A compressor is used to compress air from an initial state of 100 kPa and 300 K to a final state of 800 kPa. Determine the work done on the air and the final temperature if the compression process is isentropic.
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To solve this problem, we can use the isentropic process equations for an ideal gas:
P₁ * V₁^γ = P₂ * V₂^γ (1)
T₁ * V₁^(γ-1) = T₂ * V₂^(γ-1) (2)
Where:
P₁ = initial pressure = 100 kPa
V₁ = initial volume (unknown)
T₁ = initial temperature = 300 K
P₂ = final pressure = 800 kPa
V₂ = final volume (unknown)
T₂ = final temperature (unknown)
γ = specific heat ratio = Cp/Cv for air = 1.4 (approximately)
First, let's calculate the initial volume V₁ using the Ideal Gas Law:
P₁ * V₁ = n * R * T₁
Where:
n = number of moles of air
R = gas constant = 8.314 J/(mol·K) (approximately)
Using the value of R, we can convert the initial pressure from kPa to Pa:
P₁ = 100 kPa = 100,000 Pa
Rearranging the Ideal Gas Law equation, we can solve for V₁:
V₁ = (n * R * T₁) / P₁ (3)
Next, we can use equation (1) to relate the initial and final volumes:
P₁ * V₁^γ = P₂ * V₂^γ
Substituting the expression for V₁ from equation (3) and rearranging the equation, we can solve for V₂:
V₂ = (V₁^γ * P₁) / P₂ (4)
Substituting the values into equations (3) and (4), we find:
V₁ = (n * R * T₁) / P₁ ≈ (n * 8.314 J/(mol·K) * 300 K) / 100,000 Pa
V₂ = (V₁^γ * P₁) / P₂ ≈ ((n * 8.314 J/(mol·K) * 300 K) / 100,000 Pa)^1.4 * 100,000 Pa / 800,000 Pa
Now, let's calculate the work done on the air using the isentropic work equation:
W = (P₂ * V₂ - P₁ * V₁) / (γ - 1)
Substituting the values into the equation, we find:
W = (800,000 Pa * V₂ - 100,000 Pa * V₁) / (1.4 - 1)
Finally, let's calculate the final temperature T₂ using equation (2):
T₂ = (T₁ * V₁^(γ-1)) / V₂^(γ-1)
Substituting the values into the equation, we find:
T₂ = (300 K * V₁^(1.4-1)) / V₂^(1.4-1)
Unfortunately, without knowing the value of n (number of moles of air), we cannot calculate the exact values for V₁, V₂, W, and T₂. However, we can still solve this problem once we know the value of n.