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The irreversibility of the thermoelectric cooling (TEC) model could analyze and optimize refrigeration performance. In present work, a one-dimensional thermal conductivity model of the internal irreversible thermoelectric element was first established. Subsequently, two categories of evaluation indexes were further analyzed, i.e., cooling capacity Qc and coefficient of performance (COP). The thermodynamic model of TEC was then established jointly with finite time thermodynamics. The influences of current and the ratio of heat transfer areas between cold and hot sides on the steady-state characteristics of TEC were further discussed under Newtonian linear heat transfer. In addition, a transient thermodynamic model of TEC equipment was built to compare the effects of pulse width, pulse gradient, and pulse current on the cold side temperature of the TEC module. Theoretical results demonstrated that the effective working range of the steady-state operating current is 2A ≤ I ≤ 25A, and the area ratio of heat transfer between cold and hot sides is 0.07 ≤ x ≤ 1. The cooling capacity (Qc) and coefficient of performance (COP) could reach up to about 50W and 2.0, respectively. In addition, the increase of external heat transfer capacity of the hot side could reduce the transient supercooling temperature and the peak overshoot temperature, simultaneously. Afterward, the cooling capacity was remarkably enhanced. Current research could provide a reliable support for the optimization design and performance improvement of the thermoelectric cooler. Thermal conductivity model of internal irreversible thermoelectric element was established; Effects of cold and hot ends on the TEC were discussed under Newtonian linear heat transfer; Effects of pulse width, gradient and current on TEC cold end temperature were investigated; Heat transfer capacity of TEC hot end could reduce supercooling and overshoot temperatures; The irreversibility of TEC model will enhance its potentials for low grade energy exploitation. [ABSTRACT FROM AUTHOR]

The present study presents a comprehensive analysis of effects of porous fins on mixed convection heat transfer in lid-driven square cavities, where the top lid has the two-way movement. Porous medium with varying permeability, instead of the solid one, could widely modify its baffling effect on fluid flow and could also be utilized to control fluid flow and heat transfer. Fluid flow within the cavity was solved through the Navier–Stokes equations, while that within a saturated porous medium was governed by the Darcy–Forchheimer model. Numerical results indicate that the adding porous fins with excellent permeability could enhance heat transfer dramatically, especially for more fins. The rate of heat transfer enhancement due to an increase in Darcy number decreases, and similar trends were observed for the quantitative variations of porous fins. Besides, positions of porous fins have significant effects on fluid flow and heat transfer. The correlations of average Nusselt numbers, as functions of various governing parameters, have been proposed. The present investigations could be beneficial to the design of the microelectronic cooling through the installation of porous-alike materials or modules. [ABSTRACT FROM AUTHOR]

The effects of porous fins on mixed convection inside lid-driven square enclosures were reported in the present work. The porous medium with varying permeability, instead of the solid one, could widely change the baffling performance on the fluid flow, where this characteristic could be beneficial for controlling fluid flow and energy transport, typically electronic cooling process. The top lid could have the two-way movement. The working fluid in the cavity was governed by the N-S equations while that within porous medium was determined by the non-Darcy model called the Darcy-Forchheimer model based on representative element-averaging method. Relevant governing parameters, including Richardson number, Darcy number, quantities, length and distribution ratio of porous fins, are sensitively varied to identify their effects and roles on mixed convection heat transfer. Numerical results illustrate that the mechanism of main circulation development is modified by the additional fins. The adding porous fins with excellent permeability enhance heat transfer dramatically, while these fins with tiny Darcy number deteriorate heat transfer rate. The rate of heat transfer enhancement due to the increasing of the length and quantities of fins decreases. Furthermore, the distribution ratio shows the significant effects on the fluid flow and heat transfer. Present investigations could benefit the microelectronic cooling through the installation of porous-alike materials or modules. [ABSTRACT FROM AUTHOR]

Surface effect, inertia and thermal softening are important factors affecting the elasto-plastic evolution of voids. In this study, we theoretically examine the dynamic evolution of a nano-void in an elasto-plastic medium, particularly focusing on influences of surface energy, inertia and thermal softening. A two-stage strategy of analyzing surface effect is adopted, i.e. the first stage which is a quasi-static stage from a fictitious stress-free configuration to the actual initial configuration, and the second one which is the dynamic process of deformation under both surface stress and external dynamic loadings. The void will grow dynamically and quickly under high external loading, and the accelerations of material points in the neighborhood of the void are extremely high, resulting in a profound inertia effect. Under impact-like loading conditions, the plastic work done during the elasto-plastic growing process of the void is mainly transformed into heat, leading to thermal softening of material. Furthermore, heat transfer can be well neglected due to the transient characteristic of the problem studied. Tendencies related to all above influence factors are systematically analyzed. [ABSTRACT FROM AUTHOR]

In former theoretical researches of nanofluid flows, numerical investigations could not agree with experimental observations, particularly regarding whether the mixing nanoparticles will enhance or deteriorate the heat transfer. In the present work, thermal driven buoyancy flows of nanofluids in a square enclosure were modeled by the use of homogeneous assumptions and the effective kinematic viscosity and thermal conductivity formulas. Thoroughly developed heat transfer coefficient is subsequently proposed, aiming to critically evaluate the performance of nanofluid heat transport. Numerical results are presented over a wide range of thermal Rayleigh number (103 ≤ Ra ≤ 106) and nanoparticles volume fraction (0.001 ≤ φ ≤ 0.04). Present modeling results accurately predict both the enhancement and deterioration of the natural convection heat transfer, fully validated by former experimental observations. Overall, mathematical models and Nusselt number definitions proposed in the present work effectively enhance the reliability of numerical modeling researches on the nanofluid heat transfer. Present clarification research on the Nusselt unifications could benefit future development of thermal carrier fluid enhanced by nano-particles. [ABSTRACT FROM AUTHOR]

Combined heat and moisture transportation in an enclosure has been numerically investigated, which could benefit the sustainable building energy conservations and electronic cooling designs. An adiabatic and impermeable partition of finite thickness is considered, placed in the enclosure following an ordered arrangement. Effects of length and location of the partition, buoyancy ratio and thermal Rayleigh number on convective heat and moisture transfer rates in the enclosure are discussed. Firstly, this situation of the partition placed in the horizontal wall is studied, where inhibition effect of partition is observed. It is seen that the location of partition put relatively weaker influences on the heat and mass transfer in the regime of thermal-driven flow, when its length exceeds the critical value. Additionally, inhibition effect is more pronounced as the partition is fixed in center of vertical wall. Furthermore, local heat and mass transfer rates could be suppressed when the buoyancy ratio becomes negative. Finally, thermal Rayleigh number greatly affects the transport structures of fluid, heat and moisture, whatever aiding flow or opposing flow situations. Heat and mass transfer potentials could be promoted with increasing thermal Rayleigh numbers. Present work could be adopted to optimize the enclosure flows simultaneously with heat and moisture transport. [ABSTRACT FROM AUTHOR]

In the present work, an open-type thermoelectric heating system with multiple channels was developed. A mathematical model of heat transfer, based on one-dimensional treatment of thermal and electric power, is conducted. The heating coefficient and production are both correlated in terms of temperature difference, thermal conductivity, electric resistance and electric current. The looped air circulation was designed to simultaneously recycle heat and enhance heater system performance. Experimental investigations were conducted to identify thermal performance of the thermoelectric heater. Effects of airflow rates through the heating side and cooling side, temperatures of heating side and cooling side on the performance were investigated. The heating coefficient was calculated upon that surface temperatures of hot and cold sides were recorded. The results show that the average heating coefficient of the thermoelectric heating system could reach to 1.3, which is greater than that of a typical electric heater with heating coefficient of less than one. The optimal isolation thickness for this thermoelectric heater, i.e., 14 mm, is confirmed by the experimental rig system. Generally, heating coefficient was found to increase first and decrease afterwards when the current was continuously increasing. Analytical and experimental results demonstrate that the optimum performance of the thermoelectric heat recovery heater strongly depends on the intensities of these operating parameters. [ABSTRACT FROM AUTHOR]

In the present study, a thermoelectric mini cooler coupling with a micro thermosiphon cooling system has been proposed for the purpose of CPU cooling. A mathematical model of heat transfer, depending on one-dimensional treatment of thermal and electric power, is firstly established for the thermoelectric module. Analytical results demonstrate the relationship between the maximal COP (Coefficient of Performance) and Q c with the figure of merit. Full-scale experiments have been conducted to investigate the effect of thermoelectric operating voltage, power input of heat source, and thermoelectric module number on the performance of the cooling system. Experimental results indicated that the cooling production increases with promotion of thermoelectric operating voltage. Surface temperature of CPU heat source linearly increases with increasing of power input, and its maximum value reached 70 °C as the prototype CPU power input was equivalent to 84 W. Insulation between air and heat source surface can prevent the condensate water due to low surface temperature. In addition, thermal performance of this cooling system could be enhanced when the total dimension of thermoelectric module matched well with the dimension of CPU. This research could benefit the design of thermal dissipation of electronic chips and CPU units. [ABSTRACT FROM AUTHOR]

Abstract: Combined natural convective heat and moisture transports in a moist-air-filled enclosure with four free vent ports are numerically investigated. Four situations of ambient air states, hot and humid (I), hot and arid (II), cold and arid (III), and cold and humid (IV), are taken into consideration. Convective transports of semi-enclosed air, heat and moisture are respectively analyzed using the contours of streamfunction, heatfunction and massfunction, in addition to the isotherms and iso-concentrations. Overall convective heat transfer rate (Nu) and moisture transfer rate (Sh) of the internal concentrated heat and moisture source have been correlated with the thermal Rayleigh number respectively within the domain of the heat transfer driven flows and that of moisture transfer driven flows. When different initial convective flow conditions were imposed in the cases (I) and (IV), dual steady flow states of semi-enclosed heat and moisture convection are observed, and heat and moisture transport potentials can be enhanced or inhibited depending on the flow solution branches. These results can be adopted to guide the design of natural ventilation in the humid regions. [Copyright &y& Elsevier]

Abstract: Slot ventilated enclosure flows have been simulated, respectively in displacement ventilation and mixed ventilation covering from the forced convection dominated flow to the natural convection dominated flow. Direct convection simulation together with the turbulent streamlines and turbulent heatlines demonstrate that the enclosure flow pattern, indoor thermal level and heat transfer potential will depend on the interactions of external forced flow and thermal buoyancy driven flows, i.e., Reynolds number and Grashof number. In subsequent inverse convection modeling, the inverse determination of enclosure wall heat flux profiles was conducted by the use of adjoint methodology, in which the direct, sensitivity and adjoint problems are formulated and solved by finite volume method. The effects of the supplying air flow rate, thermal source strength, ventilation mode, flux functional forms, and the measurement errors on the accuracy of inverse turbulent convection estimation have been investigated. The inverse solutions of turbulent convections are of low level accuracy as the flow becomes thermal-driven turbulent flows, and they deteriorate as the noise levels increase. This work is of fundamental importance for the room air flow design and measurements involving the turbulent thermal convections. [Copyright &y& Elsevier]

Abstract: Thermal transport and transient dispersion of pollutants emitted from two discrete strips within the displacement ventilation enclosure have been modeled numerically. Following the full numerical simulation of turbulent air flows, the inverse determinations of multiple pollutant sources were conducted by the use of quasi reversibility methodology. Direct simulation together with the turbulent streamlines and turbulent heatlines demonstrate that the enclosure flow pattern, enclosure air thermal level and heat transfer potential will depend on the interactions of external forced flow and thermal buoyancy driven flows, i.e., Reynolds number (2×103 ⩽ Re ⩽104) and Grashof number (106 ⩽ Gr ⩽1010). In subsequent forward time and backward time modeling of airborne pollutant transports, temporal evolutions of enclosure average concentration and pollutant exhaust are shown to depend on the supplying velocity (Re), thermal plume (Gr), pollutant diffusivity (0.1⩽ Sc ⩽2), and the pitch between both sources (0.2H ⩽ dPSL = dPSR ⩽0.7H). Reverse time modeling of airborne spread has demonstrated that increasing the spread rate and the concentration sensitivity of airborne pollutants will facilitate the identification of pollutant sources. [Copyright &y& Elsevier]

Abstract: Simultaneous transport of heat and moisture by conjugate natural convection in a partial enclosure with a solid wall is investigated numerically. Moist air motions are driven by the external temperature and concentration differences imposed across enclosures with different ambient moisture conditions. The Prandtl number and Schmidt number used are 0.7 and 0.6, respectively. The fluid, heat and moisture transports through the cavity and solid wall are, respectively, analyzed using the streamlines, heatlines and masslines, and the heat and mass transfer potentials are also explained by the variations of overall Nusselt and Sherwood numbers. The numerical simulations presented here span a wide range of the main parameters (heat and mass diffusion coefficient ratios, solid wall thickness and thermal Rayleigh numbers) in the domain of aiding and opposing buoyancy-driven flows. It is shown that the heat transfer potential, mass transfer potential, and volume flow rate can be promoted or inhibited, depending strongly on the wall materials and size, thermal and moisture Rayleigh numbers. [Copyright &y& Elsevier]

Abstract: The numerical study presented in this work describes the direct and inverse mixed convection problems in a slot-ventilated enclosure subjected to an unknown heat flux on one side. Particularly, the interaction of internal natural convection with the cold ventilated flow leads to various flow fields depending on the Richardson number, Reynolds number, and the functional form of the imposed boundary heat flux. Fluid and heat transport structures across the enclosure are visualized by the streamlines and heatlines, respectively. Subsequently, an iterative conjugate gradient method is applied such that the gradient of the cost function is introduced when the appropriate sensitivity and adjoint problems are defined for a domain of arbitrary geometries. In this approach, no a priori information is needed about the unknown boundary heat fluxes to be determined. The accuracy of the heat flux profile solutions is shown to depend strongly on the values of Reynolds number and flux functional forms. Effects of measurement errors on the accuracy of estimation are also investigated. The present work is significant for the flow control simultaneously involving the natural convection and forced convection. [Copyright &y& Elsevier]

The present work is concerned with natural convection heat transfer and fluid flow in a vertical enclosure subject to periodic temperature boundary condition imposed at the right sidewall with a conducting body placed at the center of the enclosure. A close inspection is concentrated to the effects of the body size and thermal conductivity ratio on the resonant frequencies for unsteady state. The body size varies from 0.1 to 0.9 the height of the enclosure, and the thermal conductivity ratio from 0.1 to 20. The results are presented in terms of amplitude of cycle averaged Nusselt number, fluctuating velocity and temperature contours and its intensity. The vertical and horizontal temperature excursions are also shown. It is found that the resonant frequency decreases with increasing the body size and thermal conductivity ratio. The disturbance of hot wall travels the core region, and will be interrupted by the centered body. Double-peak structure of the vertical velocity intensity would be observed at resonance. [ABSTRACT FROM AUTHOR]

Abstract: This paper aims to prolong the heat pump frost time and reduce its growth with heat recovery facility, which should mix the exhausted indoor and outdoor air before entering the evaporator. An ideal mathematic model is developed for heat transfer, frost generation and airside pressure drop. The properties of the mixture would be obtained by solving the mass and energy conservation equations. A parametric analysis is performed to investigate the effects of air inlet temperature, relative humidity and air mass flow rate on total heat transfer coefficient, frost thickness and airside pressure drop, respectively. The results show that rationalizing the ratio of indoor and outdoor air could prolong frosting time and reduce the frost thickness greatly. The total heat transfer coefficient, frost thickness and airside pressure drop increase monotonically with time going, but are not proportional. Decreasing the mixture inlet air temperature and relative humidity could essentially reduce frost growth on the tube surfaces. This can also be observed when increasing the air mass flow rate. [Copyright &y& Elsevier]

High thermal conductivity and simple structure of two-phase closed thermosyphons (TPCTs) facilitate it extensively applied in low-grade thermal recovery, such like geothermal and solar energy exploitation. In present work, by incorporating threaded grooves into the evaporator section of the TPCTs, heat transfer performance could be significantly enhanced. Thermal transport mechanism of thermosyphons with various threaded groove structures was comprehensively investigated, and corresponding thermo-hydrodynamic performance was modelled through CFD/VOF simulations. Numerical procedures were validated well after comparison with experimental ones felled within 5.0 %. Under various heating power levels and filling ratios, heat transfer performance of thermosyphons with threaded grooves evidently surpassed that of smooth thermosyphons. Depending on delicate numerical results, critical point at 33 % filling ratio and 90 W heating power were confirmed that total thermal resistance of the grooved thermosyphon decreased almost close to 4.6 %. Furthermore, deviating from that critical point, higher heating power and lower filling ratio instead confined heat transfer performance of the threaded TPCT, which was primarily due to the rate of bubble generation and growth being significantly was slower than its detachment rate from the wall. In addition, heat and mass transfer performance of thermosyphons with threaded grooves of various pitches and apex angles were further analyzed under various conditions. Our results indicated that, when the groove apex angle turned to 90°, overall thermal transportation capability of the TPCT achieved optimal, with a decline in thermal resistance of up to 6.5 % compared to thermosyphons with smaller apex angles. Apex angle primarily affected the number of nucleation sites and the bubble detachment rate. Additionally, as the screw pitch decreased, boiling heat transfer enhancement, leading to more robust boiling heat transfer of TPCTs. Under high heating power, thermosyphons with larger screw pitch exhibited superior heat transfer performance. Overall, this innovative TPCTs with threaded grooves could be well applied in low-grade energy exploitation, particularly like as geothermal and solar energy fields. [Display omitted] • A VOF/CFD model was proposed to simulate the thermo-hydrodynamic performance of grooved thermosyphons. • The threaded groove structure enhanced the thermosyphons thermal performance by up to 5 %. • The groove apex angle of thermosyphons was optimized and confirmed around 90°. • Thermosyphons with larger screw pitch exhibited superior heat transfer performance. [ABSTRACT FROM AUTHOR]

High sunlight concentration on photovoltaic cells causes a substantial increase in the temperature of semiconductor, which leads to a decrease in conversion efficiency and irreversible faults of PV modules. Thereby, an ultra-thin Fan Shaped-Plate Pulsating Heat Pipe (FS-PPHP) was innovatively proposed by optimizing the traditional parallel channel structure in the thermal design for efficient cooling small scale HCPV cells. The effects of filling ratios, angles, working fluids and heat inputs on thermal transportation performance of FS-PPHP were comprehensively analyzed and discussed. The results indicated that the variable diameter design of the evaporation and condensation sections facilitates the working fluid return to the heating section and enlarges the imbalance pressure potential between adjacent channels, ensuring smoother startup of the FS-PPHP at various conditions. And the FS-PPHP exhibits excellent temperature oscillation characteristics at a filling ratio of 57 % and angle of 45° under variable input power, with a minimum thermal resistance of 0.5012 °C/W. Compared to deionized water, utilizing pure acetone as the working medium in the FS-PPHP reduces the average thermal resistance by 23 %, demonstrating superior heat transfer capability of FS-PPHP. Subsequently, the FS-PPHP was applied for cooling HCPV cells under simulated solar radiation, and its effect on the thermal and the output power characteristics of the HCPV cells was explored. The FS-PPHP could significantly reduce cell temperatures and enhance the generated electricity performance of HCPV modules, it was observed that in conjunction with from the FS-PPHP, the temperature of the HCPV cell ranged from 62.8 to 63.9 °C for solar irradiation of 4044.44 W/m2. Compared to natural cooling, this configuration resulted in a 56.1 % increase in output power and a 66.8 % average temperature reduction. [Display omitted] • A Fan Shaped- Plate Pulsating Heat Pipe (FS-PPHP) for HCPV cells cooling was firstly developed; • Superior thermal performance of FS-PPHP was theoretically and experimentally confirmed; • Power generation and thermal management of HCPV cells have been enhanced by FS-PPHP; • Present search and results could benefit the future thermal managements in chip and relevant units. [ABSTRACT FROM AUTHOR]

To address the problems of low power generation efficiency and low security of solar photovoltaic cells, a novel and versatile PV panel cooling strategy was proposed; which employed an absorbent hydrogel evaporative (AHE) cooling with 3D porous copper foam (CF) composite structure as an effective cooling component. By comparing natural cooling, comprehensive indoor simulated and outdoor experimental studies were conducted to explore the feasibility of enhancing the electrical output performance of PV cells. The effects of solar irradiation, environment humidity, ambient temperature and wind speed on heat transfer performance and the generated electricity power efficiency of PV with CF-AHE cooling panel were comprehensively analyzed and discussed. Present research demonstrated that the CF-AHE cooling layer of three solar irradiations (0.8, 1.0 and 1.2 sun conditions) could remove 449∼713W/m2 of heat from a photovoltaic cell, which significantly out-performed that of general cooling methodology depending on wind or buoyancy driven ventilation. The results further indicated that CF-AHE significantly reduces the cell temperature, enhancing the temperature uniformity of PV cell modules, i.e., the PV cell temperature ranges from 43–46 °C, markedly lower than the 53–66 °C observed with natural cooling. Additionally, average electrical efficiencies were enhanced by 4.69 %, 8.53 % and 12.84 % compared with that of natural cooling method, respectively. Subsequently, in the field test conducted in Wuhan city of China , current results further showed that our proposed cooling unit has boosted the power generation of PV panels by 14.01 % and reduced PV surface temperature by no less than 10 °C, simultaneously. Therefore, CF-AHE cooling structure can furnish excellent heat transfer characteristics and efficient electrical generation performance of PV panel. This research will provide valuable guidance for design of photovoltaic-AHE cooling systems and verifies the feasibility of such systems. [Display omitted] • Nano structures of porous copper foam and absorbent hydrogel were firstly designed. • An absorbent hydrogel evaporative (AHE) cooling with 3D porous copper foam (CF) was proposed. • Power generation and thermal management of PVs could be simultaneously enhanced by CF-AHE. • Potentials on commercial PVs have been demonstrated both by on-site and lab experiments. • AHE-CF could be especially advantageous in the regions of high temperature and humidity. [ABSTRACT FROM AUTHOR]

For energy efficient ventilation and low carbon design, solar chimney has been extensively applied on buildings. In the present work, three representative solar chimneys were introduced, i.e., Model 1 with top-horizontal outlet, Model 2 with upper-vertical outlet and Model 3 with middle-vertical outlet. Updraft ventilation from the built enclosure to the outlet and heat transfer from the absorber to the fluid by heat convection were numerically and theoretically investigated, and their limitations and correlations with governing parameters were also discussed. Streamlines and heatlines were used to visualize transport paths of air and heat respectively. Reverse flow could not be observed in the solar chimney channels of Model 2 and Model 3; Therefore, total volume flow rate induced by the solar chimneys Model 2 and Model 3 and convection heat transfer rate of the absorber increases positively with thermal Rayleigh numbers (Ra). Model 2 chimney produces greater thermal buoyancy than that by Model 3, and its air flow rate is higher than that of Model 3. Generally, volume flow rate induced in Model 1 is higher than those of Model 2 and Model 3 as Ra is no more than 2.5 × 106, and simultaneously, convection heat transfer rate Nusselt number (Nu) is also greater than those of Model 2 and Model 3. When Ra exceeded 2.5 × 106, reverse air flow was intensified further, Nu of Model 1 started to decline. The three models with discrete heat sources could induce more air from indoor than that respective model without discrete heat sources. The maximum increment rate is obtained by the Model 1 solar chimney with discrete heat sources, then Model 2 and the least done by Model 3. Their power relationships between Nu and Ra , V*and Ra are regressed respectively. The dependence of volume flow rate on broad thermal Rayleigh numbers covering all the three flow regimes showed that there were linear correlations between discrete numerical volume flow rates and the scaling predictions, except in Model 1 for high Ra (exceeding critical value 9.0 × 105), where volume flow rate was remarkably reduced due to reverse air flow. This research could provide useful theoretical information for applying small sized vertical solar chimneys attached to the building sidewall to effectively reduce built energy consumption. [ABSTRACT FROM AUTHOR]

• A novel coaxial condensing heat pipe applied in the solar CCHP/PVT system was proposed. • Thermal, electrical and exergy efficiencies of the solar CCHP/PVT system were defined. • Proposed CCHP/PVT system has better performance in thermal and electrical efficiencies. • Current theoretical models and codes were well validated by former experiments and results. • CCHP/PVT was favored for solar exploitation, particularly in the solar energy poor regions. Heat pipes offer tremendous potential for utilization in the energy and construction industries due to their excellent heat transmission efficiency. The current study involved the development of a theoretical model for thermal transport in a coaxial condensing heat pipe (CCHP) connected with solar photovoltaic and thermal (PVT) systems. Subsequently, parameter studies were conducted to analyze their impact on system performance, including irradiation intensity, surrounding temperature, inlet temperature, mass flow rate and PV coverage factor. In addition, temperature variation, thermal and electrical conversion capabilities of the CCHP/PVT system on typical days were discussed utilizing meteorological conditions in Wuhan city as inputs for the analysis. Our findings showed that the morning is when thermal efficiency is at its highest across the seasons, and it remained between 50% and 55%. Compared to natural cooling and conventional heat pipe cooling, the CCHP/PVT system reduced the temperature of the PV panels by approximately 30.3% and 16.3%, respectively. The proposed CCHP/PVT system has a respectively 14.4% and 5.2% enhancement in thermal and electrical efficiencies in comparison with those conventional heat pipes. Here, theoretical results agree well with former published ones, with average errors of no more than 10%. Our parametric investigations were then put into practice to assess the overall performance and to serve as a theoretical foundation for later development. It was really beneficial to boost the efficiency of solar energy utilization in the Yangtze River, China, where solar potentials were relatively poor than north western China. [ABSTRACT FROM AUTHOR]

Combined thermal and moisture convections in an enclosure partially filled with porous medium are numerically and analytically investigated, aiming to enhance moisture transport in the thermal energy storage unit. Two representative configurations of porous layers were taken into considerations, being placed centrally in the space or attached to the vertical walls. Moist air motions are simultaneously driven by the internal heat generation and external concentration difference imposed across the enclosure. Effects of Darcy number, mass diffusion coefficient, thermal Rayleigh number and buoyancy ratio on the heat and moisture transfer across the enclosure are discussed. Heat and mass transfer of the fluid/porous interface is analyzed as a function of the permeability of the porous layer. In the extreme case of high permeability and solutal-driven flow, a scale analysis is applied to predict the order of magnitudes involved in the boundary layer regime. Also, correlations for the average Nusselt and Sherwood numbers based on discrete numerical results are proposed. There is an agreement between the analytical and numerical results of moisture transfer rate, while a slight difference of heat transfer rate is observed due to different configurations of porous layers were imposed. Present research could benefit future development of sustainable building energy storage. [ABSTRACT FROM AUTHOR]

An objective-oriented optimization procedure consisting of a simplified conjugated gradient methodology and a two-dimensional fluid and thermal energy transfer model is implemented to discover optimal morphologies of local heating elements. Direct heat transfer problem and inverse optimization problem are subsequently investigated. Full simulation shows that thermal Rayleigh number, enclosure inclination, heating strength ratio and size ratio of local heating sources have significant effects on the natural convection heat transfer in the inclined enclosure, asymptotically modeling like solar energy collectors or electronic boxes. The fluid flow and energy transfer inside the enclosure are analyzed in some representative situations, by the simultaneous use of streamlines, isotherms and heatlines. Inverse natural convection solutions on the maximization of global conductance are addressed, concerning on the effects of thermal Rayleigh number, inclination angle, heater strength ratio and heater length ratio. Mathematical correlations have been proposed by the multiple linear regressions to identify the role of governing parameters on maximizing global conductance and optimal morphologies of the discrete heat sources, concerning on the unique global heating flux. Present numerical methodology and inverse procedures could benefit free cooling of electronic components and effective solar collection elements. [ABSTRACT FROM AUTHOR]

Natural convection on a heated and polluted strip within a partial enclosure is investigated, where the baffle is attached to the right wall. Numerical solutions demonstrate that the baffle in the partial enclosure could enhance heat and mass transfer rates only when Ra (thermal Rayleigh number) is higher than the critical value and its dimensionless vertical deviation between the baffle and horizontal x -axis, represented by E , lies between −0.8 and −0.5. When Ra ≥ 10 5 and E = −0.50 are imposed, heat and mass transfer rates for the dimensionless length of the baffle L = 0.8 are higher than those of L = 0.2 and L = 0.5; whereas, for Ra ≥8.0 × 10 5 and E = −0.8, convective transfer rates of L = 0.5 and L = 0.8 are higher than those of L = 0.2. These trends could be reversed when the regime of low Ra is established. Steady transition flows are observed as Ra varies from 1.25 × 10 5 towards 1.30 × 10 5 , where L = 0.2 and E = −0.6 are maintained; As Ra turns up to 8.00 × 10 5 from 7.90 × 10 5 , Nu and Sh could be enhanced sharply for L = 0.8 and E = −0.7. Moreover, huge divergences are observed for temperature and concentration distributions along the central axis when the steady transition flow appears in the enclosure. Present work could be significant for natural convection optimization and passive control of heat and pollutant removals from the building enclosures or electronic boxes. [ABSTRACT FROM AUTHOR]

This work uses an optimization procedure consisting of a simplified conjugate-gradient methodology and a two-dimensional fluid flow and heat transfer model to identify heat transfer capability of the enclosure with heat conducting partitions. The objective function is constructed by maximizing overall heat transfer rate (Nusselt number), upon the fact that overall volume of partitions is maintained constant whereas the height and position of these partitions could be varied. The pressure-based SIMPLE procedure was developed in a unification to solve the direct problem and the auxiliary problem. Direct and inverse natural convection problems are subsequently investigated. Direct simulation shows that partitions could put heavy effects on the natural convection heat transfer in the enclosure. Enclosed fluid flow and heat transfer are analyzed for some representative situations, by the simultaneously use of streamlines, isotherms and heatlines. Inverse problem solutions on the maximization of heat transfer rate are addressed, respectively regarding of thermal Rayleigh number, partitions location, partitions width, partitions total-length and thermal conductivity ratio. A correlation has been proposed to identify the role of governing parameters on maximizing overall Nusselt number. Present procedures and numerical results could benefit future electronic cooling and reduce materials consumed in heat transfer engineering. [ABSTRACT FROM AUTHOR]

The application of porous media for electronic cooling process, instead of solid one, generally strengthens heat conduction while weakens convection insignificantly at high Darcy number. In the present work, effects of morphology and topology of porous fins on the laminar natural convection heat transfer were investigated in a differentially heated enclosure. Volume averaged Darcy-Forchheimer model was applied to solve the transport process within the porous media while the Navier-Stokes equations were employed within pure fluid region. Relevant governing parameters, including thermal Rayleigh number, Darcy number, thermal conductivity of the porous matrix, designs of porous fins, are sensitively varied to identify their effects and roles on the natural convection flows. Depending on thousands of numerical data, the correlation has been developed for all designs of porous fins. Numerical results illustrate that the adding porous fins with excellent permeability and heat conduction contribute to the remarkable heat transfer enhancement while the adding fins, acting like solid ones and having poor heat conduction, could result in an increase of thermal resistance and the deterioration of heat transfer. Numerical results further show that there exists an optimal design of porous fins to achieve the best performance of heat transfer if some conditions were satisfied. Overall, this study could benefit the electronic cooling by the installation of porous-alike materials. • Electronic passive cooling is modeled by the natural convection in an enclosure. • Thermal conductivity and Darcy number of porous matrix were broadly tested. • Morphology and topology of porous fins on the natural flow were analyzed. • Porous fins flush mounted on the hot wall affect heat transfer rates significantly. • Porous fins maximize the heat transfer rate if some conditions were satisfied. [ABSTRACT FROM AUTHOR]