Question

(25 pts) A well-insulated and well-sealed 2-m x 3-m x 4-m room is initially at Tal = 22 °C and p = 100 kPa. A mass of mw = 20 kg of liquid water at Tw./ = 80 °C is brought into the room and the system is allowed to reach equilibrium conditions (state 2). 2m x 3m x 4m ROOM 22°C 100 kPa Specific heat values for the air and water may be taken as Cp,air = 1.005 kJ/kg-K; Cv,air = 0.718 kJ/kg-K, and water = 4.2 kJ/kg-K. Also, Rair = 0.287 kJ/kg-K. Water 80°C Heat Although you could easily find the final equilibrium conditions yourself, they are provided here for you to use: mair = 28.3 kg; T2=69 °C; and p2 = 116 kPa. (Remember, the room is sealed.) (Neglect the volume of the water relative to the room.) a. (10 pts) Determine the change in the entropy of the room air plus water (Sair + Sw) in going from state 1 to state 2, in kJ/K. b. (5 pts) Determine the total entropy generation, Ogen, for this system, in kJ/K, for process 1 - 2. c. (10 pts) NOW, suppose that the insulation is removed and the entire contents are cooled, from the T2 = 69 °C and p2 = 116 kPa condition, by heat transfer to surroundings at Tsurr = 22 °C until everything (air plus water) is at T3 = 22 °C. Although you could easily determine the amount of heat transfer needed for this cooling, it is provided here for you to use: Q2-3 = - 4900 kJ. Determine the total entropy generation (system plus surroundings) for this process (2-3), Open fox , in kJ/K. (Hint: You can work part c. without having worked parts a. and b.)

Answer 1

Dotz sir Initial temperature Tay = 22°C = 295k Pressure Pai= lookea ma= 28.3 kg Rai = 0.287 kJ / kg ta Op.cie = 1.005 13/ks K. Grair = 0.718 kJ/kgk. For water in on Tw=80°c = 353k Cuz 4.2 1/kk mwe 2 kg Tz = 69°C = 342k P2 = 116 Kla - Change in entropy of room as wtf sain a ma conta in I am so he A Som = mucun Iz + main { cp lu TZ . . . . ] 2 m 12 | m .cii - R 20X4:2x10 to 142 llic 54 १५८ _यर HE - 0-2877costan - 2659.21.5 + 2013 | a 339.9 ~ 340 /k z 0.34 KB Ko

Date Poge 6 foom is well insulated in Hence, Total entropy generation systein will be gew. ---- for this Sgenic Assyst- og = ma con la mafan, - Ty=69c a 392k sa To = 22' 295k 160= - 4900 Ks P2 = 101:325 kPa , l2 = 116kla c. 2oxarla 295 + 08.3 pooglen 295 -0.2674 loloses! 342 at 32 116 T + 4900 95 = -12.42 + 263 X (-0.1486 +0.0388) + 4900 295 < -12.42 * 3.12 + 16.61 sen a 1-07 KK