Carbon Dioxide and R410a Flow Boiling Heat Transfer, Pressure Drop, and Flow Pattern in Horizontal Tubes at Low Temperatures

Park, C.Y.; Hrnjak, P.S.

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https://hdl.handle.net/2142/12918 Copy

Description

Title

Carbon Dioxide and R410a Flow Boiling Heat Transfer, Pressure Drop, and Flow Pattern in Horizontal Tubes at Low Temperatures

Author(s)

• Park, C.Y.
• Hrnjak, P.S.

Issue Date

2007-01

Keyword(s)

• R744
• heat transfer
• pressure drop
• flow regimes

Abstract

Carbon dioxide (CO2) has been seriously considered as an alternate refrigerant for HCFC and HFC fluids, due to the increasing interest of environmentally safe refrigerants in air-conditioning and refrigeration systems. In this study, CO2 flow boiling heat transfer coefficients and pressure drop are measured in macro-scale (6.1 and 3.5 mm) tubes at evaporation temperatures of –15 and –30 °C. The measured results show that the nucleate boiling is a main heat transfer mechanism in the 6.1 mm tube and the contribution of convective boiling becomes greater with the decrease of tube diameters and the increase of mass fluxes. The surface roughness of the 6.1 and 3.5 mm tube are presented by SEM and AFM images and surface profiles, and it is shown that the rougher surface of the 6.1 mm tube can affect the flow boiling heat transfer. The CO2 heat transfer coefficients and pressure drop are measured in a mini-scale (0.89 mm) multi-ported tube at the evaporation temperature of –30 °C. Also, R410A and R22 flow boiling heat transfer coefficients and pressure drop in a macro-scale (6.1 mm) tube were measured, and they are compared with CO2. This comparison presents that the CO2 flow boiling heat transfer coefficients are higher than R410A and R22 at low vapor qualities, and CO2 pressure drop is significantly lower than R410A and R22. This advantageous characteristic for CO2 could be explained by properties such as surface tension, reduced pressure, and the density ratio of liquid to vapor. The prediction of heat transfer coefficients and pressure drop was performed by general correlations and the calculation results are compared with measured values. Two-phase flow patterns were visualized for CO2 and R410A in the 6 and 3 mm glass tubes, and they are compared with the Weisman et al. and the Wojtan et al. flow pattern maps. The flow pattern maps can determine the flow patterns relatively well, except the transition from intermittent to annular flow.

Publisher

Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.

Series/Report Name or Number

Air Conditioning and Refrigeration Center TR-258

Type of Resource

text

Language

en

Permalink

http://hdl.handle.net/2142/12918

Sponsor(s)/Grant Number(s)

Air Conditioning and Refrigeration Project 183

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