Long Soln Flashcards
A single-effect evaporator is concentrating a feed of 9072 kg/h of a 10 wt % solution of NaOH in water to a product of 50% solids. The pressure of the saturated steam used is 42 kPa (gage) and the pressure in the vapor space of the evaporator is 20 kPa (abs). The overall heat-transfer coefficient is 1988 W/m2-K. The feed temperature is 288.8 K. The heating surface required
340 m2
The engine cylinder of a motorcycle is constructed of 2024-6 aluminum alloy and is of height H = 0.15 m and outside diameter D = 50 mm. Under typical operating conditions the outer surface of the cylinder is at a temperature of 500 K and is exposed to ambient air at 300 K, with a convection coefficient of 50 W/m? • K. Annular fins are integrally cast with the cylinder to increase heat transfer to the surround ings. Consider five such fins, which are of thickness t = 6 mm, length L = 20 mm, and equally spaced. What is the increase in heat transfer due to use of the fins?
454 W
The wall of an industrial furnace is constructed from 0.15-m-thick fireclay brick having a thermal conductivity of 1.7 W/m • K. Measurements made during steady-state operation reveal temperatures of 1400 and 1150 K at the inner and outer sur-faces, respectively. What is the rate of heat loss through a wall that is 0.5 m by 1.2 m on a side?
1700 W
An uninsulated steam pipe passes through a room in which the air and walls are at 25°C. The outside diameter of the pipe is 70 mm, and its surface temperature and emissivity are 200°C and 0.8, respectively. What are the surface emissive power and irradiation? If the coefficient associated with free convection heat transfer from the surface to the air is 15 W/m’ • K, what is the rate of heat loss from the surface per unit length of pipe?
998 W/m
A spherical, thin-walled metallic container is used to store liquid nitrogen at 77 K. The container has a diameter of 0.5 m and is covered with an evacuated, reflective insulation composed of silica powder. The insulation is 25 mm thick, and its outer surface is exposed to ambient air at 300 K. The convection coefficient isknown to be 20 W/m? - K. The latent heat of vaporization and the density of liquid nitrogen are 2 X 10* J/kg and 804 kg/m’, respectively. What is the rate of heat transfer to the liquid nitrogen?
13.06 W
A spherical, thin-walled metallic container is used to store liquid nitrogen at 77 K. The container has a diameter of 0.5 m and is covered with an evacuated, reflective insulation composed of silica powder. The insulation is 25 mm thick, and its outer surface is exposed to ambient air at 300 K. The convection coefficient isknown to be 20 W/m? - K. The latent heat of vaporization and the density of liquid nitrogen are 2 X 10* J/kg and 804 kg/m’, respectively. What is the rate of liquid boil-off?
7 L/day
Steam condensing on the outer surface of a thin-walled circular tube of diameter D = 50 mm and length L = 6 m maintains a uniform outer surface temperature of 100°C. Water flows through the tube at a rate of in = 0.25 kg/s, and its inlet and outlet temperatures are Tm = 15°C and Tmo = 57°C. What is the average convection coefficient associated with the water flow?
755 W/m2K
A single-effect evaporator is concentrating a feed of 9072 kg/h of a 10 wt % solution of NaOH in water to a product of 50% solids. The pressure of the saturated steam used is 42 kPa (gage) and the pressure in the vapor space of the evaporator is 20 kPa (abs). The overall heat-transfer coefficient is 1988 W/m2-K. The feed temperature is 288.8 K. The steam economy
0.81
The model ‘6SE-TCA3 Perkins’ diesel engine have a stroke of 190 mm and a bore of 160 mm. If its clearance volume is 5% of the swept volume, determine the pressure and temperature at the end of compression when the inlet condition is 1 bar, 27o C.
P 67.2 bar
T 956 K
A closed rigid container has a volume of 1 m 3 and holds air at 345 kPa and 20°C. Heat is added until the temperature is 327°C. Determine the change in Internal Energy:-
a) Using an average value of the specific heat.
b) Taking into account the variation of specific heat with temperature.
a 932 kJ
b 1018.7 kJ
An adiabatic steam turbine expands steam from a pressure of 6 MPa and a temperature of 500°C to a pressure of 10 KPa The isentropic efficiency of the turbine is 0.82 and changes in kinetic and potential energy may be neglected. Determine the state of the steam at exit from the turbine and the specific work transfer.
mixture 0.917
849 kJ/kg
A steam turbine receives steam at 2 MPa and 250o C, and exhausts at 0.1 MPa, 0.85 dry.
a) Neglecting heat losses and changes in ke and Pe, estimate the work output per kg steam.
b) If, when allowance is made for friction, radiation, and leakage losses, the actual work obtained is 80% of that estimated in (a), calculate the power output of the turbine when consuming 600 kg of steam per minute.
a 539 kJ/kg
b 4.31 MW
A boiler receives feed water at 40o C and delivers steam at 2 MPa and 500o C. If the furnace is oil fired, the calorific value of oil being 42000 kJ/kg and 4000 kg oil are burned while 45000 kg of steam are produced, determine :
a) the heat supplied in the boiler.
b) the efficiency of the boiler.
a 1.484 x 10^8 kJ
b 88%
Air, which may be considered a perfect gas, enters an adiabatic nozzle with negligible velocity. The entry pressure is 6 bar and the exit pressure is 1 bar; the entry temperature is 760 K. The flow throughout the nozzle is reversible and the mass flow rate is 2 kg/s. Calculate the exit velocity.
782 m/s
Self-ignition would occur in an engine using certain brand of petrol if the temperature due to compression reaches 350o C; when the inlet condition is 1 bar, 27o C.
Calculate the highest compression ratio possible in order to avoif self-ignition, if the compression is according to
a) adiabatic, with index of 1.4; and
b) polytropic, with index of 1.3
a 6.2
b 11.4
