6.1. HEAT domain¶

6.1.1. Core quantities¶

In the heat domain the following core quantities are used:

Total pressure \(p_t\) [N/m²]
mass flow rate \(\dot{m}\) [kg/s]
Specific internal energy \(u\) [J/kg]

The total pressure (\(p_t\)) is defined as:

(6.1.1)¶\[p_{t} = \rho gh + \frac{\rho v^{2}}{2}\]

and the mass flow rate (\(\dot{m}\)) is defined as:

(6.1.2)¶\[\dot{m} = \rho Av\]

The specific internal energy is a function of the temperature, \(T\):

(6.1.3)¶\[u = u(T)\]

It is used to calculate the amount of energy needed to raise the temperature of the fluid to another temperature. The amount of energy needed is the difference between the specific internal energy at the given temperatures:

(6.1.4)¶\[\Delta u = c_p \Delta T\]

The following symbols are used:

Variable	Description	Units
p	The manometric (or piezometric) pressure	N/m²
\(\dot{m}\)	mass flow	kg/s
\(\rho\)	density	kg/m³
g	gravitational acceleration	m/s²
h	pressure head	m
v	velocity	m/s
A	cross sectional area	m²
u	specific internal energy	J/kg
\(T\)	temperature	K
\(c_p\)	specific heat at constant pressure	J/kg K

The pressure (p)_, discharge (Q), (energy) head (H) and temperature are derived from the above given core quantities. These core quantities are calculated as:

(6.1.5)¶\[p = p_{t} + \frac{\rho v^{2}}{2}\]

(6.1.6)¶\[Q = v A\]

(6.1.7)¶\[H = z + \frac{p}{\text{ρg}} + \frac{v^{2}}{2g}\]

with:

Variable	Description	Units
p_t	total pressure	N/m²
Q	discharge (volume flow)	m³/s
H	energy head	m
z	elevation	m

The temperature \(T\) in the user interface is displayed in degree Celsius. This is the only unit that can be chosen for temperature due to limitations in the unit system. Controls using temperature should also use degree Celsius.

6.1.2. Fluid properties¶

In Wanda Heat the properties of the fluid depend on the temperature. Therefore, a table with “Temperature dependent fluid properties” needs to be defined before starting any simulation (see Fig. 6.1.1). This table can be found in the “Fluid window” under the “Model” menu.

../_images/image1065.png — Fig. 6.1.1 Example of a fluid window.¶

Fluid window

The following properties depend on the actual temperature:

Density [kg/m³]
Kinematic viscosity [m²/s]
Vapour pressure [bar.a]
Specific heat [J/kg/K]
Thermal conductivity coefficient [W/mK]

The above properties of the fluid have to be specified within the computational range (the range of temperatures Wanda encounters during the computation). An error will be displayed if Wanda computes a temperature anywhere outside this range at any time (‘Temperature outside table range’).

It should be noted that Wanda linearly interpolates between the temperatures at which the values are specified in the table. An erroneous solution may result if the fluid properties do not vary linearly over the table rows (i.e., to few table rows are defined to capture the variation in fluid properties).

../_images/image1066.png — Fig. 6.1.2 Fluid table example¶

The fluid window contains also the property fields “Density”, “Vapour pressure” and “Kinematic viscosity”. These are ignored by WANDA Heat.

By default the fluid property table for water is loaded (stored in program directory Wanda4Property TemplatesExamplesFluids). The user might build a database of fluid properties to be loaded / saved in the fluid window. Fluid property template files can be loaded into the fluid properties window by clicking on the ‘open property template file’ button or pressing ‘Ctrl + o’ in the fluid window. In a similar way the user might save (key: ‘Ctrl + S’) fluid property templates.

6.1.3. Overview of Heat Components¶

The Heat components listed below are currently available in wanda. Your license specifies if you are authorised to use them.

Table 6.1.1 Table with an overview of the heat components.¶
Type	Symbol	Short description
Heat air vessel		Vertically positioned, prismatic (constant area), nonvented air vessel
Heat boundary: Heat BoundPT		Pressure temperature boundary condition
Heat boundary: Heat BoundMT		Mass flow temperature boundary condition
Heat boundary: Heat BoundT(PM)		Temperature pressure or mass flow boundary condition
Check valve / Non-return valve		Ideal check valve; closes if \(Q < 0\), and opens if \(p_1 - p_2 > \Delta p_{reopen}\)
Heat exchanger: Heat supply QHeat in		Supply heat to or extract heat from the fluid by directly specifying a heat input.
Heat exchanger: Heat supply Tdown		Supply heat to or extract heat from the fluid by specifying a temperature at downstream Heat node.
Heat exchanger: Heat supply QHeat with limits on T		Supply heat to or extract heat from the fluid by directly specifying a heat input, with user specified limits for the minimum and maximum temperatures
Heat exchanger: Heat exchanger		Exchange heat with surroundings due to temperature difference between fluid and ambient temperature
Heat exchanger: Heat demand		Heat demand for district heating systems with different input parameters for heating and warmp (tap) water
Pipe		Heat pipe including friction model, friction generated heat and heat transfer to or from the surroundings.
Pump		Complete pump model with various data and drives; positive and negative speed.
Surge tower		Surge tower with storage area independent of liquid level.
Heat resist		Surge tower with storage area independent of liquid level.
Valve		Control or block valve with choice out of four predefined Deltares standard head loss characteristics or user characteristics (Cv Kv, Xi).
Converters		Converter to enable the connection of liquid component to heat components
4-Way Heat exchanger		Exchange heat with surroundings due to temperature difference between fluid and ambient temperature.
4-Way Heat exchanger		Exchange heat with surroundings due to temperature difference between fluid and ambient temperature.
Gas boiler		Supply heat to the fluid by gas combustion
Solar collector		Heat supply via a solar collector

6.1.4. Component properties¶

All input and output properties are displayed in the property window (selection property window: Shift-F11). The property window can be divided in 5 parts:

Table 6.1.2 Different parts of the property window with their respective properties.¶
Part of property window	Properties
General input data	Name, comment, keywords etc
Component specific input data	Type dependent
Action table	Type dependent for active types only (actions)
General output data	Messages, default HEAT output variables
Component specific output data	Type dependent (including pressure loss, temperature loss, mass)

The default HEAT output variables (for each connect point) are: discharge, energy head, pressure, velocity, density, temperature and mass flow rate.

The visibility of some properties can be managed using the checkboxes in the upper part of the Mode & Options window in the “Model” menu.

The properties are type dependent. They are described for each component type separately. Some details about the action table are described below.

6.1.5. Hydraulic and thermal action tables¶

Hydraulic or thermal transients in a pipeline system are caused by changes in the flow conditions or thermal boundary conditions. These changes are initiated by manoeuvring Heat components in the system, called actions. Not all components in a pipeline system can be activated. A component is categorised as either an active or a passive component, depending on its manoeuvrability.

An action is described using a control parameter specified as a function of time. The control parameter depends on the component type. In WANDA, a control parameter function is specified through an action table in the properties of the component or by connecting a control system, see WANDA Control. The control system overrules the component specific action table.