Materials selection and compatibility between construction materials and working fluids are important issues, in particular with regard to corrosion and/or operation at elevated temperatures.
Requirement for low cost, light weight, high conductivity, and good joining characteristics often leads to the selection of aluminum for the heat transfer surface.
On the other side, stainless steel is used for food processing or fluids that require corrosion resistance.
In general, one of the selection criteria for exchanger material depends on the corrosiveness of the working fluid.
A summary Table is provided as a reference fo rcorrosive and noncorrosive environments
Tube wall thickness
- The wall thickness of heat exchanger tubes is standardized in terms of Birmingham Wire Gage BWG of the tube.
- Small tube diameters (8 to 15mm) are preferred for greater area to volume density but are limited for the purposes of cleaning.
- Large tube diameters are often required for condensers and boilers.
Tube length affects the cost and operation of heat exchangers.
- Longer the tube length (for any given surface area),
- Fewer tubes are needed, requiring less complicated header plate with fewer holes drilled
- Shell diameter decreases resulting in lower cost
Typically tubes are employed in 8, 12, 15, and 20 foot lengths. Mechanical cleaning is limited to tubes 20 ft and shorter, although standard exchangers can be built with tubes up to 40 ft.
There are, like with anything limits of how long the tubes can be.
- Shell-diameter-to-tube-length ratio should be within limits of 1/5 to 1/15
Maximum tube length is dictated by
- Architectural layouts
- Transportation (to about 30m.)
No comments:
Post a Comment