Preparation and evaluation of stable nanofluids for heat transfer application: A review

•High heat load, a barrier in industries can be overcome by using nanofluids.•Nanofluids have higher thermal conductivity compared to conventional fluids.•For heat transfer applications, nanofluids must have long term stability.•Preparation of a long term stable nanofluids is challenging.•Study focuses on preparation, analysis & application challenges of nanofluids.

High heat load is becoming a barrier in industrial development. This high heat load can be overcome by increasing the rate of heat transfer. Heat transfer rate can be increased by increasing temperature gradient, area of heat transfer or by improving thermo physical properties of heat transfer fluids. Emergence of modern technology provides a great opportunity to process and produce particles in the size range of 1–100 nm called nanoparticles having high specific surface area. Colloidal suspension of nanoparticles into the conventional fluid called nanofluid has higher thermal conductivity compared to conventional fluids. Long term stability of nanofluid is one of the basic requirements for its better utilization in heat transfer applications. Preparation of a long term stable nanofluid is one of the main technical challenge. The main focus of this study is to review the work carried out by various researchers in the last two decades and to summarize the preparation and analytical techniques used for preparation of stable nanofluids. The paper also discusses some new challenging issues that need to be solved for better industrial application of nanofluids.