In order to investigate the heat transfer coefficient of quenching oil at different flow rates, the ultrasonic Doppler velocimeter was adopted to measure the flow rates in given quench tank. The heat transfer coefficients were measured on the surface flat samples and calculated with the inverse heat conduction method. The results show that the peak values of heat transfer coefficient increase with the increment of flow rates. When agitation produces air bubbles in quenching oil, the cooling capacity of the quenchant declines sharply. It is demonstrated that heat transfer coefficient can perfectly describe the heat transfer at the interface between workpiece and quenchant.
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