Local Resistance (MA)
Resistance in the pipe in the humid air network.
blockType: EngeeFluids.MoistAir.Fittings.LocalResistance
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Path in the library: |
Description
Block Local Resistance (MA) simulates pressure losses related to the resistance of a pipe, which is set by the user, in a humid air network. In the block, you can set different loss coefficients for forward and reverse flows through the pipe section.
The loss coefficient can be set to a constant value determined by the pressure in the pipe, or it can be found from the user table of loss coefficients and the corresponding Reynolds numbers.
Constant loss ratio
If for the parameter Local loss parameterization the value is set Constant, then the resistance coefficients of the sections can be considered constant in a given speed range. The loss coefficient is calculated as follows:
where
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and — parameter values Forward flow loss coefficient (from A to B) and Reverse flow loss coefficient (from B to A) accordingly;
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— pressure drop.
Critical pressure drop — this is the pressure difference determined by the critical Reynolds number , which is a transition point between laminar and turbulent flow modes:
where
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— the loss coefficient determined by the critical pressure and based on the average value of the loss coefficients in the forward and reverse directions;
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— kinematic viscosity of the liquid;
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— the average density of the liquid;
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— the hydraulic diameter of the section, which is the equivalent diameter of a pipe with a non-circular section: , where — parameter value Flow area.
Tabular parameterization method
If for the parameter Local loss parameterization the value is set Tabulated data - loss coefficient vs. Reynolds number The loss coefficient can be determined by interpolating the Reynolds number and loss coefficient data. The vector of Reynolds numbers can have both positive and negative values, which indicates a forward and reverse flow, respectively.:
Conservation of mass
The law of conservation of mass is fulfilled for the pipe section:
where
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and — the mass flow rate of the mixture in ports A and B, respectively;
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and — the mass flow rate of water vapor in ports A and B, respectively;
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and — the mass flow rate of impurity gases in ports A and B, respectively;
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and — the mass flow rate of water droplets in ports A and B, respectively.
The mass flow rate through the pipe section is
where — the coefficient of flow loss.
Ports
Conserving
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B
—
humid air port
humid air
Details
A non-directional port connected to the inlet or outlet of humid air from a pipe section. When the flow direction is positive, moist air flows from port A to port B.
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A
—
humid air port
humid air
Details
A non-directional port connected to the inlet or outlet of humid air from a pipe section. When the flow direction is positive, moist air flows from port A to port B.
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Parameters
Main
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Flow area —
the cross-sectional area of the site
m^2 | um^2 | mm^2 | cm^2 | km^2 | in^2 | ft^2 | yd^2 | mi^2 | ha | ac
Details
The cross-sectional area of the pipe section.
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| Default value |
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| Evaluatable |
Yes |
# Forward flow loss coefficient (from A to B) — loss factor for flow from A to B
Details
The loss coefficient related to pressure loss for flows from port A to port B.
Dependencies
To use this parameter, set for the parameter Local loss parameterization meaning Constant.
| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Local loss parameterization —
the method of calculating the loss coefficient
Constant | Tabulated data - loss coefficient vs. Reynolds number
Details
A method for calculating the loss coefficient in a pipe section. The loss coefficient can be set to a constant value determined by the pressure in the pipe, or it can be determined from a custom table of loss coefficients and their corresponding Reynolds numbers.
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| Default value |
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| Evaluatable |
No |
# Loss coefficient vector — vector of loss coefficients
Details
Vector of loss coefficients for tabular parameterization of the loss coefficient. The elements of the vector must correspond exactly to the elements of the parameter. Reynolds number vector. The elements of the vector must be larger 0.
Dependencies
To use this parameter, set for the parameter Local loss parameterization meaning Tabulated data - loss coefficient vs. Reynolds number.
| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
# Reverse flow loss coefficient (from B to A) — loss factor for flow from B to A
Details
The loss coefficient related to pressure loss for flows from port B to port A.
Dependencies
To use this parameter, set for the parameter Local loss parameterization meaning Constant.
| Default value |
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| Evaluatable |
Yes |
# Reynolds number vector — a vector of Reynolds number values
Details
A vector of Reynolds numbers for tabular parameterization of the loss coefficient. The elements of the vector must correspond exactly to the elements of the parameter. Loss coefficient vector. The elements of the vector must be set in ascending order.
Dependencies
To use this parameter, set for the parameter Local loss parameterization meaning Tabulated data - loss coefficient vs. Reynolds number.
| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
# Laminar flow pressure ratio — the pressure ratio at which the flow transitions between laminar and turbulent modes
Details
The ratio of outlet pressure to inlet pressure at which the flow transitions between laminar and turbulent flow modes.
| Default value |
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| Program usage name |
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| Evaluatable |
Yes |