The purpose of the paper is to experimentally assess the effect exerted by subcooling degree and heat-up rate (i.e., the rate of increase of thermal flux) on the phenomenon of nucleate boiling in the presence of an electric field. To this aim, an experimental facility was set up to investigate pool boiling on a heated platinum wire of 0.2-mm diameter. The working fluid was R-113 (C 2Cl 3F 3). A cylindrical electric field (up to 21 MV/m at the heater surface) was imposed. The power was increased along a linear ramp, at a rate ranging from 2.5 mW/s to 6 W/s. Subcooling degrees up to 22 K (Ja = 0.146) were investigated. The results of zero-field measurements are in agreement with previous ones in the literature. The effect exerted by the electric field consists mainly of a strong increase in critical heat flux, whereas, for a given heat flux, the nucleate boiling performance can be either weakly degraded or slightly enhanced. The critical heat flux was found to remain nearly constant with increasing transient velocity up to a given heat-up rate and then to increase with it. The effect of subcooling on nucleate boiling is quite complex but, in any case, quite weak in the entire investigated range.
Nucleate pool boiling in the presence of an electric field: effect of subcooling and heat-up rate
DI MARCO, PAOLO;GRASSI, WALTER
1997-01-01
Abstract
The purpose of the paper is to experimentally assess the effect exerted by subcooling degree and heat-up rate (i.e., the rate of increase of thermal flux) on the phenomenon of nucleate boiling in the presence of an electric field. To this aim, an experimental facility was set up to investigate pool boiling on a heated platinum wire of 0.2-mm diameter. The working fluid was R-113 (C 2Cl 3F 3). A cylindrical electric field (up to 21 MV/m at the heater surface) was imposed. The power was increased along a linear ramp, at a rate ranging from 2.5 mW/s to 6 W/s. Subcooling degrees up to 22 K (Ja = 0.146) were investigated. The results of zero-field measurements are in agreement with previous ones in the literature. The effect exerted by the electric field consists mainly of a strong increase in critical heat flux, whereas, for a given heat flux, the nucleate boiling performance can be either weakly degraded or slightly enhanced. The critical heat flux was found to remain nearly constant with increasing transient velocity up to a given heat-up rate and then to increase with it. The effect of subcooling on nucleate boiling is quite complex but, in any case, quite weak in the entire investigated range.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
