Experimental and numerical study on convective boiling in a staggered array of micro pin-fin microgap

Liang Han Chien, Yi Ting Cheng, Ying Liang Lai, Wei Mon Yan*, Mohammad Ghalambaz

*Corresponding author for this work

Research output: Contribution to journalJournal Article peer-review

40 Scopus citations

Abstract

The flow patterns, heat transfer and pressure drop of convective boiling of dielectric fluid, FC-72, in a micro-gap are investigated experimentally. The surface of the microgap is enhanced with a staggered array of micro pin-fins. The enhanced surface of the microgap with the size of 10 × 10 mm2 is subject to an electrical heat source. The micro-pin-fins are etched as cubic columns of 100 μm size and arranged in a staggered arrangement with 400 μm pitch in both transverse and longitudinal directions. The inside of the micro pin-fins is nucleated with a cavity of cylindrical shape with diameter of 60 μm and an opening with a size of either 15 μm or 45 μm width. The opening of the cavities of the micro-pin-fins is aligned toward the down-stream. For the case of single-phase flow, a numerical analysis is performed, and the pressure drop and velocity fields are investigated in the micro-gap. The experiments were performed for various mass fluxes ranging from 94 to 275 kg/m2s and heat flux ranging from 0 to 10 W/cm2, and at two saturation temperatures of 35 and 50 °C. For the case of single-phase heat transfer, the experimental results are compared with the pin-fins having 45 μm cavity opening and found that the effect of cavity opening is significant when the mass flux is high. The surface-superheat at the onset of boiling is reduced by reducing the cavity opening-width from 45 to 15 μm. The microgap having nucleation cavity with cavity opening-width of 15 μm results in a 3.44 °C smaller surface-superheat than that of 45 μm opening-width. The convective heat transfer coefficient increases with the increase of mass flux, regardless of the flow type. Moreover, the variation of the pin-fin opening-widths does not influence the convection heat transfer rate. For single-phase flow, the heat flux shows a negligible effect on pressure drop, and the pressure drop increases with increasing mass flux. For two-phase flow, the pressure drop increases drastically with increasing heat flux. A smaller cavity opening-width results in a smaller pressure drop when the mass flux is high. The flow observation shows two distinct flow patterns in the microgap at the beginning of the bubble nucleation.

Original languageEnglish
Article number119203
JournalInternational Journal of Heat and Mass Transfer
Volume149
DOIs
StatePublished - 03 2020
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2019

Keywords

  • Columnar nucleation pin-fin
  • FC-72
  • Micro-pin-fin
  • Microgap
  • Nucleate boiling heat transfer
  • Staggered array

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