Masters Theses

Date of Award

5-1995

Degree Type

Thesis

Degree Name

Master of Science

Major

Chemical Engineering

Major Professor

Joseph J. Perona

Committee Members

Ken Kirby, Pete Counce

Abstract

In an effort to validate Lithium Bromide/Water (LiBr/H2O) absorption chiller design specifications using theoretical cycle calculations, a computer code was written to calculate overall heat transfer coefficient times area (UA) values in heat exchangers with horizontal tube bundles. Specifically, component models were developed for absorbers, generators, evaporators, and condensers. These component models were linked to the DOE/ORNL-sponsored ABSIM computer model to integrate the design specifications with the cycle analysis. ABSIM is a user-oriented computer model for simulation of absorption systems. The UA values from the component models were compared to experimentally determined values based on operating data from a double-effect LiBr/H2O absorption chiller. These comparisons were used as a tool to validate the component models. Since the triple-effect absorption chillers are simply modular extensions of the double-effect absorption machine, it can be inferred that the component models are valid for these cycles. The calculated UA values matched the experimentally determined UA values within 20% for the evaporator, 10% for the condenser, 15% for the absorber, and within 45% for the generator. The experimental data used for comparisons was primarily taken over a narrow range of operating conditions. It would be desirable to obtain follow-on experimental data over a larger range of load conditions to perform additional comparisons between experimental and calculated values. It is also desirable to obtain data from chillers of alternate designs to perform additional comparisons, and to develop an alternate correlation, either empirical or theoretical, for the generator. UA values can be used to calculate cycle performance. The utility of valid component UA values was demonstrated using a parametric analysis by varying component UA values and calculating cycle performance using ABSIM. Based on the cycle performance calculations, optimum sized components for the base operating case triple-effect cycle are recommended. The optimum sized components performed at an efficiency comparable to the base case at a lower relative cost across all heat loads. In addition, the optimized cycle offers the ability to run the chiller at much higher heat loads than the base case.

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