Specific Dissipation Heat Exchanger Interface (G)
The thermal interface between the gas and the environment.
blockType: EngeeFluids.HeatExchangers.SpecificDissipation.Interfaces.Gas
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Path in the library: |
Description
Block Specific Dissipation Heat Exchanger Interface (G) simulates the pressure drop and temperature change of a gas as it passes through a thermal interface, for example, through a heat exchanger. Heat transfer through the thermal interface is not taken into account. See the block diagram Heat Exchanger (G-G) for an example of combining two blocks.
The pressure drop is calculated as a function of mass flow based on tabular data set at a certain reference pressure and temperature. The calculation is based on linear interpolation if the mass flow rate falls within the limits of the tabular data, and on extrapolation to neighboring elements otherwise. In other words, adjacent data points are connected by rectilinear segments, with the segments at the boundaries of the mass flow extending horizontally outward.
Linear interpolation (left) and extrapolation by neighboring elements (right)
The calculations of the unit are based on the states and properties of temperature, density, and specific internal energy of the liquid at the entrance to the thermal interface. The input changes abruptly from one port to another when a reverse flow occurs, which leads to gaps in the values of these variables. To eliminate these gaps, the unit smooths out the corresponding variables at mass flow values below the set threshold value.
Smoothing the input temperature below the mass flow threshold
Mass balance
The mass can enter and exit the thermal interface via ports A and B. The volume of the interface is fixed, but the compressibility of the liquid means that the mass inside the interface can vary depending on pressure and temperature. The compressibility of the gas is always taken into account, and its value corresponds to the value specified in the unit settings. Gas Properties (G). The mass balance in the interface can be expressed as follows:
where
-
— the mass of the internal volume of the thermal interface fluid;
-
— internal pressure of the liquid;
-
— internal temperature of the liquid;
-
— mass flow through non-directional ports connected to gas.
Energy balance
Energy can enter and exit the thermal interface in two ways: with liquid flow through ports A and B and with heat flow through port H. The liquid inside the interface does not do any work. Therefore, the rate of energy accumulation in the internal volume of the interface fluid should be equal to the sum of the energy flows through all three ports.:
where
-
— total energy in the internal volume of the thermal interface fluid;
-
— energy flow coming through non-directional ports connected to gas;
-
— the rate of heat flow coming through a non-directional heat-related port.
Balance of impulses
The differential pressure calculation is based entirely on the tabular data you provided. The causes of the pressure drop are not considered, except for their possible effect on these data. The total pressure difference between one non-directional gas-related port and another is calculated based on the individual pressure differences between each non-directional gas-related port and the internal volume of the liquid:
where
-
— liquid pressure in non-directional ports connected to gas;
-
— pressure difference between the non-directional ports connected to the gas and the internal volume of the liquid:
where — pressure in the internal volume of the liquid.
Tabular data are provided for the reference pressure and temperature, on the basis of which the third reference parameter is calculated — the reference density. The ratio of the reference density to the actual density in the port serves as a correction factor in the individual differential pressure equations, each of which is defined as
where
-
— tabular differential pressure function;
-
— density of liquid in non-directional ports connected to gas.
The asterisk indicates a non-directional gas-related port (A or B) where a parameter or variable is defined. Lower index indicates a reference value. The density at the interface entrance is smoothed below the threshold value of the mass flow due to the introduction of a hyperbolic term :
where — smoothed density at the entrance, — non-smoothed density at the same input and — the density in the internal volume of the liquid. The hyperbolic smoothing term is defined as
where — the average value of the mass flow through non-directional ports associated with gas, and — the threshold value of the mass flow rate set in the dialog box of the block. This threshold value determines the width of the mass flow area within which the density of the liquid is smoothed. The average mass flow rate is defined as
Ports
Conserving
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A
—
fluid port
gas
Details
The port through which gas can enter and exit the thermal interface.
| Program usage name |
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B
—
fluid port
gas
Details
The port through which gas can enter and exit the thermal interface.
| Program usage name |
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H
—
thermal regime at the fluid inlet
warmth
Details
A non-directional port used to set up the thermal regime in a non-directional gas-related port.
| Program usage name |
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Output
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CP
—
isobaric specific heat of a gas, kJ/(kg·K)
scalar
Details
Isobaric specific heat capacity of a gas in the internal volume of a thermal interface liquid.
| Data types |
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| Complex numbers support |
No |
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M
—
mass gas consumption, kg/s
scalar
Details
The mass flow rate of gas in the internal volume for the interface fluid. The output signal is positive when the flow rate is directed from port A to port B, and negative otherwise.
| Data types |
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| Complex numbers support |
No |
Parameters
Pressure Loss
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Mass flow rate vector —
the mass flow rate at which it is necessary to specify the pressure drop data
kg/s | N*s/m | N/(m/s) | lbf/(ft/s) | lbf/(in/s)
Details
An array of mass flow values for which tabular pressure drop data must be specified.
| Units |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Pressure drop vector —
pressure drop data corresponding to the specified mass flow values
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar
Details
An array of pressure drop values from the inlet to the outlet corresponding to the tabular mass flow data.
| Units |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Reference inflow temperature —
the temperature at which tabular pressure drop data is set
K | degC | degF | degR | deltaK | deltadegC | deltadegF | deltadegR
Details
The temperature at which tabular pressure drop data is set.
| Units |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
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Reference inflow pressure —
the pressure at which tabular pressure drop data is set
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar
Details
The pressure at which tabular pressure drop data is set. The block uses this parameter to calculate the third reference parameter, the reference density. The reference value is used to scale the pressure drop tabular data for pressure and temperature values that differ from the nominal conditions.
| Units |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
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Mass flow rate threshold for flow reversal —
the mass flow rate below which numerical data needs to be smoothed
kg/s | N*s/m | N/(m/s) | lbf/(ft/s) | lbf/(in/s)
Details
The mass flow rate, below which there is a smooth change in the flow direction to prevent discontinuities in the simulation data.
| Units |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
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Gas volume —
the volume of gas inside the heat exchanger
l | gal | igal | m^3 | cm^3 | ft^3 | in^3 | km^3 | mi^3 | mm^3 | um^3 | yd^3 | N*m/Pa | N*m/bar | lbf*ft/psi | ft*lbf/psi
Details
The volume of gas in the heat exchanger at any given time. During the simulation, the volume remains constant.
| Units |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
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Cross-sectional area at ports A and B —
flow cross-sectional area at the gas supply ports
m^2 | cm^2 | ft^2 | in^2 | km^2 | mi^2 | mm^2 | um^2 | yd^2
Details
The cross-sectional area of the flow at the gas supply ports. Ports A and B are assumed to be the same size.
| Units |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |