BRANCH--- MECHANICAL ENGINEERING.�SEMESTER--- 4th �SUBJECT---- THERMAL ENGINEERING-II�TOPIC------- PROPERTIES OF STEAM�FACULTY---- Er. CHANDAN KUMAR NAYAK�

STEAM AND ITS PROPERTIES

• Steam is the gaseous phase of water. It utilizes heat during the process and carries large quantities of heat later. Hence, it could be used as a working substance for heat engines.
• Steam is generated in boilers at constant pressure. Generally, steam may be obtained starting from ice or straight away from the water by adding heat to it.

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FORMATION OF STEAM

• temperature-Enthalpy Diagram t-h diagram)
• The graphical representation of transformation of 1 kg of ice into 1 kg of superheated steam at constant pressure (temperature vs. enthalpy) is known as t-h diagram. shows the various stages of formation of steam starting from ice shows the corresponding t-h diagram.

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TYPES STEAM

The steam during the steam generation process can exist in three types:

1. Wet steam (saturated steam)
2. Dry steam (dry saturated steam)
3. Superheated steam

1. WET STEAM :

• Both the water molecules and steam coexist to form a two phase mixture, called wet steam.
• Which will be in thermal equilibrium because both of them will be at the same saturation temperature.

2. DRY SATURATED STEAM:

• A steam at the saturation temperature corresponding to a given pressure and having no water molecules in it is known as dry saturated steam or dry steam.

• Since the dry saturated steam does not contain any water molecules in it, its dryness fraction will be unity.

3. SUPERHEATED STEAM:

• When a dry saturated steam is heated further at the given constant pressure, its temperature rise beyond its saturation temperature. The steam in this state is said to be superheated.

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ENTHALPY OF STEAM

• Enthalpy Of liquid:

hf=Cpw(tf-0)

• Enthalpy of Dry saturated steam:

hg=hf + hfg

• Enthalpy of Wet steam:

h=hf + xhfg

• Enthalpy of Superheted steam:

hsup= hg + Cps(Tsup –Tsat )

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SPECIFIC VOLUME OF STEAM

• Specific volume of saturated water: vf
• Specific volume of dry saturated steam: vg
• Specific volume of wet steam:

v = xvg +(1-x)vf

• Specific volume of superheated steam:

Vg/Ts = Vsup/Tsup

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INTERNAL ENERGY OF STEAM

• It is defined as the difference between the enthalpy of steam and external work of evaporation.

Internal energy of dry steam : ug = hg – pvg kJ/kg

Internal energy of wet steam : u = hf + xhfg – pxvg kJ/kg

Internal energy of superheated steam : usup = hsup – pvsup kJ/kg

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• Internal Latent heat:

It is algebraic difference between the enthalpy of evaporation at given pressure and work of evaporation.

Internal Latent heat : hfg - pv

BUCKET OR BARREL CALORIMETER

• In this calorimeter a known mass of water and then heat loss by steam is equated to heat gained by water. The steam is passed through a sample tube into bucket calorimeter contains known weight of water.
• The weight of calorimeter with water before mixing steam & after mixing the steam is measured by thermometer.

THROTTLING CALORIMETER

• This types of calorimeter is used to measure dryness fraction of steam whose dryness fraction is considerably high.
• The steam sample is passed through a throttle valve & is allowed to throttle down to pressure unit until it comes out in dry saturated or super heated condition.
• The pressure & temperature of steam coming out of throttling calorimeter is measured with water manometer & thermometer respectively.

• Thank you..!!!