The Effect of Thermal Quench Cycling on the Stability and Heat Transfer Characteristics of Transesterified-Epoxidized Used Cooking Oil Blended Quench Medium

Mineral oil is a widely used quench media in the heat treatment industries. They are derived from petroleum crude oil, and are toxic, and non-biodegradable. Therefore, in order to minimize the use of mineral oil, the fatty acid methyl esters (FAME) derived from the used cooking oil through the transesterification process can be blended with mineral oil. However, due to the high amount of unsaturation, blending of FAME in mineral oil would decrease the thermal-oxidative stability of the oil. Therefore, in the present work, to improve the stability of the mineral/FAME blend quenchant, the unsaturation in the FAME is decreased through epoxidation. The stability of epoxidized FAME/mineral blended oil is assessed by thermogravimetric analysis and thermal quench cycling. The quench cycles were performed using an ISO 9950 Inconel 600 standard probe. The viscosity and cooling performance of the oil were assessed periodically after the 1st, 10th, 50th, and 100th quench cycle. Investigation of cooling performance was performed by carrying out cooling curve analysis and estimating metal/quenchant interfacial heat flux tranisents. The results indicated that the thermal stability of the blend quenchant was improved with the epoxidation of FAME. The relative increase in viscosity was lower for blend quenchants than that for the mineral oil. The epoxidized FAME/mineral oil blend showed comparable cooling performance as that of mineral oil as the number of quench cycles were increased.