JNTU
JNTU B.Tech III THERMODYNAMICS FOR PETROLEUM ENGINEERS Previous Question Paper (October - 2020 - R16)
Answer any five questions. All questions carry equal marks.
Main
A steam turbine operates adiabatically with a power output of 4000 kW. Steam enters the turbine at 2100 kPa and 475°C. The exhaust is saturated steam at 10 kPa that enters a condenser, where it is condensed and cooled to 30°C. What is the mass flow rate of the steam, and at what rate must cooling water be supplied to the condenser, if the water enters at 15°C and is heated to 25°C?
Answer
To determine the mass flow rate of steam (m_s) and the cooling water flow rate (m_w), we apply the steady-state energy balance to the turbine and the condenser.
1. Turbine Analysis:
From steam tables at 2100 kPa and 475°C, the inlet enthalpy (h_1) is approximately 3410.3 kJ/kg. At the turbine exhaust (10 kPa, saturated steam), the enthalpy (h_2) is approximately 2584.7 kJ/kg. The power output (W) is 4000 kW.
Substituting the values:
2. Condenser Analysis:
The steam enters the condenser at 10 kPa (saturated vapor, h_2 = 2584.7 kJ/kg) and leaves as saturated liquid at 30°C (h_3 = 125.7 kJ/kg). The heat rejected by the steam (Q_out) is:
For the cooling water, the heat gained equals the heat lost by the steam. Using the specific heat of water (c_p = 4.18 kJ/kg·K) with inlet temperature T_in = 15°C and outlet T_out = 25°C:
The mass flow rate of the steam is 4.845 kg/s, and the cooling water must be supplied at a rate of 285.13 kg/s.
An ideal gas initially at 600 K and 10 bar undergoes a four-step mechanically reversible cycle in a closed system. In step 1-2, pressure decreases isothermally to 3 bar; in step 2-3, pressure decreases at constant volume to 2 bar; in step 3-4, volume decreases at constant pressure; and in step 4-1, the gas returns adiabatically to its initial state. Take CP = (7/2)R and CV = (5/2)R.
Sketch the cycle on a PV diagram.
Answer
The cycle is represented on a PV diagram as follows: State 1 to 2 is an isothermal expansion curve. State 2 to 3 is a vertical line downward (constant volume). State 3 to 4 is a horizontal line to the left (constant pressure). State 4 to 1 is an adiabatic compression curve returning to the initial point.
Determine (where unknown) both T and P for states 1, 2, 3, and 4.
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Calculate Q, W, ΔU, and ΔH for each step of the cycle.
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State the limitations of first law of thermodynamics.
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Discuss about the PVT behavior of pure substances.
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Describe about the principle of conservation of mass and energy for flow systems.
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Estimate the fugacity of isobutylene as a gas:
At 280°C and 20 bar;
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At 280°C and 100 bar.
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Explain the correlation for the estimation of residual and excess Gibbs energy in vapor liquid equilibria.
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What is correlation for petroleum fluids?
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Explain about the vapour liquid-liquid-equilibria.
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At 25°C the solubility of n-hexane in water is 2 ppm (molar basis), and the solubility of water in n-hexane is 520 ppm. Estimate the activity coefficients for the two species in the two phases.
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A binary liquid mixture is only partially miscible at 298 K. If the mixture is to be made homogeneous by increasing the temperature, what must be the sign of VLE?
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