Boiling heat transfer and pressure drop of R-600a flowing in the mini-channels with fillisters

This study investigated the boiling heat transfer and pressure drop of hydrocarbon refrigerant (R-600a) flowing in six minichannels with fillisters made by electrical-discharge machining. The tests were run at a inlet pressure of 259–293 kPa and under saturated conditions, with the Reynolds number of 4,400–11,000 (i.e. mass flux of 195–487 kg/m2 s), heat flux of 1,790–8,950 W/m2 and outlet vapor quality of 0.041–0.25. Effects of the geometries of the fillisters, Reynolds number, heat flux and refrigerant quality on the heat transfer coefficient, friction factor and enhancement performance ratio were examined. The results of the minichannels with fillisters (Tests 1–4) compared to the minichannels without any fillister (Test 5) showed that the heat transfer coefficients increase about 1.05–1.34, 1.11–1.25, 1.23–1.59 and 1.07–1.21-fold, respectively. In addition, the friction factors for Tests 1, 2, 3 and 4 were about 3.3–9.4, 11.2–15.6, 14.7–21.9 and 5.0–6.3 % larger compared to that of the minichannels without any fillisters for Test 5. It was also found that Test 3 had the best enhancement of the performance. In summary, this study strongly suggests the use of fillisters constructed in minichannels.