Ayla Dogan

Metal foam heat sinks are preferred in electronic cooling systems with their advantages such as superior properties in heat transfer, light weight and ability to mix the cooling fluid. It is very difficult to conduct extensive experimental studies wi...

The thermal management of electronic devices has become a major problem in recent years. Therefore, there is a growing need for research on many new materials and innovative fluids due to the developing technology and increasing cooling need in electronic systems. In this paper, heat transfer from a plate fin and pin fin type heat sinks that were placed in a water block that are used in electronic systems was investigated. A base fluid (pure water) and 0.1% mass concentration Al₂O₃-H₂O nanofluid were used as cooling fluids. The experiments were carried out for volumetric flow rates varying between 100 and 800 mL/min and heat flux values of 454.54 W/m² and 1818.18 W/m². The results demonstrated that the Al₂O₃-H₂O nanofluid on the empty surface provided a maximum improvement of 10.5% in heat transfer compared to the base fluid. In the use of plate finned heat sink, the maximum amount of improvement in heat transfer compared to the empty surface was obtained approximately 64.25% for the base fluid and 82.8% for the nanofluid. A similar comparison was made for the pin-fin heat sink, a maximum thermal improvement of 56.4% in the base fluid and 70.27% in the use of nanofluid was determined.

With the developing technology, the dimensions of electronic systems are becoming smaller, and their performance and the amount of energy they need increases. This situation causes the electronic components to heat up more and the existing cooling systems to become inadequate. In this study, instead of the fins used in existing systems, 10 PPI and 40 PPI PHS were placed inside a water block, and the Al₂O₃-H₂O nanofluid at a mass fraction of 0.1% was used as the cooling fluid. Experiments were carried out under constant heat flux of 454.54 W/m² and 1818.18 W/m², with volumetric flow rates varying between 100 mL/min and 800 mL/min. The heat transfer results were compared with the results obtained from the base fluid and the empty surface. The results showed that the nanofluid reduced the surface temperatures compared to the base fluid. Especially when PHSs were used together with the nanofluid, a significant increase in heat transfer occurred compared to the empty surface. The highest heat transfer was observed when both the nanofluid and 40 PPI PHS were used together. In addition, the highest thermal performance value was determined as 1.25 times compared to the empty surface when the nanofluid and 10 PPI PHS were used together.

In this study, three dimensional mixed convection heat transfer from discrete heat sources placed in a horizontal rectangular channel has been investigated numerically. 8x4 flush-mounted discrete heat sources were mounted on the lower and upper surfaces of the channel. Air is used as working fluid (Pr0.7). The heaters at the bottom and at the top wall were kept at a constant heat flux. Side walls, upper and lower walls are insulated and considered adiabatic. Nusselt number distributions and the effect of the Grashof number (5.8x106≤ Gr* ≤ 2.3x107) and Reynolds number (150 ≤ Re ≤ 971) on the buoyancy-driven secondary flow have been investigated. Distributions of velocity vectors and temperature contours have been determined by the numerical method, and the results have been presented in detail. Governing equations were solved by the control volume method using suitable boundary conditions. The numerical parametric study was made for aspect ratio of AR=8, at various Reynolds and Grashof numbers.

In this study, the effect of both hexagonal pin fins (HPFs) and cylindrical pin fins (CPFs) into the rectangular channel on heat transfer augmentation, Nusselt number and friction factor were experimentally investigated. In planning of the experiments, different Reynolds number, pin fin array, pin fin geometry and the ratio of the distance between pin fin spacing (s) to the pin fin hydraulic diameter (s/D_h) were chosen as the design parameters. Air was used as the fluid. The Reynolds number, based on the channel hydraulic diameter of the rectangular channel, was varied from 3188 to 19531. In the experiments, the heating plate was made of stainless steel foil. The foil was electrically heated by means of a high current DC power supply to provide a constantly heated flux surface. The heat transfer results were obtained using the infrared thermal imaging technique. The heat transfer results of the hexagonal pin fins (HPFs) and cylindrical pin fins (CPFs) are compared with those of a smooth plate. Best heat transfer performance was obtained with the hexagonal pin fins. The maximum thermal performance factor ((Ƞ), was obtained as Re = 3188, staggered array, s/D_h = 0, Ƞ = 2.28.

One of the most important component of computers is processors (CPU). Because of the reasons like running too many programs simultaneously and playing games may cause the processor to overheat. This situation may cause unwanted computer malfunction. The CPU capacity and heat quantities increase with increasing the CPU speed and its performance. In order to run the system effectively, this heat must be removed and the critical surface temperature of the CPU must be kept below approximately 85 °C. In this present study, aluminum open cell metal foam (Al-6101) heat sink having pore density of 10 and 40 PPI (pore per inch) was used instead of the conventional plate type aluminum heat sink. 10 and 40 PPI aluminum metal foam materials are compared with each other and the results are presented in graphics at different fan speeds (1140, 1742, 2439, 2944, 3308 and 4187 rpm). According to the results, in %0-10 CPU usage (standby), lower surface temperatures were reached while using 10 PPI aluminum metal foam material. However, in %100 CPU usage, lower surface temperatures were reached while using 40 PPI aluminum metal foam material.

In this present study, the forced convection heat transfer from aluminum foam heat sinks with 10, 20, 40 PPI pore density placed in a discrete form in a partially open cavity were experimentally investigated. Air was used as working fluid. The uniform heat flux was applied to 3 × 3 array of foam heat sinks horizontally mounted in the cavity. The experimental studies were performed for the 3363–9743 range of Reynolds number and the 2.7 x 10⁶ and 7.5 x 10⁶ range of modified Grashof number. The effects of the Reynolds number, the modified Grashof number and the pore density of foam heat sink on the heat transfer were investigated. The results obtained were compared with the results obtained without foam heat sink cases. In addition, the most heated elements within the cavity were identified and solution proposals were presented. In addition, the most heated elements within the cavity were identified and solution proposals were presented.

This work experimentally studied heat transfer associated with three aluminum-foam heat sinks having various porosity size of 10, 20, and 40 PPI (pore per inch). Air was used as the coolant. Aluminum-foam heat sinks have been placed in discrete form on heat sources in a rectangular channel in order to investigate the heat transfer effect on the electronic equipment performance. The lower surface of the channel was equipped with 8 × 2 aluminum-foam heat sinks placed on copper blocks subjected to a uniform heat flux. All the channel surfaces were insulated. The experimental study was made for Reynolds numbers varying from 531 to 2461, while the Grashof number ranged from 4.2 × 107 to 2.7 × 108. The results show that the row-averaged Nusselt number values increase with increasing Grashof number for all pore densities. While the first row of the foam is affected by forced convection flow, with increase in the buoyancy-induced flow and the onset of instability, the row-averaged Nusselt number increases around the middle section of the rows because of the heat transfer enhancement. Comparisons made between the foams having different pore densities show that the 10 PPI aluminum-foam heat sink displays 3% and 18% higher Nusselt number values than those of the 20 PPI and the 40 PPI, respectively, because of its high permeability and low pore density characteristics. The results obtained also represent that the aluminum-foam heat sinks show 2 to 3 times higher thermal performance than those of no aluminum-foam case in the channel.

Natural convection heat transfer from aluminum (Al-6101) foam blocks with different pore densities (10, 20, and 40 pore per inch (PPI)) were investigated experimentally. Air was used as the working fluid. The test section was equipped with 3 × 3 aluminum foam blocks placed on copper plates and subjected to a uniform heat flux. The modified Rayleigh number Ra* varied between 8.33 × 105 and 5.24 × 106, while the foam height varied between 10 and 30 mm. The effects of block height and pore density of the aluminum foam on the heat transfer enhancement were determined. For the highest Rayleigh number, the results show that the thermal performance of the aluminum foam having H = 30 mm average Nusselt number obtained for pore density of 40 PPI is about 1.5 and 1.36 times higher than for 10 PPI and 20 PPI, respectively, and also 3.85 times higher than without a foam case in a cavity.