Browsing by Author "Wang, Chi-chuan"

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Heat transfer simulation of annular elliptical fin-and-tube heat exchanger by transition SST model
(2020-08-01)
Nemati, H.
;
Rahimzadeh, A. R.
;
Wang, Chi-chuan
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機械工程學系
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Department of Mechanical Engineering
In this study, thermo-fluid characteristics of elliptical annular finned tube heat exchanger were numerically studied in detail. Transition SST model was utilized to simulate turbulent flow. Effects of air velocities, horizontal to vertical fin diameter ratios, and fin densities were examined in detail. The simulations indicate superior performance of elliptical fin layout. It was shown that pressure drop of annular elliptical fin can be only one half of that of a circular annular fin while containing comparable heat transfer performance. The vertical elliptical annular fin may even contain a higher heat transfer performance over circular fin. Correlations are proposed to estimate theNunumber and pressure drop based on the annular circular fin. The maximum deviations between the proposed correlations and simulations regarding pressure drop and heat transfer coefficient are 5.6% and 3.2%, respectively. For further elaboration of the superiority of the elliptical layout from the second law perspective, normalized entropy generation was also studied. In all cases, the entropy generation rate in circular fin was higher than that of an elliptical fin.
INVESTIGATING MICRO-FIN AND SMOOTH TUBES IN HORIZONTAL TWO-PHASE FLOW BOILING USING R-1234ze and R-134a REFRIGERANTS
(2016)
Abdul, Kaggwa
;
Wang, Chi-chuan
;
機械工程學系
;
Department of Mechanical Engineering
Global warming is becoming a major issue to the environmental perspective of view and one of the several causes is the release of refrigerants to the atmosphere. This research investigates refrigerant R-1234ze that is considered to substitute R-134a. A microfin and smooth tube with 9.5mm outer diameter was used in a two-phase flow horizontal convective boiling to study the pressure drop and the enhancement of heat transfer coefficients. The brazed microfin inside a stainless steel tube was heated electrically with current. Thermocouples were inserted in the wall to measure the temperature distribution. The measurements were carried out at saturation temperature of 20 degrees C by varying the refrigerant mass velocity between 50 kg/m(2)s and 200 kg/m(2)s, the vapor quality from 0.1 to 0.9, at different heat fluxes. Results from the two refrigerants and tubes were analyzed and compared basing on the values of the two-phase heat transfer coefficient and pressure drop.