In-tube evaporation heat transfer and pressure drop characteristics of enhanced tubes ∅ 7mm and 9.52mm O.D with various groove shapes were experimentally investigated.
The test section was horizontal double-pipe counterflow heat exchanger with the length of 1680 mm. The refrigerant R-22 was heated by water in annulus. Test conditions were simulated with practical operating range of domestic air-conditioner ; heat flux and quality were 20 kW/m2 and 0.2 to 1.0 respectively. Mass flux was 200 kg/m2s for ø 7 mm and 150 kg/m2s for ø 9.52 mm. Oil circulation rate was 0.25 to 0.78 wt%.
The results showed that in-tube evaporation heat transfer and pressure drop varied with grooved shapes and heat transfer area enhancement. Based on experimental data, a new correlation was proposed for predicting the frictional pressure drop during evaporation inside horizontal smooth and single grooved tubes. This correlation yielded a good agreement with the experimental value within ±25%.