Convective Heat Transfer

Heat transfer by convection

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Libraries:
Simscape / Foundation Library / Thermal / Thermal Elements

Description

The Convective Heat Transfer block represents heat transfer by convection between two bodies by means of fluid motion. The Newton law of cooling describes the transfer,

$$Q=k\cdot A\cdot (T_A-T_B),$$

where:

• Q is the heat flow.

• k is the convection heat transfer coefficient.

• A is the surface area.

• T_A and T_B are the temperatures of the two bodies.

The heat transfer coefficient, k, can be either constant, which you specify by using the Heat transfer coefficient parameter, or variable, which you specify by using the physical signal at port K.

A and B are thermal conserving ports associated with the points between which the heat transfer by convection takes place. Because the block positive direction is from port A to port B, the heat flow is positive if it flows from A to B.

Variables

To set the priority and initial target values for the block variables prior to simulation, use the Initial Targets section in the block dialog box or Property Inspector. For more information, see Set Priority and Initial Target for Block Variables.

Nominal values provide a way to specify the expected magnitude of a variable in a model. Using system scaling based on nominal values increases the simulation robustness. Nominal values can come from different sources, one of which is the Nominal Values section in the block dialog box or Property Inspector. For more information, see Modify Nominal Values for a Block Variable.

Examples

House Heating System

Model a simple house heating system. The model contains a heater, thermostat, and a house structure with four parts: inside air, house walls, windows, and roof.

• Open Model

Lithium-Ion Battery Pack with Fault

Simulate a battery pack consisting of multiple series-connected cells in an efficient manner. It also shows how a fault can be introduced into one of the cells to see the impact on battery performance and cell temperatures. For efficiency, identical series-connected cells are not just simply modeled by connecting cell models in series. Instead a single cell is used, and the terminal voltage scaled up by the number of cells. The fault is represented by changing the parameters for the Cell 10 Fault subsystem, reducing both capacity and open-circuit voltage, and increasing the resistance values.

• Open Model

Two-Phase Fluid Refrigeration

Models a vapor-compression refrigeration cycle using two-phase fluid components. The compressor drives the R-134a refrigerant through a condenser, an expansion valve, and an evaporator. The hot gas leaving the compressor condenses in the condenser via heat transfer to the environment. The pressure drops as the refrigerant passes through the expansion valve. The drop in pressure lowers the saturation temperature of the refrigerant. This enables it to boil in the evaporator as it absorbs heat from the refrigerator compartment. The refrigerant then returns to the compressor to repeat the cycle. The controller turns the compressor on and off to maintain the refrigerator compartment temperature within a band around the desired temperature.

• Open Model

Ports

Input

K — Heat transfer coefficient control signal, W/(K*m^2)

physical signal

Input physical signal that controls the heat transfer coefficient. The signal saturates when the value is outside the minimum limit specified by the Minimum heat transfer coefficient block parameter.

Dependencies

To enable this port, set the Convection type parameter to Variable.

Conserving

A — Body A

thermal

Thermal conserving port associated with body A.

B — Body B

thermal

Thermal conserving port associated with body B.

Parameters

Convection type — How to specify heat transfer coefficient

Constant (default) | Variable

Whether to specify the heat transfer coefficient of the material as a block parameter or an input signal:

• Constant — The heat transfer coefficient, specified by the Heat transfer coefficient parameter, remains constant during simulation.

• Variable — The input physical signal at port K specifies the heat transfer coefficient, which can vary during simulation. The Minimum heat transfer coefficient parameter specifies the lower bound for the heat transfer coefficient.

Area — Area of heat transfer

1e-4 m^2 (default) | positive scalar

Surface area of the heat transfer.

Heat transfer coefficient — Convection heat transfer coefficient

20 W/(K*m^2) (default) | positive scalar

Convection heat transfer coefficient.

Dependencies

To enable this parameter, set Convection type to Constant.

Minimum heat transfer coefficient — Lower bound for heat transfer coefficient

1e-3 W/(K*m^2) (default) | positive scalar

Lower bound for the convection heat transfer coefficient. The input signal at port K saturates at this value to prevent the heat transfer coefficient from further decreasing.

Dependencies

To enable this parameter, set Convection type to Variable.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2007b

R2022b: Model variable heat transfer coefficient

The new Convection type parameter lets the heat transfer coefficient be either constant, which you specify by the Heat transfer coefficient parameter, or variable, which you specify as a physical signal at port K.

In the default configuration, with Convection type parameter set to Constant, the block functions as in previous releases.