The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California

Hot Water Suply

The particles of water touching the sides of the vessel become cooled by the transmission of heat from them through the metal to the outer atmosphere. Hence, the particles of water touching the sides will descend more rapidly than those some distance from it, and the circulation within the water will, in general, be about as shown by the arrows for the case illustrated. Circulation within an undivided volume of water, as in the vessel of Fig. 1, is called local circulation.
The transmission of heat through a liquid, by a motion of its particles, is called convection.

3..In Fig. 2 is shown a U tube connected near the top by a cross pipe, to which a water-tight valve as attached. If this valve is closed and cold water is poured into the loop until the surface in the tube b is at the dotted line c, the surface of the water in the tube d will also be at the dotted level line c; that is, the level of the water in both tubes will be the same, because the temperature of the water is the same in both tubes." If the valve a is opened, the water will not flow from one tube into the other, because no hydrostatic head will be present to produce a current. Suppose that the valve a is closed and heat is applied to the base of d by a flame, as shown. the water in d will become heated, and will occupy a greater space. Hence, the surface of the water in the tube d will rise from its original level c to a new level, as e. It will be noticed that while the columns of water in b and d are equal in weight, they are unequal in height, the warmer column being the higher one. If the valve a is now opened, the pressure due to the head of water between the levels c and e will cause the water in the top of d to flow through the horizontal tube into b. The head of water f between the levels c and e is known as the circulation head.

While the pressure due to the circulation head b is very low, it is sufficient to overcome the friction of the water against the inner surface of the tubes and to cause a free flow of water into b. Weight is thus transferred from d to b, d becoming a little lighter and b a little heavier. The two columns of water no longer balance; hence, b sinks and d rises. The cool water from b passes into the base of d and absorbs the heat. The water is thus expanded, its weight is diminished, and it is crowded upward by the cooler and heavier water coming in beneath it; that is, a circulation is established.