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Accurate heating load prediction is essential to supply-demand collaboration in district heating systems and energy sustainability. With the development of the Internet of Things technology, massive monitoring data is collected that provides abundant data sources for the prediction models. However, the missing data from equipment anomalies, network transmissions and the complexity of heat load changing cause difficulty in realizing accurate heat load prediction. Therefore, the hybrid model based on bidirectional long short-term memory network and temporal convolutional network proposed in this paper to improve the accuracy of the heat load prediction from the aspects of reconstruction of missing values and extraction of complex features. The bidirectional long short-term memory algorithm imputes missing values based on bi-directional features of existing data and provides solid data foundation for subsequent training of predictive models. The temporal convolutional network achieves high-level feature extraction and parallel computation, which contributes to the effective modeling of complex changes in heat load and the realization of accurate heat load prediction. Comparative study was conducted with four heat exchange stations of actual environment to evaluate the performance of the prediction model. The results showed the mean absolute percentage error of the hybrid model decreased to 2.47% which is lower than the State-of-the-Art models, such as long short-term memory, temporal convolutional network, and support vector regression etc. The superior results further validated the feasibility of this hybrid model in heat load prediction. • The missing values in heating system were reconstructed by deep learning model. • A hybrid heating load prediction model was proposed considering missing values. • Detailed experiments were conducted to validate the model's superiority. [ABSTRACT FROM AUTHOR]

Abstract This paper presents analyses of complex flows and heat transfer induced by twin oblique turbulent slot-jets of different directions (divergent, convergent or parallel) impinging a heated wall. A comparison of the heat transfer characteristics between perpendicular and three cases of twin oblique jets (parallel, convergent and divergent). The twin slot jets are located on a confining adiabatic wall at a distance of 8 slot jet width. Convective heat is investigated numerically examining the effect of Reynolds number (Re) and jet inclination angle (α). This problem is relevant to a wide range of practical applications including nuclear engineering devices, manufacturing, material processing, electronic cooling, drying paper or textile, tempering of glass, etc. All computations are performed using two dimensional large eddy simulations (LES) approach with Smagorinsky sub-grid scale (SGS) models. For all directions and inclinations of the jets, the location of the stagnation points is changed and hence, the location and magnitude of the maximum Nusselt number on the heated wall vary. When Reynolds number increases, Nusselt number is improved for all types of inclination. The averaged Nusselt number shows that the perpendicular impingement gives better heat transfer than that of the oblique jets. The poor heat transfer is obtained for the parallel oblique jets. For the same angle, divergent jets give smallest heat transfer than the convergent jets. Graphical abstract Twin-jets flow configuration. (a) Perpendicular (b) Divergent (c) Parallel (d) Convergent. Image 1 Highlights • Four types of flow patterns of impinging twin jet are studied by Large Dissipation Simulation. • Nusselt number is enhanced for all types of inclination for increasing Reynolds number. • Averaged Nusselt number of the perpendicular impingement gives better heat transfer than that of the oblique jets. • The poor heat transfer is obtained for the parallel oblique jets. • For the same angle, divergent jets give smallest heat transfer than the convergent jets. [ABSTRACT FROM AUTHOR]

Solar-based radiant heating systems represent a sustainable, and relatively low-cost, technology to raise the temperature of the interior thermal mass of our buildings. Through the use of direct absorption solar thermal collectors, the same working fluid which absorbs the solar energy can be used to transfer the energy for storage in the thermal mass of the structure using a network of pipes embedded in concrete floors. This study investigates a promising working fluid which can be used in such systems – one which is based on multi-walled carbon-nanotubes suspended in normal base fluids. A major stumbling block affecting the wide spread use of carbon-nanotube nanofluids is their low dispersion stability at elevated temperatures, which significantly reduces the absorption capabilities of the nanofluids and could lead to clogging of the pumps used to circulate the fluids. In this paper, we report on a scalable UV-ozone (UVO) treatment technique to produce highly stable dispersions for the elevated temperatures experienced by working fluids in radiant heating systems. To probe suitability of UVO treated multi-walled carbon-nanotube (MWCNTs) for solar-assisted radiant heating systems, this paper investigates the effects of exposure time and temperature on stability, optical absorbance properties, the extent of functionalisation, and the photothermal conversion performance of UVO-treated MWCNT nanofluids. No agglomeration or degradation of the MWCNTs was observed at elevated temperatures (up to 150   °C), highlighting the stability of proposed nanofluids. [ABSTRACT FROM AUTHOR]

In this paper Double Multi Relaxation Time Lattice Boltzmann method (DMRT-LBM) is utilized to investigate the particle motion in a modeled room for the first time. The effect of indoor heating system location has been considered on both particle deposition and convective heat transfer so six different positions have been selected for the heating system. Results are shown for two Rayleigh numbers (104 and 105) and different particle sizes (1 μ m and 10 μ m). To study the particle motion, after the flow reaches steady state, 50 000 particles are randomly injected to the room and the number of deposited particles on the walls has been reported for 100 s. Considering the present results, when the heating system is in the middle of the wall, the maximum heat transfer rate is seen for both Rayleigh numbers. Also, the number of deposited 1 μ m particles on the walls for all locations of the heating system is zero for R a = 104, so the number of suspended particles is the maximum. For both Rayleigh numbers and 10 μ m particles, the number of deposited particles is maximum when the heating system is fixed on the top of the wall. It is also concluded that when the heating system is located on the top of the wall, the number of suspended 1 μ m particles for R a = 105 reaches its maximum value. [ABSTRACT FROM AUTHOR]

It is difficult to alter the thermal performance of a minichannel heat sink with a fixed structure under constant operating conditions. In particular, if the local heat transfer of the substrate cannot be regulated in real time, the dynamic heat dissipation needs of high-power electronic components cannot be met in the electrical servo systems of flight vehicles. In this paper, a new minichannel heat sink structure based on the classical rectangular channel is proposed and a piezoelectric oscillating fin (POF) is introduced to replace the fixed fin. The thermal performance of the heat sink can then be regulated using the swing of the POF, with supercritical carbon dioxide (S–CO 2) as the coolant. Transient numerical simulations are applied to investigate the influence of various POF operating parameters on the heat transfer of the channel, such as the oscillation amplitude and frequency. The results demonstrate that a channel with a POF can allow for dynamic and rapid adjustment of the thermal performance through control of the oscillation frequency and amplitude of the POF, with a constant channel configuration, coolant, and operating conditions. The heat transfer can be enhanced significantly by the swing of the POF, with the local Nusselt number growing up to 8.3 times and the overall one up to 1.14 times. Both the oscillation frequency and amplitude have a positive correlation with the intensity of heat transfer. The POF also contributes to a greater pressure drop and fluctuation in pumping power. A comprehensive evaluation coefficient shows that the POF is effective at improving the overall thermal performance with a low-frequency swing, while high-frequency operation enhances the local heat transfer and decreases the local temperature near the tail end of the POF. Finally, considering the effects of the frequency and amplitude of the POF, as well as the variable thermophysical properties of the supercritical coolant, a heat transfer correlation based on the Dittus–Boelter equation is established to predict the thermal performance of the channel with a POF. This prediction has a maximum error of ±0.56%. • A minichannel introducing piezoelectric oscillating fin (POF) to replace the fixed fin is proposed. • The thermal performance of the minichannel heat sink is regulated using the POF and S–CO 2. • The influence of oscillation frequency and amplitude of the POF on heat transfer is investigated. • A heat transfer correlation for POF channel based on the Dittus–Boelter equation is established. [ABSTRACT FROM AUTHOR]

Experimental Advanced Superconducting Tokamak (EAST) is one of the important steady-state divertor Tokamak physical experiment platforms in the world. The main functions of the high-temperature and high-pressure Divertor Primary Heat Transfer System (DIV PHTS) are to provide high-pressure cooling water for the divertor to remove the heat load deposited on the divertor under the plasma operation mode and to provide high-temperature nitrogen gas for the divertor system to achieve vacuum condition during the baking mode. The stability and reliable operation of the DIV PHTS play an important role in the EAST tokamak plasma physics experiment. The high-temperature and high-voltage electrical insulation break are one of the important components of the system. The main function of the Electrical Insulation Break (EIB) is to break the closed circuit of the heat transfer system to avoid eddy current during plasma discharge affecting the magnetic field distribution characteristics of the tokamak. On the other way, it also needs to meet the requirement, there is no leak of the cooling water and nitrogen gas during cooling and baking operation mode. This paper proposes the design of an electrical insulating break (EIB) to meet the design requirements of EAST tokamak at first. Then the electric field analysis is carried out by using a finite element model to evaluate its electrical insulation characteristics. And the sealing structural characteristics are verified by applying the finite element method under two design modes. Finally, the sealing test result under the high-temperature baking and high-pressure cooling modes are presented to validate the design. [ABSTRACT FROM AUTHOR]

The Experimental Advanced Superconducting Tokamak (EAST) had been under major upgrading from 2020 to 2021 in China. In this campaign of major upgrading, the new lower tungsten divertor is successfully installed to achieve the targets of long pulse and high β H-mode plasma operation. High temperature and high pressure Divertor primary heat transfer system (DIV PHTS) is also developed to remove the plasma deposition heat load on the Divertor. This paper presents a description of the design and construction of DIV PHTS for EAST Tokamak. Starting from the requirements specified in the Technical Specifications of DIV PHTS, the process to meet the Divertor cooling and baking requirement is designed and validated by the supported thermal-hydraulic analysis. Then, the piping stress analysis under different types of load combinations is performed to verify the structural design requirements. General layout design is also performed based on the component requirement and the allocated space in the EAST Tokamak hall. Finally, the procurement and test of the system main equipment is also given. [ABSTRACT FROM AUTHOR]

HVAC systems in buildings are composed of many subcomponents which consume energy in huge amounts. In recent years, energy consumption becomes very important aspect due to the lack of energy resources and environmental reasons. In terms of energy consumption, the components of HVAC systems account for large portion of total energy used in buildings. Therefore optimization of energy consumption in HVAC applications is an essential requirement in terms of thermodynamic and economic point of views. Besides, the efforts for decreasing energy consumption turn into economic recovery. It also provides benefits for human health and cleaner environment. In this paper, as originality, thermodynamic and economic analyses of an existing social and cultural building which has a heating and cooling area of 8852 m 2 are presented by comparing of a conventional HVAC and a VRF system. A novel contribution is given to the open literature by comparing two systems with actual data measured from the existing system. The other originality is to apply and test a VRF system to a complex-structured building. This study is a rare one which contains insulation, heating and cooling accounts of a building together. In this paper, VRF system is modelled to the existing building for the comparison of the conventional HVAC system. Both systems have been compared in terms of heating and cooling capacity, initial, operation and maintenance costs. It is found that the VRF system is more economic and efficient such that the VRF system is found to have 44% cost profit when compared with the conventional HVAC system. [ABSTRACT FROM AUTHOR]

Highlights • A two-phase flow visualisation and heat transfer experiment bench was established. • Flow patterns at various crank angles in an open cooling gallery were captured. • The effects of motor speed and heating on flow patterns were discussed. • The temperature distribution was obtained and the effect of speed was discussed. • Transition from laminar flow to turbulent flow has been identified. Abstract The demand of increasing power density of the Internal Combustion Engine promotes the technology development using internal cooling gallery of the piston. The oil flow and heat transfer performance of the piston internal cooling gallery have great influence on the cooling performance, which affects the thermal conditions of the piston and of the entire engine. The experimental study using visualising method is therefore critical and important to observe the flow patterns inside the piston gallery. In this paper, we presented the visualised study of two-phase flow patterns within an open cooling gallery by using a high-speed camera at various crank angles. The effects of motor speed both on the flow patterns and temperature distribution were investigated and the heat transfer mechanisms in gas-liquid two-phase flow during reciprocating motion were explored. Based on the study, the period-doubling phenomenon, which represented the transition from laminar flow to turbulent flow, was observed when the speed was around 400–500 rpm. Results indicated the increase of motor speed can effectively improve the cooling performance. Results also showed when the speed was higher than 600 rpm, the reduction of temperatures was quite close, which proven the existence of optimal or minimum requirement of motor speed to achieve good quality cooling performance. The results obtained in this study could be used as a critical reference for numerical studies and important experimental reference to further investigate the design and optimisation of engine cooling gallery for vehicle application. [ABSTRACT FROM AUTHOR]

The paper deals with the study of the heat transfer phenomena within a vertical enclosure containing PCM integrated inside a test cell with the dimension of (0.5, 0.5, 0.5 m 3 ). An experimental framework was conceived and installed in the Thermal Processes Laboratory in Borj Cedria, Tunisia. The experimental investigation was carried out by measuring the temperature and the heat fluxes exchanged throughout the PCM vertical enclosure. It was found that during the heating phase the temperature inside the test cell equipped with the PCM vertical enclosure is about 28 °C. It was also found that once the PCM vertical enclosure is omitted the cell temperature inside the test cell ranges between 29 and 40 °C. A complete model was also formulated by taking into account various modes of heat transfer inside the PCM vertical enclosure. The numerical model was performed by following the temperature changes at the bottom position and at the high position of the PCM vertical enclosure. The numerical model followed also the evolution of the melting front during the melting process. The model was then exploited for the evaluation of the melting front evolution during the charging and the discharging processes. Another TRNSYS simulation was achieved to evaluate the feasibility of integrating the PCM vertical enclosure in a real building envelop. The results of the TRNSYS simulation showed that the integration of a well dimensioned PCM vertical enclosure enhances the thermal comfort of the occupant by reducing the thermal fluctuation and by improving the thermal inertia of the walls. [ABSTRACT FROM AUTHOR]

Measurements from the operation of Heating, Ventilation and Air conditioning (HVAC) system are collected by Building Automation System (BAS) mostly for control purpose. In many air handling units (AHUs) the airflow meter is not installed on the outdoor air stream to reduce the initial costs. To provide such a missing information needed for the ongoing commissioning of HVAC system, a virtual flow meter (VFM) should be implemented in the BAS. This paper presents VFMs for the heating season when the heat recovery coils are used. Two models are presented which predict the outdoor air ratio (factor α), in the absence of such an air flow meter, by using BAS trend data. Two energy balance equations, one for the air mixing box and another for the heat recovery coils, are coupled. The results from a case study building show that the two models predict the daily average outdoor air ratio of 0.89 and 0.87, respectively, compared with the reference daily average ratio of 0.86. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of forced convection effects on transient boiling heat transfer of water on plate-type heaters, at atmospheric pressure, under exponentially escalating heat fluxes. It complements the work performed under pool boiling conditions presented in the companion paper (Part I). Infrared (IR) thermometry and high-speed video (HSV) were used to gain insight into the physical phenomena and generate data that can be used for development and validation of accurate models of transient flow boiling heat transfer. Exponential power escalations with periods in the range from 5 to 500 ms, and subcooling of 10, 25 and 75 K were explored. The Reynolds number was varied from 25,000 to 60,000, depending on the subcooling. Single-phase heat transfer, onset of the boiling driven (OBD) heat transfer regime and overshoot (OV) conditions were identified. The experimental data suggest that during the single-phase heat transfer regime, forced convection is the dominant heat transfer mechanism for long periods, whereas transient conduction is more important for short periods. A criterion based on the normalized time scale for turbulent heat transfer is shown to capture all single-phase heat transfer data on a single curve. At a given period, OBD heat flux and wall superheat, as well as OV wall superheat increase with increasing subcooling and increasing Reynolds number. For a given Reynolds number and a given subcooling, they decrease with increasing periods at short periods, when the dominant heat transfer mechanism is transient conduction, whereas they barely change for long periods, as the dominant single-phase heat transfer mechanism is forced convection. Once boiling is fully developed, the heat transfer coefficient is proportional to the wall superheat to the fourth power and increases with increasing subcooling. [ABSTRACT FROM AUTHOR]

For a linear heat transfer system, the unit step response of the temperature field to any system inputs, such as internal and external heat sources, is specific. This means that there is a definite temperature response correlation between any spatial points in the system spatiotemporally, which is independent of the system inputs. It is significant to achieve a quantitative description of the temperature response spatiotemporal correlation between the spatial points for solving the temperature field reconstruction problem of the heat transfer system with unknown inputs. In this paper, a temperature response spatiotemporal correlation model (RSTCM) of the heat transfer system is established originally to reveal the inherent quantitative relationship between the responses of any system spatial points theoretically. Firstly, an external description of the spatiotemporal mapping relationship of the heat transfer process is established according to the heat transfer equations. Furthermore, a basic RSTCM form is proposed and a response spatiotemporal correlation matrix is determined with the help of the external description. Finally, considering the ill-posed characteristic of the response spatiotemporal correlation problem, the regularization technology is employed to transform the original problem into a well-pose problem and to provide a response spatiotemporal correlation matrix with regularization. Effectiveness of the RSTCM is verified by the existing heat transfer experimental data. Besides, adaptability of the proposed model is demonstrated by the achieved numerical experiment results on a two-dimensional heat transfer system. [Display omitted] • The temperature response spatiotemporal correlation is revealed for a heat transfer system. • A temperature response spatiotemporal correlation model (RSTCM) of the heat transfer system is established. • The response spatiotemporal correlation matrix is constructed by regularization. • Effectiveness of the RSTCM is verified by experimental data. • The RSTCM lays a foundation for temperature field reconstruction independent of heat sources. [ABSTRACT FROM AUTHOR]

Current heat transfer systems in the industry may result in problems such as low efficiency and environmental pollution. In this paper, the influence of heater power, speed and direction of rotation cylinders, and underfloor heating power are investigated on the Nusselt number in a water-filled enclosure with Pr = 5.4 numerically and experimentally based on the Arduino control unit. The enclosure is under constant heat flux from the bottom wall. Using the mixed-Taguchi method and according to different considered cases, 36-state experiments were designed in the range of 2 × 10 8 < R a < 8 × 10 8 and R e < 4000. The problem was simulated by using the Realizable k-ε turbulence model, in 3D steady-state mode. Isotherms and streamlines were reported for each case and analysis revealed that the speed of rotation and the heater power has a more important role than other parameters on the heat transfer rate. In the best situation with a maximum speed of cylinders (S = S (max)), maximum floor heating system ( q f ˙ = q f ˙ (max)) , and maximum power of the heater ( q r ˙ = q r ˙ (max)) the Nusselt number is 110.5 with an almost 22% increase in heat transfer rate. A polynomial surf fit for Nusselt number according to Re, Ra proposed and there are three parts to the variation range of Nusselt numbers based on Richardson numbers. [Display omitted] [ABSTRACT FROM AUTHOR]

The following comments address an inappropriate implementation of a theoretical relationship and some incorrect qualitative and quantitative findings in the paper, as mentioned above. Therefore, this analysis clarifies the article "Numerical study on the conjugate effect of joule heating and magneto-hydrodynamics mixed convection in an obstructed lid-driven square cavity." [International Communications in Heat and Mass Transfer 37 (2010), 524–534]. [ABSTRACT FROM AUTHOR]

Nowadays, utilization of micro/mini channel heat sinks (MCHS) has become a popular solution for cooling of electronic systems and maintaining their operating temperature in a desired range. Increasing the contact surface area between fluid and solid zones by geometrical modifications is a promising solution that significantly affects thermal performance and heat transfer in these systems. In this paper, considering thermohydraulic performance, the effect of creating grooves on the middle-placed barriers of a minichannel heat sink is investigated to access a criterion for favorable temperature performance. Evaluating different geometrical parameters of barriers and grooves including cross section, depth and position of horizontal groove as well as vertical groove distance, simultaneous employment of optimal horizontal and vertical groove in the channel at different Reynolds numbers is studied. Outputs including channel base temperature, friction factor ratio and total thermal resistance are studied to evaluate the performance of the proposed minichannel. Results indicate that vortex formation adjacent to solid walls considerably enhances the heat transfer and variation of each geometrical parameters offers a performance enhancement. Moreover, the best thermal performance is obtained by simultaneous employment of the horizontal rectangular groove (x = 0.45 mm, y = 0.2 mm and h g = 0.6 mm) and the vertical groove (d g = 0.4 mm). In the optimal case, the channel base temperature and the total thermal resistance reduces by 11.88 K and 27%, respectively. [ABSTRACT FROM AUTHOR]

This paper deals with the analytical and experimental analysis of heat transfer in the xylem of trees and the determination of stem water content (WC). The aim of this paper was to derive and verify a new approach to WC calculation from measured temperature differences around a continuously heated needle. The configuration of heater and thermocouples of the heat field deformation (HFD) method for sap flow measurements was taken for this purpose. The suggested formula is derived from the heat conduction equation with a continuous linear source of heating. The ability of the HFD method to non-destructively determine the radial distribution of the local conditions of sap flow measurements under zero flow (referred to as K-value) was used to derive the radial distribution of WC. Examples of the application of our method on several contrasting species with different plant hydraulic architecture are given where calculated WC along stem xylem radius was compared with its direct gravimetrical measurements or with relative determination of wetness of cross-sectional stem discs using a modified differential translucence method. The proposed method enables water content measurements during continuous linear heating and is important for information about WC and sap flow together per day or season when there is possible to extrapolate the temperature difference for zero flow condition. [ABSTRACT FROM AUTHOR]

Despite a variety of techniques available for thermal conductivity measurement, there is a lack of methods to directly measure the radial thermal conductivity of a cylinder. This presents a critical gap in heat transfer metrology, particularly in presence of anisotropic thermal conduction, such as in a Li-ion cell, where radial thermal conductivity plays a key role in determining performance and safety. This paper reports a technique for measurement of radial thermal conductivity of a cylinder by accounting for variable heat flux into the cylinder when heated on the outside. It is shown that heat flux into the cylinder from a thin heater wrapped around its surface varies significantly with time. This variation, which was neglected in past work, is accounted for by developing a variable heat flux model for experimental data analysis. For two different materials, measurements of radial thermal conductivity using this approach are shown to be in close agreement with standard thermal conductivity measurement using the transient plane source method. Radial thermal conductivity of a 26650 Li-ion cell is measured to be 0.39 W/mK. Besides contributing a new approach for thermal metrology in cylindrical systems, this work also improves the understanding of thermal phenomena in Li-ion cells. [ABSTRACT FROM AUTHOR]

Latent heat thermal energy storage is an attractive technique as it can provide higher energy storage density than conventional heat energy storage systems and has the capability to store heat of fusion at a constant (or a near constant) temperature corresponding to the phase transition temperature of the phase change material (PCM). This paper provides a state-of-the-art review on phase change materials (PCMs) and their applications for heating, cooling and electricity generation according to their working temperature ranges from (−20 °C to +200 °C). Four working temperature ranges are considered in this review: (1) the low temperature range from (−20 °C to +5 °C) where the PCMs are typically used for domestic and commercial refrigeration; (2) the medium low temperature range from (+5 °C to +40 °C) where the PCMs are typically applied for heating and cooling applications in buildings; (3) the medium temperature range for solar based heating, hot water and electronic applications from (+40 °C to +80 °C); and (4) the high temperature range from (+80 °C to +200 °C) for absorption cooling, waste heat recovery and electricity generation. Different types of phase change materials applied to each temperature range are reviewed and discussed, in terms of the performance, heat transfer enhancement technique, environmental impact and economic analysis. The review shows that, energy saving of up to 12% can be achieved and a reduction of cooling load of up to 80% can be obtained by PCMs in the low to medium–low temperature range. PCM storage for heating applications can improve operation efficiency from 26% to 66%, depending on specific applications. Solar thermal direct steam generation (DSG) is the most common electricity generation application coupled with PCM storage systems in the high temperature range, due to the capability of PCMs to store and deliver energy at a given constant temperature. The recommendations for future research are also presented which provide insights about where the current research is heading and highlights the challenges that remain to be resolved. [ABSTRACT FROM AUTHOR]

The complex interactions between the inclined terrain and the flow generated by the fire make the slope one of the most influencing factors on fire spread. In order to gain a deeper understanding of the mechanisms involved in wildfires spreading upslope, the investigation of flow dynamics and heat transfers is fundamental. This paper reports a series of fire spread experiments conducted across a porous bed of excelsior in a large-scale facility, under both no-slope and 30° up-slope conditions. The coupling of particle image velocimetry and video imaging allowed characterizing the flow pattern with respect to the fire front. Simultaneous heat flux measurements with high scan rate were also performed at the edge of the fuel bed. From the collected data, the increase of the rate of spread with increasing slope is attributed to a major change in fluid dynamics surrounding the flame. For horizontal fire spread, flame fronts exhibit quasi-vertical plume resulting from the buoyancy forces generated by the fire. These buoyancy effects induce an inward flow of ambient air that is entrained laterally into the fire from both sides. Flame radiation is the dominant fuel preheating mechanism. Under upslope conditions, the fire plume is tilted toward the unburnt vegetation, increasing radiation levels. The air entrainment at the burnt side of the fire strongly influences the downstream flow, which becomes attached to the surface over a characteristic length scale. Ahead of the flame front, the induced wind blows away from the fire rather than toward it, enhancing convective heating. Periodical forward bursts of flame combined with distant fuel ignitions were also observed. The heat flux measurements confirmed the existence of such convective mechanisms. [ABSTRACT FROM AUTHOR]

The melting process and the solidifying process of phase change material (PCM) are usually considered symmetrical in the traditional PCM heat transfer models, but there are inevitable calculation errors using these models. In this paper, a new heat transfer model of PCM based on the energy asymmetry was built, and it was validated by experimental data. It was found that the two main reasons for the energy asymmetry of the PCM were the melting temperature range and the solidifying temperature range were not the same and the supercooling problem during the cooling process. No matter for only one thermal cycle or for the multiple thermal cycles, the results from the asymmetrical model and the symmetrical model were different. Apparently, compared with the symmetrical model, the asymmetrical model had higher accuracy, and the heating/cooling process in the asymmetrical model was more consistent with the real heating/cooling process of the PCM. [ABSTRACT FROM AUTHOR]

The paper presents results of experimental research into the transmission of infrared radiation through water film. Experiments substantiate a hypothesis about the considerable role of radiative heat transfer when heating heterogeneous water drops containing opaque solid particles in high-temperature gases. We measure the temperatures of water film surface, the bottom of a cylindrical plastic cuvette and a graphite substrate. During the experiments, the typical thickness of the water film, the bottom of the plastic cuvette and the graphite substrate is 1 mm. The temperature measurements are implemented for carbonated, distilled and tap water. Results of a comparative analysis of these measurements are presented as well. The hypothesis is formulated about a significant variation in the optical properties of water under temperature fluctuations. This assumption is based on the hydrophobic properties of amphiphilic molecules. Importantly, the experimental data enable the study of rapid evaporation of a liquid at internal and external interfaces of water drops containing solid opaque particles with a further explosive fragmentation of water film. This mechanism relies on heating of the particle surface above the boiling point of water. [ABSTRACT FROM AUTHOR]

The main concern in this paper is to analyze the heat, mass and motile microorganisms transfer rate in the magnetohydrodynamic (MHD) convective flow of tangent hyperbolic material. Analysis is studied in presence of both nanoparticles past an exponential surface. Nanofluid containing gyrotactic microorganisms in addition to nanoparticles is considered. Analysis is carried out in presence of an inclined magnetic field. In fact the idea here is to use the microorganisms just to stabilize the suspended nanoparticles due to bioconvection generated by the combined effects of buoyancy forces and magnetic field. Brownian motion, thermophoretic and Newtonian heating are also studied. The resulting systems of nonlinear systems have been solved by homotopic procedure. The velocity, temperature, nanoparticle concentration and density of motile microorganisms are examined graphically. The skin friction coefficient, local Nusselt, Sherwood and motile microorganism numbers are numerically discussed for the active involved parameters. It is observed that velocity profile is decreased by both magnetic parameter and angle of inclination. It is also noted that the temperature profile increases for larger Nb but it decreases for nanoparticle concentration. [ABSTRACT FROM AUTHOR]

• An improved thermodynamic analysis method is presented and validated. • Unsteady local conductive and radiative entropy generation rates are analyzed. • Exergy storage rate and exergetic efficiency is obtained. • An uniform and centralized heating strategy is proposed. This paper presents an improved thermodynamic analysis method used to evaluate the irreversibility and efficiency of a coupled conductive-radiative heat transfer process. The exergy analysis of the conductive-radiative process is developed based on the exergy balance equation. In the method, the local entropy generation rates due to the radiative heat transfer and heat conduction processes are calculated. Based on the entropy generation analysis, an exergy analysis is performed, the stored exergy of the system and the exergetic efficiency are determined, and the thermodynamic efficiency of the system is further evaluated. The results are verified by the principle of exergy balance and the exergy generation rate calculated by the method does not deviate from the theoretical value by more than 0.1%. Four heat source distributions are specified in the numerical analysis, which include completely uniform, partially uniform, and non-uniform heat source distributions in the numerical analysis. The effects of heat source distribution, conductive-radiative coefficient and total heat generation rate of medium on entropy generation and stored exergy of system are investigated. The numerical results show that the average temperatures and exergy storage rate of the systems with partially uniform heat source distribution are 5.1–79.7 K and 6.8–49.8% higher than the other distributions, and uniform and centralized heat generation in the internal region of the system is proposed. The total stored exergy of the systems has a tendency to first increase and then decrease, reaching its maximum at N = 1 as the conduction and radiation coefficients increase, and increasing as the total heat generation rate increases. [ABSTRACT FROM AUTHOR]

Abstract: Due to the unique properties of near-critical fluid, trans-critical/supercritical CO2 based natural circulation loop (NCL, or thermosyphon) has been proposed in many energy conversion systems, such as solar heater, waste heat recovery, next generation nuclear cooling, etc. This paper presents an experimental investigation of a near-critical CO2 thermosyphon. The closed thermosyphon is specially designed for high pressure experiments, where natural convection is achieved only by heating and cooling of fluid in the loop. The system is operated in wide range of pressures from around 6.0 to 15.0MPa in the near-critical region. It is found that the NCL flow will change from unstable sub-critical two-phase flow to stable liquid flow, and then become stable supercritical circulation with the increase of system initial pressure. The heat transfer behaviors are analyzed for stable flow conditions mainly for supercritical region. General variations of the fluid temperature, mass flow rate and loop pressure are presented in this paper. In the steady supercritical region, the heat transfer performance of the cooler show very small changes with bulk mean fluid temperature, and at the heater better heat transfer is found for conditions close to the pseudo-critical point. The heat transfer dependency on operation pressure and evolution mechanisms are also discussed in detail in this paper. [Copyright &y& Elsevier]

Abstract: Experimental measurements in a spray cooling test rig were carried out for two different heater surface roughnesses and for two different types of nozzles with the dielectric refrigerant R134a. In this paper, results of the sprayed refrigerant film thickness measurements are presented. The influence of the volumetric flow rate, the surface roughness and the type of nozzle (through the spray parameters) on the total average film thickness is analyzed and discussed. In a companion paper, results of the heat transfer measurements are presented. It has been found that there is a relation between the variations of the average Nusselt number and of the film thickness along the spray cooling boiling curve. The heat transfer regimes along that curve are related not only to a variation in the average Nusselt number but also to changes in the film thickness. The qualitative analysis of those variations served to better understand the heat transfer mechanisms occurring during the spray cooling. [Copyright &y& Elsevier]

In continental climates heating accounts for a significant part of the total energy consumption of a residential building with average thermal characteristics of the envelope. Solar heat gains have to be used wisely in order to reduce the energy need for heating. Glazed ratio of the facades, orientation of the transparent area and thermal mass has to be properly chosen in order to obtain the desired utilization factor. In this paper the effects of window size, thermal mass and window orientation on the balance point temperature are analysed in case of a reference room. The calculation methodology given by EN ISO 13790 standard was used. Measurements were done in order to validate the model. Performing the calculus on 48 different cases it was shown, that differences of even 11% can appear between the energy demands for heating (for similar overall heat transfer coefficients of the external building elements). [ABSTRACT FROM AUTHOR]

Analytical methods for the evaluation of temperature distribution of steel members in fire are readily available in codes of practice. These methods are usually based on uniform sections under fully engulfed fire conditions. In reality, structural members are often subject to partial heating fire conditions such as members passing through multiple fire compartments or subject to localised fires. At present, little guidance is given for temperature calculation of steel members subject to partial heating fire conditions. Evaluating the temperature distribution of steel members in such situations is important as the results may determine the extent of fire protection required for these members. This paper describes a numerical study on the temperature distribution of a partially heated steel member using a simple finite difference scheme with parametrically coded generic elements. The results are compared with the approximated method given in Eurocodes whereby the average temperature of a partially heated steel member can be calculated. It is shown that the proposed finite difference scheme can accurately predict the temperature distribution of steel members and provides a means for assessing their fire protection requirements. [ABSTRACT FROM AUTHOR]

This paper reports the results of an experimental investigation of the heat transfer performance of a phase change material (PCM) based composite 72 pin fin heat sink subjected to individual heat loading of 4 discrete heaters of equal area. The investigation is then followed by multi objective optimization of the individual heat inputs, wherein the total power of the heaters is fixed. The PCM used is n-eicosane and the heat sink is made of aluminium. First, in house experiments are conducted for different combinations of power. The hotspots imposed by spatially non uniform heat flux are seen to have a considerable effect on the melting and solidification cycle and hence on the thermal performance of the heat sink. The diversity in the performance of heat sink motivates us to perform a multi objective optimization using Non-dominated sorting genetic algorithm (NSGA-II) to determine the optimum combination of the discrete power levels, that stretches the charging period and minimizes the discharging period of the heat sink simultaneously. The solutions obtained thus obtained are validated by conducting in house experiments. This study establishes the fact that discrete heating scenarios have to be considered in the future optimization of the heat sinks. [ABSTRACT FROM AUTHOR]

Lack of understanding of flow boiling behavior in reduced gravity poses a major challenge to the development of future space vehicles utilizing two-phase thermal control systems (TCSs). A cost effective method to investigating the influence of reduced gravity on flow boiling is to perform ground experiments at different orientations relative to Earth gravity. This paper is the first part of a two-part study aimed at exploring flow boiling mechanisms of FC-72 in a rectangular channel heated along one wall or two opposite walls. Experiments are performed in vertical upflow, vertical downflow and horizontal flow, subject to large variations in mass velocity, inlet quality and wall heat flux. Detailed measurements are used to investigate the influences of orientation, and therefore gravity, on boiling curve, local and average heat transfer coefficients, and pressure drop, and their relationship with interfacial behavior is captured with high-speed video. For horizontal flow, the effects of gravity are reflected in appreciable stratification across the channel at low mass velocities, with gravity aiding vapor removal from, and liquid return to the bottom heated wall, while accumulating vapor along the top heated wall. For vertical upflow and vertical downflow, with both single-sided and double-sided heating, there is far better symmetry in vapor formation along the channel. The heat transfer coefficient shows significant variations among the different orientations and heating configurations at low mass velocities, but becomes insensitive to orientation above 800 kg/m 2 s, proving inertia around this mass velocity is effective at negating any gravity effects. For low mass velocities, pressure drops are fairly equal for vertical upflow and vertical downflow, but greater than for horizontal flows. However, fairly equal pressure drops are achieved at high mass velocities for all orientations. Overall, this study proves that gravity effects on two-phase pressure drop and two-phase heat transfer are dictated mostly by mass velocity and, to a lesser extent, by inlet quality. [ABSTRACT FROM AUTHOR]

This paper investigates into the heat transfer from the wall to solids moving inside an indirectly heated rotary reactor with flights. The cluster renewal mechanistic model was used to develop a model for estimating the effective heat transfer coefficient (EHTC) from wall to solids. The overall heat transfer coefficient (OHTC) considered the heat transfer from the reactor wall to solids, and that from the wall to gases in the reactor whose wall temperature is maintained at constant temperature. Predictions from the OHTC model showed a good agreement with values measured in the reactor fed with brass particles. The model for estimating the EHTC was compared with the published experimental values of Herz et al. (2012), and showed a better agreement than the existing models. The developed model could therefore be applied for designing rotary torrefier or used for overall performance model of rotary torrefier. [ABSTRACT FROM AUTHOR]

• Simplified models for heat transfer and surface temperature were established. • Calculated heat transfer and surface temperature agreed well with experimental data. • Heat transfer and surface temperature linearly changed with mean water temperature. • The pipe space clearly affected the heat transfer and surface temperature. • Heat transfer and surface temperature varied greatly as the transition changed. Prefabricated radiant heating and cooling (RHC) system is a typical form of high efficiency and lightweight radiant terminal, which has been extensively used in the residential and non-residential buildings. Heat transfer and surface temperature are the key parameters for rational design of a prefabricated RHC system. Therefore, in this paper, based on the analysis of the heat transfer mechanism, simplified models and numerical models were established for calculating the heat transfer and surface temperature of the prefabricated floor or ceiling RHC system. Compared with experimental test results, when the supply water temperature increased from 35 °C to 50 °C under heating condition or from 13 °C to 19 °C under cooling condition, the relative errors calculated by the simplified models were between −10.8% and 3.7% and between −3.8% and 5.0% for the heat transfer and surface temperature of the prefabricated floor RHC system, and ranged from 0.8% to 6.9% and from −0.7% to 0.3% for the prefabricated ceiling RHC system. Moreover, the calculated heat transfer and surface temperature of the prefabricated ceiling or floor RHC system using the simplified models were highly consistent with the numerical simulation results. Hence, the calculation accuracy of the proposed simplified models for the heat transfer and surface temperature can meet the requirements of engineering application, which will provide the support for the rational design of a prefabricated floor or ceiling RHC system. [ABSTRACT FROM AUTHOR]

Abstract: The article described the dilatancy technology of district heating system with high-temperature heat pump (HTHP). For the exploitation of low-temperature return network sources, a high-temperature heat pump with a heat exchanger was planned. As the core technology of the dilatancy district heating system, HTHP units and heat exchanging systems had been described detailedly through theoretical and experimental analysis. The model was proved to be in good agreement with the experiment data. It could be used for engineering design. In this paper the district heating system in Datong was taken as a case study. The main characteristics of the dilatancy district heating system had been presented in the form of diagrams. The principal advantage of dilatancy technology in the district heating system lies in increasing the temperature difference, reducing the diameters and the initial investment of primary side network. This paper shows clearly the analysis of the dilatancy technology for characterising and improving the performance of district heating systems. [Copyright &y& Elsevier]

Abstract: In certain building applications, the PV installation is extended to cover also south- or west-facing walls, taking care to circulate cooling air to the back of the panels. The cooling effect maintains a high conversion efficiency of the PV panels and the heated air may be exploited by the HVAC or service water heating system. Sizing and design of the double façade system is critical to its energetic performance. In this paper, the results from flow visualization and hot wire anemometry measurements performed on the basic structural module of a double-skin photovoltaic (PV/T) façade are discussed. The concept and its feasibility have been presented in a previous paper. The results of transient outdoor measurements with the testing device have been reported elsewhere. The air flow and turbulence field inside the cavity is analyzed in the present paper by means of indoor measurements with the testing device. The results are combined with CFD computations to calculate heat transfer coefficients and improve our understanding and modeling of the specific PV/T concept. [Copyright &y& Elsevier]

Abstract: This paper presents a review of studies on natural convection heat transfer in the triangular enclosure namely, in attic-shaped space. Much research activity has been devoted to this topic over the last three decades with a view to providing thermal comfort to the occupants in attic-shaped buildings and to minimising the energy costs associated with heating and air-conditioning. Two basic thermal boundary conditions of attic are considered to represent hot and cold climates or day and night time. This paper also reports on a significant number of studies which have been performed recently on other topics related to the attic space, for example, attics subject to localized heating and attics filled with porous media. [Copyright &y& Elsevier]

Abstract: The paper gives the basic results of experimental investigation of hydrodynamics and heat transfer in heat-absorbing devices of the ITER thermonuclear reactor, which are subjected to one-side heating. The entire array of experimental data is obtained in the following range of parameters of water flow: pressure p =0.7–2.0MPa, mass flux G =340–25,000kg/(m2 s), inlet water temperature T in =15–60°C. The experiments are performed with turbulent swirl flows of water for twisted tapes with the flow swirl coefficient k =0.90, 0.66, 0.49, 0.39, 0.25, 0.19, and 0, as well for test sections without a tape. Given in the first part of the paper are the data on pressure drop and single-phase convective heat transfer. Appropriate calculation formulas are derived, which reliably generalize the experimental data. [Copyright &y& Elsevier]

Abstract: The authors have conducted measurements of liquid–vapor behavior in the vicinity of a heating surface for saturated and subcooled pool boiling on an upward-facing copper surface by using a conductance probe method. A previous paper [A. Ono, H. Sakashita, Liquid–vapor structure near heating surface at high heat flux in subcooled pool boiling, Int. J. Heat Mass Transfer 50 (2007) 3481–3489] reported that thicknesses of a liquid rich layer (a so-called macrolayer) forming in subcooled boiling are comparable to or thicker than those formed near the critical heat flux (CHF) in saturated boiling. This paper examines the dryout behavior of the heating surface by utilizing the feature that a thin conductance probe placed very close to the heating surface can detect the formation and dryout of the macrolayer. It was found that the dryout of the macrolayer formed beneath a vapor mass occurs in the latter half of the hovering period of the vapor mass. Two-dimensional measurements conducted at 121 grid points in a 1-mm×1-mm area at the center of the heating surface showed that the dryout commences at specific areas and spreads over the heating surface as the heat flux approaches the CHF. Furthermore, transient measurements of wall void fractions from nucleate boiling to transition boiling were conducted under the transient heating mode, showing that the wall void fraction has small values (<10%) in the nucleate boiling region, and then steeply increases in the transition boiling region. These findings strongly suggest that the macrolayer dryout model is the most appropriate model of the CHF for saturated and subcooled pool boiling of water on upward facing copper surfaces. [Copyright &y& Elsevier]

• Building integrated earth-to-air heat exchanger for global footprint reduction. • Offering similar energy gains than traditional earth-to-air heat exchanger. • Two time-dependent 3-dimensional finite volume models are developed and coupled. • Coupled heat and moisture transfers and complex boundary conditions are considered. • Successful validation against in-situ temperature and water content measurements. This paper investigates an innovative earth-to-air heat exchanger (EAHE), namely the geothermal foundation Fondatherm®. This system solves numerous technical problems inherent to a traditional EAHE. However, an accurate understanding of its thermal behavior is crucial to ensure the best energy gain and its economic viability. This current paper focuses on a numerical study of the ventilated foundation. A time-dependent three-dimensional finite volume numerical model is developed. This model considers coupled heat and moisture transfers as well as complex boundary conditions such as the weather, the building and the water table simultaneous influences. A matric-head based system of equations is used to represent the heat, vapor and liquid transfers within the soil. It is combined to a capillary pressure-based formulation of the heat and vapor balance equation for the concrete foundation. Furthermore, a numerical method built on a switching from a potential- to a flux-based system of equations is proposed. It is added to a variable time-step method of resolution and allow to handle the greatest hygric loads variations at the ground surface. The numerical code is successfully validated against analytical solutions for simple cases, and against experimental and in situ measurements. [ABSTRACT FROM AUTHOR]

• Heat exchange performance optimization study of the coaxial deep borehole heat exchanger. • Optimal insulation backfill depth for deeply buried pipes. • Multi-factor orthogonal simulation experiment. • Multiple linear regression analysis for optimal insulation backfill depth. Coaxial deep borehole heat exchanger (DBHE) coupled with ground source heat pump (GSHP) system has been widely applied in building heating. Insulation backfill is essential for the heat transfer performance of DBHE in colder regions. However, few studies focus on the combined influence of multi-factors on the optimal insulation backfill depth. In this paper, an orthogonal experiment was designed to explore the influence of multi-factors on the optimal insulation backfill depth of DBHE by using a numerical heat transfer model. Sensitivity analysis concluded that heat transfer factors such as inlet flow rate (A), inner pipe thermal conductivity (B), inlet temperature (C), geothermal gradient (D), and pipe depth (E) all affected insulation backfill depth of DBHE, and the comparison order of significance are C > D > B > A > E. An optimal insulation backfill depth exists for different DBHE heat transfer conditions. Compared with no insulation backfill, the average heat extraction of buried pipe under optimal insulation backfill conditions increased by 6.09 kW, with an average growth rate of 8.78 %. In addition, multiple linear regression analysis was utilized to examine the relationship between affecting factors and the optimal insulation backfill depth, based on the findings of orthogonal tests. The outcomes revealed that inlet temperature, inner pipe thermal conductivity, and pipe depth were positively correlated, with the highest standardized positive correlation value of 0.755 for inlet temperature. In contrast, inlet flow and geothermal gradient were negatively correlated, with the highest standardized negative correlation coefficient of −0.420 for the geothermal gradient. The linear regression equation could predict the magnitude of optimal insulation backfill depth with diverse input parameters. The relative error between the predicted and simulated values of the equation was less than 5 %. The findings of this research can guide the popularization and application of the GSHP coupled with the DBHE system in colder regions. [ABSTRACT FROM AUTHOR]

• A new methodology to investigate the impact of thermal mass is defined. • The use of unrepresentative boundary conditions could lead to inaccurate conclusions. • High thermal mass helps to decrease and regulate the internal temperature. • High thermal mass could increase energy use in the summer and winter seasons. • Isolating thermal mass through internal insulation results in better energy performance than external insulation. Contradictory conclusions have been reported on whether thermal mass reduces or increases energy demand in hot and cold climates. A novel approach to measuring the impact of thermal mass on the building's energy consumption is presented. The method aims to better represent reality and applies two different control conditions simultaneously in a numerical model: the first condition, which has been used in past studies, adjusts the internal boundary condition based on the time duration of heating/cooling activation (simulating an occupancy pattern) and the second, which has not been used in past studies, adjusts the internal boundary condition based on both the time duration and the internal temperature (simulating an occupancy pattern and the thermostatic control system). When investigating the impact of thermal mass on the internal temperature in a scenario where no heat is transferred into the building, the high thermal mass outperforms the low thermal mass, showing a time-shifting effect, long time lag, and small decrement factor. However, when modelled using the method presented in this paper, high thermal mass results in greater energy consumption during summer and winter periods in Saudi Arabia. During transition seasons where temperature swings occur on either side of the indoor set-point temperatures, thermal mass reduces thermal transmission. The impact of thermal mass is also investigated for several climatic conditions in Saudi Arabia. Simulation results show that an internally exposed thermal massive wall section results in greater energy consumption when compared to a similar building with isolated thermal mass (i.e. insulated internally). This is due to the fact that even though the internal temperature inside the building is being cooled/warmed up to the set-point, the thermal mass continues to transfer heat that is absorbed by the building's fabric from/to the interior, placing a greater demand on the cooling/heating system. Over the course of a year, however, the impact of thermal mass is negligible when compared to other factors, such as the insulative properties of the building's fabric. [ABSTRACT FROM AUTHOR]

• Raj et al.'s gravity scaling parameters can't be applicable to the controlled wall heat flux condition. • Microgravity boiling mechanisms on chip S 2 × 2 transform from the SDB to BDB regime. • m BDB for controlled wall temperature condition is larger than that for controlled wall heat flux condition. • m BDB for controlled wall heat flux boiling is affected by both T * and L h / L c. • Gravity scaling parameters for controlled wall heat flux boiling were developed. With the ability of dissipating large amount of latent heat in nearly isothermal process, pool boiling heat transfer is an efficient solution for cooling problem of different sized electronic devices in different gravities. For the practical heat dissipation of electronic device usually occurs at controlled wall heat flux condition, it is essential to reveal pool boiling heat transfer characteristics at different sizes and gravities under controlled wall heat flux condition. In this paper, boiling heat transfer mechanisms on two sized smooth silicon chips (chip S 1 × 1 and chip S 2 × 2) in ground gravity and microgravity were studied. It was found that the gravity scaling parameters developed under controlled wall temperature condition cannot be applicable to the controlled wall heat flux condition. Under controlled wall heat flux condition, the microgravity boiling heat transfer performance on chip S 1 × 1 is in surface tension dominated boiling (SDB) regime in the whole heat flux range. While for chip S 2 × 2, it is in SDB regime when heat flux is smaller than 6.44 W·cm−2, but enters into buoyancy dominated boiling (BDB) regime when heat flux is larger than 6.44 W·cm−2. The critical point of the two boiling mechanisms occurs when the threshold gravitational acceleration equals to the experimental microgravity. In BDB regime, the power law coefficient reflecting the gravity effect on nucleate boiling heat transfer performance (m BDB) for controlled wall temperature condition is larger than that for controlled wall heat flux condition, indicating a greater impact of gravity level under controlled wall temperature condition. Moreover, m BDB for controlled wall temperature condition is affected only by non-dimensional wall temperature T *. While for controlled wall heat flux condition, m BDB increases with increasing T * but decreases with increase in heater size, and heater size has a greater influence on m BDB. Based on the available data, the gravity scaling parameters for controlled wall heat flux boiling were developed, which can accurately predict the microgravity boiling heat transfer performance on two sized chips. [ABSTRACT FROM AUTHOR]

The effective thermal management of the heat generating components is important for job scheduling in multi core processors used in several electronic devices. In the present paper, natural convection in an enclosure with alternately active heat sources for different switch over time period is studied. Laminar, incompressible 2-D code with Finite Volume Method (FVM) has been used to solve the transient equations of continuity, momentum and energy. The study is limited for the Rayleigh number (Ra) varying from 10 3 to 10 6 and Prandtl number of 0.71. For the range of Rayleigh number and time period studied here, heat transfer is found to be more than that of the steady operation of a single heater for all switch-over time periods. Some nonlinear characteristics on hydrodynamics and heat transfer are observed at higher Rayleigh numbers for longer switchover time period. The analysis also shows that the decrease in time period results in increase in heat transfer. [ABSTRACT FROM AUTHOR]

The paper examines implementation of heat saving measures in buildings in 2050, under the assumption that heat and power supply comes solely from renewable resources in Denmark. Balmorel – a linear optimisation model of heat and power sectors in Denmark is used for investigating economically viable levels of heat savings, which can be implemented by reducing heat transmission losses through building elements and by installing ventilation systems with heat recovery, in different future Danish heat and power system scenarios. Today almost 50% of heat demand in Denmark is covered by district heating. A further expansion of district heating network in Denmark is assessed and penetration of heat savings is analysed in this context. If all heat saving measures, included in the model, are implemented, heat demand in Danish buildings in 2050 could be reduced by around 40%. Results show that it is cost effective to reduce from approximately 12% to 17% of future heat demand in buildings depending on assumed lifetime and costs of heat saving measures. Individual heating areas have higher penetration of heat savings than district heating areas. When district heating systems are expanded, an overall penetration of heat savings slightly decreases along with lower capacity investments and system costs. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a numerical study of heat transfer from spheres settling under gravity in a box filled with liquid. Three-dimensional Lattice Boltzmann Method is applied to simulate fluid-particle interaction. Firstly the developed numerical model is validated in comparison with experimental and numerical data for a falling sphere in a box filled with liquid. Then the effects of Reynolds, Prandtl and Grashof numbers (Re, Pr, Gr) are investigated for a settling particle at fixed/varied temperature. The time variations of velocity, height and Nusselt number of the settling particle are also investigated. The results depict that the maximum settling velocity of the particle at varied surface temperature is higher at lower Reynolds numbers. As the Reynolds number increases, the settling velocity of the particle for both cases of constant and varied temperature is the same. However, the Nusselt number of the particle at varied temperature is lower compared with that for the particle at constant surface temperature. Increasing the Grashof number leads to slower settling and larger average Nusselt number. Finally sedimentation of 30 hot spherical particles in an enclosure and their hydraulic and heat transfer interactions with the surrounding fluid are studied. The results depict how the presence of heat transfer phenomena can significantly alter the behavior of settling particles. [Copyright &y& Elsevier]

• A new enclosed melting system was built for deicing the bottom of a train. • A new method was used for simulating gravity shedding melting in complex models. • The effect of supply air properties on system performance was studied. In winter, a large amount of icing and snowing occurs in outdoor equipment and systems, which adversely affects their lifespan. The melting process is divided into two parts: convection melting and gravity shedding melting. This paper is based on an experiment with a real high-speed train unit, and it establishes a three-dimensional computational fluid dynamics model of the bogie area to validate the mathematical model of the winter ice melting experiment. A numerical simulation was used to calculate the airflow in the baffle-enclosed space and to predict the effects of interactions between air and the ice body on heat transfer and phase change. The influence of air velocity and temperature on the heat transfer was analyzed. The computational simulation effectively quantifies the amount of heat transfer and energy consumption under different conditions. This paper also presents a research method for the simulation of gravity shedding in complex models. These models provide information for the construction of similar ice melting models. This paper has suggested that for thin ice bodies, convection melting was the dominant strategy. For thick ice bodies, however, gravity shedding melting became dominant. The study also confirmed that enclosed hot-air ice-melting systems gave a better energy performance than unenclosed systems. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the experimental study on transient heat transfer at boiling and development of crisis phenomena in the falling film of subcooled liquid at stepwise heat generation. Experimental data with a high temporal and spatial resolution were obtained with the use of high-speed infrared thermometry and high-speed video recording synchronized simultaneously. It is shown that at vapor bubble appearance and condensation the convective streams are formed there, which lead to a decrease in temperature in the area behind the active nucleation site and local increase in heat transfer intensity. At the same time on the free surface of liquid film the so-called “temperature waves” propagating along the liquid flow are formed. The boiling curves were obtained on the basis of experimental data, and comparison with the known models for description of heat transfer at pool boiling of saturated liquid was performed. It is shown that mechanism of appearance and development of crisis phenomena depended significantly on the Reynolds numbers. Crisis development at high Reynolds numbers relates to dry spot formation at quasi steady-state boiling and their following expansion by the mechanism of longitudinal heat conductivity in the heating wall. The wave development on the free surface at low Reynolds number (Re =601), studied in current research, leads to the breakdown of the film without nucleate boiling due to the action of thermocapillary forces. The critical heat fluxes under these conditions are significantly lower than the critical values obtained for high Reynolds numbers at boiling in the falling films of subcooled water. [Copyright &y& Elsevier]

Abstract: This paper is focused on simultaneous two-dimensional temperature and velocity field measurements to study heat transfer processes of ambient temperature nitrogen jets impinging on a heated wall. Instantaneous temperature fields were measured by laser-induced fluorescence (LIF) of toluene seeded as a tracer in the nitrogen carrier flow. High repetition rate particle image velocimetry (PIV) data were recorded simultaneously to investigate interactions between velocity and temperature fields. Different heat transfer phenomena were observed by parametric variation of Reynolds number, turbulence intensity and surface temperatures. Whereas laminar flows at low Reynolds numbers exhibited a smooth thermal boundary layer, highly dynamic flares were observed ejecting hot gas from the near wall region into the free stream at increased Reynolds numbers. Rotating vortex structures were identified as the leading source of flare generation. Additionally, turbulent heat flux was quantified and shown to significantly contribute to increased heat transfer rates. [Copyright &y& Elsevier]

Abstract: This paper studied the annual thermal performance of a photovoltaic wall (PV wall) mounted on a multi-layer façade. Based on some developed unsteady-state heat transfer models for a PV wall and a normal wall, the annual thermal performance of two types of walls was simulated. Compared with a normal wall, the south-facing PV wall could reduce heat gain through the envelope by 51% in summer under Hong Kong weather conditions. The impact of the PV wall on the envelope’s heat gain and heat loss in winter was investigated for the first time, and the results indicated that the PV wall could not only significantly reduce the heat gain through the envelope in daytime, but also reduce the heat loss at nighttime. The heat gain and heat loss through the PV wall in winter were reduced by 69% and 32% respectively compared with a normal wall. Totally, an annual thermal energy consumption reduction of 52.1kWh was achieved by replacing each square meter of a south-facing normal wall by a PV wall, which is equivalent to a saving of 18.6kWh of electric energy for the air conditioning system in a building. The impact of the thickness of an air duct on the thermal performance of the PV wall was also discussed. [Copyright &y& Elsevier]

Abstract: EHD effects on bubble nucleation and its subsequent growth dynamic on a small heater in pool boiling of R113 are investigated experimentally in this paper. The small heater, 5mm×5mm in size, is made of an ITO film consisting of Pyrex glass and ITO-coatings. A non-uniform electric field is generated by a vertical needle at high potential and the small heater at low potential as electrodes. A high-speed camera is used to record the changing shape of a single R113 vapor bubble during its nucleation and its subsequent rise from the small heater at different heat fluxes with and without an externally imposed electric field. Effects of electric field strength and imposed heat flux on the bubble growth time, waiting time, departure frequency, dynamic contact angle and movement of triple contact line are presented. It is found that the electric field enhances nucleate boiling heat transfer of a single R113 bubble in the present experiment. [Copyright &y& Elsevier]

Abstract: The falling film liquid desiccant air conditioning system is a promising technology. The wetted area, as a key factor affecting the system performance, is significantly influenced by the plate surface temperature. With a single channel internally heated regenerator, this paper experimentally investigated the impact of plate temperature on the wetted area and system performance, by obtaining the film area and temperature with a thermal camera. LiCl was chosen as the desiccant. By reducing the film contraction in the transverse direction, the increase of plate surface temperature could enhance the wetted area significantly, especially for the low solution mass flow rate. The growth rate of area increased from 0.0017 to 0.0022m2/°C when the flow rate reduced from 0.062 to 0.034kg/s. The regeneration performance also increased with the temperature. A theoretical model with an analytical solution was developed to obtain the wetted area by describing the film contraction caused by the Marangoni effect. A good match was observed for the prediction and experimental results, with an average error of 10.8%. Furthermore, the wetted width was numerically found to also increase with the decrease of film thickness and contact angle, and its change with the solution concentration was slight. This research helps researchers and engineers to accurately predict the wetted area of falling film and to improve the heat and mass transfer performance of liquid desiccant regeneration system. [Copyright &y& Elsevier]