Engee documentation

Local Resistance (TL)

Hydraulic resistance in a pipe in a thermal liquid network.

local resistance tl

Description

Block Local Resistance (TL) simulates the pressure losses associated with the user-defined pipe resistance in a thermal liquid network. In the block it is possible to set different values of loss coefficients for forward and return flows through the pipe section.

The loss coefficient can be set as a constant value determined by the pressure in the pipe, or it can be obtained from a custom table of loss coefficients and their corresponding Reynolds numbers.

Constant loss factor

The drag coefficients of the sections where they can be considered constant over a given velocity range are calculated as:

where

  • and - values of parameters Forward flow loss coefficient (from A to B) и Reverse flow loss coefficient (from B to A) respectively;

  • - pressure drop .

The critical pressure drop is the pressure difference determined by the critical Reynolds number Critical Reynolds number, , which is the transition point between laminar and turbulent flow regimes:

ρν

where

  • - loss coefficient determined by the critical pressure and based on the average value of loss coefficients in the forward and reverse directions;

  • ν - kinematic viscosity of the fluid;

  • ρ - average density of the fluid;

  • - hydraulic diameter of the section, which is the equivalent diameter of a pipe with a non-circular cross-section: π , where is the value of the parameters Flow area.

Tabular method of parameterization

The loss factor can be determined using user provided Reynolds number and loss factor data. The vector of Reynolds numbers can have both positive and negative values, indicating forward and reverse flow respectively:

Law of conservation of mass

The law of conservation of mass is fulfilled for a section of pipe,

.

The mass flow rate through the pipe section is calculated as:

ρ ,

where is the flow loss coefficient, which is chosen between the values of parameters Forward flow loss coefficient (from A to B) и Reverse flow loss coefficient (from B to A) depending on the flow direction in the block.

Energy conservation

The unit provides energy conservation as follows:

where

  • - is the energy flow at port A;

  • - is the energy flow at port B.

Ports

Conserving

# A — thermal liquid port
thermal liquid

Details

Port of isothermal liquid, corresponds to the inlet or outlet of liquid from a section of pipe. When the flow direction is positive, the liquid flows from port A to port B.

Program usage name

port_a

# B — thermal liquid port
thermal liquid

Details

Port of isothermal liquid, corresponds to the inlet or outlet of liquid from a section of pipe. When the flow direction is positive, the liquid flows from port A to port B.

Program usage name

port_b

Parameters

Main

# Local loss parameterization — method for calculating hydraulic losses
Constant | Tabulated data - loss coefficient vs. Reynolds number

Details

Method for calculating the loss coefficient in a pipe section.

The loss factor can be set as a constant value determined by the pressure in the pipe, or it can be obtained from a custom table of loss factors and their corresponding Reynolds numbers.

Values

Constant | Tabulated data - loss coefficient vs. Reynolds number
Default value

Constant
Program usage name

resistance_loss_model
Evaluatable

No

# Forward flow loss coefficient (from A to B) — loss factor for flow from A to B

Details

Loss factor associated with pressure loss for flows from port A to port B.

Default value

1.0
Program usage name

loss_coefficient_a_b
Evaluatable

Yes

# Reverse flow loss coefficient (from B to A) — loss factor for flow from B to A

Details

Loss factor due to pressure loss for flows from port B to port A.

Default value

1.0
Program usage name

loss_coefficient_b_a
Evaluatable

Yes

# Reynolds number vector — vector of Reynolds number values in the case of the tabular parameterization method

Details

Vector of Reynolds number values for tabular parameterization of the loss factor. The vector must correspond element by element to the vector Loss coefficient vector. The elements in the vector are given in ascending order.

Dependencies

To use this parameter, set the parameters to Tabulated data - loss coefficient vs. Local loss parameterization value `Tabulated data - loss coefficient vs. Reynolds number.

Default value

[-500.0, -200.0, -100.0, -50.0, -40.0, -30.0, -20.0, -10.0, 10.0, 20.0, 30.0, 40.0, 50.0, 100.0, 200.0, 500.0, 1000.0, 2000.0]
Program usage name

Re_vector
Evaluatable

Yes

# Loss coefficient vector — loss factor vector

Details

Vector 1 on loss factor vector for tabular parameterization of the loss factor, where is the length of the vector of Reynolds number values. The elements of the vector must be greater than 0.

Dependencies

To use this parameter, set the parameters to Local loss parameterization value Tabulated data - loss coefficient vs. Reynolds number.

Default value

[0.65, 0.75, 0.90, 1.15, 1.35, 1.65, 2.3, 3.10, 4.0, 2.70, 1.80, 1.46, 1.30, 0.90, 0.65, 0.42, 0.30, 0.20]
Program usage name

loss_coefficient_vector
Evaluatable

Yes

# Flow area — sectional area
m^2 | cm^2 | ft^2 | in^2 | km^2 | mi^2 | mm^2 | um^2 | yd^2

Details

Cross-sectional area of the pipe section.

Values

m^2 | cm^2 | ft^2 | in^2 | km^2 | mi^2 | mm^2 | um^2 | yd^2
Default value

1e-3 m^2
Program usage name

flow_area
Evaluatable

Yes

# Critical Reynolds number — upper limit of Reynolds number for laminar flow

Details

Upper limit of Reynolds number for laminar flow regime.

Default value

150.0
Program usage name

Re_critical
Evaluatable

Yes