James E. Bryan

Heat transport enhancement of monogroove heat pipe with electrohydrodynamic pumping

The enhancement of the heat transport capacity of a monogroove heat pipe with electrohydrodynamic (EHD) pumping was investigated. The EHD pump was located on the liquid channel in the adiabatic section of the heat pipe. The heat pipe e uid used in all experiments was R-123, a new alternative refrigerant. The two experimental goals were to determine the magnitude of heat transport enhancement that could be achieved using the EHD pump and to demonstrate the controllability and recovery of the heat pipe during dryout. Both were successfully accomplished. Over 100% enhancement in the transport capacity was achieved using the EHD pump operating at 20 kV. This enhancement could be maintained with less than 0.08 W of electric power to the EHD pump. The EHD pump was also able to provide immediate recovery from dryout when the heat pipe had been experiencing progressive evaporator dryout for over 70 min at 400 W.

Experimental study of ion-drag pumping using various working fluids

An ion-drag pump in a vertical axisymmetric configuration was built. Different dielectric fluids were compared to establish which produced the best pumping performance. Experimental results showed that pumping performance depended on fluid properties, primarily fluid viscosity and electrical conductivity. Two fluids, dodecylbenzine and Envirotemp 200, were studied at various doping levels. In both fluids a decrease in the charge relaxation time caused a decrease in efficiency. >

Characteristics of Nucleate Boiling With Gold Nanoparticles in Water

An experiment was designed to test the pool boiling performance of 3 nm gold nanofluid on a flat circular copper coupon. Compared to pure water, an increase of up to 175% in the critical heat flux was seen with gold nanofluids. However, a 25-30% deterioration in the heat transfer coefficient was also observed. The heating surface was observed before and after boiling with a scanning electron microscope. A thin, dark film was observed on the surface, which was due to the deposition of gold particles.Copyright

Influence of Flow Regime, Heat Flux, and Mass Flux on Electrohydrodynamically Enhanced Convective Boiling

The influence of quality, flow regime, heat flux, and mass flux on the electrohydrodynamic (EHD) enhancement of convective boiling of R-134a in a horizontal smooth tube was investigated in detail. The EHD forces generated significant enhancements in the heat transfer coefficient, but the enhancements were highly dependent on the quality, flow regime, heat flux, and mass flux. The experimental data provided evidence that an optimum END enhancement exists for a given set of these variables with a specific electrode design. However, experimental data also provided evidence that the EHD forces can drastically reduce the rate of heat transfer at certain conditions

Electrohydrodynamically Enhanced Convective Boiling: Relationship Between Electrohydrodynamic Pressure and Momentum Flux Rate

The relationship between the mean radial electrohydrodynamic (EHD) pressure and the rate of the axial momentum flux and its influence on heat transfer enhancement and pressure drop in EHD-enhanced convective boiling of R-134a in a horizontal smooth tube was investigated in detail. A simple theory, which included the characteristics of two-phase flow, was developed to determine the mean radial EHD pressure. The amount of heat transfer enhancement and the pressure drop penalty were dependent upon the size of the mean radial EHD pressure relative to the rate of the axial momentum flux. The influence of the mass flux, change in quality, and saturation temperature on the mean radial EHD pressure relative to the rate of the axial momentum flux was also studied. This study has provided a greater understanding of EHD enhancement of the convective boiling heat transfer

Effect of frequency on heat transfer enhancement in temperature-induced electrohydrodynamic pumping

An induction electrohydrodynamic (EHD) pump in an axisymmetric configuration was designed and built to examine the heat transfer enhancement which accompanies fluid pumping under laminar flow conditions. The apparatus was operated at several tilt angles between 0 (horizontal) and 90/spl deg/ while the augmentation of heat transfer was measured and compared to typical forced pumping and natural circulation. The increase in the overall conductance value for EHD pumping compared to typical forced pumping and natural circulation was as high as 105 and 122%, respectively. This corresponded, to a much higher increase in the inside convection coefficient, which was the only resistance to heat transfer being affected by induction pumping. The operating frequency had an effect on the peak overall conductance value. >

Control of Liquid Impingement With Electrical Field

An initial experimental study was performed to better understand the effect of various operating and geometrical parameters on mode transition in EHD spray impingement. Detailed experimental data is provided for the different modes observed with ethanol. Previous research has focused on the effects of applied voltage and volume flow rate with limited experimental data. Using high-speed digital video imaging, details of eight different spray modes are presented.Copyright

Electrohydrodynamically Enhanced Convective Boiling of Alternative Refrigerants: Fundamental Understanding and Applicability

Electrohydrodynamically (EHD) enhanced convective boiling, based on the extraction phenomenon, is experimentally investigated. The working fluids are R-134a and R-404A refrigerants. Both smooth and enhanced tubes are investigated in a horizontal configuration. The heat transfer enhancement and suppression with the corresponding pressure-drop data are presented. The ratio of EHD power consumption relative to the heat transferred was less than 1.5% for the data presented. A theoretical analysis is presented to determine the contributing terms of the EHD power consumption, and it was determined that the electric conduction mechanism was the primary contributing factor to current flow. The transient application of EHD, in the case that resulted in the suppression of the heat transfer under steady-state conditions, provided transient enhancements for convective boiling of R-404A in a horizontal smooth tube. Additionally, applicability of the EHD extraction phenomenon to convective boiling is discussed.

Modeling Dielectrophoretic Force Induced Bubble Motion in Micro-Channels

Using electrostatic forces to control bubble motion in meso to micro-scale channels filled with dielectric liquid is a promising and experimentally validated approach. In this study, dielectrophoretic force induced bubble motion in micro-channels is investigated in terms of a simple model, which has been verified by comparing with experimental data for bubble motion in meso-scale channels. Dielectrophoretic force, pressure drop across a gas bubble, viscous friction at channel wall, and inertial force related to fluid acceleration or deceleration when applied electrostatic field changes with position and time are parameterized and included explicitly in the model. For wide ranges of considered model parameters, including fluid properties, channel and electrode geometry, and applied electric field as well, modeling predictions for dynamic bubble motion in micro-channels are obtained and compared with the counterpart in meso-channel case. The results of this study show that with the channel size decreasing from meso-scale to micro-scale, the effect of inertial force becomes less important and negligible, while the pressure drop across the bubble increases significantly. In addition, it is demonstrated that the fringing field of the planar electrodes becomes more important and must be considered at micro-scale.© 2006 ASME

Theoretical study of an electrostriction pump

A numerical solution for an electrohydrodynamic pump based on the electrostriction phenomenon has been developed. Specifically, the performance of a single pair electrostriction pump has been analyzed at various levels of applied voltage. The results indicate that the pressure head generated by the electrostriction pump increases exponentially with the applied voltage.