Boiling heat transfer in compact heat exchangers

Conference · Sat Dec 31 04:00:00 EST 1994

OSTI ID:27051

Tran, T N; Wambsganss, M W ^[1]; France, D M ^[2]

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1. Argonne National Lab., IL (United States)
2. Illinois Univ., Chicago, IL (United States). Dept. of Mechanical Engineering

Small circular and noncircular channels are representative of flow passages in compact evaporators and condensers. This paper describes results of an experimental study on heat transfer to the flow boiling of refrigerant- 12 in a small circular tube of diameter = 2.46 mm. The objective of the study was to assess the effect of channel size on the heat transfer coefficient and to obtain additional insights relative to the heat transfer mechanisms. The flow channel was made of brass and had an overall length of 0.9 m. The channel wall was electrically heated, and temperatures were measured on the channel wall and in the bulk fluid stream. Voltage taps were located at the same axial locations as the stream thermocouples to allow testing over an exit quality range of 0.21 to 0.94 and a large range of mass flux (63 to 832 kg/m{sup 2}s) and heat flux (2.5 to 59 kW/m{sup 2}). Saturation pressure was nearly constant, averaging 0.82 MPa for most of the testing; a few test data were also taken at a constant lower pressure of 0.52 MPa. Local heat transfer coefficients were determined experimentally. Analysis provided additional support for the conclusion, arrived at from previous studies, that a nucleation mechanism dominates for flow boiling in small channels; nevertheless, a convective-dominant region was identified at very low values of wall superheat (<{approx}3{degrees}C). Previous flow boiling studies in small channels, that did not include wall superheats this low, did not encounter the convective dominant mechanism. Conversely, cryogenic studies at very low wall superheats ({approx}l{degree}C) did not encounter the nucleation dominant regime. The apparent discrepancy is explained by the results of this study.

• Research Organization: Argonne National Lab., IL (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 27051
• Report Number(s): ANL/ET/CP--84414; CONF-941128--5; ON: DE95005850
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
BOILING
HEAT EXCHANGERS
HEAT TRANSFER
MASS TRANSFER
SIZE
TESTING