Jiann-Cherng Chu

Fluid Dynamics in Microchannels

1.1 Need for microchannels research In contrast to external flow, the internal flow is one for which the fluid is confined by a surface. Hence the boundary layer develops and eventually fills the channel. The internal flow configuration represents a convenient geometry for heating and cooling fluids used in chemical processing, environmental control, and energy conversion technologies [1]. In the last few decades, owing to the rapid developments in micro-electronics and biotechnologies, the applied research in micro-coolers, micro-biochips, micro-reactors, and micro-fuel cells have been expanding at a tremendous pace. Among these micro-fluidic systems, microchannels have been identified to be one of the essential elements to transport fluid within a miniature area. In addition to connecting different chemical chambers, microchannels are also used for reactant delivery, physical particle separation, fluidic control, chemical mixing, and computer chips cooling. Generally speaking, the designs and the process controls of Micro-Electro-MechanicalSystems (MEMS) and micro-fluidic systems involved the impact of geometrical configurations on the temperature, pressure, and velocity distributions of the fluid on the micrometer (10-6 m) scale (Table 1.1). Therefore, in order to fabricate such micro devices effectively, it is extremely important to understand the fundamental mechanisms involved in fluid flow and heat transfer characteristics in microchannels since their behavior affects the transport phenomena for the bulk of MEMS and micro-fluidic applications. Overall, the published studies based on an extensive literature reviews include a variety of fluid types, microchannel cross-section configurations, flow rates, analytical techniques, and channel materials. The issues and related areas associated with the microchannels are summarized in the following table (Table 1.2).

Investigation of the Flow Mal-Distribution in Microchannels

This study examines the mal-distribution problem in microchannel manifolds. The tubes are of triangular shape with hydraulic diameter of 25 and 50 μm. Ranges of the Reynolds number are from 0.1 to 9. The test results indicate that the mal-distribution decreases with the rise of flow rate. For an inlet flow rate of 0.1 mL/min at the distributor inlet, the maximum difference of the translational velocity among manifolds is about 45%. The difference is reduced to 33% if the flow rate is increased to 0.153 mL/min. The maximum translational velocity inside the manifolds is located at the edge of the manifolds and the center portion has the smallest translational velocity. This is because of the spread and turn around water that helps to contribute the increase of flow rate nearby the edge.Copyright

Single-Phase Heat Transfer and Fluid Flow Phenomena of Microchannel Heat Exchangers

Thanhtrung Dang1, Jyh-tong Teng2, Jiann-cherng Chu2, Tingting Xu3, Suyi Huang3, Shiping Jin3 and Jieqing Zheng4 1Department of Heat and Refrigeration Technology, Hochiminh City University of Technical Education,Hochiminh City, 2Department of Mechanical Engineering, Chung Yuan Christian University, Chung-Li, 3School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, 4College of Mechanical Engineering, Jimei University, Xiamen, Fujian, 1Vietnam 2Taiwan 3,4P. R. China