Critical Heat Flux for Downward Facing Boiling on a Coated Hemispherical Surface

The objective of this paper is to investigate the droplet evaporation lifetime and boiling curve on hot copper surface using ethanol liquid. We focus our study to find the Critical Heat Flux (CHF) and Leidenfrost temperature in the boiling curve. Copper material which has a high thermal conductivity, k was chosen as a test material. The copper material dimension was approximately 28.0 mm in height and 50.0 mm in diameter. The copper surface was modified into hemispherical surface in order to maximize the evaporation lifetime. The hemispherical surface was constructed using Electrical Discharge Machining (EDM). After completing the EDM process, the dimension of the hemispherical surface area was approximately 15.0 mm in depth and 30.0 mm in diameter. Meanwhile, ethanol liquid which has a low boiling point of 78 °C was chosen as a test fluid. The droplet diameter was approximately 3.628 mm. The impact height was set to be around 4.0 mm corresponding to drop impact velocity of 0.886 m/s. As a result, it was found that the critical heat flux (CHF) and Leidenfrost temperature range on hemispherical copper surface was approximately TCHF = 100.4-117.7 °C and TL = 170.0-175.8 °C, respectively.

Download Full-text

Critical Heat Flux for Downward Facing Boiling on a Coated Hemispherical Surface

Volume 3 ◽

10.1115/ht-fed2004-56056 ◽

2004 ◽

Cited By ~ 4

Author(s):

J. Yang ◽

M. B. Dizon ◽

F. B. Cheung ◽

J. L. Rempe ◽

K. Y. Suh ◽

...

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Steady State ◽

Critical Heat Flux ◽

Heat Transfer Performance ◽

Transfer Performance ◽

Copper Coatings ◽

Hemispherical Surface ◽

The Right ◽

Effect Of Surface

An experimental study was performed to investigate the effect of surface coating on the critical heat flux for downward facing boiling on the outer surface of a hemispherical vessel. Steady-state boiling experiments were conducted in the SBLB (subscale boundary layer boiling) facility using test vessels with metallic microporous coatings to obtain the local boiling curves and the local CHF limits. Similar heat transfer performance was observed for microporous aluminum and microporous copper coatings. When compared to the corresponding data without coatings, the boiling curves for the coated vessels were found to shift upward and to the right. This meant that the CHF limit and minimum film boiling temperatures were located at higher wall superheats. In particular, the microporous coatings were found to enhance the local CHF values appreciably at all angular locations explored in the experiments. Results of the present study showed that the microporous aluminum coating was very durable. Even after many cycles of steady state boiling, the vessel coating remained rather intact, with no apparent changes in color or structure. Although similar heat transfer performance was observed for microporous copper coatings, the latter were found to be much less durable and tended to degrade after several cycles of boiling.

Download Full-text