Experimental Study on the Saturated Boiling Heat Transfer Characteristics of Water in Parallel Rectangular Channels

Aiming at the boiling heat transfer problem under the conditions of high temperature and high pressure between the narrow channels of the plate fuel in ship nuclear reactor, experimental studies on the heat transfer and flow distribution rules of vertical upward flow of water in two parallel narrow rectangular channels were performed. The electric heating simulation body of plate-type fuel was designed, the parallel rectangular narrow-slit channel circulation structure used at high parameters was fabricated, and the problems of sealing, insulation and thermal expansion of the test section at high temperature and high pressure were solved. The test section has two parallel rectangular channels with the aspect ratio of 39.4. The experimental pressure ranges from 2.1 to 10 MPa, mass flux from 1 000 to 1 500 kg•m-2•s-1, heat flux from 100 to 300 kW•m-2 and inlet temperature of subcooled water from 80 to 299℃. The results show that no significant difference of the heat transfer characteristics between the rectangular channel with a gap size of 2 mm and the conventional circular channel was observed. In the saturated boiling region, heat flux became the dominant factor of boiling heat transfer, and the effects of mass flow rate were weakened. In addition, the effects on the heat transfer characteristics between the parallel channels resulting from wall temperature, mass flow rate, heat flux and system pressure were analyzed, and it was found that the relative deviations of heat transfer coefficients between the two parallel channels were less than ±7% at same position and in the same working conditions. It is concluded that the flow distributions in the two parallel rectangular channels tend to be uniform. Moreover, the experimental data were compared with 5 existing boiling heat transfer correlations, and a new correlation was proposed based on the Kim formula. The proposed heat transfer correlation is in good agreement with the experimental data, and about 77.1% and 96.4% of the experimental points have deviations from the correlation within ±10% and ±20%, respectively. © 2021, Editorial Office of Journal of Xi'an Jiaotong University. All right reserved.