Radiation CFD Simulation

What is Radiation Heat Transfer?

Within the atoms of each substance, electrons and protons move and vibrate relative to each other. This vibration creates electromagnetic waves, which spread into the surrounding environment, whether within the material or not. When these electromagnetic waves encounter the charged particles of other atoms, such as protons and electrons, they cause these particles to vibrate. As a result, the temperature of the material increases. This process is called radiation heat transfer and is the mechanism by which heat from the sun is transferred to the Earth.

What is Blackbody Radiation?

When an electromagnetic wave reaches a material, it can have three possible interactions: a part of the wave is absorbed by the material, a part passes through the material, and a part is reflected. For simplicity in expressing the concepts of heat transfer and solving related problems, the concept of a blackbody is introduced. A blackbody is an idealized object that absorbs all incident electromagnetic waves without transmitting or reflecting any of them. It also emits all the absorbed energy immediately.

A blackbody is perceived as black because it absorbs all electromagnetic waves, including visible light. However, not every material that appears black to the human eye is a blackbody. This is because a material can appear black by absorbing light only within the range of human vision, but it might still reflect or transmit electromagnetic waves outside this range.

What is a Radiator?

A radiator is a heat exchanger that can be seen in various HVAC systems in homes and in automotive applications. While radiation heat transfer is usually ignored in radiator calculations, it is possible to consider it in CFD (Computational Fluid Dynamics) analysis, particularly in the CFD analysis of automobile radiators. This analysis can help determine the role of radiation heat transfer in overall heat exchange and whether it can be ignored. Radiator CFD analysis provides detailed insights into the thermal performance and fluid flow characteristics, allowing for optimization of the radiator design.

What is Stefan-Boltzmann Law?

This law expresses the energy emitted per unit area of the blackbody per unit time. The emitted energy includes the energy of all electromagnetic waves with different wavelengths. In the equation of this law, 𝑇 is the body temperature [K] and σ is the Stefan-Boltzmann constant (5.67×10⁻⁸ [W.m⁻².K⁻⁴]).

If the substance is not a blackbody, the amount of radiation it emits is multiplied by a factor called emissivity, which is a number between zero and one. Emissivity (ϵ) represents the efficiency of the material in emitting thermal radiation compared to a blackbody.

Applications of Radiation Heat Transfer

Radiation heat transfer plays a crucial role in many practical applications across various fields. Here are some of the key applications:

Spacecraft and Satellite Thermal Management

Sunlight hits space structures and transfers thermal energy to them. Additionally, the systems and humans inside these structures generate heat. To manage the temperature inside space structures, which are located in a vacuum, engineers rely on radiation as the primary means of heat transfer. They adjust the heat output and input to the space structure through radiation.

If the temperature increases, heat will quickly radiate away from the structure. If the temperature decreases, heat will be generated inside the structure, or the heat from the sun will be absorbed. Before launching, engineers test space structures on the ground by creating a vacuum in a laboratory environment and shining xenon lamp light on them. The light from these lamps closely simulates sunlight. Engineers also use CFD radiation simulations to model and predict thermal behavior under various conditions.

Solar Energy Systems

By concentrating sunlight on an area using mirrors and lenses, its thermal energy can be harnessed for various applications. For example, in some power plants, this method is used to heat fluids. In domestic settings, this technique is employed to heat water or for cooking. Engineers often use radiation CFD simulations to optimize the design and efficiency of these systems.

A solar thermal power plant energy farm. By concentrating sunlight with mirrors at one point, the thermal energy is focused on the heat exchanger, increasing the temperature of the fluid.

Building Heating and Cooling

To manage the temperature of a building, it is very important to design it according to the ambient weather to absorb or reflect the thermal energy of sunlight. In cold environments, significant heat can be absorbed by using darker colors for the building’s exterior. Additionally, by concentrating sunlight on a fluid, this hot fluid can be used in HVAC systems to increase the building’s temperature. In hot environments, using lighter colors for the building’s exterior reduces the absorption of thermal energy. This method is very effective for maintaining a cooler interior. CFD radiation heat transfer simulations are often utilized to optimize the design and efficiency of these systems.

Medical Treatments

Radiant thermal energy is utilized in various medical applications, typically generated by high-energy electromagnetic wave lasers. This method is employed for the destruction of cancer cells. Multiple lasers direct light from different angles towards a specific point. Individually, each beam lacks sufficient energy to harm body tissues significantly. However, their combined focus at a single point enables the desired tissue to be effectively targeted and treated. CFD radiation heat transfer simulations by ANSYS Fluent are often used to model and optimize these treatments.

The thermal camera shows the temperature differences of objects by detecting the infrared radiation they emit.

Simulation of Radiation Heat Transfer by ANSYS Fluent

ANSYS Fluent is a powerful computational fluid dynamics (CFD) simulation software based on the finite volume method. This versatile software excels at simulating radiation heat transfer, a critical aspect in many engineering applications. Fluent is capable of accurately modeling multiple heat transfer mechanisms, including conduction, convection, and radiation, simultaneously within a system. It allows for precise adjustments and definitions of even the smallest details of radiant heat transfer.

This capability makes it an invaluable tool for engineers seeking to optimize thermal performance in various materials and structures, ensuring comprehensive and reliable simulation results for complex thermal systems.

Temperature contour, adopted from “Active Cooling in Photovoltaic System CFD Simulation”

CFDLAND expertise in Radiation Heat Transfer Modeling Using ANSYS Fluent Software

Discover the exceptional capabilities of CFDLAND, where we have completed numerous high-quality CFD projects, many of which are showcased in our CFDSHOP. Browse our ready-to-use projects in the field of radiant heat transfer at the top of this page—you might find exactly what you need. Trust our team of experts to handle your simulation projects. Simply place your order through ORDERPROJECT, and prepare to be amazed by the outstanding results we deliver.