Mechanical Engineering Principles

THE MEASUREMENT OF TEMPERATURE 277

Assignment 7

This assignment covers the material

contained in chapters 21 and 24.

The marks for each question are shown

in brackets at the end of each question.

When required take the density of water to be
1000 kg/m^3 and gravitational acceleration as
9 .81 m/s^2.

1. A circular piston exerts a pressure of
   150 kPa on a fluid when the force
   applied to the piston is 0.5 kN. Calculate
   the diameter of the piston, correct to the
   nearest millimetre. (6)


2. A tank contains water to a depth of
   500 mm. Determine the water pressure

(a) at a depth of 300 mm, and

(b) at the base of the tank. (6)

3. When the atmospheric pressure is
   101 kPa, calculate the absolute pressure,
   to the nearest kilopascal, at a point
   on a submarine which is 50 m below
   the seawater surface. Assume that the
   density of seawater is 1030 kg/m^3 .(5)


4. A body weighs 2.85 N in air and 2.35 N
   when completely immersed in water.
   Determine

(a) the volume of the body,

(b) the density of the body, and

(c) the relative density of the body.

(9)

5. A submarine dives to a depth of 700 m.
   What is the gauge pressure on its surface
   if the density of seawater is 1020 kg/m^3.
   (5)


6. State the most appropriate fluid flow
   measuring device for the following app-
   lications:

(a) A high accuracy, permanent instal-

lation, in an oil pipeline.

(b) For high velocity chemical flow,

without suffering wear.

(c) To detect leakage in water mains.

(d) To measure petrol in petrol pumps.

(e) To measure the speed of a viscous

liquid. (5)

7. A storage tank contains water to a depth
   of 7 m above an outlet pipe, as shown
   in Figure 22.12 on page 254. The sys-
   tem is in equilibrium until a valve in
   the outlet pipe is opened. Determine the
   initial mass rate of flow at the exit of
   the outlet pipe, assuming that losses at
   the pipe entry= 0 .3v^2 , and losses at
   the valve= 0 .2v^2. The pipe diameter
   is 0.05 m and the water density,ρ,is
   1000 kg/m^3. (15)


8. Determine the wind pressure acting on
   a slender building due to a gale of
   150 km/h that acts perpendicularly to
   the building. Take the density of air as
   1 .23 kg/m^3 .(5)


9. Some gas occupies a volume of 2.0m^3
   in a cylinder at a pressure of 200 kPa.
   A piston, sliding in the cylinder, com-
   presses the gas isothermally until the
   volume is 0.80 m^3. If the area of the pis-
   ton is 240 cm^2 , calculate the force on the
   piston when the gas is compressed.
   (5)


10. Gas at a temperature of 180°C has its
    volume reduced by a quarter in an iso-
    baric process. Determine the final tem-
    perature of the gas. (5)


11. Some air at a pressure of 3 bar and at a
    temperature of 60°C occupies a volume
    of 0.08 m^3. Calculate the mass of the
    air, correct to the nearest gram, assuming
    the characteristic gas constant for air is
    287 J/(kg K). (5)


12. A compressed air cylinder has a volume
    of 1.0m^3 and contains air at a tempera-
    ture of 24°C and a pressure of 1.2 MPa.
    Air is released from the cylinder until the
    pressure falls to 400 kPa and the tem-
    perature is 18°C. Calculate (a) the mass
    of air released from the container, and
    (b) the volume it would occupy at S.T.P.
    (Assume the characteristic gas constant
    for air to be 287 J/(kg K)). (10)