Degree Type

Dissertation

Date of Award

1994

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

First Advisor

Michael Pate

Abstract

Shell-side condensation heat transfer data were obtained for refrigerants HFC-134a and HCFC-123, the scheduled non-CFC replacements for CFC-12 and CFC-11, respectively, using tube bundles constructed from 19.1 mm o.d. 26-fpi, 40-fpi, Turbo C-II, and GEWA SC tubes. HCFC-123 bundle data were obtained for non-condensible gas concentrations of 0.5, 1.0, 2.0, and 5.0% at four heat fluxes between 18,000 W/m2 and 34,000 W/m2. HCFC-123 vapor shear and liquid inundation studies were also conducted to simulate bundle depths of 25 tube rows at heat fluxes ranging from 17,500-31,000 W/m2 and vapor velocities between 2.5 and 4.5 m/s. Liquid inundation tests with HFC-134a were conducted to simulate bundle depths up to 30 rows at heat fluxes between 26,000 and 56,000 W/m2. All tests were conducted at a refrigerant saturation temperature of 35∘C;The Turbo C-II generally performed the best at non-condensible gas concentrations up to 5.0%, followed by the 40-fpi, GEWA SC and 26-fpi geometries. The Turbo C-II was also found to be the most susceptible to even small gas concentrations (0.5%), with drops in average bundle heat transfer coefficients of 50% and 35% at the lowest heat flux (20 kW/m2) and highest heat flux (34 kW/m2) respectively. Row-by-row data showed that non-condensibles work to smooth out individual row performance, so that at the highest gas concentrations all rows within a bundle perform very similarly. High concentrations of nitrogen also cause the different bundles to perform similarly, within approximately 13% of each other. Vapor shearing effects in the non-condensible gas layer were found to have a large effect with all tube geometries, particularly at the highest heat fluxes;In inundation with HFC-134a, the Turbo C-II had the highest heat transfer coefficients, followed by the GEWA SC, the 40-fpi, and the 26-fpi tubes. At the lowest inundation rates the Turbo C-II heat transfer performance was approximately 2.5 times that of the GEWA SC and more than four times that of the 26-fpi. However, at the highest inundation rates the Turbo C-II performed almost equally to the GEWA SC and differed from the other tubes by less than 10%;Inundation with HFC-134a had very little effect on those tubes with continuous fins, particularly the 26-fpi and the GEWA SC. The Turbo C-II was most affected by HFC-134a inundation, with heat transfer coefficients dropping nearly 80% through a Reynolds number of 2900;The inundation effects are much more pronounced with HCFC-123 than with HFC-134a. The Turbo C-II performance dropped nearly 80% from the lowest to the highest condensate Reynolds numbers. Decreases of approximately 20%, 20%, and 45% were seen for the 26-fpi, 40-fpi, and GEWA SC tubes, respectively, over the same test range. (Abstract shortened by UMI.)

DOI

https://doi.org/10.31274/rtd-180813-12923

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Lance Edward Rewerts

Language

en

Proquest ID

AAI9518434

File Format

application/pdf

File Size

221 pages

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