Some Factors in the Design of Surface Condensing Plant

Abstract

It is suggested that the poor performance of certain large surface condensers is due to pressure drop on the steam side. Tests are given showing the pressure drop for various patterns of tube plates and illustrating the steps taken to reduce it. The effect of pressure drop upon the mean temperature difference is discussed. The limitations of accepted formulae are criticized and the results of more accurate analysis are presented. The results of Eagle and Ferguson's tests on heat transmission from tube to water are presented in terms of the external surface for the range of normal condensing plant. Utilizing these results, the overall rates of heat transmission from a large number of tests on commercial condensers are analysed in order to obtain the rate of heat transmission from steam to tube, and after a discussion of the results a mean value is suggested. A set of curves of overall rates of heat transmission on this basis is presented as applicable to brushed tubes. A method of obtaining the net heat rejected to the circulating water in power plant is developed and the departure from the conventional figure of 1,000 B.Th.U. per lb. is brought out. The results obtained on a series of tests on individual tubes in a complete condenser are analysed and commented upon. The paper also deals with the effect of tube fouling upon the overall rate of heat transmission, and methods of obtaining a margin in surface to allow for this are discussed. The effect of pressure drop upon the duty of an air extraction plant and certain problems arising therewith are discussed. Some actual air leakage tests are given and compared with recognized standard allowances. The authors deal with the friction on the water side of condensers and give test figures of the friction in the tube with various methods of tube plate fastenings. Recommended standard values of the various factors for assessing condenser water friction are given, together with tests from commercial installations. The paper concludes with a treatment of the problem of syphonic return in condenser circulating water systems and gives a method of calculating the syphonic efficiency.