Thermodynamics and Marks

Topics: Thermodynamics, Heat, Viscosity Pages: 6 (987 words) Published: February 22, 2013
HERIOT WATT UNIVERSITY

SCHOOL OF ENGINEERING AND PHYSICAL SCIENCES

DEGREE OF BENG IN MECHANICAL ENGINEERING

First Year

Mechanical Engineering Science 3

??day ?? June 2007??:?? – ??:??

Answer TWO questions from each section A & B.
Section A

Q1. a) For a Newtonian fluid state an expression for the shear stress. [4 marks]

b) An ice hockey puck traverses the ice on a thin sheet of water. A puck struck by an ice hockey player Initially travels at a speed of 20 m/sec, the thin layer of water between the puck and the ice has a thickness of 0.2 mm calculate the shear stress if the viscosity of the water is 0.0018 kg/m sec. [8 marks]

A puck has an approximate diameter of 80 mm, calculate the initial drag force on the puck. [5 marks]

c) In the figures below the viscosity as a function of temperature is graphed for two fluids, Fluid A and Fluid B; given no other information, identify which fluid is a liquid and which is a gas. Justify your answer.

Fluid A Fluid B [pic]
[pic]

Figure Q1
[8 marks]
.

Q2.Figure Q2a shows a mercury manometer, (mercury s.g.=13.6) connected to a pipeline transporting oil (oil s.g.=0.85), the other arm of the manometer is exposed to the atmosphere. What is the absolute pressure in the pipeline? [pic]

Figure Q2a
[10 marks]

Another mercury manometer is connected to two oil pipelines (oil s.g.=0.85) labelled A and B, as shown below in Figure Q2b. Calculate the pressure difference pB-pA.

[pic]
Figure Q2b

[10 marks]

Suppose a pressure gauge was fitted to pipeline A and it measured a pressure of 2 bar. What would the absolute pressure in pipeline B be? Give your answer in bar. [5 marks]

Q3. a)A hot air balloon has a volume of 1,000 m3(1 thousand m3). Taking the surrounding air density to be 1.21 kg/m3 calculate the buoyancy force. [5 marks]

Taking the pressure and temperature of the hot air to be 1 bar and 200oC respectively calculate the mass of hot air (Specific gas constant R=287 J/kg K)? [5 marks]

If the balloon and basket have a mass of 100 kg combined and a typical passenger has a mass of 70 kg, how many people can ride in the balloon? [8 marks]

b) An experimental model boat has been constructed by a team of young engineers and it has been found to be unstable. A number of suggestions are made to improve the boats stability that all involve attaching buoyancy aids (blocks of polystyrene) to the outside of the boat, see the figure below.

[pic]

Figure Q3

Of the three configurations rank them in order of most stable to least stable. Justify your ranking. [7marks]

Section B./
Section B

Q4.With the aid of a sketch on a pV diagram, describe the processes which occur in the cylinder of a 4-stroke, spark-ignition engine during its operation. [10 marks]

An engine test was carried out on a 6 cylinder 4 stroke engine with a total swept volume of 3000cm3. The following data were obtained:

Indicator diagram
Length (x axis on the indicator diagram)160mm
Spring constant75kN/m2 per mm
Net diagram area1600mm2

Engine speed2500 rev/min
Torque170Nm

Calculate:
a) the indicated work during one cyclefor one cylinder [5 marks] b) the indicated power output of the engine [4 marks] c) the brake power output of the engine [2 marks] d) the brake specific fuel consumption in kg/(kW h) if 150 cm3 of fuel is consumed in a 1 minute test (fuel density = 750 kg/m3) [4 marks]

Q5.(a) Coal fuelled power plant for generating electricity uses steam/water in a cycle. Name the thermodynamic devices in the cycle and show how they are linked together. [5 marks]

A power plant burns 0.5 metric tonnes of coal in an hour and in that time produces 6000 MJ of...
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