TUT1-PROPERTIES OF FLUIDS
Question 1
Calculate the dynamic viscosity of an oil which is used for
lubrication between a square plate of size 0.8 m x 0.8 m and
an inclined plane with angle of inclination 30 degrees as shown
in Fig. 1. The weight of the square plate is 300 N and its slides
down the inclined plane with a uniform velocity of o.3 m/s.
The thickness of the oil film is 1.5 mm.
Fig.1
Question 2
A flat plate 0.3 m2 in area moves edgewise through oil
between large, fixed parallel planes 10 cm apart (Fig. 2a & 2b).
If the velocity of the plate is 0.6 m/s and the oil has a kinematic
viscosity of 0.45 × 10-4 m/s and a specific gravity of 0.8,
calculate the drag force when: (i) the plate is 2.5 cm from one
of the planes; (ii) the plate is equidistant from the plane.
Question 3
The dynamic viscosity of an oil used for lubrication between a
shaft and sleeve is 0.6 Ns/m2(Fig. 3). The shaft is of diameter
0.4 m and rotates at 190 rpm. Calculate the power loss in the
bearing for a sleeve of length 90 mm. The thickness of the oil
film is 1.5 mm.
Fig.3
Question 4
Calculate the capillary effect in millimetres in a glass tube of 4
mm diameter when immersed in (a) water and (b) mercury.
The temperature of the liquid is 20℃ and the values of the
surface tension of water and mercury at 20℃ in contact with
air are 𝜎 = 0.073575 𝑁⁄𝑚 and 𝜎 = 0.51 𝑁⁄𝑚 respectively.
The angle of contact for water is zero and that of mercury is
130°. The density of water at 20℃ is 998 𝑘𝑔⁄𝑚3 .
Question 5
(a). The pressure inside a 50-mm-diameter soap bubble is 2.5
N/m2 above the atmosphere. Calculate the surface tension of
the soap film. (b) Air is introduced through a nozzle into a tank
of water to form a stream of bubbles. If the bubbles are
intended to have a diameter of 2 mm, calculate by how much
the pressure of the air at the nozzle must exceed that of the
surrounding water. Assume that the surface tension of water
is 0.073 N/m. What would be the absolute pressure inside the
bubble if the surrounding water was 100 kPa?