# QUESTIONS ON ENERGY CONVERSION SYSTEMS

QUESTIONS ON ENERY CONVERSION SYSTEMS

Question 1

(a) For small flow rates, the volume flow rate Q through a small square-section tube of

side h and length L is a function of dynamic viscosity ?, pressure drop per unit length

?p/L and h. Using Buckingham pi theorem, express the relation between variables in a

non-dimensional form.

(b) Reynolds number is probably the most widely used non-dimensional number in

Fluid dynamics. Explain its physical meaning by reference to a creeping flow (a very

slow motion) and a high speed subsonic flow

Question 2

Two reversible Carnot engine operate in series between a source at 800oC and a sink

at 30oC. The amount of heat taken from the high temperature reservoir is 5 kW. If the

efficiency of the first engine operating with the source is 1.2 times the efficiency of the

second engine, calculate

(a) the temperature at which heat is supplied to the second engine

(b) the work done by each engine

(c) the heat rejected to sink

Question 3

(a) Calculate the heat and work transfers, cycle efficiency, work ratio and specific

steam consumption of a Carnot cycle, using steam between pressures of 66 and

0.04 bar. Recalculate the problem with introduction of isentropic efficiencies of 85%

for the compression and expansion processes of the ideal cycle.

(b) By reference to a line diagram of the above cycle, identify how irreversibility might

have occurred during heat input to the boiler. Also show how the first and second laws

of thermodynamics are not violated by considering the energy flow through the turbine.

(a) For small flow rates, the volume flow rate Q through a small square-section tube of

side h and length L is a function of dynamic viscosity ?, pressure drop per unit length

?p/L and h. Using Buckingham pi theorem, express the relation between variables in a

non-dimensional form.

(b) Reynolds number is probably the most widely used non-dimensional number in

Fluid dynamics. Explain its physical meaning by reference to a creeping flow (a very

slow motion) and a high speed subsonic flow

Question 2

Two reversible Carnot engine operate in series between a source at 800oC and a sink

at 30oC. The amount of heat taken from the high temperature reservoir is 5 kW. If the

efficiency of the first engine operating with the source is 1.2 times the efficiency of the

second engine, calculate

(a) the temperature at which heat is supplied to the second engine

(b) the work done by each engine

(c) the heat rejected to sink

Question 3

(a) Calculate the heat and work transfers, cycle efficiency, work ratio and specific

steam consumption of a Carnot cycle, using steam between pressures of 66 and

0.04 bar. Recalculate the problem with introduction of isentropic efficiencies of 85%

for the compression and expansion processes of the ideal cycle.

(b) By reference to a line diagram of the above cycle, identify how irreversibility might

have occurred during heat input to the boiler. Also show how the first and second laws

of thermodynamics are not violated by considering the energy flow through the turbine.

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