HEAT EXCHANGER

Topics: Heat exchanger, Heat transfer, HVAC Pages: 16 (5023 words) Published: January 5, 2015
heat exchanger is a device built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact.[1] They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, natural gas processing, and sewage treatment. One common example of a heat exchanger is the radiator in a car, in which the heat source, being a hot engine-cooling fluid, water, transfers heat to air flowing through the radiator (i.e. the heat transfer medium). Contents

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1 Flow arrangement
2 Types of heat exchangers
2.1 Shell and tube heat exchanger
2.2 Plate heat exchanger
2.3 Adiabatic wheel heat exchanger
2.4 Plate fin heat exchanger
2.5 Fluid heat exchangers
2.6 Waste heat recovery units
2.7 Dynamic scraped surface heat exchanger
2.8 Phase-change heat exchangers
3 Direct contact heat exchangers
4 HVAC air coils
5 Spiral heat exchangers
5.1 Construction
5.2 Self cleaning
5.3 Flow Arrangements
5.4 Applications
6 Selection
7 Monitoring and maintenance
7.1 Fouling
7.2 Maintenance
8 In nature
8.1 Humans
8.2 Birds, fish, whales
9 In industry
10 In aircraft
11 A model of a simple heat exchanger
12 See also
13 References
14 External links
[edit] Flow arrangement
Countercurrent (A) and parallel (B) flows
Fig. 1: Shell and tube heat exchanger, single pass (1-1 parallel flow) Fig. 2: Shell and tube heat exchanger, 2-pass tube side (1-2 crossflow) Fig. 3: Shell and tube heat exchanger, 2-pass shell side, 2-pass tube side (2-2 countercurrent) There are two primary classifications of heat exchangers according to their flow arrangement. In parallel-flow heat exchangers, the two fluids enter the exchanger at the same end, and travel in parallel to one another to the other side. In counter-flow heat exchangers the fluids enter the exchanger from opposite ends. The counter current design is most efficient, in that it can transfer the most heat from the heat (transfer) medium. See countercurrent exchange. In a cross-flow heat exchanger, the fluids travel roughly perpendicular to one another through the exchanger. For efficiency, heat exchangers are designed to maximize the surface area of the wall between the two fluids, while minimizing resistance to fluid flow through the exchanger. The exchanger's performance can also be affected by the addition of fins or corrugations in one or both directions, which increase surface area and may channel fluid flow or induce turbulence. The driving temperature across the heat transfer surface varies with position, but an appropriate mean temperature can be defined. In most simple systems this is the "log mean temperature difference" (LMTD). Sometimes direct knowledge of the LMTD is not available and the NTU method is used. [edit] Types of heat exchangers

[edit] Shell and tube heat exchanger
A Shell and Tube heat exchanger
Main article: Shell and tube heat exchanger
Shell and tube heat exchangers consist of a series of tubes. One set of these tubes contains the fluid that must be either heated or cooled. The second fluid runs over the tubes that are being heated or cooled so that it can either provide the heat or absorb the heat required. A set of tubes is called the tube bundle and can be made up of several types of tubes: plain, longitudinally finned, etc. Shell and Tube heat exchangers are typically used for high pressure applications (with pressures greater than 30 bar and temperatures greater than 260°C).[2] This is because the shell and tube heat exchangers are robust due to their shape. There are several thermal design features that are to be taken into account when designing the tubes in the shell and tube heat exchangers. These include: Tube diameter: Using a small tube diameter makes the heat exchanger both economical and compact. However, it is more likely for the heat exchanger to...
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