Research on heat transfer characteristic inside microchannels has become important topic as the advancement in the field of micro-scale technology such as micro electro-mechanical system. The impacts of miniaturization of the system involving high heat transfer processes create challenges for better system’s thermal management which can only be solved by enhancement of the performance and efficiency of applied heat exchanger devices. Microchannels have been considered as the potential solution for such devices due to their high thermal performance characteristic with low space requirements.
As for current development, the fabrication methods of microchannels, which limit the microchannels applications in the early developments, have emerged beyond the ability to model the thermal system on the microchannels of such scale. Micromachining of silicon wafers, micro-extrusion of aluminum elements [1], anisotropic wet chemical etching and sawing, anisotropic dry etching, hybridization and system-on-chip integration [2] are examples of micro-fabrication methods capable of manufacturing microchannels.
Early research in microchannels heat exchanger can be traced back to works by Tuckerman and Pease [3] for a very-large-scale-integrated circuits cooling. In fact, microchannels application can be found in cooling devices for computer’s microprocessors and electronic components, laser diodes, radar and aviation components, and microchemical reactors. For larger system, microchannels have been employed in compact heat exchanger for air conditioning system in automotive and domestic applications. Various microchannel configurations are used in these applications, including important feature of refrigerant headers which provide minimum effects on the upstream flow during two-phase flows inside the microchannel passages.
Despite the extensive applications of microchannels in heat exchanger devices, as for current applications, the devices are being implemented based on extensive testing which are expensive and time consuming. There has not been a fully-reliable thermal design methods for such applications due to the limited understanding in thermal-hydraulic phenomena occurred in micro-scale channels, importantly for two-phase flow boiling heat transfer mechanism.
Important issues on microchannels include two-phase flow patterns, flow boiling heat transfer mechanism and model developments, two-phase pressure drop and prediction methods, and critical heat flux.
References:
[1] Thome, John R., 2004. Boiling in microchannels: a review of experiment and theory, Int. J. Heat and Fluid Flow 25 pp. 128-139
[2] Kandlikar, Satish G. and Grande, William J., 2003. Evolution of Microchannel Flow Passages-Thermohydraulic Performance and Fabrication Technology, Heat Transfer Eng. 24(1) pp. 3 – 17
[3] Tuckerman, D.B. and Pease, R.F., 1981. High Performance Heat Sinking for VLSI, IEEE E. Device Letters, EDL-2 pp. 126-129
