Chapter 1 Problems: Chapter 2 2.4. Examples: Thermo Examples and Problems (1).docx - Google Docs When a system is taken from state a to state b along path acb, 100

J of heat flows into the system and the system does 40 J of work. A.) How much heat flows into the system along path aeb if the work done by the system is 20 J? B.) The system returns from b to a along path bda. If the work done on the system is 30 J, does the system absorb or liberate heat? How much? google.com/document/d/1eWxl-CON8Or3rdhs-1 SryWOe-VtnQj5P/edit?pli=1 Copyright © McGraw-H Educaber, Permission required for reproduction or display Ø V Scanned with CamScanner 1 2.9. Air at 1 bar and 298.15 K (25°C) is compressed to 5 bar and 298.15 K by two different mechanically reversible processes: (a) Cooling at constant pressure followed by heating at constant volume. (b) Heating at constant volume followed by cooling at constant pressure. Calculate the heat and work requirements and AU and AH of the air for each path. The following heat capacities for air may be assumed independent of temperature: C, = 20.78 and Cp= 29.10 J mol¹ K-¹ Assume for air that PV/T is a constant, regardless of the changes it undergoes. At 298.15 K and 1 -1 bar the molar volume of air is 0.02479 m³ mol Seignoin 30 doll erside med Scanned with CamScanner 2.10 -1 Calculate the internal-energy and enthalpy changes for air when changed from an initial state of 40(°F) and 10(atm), where its molar volume is 36.49(ft)³(lb mole)¹, to a final state of 140(°F) and 1(atm). Assume for air that PV/T is constant and that C₁= 5 and Cp 7(Btu)(lb mole) ¹ (°F)-¹ Find SU,AH T₁= 40°F P₁ = 10 atm V₁ = 36.493 6² Ibmol T₂ = 140°F P₂=latm V₂= • To know the state of the Systen, we find V₂. Pevz Tz P₁V₁ 라 PE R jor Example 2. 15 (10)(36.44) (1) V₂ (40+ 4596) (140+459), V₂ = 438 36³ = Air (ideal Gas), Closed System AU= Q+W, H = U+ PV, W= Spdv ( Flow rate=4.15 g s-1 t = 0°C 1 Set I R = F²+ 454.67 1 Ibmol The following data are taken from a flow calorimeter with water as the test fluid: t = 300°C 2 Rate of heat addition from resistance heater = 12,740 W It is observed that the water is completely vaporized in the process. Calculate the enthalpy of steam at 300°C and 3 bar based on H = 0 for liquid water at 0°C. P = 3 bar 2 3rdhs-1.SWOe-VtnQi5P/edit?pli=1 36 Scanned with CamScanner 438 Example 2.16 Air at 1 bar and 25°C enters a compressor at low velocity, discharges at 3 bar, and enters a nozzle in which it expands to a final velocity of 600 m s-1 at the initial conditions of pressure and temperature. If the work of compression is 240 kJ per kilogram of air, how much heat must be removed during compression? Problems: ment/d/1eWxl-CON8Or3rdhs-1SryWOe-VtnQj5P/edit?pli=1 Scanned with CamScanner 2.8. A tank containing 20 kg of water at 20°C is fitted with a stirrer that delivers work to the water at the rate of 0.25 kW. How long does it take for the temperature of the water to rise to 30°C if no heat is lost from the water? For water, CP = 4.18 kJ-kg-1 °C-1. 2.9. Heat in the amount of 7.5 kJ is added to a closed system while its internal energy decreases by 12 kJ. How much energy is transferred as work? For a process causing the same change of state but for which the work is zero, how much heat is transferred? Scanned with CamScanner