Heat Leaks Through a Glass Window that Has a Size of 5 m x 3 m The Temperature of the Air Inside the Window is 20°C: Physics Assignment, NUS, Singapore

Question1

Heat leaks through a glass window that has a size of 5 m x 3 m. The temperature of the air inside the window is 20°C. The outside atmospheric air temperature is 28°C. The convective heat transfer coefficients on the inside and outside of the window are 14W/m2K and 45 W/m2K respectively. The glass is 15 mm thick and its thermal conductivity is 0.8W/mK. Calculate the:

A. Rate of heat leakage through the glass window,and

B.Surface temperatures on both sides of the glass window.

Question2

A perfect gas requires 117 kJ/kg when heated at constant pressure from 25°C to 95°C. The same gas requires 107kJ/kg when heated at a constant volume between the same temperature limits. Calculate the:

A.the principal specific heat capacities of the gas,

B.the ratio of the principal specific heat capacities,

C. the value of the gas constant, and

D. the molar mass soft the gas if the universal gas constant is 8314J/kg.

E.Explain why a higher quantity of heat is required by the gas when heated at constant pressure than at constant volume for the same temperature limits.

Question3

0.23 m3 of air at 101.3 kPa and 33 °C is compressed according to the law PV1.15 = constant until the pressure is 658.45 kPa in a reciprocating cylinder. Take the molar mass of air, Cp, and the universal gas constant to be 29g/mol,1 .005kJ/kg, and 8.314kJ/kg respectively. Assuming air to be a perfect gas, calculate the:

A.Volume of the air after compression,

B.Final temperature of the air after compression, and

C.Heat transferred to the cylinder wall.

Question4

A furnace wall consists of 270-mm firebrick and 225-mm building brick, separated by an air gap of 75 mm. The furnace inner wall surface temperature is 750°C and the ambient temperatureis32°C. The convective heat transfer coefficient from the outer wall surface to the surrounding and the air gap is 20W/m2K and 5W/m2K respectively. The thermal conductivities of the fire brick and building brick are1.2W/mK and 0.7W/m K respectively.Neglect the effects of radiation, calculate the:

A.rate of heat loss per unit area,

B.outer wall surface temperature, and

C.temperature a teach interface.

D.Suggest two methods store duce the outer wall surface temperature without out hanging the wall and its thickness.

Question5

Carbon dioxide expands reversibly in a perfectly insulated piston-cylinder assembly from 320kPa, 120°C to a volume of 0.12m3.Theinitialvolumewas0.04m3.The molarmass of carbondioxide and is 44 g/mol. Take Cvand universal gas constant to be 0.655 kJ/kg and 8.314kJ/kg respectively. Assuming carbon dioxide to be a perfect gas, calculate the:

A.Work done during the expansion, and

B. Change in internal energy of the gas.

C.Sketch and label fully the pressure-Volume graph of the process.

D.Explain, why the answer obtained in(b)increases order, eases.

Question6

0.08 kg of argon occupying a volume of 0.05 m3at 112.5 kPa is compressed reversibly according to the law PVn = constant until the pressure is 562.5 kPa in a cylinder. The molar mass of argon and the universal gas constant are 39.94 g/mol and 8.314 kJ/kg respectively. Assume argon to be a perfect gas and takeγ=1.667. Calculate the heat transferred to or from the cylinder wall when:

a. n =1.28,and

b.n =1.

c.Draw and label fully a graph for work done versus n for values of n = 1.0, 1.1, 1.2, 1.28,and1.4.

d.State your observations from the graph drawing(c)