Degree Type

Dissertation

Date of Award

1993

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

First Advisor

Michael B. Pate

Abstract

Mandates currently in place by the Environmental Protection Agency require use of new environmentally acceptable refrigerants by 1996. Implementation of these new refrigerants by refrigeration and air-conditioning manufactures requires design data for the various components of these systems. This study focused on obtaining design data for evaporators and condensers of vapor compression systems. Specifically, a new environmentally acceptable refrigerant HFC-134a, which is targeted as a replacement for refrigerant CFC-12, was tested in an instrumented evaporator and condenser and their performance measured;Heat transfer coefficients and pressure drops were measured during evaporation and condensation of HFC-134a and CFC-12 in smooth and micro-fin tubes. Two different diameter smooth tubes and micro-fin tubes were tested: 9.52-mm outside diameter tubes and 12.7-mm outside diameter tubes. Micro-fin tubes are characterized by the numerous small fins that spiral down the inner surface of the tube. The micro-fin tubes used in this study had 60 fins with a spiral angle of 17° and fin heights of 0.2 mm. The heat transfer coefficients and pressure drops measured in this study were averages over the 3.66-m long test tubes. The refrigerant mass flux was varied from 125 kg/m[superscript]2·s to 375 kg/m[superscript]2·s in both the smooth and micro-fin tubes;The experimental data showed a significant increase in the performance of HFC-134a in the micro-fin tube as compared to the smooth tube. Specifically, evaporation heat transfer coefficients were increased by 50% to 100% with only a 10% to 30% increase in evaporation pressure drop, while condensation heat transfer coefficients were increased by 100% to 200% with a 40% to 100% increase in condensation pressure drop. Similar results were obtained for pure CFC-12 in the micro-fin tube;The effects of lubricant concentration (\prec5%) on the performance of HFC-134a and CFC-12 were also studied. HFC-134a was tested with a penta erythritol ester mixed-acid lubricant and a penta erythritol ester branched-acid lubricant. CFC-12 was tested with a naphthenic lubricant. Lubricant concentration in general decreased the heat transfer performance of refrigerants. The only exception was evaporation at low lubricant concentrations were the heat transfer coefficients were slightly enhanced by refrigerant/lubricant mixtures. Pressure drop during evaporation and condensation was increased by the addition of lubricant in most cases.

DOI

https://doi.org/10.31274/rtd-180813-11226

Publisher

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

Copyright Owner

Steven J. Eckels

Language

en

Proquest ID

AAI9334977

File Format

application/pdf

File Size

379 pages

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