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Design Procedure

DOI 10.1615/hedhme.a.000268

3.4.9 Design procedure

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:

  1. Determine suitable types of condensers. See Chart 1 and Chart 2 in Section 261.
  2. Determine the heat load.
  3. Select the coolant temperatures and calculate an overall logarithmic mean temperature difference.
  4. Estimate an overall coefficient from Table 1 or by prior experience using estimated individual coefficients.
  5. Calculate the area.
  6. Select a tube size, pitch, and length and determine the number of tubes, shell size, and baffling, if required.
  7. 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 1618-mm-high aluminum fins with spacing of 2.53 mm. Coefficients are based on tube area.
VaporCoolantU, W/m2 K
AlcoholWater550–1,100
DowthermTall oil340–450
DowthermDowtherm450–680
High-boiling hydrocarbons under vacuumWater100–280
Low-boiling hydrocarbonsWater450–1,140
HydrocarbonsOil140–230
Organic solventsWater550–1,140
KeroseneWater170–370
KeroseneOil110–170
NaphthaWater280–430
NaphthaOil110–170
SteamFeed water2,200–5,700
Vegetable oilsWater110–280
Organic-steam, azeotropeWater220–450
Air coolersa
SteamAir730–800
AmmoniaAir550–680
Light hydrocarbonsAir450–540
Light naphthaAir400–450
FreonsAir340–450
Heavy naphthaAir340–400

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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