Heat exchanger

Table of Contents

Properties

The heat exchanger is modelled as a volumetric energy source where the energy transfer between two fluid streams is based on an effectiveness, specified as a function of the mass flow rates.

\[ Q_t = e \left(\dot{m}_1 , \dot{m}_2 \right) \left(T_2 - T_1\right) \dot{m}_1 C_p, \]

where:

\( Q_t \) = total heat source
\( e(\dot{m}_1,\dot{m}_2) \) = effectiveness table
\( \dot{m}_1 \) = net mass flux entering heat exchanger [kg/s]
\( \dot{m}_2 \) = secondary mass flow rate [kg/s]
\( T_1 \) = primary inlet temperature [K]
\( T_2 \) = secondary inlet temperature [K]
\( C_p \) = specific heat capacity [J/kg/K]

The energy source is distributed across the cells according to:

\[ Q_c = \frac{V_c |U_c| (T_c - T_{ref})}{\sum(V_c |U_c| (T_c - T_{ref}))}, \]

where:

\( Q_c \) = energy source for cell
\( V_c \) = volume of the cell [m3]
\( U_c \) = local cell velocity [m/s]
\( T_c \) = local call temperature [K]
\( T_{ref} \) = min or max(T) in cell zone depending on the sign of \( Q_t \) [K]

Optional entries:

  • primaryInletT : sets the primary inlet temperature. If not set, the flux-averaged temperature is used
  • targetQdot : the secondary inlet temperature is derived from a target heat rejection

Usage

The option is specified using: 

heatExchanger1
{
    type            effectivenessHeatExchanger;
    selectionMode   cellZone;
    cellZone        porosity;

    secondaryMassFlowRate   1.0;
    secondaryInletT 336;
    faceZone        facesZoneInletOriented;
    outOfBounds     clamp;
    file            "effTable";

    // Optional
    // primaryInletT 293;
    // targetQdot   1500;
}

The two-dimensional effectiveness table is specified according to, e.g. for the table

mfr2,1 mfr2,2 mfr2,3
mfr1,1 A B C
mfr1,2 D E F
mfr1,3 G H I

the equivalent entry becomes: 

(
    (
        mfr1,1
        (
            (mfr2,1    A)
            (mfr2,2    B)
            (mfr2,3    C)
        )
    )
    (
        mfr1,2
        (
            (mfr2,1    D)
            (mfr2,2    E)
            (mfr2,3    F)
        )
    )
    (
        mfr1,3
        (
            (mfr2,1    G)
            (mfr2,2    H)
            (mfr2,3    I)
        )
    )
);

Further information

Tutorials

  • none

Source code

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