Effective Heat Transfer Coefficient Research Articles

Evaluation of heat mass performances for freeze drying of mint leaves

Mint leaves are one of the most used medicinal and aromatic plants in the world, having a wide range of minerals and vitamins. It is necessary to prevent nutrient content and quality loss during the drying of the leaves. This study aimed to perform the drying of mint leaves and to experimentally specified the effective diffusion coefficient, activation energy, and heat and mass transfer coefficients values throughout the drying process. Mint leaves were dried using a laboratory-scale dryer with three different drying temperatures (30, 40, and 50°C) and three different chamber pressures (50, 60, and 70 kPa). As a result, heat transfer coefficients varied from 0.3347 to 0.3353 W/m2K, and mass transfer coefficients varied from 3.33 × 10−10 to 2.27 × 10−9 m/s for different drying conditions. The effective moisture diffusivity during drying varied from 5.01 × 10−14 to 4.80 × 10−13 m2/s. The activation energy for mint leaves during drying varied from 79.07 to 76.44 kJ/mol at different drying temperatures. Practical applications Drying is an energy-intensive process that involves simultaneous heat and mass transfer. In this study, the heat and mass transfer coefficients of mint leaves at different drying temperatures and pressures were studied. In order to optimize the drying process, the heat and mass parameters of the product must be fully understood. Understanding these parameters can easily provide a basis for designing dryers with the best energy saving.

Similarity of energy balance in mechanically ventilated compartment fires: An insight into the conditions for reduced-scale fire experiments

When evaluating energy balance and temperature in reduced-scale fire experiments, which are conducted as an alternative to full-scale fire experiments, it is important to consider the similarity in the scale among these experiments. In this paper, a method considering the similarity of energy balance is proposed for setting the conditions for reduced-scale experiments of mechanically ventilated compartment fires. A small-scale fire experiment consisting of various cases with different compartment geometries (aspect ratios between 0.2 and 4.7) and heights of vents and fire sources was conducted under mechanical ventilation, and the energy balance in the quasi-steady state was evaluated. The results indicate the following: (1) although the compartment geometry varies the energy balance in a mechanically ventilated compartment, the variation in the energy balance can be evaluated irrespective of the compartment size and geometry by considering scaling factor F (∝heffAwRT, where heff is the effective heat transfer coefficient, Aw is the total wall area, and RT is the ratio of the spatial mean gas temperature to the exhaust temperature); (2) the value of RT, which is a part of F, reflects the effects of the compartment geometry and corresponds to the distributions of the gas temperature and wall heat loss.

Measurement and determination of local film cooling performance along a transonic turbine blade tip with viscous dissipation

Presented are experimental and analytic procedures for the measurement and determination of film cooling performance parameters for a transonic flow environment along a turbine blade tip, which account for the influences of viscous dissipation. Such viscous dissipation magnitudes are vital to ascertain appropriate driving temperatures for convective heat transfer within high velocity, compressible environments. A key step in this procedure is the separation of adiabatic surface temperature magnitudes due to the thermal field from adiabatic surface temperature values associated with flow effects related to viscous dissipation. These latter adiabatic surface temperature magnitudes, from flow effects only, are determined with no film cooling, which, when considered relative to flow stagnation temperature, are directly related to local Mach number values within the tip gap flow along the blade tip surface. After the separation is implemented, adiabatic surface temperature variations from film cooling thermal effects only are provided relative to local baseline values with no film cooling. Resulting local adiabatic film cooling effectiveness and local heat transfer coefficients are subsequently determined which are based entirely upon locally measured temperatures (without the use of global temperature parameters), which is the most appropriate perspective for presentation of spatially-resolved surface heat transfer characteristics. Associated data are provided for the surface of a blade tip with a squealer rim and recess, with and without film cooling. An array of five film cooling holes, located along the upper pressure side of a two-dimensional turbine blade, are employed to provide the film coolant, with a local blowing ratio BR of 3.02. Ratios of tip gap to true blade span are 0.66%, and 1.16%. Experimental procedures employed to obtain the spatially-resolved surface data include infrared thermography, transient testing techniques, and the impulse response method for transient data analysis.

Pool boiling enhancement via nanotexturing and self-propelled swing motion for bubble shedding

Vapor bubbles were shed from the heater surface by self-propelled swinging resulting from rising bubbles for improved heat dissipation. The heating wire was electroplated, and thus nanocones were formed on its surface. This nanotextured wire was attached to polyamide tape and underwent Joule heating. The vapor bubbles on the wire induced the self-propelled motion of the heater plates assembled in a “Λ” shape suspended at the tip. The growing bubbles experienced competing forces in the form of buoyancy and surface tension. Eventually, buoyancy dominated and, as a result, the heater plate was propelled in the direction of the rising bubbles. The nanotextured surface increased the number of bubble nucleation sites, and thus, the displacement of the swing motion was magnified accordingly, owing to enhanced bubble detachment. The sustainable swing motion was motorized to enable the temperature of the wire heater to be accurately measured. In these motorized experiments, the critical heat flux (CHF) and effective convective heat transfer coefficient (heff) increased when the amount of nanotexturing on the heating wire increased, which confirmed the benefits of nanotexturing on pool boiling in which self-propelled swing motion was utilized to shed the nucleated bubbles.

Measurement and determination of local film cooling performance along a transonic turbine blade tip with viscous dissipation

Abstract Presented are experimental and analytic procedures for the measurement and determination of film cooling performance parameters for a transonic flow environment along a turbine blade tip, which account for the influences of viscous dissipation. Such viscous dissipation magnitudes are vital to ascertain appropriate driving temperatures for convective heat transfer within high velocity, compressible environments. A key step in this procedure is the separation of adiabatic surface temperature magnitudes due to the thermal field from adiabatic surface temperature values associated with flow effects related to viscous dissipation. These latter adiabatic surface temperature magnitudes, from flow effects only, are determined with no film cooling, which, when considered relative to flow stagnation temperature, are directly related to local Mach number values within the tip gap flow along the blade tip surface. After the separation is implemented, adiabatic surface temperature variations from film cooling thermal effects only are provided relative to local baseline values with no film cooling. Resulting local adiabatic film cooling effectiveness and local heat transfer coefficients are subsequently determined which are based entirely upon locally measured temperatures (without the use of global temperature parameters), which is the most appropriate perspective for presentation of spatially-resolved surface heat transfer characteristics. Associated data are provided for the surface of a blade tip with a squealer rim and recess, with and without film cooling. An array of five film cooling holes, located along the upper pressure side of a two-dimensional turbine blade, are employed to provide the film coolant, with a local blowing ratio BR of 3.02. Ratios of tip gap to true blade span are 0.66 percent, and 1.16 percent. Experimental procedures employed to obtain the spatially-resolved surface data include infrared thermography, transient testing techniques, and the impulse response method for transient data analysis.

Estimation of Heat Generation in Semiconductors Centrally Mounted on Printed Circuit Boards

This work proposes a method to estimate the heat dissipation of components that are centrally soldered to printed circuit boards (PCBs). The power losses of a ball grid array (BGA) package and a MOSFET are estimated via a 1-D thermal model in tandem with a heat flux sensor. The former device is soldered to a multilayer PCB with complex copper traces, whereas the latter is mounted on a PCB without internal copper layers and relatively simple trace patterns. Thermal analyses demonstrate that the 1-D model is capable of representing heat conduction with good agreement in the board without internal copper layers. However, the multilayer PCB requires an adjustment coefficient based on the thermal conductance of the board. Said coefficient is employed to adjust the effective heat transfer coefficient of the multilayer PCB. With the aid of the adjustment coefficient, results show that the 1-D thermal model in combination with a heat flux sensor is capable of predicting heat dissipation within 15% of the actual power loss for both devices.

Transonic Turbine Blade Tip Heat Transfer with Pressure Side Film Cooling

Investigated are spatially resolved distributions of surface adiabatic film cooling effectiveness and surface heat transfer coefficients for a transonic turbine blade tip, with a unique and innovative film cooling arrangement, wherein a single row of five film cooling holes, located on the pressure side of the blade very near to the blade tip, provides thermal protection to the blade tip. The blade tip contains a squealer rim, and a squealer recess region. The present tip gap magnitude is 1.2% of the true blade span. When blade upper pressure side data are considered, heat transfer coefficient ratio variations are due, in part, to a horseshoe-shaped vortex structure, which forms around each film cooling jet, and then advects downstream. Spatially resolved distributions of surface adiabatic film cooling effectiveness show that the coolant advects to the upper edge of the blade pressure surface, along the pressure side rim, over the squealer recess region, and then sometimes collects in a substantial manner along portions of the suction side rim. As a result, local effectiveness values are generally higher on the suction side rim relative to pressure side rim values when compared at a particular value of blowing ratio.

Computational study for natural convection effects on temperature during batch and continuous industrial scale radio frequency tempering/thawing processes

Radio frequency (RF) processing have been used for tempering and thawing. There have been significant experimental and mathematical model based studies for this process especially in the last two decades. The modeling studies applied the convective boundary condition with effective heat transfer coefficient and constant medium temperature in through field flat plate RF systems. The objective of this study was first to develop a mathematical model for conjugate heat transfer (natural convection) in a staggered through field electrode RF system and to use this model for natural convection effects in industrial scale processes. For this purpose, the developed comprehensive mathematical model was experimentally validated using the data from frozen tuna samples. The air temperature variation was also used for validation. Then, the developed model was used in industrial scale process simulations with the presence of natural convection. The industrially preferred flat plate systems were used in this part to determine the temperature and electric field evolutions. The results demonstrated the significant effect of the natural convection on sample surface temperature distribution and temperature change of air within the cavity. The evolved natural convection resulted in the variation of the heat transfer coefficient along the sample surfaces with significant changes in temperature. Based on these results, it might be concluded that the effect of air temperature change within the cavity during an RF processes should also be controlled and considered for industrial system design and process optimization.

Boiling-condensation heat transfer and flow characteristics in ultrathin limited enclosed space based on numerical simulation and visualization experiment

Boiling-condensation heat transfer in ultrathin flat heat pipes are complicated and difficult to observe. In this study, a visualization experiment and simulation analysis in an ultrathin limited enclosed space were carried out. Width of the ul?trathin enclosed space was 1 mm, with anhydrous ethanol as the working medium. The enclosed space was oriented vertically with the heating section on the bottom and the cooling section on the top. Flow characteristics of the anhydrous ethanol were photographed using a high speed camera through the quartz cover. The boiling-condensation heat transfer and fluid-flow in the limited enclosed space were simulated. Effective heat transfer coefficient calculated based on the experimental data varied from 1.0-1.1 W/?C, while that of the inner wall obtained by the simulation varied within the range of 1.068-1.076 W/?C. The maximum error was 2.9%, which verified the reliability of the simulation results. By analyzing the pressure change in condensation section, it was found that the boiling-condensation heat released in the enclosed space changed periodically, because of the growth and bursting of bubbles and falling of the working medium due to gravity. Restricted by the thickness, the bubbles produced by boiling of the working medium grew in flat and irregular shapes, promoting the upward movement of the rest of the liquid working medium, and a liquid film was formed at the heated inner surface for evaporation heat transfer, which enhanced the heat transfer capacity of the heating section.

Computational Analysis of Conventional and Helical Finned Shell and Tube Heat Exchanger Using ANSYS-CFD

The summary of the proposed work is to compare the rate of heat transfer, logarithmic mean temperature difference (LMTD) and effectiveness (ε) for a conventional shell and tube heat exchanger with and without helical finned surfaces on tube side of heat exchanger. It is shown that the inlet velocity of cold fluid at the tube side varies, while the inlet velocity of hot fluid at the shell side remains constant. The percentage variations of heat transfer rates with theoretical and simulation methods are compared. The geometry is modelled in ANSYS design modeler and analysis have been carried out in ANSYS-CFD. The inlet velocity of shell side hot fluid is varied in both types of heat exchangers. The proposed work is tested for two configurations of counter flow heat exchanger (conventional and helical finned surfaces) under different shell side inlet velocities of fluids. Helical finned tube heat exchanger with counter flow has a higher LMTD than a conventional counter flow heat exchanger. Variation in heat transfer rates and heat transfer coefficients were observed in heat exchanger influenced by shell side hot fluid velocity. The study shows that helical finned tube surfaces have improved heat transfer rates, LMTD, effectiveness (ε) and overall heat transfer coefficients compared to the conventional heat exchangers.

Legitimacy of the Local Thermal Equilibrium Hypothesis in Porous Media: A Comprehensive Review

Local thermal equilibrium (LTE) is a frequently-employed hypothesis when analysing convection heat transfer in porous media. However, investigation of the non-equilibrium phenomenon exhibits that such hypothesis is typically not true for many circumstances such as rapid cooling or heating, and in industrial applications involving immediate transient thermal response, leading to a lack of local thermal equilibrium (LTE). Therefore, for the sake of appropriately conduct the technological process, it has become necessary to examine the validity of the LTE assumption before deciding which energy model should be used. Indeed, the legitimacy of the LTE hypothesis has been widely investigated in different applications and different modes of heat transfer, and many criteria have been developed. This paper summarises the studies that investigated this hypothesis in forced, free, and mixed convection, and presents the appropriate circumstances that can make the LTE hypothesis to be valid. For example, in forced convection, the literature shows that this hypothesis is valid for lower Darcy number, lower Reynolds number, lower Prandtl number, and/or lower solid phase thermal conductivity; however, it becomes invalid for higher effective fluid thermal conductivity and/or lower interstitial heat transfer coefficient.

Delay time of gases's catalytic heterogeneous ignition on various sizes's catalyst particles

In this work, catalytic ignition delay time of combustible gas's small impurities in air on a spherical metal particle of various diameters is analytically determined by the example of gas-air mixtures's flameless combustion with hydrogen impurities on a platinum particle. It is shown that stable flameless combustion is observed after an induction period for particles of a certain range. It has been established that catalytic ignition time of gases is divided into three stages: 1. inert heating, the duration of which still depends on the combustible gas concentration; 2. the stage of self-acceleration and catalyst temperature rise during the course of the catalytic reaction in the transition region; 3. stage of diffusion inhibition and reaching stable catalytic combustion. The characteristic relaxation time was used in a dimensionless form. To determine the duration of the second stage, a modified Frank-Kamenetsky approach is applied. The duration of diffusion inhibition stage in the dimensionless form is practically independent of catalyst particle's diameter, although the catalytic combustion temperature decreases with an increase in the catalyst diameter. Heat transfer by radiation, the role of which increases with the growth of the catalyst size, is included in the effective heat transfer coefficient, which allows maintaining the classical ideology to solving the problem of the induction period.

Three-dimensional lattice Boltzmann investigation on pore scale liquid–vapor distribution patterns and heat transfer performance of a loop heat pipe heterogeneous porous wick evaporator

The pore scale numerical simulations on evaporation of a three-dimensional heterogeneous porous wick capillary evaporator used in a loop heat pipe (LHP) are realized through using a lattice Boltzmann method with liquid–vapor phase change. The dynamic liquid–vapor interface characteristics are obtained. The steady-state wick state and heat transfer performance as well as the influences of wick porosity and surface wettability are discussed. It is found that as heat flux increases, the wick state changes from the fully saturated state at low heat fluxes, to the partial dryout state at medium heat fluxes, and finally to the complete dryout state at high heat fluxes. The effective heat transfer coefficient of evaporator firstly grows slowly for the saturated wick, then increases rapidly and reaches a maximum value at partial dryout wick state, but afterwards drops sharply when the wick starts to be complete dryout. With the decreasing of wick porosity and contact angle, the heat flux to achieve the maximum effective heat transfer coefficient is increased and the complete dryout state is postponed. In the present range of parameters, the maximum effective heat transfer coefficient is improved by reducing wick porosity, while it is barely affected by contact angle.

Numerical prediction on deposition growth and heat transfer characteristics burning high–sodium pulverized coal

In this paper, a transient numerical model, which both considered fly–ash particle deposition and alkali vapor condensation, is proposed to predict the ash deposition propensity on a single heat transfer surface. Four deposition mechanisms are considered comprehensively, named inertial force, thermophoresis force, direct condensation, and heterogeneous nucleation. The condensation behavior caused by high content of AAEM was quantitatively evaluated according to the partial pressure of alkali vapor and the changing saturation pressure. The dynamic mesh technology based on an advisable strategy was performed to reflect the actual shape of fluid–solid interface in deposition process. Furthermore, a resistance network model (RNM) is established to calculate the effective heat transfer coefficient, and the temperature of deposition surface is solved based on the principle of energy conservation, in order to analyze the heat transfer performance of deposition layer. The contribution of each of the four essential mechanisms to tendency of deposition and condensation in different areas is evaluated. The different cases are used to investigate the effects of five typical furnace temperatures and six prime particle sizes on deposition and heat transfer characteristics. The proposed model has been validated and shown to predict deposition rate effectively and heat transfer parameters for ZD coal burned in 300 kW test furnace.

Thermal conductivity of porous oxide layer: A numerical model based on CT data

This paper presents a novel method to determine the effective thermal conductivity of porous oxides formed on steel. This advanced approach enables more accurate numerical modeling of the oxide layer impact on the spray cooling of steel. Although the thermal conductivity of the oxide layer is highly influenced by the porous structure of iron oxides, the microstructure of the oxide layer was generally not considered in the studies of the thermal conductivity. In this paper a detailed 3D finite element model of the oxide layer based on a data acquired by computed tomography was created. The image acquisition and image processing are described. An unconventional method of converting image voxels directly into finite elements was used. Two distinct segmentation approaches were implemented and results of simulations were averaged. Obtained temperature-dependent results of the effective conductivity of the oxide layer was used as an input material parameter for the subsequent numerical simulation of the spray cooling of steel. The impact of the oxide layer with different thicknesses was quantified by plotting the temperature-dependent effective heat transfer coefficient. The limitations of the commonly used alternative analytical approach were identified.

Performance evaluation of three latent heat storage designs for cogeneration applications

Well-integrated thermal energy storage units can enhance flexibility and profitability for a cogeneration system by enabling its decoupling of electricity and heat production. In the present study, novel latent heat thermal energy storage technologies are numerically investigated on their thermal and economic performance to evaluate their implementation at an existing combined cycle power plant. Three commercially available storage designs are analyzed: one shell-and-tube heat exchanger design based on planar spiral coils, and two types of advanced macro-encapsulated designs with capsules resembling ellipsoid and slab in shape, respectively. For the spiral coil design, three-dimensional flow velocity and temperature fields are simulated with finite volume method to predict the transient storage heat transfer process, including the effect of secondary flow induced by centrifugal forces. For the macro-encapsulated designs, effective heat transfer coefficients between heat transfer fluid (HTF) and phase change material (PCM) are inferred from scaled-down storage prototyping and testing. A one-dimensional two-phase packed bed model was developed based on the apparent heat capacity-based enthalpy method to numerically study the heat transfer in macro-encapsulated PCM. With an operating temperature range of 46–72 °C and a HTF supplying flowrate range of 4.2–8.4 m3/h defined by the cogeneration strategy, thermal power and accumulated storage capacity are calculated and compared for the first three hours of charge and the first hour of discharge for the three designs. The effect from increasing the HTF flowrate to accelerate charging/discharging processes is indicated by the simulation results. Performance comparison among the three designs shows that the slab capsule design exhibits the highest accumulated storage capacity (710 kWh) and state of charge (40%) after three hours of charge, though it has a lower theoretical total storage capacity (1760 kWh) than the spiral coil design (1830 kWh). The ellipsoid capsule design shows a slightly lower accumulated storage capacity (700 kWh) than the slab design for 3-hr charge and an equivalent accumulated storage capacity/depth of discharge (250 kWh/14%) as the latter. Furthermore, the storage power cost of the slab capsule design is the lowest, by 6–12% lower than the spiral coil design and by 2–3% lower than the ellipsoid capsule design. However, with the highest design flowrate of 8.4 m3/h, the low state of charge (below 40%) after three hours and the low depth of discharge (below 14%) after one hour indicate that redesigning the heat transfer boundary conditions and the configurations of the three units are necessary to meet desirable storage performance in cogeneration applications.

Heat transfer growth of sonochemically synthesized novel mixed metal oxide ZnO+Al2O3+TiO2/DW based ternary hybrid nanofluids in a square flow conduit

In the current investigation, the heat transfer development with the turbulent flow of novel metal oxide-based ternary composite nanofluids of ZnO + Al2O3+TiO2/DW at varying wt.% concentrations (0.025, 0.05, 0.075, and 0.1) in a square heat exchanger below constant heat flux conditions was discussed. The new ternary composite nanofluids were synthesized by using the sonochemical technique. The ZnO + Al2O3+TiO2/DW based ternary composite nanofluids with their respective wt. % reveals an enhancement in effective thermal conductivity and heat transfer coefficient local and average with Reynolds numbers varying from 4550 to 20,367. The extreme growth in overall effective thermal conductivity was noticed up to 1.149 W/m-K at 0.1 wt% for ternary hybrid composite nanofluids at a maximum temperature 45 °C. Similarly, at 0.075 wt%, 0.05 wt%, and 0.025 wt% the overall effective thermal conductivity was recorded 1.118 W/m-K, 1.091 W/m-K, and 1.079 W/m-K correspondingly, which is greater than that of base fluid (DW), with improved thermo-physical characteristics for novel ZnO + Al2O3+TiO2/DW ternary hybrid composite nanofluids. Also, it shows an improvement in local and average heat transfer with a maximum growth of 0.1 wt %. The maximum heat transfer was observed for ZnO + Al2O3+TiO2/DW based Ternary hybrid composite nanofluids at 0.1 wt % concentrations, up to 900–5700 W/m2K, which is 89% higher than distilled water. While, an enhancement of 900–3870 W/m2K, 900–3350 W/m2K, 900–2750 W/m2K were observed for the other three wt. % 0.075, 0.05 and 0.025, respectively. The study revealed that the metal oxide based ternary hybrid composites nanofluids are suitable for nano coolant applications due to improved thermophysical characteristics and also it is applicable for energy management in industrial applications.

Effects of non-isothermal oxidation on transient conjugate heat transfer of the cryo-supersonic air-quenching

In this paper, the effects of non-isothermal oxidation on transient conjugate heat transfer of the cryo-supersonic air-quenching are investigated based on a double-layered oxidation kinetics model, while a unified conjugate heat transfer formula is developed to synthetically consider the near-wall turbulence, non-isothermal oxidation, and surface radiation. The comparison between numerical and experimental results are also presented to check the validity of the developed model. The results indicate that the film growth has some degree of inhibition to the conjugate heat transfer, in particular, the stagnation temperature increases linearly by about 5 K per 100 ?m increase in film thickness, and the effective conjugate heat transfer coefficient in the stagnation region decreases linearly by about 55 Wm?2K?1 per 100 ?m increase in film thickness. Moreover, the oxide film would have little impact on transient conjugate heat transfer when the near-wall velocity is higher due to the effect of viscous dissipation.

Pool boiling enhancement by nanotextured surface of hierarchically structured electroplated Ni nanocones

Electroplated Ni nanocones (NiNCs) with a hierarchical structure were used to enhance the pool boiling properties of a surface. The electroplating time was varied to produce NiNCs with varying texturing parameters, which affected the morphology, roughness, and surface area of the boiling surface. These parameters affected the number of boiling nucleation sites and the surface wettability. The resulting values of the critical heat flux (CHF) and effective heat-transfer coefficient (heff) were derived. The heat flux (q″) sharply increased when the superheating temperature (ΔTsat) exceeded the temperature at the onset of nucleate boiling, which distinguished the natural convection regime from the boiling regime. Optimal texturing was obtained at an electroplating time of tep = 5 min and increased the CHF by 36% compared to that of the bare Cu substrate: q″opt = 214 and q″bare = 157 kW⋅m−2. The value of heff increased correspondingly from 5.7 to 10.5 kW⋅m−2⋅°C−1. The Rayleigh and Nusselt (Nu) numbers in the natural convection regime were also the highest for the optimal texturing case. The total surface area was the largest when the surface roughness reached a maximum. A dimensionless parameter, the relative roughness (r*), was introduced to represent the ratio of the surface roughness (R) to the total surface area (A). The CHF, ΔTsat, bubble diameter (Db), boiling Nusselt number (Nub), and experimental factors (CCHF and Cheff) can be linearly expressed in terms of r*, confirming the importance of textured surfaces for the enhancement of the pool boiling performance.

Efficient Thermoelectric Transformation of Daily Thermal Fluctuations into Electricity

We present an enhanced micro-energy harvester design that couples a thermoelectric module to a heat storage unit formed by a Phase Change Material embedded within a metallic foam. The effect of the thermal resistance between the thermoelectric material and the ambient is investigated through an effective heat transfer coefficient. A case study is analyzed to transform daily thermal fluctuations into electricity during a full day on ground conditions in a Southern Hemisphere typical winter day, using hexadecane as PCM and aluminium as metallic foam. For base PCM as a heat storage unit, the micro-harvester generates 0.01 J after a full day of operation. However, the metallic foam multiplies the electric energy production: from 0.23 J for ∈ = 0.95 to 0.49 J for ∈ = 0.85. Importantly, the relative boost in electric energy production is robust across a wide range of thermal resistance loads.