Carbon dioxide is a natural refrigerant that has been considered for certain
refrigeration and air conditioning applications. The coefficient of performance (COP) of
carbon dioxide cycles is low compared to classical vapor compression cycles. The aim of
this portion of the thesis is to present a thermodynamic analysis of carbon dioxide cycles
in order to evaluate the potential performance of a refrigeration cycle using carbon
dioxide. A thermodynamic model for the cycle is proposed which can simulate the
operation of a carbon dioxide refrigeration cycle. This model takes into account the
practical effects of the thermo-physical properties of carbon dioxide as a refrigerant in a
trans-critical cycle. One and two-stage compression processes were considered for
comparison purposes. A sensitivity analysis has been conducted so that cycle
performance can be estimated. The effect of cycle components on system capacity and
cycle performance was investigated.
The second portion of the thesis deals with the concept of reheat air conditioning,
and looks at the performance of different reheat cycles. The thesis looks at reheat
systems that utilize different placements of the reheat coil. The overall performance of
these reheat systems is then calculated. These systems require no additional electric
power to reheat the air after it is cooled and dehumidified in the evaporator. Instead, they
use heat from the condenser heat exchanger to reheat the air during partial load
conditions. Four different reheat configurations are discussed and analyzed to determine
performance levels. Visual Basic programs were written for each of the four cycles to
simulate the different configurations and to evaluate key performance parameters.
Graphs were developed based on these programs, where critical variables were changed
to monitor trends in coefficient of performance. The thermodynamic cycle of each reheat
configuration is developed, with equations presented with figures depicting the cycles.
Refrigerant 134a was used in the programs throughout the reheat section of the thesis.
The reheat coefficient of performance is used as the basis for cycle comparison. The
relative performance of the four cycles is illustrated in the figures and explained in the
Results and Discussion section at the end of chapter 3.
| Identifer | oai:union.ndltd.org:USF/oai:scholarcommons.usf.edu:etd-5072 |
| Date | 05 May 2006 |
| Creators | Brown, Mark |
| Publisher | Scholar Commons |
| Source Sets | University of South Flordia |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Graduate Theses and Dissertations |
| Rights | default |
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