Review of spray cooling – Part 1: Single-phase and nucleate boiling regimes, and critical heat flux

Spray cooling heat transfer: Technology overview and assessment of future challenges for micro-gravity application

For many years, spray cooling has been known as a promising technology for the removal of high heat fluxes. However, that promise has yet to be fully realized. This work presents a current understanding of the mechanisms of spray cooling and its limitations. To address these limitations, a novel spray nozzle array is described that allows for scalable, high-performance cooling. However, fluid management remains a challenging concern that may limit the application of this technology.

Next Generation Spray Cooling: High Heat Flux Management in Compact Spaces

Experiments were conducted to study the effects of enhanced surfaces on heat transfer during spray cooling. The surface enhancements consisted of cubic pin fins, pyramids, and straight fins (uniform cross sectional straight fins) machined on the top surface of copper heater blocks. Each had a cross-sectional area of 2.0 square cm. Measurements were also obtained on a heater block with a flat surface for baseline comparison purposes. A 2x2 nozzle array was used with PF-5060 as the working fluid. Thermal performance data was obtained under nominally degassed (chamber pressure of 41.4 kPa ) and gassy conditions (chamber with N2 gas at 101 kPa). The results show that the straight fins had the largest enhancement in heat flow. Critical heat flux (CHF) for this surface showed an increase of 55% in comparison to the flat surface for the nominally degassed condition. The cubic pin finned and pyramid surfaces provided slightly more than half the heat flux enhancement (30% - 40% greater than the flat surface) of the straight fins. The gassy case showed that the straight fins again provided the largest enhancement (48%) in CHF relative to the flat surface. This was followed by the cubic pin fins, and pyramids which had increases of 31% and 18% respectively. No significant effect was observed in the surface temperature at which CHF occurs for either portion of the study.

/pdf/investigation-of-enhanced-surface-spray-cooling-cbj3wq88yt.pdf

Investigation of Enhanced Surface Spray Cooling

Spray cooling is a novel solution for high heat flux applications, whose need is becoming apparent with the advance of high power density electronic systems (lasers, radars, etc). The aim of this investigation is to explore thermal management solutions for space‐based systems and the effects of varying gravity on heat transfer. Previous modeling done by Selvam, Lin, and Ponnappan (2006) used a liquid film thickness of ≈ 40 μm on the heater wall. The two‐phase flow modeling is done using the level set method to identify the interface of vapor and liquid as explained in Selvam, Lin, and Ponnappan (2005; 2006). Modifications to the incompressible Navier‐Stokes equations for surface tension, viscosity, gravity and phase change are discussed in detail. The equations are solved using finite difference method. The computed heat flux in thick layers is compared with previous thin layer heat flux. The computed liquid and vapor interface and temperature distributions are also visualized for better understanding of ...

Spray Cooling Modeling: Liquid Film Thickness Effect on Heat Transfer

Spray cooling is a high heat flux removal technique considered for systems such as advanced lasers and high power density electronics. Several experiments have been conducted using spray cooling in recent years and various designs of spray cooling devices are continually emerging. At this time, one of NASA’s missions is to enhance future space science capabilities through the application of power lasers and electronics. However, the usage of systems having high heat fluxes can only be achieved with the corresponding development of high power thermal control systems. For the reliable performance of these high‐heat‐flux systems, proper thermal management is imperative. The study presented reviews the fabrication of a spray cooling system aimed at addressing issues pertinent to space applications. These issues include heat flux capability, orientation, and volumetric packaging. Computer modeling of spray cooling under microgravity conditions as well as comparison to the analogous 1‐g condition was also performed to gain insight into microgravity behavior.

Brian L. Rowden

Papers

Spray Cooling Development Effort for Microgravity Environments