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In this paper, a vertical gypsum plate with thermal capacity placed in an open cavity under dynamic temperature decrease is numerically investigated in order to assess the evolution of the thermal and kinetic structure of the boundary layer and the convective heat transfer coefficient h over time. The particularity of this work resides in the fact that the system was made to simulate the case of a plate with thermal capacity under nocturnal conditions where the temperature is constantly decreasing. Thus, a two-dimensional CFD model is developed under the Ansys Fluent 14.5 environment and is validated using experimental data obtained for a plasterboard studied under dynamic temperature changes. This study contributes to give precise results about temperature, flux, convective heat transfer coefficient and velocity in the vicinity of a vertical wall with a thermal conductivity at the building scale. All the phenomena that occur in the vicinity of the heat capacitive vertical plate (gypsum) are analyzed and explicitly discussed. The main results of this study show that after simulating 1 h real time we observe that turbulent flow begins to appear at the top level of the plate and after this moment the three flows (laminar, transitional and turbulent) coexist. Finally, mean convective heat transfer coefficient depends on the thermal storage capacity of the adjacent material. The average value of convective heat transfer coefficient increases over time by obtaining for a plasterboard ( C p = 1100 J/kg K) value of 1.8 W/m 2 K and for a phase change material in a solid state ( C p = 4350 J/kg K) value of 2.4 W/m 2 K at steady state. [ABSTRACT FROM AUTHOR]

The Selective Laser Melting (SLM) fabrication process is complex and it is crucial to understand the phenomena that will occur to better control it. In this paper, an FE model on SLM that considers powder-to-solid transition together with an effective method to achieve volume shrinkage and material removal has been created. Experiments were conducted to validate the model. A detailed discussion on the progression of the melt pool and the rate of temperature change has been made. Parametric study with the laser power and scan speed as variables has been conducted to identify their relationships with the melt dimensions, melting and evaporation of powder and rates of temperature change. [ABSTRACT FROM AUTHOR]

In this paper, a numerical investigation of thermal and thermodynamic performance of a receiver for a parabolic trough solar collector with perforated plate inserts is presented. The analysis was carried out for different perforated plate geometrical parameters including dimensionless plate orientation angle, the dimensionless plate spacing, and the dimensionless plate diameter. The Reynolds number varies in the range 1.02 × 10 4 ⩽ Re ⩽ 7.38 × 10 5 depending on the heat transfer fluid temperature. The fluid temperatures used are 400 K, 500 K, 600 K and 650 K. The porosity of the plate was fixed at 0.65. The study shows that, for a given value of insert orientation, insert spacing and insert size, there is a range of Reynolds numbers for which the thermal performance of the receiver improves with the use of perforated plate inserts. In this range, the modified thermal efficiency increases between 1.2% and 8%. The thermodynamic performance of the receiver due to inclusion of perforated plate inserts is shown to improve for flow rates lower than 0.01205 m 3 /s. Receiver temperature gradients are shown to reduce with the use of inserts. Correlations for Nusselt number and friction factor were also derived and presented. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of naphtha (RON = 65.6) and commercial gasoline (RON = 94.0) on Multiple Premixed Compression Ignition (MPCI) mode. The experiment is conducted on a single cylinder research diesel engine with compression ratio of 16.7. The engine is operated at an engine speed of 1600 rpm for the IMEP from 0.4 to 1.4 MPa. Commercial diesel (CN = 56.5) is also tested in Conventional Diesel Combustion (CDC) mode as a baseline. At each operating point, the injection strategy and intake conditions are adjusted to meet with the criteria (NO x < 0.4 g/kW h, soot < 0.06 m −1 , MPRR < 1 MPa/deg and CA50 < 20 CAD ATDC). The typical two-stage combustion characteristics of MPCI are obtained in both naphtha and gasoline. Stable combustion is achieved by naphtha in wide load range, while the engine fuelled with gasoline cannot operate stably at 0.4 MPa IMEP. The COV of IMEP of gasoline MPCI is higher than that of naphtha and diesel. However, gasoline has the low MPRR and the retarded CA50 at medium and high loads due to its longest ignition delay. As a result of low exhaust loss for naphtha and low heat transfer loss for gasoline, the thermal efficiencies are higher for both naphtha and gasoline in MPCI mode than diesel in CDC mode, even though diesel has the highest combustion efficiency. The separated combustion in MPCI leads to low cylinder temperature, and moderate EGR ratio (less than 30%) is needed to control NO x emissions under the limit of EURO VI. [ABSTRACT FROM AUTHOR]

This paper presents a numerical investigation of thermal transport in a parallel-plate channel comprised of superhydrophobic walls. The scenario analyzed is laminar, fully developed, steady flow with constant properties. The superhydrophobic walls considered here have alternating micro-ribs and cavities aligned perpendicular to the flow direction and are made of a highly conductive material. The cavities are assumed to be non-wetting and contain air whereas the bulk liquid is water. The thermal transport through the ribs is considered to have a constant heat flux while the thermal transport through the air/liquid interface over the cavity is considered to be negligible. Numerical results have been obtained for a range a Peclet numbers, cavity fractions, and relative channel widths. A limited number of results were also obtained where the rib was maintained at a constant temperature condition for comparison. In general, the thermal transport is a strong function of all the parameters explored. By comparison to previous analytical work, the influence of axial conduction is found to be significant and is most pronounced at large relative channel widths, low Peclet numbers, and large cavity fractions. Lastly, the ratio of temperature jump length to hydrodynamic slip length is presented in terms of the varied parameters and is compared to previous results where axial conduction is neglected and other work where diffusion is assumed dominant. [ABSTRACT FROM AUTHOR]

In this paper a further development of methodology for decreasing the capital cost for Total Site heat recovery by use of different utility levels is proposed. The capital cost of heat recovery system is estimated for certain temperature level of intermediate utility applying Total Site Profiles. Heat transfer area is reduced by selection of appropriate temperature of intermediate utility. Minimum of heat transfer area depends on slopes of Total Site Profiles in each enthalpy interval. This approach allows estimating the minimum of heat transfer area for heat recovery on Total Site level. Case study is performed for fixed film heat transfer coefficients of process streams and intermediate utilities. It indicates that the total heat transfer area of heat recovery can be different up to 49.15% for different utility temperatures. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of phase change material (PCM) melting in a transparent rectangular enclosure with and without horizontal partial fins. The enclosure was heated isothermally from one side while the other walls were thermally insulated. Experiments were performed with wall temperatures of 55, 60 and 70 °C ( 3.6 × 10 8 ⩽ Ra ⩽ 8.3 × 10 8 ) for finned and unfinned enclosures. Visualization of the melting process and the temperature field were performed directly. Both qualitative and quantitative information about the melting phenomena were obtained using digital photographs of the instantaneous melt front evolutions and temperature recordings at the vertical mid-plane of the enclosure. Temperature histories revealed that the thermally stratified region became smaller as the number of fins increased. Experimental data were used to calculate melt fractions, heat transfer rates and Nusselt numbers during the melting process. Furthermore, two correlation equations were developed using the dimensionless parameters to predict the Nusselt number and melt fraction. Also, in order to evaluate the improved thermal performance of the enclosure in the presence of partial fins, two other parameters were defined, melting enhancement ratio and overall fin effectiveness. Experimental results indicated that increasing the number of fins decreased the melting time and increased the total heat transfer rate while the surface-averaged Nusselt number reduced. Melting enhancement ratio and overall fin effectiveness increased with increasing the number of fins and decreased with raising the wall temperature. Melting enhancement ratios decreased with time after reaching some maximum values indicating that partial fins are more beneficial during the initial time of the melting. [ABSTRACT FROM AUTHOR]

This paper reports on the development and the thermal tests of two superfluid helium heat pipes. They feature a copper braid located inside a 6 mm outer diameter stainless tube fitted with copper ends for mechanical anchoring. The copper braid is the support of the Rollin superfluid helium film which is essential in the heat transfer. The extremely low thickness of the liquid film allows for a low filling pressure, making the technology very simple without the need for any external hot reservoir and with the possibility to easily bend the tube. We present the design and discuss the thermal performance of two heat pipes tested for several filling pressures, adverse tilt angles and in 1.4–2.0 K temperature range. A minimum filling pressure (0.6 MPa) is needed to get significant transport capacity. A 12 mW transport capacity is achieved for 3.0 MPa filling pressure. It is shown that the long heat pipe (1.2 m) and the short one (0.25 m) have similar thermal performance in adverse tilt. At 1.7 K the long heat pipe, 120 g in weight, reaches a transport capacity of 5.7 mW/4.2 mW for a tilt angle of 0 / 60° and a thermal conductance of 600 mW/K for 4 mW transferred power. When the condenser reaches the super-fluid transition temperature, the Rollin film accelerates the cool down of the evaporator down to 1.7 K with a heating power applied to the evaporator. [ABSTRACT FROM AUTHOR]

The combined heat and mass transfer mechanisms owing to the temperature and humidity ratio differences and their influence on the efficiency of different exponential type porous fin configurations are analyzed in this paper. The closed-form temperature solutions for an exponential impermeable dry fin as obtained in an earlier publication (Turkyilmazoglu, 2012) are extended here to the case where the surface of the fin is fully wet and porous. A comparison with the traditional straight porous fins proves that the fin tip temperature and efficiency of the exponential porous wet fins are much better than those of corresponding to the straight porous wet fins. [ABSTRACT FROM AUTHOR]

In this paper we report the extension of an earlier reported DNS method (Deen et al., 2012; Deen and Kuipers, 2013) based on a novel Immersed Boundary Method (IBM) which incorporates the fluid-solid coupling at the level of the discrete field equations. The extended method is used to study coupled mass and heat transport in dense fluid-particle systems where the coupling arises as a consequence of an exothermal chemical reaction proceeding at the exterior surface of the particles. Following a detailed verification (using an independent numerical technique) and validation (using established empirical correlations) we apply our DNS technique to study coupled mass and heat transfer in a dense fluid-particle system. In addition a comparison is made with results obtained from a simple one-dimensional (1D) heterogeneous reactor model which uses empirical closures for the fluid-particle mass and heat transfer coefficients. The main features of the complex transient temperature profiles obtained from our DNS agree quite well with the corresponding profiles obtained from the 1D heterogeneous reactor model. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we proposed a modified vacuum directional solidification system for producing multicrystalline silicon (mc-Si). A transient numerical model was carried out to simulate the process of mc-Si vacuum directional solidification which cannot be directly monitored. The temperature distribution, melt convection, melt–crystal (m/c) interface and thermal stress have been simulated. Simulation results show that the modified system is particularly suitable for growing high-quality crystal of mc-Si. The thermal stress of the silicon crystal decreases considerably due to the lower temperature gradient by installing a conical insulation unit, the m/c interface keeps slightly convex and the melt flow along the axis direction is relatively stronger by improving the heat transfer. The results of the experiment show that this modified system of mc-Si can obtain better crystal quality than the traditional vacuum directional solidification system. [Copyright &y& Elsevier]

Based on the need for decommissioning and as a consequence of the Fukushima accident, research into spent fuel pools (SFPs) has become an important topic for nuclear safety analysis. In this paper, a three-dimensional (3-D) computational fluid dynamics (CFD) methodology is proposed to investigate the transient behaviors of flow and heat transfer for the coolant within a rod bundle in a SFP. A cell with a 17 × 17 rod bundle in a SFP of the Maanshan nuclear power plant (NPP) is practically simulated, instead of using the porous media assumption employed in previous simulations. Normal operation conditions are adopted in the present transient simulations. The thermal-hydraulic characteristics of coolant in a rod bundle can be reasonably captured by the present CFD model. These characteristics include the flow acceleration and heat transfer enhancement in the support grids, the secondary flow between the rods, and the non-uniform distributions of velocity and temperature on the cross-section of the rod bundle. In future, this 3-D transient CFD model can be extended to investigate accidents that might occur in the SFP. Such investigations can be useful in providing the transient characteristics of localized flow and heat transfer for the coolant to assist the tradition system codes in simulating the accident scenarios. [ABSTRACT FROM AUTHOR]

Abstract: The full-spectrum correlated-k distribution method has been shown to be exact for thermal radiation in molecular gas-particulate mixtures which obey the correlation assumption. Unfortunately, this assumption breaks down for molecular gases with strong temperature or concentration gradients. There has previously been no way to effectively quantify the model-form uncertainty introduced by the failure of the correlation assumption. This paper examines the effect of temperature gradients in CO2 and proposes a technique to generate probability density functions for the gray-gas absorption coefficients used in the full-spectrum correlated-k distribution method. The uncertainty in the absorption coefficients may then be propagated forward to ascertain confidence intervals for important quantities such as heat flux or intensity distributions. [Copyright &y& Elsevier]

Abstract: This paper proposes a new approach based on VSP method (Vorticity–Stream function–Poisson equation method), to study numerically fully developed laminar flow characteristics and heat transfer behaviors of helical ducts with rectangular cross section. The aim is to guide heat transfer enhancement for helical rectangular ducts. Based on the numerical results, synergies between velocity field and temperature field have been investigated through field synergy principle. The effects of curvature, torsion, aspect ratio, Reynolds number, and Prandlt number on velocity field, temperature field and field synergy have been examined. The results show that the secondary flow of the central regions is weaker than that in other locations of the cross section. With reference to the entire cross section, the best values of synergy between velocity field and temperature field can be found in the center of the section. Increasing the curvature, Reynolds number and Prandtl number causes the mean synergy angles of the cross section to increase. This result indicates that it is more important to improve the field synergy for high Prandlt number fluid, especially at high Reynolds number. As the torsion increases, the average synergy angles decreases. The mean synergy angles reach the maximum value when the aspect ratio is equal to one; therefore, one can conclude that the field synergy of helical ducts with square cross section is the worst. To enhance heat transfer performance of helical rectangular ducts, for small aspect ratio, the main important aspect is to improve the secondary flow in the center of the cross section. On the contrary, for moderate values of the aspect ratio, the most important aspect is to improve the field synergy of the region near the upper and the lower wall. The correlations of friction factor and Nusselt number have been also developed for helical ducts with rectangular cross section. [Copyright &y& Elsevier]

Abstract: This study is aimed to clarify transient heat transfer process between the surface of solid and the neighboring helium gas in Very High Temperature Reactor (VHTR) or Intermediate Heat Exchanger (IHX). In this paper a series of plate heaters with different widths under various pressures inside a circular channel have been tested for forced convective flow. The heat generation rate of the plate heater was increased with a function of Q 0exp(t/τ) (where t is time and τ is period of heat generation rate or e-fold time). The heaters were platinum plates with a thickness of 0.1mm and widths of 2mm, 4mm and 6mm. The heat flux, surface temperature, and transient heat transfer coefficients were measured for helium gas passing by horizontal plates under wide experimental conditions such as velocities, pressures, widths of plate and periods of heat generation rate. It was clarified that the heat transfer coefficient approaches the quasi-steady-state value when the period is more than around 1s and it becomes higher when the period is shorter than around 1s. It was found that the heat transfer coefficient becomes higher with the increase of gas pressure under the same velocity and period of heat generation rate. It was also found that the widths have a great influence on the heat transfer coefficient: the heat transfer coefficients of narrow heaters are much higher than those of wide ones under the same velocity and the same pressure. Based on the experimental data, empirical correlations were obtained for both quasi-steady state heat transfer and transient state one at various plate-widths. [Copyright &y& Elsevier]

Abstract: Numerous factors, including the meteorological and the geographical conditions as well as the configurations of the fin tube bundles, can affect the performance of an air-cooled condenser (ACC) in a power generating unit. In this work a new model is presented to rapidly and accurately predict the flow and heat transfer characteristics of an ACC under the influence of natural wind. This reduced-order model is based on proper orthogonal decomposition (POD) of the three-dimensional velocity and temperature fields and encompasses natural wind directions ranging from 0° to 90°. In the process of operation in the present paper, a combined procedure involving spare and complementary POD is formulated to treat the issue of high nonlinearity associated with the large variable gradients which generate vortices around the ACC. A flux matching procedure is also introduced for estimation of the weight coefficients of the POD modes. The velocity and temperature fields of four typical test cases were estimated with maximum relative errors of 1.75% and 0.19%, respectively. At the same time, the degree of freedom was reduced by 105 compared to calculations made using computational fluid dynamics. The present research may provide a new and more reliable approach to real-time operational control of ACCs in power plants under polytropic natural wind conditions. [Copyright &y& Elsevier]

In this paper, a novel rotary magnetic refrigerator is described, and initial experimental results are presented. The prototype employs a two-pole magnetic system based on a double U configuration of permanent magnets with an air gap of 43 mm and 1.25 T. The magnetocaloric refrigerant is confined within eight static regenerator enclosures, which are alternatively magnetized and demagnetized with the rotation of the magnets. A rotary valve mechanically coupled with the field generator imparts the direction of heat transfer fluid through the regenerators. Using a total mass of 1.20 kg of gadolinium spheres (of 400-500 microns) as refrigerant and distilled water as regenerating fluid, the device produced a maximum temperature span of 13.5 K under zero applied thermal load with an utilization factor of 1.40 and a heat rejection temperature of 298 K. [ABSTRACT FROM AUTHOR]

Abstract: This paper theoretically analyses the problem of coal stockpile self-heating under free convection (no wind) conditions. Scale analysis has been used to drive expressions for the stockpile temperature and inflection point (when the stockpile is completely dry) as functions of the key parameters including the coal type, moisture content, and particle diameter as well as the ambient air temperature. Theoretical predictions are then successfully compared with experimental data and CFD simulations results available in the open literature. [Copyright &y& Elsevier]

Abstract: In this paper, a two-dimensional (2D) multiple-relaxation-time (MRT) lattice Boltzmann (LB) model is developed for simulating convection heat transfer in porous media at the representative elementary volume scale. In the model, a D2Q9 MRT-LB equation is adopted to simulate the flow field, while a D2Q5 MRT-LB equation is employed to simulate the temperature field. The generalized model is employed to model the momentum transfer, and the effect of the porous media is considered by introducing the porosity into the equilibrium moments, and adding a forcing term to the MRT-LB equation of the flow field in the moment space. The present MRT-LB model is validated by numerical simulations of several 2D convection problems in porous media. The present numerical results are in excellent agreement with the analytical solutions and/or the well-documented data reported in previous studies. It is also found that the present MRT-LB model shows better numerical stability than the LBGK model. [Copyright &y& Elsevier]

The paper deals with the process of evaporation of large water drops with the initial mass of 1g deposited on a hot surface, the temperature of which is higher than Leidenfrost point. The behavior of water drops was examined at the test stand, at which three independent measurement paths were available, namely those of instantaneous mass measurements, temperature recording and sequential recording of the thermal field of the drop upper surface. Thus obtained sets of drop mass, drop temperature, and its area size, for pre-defined temperature of the heating cylinder having a great thermal capacity, were used to compute instantaneous values of the heat transfer coefficient. The methodology of investigations was discussed in detail. Measurement uncertainties were analysed using the total differential method. On the basis of thermographic images, recorded with a thermovision camera, of the drop upper surfaces, substantial thermal diversity of drops was found. The difference between the maximum and minimum temperatures periodically amounts to above 9°C, and standard deviation from the area of their upper surfaces amounts even to 2°C. Measured instantaneous values of the heat transfer coefficient were approximated with a power function, dependent on the heating surface temperature and a momentary drop size. This relation was selected in accordance with the developed approximation procedure, at the imposed condition of the minimum of the mean square error. Consequently, a constant value of exponent and a dependence on the heating wall temperature were obtained. It was shown that values of measured and approximated heat transfer coefficients are contained in the interval defined by the value of the relative error ranging from −13% to +9%. An approximation of the perpendicular projection of the drop area in the form of polynomial is proposed. Under these assumptions, an analytical solution to the energy balance equation is given. Exemplary computations provided in the study indicate a very good effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we determine the fundamental relation between global performance and flow configuration (constructal design) in the case of steam power generation with superheater and reheater placed in parallel in the same stream of hot gases of combustion. The superheater heats the steam for the high pressure turbine, and the reheater supplies steam to the low pressure turbine. Both turbines operate irreversibly. We consider superheaters and reheaters with balanced counter flows and unbalanced counter flows. The total heat transfer area (or the overall number of heat transfer units) is finite. We show that the heat transfer area can be allocated to the superheater and reheater such that the overall power output is maximum. The optimal area allocation ratio is reported for two scenarios: designs with and without a maximum allowable steam temperature. [Copyright &y& Elsevier]

Abstract: Humidification–dehumidification is a promising technology for decentralized, small-scale desalination, but conventional dehumidifiers are expensive due to the large surface area required. Direct-contact dehumidification in bubble columns has been shown to significantly decrease dehumidifier size and cost. In this paper, the heat flux and parallel-flow effectiveness of a bubble column dehumidifier are investigated experimentally using significantly smaller cooling coils than in previous work. In addition, a model is developed which predicts the heat transfer rate with an average error of less than 3%. It is found that heat flux rises and effectiveness decreases with decreasing coil area. Increasing air flow rate and air temperature both lead to increased heat flux but decreased effectiveness. Neither bubble-on-coil impact nor column height are found to significantly affect heat flux or effectiveness. The conflicting findings of previous research on bubble-on-coil impact are explained by the other trends identified in this work. Modeling results for salt water temperature and tube diameter are presented. Additional heat transfer in the air gap above the column liquid is explored, but found to be minimal for well-designed columns with low temperature pinch. These findings will inform the design of bubble column dehumidifiers for high heat recovery and low capital cost. [Copyright &y& Elsevier]

Suspended nanoparticles inside the nanofluids can modify the characteristics of heated surfaces and the physical properties of the base liquids, offering a great opportunity to optimize boiling heat transfer. This paper reviews the mechanisms of nanoparticle deposition and the effects induced by deposited nanoparticles on surface roughness, force balance at the triple line, surface wettability, active nucleation site density, receding and advancing contact angles, boiling heat transfer coefficient and critical heat flux. Both enhancement and deterioration effects on boiling heat transfer coefficient and critical heat flux have been discussed. Most of the existing experimental data confirms the enhancement of critical heat flux using alumina nanofluid, however there is no consistency about its boiling heat transfer coefficient. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a detailed investigation on temperature overshoot characteristic of a realistic thermoelectric module (TEM) that operated with a square current pulse. A numerical model for TEM is developed and validated. Based on the model, obtained simulation results reveal that the transient temperature variation of realistic TEM cold side is more moderate due to the effect of the metal strips and the ceramic plates. Furthermore, the temperature overshoot characteristic of TEM cold side is analyzed for different current pulse parameters and operation conditions. For the square current pulse operation, the temperature overshoot occurs only when the current pulse amplitude is greater than a critical value, which is jointly determined by original steady current, cooling load and thermal conductance of heat sink. From the results obtained here, we propose a general principle to make a judgment whether a temperature overshoot will occur under a square current pulse operation. The present study will provide beneficial guidance for design of a TEM under current pulse operations. [Copyright &y& Elsevier]

Abstract: This work intends to be a novel application of probabilistic tools to improve the comprehension of heat transfer phenomena during a roller-compacted-concrete (RCC) dam construction. A probabilistic thermal model is proposed to propagate uncertainties on some RCC’s physical properties. A thermo-chemo-mechanical model is used to describe the RCC behaviour. A global sensitivity analysis is performed via the RBD-FAST method in order to evaluate the influence of some parameters which are given a random character. Heterogeneity on those parameters is further taken into account by means of bi-dimensional random fields. A variance reduction of the model output is observed while using random fields to propagate uncertainties. It shall be enhanced here that the present paper only concerns the thermal behaviour of the RCC dam during construction. In this sense, the temperature, hydration degree and ageing fields are modelled. [Copyright &y& Elsevier]

Abstract: This paper investigates the applicability of a simple fire resistance design method for axially loaded thin-walled steel studs in wall panel assemblies when exposed to parametric fires from one side. The simple method includes calculations of cross-section temperatures and ultimate load carrying capacities at elevated temperatures. The simplified calculation method for heat transfer in the cross-section is based on dividing the cross-section into a number of segments. The thermal properties of these layers are based on weighted averages of the thermal properties of the components contained within. The structural capacity calculation method is based on the Direct Strength Method. Results from the design method are compared with the results from Finite Element simulations for heat transfer and structural analysis (236 models). The calculation results are in good agreement with the simulation results and the proposed method may be used in performance-based fire engineering design of such construction. [Copyright &y& Elsevier]

Abstract: In this paper, free convection of ferrofluid in a cavity heated from below in presence of external magnetic field is studied numerically using the Lattice Boltzmann method. The enclosure is filled with a mixture of kerosene–cobalt. This investigation was compared with other experimental and numerical works and found to be in excellent agreement. Effects of Rayleigh number, magnetic coefficient, heat source length and volume fraction of cobalt on flow and heat transfer characteristics are examined. Results show that particles with a smaller size have better ability to dissipate heat, and a larger volume fraction would provide a stronger driving force which leads to increase in temperature profile. The Nusselt number has direct relationship with the Rayleigh number and heat source length while it has reverse relationship with size of nanoparticle and volume fraction of cobalt. [Copyright &y& Elsevier]

Abstract: In this paper, the overall heat transfer coefficient of water based iron oxide nanofluid in a compact air-cooled heat exchanger has been measured experimentally under laminar flow conditions. The concentrations of 0.15, 0.4 and 0.65 vol.% of stabilized Fe2O3/water nanofluid have been examined with variation of flow rates in the range of 0.2–0.5 m3/h. For better dispersion of iron (III) oxide nanoparticles in water, 0.8 wt% polyethylene glycol has been added and pH has been adjusted to 11.1. The air-cooled heat exchanger is consisted of 34 vertical tubes with stadium-shaped cross section and air makes a cross flow through the tube bank with variable flow rates ranging from 740 to 1009 m3/h. Also, hot working fluid enters the heat exchanger at different temperatures including 50, 65, and 80 °C. The results demonstrate that increasing the nanofluid flow rate and concentration and the air Reynolds number can improve the overall heat transfer coefficient and heat transfer rate whereas enhancing the inlet temperature has a negative effect on the overall heat transfer coefficient and a positive effect on the heat transfer rate. Meanwhile, the maximum enhancements of the overall heat transfer coefficient and heat transfer rate compared with base fluid (distilled water) are respectively equal to 13% and 11.5% which is occurred at the concentration of 0.65 vol.%. [Copyright &y& Elsevier]

Abstract: In this paper steady state forced convective heat transfer from a stationary unconfined spheroid to an incompressible power law fluid is studied numerically. The spheroid is assumed to be maintained at a constant wall temperature. The effect of Reynolds number (Re), Prandtl number (Pr), aspect ratio (E) and power law index (n) on the average Nusselt number was studied. The range of parameters investigated in this study is: 5⩽ Re ⩽100; 5⩽ Pr ⩽100; 0.5⩽ n ⩽1.5; and 0.5⩽ E ⩽1.5. The variation of local Nusselt number on the surface of both oblate and prolate spheroids was obtained. Further the Nusselt numbers for spheres lies between the prolate and oblate spheroids for all power law indices. A correlation was developed using least squares regression analysis. [Copyright &y& Elsevier]

Abstract: This paper introduces a new methodology for the generation of thermal response factors of geothermal bore fields using the concept of g-functions introduced by Eskilson. Boreholes are divided into segments to consider the variation of the heat extraction rates along the length of the boreholes and the analytical finite line source (FLS) solution is used to calculate the temperature variations at the wall of each borehole segment along the axial direction. The proposed methodology accounts for the time variation of the heat extraction rates among boreholes and along the length of individual boreholes to obtain a uniform borehole wall temperature equal for all boreholes in accordance with the original boundary conditions proposed by Eskilson. In addition, the methodology is generalized to account for boreholes of different lengths and buried depths. g-Functions calculated with the proposed methodology are compared to the numerical technique used by Eskilson to derive the g-functions for fields of 1 to 12×12 boreholes. The difference between the two models is within 5% for all studied bore fields, except for fields of boreholes located on a single row. The variation of the heat extraction rates of individual boreholes along their length as well as in time also showed good agreement with the numerical model. It is shown that using 12 borehole segments is adequate to calculate the g-functions in most practical cases. For instance, the error on the g-function of a 10×10 bore field calculated using 12 borehole segments is 2.2% after 20years and 4.7% at steady-state. [Copyright &y& Elsevier]

Abstract: The present paper deals with the longitudinal heat transportation by an oscillatory flow in a curved tube heat transportation pipe. The velocity and temperature fields during oscillatory water flow in a curved tube with inner diameter of 10mm were numerically simulated using the commercial software FLUENT. To clarify the effect of the curvature on heat transportation, the ratio of the tube radius to the curvature radius was varied from 0.0125 to 0.075, and oscillatory flow frequency was varied from 0.1 to 2.0Hz. The effective thermal diffusivity exhibited a peak at a curvature ratio around 0.05–0.07 and reached a value 12 times higher than that of a straight tube. It was also found that the dispersion of fluid particles due to secondary flow caused the enhancement of heat transportation. [Copyright &y& Elsevier]

This paper presents the effects of saturation temperature and inclination angle on convective heat transfer during condensation of R134a in an inclined smooth tube of inner diameter of 8.38mm. Experiments were conducted for inclination angles ranging from −90° (vertical downwards) to +90° (vertical upwards) for mass fluxes between 100kg/m2 s and 400kg/m2 s and mean vapour qualities between 0.1 and 0.9 for saturation temperatures ranging between 30°C and 50°C in a test matrix of 637 test data points. The results showed that saturation temperature and inclination angle strongly influenced the heat transfer coefficient. With respect to saturation temperature, an increase in saturation temperature generally led to a decrease in heat transfer coefficient irrespective of the inclination angle. The effect of inclination angle was found to be more pronounced at mass fluxes of 100kg/m2 s and 200kg/m2 s for the range of mean vapour qualities considered. Within the region of influence of inclination, there was an optimum angle, which was between −15° and −30° (downward flow). The inclination effect corresponded to the predominance of the effect of gravity on the flow distribution. An increase in saturation temperature increased the effect of inclination on two-phase heat transfer. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, numerical study of the gas flow velocity space is presented in a convection type reflow oven. Convection reflow ovens usually apply the nozzle-matrix heater system which generates numerous gas streams perpendicularly to surface of the soldered assembly. The ovens are divided into zones; every zone contains an upper and a lower nozzle-matrix. The temperature can be independently controlled in each zone; however the velocity of the influent streams is usually fixed. The gas flow velocity space is one of the most important parameter of the local heat transfer coefficient in the oven. The gas flow space cannot be examined by classical experimental methods due to the extreme circumstances in the reflow oven. Therefore the effect of the soldered assembly, the different component sizes, the position of the conveyor belt and the vent hood between the zones on the gas flow velocity space was studied by CFD simulations. These results can be useful during the overview of the actual assembly design and manufacturing rules. [Copyright &y& Elsevier]

Abstract: The problem of unsteady natural convection induced by a temperature difference between a cold outer square enclosure and a hot inner circular cylinder is studied in this paper. The cylinder temperature is assumed to vary sinusoidally with time about a fixed mean temperature. The coupled momentum and energy equations have been solved numerically over a wide range of values of the amplitude and the frequency of the source temperature signal, as well as the source radius. It is found that the heat transfer rate tends to increase by oscillating the source temperature signal. The maximum heat transfer augmentation was obtained for frequency between 25π and 30π for a high amplitude and a moderate source radius. [Copyright &y& Elsevier]

Abstract: In this paper, the optical absorption and heat transfer coefficients of a single suspended 4.3μm diameter carbon fiber have been measured in the experiment. The test fiber was first heated locally by a laser beam and the temperature rise was measured from the shifts in the Raman G-band frequency, and then the laser heating was replaced by an electrical current heating, the electrical power was adjusted to have the same temperature rise. Since the electrical power can be measured accurately, the absorbed laser power can be extracted from one-dimensional heat conduction analysis and the heat transfer coefficient can be obtained as well. The present experimental results show that the optical absorption of 4.3μm diameter carbon fiber is 39.62% and the heat transfer coefficient is 4150Wm−2 K−1, which agrees well with the prediction of published experimental empirical formula. [Copyright &y& Elsevier]

Abstract: This paper outlines an analytical model to predict the temperature of fully-inflated balloon on float at high altitude in stratosphere. Simplified radiative and convective heat transfer models are developed to estimate absorption and emission heat of balloon film and lifting gas within balloon. Thermal equilibrium equations for the balloon system in the day time and night time are derived by incorporating radiative and convective heat transfer models. The new model is applied to calculate the day and night temperatures of the balloon system on float at a high-altitude in stratosphere and reasonable correlation is achieved between the predictions obtained from new models and from prior flight testing data, demonstrating the effective use of the proposed models. [Copyright &y& Elsevier]

Highlights: [•] Four heat flux tubes for measuring heat flux to water walls were developed. [•] The inverse procedure was used to determine: absorbed heat flux, water-side heat transfer coefficient and fluid temperature. [•] Tests calculations and measurements in a steam boiler were carried out to validate the method proposed in the paper. [•] The flux tubes and inverse procedure are especially appropriate for measuring heat flux in once-through boilers. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a three-dimensional finite element model to investigate the interface damage occurred between prefabricated slab and CA (cement asphalt) mortar layer in the China Railway Track System (CRTS-II) slab track system. In the finite element model, a cohesive zone model with a non-linear constitutive law is introduced and utilized to model the damage, cracking and delamination at the interface. Combining with the temperature field database obtained from the three-dimensional transient heat transfer analysis, the interface damage evolution as a result of temperature change is analyzed. A three-dimensional coupled dynamic model of a vehicle and the slab track is then established to calculate the varying rail-supporting forces which are utilized as the inputs to the finite element model. The non-linearities of the wheel–rail contact geometry, the wheel–rail normal contact force and the wheel–rail tangential creep force are taken into account in the model. Setting the maximum interface damaged state calculated under temperature change as the initial condition, the interface damage evolution and its influence on the dynamic response of the slab track are investigated under the joint action of the temperature change and vehicle dynamic load. The analysis indicates that the proposed model is capable of predicting the initiation and propagation of cracks at the interface. The prefabricated slab presents lateral warping, resulting in severe interface damage on both the sides of the slab track along the longitudinal direction during temperature drop process, while the interface damage level does not change significantly under vehicle dynamic loads. The interface damage has great effects on the dynamic responses of the slab track. [Copyright &y& Elsevier]

Abstract: Heat transfer performance with nanofluids depends on the thermo physical properties of the suspension. Surface tension is an important property for heat transfer calculation. In this paper, various parameters that effect on the surface tension of nanofluids such as nanofluid preparation method, effect of volume fraction, temperature, and surfactants on nanofluids have been studied. Additionally, precise assessments on the theoretical correlations related to the surface tension of nanofluids have also been included. Based on the existing experimental results, surface tension augments respectively with volume fraction intensification. Surface tension of nanofluids decreases accordingly with the increase of temperature and surfactant concentration. Nevertheless, there have been some contradictory results on the effect of volume fraction and surfactant on surface tension of nanofluids. [Copyright &y& Elsevier]

Abstract: There is a significant push to increase the output power of thermoelectric generators (TEGs) in order to make them more competitive energy harvesters. The thermal coupling of TEGs has a major impact on the effective temperature gradient across the generator and therefore the power output achieved. The application of micro fluidic heat transfer systems (μHTS) can significantly reduce the thermal contact resistance and thus enhance the TEG's performance. This paper reports on the characterization and optimization of a μTEG integrated with a two layer μHTS. The main advantage of the presented system is the combination of very low heat transfer resistances with small pumping powers in a compact volume. The influence of the most relevant system parameters, i.e. microchannel width, applied flow rate and the μTEG thickness on the system's net output performance are investigated. The dimensions of the μHTS/μTEG system can be optimized for specific temperature application ranges, and the maximum net power can be tracked by adjusting the heat transfer resistance during operation. A system net output power of 126 mW/cm2 was achieved with a module ZT of 0.1 at a fluid flow rate of 0.07 l/min and an applied temperature difference of 95K. It was concluded that for systems with good thermal coupling, the thermoelectric material optimization should focus more on the power factor than on the figure of merit ZT itself, since the influence of the thermal resistance of the TE material is negligible. [Copyright &y& Elsevier]

Abstract: An increased interest in absorption chillers has been observed [1] because these systems can utilize solar, geothermal and biomass energy sources, but also because they are quiet, vibration-free, require little maintenance and are ecological [2]. Instead of a compressor system, which uses electricity, an absorption cooling system, using renewable energy and kinds of waste heat energy, may be used for cooling. This paper presents the simulation of a single stage solar absorption chiller operating with an ammonia–water mixture under steady state conditions. This simulation is based on heat and mass balances for each component. The heat and mass transfers in the absorber, the condensation of binary vapor of ammonia–water in the condenser and a thermosyphon desorber placed under the purification column were modeled. The numerical model was compared and validated with experimental data obtained with a solar absorption chiller. The calculated results agree well with experimental data. Simulations based on experimental data were used to predict the temperature and concentration profiles in each heat exchanger. A parametric study was conducted to investigate the effect of evaporator and desorber temperature on the absorption chiller's performance. The COP decreases by 25% with a decrease of 10 °C in evaporator temperature and the COP increases by 4% with an increase of 10 °C in desorber temperature. [Copyright &y& Elsevier]

Abstract: Heat may transport as waves under ultrafast heat pulse conditions. In this paper, our numerical analyses considering typical thermal wave modes, i.e. Cattaneo–Vernotte (CV), dual-phase-lagging (DPL), and thermomass (TM), disclose that dispersion may occur during the heat propagation processes like water, sound, and light waves. The unified implicit finite difference method for the Fourier, CV, DPL, and TM models was adopted to analyze the heat propagation process in solids. The validity of this numerical method for the Fourier, CV, DPL and TM models was confirmed. The dispersion of thermal waves was observed in their propagation processes for the first time. As the thermal waves moving forward, many peaks appear in the rear of the thermal waves relative to the propagation direction. The underlying mechanism for the dispersion of the thermal waves is that they can travel faster in the points with higher temperature considering the temperature dependence of the relaxation time. For the CV-waves and DPL-waves, the origins of the dispersion are both due to the inertia term of heat flux to time . For the TM-waves, the origins are due to the inertia term of heat flux to time, inertia term of temperature to time, and inertia term of heat flux to space in the TM model, and effects of the inertia term of temperature to space on the dispersion can be neglected, where the inertia term to space comes from the nonlocal effects. The dispersion of the TM-waves is mainly dominated by the inertia term of heat flux to time. In the TM model, the characteristic time τTM decreases with the increase of temperature, and therefore the dispersion will appear in the propagation process of the TM-wave. For actual materials, if considering that τq decreases with the temperature increasing, the dispersion of the CV-wave and DPL-wave will also appear under the appropriate amplitude of heat flux pulse, relaxation times τq and τT . The increase of the amplitude of heat flux pulse and the decrease of the initial temperature both can enhance the dispersion of the TM-wave. The increase of the amplitude of heat flux pulse and the relaxation time τq can both enhance the dispersion of the CV-wave and DPL-wave, while the increase of the relaxation time τT will weaken the dispersion of the DPL-wave. [Copyright &y& Elsevier]

Abstract: In this paper we explore the opportunity to maximize the production of power in a steam-turbine power plant by properly configuring the hardware at the interface between the stream of hot gas produced by the furnace and the steam that circulates through the power producing cycle. The interface consists of four heat exchangers, superheaters and reheaters, in parallel flow and counter flow. The search for better configurations is based on constructal design, and consists of searching for the distribution of heat exchanger surface (number of heat exchangers, types, sizes) such that the total power output of the turbines is maximum, subject to fixed total size for the heat transfer surface, and fixed maximum allowable steam heat exchanger wall temperature. The emergence of the more effective configurations is documented along with the migration of the spot of maximum temperature along the flow path. [Copyright &y& Elsevier]

Abstract: The accurate prediction of heat transfer behavior in packed bed is of great importance to the design and operation of this kind of facility. In this paper, heat transfer between packed bed and adjacent wall in heat recovery processing is investigated theoretically and experimentally. A bed-to-wall heat transfer model is presented with consideration of two essential components including particle-to-wall contact heat transfer and heat conduction through the thermal penetration layer. Details of model parameter determination are provided. Through comprehensive sensitivity analysis of those parameters, it is shown that particle temperature, particle residence time and particle diameter are critical parameters to heat transfer coefficient. Besides, surface roughness, solid thermal conductivity and environmental gas species are all influencing factors of the overall heat transfer coefficient. In particular, a dimensionless particle residence time is introduced to characterize the combining effect of residence time, effective thermal conductivity and wall contact heat transfer. Meanwhile, a revised simplified formula for calculating particle contact heat transfer coefficient is correlated as well, which provides better prediction than the one widely adopted in previous studies. Furthermore, experimental heat transfer test on an industrial packed bed char cooler is performed for validating the model predicting capability in heat recovery process. The systematical test on a bench scale packed bed heat exchanger has also been carried out. Parametric analysis of the experimental data is consistent with the conclusions drawn from the model analysis section. The model provides good predicting accuracy on the overall heat transfer coefficient from the bench scale facility as well as data from the field test by correlating 95% of the measured data within ±20%. The implementation of the proposed model shows good prediction of heat transfer coefficient in packed bed for heat recovery purpose. It is recommended that the model can be applied in industrial design. [Copyright &y& Elsevier]

Abstract: The feature of fluids at pressures just above the critical value which makes them of particular interest is that they change in a continuous manner from being liquid-like to gas-like with increase of temperature at constant pressure. As a consequence of the extreme dependence of fluid properties on temperature, non-uniformity of density can lead to important effects on the mean flow and turbulence fields and heat transfer effectiveness. When the author and his colleagues first commenced research on supercritical pressure fluids many years ago it was decided to begin with a novel experiment specifically designed to include effects of strong non-uniformity of fluid properties whilst avoiding other complications associated with the temperature dependence of density. This fundamental experiment on stably stratified turbulent flow of supercritical pressure carbon dioxide between two horizontal planes, with the upper one heated and the lower one cooled, in such a way that there was no net heat transfer to the fluid, yielded evidence of a special mechanism for enhancement of turbulent mixing. Later, experiments with uniformly heated vertical tubes using carbon dioxide at pressures very near to the critical value gave results, which exhibited further striking features. Severe localized non-uniformity of heat transfer developed in the case of upward flow, but was not found with downward flow. Gravitationally induced motion caused effects on heat transfer which could only be explained by postulating drastic modification of turbulence. Such results stimulated the development of physically based ideas concerning the mechanisms which might be involved and led to the development of a semi-empirical model of buoyancy-influenced turbulent flow and heat transfer. The main aim of this paper is to show how such early work is now providing a basis for correlating experimental data and enabling the complicated phenomena encountered in those early experiments to be properly accounted for in thermal design procedures. [Copyright &y& Elsevier]

Abstract: The optimal working fluid inventory of a prototype of a cryogenic loop heat pipe (CLHP) is studied in this paper. The CLHP prototype operates within a temperature range of 77–126K with nitrogen as the working fluid. The possible fluid inventory range is calculated based on analysis of phase distribution of vapor and liquid within the loop in a normal operation mode. Furthermore, a series of experiments are carried out with various filling pressures of the gaseous nitrogen at room temperature for validation of the fluid inventory range and identification of the optimal fluid inventory. The experimental results are compared with the calculation results, and the effect of different filling pressure on the performance of the CLHP is analyzed. [Copyright &y& Elsevier]

Abstract: One of the main challenges of the ITER fusion reactor is to effectively remove large amount of heat deposited to the surface of the plasma facing components. The tokamak cooling water system (TCWS) will accomplish the objective of removing about 1GW of peak heat load from in-vessel components while maintaining pressures and temperatures of the coolant within acceptable and safe limits during different operational scenarios. A study of feasibility has been launched for the IBED PHTS (Integrated Blanket, Edge localized mode coils (ELMs) and Divertor Primary Heat Transfer System; it consists of five independent cooling trains (four operational and one in stand-by), one steam pressurizer, supply and return headers, ring manifolds and connections to the all in-vessel components (i.e. First Wall Blanket, Divertor, ELM, Diagnostics and other Ports clients). The dynamic behaviour of the IBED PHTS has been investigated by means of RELAP5® code to simulate the response of the system during plasma pulse and baking operations. Due to the plasma heat deposition on the surfaces of the in-vessel components and subsequent increase in hot leg temperature, a large amount of water volume is transferred from the hot legs of the circuit to the surge-line of the pressurizer during each burn cycle. This causes rapid increase of pressure and temperature of the system and the following actions are proposed to counteract these variations: spray injection in the upper dome of the pressurizer from the Chemical and Volume Control System (CVCS) to reduce the pressure and active control of flow rates through heat exchangers and their bypass loops to regulate the heat transfer from the primary system to the environment via secondary and tertiary loops. This paper focuses on the prediction of the thermal hydraulic behaviour of the IBED PHTS during plasma pulses and baking scenarios, describing the various activity of the analysis, the geometrical assessment of the circuit and the modelling with RELAP5® code. The results have been compared with design and operational requirement. Possible strategies to enhance the system performances have been formulated. [Copyright &y& Elsevier]

Abstract: An understanding of the complex phenomena involved in droplet combustion, such as two-phase flows and heat/mass transfer, is a necessary step towards improving combustion efficiency and reducing pollutant emissions. This paper is focused on an analysis of the droplet temperature evolution across the flame front in two-phase flow systems. In this experiment, the flame was stabilized on a rod at atmospheric pressure and the fuel was liquid at injection, which implies the presence of fuel droplets close to the flame front. However the flame was partially premixed because part of the fuel vaporized quickly and contributed to the stabilization of the flame. The configuration was two-dimensional and so called “V-shape” flame. Two different flow conditions were investigated: a pseudo-laminar flow as the reference case (R) and a low-turbulence level flow (LT). The evolution of the mean fuel droplet temperature across the flame brush was quantified. The shape of the fuel droplet temperatures histogram became clearly bimodal for high values of the mean progress variable , indicating the presence of droplets in the measurement volume that were heated up by the burnt gases and the flame. The temperature evolution and the statistics across the flame front can be used to compare the numerical and the physical models applied to two-phase combustion. [Copyright &y& Elsevier]

Abstract: Cold crucible directional solidification (CCDS) is a promising technique to prepare TiAl alloys with an industrial size and no contamination. Heat transfer in mushy zone significantly influences the solidification interface shape and grain growth during CCDS. In this paper heat transfer characteristics were investigated at different stages in CCDS. Heat transfer models in mushy zone were established and a dimensionless parameter K (axial-to-radial heat flux density ratio) was defined and used to characterize the direction of heat flux, the effects of the temperature gradient (GL ), the current frequency (f) and the pulling rate (u) were evaluated. Ti–46Al–6Nb ingots were directionally solidified by a square cold crucible (the inner section size is 36×36mm) under different pulling rates. Results show that the interface shape can be adjusted to be more planar by increasing the GL , heightening the f and decreasing the u. The superheat of the melting pool in CCDS will decrease with the increasing of u. In addition, the macrostructures of these Ti–46Al–6Nb ingots well verify the theoretical results. [Copyright &y& Elsevier]

Abstract: In this paper, a new boundary-domain integral equation for solving energy equation in convective heat transfer problems is derived. The derived integral equation accounts for fluid velocity which is computed using the velocity boundary-domain integral equations presented in [2,3] (X.W. Gao, 2004, 2005). Numerical implementation of these integral equations is discussed for steady incompressible fluid flows, in which the velocity and pressure integral equations are uncoupled from the temperature equation, and thus can be solved separately. By substituting the velocity, velocity gradient, and pressure integral equations into the energy integral equation, temperatures can be computed without iterative processes. Two numerical examples for 2D problems are given to validate the proposed method. [Copyright &y& Elsevier]