Thermal Power Engineering Answers

In the single-phase half-wave rectifier shown below, assume that I, is constant (load inductance L is very large). (a) Sketch the load voltage waveform v for a= 90°and find its average value V4c

Single phase full-wave fully controlled rectifier bridge is operated from a 110 V, 60 Hz supply Draw the load voltage and current and switch voltage waveforms along with supply voltage assume that 40°.

The single-phase half-wave controlled rectifier supplies a resistive load draws an average current of 1.62 A. If the converter is operated from a 240 V, 50 Hz supply and if the average value of the output voltage is 81V, calculate the following: (a) The firing angle a. (b) Load resistance. (c)The rms load voltage. (d) The rms load current. (e) The output d.c. power (f) The ripple factor .

2.6 Air flows steadily at a mass flow rate m of 0.85 kg/sec through an air
compressor. The air enters the compressor by a velocity c1 of 6.5 m.s–1,
pressure p1 of 0.95 bar and a specific volume v1 of 1.85 m3/kg, and leaves
the compressor at a velocity c2 of 9.5 m.s–1, pressure p2 of 16.5 bar and a
specific volume v2 of 0.45 m3/kg. The specific internal energy u2 of the air
leaving the compressor is 215 kJ/kg greater than that of the air entering.
Cooling water in a jacket surrounding the cylinder absorbs heat from the air
Qout at the rate of 135 kJ/kg.
a. the mechanical power P required to drive the compressor in kW if the
mechanical efficiency turbine is 80%,
b. the specific change of the air enthalpy h in kJ/kg, and
c. the cross-sectional area at the exit pipe A2 in m2.

Two Carnot engines operate in a series between two reservoirs maintained at 500 oC and 40 oC, respectively. The energy rejected by the first engine is utilized as energy input to the second engine. Determine the temperature of this intermediate reservoir between the two engines, if the efficiencies of both engines are the same?

A cylinder contains N2, at a pressure of 200 kPa and a temperature of 80°C. As a result of cooling at night, the cylinder pressure is reduced to 190 kPa and the temperature is 30°C. How much work does the gas do?

100 kg/min of steam at 34 bars, 340°C (h=3082.0kJ/kg) expands through a turbine isentropically until the pressure becomes 0.25 bars (h= 2540.37kJ/kg). Find the work in hp.

Show that coefficient of performance of heat pump and refrigerator can be related as COP ref =COP hp-1

Hot combustion gases of a furnace are flowing through a square chimney made of concrete (k = 1.4 W/m-K). The flow section of the chimney is 20 cm x 20 cm, and the thickness of the wall is 20 cm. The average temperature of the hot gases in the chimney is T, = 300°C, and the average convection heat transfer coefficient inside the chimney is h; = 70 W/m-K. The chimney is los ing heat from its outer surface to the ambient air at T = 20°C by convection with a heat transfer coefficient of h,= 21 W/m2K and to the sky by radiation. The emissivity of the outer surface of the wall is e=0.9, and the effective sky temperature is estimated to be 260 K. Using the finite difference method with Ax = Ay = 10 cm and taking full advantage of symmetry, determine the tem pressure at the nodal points of a cross section and the rate of heat loss for a 1-m-long section of the chimney.

Dry saturated steam at 7bar expands reversibly in a cylinder behind a piston until the process is 0.1bar. If heat is supplied continuously during the process in order to keep the temperature constant, Calculate the change of internal energy per unit mass of steam.