Research Papers

Boiling of R134a in a Plate-Fin Heat Exchanger Having Offset Fins

[+] Author and Article Information
Chennu Ranganayakulu

Aeronautical Development Agency,
P.B. No. 1718,
Vimanapura Post,
Bangalore 560017, India
e-mail: chennu_r@rediffmail.com

Stephan Kabelac

Institut für Thermodynamik,
Leibniz Universität Hannover,
Hannover 30167, Germany
e-mail: kabelac@ift.uni-hannover.de

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received April 24, 2014; final manuscript received January 29, 2015; published online August 11, 2015. Assoc. Editor: P.K. Das.

J. Heat Transfer 137(12), 121002 (Aug 11, 2015) (10 pages) Paper No: HT-14-1235; doi: 10.1115/1.4030910 History: Received April 24, 2014

This paper presents experimental results on boiling heat transfer of R134a in a compact plate fin heat exchanger. The exchanger is made of aluminum and has high density offset fins (30 fins/in.). Such heat exchangers are widely used in air separation industry and aerospace applications because of their high compactness and low weight. The test heat exchanger is attached to a vapor cycle refrigeration basic module to study the effects of boiling phenomena and its influence on performance as there is limited information available for this type of fins. This in turn allows for discussion on boiling mechanism of R134a inside the fins using the water circuit on the other side of the test heat exchanger. The water side single phase heat transfer coefficient (Colburn j factor) is calculated using the cfd tool fluent and validated with available open literature. The results are presented for heat fluxes up to 5500 W/m2 and mass fluxes up to 20 kg/(m2s) with water side flow rate varying from 0.033 to 0.17 kg/s for water temperatures of 10, 15, 20, 25, and 30 °C.

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Fig. 1

Test rig schematic diagram

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Fig. 2

Details of the test heat exchanger

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Fig. 3

Authors comparison of j and f data along with CFD results for an offset fin compact heat exchanger of the type 2.54 S-30-0.1016 with offset fin length of 3.175 mm

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Fig. 4

Computational domain of offset fin

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Fig. 5

Grid independency graph—CFD analysis

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Fig. 6

CFD results of j and f data of offset fin of the type 2.54 S-30-0.1016 with offset fin length of 1.588 mm for water and air

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Fig. 7

Pressure drop values on water side

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Fig. 8

(a) Pressure drop values on refrigerant side and (b) comparison of the mean friction factor f with estimated values using equivalent Re numbers on the refrigerant side

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Fig. 9

Overall heat transfer coefficient U versus heat flux q on the refrigerant side

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Fig. 10

Heat transfer coefficient hr versus heat flux q on the refrigerant side

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Fig. 11

Heat transfer coefficient hw versus heat flux q on the water side

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Fig. 12

Heat transfer coefficient hcon versus mass flux GR

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Fig. 13

Refrigerant side heat transfer coefficient hnuc versus Z

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Fig. 14

Heat transfer coefficient hnuc versus mass flux Gr




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