Protruding Heat Sources Research Articles

Experimental study on air impinging jet for effective cooling of multiple protruding heat sources

Air Impinging Jet is an effective cooling method for various applications, ensuring optimal performance and reliability of heat-generation systems. In the present work, a novel technique of cooling discrete protruding heat sources mounted in a rectangular channel by using a double air jet is introduced experimentally. A constant and uniform heat flux is produced from protruding heat source surfaces where the bottom and the upper channel walls are insulated. The effects of various parameters on the heat source cooling performance such as the Nusselt number for single and double air jets are obtained. Various parameters such as the air Reynolds number, aspect ratio, double jet position ratio, and jet inclination angle are investigated. The results show that those parameters effectively affect the average temperatures and the standard deviation of all protruding heat sources. It is indicated that the maximum value of the average Nu number occurs at the heat source just underneath the impinging air jet compared to other downstream heat sources. The highest average Nu is achieved at a position ratio of 3/7 and an inclination angle of 10o. The cooling system accomplishes an acceptable Nu and temperature uniform distribution for a position ratio of 4/7 compared to the other position ratios. The improved performance and longevity of heat sources are achieved by the innovative double-air jet method, which archives a consistent temperature distribution for all projecting heat sources.

Lattice Boltzmann simulation of natural convection heat transfer phenomenon for thermal management of multiple electronic components

Thermal management of electronic components is becoming a vital necessity in view of the rapid development of electronics technology. It is a concern imposed by the miniaturization of electronic chipsets. The present work addresses this issue numerically, using the lattice Boltzmann method (LBM). It consists of an air-filled heat sink containing multiple protruding electronic components. The problem is modelled using 2D continuity, momentum, and energy conservation equations. The thermal and dynamic fluid flow are analysed for various enclosure inclinations (0°, 45°, and 90°) and Rayleigh numbers (Ra=103-106). A twin protruding heat sources are considered at the bottom wall. The top cold wall can be at a uniform temperature (case 1) or consisting of two protruding sinks maintained at a constant temperature (case 2). The results showed that the maximum heat transfer rate corresponding to Nusselt number (Nu¯=5.51) is achieved for Ra=106 on the hot wall for the horizontal cavity in case 1, illustrating the cavity with top cold uniform wall. Indeed, the heat transfer is improved by 80% by varying the Rayleigh number (Ra) from 103 to 106. Furthermore, for case 2 with a twin cold protruding, a quite complicated heat transfer behaviour is observed on the hot wall. For Ra>106, the horizontal cavity outperforms the other cavities in terms of heat transfer rate, however the horizontal position is the less performant for Ra<104. With a horizontal disposition and Ra=106, the heat exchange ratio is improved by 32.32% in case 2 compared to case 1. The outcomes of this study provide insights into design and implementation of natural convection cooling solutions for electronic devices, which can have significant practical implications in various industries.

Conjugate turbulent natural convection with thermal radiation in a vertical and inclined wall with heat sources

This work presents an experimental and numerical study of turbulent conjugate natural convection heat transfer in a plate for vertical and inclined positions containing protruding heat sources mounted on a conductive substrate, with thermal radiation effects. Experiments were performed with seven aluminum protruding heat sources uniformly mounted over an upper substrate fiberglass plate. Insulation and a guard heater were used at the back of the substrate plate. The temperature was measured for each power input and downward inclination angle. Numerical simulations were performed to explore the effects of conductivity, upward and downward inclinations, and heater emissivity. The conjugate problem was numerically addressed for a two-dimensional model, steady-state and incompressible flow under turbulent flow conditions. The main effort was to investigate the effects of power dissipation, conductivity plate-fluid ratio, plate inclination angle, and emissivity of the heater on temperature and Nusselt number distribution. The range of the modified Rayleigh number covers the values between 9 × 105 and 1.3 × 1010. The results found that heat loss by radiation was greater than 35%, the heat transfer became less efficient as the downward angle increased, and a jump in the average Nusselt number was found for upward cases due to plume detachment. A correlation for the Nusselt number was also developed.

Thermal Analysis of Melting Occurring Inside a Finned Rectangular Enclosure Equipped with Discrete Pulsed Protruding Heat Sources

This paper numerically investigates the effect of the location of a horizontal fin on the melting of a phase change material (PCM) inside a rectangular enclosure heated by multiple discrete pulsed protruding heat sources. The fin and the phase change material filling the enclosure store the thermal energy extracted from the heat sources, in sensible and latent forms. The heat sources are assumed to simulate electronic components undergoing a superheating technical issue. By extracting heat from the electronics, the PCM plays the role of a heat sink. To analyze the thermal behavior and predict the cooling performance of the proposed cooling system, we derive a nonlinear mathematical model based on mass, momentum and energy conservation laws. Several numerical investigations are conducted to quantify the influence of the fin position on the thermal behavior and the cooling performance of the heat sink. Predictions include the transient maximum temperature occurring inside the heat sources and the liquid volume. A comparison between our numerical results and experimental data selected from the literature shows a good agreement. The main conclusion is that the presence of the fin leads to a slight increase in the melting time.

Enhancing Mixed Convection Heat Transfer from Multiple Protruding Heat Sources Using Inclined Obstacles. (Dept. M)

Enhancing Mixed Convection Heat Transfer from Multiple Protruding Heat Sources Using Inclined Obstacles. (Dept. M)

Guided Air by Convection to Cool-Down Inclined Channel Supported by Two Heat Sources

This paper presents the numerical study of the laminar mixed-convection heat transfer of two identical protruding heat sources mounted in an inclined channel with obstacle. The control volume method and the SIMPLER algorithm are used to solve the dimensionless governing equations of mass, momentum, and energy for mixed convection. The effects of the obstacle, the channel inclination and the Reynolds number 5 ≤Re≤ 30 on streamlines and isotherms as well as on the heat transfer rate at the surface of each component are investigated for Pr=0.71 and Gr=105. The finding results show that for the channel inclination angle in the range 30° ≤φ≤60°, the obstacle has a large effect on the rate of transfer. In addition, by analyzing the effect of the obstacle size, it has been found out that the obstacle height has a strong effect on the cooling rate of the area between the two sources while the obstacle width effect is less noticeable.

Lattice Boltzmann Computations of Natural Convection Heat Transfer of Nanofluid in a Square Cavity Heated by Protruding Heat Source

Abstract This paper reported the mathematical modeling and numerical simulation of natural convection flow of Cu/water nanofluid in a square enclosure using the lattice Boltzmann method (LBM). The cavity is heated from below by heat source and cooled by the top wall. The vertical walls are adiabatic. After validating the numerical code against the numerical and experimental data, simulations were performed for different Rayleigh numbers (104–0.5 × 107), nanoparticles volume fractions (0–8%), and cavity inclination angle (0 deg–90 deg). The effects of the studied parameters on the streamlines, on isotherms distributions within the enclosure, and on the local and average Nusselt numbers are investigated. It was found that heat transfer and fluid flow structure depend closely on the nanoparticle concentration. Results show differences in stream separation between a base fluid and the nanofluid. Also, adding small nanoparticles fractions, less than 6%, to the base fluid enhances the heat transfer for higher Rayleigh numbers and cavity inclination angle less than 30 deg. It is concluded that the optimal dilute suspension of copper nanoparticles can be applied as a passive way to enhance heat transfer in natural convection engineering applications.

A Numerical Investigation of Flow and Heat Transfer of Laminar Multiple Slot Jets Impinging on Multiple Protruding Heat Sources

The flow and heat transfer behavior of laminar incompressible slot jets impingement cooling of an array of heated surfaces in a channel have been investigated numerically. The computations are done for a variety of values of slot jets Reynolds number, channel height and distance between two heated blocks. The influences of these geometrical and physical parameters are predicted. The results, streamline contour, velocity profile, isothermal contour, local Nusselt number, and average Nusselt number are compared and documented. The first and second recirculation cells size are gradually increased, and the highest heat transfer rate is attained when Reynolds number increased. However, the heat transfer rates are decreased when channel height increased. The peak local Nusselt number value is noticed at stagnation point of the first block by first jet, and the second peak local Nusselt number value is observed at fourth block by second jet. The distances between two blocks play a significant role in the downstream velocity which leads to create the strong recirculation cells in between the two heated blocks when the distance between the two blocks increased.

Buoyancy driven turbulent plume induced by protruding heat source in vented enclosure

The buoyancy driven thermal plume behavior inside a partial square enclosure with protruding isothermal heat source block is numerically investigated. The turbulent flow is modeled by using unsteady Favre-averaged Navier-Stokes (UFANS) equation with buoyancy modified Lam Bremhorst low Reynolds number k−ϵ model. A Simplified Marker and Cell algorithm (SMAC) is used to solve the governing equations and the computations are performed using an in-house code based on Finite difference method. The heat transfer characteristics and the bidirectional exchange across the vent are analyzed for different Grashof number 108 ≤ Gr ≤ 1011. Further, the thermal plume patterns are investigated by mounting the heat source block at five different locations δ = 0.25 H, 0.35 H, 0.5 H, 0.65 H and 0.75 H. A significant enhancement in the net mass flow rate and average Nusselt number is observed by increasing the Grashof number. It is found that the heat source location has strong influence on the vent bidirectional exchange rate, thermal mixing and heat transfer characteristics inside the enclosure. The present model is validated with the experimental and numerical benchmark results available in literature.

Experimental and numerical investigation of natural convection in a discretely heated vertical channel: Effect of the blockage ratio of the heat sources

This study deals with the buoyancy induced flow and heat transfer in a parallel plate channel with a heat source array, which simulates an electronic package. The heat source array consists of four discrete protruding heat sources made of copper. The focus of this study is concentrated on the effect of heat source blockage ratio (br) on recirculating flow and cooling performance of the system. Studies are conducted both for flush mounted or protruding heat source cases. Four different values of the blockage ratio of the protruding heat sources (br = 0.125, 0.25, 0.375 and 0.5) are considered. The range of the modified Grashof number covers the values between 9.6 × 105 and 1.53 × 107. In the experiments, flow visualization and temperature measurements are conducted. Numerical studies are performed via ANSYS Fluent software. From the experimental results and numerical studies, it is found that buoyancy induced flow and cooling performance is significantly affected by the blockage ratio of the heat source array.

Studies on Three-Dimensional Mixed Convection with Surface Radiation in a Rectangular Channel with Discrete Heat Sources

ABSTRACTThe flow behavior and heat transfer characteristics of conjugate heat transfer under mixed convection for a three-dimensional laminar flow in a rectangular channel with six protruding heat sources, mounted on the lower wall of the channel, have been studied numerically and experimentally. At higher temperatures, radiation plays an important role. This work reports the effect of radiation on conjugate mixed convection heat transfer. Air is taken as a cooling medium and is considered to be radiatively non-participating medium. The parameters considered for the study are positions (streamwise and spansise) of the heat sources, Reynolds number, emissivity of the heat sources, and the thermal conductivity of a printed circuit board (PCB) having constant fluid properties with the Prandtl number being 0.707. The Boussinesq approximation has been used. Commercial software ANSYS Fluent has been used for numerical analysis, and experiments have been carried out in a small-sized wind tunnel. The ranges of Reynolds number, emissivity, and thermal conductivity of PCB are 115–690 (corresponding inlet velocity of 0.25–1.5), 0–0.9, and 0.038–1.4 W/mK, respectively. Results indicate that the radiative heat transfer is significant at lower Reynolds number and lower thermal conductivity of PCB. The streamwise spacing of heat sources has larger influence compared to the spanwise spacing.

Effect of Magnetic Field on Natural Convection and Entropy Generation in Al2O3/Water Nanofluid-Filled Enclosure With Twin Protruding Heat Sources

In this paper, the effect of magnetic field on natural convection of Al2O3/water nanofluid in an enclosure containing twin protruding heat sources placed on top and bottom walls arranged in-line and staggered manner is presented. For this purpose, coupled equations governing fluid flow and heat transfer are solved in Cartesian framework using streamline upwind/Petrov–Galerkin (SUPG) finite element method. Numerical computations are performed to predict the fluid flow, heat transfer, and entropy generation for a wide range of Hartmann number (0.0 ≤ Ha ≤ 100.0), Rayleigh number (103≤Ra≤106), and nanoparticle volume fraction (0.0≤ϕ≤0.1). The simulated results indicate that, for both in-line and staggered arrangement, the entropy generation due to heat transfer is significant along isothermal surfaces, whereas entropy generation due to fluid friction is higher at no-slip walls and along the regions of contact between adjacent recirculation cells. For both in-line and staggered arrangement, increase in global total entropy generation and average Nusselt number along top and bottom heat sources is obtained with decreasing Ha and increasing Ra. Furthermore, for both in-line and staggered arrangement, variation in global total entropy generation and average Nusselt number along top and bottom heat sources with increasing nanoparticle volume fraction, depend on both Ha and Ra.

Inverse conjugate mixed convection in a vertical substrate with protruding heat sources: a combined experimental and numerical study

This paper reports the results of a combined numerical and experimental study to estimate the heat inputs of three protruding heat sources of the same size placed on a vertically placed PCB board of height 150 mm, depth 250 mm, and thickness 5 mm. First, limited measurements of temperatures were recorded at eight locations along the height of the back of the PCB board for different (and known) values of heat inputs of the protruding heat sources and different velocities. These were followed by three-dimensional calculations of fluid flow and conjugate heat transfer for various heat transfer coefficients on the backside of the PCB board. The difference between the CFD predicted and experimentally measured temperature distributions on the back of the PCB board was minimized using least squares and the best value of heat transfer coefficient was obtained. Using this ‘data assimilated’ CFD model, detailed CFD simulations were done for various values of heat input values and Reynolds numbers (each of these can be different from one another) of the flow. The temperatures at the same eight locations at the back of the PCB board were noted. An artificial neural network was then developed with ten inputs (eight temperatures together with the input velocity and the ambient temperature) to estimate the three outputs (three heat inputs) after carrying out extensive studies on the architecture of the network. This inverse solution was then tested with experiments for validating the ANN approach to solve the inverse conjugate heat transfer problem. Finally, with the ANN estimated heat inputs, CFD simulations were again run to compare the temperature distribution at the back of the PCB board with measurements.

A numerical investigation of heat transfer and entropy generation during jet impingement cooling of protruding heat sources without and with porous medium

In the present study, fluid flow and thermal characteristics associated with forced convection cooling of an array of discrete protruding heat sources mounted on impingement plate of channel by an impinging laminar jet is investigated for various Reynolds number (Re) and channel height (H/L). It is observed that, the magnitude of average Nusselt number for all heat sources increases with increasing Re and decreasing H/L, except the regions of heat sources covered by recirculation bubbles which may be due to accumulation of heat resulting in hot spots. In order to eliminate these hot spots, a porous layer is attached to the impingement plate. A parametric study is conducted to predict the performance of porous layer on fluid flow pattern, heat transfer and entropy generation for various values of Darcy number (Da), Reynolds number (Re), channel height (H/L), porosity (∊) and porous layer thickness (h/H). For the purpose, equations governing two-dimensional, time-dependent, incompressible and laminar flow are solved in a Cartesian framework by using Streamline Upwind Petrov–Galerkin (SUPG) Finite Element (FE) method. The generalized Darcy–Forchheimer–Brinkman model is adopted to model the flow in porous medium. The recirculation bubbles on heat sources are completely eliminated with the inclusion of porous layer at Darcy number, Da=10-2. The magnitude of overall Nusselt number and global entropy generation due to heat transfer (Sθ,Ω‾) and fluid friction (Sψ,Ω‾) increases with increasing Da,Re,h/H and decreasing ∊ and H/L. The optimum configuration for maximum heat transfer and minimum entropy generation is observed at Da=10-2,Re=1000,H/L=1.0,h/H=0.75 and ∊=0.5.

A Simple Thermal Model for Mixed Convection From Protruding Heat Sources

This paper reports the results of numerical and experimental investigations of conjugate mixed convection from a vertical channel with sets of protruding heat sources. The goal of this study is to investigate the possibility of obtaining reasonably accurate results with a simpler or compact thermal model that replaces a set of protruding heat sources with a heat source of appropriate thickness that occupies the whole of the channel wall. Commercially available FLUENT 6.3 was used for the simulations. In order to validate the numerical results, a low-speed vertical wind tunnel has been employed. These are followed by three-dimensional simulations for various heat transfer coefficients on the back side of the printed circuit board (PCB). The differences between the computational fluid dynamics (CFD) predicted and experimentally measured temperatures were minimized using least squares and the optimum value of heat transfer coefficient was obtained for use in the simple model. The effect of Reynolds number on heat transfer has been analyzed for both the full CFD and simpler thermal models. The variation of error in the maximum temperature between the full CFD model and the simpler thermal model under different conditions, as the number of chips changes from three to eight, is studied.

Computation of melting with natural convection inside a rectangular enclosure heated by discrete protruding heat sources

This paper presents the results of a numerical investigation of the heat transfer by natural convection during the melting of a phase change material (PCM, n-eicosane with melting point of 36°C) contained in a rectangular enclosure. This latest is heated by three discrete protruding heat sources (simulating electronic components) placed on one of its vertical walls. The power generated by heat sources is dissipated in PCM. The advantage of using this cooling scheme is that the PCMs are able to absorb high amount of heat generated by the heat sources, without acting the fan during the charging process (melting of the PCM). The thermal behavior and thermal performance of the proposed PCM based-heat sink are numerically investigated by developing a mathematical model based on the mass, momentum and energy conservation equations. The obtained numerical results show the impact of various key parameters on the cooling capacity of the PCM-based heat sink. Correlations encompassing a wide range of parameters were developed in terms of the dimensionless secured operating time (time required by one of the electronic components before reaching its critical temperature, Tcr∼75°C) and the corresponding liquid fraction, using the asymptotic computational fluid dynamics (ACFD) technique.

Experimental and Numerical Investigation of Mixed-Convection Heat Transfer from Protruding Heat Sources in an Enclosure

Heat transfer from a 5-by-4 array of protruding heat sources in the bottom wall of an adiabatic enclosure is investigated experimentally and numerically. The enclosure has a fixed inlet and different outlets. Flow velocity and applied heat fluxes are varied. Steady-state temperatures of the heat sources, air inlet and outlet temperatures, and enclosure wall temperature are measured. Results indicate that the first row is the coolest, and the Nusselt numbers of the heat sources, which are near the enclosure wall, are higher than those in the inner side. There is a good agreement between the experimental and numerical results.

Conjugate Mixed Convection with Surface Radiation from a Vertical Channel with Protruding Heat Sources

In this article, the results of a numerical investigation of conjugate mixed convection from a vertical channel with discrete protruding heat sources mounted on the right side wall of a vertical channel have been presented. The flow is considered to be laminar, two-dimensional, hydrodynamically, and thermally developing. All geometric parameters such as the size of the protruding heat sources and the spacing between the protruding heat sources, the spacing between the channel walls, and the thickness of the channel walls are fixed. The parameters such as Reynolds number (Re S ), modified Grashof number , ratio of thermal conductivity of heat sources and thermal conductivity of fluid (k p /k f ), ratio of thermal conductivity of channel walls and thermal conductivity of fluid (k s /k f ), emissivity of heat sources (ϵ p ), and emissivity of channel walls (ϵ s ) are varied to understand the flow and heat transfer characteristics. A correlation for the nondimensional maximum temperature has also been developed for this configuration using the method of asymptotic expansion method.

ANN based estimation of heat generation from multiple protruding heat sources on a vertical plate under conjugate mixed convection

Inverse Heat Transfer Problems (IHTP) are characterized by estimation of unknown quantities by utilizing any given information of the system. In this study, the inverse problem of estimation of heat generation in multiple two dimensional protruding heat sources on a vertical plate, a geometry frequently encountered in the cooling of electronic equipment, is carried out from the information available on the temperature distribution on the substrate on which these sources are mounted. A non-iterative method is applied utilizing Artificial Neural Networks (ANN) and covariance analysis to estimate the heat generation in the protruding heat sources on a vertical plate. The forward model involving laminar, two dimensional, steady, incompressible fluid flow and mixed convection heat transfer is numerically solved with FLUENT 6.3 for known values of heat generation in the protruding sources and the temperature distribution thus obtained on the PCB substrate is utilized to train the ANN for the inverse model. Parametric studies are conducted on the forward model to investigate the effect of Richardson number, Reynolds number, the chip and substrate conductivities on the heat dissipation to the fluid flowing over the heat sources. The trained networks are finally used to estimate the heat generation from the sources for a given temperature distribution on the substrate wall generated, for known values of the heat generation rates, which serve as the “measured” temperature distribution. Use is made of covariance analysis in order to identify the important temperature locations sufficient to carry out the inverse analysis. Finally, a systematic investigation on the effect of noise in the temperature “measurements” on the estimates also has been carried out.

Cooling Management of Highly Powered Chips Packed in an Insulated Cavity Filled with a Phase Change Material

This work describes and analyses a novel computer's thermal management system based on a phase change material (PCM) heat storage reservoir. The proposed heat sink consists of a PCM filled enclosure heated by substrate-mounted protruding heat sources (micro processors). PCMs, characterized by high energy storage density and small transition temperature interval, are able to store a high amount of generated heat; which provides a passive cooling of microprocessors. The advantage of this cooling strategy is that the phase change materials are able to absorb a high amount of generated heat without energizing the fan. The proposed strategy is suitable and efficient for situations where the cooling by air convection is not practical (thermal control of recent multiprocessors computers, for example). The problem is modelled as, two dimensional, time dependent and convection–dominated phenomena. A finite volume numerical approach is developed and used to simulate the physical details of the problem. This approach is based on the enthalpy method which is traditionally used to track the motion of the liquid/solid front and obtain the temperature and velocity profiles in the liquid phase. The study gives an instruction on the presentation of PCM heat sink used for cooling management of recent computers. Numerical investigations have been conducted in order to examine the impact of several parameters on the thermal behaviour and efficiency of the proposed PCM-based heat sink. Correlation for the secured operating time (time required by the heat sink before reaching the critical temperature, Tcr) is developed.