In Japan, a carbon dioxide (CO{sub}2) heat pump water heater for residential use was developed for sale in 2001 to conserve energy and help prevent global warming. In order to develop a more efficient and more compact CO{sub}2 heat pump, it is necessary to develop a compact and highly efficient evaporator, and important to understand the CO{sub}2 flow boiling heat transfer coefficient. An experimental study was conducted here to measure the pure CO{sub}2 (99.999% purity, without oil) heat transfer coefficient in a horizontal copper tube (outer diameter (O.D.): 6 mm, thickness: 0.4 mm, length: 4 m). The test conditions were: CO{sub}2 mass flux from about 200 to about 700 kg/(m{sup}2s) (heat flux from about 10 to about 40 kW/m{sup}2), quality at inlet of test section 0.17, CO{sub}2 super heat at outlet of test section 5 K, and saturation temperature from 0 to 10°C. The measured heat transfer coefficient was compared with calculated values by means of several correlations.
展开▼
