Spray Cooling of High Aspect Ratio Open Microchannels

Abstract

Direct spraying of dielectric liquids has been shown to be an effective method of cooling high-power electronics. Recent studies have illustrated that even higher heat transfer can be obtained by adding extended structures, particularly straight fins, to the heated surface. In the current work, spray cooling of high-aspect-ratio open microchannels was explored, which substantially increases the total surface area and allows more residence time for the incoming liquid to be heated by the wall. Five such heat sinks were constructed, and their thermal performance was investigated. These heat sinks featured a projected area of 1.41×1.41cm2, channel width of 360μm, a fin width of 500μm, and fin lengths of 0.25mm, 0.50mm, 1.0mm, 3.0mm, and 5.0mm. The five enhanced surfaces and a flat surface with the same projected area were sprayed with a full cone nozzle using PF-5060 at 30°C and nozzle pressure differences from 1.36–4.08atm(69–121ml∕min). In all cases, the enhanced surfaces improved thermal performance compared to the flat surface. Longer fins were found to outperform shorter ones in the single-phase regime. Adding fins also resulted in the onset of two-phase effects (and higher-heat transfer) at lower wall temperatures than the flat surface. The two-phase regime was characterized by a balance between added area, changing flow flux, flow channeling, and added conduction resistance. Spray efficiency calculations indicated that a much larger percentage of the liquid sprayed onto the enhanced surface evaporated than with the flat surface. Fin lengths between 1mm and 3mm appeared to be optimum for heat fluxes as high as 124W∕cm2 (based on projected area) and the range of conditions studied.

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

“…The temperature gradients near the contact line on a smooth surface were examined using thermochromic liquid crystals and were proven to be larger than those in other areas, making the hypothesis reasonable. Their results validated and extended the triple contact line length enhancement mechanism proposed by Horacek et al [115,116]. In their following research, it was found that the substrate temperature and heat flux distributions had a local minimum and a local maximum beneath the three-phase contact line, respectively, which is resulted from strong local evaporation.…”

Air Cooling of Power Electronics Through Vertically Enhanced Manifold Microchannel Systems (VEMMS)

“…Thermal management of the switches has become a primary design goal in the packaging of power converters. Many aggressive cooling methods, such as jet cooling, spray cooling, and two-phase cooling, have been and are being developed which are capable of handling heat fluxes above 100 W/cm 2 , with some capable of dissipating near or above 1 kW/cm 2 [1][2][3][4][5]. However, such cooling methods usually involve additional complexity and lack sufficient understanding of the fundamental physics of liquid-vapor flow interaction, making accurate and reliable analysis and design optimization more difficult [6].…”

The Effect of Water Droplet Size, Temperature, and Impingement Velocity on Gold Wettability at the Nanoscale

“…Thus, temperature influences the molecular arrangement of droplets and can be used to change the wettability of a substrate [18,21]. Nanodroplets are relevant to many processes that occur at high temperatures such as physical vapor deposition and spray-cooling [22]. In this work, droplets were simulated at the boiling temperature (373 K) of water and at room temperature which enabled the influence of temperature to be investigated in relation to droplet sizes and impingement velocities of the droplet.…”