Heat Transfer Engineering, 27(9):20–27, 2006 Copyright C  Taylor and Francis Group, LLC ISSN: 0145-7632 print / 1521-0537 online DOI: 10.1080/01457630600845598 Two-Phase Flow Visualization in Chevron and Bumpy Style Flat Plate Heat Exchangers E. W. JASSIM, T. A. NEWELL, and J. C. CHATO Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA Adiabatic flow visualization in a chevron plate, a 1:1 aspect ratio bumpy plate, and a 2:1 aspect ratio bumpy plate heat exchangers were investigated for vertical upward flow with R134a. Qualities ranging from 5% to 90% and mass fluxes of 60, 90, and 125 kg/m 2 -s were investigated. The flow visualization experiments were conducted at a 10 ◦ C inlet temperature. Four flow regimes were observed for the flat plate geometries investigated: bubbly flow, rough annular flow, smooth annular flow, and mist flow. The four flow regimes are mapped out on a mass flux versus quality basis for each geometry. The chevron geometry was seen to undergo flow transitions at lower qualities and mass fluxes than the bumpy plate geometries, and the 2:1 aspect ratio bumpy plate geometry was seen to undergo flow transitions at lower qualities and mass fluxes than the 1:1 aspect ratio bumpy plate geometry. INTRODUCTION Flat plate heat exchangers have been in commercial use since 1923, according to Raju and Chand [1]. They are widely used in a liquid-to-liquid configuration for food processing, dairy, and other industrial applications, and their compact size presents a clear advantage over shell and tube-style heat exchangers in some applications. Because the single-phase flow configuration in flat plate heat exchangers has been used for a long period of time, there is much single-phase flat plate literature available. Currently, flat plate heat exchangers are being used in two-phase configurations for automotive evaporators, oil coolers, and other industrial applications. Chevron-style flat plate heat exchangers are used for industrial refrigeration, and bumpy style flat plate heat exchangers are commonly used for automotive air con- ditioners. There is limited information in the literature about two-phase flow in flat plate heat exchangers, especially with new refrigerants such as R134a. Furthermore, the relationship between “chevron” and “bumpy” style flat plate heat exchangers have yet to be fully identified in literature. The authors would like to thank the Air Conditioning and Research Center (ACRC) at the University of Illinois for their financial support. The authors would also like to thank Frank Sup, an undergraduate at the University of Illinois, for his assistance in the flow visualization. Address correspondence to Dr. E. W. Jassim, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA. E-mail: emadjassim@yahoo.com This paper will focus on adiabatic flow visualization of R134a in chevron style and two types of bumpy style flat plate evapo- rators with upward flow conditions—a 1:1 aspect ratio bumpy plate and a 2:1 aspect ratio bumpy plate. Flat plate heat exchang- ers generally consist of complex passageways for the two-phase refrigerant flow. Chevron flat plate heat exchangers consist of passageways that have limited groove-to-groove access, while bumpy plate heat exchangers have a more direct connection across groove (bump) rows. The 2:1 aspect ratio bumpy plate has less of a direct connection across groove (bump) rows than the 1:1 aspect ratio plate geometry. Consequently, the 2:1 aspect ratio bumpy plate represents an intermediate step between the chevron and 1:1 aspect ratio geometries. The rationale behind the plate designs was to provide a means of comparing chevron plates to dimpled plates. The single and two-phase pressure drop characteristics of all three heat exchanger geometries tested are presented by Jassim and colleagues [2, 3]. Moreover, the pressure drop characteristics of the chevron plate were found to be very similar to that found by Luo and Yu [4] and Luo and Zhang [5]. They both used chevron geometry heat exchangers similar to the chevron geometry tested in this paper. Both papers used a 60 ◦ C chevron angle, which is the angle between the corrugated channel and the flow direction. The pressure drop characteristics of Luo and Zhang [5] were closer to that of the chevron geometry tested in this paper because the geometries were most similar. 20