Jamal Seyed-Yagoobi

Electrohydrodynamically induced dielectric liquid flow through pure conduction in point/plane geometry

Mildly polar liquids generally exhibit an ohmic behavior when subjected to electric fields of limited values. The resulting conduction is then associated with heterocharge layers of finite thickness in the vicinity of the electrodes. In the absence of charge injection or induction, a simple conduction model based on the processes of dissociation of a neutral electrolytic species and recombination of the generated ions is presented. This model is first applied to parallel plane electrode geometry to describe the build-up of the heterocharge. Then, the case of point/plane configuration is considered where the effect of Coulomb force is different in the two layers next to the electrodes. A net motion toward the point electrode is predicted to occur. With a rough approximation for the harmonic field, an analysis is presented which leads to an expression for the axial component of the net force exerted on the liquid. A simple static pump is designed and built to experimentally investigate the pressure head generated through pure conduction. Two working fluids (refrigerant R-123 and n-hexane) and two different electrode designs are considered in this study. The experimental results are qualitatively compared to the theoretical predictions.

Experimental study of electrohydrodynamic pumping through conduction phenomenon

In an isothermal liquid, only the Coulomb force which is the force acting on the free charges, can contribute to net electrohydrodynamic (EHD) motion. In the absence of a direct charge injection, pumping of an isothermal liquid can be achieved due to the charges associated with the heterocharge layers of finite thickness in the vicinity of the electrodes. These charges are based on the process of dissociation of a neutral electrolytic species and recombination of the generated ions. This type of pumping is referred to as conduction pumping. The conduction pumping mechanism is experimentally investigated here with three different electrode designs. Sufficient pressure heads are generated with very low electric power requirements making the EHD conduction pumping attractive to certain applications in the presence and absence of gravity, such as capillary pumped loops and heat pipes.

SUPERHEATED STEAM IMPINGEMENT DRYING OF TORTILLA CHIPS

ABSTRACT Low-fat snack products are the driving forces for the drying of tortilla chips before frying. Super-heated steam impingement drying of foods has the advantage of improved energy efficiency and product quality. The temperature profile, drying curves, and the physical properties (shrinkage, crispiness, starch gelatinization and microstructure) of tortilla chips dried at different superheated steam temperatures and heat transfer coefficients were measured. Results indicated that the steam temperature had a greater effect on the drying curve than the heat transfer coefficient within the range of study. The microstructure of the samples after steam drying showed that higher steam temperature resulted in more pores and coarser appearance. The modulus of deformation and the shrinkage of tortilla chips correlated with moisture content. A higher steam temperature caused less shrinkage and a higher modulus of deformation. The pasting properties showed that samples dried under a higher steam temperature and...

Theoretical/numerical study of electrohydrodynamic pumping through pure conduction phenomenon

In an isothermal liquid, only the Coulomb force which is the force acting on the free charges, can contribute to net electrohydrodynamic (EHD) motion. In the absence of a direct charge injection or induction, the charges can be generated through the dissociation process of the fluid. The generated charges by dissociation are redistributed by the applied electric field, resulting in the heterocharge layers around the electrodes. The pumping of an isothermal liquid without ion injection is associated with the heterocharge layers of finite thickness in the vicinity of the electrodes. This type of pumping is referred to as the conduction pumping. This paper investigates the conduction pumping mechanism theoretically through the numerical solutions. For this purpose, a theoretical model for the static case (i.e., without a flow motion) is established and a numerical code using the finite volume method is developed. Electric potential, electric field, charge density and electric body force distributions for the selected electrodes configuration are presented. The generated pressure as a function of applied voltage is also presented. The numerical results confirmed the EHD conduction pumping concept theoretically.

Understanding of electrohydrodynamic conduction pumping phenomenon

Electrohydrodynamic (EHD) phenomena can be applied to enhance and control mass and heat transfer in both terrestrial and microgravity environments. The emerging EHD conduction pumping technique shows its potential as an active control method of the flow distribution. The EHD conduction pumping is associated with the heterocharge layers of finite thickness in the vicinity of the electrodes, which are based on the process of dissociation of the neutral electrolytic species and recombination of the generated ions. This paper theoretically and experimentally studies the EHD conduction phenomenon in a dielectric liquid. The analytical solutions provide the non-dimensional distributions of electric field and charge density in the vicinity of the electrodes. The characteristic heterocharge layer thickness is also theoretically predicted. Measured pressure heads and current levels are compared with the theoretical results. The EHD conduction pump presented here is capable of electrically driving and controlling t...

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.

Induction Electrohydrodynamic Pump in a Vertical Configuration: Part 1—Theory

An induction electrohydrodynamic (EHD) pump in an axisymmetric, vertical configuration is studied theoretically. The model includes the effect of entrance conditions, buoyancy effects, secondary flow, and Joule heating. Primarily the forward (cooled wall) and to a lesser extent the backward (heated wall) modes are investigated. A finite difference technique is used to obtain the numerical solutions. A set of these solutions is presented to show the influence of the controlling factors of operating an induction EHD pump. The results indicate that the entrance temperature profile plays an important role in the operation of the pump because steeper profiles produce higher velocities. The pump must be operated at an optimum frequency, wavelength, and electric conductivity level.

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. >

Electrically Induced Dielectric Liquid Film Flow Based on Electric Conduction Phenomenon

Electrohydrodynamic (EHD) conduction pumping is associated with the heterocharge layers of finite thickness in the vicinity of the electrodes, generated by the process of dissociation of the neutral electrolytic species and recombination of the generated ions. The theoretical formulation for EHD conduction pumping of liquid film is presented and fundamentally analyzed with the aid of numerical solutions. This model includes fluid dynamics governing equations under laminar and isothermal conditions which are modified to account for the presence of electric body force. The model also includes charge transport equations which are related to the dissociation/recombination phenomenon along with Maxwells relations that govern the electric field distribution. This paper determines how liquid film flow is generated based on the electric conduction phenomenon. Specifically, the role of controlling dimensionless parameters on the heterocharge layers and flow structures along with the impact of liquid film velocity on charge distribution are illustrated and fundamentally analyzed. In addition, the contribution of unique electrode designs toward electric body force distribution and flow pattern is investigated followed by the effect of interaction between adjacent electrode pairs in multi-pair configurations on generated flow rate. Further, a brief discussion of the conduction pumping efficiency is presented. Finally, the numerical results are verified against experimental data.

An experimental investigation of an ion-drag pump in a vertical and axisymmetric configuration

Electrohydrodynamic (EHD) pumping is produced by the interaction of electrical fields and free charges in an insulating fluid medium. Pumping is achieved when electrical fields are generated that drag the charges along in a given direction. An ion-drag pump in a vertical, axisymmetric configuration was built. The electrodes were designed from the fluid mechanics standpoint. Pumping velocities as high as 30 cm/s (1 kg/s corresponding flow rate) at 23.6 kV have been achieved. It is noted that this improvement in the pump performance makes the ion-drag pump attractive for industrial applications.<<ETX>>