Numerical simulation of electrohydrodynamic effect on single and two-phase heat transfer

Zhang, H, 2004. Numerical simulation of electrohydrodynamic effect on single and two-phase heat transfer. PhD, Nottingham Trent University.

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Abstract

The effects of an electric field on single- and two-phase heat transfer have been numerically investigated. The aim of this work is to establish analytical and mathematical models for the coupled electric, flow and thermal fields in single- and two-phase flows and to analyze the EHD effects on natural convection and nucleate boiling and provide numerical predictions of temperature, electric and velocity fields both in pure liquid and in the vicinity of single bubbles attached to a heat transfer surface under the application of electric fields.

Physical and mathematical models to describe the phenomenon of EHD effects on natural convection are proposed. A current in a dielectric field is physically modelled as a directed motion of electrically charged particles injected into a fluid. The Navier-Stokes equations, with an electric body force and the Joule heat are added to the momentum and energy equations respectively, are coupled with the electric field equations. The governing equations for the coupled electric, flow and thermal fields are discretized using Finite Volume Method (FVM) and solved using the SIMPLE method with a non-staggered grid arrangement. A modified momentum interpolation scheme is proposed to eliminate the defects of Rhie and Chow's interpolation scheme. The algorithm is developed into a FORTRAN code and is validated.

Natural convection enhanced by electric fields is widely investigated. This includes the natural convection in rectangular and cylindrical enclosures, enhanced by uniform and non-uniform electric fields respectively. The effects of the Rayleigh number and the fluid viscosity and electrical conductivity on the obtaining of good heat transfer enhancement are numerically investigated.

In order to understand the mechanism of EHD enhancement of heat transfer at the gas-liquid interface during nucleate boiling, a simplified physical model for a bubble attached to a heated wall is considered. Treatments at the gas-liquid interface and the triple-phase point are applied. Based on these, numerical study of EHD effect on heat and flows around a single R134a bubble attached to a superheated wall are carried out. Analysis is carried out for the flow and heat transfer at the vicinity of the gas-liquid interface when different electric voltages are applied. The bubble model is further employed to study the EHD effects on the fluids with different charge relaxation time. Four refrigerants, R134a, R123, R12 and R113, are studied and compared.

The numerical methods and the models for the coupled electric, flow and thermal fields are employed to carry out a preliminary study of the EHD effect on a growing bubble at different stages.

Item Type:	Thesis
Creators:	Zhang, H.
Date:	2004
ISBN:	9781369313284
Identifiers:	Number Type PQ10183036 Other
Divisions:	Schools > School of Architecture, Design and the Built Environment
Record created by:	Linda Sullivan
Date Added:	28 Aug 2020 14:41
Last Modified:	22 Jun 2023 08:34
URI:	https://irep.ntu.ac.uk/id/eprint/40592

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