The Shell and Tube Heat Exchanger diagram show the heat exchanger works. As illustrated in the diagram below, the heat exchanger works by burning natural gas, making a line or grid of hot gas jets that fire upward over water flowing through a network of pipes. As the water pumps through the pipes, it absorbs the heat energy and heats up. We mean this arrangement by a heat exchanger: the gas jets cool down, and the water heats up. In simpler words, the heat exchange between two objects is proportional to the difference in their temperatures. For heat loss, internal heat has to be transported from the various tissues and organs to the cooler body surface.