Lesson 3 - Principles of Heat Transfer and Conduction SAQ

* Indicate whether the following statements are true or false. If you think they are false, state why:

a)    The SI unit of energy is the joule (J).

b)    Sensible energy is the energy released or absorbed during a phase change.

c)    When a high temperature object touches a lower temperature object, heat is transferred from the lower temperature object to the higher temperature object via conduction.
 

* 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.
 

** Calculate the amount of heat that needs to be removed to cool 500 hL (52,650 kg) wort with SG of 1.053 from 90° to 20°C. The specific heat capacity of wort is roughly 4,000 J kg^-1 K^-1.
 

** How much thermal energy is released when 3,000 kg steam is condensed? The heat of vaporisation of water is 2,257 kJ kg^-1 .
 

** Use Fourier’s law for steady state heat conduction to determine the rate of heat exchange from the ambient air into a stainless steel tank filled with beer at 1°C. You may assume the temperature of the air on the outside of the tank is 20°C, the thickness of the tank wall is 25.4 mm and the heat transfer surface area is 7.0 m². The thermal conductivity of stainless steel is 17 Wm^-1 K^-1. Describe why it is important to know this value in a brewery.