OM INSTITUTE OF TECHNOLOGY, VANTA VACHHODA Subject : EME Subject code:2110006 Internal energy of steam BRANCH: MECHANICAL GUIDE- MR.Neelesh Gupta RANA KALPESH A : 131030119047

index INTRODUCTION DEFINITION INTERNAL LATENT HEAT MEASUREMENT OF DRYNESS FRACTION UNDERSTAND AND CONSTUCTION OF SEPARATING CALORIMETER

Introduction The enthalpy of the total heat energy of a dry saturated steam at a given pressure will be equal to the sum of the sensible heat, latent heat and external work for evaporation. But the heat energy of external work of evaporation of is not present in the steam as it has been spent In doing external work. The actual energy possessed in the steam comprises of only the sensible heat and latent heat. This actual energy stored in the steam is called internal energy.

Definition Internal Energy of Steam It is defined as the difference between the enthalpy of steam and external work of evaporation. It is obtained by subtracting the external work of evaporation from the enthalpy and is denoted by u

Mathematically 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

Internal latent heat It is the algebraic difference between the enthalpy of evaporation at given pressure and work of evaporation. Internal latent heat = hfg - pv where, hfg = enthalpy of evaporation at given pressure in kj/kg p = pressure of steam Pa v = specific volume of steam(dry, wet or super heated), m3/kg

Measurement of dryness fraction There are four methods of determining the dryness fraction of steam. Bucket or Barrel calorimeter Throttling calorimeter Separating calorimeter Combined separating and throttling calorimeter

Separating calorimeter This calorimeter show in figure is used for measuring dryness fraction of very wet steam. This calorimeter works on principal of separating the water particles from a sample of steam and finding their mass fraction in the sample.

Construction Separating calorimeter consist of inner chamber and other chamber. Perforated tray is provided at the top of inner chamber. Due to inertia of water droplet, wet steam is separated droplet is collected in inner chamber while steam is condensed in barrel calorimeter. Control valve and sampling tube performs same function as that in barrel calorimeter.

WORKING The steam is supplied to the calorimeter from the main steam pipe through a sampling tube. Entering steam strikes against the perforated tray in the inner vessel of calorimeter. By centrifugal force and inertia of droplets, the water particles are separated from steam and they are collected in inner chamber. Dry steam passes through the annular space between inner and outer vessel. The steam is condensed in barrel calorimeter. The quantity of steam condensed can measured by a weighing and quantity of water droplet separated can be measured from scale.

Calculation Let mw = Mass of water collected in inner chamber, in kg ms = mass steam condensed in barrel calorimeter, x = Dryness fraction As per definition of dryness fraction, :> x= ms/ms + mw

Limitation This calorimeter gives only approximate value of dryness fraction.

Reference Elements of Mechanical Engineering (Books India Publication) H.G KATARIYA, J.P.HADIYA, S.M BHATT