| Summary: | 碩士 === 國立中央大學 === 機械工程研究所 === 91 ===
Abstract
A numerical study was performed to analyze the laminar and turbulent flow and heat transfer characteristics for various types microchannel flow. The types of microchannel flow including the parallel plate, circular tube and the trapezoidal duct, where the hydraulic diameter ranging from 50μm to 4mm. Numerical solution using the software FEMLAB are compared with experiment and theory. In addition, the roughness viscosity model (RVM) was adopted to simulate the roughness effect in the circular tube (Dh=50—101μm). Results show that when Re<400, predictions of friction factors (f) of the laminar flow in the trapezoidal duct are agreed with the experimental data and the theory. For laminar microtube flow, solutions using RVM would induce higher flow resistance and thus reduce the volume flowrate. Prediction of friction factors matches experimental data but are lower than conventional theory. When Re>1500, present solutions using RVM disagree with Mala’s (1999) RVM solutions due to the early transition to turbulent flow at Re=1500. Calculation for turbulent microtube flow are performed using the k-ε model and law of the wall, and higher f’s (about 30%) values than experiment and theory is found in the flow regime of 4000<Re <10000.
For the case of heat transfer in the parallel plate, calculations of the local Nu compare well with available experimental measurement for the channel height equal to 0.4mm and 0.7mm. In the microtube flow at high Re (Re=1687), both experimental and numerical results of Nu close to the exit of tube are higher than the classical theory. Based on experiment’s explanation, the tube is not long enough for flow reaching the thermal fully developed condition, and thus cause experimental and numerical data higher than the theatrical value.
|
|---|
