Determination of Dryness Fraction of Steam MCQ Quiz in தமிழ் - Objective Question with Answer for Determination of Dryness Fraction of Steam - இலவச PDF ஐப் பதிவிறக்கவும்

Explanation:

A separating and throttling calorimeter is a combination of separating and a throttling calorimeter.

The Separating calorimeter:

• It consists of two concentric chambers, the inner chamber and the outer chamber, which communicate with each other through an opening at the top.
• As the steam discharges through the metal basket, which has a large number of holes, the water particles due to their heavier momentum get separated from the steam and collect in the chamber.
• The comparatively dry steam in the inner chamber moves up and then down aging through the annular space between the two chambers and entering the Throttling Calorimeter.
• It is a vessel used initially to separate some of the moisture from the steam, to ensure superheat conditions after throttling. The steam is made to change direction suddenly; the moisture droplets, being heavier than the vapor, drop out of suspension and are collected at the bottom of the vessel.

The Throttling Calorimeter:

• It is a vessel with a needle valve fitted on the inlet side.
• The steam is throttled through the needle valve and exhausted to the condenser. The state of steam for the separating and throttling calorimeter should be in superheated vapor just after throttling.
• Then only pressure and temperature can be measured by a manometer and thermometer and then using the steam table enthalpy of superheated vapor is determined.
• From the steady flow energy equation, we can find the enthalpy after throttling and dryness fraction.
• The throttling calorimeter is a device that can use to measure the quality of wet steam.

Explanation:

Throttling Calorimeter: A throttling calorimeter is based on the principle of throttling the wet steam so that it becomes superheated.

Separating Calorimeter: It is a vessel used initially to separate some of the moisture from the steam, to ensure superheat conditions after throttling.

Combined Separating and Throttling Calorimeter

A combined separating and throttling calorimeter is therefore found most suitable for accurate measurement of dryness of steam reducing the drawback of Separating Calorimeter (i.e. water particles from wet steam are not fully separated) and the drawback of Throttling Calorimeter (i.e. not suitable for very wet steam).

a1 = dryness fraction of steam considering separating calorimeter

a2 = dryness fraction of steam considering the throttling calorimeter

x = actual dryness fraction of steam in the sample

The actual dryness fraction of steam in the sample is:

X = a₁a₂

Concept:

Dryness fraction is defined as the ratio of the mass of dry steam (vapour) to the combined mass of dry steam (vapour) & mass of liquid in the mixture. It is denoted by x.

\(Dryness\;fraction\;\left( x \right) = \frac{{mass\;of\;vapour\;\left( {{m_v}} \right)}}{{mass\;of\;vapour\;\left( {{m_v}} \right) ~+~ mass\;of\;liquid\;\left( {{m_l}} \right)}}=\frac{mass~of~vapor~(m_v)}{total~mass}\)

Calculation:

Given:

m_v = 5 kg, total mass = 55 kg

\(x=\frac{5}{55}=0.09\)

Additional Information

For saturated liquid x = 0

For saturated vapour = 1

The value of dryness fraction lies between 0 and 1.

Concept:

Dryness Fraction is given by:

\(x = \frac{{mass\;of\;vapour}}{{mass\;of\;vapour\; + \;mass\;of\;liquid}} = \frac{{{m_v}}}{{{m_v} + {m_l}}}\)

x = 0 signifies saturated liquid.

x = 1 signifies saturated vapour.

Calculation:

Given:

m_v = 0.8 kg, (m_v + m_f) = 1 kg

Dryness Fraction:

\(x = \frac{{mass\;of\;vapour}}{{mass\;of\;vapour\; + \;mass\;of\;liquid}} = \frac{{{m_v}}}{{{m_v} + {m_l}}}\)

\(x = \frac{{{m_v}}}{{{m_v} + {m_l}}}=\frac{0.8}{1}=0.8\)

Explanation:

The dryness fraction is defined as the ratio of the mass of dry steam and the combined mass of dry steam & mass of water in the mixture. It is denoted by x.

\(Dryness\;fraction\;\left( x \right) = \frac{{mass\;of\;vapour\;\left( {{m_v}} \right)}}{{mass\;of\;vapour\;\left( {{m_v}} \right)\; + \;mass\;of\;liquid\;\left( {{m_l}} \right)}}\)

For saturated liquid x = 0

For saturated vapour = 1

The value of the dryness fraction of a substance in a saturated liquid vapor mixture lies between 0 and 1.

Concept:

\(Dryness\;Fraction\;\left( x \right) = \frac{{Mass\;of\;dry\;vapor\;in\;the\;wet\;steam\;}}{{Total\;mass\;of\;wet\;steam}}\)

Calculation:

Given:

Mass of dry vapor = 0.9 kg, Mass of moisture = 0.1 kg

The total mass of wet steam = 1 kg

Dryness fraction is:

\(x = \frac{{Mass\;of\;dry\;vapor\;in\;the\;wet\;steam\;}}{{Total\;mass\;of\;wet\;steam}}\)

\(x = \frac{{0.9}}{1} = 0.9\)

Important Points

• Dryness fraction defines the quality of wet steam.
• For the saturated liquid, the value of dryness fraction is zero.
• For the dry saturated steam, its value is unity.
• It also can be defined as the part of the latent heat absorbed by the steam at a given pressure to reach the existing condition.

Concept:

Using a separating calorimeter, the Dryness fraction (x) of steam is calculated as the ratio of mass of dry steam to the total mass of steam.

\(x=\frac{m_s}{m_s + m_w}\times100\;\)

where m_S = amount of steam condensed, m_w = water obtained from the separator 

Calculation:

Given:

m_s = 5.1 kg, m_w = 1.7 kg.

\(x=\frac{5.1}{5.1+1.7}\times100=75\;\%\)

Concept:

Dryness fraction:

Dryness fraction (x) of steam is defined as the ratio of the mass of the dry steam to the total mass of both dry steam and liquid.

\(x = \frac{m_g}{m_f\; +\; m_g}\;\left( {0 \le x \le 1} \right)\)

where mg = mass of the dry steam or vapour and mf = mass of liquid.

Calculation:

Given:

m_g = 3, m_f = 2

\(x = \frac{m_g}{m_f\; +\; m_g}\)\(= \frac{{{3}}}{{{2}\; + \;{3}}} = 0.6\)

∴  The dryness fraction of the liquid-vapour mixture is 0.6

Explanation:

The mass fraction of the vapor phase in the two-phase liquid-vapor region is called, vapor quality or dryness fraction.

\(Dryness\;fraction\ (x) = \frac{{mass\;of\;vapour(m_v)}}{{mass\;of\;liquid\;(m_l) \;+\; mass\;of\;vapour\;(m_v)}}\)

• This ratio is used to define the quality of steam produced.
• The value of dryness fraction ranges from zero to one.
  • if the value of the dryness fraction is less than one i.e. (x < 1) then steam is called wet steam.
  • if the value of the dryness fraction is one (x = 1) than it steam is called dry saturated steam.
  • for saturated liquid condition value of dryness-fraction is zero (x = 0).

Calculation:

Given:

Mass of water (m_l) = 2 kg, Mass of steam (m_v) = 60 kg

\(Dryness\;fraction\ (x) = \frac{{mass\;of\;vapour(m_v)}}{{mass\;of\;liquid\;(m_l) \;+\; mass\;of\;vapour\;(m_v)}}\)

\(Dryness\;fraction\;(x) = \frac{{60}}{{2\;+\;60}}\Rightarrow\frac{60}{62}\)

∴ x = 0.9677 ≈ 0.96

Concept:

Throttling Calorimeter: A throttling calorimeter is based on the principle of throttling the wet steam so that it becomes superheated.

Separating Calorimeter: It is a vessel used initially to separate some of the moisture from the steam, to ensure superheat conditions after throttling.

Combined Separating and Throttling Calorimeter

A combined separating and throttling calorimeter is therefore found most suitable for accurate measurement of dryness of steam reducing the drawback of Separating Calorimeter (i.e. water particles from wet steam are not fully separated) and the drawback of Throttling Calorimeter (i.e. not suitable for very wet steam).

x1 = dryness fraction of steam considering separating calorimeter

x2 = dryness fraction of steam considering the throttling calorimeter

x = actual dryness fraction of steam in the sample