Steam and its properties and steam table

this slide content what is steam its types and various formula and introduction to steam table

1. STEAM AND ITS PROPERTIES Prepared by.. Prof.Sachin Kumar Nikam

2. 01 02 03 CONTENT

3. STEAM:- the vapor into which water is converted when heated, forming a white mist of minute water droplets in the air. Or Steam  is the hot mist that forms when water boils Steam  is water in the gas phase. It is commonly formed by boiling or evaporating water.  Steam  that is saturated or superheated is invisible;   Formation of steam: DEFINITION Steam can be formed by boiling water in a vessel. But to use it effectively as a working or heating medium, it has to produce in a closed vessel under pressure. Steam formed at a higher pressure has higher temperature and can be made to flow easily through insulated pipes from steam generator to point of use. A simple arrangement of formation of steam at constant pressure is shown.

4. Consider 1 kg of ice at temperature -10 C which is below the freezing point. Let it be heated at constant pressure P. The temperature of ice starts increasing until it reaches the melting temperature of ice i.e., 0 C and during this course ice absorbs its sensible heat. On further addition of heat, ice starts melting, its temperature remains constant at 0 C and it absorbs latent heat of fusion and converts completely into water at 0 C.

5. On further addition of heat, the temperature of water starts rising until it reaches the boiling temperature or saturation temperature corresponding to pressure P. This heat absorbed by water in sensible heat.

6. After the boiling temperature is reached, it remains constant with further addition of heat and vaporization take place. The water absorbs its latent heat and converts into dry saturated steam remaining at same saturation temperature. The intermediate stage of water and dry saturated steam is wet steam, which is actually a mixture of steam and water. If further the heat is added, the temperature of this dry saturated steam starts rising from saturation temperature and it converts into superheated steam. This heat absorbed is again the sensible heat. The total rise in temperature of superheated steam above the saturation temperature is called degree of superheat. We must know here that the saturation temperature, latent heat and other properties of steam remain same at constant pressure but varies with the variation of pressure. Pressure –Temperature Relationship of Water & Steam: If water is heated beyond the boiling point, it vaporizes into steam, or water in the gaseous state. However, not all steam is the same. The properties of steam vary greatly depending on the pressure and temperature to which it is subject. Saturated (dry) steam results when water is heated to the boiling point (sensible heating) and then vaporized with additional heat (latent heating). If this steam is then further heated above the saturation point, it becomes superheated steam (sensible heating ).

7. TRIPLE POINT  is the temperature and pressure at which solid, liquid, and vapor phases of a particular substance coexist in equilibrium. It is a specific case of thermodynamic phase equilibrium. The term "triple point" was coined by James Thomson in 1873.

8. CRITICAL POINT a point on a phase diagram at which both the liquid and gas phases of a substance have the same density, and are therefore indistinguishable. In water, the critical point occurs at around 647 K (374 °C or 705 °F) and 221.5 bar   Qualities of  Steam: Produced from water. Clean, odorless, and tasteless. Easily distributed and controlled. Heat can be used over and over. High usable heat content. Gives up its heat at constant temperature. Well-known characteristics. Pressure, temperature, volume . Types of steam: Steam has following type as per moisture content. Wet Steam Dry steam Superheated steam

9. Wet Steam :- W hen the moisture present in the steam it is known as wet steam. This is the most common form of steam actually experienced by most plants. When steam is generated using a boiler, it usually contains wetness from non-vaporized water molecules that are carried over into the distributed steam. Even the best boilers may discharge steam containing 3% to 5% wetness. As the water approaches the saturation state and begins to vaporize, some water, usually in the form of mist or droplets, is entrained in the rising steam and distributed downstream. Dry steam :- Dry Steam is saturated steam that has been very slightly superheated. This is not sufficient to change its energy appreciably, but is a sufficient rise in temperature to avoid condensation problems, given the average loss in temperature across the steam supply circuit. Dryness fraction x = 1. Superheated Steam :- Superheated steam is created by further heating wet or saturated steam beyond the saturated steam point. This yields steam that has a higher temperature and lower density than saturated steam at the same pressure. Superheated steam is mainly used in propulsion/drive applications such as turbines, and is not typically used for heat transfer applications .

10. IMPORTANT TERM RELATING STEAM FORMATION: SPECIFIC HEAT:- The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. The relationship between heat and temperature change is usually expressed in the form shown below where c is the specific heat. The relationship does not apply if a phase change  is encountered, because the heat added or removed during a phase change does not change the temperature. The equation is Q= m c ΔT We have: Q: Sensible heat m: Mass of the body ΔT: Change of the temperature c: Specific heat coefficient of the material   The specific heat of water is 1 calorie/gram °C = 4.186 joule/gram °C which is higher than any other.

11. SENSIBLE HEAT OF WATER : It is defined as the quantity of heat absorbed by 1 kg of water when it is heated from 0°C (freezing point) to boiling point. It is also called total heat ( or enthalpy ) of  water . I f 1 kg of water is heated from 0°C to 100°C the sensible heat added to it will be 4.18 × 100= 418 kJ but if water is at say 20°C initially then sensible heat added will be 4.18 × (100 – 20)= 334.4 kJ. This type of heat is denoted by letter h f and its value can be directly read from the steam tables . LATENT HEAT  ( L ): It is defined as the amount of thermal energy (heat,  Q ) that is absorbed or released when a body undergoes a constant-temperature process. The equation for specific latent heat is: L  =  Q  /  m where: L  is the specific latent heat Q  is the heat absorbed or released m  is the mass of a substance

12. The most common types of constant-temperature processes are phase changes, such as melting, freezing, vaporization, or condensation. The energy is considered to be "latent" because it is essentially hidden within the molecules until the phase change occurs. It is "specific" because it is expressed in terms of energy per unit mass. The most common units of specific latent heat are  joules per gram (J/g) and kilojoules per kilogram (kJ/kg). Specific latent heat is an intensive property of matter. Its value does not depend on sample size or where within a substance the sample is taken . Types of Latent Heat: Latent Heat of Fusion : Latent  heat of fusion is the heat absorbed or released when matter melts, changing phase from solid to liquid form at a constant temperature. Latent Heat of Vaporization : The latent heat of vaporization is the heat absorbed or released when matter vaporizes, changing phase from liquid to gas phase at a constant temperature .

13. Latent Heat of Fusion Latent Heat of Vaporization :

14. Table of Specific Latent Heat Values: Material Melting Point (°C) Boiling Point (°C) SLH of Fusion kJ/kg SLH of Vaporization kJ/kg Ammonia −77.74 −33.34 332.17 1369 Carbon Dioxide −78 −57 184 574 Ethyl Alcohol −114 78.3 108 855 Hydrogen −259 −253 58 455 Lead 327.5 1750 23.0 871 Nitrogen −210 −196 25.7 200 Oxygen −219 −183 13.9 213 Refrigerant R134A −101 −26.6 — 215.9 Toluene −93 110.6 72.1 351 Water 100 334 2264.705 Examples of Latent and Sensible Heat Daily life is filled with examples of latent and sensible heat: Boiling water on a stove occurs when thermal energy from the heating element is transferred to the pot and in turn to the water. When enough energy is supplied, liquid water expands to form water vapor and the water boils. An enormous amount of energy is released when water boils. Because water has such a high heat of vaporization, it's easy to get burned by steam .

15. Similarly, considerable energy must be absorbed to convert liquid water to ice in a freezer. The freezer removes thermal energy, allowing the phase transition to occur. Water has a high latent heat of fusion, so turning water into ice requires the removal of more energy than freezing liquid oxygen into solid oxygen, per unit gram . Latent heat causes hurricanes to intensify. Air heats as it crosses warm water and picks up water vapor. As the vapor condenses to form clouds, latent heat is released into the atmosphere. This added heat warms the air, producing instability and helping clouds to rise and the storm to intensify . Sensible heat is released when soil absorbs energy from sunlight and gets warmer . Cooling via perspiration is affected by latent and sensible heat. When there is a breeze, evaporative cooling is highly effective. Heat is dissipated away from the body due to the high latent heat of vaporization of water. However, it's much harder to cool down in a sunny location than in a shady one because sensible heat from absorbed sunlight competes with the effect from evaporation .

16. x =   DRYNESS FRACTION:  The term dryness fraction is related with wet steam. It is defined as the ratio of the mass of actual dry steam to the mass of steam containing it. It is usually expressed by the symbol ‘x’ or ‘q’. If M s =Mass of dry steam contained in steam considered and M w =weight of water particles in suspension in the steam considered Then SPECIFIC VOLUME  : Gases (steam is a gas) occupy less space under higher pressure than under lower pressure. This means 1 kilogram of steam occupies different volumes, depending upon its pressure. The term specific volume refers to the volume that one kg of steam occupies at a given pressure and temperature. V S = V/M V S = V Where V = Volume in m 3 M= 1kg or unit mass

17. Specific  volume of saturated water ( v f ) It is defined as volume of 1kg of water at saturation temperature corresponding to the given pressure. It is denoted by  v f . It can be calculated experimentally. It slightly increases with increase in saturation temperature and hence the pressure. The reciprocal of sp -volume is equal to density . Specific  volume of dry saturated steam (v g ) It is defined as volume of 1kg of dry saturated steam corresponding to the given pressure. It is denoted by v g  and can be calculated experimentally. As dry saturated steam is a gas, its specific volume decreases with increase in pressure or the saturation temperature. Specific  volume of wet steam of quantity x It is the volume of 1kg of wet steam and is denoted as = x.v g Where x = Dryness fraction v g  = Specific volume of dry saturated steam Specific volume of Superheated Steam ( v sup ): It is the volume of 1kg of superheated steam and can be determined by assuming that the steam behaves as a perfect gas i.e., obeys the gas laws. It is denoted by 

18. V sup = Let P = pressure under which steam is superheated . Since, P = constant, t sup  =temperature of superheated steam v g  = Specific volume of dry saturated steam t s  = saturation temperature at pressure P. Table of Common Specific Volume Values Engineers and scientists typically refer to tables of specific volume values. These representative values are for standard temperature and pressure (STP), which is a temperature of 0 °C (273.15 K, 32 °F) and pressure of 1 atm .   Substance Density Specific Volume (kg/m 3 ) (m 3 /kg) Air 1.225 0.78 Ice 916.7 0.00109 Water (liquid) 1000 0.00100 Salt Water 1030 0.00097 Mercury 13546 0.00007

19. ENTHALPY: The total heat content of a substance is called enthalpy, so the total heat content by steam is termed as its enthalpy. It is denoted by ‘H’. SI unit is KJ ‘ h ‘ is generally used term which represents specific enthalpy, unit for which is KJ/Kg . Enthalpy of wet steam is given by: h = h f + xh fg Where h f = sensible heat of saturated liquid. h fg = Latent heat of vaporization x= Dryness fraction Enthalpy of dry steam is given by : h = h f + h fg =h g Where h f = sensible heat of saturated liquid. h fg = Latent heat of vaporization x= Dryness fraction = 1

20. Enthalpy of superheated steam is given by: h sup = h f + h fg + c ps ( T sup - T s ) Where h f = sensible heat of saturated liquid. h fg = Latent heat of vaporization h sup = E nthalpy of Superheated steam. T sup = Superheating temperature C ps = specific heat T s = saturation temperature ENTROPY OF STEAM: Specific entropy of saturated water ( s f ) The specific entropy of saturated water at a particular pressure P and saturation temperature T s  is given as the change in entropy during conversion of one kg of water at 0 C into saturated water at that pressure. The water at freezing point 0 C or 273 K is considered as datum where, absolute entropy is taken as zero. If C W  is specific heat of water then the change in entropy of 1kg water during temperature change from 273   K to T   K is given as

21. As the Initial entropy at 273 K is zero, so this change in entropy above 273 K is taken as entropy of water at temperature T. In case of Saturated Water, T= T s Change  in specific entropy during evaporation, ( s fg ) During evaporation heat added =  h fg  = Latent heat of water Temperature remains constant during evaporation and is equal to saturation Temperature T s . Specific entropy of wet steam: Specific entropy of wet steam is equal to sum of specific entropy of saturated water and change in specific entropy during evaporation of dry fraction of steam. s =  s f  +  xs fg   Where s f = specific entropy   S fg = specific entropy during evaporation.

22. Specific entropy of dry saturated steam ( s g ) It is the entropy of one kg of dry saturated steam and is given as the sum of entropy of 1kg of saturated water and entropy change during evaporation. It is denoted by  s g . Thus      s g  =  s f  +  s fg   Specific entropy of superheated steam ( s sup ) It is the sum of specific entropy of dry saturated steam and entropy change during superheating from saturation temp T s  to superheated temp  T sup . Change in entropy during superheating Total specific entropy of superheated steam

23. STEAM TABLE In engineering problems for any fluid which is used as working fluid, the six basic thermodynamic properties required are: Pressure, Temperature. Volume. Internal energy. Enthalpy. Entropy. These properties must be known at different pressure for analyzing the thermodynamic cycle used for work producing devices. The values of these properties are determined theoretically or experimentally and are tabulated in the form of table which are known as STEAM TABLE. Following are the thermodynamic properties of steam which are tabulated in the form of table:

24. p = absolute pressure in bar t s = Saturation temperature C h f  = Specific enthalpy of saturated water (kJ/kg) h fg  = Latent heat of evaporation (kJ/kg) h g  = Specific enthalpy of dry saturated steam (kJ/kg) v f  = Specific volume of saturated water (liquid). (m 3 /kg) v g  = Specific volume of saturated steam (gas). (m 3 /kg) s f = Entropy of saturated liquid ( kJ/ kg.Kelvin ) s g   = Entropy of saturated vapor ( kJ/ kg.Kelvin ) s fg   = Entropy of vaporization ( kJ/ kg.Kelvin ) Also h fg = h g - h f   change of enthalpy during evaporation. s fg = s g - s f   change of entropy during evaporation. v fg = v g - v f   change of volume during evaporation . The above mentioned properties at different pressure and temperature are tabulated in the form of steam table.

25. Two Formats: Pressure Based and Temperature Based Since saturated steam pressure and saturated steam temperature are directly related to one another, saturated steam tables are generally available in two different formats: based on pressure and based on temperature. Both types contain the same data that is simply sorted differently . Pressure based table: in this types of table pressure given in the first column and then corresponding values based on it. PRESS. (GAUGE) TEMP. SPECIFIC VOLUME SPECIFIC ENTHALPY kPaG °C m 3 /kg kJ/kg P T V f V g H f H fg H g 99.97 0.0010434 1.673 419.0 2257 2676 20 105.10 0.0010475 1.414 440.6 2243 2684 50 111.61 0.0010529 1.150 468.2 2225 2694 100 120.42 0.0010607 0.8803 505.6 2201 2707

26. Temperature based table: in this type of table temperature given in the first column and then corresponding values based on it. TEMP. PRESS. (GAUGE) SPECIFIC VOLUME SPECIFIC ENTHALPY °C kPaG m 3 /kg kJ/kg T P V f V g H f H fg H g 100 0.093 0.0010435 1.672 419.1 2256 2676 110 42.051 0.0010516 1.209 461.4 2230 2691 120 97.340 0.0010603 0.8913 503.8 2202 2706 130 168.93 0.0010697 0.6681 546.4 2174 2720 140 260.18 0.0010798 0.5085 589.2 2144 2733 150 374.78 0.0010905 0.39250 632.3 2114 2746

27. How to use steam table: First things we have to understand how much values given in the question. Pressure based values or temperature based values on which other properties depends. If pressure given in the question and all the properties we have to find on the basis of it. Then go to steam table find values in S.I. Units. Then find Pressure Based Saturated Steam Table and search given pressure say 20 kpa or bar then find the corresponding values of T, hf , hg, hjg , vf , vg, or if required sf , sg , sfg . Simliary find Temperature Based Saturated Steam Table and search given temperature say 100 then find the corresponding values of p, hf , hg, hjg , vf , vg, or if required sf , sg , sfg . Please see in the table provided in previous slide.