2300_hw_7_sol

# 2300_hw_7_sol - Homework#7 Solutions 1 4-49C It can be used...

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Homework #7 Solutions: 1. 4-49C It can be used for any kind of process of an ideal gas. 2. 4-54C The energy required is mc p D T , which will be the same in both cases. This is because the c p of an ideal gas does not vary with pressure. 3. 4-61 Neon is compressed isothermally in a compressor. The specific volume and enthalpy changes are to be determined. Assumptions At specified conditions, neon behaves as an ideal gas. Properties The gas constant of neon is R = 0.4119 kJ/kg K and the constant-pressure specific heat of neon is 1.0299 kJ/kg K (Table A-2 a ). Analysis At the compressor inlet, the specific volume is /kg m 207 . 1 kPa 100 K) 273 K)(20 /kg m kPa (0.4119 3 3 1 1 = + = = P RT v Similarly, at the compressor exit, /kg m 2414 . 0 kPa 500 K) 273 K)(20 /kg m kPa (0.4119 3 3 2 2 = + = = P RT The change in the specific volume caused by the compressor is /kg m 0.966 3 - = - = = D 207 . 1 2414 . 0 1 2 - Since the process is isothermal, kJ/kg 0 = D = D T c h p 4. 4-66 A resistance heater is to raise the air temperature in the room from 7 to 23°C within 15 min. The required power rating of the resistance heater is to be determined. Assumptions 1 Air is an ideal gas since it is at a high temperature and low pressure relative to its critical point values of -141 ° C and 3.77 MPa. 2 The kinetic and potential energy changes are negligible, D D ke pe @ @ 0 . 3

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2300_hw_7_sol - Homework#7 Solutions 1 4-49C It can be used...

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