| Abstrakt: |
New experimental data are presented for single-tube water heaters supplied with exhaust steam. These, together with various data from the literature, are analyzed by the graphical method of E. E. Wilson, by means of which the overall resistance to heat transfer, 1/U, may be successfully resolved into its component parts. Furthermore, by employing a coefficient of 2000 for the steam side, and by using the equation of McAdams and Frost for the water-side coefficient, it is possible to predict the value of U for various water velocities and temperatures. These predicted values compare closely with published test data, both for vacuum condensers and feedwater heaters operated with exhaust steam, covering a range of sizes from 80 to 50,000 sq. ft. For abnormal amounts of air or scale, proper allowances should be made by applying the resistance concept. The equation previously published for the heat transfer on the water side is found to be satisfactory for vacuum condensers and exhaust heaters. However, in analyzing laboratory data for single-tube apparatus heated by steam materially above atmospheric pressure, it was found that this equation gave unduly conservative results, the discrepancy increasing with increase in steam pressure. This may be due to the boiling of the water on the inner wall of the pipe, to the evolution of dissolved air, etc. Fortunately, since commercial tubular apparatus are usually operated either under vacuum or with exhaust steam, this complication is of minor importance in plant practice. |
