Natural Convection Heat Transfer Performance Research Articles

Introducing Passive Nuclear Safety in Water-Cooled Reactors: Numerical Simulation and Validation of Natural Convection Heat Transfer and Transport in Packed Beds of Heated Microspheres

Abstract The development of an accident tolerant nuclear fuel for water-cooled reactors would redefined the status of these reactors from traditional active safety to passive safety systems. As a possible solution toward enhancing the safety of light-water reactors (LWRs), loose-coated particles of enriched uranium dioxide (UO2) fuel with the ability to retain gaseous and metallic fission products in the case of a loss of cooling event can be introduced inside Silicon-Carbide cladding tubes of the fuel assembly (see Figs. 1(a) and 1(b)). These coated particles are treated as a bed from where heat is transferred to the cladding tube and the helium gas movement is due to natural convection. A slender geometrical model with tube-to-particle diameter ratio N = 2.503 and porosity ε = 0.546 mimicking the proposed nuclear fuel in the cladding was numerically simulated. This study is to investigate the heat transfer characteristics and flow distribution under buoyancy driven force expected in the cladding tube of the proposed nuclear fuel using a commercial code. Random packing of the particles is achieved by discrete element method (DEM) simulation with the aid of starccm+. The temperature contour and velocity vector plots obtained can be said to be good illustration of anticipated heat transfer and transport phenomenon to occur in the proposed fuel design. Simulated results for particle-to-fluid heat transfer coefficient, Nusselt number, and Rayleigh number which are of prime importance when analyzing natural convection heat transfer performance in fixed bed reactors were validated. Results from this work show close agreement with results obtained in established numerical and experimental works.

Analysis of Fin Interruptions on the Natural Convection of Heat Sinks

For heat sinks with high fins used in outdoor high-power electronic equipment, this paper proposes a natural convection heat transfer calculation method based on the chimney effect and uses this method and numerical simulation to analyze the heat transfer performance of the heat sinks with interrupted fins. Results show that the interrupted fins effectively improve the convective heat transfer coefficient of the fins by breaking the thermal boundary layer of the fins, and have a significant effect on the air flow between the fins. When the fin interruption length is 1mm and the number of interrupts is 15, the natural convection heat transfer performance of the heat sink is the best. Compared to heat sinks of the same size without interrupted fins, the thermal performance has been improved by 80% while reducing weight by 7%.

Effect of structural characteristics on the natural convective heat transfer performance of copper foam

• Copper foam with highly controllable structure was manufactured. • The relationship between structure and heat transfer performance was studied. • When the porosity is > 78%, the heat transfer performance drops sharply. • The optimal porosity and pore size for convective heat transfer have been found. • Side-heated foams exhibit better heat transfer than the bottom-heated foams. The effects of porosity, pore diameter and heating direction on the heat transfer performance of copper foam under natural convection were experimentally investigated. The open cell copper foam with highly controllable porosity ranging from 65% to 85% and mean pore diameters of 330 μm, 560 μm, 850 μm and 1200 μm were manufactured using a space holder method. The natural convective heat transfer coefficient of the copper foam was measured using a purpose-designed device. The influence mechanism of porosity, pore diameter and heating direction on heat transfer was analysed and discussed. The results showed that when the porosity is less than 75%, the effect of porosity on heat transfer is not significant, but as the porosity increases further, the heat transfer performance decreases significantly. The optimal pore size was found to be 850 μm, while the heat transfer performance of other pore sizes depends on the porosity. It was also found that the samples heated from the side generally showed better heat transfer performance than the samples heated from the bottom. The influence of porosity and pore size on natural convective heat transfer performance is mainly caused by changes in thermal conductivity and permeability. This research provides important guidance for the design of future heat sinks.

Influence of dome shape on flow structure, natural convection and entropy generation in enclosures at different inclinations: A comparative study

Flow structure is an essential aspect for the intensity of natural convective heat transfer in enclosures. Improvements in the enclosure geometry affecting the flow structure can increase the natural convective heat transfer performance. As the dome shaped walls can change the flow direction in a way to improve the flow circulations and natural convection, the present work numerically investigates laminar flow and natural convective heat transfer of air in dome shaped enclosures with three different dome inclinations. The dome shape can be designed for such enclosures by either filleting the corners of a rectangular cavity or replacing one of the adiabatic walls of a square cavity with a dome shaped wall. Therefore, the impact of dome shape utilization is analyzed from these two perspectives by separately considering the rectangular and square enclosures as reference cases. To broaden the investigation for various circumstances, three different Rayleigh numbers and four different cavity inclination angles are considered. Furthermore, the non-dimensional entropy generation rates are computed for each enclosure to evaluate their performance in terms of second law of thermodynamics. The results show that the dome shape wall significantly changes the flow structure by providing a smoother circulation, which facilitates more intensified convection currents by directing the hot fluid to the colder region of the enclosure, hence, establishing a more effective natural convective heat transfer. The computed results reveal that the mean Nusselt number can be augmented up to 22.5 and 25.0% by the utilization of dome shaped enclosure compared to the equivalent rectangular and square enclosures, respectively. The impact of the dome is dependent on the cavity inclination and generally decreases as Ra increases. Besides, the dome shaped enclosure codified by D45 gives the lowest entropy generation value.

Natural convection heat transfer performance of additively manufactured tube bundle heat exchangers with novel fin design

We studied the heat transfer of finned heat exchanger configurations with a novel design. These novel fin designs use integrated pins to enhance the heat conduction from the fin base to the fin tip as well as the air-side heat transfer on the fin surface. Oval tubes with conventional circular plain fins (CPF) as well as novel circular integrated pin fins (CIPF) and serrated integrated pin fins (SIPF) were additively generated by a Selective Laser Melting (SLM) process and installed at the bottom of a 6.5 m long chimney. All heat exchanger designs were tested in a 2-row and 3-row configuration with Rayleigh numbers between 25,000 and 120,000. We found the average Nusselt number of SIPF to be higher and the Nusselt number of the CIPF to be lower than for the CPF. Moreover, the 2-row configuration achieved a higher Nusselt number compared to the 3-row configuration for all heat exchanger designs. The analysis of the individual tube rows showed the highest Nusselt numbers at the first tube row and the lowest one at the last tube row for both configurations. However, for the SIPF the difference between the first and second tube row is smaller compared to the CPF and CIPF. In order to evaluate the compactness of the heat exchanger, the volumetric heat flux density was considered. Similar to Nusselt number the volumetric heat flux density enhanced for the SIPF and reduced for the CIPF compared to the conventional design. Also the 2-row configuration reached greater thermal performance compared to the 3-row configuration. Additionally, the volume and the surface area of the heat exchanger are 6.9% and 30.7% lower for the SIPF compared to the CPF. The experimental data were used to develop an empirical heat transfer correlation between Nusselt number, Rayleigh number, fin design and tube row number.

Heat Transfer Performance of Different Fluids During Natural Convection in Enclosures with Varying Aspect Ratios

The heat transfer process takes place in numerous applications through the natural convection of fluids. Investigations of the natural convection heat transfer in enclosures have gained vital importance in the last decade for the improvement in thermal performance and design of the heating/cooling systems. Aspect ratios (AR=height/length) of the enclosures are one of the crucial factors during the natural convection heat transfer process. The investigated fluids consisting of air, water, engine oil, mercury, and glycerine have numerous engineering applications. Heat transfer and fluid flow characteristics are studied in 3-dimensional rectangular enclosures with varying aspect ratios (0.125 to 150) using computational fluid dynamics (CFD) simulations. Studies are carried out using the five different fluids having Prandtl number range 0.01 to 4500 in rectangular enclosures with the hot and cold surface with varying temperature difference 20K to 100K. The Nusselt number and heat transfer coefficients are estimated at all conditions to understand the dependency of ARs on the heat transfer performance of selected fluids. Temperature and velocity profiles are compared to study the flow pattern of different fluids during natural convection. The Nusselt number correlations are developed in terms of aspect ratio and Rayleigh number to signify the natural convection heat transfer performance.

Impact of wavy texture and hybridity of nanofluid on heat transfer augmentation over the frustum of cone geometry

In this article, the impact of water-based hybrid nanofluid on heat transfer characteristics along the wavy frustum of the cone is examined. We considered hybrid nanofluid containing Cu and TiO2 nanoparticles. Non-similar form of the constitutive equations is obtained by using an appropriate set of transformations and results are achieved by employing transformed into compact non-similar form and are solved by the famous numerically implicit finite difference scheme known as Keller-box technique. The influence of the hybrid nanoparticles? volume fraction, frustum of cone half-angle, and the wavy texture parameters on the Nusselt number and skin friction are scrutinized and comparison is made between the wavy frustum of the cone and flat frustum of the cone through numerical data. It is observed that the rise in the truncated cone half-angle leads to an increase in skin friction and Nusselt number. The TiO2-water nanofluid has lower heat transfer rates as compared to Cu-TiO2 hybrid nanofluid. The increasing of the truncated cone half-angle enhances the heat transfer rates. Generally, the results established from this analysis can be used as a benchmark for improving the natural convection heat transfer performance along the frustum of cone wavy texture.

Experimental Research and Development on the Natural Convection of Suspensions of Nanoparticles-A Comprehensive Review.

Suspensions of nanoparticles, widely known as nanofluids, are considered as advanced heat transfer media for thermal management and conversion systems. Research on their convective thermal transport is of paramount importance for their applications in such systems such as heat exchangers and solar collectors. This paper presents experimental research on the natural convection heat transfer performances of nanofluids in different geometries from thermal management and conversion perspectives. Experimental results and available experiment-derived correlations for the natural thermal convection of nanofluids are critically analyzed. Other features such as nanofluid preparation, stability evaluation and thermophysical properties of nanofluids that are important for this thermal transfer feature are also briefly reviewed and discussed. Additionally, techniques (active and passive) employed for enhancing the thermo-convection of nanofluids in different geometries are highlighted and discussed. Hybrid nanofluids are featured in this work as the newest class of nanofluids, with particular focuses on the thermophysical properties and natural convection heat transfer performance in enclosures. It is demonstrated that there has been a lack of accurate stability evaluation given the inconsistencies of available results on these properties and features of nanofluids. Although nanofluids exhibit enhanced thermophysical properties such as viscosity and thermal conductivity, convective heat transfer coefficients were observed to deteriorate in some cases when nanofluids were used, especially for nanoparticle concentrations of more than 0.1 vol.%. However, there are inconsistencies in the literature results, and the underlying mechanisms are also not yet well-understood despite their great importance for practical applications.

Experimental Investigation into Natural Convection of Zinc Oxide/Water Nanofluids in a Square Cavity

The public domain is inundated with discrepancies in numerical and experimental findings on the natural convection heat transfer performance of nanofluids in a cavity. This paper presents the experimental investigation of the natural convection of deionized water (DIW)-based zinc oxide (ZnO) nanofluid in a rectangular cavity. The ZnO nanoparticles (20 nm) were dispersed in DIW to formulate nanofluids at various volume concentrations (0.10, 0.18, 0.36, 0.50 and 1.0 vol.%). The spectrophotometer and zeta potential were used to verify the stability of ZnO/DIW nanofluid at various temperatures and concentrations. ZnO/DIW nanofluids and DIW were charged into a rectangular cavity with the opposite vertical walls under varying temperature differences. The natural convection of ZnO/DIW nanofluid was performed at Rayleigh number range of 7.45 × 107 and 9.20 × 108. Zeta potential values revealed stable nanofluids with no sedimentation of nanoparticles observed within 24 h. At 0.10 vol.% and temperature difference of 32 °C, the ZnO/DIW nanofluid was observed to enhance the heat transfer coefficient by 9.14% relative to DIW. Further increase in volume concentration resulted in the attenuation of heat transfer. Additionally, the Nusselt number and heat transfer rate were augmented by 8.42% and 6.75% at 0.10 vol.%, respectively.

Rib shape and nanoparticle diameter effects on natural convection heat transfer at low turbulence two-phase flow of AL2O3-water nanofluid inside a square cavity: Based on Buongiorno’s two-phase model

In this study, the effects of the rib shape with constant height, width and pitch and nanoparticle diameter on natural convection heat transfer of low turbulence flow of AL2O3-water nanofluid inside a square cavity is numerically simulated based on Buongiorno’s model. Two rib-ed vertical walls are with different constant temperatures (Th>Tc), while the top and bottom walls are insulated. Heat transfer of nanofluid in rib-ed square cavity is investigated at Rayleigh numbers107, 108 and 109 for various Prandtl numbers 7.0659, 7.3593 and 7.8353. The CFD simulation of AL2O3-water nanofluid is studied for 1–3% volume fractions ranges. Also, the effect of the various diameters of nanoparticle 50, 100 and 150 nm on natural convection heat transfer performance is analyzed. The comparison of present numerical and experimental results shows that due to the thermophoresis and the Brownian motion effects, obtained numerical results are acceptable. Results indicate that at high Rayleigh number, low volume fraction has better performance and trapezoidal rib is the best. Also, by reducing nanoparticle diameter, nanofluid heat transfer and NBT increase considerably. However, by increasing nanoparticle diameter, convection heat transfer decreases greatly and even gets less than base fluid and smooth walls.

A review of magnetic field influence on natural convection heat transfer performance of nanofluids in square cavities

The emergence of nanofluids as high-performance thermal transport media has drawn great research attention in the field of heat transfer. Owning to the huge importance of natural convection applications in environmental, agricultural, manufacturing, electronics, aviation, power plants, and industrial processes, heat transfer and flow characteristics of these special fluids in various cavities have been extensively researched. This review paper has paid serious attention to the benefits of controlling the natural convection heat transfer and flow performance of nanofluids in square cavities using magnetic field sources in addition to the aspect ratio, porous media, cavity and magnetic field inclination, hybrid nanofluids, etc. The influence of several variables such as heat distribution methods, thermal and concentration boundary conditions, governing parameters, magnetic field types, numerical schemes, thermophysical correlation types, nanofluid types, slip conditions, Brownian motion, and thermophoresis on the magnetohydrodynamic (MHD) natural convection behaviours of nanofluids in square cavities has been reviewed. The paper focused on the application of numerical and experimental methods to hydromagnetic behaviours of nanofluids in square-shaped enclosures. The concept of bioconvection, bio-nanofluid (green nanofluid), ionic nanofluid, and hybrid nanofluid has also been reviewed in relation to natural convection for the first time. Special cases of MHD natural convection in cavities involving micropolar and hybrid nanofluids are also presented herein. Convective heat transfer in square cavities has been demonstrated to be altered due to the presence of magnetic fields.

Heat transfer in a liquid under focused ultrasonic field

The ultrasonic heat transfer enhancement has a strong dependence on the sound intensity. The higher the local sound intensity is, the better the heat transfer enhancement achieves. Therefore, a focused ultrasonic field is proposed in cavities with elliptical cross-section based on interference criterion and standing wave criterion. To design a cavity with focused ultrasonic field, sound source and heat source are purposely located at the two focus points where sound intensity could be reinforced. There is a compromise between the value of the standing wave coefficient and the time-averaged sound pressure. The profile of heat transfer coefficient is found to be spatially consistent with the simulated time-averaged sound pressure distribution. The cavities with focused ultrasonic field always present larger heat transfer coefficient of natural convection heat transfer than the ordinary ones and the cavity with standing wave coefficient k2 = 8 presents better natural convection heat transfer performance than the cavity with standing wave coefficient k2 = 6. For the sub-cooled boiling heat transfer, bubble plays an important role on the ultrasonic heat transfer enhancement effect. At larger heat flux or smaller sub-cooled temperature, bubbles gather together to form bubble cloud that presents large thermal resistance. The cavitation collapse can disperse the bubble cloud.

Enhancement of Free Convection From Horizontal-Base Straight-Fin Heat Sink by Partial Shrouding

Abstract This work presents a simple method to improve natural convection heat transfer performance of horizontal-base straight-fin heat sink by adding partial shroud plates on top of the heat sink at both ends. Experiments are conducted in conjunction with a detailed three-dimensional (3D) computational study. The numerical model is validated using experimental results. With partial shrouding, the modification and effective utilization of airflow surrounding the heat sink leads to significant heat transfer enhancement. The installation of shroud plates effectively improves the mass flowrate of air admitted into the fin channel. Further, the airflow drawn above the heat sink dissipates heat from the upper surface of the shroud plate. There is also a significant heat dissipation from the lower surface of the shroud plate which is exposed to cold air drawn from the side-end of the heat sink. The heat transfer from the existing optimal conventional heat sink is improved by 17% with the introduction of shroud plates. An optimal width of the shroud plate is identified to exist for the maximum heat transfer. The percentage enhancement in heat transfer achieved by partial shrouding increases with a decrease in the fin height and with an increase in the fin spacing. The proposed compact heat sink design would be of application in enhancing passive heat dissipation from light-emitting diode (LED) lights and other electronic devices, especially when size constraints exist.

Experimental and numerical investigation of natural convection heat transfer of W-type fin arrays

In this paper, a W-type finned heat sink for natural convection is proposed based on the research of inclined-plate fins. As thermal radiation considered, the natural convective heat transfer performance of W-type fins on a vertical substrate was numerically studied with respect to the variations of geometry. The parallel-plate finned heat sink with and without the surface coating were experimentally studied, to validate the numerical results and the influence of radiation. Moreover, the W-type finned heat sink was experimentally investigated. Experimental results indicate that the W-type finned heat sink achieves the cooling effect of a maximum temperature drop of 4.6°C and an average temperature drop of 2.9°C. Compared to the optimized parallel-plate finned heat sink, the area of heat dissipation decreased by 10%. The optimization results indicate that the average temperature of the substrate tends to decrease first and then increase with the increment of the fin spacing, inclined angle and gap clearance. Meanwhile, there exist peak values for mean heat transfer coefficient of the whole heat sink with the fin spacing, the inclined angle and the gap clearance varied. Furthermore, a characteristic parameter coupled with a series of dimensionless variables is proposed, and the correlation for the inclined plate finned heat sink is suggested with deviation within 12%. It is concluded that for the W-type finned heat sink, the air input is effectively increased in the direction perpendicular to the substrate, leading to smaller thermal resistance. The thermal boundary layer is thinned. Synergy analysis shows that the intersection angle between the direction of velocity and the temperature gradient reduced.

Heat discharging and natural convection heat transfer performance of coil heat exchanger in single molten salt tank

There has been an increasing attention on single-tank thermal energy storage, attracted by the low cost, high efficiency and compactness in the operation. The most researches on single-tank thermal energy storage focused on temperature stratification to improve its heat discharging efficiency using water as heat storage media. The present research aims at investigating heat discharging performance by improving natural convection heat transfer of molten sat around coil heat exchanger in single heat storage tank. The effect of different parameters of the coil heat exchanger on the heat discharging performance, flow field and temperature distribution are analyzed and discussed in the single molten salt tank. The results show that the heat discharging performance of the coil heat exchanger can be enhanced by increasing the buoyancy-driven flow around the coil heat exchanger. The heat discharging efficiency can be improved by the optimal arrangement of coil heat exchanger for the highest velocity can be induced around it, which results in a fully mixed of molten salts and its temperature turns to uniform, instead of temperature stratification. Based on the results, a correlation among the natural convection Nu number with Ra number and other heat exchanger parameters in a single molten salt tank is obtained by numerical results. The research results provide a theoretical basis and paradigm for the design of single thermal storage tank energy storage system.

Experimental Observation of Natural Convection Heat Transfer Performance of a Rectangular Thermosyphon

This study experimentally investigates the natural convection heat transfer performance of a rectangular thermosyphon with an aspect ratio of 3.5. The experimental model is divided into a loop body, a heating section, a cooling section, and two adiabatic sections. The heating section and the cooling section are located in the vertical legs of the rectangular loop. The length of the vertical heating section and the length of the upper and lower horizontal insulation sections are 700 mm and 200 mm, respectively, and the inner diameter of the loop is 11 mm. The relevant parameters and their ranges are as follows: the input thermal power is 30–60 W (with a heat flux in the range of 60–3800 W/m2); the temperature in the cooling section is 30, 40, or 50 °C; and the potential difference between the hot and cold sections is 5, 11, or 18 for the cooling section lengths of 60, 45, and 30 cm, respectively. The results indicate that the value of the dimensionless heat transfer coefficient, the Nusselt number, is generally between 5 and 10. The heating power is the main factor affecting the natural convection intensity of the thermosyphon.

Experimental study of the natural convection heat transfer performance for finned oval tubes at different tube tilt angles

The natural convection heat transfer of finned oval tubes was studied for different tube tilt angles (0° to 40°), fin spacing (6mm to 16mm) and Rayleigh numbers (11,000 to 130,000). Fin efficiency was determined by temperature measurements along the fin surface and temperature gradient calculations. Nusselt number and volumetric heat flux density were chosen as assessment parameters for the thermal performance. A comparison of the experimental data with correlations from literature was made and good agreement was found. Furthermore, the uncertainty of the measurements was evaluated. In the horizontal tube orientation (0°) the Nusselt number increases with fin spacing. However, the fin efficiency and the volumetric heat flux density reduce. The tilt angle of the longitudinal tube axis was found to have an essential impact on the thermal performance, in particular when the fin spacing is high. For the higher fin spacing values the horizontal orientation gives highest Nusselt number and volumetric heat flux density. At tube tilt angle of 40° the thermal performance becomes lowest for all fin spacing values. When the fin spacing is low, the effect of tube tilt angle is minor. From the experimental results correlations between Nusselt number, Rayleigh number, fin spacing and tube tilt angle are proposed to assist the future design of heat exchanger with tilted finned oval tubes.

Natural convection heat transfer characteristics of molten salt with internal heat generation

Molten salt is a promising heat transfer fluid with its high heat capacity, high boiling point, and chemical stability. In liquid fueled molten salt reactors and spent fuel reprocessing unit, molten salt carries heat generating fuel itself in a liquid state. To investigate the natural convection heat transfer performance of molten salt, a vertical heater vertical cooler rectangular loop filled with chloride salt containing liquid fuel, NaCl-KCl-(Pu, 238U)Cl3, is simulated using an open source CFD package, OpenFOAM under various heat input conditions; external heat flux, internal heat generation (IHG), and a combined heat input type condition. Different aspects of natural convection heat transfer according to heat input condition are found for same amount of total heat. The external heat flux condition generates a high temperature gradient near the heater wall with very thin thermal boundary layer due to the low thermal conductivity of molten salt. On the other hand, the IHG condition has a relatively flat temperature profile from its uniform volumetric heating. Due to the different behaviors of temperature evolution, local upward flow is formed only at the wall region under the heat flux condition, but global natural circulation flow is promoted under IHG condition. The combined type condition is largely dependent on how much heat exists in heat flux type, which strongly influences local heat and fluid phenomena in natural convection heat transfer. Molten salt has a high dependence on the heat input condition from its thermo-physical properties. Therefore, the distinct characteristics of molten salt and heat input conditions should be considered, when designing and analyzing the molten salt systems with both external and internal heating conditions.

Buoyancy-Induced Natural Convective Heat Transfer Along a Vertical Cylinder Using Water–Al2O3 Nanofluids

Buoyancy-induced natural convective heat transfer along a vertical cylinder immersed in Water–Al2O3 nanofluids for various concentrations (0, 0.05, 0.1, 0.2, 0.4, 0.6 vol %) under constant heat flux condition was investigated experimentally and presented. Thermal stratification was observed outside the boundary layer in the ambient fluid after steady-state condition is achieved as the fluid temperature goes on increasing along the axial direction. Temperature variations of the cylinder along the axial direction and temperature variations of fluid in radial direction are shown graphically. It is observed that the temperatures of the cylinder and the fluid increases along the axial direction and the fluid temperature decreases in the radial direction. Experiments were conducted for various heat inputs (30 W, 40 W, 45 W, and 50 W) and volume concentrations and observed that the addition of alumina nanoparticles up to 0.1 vol % enhances the thermal performance and then the further addition of nanoparticles leads to deterioration. The maximum enhancement in the natural convection heat transfer performance is observed as 13.8%, i.e., heat transfer coefficient is increased from 382 W/m2 K to 435 W/m2 K at 0.1 vol % particle loading.

Investigation of natural convection heat transfer performance of the QFN-PCB electronic module by using nanofluid for power electronics cooling applications

Natural convection heat transfer of Cu-water nanofluid in a 3 × 3 array of a typical isothermal quad flat non-lead (QFN) embedded printed circuit board (PCB) module which can be bounded with respect to the sealed non-Darcy porous enclosure is numerically investigated. The Darcy-Brinkman-Forchheimer model is adopted to model the fluid flow in the porous medium under the presence of an external magnetic field. The transport governing equations are solved by the finite volume method based on the SIMPLE algorithm and the power law scheme. Main efforts focus on the effects of the parameters such as a nanoparticle volume fraction, Hartmann number, Darcy number and the enclosure side aspect ratio on the fluid flow and heat transfer characteristics inside the enclosure. The obtained results indicate that the influence of nanofluid of the overall Nusselt number increases with increasing the Darcy number, but decreases with increasing the Hartmann number. The overall Nusselt number attains its maximum value in the range of enclosure side aspect ratio from 1.5 to 3 with respect to the Darcy number. Moreover, the proposed correlations improve the efficiency, reliability and stability of the electronic device encountered in various applications in electronic industries.