Visit Thermtest at the Thermal Management Expo Europe 2024!
November 11, 2024
Let’s see how radiation heat transfer plays a fundamental role in everyday life and technology.
Radiation heat transfer is an important concept in physics, and it plays a vital role in everyday life. Radiation is one of three ways heat transfers, the other two being conduction and convection. In contrast with convection and conduction, radiation does not require a medium to travel through. Many natural phenomena and technologies we use every day can be explained by understanding radiation heat transfer. This blog is focused on the practical understanding of radiation heat transfer and examples that confirm its significance.
Radiation is the transfer of thermal energy from a hot surface to a cool surface by electromagnetic waves, mostly through infrared radiation. In contrast to conduction and convection, radiation can transfer energy through an empty space. In simpler terms, radiation can happen in a vacuum or through matter. Consider the following factors that affect radiation heat transfer:
Temperature: Radiation emitted from a body depends on the amount of heat a body possesses or on the temperature of the body. Stefan-Boltzmann’s law states that the radiant energy given out by a surface is proportional to the fourth power of its absolute temperature.
Surface properties: Emissivity is a property of a surface that measures a material’s ability to emit energy as thermal radiation. An ideal reflector will have a rating of zero while an ideal emitter will score a rating of one, where one represents a perfect black body that emits the maximum possible radiation. Materials have an emissivity that ranges from low to high, with darker and rougher surfaces having a higher value.
Distance: According to the inverse square law, the intensity of radiation from the source reduces with the square of the distance from the source.
The angle of incidence: The amount of radiation received by a surface from an energy source also depends on the angle it is being applied. If an applied beam strikes a surface perpendicularly, maximum absorption will be obtained, but if it strikes obliquely, absorption will be less.
These factors make it possible to explain why radiation heat transfer has various uses and consequences in our lives.
The concept of radiation heat transfer envelops and influences everything, from the warmth one receives on a sunny day to cooking technology. Let’s look at five examples in daily life:
The heat we receive from the Sun is one of the most common (and most powerful) examples of radiation. The Sun radiates thermal energy and has a heating effect on Earth’s surface, which is important for our planet’s climate and life. Solar panels can capture this radiant energy and convert it into electrical power as a renewable energy source. Sunlight may also be applied directly to heat water or buildings using solar thermal systems.
Figure 1: Sun radiating heat to the Earth’s surface.
Infrared heaters work by emitting infrared radiation, which directly heats the objects and people in the path of the radiation, rather than heating the air. These are commonly used for intermittent heating of residential places and open areas such as patios. They are usually regarded as more energy friendly since they directly heat objects, rather than the space around them.
Figure 2: Infrared heaters shedding heat on people directly.
The microwave oven uses radiation to heat food. Microwaves make the water molecules in the food vibrate, thus cooking the food from the inside out and generating heat through friction. Therefore, the concept of radiation depicts the point that electromagnetic radiation of other wavelengths can have diverse responses, such as heating.
Figure 3: Microwave oven using heat radiation to warm the food.
Radiant floor heating is a method used for heating a building by installing heat-conducting materials under the floors. The heat conducted upwards helps to keep the room at a comfortable temperature. This method gives off heat uniformly helping to keep the space comfortable and allows a more effective use of energy by minimizing heat loss and recirculating warm air.
Figure 4: Floor heating systems installed to heat the building.
Heat lamps are used as food warmers in restaurants and buffets. They radiate infrared energy which keeps food warm without drying or overcooking it. Here, the radiation directly heats the food, maintaining an ideal temperature until it is served. Therefore, the concept of thermal radiation is applied in the food industry to maintain meals at an optimal serving temperature, ensuring high food quality and safety.
Figure 5: Heat lamps helping to keep the food at optimal temperature ensuring quality and safety.
Radiation is a crucial heat transfer mechanism. From the natural warmth of sunlight to the technologies used in home and industry appliances, radiation plays a key role in heating systems and energy transfer. The examples discussed show how radiation is crucial for our earth and personal well-being.
For a more detailed exploration of heat transfer principles and its various mechanisms, visit the Basics of Heat Transfer page.
Radiation heat transfer is a process where thermal waves are emitted that may be absorbed, reflected, or transmitted through a colder body. It does not require any medium for its transmission and, therefore, can conduct heat through matter or even across vacuums.
Radiation heat is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) is converted to electromagnetic radiation.
Convection involves the transfer of thermal energy via the movement of fluids. This process occurs when molecules within a liquid, gas, or liquid-gas mixture move in bulk, carrying heat with them. Radiation, on the other hand, involves transferring of heat in the form of electromagnetic waves, which can take place even through a vacuum.
The basic law for radiation heat transfer is embodied in the Stefan-Boltzmann law, stating that the total radiant heat energy per unit of time emittance from a black body is directly proportional to the fourth power of its absolute temperature.
Britannica, T. E. (2024, June 13). Thermal Radiation. Retrieved from Britannica: https://www.britannica.com/science/thermal-radiation
Frank P. Incropera, D. P. (2007). Fundamentals of Heat and Mass transfer. John Wiley & Sone.
Heat Transfer Methods – Conduction, Convection and Radiation Introduction. (2016). Retrieved from bccampus: https://pressbooks.bccampus.ca/introductorygeneralphysics2phys1207/chapter/14-4-heat-transfer-methods/
Radiation. (n.d.). Retrieved from Lumen learning: https://courses.lumenlearning.com/suny-physics/chapter/14-7-radiation/
Stewart, M. (2011). Radiation Heat Transfer. Retrieved from Science Direct: https://www.sciencedirect.com/topics/engineering/radiation-heat-transfer
Convection Heat Transfer – What is it and Examples in Real Life (n.d.). Retrieved from Thermtest: https://thermtest.com/examples-of-convection-heat-transfer