Showing 514–522 of 728 results

  • A CI is desired for the true average stray-load loss

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    A CI is desired for the true average stray-load loss ? (watts) for a certain type of induction motor when the line current is held at 10 amps for a speed of 1500 rpm. Assume that stray-load loss is normally distributed with

    ? = 3.3. (Round your answers to two decimal places.)

    (a) Compute a 95% CI for ? when n = 25 and x = 57.8.

    (b) Compute a 95% CI for ? when n = 100 and x = 57.8.

    (c) Compute a 99% CI for ? when n = 100 and x = 57.8.

    (d) Compute an 82% CI for ? when n = 100 and x = 57.8.

    (e) How large must n be if the width of the 99% interval for ? is to be 1.0? (Round your answer up to the nearest whole number.)

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  • Unit Eleven Homework Solutions

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    1. Consider a 210 MW steam power plant that operates on a simple ideal Rankine cycle. Steam enters the turbine at 10 MPa and 500oC and is cooled in the condenser to a pressure of 10 kPa. Show the cycle on a T-s diagram with respect to the saturation lines and determine (a) the quality of steam at the turbine exit, (b) the thermal efficiency of the cycle, and (c) the mass flow rate of the steam.
    2. Consider a solar-pond power plant that operates on a simple ideal Rankine cycle with refrigerant-134a as the working fluid. The refrigerant enters the turbine as a saturated vapor at 1.6 MPa and leaves at 0.7 MPa. The mass flow rate of the refrigerant is 6 kg/s. Show the cycle on a T-s diagram with respect to the saturation lines and determine (a) the thermal efficiency and (b) the power output of the plant.
    3. Consider a steam power plant that operates on a simple ideal Rankine cycle and has a net power output of 45 MW. Steam enters the turbine at 7 MPa and 500oC and is cooled in the condenser to a pressure of 10 kPa by running cooling water from a lake through the condenser at a rate of 2000 kg/s. Show the cycle on a T-s diagram with respect to the saturation lines, and determine (a) the thermal efficiency of the cycle, (b) the mass flow rate of the steam, and (c) the temperature rise of the cooling water.
    4. A steam power plant operates on an ideal regenerative Rankine cycle. Steam enters the turbine at 6 MPa and 450oC and is condensed in the condenser at 20 kPa. Steam is extracted from the turbine at 0.4 MPa to heat the feedwater in an open feedwater heater. Water leaves the feedwater heater as a saturated liquid. Show the cycle on a T-s diagram and determine (a) the net work per kilogram of steam flowing through the boiler and (b) the thermal efficiency of the cycle.
    5. Repeat problem 4 with the open feedwater heater replaced by a closed feedwater heater. Assume that the feedwater leaves the heater at the condensation temperature of the extracted steam and that the extracted steam leaves the heater as a saturated liquid and is pumped to the line carrying the feedwater.
    6. A steam power plant operates on an ideal reheat-regenerative Rankine cycle and has a net power output of 80 MW. Steam enters the high-pressure turbine at 10 MPa and 550oC and leaves at 0.8 MPa. Some of the steam is extracted at this pressure to heat the feedwater in an open feedwater heater. The rest of the steam is reheated to 500oC and is expanded in the low pressure turbine to the condenser pressure of 10 kPa. Show the cycle on a T-s diagram and determine (a) the mass flow rate of steam flowing through the boiler and (b) the thermal efficiency of the cycle.
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  • EGR 334: Thermodynamics Review Problems Solutions

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    Problem 1) A reversible power cycle operates between a thermal reservoir at 1540°F and 40°F.
    a) What is the maximum thermodynamic efficiency of the cycle?

    1. b) This cycle is found to have Wcycle = 50 Btu, what is Qout?

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    Problem 2) An inventor claims to have devised a refrigeration cycle that at steady state requires a net power input of 0.8 hp to remove 13,000 Btu/hr of energy by heat transfer from the freezer compartment at -10°F and discharge energy by heat transfer to a kitchen at 65°F.
    a) What is the maximum thermodynamic coefficient of performance for the cycle?

    1. b) Is this process thermodynamically possible? Why or why not?

    Problem 3) One kilogram of water executes a Carnot power cycle. The following table describes the thermodynamic cycle.

    1. a) Complete the following tables
    State 1 2 3 4   Process Q (kJ) W (kJ)
    p (bar) 40 40 1.5 1.5   1 – 2    
    T (°C)           2 – 3    
    x 0.15 1 0.801 0.32   3 – 4    
    v (m3/kg)           4 – 1    
    u (kJ/kg)                
    s (kJ/kg-K)                

    1. b) Draw the cycle on the p-v and T-s diagrams.

    Problem 4) A 2 m3 ridged, insulated container is filled with 4.76 kg of air and fitted with a paddle wheel. The container and its contents are initially at 293 K. The paddle wheel does 710 kJ of work on the air. Treat the air as an ideal gas with cv = 0.72 kJ/kg·K.

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    1. a) What is the initial pressure?

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    1. b) What is the final temperature?

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    1. b) How much entropy is produced?

    Problem 5) Steam enters a turbine operating at steady state at 6 MPa, 600°C with a mass flow rate 125 kg/min and exits as a saturated vapor at 20 kPa. The turbine produces energy at a rate of 2 MW. Kinetic and potential energy effects are negligible. The rate of heat loss from the turbine occurs to the air around the turbine at 27°C.

    1. a)   What the rate of entropy production for within the turbine?
    2. b)   What is the isentropic efficiency of the turbine?

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  • EGR 334 Thermodynamics: Homework 18

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    EGR 334 Thermodynamics:   Homework 18

    Problem 4: 95

    A turbine operating at a steady state that provides power to an air compressor and an electric generator. Air enters the turbine with a mass flow rate of 5.4 kg/s at 527 deg C and exits the turbine at 107 deg C, 1 bar. The turbine provides power at a rate of 900 kW to the compressor and at a rate of 1400 kW to the generator.   Air can be modeled as an ideal gas, and kinetic and potential energy changes are negligible. Determine

    1. a) the volumetric flow rate of the air at the turbine exit, in m3/s and
    2. b) the rate of heat transfer between the turbine and its surroundings in kW.

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    EGR 334 Thermodynamics:   Homework 18

    Problem 4: 98

    A refrigeration system consists of a heat exchanger, an evaporator, a throttling valve, and associated piping. Data for steady state operation with R134a are given in the figure. There is no significant heat transfer to or from the heat exchanger, valve, and piping. Ignore KE and PE. Determine the rate of heat transfer between the evaporator and its surroundings in Btu/h.

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    EGR 334 Thermodynamics:   Homework 18

    Problem 4: 102

    Steady state operating data for a simple steam power plant are provided in the figure. Stray heat transfer, KE and PE effects are small. Determine

    1. a) thermal efficiency
    2. b) mass flow rate of cooling water in kg/kg of stream flowing.

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  • Determine the thermal efficiency and the mass flow rate of the cooling water

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    uploaded image

    Steady-state operating data for a simple steam power plant are provided in figure. Stray heat transfer and kinetic and potential energy effects can be ignored. Determine the (a) thermal efficiency and (b) the mass flow rate of the cooling water, in kg per kg of steam flowing.

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  • A person is working near the secondary of a transformer

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    A person is working near the secondary of a transformer . The primary voltage is 120 V at 60.0 Hz. The capacitance C, which is the stray capacitance between the hand and the secondary winding, is 20.0 ρF. Assuming the person has a body resistance to ground of Rb = 50.0 kΩ, determine the rms voltage across the body.

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  • Determine the power developed by the turbine in hp.

    $2.00

    Water vapor at 800 lbf/in^2 and 1000 degrees F enters a turbineoperating at steady state and expands to 2 lbf/in^2. The mass flowrate is 5.56 lb/s and the isentropic turbine efficiency is 92%.Stray heat transfer and kinetic and potential energy effects arenegligble. Determine the power developed by the turbine in hp.

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  • Will the beam strike the moon?

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    A laser beam is to be directed towards the center of the moon, but the beam strays 0.25 degree from its intended path. The radius of the moon is about 1000 miles, and the distance from the moon to the earth is 240,000 miles. Will the beam strike the moon? (You may treat the moon as a flat disc for the purposes of this problem.)

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  • Determine the power developed by the turbine, in hp

    $1.00

    Water vapor at 800lbf/in^2, 1000 degree F enters a turbine operating at a steady state and expands to 2 lbf/in^2. The mass flow rate is 5.56 lb/s, and the isentropic turbine efficiency is 92%. Stray heat kinetic and potential energy effects are negligible. Determine the power developed by the turbine, in hp.

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