Experimental study of heat transfer during quenching of a heated rod

Quenching experiments of a cylindrical rod were conducted in a distilled water pool in order to investigate the behavior of the critical heat flux (CHF) and the minimum heat flux (MHF). The effects of liquid subcooling, initial rod temperature, and surface condition on CHF and MHF were investigated during the quench process. The test specimen is a hollow stainless steel rod. The specimen has two thermocouples, one at the inner diameter and the other embedded inside the wall. Both thermocouples are located at the same axial elevation. During the experiment, all thermocouple readings were taken by a data acquisition system. In addition, a video was recorded by a high-speed video camera for visualization of the boiling phenomenon. The surface heat flux was calculated using a one-dimensional inverse heat conduction code at each location. It has been found that the MHF and CHF were significantly influenced by the degree of subcooling. However, the MHF and CHF values were almost independent of initial rod temperature and surface condition for the tested substrate material. The calculated surface heat flux based on each thermocouple location was found to be consistent during the film boiling regime. The inconsistency in the evaluated surface heat fluxes at both locations begins after the MHF point and reaches a maximum near the CHF. After the CHF point, the inconsistency decays dramatically. The variation in CHF values could be related to the axial conduction effect due to the large temperature gradient above and below the quench front.