Design Procedure
DOI 10.1615/hedhme.a.000268
3.4.9 Design procedure
A. C. Mueller
A. Overall design procedure
All calculations start with an assumed design, which is then rated to determine its capacity. Suitable modifications are made to the assumed design in order to approach the required capacity and the final design. To obtain the assumed design, follow these steps:
- Determine suitable types of condensers. See Chart 1 and Chart 2 in Section 261.
- Determine the heat load.
- Select the coolant temperatures and calculate an overall logarithmic mean temperature difference.
- Estimate an overall coefficient from Table 1 or by prior experience using estimated individual coefficients.
- Calculate the area.
- Select a tube size, pitch, and length and determine the number of tubes, shell size, and baffling, if required.
- Steps 1 to 6 result in a guessed design. Three options are now available:
- (a) Go to a computer program and rate. A number of trials may be required to obtain a final design.
- (b) Make a preliminary hand calculation design by use of the approximate average condensing coefficient equations.
- (c) After step 7(b), proceed to use the stepwise calculations and equations or go to the computer programs for final checking. After doing step 7(b), the number of trials on the computer should be substantially less than in 7(a).
Table 1 Overall coefficients for estimating condensers
| a Based on 50-mm tubes with 16–18-mm-high aluminum fins with spacing of 2.5–3 mm. Coefficients are based on tube area. | ||
| Vapor | Coolant | U, W/m2 K |
|---|---|---|
| Alcohol | Water | 550–1,100 |
| Dowtherm | Tall oil | 340–450 |
| Dowtherm | Dowtherm | 450–680 |
| High-boiling hydrocarbons under vacuum | Water | 100–280 |
| Low-boiling hydrocarbons | Water | 450–1,140 |
| Hydrocarbons | Oil | 140–230 |
| Organic solvents | Water | 550–1,140 |
| Kerosene | Water | 170–370 |
| Kerosene | Oil | 110–170 |
| Naphtha | Water | 280–430 |
| Naphtha | Oil | 110–170 |
| Steam | Feed water | 2,200–5,700 |
| Vegetable oils | Water | 110–280 |
| Organic-steam, azeotrope | Water | 220–450 |
| Air coolers a | ||
| Steam | Air | 730–800 |
| Ammonia | Air | 550–680 |
| Light hydrocarbons | Air | 450–540 |
| Light naphtha | Air | 400–450 |
| Freons | Air | 340–450 |
| Heavy naphtha | Air | 340–400 |
Note that condensers can be designed to perform the required duty that have unacceptable physical dimensions, for example, very short but large-diameter shells. Thus condenser design involves not only duty performance but also an economic consideration and suitable physical arrangements for plant installations. Thus, there is no one correct design.
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