Experimental study of evaporation heat transfer of R-134a inside a corrugated tube with different tube inclinations

Flow pattern visualization and heat transfer characteristics of R-134a during evaporation inside a smooth tube with different tube inclinations

“…From this figure it is found that for all the tube inclination angles the heat transfer coefficient increases with the increase of vapor quality until a vapor quality near 70% when it begins to decrease because of dryout. This trend had been observed previously during flow boiling inside inclined microfin tubes [8].…”

“…Fig. 9 also shows that the tube inclination angle has considerably influenced the heat transfer coefficient and this influence for the smooth tube is more prominent than the microfin tube [8]. Moreover, the smooth tube with + 90°inclination angle (vertical upward flow) turns out to be the best performing tube at low vapor quality, and the tube having inclination angle of −90°(vertical upward flow) has the lowest heat transfer coefficient.…”

“…Experimental apparatus applied in the present study is similar to our prior work [8]. The test apparatus consisted of a test-evaporator having a test-section length of 1100 mm.…”

“…Moreover, a comparison of heat transfer characteristics during evaporation inside the smooth tube with the microfin tube [8] is carried out. The experimental results have been conducted at four mass velocities of 53, 80, 107 and 136 kg/m 2 s.…”

“…Furthermore, evaporation heat transfer of R-134a flow inside inclined microfin tubes [7] and corrugated tubes [8] has been studied previously. The experiments were performed for seven different tube inclinations in a range of − 90°to + 90°.…”