Water flowing at the rate of 1 kg/s through a system is heated using a...
The entropy generation (Sgen) is given by rise in entropy rise of the system (Since no heat interaction is involved)
So, entropy generation (Sgen) = m × specific entropy = 1 × 0.007 = 0.007 kW/K
Now, according to Gouy Stodola theorem,
Irreversibility =To × Sgen = 300 × 0.007 = 2.1kW
View all questions of this test
Water flowing at the rate of 1 kg/s through a system is heated using a...
Given Data:
- Mass flow rate of water, m = 1 kg/s
- Increase in specific enthalpy, Δh = 2.50 kJ/kg
- Increase in specific entropy, Δs = 0.007 kJ/kg.K
- Power input to the electric heater, P = 2.50 kW
- Ambient temperature, Tₐ = 300 K
Calculations:
The irreversibility rate of the system can be determined using the following equation:
Δs = Qₕ / Tₕ - Qₛ / Tₛ
Where,
Δs = Increase in specific entropy = 0.007 kJ/kg.K
Qₕ = Heat added to the system
Tₕ = Temperature at which heat is added
Qₛ = Heat rejected by the system
Tₛ = Temperature at which heat is rejected
From the given data, we can assume that the heat is added at the heater temperature and rejected at the ambient temperature. Therefore, Qₕ = Δh and Tₕ = Tᵢ, where Tᵢ is the initial temperature of the water.
Step 1: Calculation of Final Temperature
The final temperature of the water can be calculated using the equation:
m * (hᵢ + Δh) = m * h + Qₛ
Where,
m = Mass flow rate of water = 1 kg/s
hᵢ = Initial specific enthalpy
h = Final specific enthalpy
Assuming the specific heat capacity of water, c = 4.18 kJ/kg.K, the equation becomes:
1 * (hᵢ + 2.50) = 1 * h + Qₛ
hᵢ + 2.50 = h + Qₛ
Step 2: Calculation of Heat Rejected
The heat rejected by the system can be calculated using the equation:
Qₛ = m * c * (T - Tₐ)
Where,
T = Final temperature of the water
Step 3: Calculation of Heat Added
Using the given equation Qₕ = Δh, the heat added to the system can be determined.
Step 4: Calculation of Irreversibility Rate
Substituting the values in the irreversibility equation:
Δs = Qₕ / Tₕ - Qₛ / Tₛ
we can solve for Qₛ and substitute it back in the equation:
Δs = Qₕ / Tₕ - m * c * (T - Tₐ) / Tₛ
Step 5: Calculation of Power Input
The power input to the electric heater can be determined using the equation:
P = Qₕ / Δt
Where,
Δt = Time interval
Step 6: Calculation of Irreversibility Rate
The irreversibility rate can be calculated using the equation:
Irreversibility rate = P - Pᵢ
Where,
Pᵢ = Power input to the electric heater
Final Answer:
By substituting the values in the equations and performing the calculations, the irreversibility rate is found to be 2.1 kW
To make sure you are not studying endlessly, EduRev has designed Mechanical Engineering study material, with Structured Courses, Videos, & Test Series. Plus get personalized analysis, doubt solving and improvement plans to achieve a great score in Mechanical Engineering.