Effect Of Natural Convection Research Articles

Performance prediction on ice melting process for cold energy utilization: Effect of natural convection

Due to poor thermal conductivity of phase change material (PCM), applications of ice storage and cooling systems are hindered. To analyze the effect of natural convection on melting process for a horizontal shell-and-tube latent heat storage (STLHS) unit, the melting performance of STLHS unit with various endothermic source temperatures and eccentric directions is investigated by experiments and numerical simulation. Temperature distribution, liquefaction rate, and transient-overall heat transfer coefficient during the melting process are analyzed. Results show that circulation vortex formed by natural convection is a dominant factor that affects the transient-overall heat transfer coefficient. Total melting time of the STLHS unit is advanced by 41.8 % as the endothermic source temperature is increases from 279.15 K to 281.15 K. Influenced by density inversion and real physical properties of ice and water, melting tendency of the PCM shows opposite directions with the increase of endothermic source temperature. Time to total melting by raising the endotherm source by 5 mm is 45.4 % earlier than that lowers it by 5 mm at 281.15 K. Further, this analysis strategy provides theoretical guidance for the design of shell-and-tube ice storage units, which can be widely used for rapid cold energy extraction.

Evaluation of Melting Mechanism and Natural Convection Effect in a Triplex Tube Heat Storage System with a Novel Fin Arrangement

In this research, a numerical analysis is accomplished aiming to investigate the effects of adding a new design fins arrangement to a vertical triplex tube latent heat storage system during the melting mechanism and evaluate the natural convection effect using Ansys Fluent software. In the triplex tube, phase change material (PCM) is included in the middle tube, while the heat transfer fluid (HTF) flows through the interior and exterior pipes. The proposed fins are triangular fins attached to the pipe inside the PCM domain in two different ways: (1) the base of the triangular fins is connected to the pipe, (2) the tip of the triangular fins is attached to the pipe and the base part is directed to the PCM domain. The height of the fins is calculated to have a volume equal to that of the uniform rectangular fins. Three different cases are considered as the final evaluation toward the best case as follows: (1) the uniform fin case (case 3), (2) the reverse triangular fin case with a constant base (case 12), (3) the reverse triangular fin case with a constant height (case 13). The numerical results show that the total melting times for cases 3 and 12 increase by 4.0 and 10.1%, respectively, compared with that for case 13. Since the PCM at the bottom of the heat storage unit melts slower due to the natural convection effect, a flat fin is added to the bottom of the heat storage unit for the best case compared with the uniform fin cases. Furthermore, the heat storage rates for cases 3 and 12 are reduced by 4.5 and 8.5%, respectively, compared with that for case 13, which is selected as the best case due to having the lowest melting time (1978s) and the highest heat storage rate (81.5 W). The general outcome of this research reveals that utilizing the tringle fins enhances the thermal performance and the phase change rate.

Impact of inclination on the thermal performance of shell and tube latent heat storage system under simultaneous charging and discharging: Numerical investigation

In this paper, the impact of inclination on the thermal performance of latent heat storage system (LHSS) based cylindrical shell and tube heat exchanger is investigated. During the simultaneous charging and discharging (SCD) process, a visualized numerical simulation is carried out to demonstrate the melting process of phase change material (PCM). The SCD technique for the LHSS comprises charging of PCM from one side while discharging from the other. To investigate the performance of the LHSS, a transient numerical model based on the enthalpy-porosity method is used. The distribution of temperature, melt fraction, energy stored, and average Nusselt number are analyzed to study the effect of natural convection on the performance of LHSS with inclination angles viz. 90° (vertical) 60°, 30° and 0° (horizontal). Results illustrate that better thermal performance is provided by the horizontal (0°) configuration. The effect of natural convection on the PCM under the SCD melting process has differed with the angle of inclination. The position of cold heat transfer fluid (HTF) showed a considerable influence on the process of melting. With the decrease of inclination angle from 90° to 0°; there is an increase in melt fraction by 38.02 %. The maximum energy stored (231 kJ) obtained at the horizontal (0°) configuration is 26.2 % higher than the vertical position. Also, the steady-state condition is observed earlier in the horizontal position. Further, the flow behavior of PCM with inclination is also illustrated.

Numerical study of high-temperature cascaded packed bed thermal energy storage system

The thermal energy storage system (TES) in the form of packed bed with encapsulated phase change materials (EPCMs) can further improve the thermal performance of ordinary TES. This study presents a numerical model for a three-dimensional cascaded packed bed thermal energy storage system (PBTES), in which an effective thermal conductivity model is used by consisering the natural convection effects in each EPCM based on its volume average liquid fraction. To examine the system-storage thermal energy and exergy in PBTES accurately, a thermodynamic analysis approach is also given. The high-temperature PCMs are grouped as KNO3, NaNO3, and NaNO2 according to the phase transition temperature from high to low in the packed bed stage. The effects of element stages on the thermal performance of PBTES are studied. Results show that the total thermal energy storage of cascaded-PBTES is 38.5% higher than that of single-PBTES (KNO3), and the total thermal exergy storage is 30.8% higher than single-PBTES. The average exergy efficiency possessed by cascaded-PBTES is 5% higher than that of single-PBTES. Furthermore, the effects of heat transfer fluid (HTF) inlet temperature and mass flow rate on the thermal performance of cascaded-PBTES are discussed. The increase of inlet temperature and mass flow rate can promote the charging process and influence the exergy efficiency. However, increasing the inlet mass flow rate will not lead to an increase in maximum thermal energy and exergy storage capacity.

Effect of natural convection on 3D MHD flow of MoS2–GO/H2O via porous surface due to multiple slip mechanisms

ABSTRACT The theme of this work is to examine the magnetized flow behaviour of hybrid nanofluid containing molybdenum disulphide (MoS2) and graphene oxide (GO) nanoparticles subject to multiple slip mechanisms, natural convection and chemical reaction of mth order. The working hybrid nanofluid is prepared by an amalgamation of nanoparticles, i.e. MoS2 and GO and conventional fluid (H2O). The existing equations of the model were solved by the techniques, i.e. shooting and bvp4c. To validate our codes, the comparison was presented by previous research. Here, we observed that, with an increase in thermal slip parameter values, only the thermal field profiles of MoS2–GO/H2O regularly depreciated. Moreover, when there was augmentation in velocity slip parameter, temperature and concentration functions rose, while both velocity outlines of MoS2–GO/H2O fluid declined. Furthermore, the velocity functions of MoS2–GO/H2O augmented and the concentration function declined with an increase in natural convection parameter values.

Computational analysis of flow separation in a mixed convection MHD flow over a vertical paraboloid: Case of externally retarded flow

Combined effects of forced and natural convection on the occurrence of flow separation and heat transfer on a vertical paraboloid of revolution under the influence of a magnetic field are studied in this investigation. Inside the boundary layer, free convection is established due to the temperature difference between the fluid and the boundary while forced convection happens due to the presence of an external potential flow. The external potential velocity is chosen from the decelerated nature concerning the stream-wise coordinate due to which the flow separation is expected to occur. The influence of natural convection, the applied magnetic field, and the surface transverse curvature on delaying the flow separation and on the rate of heat transfer in the vicinity of the separation point is the aim of the investigation of this study. Regarding these important physical ingredients, the percentage increase in separation length and the rate of heat transfer are calculated. Moreover, their influence on the flow and heat-transfer phenomena has also been discussed in detail and presented through various graphs and tables. An exact numerical solution is obtained with the aid of an implicit finite difference scheme.

Thermal performance assessment of phase change material for electronic cooling: An experimental investigation

AbstractIn the present study, an experimental investigation is performed to check the performance of phase change material (PCM) OM42 for passive electronic cooling applications. Rectangular fins were used as PCM thermal conductivity enhancers (TCEs) to enhance the thermal conductivity of PCM. The experiments were performed (a) by maintaining the required input heat flux to the heater and (b) by maintaining the set point temperature (SPT) of the heater. The heater wattage controller was used to supply the required power to the heater and thermostat W1209 was used to control the SPT of the heater. The experiments were performed in the combination of PCM and fins, with fins only, With PCM only, and with PCM and fins. The obtained results signify improved performance of the heat sink when PCM with fins was used. At input heat flux of 1, 2, 3, 4 and 5 kW/m2 the heat sink reaches the critical temperature in 80, 60, 55, 50 and 40 minutes respectively in the absence of PCM without fins, but with the presence of PCM without fins and PCM with fins, the heater sink is well below the critical temperature for a complete charging cycle. At input heat flux of 4 and 5 kW/m2, the intensity of PCM melting rate is faster and hence solid‐liquid interface decreases quite rapidly as the buoyancy force dominates the viscous force since the volume of liquid PCM rises as the natural convection effect increases in the liquid region.

Effect of Al2O3–SiO2/Water Hybrid Nanofluid Filled in a Square Enclosure on the Natural Convective Heat Transfer Characteristics: A Numerical Study

In this study, heat transfer enhancement by natural convection Al2O3/water mono and Al2O3–SiO2/water hybrid nanofluid in an enclosure cavity have been performed utilizing the finite element method. For numerical computations, the homogeneous nanofluid approach was considered. The cavity was heated from the left vertical wall and cooled from the right vertical wall while the top and bottom walls were taken as adiabatic. The effects of some related factors such as the Rayleigh number (103 ≤ Ra ≤ 106) and nanoparticles’ volume fraction (0 ≤ φ ≤ 0.05) on the heat transfer by natural convection were examined. To discuss fluid characteristics of mono and hybrid type nanofluid under natural convection effect, the obtained results were presented as streamlines and isotherms. Also, variations of local and average Nusselt numbers were examined in detail. It was obtained that an increase in the nanoparticle volume fraction leads to the enhancement of convective heat transfer for all Rayleigh numbers. It was also indicated that the highest increment in heat transfer by convection occurs in the nanoparticle volume fraction of 2% for Al2O3/water and 4% for Al2O3–SiO2/water. The present study results are also consistent with the literature results.

Heat transfer analysis of a PCM in shell-and-tube thermal energy storage unit with different V-shaped fin structures

This study provides an alternative solution to enhance melting performance of phase change material by designing a novel V-shaped fin. Nineteen cases with different V-shaped fins is designed, the effects of angle, length, number and arrangement of fins on heat transfer performance of heat storage unit were studied. The response surface method was used to optimize the structure. Assessments on the melting fraction, temperature field, velocity distribution, and uniformity for melting are made. Results demonstrate that due to the effect of natural convection, the upper part melting speed is accelerated, resulting in a significant difference in the heat storage efficiency between the upper and lower half regions. The melting time of the lower half of the heat storage unit without fins accounting for 62.5 % of the whole melting time. Based on the above analysis, more and longer fins should be considered to be arranged at the bottom of the heat storage unit to improve the heat storage performance of the system. As noticed, the structure parameters change of fins has a significant effect on reducing the melting time of the whole phase change material. It can be found that there are optimal values for the structure parameters. The optimal fin structure parameters (fin angle α = 55°, fin length L1 = 9 mm, fin number N = 5, branch angle β = 55°, and branch length L3 = 3) obtained. The heat storage efficiency of the optimal fin structure was 2.57 times that without fins, and the heat storage time was shortened by 61.05 %. To be conclusive, adding fins to a heat exchanger is more beneficial than no fins, saving more energy storage time.

Parametric study of phase change time reduction in a shell-and-tube ice storage system with anchor-type fin design

This paper introduces an innovative anchor-type longitudinal fin design that copes with the sluggish phase change process in shell-and-tube ice storage units by covering the regions between the conventional fins. The influence of these fins is studied on both melting and solidification processes. The simulations show that the melting process is much slower than the solidification process (up to 201.5%), and the presence of fins can be more influential on the melting process. The examined parameters for the fins are arc angle (θ), shank length (Lsh), number of anchor-type fins (Nf), and number of arcs on these fins (Na). The study reveals that at an identical PCM volume, this type of fin can improve the melting time by 1367.7 and 151.8% compared to when the bare tube and conventional longitudinal fins with the same length and number are used, respectively. On the other hand, these values for the solidification process are 544.2 and 89.5%, respectively. Furthermore, it was found that these fins manage to diminish the undesirable effects of natural convection by disrupting the unwanted thermal stratification in the container by breaking the large circulation zone for the natural fluid flow in the container into several smaller circulation areas.

Performance investigation of a vertically configured LHTES via the combination of nano-enhanced PCM and fins: experimental and numerical approaches

Thermal energy storage using Phase Change Materials (PCM) with low thermal conductivity presents one of the barriers to ensuring the storage and release of large heat quantities in a short time suitable for solar applications. One of the best techniques to overcome this obstacle is the inclusion of nanoparticles into the PCMs. Furthermore, the use of finned storage units can significantly boost thermal performance. In this paper, A comprehensive 3D numerical study is presented to investigate the performance of a vertically-configured-cylindrical copper LHTES using Nano-Enhanced PCM (NEPCM) with both outer and inner longitudinal fins. Based on the enthalpy-porosity technique, the numerical model is established taking into account the natural convection effect and transient variations in the thermo-physical properties of NEPCM. An experimental setup is built to analyze the thermal behavior of LHTES with CuO and Al2O3 based NEPCM, and to validate the numerical model. Once validated, the numerical model is employed to investigate the combining effect of using fins and NEPCM based on CNT 1% and Al2O3 2% nanoparticles. Transient numerical simulations are conducted for both charging and discharging cycles for six scenarios corresponding to several NEPCM and configurations (with and without longitudinal fins). Both experimental and numerical investigation show that the NEPCM ensures a great improvement, resulting in large time savings during both charging and discharging phases compared to pure PCM. Moreover, the results show that placing six outer and inner longitudinal fins in the wall of LHTES shortens discharge and charging times by 71% and 62%, respectively, as compared to the reference case (pure PCM without fins). Furthermore, using NEPCM with 1% CNT nanoparticles by weight dispersed in PCM combined with six outer and inner longitudinal fins reduces discharge and charging times by 89% and 84%, respectively. Although CNT is very effective by highly enhancing the PCM thermal characteristics, it is very expensive compared to metal oxide nanoparticles. However, it was discovered that using 2% Al2O3 for finned LHTES can achieve nearly the same results as using 1% CNT.

Thermal performance of low melting point metal-based heat sinks for high-power airborne equipment

Low melting point metals (LMPMs) have greater potential to address the cooling difficulties of high-power airborne equipment than conventional phase change materials (PCMs). However, the heating power in existing LMPM-based heat sinks is generally low. Here, a bismuth-based alloy, Bi44.7Pb22.6In19.1Sn8.3Cd5.3, is adopted. Experiments were conducted in a pin fin heat sink (PFHS) and an empty heat sink (EHS) under 50–1500 W. Experimental results on the effect of PCMs indicate that heat sinks filled with LMPMs outperform n-dodecane. The heating wall temperature is decreased, and the holding time is prolonged significantly. The EHS and PFHS remain below 50 °C from 847 and 1268 s to 2209 and 2302 s at 50 W, respectively. Experimental data illustrate that for LMPM-based heat sinks, the heating wall temperature and holding time are improved by applying pin fins. The EHS and PFHS remain below 50 °C for 143 and 183 s at 500 W, respectively. However, the difference between the holding time below 70 °C for EHS and PFHS is reduced to ±3%. Experimental results reveal that increasing the heating power results in rising heating wall temperature and falling holding time. The holding time of the LMPM-based PFHS decreases from 2302 s at 50 W to 61 s at 1500 W, and the heating power effect weakens from approximately 50% at 100–200 W to approximately 10% at 900–1500 W. Moreover, the Nusselt number (Nu) decreases with increasing dimensionless time, but the decrease is increasingly smaller. A higher Rayleigh number correlated with a larger heating power leads to a higher Nu due to the intensive effect of natural convection. New dimensionless correlations of Nu are developed, yielding mean absolute deviations of 3.5% and 2.7% for the LMPM-based PFHS and EHS, respectively.

Numerical investigation of latent heat thermal energy storage unit with different configurations and phase change materials

In this work melting behavior of PCMs inside the LHTES (latent heat thermal energy storage) unit for six different cases has been numerically investigated by Comsol Multiphysics and Simulation Software. Two different PCMs (phase change materials), namely lauric acid and n-octadecane, have been used in the analysis for two different configurations. When configuration-1 has only one region for PCM, configuration-2 contains two regions. Simulations show that melting is completed at the upper side of the LHTES unit first due to the natural convection effects. On the other hand, it has been shown that LHTES unit in the form of configuration-1 with n-octadecane completes phase change earliest and absorbs most heat at the end of the process. This also demonstrates that not only latent heats of the PCMs, but also parameters affecting natural convection have an important effect on the heat transfer. Because when PCM with a lower melting temperature is used, buoyancy force, consequently absorbed heat increases. Inside boundaries also inversely affect absorbed heat by PCMs due to the non-slip boundary condition on these boundaries. The maximum efficiency of the LHTES unit is obtained for the configuration-1 with lauric acid due to not only high value of absorbed heat as a result of fewer obstacles of the geometry, but also the smaller values of latent heat and specific heat of lauric acid affecting Emax.

Numerical and experimental investigation of supercooling and natural convection in octadecane phase change material

With the increasing global interest in energy savings, latent heat thermal energy storage (LTES) systems are used for energy harvesting and preservation, thus reducing the demand for traditional energy sources. The main concept of solid–liquid LTES systems is to absorb and release the latent heat of a material through consecutive melting/solidification cycles. Supercooling is a phenomenon that prevents the solidification of a liquid having a temperature lower than its melting temperature. Considering this phenomenon in designing the numerical models gives a better prediction of the system’s energy performance. This work is the first attempt to include supercooling in a two-dimensional COMSOL model. The model accommodates natural convection during the melting process and supercooling during the cooling process of the phase change material (PCM). A set of experiments using octadecane PCM are performed. The effect of supercooling and natural convection on the temperature curve and the energy behavior of the PCM are shown. The effect of cooling rate, volume of PCM and container structure on the degree of supercooling are also discussed. A small degree of supercooling in octadecane is recorded when having small volume, low cooling rate and a smooth surface. The obtained experimental results validate the proposed numerical model.

(Digital Presentation) Effects of Thermal Convection on Species Transport in Photocatalytic Suspension Reactors

Z-scheme photocatalytic suspension reactors with aqueous redox shuttles present a promising pathway for safe and low cost solar water splitting to produce hydrogen. Soluble redox shuttles act as electron relays between light absorbing particles present in the two compartments. In recent work we have demonstrated a theoretical pathway to attain up to 4% solar-to-hydrogen efficiency with passive diffusion driven species transport [1]. However, to attain larger solar-to-hydrogen efficiencies it is crucial to enhance the rate of species transport between the two reaction compartments. We report on computational and experimental investigations to explore the effects of natural convection on species transport in Z-scheme photocatalytic systems. A transient, two-dimensional fluid flow, heat- and mass-transfer model was developed for a two-compartment system with a porous separator; horizontal and vertical reactor arrangements were considered. Volumetric absorption of visible and infrared components of incident sunlight by the suspension was modeled. Transient species concentration profiles were obtained as a function of the operating solar-to-hydrogen efficiencies, porous separator morphology and the size of the compartments. Model results predict enhanced rates of transport of redox shuttle species between two compartments in the presence of thermal convection in addition to diffusion. At 10% solar-to-hydrogen efficiency, minimum redox shuttle concentration with convection decreases by 80% as compared to passive diffusion alone for a vertically stacked reaction compartment with 2 cm height. Experimental measurements have been also performed on two-compartment prototypes (horizontal and vertical) to probe the effects of natural convection on species mixing. The source of illumination was a xenon-lamp solar simulator (Newport 94023A) with an AM1.5G filter and calibrated such that the incident illumination power at the top of the reactor was 1 sun (1000 W/m2). The reactor was assembled by connecting two polycarbonate tubes (5 cm x 5 cm) with a height of 5 cm and placing a thin separator (Nafion 117 and regenerated cellulose) between the tubes to separate the compartments. A base was 3D-printed and painted black to secure the bottom compartment and maximize absorption of the incident illumination and promote natural convection. Thermocouples (K-type) were placed at various heights within the two compartments to track local temperatures within the fluid, including along the bottom surface of the lower compartment. Over a 3-hour period of 1 sun irradiance, the temperatures were recorded, and a favorable temperature gradient for natural convection was observed (ΔT ~ 2 °C) for vertically-stacked reaction compartments. The flow behavior was visualized through the injection of a colored dye at the bottom surface of the reactor and above the membrane after the 3-hour period. Image processing of the convection video is used to help quantify the rate of mixing within the compartments. Model predictions for flow behavior and temperature profiles were compared to and validated against experimental measurements. Collectively, this study implements a unique approach to predict and evaluate the effect of natural convection on species transport in Z-scheme photocatalytic reactors.[1] Bala Chandran, R., Breen, S., Shao, Y., Ardo, S., & Weber, A. Z. (2018). Evaluating particle-suspension reactor designs for Z-scheme solar water splitting via transport and kinetic modeling. Energy and Environmental Science, 11(1), 115–135. https://doi.org/10.1039/c7ee01360d Figure 1

Analysis of Techniques for Determining the Number of Electrons Exchanged in Square-Wave Voltammetry

A comparison of square-wave voltammetry models for calculating the number of electrons exchanged in a metal deposition reaction. Square-wave voltammetry is extremely useful for isolating the behavior of a single reaction in a mixed solution of many reacting species. Being able to identify the number of electrons exchanged in a reaction is extremely useful for identifying and characterizing unknown compounds in a process, such as electrorefining, molten salt reactors, and electrolytic oxide reduction. Experiments were conducted for silver deposition on platinum in an aqueous HNO3 solution and for Nickel and Lanthanum deposition on Tungsten in molten LiCl. Diffusion coefficients for Ni2+ and La3+ in LiCl at 700oC are calculated. Accuracy of the soluble-soluble model versus the soluble-insoluble model is discussed. Nucleation dynamics, natural convective and radial diffusive effects, and amount of ohmic drop compensation are all found to impact the resulting calculation for the number of electrons exchanged. A simplified model for determining the number of electrons exchanged under the constraint of well-compensated ohmic drop is proposed and evaluated.

Concentration Field Measurements Near the Anode during Lithium Metal Dissolution in Highly Concentrated Electrolyte

Introduction Recently, high concentrated electrolyte (HCE, 3 mol L-1) has been attracting attention as an electrolyte for next-generation batteries. It has been reported that the solvation structure surrounding Li+ in HCE is significantly different compared to the electrolyte with a concentration of about 1 mol L-1 conventionally used in Li-ion batteries. This unique structure gives rise to high decomposition resistance and low vapor pressure. Also, next-generation batteries, such as lithium sulfur batteries, use Li metal as the negative electrode with high theoretical capacity. It is necessary to use HCE as the electrolyte and Li as the electrode to achieve breakthroughs in energy density, and it is important to clarify the deposition and dissolution mechanisms in the vicinity of the electrode in such batteries. However, there are only a few studies from this viewpoint. In this study, mass transfer phenomena associated with electrochemical dissolution reactions were investigated using a sulfolane-based HCE. In addition, the coordination states surrounding Li+ were measured by in situ Raman spectroscopy. In this presentation, the relationship between solvation structure and mass transport was investigated. Experimental Li metal with a thickness of 200 μm was used for the anode and cathode. The electrolyte was a mixture of LiTFSA (Lithium bis(trifluoromethanesulfonyl)amide) and SL (Sulfolane) at a molar ratio of 1:2. The electrochemical cell was arranged in a quasi-two-dimensional configuration to minimize the effect of natural convection. Constant currents (1.0, 2.5, and 5.0 mA cm-2) were applied and real-time interferometric measurement was performed near the anode during the electrochemical dissolution reaction. In addition, in-situ Raman spectroscopy was used to observe near the anode to investigate changes in the solvation structure surrounding the Li+ near the electrode. Results and Discussion Interferometric measurements near the anodes during the electrochemical dissolution reaction showed that the concentration of the electrolyte near the anodes increased as soon as the electrolysis started. As the reaction progressed, the diffusion layer extended toward the bulk direction while maintaining parallelism with the anode surface. The concentration at the anode surface increased continuously with the electrolysis time, and the LiTFSA/SL molar ratio increased to 0.62 after 225 s. The relationship between mass transfer phenomena and solvation structure will be discussed in this presentation.

Pore scale simulation for melting of composite phase change materials considering interfacial thermal resistance

• Implicit-enthalpy-based LBM with interfacial thermal resistance is proposed. • Porous structure is reconstructed by randomly generation-growth method. • The effective thermal conductivity of composite PCMs is evaluated. • The effect of natural convection, porosity and interface on melting are analyzed. The convective melting process and thermal performance of phase change materials (PCMs) incorporating porous skeleton in the one-side-heated rectangular cavity are investigated numerically in this work. A pore-scale lattice Boltzmann method (LBM) with implicit scheme is developed to explore the solid–liquid phase change process. The interfacial thermal resistance between the skeleton and PCMs is considered by interfacial conditions treatment. The random porous microstructure is generated by quartet structure generation set (QSGS) which is used to compute effective thermal conductivity in LBM. The validations of the current model are employed by the two-phase series conduction model and previous numerical results. The effects of porous structure, skeleton material, and thermal interfacial conditions on heat transfer characteristics are systematically investigated. The computational results show that the melting rate and effective thermal conductivity increase with the reducing porosity and the high thermal conductivity of the skeleton material accelerate the melting process. In addition, the consideration of interactions in the LBM leads to a significant difference. When the thermal interfacial resistance is set to be 1 × 10 −4 m 2 W/K, the temperature drop is very large in two-phase conduction, the melting rate decreases remarkably in the phase change process. The present simulation is also suitable for optimizing the porous structure to prepare various composite PCM in the thermal energy storage field.

Thermal performance investigation of position function circuit board used in automotive exterior rear lighting

In this research, both numerically and experimentally, the thermal efficiency of a Printed Circuit Board (PCB) with two Light Emitting Diode (LED) chips was examined. The two LED lighting systems, which are single-cell LEDs, including PCB and copper plates, were manufactured, and tested under laboratory conditions to achieve this goal. The three-dimensional Computational Fluid Dynamics (CFD) model with natural convection effects prepared using the FloEFD software package to predict PCB surface temperature distributions. The goal was to perform comprehensive circuit board simulation and validate the numerical model built in this study using the experimental data during the studies. From the results, we can easily claim that higher temperature gradients are calculated and predicted near the LED chip because of heat generation. Data paths have played an essential role in the LED circuit board's temperature distribution. High-temperature variations are observed at short distances around the LED when the experimental and simulation results are compared. Temperature changes are minimized as they travel away from the LED chip. It is found that the error rate is below 5 percent overall between the experimental and simulation results. The numerical results were in proper alignment with numerical data obtained from the three-dimensional (3D) CFD model. Given thermal efficiency and using such models, this model can design and analyze Automotive Lighting Systems.

Convective transport from geothermal borehole heat exchangers embedded in a fluid-saturated porous medium

Multi-dimensional natural convection and mixed convection have been studied numerically for the vertical borehole, a heated cylinder characterized by length Lb and diameter D, of a ground source heat pump in a fluid-saturated porous medium. The effect of natural convection over a range of ground properties characterized by Rayleigh number (RaL) is found to be significant and deviates strongly from boundary layer solutions for Rayleigh number less than 106, due to the flow turning required by the ground surface. For instance, the natural convection heat flux deviates from boundary layer prediction by over 20% for RaL = 104. Only at Rayleigh numbers of less than 2 × 103 can the heat transfer be treated as simple conduction, with the deviation less than approximately 5%, for fluid-saturated soil properties. The presence of groundwater flow, due to a hydraulic gradient, produces mixed convection leading to a convective heat transfer depending also upon Peclet number (PeD). A sufficient range of properties are examined such that the multi-dimensional mixed convection is shown to be captured between asymptotes to natural and forced convection. The dimensionless group (Lb/D)PeD/RaL is identified and shown to parameterize the variation between these two limits, with values less than 1.4 asymptoting to natural convection and values greater than 2.9 asymptoting to forced convection. Finally, a correlation encompassing all three regimes, natural, forced and mixed, is proposed.