A STUDY OF HEAT TRANSFER DURING POOL BOILING OF WATER OVER A LARGE DIAMETER TUBE

Abstract

The present investigation was undertaken to obtain experimental data for pool boiling of saturated water at atmospheric pressure on an electrically heated tube in its horizontal orientation. The heating tube was made of zircaloy having outside and inside diameter of 111 mm and 108 mm respectively with effective heating length of 530 mm. The J type thermocouples were used to measure the wall temperature of heating tube and that of the boiling water. The wall temperatures were measured at the six positions at a cross-section which was midway of the heated tube length. The thermocouples are spaced by angle it / 3 radians with one each at top and bottom positions. From the experimental data it is observed that the wall temperature varies circumferentially. It increases from top to side to bottom position continuously for a given value of heat flux. But the bulk temperature of water did not vary appreciably. They are almost equal to saturation temperature corresponding to pressure on the boiling liquid. When the value of heat flux is raised, the behavior of temperature distribution remains same but the temperature at top, side and bottom positions assume higher values. With further increase in heat flux the values of wall temperature increases correspondingly. The data analysis of average wall temperature of the tube has resulted in a generalized correlation relating the wall temperature, (OT,,,) to heat flux. The average value of heat transfer coefficient was found to increase with rise in heat flux and it is directly proportional to the heat flux raised to the power of 0.7. Based on the data of present investigation and those due to earlier investigations, generalized correlations have been proposed for the prediction of average heat transfer coefficient at atmospheric pressure.