Nihon Kikai Gakkai ronbunshu (Oct 2014)
Prediction of thermal transport characteristics of microgroove evaporator (Validation of prediction model by measurement of transported heat and capillary-rise length)
Abstract
A microgroove evaporator is expected to achieve a high heat transfer coefficient despite its simple structure. However, the mechanism of high heat flux in association with the groove structure is still not clear enough to design its thermal performance. In this research, we propose the numerical simulation model of evaporation in a single groove that enable predicting its thermal transport characteristics and capillary-rise length. The proposed simulating method consists of three steps. First, we calculate the cross sectional profiles of working liquid meniscus in a rectangular groove. Secondary, the evaporative rate, the capillary force and the flow resistance that correspond to each cross sectional profile are calculated assuming one-directional viscous flow and the evaporation limit at vapor-liquid interface. Finally, the capillary-rise length and the evaporative rate of single groove are calculated using the steady-state momentum and mass conservation equations of working liquid. We verified the proposed method by comparing the calculated meniscus profile with the microphotos taken by Confocal Laser Scanning Fluorescent Microscopy. We also perform experiments for measuring the capillary-rise length and transported heat rate (evaporative rate) of several microgroove evaporators in a certain condition (superheat: 6K, inclination: 60 degree) to compare these values with the calculated values. Both experimental results showed good agreements proving that the proposed simulation method might be useful for designing microgroove evaporator. From the experimental and numerical results, we found that the capillary-rise length is maximum at the groove width of 200µm, and that the broader the groove width is, the lower the effective heat flux and the higher the transported heat rate per groove are.
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