Heat transfer characteristic of water at near critical pressure in circumferentially non-uniformly heated vertical tubes

Experiments on heat transfer and characteristic of water in circumferential non-uniformly heated, vertical up flow tube at near critical pressure have been carried out at Xi'an Jiaotong University. The wall temperature and heat flux distribution along the cross section of the tube were obtained in the experiments. The critical heat flux, critical mass flow rate and critical mass quality have been analyzed. The effect of the heating method on the heat transfer characteristic has also been obtained. Experimental conditions included pressures of 19-22 MPa, mass flow velocities of 600-1200 kg/m2 s, and heat fluxes of 200-600 kW/m2. The experimental results showed that, for the non-uniformly heated tube, film boiling and nucleate boiling can coexist simultaneously at the different sides of one cross section of the tube when heat transfer deterioration occurs at high flux side. When the heat transfer deterioration occurs, the local critical peak heat flux of the non-uniformly heated tube and the critical heat flux of the uniformly heated tube are almost the same. So, the heat transfer deterioration is caused by the local heating condition of the non-uniformly heated tube. The minimum heat transfer coefficient of the non-uniformly and of the uniformly heated vertical tubes differs only a little when heat transfer deterioration occurs. Finally, the experimental correlations used to calculate the critical heat flux and the minimum heat transfer coefficient were given. (authors)