An apparatus for noiselessly heating water by direct contact in a closed circuit is shown in Fig. 126. This apparatus is known as a commingler, and takes the place of, and is connected to, a storage tank in the same manner as a waterback or heater. Water from the hot water tank enters the com-mingler through the pipe a passes up through the body of the casting and flows back through the pipe b into the tank. Steam is supplied to the heater through the pipe c, passes down pipe d and escapes into the body of the commin-gler through the small holes shown in the nozzle, e.

The admission of steam to the body of the water in this manner prevents the noise that is experienced when steam enters a body of cold water directly and without being previously broken up, as is done by these holes. Sometimes a portion of the interior of the casting is filled with small pebbles surrounding the nozzle, the effect being to still further break up the steam, which has to force its way through these pebbles before striking the main body of water in the casting.

Fig. 126

To use this apparatus in a closed circuit the steam pressure must be greater than the water pressure, and a check-valve should be placed in the steam pipe to prevent water flowing from the commingler to the steam boiler when the steam pressure is low. Heat Transmitted by Steam to Water - When steam is brought in contact with water of lower temperature than the steam, it almost instantly parts with all of its latent heat and all of its sensible heat above the temperature of the water. Thus, when a pound of steam is brought in contact with water it imparts as many B. T. U. to the water as there are B. T. U. in a pound of steam at that pressure above the temperature of the water. For instance, there are 1141.1 B. T. U. in one pound of steam at atmospheric pressure reckoning from the freezing point, and if allowed to expand in water with a temperature of 60 degrees Fahr., the steam will part with all of its heat until the temperature of the water of condensation is equal to the temperature of the water to be heated. In doing so it will impart 1141.1+32-60=1113.1 B. T. U. to the water, and will increase its bulk by one pound, or about 1/8 gallon. The number of B. T. U. in a pound of steam varies with its temperature and pressure.

The number of B. T. U. contained in one pound of water at different temperatures, also the number of B. T. U. required to raise one pound of water from different temperatures to boiling point at atmospheric pressure, may be found in the following table:

Table LII - B. T. U. In Water At Different Temperatures