Spray Cooling on Enhanced Surfaces: A Review of the Progress and Mechanisms

Abstract

The rapid development of electronics, energy and propulsion systems has led us to the point where their performances are limited by cooling capacities. Heat fluxes of 10~100, even over 1,000 W/cm2 need to be dissipated with minimum coolant flow rate in next-generation power electronics. Spray cooling is a high heat flux, uniform and efficient cooling technique proven effective in various applications. However, its cooling capacity and efficiency need to be further improved to meet next-generation ultrahigh-power applications. Engineering of surface properties and structures can fundamentally affect the liquid-wall interactions, thus becoming the most promising way to enhance spray cooling. However, the unclear mechanisms of surface-enhanced spray cooling cause lack of guiding principles for surface design. Here, progress in spray cooling on surfaces with structures of different scales are reviewed and their performances evaluated and compared. Spray cooling can achieve critical heat flux (CHF) above 945 W/cm2 and heat transfer coefficient (HTC) up to 57 W/cm2K on structured surfaces for pressurized nozzle and CHF and HTC up to 1250 W/cm2 and 250 W/cm2K, respectively, on a smooth surface with the assistance of secondary gas flow. CHF enhancement of 110% was achieved on hybrid micro- and nanostructured surfaces. A clear map of enhancement mechanisms is proposed after analysis. Some future concerns are also proposed. This work helps the understanding and design of engineered surfaces in spray cooling and provides insights for interdisciplinary applications of heat transfer and advanced engineering materials.

The Simultaneous Analysis of Droplets’ Impacts and Heat Transfer during Water Spray Cooling Using a Transparent Heater

“…As can be seen from the comparison, the general view and the exponents at the similar numbers of expression (10) are close to expressions (7) and (8). In addition, as the characteristic dynamic scales of nucleate boiling, the capillary constant and the evaporation rate are used in (10). These parameters are similar to those used for spray cooling description (Figure 9a,b).…”

“…In this regard, many studies are devoted today to the processes during spray cooling, the description of which could be found in recent review papers [3,4,10]. At the same time, the analysis of these works shows that some issues related to the dynamics of liquid irrigation and heat transfer during spray cooling still remain open.…”

Experimental Correlation for Splashing Condition of Droplets on Solid Substrates

“…However, droplet behavior has great potential to applications in a variety of industrial, agricultural, medical, and biological fields. Especially, droplet impingement behavior is related to inkjet printing [1], spray cooling [2,3], spray painting [4], fuel injection [5], and pesticide spray in agriculture [6] and so on. In such applications, the precise predictions of the droplet behaviors such as the spreading size of the droplet, the contact time between liquid and solid surface during the impingement process and splashing or not are very important for an estimation of effective heat transfer, efficient consumption of the pesticide, coating material, and the inkjet process.…”

Experimental investigation of spray cooling performance in non‐boiling zone on rough superhydrophilic/hydrophobic surfaces

“…4 Spray cooling is considered as an appropriate technique for high power and high heat flux conditions, with the main advantages including low thermal resistance, large heat dissipation capacity, and good temperature uniformity. When using an atomizing nozzle with water as a cooling medium, the critical heat flux can reach 1000 W/cm 2 when the degree of superheat stays below 60 C. 5 When the pressure is kept constant and the hot surface temperature is lower than the boiling point of the cooling medium, the spray cooling can stay in the nonboiling zone, where the forced convection and the thin liquid film evaporation mainly contribute to the heat transfer process. Many researches have been done in this field in the past decades.…”