Thermophysical Properties and Heat Transfer Performance of Novel Dry-Ice-Based Sustainable Hybrid Lubri-Coolant

It is a well-known fact that the consumption of conventional cutting fluids in metalworking industries leads to severe health and environmental issues. Owing to the EPA (Environmental Protection Agency) increasing regulations regarding pollution and contamination, there is a dire need for a greener fluid with excellent cooling and lubrication characteristics to diminish the environmental impact of cutting fluids, as well as to improve machinability. Cryogens are greener and excellent coolants but poor lubricants, while ester oils are excellent lubricants and poor coolants. Therefore, a hybrid lubri-coolant cutting fluid with synergistic cooling and lubrication characteristics could be a desideratum to replace conventional cutting fluid. To investigate a newly proposed hybrid lubri-coolant, thermophysical properties (density, thermal conductivity, specific heat, and viscosity), heat transfer properties (surface temperature, heat flux, and heat transfer coefficient), and machinability properties (tool life, etc.) are key characteristics of the fluids that decide phase change and heat dissipation capabilities during their application in machining. In the current experimental study, hybrid ethanol–ester oils with/without dry ice (−78 °C) are proposed as cutting fluids and holistically investigated in terms of thermo-physical properties, heat transfer properties, and machinability properties under different cutting conditions. Experimental findings have depicted a 20%, 10%, and 5% decrease in density, specific heat, and viscosity, respectively, with a 15% increase in the thermal conductivity of the fluid with the addition of dry ice. The dry-ice-based hybrid lubri-coolant sprayed onto a Ti-6Al-4V plate enhanced the heat transfer coefficient significantly by 17% compared to hybrid lubri-coolant without dry ice. Besides, hybrid ethanol–ester oil dry ice was treated as a trendsetter and indicated an 11% improvement of the tool life at a cutting speed of 75 m/min and a feed rate of 0.04 mm/z. Therefore, dry-ice-based hybrid lubri-coolant can be applied as a cutting fluid by practitioners in aerospace, automotive, prosthetic body parts manufacturing, and manufacturing industries.