Design and rating methods for heat exchangers.
LMTD: ΔT_lm=(ΔT₁-ΔT₂)/ln(ΔT₁/ΔT₂) when inlet and outlet temperatures known. ε-NTU method uses NTU=UA/C_min and effectiveness ε=Q/Q_max when outlet temperatures unknown. Correction factors F for multi-pass and cross-flow.
A counterflow exchanger with NTU=3 has effectiveness about 0.95 at C_r=1.
The LMTD and NTU methods are the standard design and rating tools for heat exchangers, so they determine the size of any exchanger.
Design and rating methods for heat exchangers.
The LMTD and NTU methods are the standard design and rating tools for heat exchangers, so they determine the size of any exchanger.
The log mean temperature difference, a driving force averaged along the exchanger that is used with the overall heat transfer coefficient.
When outlet temperatures are unknown, as in rating problems, because effectiveness can be found from NTU and the capacity ratio.
Typical applications include sizing the area of an exchanger for a required heat duty, rating an existing exchanger to see if it will meet a new process condition and checking whether an exchanger with a given area will reach a target outlet temperature.
Study "Heat exchangers" first (topic 93 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
Counterflow maximises ΔT_lm. C_r=C_min/C_max. Charts or formulas.
A counterflow exchanger with NTU=3 has effectiveness about 0.95 at C_r=1.
The next topic is "Boiling and condensation", which builds directly on this one.
It is classed as Advanced in Thermodynamics & Fluids (topic 94 of 105). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Thermodynamics & Fluids.
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