ASHRAE F05-2009 (I-P)

Two-phase flow is encountered extensively in the HVACR industries. A combination of liquid and vapor refrigerant exists in flooded coolers, direct-expansion coolers, thermosiphon coolers, brazed and gasketed plate evaporators and condensers, and tube-in-tube evaporators and condensers, as well as in air-cooled evaporators and condensers. In heating system pipes, steam and liquid water may both be present. Because the hydrodynamic and heat transfer aspects of two-phase flow are not as well understood as those of single-phase flow, no comprehensive model has yet been created to predict pressure drops or heat transfer rates. Instead, the correlations are for specific thermal and hydrodynamic operating conditions. This chapter introduces two-phase flow and heat transfer processes of pure substances and refrigerant mixtures. Thus, some multiphase processes that are important to HVACR applications are not discussed here. The 2008 ASHRAE HandbookHVAC Systems and Equipment provides information on several such applications, including humidification (Chapter 21), particulate contaminants(Chapter 28), cooling towers (Chapter 39), and evaporative air cooling (Chapter 40). See Chapter 41 of the 2006 ASHRAE HandbookRefrigeration for information on absorption processes.

Chapter Table of Contents

Boiling
Condensing
Pressure Drop
Enhanced Surfaces
Symbols

ISBN: 978-1-933742-54-0
ISSN: 1523-7222

Units: I-P

Citation: 2009 ASHRAE Handbook -- Fundamentals: Chapter 5, Two-Phase Flow



Product Code(s): D-F052009IP

Chapter Table of Contents

Boiling

Condensing

Pressure Drop

Enhanced Surfaces

Symbols