The primary function of a heat exchanger is to:

The primary function of a heat exchanger is indeed to heat or cool one fluid by means of another fluid. Heat exchangers operate on the principle of transferring thermal energy between two fluids at different temperatures without them mixing. This dual functionality of either heating or cooling makes them essential in various applications, such as in HVAC systems, engine cooling, and industrial processes.

When one fluid is heated, it transfers its thermal energy to the colder fluid, thereby increasing the temperature of the latter. Conversely, if the primary goal is to cool one fluid, it absorbs heat from the warmer fluid. This versatile operation is crucial in systems that require precise temperature control for efficiency and safety.

Other options, while related to heat exchangers, do not capture the full range of their capabilities. For instance, focusing solely on one fluid's temperature increase misses the broader application of transferring heat efficiently between two different fluids. Similarly, the mention of cooling one fluid by means of another, while true, limits the function to just cooling rather than also acknowledging the heating aspect. The stabilization of pressure in the system is a function that may arise indirectly from the operation of heat exchangers, but it is not their primary purpose. Therefore, the comprehensive functionality described in the correct answer clearly aligns with the operational