What is Heat Exchanger?
A heat exchanger is a device designed to transfer heat between two or more fluids without allowing them to mix. The fluids can be liquids, gases, or a combination of both. They are separated by a solid wall (to prevent mixing) which allows thermal energy to pass from the hotter fluid to the colder one.
Think of it as a “heat bridge” between two separate streams.
The Analogy: A Car Radiator
The most common everyday example is a car radiator.
- Hot Fluid: Engine coolant that has absorbed heat from the engine.
- Cold Fluid: Ambient air being forced through the radiator fins by a fan and the car’s motion.
- Process: The hot coolant flows through tubes. The cooler air passes over the outside of these tubes (and thin fins attached to them). Heat transfers from the coolant to the air, cooling the engine and heating the passing air.
How Does It Work? The Basic Principle
Heat exchangers operate on the fundamental principles of thermodynamics, specifically the Second Law: heat always flows from a hotter object to a colder object.
The rate of heat transfer is influenced by:
- Temperature Difference (ΔT): A larger difference means faster heat transfer.
- Surface Area (A): More surface area between the fluids allows for more heat to be transferred. This is why heat exchangers often have fins or complex internal structures.
- Heat Transfer Coefficient (U): A property that represents how well the materials and fluids involved conduct heat.
The basic heat transfer equation is: Q = U × A × ΔT
Where Q is the rate of heat transfer.