IJames Watt - mproving the Broiler
James Watt made a new boiler for the experimental investigation on which he was about to enter that could measure the quantity of water evaporated and the steam condensed at every stroke of the engine.
James Watt Rediscovers Latent Heat
He soon discovered that it required a very small quantity of steam to heat a very large quantity of water, and immediately started to determine with precision the relative weights of steam and water in the steam cylinder when condensation took place at the down stroke of the engine. James Watt independently proved the existence of "latent heat", the discovery of another scientist, Doctor Black. Watt went to Black with his research, who shared his knowledge with Watt. Watt found that, at the boiling point, his condensing steam was capable of heating six times its weight of water used for producing condensation.
James Watt's Separate Condenser
Realizing that steam, weight for weight was a vastly greater absorbent and reservoir of heat than water, Watt saw the importance of taking greater care to economize it than had previously been attempted. At first, he economized in the boiler, and made boilers with wooden "shells" in order to prevent losses by conduction and radiation, and used a larger number of flues to secure more complete absorption of the heat from the furnace gases. He also covered his steam pipes with nonconducting materials, and took every precaution to secure the complete utilization of the heat of combustion. He soon discovered that the great source of loss was to be found in defects which he noted in the action of the steam in the cylinder. He soon concluded that the sources of loss of heat in the Newcomen engine which would be greatly exaggerated in a small model were:- First, the dissipation of heat by the cylinder itself, which was of brass, and was both a good conductor and a good radiator.
- Secondly, the loss of heat consequent upon the necessity of cooling down the cylinder at every stroke, in producing the vacuum.
- Thirdly, the loss of power due to the pressure of vapor beneath the piston, which was a consequence of the imperfect method of condensation.
Continuing his research, he measured the amount of steam used at each stroke, comparing it with the quantity that would just fill the cylinder, he found that at least three fourths was required. The quantity of cold water necessary to produce the condensation of a given weight of steam was determined next; and he found that one pound of steam contained enough heat to raise about six pounds of cold water, as used for condensation, from the temperature of 62° to the boiling point. James Watt was compelled to use, at each stroke of the Newcomen engine, four times as much injection water as the amount used to condense a cylinder full of steam. This confirmed his previous conclusion that three-fourths of the heat supplied to the engine was wasted.
