Thermodynamic optimization of evaporators with zeotropic refrigerant mixtures
Ragazzi, Franco
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/23469
Description
Title
Thermodynamic optimization of evaporators with zeotropic refrigerant mixtures
Author(s)
Ragazzi, Franco
Issue Date
1995
Doctoral Committee Chair(s)
Pedersen, Curtis O.
Department of Study
Engineering, Mechanical
Discipline
Engineering, Mechanical
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Language
eng
Abstract
A study was conducted to determine the influence of heat exchanger design on the performance of residential air-conditioning systems using zeotropic mixtures as HCFC-22 alternatives.
A computer simulation of the evaporator was developed to model various evaporator designs, and was validated with experimental data collected under controlled air and refrigerant conditions with both HCFC-22 and a zeotropic mixture of HFC-32/HFC-134a/HFC-125 (23%/52%/25%). The model predictions of heat transfer, pressure drop, and temperature profiles were in very good agreement with the experimental data.
An effectiveness-type model for combined heat and mass transfer was developed and implemented in the simulation, resulting in increased computational speed and stability. The model was compared to two others in the literature, and their predictions of the total rate of heat transfer were found to be in reasonable agreement. A discretized solution of the differential heat and mass transfer equations resulted in the best latent load predictions.
An irreversibility-based objective function, chosen to quantify evaporator thermodynamic performance, showed a clear dependency on design and operating conditions. A trade-off between irreversibilities due to heat transfer and air pressure drop was found with an increasing number of exchanger rows, and the presence of a minimum suggested a possible optimum design. The effects of refrigerant circuitry and glide matching on exchanger performance were also investigated.
Finally, a link was established between the second-law optimization of the evaporator and its actual performance in a full air-conditioning system. The evaporator model was implemented in a system simulation, and its thermodynamic performance was found to significantly affect that of other components under certain operating conditions. A complete analysis of the interaction between all system irreversibilities is recommended, based on the results of this study.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
