Abstract
Pool boiling experiment is one of the most fundamental methods to study boiling heat transfer and two phase flow phenomena. Our team used to conduct a quench experiment by quenching stainless steel ball and zircaloy ball with initial temperature at 1000℃ in seawater and deionized water to simulate the situation that the emergency core cooling system in nuclear power plant injects water to the core when the core uncovered accident occurs. The results demonstrate that seawater can significantly reduce the quenching time because the ions in it may inhibit the formation of vapor film at ultra-high temperature during quenching. In other words, the extreme hot surface can still contact with the liquid coolant and enhance the heat transfer coefficient. In this experiment, we design a steady-state pool boiling experiment to explore the different phenomena and the physics involved between ionic solution and deionized water. The test section is a platinum wire heater with a diameter of 0.3 mm and a length of 11.3 cm. It is coated with electronic insulation adhesive to prevent electrochemical reaction in ionic solution. A stainless steel tank with a length of 23 cm, width of 22 cm and height of 20 cm is employed as the pool for the boiling experiments. The pool is always filled with 6 L, equivalent to a depth of 11.5 cm of test working fluid in each test. A hot plate below the tank is used to control the bulk liquid temperature, which is measured by four T-type thermocouples connected to MX100 data acquisition system. The wall superheat can be acquired by the Kelvin 4-wire measurement method. The boiling curve can then be acquired. The results demonstrate that the bubbles for boiling in deionized water are usually much bigger than that in seawater or sodium chloride solution at the same heat flux. As the heating power is increased, the bubbles in deionized water may grow up obviously due to frequent bubble coalescence, while the bubble diameter approximately the same in ionic solution owing to lack of bubble coalescence. In sodium chloride solution, high departure frequency and non-coalescence bubbles may induce significant disturbance to the liquid near the surface and result in much better heat transfer performance and higher critical heat flux. In seawater, however, some magnesium salt may deposit on the heating wire, especially near the cathode and thus increase the thermal resistance. This may deteriorate heat transfer and heat transfer coefficient may be smaller than that in deionized water at high heat flux. In deionized water, the frequent bubble coalescence may eventually form a stable vapor film on the test section and heat transfer mode changes from nucleate boiling to film boiling. Compare with the other two working fluids, the critical heat flux in deionized water is much lower than that in seawater and sodium chloride solution.