Date of Award
Master of Science
An experimental study on heat transfer during condensation of refrigerant R-134a in microchannel tubes was conducted. Investigations were carried out on 3 circular and 6 non-circular channels. The non-circular channels included barrel, N-shaped, rectangular, square, and triangular extruded tubes, and a channel with a corrugated insert that yielded triangular microchannels. The hydraulic diameters ranged from 0.424 mm to 1.524 mm. Local heat transfer coefficients over the range of mass fluxes 150 < G < 750 kg/m2-s were measured in small increments for the entire saturated vapor-liquid region, spanning several different two-phase flow regimes. In the three circular tubes, the hydraulic diameter did not have a significant influence on heat transfer coefficients for low qualities, whereas the heat transfer coefficient increased as the diameter decreased for higher qualities. Data for the barrel, square, and triangular extruded tubes and the triangular corrugated insert tube were compared with the data for the circular tube with a similar hydraulic diameter to document the effect of channel shape. The triangular extruded and corrugated insert tubes have the highest heat transfer coefficients, with the effect of tube shape not being very significant for the other tube shapes. Most of the heat transfer correlations available in the literature were found to over-predict the data from the present study. In other instances, the trends (i.e., the slope of heat transfer versus quality plots) were either much steeper or more gradual than what was observed in the present study. Hence, condensation heat transfer models for annular, mist, and intermittent flow were developed using the data for both the circular and non- circular tubes. Quality-based averaging was used to account for the presence of multiple regimes for a given condition. The models predicted 90% of the circular data to within ±25% and 84% of the non-circular data to within ±30%. These models are expected to be valid for the following range of conditions: 0.424 mm < D[Subscript h] < 1.524 mm, 150 kg/m2-s < G < 750 kg/m2-s, and 1,240 kPa < P < 1,725 kPa.
Todd Matthew Bandhauer
Bandhauer, Todd Matthew, "Heat transfer in microchannel geometries during condensation of R-134a" (2002). Retrospective Theses and Dissertations. 19790.