3 3 Long Exams 60% Final Exam 20% 3 Machine Problems 15% Classwork 5% Course Assessment3 Long Exams 60% Final Exam 20% 3 Machine Problems 15% Classwork 5%
4 Policies to RememberSubmit 12 sheets of colored pad paper at least the day before an exam. Get an official excuse slip from the College if you miss an exam and you have a valid excuse. No exemptions will be given for the final exam.
5 Policies to RememberQuizzes may be given from time to time. All quizzes shall be written in bluebooks. No makeup shall be given to missed quizzes.
7 Transport Phenomena What exactly are "transport phenomena"? Transport phenomena are really just a fancy way that Chemical Engineers group together three areas of study that have certain ideas in common.These three areas of study are:Fluid mechanicsHeat transferMass transferTransport processes
8 Transport ProcessesMomentum Transport – transfer of momentum which occurs in moving media (fluid flow, sedimentation, mixing, filtration, etc.)Heat Transport – transfer of energy from one region to another (drying, evaporation, distillation)Mass Transport – transfer of mass of various chemical species from one phase to another distinct phase (distillation, absorption, adsorption, etc.)
11 Why Study Transport Phenomena? ChemicalEngineeringThermodynamicsTransportPhenomenaMaterialsSciencePROCESSEQUIPMENTDESIGNChemicalReactionKineticsProcessEconomics
12 Levels of AnalysisMACROSCOPICMICROSCOPICMOLECULAR
13 Levels of Analysis MACROSCOPIC MICROSCOPIC MOLECULAR Use of macroscopic balancesOverall assessment of a systemMICROSCOPICMOLECULAR
14 Levels of Analysis MACROSCOPIC MICROSCOPIC MOLECULAR Small region/volume element is selectedUse of equations of changeVelocity, temperature, pressure and concentration profiles are determinedMICROSCOPICMOLECULAR
15 Levels of Analysis MACROSCOPIC MICROSCOPIC MOLECULAR Molecular structure and intermolecular forces become significantComplex molecules, extreme T and P, chemically reacting systemsMICROSCOPICMOLECULAR
17 Dimensional AnalysisCheck the dimensional consistency of the following empirical equation for heat transfer between a flowing fluid and the surface of a sphere: h – heat transfer coefficient (W/m2-K) D – diameter of sphere (m) k – thermal conductivity of fluid (W/m-K) G – mass velocity of fluid (kg/m2-s) μ – viscosity (kg/m-s) cp – heat capacity (J/kg-K)
18 Dimensional AnalysisWe use the following convention: Energy unit – E Mass unit – M Length unit – L Time unit – t Temperature unit – T
19 Dimensional AnalysisFor the heat transfer coefficient: For thermal conductivity: For diameter: For viscosity:
20 Dimensional AnalysisFor mass velocity: For heat capacity: Combining:
23 Material BalanceAn evaporator is fed continuously with 25 metric tons/h of a solution consisting of 10% NaOH, 10% NaCl, and 80% H2O. During evaporation, water is boiled off, and salt precipitates as crystals, which are settled and removed from the remaining liquor. The concentrated liquor leaving the evaporator contains 50% NaOH, 2% NaCl, and 48% H2O. Calculate the MT of water evaporated per hour, the MT of salt precipitated per hour, and MT of liquor produced per hour.
25 Material Balance25 MT/h0.1 NaOH0.1 NaCl0.8 H2OM (mother liquor)0.5 NaOH0.02 NaCl0.48 H2OEVAPORATORH (water)1.0 H2OC (crystals)1.0 NaClH = water evaporated per hour = 17.6 MT/h C = salt precipitated per hour = 2.4 MT/h M = liquor produced per hour = 5 MT/h
26 Material BalanceDry gas containing 75% air and 25% NH3 vapor enters the bottom of a cylindrical packed absorption tower that is 2 ft in diameter. Nozzles in the top of the tower distribute water over the packing. A solution of NH3 in H2O is drawn at the bottom of the column, and scrubbed gas leaves the top. The gas enters at 80°F and 760 mm Hg. It leaves at 60°F and 730 mm Hg. The leaving gas contains, on the solute-free basis, 1.0% NH3. If the entering gas flows through the empty bottom of the column at velocity (upward) of 1.5 ft/s, how many ft3 of entering gas are treated per hour? How many pounds of NH3 are absorbed per hour?
27 Material Balance Volume of gas entering = velocity diameter of tower G (scrubbed gas)0.01 NH3(solute-free)W (water)1.0 H2OSCRUBBERD (dry gas)0.75 air0.25 NH3S (water + ammonia)x H2Oy NH3Volume of gas entering = velocity diameter of tower
28 Material BalanceConvert solute-free basis percentage to mass fraction: We now rewrite our diagram:
29 Material BalanceG (scrubbed gas)NH3airW (water)1.0 H2OSCRUBBERD (dry gas)0.75 air0.25 NH3S (water + ammonia)x H2Oy NH3Determine the number of moles of dry gas entering the scrubber. Assuming ideal gas behavior,
30 Material BalanceDetermine the number of moles of dry gas entering the scrubber. Assuming ideal gas behavior and a basis of 1 hour:
31 Material BalanceG (scrubbed gas)NH3airW (water)1.0 H2OSCRUBBERD (dry gas) = lbmol0.75 air0.25 NH3S (water + ammonia)x H2Oy NH3Air balance: 0.75(42.35) = G G = amount of dry gas = lbmol dry gas
33 Material Balance Pounds of NH3 absorbed: G (scrubbed gas) 0.0099 NH3 airW (water)1.0 H2OSCRUBBERD (dry gas) = lbmol0.75 air0.25 NH3S (water + ammonia)x H2Oy NH3Pounds of NH3 absorbed:
34 Energy BalanceAir is flowing steadily through a horizontal heated tube. The air enters at 40°F and at a velocity of 50 ft/s. It leaves the tube at 140°F and 75 ft/s. The average specific heat of air is 0.24 Btu/lb-°F. How many Btu’s per pound of air are transferred through the wall of the tube?