modelCavityAirflow
Model for air flow through a cavity
Information
Assumptions and limitations
The cavity model assumes that the temperature difference between both zones is constant along the zone heights and that this causes a pressure difference between the zones due to buoyancy. We assume that the pressure at the height of the center of the opening is equal in both zones. Based on this pressure difference, the mass flow rate is computed using Bernoulli, from which a heat flow rate is computed. This model deals with stratification in a very simplified way. Very large openings can lead to small time constants, which can cause problems for the time integrator. Only thermal effects are modelled: there is no mass transport of air or moisture. The influence of the cavity on the radiative heat exchange is not modelled.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Boolean | linearise | false | =true, to linearise the relation between heat flow rate and temperature difference |
| Real | CD | 0.65 | Discharge coefficient |
| Modelica.Units.SI.Length | h | 2 | Height of (rectangular) cavity in wall |
| Modelica.Units.SI.Length | w | 1 | Width of (rectangular) cavity in wall |
| Modelica.Units.SI.Acceleration | g | Modelica.Constants.g_n | Gravity, for computation of buoyancy |
| Modelica.Units.SI.Pressure | p | 101300 | Absolute pressure for computation of buoyancy |
| Modelica.Units.SI.Density | rho | p/r/T | Nominal density for computation of buoyancy mass flow rate |
| Modelica.Units.SI.SpecificHeatCapacity | c_p | 1013 | Nominal heat capacity for computation of buoyancy heat flow rate |
| Modelica.Units.SI.Temperature | T | 293 | Nominal temperature for linearising heat flow rate |
| Modelica.Units.SI.TemperatureDifference | dT | 1 | Nominal temperature difference when linearising heat flow rate |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a | port_a | Port for connections between layers | |
| Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_b | port_b | Port for connections between layers |
Revisions
-
June 5, 2018 by Filip Jorissen:
First implementation