Devices that transfer energy between fluids at different temperatures.

Only work interaction : Flow work

(heat loss to the surroundings)

Classification Types of Heat Exchangers Transfer Process Direct contact Indirect contact Compactness Area density: ratio of the heat transfer surface area to the volume of the heat exchanger Compact heat exchangers: area density 700 m2/m3 Construction Type Tubular heat exchangers (shell-and-tube heat exchangers) Plate heat exchangers Tube-fin heat exchangers Plate-fin heat exchangers Regenerative heat exchangers (static, dynamic) Flow Arrangement Parallel-flow Counter flow Cross-flow (mixed, unmixed) Multipass flow State of Working Fluid Single-phase Multi-phase		Shell-and-Tube Heat Exchanger Automobile Radiator (Reference: F. Kreith and M. S. Bohn, Principles of Heat Transfer, 5th Ed., West Publishing Company, St. Paul, 1993.)

Flow-restricting devices (valves, porous plugs) used to reduce the pressure of a gas or a liquid. The pressure drop in the fluid is often accompanied by a significant change in temperature. The temperature change depends on the Joule-Thomson coefficient. Unlike turbines, they produce a pressure drop without involving any work.

Example of Flow-Restricting Device: Valve

Throttling Devices
Conservation of Mass
Conservation of Energy	or
Ideal Throttling Process ( )	or

The final outcome of a throttling process depends on which of the two quantities increases during the process. If the flow energy increases during the process () , it can do so at the expense of the internal energy. As a result, internal energy decreases, which is usually accompanied by a drop in temperature.

If the product pv decreases, the internal energy and the temperature of a fluid will increase. In the case of an ideal gas (h = h(T)), the temperature has to remain constant during a throttling process.

When analyzing an unsteady-flow process, it is important to keep track of the mass and energy contents of the control volume as well as the energy interactions across the boundary.

Examples for Unsteady-Flow Processes
Inflating a Tire	Filtration System of an Aquarium	Cooking with an Ordinary Cooker

Uniform-Flow Processes
1. At any instant during the process, the state of the control volume is uniform. The state of the control volume may change with time, but it will do so uniformly.
2. The fluid properties may differ from one inlet (or exit) to another, but the fluid flow at an inlet (exit) is uniform and steady. That is, the properties do not change with time or position over the cross-section of an inlet (exit).
Conservation of Mass
Conservation of Energy	When the changes in kinetic and potential energy are negligible: