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BME 200 Conservation Principles in BME 07 March 24, 2022 Class Participation 7 (CP 07): Cooling of Nitrogen gas for refrigeration A stream of nitrogen (N,) gas flowing at a rate of 100 mol/min is cooled from 30C to 1C at steady-state and constant pressure of 1 atm. Assuming that nitrogen behaves as an ideal gas, calculate the rate at which heat is removed to cool the gas to this temperature (Answer: 0 = - 842 kJ/min) If needed, use data from Tables B.1 and B.2 of Felder (2016) on Canvas. Nitrogen gas, 30C 100 mols min Nitrogen gas, 1C Cooler Heat SOLUTION This is an open system, so the Energy Balance is applied with the Cooler as the Control Volume V de = 0W.+mich, *** +970 - Xm-c +9=) In the equation below, cross-out the terms that can be removed, indicating why this is appropriate for the problem de dt --0-wa+mall, - Em(,++92) - 2m (++9= V ) - . .) Write the final equation, changing the mass into molar flowrate since we will use it as kJ mol Fill up the Enthalpy table below Note that we want the specific enthalpy of the input to be zero. What reference state was chosen to make this possible? Reference state Substance (mol min) Nor H. (kJ/mol) Now (mol min Hor Hour (kJ/mol) N 0 is the specific enthalpy of nitrogen gas in the outlet at 1C relative to pure nitrogen at its reference temperature of 20C. In other words, it is the specific enthalpy change for the process CH. (g. 30C. Pin inlet) CH. (g. 1C, Pin outlet) BME 200 Conservation Principles in BME 07 March. 24, 2022 We neglect the effect of pressure on enthalpy (ideal-gas behavior) so the enthalpy change is calculated for the cooling of pure nitrogen at whatever pressure the process is under This is a case of change in ft due to change in temperature. # = S(CM), dr You need (Cp)nz the specific heat of N, gas as a function of temperature. Where can you find it? 1C 30C Write the expression for (C) Ny, with units of (kJ/moleC) and T in C 10 Solso for it,- S0(CM) 30C Calculate the rate at which heat is removed out - .. - , .. - . - ins