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Research Papers

Comparison of the Straight Adiabatic Capillary Tube Expansion Devices Used in Refrigeration Systems Operating With Refrigerants R134a and R1234yf

[+] Author and Article Information
S. S. Harish Kruthiventi

Refrigeration and Air Conditioning Laboratory,
Department of Mechanical Engineering,
Indian Institute of Technology Madras,
Chennai 600036, India
e-mail: harish.kruthiventi@gmail.com

G. Venkatarathnam

Refrigeration and Air Conditioning Laboratory,
Department of Mechanical Engineering,
Indian Institute of Technology Madras,
Chennai 600036, India
e-mail: gvenkat@iitm.ac.in

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received July 1, 2015; final manuscript received November 23, 2015; published online February 3, 2016. Assoc. Editor: Amir Jokar.

J. Thermal Sci. Eng. Appl 8(2), 021015 (Feb 03, 2016) (7 pages) Paper No: TSEA-15-1178; doi: 10.1115/1.4032366 History: Received July 01, 2015; Revised November 23, 2015

Capillary tube expansion devices are used extensively in small refrigeration and unitary air conditioning systems. R1234yf is likely to replace R134a in the next few years in many small refrigeration systems worldwide because of the new environmental regulations being proposed. In this paper, we compare the length and diameter of capillary tube required when R134a and R1234yf are used in a typical small refrigeration system. The minimum diameter of the capillary tube required has been estimated using the speed of sound of the refrigerant leaving the capillary tube in the two-phase state. The two-phase speed of sound routine developed by us can be used with both pure fluids and mixtures.

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References

Figures

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Fig. 1

Procedure for the sizing of capillary tube diameter

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Fig. 2

Comparison of the speed of sound of water–air mixture at P = 1 bar and T = 298.15 K calculated in this work with that measured by Karplus [21]

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Fig. 3

Variation of speed of sound with vapor fraction for refrigerant R134a at an evaporating temperature of −20 °C

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Fig. 4

Variation of the critical mass flux of the refrigerant under choked flow conditions with condensing temperature at an evaporating temperature of −20 °C and zero degrees of subcooling

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Fig. 5

Variation of speed of sound at capillary tube outlet under choked flow conditions with condensing temperature at an evaporating temperature of −20 °C and zero degrees of subcooling

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Fig. 6

Variation of vapor fraction at capillary tube outlet under choked flow conditions with condensing temperature at an evaporating temperature of −20 °C and zero degrees of subcooling

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Fig. 7

Variation of ratio of the mass flow rate of R1234yf and that of R134a under choked flow conditions with condensing temperature at an evaporating temperature of −20 °C and different degrees of subcooling

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Fig. 8

Variation of ratio of the diameter of R1234yf and that of R134a under choked flow conditions with condensing temperature at an evaporating temperature of −20 °C and different degrees of subcooling

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Fig. 9

Variation of critical mass flux through a capillary tube operating with R1234yf under choked flow condition and different degrees of subcooling with condensing temperature

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Fig. 10

Variation of the ratio of length of capillary tube required with R1234yf and R134a with condensing temperature for the same refrigeration capacity, and choking at the capillary tube exit

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Fig. 11

Minimum diameter of capillary tubes for a 100 W cooling capacity refrigerator operating with R134a and R1234yf at an evaporating temperature of −20 °C, subcooling/superheating of zero

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