modelPipeFreeConvection
Extends from Modelica.Thermal.HeatTransfer.Interfaces.Element1D (Partial heat transfer element with two HeatPort connectors that does not store energy).
Information
The magnitude of convective heat from the heating pipes to the air depends on the pipe position, which implies a free exchange (i.e. pipes in free air) or a hindered exchange (i.e. pipes situated close to the canopy and near the floor). In free convection, the Nusselt (Nu) number describing the exchange process can be defined as a function of the Rayleigh (Ra) number [1]. Therefore, the free exchange is modeled based on the Nu-Ra relation. The hindered exchange, considered to be forced, is modeled by experimental correlations derived by [2]. The user should indicate which exchange is modeled by means of the Boolean parameter 'freePipe'. The diameter of the pipes and the installed pipe length per ground area are also parameters, required to compute the heat exchange coefficient.
[1] Luc Balemans. Assessment of criteria for energetic effectiveness of greenhouse screens. PhD thesis, Agricultural University, Ghent, 1989.
[2] G.P.A Bot. Greenhouse climate : from physical processes to a dynamic model. PhD thesis, Wageningen University, 1983.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Units.SI.Area | A | floor surface | |
| Modelica.Units.SI.Length | d | characteristic dimension of the pipe (pipe diameter) | |
| Modelica.Units.SI.Length | l | length of heating pipes per m^2 floor surface | |
| Boolean | freePipe | true | true if pipe in free air, false if hindered pipe |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| HeatPort_a | port_a (from Element1D) | ||
| HeatPort_b | port_b (from Element1D) |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| SI.HeatFlowRate | Q_flow (from Element1D) | Heat flow rate from port_a -> port_b | |
| SI.TemperatureDifference | dT (from Element1D) | port_a.T - port_b.T | |
| Modelica.Units.SI.CoefficientOfHeatTransfer | HEC_ab | ||
| Real | alpha |