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Purdue University Purdue e-Pubs International Compressor Engineering Conference School of Mechanical Engineering

2008 Effects of Surface Roughness Upon Gas Leakage Flow Through Small Clearances in CO2 Scroll Compressors Noriaki Ishii Osaka Electro-Communication Univ.

Tatsuya Oku Mayekawa Mfg. Co. Keiko Anami Ashikaga Institute of Technology Charles W. Knisely Bucknell University Kiyoshi Sawai Matsushita Electric Industrial Co. See next page for additional authors Follow this and additional works at: https://docs.lib.purdue.edu/icec This document has been made available through Purdue e-Pubs, a service of the Purdue University Libraries. Please contact [email protected] for additional information. Complete proceedings may be acquired in print and on CD-ROM directly from the Ray W. Herrick Laboratories at https://engineering.purdue.edu/ Herrick/Events/orderlit.html Ishii, Noriaki;

Oku, Tatsuya;

Anami, Keiko;

Knisely, Charles W.;

Sawai, Kiyoshi;

Iida, Noboru;

Morimoto, Takashi;

and Fujiuchi, Kenji, Effects of Surface Roughness Upon Gas Leakage Flow Through Small Clearances in CO2 Scroll Compressors (2008). International Compressor Engineering Conference. Paper 1851. https://docs.lib.purdue.edu/icec/1851 Authors Noriaki Ishii, Tatsuya Oku, Keiko Anami, Charles W. Knisely, Kiyoshi Sawai, Noboru Iida, Takashi Morimoto, and Kenji Fujiuchi This article is available at Purdue e-Pubs: https://docs.lib.purdue.edu/icec/1851 1429, Page

1 International Compressor Engineering Conference at Purdue, July 14-17,

2008 Effects of Surface Roughness upon Gas Leakage Flow through Small Clearances in CO2 Scroll Compressors Noriaki ISHII1 , Tatsuya OKU2 , Keiko ANAMI3 , Charles W. KNISELY4 , Kiyoshi SAWAI5 , Takashi MORIMOTO5 , Kenji FUJIUCHI6

1 Division of Mechanical Engineering, Osaka Electro-Communication University, Neyagawa-City, Osaka, Japan Tel: +81-720-20-4561;

E-mail: [email protected]

2 Mayekawa MFG. Co., Ltd., Research and Development Center, Moriya-City, Ibaraki , Japan Tel: +81-297-48-1364, Fax: +81-297-5170, E-mail: [email protected]

3 Division of Mechanical Engineering, Ashikaga Institute of Engineering, Ashikaga-City, Tochigi, Japan

4 Mechanical Engineering Department, Bucknell University, Lewisburg PA 17837, USA

5 Appliance Development Center,

6 Air Conditioning Devices Business Unit, Matsushita Home Appliance Company, Matsushita Electric Industrial Co., Ltd. Kusatsu-City, Shiga, Japan. ABSTRACT This study presents empirical values of the friction factor for CO2 gas leakage through thin rectangular cross- sectional openings of small axial and radial clearances between the orbiting and fixed scrolls of scroll compressors. Leakage flow experiments are conducted for different relative roughness of leakage channel surface. The pressure drop due to leakage is measured using a maximum pressure of

3 MPa. The Darcy-Weisbach equation for incompressible, viscous fluid flow through the thin rectangular cross-section is applied to calculate the pressure drop characteristics, where the empirical friction factors are determined and plotted on a Moody diagram. As a result, it is shown that the empirical friction factors for both axial and radial clearance leakage flows take on essentially the same values, strongly dependent on the relative roughness of leakage channel surface. Subsequently, the empirical friction factor is incorporated into computer simulations for a CO2 scroll compressor with small cooling capacity to determine its optimal performance. As a result, it is shown that CO2 scroll compressors can achieve higher performance levels by increasing the relative roughness of scroll wrap surfaces. 1. INTRODUCTION In recent years, scroll compressors, because of their low vibration, low noise and high efficiency, have become an increasingly popular choice for compressors not only in the conventional refrigerant air-conditioning systems but also in the air-conditioning systems using CO2 as the refrigerant. Scroll compressors have small axial and radial clearances between the orbiting and fixed scrolls. The leakage of the compressed refrigerant gas through these small clearances has a strong detrimental effect on the volumetric efficiency. In order to carry out accurate performance simulations of scroll compressors, a reliable method of calculating the leakage flow through these clearances is needed. Previous studies by Ishii et al. (1996a) and Oku et al., (2005, 2006) present a very simple method for calculating the refrigerant gas leakage flows through the axial and radial clearances in a scroll compressor based on the Darcy- Weisbach equation for incompressible, viscous fluid flow through a thin rectangular cross-section, in which the gas 1429, Page