ANS:C - cooling by flow of air over the surface.

Cooling by the flow of air over the surface refers to a method of dissipating heat from an object by exposing it to moving air. This process relies on the principle of convective heat transfer, where heat is transferred from the object to the surrounding air as it moves past. Here's how cooling by the flow of air over the surface works:

1. Convective Heat Transfer: As the object moves through the air or as air flows over the object, heat is transferred from the warmer object to the cooler air through convection. This occurs because air molecules in direct contact with the surface of the object gain heat energy and become less dense, causing them to rise. Cooler air then moves in to replace the rising warm air, and the process continues, resulting in the transfer of heat away from the object.
2. Enhanced Heat Dissipation: The flow of air over the surface helps to carry away the heat absorbed by the object, allowing it to cool down more rapidly than if it were stationary. The rate of heat transfer through convective cooling depends on factors such as the velocity of the air, the temperature difference between the object and the air, and the surface area and geometry of the object.
3. Applications: Cooling by the flow of air over the surface is commonly used in various engineering applications to dissipate heat from objects such as electronic components, machinery, engines, and industrial equipment. It is often facilitated by fans, blowers, or natural airflow in outdoor environments.

While cooling by the flow of air over the surface can be effective for dissipating heat under certain conditions, it may not be sufficient to prevent overheating during extreme thermal environments such as re-entry into Earth's atmosphere for satellites. In such cases, additional thermal protection measures, such as ceramic heat shields or ablative materials, are typically required to withstand the high temperatures encountered during re-entry. In summary, cooling by the flow of air over the surface is a method of dissipating heat from an object by exposing it to moving air, which promotes convective heat transfer and helps to reduce the object's temperature.