Temp Efficiency Hand Out

Is My Design OK? Temperature Efficiency in Design Webinar

©Heat Transfer Research, Inc. All rights reserved Confidential: For Member use only.

Baseline Case (Slide 5) Modified Case – Obtain WMTD (Slide 17)



Thermally Unmixed Shellside Flow (Slide 27) Partial Thermally Unmixed Flow (Slide 29)



Unbalanced Pass Example – Three Tubepasses (Slide 32) Unbalanced Pass Example – Moved Pass Lane (Slide 34)



Using Xist to Obtain WMTD

1 Record the EMTD for the original design

2 Make the following adjustments to the Geometry in Xist

Select Rating mode

Use the Flow rates and terminal temperatures from the case you are updating

Change the Shell Geometry to TEMA type BEM

Change the number of Tubepasses to 1

Ensure the Flow Direction is specified as Countercurrent

Select Rod for the baffle Type

3 Run the case. The EMTD on the output summary is the value for WMTD.

4 Calculate the temperature profile efficiency for the existing design. (This value will be between 0 and 1.) E = EMTD / WMTD = 8.6/19.3 = 0.45

Rules of Thumb

E > 0.80 is acceptable, E < 0.70 requires investigation

Options for improving E without changing the process 1. Heat Exchanger Shells – Flow Geometry/Shell Pass 2. Baffle Geometry – Thermally Unmixed Flow 3. Bundle Pass Geometry – Unbalanced Passes

Comparison of E - Examples



Nomenclature

Variable Description SI Units

AMTD Arithmetic mean temperature difference °C

CMTD Corrected mean temperature difference °C

E Temperature profile efficiency —

EMTD Effective mean temperature difference °C

F MTD correction factor (Ratio of the true mean temperature difference) —

i Increment —

LMTD Log mean temperature difference °C

LMTDi Log mean temperature difference for increment i °C

MTD Mean temperature difference °C

n Number of increments —

Q Heat duty W

Qi Heat duty for increment i W

Qtotal Total calculated duty W

Tin Inlet temperature – hot stream °C

tin Inlet temperature – cold stream °C

Tout Outlet temperature – hot stream °C

tout Outlet temperature – cold stream °C

Uop Operating heat transfer coefficient W/m2 K

WMTD Weighted mean temperature difference °C

Temp Efficiency Hand Out

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Transcript of Temp Efficiency Hand Out