جستجوی مقالات مرتبط با کلیدواژه "heat sink" در نشریات گروه "مکانیک"

The most obvious feature of heat sinks is their ability to transfer heat and their cooling properties. In this research, a vertical single-channel active heat sink with Galinstan liquid metal fluid was used and the discretization of Navier Stokes equations was done using the second-order upwind finite volume method. Investigation of Mixed Convection heat transfer with Richardson numbers 0.45, 1 and 10 has been done in both directions of flow from top to bottom and flow direction from bottom to top and the effects of external magnetic field in two directions perpendicular to the flow axis have been investigated. The results showed that the flow direction from bottom to top with a Richardson number of 10 without the presence of a magnetic field improved the Nusselt number by 11.30% compared to the flow direction from top to bottom. With the Richardson number of 1 and the flow direction from bottom to top, the effect of applying the magnetic field in the Z direction (perpendicular to the current axis) with the Hartmann number of 129, 164.5, and 194, respectively, is 11.29, 13.63, and 15.88 percent of the Nusselt number has been improved. With the Richardson number of 1 and the flow direction from the bottom to the top, the effect of applying the magnetic field in the X direction (perpendicular to the flow axis) with the Hartmann number of 64.6, 129 and 194, respectively, is 7.08, 8.28 and 8.76% of the Nusselt number has improved.

A strong magnetic field provides a new method of heat transfer with high heat flux. A numerical simulation for a heat sink with high heat flux under an external uniform magnetic field in three different directions is used to investigate the flow field and displacement heat transfer between liquid metal and hot surfaces. Due to its high density and large thermal and electrical conductivity coefficients, gallinsten liquid metal has been used as a working fluid. Discretization of the Navier-Stokes equations is performed by the upstream second-order finite volume method. The results show that the effect of applying a magnetic field in the Y and Z directions (perpendicular to the flow axis) on the heat sink with a Hartmann number of 88, improves the displacement heat transfer coefficient by 15% and 8%, respectively. The best efficiency in increasing the heat transfer was obtained by applying the magnetic field in the Y direction. By applying the magnetic field in the Y direction to the heat sink, the displacement heat transfer coefficient was increased by 11.9% for Hartman number of 44, 15% for Hartman number of 88, and 17.7% for Hartman number of 132, compared to zero Hartman number. By applying the magnetic field in Z direction to the heat sink, the displacement heat transfer coefficient was increased by 4.3% for Hartmann number of 44, 8% for Hartmann number of 88, 11.4% for Hartmann number of 132 and 22.1% for Hartmann number of 330, compared to Hartmann number of zero. Also, the results show that the effect of applying a magnetic field perpendicular to the flow axis has increased the velocity gradient. As a result, the pressure drop and friction coefficient of the heat sink have increased.

Increasing the heat transfer rate in various industries in order to improve the efficiency of equipment, prevent damage to parts and reduce costs is one of the essential discussions in the industry. One of the solutions to increase heat transfer is the use of active heat sink. In this research, an active heat sink with Galinsten liquid metal fluid was used and the discretization of Navier-stokes equations was done using the second order upstream finite volume method. The effect of applying the magnetic field in the Y direction (perpendicular to the flow axis) to the heat sink has caused the creation of a force against the flow direction called the Lorentz force, which has caused the M-shaped velocity distribution. According to the constant flux boundary condition, increasing the flow velocity in the vicinity of the walls has caused the surface temperature to decrease and the heat transfer to improve. The results showed that the effect of applying a uniform external magnetic field in both Y and X directions with a Hartmann number of 517 improved the Nusselt number by 38% and 13%, respectively, compared to a Hartmann number of zero. The effect of applying a magnetic field in the Y direction to the heat well with a Hartmann number of 517, 38%, Hartmann number of 258, 22% and Hartmann number of 129, 13% has improved the heat transfer.

In the present study, two geometries of microtube and microchannel are used simultaneously in a heatsink. The aim is to improve the performance of micro heatsink in cooling digital processors. ANSYS FLUENT software is employed to solve the governing equations. The second-order upwind method is utilized to solve the momentum equation and the SIMPLE method is employed for coupling the velocity and pressure fields. The results show that the fluid flow temperature changes less along with the micro heatsink by increasing the Reynolds number due to the high flow rate. Also, the surface temperature of the processor decreases significantly by enhancing the concentration of nanoparticles and improving the heat transfer performance. Hence, at Re =700 and a volume fraction of 0.5%, the average outlet temperature of the system is 316.1 K. It is equal to 319.03 K for a volume fraction of 1%. The addition of microtubes also causes a significant increment in the overall thermal efficiency of the system. For example, at Re = 300, the heat transfer coefficient for the base fluid flow with microtubes is approximately 58.4% higher than that for the system without microtubes. At Re =700 and 1500, this enhancement is 63.3% and 50.9%, respectively. This indicates that the presence of microtubes improves the performance of the heatsink and the access of heat transfer in different parts of the equipment to the cooling fluid flow. It reduces the thermal resistance of far points of the processor, leading to more heat absorption from the CPU surface.

In the present study, the cooling of a pack of lithium-ion batteries in micro-channel heatsink with wavy microtubes was investigated in the presence of silver/water-ethylene glycol (50:50) nanofluid. ANSYS FLUENT software and SIMPLE method are used to solve the equations and coupling of velocity and pressure fields. The results show that this system can maintain the lithium-ion temperature between 295 and 305 K. At all studied concentrations, the maximum temperature difference at the surface is 5 and 7 K, respectively. It is also found that increasing the nanofluid concentration provides a more uniform temperature. At higher Reynolds numbers, although the temperature distribution is more uniform, increasing the nanofluid concentration has no significant effect. For example, at Re = 300, the improvement of surface temperature uniformity is 4.5% with increasing the concentration from zero to 1%. On the other hand, an increment in the Reynolds number has a negative effect on the pumping power of the coolant. Also, the rate of thermal and frictional entropy generation decreases with the volume fraction of nanoparticles, so that at a concentration of 1%, the rate of reduction of frictional entropy relative to pure fluid is 9%.

Electronic devices with different and wide applications must operate under critical temperature for long life and safe operation. Therefore, excess heat must be properly removed from these devices. Recently, the use of phase change materials (PCM) has been considered as one of the effective methods for removing heat from electronic devices. Despite the high energy storage capacity of PCM, the low thermal conductivity of them is a limiting factor for the use of these materials. Therefore, current research has focused on improving the thermal performance of PCM using thermal conductivity enhancer (TCE). Metallic fins, nanoparticles mixed with PCM, and metallic foams are used as thermal conductivity enhancer. In the three methods mentioned as thermal conductivity enhancers, it is observed that the presence of metal fins leads to more uniformity of the base temperature of the heat sink and decreasing the base temperature. The use of nanoparticles provides appropriate and acceptable performance for temperature management of heat sink. Also, metal foams offer good performance due to their higher surface to volume ratio, better heat conductivity and lower weight. In this paper, various studies about enhance PCM performance for cooling electronic components under constant heat load are investigated and compared.

In this study, management of the electronic board temperature using an aluminum heat sink with9 fins containing phase change material (PCM) was investigated, experimentally. The critical temperature of the electronic board was 85 ° C and according to this temperature, stearic acid was selected as PCM for temperature management of the system. Experiments were performed in the wide power range and in different volume fractions of PCM. Using PCM at 11% volume fractions at power of 4 W significantly increased 20 minutes the operating time of the electronic board. Increasing the volume fraction of PCM from 11% to 50% at the power of 6 W, increased PCM melting range by 878 seconds and increased the operating time by 14 minutes. Experiments with alternative power (10 minutes on and 80 minutes off) in several consecutive heating-cooling cycles and at high powers (10, 15 and 18 watts) showed that the sensitivity of heat sink performance to PCM volume percentage at high powers is more than in low powers.

In this paper, numerical simulation of the convection heat transfer in micro-channel heat sinks is investigated. The main objective of this research is to study the effect of diameter, distance between fins and fins height, as well as the inlet fluid velocity on the average temperature fins, average temperature of fluid at outlet, temperature distribution in longitudinal direction of the micro-channel and heat flux passing fins. For this purpose, the cooling fluid flow passing through a micro-channel heat sinks with bar fins which have the elliptical cross-section and placed in a linear arrangement is simulated using a finite volume method. Simulation results indicate that changes in diameter and distance between the fins as well as the velocity of the inlet fluid have a significant effect on the heat transfer rate of the heat sink, but the temperature variations due to the change in the height of the fins are low.

In present work, for the first time, gas flow with considering slip velocity and temperature jump boundary condition is studied in a heat sink consisting rectangular fins and microchannels with calculating conjugated heat transfer.In this paper, helium gas flow with Knudsen number between 0.048 to 0.06 has been studied. Heat flux applied to the bottom of aluminum heat sink is 500W/m2. The governing equation for fluid flow has been discretized using second order upwind method and solved with using Coupled algorithm in Ansys-Fluent commercial software.Results show that inlet and local Knudsen numbers decrease with increasing pressure ratio and also local Poiseuille number decreases with increasing inlet Knudsen number. Also with increasing inlet Knudsen number (reduction of pressure ratio), first the average Nusselt number decreases and then increases.In this case, the average Nuselt number decreases about 54.4% with increasing Knudsen number from 0.006 to 0.024 and the average Nusselt number increases with increasing Knudsen number from 0.024 to 0.048.With increasing Knudsen number, thermal resistance increases continuously. The results show that with increasing inlet Knudsen number, slip effects are pronounced and slip and jump temperature coefficients increase.

Nowadays, with the advancement of technology, high-speed electronic instruments with small sizes are required. Regarding the low density of metal foams, they are recommended for many applications in order to energy absorption and heat transfer purposes. In this paper, the heat sinks made of metal-foams are simulated and the results are compared with simple finned heat sinks. In the heat sinks that made from aluminum foams with porosity value of 95.6%, the amount of heat transfer coefficient of displacement increases up to 31.127%. In another part of the dissertation, a finned heat sink, which metal-foam is placed between its fins is modeled. Obtained results show that, the Nusselt number in the heat sinks that made of aluminum foam with porosity of 95.6%, in the finned mode could increase up to two times. Finally, the effects of parameters such as the amount of mass discharge, the heat sink height and the amount of porosity of heat sink foam on the amount of heat transfer through heat sinks is determined at the end part.