Answered: Calculate the rate of heat transfer…

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Question

A 5-cm thick slice of bread (k = 0.23 W/m°C) is placed on top of a hot plate at a temperature of 85oC. The top surface of the bread slice is maintained at 25°C.a.Calculate the rate of heat transfer from bottom to top of the slice in W/m2

Expert Solution

Step 1

Thermal Conductivity

The thermal conductivity of a substance is the measure of the ability of the substance to conduct heat. It can be defined as the rate at which heat is transferred through a unit cross-section of a material when a temperature gradient exists perpendicular to the heat flow. It is denoted by $K$ and its SI unit is $W m^{- 1} K^{- 1}$ .

The amount of heat $Q$ flowing through a slab of the cross-sectional area $A$ and of thickness $x$ in time $t$ from the side at a higher temperature $θ_{1}$ to the side of lower temperature $θ_{2}$ is given by

$Q = \frac{K A (θ_{1} - θ_{2}) t}{x}$

Therefore the amount of heat supplied per unit area per unit time is given by

$\frac{Q}{A t} = \frac{K (θ_{1} - θ_{2})}{x}$