Enhancement of Heat Transfer Characteristics of Liquid Quenchants

ABSTRACT: In order to achieve greater cooling rates and shorter full film phase of liquid quenchants two approaches were investigated. First, enhancement of base fluid thermal properties by addition of TiO2 nanoparticles of 50 nm average particle size. Nanofluids are colloidal suspensions of nanoparticles in base fluids. In the second testing method, cooling was performed in ultrasonic bath, with frequency of 50 kHz and power of 120 W. Ultrasound allows improvement of boiling and convective heat transfer through means of acoustic streaming. Standard liquid quenchants, water, polymer solution and quenching oil, and their cooling curves have been measured with and without ultrasound treatment and compared. All of the cooling curves were measured and recorded by IVF smart quench system using stainless steel probe with 12.5 mm diameter in accordance with ISO 9950 standard. Cooling rate vs. temperature and time was compared for all of the investigated media, as well as heat transfer coefficient. The addition of TiO2 powder caused a shorter full film phase for some nanofluids and maximum increase in CR for 26%. All experiments by ultrasound treatment of the quenchants without nanoparticles provided shorter full film phase and increase in maximum cooling rate of 20%. At polymer concentrations of 30% PAG neither TiO2 nanoparticles nor presence of ultrasound had any significant effect on the cooling curve. Distortions for each liquid quenchant was performed using ring probe. Keywords: quenching, TiO2 nanoparticles, ultrasound