Mechanical Engineering Answers

Question No. 17      (a) Design a bushed pin type flexible coupling for connecting a motor shaft to a pump shaft for the following service conditions.

Power to be transmitted = 40 kW.

Speed of the motor shaft = 1000 RPM.

Diameter of the motor shaft = 50 mm

Diameter of the pump shaft = 45 mm.

The bearing pressure in the rubber bush and allowable stress in the pins are to be limited to 0.45 N/mm² and 25 MPa respectively.

(b) List the factors to be considered while selecting the material for design of Machine element.

A furnace wall consists of 250mm fire brick, 125mm thick insulating brick and 250mm thick building brick. The inside wall is at a temperature 600 degrees Celcius and atmospheric temperature is 20 degrees Celsius. The heat transfer coefficient for outside surface is 10 w/m^2k and thermal conductivity of fire brick, insulating brick and building brick are 1.4, 0.2 and 0.7 w/mk respectively. Neglecting radiation calculate the rate of heat loss per unit surface area, the temperature at each interface through the wall and temperature at the outside surface of the wall.

A steam main of 150mm outside diameter containing wet steam at 28bar is insulted with an inner layer of diatomaceous earth, 40mm thick and an outer layer of 85% magnesium 25mm thick. The inside surface of the pipe is at the steam temperature and heat transfer coefficient for the outside surface of the lagging is 17w/m^2k. The thermal conductivities of diatomaceous earth and 85% magnesium are 0.09 and 0.06 w/mk respectively.

Neglecting radiation and thermal resistance of the pipped wall calculate : the rate of heat loss per unit length of the pipe and temperature of the outside surface of the lagging when room temperature is 20 degrees celcius

(a) Explain various process of Carnot cycle with the help of P-V and T-S diagrams and mention various assumptions made in the analysis of Carnot cycle.

(b) The following details refers to a four stroke engine:

Cylinder diameter = 220 mm

Length of stroke = 330 mm

Speed = 5 rev/second

Effective brake load = 500 N

Mean circumstances of the brake drum = 4·5 m

IMEP = 5·6 bar

Calculate

(a) Indicated power, (b) Brake power and (c) Mechanical efficiency.

What are different methods adopted in cooling of an I.C engine. Explain in details.

(a) A Diesel engine has a bore of 200 mm and stroke of 320 mm. Cut – off takes place at 9% of stroke. Find the air – standard efficiency if clearance volume is 0.000593 m³.

(b) An engine working on Otto cycle has a compression ratio of 6. Find the air – standard efficiency of the cycle.

A water manometer shows a pressure, in a vessel of 400mm below atmospheric pressure. If the atmospheric pressure is measured as 763 mm Hg. Determine absolute pressure in the vessel in kN/m²

Steam turbine is receiving 1,073 lb/hr of steam, determine the kW output of the turbine if the work done by steam is 2,121 BTU/lb.

The throat and exit area of a convergent divergent nozzle in a wind tunnel are 4 cm and 10 cm respectively. The reservoir conditions are 10 bar and 95°C. Find out the Mach number, pressure and temperature of the air at the test section. Also find the mass flow rate.

A perfect gas having c_P = 1017.4 J/kg-K and m = 28.97 flows adiabatically in a converging passage with a mass flow rate m = 29.188 kg/s. At a particular cross section, M = 0.6, T = 550 K, and P = 2.0 middot 10^5 N/m^2. Calculate the area of the cross-section of the passage at that point.