Mechanical Engineering Answers

Background A villager in South Africa has an inhabitant of five hundred people. It is 200 km from the nearest Eskom substation based on line of sight. Presently, the only source of electric power in the village is diesel generator. Due to Covid-19, the company that used to maintain the generator has folded up, consequently, the villagers have no electricity. Aim Design a standalone (off grid) Photovoltaic (PV) system with special reference to the village in South Africa with the following PV panel generation factors: Group Number PV panel generation factor A 8.5 B 8 C 7.8 D 7 E 7.5 G 7.2 F 8.4 G 7.5 Use any medium of communication available to group yourselves into a maximum of eight (8) members per group and name your groups as per the group numbers in the table above respectively. A typical platform to be used for communication could be myUnisa (discussion forum), Whatsup, Zoom, MS Teams etc. Choose PV panel generation factor based on the group number.

A jet of water with 50 mm diameter impinges on a curved vane

and is deflected through 135º. The vane moves in the same

direction as that of jet with a velocity of 5 m/sec. If the rate of

flow of water is 30 lt/sec, determine (a) force on the vane in the

direction of motion, (b) work done per sec and (c) efficiency.

A 20 cm diameter jet of water strikes a curved vane with a velocity of 30 m/s. The inlet vane angle is zero and the outlet angle is 25°. Find the resultant force on the vane

(a) when the vane is fixed;

(b) when the vane is moving with a velocity of 15 m/s in the direction of jet.

A thick cylinder of internal and external radii 300 mm and 500 mm respectively is subjected to a gradually increasing internal pressure P. Determine the value of P when:

(a) the material of the cylinder first commences to yield;

(b) yielding has progressed to mid-depth of the cylinder wall;

(c) the cylinder material suffers complete “collapse”.

Take uY = 600 MN/m’.

A foot-lever is 1 metre from the center of shaft to the point of application of 600 N load. Find: i) diameter of the shaft, ii) dimensions of the key, iii) dimensions of rectangular arm of the foot lever at 60 mm from the center of shaft assuming width of the arm as 3 times thickness. The allowable tensile stress may be taken as 75 N/mm2 and allowable shear stress as 70 N/mm2.

The properties of a system, during a reversible constant pressure non￾flow process at p = 1.6 bar, changed from v1 = 0.3 m3/kg, T1 = 20°C to v2 = 0.55 m3/kg, T2 = 260°C.

The specific heat of the fluid is given by

cp = 1.5+74/(T+45)kJ/kg°c

 , where T is in °C.

Determine : (i) Heat added/kg ;

(ii) Work done/kg ;

(iii) Change in internal energy/kg ;

(iv) Change in enthalpy/kg

A foot step bearing has a shaft 140 mm diameter is counter bored with a hole of 70 mm diameter al the end. The shaft rotates at 120 rpm. Calculate

(a) The axial load

(b) Frictional Torque

(c) Heat generated al the bearing if the allowable bearing pressure is 0.8 MN/m² by using Uniform wear theory.

Take coefficient of friction, mu = 0.045