Spray Cooling: From Physics to Practice

Presenter: Cameron Tropea, Phd, Technische Universität Darmstadt, Germany
Location: 1043 ERF

Abstract: Spray Cooling counts as a particularly promising technology for high rates of heat removal at high temperatures. Nevertheless, the predictive capabilities are still very rudimentary, relying heavily on empirical correlations, often with limited transferability outside the conditions from which they were developed. On the other hand, over the last decade significant progress has been made in theoretically predicting the heat transfer involved in a single drop impacting onto a heated substrate. The present study is devoted to utilizing these advancements to improve the theoretical and predictive foundations of spray cooling. Having such capabilities then opens avenues for optimization for a given application in terms of spray parameters, i.e. drop size and velocity distributions and number density or number flux at the substrate surface.

The presentation begins with a brief review of heat transfer solutions for single drop impacts and then outlines the challenges faced when moving from single drops to sprays. For instance, conditions under which an approach based on superposition are derived and the associated heat flux values as a function of spray parameters are computed. Another important aspect involved in practical applications is that the heated surface is often a complex geometry, differing from the flat plate situation often used in basic studies of heat transfer. Such geometries, usually involving oblique impacts, affect not only the hydrodynamics of impact, but also the local number flux of drops. Furthermore, in practical applications there is often relative movement between the spray and the substrate. This introduces two degrees of transient behaviour, one because the substrate is cooling down and another because of the local changes in spray parameters in different regions of the spray. This then necessitates that the problem is treated as a conjugate heat transfer problem, whereby the temperature distribution inside the substrate must also be solved and not just the instantaneous heat transfer on the substrate surface.

This novel approach to computing the heat transfer for spray cooling applications will be illustrated using computations of the heat transfer from a heated cylinder in both the Leidenfrost and nucleate boiling regimes. Conditions for optimum heat transfer will be elucidated.

Speaker Bio: Cameron Tropea graduated from the University of Toronto in engineering sciences, followed by a master’s degree in mechanical engineering (1977). He completed his Dr.-Ing. in civil engineering at the Technical University of Karlsruhe (1982) and his habilitation in fluid mechanics at the University of Erlangen-Nürnberg (1991) where he was appointed as professor of fluid mechanics until 1997. This was followed by an appointment as head of the Institute of Fluid Mechanics and Aerodynamics at the Technische Universität Darmstadt. Since 2003, he is editor-in-chief of the SpringerNature journal Experiments in Fluids and was past director of the Center of Smart Interfaces (CSI) in the period 2007-2014. His research interests include optical measurement techniques in fluid mechanics, interfacial transport and wetting phenomena, atomization and spray processes and unsteady aerodynamics. He has been a member of the Scientific Commission of the Council of Science and Humanities in Germany (Wissenschaftsrat) in the period 2016-2022. Tropea retired from the TU Darmstadt in April 2020 and presently holds the Henry Ford Visiting Professorship Chair at IIT Madras and a VAJRA faculty position at IISc Bangalore.