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Experiments On The Rate Of Heat Transfer From A Hot Gas To A Cooler Metallic Surface Author:Various EXPERIMENTS ON THE RATE OF HEAT TRANSFER FROM A HOT GAS TO A COOLER METALLIC SURFACE THE BABCOCK WILCOX CO. In NEW YORK tmmi mwm EXPERIMENTS ON THE RATE OF HEAT TRANSFER FROM A HOT GAS TO A COOLER METALLIC SURFACE SECTION PAGE I INTRODUCTION 7 II DESCRIPTION OF THE EXPERIMENTAL APPARATUS 13 III PRELIMINARY EXPERIMENTS 23 IV METHOD OF CONDUCTING ... more »EXPERIMENTS AND RECORDING RESULTS 27 V DETERMINATION OF RADIATION LOSSES ... 30 VI MEASUREMENT OF METAL TEMPERATURES . . 32 VII THE DETECTION AND CORRECTION OF ERRORS CHECKS ON RECORDED DATA AND COMPUTED RESULTS 38 VIII METHODS OF MAKING COMPUTATIONS ... 45 IX SUPPLEMENTARY EXPERIMENTS 64 X DISCUSSION OF RESULTS 66 APPENDIX A DERIVATION OF CORRECTIVE FORMULA FOR HEAT ABSORPTION 68 f APPENDIX B DERIVATION OF HEAT TRANSFER FORMULA 70 APPENDIX C THE SPECIFIC HEAT OF GASES . . . f73 APPENDIX D CALIBRATION OF THERMO-COUPLES . . 81 INTRODUCTION WHILE there has been within recent years a number of experiments dealing with the subject of Heat Transmission, it is apparent from a study of the literature on the subject that not only is there a marked uncer tainty as to the actual value of the numerical coefficients involved, but also a considerable lack of information with reference to the theory. The 35th Edition of Steam gives a brief account of what was known at the end of the year 1913 of the laws governing the transfer of heat from a hot gas to a cooler metallic surface, and since that time there have been practically no additional contributions to the literature on the subject. The experiments of H. P. Jordan, an account of which is given in the Proceedings of the Institute of Mechanical Engineers, 1909, appear to be the most reliable and are, in fact, the only experiments that seem to offer anything from the viewpoint of practical design. The methods employed by Jordan in working up his results corresponded with the methods used by The Babcock Wilcox Co. some years ago in the determination of average heat transfer rates in boilers from evaporative tests. Jordans results, however, and those of The Babcock Wilcox Co. differed very materially in the numerical value of the constants determined. Because of this wide discrepancy in results, and with a view to arriving at some definite conclusions on the laws governing heat transfer as applied to actual practice, as distinguished from the purely theoretical aspect of the subject, the experiments described in this paper were undertaken. Before criticising Jordans results it would be well to point out a few deductions from the elementary theory covering the transfer of heat. As ordinarily used, the heat transfer rate is Quantity of heat Temperature difference x Area x Time A quantity of heat dimensionally is equal to the product of a mass times a temperature difference hence, the ratio Quantity of heat Temperature difference Steam, Its Generation and Use, 35th Edition, 1913. The Babcock Wilcox Co. has the dimension M, and the area and time, of course, have the dimensions L 2 and T. Therefore the dimension of the transfer rate coefficient is The dimension of the coefficient of conductivity, as ordinarily used, is obviously Hence, considered dimensionally, the transfer rate could be equal to a coefficient of conductivity divided by a length, which in the case of a cylindrical tube must be the diameter of the tube. It is also evident that from the dimensions the transfer rate can be equal to a velocity times a density, and again, considering a flow through a cylindrical tube, the velocity and density can be taken as the mean density of the gas, which gives Osborne Reynolds law. It has been recently demonstrated by the experiments of Stanton and Pannell that the motion of a viscous fluid of con stant viscosity depends only on the coefficient of viscosity and the density...« less
