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Test: U-Tube Manometer - Civil Engineering (CE) MCQ


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10 Questions MCQ Test Fluid Mechanics for Civil Engineering - Test: U-Tube Manometer

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Test: U-Tube Manometer - Question 1

The absolute pressure of gas A in the bulb in 'mm of Hg' is

Detailed Solution for Test: U-Tube Manometer - Question 1

Concept:
U-tube Manometer:

  • It is a transparent glass tube bent in a U shape initially both ends are open to the atmosphere after that one end of the U-tube is connected to the point at which the pressure of the liquid is to be measured and another end is open to the atmosphere.
  • The U-tube is filled with the manometric fluid whose Specific gravity should be higher than the liquid whose pressure is to be measured. initially, the level of the manometric fluid will be same in the both of the limbs.

U-tube manometer for gauge pressure:

  •  to calculate the gauge pressure let at point P, you may simply use the hydrostatic law and balance the column concepts So the pressure at the point P will be;
  • PA = ρ1gh1 - ρ2gh2
  • here, h2 and h1 height of the right and left limbs above the reference line X-X.
  • The absolute pressure at point A, Pabsolute = PA + Patm

Calculation:
Given:


Pabsolute = Patm + ρwgh1 + ρHggh2 - ρwgh3 
where,  Patm = 101.32 kPa, ρ = 1000 Kg/m3 , ρHg = 13600  Kg/m3, h1 = 0.05 m, h2 = 0.02 m, h3 = 0.17 m.
Pabsolute = 101.32 × 1000 + 1000 × 9.81 × 0.05 + 13600 × 9.81 × 0.02 - 1000 × 9.81 × 0.17
Pabsolute = 102887.28 Pa
Head in terms of Hg column is given by:
hHg  × ρHg × g = Pabsolute 
hHg × ρHg × g = 102887.28
hHg = 771.17 mm

Test: U-Tube Manometer - Question 2

Differential manometers are the devices used for measuring the difference of pressure between:

Detailed Solution for Test: U-Tube Manometer - Question 2

Concept:
Differential Manometers:

  • Differential manometers are devices used for measuring the difference of pressures between two points in a pipe or in two different pipes.
  • A differential manometer consists of a U-tube, containing a heavy or light liquid, whose two ends are connected to the points, whose difference of pressure is to be measured.
  • The most common types of differential manometers are
  1. U-tube differential manometer
  2. Inverted U-tube differential manometer
  • The tube generally contains mercury or any other liquid whose specific gravity is greater than the specific gravity of the liquid whose pressure is to be measured.

U-tube differential manometer

  • It consists of a U-tube containing a heavy liquid. 
  • The two ends of the tube are connected to the points whose difference is to be measured. 
  • It is used for measuring the difference of pressure between two points in the flow section to which it is connected.

Differential inverted U-tube manometer: 

  • It consists of an inverted U-tube containing a light liquid.
  • The two ends of the tube are connected to the points whose difference is to be measured.
  • It is used for measuring the difference of pressure between two points in the flow section to which it is connected.
  • It is used in two conditions
    • In underground pipeline
    • When the specific gravity of manometric fluid is less than 1

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Test: U-Tube Manometer - Question 3

In a U tube manometer filled with mercury and measuring the pressure of air in a container, the difference in height of the two columns is 12 cm. If the specific weight of mercury is 13.6 kg/liter, then what is the pressure measured by the manometer? (g = 10 m/sec2)

Detailed Solution for Test: U-Tube Manometer - Question 3

Concept:
Pressure intensity at any point in a fluid, P = ρ×g×h
Where,
ρ = mass density of fluid which is assumed to be constant along with the depth, g = acceleration due to gravity, h = height of fluid measured from the free surface.
1 litre = 10-3 m3
1 bar = 105 pascal
Calculation:
Given:

S = 13.6 kg/liter, ρ = 13.6 × 10kg/m3, h = 12 cm = 0.12 m
P = ρ×g×h = 13600 × 0.12 × 10 = 16320 pascal = 0.1632 bar

Test: U-Tube Manometer - Question 4

A U - tube manometer

Detailed Solution for Test: U-Tube Manometer - Question 4

U-tube Manometer:
(i) It consists of a glass tube in U shape, one end of which connected to the gauge point and another end open to the atmosphere.
(ii) The tube contains a liquid of specific gravity greater than that of the fluid of which the pressure is to be measured.
(iii) The choice of the manometric liquid depends on the range of pressure to be measured For the low-pressure range, liquid of lower SG is used and for the high range, generally, mercury is used.
(iv) A U-tube manometer is used inverted if the pressure differential is small (density of the manometric fluid is less than fluid) and A U-tube manometer is used upright if the pressure differential is large (density of the manometric fluid is large)
Limitation:

  • This method requires reading of fluid level at two or more points since the change in pressure causes a rise in one limb and drop in another.
Test: U-Tube Manometer - Question 5

It is required to find the pressure difference between two horizontal pipes through which water is flowing using an inverted manometer. Two monomeric fluids with specific gravities 13.6 and 0.8 and are available. Which manomeric fluid is to be used now?

Detailed Solution for Test: U-Tube Manometer - Question 5

Concept:
Differential Manometers:

  • Differential manometers are devices used for measuring the difference of pressures between two points in a pipe or in two different pipes.
  • A differential manometer consists of a U-tube, containing a heavy or light liquid, whose two ends are connected to the points, whose difference of pressure is to be measured.
  • The most common types of differential manometers are
  1. U-tube differential manometer
  2. Inverted U-tube differential manometer
  • The tube generally contains mercury or any other liquid whose specific gravity is greater than the specific gravity of the liquid whose pressure is to be measured.

U-tube differential manometer

  • It consists of a U-tube containing a heavy liquid. 
  • The two ends of the tube are connected to the points whose difference is to be measured. 
  • It is used for measuring the difference of pressure between two points in the flow section to which it is connected.


Differential inverted U-tube manometer: 

  • It consists of an inverted U-tube containing a light liquid.
  • The two ends of the tube are connected to the points whose difference is to be measured.
  • It is used for measuring the difference of pressure between two points in the flow section to which it is connected.
  • It is used in two conditions
    • In underground pipeline
    • When the specific gravity of manometric fluid is less than 1

Test: U-Tube Manometer - Question 6

In a differential manometer a head of 0.6 m of fluid A in limb 1 is found to balance a head of 0.3 m of fluid B in limb 2. The ratio of specific gravities of A to B is

Detailed Solution for Test: U-Tube Manometer - Question 6

Concept:
Hydrostatic law:

In a static fluid, the pressure depends on the vertical depth from the surface and it is independent of the shape and size of the container.

Calculation:
Given:


Specific gravity ∝ density
∴ 
= 0.5

Test: U-Tube Manometer - Question 7

U type of configuration is possible in _____ for pressure measurement.

Detailed Solution for Test: U-Tube Manometer - Question 7
  • Manometers are devices in which columns of a suitable liquid are used to measure the difference in pressure between two points or between a certain point and the atmosphere.
  • A manometer is needed for measuring large gauge pressures. It is basically the modified form of the piezometric tube.

 

  • A common type of manometer is like a transparent "U-tube" as shown in Figure:

These are of two types:

  1. Simple manometers
  2. Differential manometers

A simple manometer consists of a glass tube having one of its ends connected to a point where pressure is to be measured and another end remains open to atmosphere.

Test: U-Tube Manometer - Question 8

A pipe contains an oil of specific gravity 0.9. A differential manometer connected at the two points A and B shows a difference in mercury levels as 15 cm. The difference of pressure at the two points A and B will be (Note: consider the density of mercury as 13600 kg/m3)

Detailed Solution for Test: U-Tube Manometer - Question 8

Concept:
Differential manometer:

Differential manometers are the devices used for measuring the differences of pressures between two points in a pipe or in two different pipes. 
Most common types of differential manometers are:
1) U-tube differential manometer
A differential manometer consists of a U-tube, containing heavy liquid, whose two ends are connected to the points, whose difference of pressure is to be measured.


h = Difference of mercury level in the U-tube
y = Distance of the centre of B, from the mercury level in the right limb
x = Distance of the centre of A, from the mercury level in the right limb
ρ1 = Density of liquid at A
ρ2 = Density of liquid at B
ρg = Density of heavy liquid or mercury
Hence the difference in the pressure between A and B, when A and B are at different level is given by,
PA – PB = h × g × (ρg – ρ1) +ρ2gY – ρ1gX  
Hence the difference in the pressure between A and B, when A and B are at same level is given by,
PA – PB = g × h × (ρg – ρ1)    
2) Inverted U-tube differential manometer
It consists of an inverted U-tube, containing light liquid. It is used for measuring difference of low pressures
Calculation:
Given,

Oil specific gravity = 0.9
Difference in mercury level = 15 cm = 0.15 m
ρhg = 13600 kg/m3 
ρoil = 0.9 × 1000 = 900 kg/m3


PA + [900 × g × (Y + 0.15)] = PB + (900 × g × Y) + [0.15 × g × 13600]
PA - PB = (13600 × g × 0.15) - (900 × g × 0.15)
PA - PB = 18688 N/m2

Test: U-Tube Manometer - Question 9

A simple U tube manometer connected to a pipe in which liquid is flowing with uniform speed will give which kind of pressure?

Detailed Solution for Test: U-Tube Manometer - Question 9

Concept:
U tube manometers:

  • A U-tube manometer is the simplest pressure measurement device.
  • Its name comes from the U-shape formed when the two ends of a flexible tube full of liquid are raised to keep the liquid from coming out the ends.
  • A simple U tube manometer connected to a pipe in which liquid is flowing with uniform speed will give Gauge pressure.

Gauge pressure:
Gauge pressure is the pressure relative to atmospheric pressure. Most of the pressure measuring devices are calibrated to read gauge pressure.

  • Gauge pressure is positive for pressures above atmospheric pressure.
  • Gauge pressure is negative for pressures below atmospheric pressure.
  • Gauge pressure is zero at atmospheric pressure.

Atmospheric pressure:
Atmospheric pressure or barometric pressure is the pressure within the atmosphere of Earth. Atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point.
Patm = 1.013 bar.
Absolute pressure:
Absolute pressure is the sum of gauge pressure and atmospheric pressure.
Pabs = Pgauge + Patm .

Test: U-Tube Manometer - Question 10

Differential pressure head measured by mercury oil differential manometer (specific gravity of oil is 1.0) equivalent to a 600 mm difference of mercury levels will be nearly:

Detailed Solution for Test: U-Tube Manometer - Question 10

Manometer:
It is the device used for measuring pressure at a point in a fluid by balancing the column of fluid with the same or another column of liquid. manometers can be classified as follow:
1. simple manometer:

  • Piezometer.
  • U tube manometer.
  • Single column manometer.

2. Diffrential type mano meter:
A Differential type manometer is a type of manometer which is used to measure the pressure difference between two points in a pipe.
U - tube differential manometer:
case-1

The below figure shows a differential manometer whose two ends are connected with two different points A and B at the same and contain the same liquid.


Where,
h = Difference in mercury level in the U- tube.
h1 = Distance of center at A from mercury level at the right limb.
S1 = S2 =Speciic gravity of liquid at two points A and B.
S = specific gravity of heavy liquid or mercury in a U tube.
hA = Pressure head at A.
hB = Pressure head at B.
Difference in pressure head 
hA - hB = h(S - S1).
Case - 2:

The figure below shows a differential manometer whose two ends are connected with two different points A and B at different levels and containing different liquids.


Where,
h1 = Distance of the center of A from the mercury level at the left limb.
h2 = Distance of the center of B from the mercury level at the right limb.
S1 = Specific gravity of liquid in pipe A.
S2 = Specific gravity of liquid in pipe B.
The difference in pressure head at pint A and B.
hA - hB = h(S - S1) + h2S2 - h1S1.
Calculation:
Given:
S1 = 1.0
S = 13.6 (Specific gravity of mercury).
h = 600 mm.
Pressure difference = 600 × ( 13.6 - 1.0 ).
Pressure difference = 7560 mm = 7.56 m.
The correct answer is 7.56 m .

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