Molecular Physics | Thermodynamics Answers

. An air receiver of volume 5.5 m3 contains air at 16 bar and 42°C. A valve is

opened and some air is allowed to blow out to atmosphere. The pressure of the air in the receiver

drops rapidly to 12 bar when the valve is then closed.

Calculate the mass of air which has left the receiver

In a steam engine the steam at the beginning of the expansion process is

at 7 bar, dryness fraction 0.98 and expansion follows the law pv1.1 = constant, down to a pressure

of 0.34 bar. Calculate per kg of steam :

(i) The work done during expansion ;

(ii) The heat flow to or from the cylinder walls during the expansion.

A mercury thermometer is at an initial temperature of 24 C and it is placed in a glass of water at 8 C. The thermometer has a spherical reservoir of diameter D = 1.4 cm3 , and a column of diameter d = 1.00 mm. At 4 C the mercury fills the reservoir but does not enter the column. The linear expansion coefficient of mercury  = 6.00 × 104 K1 . The mercury column has initial height hi and it decreases to a final height hf = hi/2 during the process of arriving at equilibrium with the water. (a) Explain why the process is not a quasi-equilibrium process. (3) (b) Calculate the temperature of the water.

Two steel rings of radial thickness 30 mm, common radius 70 mm and length 40 mm are 

shrunk together to form a compound ring. It is found that the axial force required to separate 

the rings, i.e. to push the inside ring out, is 150 kN. Determine the shrinkage pressure at the 

mating surfaces and the shrinkage allowance. E = 208 GN/mZ. The coefficient of friction 

between the junction surfaces of the two rings is 0.15. 

Dry saturated steam at 100 bar expands isothermally and reversibly to a

pressure of 10 bar. Calculate per kg of steam :

(i) The heat supplied ;

(ii) The work done

. Air at a temperature of 20°C passes through a heat exchanger at a

velocity of 40 m/s where its temperature is raised to 820°C. It then enters a turbine with same

velocity of 40 m/s and expands till the temperature falls to 620°C. On leaving the turbine, the air

is taken at a velocity of 55 m/s to a nozzle where it expands until the temperature has fallen to

510°C. If the air flow rate is 2.5 kg/s, calculate :

(i) Rate of heat transfer to the air in the heat exchanger ;

(ii) The power output from the turbine assuming no heat loss ;

(iii) The velocity at exit from the nozzle, assuming no heat loss.

Take the enthalpy of air as h = cpt, where cp is the specific heat equal to 1.005 kJ/kg°C and

t th

 In an air compressor air flows steadily at the rate of 0.5 kg/s through an

air compressor. It enters the compressor at 6 m/s with a pressure of 1 bar and a specific volume

of 0.85 m3/kg and leaves at 5 m/s with a pressure of 7 bar and a specific volume of 0.16 m3/kg. The

internal energy of the air leaving is 90 kJ/kg greater than that of the air entering. Cooling water

in a jacket surrounding the cylinder absorbs heat from the air at the rate of 60 kJ/s. Calculate :

(i) The power required to drive the compressor ;

(ii) The inlet and output pipe cross-sectional areas

A 2.2-cm-outer-diameter pipe is to span across a river at a 30-m-wide sec￾tion while being completely immersed in water (). The average

flow velocity of water is 4 m/s and the water temperature is 158C. Determine

the drag force exerted on the pipe by the river.

The specific heat capacity of ethanol is 2440J/kg °C. How many joules of energy will be required to heat 150g ethanol to 35°C if the starting temperature is 22°C?