Research Papers: Evaporation, Boiling, and Condensation

Flow Boiling Heat Transfer, Pressure Drop, and Flow Pattern for CO2 in a 3.5mm Horizontal Smooth Tube

[+] Author and Article Information
Chang Yong Park

School of Mechanical Design and Automation Engineering, Seoul National University of Technology, 172 Gongneung-2Dong, Nowon-Gu, Seoul 139-743, Korea

Pega Hrnjak1

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 1206 West Green Street, Urbana, IL 61801pega@uiuc.edu


Corresponding author.

J. Heat Transfer 131(9), 091501 (Jun 19, 2009) (12 pages) doi:10.1115/1.2909079 History: Received April 17, 2007; Revised August 07, 2007; Published June 19, 2009

CO2 flow boiling heat transfer coefficients and pressure drop in a 3.5mm horizontal smooth tube are presented. Also, flow patterns were visualized and studied at adiabatic conditions in a 3mm glass tube located immediately after a heat transfer section. Heat was applied by a secondary fluid through two brass half cylinders to the test section tubes. This research was performed at evaporation temperatures of 15°C and 30°C, mass fluxes of 200kgm2s and 400kgm2s, and heat flux from 5kWm2 to 15kWm2 for vapor qualities ranging from 0.1 to 0.8. The CO2 heat transfer coefficients indicated the nucleate boiling dominant heat transfer characteristics such as the strong dependence on heat fluxes at a mass flux of 200kgm2s. However, enhanced convective boiling contribution was observed at 400kgm2s. Surface conditions for two different tubes were investigated with a profilometer, atomic force microscope, and scanning electron microscope images, and their possible effects on heat transfer are discussed. Pressure drop, measured at adiabatic conditions, increased with the increase of mass flux and quality, and with the decrease of evaporation temperature. The measured heat transfer coefficients and pressure drop were compared with general correlations. Some of these correlations showed relatively good agreements with measured values. Visualized flow patterns were compared with two flow pattern maps and the comparison showed that the flow pattern maps need improvement in the transition regions from intermittent to annular flow.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Simplified schematics of test facility

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Figure 2

Schematics for (a) the test section, (b) the cross section of the test tube, and (c) dimension of the test tube

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Figure 3

Comparison of the measured and predicted R22 flow boiling heat transfer coefficients to validate the test results for a 6.1mm tube at the evaporation temperature, heat flux, and mass flux of −15°C, 10kW∕m2, and 400kg∕m2s, respectively

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Figure 4

CO2 flow boiling heat transfer coefficients for the 3.5mm tube as a function of mass flux, heat flux, vapor quality, and evaporation temperatures

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Figure 5

The ratio of CO2 flow boiling heat transfer coefficients for the 3.5mm to those for the 6.1mm tube at identical conditions

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Figure 6

Tube surface images with a SEM for the (a) 3.5mm tube (×5000) and (b) 6.1mm tube (×5000)

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Figure 7

Surface profile measured by a profilometer to the axial direction on the (a) 3.5mm and (b) 6.1mm tubes and to the circumferential direction on the (c) 3.5mm and (d) 6.1mm tubes

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Figure 8

Surface image measured by an AFM for the (a) 3.5mm and (b) 6.1mm tubes

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Figure 9

Surface roughness effect on pool boiling heat transfer coefficients based on Gorenflo’s (26) correlation at boiling temperatures of (a) −15°C and (b) −30°C

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Figure 10

Pressure drop of adiabatic two-phase flow in the 3.5mm tube for evaporation temperatures of −15°C and −30°C, mass fluxes of 200kg∕m2s and 400kg∕m2s, and vapor qualities from 0.1 to 0.8

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Figure 11

Flow patterns in the 3mm glass tube at a saturation temperature of −15°C for mass fluxes of (a) 200kg∕m2s and (b) 400kg∕m2s

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Figure 12

Comparison of the visualized flow patterns in the 3mm glass tube with the flow pattern map presented by (a) Weisman (15) and (b) Wojtan (16) at −15°C, and (c) Wojtan (16) at −30°C



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