Sort of. A car radiator runs hot water through the radiator and air passes around it which heats the air and cools the radiator. A boiler can work two ways. It can have water in tubes (pipes) in the fire chamber so the fire heats the water in the tubes (which is then used for power or for heat) or______the fire can actually be fed into tubes (on its way to the chimney) and the water can be surrounding the tubes. So a radiator heats air with water. The water in the car radiator is heated by going around the cylinders.
Two fluids of different temperatures are brought into close contact but are prevented from mixing by a physical barrier. The temperature of the two fluids will tend to equalize. By arranging counter-current flow it is possible for the temperature at the outlet of each fluid to approach the temperature at the inlet of the other. The heat contents are simply exchanged from one fluid to the other and vice versa. No energy is added or removed. Since the heat demands of the process are not constant, and the heat content of the two fluids is not constant either, the heat exchanger must be designed for the worst case and must be controlled to make it operate at the particular rate required by the process at every moment in time. The heat exchanger itself is not constant. Its characteristic changes with time. The most common change is a reduction in the heat transfer rate due to fouling of the surfaces. Exchangers are initially oversized to allow for the fouling which gradually builds up during use until the exchanger is no longer capable of performing its duty. Once it has been cleaned it is again oversized.
