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MICRO/NANOSCALE HEAT TRANSFER—PART I

Pressure Drop During Two-Phase Flow of R134a and R32 in a Single Minichannel

[+] Author and Article Information
Alberto Cavallini

Dipartimento di Fisica Tecnica, University of Padova, Padova 35131, Italyalcav@unipd.it

Davide Del Col

Dipartimento di Fisica Tecnica, University of Padova, Padova 35131, Italydavide.delcol@unipd.it

Marko Matkovic

Dipartimento di Fisica Tecnica, University of Padova, Padova 35131, Italymarko.matkovic@unipd.it

Luisa Rossetto

Dipartimento di Fisica Tecnica, University of Padova, Padova 35131, Italyluisa.rossetto@unipd.it

J. Heat Transfer 131(3), 033107 (Jan 21, 2009) (8 pages) doi:10.1115/1.3056556 History: Received April 14, 2008; Revised August 29, 2008; Published January 21, 2009

Condensation in minichannels is widely used in air-cooled condensers for the automotive and air-conditioning industry, heat pipes, and compact heat exchangers. The knowledge of pressure drops in such small channels is important in order to optimize heat transfer surfaces. Most of the available experimental work refers to measurements obtained within multiport smooth extruded tubes and deal with the average values over the number of parallel channels. In this context, the present authors have set up a new test apparatus for heat transfer and fluid flow studies in single minichannels. This paper presents new experimental frictional pressure gradient data, relative to single-phase flow and adiabatic two-phase flow of R134a and R32 inside a single horizontal minitube, with a 0.96 mm inner diameter and with not-negligible surface roughness. The new all-liquid and all-vapor data are successfully compared against predictions of single-phase flow models. Also the two-phase flow data are compared against a model previously developed by the present authors for adiabatic flow or flow during condensation of halogenated refrigerants inside smooth minichannels. Surface roughness effects on the liquid-vapor flow are discussed. In this respect, the friction factor in the proposed model is modified, in order to take into consideration also effects due to wall roughness.

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Experimental test rig: desup=desuperheater, MF=mechanical filter, HF=dehumidifier, PV=pressure vessel, CFM=Coriolis-effect mass flow meter, P=pressure transducer, T=temperature transducer, DP=differential pressure transducer, and TV1 and TV2=throttling valves

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Figure 2

The test section

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Figure 3

Experimental and calculated friction factors for a 0.96 mm inner diameter circular single minichannel

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Figure 4

Overall experimental pressure losses during adiabatic two-phase flow of R134a and R32 at 40°C saturation temperature and different mass velocities G(kg m−2 s−1) in the 0.96 mm inner diameter circular single minichannel. Calculated trends (dashed lines) by the model, which do not consider surface roughness (Eq. 1,2,3,4,5,6,7,8,9,10,11), are also reported.

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Figure 5

Calculated (Eqs. 1,2,3,4,5,6,7,8,9,10,11) versus experimental pressure drop

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Figure 6

Overall experimental pressure losses during adiabatic two-phase flow of R134a and R32 at around 40°C saturation temperature and different mass velocities G(kg m−2 s−1) in the 0.96 mm inner diameter circular single minichannel. Calculated trends (dashed lines) by the model, modified for the surface roughness effect with Eq. 5, are also reported.

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Figure 7

Calculated (model modified with Eq. 5) versus experimental pressure drop

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Figure 8

Comparison between predictions from Cavallini (15) model modified with Eq. 5 and experimental data by Cavallini (8) and Coleman (9).

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