Enhancement of heat transfer characteristics of liquid quenchants

摘要

In order to achieve greater cooling rates (CR) and shorter full-film phase of liquid quenchants, two approaches were investigated. First, an enhancement of base fluid thermal properties by addition of TiO_2 nanoparticles of 50 nm average particle size. Nanofluids are colloidal suspensions of nanoparticles in base fluids. In the second testing method, cooling of the base fluids was performed in an ultrasonic bath, with frequency of 50 kHz and power of 120 W. Ultrasound allows an improvement in boiling and convective heat transfer through means of acoustic streaming. Standard liquid quenchants, water and polymer solution, and their cooling curves were measured with and without ultrasound treatment, and compared. All of the cooling curves were measured and recorded by IVF SmartQuench system using Inconel 600 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 the heat transfer coefficient (HTC). The addition of TiO_2 powder caused a shorter full-film phase for some nanofluids and maximum CR increase by 26 %. All experiments by ultrasound treatment of the quenchants without nanoparticles provided shorter full-film phase and an increase in maximum cooling rate by 20 %. At polymer concentrations of 30 %PAG neither the TiO_2 nanoparticles, nor the application of ultrasound had any significant effect on the cooling curve.