Mechanical Engineering Answers

The 6-pole,wound-rotor induction motor is excited by a 3-phase, 60 Hz source. Calculate the

frequency of the rotor current under the following conditions:

(i) at standstill

(ii) motor turning at 500 rpm in the same direction as the revolving field

(iii) motor turning at 500 rpm in the opposite direction to the revolving field

(iv) motor turning at 2000 rpm in the same direction as the revolving field

Realize the following two filters using electrical circuits consisting of resistor(s) (R), and capacitor(s) (C), obtain their step responses based on the circuits using the software. 2.1 𝑉𝑜𝑢𝑡1 𝑉𝑖𝑛1 = 𝑠 𝑠+5 (10) 2.2 𝑉𝑜𝑢𝑡2 𝑉𝑖𝑛2 = 1 2𝑠+1

Refer to Fig 3 when answering question 3. In the circuit , , and . The switch was at position a for a very long time and is switched to position b at t=0. c b a - + V0 Ra Rb () c v t () ci t Fig 3. (i) Find the capacitor voltage, as a function of time after the switch closes to position b at using the analytical approach (5). (ii) What will be the value of current at the instance of the switch change? (5) (iii) At what point in time will the potential difference across the capacitor be 15% of the original value? (5) (iv) Build the circuit of Fig 3 in PSpice or Multism. Simulate and measure the power and energy dissipated in the circuit between t=0s and t=15ms (10

Water at the rate of 4 kg/s is heated from 40o

C to 55o

C in a shell and tube heat 

exchanger. On the shell side one pass is used with water as the heating fluid 

and at a mass flow rate of 2kg/s, and entering the heat exchanger at 95o

C. The 

overall heat transfer coefficient is 1500 W/m2

K. and the average water velocity 

in the 2 cm diameter tubes is 0.5m/s. Because of space limitations, the tube 

length must not exceed 3 m. Calculate the number of tube passes , the number 

of tubes per pass and the length of the tubes, keeping in mind the design 

constraints

Formulate the recurrence and derive closed form for Josephous problem.

Problem 18.

A 400 kVA transformer has a

primary winding resistance of 0.5 and a

secondary winding resistance of 0.001. The iron

loss is 2.5 kW and the primary and secondary

voltages are 5 kV and 320 V, respectively. If the

power factor of the load is 0.85, determine the

efficiency of the transformer (a) on full load, and

(b) on half load.

Problem 9.

A single-phase, 50 Hz transformer

has 25 primary turns and 300 secondary turns. The

cross-sectional area of the core is 300 cm2. When

the primary winding is connected to a 250 V supply,

determine (a) the maximum value of the flux

density in the core, and (b) the voltage induced in

the secondary winding.

Problem 5.

A 5 kVA single-phase transformer

has a turns ratio of 10:1 and is fed from a 2.5 kV

supply. Neglecting losses, determine (a) the full

load secondary current, (b) the minimum load

resistance which can be connected across the

secondary winding to give full load kVA and (c) the

primary current at full load kVA.

A machine of mass 500kg is mounted through four rubber mountings that exhibit linear elasticity and viscous damping.in the installation of the machine ,each pad was observed to undergo a compression of 15mm. During the trial run of the machine ,the system was observed to execute free samples vibration such that it made 50 oscillations in 15 seconds.For this system,find;

a)the stiffness and damping coefficient of each mounting.

b)the minimum number of oscillations and consequently the time it will take for the amplitude of oscillations to be reduced to 1%.