Why does the heat transfer rate of an insulated cylinder first increase before reducing as the thickness of the insulation is increased?

The thicker the insulation, the lower the heat transfer rate. This is due to the fact the outer surface have always the same area. As can be seen, if r1 < rcr, as it is in this case, the total resistance decreases and the heat rate therefore increases with the addition of insulation.

What is the critical radius of insulation explain its significance over pipes and cable?

The critical radius of insulation is a counterintuitive concept within the study of heat transfer. The theory states that adding insulation to a cylindrical or spherical object will increase the rate of heat loss rather than decrease it, if the radius (thickness) of the insulation is at its “critical” value.

What happens when the radius of insulation on a pipe exceeds the critical value?

When the thickness of insulation on a pipe exceeds the critical value the heat flow rate. Options are : Increases.

What happens with the heat flow rate when the thickness of insulation on a pipe exceeds the critical value and why?

The value of Router for which the heat transfer rate is maximum is called the critical radius of insulation. The thickness up to which heat flow increases and after which heat flow decreases is termed as Critical thickness. And it starts decreasing after the critical thickness of insulation.

How does distance affect heat transfer?

The closer the distance to the object by the source of fire, then intensity of radiation will be greater. So that every object in the room has the same risk in the fire even if not directly exposed by fire[2].

What is meant by critical radius of insulation?

The critical radius of insulation is the thickness of insulation at which the rate of heat transfer through the body is maximum. It means that the rate of heat transfer increases with an increase in the thickness of insulation up to the critical radius of insulation.

Why do we need critical radius of insulation?

As we increase the layer of insulation on a cylindrical or spherical surface, the area exposed to the surrounding also increases. The increased surface area increases the convective heat transfer. Therefore up to the critical radius of insulation, the rate of heat transfer increases.

What is mean by critical radius of insulation?

resistance of insulation, but decreases the convection resistance of the surface because of the increase in the. outer surface area. Due to these opposite effects, a critical radius of insulation is defined as the outer radius. that provides maximum rate of heat transfer.

How does heat flux change with increasing excess temperature?

As the excess temperature increases, radiation heat transfer through the vapor film becomes significant and increases the heat flux. The maximum heat flux (Point A) is the critical heat flux (CHF).

How does heat decrease with distance?

Inverse Square Law: For point sources, intensity of the radiation varies inversely with the square of the distance from the source. Doubling the distance reduces intensity of the radiation by a factor of four (1/4 of its original value).

Why does temperature decrease with distance?

By natural convection, heated air will flow upwards, and this will carry a lot of energy that way. Walking slightly further away might remove the convection effect entirely. This will feel like a huge decrease in heating.