manal950 said:
Here we have question with answer
Could please explain to me the answer of this question ?
You want the surface area of the pipe, not the cross-sectional area.
There are three possible modes of heat transfer: conduction, convection, and radiation. Heat transfer by conduction doesn't work so well for a gas, it's main method of transport is convection.
It is Boltzmann's constant. See: Stefan-Boltzmann Lawmanal950 said:
The surface area of a cylinder is given by the circumference multiplied by the length. The circumference is given by ##2 \pi r## or ##\pi D##, where D is the diameter of the cylinder.
(Circle?)
Radiation and convection are two different modes of heat transfer. Radiation is the transfer of heat through electromagnetic waves, while convection is the transfer of heat through the movement of fluids (liquids or gases).
Radiation and convection both contribute to the overall temperature of a system. Radiation can cause an increase in temperature when heat is absorbed, while convection can lead to a decrease in temperature as heat is transferred away.
It depends on the system and the conditions. In some cases, radiation may be more efficient, while in others, convection may be more efficient. For example, in a vacuum, radiation is the only way heat can be transferred, making it the most efficient mode of heat transfer.
In radiation, the rate of heat transfer is directly proportional to the surface area. In convection, the rate of heat transfer is also affected by surface area, but other factors such as the temperature difference and fluid velocity also play a role.
Yes, radiation and convection can occur simultaneously. In fact, most heat transfer processes involve a combination of both modes. For example, heat from the sun reaches the Earth through radiation, but convection also plays a role in distributing heat throughout the atmosphere.