Numerical investigation on the thermo-hydraulic performance of eccentric microchannels

• Main Author: Soh, Wei Zhen
• Other Authors: Ooi Kim Tiow
• Format: Final Year Project
• Language: English
• Published: 2019
• Subjects: Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/78764
• Institution: Nanyang Technological University

The increasing need for power density in many industrial processes led to the numerous efforts to seek better heat transfer method. Tuckerman and Pease introduced the use of microchannels in 1981, which boost the thermal efficiency due to the high surface area to volume ratio of the micro-sized channels. The ability to realise a microscale gap by superimposing two macro geometries has been demonstrated. However, due to the complexity and high cost of manufacturing concentric micro-sized channels, this method of heat transfer is still not widely used today. Thus, the author aims to investigate the effects of eccentricity on the single-phase convective heat transfer and fluid flow in a microscale channel. By doing so, the author hopes to be able to conclude whether the control of concentricity in microchannels is dispensable so that microchannels can be manufactured at a more competitive cost. In this study, numerical investigations will be carried out on three types of microchannels, namely concentric, uniformly eccentric and skewed annular, using single-phase liquid water flow. The microchannel will be modelled using a hollow copper block of 20 mm in diameter and length of 30 mm. A cylindrical steel insert will be placed within the copper tube to form the annular microchannel. For each type of microchannel, two steel insert diameters of 19.0 mm and 19.4 mm will be used to investigate the effect on heat transfer caused by using different radius ratio. Reynolds number is varied from 550 to 2300 in this study, with a constant step of 350. The copper block is subjected to a constant heat flux of 58946.3Wm-2. The continuity, energy and momentum equations are solved using a commercial solver, ANSYS Fluent. The results show that different types of eccentricity indeed cause deviations in the heat transfer capability of the microchannel. However, it can be concluded that smaller radius ratio causes lesser deviation from the results of the concentric microchannel. The results of the cases with radius ratio of 0.95 mostly stay within the range of 5% from the concentric cases. In addition, uniformly eccentric cases experience greater deviation as compared to the skewed microchannels. In fact, skewed annular with low radius ratio and higher eccentricity ratio demonstrated heat transfer capability that is more comparable to the concentric annular. With these results, it shows that there is possibility of developing a microchannel heat exchanger at a more competitive cost, given that the effects caused by eccentricity are negligible.