Q1: Heat transfer by __________ is almost absent in case of fluidised bed drying operation.

ANS:A - radiation

Radiation is a method of heat transfer that does not require a medium to carry the heat. Instead, heat is transferred through electromagnetic waves, typically in the form of infrared radiation. Here's how radiation works:

1. Electromagnetic Waves: Heat energy is emitted in the form of electromagnetic waves from a warmer object to cooler surroundings. These waves travel at the speed of light and can transfer energy over large distances without the need for direct contact between the hot object and the cooler object.
2. Every Object Emits Radiation: All objects with a temperature above absolute zero (-273.15°C or 0 Kelvin) emit radiation. The amount of radiation emitted by an object depends on its temperature and its emissivity, which is a measure of how efficiently the object emits radiation compared to a perfect blackbody radiator.
3. Heat Exchange: When two objects at different temperatures are in close proximity, heat exchange occurs through radiation. The hotter object emits radiation, which is absorbed by the cooler object, causing its temperature to rise. Conversely, if the cooler object has a higher temperature, it emits radiation that is absorbed by the hotter object, resulting in a decrease in its temperature.
4. Key Factors Affecting Radiation:
   • Temperature: The rate of radiation increases with the temperature of the emitting object raised to the fourth power, according to Stefan-Boltzmann law. This means that hotter objects emit significantly more radiation than cooler objects.
   • Surface Area and Geometry: The surface area and geometry of the objects involved affect the rate of radiation exchange. Objects with larger surface areas and certain shapes may emit or absorb radiation more effectively.
   • Emissivity: Emissivity is the efficiency with which an object emits radiation compared to a blackbody radiator. Objects with higher emissivity values emit radiation more efficiently.
5. Applications:
   • Thermal Insulation: Understanding radiation is essential in designing effective thermal insulation materials and systems to minimize heat transfer.
   • Space Heating and Cooling: Radiation plays a role in heating and cooling systems, such as radiators, underfloor heating, and infrared heaters.
   • Solar Energy: Solar panels capture radiant energy from the sun to generate electricity or heat water for various applications.
   • Cooking: Infrared radiation is used in cooking processes such as grilling, broiling, and toasting.