1COMPACT EXCHANGERS FOR PHASE CHANGE

Compact heat exchangers are being increasingly considered for duties involving phase change processes of boiling and condensation. In many cases such applications are completely new and no previous experience or information on exchanger performance is available. Understanding the thermal-hydraulic characteristics of flow passages of compact heat exchangers for phase change duties is therefore vitally important. Even for those compact heat exchangers, which have long been used for boiling and condensation duties, design procedures based on local two-phase characteristics are clearly preferred. This paper reviews the currently available information about phase change in small diameter channels, which are typical of the compact heat exchanger passages. These channels often exhibit different two-phase heat transfer characteristics when compared to 'normal', large diameter tubes. These differences caused by narrowness, and in some cases, non-circular nature of the flow channels are discussed. Some general considerations regarding the effectiveness of single phase heat transfer enhancement features for two-phase applications, the use of fin efficiency term fo