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Study of flow boiling characteristics of R134a in annulus of enhanced surface tubing

Abstract:

The paper presents an experimental study of the flow‐boiling heat‐transfer characteristics of R12 and R134a in the annulus of a horizontal enhanced‐surface‐tubing evaporator. The test section has an inner‐tube bore diameter of 17.5 mm, an envelope diameter of 28.6 mm and an outer smooth tube of 32.3 mm inside diameter. The ranges of heat flux and mass velocity covered in the tests were 5–25 kW/m2 and 180–290 kg/m2/s, respectively, at a pressure of 365 kPa. In order to establish the flow regime conditions at the inlet to the test section, the test rig allows for the visualization of refrigerant flow through the preheater. The experiments show two regions of heat transfer: a nucleate boiling region where the heat transfer depends mainly on heat flux, and a forced convective region where the heat transfer depends only on the refrigerant flow rate. Copyright © 1993 John Wiley & Sons, Ltd.