Mollier diagram

MOLLIER DIAGRAMPrepared By:Sumit Khachane

About the Mollier Chart DiagramThe Mollier chart is also known as H-S or H-X diagram or enthalpy pressure diagram. Where the letter H stands for enthalpy and the X or S for the relative water vapor fraction. The graph is bound by the line where complete saturation of air with water is achieved. On this line, the saturation line, air contains the maximum amount of water. In this situation the percentage of relative humidity equals 100%. The Mollier diagram is a graphical representation of 3 components: Firstly, the enthalpy H, as illustrated in "Heat-content". In the Mollier diagram, to be read in the example below, the enthalpy is shown in h(kJ / kg). Secondly, the water content of air. This is shown in the form of the moisture content x [g / kg] at the upper side of the Mollier diagram. Thirdly, the temperature which is on the left axis of the Mollier diagram.

DetailsOn the diagram, lines of constant pressure, constant temperature and volume are plotted, so in a two-phase region, the lines of constant pressure and temperature coincide.Thework doneonvapor cyclesis represented by length, so it can be measured directly.Lines of constantdryness fraction , sometimes called thequalityof the steam, are drawn in the wet region and lines of constant temperature are drawn in the superheated region. In general such charts do not show the values ofspecific volumes, nor do they show the enthalpies of saturated water at pressures which are of the order of those experienced in condensers in athermal power station.Hence the chart is only useful for enthalpy changes in the expansion process of the steam cycle. Dew PointThe Dew Point is the temperature at which water vapor starts to condense out of the air, the temperature at which air becomes completely saturated. Above this temperature the moisture will stay in the air.If the dew-point temperature is close to the air temperature, the relative humidity is high, and if the dew point is well below the air temperature, the relative humidity is low.The Dew Point temperature can be measured by filling a metal can with water and ice cubes. Stir by a thermometer and watch the outside of the can. When the vapor in the air starts to condensate on the outside of the can, the temperature on the thermometer is pretty close to the dew point of the actual air. The dew point temperature can be read by following a vertical line from the state-point to the saturation line. Dew point is represented along the 100% relative humidity line in the Mollier diagram.

Dry-Bulb TemperatureThedry-bulb temperature(DBT) is thetemperatureof air measured by a thermometer freely exposed to the air but shielded from radiation and moisture. DBT is thetemperaturethat is usually thought of as air temperature, and it is the true thermodynamictemperature. Dry bulb temperature is usually referred to as air temperature, is the air property that is most common used. When people refer to the temperature of the air, they are normally referring to its dry bulb temperature. Dry-bulb temperature - Tdb, can be measured by using a normal thermometer. The dry-bulb temperature is an indicator of heat content and is shown along the left axis of the Mollier diagram. The horizontal lines extending from this axis are constant-temperature lines.Wet-Bulb Temperature Thewet-bulb temperatureis thetemperaturea parcel of air would have if it were cooled to saturation (100% relative humidity) by the evaporation of water into it, with the latent heat being supplied by the parcel. Awet-bulbthermometer indicates atemperatureclose to the true (thermodynamic)temperature. Wet bulb temperature is associated with the moisture content of the air. Wet bulb temperature can be measured with a thermometer that has the bulb covered with a water-moistened bandage with air flowing over the thermometer. Wet bulb temperatures are always lower than dry bulb temperatures but they will be identical with 100% relative humidity in the air (the air is at the saturation line). On the Mollier diagram, the wet-bulb lines slope a little upward to the left (dotted lines).Heating of air

Cooling and Dehumidifying air

Mixing of air of different condition

Humidifying, Adding steam or water

Psychometric chartThe psychometric chart is a variant of the Mollier diagram used in some parts of the world.

Application and UsageIt can be used in practical applications such asmalting, to represent the grain-air-moisture system.The underlying property data for the Mollier diagram is identical to apsychrometric chart. At first inspection, there may appear little resemblance between the charts, but if the user rotates a chart ninety degrees and looks at it in a mirror, the resemblance is apparent.The Mollier diagram coordinates are enthalpyhand humidity ratiox. The enthalpy coordinate isskewedand the constant enthalpy lines are parallel and evenly spaced. The Mollier diagram is preferred by many users in Scandinavia, Eastern Europe, and Russia.THANK YOU