By What is the rate of heat transfer from the sphere?
A hollow sphere of inner radius 30 mm and outer radius 50 mm is electrically heated at the inner surface at a rate of 105W/m2. At the outer surface, it dissipates heat by convection into a fluid at 100°C and a heat transfer coefficient of 400 W/m2 K.
How do you calculate resistance in heat transfer?
In heat transfer resistance modeling, we look for regions which have relatively large temperature differences, and compute the heat transfer resistance across those regions.
- Figure 12.
- DV = I R or R = DV/ I (Ohm’s Law)
- DT = (Q/A) R or R = DT / (Q/A) (on a per unit area basis)
- Convection resistance.
Which mode of heat transfer does not need any medium for heat transfer?
radiation
Transfer of heat by radiation does not need any material medium. Energy from the sun comes to us by radiation.
What is the surface area of the sphere?
Therefore, the Surface Area of a Sphere with radius r equals 4πr2 .
Why cork is a good insulator?
Cork is made up of hollow polyhedral cells, which means that each cell has 14 sides. The cell walls are flexible, strong, waterproof and airtight, resulting in an insulating material with a low density. Due to the structure of the cork cells, it is not only a thermal insulator, but an acoustical one as well.
What is R value and K value?
The performance of your insulation can be measured in terms of both “r value” and “k value,” but these numbers tell you two different things. K-values measure how much heat passes through a material, while R-values measure how well the material prevents heat from passing through.
Is the heat transfer coefficient of a sphere a dimensionless variable?
The heat transfer coefficient for the sphere/bath system accounts for the resistance associated with heat loss from the sphere to the fluid and is a function of the local mixing properties of the bath as well as the fluid thermal properties. To solve this problem it is convenient to introduce the following dimensionless variables:
What is the formula for the heat transfer coefficient?
Radiation. Here, Hc is the heat transfer coefficient. Here σ is known as Stefan Boltzmann Constant. From the definition of specific heat capacity, we can say that, it is the total amount of heat that is to be supplied to a unit mass of the system, so as to increase its temperature by 1 degree Celsius.
What is the expression for the thermal conduction resistance through a hollow sphere?
1. What is the expression for the thermal conduction resistance to heat transfer through a hollow sphere of inner radius r1 and outer radius r2 and thermal conductivity k? 1. 2. 3. 4. None of these 2.
How to write the heat flow equation through a sphere?
The expression for steady state temperature distribution in a spherical wall can be set up by integrating the Fourier rate equation between the limits – Quite often it is considered advantageous to write the heat flow equation through a sphere in the same form as that for heat flow through a plane wall.