Pressure Measuring Instruments MCQ Quiz in मल्याळम - Objective Question with Answer for Pressure Measuring Instruments - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Concept:

Case 1: When only mercury is filled in the U Tube manometer, then the level of mercury in both limb is the same and have reference axis x-x.

Case 2: When 13.6 cm of water is poured into the right limb of the U Tube manometer then because of water, the level of mercury down by x unit in the right limb, and that x unit of mercury rises in the left limb, and also reference axis changes from x-x to y-y. Because of this level of mercury in the left limb rises by x unit from its initial level.

Calculation:

Given:

ρn = 1000kg/m3, ρmg = 13600kg/m3, amount of water poured = 13.6 cm

Pressure Equation for the system, having y-y as the reference axis

P_atm + 2x cm of mercury = Patm + 13.6 cm of water

2x × 13600 × g = 13.6 × 1000 × g

2x = 1

x = 0.5 cm

Concept:

The barometer is an instrument used to measure the pressure of air. There are two typed of barometers, the mercury manometer and, aneroid barometer.

Mercury barometer: In a mercury barometer a tube filled with mercury is placed upright with its open end down into a container of more mercury.

Air pressure on the mercury in the container keeps the mercury from draining out of the tube.

Aneroid barometer: An aneroid barometer uses a flexible metal bellows instead of mercury to measure air pressure.

Calculation:

The gauge pressure = P_abs - P_atm

At atmospheric pressure the gauge pressure = 0

Now if we write the equation for pressure in vertical column then,

P_atm – ρ_m × g × h – P_vapour = 0

⇒ P_atm = ρ_m × g × h + P_vapour

Now Since At atmospheric pressure the gauge pressure = 0

(P_vapour­)_gauge = -ρ_m × g × h

∴ Gauge pressure of vapour will be negative.

Concept:

Hydrostatic Law:

It states that the rate of increase of pressure in a vertical direction is equal to the weight density of the fluid at that point.

\(\frac{{\partial P}}{{\partial Z}} = - pg\;\left[ {Going\;Upward} \right]\)

\(\frac{{\partial P}}{{\partial Z}} = + pg\;\left[ {Going\;Downward} \right]\)

P = ρgh

Calculation:

Given:

Equating the pressure on the same datum line

\(\begin{array}{l} p + {\rho _1}{h_1} - {\rho _2}h - {\rho _3}\left( {{h_1} - h} \right) = p\\ \therefore h = \left(\frac{{{\rho _1}\;-\;{\rho _3}}}{{{\rho _2}\;-\;{\rho _3}}}\right){h_1} \end{array}\)

Concept:

Inclined manometer: The U- tube is at some angle, and the pressure calculated always uses vertical height.

• P = ρghsinθ 

where, θ = angle of the tube from horizontal, h = height of water difference in the tube

P = pressure in the tube, ρ = density of liquid

Calculation:

Given:

ρ = 800 kg/m3, h = 10cm = 0.1 m, g =9.81 m/s²

h' = hsinθ , P = ρgh'

h' = 0.1 × sin(20)^∘ = 0.034 m

P = 800 × 9.81 × 0.034

P = 268.42 N/m2

Concept:

U tube manometers:

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 .

Explanation:

Some of the important and desirable properties of the manometric liquids are:

(i) High chemical stability

(ii) Low viscosity

(iii) Low capillary constant

(iv) Low coefficient of thermal expansion

(v) Low volatility

(vi) Low vapour pressure

For amplifying the deflection in a liquid column manometer, liquids with lower density could be used or one of the limbs of the manometer may be inclined.

Commonly used manometric liquids are mercury, water or alcohol. Water and alcohol are used for measure low pressures while mercury is used for higher pressures.

Explanation:

Sensitivity:

Sensitivity is directly proportional to the length of fluid travel for a particular pressure difference.

\(\begin{array}{l} {\left( {Sensitivity} \right)_{U - tube}} \propto \;x\\ {\left( {sensitivity} \right)_{Inclined\;tube}} \propto \frac{x}{{\sin \theta }} \end{array}\)

\(\frac{(Sensitivity)_{Inclined\;tube}}{(Sensitivity)_{U-Tube}}=\frac{1}{\sin \theta}\)

McLeod gauge:

• The Mcleod gauge is used for the measurement of very low pressure or ultra-high vacuum pressure.
• It is nothing but special development sealed U-tube manometer, in which low-pressure fluid is compressed to high pressure and then it read by basic manometer techniques.
• The operation of Mcleod gauge is based on Boyle's law.
• The Mcleod gauge has excellent accuracy of  ±1%.
   

Bourdon Tube:

• Bourdon gauges are available to cover a large range of pressures. Bourdon gauges are purely mechanical devices utilizing the mechanical deformation of a flattened but bent tube that winds or unwinds depending on the pressure difference between the inside and the outside. The motion is against a spring torque such that a needle attached to the shaft indicates directly the pressure difference.

Manometer:

• 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 the atmosphere. Common types of simple manometers are:
  • Piezometer
  • U-tube Manometer
  • Single Column Manometer
• Differential Manometers measure the difference of pressure between two points in a fluid system and cannot measure the actual pressures at any point in the system. It consists of a U-tube, containing a heavy liquid, whose two ends are connected to the points whose difference of pressure is to be measured.

Explanation:

Concept:

U-tube manometer:

• The U-tube manometer is a U-shape bent glass tube, whose one end is open to the atmosphere and other end is connected to a section where the pressure of the liquid is to be measured.
• The U-tube manometer is filled with a liquid whose specific gravity is more than as compared to the liquid whose pressure is to be measured.

• The gauge pressure at point B in the above-shown U-tube manometer is calculated by using hydrostatic law and is given as:

The pressure of liquid above section A-A in the right column = \(\rho_{2}gh_{2}\)

The pressure of liquid above section A-A in the left column = \(P_B+\rho_{1}gh_{1}\)

Equating the above two pressure, we get the gauge pressure at point B as:

\(P_B+\rho_{1}gh_{1}=\rho_{2}gh_{2}\)

Calculation:

Given:

In this problem, the pressure at point B is:

Pressure of liquid above A-A in right column = 0

Pressure of liquid above A-A in left column = \(P_B+\rho_{1}gh_{1}+\rho_{2}gh_{2}\)

Equating both the pressure, we get:

\(P_B+\rho_{1}gh_{1}+\rho_{2}gh_{2}=0\)

\(P_B=-(\rho_{1}gh_{1}+\rho_{2}gh_{2})\)

Thus, option (2) is correct answer.

Explanation:

The correct statements are:-

(i) manometers are easy to operate

(ii) manometers do not require frequent calibration

Key Points :

• manometers are a device used to measure the pressure of the fluid by balancing of the fluid column
• They are generally made up of Glass
• They are generally a tube of Glass in U - Shape
• They are simple in construction and are easy to operate
• They do not require frequent calibration
• They are generally calibrated once a year.

Additional Information

Types of manometer :

• piezometer is wed to measure very low pressure
• Differential monometers are used to measure the difference of pressure between two points.