Pure Substance Lecture Notes PDF

Lecture 17: Properties of Pure substance BMEE203L: Engineering Thermodynamics Nishant Tiwari Assistant Professor (Senior) Department of Thermal and Energy Engineering School of Mechanical Engineering Vellore Institute of Technology Vellore 632014 (Tamil Nadu), India (WhatsApp No.: 09424974455) nisha...

Lecture 17: Properties of Pure substance BMEE203L: Engineering Thermodynamics Nishant Tiwari Assistant Professor (Senior) Department of Thermal and Energy Engineering School of Mechanical Engineering Vellore Institute of Technology Vellore 632014 (Tamil Nadu), India (WhatsApp No.: 09424974455) [email protected] Office: 302-G, SJT Annex T-v diagram for isobaric heating of water 2  T-v chart for water Isobars Isotherms 4  T-v chart for water As we increase pressure the two- phase region shortens 5  Critical point The point at which the saturated liquid and saturated vapor states are identical The corresponding temperature is called critical temperature and pressure is called critical pressure. 6  Quality or dryness fraction of vapor vg x v  v  1 x v f  xvg v = v f + x) (vg- v f ) Mixture specific volume: v v = v f + x(vfg)  Quality or dryness fraction of vapor vapor fraction within the Quality is an intensive property saturated mixture Can be used with other independent Saturated vapor: x = 1 intensive property like P or T for Saturated liquid: x = 0 defining state of saturated mixture 15 A rigid tank contains 50 kg of saturated liquid water at 90°C. Determine the pressure in the tank and the volume of the tank  Example 2 Mixture of liquid water and steam (quality = 0.3) is present in a piston cylinder assembly at 30°C (volume 1 L). This assembly is now heated to 72°C in an isobaric manner. (a) 4.246 kPa (a) What is the pressure within the cylinder? (b) What is the final volume of the cylinder? (b) 3.78 L (c) What is the mass of liquid + vapor mixture (in g) ? (c) 0.1013 g (d) What is the final state of water ? (d) Superheated 18  P-v chart for water Isobars 7 P-T chart for water 8 P-T chart including solid phase A-B: Melting/freezing A B C-D: Boiling/condensation C D E-F: Sublimation/deposition E F 9 P-v-T chart for water 10 P-v-T chart for substance that contract on freezing 11  Application of triple point Ptr & Ttr are fixed for a pure substance Vapor Liquid Cool using dry ice Ice 611.73 Pa The cell is filled with pure deionized 0.01°C water and then evacuated. The top portion is not air but water vapor Can be used for calibration of sensors If you achieve 3 phases simultaneously, then Ptr , Ttr is obtained. What is the problem in using freezing point and boiling point of water? 12  Significance of critical point Supercritical fluid Pcr Tcr Fluid with temperature greater than critical temperature and pressure higher than critical pressure is called “Supercritical Fluid” 13 Complete the following table of properties for 1 kg of water (liquid,vapour or mixture) T (oC) p, kPa h, kJ/kg x Phase description (a) 200 0.7 (b) 140 1800 (c) 950 0 (d) 80 500 (e) 800 3161.7 T (oC) p, kPa h, kJ/kg x Phase description (a) 120.21 200 2045.8 0.7 Saturated Mixture (b) 140 361.53 1800 0.565 Saturated Mixture (c) 177.66 950 752.74 0 Saturated Liquid (d) 80 500 335.37 --- Compressed Liquid (e) 350 800 3161.7 --- Saturated Vapor Ten kg of water at 45°C is heated at a constant pressure of 10 bar until it becomes superheated vapour at 300°C. Find the change in volume, enthalpy, and internal energy Water at 40°C is continuously sprayed into a pipeline carrying 5 tonnes of steam at 5 bar, 300°C per hour. At a section downstream where the pressure is 3 bar, the quality is to be 95%. Find the rate of water spray in kg/h. A rigid closed tank of volume 3 m3 contains 5 kg of wet steam at a pressure of 200 kPa. The tank is heated until the steam becomes dry saturated. Determine the final pressure and the heat transfer to the tank.  Example 3 A piston cylinder arrangement contains water at 250 kPa, 200°C. The 50 kg piston has a diameter of 0.1 m and initially pushes against a set of stops. Initially the piston is at 0.25 m from bottom of the cylinder. The atmosphere is at 100 kPa. The cylinder is now cooled to 20°C. At what temp does the piston begin to move down? (a) 113.8°C What is the final pressure within the cylinder ? (b) 162.4 kPa What is the piston height when the temp reaches 20°C? (c) 0.03 m 20