Mechanical Engineering Answers

The turning moment diagram for a four stroke gas engine may be assumed for simplicity to be repre-

sented by four triangles, the areas of which from the line of zero pressure are as follows:

Expansion stroke = 3550 mm2; exhaust stroke = 500 mm2; suction stroke = 350 mm2; and compres- sion stroke = 1400 mm2. Each mm2 represents 3 N-m.

Assuming the resisting moment to be uniform, find the mass of the rim of a flywheel required to keep the mean speed 200 r.p.m. within ± 2%. The mean radius of the rim may be taken as 0.75 m. Also determine the crank positions for the maximum and minimum speeds

An ice-skating rink is located in an indoor shopping mall with an environmental air temperature of 22◦C and radiation surrounding walls of about 25◦C. The convection heat-transfer coefficient between the ice and air is about 10 W/m2 · ◦C because of air movement and the skaters’ motion. The emissivity of the ice is about 0.95. Calculate the cooling required to maintain the ice at 0◦C for an ice rink having dimensions of 12 by 40 m. Furthermore, the rink is located on the 2nd floor with which the room air temperature of the 1st floor is 24◦C with convection heat-transfer coefficient between the concrete floor (see appendix Table A3 for normal weight concrete) of the 2nd floor is about 12 W/m2. ◦C. Thickness of the concrete is 4 inches. The Obtain a value for the heat of fusion of ice and estimate how long it would take to melt 3 mm of ice from the surface of the rink if no cooling is supplied.

A dump truck hoists a box to an angle of 25° from the horizontal and pulls ahead 10 ft. Calculate the displacement of point A

 A mass of 0.9 kg of fluid, initially at a pressure of 15 bar and a temperature of 250oC, expands reversibly and polytropically to 1.5 bar. Find the final temperature, work and heat transfers and the change of entropy, if the index of expansion (n) is 1.25.

8. A 75% efficient cooling tower has a water entering at 45o C and wet bulb temperature of air entering at

25 oC. Find the water exit temperature of water.

A. 32oC B. 30oC C. 34.34oC D. 23.44oC

7. A 6 x 5 x 4 m room has a pressure of 101 kpa and temperature of 30oC (Psat = 5 kpa). If percent

relative humidity is 65%, find the mass of vapor (RV = 0.423 KJ/kgoK).

6. Air in a conditioned space has 26 oC db and 70% RH, find the wet bulb depression.

To a closed system 150 kJ of work is supplied. If the initial volume is 0.6 m3 and pressure of the system changes as p = 8 – 4V, where p is in bar and V is in m3, determine the final volume and pressure of the system.

An element in biaxial stress is subjected to stresses σx = −16 MPa and σy =42 MPa, as shown in the figure. Using Mohr's circle, determine:

(a) the stresses acting on an element oriented at a slope of 1 on 2.5 (see Fig Q1)

(b) the maximum shear stresses and associated normal stresses. Show all results on sketches of properly oriented elements.

It is required to lift a load of 1.2 tons through a height of 320

mm by using a screw jack under the following condition:

• The available material of the screw is plain carbon steel

which has elastic strength in tension and compression of

200 MPa and in shear 120 MPa respectively.

• The available material of the nut is phosphor-bronze for

which the elastic limit may be taken as 100 MPa in

tension, 90 MPa in compression and 80 MPa in shear.

• The bearing pressure between the nut and the screw is

not to exceed 20 N/mm?.

Design and draw the screw jack. The design should include

the design of:

1) The screw,

2) Nut,

3) Handle and Cup, and

4) Body.

Draw to full scale an isometric and multi-views for the screw

jack.

The design report should include the following:

• Calculation sheet.

• Detail drawing (soft).

• References including material data sheets and used

curves and tables.

• Assume any missing data.