DISCUSSION ON EFFICIENCY OB STEAM-ENGIXES. [Minutes of Capt. Sankey. what absolute thermal efficiency did, as mentioned on the first page of the Paper. The standard thermal efficiency was useful for quite a different purpose, and the standard engine discussed in the Paper had reference only to steam-engines ; but a gas-engine could be compared with its B + diagram, as shown in Fig. 1, in an exactly similar manner, and the standard thermal efficiency of a gas-engine obtained. Thab there ought to be two thermal efficiencies, one to compare the absolute conversion into work by an engine, and the other to ascertain the degree of perfection under the conditions in which the engine was placed, Mr. Beaumont appeared to be in agreement with the Paper. He had laid on the Table a few copies of the B + chart, which was a graphic representation of the properties of steam. This chart showed the temperatures, pressures, and volumes of saturated steam and also the volumes of 1 lb. of H,O under various conditions (using that term to mean a mixture of steam and water) ; also the total heat expressed i n British thermal units required to evaporate water at constant pressure from 32" F.
STEAM-ESGINE TRIALS. CORRESPONDENCE ON NON-CONDENSING [Niuutes of Mr. Bodmer. he would take the data from Table I, under the trial letter and numbers S-(p. lG1). Here there was a mean admission pres-110 4.4 sure of 106.34 lbs. per square inch, a mtio of expansion of 4.57, which might be taken as corresponding, with sufficient accuracy for the purpose of illustration, to a terminal pressure of 21 lbs. absolute. Assuming the steam to be initially dry, and calculating the quantity condensed by the time tho pressure was reduced by expansion to 21 lbs., he found this quantity to amount to about 9 per cent. of the total weight of steam used. The percentage of feed-water missing at the end of the stroke was given as 21-53, but should be, in his opinion, strictly speaking, only 21-5 3-9 = 11-53, as otherwise 9 per cent. of feed-water would, by the Author's method, appear to be missing even with a non-conducting cylinder ; whereas this proportion of condonsation was the inevitable result of the adiabatic expansion of initially dry steam. The formula, as given by Clausius and Rankine for calculating the proportion of steam condensed (or re-evaporated) during adiabatic expansion, was-Y x1 T1 T X-=-+ c hyp low-1, * Minutes of Proceedings Inst. C.E. vol. hxii. p. 275. CORRESPONDENCE ON SON-CONDENSING
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