Quenching is one of the important industrial processes in which the rate of heat transfer plays a vital role. Recently, nanofluids have been used for heat transfer applications by researchers because of their higher heat transfer performance. In this paper, water based CNT nanofluid having 0.25 wt% of CNTs has been used as quenchant and the effect of nanofluid temperature on the heat transfer rate has been studied during quenching. CNT nanofluid was prepared by suspending chemically treated CNTs in de-ionized water. Cylindrical quench probes made of 304L stainless steel were quenched in 2 liters of water and CNT nanofluid. During quenching, the CNT nanofluid was maintained at 30 °C, 40 °C and 50 °C using an external temperature bath and the temperature history was recorded at the selected location inside the probe using a data acquisition system.

The heat flux and temperature at the quenched surface were estimated based on the Inverse Heat Conduction method by using the measured temperature data as input. The peak cooling rate and heat flux were higher during quenching in CNT nanofluid maintained at 30 °C as compared to water, which is due to the higher effective thermal conductivity of CNT nanofluid. When the CNT nanofluid was maintained at 40 °C, the peak cooling rate and heat flux were still higher than when it was maintained at 30 °C. But, the peak cooling rate and heat flux started decreasing when the CNT nanofluid temperature was further increased to 50 °C. The enhanced heat transfer performance during quenching in CNT nanofluid at a slightly higher temperature is attributed to the increase in Brownian motion of CNTs in nanofluid. When the CNT nanofluid temperature was further increased, the effect of bath temperature became predominant than the effect of CNTs and affected the quenching heat transfer.