LMTD

This function computes the log-mean temperature difference (LMTD) for ideal counterflow or co-current heat exchangers from inlet and outlet temperatures. LMTD is the effective driving force used in exchanger design equations.

\Delta T_{\mathrm{LMTD}}=\frac{\Delta T_1-\Delta T_2}{\ln(\Delta T_1/\Delta T_2)}

It correctly handles limiting cases where the terminal temperature differences become equal.

Excel Usage

=LMTD(Thi, Tho, Tci, Tco, counterflow)

Thi (float, required): Hot fluid inlet temperature (K).
Tho (float, required): Hot fluid outlet temperature (K).
Tci (float, required): Cold fluid inlet temperature (K).
Tco (float, required): Cold fluid outlet temperature (K).
counterflow (bool, optional, default: true): Whether the exchanger is counterflow (true) or co-current (false).

Returns (float): Log-mean temperature difference (K), or an error message if invalid.

Example 1: Counterflow temperature difference

Inputs:

Thi	Tho	Tci	Tco	counterflow
100	60	30	40.2	true

Excel formula:

=LMTD(100, 60, 30, 40.2, TRUE)

Expected output:

43.2004

Example 2: Co-current temperature difference

Inputs:

Thi	Tho	Tci	Tco	counterflow
100	60	30	40.2	false

Excel formula:

=LMTD(100, 60, 30, 40.2, FALSE)

Expected output:

39.7525

Example 3: Counterflow with equal temperature difference

Inputs:

Thi	Tho	Tci	Tco	counterflow
100	60	20	60	true

Excel formula:

=LMTD(100, 60, 20, 60, TRUE)

Expected output:

40

Example 4: Co-current with equal temperature difference

Inputs:

Thi	Tho	Tci	Tco	counterflow
100	60	20	60	false

Excel formula:

=LMTD(100, 60, 20, 60, FALSE)

Expected output:

0

Python Code

Show Code

from ht.air_cooler import LMTD as ht_LMTD

def LMTD(Thi, Tho, Tci, Tco, counterflow=True):
    """
    Compute the log-mean temperature difference for a heat exchanger.

    See: https://ht.readthedocs.io/en/latest/ht.air_cooler.html

    This example function is provided as-is without any representation of accuracy.

    Args:
        Thi (float): Hot fluid inlet temperature (K).
        Tho (float): Hot fluid outlet temperature (K).
        Tci (float): Cold fluid inlet temperature (K).
        Tco (float): Cold fluid outlet temperature (K).
        counterflow (bool, optional): Whether the exchanger is counterflow (true) or co-current (false). Default is True.

    Returns:
        float: Log-mean temperature difference (K), or an error message if invalid.
    """
    try:
        return ht_LMTD(Thi=Thi, Tho=Tho, Tci=Tci, Tco=Tco, counterflow=counterflow)
    except Exception as e:
        return f"Error: {str(e)}"

Online Calculator

Thi *

Hot fluid inlet temperature (K).

Tho *

Hot fluid outlet temperature (K).

Tci *

Cold fluid inlet temperature (K).

Tco *

Cold fluid outlet temperature (K).

counterflow

Whether the exchanger is counterflow (true) or co-current (false).