2021.04.21

Points of this article

・A fluid is something that flows, whether a gas, a liquid, or the like.

・Convection is a phenomenon of heat movement in which a fluid that has received heat moves, thereby transferring heat.

・Natural convection is flow driven by the buoyancy that arises from temperature differences in the fluid.

・Forced convection is flow driven by external factors, such as a fan or a pump.

・Thermal resistance in convection is the reciprocal of the product of the convective heat transfer coefficient hm and the surface area A of the object emitting heat.

In succession to the previous article on thermal resistance in heat conduction, this article discusses thermal resistance in convection.

There are a number of kinds of convection; below we provide definitions, along with terminology. The diagram is a conceptual image of convection.

Fluids | Something that flows, such as gases and liquids |
---|---|

Convection | A movement phenomenon in which heat is transported by movement of a fluid that has received heat *Where no fluid is present (vacuum), heat movement by convection cannot be expected to occur |

Natural convection | Flow is driven solely by buoyancy due to temperature differences in a fluid |

Forced convection | Flow is driven by an external factor, such as a fan or pump |

The following equations represent thermal resistance in convection.

Thermal resistance in convection is the reciprocal of the product of the convective heat transfer coefficient hm and the surface area A of the object emitting heat. From the equation, we see that as the surface area of the object increases, the thermal resistance of convection decreases.

The convective heat transfer coefficient hm differs depending on the type of convection. We have presented hm values for both natural convection and for forced convection (laminar and turbulent flow).

Downloadable materials, including lecture materials from ROHM-sponsored seminars and a selection guide for DC-DC converters, are now available.

- About Thermal Design
- Changes in Engineering Trends and Thermal Design
- A Mutual Understanding of Thermal Design
- Fundamentals of Thermal Resistance and Heat Dissipation: Heat Transmission and Heat Dissipation Paths
- Fundamentals of Thermal Resistance and Heat Dissipation: About Thermal Resistance
- Fundamentals of Thermal Resistance and Heat Dissipation : Thermal Resistance in Conduction
- Fundamentals of Thermal Resistance and Heat Dissipation : Thermal Resistance in Emission
- Thermal Resistance Data: JEDEC Standards, Thermal Resistance Measurement Environments, and Circuit Boards
- Thermal Resistance Data: Actual Data Example
- Thermal Resistance Data: Definitions of Thermal Resistance, Thermal Characterization Parameters
- Thermal Resistance Data: θJA and ΨJT in Estimation of TJ: Part 1
- Thermal Resistance Data: θJA and ΨJT in Estimation of TJ: Part 2
- Estimating TJ: Basic Calculation Equations
- Estimating TJ: Calculation Example Using θJA
- Estimating TJ: Calculation Example Using ΨJT
- Estimating TJ: Calculation Example Using Transient Thermal Resistance
- Estimation of Heat Dissipation Area in Surface Mounting and Points to be Noted
- Surface Temperature Measurements: Thermocouple Types