Modelling and simulation techniques for forced convection heat transfer in heat sinks with rectangular fins

The official published version of this article can be found at the link below.This paper provides a comprehensive description of the thermal conditions within a heat sink with rectangular fins under conditions of cooling by laminar forced convection. The analysis, in which increasing complexity is progressively introduced, uses both classical heat transfer theory and a computational approach to model the increase in air temperature through the channels formed by adjacent fins and the results agree well with published experimental data. The calculations show how key heat transfer parameters vary with axial distance, in particular the rapid changes in heat transfer coefficient and fin efficiency near the leading edges of the cooling fins. Despite these rapid changes and the somewhat ill-defined flow conditions which would exist in practice at the entry to the heat sink, the results clearly show that, compared with the most complex case of a full numerical simulation, accurate predictions of heat sink performance are attainable using analytical methods which incorporate average values of heat transfer coefficient and fin efficiency. The mathematical modelling and solution techniques for each method are described in detail.This work was part of a project funded by Solas Technology Limited, Ireland

Optimization of Heat Sinks in a Range of Configurations.

In this study, different heatsink geometries used for electronic cooling are studied and compared to each other to determine the most efficient. The goal is to optimize heat transfer of the heat sinks studied in a range of configuration based on fin geometry. Heat sinks are thermal conductive material devices designed to absorb and disperse heat from high-temperature objects (e.g. Computer CPU). Common materials used in the manufacturing of heat sinks are aluminum and copper due to their relatively high thermal conductivity and lightweight [1]. Aluminum is used as the material for the heatsinks studied in this research project. To start, experimental results from a wind tunnel test conducted were compared to numerical results generated to establish a validation case. Best practices in running numerical simulations on heat sinks along with suitable models for simulating real-world conditions were determined and analyzed. The two main thermal performance-evaluating parameters used in this project are pressure drop (ΔP) and thermal resistance (R). Thirteen numerical CFD simulations were run on different heatsink fin extrusion geometries including the traditional rectangular plate, arc plate, radial plate, cross pin, draft pin, hexagonal pin, mixed shape pin fin, pin and plate, separated plate, airfoil plate, airfoil pin, rectangular pin, and square zig-zag plate heat sinks. It was observed that different fin geometries and dimensions affect the performance of heat sinks to varying extents. The square zig-zag plate heat sink from results obtained had the lowest thermal resistance of 0.25 K/W with the separated plate having the lowest pressure drop of 11.94 Pa. This information is relevant in the selection of fan type, size, and model of heat sink for electronics cooling. Also, another important conclusion drawn from this project is the existence of no definite correlation between the thermal resistance (R) and pressure drop (ΔP) parameters when evaluating heatsink performance

Enhancing the performance of concentrating photovoltaics through multi-layered microchannel heat sink and phase change materials

Concentrating Photovoltaic technology is considered now as a promising option for solar electricity generation along with the conventional flat plate PV technology especially in high direct normal irradiance areas. However, the concentrating photovoltaic industry sector still struggles to gain market share and to achieve adequate economic returns due to challenges such as the high temperature of the solar cell which causes a reduction its efficiency. The work presented in this thesis is targeted to influence the overall performance of a high concentrated photovoltaic system by integrating both the multi-layered microchannel heat sink technique and a phase change material storage system. The proposed integrated system is composed of a multi-layered microchannel heat sink attached to a single solar cell high concentrated photovoltaic module for thermal regulation purposes. This is expected to reduce the solar cell temperature hence increasing the electrical output power. The high concentrated photovoltaic and multi-layered microchannel heat sink system is then connected to a phase change material thermal storage system to store efficiently the thermal energy discharged by the high concentrated photovoltaic and multi-layered microchannel heat sink system. The first part of the thesis discusses the influence of the multi-layered microchannel heat sink on the high concentrated photovoltaic module using both the numerical and experimental approaches. The multi-layered microchannel heat sink has been integrated for the first time with the single cell receiver and tested successfully. A numerical analysis of the high concentrated photovoltaic and multi-layered microchannel heat sink system shows the potential of the heat sink to reduce the solar cell maximum temperature and its uniformity. The thermal behaviour of the multi-layered microchannel heat sink under non-uniform heat source was experimentally investigated. The results show that in extreme heating load of 30W/cm² and in heat transfer fluid flow rate of 30ml/min, increasing the number of layers from 1-layer to 4-layers reduced the heat source temperature from 88.55°C to 73.57°C, respectively. In addition, the single layer multi-layered microchannel heat sink suffers of the most heat source temperature non-uniform compared to the heat sinks with higher number of layers. Also, the results show that increasing the number of layers from 1-layer to 4-layers reduced the pressure drop from 16.6mm H2O to 3.34 mm H2O. The indoor characterization of the high concentrated photovoltaic and multi-layered microchannel heat sink system investigated the effect of the number of layers, the homogeniser materials, and the heat transfer fluid flow rate and inlet temperature on the electrical and thermal performance of the system. The results show that the maximum power of the high concentrated photovoltaic module with glass homogeniser is 3.46W compared to 2.49W when using the crystal resin homogeniser for the 2-layers multi-layered microchannel heat sink and 30ml/min under 1000W/m² irradiance intensity. Increasing the number of layers from 1-layer to 3-layers on the high concentrated photovoltaic and multi-layered microchannel heat sink system increased the maximum electrical power by 10% and decreased the solar cell temperature 3.15°C for the heat transfer fluid flow rate of 30ml/min. This gives an increase in the maximum electrical power of 98.4mW/°C. The outdoor characterisation of the high concentrated photovoltaic and multi-layered microchannel heat sink system performance was evaluated at the University of Exeter, Penryn Campus, UK. The achieved maximum output electrical power of the system was 4.59W, filling factor of 75.1%, short circuit current of 1.96A and extracted heat of 12.84W which represents of 74.9% of the maximum solar irradiance of 881W/m². In addition, the maximum solar cell temperature reached to 60.25°C. Secondly, the experimental studies were carried out in order to investigate the performance of the phase change material storage system using paraffin wax as the PCM materials. The thermal storage system performance was evaluated in various conditions. The results show that inclination of the phase change material storage influences the melting behaviour of the phase change material where the phase change material storage of 45º inclination position melts faster than the phase change material storages in the 0º and 90º inclination positions. The phase change material melting time is reduced in the PCM storage of 45º inclination position by 13% compared to the 0º inclination position. The last part of the thesis discusses the integration of the phase change material storage with the high concentrated photovoltaic and multi-layered microchannel heat sink system. A 3D numerical model was developed to predict the behaviour of the integrated high concentrated photovoltaic and multi-layered microchannel heat sink system with the phase change material storage system using variable source conditions. The results show a higher heat absorption rate on phase change material storage that uses a lower melting temperature phase change material compared to the higher phase change material melting temperature. The multi-stages storage with different phase change materials melting temperature showed a lower heat absorption compared to the phase change material arrangement with the lower melting temperature. Also, the rate of the absorbed heat fluctuation is less affected by the phase change material arrangement with higher melting temperature

A review of metal foam and metal matrix composites for heat exchangers and heat Sinks

Recent advances in manufacturing methods open the possibility for broader use of metal foams and metal matrix composites (MMCs) for heat exchangers, and these materials can have tailored material properties. Metal foams in particular combine a number of interesting properties from a heat exchanger's point of view. In this paper, the material properties of metal foams and MMCs are surveyed, and the current state of the art is reviewed for heat exchanger applications. Four different applications are considered: liquid-liquid, liquid-gas, and gas-gas heat exchangers and heat sinks. Manufacturing and implementation issues are identified and discussed, and it is concluded that these materials hold promise both for heat exchangers and heat sinks, but that some key issues still need to be solved before broad-scale application is possible

Numerical Validation of Cooling Performance of Phase Change Materials Integrated Into Heat Sinks for Electronics Cooling

This study aims to analyze the cooling performance of phase change materials (PCMs) integrated into metallic heat sinks (HSs) both experimentally and numerically. For the experimental part of the study, a test setup has been constructed to test PCM integrated heat sinks. The heat sinks are prepared as metallic containments having fins with fixed inter-fin spacing. The volume between the heat sink fins is filled with PCM namely: a paraffin wax, salt hydrate-calcium chloride and milk-fat, then the whole system is sealed for testing under various heat loads at 4W, 6W, 8W and 10W. Four modes of operation are experimentally tested in this study: HS under natural convection, HS integrated with PCM under natural convection, HS under forced convection, and HS integrated with PCM under forced ventilation. The temperature of heat generating surface and the heat sink surface are monitored over time to evaluate the PCM thermal performance. From the results, the time lag and temperature drop in case of with PCM compared to without PCM shows the cooling effect of adding PCM under both natural and forced ventilation modes of heat removal. It found that inclusion of each of the three types of PCM into heat sinks with natural convection shows higher temperature drop (up-to 15 °C) in first 15 min of heating than inclusion of fan (forced convection) without PCM. However, the combination of both the fan ventilation and the PCM always maintain the lower temperature other three modes. This leads to conclusion that implementing a PCM in the heat sink will be very useful in thermal management of the electronic device and the application is more suitable under cyclic thermal loading conditions since in all cases the PCM completes melting in certain time and then shows a temperature rise. It is recommended to use forced convection combined with PCM filled in HS to increase the cooling effect while using PCM will be recommended for short time operation or cyclic operation such as switching operations where PCM can be regenerated to solid during off duty cycle to be ready for the next cycle of heat absorption. It is also recommended to use PCM integrated into a HS to provide a backup passive cooling support especially in case of failure of the fan system during operation as an additional safety cover. For the numerical part of the study, a three dimensional transient heat transfer numerical model using commercial ANSYS CFD software is developed and is validated against the experimental results. Next the numerical model is used to optimize the heat sink geometry, the PCM amount and the viii cooling-heating response in order to identify potential applications in electronic packaging in terms of temperature drop and charging-discharging cycle time. From parametric study, it is observed that a narrow melting point, not mixing of the PCM, good thermal conductivity, higher density, rectangular fin type and a reasonable package size are optimum for the temperature control of electronic devices employing heat sink with PCM

Turbulent heat transfer analysis of a three-dimensional array of perforated fins due to changes in perforation sizes

Turbulent heat transfer characteristics of three-dimensional and rectangular perforated fins, including perforation like channels along the length of the fins, are investigated. Both dimensions and numbers of perforations are changed at the highest porosity in the study of Shaeri and Yaghoubi [7] to determine the effects of perforation sizes on the heat transfer characteristics of the perforated fins. Results show that at a specific porosity, a fin with a higher number of perforations enhances the heat transfer rate more efficiently. Also, total drag is not only remarkably lower in perforated fins compared with a solid fin, but also becomes smaller by decreasing the number of perforations

Theoretical and experimental analysis of the performances of a heat sink with vertical orientation in natural convection

In the various areas in which electrical components are used, the problem of heat dissipation generated due to the absorption of electrical energy assumes great interest and is worthy of an in-depth study. In steady state conditions, the thermal power generated can equal the electrical power absorbed and leads to an alteration in the physical properties of electrical components compromising their performance and correct functioning. One of the most frequently adopted solutions consists in the application of a heat sink on the surface to be cooled. Experimental tests were conducted using an infrared thermal camera, an internal climate control unit for the recording of the thermo hygrometric conditions of the environment and a finite element software (ProENGINEER) to simulate the thermal behaviour of the heat sink in order to analyse the modalities of thermal exchange of the heat sink. The results obtained were subsequently compared with the heat sink properties provided by the manufacturer. The main objective of the work is that of providing a methodology that blends the use of thermographic and simulation techniques with finite elements, in order to render the development of a theoretical–experimental correlation possible for any physical condition and geometrical configuration taken into consideration. This methodology is confirmed in the field of technological development of electrical components, where at each stage of the planning process exists a marked intertwining of computing, electronics, mechanics and heat transmission