ME354 Thermodynamics 2

Availability/Exergy Problems

Problem 3: 1

Determine the availability of water at its critical point.

Answer: n_2nd = 734.04 kJ/kg

Solution

(27.7 KBytes)

Problem 3: 2

Steam is expanded in an adiabatic steady-flow steam turbine from 1000 kPa, 280 oC to 120 oC. Calculate the second law effectiveness of this turbine when its efficiency is 70%. Assume that the system is an adiabatic, steady-flow stream turbine with a single inlet and outlet.

Answer: n_2nd = 0.846

Solution

(38.9 KBytes)

Problem 3: 3

Steam expands adiabatically in a turbine from 2 MPa, 400 oC to 0.4 MPa, 250 oC. Calculate: (i) the isentropic efficiency of the process; (ii) the loss of exergy of the system assuming an atmospheric temperature of 15 oC; (iii) the effectiveness of the process

Answer:

(i)	isentropic efficiency = 69.6%
(ii)	loss of exergy = 355.9 kJ/kg
(iii)	effectiveness = 79.6%

Solution

(43.7 KBytes)

Problem 3: 4

Air at 15 oC is to be heated to 40 oC by mixing it in a steady flow with a quantity of air at 90 oC. Assuming that the mixing process is adiabatic and neglecting changes in kinetic and potential energy, calculate the ratio of the mass flow of air initially at 90 oC to that initially at 15 oC. Calculate also the effectiveness of the heating process if the atmospheric temperature is 15 oC.

Answer:

(a)	loss of exergy (90 oC) = 3.65 kJ/kg
(b)	increase of exergy (15 oC) = 1.195 kJ/kg
(c)	effectiveness = 32.7%

Solution

(35.0 KBytes)

Problem 3: 5

A liquid of specific heat 6.3 kJ/kg K is heated at approximately constant pressure from 15 to 70 oC by passing it through tubes which are immersed in a furnace. The furnace temperature is constant at 1400 oC. Calculate the effectiveness of the heating process when the atmospheric temperature is 10 oC.

Answer:

effectiveness = 12.1%

Solution

(49.8 KBytes)

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