How can you model a temperature gradient in a constant moist air volume?

I am trying to simulate a room filled with moist air. Inside the room is a heat source. To control the temperature of the room cold air is coming in at the bottom of the room and hot air ist exiting at the top of the room. For other parts of the simulation it is essential that the temperature of the exiting air is correct. Therefore the temperature gradient of the air from top to bottom needs to be simulated. However modeled with the constant volume chamber (MA) block, the temperature inside the volume is constant. This results in the air exiting the room with the mean temperature of the room and NOT with the higher temperature at the top of the room measured in the real system.

Any ideas on how to get the correct exit temperature at the top of the room?

Answer 1

[Ayush Anand]

Hi,

I understand you want to simulate the temperature gradient in a room with a heat source and airflow. For the situation you have described, the spatial temperature variation due to convection and the heat source should be considered, moving away from assuming a well-mixed, constant volume chamber. This can be achieved by dividing the room into several interconnected chambers or by using a computational fluid dynamics (CFD) approach.

Here's a simplified method using multiple chambers to simulate the temperature gradient:

1. Divide the Room into Layers: Conceptualize the room as a series of horizontal layers or zones stacked on top of each other. Each layer represents a portion of the room with its own temperature.
2. Connect the Layers: Model the interaction between layers using thermal conduction and convection blocks.
3. Model the Heat Source: Include the heat source in the appropriate layer(s), representing the actual location of the heat source within the room.
4. Inlet and Outlet Airflows: Model the cold air inlet at the bottom layer and the hot air outlet at the top layer.
5. Thermal Mass and Heat Transfer Coefficients: Assign thermal mass and heat transfer coefficients to each layer to accurately simulate the heat capacity and exchange between layers.
6. Control System: Implement a control system to regulate the temperature by adjusting the cold air inflow based on the temperature of the top layer.

You can read this example on a sample thermal model of a house for more insight: https://www.mathworks.com/help/releases/R2022b/simulink/slref/thermal-model-of-a-house.html

I hope this helps resolve your query!