Tarik Al-Shemmeri. Engineering Thermodynamics (776123), страница 10
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Laws of ThermodynamicsEngineering ThermodynamicsWorked Example 3.35Determine for a unit mass of air, the change in enthalpy when heated from zero C to 100 OC if:i.ii.Cp = 1 kJ/kgK constantCp = 0.95 + 0.00002 * T – 0.03x10-6 xT2Solutioni.change in enthalpydh= m Cp ( T2 –T1)= 1 x 1 x (100 – 0 )= 100 kJ/kgii.∆h = ∫ Cp.dTUsing the definition of specific heat in terms of temperature, the change in enthalpy:100∆h = ∫ (0.95 + 0.02 x10 −3 T − 0.03x10 −6 T 20Integrating between the limits of temperatures from zero to 100:∆h = [ 0.95T + 0.01x10 −3 T 2 − 0.01x10 −6 T 3]1000∆h = 96.09 kJ / kgThe difference between the calculated values in (i) and (ii) is about 4% which is due to the fact thatthe specific heat capacity is not strictly constant for different temperatures.Download free ebooks at bookboon.com1003.
Laws of ThermodynamicsEngineering ThermodynamicsWorked Example 3.36A burner heats air from 20 to 40oC at constant pressure. Determine the change in entropy for a unitmass of air going through the heater, assuming that for airCp = 1 kJ/kgKSolution:Constant pressure process, the change in entropy is calculated as:∆S = m.Cp. ln= 1x1x lnT2T1303293= 0.03356 kJ / kgKDownload free ebooks at bookboon.com1014.
Thermodynamics Tutorial problemsEngineering Thermodynamics4. Thermodynamics Tutorial problems4.1 First Law of Thermodynamics N.F.E.E Applications1. In a non-flow process there is heat transfer loss of 1055 kJ and an internal energy increaseof 210 kJ. Determine the work transfer and state whether the process is an expansion orcompression.[Ans: -1265 kJ, compression]2. In a non-flow process carried out on 5.4 kg of a substance, there was a specific internalenergy decrease of 50 kJ/kg and a work transfer from the substance of 85 kJ/kg. Determinethe heat transfer and state whether it is gain or loss.[Ans: 189 kJ, gain]3.
During the working stroke of an engine the heat transferred out of the system was 150kJ/kg of the working substance. If the work done by the engine is 250 kJ/kg, determine thechange in internal energy and state whether it is decrease or increase.[Ans: -400 kJ/kg, decrease]Please click the advertdongenergy.com/jobEverybodyis talking......about future energy supply. We are not.Stop talking and make a careermoving energy forward.Ambitious engineers andfinance students go todongenergy.com/jobDownload free ebooks at bookboon.com1024. Thermodynamics Tutorial problemsEngineering Thermodynamics4.
Steam enters a cylinder fitted with a piston at a pressure of 20 MN/m2 and a temperature of500 deg C. The steam expands to a pressure of 200 kN/m2 and a temperature of 200 deg C.During the expansion there is a net heat loss from the steam through the walls of thecylinder and piston of 120 kJ/kg. Determine the displacement work done by one kg ofsteam during this expansion.[Ans: 168.6 kJ/kg]5. A closed rigid system has a volume of 85 litres contains steam at 2 bar and dryness fractionof 0.9.
Calculate the quantity of heat which must be removed from the system in order toreduce the pressure to 1.6 bar. Also determine the change in enthalpy and entropy per unitmass of the system.[Ans: -38 kJ]6. 2 kg of air is heated at constant pressure of 2 bar to 500 oC. Determine the change in itsentropy if the initial volume is 0.8 m3.[Ans: 2.04 kJ/K]4.2 First Law of Thermodynamics S.F.E.E Applications1.
A boiler is designed to work at 14 bar and evaporate 8 kg/s of water. The inlet water to theboiler has a temperature of 40 deg C and at exit the steam is 0.95 dry. The flow velocity atinlet is 10 m/s and at exit 5 m/s and the exit is 5 m above the elevation at entrance.Determine the quantity of heat required. What is the significance of changes in kinetic andpotential energy on the result?[Ans: 20.186 MW]2.
Steam flows along a horizontal duct. At one point in the duct the pressure of the steam is 1bar and the temperature is 400°C. At a second point, some distance from the first, thepressure is 1.5 bar and the temperature is 500°C. Assuming the flow to be frictionless andadiabatic, determine whether the flow is accelerating or decelerating.[Ans: Decelerating]3. Steam is expanded isentropically in a turbine from 30 bar and 400°C to 4 bar.
Calculatethe work done per unit mass flow of steam. Neglect changes in Kinetic and Potentialenergies.[Ans: 476 kJ/kg]4. A compressor takes in air at 1 bar and 20°C and discharges into a line. The average airvelocity in the line at a point close to the discharge is 7 m/s and the discharge pressure is3.5 bar. Assuming that the compression occurs isentropically, calculate the work input tothe compressor. Assume that the air inlet velocity is very small.Download free ebooks at bookboon.com1034.
Thermodynamics Tutorial problemsEngineering Thermodynamics[Ans:-126.6 kW/kg]5. Air is expanded isentropically in a nozzle from 13.8 bar and 150°C to a pressure of 6.9 bar.The inlet velocity to the nozzle is very small and the process occurs under steady-flow,steady-state conditions. Calculate the exit velocity from the nozzle knowing that the nozzleis laid in a horizontal plane and that the inlet velocity is 10 m/s.[Ans: 390.9 m/s]4.3 General Thermodynamics Systems1. A rotary air compressor takes in air (which may be treated as a perfect gas) at a pressure of1 bar and a temperature of 20°C and compress it adiabatically to a pressure of 6 bar. Theisentropic efficiency of the processes is 0.85 and changes in kinetic and potential energymay be neglected.
Calculate the specific entropy change of the air. Take R = 0.287 kJ/kgK and Cp = 1.006 kJ/kg K.[Ans: 0.07 kJ/kg K]2. An air receiver has a capacity of 0.86m3 and contains air at a temperature of 15°C and apressure of 275 kN/m2. An additional mass of 1.7 kg is pumped into the receiver. It is thenleft until the temperature becomes 15°C once again. Determine,a) the new pressure of the air in the receiver, andb) the specific enthalpy of the air at 15°C if it is assumed that the specific enthalpy of theair is zero at 0°C.Take Cp = 1.005 kJ/kg, Cv = 0.715 kJ/kg K[Ans:442 kN/m2, 15.075 kJ/kg]3.
Oxygen has a molecular weight of 32 and a specific heat at constant pressure of 0.91 kJ/kgK.a) Determine the ratio of the specific heats.b) Calculate the change in internal energy and enthalpy if the gas is heated from 300 to400 K.[Ans: 1.4, 65 kJ/kg, 91 kJ/kg]4. A steam turbine inlet state is given by 6 MPa and 500°C. The outlet pressure is 10 kPa.Determine the work output per unit mass if the process:a) is reversible and adiabatic (ie 100% isentropic),b) such that the outlet condition is just dry saturated,Download free ebooks at bookboon.com1044. Thermodynamics Tutorial problemsEngineering Thermodynamicsc) such that the outlet condition is 90% dry.[Ans:1242.7 kJ/kg, 837.5 kJ/kg, 1076.8 kJ/kg]5.
Determine the volume for carbon dioxide contained inside a cylinder at 0.2 MPa, 27°C:a) assuming it behaves as an ideal gasb) taking into account the pressure and volume associated with its molecules[Ans: 0.2833m3/kg]6. A cylindrical storage tank having an internal volume of 0.465 m3 contains methane at 20°Cwith a pressure of 137 bar. If the tank outlet valve is opened until the pressure in thecylinder is halved, determine the mass of gas which escapes from the tank assuming thetank temperature remains constant.[Ans: 20.972 kg]7. Find the specific volume for H20 at 1000 kN/m2 and 300°C by using:a) the ideal gas equation assuming R = 461.5 J/kg Kb) steam tables[Ans: 0.264m3/kg, 0.258 m3/kg]Please click the advertdongenergy.com/jobdDear highly educated engineeringand finance students,if you are driven, ambitious, open-mindedand focused - we have a challenge for you.Actually, the greatest challenge in theworld.
Curious? Visit dongenergy.com/jobBest wishesDONG EnergyDownload free ebooks at bookboon.com1054. Thermodynamics Tutorial problemsEngineering Thermodynamics8. Determine the specific volume of steam at 6 MPa using the steam tables for the followingconditions:a)b)c)d)dryness fraction x = 0dryness fraction x = 0.5dryness fraction x = 1its temperature is 600oC[Ans: 0.001319, 0.01688, 0.03244, 0.06525 m3/kg]9. Steam at 4 MPa, 400oC expands at constant entropy till its pressure is 0.1 MPa.Determine:a) the energy liberated per kg of steamb) repeat if the process is 80% isentropic[Ans: 758 kJ/kg, 606 kJ/kg]10. Steam (1 kg) at 1.4 MPa is contained in a rigid vessel of volume 0.16350 m3.
Determine itstemperature.a) If the vessel is cooled, at what temperature will the steam be just dry saturated?b) If cooling is continued until the pressure in the vessel is 0.8 MPa; calculate the finaldryness fraction of the steam, and the heat rejected between the initial and the finalstates.[Ans: 250oC, 188oC, 0.678; 8181 kJ]11.
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