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Building Services Tutorial 1aIntroduction to thermal energy

Answer all questions

1. a. Convert the following temperatures from degree Celsius to degree Kelvin.20 o C =

400 o C =

-10 o C =

b. Convert the following temperatures from Kelvin to Degree Celsius :

200 K =

300 K =

773 K =

2. Explain with accurate terminology, the reasons for the following observations :

a. The meat and gravy inside a hot pie burn the tongue more easily than the surrounding pastry even though all parts of the pie are at the same temperature.b. A concrete floor feels colder to walk on than carpet, even though both are at the same temperature3. Calculate the total heat required to convert 2 kg of water at 60 o C completely to steam at 100 o C. (Given the specific heat capacity of water = 4200J/kg/K and the specific latent heat of steam is 2260kJ/kg)

DATA : mass of water = 2 kg

Initial temperature of water = 60 o C

Steam is at 100 o C

Calculations :

4.An insulated hot water storage cylinder has internal dimensions of 0.6 m diameter and 1.5m in height.A heating element at the bottom of the cylinder supplies 74.81 MJ of heat to the water which is at an initial temperature of 8 o C. Ignore any heat losses from the water and heat gain by the cylinder itself.

Given : density of water = 1000 kg/m3 specific heat capacity of water = 4200J/kg/K

a. Calculate the mass of the water present in the cylinder

b. Calculate the temperature of the water after heating

c. Calculate the effective power of the heating element if the above temperature takes 4 hours

b. Heat = mc((c. Power = Heat Supplied ( Time Taken

5. Explain with accurate reference to appropriate mechanisms of heat transfer, the following effects :

a. The ability of a vacuum flask to keep liquids either hot or cold

b. The ability of silver paint on a roof to reduce heat loss from a buildingSOLUTION :

6. At standard pressure and temperature, a certain sample of gas occupies 50 litres in volume. Calculate the pressure required to compress this sample to a volume 20 litres while allowing the temperature to rise to 30oC.SOLUTION :