Research in Mechanical Engineering

HEAT TRANSFER

Staff Involved: T.T. Chandratilleke, B. Boswell, R. Narayanaswamy

Project Description(s):

Heat transfer through narrow passages

Effective removal of internal heat generated by various system components is a major design challenge in the development of modern Micro-Electro-Mechanical-Systems (MEMS) such as computers, biomedical diagnostic probes and lasers, where overheating may lead to malfunction and eventual system failure. Over the past decade, the quest for miniaturisation in modern devices has steadily raised the requirements for cooling heat flux levels making conventional heat dissipation methods inadequate. Among many alternative cooling mechanisms, forced convective heat transfer associated with flow though very narrow passages or microchannels has been identified as a leading option for the cooling needs of modern and future instruments. The programme of research in this area examines fundamental aspects of heat transfer mechanisms in microchannel flow and the possibilities of developing micro-scale heat exchangers for cooling applications in miniature devices.

Heat transfer using jet-impingement

High-speed fluid jets are widely being considered for cooling of electronic components in modern instruments due to their inherently high heat transfer characteristics. Cyclic flow interruptions in jet cooling arrangements tend to provide further heat transfer enhancement due to continuously varying thermal and hydrodynamic boundary layers that reduce thermal resistance at the heated interface. Research in this area examines the fundamental mechanisms of heat and fluid flow in continuous and interrupted jet flows. The potential of jet impingement is identified as an effective cooling technique.

Reduction on coolant fluid in machining processes

It is known that the temperature at the cutting tool-chip interface is critical for tool life, high temperatures at this point result in wear on the flank or sudden death of the tool. In most high-speed cutting processes, temperature effects outweigh the effects of cutting speed, feed rate and depth of cut on the tool. Traditionally, to increase the tool life during machining, it has been customary to apply cutting fluid during the cutting process. The addition of cutting fluid during machining reduces the high temperature in the tool tip and high frictional forces during the cutting process.

Environmental concerns, however, have brought about the need to reduce or eliminate the use of cutting fluids in metal-cutting practice. Thus, our research has considers the use of impingement cooling using air. However, to improve the heat transfer rate it is also proposed to consider Cryogenic Cooling system for cooling the tool tips. The results of these studies should allow for the development of a prototype cooling system, which may be added to existing machine tools.

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