Adequate insulation is not that important for low temperature fluids.
Answer: A
This is because the loss of available energy from such fluids would be low.
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A hot gas flowing through a pipeline can be considered as a
Answer: B
The process given here is irreversible.
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The second law affixes a quality to energy of a system at any state.
Answer: A
For example we can say that the quality of energy of a gas at say 1000K is superior to that at say 300K.
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Chemical dissociation is
Answer: D
No answer description available for this question.
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Work done in all reversible processes is equal
Answer: A
Reversible processes between the same end states must coincide and and produce equal amounts of work.
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Argon in a light bulb is at 90 kPa and heated from 20°C to 60°C with electrical power. Find the total entropy generation per unit mass of argon.
Answer: D
1s2(gen) = s2 – s1 = Cp ln (T2/T1) – R ln (P2/ P1)
= Cp ln (T2/T1) – R ln (T2/ T1) = Cv ln(T2/T1)
= 0.312 ln [ (60 + 273)/(20 + 273) ] = 0.04 kJ/kg K.
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It is better to state that “the change of state is irreversible, rather than say it is an irreversible process”.
Answer: A
This is because no irreversible path or process can be plotted on thermodynamic coordinates.
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Exergy is lost due to
Answer: D
The decrease in exergy is given by the product of lowest feasible temperature of heat rejection and the additional entropy change in the system.
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Orderly energy can be easily converted into disorderly energy.
Answer: A
An example can be, converting mechanical and electrical energy into internal energy by friction.
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A pan contains 5 L of engine oil at 20°C, 100 kPa. Now 2 L of hot 100°C oil is mixed into the pan. Find the entropy generation.
Answer: A
ρ = 885 kg/m3; From energy equation,
T2 = (mA/m2)TA + (mB/m2)TB = (5/7)20 + (2/7)100 = 42.868°C = 316.02 K
S2 – S1 = m2s2 − mAsA – mBsB = mA(s2 – sA) + mB(s2 – sB)
= 0.005 × 885 × 1.9 ln (316.02/293.15) + 0.002 × 885 × 1.9 ln (316.02/373.15)
= 0.6316 – 0.5588 = + 0.0728 kJ/K.
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