Last updated on August 10th, 2020 at 02:35 pm

Guest Post: Professor Alina Adriana Minea

Fluids are essential for many heat transfer processes in the majority of engineering equipment. Conventional heat transfer fluids include water, ethylene glycol, thermal, and engine oils. 

Modern processes present a tremendous need for enhancing thermal processes. Especially regarding finding new solutions that may favor the miniaturization of components for most of the thermal equipment. Another urgent need is to get higher heat transfer rates combined with higher energy conversion degrees.

Common heat transfer fluids actually have limited capabilities in terms of thermal properties. In turn, these limitations may impose severe restrictions in many thermal applications. Despite considerable research and efforts deployed, there remains a clear and urgent need to develop new strategies to improve the effective thermal behaviors of these fluids.

Improving Heat Transfer

Countless procedures are applied to improve heat transfer. Yet, the performance drawbacks of conventional fluids still hinder the performance enrichment and the compactness of heating/cooling equipment.

Overall, the strategies refer to the basics and considers the Newton law of convection. Improving convection heat transfer relies on two major techniques, active and passive methods. The most common one is to increase (extend) the surface heat transfer area by providing extensions or different fins (i.e. circular, pine, etc.). 

On the other hand, if one considers that the fluid itself can be improved, by increasing its convective heat transfer coefficient, it must take into account the thermal conductivity enhancement. How can this intrinsic property be enhanced? The response can be a simple one if one considers that almost all fluids have lower thermal conductivity than solids. The idea relies on improving the fluid by suspending high conductive particles. Hence, one can expect that a fluid containing solid particles may increase its conductivity. These are the bases of the nonfluids idea in the scientific community.

Nevertheless, even if this idea received great attention, several drawbacks and questions arise. How can particles remain suspended in the fluid? How to reduce clogging? What particles are suitable? How other properties are affected by particle addition? These are only a few general questions needing intensive research in the area of new heat transfer fluids.

Nanotechnology in Heat Transfer

Heat transfer augmentation techniques used to add solid particles as an additive to fluids. This approach is over 100 years old but has fallen out of favor in recent years. While effective, using solid particles as additives created nearly as many problems as they solved:

• Erosion
• Fouling
• Pressure Drop
• Sedimentation

More recent advances in materials and nanotechnology provide a better alternative: nanometer-size particles. Innovative heat transfer fluids suspended by nanometer-sized solid particles are named nanofluids. They are believed to be pioneered by Choi [1]. Although, some credit other voices that were first discovered in China a few years before Choi published its first material on this.

1995 was the year that nanofluids appeared as a pioneering research idea. Since then great efforts have been made to advance the knowledge on heat transfer fluids enhanced with nanoparticles.

Biography

Alina Adriana Minea is full professor at Technical University Gheorghe Asachi from Iasi, Romania and Director of Coordination Council of Doctoral School in Materials Engineering and has published over 140 articles and authored or co-authored 17 books, most of them in the field of heat transfer. Her research interests include heat transfer in industrial equipment, based on modifying heat chamber geometry and improving energy consumption, as well as nanofluids as heat transfer enhancement technique. She currently serves as a member of the regional editorial board of journal Thermal Sciences, as Associate Editor for Journal of Thermal Science (Springer) and International Journal of Thermophysics (Springer), as Editor for Journal of thermal science and engineering progress (Elsevier), as Editor-in Chief for IREHEAT journal. In 2013 and 2016 she received the prize for Best Reviewer from Applied Energy, Elsevier and in 2016 and 2019 the Best Researcher from Technical University Gh. Asachi from Iasi.

Her major current projects are ‘Nanouptake COST action.’ and “NanoRound”. Her current work is based on numerical and experimental studies in developing new heat transfer fluids.

Reference

1. Choi, S.U.S., Enhancing thermal conductivity of fluids with nanoparticles, in: proceedings ASME FED, vol. 231, pp. 99–105, 1995.