Supplement to Mr. Macquorn Rankine's Paper "On the Thermodynamic Theory of Steam-Engines with Dry Saturated Steam, and Its Application to Practice"

XXVIII. Supplement to Mr. Macquorn Rankine's Paper "On the Thermodynamic Theory of Steam-engines with dry saturated Steam, and its application to practice*." Received September 3,—Read December 8, 1859. The following additional information respecting the steam-ships referred to in the examples may be interesting, although it does not strictly belong to the special subject of the paper. Example I.—Paddle-steamer 'Admiral,' built by Mr. James R. Napier; engines made by Messrs. Randolph, Elder and Co.; draught 7 feet 6 inches; length 210 feet; breadth 32 feet; displacement 820 tons; speed with 774 indicated horse-power 11·9 nautical miles an hour. Effective work in driving the ship, about 604 horse-power. Available heat expended per hour in foot-pounds per indicated horse-power, \[ \frac{1,980,000}{\text{efficiency of steam}} = \frac{1,980,000}{0.123} = 16,100,000. \] Coal burned per indicated horse-power per hour, 2·97 lbs. Available heat of combustion of one pound of coal, \[ \frac{16,100,000}{2.97} = 5,420,000 \text{ foot-lbs}. \] The total heat of combustion of one pound of the coal employed being roughly estimated at 10,000,000 foot-pounds, it appears that the efficiency of the furnace and boiler was about 0·542. The boilers were improved marine boilers of ordinary proportions. Example II.—Screw-steamer 'Thetis,' built by Messrs. C. Scott and Co.; the engine made by Messrs. Rowan and Co. Available heat expended per hour in foot-lbs. per indicated horse-power, \[ \frac{1,980,000}{\text{efficiency of steam}} = \frac{1,980,000}{0.192} = 10,312,500. \] Coal burned per indicated horse-power per hour, during an experiment of one hour's duration, 1·02 lb. Available heat of combustion of one pound of the coal employed, \[ \frac{10,312,500}{1.02} = 10,110,000 \text{ foot-pounds}. \] The coal used was of very good quality; and its total heat of combustion per pound is * Philosophical Transactions, Part I. 1859, p. 177; Proceedings of the Royal Society, January 1859. estimated at 11,560,000 foot-pounds. Hence the efficiency of the furnace and boiler was \[ \frac{10,110,000}{11,560,000} = 0.88. \] In this case the short duration of the experiment on the consumption of coal, which was interrupted by a fog, makes the result less satisfactory than it would have been if the experiment had been continued, as intended, for several hours. The engine and boiler were of a kind invented some years ago by Mr. Craddock; the boiler consisting chiefly of a sort of cage of vertical water-tubes enclosing each fire-grate. The heating surface was about nine times as great, relatively to the fuel burned, as it is in ordinary marine boilers. **Example III.**—Paddle-steamer 'Callao,' built by Messrs. John Reid and Co.; the engines by Messrs. Randolph, Elder and Co.; displacement 1100 tons; speed with 1176 indicated horse-power 12·05 nautical miles per hour. Available heat expended per hour in foot-pounds per indicated horse-power, \[ \text{efficiency of steam} = \frac{1,980,000}{0.14} = 14,143,000 \text{ foot-lbs.} \] Coal burned per indicated horse-power per hour, 2·67 lbs. Available heat of combustion of 1 lb. of coal, \[ \frac{14,143,000}{2.67} = 5,300,000; \] being nearly the same as in Example I. The boilers in this case were, like those in Case I., improved marine boilers of ordinary proportions. In such boilers, 5,400,000 foot-lbs. may be considered a fair estimate of the available heat of combustion of good ordinary steam-coal.