Browsing by Author "Lee, Bing-Hung"

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A rationally based model applicable for heat pump tumble dryer
(2019-04-26)
Lee, Bing-Hung
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Sian, Rony A.
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Wang, Chi-Chuan
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機械工程學系
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Department of Mechanical Engineering
The present study proposes a rationally based heat pump clothes dryer model which is capable of handling transient behaviors of both air-side and refrigerant side. The model can take into account the geometrical variation of the heat exchangers. Yet the proposed model is free from extra constraints that were normally imposed by previous studies. The simulation shows that there exist three stages in a typical drying process, including a preheat stage, followed by a constant evaporation stage, and finally a falling drying rate period. The calculation indicates that the variation of the clothes temperature and the system suction/discharge pressure show an appreciable rise in the first stage, remain nearly unchanged at the second stage, and increase again at the final stage of drying process. Also, the corresponding maximum specific moisture extraction rate (SMER) peaks at the end of the second stage while the corresponding coefficient of performance (COP) drops continuously. The simulation also indicates that increasing the air volumetric flowrate yields a lower discharge/suction pressure, a higher COP value, and a shorter drying time. The results also suggested that a good strategy to maximize COP is initiated by a low volumetric rate during the preheat stage, increasing it during the second stage and lowering it to an intermediate flowrate at the end of the drying period. Increasing heat exchanger size, either by increasing heat exchanger width or the number of tube row, results in a lower suction/discharge pressure and a shorter drying time. Although both approaches adopt larger surface area to promote overall performance, it is found that increasing the width of heat exchanger yields more effective results.
Experimental investigation on heat transfer enhancement with twisted tape having various V-cut configurations
(2020-05-25)
Chu, Wen-Xiao
;
Tsai, Ching-An
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Lee, Bing-Hung
;
Cheng, Kai-Yueh
;
Wang, Chi-Chuan
This paper experimentally investigates the thermo-hydraulic performance of tubes with various twisted tapes (TTs) with the Reynolds number ranging from 4000 to 10,000 (at the turbulent transition region). The Nusselt number (Nu) and friction factor (f) of the tested plain tube shows good agreement with the Gnielienski and Filonenko equations. The average deviations are within 9.5% and 2.8%, respectively. For the successive TT tube, the existing correlation which includes the effect of gap between the TT insert and tube can well predict the present measurement, and the deviation upon Nu and f is within +/- 10%. Meanwhile, the successive TT with the twisted ratio of 4 can achieve the highest comprehensive thermal performance (CTP) by 1.08-1.10. Yet the Nu and f will simultaneously drop by 6.7% and 11.6% when raising the gap ratio from 0.043 to 0.135. The CTP is also pronouncedly reduced and can be negatively reversed than the plain tube at the turbulent transition region. On the other hand, it is validated that the U-cut and isosceles V-cut configurations might provide similar improvement on Nu and f compared to the successive TT. The obtuse V-cut configuration shows more pronounced improvement on Nu and f, and yields the highest CTP of 1.18-1.23 within the test range. The existing correlations applicable for the V-cut TTs are unable to predict the present measurements accurately.