multipass heat exchangers

• Correction Factor Chart

• Shell-and-Tube Heat exchanger

Analysis

• Crossflow Heat Exchanger Analysis

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CORRECTION FACTOR CHART

Multiple pass heat exchanger analysis is quite complicated

than single-pass ones. In doing the analysis for multi-pass

heat exchangers, correction factors for LMTD must be

inserted in the heat-transfer formula. The correction factors

are presented in chart form by Bowman, Mueller, and

Nagle and by the Tubular Exchanger Manufacturers

Association (TEMA). Such chart can be found in Heat

Transfer, 10th ed. by JP Holman on pages 534 – 536.

With the correction factor F, q will now be calculated as

follows:

q = UAF(LMTD or or Tm )

Where F = appropriate correction factor

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Correction-factor plot for exchanger with one

shell pass and two, four, or any multiple of

tube passes.

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Correction-factor plot for exchanger with one

shell pass and three, six, or any multiple of

tube passes.

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Correction-factor plot for exchanger with two

shell passes and four, eight, or any multiple

of tube passes

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Correction-factor plot for single-pass cross-

flow exchanger, both fluids unmixed

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Correction-factor plot for single-pass cross-

flow exchanger, one fluid mixed, the other

unmixed.

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EXAMPLE #1

Water at the rate of 68 kg/min is heated from

35 to 75C by an oil having a specific heat of

1.9 kJ/kg ·C. The fluids use a shell-and-

tube exchanger with the water making one

shell pass and the oil making two tube

passes. The oil enters the exchanger at

110C and leaves at 75C. The overall heat-

transfer coefficient is 320 W/m2·C.

Calculate the heat-exchanger area.

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EXAMPLE #1

Solution:

Solving for LMTD, or Tm

Solving for the parameters P and R:

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EXAMPLE #1

Solving for the parameters P and R:

Estimating the correction factor F:

F = 0.81

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EXAMPLE #1

Solving for heat transfer area:

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EXAMPLE #2

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EXAMPLE #2

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EXAMPLE #2

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EXAMPLE #3

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EXAMPLE #3

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EXAMPLE #3

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EXAMPLE #3

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EXERCISES

1. A shell-and-tube heat exchanger is used for the heating of oil from 20 to

30C; the oil flow rate is 12 kg/s (Cc = 2.2 kJ/kg · K). The heat exchanger has

one shell pass and two tube passes. Hot water (CH = 4.18 kJ/kg· K) enters the

shell at 75C and leaves the shell at 55C. The overall heat-transfer coefficient

based on the outside surface of the tubes is estimated to be 1080 W/m2·K.

Determine(a) the corrected logarithmic-mean temperature difference, and (b)

the required surface area in the exchanger.

2. A finned-tube crossflow heat exchanger with both fluids unmixed is used to

heat water (Cc = 4.2 kJ/kg· K) from 20 to 75C. The mass flow rate of the water

is 2.7 kg/s. The hot stream (CH = 1.2 kJ/kg· K) enters the heat exchanger at

280C and leaves at 120C. The overall heat-transfer coefficient is 160

W/m2·K. Determine (a) the mass flow rate of the heat stream, and (b) the

exchanger surface area.

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EXERCISES

3. A shell-and-tube heat exchanger is used to cool oil (CH = 2.2 kJ/kg· K) from

110 to 65C. The heat exchanger has two shell passes and four tube passes.

The coolant (Cc = 4.20 kJ/kg· K) enters the shell at 20C and leaves the shell

at 42C. For an overall tube-side heat-transfer coefficient of 1200 W/m2· K and

an oil flow of 11 kg/s, determine (a) the coolant mass flow rate; (b) the required

surface area in the exchanger.

4. A shell-and-tube exchanger having one shell pass and eight tube passes is

to heat kerosene from 80 to 130F. The kerosene enters at a rate of 2500 lbm/h.

Water entering at 200F and at a rate of 900 lbm/h is to flow on the shell side.

The overall heat-transfer coefficient if 260 Btu/h· ft2 ·F. Determine the

required heat-transfer area.

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EXERCISES

5. A shell-and-tube heat exchanger operates with two shell passes and four

tube passes. The shell fluid is ethylene glycol, which enters at 140C and

leaves at 80C with a flow rate of 4500 kg/h. Water flows in the tubes, entering

at 35C and leaving at 85C. The overall heat-transfer coefficient for this

arrangement is 850 W/m2·C. Calculate the flow rate of water required and the

area of the heat exchanger.

6. The flow rate of glycol to the exchanger in Problem 5 is reduced in half with

the entrance temperatures of both fluids remaining the same. What is the water

exit temperature under these new conditions, and by how much is the heat-

transfer rate reduced?

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