Lesson 3 - Principles of Heat Transfer and Conduction SAQ

* Provide short answers to the following questions:

a)    Define sensible heat and give an example of sensible heat in a brewery.

b)    What is Fourier’s law for steady state heat conduction, and what is it used for in a brewery?

c)    Explain where and why insulation is used in a brewery.

Response:

a)   Sensible heat is the heat you can feel or see. An example of sensible heat in a brewery is the heat removed from the wort to cool it to fermentation temperature.

b)  Fourier’s law for steady state heat conduction is an equation that models the steady state rate of heat transfer via conduction through a layer of material. It is a relationship between the thermal conductivity, temperature differential, layer thickness, and heat transfer rate over a given area. It can be used to determine how much heat is lost or gained through walls of a pipe or through the wall of a tank. It is mathematically expressed as:

Where

q is the required amount of heat flow, measured in J s^-1 (W)

A is the surface area, measured in m² 

k is the thermal conductivity, measured in W m^-1 °C^-1 

∆T =  T₂ − T₁ is the temperature drop across the layer, measured in °C or K

∆x =  x₂ − x₁ is the thickness of the layer starting at x₁ and ending at x₂, measured in m

c)  Insulation should be used anywhere it is important to prevent heat losses or gains in temperature or where there is a large temperature change. For example, insulation is often used on pipes that hold cooling water or glycol in order to prevent the warmer ambient area from changing the desired temperature of the coolant. In contrast, insulation is also often installed on steam pipes to prevent heat loss to the ambient air.