Thermal performance of ammonia-cooled micro channel heat sink

The minimization of integrated circuits in powerful electronic devices generates a large amount of heat that has to be removed effectively and efficiently. One of the methods applied is to use a microchannel heat sink. Past optimization attempts have looked at the microchannel geometry, material, and coolant types using various models to represent the heat sink. This paper reports the analytical study on the optimization of the thermal resistance and pressure drop of a rectangular microchannel heat sink using a new coolant, ammonia gas which has never been reported before. The applicability of ammonia gas as a new coolant was investigated and showed excellent performance. The effect of different channel aspect ratio, fin spacing ratio, different structural materials and Reynolds number was investigated. Significant reduction in thermal resistance was obtained with 0.213 oK/W for ammonia gas compared to that of 0.266 oK/W for air under the same operating conditions. The total pressure drop achieved was 4.82 mbar and 9.52 mbar for ammonia and air respectively. The results indicate promising potential for ammonia gas as a coolant for rectangular microchannel heat sink

Optimized heat exchanger unit in a thermoacoustic refrigerator

Due to concern over the environmental impact caused by hazardous refrigerants, the last ten years or so has seen increasing research into thermoacoustic refrigeration. A thermoacoustic refrigerator is a device which uses acoustic power to pump heat. It holds the merits of simple mechanical design, absence of harmful refrigerants and having no or few moving parts. However, the performance of the thermoacoustic refrigerator, particularly the standing wave types, is currently not competitive compared to its counterpart conventional vapor-compression refrigerator. Thermoacoustic refrigeration prototypes, built up-to-date, achieved 0.1-0.2 relative coefficient of performance (COPR) compared with that of 0.33-0.5 for the conventional vapor-compression refrigerators. The poor heat exchanger design is one of the reasons for this poor efficiency. This paper discussed the influence of the thermoacoustic refrigerator heat exchanger's parameters on its design and the optimization of the performance of the system using the Lagrange multiplier method. The results showed that, the dissipated power is less than the published value by about 49% in the cold heat exchanger and about 38.5% in the hot heat exchanger. Furthermore, the increase of the cold heat exchanger effectiveness is found to be 3%. Thus, the decrease in the dissipated power in both heat exchangers with effective cold heat exchanger increases the performance of the thermoacoustic refrigerator

CFD Investigation of the Heat Transfer between an External Heat Source and the Regenerator of a Thermoacoustic Engine

AbstractThe heat transfer between an external source to the regenerator of a thermoacoustic engine involves both convection and radiation heat transfer. In order to enhance the efficiency of the thermoacoustic engine, it is very important to investigate the heat transferred by the two modes to the regenerator. In this paper, the two modes of heat transfer, convection and radiation are under investigation numerically. This work considers the two modes of heat transfer under oscillating flow through the porous medium of the regenerator, the oscillating flow is moving in front of the hot surface of the external heat source resulting in strong convection currents. The CFD modelling and simulation was conducted using Ansys_FluentTM CFD software. The results show the strong influence of the convection currents and its strong relations to the amplitude and frequency of the vibrations of the oscillating flow. The results also show the importance of radiation heattransfer between the hot surface and the regenerator and the role it may play on the performance of the engine

Radiation Heat Transfer between the Externally Heated Surface and the Regenerator of the Thermoacoustic Engine

AbstractThe SCORE thermoacoustic engine (TAE) depends of an external heat source from the waste heat of wood burning stove or propane gas. The overall efficiency of TAE depends a lot on the efficiency of the heat transfer process from the cooking stove to the regenerator. It is important to supply most of the heat to the engine directly to the regenerator top surface for best performance of the engine. The combined and complex mode of heat transfer from the cooking stove to the engine makes this task extremely difficult to be achieved. In this work analytical calculations are used to calculate from the fundamentals the radiation heat transfer from two types of heat exchangers used by the SCORE project to transfer heat from the external heat source to the engine. The objective of this study is to understand and evaluate the proportions of heat transferred from the inner side of the external hot surface to the engine. A detailed analysis of the view factors, the surface and space resistances were conducted to calculate the radiation heat transfer in each case at different temperatures. The results obtained showed the actual radiation performance of each part of the convolution and the bulge. Although the convolution performed better in terms of the total heat transfer, but the bulge showed higher radiation. The analytical results were compared with the published numerical results

Engineering elements profile among first- and final-year engineering students in Malaysia

Under the Malaysian New Economic Model, a few strategic reform initiatives (SRI) call for globally competitive and excellent engineers. The recruitment of students into engineering programs at Malaysian higher education institutes is based solely on the students' examination results. Hence, it is not known whether students who apply for engineering programs have the correct pre-conception of what constitute engineering. This study aims at identifying engineering elements that can be integrated into school science and mathematics curriculum to introduce engineering at the school level. The engineering elements serve as the basis to produce an engineering profile database which is useful to identify potential school students to enroll in engineering programs. This paper reports the identification of engineering elements and surveys carried out among first-year and final-year engineering students studying at Universiti Teknologi Malaysia, the only research university in Malaysia that specialized in engineering. The engineering elements, namely inquiry, design, operation and sustainability, were identified through literature review and interview with experts in engineering education while a set of questionnaire was used to identify the profiles of the students. The profiles of the first-year and final-year engineering students were compared to map out the engineering elements developed among them