# L# 1

Pure substance refer to: substance with chemicals homogeneity and constant chemicals composition.

H2O is pure substance as it meets both the above requirements. Any substance which under goes a chemical reaction,can not be pure substance.

## Some important definitions:-

### Sensible heating:-

Heating of substance in single phase. It can rise in temperature of substance,’’In case of cooling in above condition it shell be called sensible cooling’’

### Latent heating:-

It is the heating of substance for causing its phase change without any change in its temperature .it will be called latent heat.

### Normal boiling point:-

It is the temperature at which vapour pressure equals to atmospheric pressure. And phase change from liquid to gas begins.

### Melting point:-

It is the temperature at which phase change from solid to liquid takes place upon supplying latent heat.

### Saturation state:-

The state at which its phase transformation takes place without any change in pressure and temperature. These can be saturated solid state,liquid state,vapour state.

### Saturation temperature:-

The temperature at which substance change its phase for any given pressure. For water at 1 atm pressure the saturation temperature 1000C

### Triple point:-.

The state at which substance can coexist in solid,liquid and gaseous phase in equilibrium.for water is 0.01oC I.e at this temperature ice water and steam can coexist in equilibrium

### Critical state:-

It that state of substance at which liquid and vapour coexist in equilibrium.

### Dryness fraction:-

It is mass of vapour in mixture of liquid and vapour at any point in liquid -vapour mixture region

It generally denoted by  ‘x’

Dryness friction = x

= mass of vapour/(mass of liquid + mass of vapour)

X= mv / (ml + mv)

### Compressed liquid or Sub cooled liquid:-

Liquid temperature less than saturation temperature corresponding to given pressure.

‘Degree of sub cooling in given temperature difference b/w liquid temperature and saturation temp. Of liquid at given pressure'

Degree of sub cooling = saturation temp. At given pressure - temp.of liquid.

### Super heated steam:-

Steam having more than the saturation temp. Corresponding to given pressure

Degree of super heat = temp. Of steam - saturation temp. At given pressure.

### P-V Diagram for water:-

 p-v diagram for water

Saturated liquid line meets saturated Vapour line is called critical point.

## Steam table and Mollier chart:-

Steam table is a tabular presentation of properties such as specific enthalpy ,entropy,internal energy, and specific volume at different saturation pressure or temperature. Steam table may be on pressure basis and on temperature basis.

## Mollier chart:-

It is the enthalpy-entropy (h-s) diagrams of steam .this diagrams is obtained on the basis of following eqn depending upon the phase transformation.

Tds = dh - vdp  (1st and 2nd law combination)

For constant pressure (dh / ds)p = T

#### h-s diagram for all phases:-1

 h-s diagram
h-s diagram:-2

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