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• The v shape pressure reflects interaction relations among 3 thermodynamic mechanisms. • FFC reflect the intensity and rate of progress of flash at unique start stage. • The factors influencing flash rate and intensity are analyzed. • FFC rises with initial temperature and valve opening degree at unique start stage. • Expanders with larger outlet area or higher working temperature have larger flash intensity. Our experiments showed that a V shape pressure drop appeared at start stage of non-equilibrium flash. V shape pressure drop firstly denoted the generating of superheat degree, which should be the starting force driving the non-equilibrium flash. Then evaporated vapor made up the pressure drop. Finally, a dynamic equilibrium was reached between the flash rate and the outflow rate, and the pressure behaved decreasing gradually. However, few published references focus on this start stage of the non-equilibrium flash. In this paper, experiments of the flash were conducted to investigate the heat and mass characteristics during V shape start stage. Dimensionless flash conversion coefficient (FCC) was proposed to normalize the flash with different initial liquid mass at start stage. The effects of initial temperature and the valve opening degree on the heat and mass characteristics of flash during the V drop start stage were studied. The results showed that the pressure of the working fluid changed dramatically during the V drop start stage. The peak of instant liquid superheat was proportional to the opening degree of the valve, which controlled the outflow rate. The flash rate increased with increasing initial temperature and valve opening degree, which had an approximately linear relationship with the flash time. FCC increased with valve opening degree. It could be deduced that flash intensity or flash rate would be higher for an expander with larger outlet area or higher working temperature. [ABSTRACT FROM AUTHOR]

• Interfacial damage of two DBBT with four interfacial CZMs under various environment conditions were analyzed. • The outdoor nature experiment was conducted to verify the transient heat transfer model of the DBBT. • The damage factors of the unitized DBBT are much larger than those of the longitudinal DBBT under evaluated temperatures. • The first and second interfaces have different damage development after considering interfacial CZMs. • Thermal responses of two DBBT increase with the increase of humidity coupling with temperature. The natural environment has a great effect on the interfacial bonding performance of ballastless track in high-speed railways, and the interfacial damage analysis models of the double-block ballastless track (DBBT) on subgrade with two connections and four interface conditions are proposed in this paper. Firstly, the cohesive zone models (CZM) parameters of two interfaces of the DBBT were calculated and the thermal responses of a 1/4 scaled DBBT in an outdoor natural environment were measured. After the validation of outdoor experimental results, the transient heat transfer models of the unitized and longitudinal DBBT with four interfacial CZMs were then established to study their interfacial damage properties under three elevated temperatures, respectively. Thermal responses of the unitized and longitudinal DBBT are also compared under the coupling effect of high temperature and humidity. Results show that the temperature and longitudinal stress generally decrease from the sleeper to the supporting layer in a natural environment. The CZM has a great effect on interfacial thermal responses, and the stresses of the track slab in the longitudinal DBBT are much larger than those of the unitized DBBT under three elevated temperatures. More importantly, the damage factors of the two interfaces of the unitized DBBT are much larger than those of the longitudinal DBBT, and the interfacial damage development of the two interfaces of the unitized DBBT is different from the longitudinal DBBT. In addition, the coupling effect of a high temperature and humidity could effectively increase the thermal responses of the track slab for two DBBTs, especially for the higher humidity that exceeds RH=65 % of the unitized DBBT. [Display omitted] [ABSTRACT FROM AUTHOR]

• We proposed one novel PV/T system – the iron filing filled tube plate PV/T system. • The performance of the iron filing filled system was researched. • The experimental results show that it improves the heat transfer. This paper proposes a novel photovoltaic/thermal (PV/T) system – the iron filing filled tube plate PV/T system (IFTP system), for solar energy collection efficiently. In the system, the Tube plate solar collector is adopted to convert solar radiation to electricity and thermal energy simultaneously. To improve the structure of the traditional tube plate PV/T module, this paper presents a new tube plate PV/T module which filled with iron filings instead of air between the absorbing plate and fluid channel to increase the heat transfer between the fluid and photovoltaic cells. After that, an IFTP system is constructed and tested according to the related standards test under laboratory conditions. Experimental research is carried out under five groups of different radiation intensity (400–800 W/m2). The experimental results demonstrate that the temperature of IFTP module in effectively reduces by 3.5–6.5 °C, and the photoelectric efficiency increases by 19.8% compared with traditional tube plate PV/T system. The IFTP system takes a shorter period of time to achieve the same temperature difference of tanks. [ABSTRACT FROM AUTHOR]

This paper is the first in a series of papers describing the temperature fields created by a circular area heat source (CHS) in various situations. In this paper, the derivation of the solution of the 3D transient heat flow from an embedded finite CHS supplying heat to an infinite medium is shown by employing different methods. The different adopted techniques include Laplace, Hankel and Fourier Cosine transforms, and solutions are based on first principles with minimum assumptions. Both isotropic and orthotropic infinite media are considered. Finite element simulations performed in COMSOL Multiphysics are provided and compared with the analytical solutions, with deviations between analytical solution and simulation of <1 mK for a typical temperature rise of 1 K. Fitting of the numerical results with the analytical solutions is performed to extract the thermal transport properties of the media, which are found to deviate by a maximum of 1.7% for all considered cases. [ABSTRACT FROM AUTHOR]

Cell to pack design concept for energy storage in automotive applications leads to a substantially increased cell size that results in temperature gradients over the surface induced by non-uniform heat transfer linked to the cooling system design, which influences the cell performance. In this paper, temperature gradient effects on life performance of a large-format cell are experimentally investigated, using a developed device that can actively control appropriate gradients in the longitudinal direction and simultaneously measure the heat generation rate (HGR). Performances under uniform and non-uniform temperature conditions (MMM: uniform temperature, LMH: low-mean-high, HLH: high-low-high) are compared and quantified. At beginning of life (BOL), the low-temperature regions in the HLH and LMH conditions dominantly limit the cell capacity, and the HLH condition suppresses the HGR at high C-rates. During aging, the cell experiences a larger capacity fade and HGR increase under the HLH than MMM condition. The analyses of half coin cell, differential capacity (dQdV), dynamic resistance and impedance reveal that the attributing mechanisms are mainly the loss of Cathode active material, potentially the loss of lithium inventory, and the increase of impedances, indicating the electrochemically promoted side reactions and corrosions in the high-temperature regions of the HLH condition. • A calorimeter with controlled temperature gradient is developed. • Heat generation rates under temperature gradients are quantified and compared. • Cell teardown, dQdV, dynamic resistance and impedance analyses are conducted. • Temperature gradient effects on cell performance during aging are analyzed. [ABSTRACT FROM AUTHOR]

With the increasing demand for oil storage, storage tanks are developing towards large-scale tanks better adaptability to extreme working conditions. The variation law of the oil temperature field and the flow field inside the tank should be accurately understood to guarantee safe and economical operation of an oil depot. Aimed at understanding the periodic variation in the ambient environment of the tank’s location and the physical properties of the crude oil, the theoretical model of unsteady heat transfer flow in a large floating roof tank was established by using the relative heat transfer theory in this paper. The numerical solution technique for the crude oil temperature field and the flow field was studied. This paper thoroughly analyzed the effect of heat transfer and flow coupling characteristics on the tank static storage process under the influences of the atmospheric temperature, solar radiation, etc. The results show that according to the variation law of the temperature field, the static storage cooling process was divided into a partial rapid cooling stage, overall rapid cooling stage, condensate reservoir growth stage and overall low-speed cooling stage. The heating process was divided into a partial low-speed heating stage and partial rapid heating stage. The solar radiation has a great influence on the temperature fluctuation, and the atmospheric temperature has a great influence on the rate of temperature decrease. The results can provide theoretical support for optimizing the design of the storage process and managing the manufacturing of a large floating roof tank. [ABSTRACT FROM AUTHOR]

In previous study on the flow of fractional viscoelastic fluid between two coaxial cylinders, due to the complexity of computation, researchers commonly assume that the flow area is a rectangular pipe. This paper studies two-dimensional magnetohydrodynamic (MHD) flow and heat transfer of fractional Oldroyd-B nanofluid between two coaxial cylinders with variable pressure. The boundary layer fractional cylindrical governing equations are firstly formulated and derived. Meanwhile, the numerical solutions are obtained by using the newly developed finite difference method combined with L1-algorithm, whose validity is confirmed by the comparison with the exact solution constructed. Results show that the fractional derivative parameters α 1 , β and exponent parameter δ related to the wall temperature have significant effects on velocity and temperature fields. Specifically, the velocity decreases with the augment of α 1 , but increases as β rises up. The temperature profiles intersect each other for different δ. Meanwhile, increasing δ leads to an increase in temperature near the wall of inner tube, but a decline near the outer cylinder, which demonstrates increasing exponent parameter can enhance heat transfer. [ABSTRACT FROM AUTHOR]

In this paper, based on the porosity characteristics of the recycled aggregate (RA) interface, the response rule and response mechanism of temperature and humidity in interior of recycled aggregate concrete (RAC) with 100% replacement ratio were studied at different temperatures, depth and bending load. Moreover, pore structures were measured to analyze the effect of temperature and relative humidity (RH) by mercury intrusion testing. The results indicated that the RAC temperature response rate was lower than NAC, and decreased from the surface. The RH response rate of the RAC was faster than that of the NAC. The effect of the bending load accelerated the response rate of RH and the cooling rate of the RAC surface but hinder the deep cooling rate. The RA partition-interface heat moisture transfer model was proposed for RH hysteresis effect. The response calculation model of temperature and RH of the RAC interior was established. [ABSTRACT FROM AUTHOR]

Actual thermal response tests, used to estimate the subsurface thermal conductivity in the geothermal domain, do not provide any estimate on the velocity of the groundwater flow and its orientation. These parameters are important for sizing geothermal borefield, since they influence the heat transfer around a geothermal borehole and the surrounding ground. To correct this shortcoming, a conceptual test has been developed in which heating cable sections inject heat in a borehole. Three temperature probes are strategically located at the borehole edge. This paper applies inverse heat transfer strategies to this thermal response test concept in order to identify the ground thermal conductivity, as well as the groundwater flow velocity and its direction. The suggested thermal response test and parameters estimation methodology are detailed. The influence of initial guessed values for the three unknown parameters was also studied. The work presented in this paper was carried out by numerical simulations. [ABSTRACT FROM AUTHOR]

The submerged combustion vaporizer (SCV) is indispensable general equipment for liquefied natural gas (LNG) receiving terminals. In this paper, numerical simulation was conducted to get insight into the flow and heat transfer characteristics of supercritical LNG on the tube-side of SCV. The SST model with enhanced wall treatment method was utilized to handle the coupled wall-to-LNG heat transfer. The thermal–physical properties of LNG under supercritical pressure were used for this study. After the validation of model and method, the effects of mass flux, outer wall temperature and inlet pressure on the heat transfer behaviors were discussed in detail. Then the non-uniformity heat transfer mechanism of supercritical LNG and effect of natural convection due to buoyancy change in the tube was discussed based on the numerical results. Moreover, different flow and heat transfer characteristics inside the bend tube sections were also analyzed. The obtained numerical results showed that the local surface heat transfer coefficient attained its peak value when the bulk LNG temperature approached the so-called pseudo-critical temperature. Higher mass flux could eliminate the heat transfer deteriorations due to the increase of turbulent diffusion. An increase of outer wall temperature had a significant influence on diminishing heat transfer ability of LNG. The maximum surface heat transfer coefficient strongly depended on inlet pressure. Bend tube sections could enhance the heat transfer due to secondary flow phenomenon. Furthermore, based on the current simulation results, a new dimensionless, semi-theoretical empirical correlation was developed for supercritical LNG convective heat transfer in a horizontal serpentine tube. The paper provided the mechanism of heat transfer for the design of high-efficiency SCV. [ABSTRACT FROM AUTHOR]

Abstract The constant undisturbed formation temperature profile controlling heat transfer into the wellbore appears counterintuitive in light of transient cooling of the formation that occurs upon fluid circulation in drilling and also heating during fluid production. This study presents a mathematical model that shows that the heat transfer occurs from the wellbore/formation interface, not from some distance away from the wellbore wherein the initial formation temperature profile remains undisturbed. This new model allows investigation of heat transfer behavior from the formation into the wellbore during drilling or fluid circulation, and from the wellbore into the reservoir in the production mode. Application of the line-source solution for the temperature diffusivity equation for a steady-state system provides the necessary ingredients for computing the temperature behaviors at different times and radii. This line-source solution can be used throughout the wellbore to determine the undisturbed formation temperature, which may be used to obtain the geothermal gradient dependent on the radius and fluid circulation time. Therefore, the initial geothermal gradient works as a time-dependent variable, and the resultant second-order polynomial relationships can describe the undisturbed formation temperature. This study provides the required tools to assess the wellbore heat-transfer behavior and their effect on the wellbore temperature profiles. Also, the new mathematical model illuminates the impact of heat transfer by comparing its performance with the original formulations. Besides, this paper presents a complete derivation of the line-source solution of the temperature diffusivity equation to justify the proposed approach. Highlights • New models proposed for variable near-wellbore geothermal gradient during fluid circulation and production. • Models are rooted in the line-source solution of the temperature diffusivity equation. • Initial formation temperature at the well bottom and geothermal gradient depend on operational time. [ABSTRACT FROM AUTHOR]

Highlights • Discrete unified gas kinetic scheme for multiscale heat transfer with arbitrary temperature difference is developed. • The Newtonian method is used to handle the nonlinear relation between the equilibrium state and the temperature. • The present scheme can predict the multiscale heat transfer problems accurately and its time step is not restricted by the relaxation time. • The effects of large temperature difference are numerically investigated in different length and temperature ranges. Abstract In this paper, a finite-volume discrete unified gas kinetic scheme (DUGKS) based on the non-gray phonon transport model is developed for multiscale heat transfer problem with arbitrary temperature difference. Under large temperature difference, the phonon Boltzmann transport equation (BTE) is essentially multiscale, not only in the frequency space, but also in the spatial space. In order to realize the efficient coupling of the multiscale phonon transport, the phonon scattering and advection are coupled together in the present scheme on the reconstruction of the distribution function at the cell interface. The Newtonian method is adopted to solve the nonlinear scattering term for the update of the temperature at both the cell center and interface. In addition, the energy at the cell center is updated by a macroscopic equation instead of taking the moment of the distribution function, which enhances the numerical conservation. Numerical results prove that the present scheme can describe the multiscale heat transfer phenomena accurately with arbitrary temperature difference in a wide range. In the diffusive regime, even if the time step is larger than the relaxation time, the present scheme can capture the transient thermal transport process accurately. Compared to that under small temperature differences, as the temperature difference increases, the variation of the temperature distribution behaves quite differently and the average temperature in the domain increases in the ballistic regime but decreases in the diffusive regime. [ABSTRACT FROM AUTHOR]

Highlights • A tree-shaped well by fracture-connected way is proposed to improve heat extraction efficiency. • The conceptual model designed is superior to doublet model. • Well's performance is affected by rock matrix permeability and injection temperature. • Distance between injection and production wells affect production temperature. Abstract A reasonable well structure can help to extract heat from the Hot Dry Rock (HDR) reservoir effectively. A tree-shaped well by the fracture-connected way is proposed to improve the efficiency of heat extraction from the geothermal reservoir. The numerical analysis of various factors based on the local thermal equilibrium method and the established model is verified by the Lauwerier's solution. The production temperature, heat extraction ratio, reservoir impedance, injection pressure, heat production power and electric power are engaged in the paper as the assessment criterion. In addition, the comparison results show that the conceptual model is superior to doublet model. Because the conceptual model has a lower flow impedance of 0.13 MPa/(kg/s) and a higher extraction ratio of 0.47, which is greater than that of doublet model. The performance of the conceptual model is significantly affected by the average perpendicular distance between the injector and producer, rock matrix permeability and injection temperature. Based on the base model, what is really significant is that the distance set as 575 m and the injection temperature set as 333.15 K when the reservoir permeability is 1 × 10−14 m2. This study can provide an alternative plan to extract larger geothermal energy in the future. [ABSTRACT FROM AUTHOR]

Highlights • CFD simulation of flow blockage accident and its induced heat transfer impairment is performed. • Three dimensional distributions of fluid and solid temperature downstream the blockage are obtained. • The influence from the blockage area and its location on the temperature peaks and inter-channel mixing is analyzed. Abstract Flow blockage accident is a severe accident. When fuel assembly is partially or totally blocked, the heat transfer between coolant and cladding is significant impaired due to a rapid decrease of coolant flow, which leads to a local increase of cladding and coolant temperature and possibly results in a release of fission products. A recirculation region is formed downstream the blockage and a temperature peak can be found in this region. In this paper, CFD modelling and simulation for a LBE-cooled 19-pin wire-wrapped bundle were carried out to consider the influence from the flow blockage on the rod surface temperature and cross flow. Three-dimensional flow and temperature distributions of LBE were obtained using commercial CFD software. The influence from the blockage area and its location was investigated as well as the axial length of blockages. It was found that flow blockages in the center of bundle result in a higher surface temperature while comparing with blockages in the side sub-channels. The cross flow between sub-channels through gaps has been evaluated and their dependency on the blockage area is also evaluated based on CFD simulation results. [ABSTRACT FROM AUTHOR]

Abstract This paper aimed to develop a computational fluid dynamics simulation for an industrial boiler. The industrial boiler is used for the sulfuric acid production. A numerical model is carried out using the commercial code "ANSYS-FLUENT". The simulations are developed for the case of the industrial boiler and a new proposed design. A clear understanding of the combustion phenomenon and the fluid flow within the boiler is provided from the simulations. The local characteristics of the fluid flow and the heat transfer such as the temperature; the velocity magnitude and the density distributions are presented and analyzed. The comparison between the numerical results and the experimental data is performed and a good agreement is found. Highlights • A numerical simulation is developed for an industrial boiler. • The fluid flow and the heat transfer characteristics are analyzed and discussed. • The numerical model is validated by comparison between numerical results and industrial measurements. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The interaction of two drops is studied experimentally: a small droplet falls on a large sessile drop located on a hot wall. The temperature of the falling droplet is 20 °C, and the wall temperature is 80 °C. It is well known that the surfactant suppresses the Marangoni flow (Ma). This paper considers the influence of surfactant in the presence of several key factors – dynamic and thermal ones. When a droplet impacts a liquid layer, the heat and mass transfer is associated with both the dynamic factor (inertial forces and pressure "jumps" inside the droplet) and the thermal factor (an increase in the surface temperature gradient). The novelty of this work is that it for the first time shows that at the moment of extremely short-term interaction of drops, there is 7–8 times increase of velocity inside the drop. In this case, the determining effect on the convection enhancement is associated with thermocapillary convection, and the role of the dynamic factor is insignificant. The influence of graphite particles and surfactant of sodium dodecyl sulphate (SDS) has been investigated. The velocity "jump" resulting from the fall of the water droplet with surfactant is 4 times smaller as compared to the fall of surfactant-free droplet. The instantaneous velocity fields inside the sessile drop have been experimentally studied using Micro Particle Image Velocimetry (Micro PIV). The obtained results are of great importance for the correct modeling of heat and mass transfer and have a wide application for sprays, as well as for the multiphase flows. [ABSTRACT FROM AUTHOR]

Abstract Diminishing fossil fuel resources have intensified the need for energy saving. Heat transfer is a basic method of energy delivery and convention, and heat transfer during the transient processes may be affected by the dynamic performances of heaters. Analysis of the heater performances during the transient process based on the second law of thermodynamics may show the room for the improvement in energy saving. Variations of boundaries, such as the flow rates and temperatures of the work fluids, may affect the dynamic behaviors of heaters. The variation rates, formats and ranges of the inlet work fluids flow rates and temperatures on the irreversibility and exergy delivery characteristics are discussed in this paper. The average exergy efficiency (η E,avg) of the heater during the transient process with different operational parameters are presented and compared. The results show that, in the identical variation range, the maximum difference in η E,avg with different flow rates and temperature variation rates of the cold work fluid are 0.3% and 0.4%, respectively. With step variation format, the maximum difference in η E,avg for the different variation ranges of the cold work fluid is 0.85%. Highlights • Real-time entropy generation rate of the heater is studied during the transients. • Effects of the variation rate and range for the controlled parameters are explored. • Step and ramp variation formats are selected to exhibit the dynamic behaviors. • Influences of the operational parameters on the exergy efficiency are studied. [ABSTRACT FROM AUTHOR]

Highlights • An experiment of wall-to-bed heat transfer in SCW fluidized bed was conducted. • Effects of velocity, temperature and pressure on heat transfer were discussed. • A wall-to-bed heat transfer correlation in SCW fluidized bed was proposed. Abstract Supercritical water (SCW) fluidized bed is a new reactor concept for hydrogen production from biomass or coal gasification. This paper presents an experimental study of wall-to-bed heat transfer characteristics for Geldart-B particles in SCW fluidized bed with the conditions of pressure ranges from 22.3 MPa to 25.7 MPa and temperature ranges from 651 K to 730 K. The effects of velocity, temperature and pressure on wall-to-bed heat transfer coefficient in SCW fluidized bed were discussed. The wall-to-bed heat transfer coefficient was found to be positively correlated with velocity and pressure, while negatively correlated with temperature within present experimental conditions. A dimensionless analysis was conducted using the Buckingham-theorem to derive the general form of an empirical wall-to-bed heat-transfer correlation in supercritical water fluidized bed for the Nusselt number, which was finalized based on the experimental data. What's more, the sold phase contributes more to the wall-to-bed heat transfer in SCW fluidized bed and the presence of solid phase enhances the heat transfer of SCW phase, which can be concluded from comparison of heat transfer between SCW fluidized bed and single phase of SCW. The experimental results and the proposed correlation in present work are useful for the design of SCW fluidized bed reactor. [ABSTRACT FROM AUTHOR]

Highlight • An idealized model of the Stirling/pulse tube cryocooler is established. • The second stage decreases the gross cooling capacity of the first stage. • The first stage may produce heat though the phase of the piston lags the displacer. • The mechanism of inter-stage cooling capacity shifting is revealed. Abstract A Stirling/pulse tube hybrid cryocooler (SPC), comprised of a Stirling cryocooler as the first stage and a pulse tube cryocooler as the second stage, features the ability of shifting cooling capacity between stages by adjusting the movement of the displacer in the first stage. Such an ability allows an SPC to accommodate itself to time-varying heat loads at different temperatures, which makes it a competitive candidate in space applications. However, due to the gas coupling, there exists a significant mutual effect between stages which endows an SPC with special thermodynamic characteristics and has a significant effect on the SPC's capability of shifting cooling capacity between stages. With the phasor analysis and the thermodynamic analysis, this paper establishes an idealized model of an SPC. The model is then used to study the effect of the second stage on the first stage and reveal the condition that an SPC is able to shift cooling capacity between stages. Also, the model is compared with a Sage numerical model and the two models are consistent on the overall trend. Though it is unable to reflect reality precisely, the idealized model can interpret the mechanism and highlight some of the essential nature of an SPC, which will eventually benefit the appropriate design of an SPC. [ABSTRACT FROM AUTHOR]

Highlights • Effects of slip velocity and wall temperature on temperature jump condition are investigated. • Modified Patterson temperature jump condition is proposed by involving viscous heat generation. • This modified jump condition can predict the surface gas temperature for the airfoil case Kn = 0.26. Abstract Recently, new type of the Smoluchowski temperature jump condition has been proposed by considering viscous heat generation in rarefied gas flow simulations, and improved prediction of the surface gas temperature in comparing with DSMC data. Two forms of the Patterson jump condition have been revisited for rarefied gas flow simulations in the literature. In this paper, the modified Patterson temperature jump condition is proposed by considering viscous heat generation. We numerically investigate the effect of the slip velocity, the wall temperature and viscous heat generation on the surface gas temperature for external high-speed rarefied gas flow simulations by using various forms of the Patterson jump condition. Three configurations such as the sharp leading-edge flat plate, the sharp 25–55-deg biconic, and micro-airfoil NACA0012 are selected for simulations with Mach number from 2 to 15.6, and Knudsen number ranging from 0.04 to 0.26. The simulation results obtained show that the modified Patterson jump condition gives good agreement with the DSMC data, and predict temperatures better than those of new type of the Smoluchowski jump condition for all cases considered. [ABSTRACT FROM AUTHOR]

Wedge-shaped hot-films are a promising alternative to hot-wires for supersonic free flow disturbance measurements if hot-wires cannot be used due to harsh flow conditions. Up to the present, wedge hot-films could not serve as quantitative tools because of an insufficient modelling of the substrate’s influence on the thermal balance. The present paper shows a static calibration of a wedge-shaped hot-film sensor that is based on a combination of an analytical, a numerical and an experimental approach. The substrate’s impact was analysed by the help of CFD simulations and modelled by a newly introduced substrate factor. The obtained sensitivities were discussed and qualitatively explained compared with standard hot-wires. A quantitative comparison of experimentally detected mass flux fluctuations proved the wedge hot-film data to match similar hot-wire results very well. The presented approach has the potential to upgrade hot-films of various shapes to tools for quantitative fluctuation measurements. [ABSTRACT FROM AUTHOR]

Abstract In the acidizing process, the problem of an uneven distribution of acid owing to excessive heterogeneity of carbonate rocks is increasing. Diverting acid with intelligent diverting characteristics is a key technology used to distribute acid uniformly in heterogeneous carbonate reservoirs. The process of diverting an acid stimulation is accompanied by some complex processes, such as a reactive mass transfer, porous media heat transfer, reaction heat release, and changes in the chemical characteristics. The current evaluation model of diverting an acid stimulation in theory has not considered such factors. In addition, an experimental evaluation method is difficult to apply to simulate the formation conditions under high temperature and pressure. Therefore, in this paper, we first evaluate the rheological properties of a novel VES diverting acid, and then establish an equation of acid viscosity change under the influence of multiple factors. Finally, a multi-reservoir diverting acidizing model with comprehensive consideration of the heat transfer, mass transfer, and chemical properties was established, and the effects of diverting the acidizing under reservoir conditions was simulated and analyzed. An experimental evaluation of novel VES diverting acid shows that the growth of a secondary wormhole is longer and the dissolution morphology is more uniform than that of the main wormhole. During the process of diversion, there is an obvious protrusion in the pressure drop curve of the acid. The simulation and analysis results show the following: The simulation of acid entering into multiple layers shows that diverting the acid can effectively increase the amount of acid entering into the low permeability layer, which results in a better development of a wormhole in a low permeability layer. It also reduces the non-uniformity of the acid distribution between the layers. The effects of the bottomhole temperature on the diverting acid viscosity exceed the effect of the reaction rate and the diffusion coefficient, which results in a higher bottomhole temperature, and worse diversion effect. The injection displacement of acid has a slight effect on the diverting effect. The higher the displacement, the better the effect of diversion. The heterogeneity of a formation has a significant effect on the diverting effect, namely, the higher the heterogeneity, the weaker the effect. Highlights • The diverting acidification model couples the near-well heat transfer model. • The new performance criterion R ahl value of diverting acid is constructed. • We propose that prepad fluid should be added to decrease the bottomhole temperature to achieve the better diversion effect. [ABSTRACT FROM AUTHOR]

This paper conducts an investigation on the temperature variations experienced by the fuel when it expands through the calibrated orifices of a commercial diesel injector. Experimental results of the temperature change across a calibrated orifice upon expansion, extracted from a previous work, are compared to the temperature predicted by computational fluid dynamic simulations under the assumption of adiabatic flow, with no heat transfer to the surroundings. The comparison points out that the simulations are able to predict the thermal effects taking place inside the orifice. Once the model is validated, the flow morphology is analyzed to explain the trends observed in the fuel temperature change across the orifice depending on the operating conditions. Two opposed effects take place inside the orifice: on the one hand, the flow is cooled in the orifice core due to depressurization; on the other hand, the fuel is importantly heated near the walls due to viscous friction. As expected, the net effect on the outlet temperature mainly depends on the orifice discharge coefficient, governed by the orifice geometry and the flow regime (Reynolds number) induced by the injection conditions. Next, the analysis is extended to a diesel nozzle, considering that the higher pressure drops achieved in it are expected to induce even more important thermal effects. The two opposed effects also take place inside the orifice. Even though their net effect is similar, the separate effect of each phenomenon is greater, leading to differences that could be relevant for the atomization and spray formation processes. Additionally, the flow pattern shows a non-uniform distribution of the flow inside the nozzle influencing the results from the thermal point of view. [ABSTRACT FROM AUTHOR]

In the present paper, several experimental and theoretical studies conducted on the thermal conductivity of nanofluids are represented and investigated. Based on the reviewed studies, various factors affect thermal conductivity of nanofluids such as temperature, the shape of nanoparticles, concentration and etc. Results indicated the increase in temperature and concentration of nanoparticles usually leads to the higher thermal conductivity of nanofluids. In addition, it is concluded that there are some novel approaches in order to obtain nanofluids with more appropriate thermal properties including using binary fluids as the base fluid or utilizing hybrid nanofluids. [ABSTRACT FROM AUTHOR]

The evaluation of thermal-hydraulics of core under decay heat removal conditions is essential to the safety evaluation of a sodium-cooled fast reactor. The inter-wrapper flow (IWF) has an influence on the thermal-hydraulics of core. However, the study of the flow and heat transfer of IWF was limited. In this paper, a 2D layered IWF model was developed, and some tests were simulated to validate the IWF model, including heat removal tests SHRT-17 and SHRT-45R conducted in the experimental fast reactor EBR-II and a natural circulation test performed during the PHENIX end-of-life experiment. In order to simulate all the components of the primary system, the IWF model is coupled with the Transient Thermal-Hydraulic Analysis Code for Sodium-cooled fast reactors (THACS). In the simulation without IWF model, the predicted peak temperature of the instrumented subassembly XX10 in EBR-II is about 150 K lower than test data, and the predicted average outlet temperature of reactor core in PHENIX is about 20 K higher than test data. While the predictions of THACS with IWF model agree well with the test data. The results show that the IWF can be accurately simulated by the IWF model, and the IWF model improves the accuracy of the simulations of the reactor core. Further, some sensitivity analyses were conducted to provide better reference for the study of sodium-cooled fast reactors. [ABSTRACT FROM AUTHOR]

This study deals with the development of a partitioned coupling strategy at the fluid–solid interface for weakly transient heat transfer problems. The thermal coupling is carried out by an iterative procedure (strong coupling) between a transient solid and a sequence of steady states in the fluid. Continuity of temperature and heat flux is ensured at each coupling time step. Emphasis is put on the choice of interface conditions at the fluid–solid interface. Two fluid–solid transmission procedures are considered in this paper: Dirichlet–Robin and Neumann–Robin conditions. These conditions are theoretically examined and it is shown that the Biot number is a key parameter for determining relevant interface conditions. Stability diagrams are provided in each case and the most effective coupling coefficients are highlighted and expressed. Numerical thermal computations are then performed for two different Biot numbers. They confirm the efficiency of the interface conditions in terms of accuracy, stability and convergence. At the end of this paper a comparison between a partitioned and a monolithic approach is presented. [ABSTRACT FROM AUTHOR]

The integration temperature difference Δ T i considers the heat transfer routes, linking the heat transfer process with the thermodynamic behavior of heat exchangers. The first and second non-dimensional integration temperature differences are defined as Δ T i, h ∗ = Δ T i / T h, i and Δ T i, s ∗ = Δ T i / ( T h, i - T 0 ) respectively, where T h,i is the heat source temperature and T 0 is the environment temperature. This paper is the first to experimentally verify the significance of the non-dimensional integration temperature differences on organic Rankine cycle (ORC) systems. The first non-dimensional temperature difference is shown to have linear relationship with the revised entropy generation numbers ( N s ). With increases of the second non-dimensional integration temperature difference, the expander powers, system thermal and exergy efficiencies had parabola distributions. They simultaneously reached maximum at Δ T i, s ∗ = 0.282 , under which the vapor cavitation in the expander disappears and the exergy losses of heat exchangers are acceptable to elevate the expander efficiency. Beyond the optimal point, the ORC performance is worsened either due to the vapor cavitation in the expander, or due to the poor thermal matches in the evaporator and condenser. The second non-dimensional integration temperature difference comprehensively reflects the effects of heat source temperatures, heating powers and organic fluid flow rates and pressures, etc. It balances exergy destructions of various components to optimize the system. Thus, it can be an important parameter index to maximize the power or electricity output for a specific heat source. The usefulness of the integration temperature difference and the future work are discussed in the end of this paper. [ABSTRACT FROM AUTHOR]

Conjugate heat transfer involving convection and conduction in a fluid flow and a solid body in contact with each other occurs commonly in engineering applications. While analytical solutions for individual convection and conduction problems are relatively easier, it is a lot more challenging to solve the combined conjugate heat transfer problem. In this paper, an iterative method is developed for analytically solving conjugate heat transfer problems. Based on an initial assumption of the temperature field at the solid–fluid interface, the temperature distributions in the fluid and solid body are determined by separately solving the governing energy conservation equations in the two domains. These solutions are used to improve the initial assumption of the interface temperature until convergence. It is found that only a few iterations of this process are needed for convergence. Temperature fields computed from this analytical approach are found to be in good agreement with finite element simulation results. The iterative analytical approach is used to solve two technologically relevant problems related to internal and external flows. Given the general nature of the iterative approach, results from this paper may be helpful in solving a variety of conjugate heat transfer problems. [ABSTRACT FROM AUTHOR]

The accurate prediction of cross-sectional temperatures within concrete filled steel hollow (CFS) sections is critical for the accurate prediction of fire resistance. Whilst there have been many thermal and structural tests conducted on CFS columns, there are few that report the full cross-sectional thermal profile, and when they are reported, the sensor density is low, hindering the ability to validate models. This paper presents furnace tests and thermal modelling on 14 unprotected and 20 protected CFS sections, and examines the effect of several parameters on cross-sectional thermal profiles, as well as assessing the accuracy of both Eurocode thermal analysis guidance and intumescent fire protection design guidance. This paper shows that; (a) the assumptions within the Eurocode guidance can lead to large over-estimations in cross-sectional temperatures; (b) proposes new thermal modelling assumptions in three key areas; and (c) shows that the current intumescent fire protection design guidance is very conservative. [ABSTRACT FROM AUTHOR]

Nonplanar solidification front causes defects in directional solidification process. The transverse temperature gradient, which can be divided into radial temperature gradient and circumferential temperature gradient, is one of the reasons causing the nonplanar solidification front. This paper presents a method by varying the wall thickness of the mould to decrease the circumferential temperature gradient and hence flatten the solidification front. The equations for calculating the wall thickness were deduced by heat transfer analysis. The optimized mould contour was obtained by solving the equations numerically. It was proved by simulation that the circumferential temperature gradient can be almost reduced by 40%. Furthermore, the starting time difference of solidification at one cross section along the circumferential direction almost reduces by half. Additionally, this paper also researches the influences of parameters of the mould and the furnace etc. on the shape of the mould and the circumferential temperature gradient. The circumferential temperature gradient decreases as the thermal conductivity and the emissivity of the mould increase. And the temperature of the cooling ring impacts little on the circumferential temperature gradient. According to the development trend of the blade manufacturing, this method may be applied widely. [ABSTRACT FROM AUTHOR]

Temperature measured from a permanent downhole gauge in a well after the well shut-in provides a unique perspective for surveillance and production management. For example, in deepwater environment, production engineer needs to know the temperature of a shut-in well before it is being restarted since different temperature profiles along the wellbore may need very different restarting strategies for flow assurance purpose. A number from the “rule-of-thumb” or running complicated numerical simulation is either not reliable or impractical. This paper presents a semi-analytical model to estimate the temperature transient behavior after the well shut-in. The temperature at a point along the wellbore, which is useful for production management and flow assurance, is solved and the solution can be easily implemented for calculating temperature history. The temperature profile solution for locations along the wellbore is also presented in the paper. Furthermore, matching the calculated temperature with the measured temperature at the same location will yield the well local heat transmissibility coefficient. The applications of the solution to this model are multiple folders and a deepwater field example is provided to demonstrate some applications and valid the results. [ABSTRACT FROM AUTHOR]

Investigations on severe accident phenomena help us in understanding the realistic accidental phenomena for the assessment of associated risk. The societal impact of radiological leakage to the environment has demanded further robustness in the line of defence of nuclear safety. Thus, to ensure the cooling and stabilization of corium within reactor containment in case of severe accident scenarios, many new reactors have been envisaged with core catcher. In this regard, corium coolability still remains an unresolved issue in spite of several efforts being taken towards its understanding. After studying the various cooling strategies, it has been demonstrated that melt coolability using bottom flooding of water is one of the most efficient techniques so far. To study the effect of decay heat on melt pool coolability under bottom flooding condition, two experiments have been performed in this paper; one without the decay heat and the other with decay heat. The test section used for carrying out these experiments consisted of two parts viz. lower part for retaining the melt from furnace, water inlet and melt quenching, and upper part for steam expansion and its outlet. The total height of the test section was 1400 mm and was made of 33 mm thick carbon steel. Total six stainless steel nozzles of diameter 12 mm were used for injecting water at the bottom of the melt pool. The lower part was surrounded by 10 radiative heaters to simulate decay heat of 10 kW which corresponds to 0.5 MW/m 3 . The experiments showed that quenching of about 25 l of melt at initial temperature of nearly 1200 °C took only a few minutes in both the cases. The debris formed in the experiments ranged between 0.5 mm fine particles to 50 mm porous chunks. The measured porosities were nearly 51% without decay heat and nearly 67% with decay heat. This paper presents the comparative experimental study of melt coolability using bottom flooding without and with decay heat scenarios. The experimental measurements show that the quenching behaviour of melt pool is not affected by decay heat, although stabilization of debris temperatures to saturation temperature takes a bit longer duration as compared to without decay heat scenarios. [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]

This paper discusses the effect of temperature polarization in Vacuum Membrane Distillation (VMD). The main motivation for using VMD in this work is that this module configuration is much simpler and more suitable for this kind of investigation than the other MD configurations such as Direct Contact Membrane Distillation (DCMD). The coupling between heat and mass transfer mechanisms at the feed-membrane interface is presented from a theoretical point of view. In addition, a new simple graphical method and a mathematical model for determining VMD flux are presented. The two methods used in evaluating the extent of temperature polarization effect on water vapor flux (flux sensitivity factors and temperature polarization coefficient (TPC)) are also analyzed and compared. The effect of integrating a heat recovery system in a large scale module on the TPC coefficient has also been studied and presented in this paper. [ABSTRACT FROM AUTHOR]

Abstract: This paper considers the numerical optimization of a T-shaped assembly of fins cooling a cylindrical solid body. The objective is to minimize the maximum excess of temperature between the solid cylindrical body and the ambient. Internal heat generation is distributed uniformly throughout the solid body. The assemblies of fins are bathed by a steady stream with constant ambient temperature and convective heat transfer. The outer surfaces of the cylindrical body are adiabatic. The total volume of the body and the total volume of the fins are fixed, but the lengths of the fins can vary. The initial simulations demonstrated that the optimal performance is achieved when the tributaries shape becomes slender and the stem thicker so that the system has more freedom to morph. However, when the number of assembly exceeds 2, the best configuration is the one that presents slender stems and shorter tributaries. The reason of this sudden change in behavior is that the tributaries length is limited by the presence of the neighbor assembly of fins: the system becomes “locked” and has no more freedom to morph. Finally, a digression on how the number of T-shaped fin assembly affects the configuration patterns concludes the paper. [Copyright &y& Elsevier]

Moving heat load problems appear in many manufacturing processes, such as lithography, welding, grinding, and additive manufacturing. The simulation of moving heat load problems by the finite-element method poses several numerical challenges, which may lead to time consuming computations. In this paper, we propose a 2D semi-analytic model in which the problem in two spatial dimensions is decoupled into three problems in one spatial dimension. This decoupling significantly reduces the computational time, but also introduces an additional error. The method is applied to a wafer heating example, in which the computational time is reduced by a factor 10 at the cost of a 4% error in the temperature field. [ABSTRACT FROM AUTHOR]

In this paper, we apply a novel immersed boundary method to simulate pore-scale level fluid flow and convective heat transfer in realistic numerically generated open-cell solid foams in a Cartesian computational domain. Five different periodic foam samples of varying porosities ( ε = [ 0.877 , 0.948 ] ) are generated by numerically mimicking the actual foam formation process (minimizing surface area). The step-by-step procedure for generating the periodic foam geometries is presented. The specific surface areas of the generated foams of different porosities are compared with real foam geometries showing a reasonable agreement. The Reynolds number ( Re ) is varied from Re ≈ 0 (creeping flow) to Re ≈ 500 , and finally drag and Nusselt correlations have been proposed. A detailed analysis is presented on the local velocity and temperature field for the fluid-solid interaction in a complex cellular porous medium. [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]

This paper studies the three-dimensional (3d) transient temperature field of a friction lining and a sliding wire rope. An efficient multigrid solver is developed. The multigrid code is validated by a comparison with a well-known analytical solution. The influence of several parameters on the temperature rise is investigated. Sliding velocity has a great influence: the larger the velocity, the larger the average temperature rise and the temperature fluctuation at a certain time. Two approximate solutions characterized by simple heat flux forms are proposed, using only a limited computational effort. A comparison of the temperature rise by the original and the two simplified schemes is performed. It is found that the heat flux shape influence is limited to the surface temperature and the temperature rise far below the contact surface depends only on the total heat flow. [ABSTRACT FROM AUTHOR]

The optimization of the battery pack in an off-grid Photovoltaic application must consider the minimum sizing that assures the availability of the system under the worst environmental conditions. Thus, it is necessary to predict the evolution of the state of charge of the battery under incomplete daily charging and discharging processes and fluctuating temperatures over day-night cycles. Much of previous development work has been carried out in order to model the short term evolution of battery variables. Many works focus on the on-line parameter estimation of available charge, using standard or advanced estimators, but they are not focused on the development of a model with predictive capabilities. Moreover, normally stable environmental conditions and standard charge-discharge patterns are considered. As the actual cycle-patterns differ from the manufacturer's tests, batteries fail to perform as expected. This paper proposes a novel methodology to model these issues, with predictive capabilities to estimate the remaining charge in a battery after several solar cycles. A new non-linear state space model is proposed as a basis, and the methodology to feed and train the model is introduced. The new methodology is validated using experimental data, providing only 5% of error at higher temperatures than the nominal one. [ABSTRACT FROM AUTHOR]

Keeping the excess temperature of heat generating mediums and circuitry devices below an allowable level is a great challenge. To facilitate the heat transfer process, it is significant to improve and optimize the geometric structure of the cooling tools. The present paper deals with the shape optimization of a tree-shaped inverted fin (‘cavity’) that is penetrated into a heat generating body and extracts the generated heat from the hot piece to a cold environment. The objective is to obtain the optimal geometry of the tree-shaped cavity that minimizes the peak (maximum) temperature of the medium subject to the volume (space) constraint. A numerical solution is performed to deliver the temperature field within the medium and the direct search method is used to reach the optimal situation. The optimization results indicate that the final (optimized) tree-shaped configuration performs the best over the existing single-root cavities introduced in the open literature. For example, the maximum excess temperature calculated in the final tree-shaped cavity with four branches was found about 50% lower compared to the best configuration investigated in the open literature. [ABSTRACT FROM AUTHOR]

Battery thermal management system (BTMS) is critical to dissipate the heat generated by the battery pack and guarantee the safety of the electric vehicles. Among the various battery thermal management technologies, the air cooling is one of the most commonly used solutions. In this paper, the cooling performance of the parallel air-cooled BTMS is improved through using the secondary vent. Computational fluid dynamics is introduced to calculate the flow field and the temperature field, finally evaluating the cooling performance of the BTMS. Mathematical analysis is conducted to explore the influences of the inlet air temperature and the heat generation rate on the battery cell temperature. The analysis results demonstrate that the temperature rise and the temperature difference of the battery pack are independent of the inlet air temperature, and are proportional to the heat generation rate for the situation of the constant heat generation rate. Subsequently, the influences of the position and the size of the secondary vent on the cooling performance of the BTMS are investigated through using the typical numerical cases. The results show that the position of the secondary vent strongly affects the maximum temperature and the maximum temperature difference of the battery pack. When the vent is on the convergence plenum, it is suggested to be located against the cooling channel around the battery cell with the maximum temperature. Compared to the vent located on the convergence plenum, the one against the outlet performs better. In this situation, the maximum temperature of the battery pack is reduced by 5 K or more, and the maximum temperature difference is reduced by 60% or more compared to the BTMS without vent for the situation of the constant heat generation rate. Moreover, the cooling performance of the BTMS becomes better as the size of the secondary vent increased, and similar conclusion can be obtained when the heat generation rate is unsteady. [ABSTRACT FROM AUTHOR]

In this study, laminar forced convection heat transfer of water-alumina nanofluid flow inside an annular microchannel in slip flow regime is investigated by lattice Boltzmann method. Uniform velocity and temperature distributions are assumed at the microchannel inlet. Internal wall is insulated and outer wall is heated uniformly with constant heat flux. In both models that are used to express the kinematic viscosity and thermal conductivity of the nanofluid, the effects of nanoparticles size and Brownian motion are considered. A lattice-Boltzmann computer code is developed and the results are compared with the existing analytical solutions in the literature. In this paper, the effect of various parameters such as nanoparticles volume fraction (0–0.05), diameter (10–100 nm), microchannel radius ratio (0.2–0.8), Reynolds number (5, 10 and 50) and the slip factor (0.005–0.1) on the flow and temperature field are studied. Furthermore, variations of slip velocity, temperature jump, friction factor and Nusselt number along the walls are provided. Results indicate that higher slip factor, radius ratio, Re and volume fractions and also smaller particle diameters, increases the Nusselt number. Also slip velocity and temperature jump increases with slip factor. Nanoparticles volume fraction doesn't have significant effect on slip velocity, while increases the temperature jump. [ABSTRACT FROM AUTHOR]

This paper numerically explores the heat transfer behaviors of cryogenic fluids in offset strip fin (OSF) channels considering the important effect of fin efficiency that combines the factors of low thermal conductivity of fin material at cryogenic temperatures and the fin geometry. A series of numerical simulations, which involve three kinds of fin materials with different thermal conductivities and the cryogenic fluids including both gases and liquids of nitrogen, normal hydrogen and classic helium 4, are carried out with well-validated 3D models. The results show that lower thermal conductivity of solid material at cryogenic temperature causes a considerable reduction in heat transfer performance of OSF fins especially for the liquids with high Prandtl number. Further analysis of the results reveals that for different cryogenic fluids, Nusselt number is strongly related to Prandtl number and fin efficiency. In particular, Nusselt number is proportional to the Pr 0.235 η f 0.9 in laminar region, regardless of Reynolds number and fin geometries. The results for different fin geometries suggest that larger fin thickness-to-length ratio can help to improve the heat transfer performance, while smaller fin thickness-to-height ratio and higher fin density no longer contribute to higher j factor (or Nusselt number) of OSF fin, especially in the case of lower thermal conductivity of fin material. There exist optimum fin thickness-to-height ratio and fin density that correspond to the maximum value of j factor for the cryogenic fluids. [ABSTRACT FROM AUTHOR]

In the present paper, a simple difference method for lattice Boltzmann algorithm is proposed to simulate conjugate heat transfer problems. In the conventional lattice Boltzmann method (LBM), the informations including temperature and heat flux exchange directly between two different media through distribution function during the streaming process, however, the continuity of heat flux at the interface between two different media cannot be guaranteed in this process. Different with the conventional LBM, we consider that the nodes near the interface get the distribution functions from the interface during the streaming process across the interface. The distribution functions at the interface can be obtained by coupling the interface conditions of temperature and heat flux with non-equilibrium extrapolation. Four test cases are used to validate the present method, including both steady and transient conjugate heat transfer with flat or curved interfaces. The results show that the present method is very easy to implement, and feasible for both steady and transient heat transfer problems. In addition, for simplicity, by approximating the real interface with a staircase shaped line, the present method can deal with curved interface easily and the results show the approximation will not contribute obvious error to the final results. [ABSTRACT FROM AUTHOR]

Thermoelectric radiant panel (TERP) system is a new prototype of radiant system with fast cooling/heating speed, stable operation, and easier system control. The full and deeper understanding of heat transfer of TERP could be beneficial for system design, operation and control. The purpose of this paper is to establish a three-dimensional analytical model of TERP in both steady and dynamic state which could be used as a useful tool for further research. The method of mirror virtual heat sources was adopted to transform original heat conduction problem to the superposition of temperature solutions of radiant panel in infinite plane. In addition, this method can offer a highly flexible treatment on boundary conditions. The basic conduction problem was solved by the method of separation of variables and the temperature field subjected to non-functional finite-plane heat source was modeled by Duhamel theorem in simulation algorithm. Thermal network RC model for TEM and copper cube was integrated with the analytical model of radiant panel for simulation of TERP. The simulation accuracy of three-dimensional temperature field of TERP was verified by comparing with experimental results in both steady and dynamic state. In order to understand the simulation difference between the previous 2-D and new 3-D model, a comparative study was implemented under different model parameters arrangements. This numerical comparative investigation can provide a basic guidance on the application of 2-D and 3-D model. And this study offered a solid and sophisticated system model for TERP. [ABSTRACT FROM AUTHOR]

Double-stage latent heat storage (LHS) unit is believed as a valid design to improve performance by separating LHS unit into two portions filled with different phase-change materials (PCMs). In this paper, double-stage LHS unit is optimized with entransy analysis. Different from those in references, optimization is conducted for LHS unit in whole cycle, i.e. charging and discharging process. Charging rate and inlet temperature of heat transfer fluid (HTF) are constrained constant. All the heat stored in charging process is released in discharging process. The criterion formulas of optimum melting temperature match is derived. The performance, i.e. discharging rate and entransy dissipation of double-stage LHS unit optimized in whole cycle, is compared with those of single-stage LHS unit and those of double-stage LHS unit optimized in only charging process. It is concluded that optimum melting temperature match exists in double-stage LHS unit in whole cycle. Performance is enhanced in double-stage LHS unit optimized in whole cycle. Constraint of discharging rate equal to charging rate is not favored in entransy analysis. Comparing with those in single-stage LHS unit, discharging rate of double-stage LHS unit optimized in whole cycle is always larger and entransy dissipation is always smaller. The difference of entransy dissipation between that of double-stage LHS unit optimized in whole cycle and that of single-stage LHS unit increases with coefficient c . It is also concluded that the double-stage LHS unit optimized in whole cycle is not the same as that optimized in only charging process. Comparing with those in double-stage LHS unit optimized in only charging process, entransy dissipation of double-stage LHS unit optimized in whole cycle is smaller, but discharging rate is also smaller. The difference of entransy dissipation between that of double-stage LHS unit optimized in whole cycle and that of double-stage LHS unit optimized in only charging process decreases with coefficient c . Optimization results are discussed in typical heat storage cases. The results are helpful to optimal design and performance improvement of LHS unit. [ABSTRACT FROM AUTHOR]

A micro-thermoelectric gas sensor (micro-TGS) uses thermoelectric voltage induced by the catalytic combustion of hydrogen or methane for selective gas detection in breath. This is accomplished under an elevated temperature using a micro-heater built on the same membrane as a hotplate, which enables selective combustion of the target gas. A temperature differential built by the catalyst on the membrane induces the offset voltage (V off ) of the micro-TGS, which limits the amplifier circuit application. In this study, we strived to suppress V off by an additive integration process of heat dissipation dots prepared using α-Al 2 O 3 paste. In this paper, we discuss the effects of these α-Al 2 O 3 dots on the thermal balance over the micro-TGS membrane by finite element method (FEM) modeling. When the dots were deposited in a symmetrical position to the combustion catalyst, V off was compensated depending on the size, numbers, and locations of the dots. The micro-TGS heat transfer control by the dots was additionally verified by 3-D FEM modeling. The changes in V off by the α-Al 2 O 3 dots in FEM modeling were greater than those of the experiments, suggesting the high thermal conductivity of the micro-TGS membrane. The deviation of the membrane thermal conductivity due to the process non-uniformity significantly influenced the V off ; however, it was effectively reduced by the additive integration of dots. [ABSTRACT FROM AUTHOR]

In this paper, a new theoretical method for upscaling the thermal conduction equation in periodic composite materials is presented. That method is named “the method of quasiperiodic fields”, and it is based on the assumption that the temperature field is quasiperiodic at the small scale. More specifically, that method allows to predict the form of the averaged governing equations, and the values of the effective transport coefficients. The new methodology involves four steps: (i) a first level averaging, (ii) the statement of a quasiperiodic problem, (iii) the development of factorized quasiperiodic problems, and (iv) the development of the closed form of the averaged thermal conduction equation. The values of the effective thermal conductivity obtained with that new method were compared with values reported in literature, and also with values obtained from direct numerical simulations. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a new frequency domain method to model the heat transfer between the injected/extracted heat and the temperature of the fluid exiting a borehole heat exchanger. The method is based on in situ measurements and focuses particularly on the short-term borehole heat transfer. It uses a rational function of the Warburg variable in the Laplace domain to model the borehole heat transfer. The rational model is transformed to a time domain model using inverse Laplace transformation. This time domain model makes it possible to calculate the temperature response on a random heat variation signal. The paper also demonstrates a new way to perform the classical thermal response test. Instead of injecting a constant amount of heat, the experiments have been performed using multiple short-duration heat injections. In this way, the obtained rational heat transfer model contains information about both the short- and the long-term heat transfer. The results obtained using the proposed modeling method are compared with those obtained from a state-of-the-art analytical method. The time domain model can be used to design a controller to optimize the performance of a Ground Source Heat Pump system, the efficiency of which depends strongly on the temperature of the fluid exiting the borehole. [Copyright &y& Elsevier]