Boiling heat transfer and critical heat flux in helical coils
Abstract
The present study was initiated to obtain more information on boiling heat transfer in coils, with particular emphasis on the effect of an outside heat flux tilt on the CHF. An experimental investigation was conducted to determine the boiling heat transfer characteristics of R-113 in electrically heated, helically coiled tubes and in straight tubes (for reference). An experimental test loop was designed and constructed for this study. Electrically heated coils of three different ratios of tube diameter to coil diameter (d/D = 0.0182, 0.0353, and 0.0649) were tested using R-112 at a pressure of 0.94 MPa and with wide ranges of mass velocity, exit sub cooling quality, and flux tilt toward the outside of the coil. A straight, horizontal tube was tested for reference. Subcooled CHF is degraded in coils relative to straight, horizontal tubes. Degradation increases with increasing d/D and mass velocity. Quality CHF is enhanced and increases with increasing d/D; CHF initially increases with increasing mass velocity but begins to decrease after a maximum is reached. The degrading effect of buoyancy on CHF in straight, horizontal tubes and in coils is shown. A Forbidden Zone is described in which severe operational problems can occur if the heat exchanger is operating with low subcooling or low quality near the inlet and high quality near the exit.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1980
- Bibcode:
- 1980PhDT........20J
- Keywords:
-
- Boiling;
- Heat Exchangers;
- Helical Flow;
- Steam;
- Cooling;
- Heat Flux;
- Heat Transfer;
- Fluid Mechanics and Heat Transfer