## Introduction to Conjugate Heat Transfer Modeling in COMSOL Multiphysics^{®}

With COMSOL Multiphysics^{®} and the add-on Heat Transfer Module, you can simulate conjugate heat transfer with laminar flow or turbulent flow. In this article, we provide a comprehensive introduction to single-phase flow, conjugate heat transfer modeling.

Note: We recommend starting with our material on modeling laminar flow and turbulent flow first if you are new to modeling fluid flow in the software.

### Modeling Conjugate Heat Transfer

#### Discussion

In this introductory video on modeling conjugate heat transfer using the software, we start by providing an overview of what is covered throughout the series of videos found in this article. Then we discuss some fundamentals of conjugate heat transfer modeling before covering some relevant settings found in the fluid flow interfaces (for both laminar and turbulent flows), in addition to the multiphysics capabilities available.

The following topics are covered in this video:

- Introduction
- Overview of what is covered throughout the series of videos

- Heat transfer mechanisms
- Heat transfer in fluids
- Settings within the fluid flow interfaces
- Compressible, weakly compressible, and incompressible flow
- Gravity property
- Viscous dissipation
- Work done by pressure changes
- Multiphysics coupling for nonisothermal flow

#### Demonstration

In this video, we show step by step how to set up a simple nonisothermal flow problem where the flow is due to natural convection. In building the model from start to finish, we demonstrate the modeling capabilities and features mentioned previously.

The following topics are covered in this video:

- Introduction
- Demo: natural convection in a cavity

- Defining parameters
- Creating geometry
- Defining the physics: fluid flow
- Compressibility settings
- Including gravity
- Reference position
*Pressure Point Constraint*condition

- Defining the physics: heat transfer
*Temperature*boundary condition

- Multiphysics coupling for nonisothermal flow
- Computing the model
- Results and visualization
- Plot density
- Evaluating hydrostatic pressure

- Extending the model
- Using an auxiliary sweep
- Using the Boussinesq approximation

### Discussion & Demo: Conjugate Heat Transfer with Laminar Flow

Thus far, we have covered modeling heat transfer in fluids in COMSOL Multiphysics. In this video, we progress to modeling heat transfer in solid domains using the software. We begin with a short lecture providing some information on modeling heat transfer in solids and the functionality for doing so, before setting up another problem where we simulate conjugate heat transfer with laminar flow.

The following topics are covered in this video:

- Discussion
- Heat transfer in solids
- Heat transfer functionality
- Thin structures
- Solid-shell connectors
- Thermal contact

- Demo
- Conjugate heat transfer with laminar flow
- Model example: heat sink

### Discussion & Demo: Conjugate Heat Transfer with Turbulent Flow

In this video, some additional aspects of modeling conjugate heat transfer with a turbulent flow are covered. We start with an overview of an example of this application, a shell and tube heat exchanger, of which the tube walls are modeled using thin layers. From there we discuss in detail how the *Nonisothermal Flow Coupling* and *Thin Layer* features are used in the model. Following this, the wall treatment used for the turbulence model is discussed. A simplified model is used to compare the effects of using different wall treatments: a low Reynold's number (Re) approach versus wall functions.

The following topics are covered in this video:

- Discussion & demo
- Conjugate heat transfer with turbulent flow
- Model example: shell-and-tube heat exchanger
- Heat transfer functionality
*Thin Layer*feature

- Wall treatment
- Comparison: wall function vs. low Re
- Comparing velocity, temperature profile, and heat flux for both solutions

### Modeling Exercise

Demonstrate the knowledge you have gained from this article by putting it into practice with the heat sink tutorial model:

- Open a new session of COMSOL Multiphysics to reproduce the heat sink model. (You can use these slides as a guide.)
- Extend the model to include a custom plot visualizing both the velocity of airflow in the channel and the temperature of the heat sink device.

The directions (attached to this article) are intentionally generalized to encourage self-guided problem solving. You can manually check your implementation with the solution model file provided here (the demo model file) or you can use the comparison tool to identify the differences.

### Further Learning

Tutorial model: Turbulent Flow Through a Shell-and-Tube Heat Exchanger Cross Section.

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