Browsing by Author "Abdul, Kaggwa"

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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.
INVESTIGATION OF THERMAL-HYDRODYNAMIC HEAT TRANSFER PERFORMANCE OF R-1234ZE AND R-134A REFRIGERANTS IN A MICROFIN AND SMOOTH TUBE
(2016-01-01)
Abdul, Kaggwa
;
Wang, Chi-Chuan
;
機械工程學系
;
Department of Mechanical Engineering
This research is based on R-1234ze that is considered a substitute for R-134a due to its low global warming potential in a microfin tube with outer diameter 9.52 mm, the number of fins 70, and fin height 0.17 mm. In comparison, a smooth tube with similar geometries was used to study pressure drop and heat transfer coefficients related to the two fluids. The microfin tube was brazed inside a stainless steel tube and heated electrically. T-type thermocouples were used to measure the temperature distribution during the phase change process. The experimental saturation temperatures and refrigerant mass velocities varied from 10-20 degrees C and 50-300 kg/m(2) s, respectively. The vapor quality ranged from 0.1 to 0.9 and heat flux from 5 to 11 kW/m(2). The results showed that heat transfer performance of R-134a in both microfin and a smooth tube was better than R-1234ze, especially at mass velocities above G = 100 kg/m(2) s. However, R-1234ze yielded better heat transfer coefficients at mass velocities lower than G = 100 kg/m(2) s. The pressure gradient of R-1234ze was markedly higher than that of R-134a at all mass flow rates.