Experimental testing of convective spray cooling with the aid of an electrical field using the Coulomb force

Abstract

Continual advances in the electronics industry and other high heat-flux fields have led to a need for increased heat transfer efficiency. Spray cooling is one of many methods for removing heat from surfaces. Experimental testing conducted at West Virginia University was sponsored by the Air Force Office of Scientific Research in collaboration with the Air Force Research Laboratory to test the effectiveness of using inductive spray charging to enhance the heat transfer rate. Modifications made to the experimental test rig built by Hunnell (2005) enabled the study of electro-hydrodynamics. Experimental testing using working fluids, FC-72 and HFE-7000, was conducted. Electrodes were designed to inductively charge spray droplets (Law, 1978). Research was performed by studying the thermophysics for different spray flow rates ranging from 6 to 10 GPH with a stepwise applied heat load ranging from 0 to 120 W, for an applied electrode voltage between 0 to 6 kV.

Effects of Contact Charging on Spray Impingement Heat Transfer Performance and Spray Behavior

“…Spray cooling performance results for the present apparatus without electrical body force effects have been presented by Hunnell (2005) and by Hunnell et al (2006) under conditions of terrestrial gravity for both vertically-downward directed and horizontal sprays. Effects of the Coulomb force via inductive charging electrode designs (Law, 1978) have been described in the thesis by Kreitzer (2006), while effects of electrodes using the electric Kelvin force have been presented in the thesis by Glaspell (2006). The present results using the Coulomb force via contact charging are consistent with these earlier results.…”

“…An initial study of the use of the electric Kelvin force has been summarized in the thesis by Glaspell (2006) and by Kreitzer et al (2006). The use of the Coulomb force via inductive charging electrode designs (Law, 1978) is described in the thesis by Kreitzer (2006) and by Kuhlman et al (2007). Both the Kelvin force studies by Glaspell (2006) and the inductive charging Coulomb force work by Kreitzer (2006) used FC-72 and a second 3M dielectric coolant, HFE-7000.…”

“…The use of the Coulomb force via inductive charging electrode designs (Law, 1978) is described in the thesis by Kreitzer (2006) and by Kuhlman et al (2007). Both the Kelvin force studies by Glaspell (2006) and the inductive charging Coulomb force work by Kreitzer (2006) used FC-72 and a second 3M dielectric coolant, HFE-7000. Also, both of these studies demonstrated small (order of 5-15%) but repeatable EHD enhancements in heat flux using HFE-7000.…”

“…Instead of using the coolant used in the AFRL work (FC-72; see Yerkes et al, 2006), a second dielectric coolant, HFE-7000, has been used due to its lower resistivity and higher dielectric constant . Detailed descriptions of the current apparatus have been given in the theses by Hunnell (2005), Glaspell (2006), and Kreitzer (2006). A schematic of the spray nozzle, heater surface, pedestal, and sump is shown in Fig.…”

“…Key thermocouples have been calibrated against an RTD standard thermometer in a stirred oil bath. Flow meter repeatability is estimated as ±3% to 5%, heater power accuracy is estimated as ±0.5 to 1 W, and temperature resolution is ± 0.1 o C, with an estimated accuracy of ±0.2 o C for all calibrated thermocouples and ±0.6 o C for uncalibrated thermocouples (Kreitzer, 2006).…”