EXPERIMENTAL INVESTIGATION OF FLOW BOILING PARAMETERS IN A TRANSVERSE GROOVED HORIZONTAL TUBE: CRITICAL HEAT FLUX, PRESSURE DROP, AND HEAT TRANSFER COEFFICIENT

Abstract

An experimental investigation was conducted to examine critical heat flux (CHF), boiling pressure drop, and local heat transfer coefficient in a horizontal channel with transverse grooves for flow boiling with R-123. Measurement of the wall temperature of the channel was done using a thermal camera. Five test sections were used for the study. A combination of groove pitch (<i>p</i>) of 18.6 and 11 mm and groove height (<i>e</i>) of 1 mm and 0.55 mm were used for the study. The groove pitch-to-height (<i>p/e</i>) ratios used were 11, 20, 18.6, and 33.8. Experiments were carried out for different heat fluxes in the range from 180 to 1259 kW/m<sup>2</sup>, six different mass fluxes from 180 to 1259 kg/m<sup>2</sup>s, and Reynolds numbers from 5834 to 51770. In the grooved channel compared with the smooth tube, an improvement in heat transfer and CHF with the higher pressure drop was found. The boiling heat transfer coefficient increases with a decrease in (<i>p/e</i>) ratio. The enhancement of heat transfer coefficient and CHF improves with a decrease in (<i>p/e</i>) ratio. The maximum enhancement of CHF for (<i>p/e</i>) ratios of 11, 18.6, 20, and 33.8 is found to be 134%, 87%, 57%, and 53%, respectively. An abrupt increase in test channel wall temperature is an indication of CHF occurring. CHF was observed at the top portion of the grooved channel and was found to be of departure from nucleate boiling type.