Mechanical Engineering Answers

A refrigerator has a COP of 1.5. That is the refrigerator removes 1.5kwh of energy from the refrigerated space for each 1kw of electricity it consumes. Is this a violation of the first law of thermodynamics? Explain

A steam powerplant operates between a boiler pressure of 30bar and a condenser pressure of 0.04bar calculate the following: 1) the heat and work transfer 2) the cycle efficiency for a carnot cycle 3) the newtwork output 4)the work ratio

A steam powerplant operates between a boiler pressure of 30bar and a condenser pressure of 0.04bar calculate the following: 1) the heat and work transfer 2) the cycle efficiency for a carnot cycle 3) the newtwork output 4)the work ratio

a cylindrical tank with hemispherical heads is constructed of steel sections that are welded circumferentially. the tank diameter is 1.25m, the wall thickness is 22mm, and the internal pressure is 1750 kpa. calculate the stress in the heads of the tank

The disc shown in the figure is supported by two

circular tubes of same cross section and different

lengths which both are connected to the disk at one

end and fixed to a wall at the other end. The internal

and external diameters of the tubes are8cmiD =

and10cmoD = , respectively. Calculate the angle

by which the disk rotates when subjected to a

torque of3kN.mT = . The tubes are made of steel

with Young’s modulus of200GPaE = and

Poisson’s ratio of0.3



60 cm and 40 cm

A four-cylinder petrol engine has a swept volume of 2000 cm3, and the clearance volume

in each cylinder is 60 cm3. Calculate the air-standard thermal efficiency. lf the induction

conditions are 1 bar and 24oC, and the maximum cycle temperature is 1400oC, calculate

the mean effective pressure based on the otto air-standard cycle.

Calculate the power that can be transmitted at 300 rpm by a hollow steel shaft of 75 mm external diameter and 50 mm internal diameter when the permissible shear stress for the steel is 70 N/mm2 and the maximum torque is 1.3 times the mean. Compare the strength of this hollow shaft with that of a solid shaft. The same material, weight and length of both the shafts are same.

Find the diameter of the solid shaft to transmit 90 KW at 160 rpm such that the shear stress is limited to 60 N/mm2. The maximum torque is likely to exceed the mean torque by 20%. Also find the permissible length of the shaft, if the twist is not to exceed 1° over the entire length. Take rigidity modulus as 0.8×105N/mm2.

A steel shaft is to require transmitting 75 KW power at 100 rpm and the maximum twisting moment is 13% greater than the mean. Find the diameter of the steel shaft if the maximum stress is 70 N/mm2. Also determine the angle of twist in a length of 3 m of the shaft. Assume the modules of rigidity for steel as 90 KN/mm2.

A thin cylindrical pipe with an inside diameter of 200 mm is 4 mm thick and fitted with end covers. It is subjected to an internal pressure of 4,8 MPa. Calculate the circumferential and longitudinal stress induced. Which axially applied compressive load would reduce the longitudinal stress to zero