Flow boiling of R134a in a large surface area microchannel array for high-flux laser diode cooling
- Colorado State Univ., Fort Collins, CO (United States)
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Packaging high average power laser diode arrays that generate heat at an area average flux in excess of 1 kW·cm-2 is a significant engineering challenge. While liquid microchannel coolers have demonstrated up to 11.9 kW·cm-2, two-phase microchannel array coolers have not achieved 1 kW cm-2 due to critical heat flux and flow instabilities. In the current study, flow boiling heat transfer was characterized by a 1 × 10 mm heated zone centered over a 5 × 10 mm array of 125 very small channels (45 × 200 μm) with R134a as the phase change fluid. The high aspect ratio channels (4.4:1) were manufactured using MEMS fabrication techniques, which yielded a large heat transfer surface area to volume ratio. A test facility was used to characterize the heat transfer performance of boiling R134a over a range of saturation temperatures (15°C to 25°C), mass fluxes (735-2230 kg·m-2·s-1), and heat duties (< 110.3 W). During the tests, the calculated outlet vapor quality exceeded 61%, and the base heat flux at the heater reached a maximum of 1.1 kW·cm-2. The resulting average experimental flow boiling heat transfer coefficients are found to be as large a 13.4 kW·m-2·K-1 over the approximately 3 mm two-phase region, with an average uncertainty of ± 2.72%. A substantial amount of heat was spread downstream via the low thermal resistance silicon floor. Specifically, between 29.5% and 55.1% of the heat dissipated in the two-phase region was dissipated over the heater. Finally, the remaining heat dissipated in the two-phase region was dissipated in the 2 mm of channel downstream of the heater. This suggests that heat spreading from the hotspot played a vital role in dissipating the heat load.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA)
- Grant/Contract Number:
- AC52-07NA27344
- OSTI ID:
- 1838601
- Report Number(s):
- LLNL-JRNL-760960; 949798
- Journal Information:
- Heat Transfer Research, Vol. 50, Issue 14; ISSN 1064-2285
- Publisher:
- Begell HouseCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Similar Records
Flow boiling heat transfer of R134a, R236fa and R245fa in a horizontal 1.030 mm circular channel
An investigation of a model of the flow pattern transition mechanism in relation to the identification of annular flow of R134a in a vertical tube using various void fraction models and flow regime maps