[1][2][3] It is typically denoted as C, listed from empirical data experimentally determined in various reference works, and is typically stated as a comparison between a hot and a cold fluid, Ch and Cc either graphically, or as a linearized equation.
It is an important quantity in heat exchanger technology common to either heating or cooling systems and needs, and the solution of many real world problems such as the design of disparate items as different as a microprocessor and an internal combustion engine.
[4][5] While itself varying, such change must be taken into account when designing a system for overall behavior to stimuli or likely environmental conditions, and in particular the worst-case conditions encountered under the high stresses imposed near the limits of operability— for example, an air-cooled engine in a desert climate on a very hot day.
If the cool fluid has a much lower heat capacity rate, that is desirable.
In practice, a cooling fluid which has both a higher specific heat capacity and a lower heat capacity rate is desirable, accounting for the pervasiveness of water cooling solutions in technology—the polar nature of the water molecule creates some distinct sub-atomic behaviors favorable in practice.