Modelling of the flow of refrigerant 134a in capillary tubes
Practical tools for the design of capillary tubes for refrigeration systems employing the traditional CFC-12 and HCFC-22 as refrigerants are widely available. Due to environmental concern of the depletion of ozone layer and global warming, CFCs and HCFCs have to be phased out eventually accord...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English |
| Published: |
2004
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| Subjects: | |
| Online Access: | http://eprints.uthm.edu.my/7609/1/24p%20AZMAHANI%20SADIKIN.pdf |
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| Summary: | Practical tools for the design of capillary tubes for refrigeration systems employing
the traditional CFC-12 and HCFC-22 as refrigerants are widely available. Due to
environmental concern of the depletion of ozone layer and global warming, CFCs and
HCFCs have to be phased out eventually according to the Montreal Protocol. As a
result, a number of alternative refrigerants including HFC-134a have emerged as
promising chlorine free alternatives to CFC-12 in domestic refrigerators and freezers.
The proper size of a capillary tube with a new refrigerant is a critical factor for the
optimum performance of a refrigeration system.
This study presents a computer model KAPILARI, which has been developed to
predict the length of capillary tube used as an expansion device in small refrigerating
and air-conditioning systems. The pressure drop through a capillary tube in the
single-phase and two-phase regions is modelled in an attempt to predict the size of
capillary tube. The model is based on the governing equations of conservation of
mass, energy and momentum. Stoecker's basic model was modified with the
consideration of various effects due to sub cooling, choked flow and friction factor
used in single-phase region.
The developed model has been validated by employing available studies and found to
agree well with the experimental data and other mathematical model predictions of
HFC-134a. The capability of the program has been tested and simulations are carried
out to investigate the effect of varying the operating and design parameters of the
system, namely cooling capacity, evaporating temperature, degree of superheat,
condensing temperature, degree of subcoo1ing and inner diameter of capillary tube,
on the length of the capillary tube. The developed model is an effective tool of
capillary tube's
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design and optimization for systems using HFC-134a |
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