An electric field acts upon a dielectric medium by means of three different body forces, capable of dramatically influencing its dynamics. In a single-phase fluid, under d.c. fields, the Coulomb force, which needs free charge, outclasses the other forces of electric nature. The physico-chemical origin of this charge, of ionic kind, and its interaction with the surrounding neutral molecules have been analyzed for the ion injection phenomenon, initially from a theoretical standpoint. Then, experiments intending to determine the effectiveness of the electrohydrodynamic process in terms of heat transfer enhancement have been conducted under five major convective regimes: (i) free advection on an upward and (ii) a downward heated plate, (iii) forced convection in a square channel, heated from one side, and (iv) mixed convection in a uniformly heated annular duct, with vertical ascending and (v) with horizontal flow. The high-voltage electrodes, tested at both polarities, are points made of several materials, manufactured by means of different techniques. Comparisons among fluids of technological relevance have been carried out, obtaining in all cases remarkable augmentation of convective heat transfer, with a negligible energy input. An important thermo-fluid dynamical analogy between electrically-induced jets and classical submerged jets, impinging on the heat transfer surface, has been highlighted. An optimal combination of working fluid and electrode configuration for an internal flow has been selected. Among the numerous applications of the electrohydrodynamic techniques, one has been chosen: a heat sink for thermal control of space components. A design solution for a cold plate has been proposed, giving a much higher performance of what is presently available for the industry and respecting the requirements for accommodation on the International Space Station.

Single-Phase Thermo-Fluid Dynamics under Electric Fields: Phenomenology and Technological Potential

TESTI, DANIELE
2006-01-01

Abstract

An electric field acts upon a dielectric medium by means of three different body forces, capable of dramatically influencing its dynamics. In a single-phase fluid, under d.c. fields, the Coulomb force, which needs free charge, outclasses the other forces of electric nature. The physico-chemical origin of this charge, of ionic kind, and its interaction with the surrounding neutral molecules have been analyzed for the ion injection phenomenon, initially from a theoretical standpoint. Then, experiments intending to determine the effectiveness of the electrohydrodynamic process in terms of heat transfer enhancement have been conducted under five major convective regimes: (i) free advection on an upward and (ii) a downward heated plate, (iii) forced convection in a square channel, heated from one side, and (iv) mixed convection in a uniformly heated annular duct, with vertical ascending and (v) with horizontal flow. The high-voltage electrodes, tested at both polarities, are points made of several materials, manufactured by means of different techniques. Comparisons among fluids of technological relevance have been carried out, obtaining in all cases remarkable augmentation of convective heat transfer, with a negligible energy input. An important thermo-fluid dynamical analogy between electrically-induced jets and classical submerged jets, impinging on the heat transfer surface, has been highlighted. An optimal combination of working fluid and electrode configuration for an internal flow has been selected. Among the numerous applications of the electrohydrodynamic techniques, one has been chosen: a heat sink for thermal control of space components. A design solution for a cold plate has been proposed, giving a much higher performance of what is presently available for the industry and respecting the requirements for accommodation on the International Space Station.
2006
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/104169
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact