Jeffrey Didion

Terrestrial and Microgravity Experimental Study of Microscale Heat-Transport Device Driven by Electrohydrodynamic Conduction Pumping

Research on heat transport in microscale has been generating much interest in the recent years due to the development of state-of-the-art high-powered electronics used in aerospace and terrestrial applications and the large amount of heat produced during their operation. Microscale two-phase-flow heat-transport devices are seen as one solution to this problem of high heat-flux removal. Microscale devices have extremely high heat fluxes due to the small heat-transfer surface area. In addition, the need for robust, nonmechanical, lightweight, low-noise, and low-vibration devices in specialized aerospace applications has led researchers to investigate electrically driven flow devices rather than their mechanical counterparts. This paper, for the first time, presents the results of an experimental study of a unique microscale heat-transport device that is driven by electrohydrodynamic (EHD) conduction pumping. Results from ground-based single-phase experiments with a microscale EHD pump are compared with experiments conducted on board a variable-gravity parabolic flight. Data show that the EHD pump functions well in both environments and can be potentially used in heat-transport devices in the absence of gravity. This is the first step in broader-scale future experimental work that will involve heat transfer, including phase change.

Performance Characteristics of Electrohydrodynamic Conduction Pump in Two-Phase Loops

The electric field applied in dielectric fluids causes an imbalance in the dissociation-recombination reaction generating free space charges. The generated charges are redistributed by the applied electric field resulting in the heterocharge layers in the vicinity of the electrodes. Proper design of the electrodes generates net axial flow motion pumping the fluid. The electrohydrodynamic (EHD) conduction pump is a new device that pumps dielectric fluids utilizing heterocharge layers formed by imposition of electrostatic fields. This paper investigates the performance characteristics of EHD conduction pump in two-phase thermal control loops. The EHD twophase loop consists of an EHD conduction pump, condenser, evaporator, transport lines, and reservoir (accumulator). The tests are performed with two different loops alternating two different EHD pumps to measure the generated pressure head and the mass flowrate at various applied voltages and sink temperatures. The power consumption of EHD conduction pumps is also determined by measuring the electric current value. The de-aerated R134a and unprocessed R134a are used as the working fluid. The dependence of EHD pump performance on the fluid temperature, effects of de-aeration of working fluid, effects of electrode design, pressure loss within EHD pump, influence of the loop size (tube diameter and length) are investigated.

Thermal Control Utilizing an Electrohydrodynamic Conduction Pump in a Two-Phase Loop With High Heat Flux Source

The electric field applied in dielectric fluids causes an imbalance in the dissociation-recombination reaction generating free space charges. The generated charges are redistributed by the applied electric field resulting in the heterocharge layers in the vicinity of the electrodes. Proper design of the electrodes generates net axial flow motion pumping the fluid. The electrohydrodynamic (EHD) conduction pump is a new device that pumps dielectric fluids utilizing heterocharge layers formed by imposition of electrostatic fields. This paper evaluates the experimental performance of a two-phase breadboard thermal control loop consisting of an EHD conduction pump, condenser, pre-heater, high heat flux evaporator (HE), transport lines, and reservoir (accumulator). The generated pressure head and the maximum applicable heat flux are experimental determined at various applied voltages and sink temperatures. Recovery from dryout condition by increasing the applied voltage to the pump is also demonstrated.Copyright

Effect of Gravity on Electrohydrodynamic Conduction Driven Liquid Film Flow Boiling

Liquid film flow boiling is used in many terrestrial thermal management applications as a heat transport mechanism. However, it suffers in microgravity applications such as spacecraft thermal management because the gravitational body force is not present to facilitate liquid film flow and bubble removal from the heater surface. One way of overcoming these constraints is to use an electrical field to move a liquid film in the absence as well as in the presence of gravity. In this experimental study, electrohydrodynamic conduction pumping is used to rewet the heater surface during liquid film flow boiling. The experiments are performed both terrestrially and onboard a variable-gravity parabolic flight. Terrestrial steady-state results show a maximum superheat reduction of 6°C and a 62% increase in critical heat flux when the electrohydrodynamic pump is moderately activated. The parabolic flight transient results indicate that, although there was an adverse effect of electrohydrodynamic on heater surface tem...

Electro-Wetting of a Heated Surface in the Presence and Absence of Gravity to Enhance Liquid Film Boiling Heat Transfer

Liquid film boiling is used in many terrestrial thermal management applications as an effective heat transport mechanism. However, it suffers in micro-gravity applications such as spacecraft thermal management as the gravitational body force is not present. The heater surface dries out as a result and heater temperature increase is unbounded. One way of facilitating liquid film boiling in micro-gravity is to use an electrical field. In this experimental study, we utilize electrohydrodynamic (EHD) conduction pumping to re-wet the heater surface during liquid film boiling in micro-gravity. EHD conduction involves electrodes embedded onto a surface that generate a pumping force in the dielectric liquid film which causes it to flow in a particular direction in this case liquid is directed toward the heater. The experiments are performed both terrestrially and on board a parabolic flight. Results indicate that activation of the EHD pump enables liquid film boiling to continue in microgravity by maintaining a liquid flow rate to the heater and lowering the surface temperature. It thereby allows us to study the complex liquid-vapor phase change phenomena in the presence of an electrical field in the absence of gravity and furthers our understanding for future application.

Demonstration of a Plug‐And‐Play Approach to Spacecraft Thermal Control System Design

The thermal demands placed on interplanetary probes and rovers can vary wildly throughout the course of a given mission. As the electronics and other equipment on these rovers become more sophisticated, heat dissipation and thermal control become more of an issue. Further complicating the thermal control problem is the fact that the mission may not place the rover or probe in a location with a constant view of deep space, which would be the lowest temperature heat sink and would provide the best heat rejection potential. Mainstream Engineering, working with the Goddard Space Flight Center, has developed a high‐lift heat pump capable of operating in microgravity that would allow the heat generated by electronic components or other subsystems to be radiated directly to the surface of a planet or moon in situations where there is no view of deep space. Performance data is presented for a prototype high‐lift system for these applications. Also discussed is the potential for a reduction in the overall system m...

A prototype electrohydrodynamic driven thermal control system (EHD-TCS)

Goddard Space Flight Center has designed and fabricated a novel, prototype thermal control system operated solely by electrohydrodynamic (EHD) forces. The EHD-TCS consists of an EHD pumping section, transport tubing, a thermal-hydraulic test section, and a condenser section. The prototype loop has been fabricated to characterize the operations of the EHD-TCS and to investigate specific applications of EHD techniques to flow management and heat transfer enhancement. This paper discusses operational issues regarding an EHD conduction pump in the EHD-TCS. In the preliminary testing presented herein, the EHD-TCS loop operated as a single-phase thermal control system. The EHD conduction pump performance is characterized in the following terms: (i) mass flow rate versus applied voltage and applied current and (ii) pressure head developed by the pump as a function of applied voltage and current. Other relevant performance issues such as determination of steady state and operational power requirements are present...

Liquid Film Boiling Heat Transfer in the Presence and Absence of Gravity

Liquid film boiling is an effective method of heat removal from a flat surface and has many terrestrial applications. It is an attractive technique for microgravity thermal control but cannot be sustained in the absence of gravity, according to theoretical prediction. However, this has not been experimentally confirmed to date for various reasons such as difficulty of performing experiments in microgravity and the associated cost. This paper presents new terrestrial and microgravity experimental results of liquid film boiling in a radial heat transport device. The microgravity experiments were performed on board a variable gravity parabolic flight. The data were expected to show that absence of gravity results in very high heater surface temperatures and eventual dryout compared to results in the presence of gravity at a given heat flux. However, this only occurred during the transition phase from 1.8-g to 0-g in the parabolic maneuver and the heater temperatures remained normal during the 0-g phase. Despite this, the results still add valuable information to the overall understanding of the liquid-vapor phase-change process in the absence of gravity. They have also laid the foundation for further experimental work such as using electrohydrodynamic (EHD) conduction pumping to facilitate liquid film boiling in microgravity, which we have presented in another study.Copyright

An experimental feasibility study on EHD-assisted capillary pumped loop (CPL)

The capillary pumped loop (CPL) is a passively pumped two-phase heat transport device that has demonstrated performance capabilities up to an order of magnitude greater than heat pipes, which are the current state-of-art. CPL technology has been developed to a near ready state for use as a thermal control device for advanced spacecraft systems. To further improve CPL performance, on a system level, the pumping head generated within the wick material must be enhanced. Utilizing the effect of a phenomenon known as liquid extraction (or EHD pumping); the Electrohydrodynamic (EHD) technique can effectively improve the liquid pumping capacity in a CPL system. EHD uses an electric field that can collect, guide, and pump liquid to the evaporating surface. This paper presents an experimental investigation of the feasibility of using EHD technology for improving CPL performances. The experimental study included EHD-enhanced pumping across a felt material that simulated a CPL wick. The results show more than 80% in...