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HW3-2011 - 3/g What are Δ H and Δ U(per weight 4(8 points...


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ECH 152A, Fall 2011, Roland Faller Homework 3, October 10, 2011, Due: October 17, Beginning of Lecture 1. (4 points) (a) What is the definition of a state function? (b) What does “reversible” mean? (c) What is “steady state”? (d) What is the difference between internal energy and enthalpy? 2. (2 point) (a) To a closed system we add 18 kJ of heat while its internal energy decreases by 34 kJ. How much work do we gain or perform? (Everything reversible) (b) If we do not gain/perform work, how much heat is exchanged (internal energy change same as in part (a))? 3. (4 points) Liquid water at 453 K and 1002 kPa has an internal energy of 762 kJ/kg and a density of 890 kg/m 3 . (a) What is the enthalpy (per weight)? (b) We change the state to 573 K and 1500 kPA. The internal energy is now 2784 kJ/kg and the specific volume 169.7 cm
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Unformatted text preview: 3 /g. What are Δ H and Δ U (per weight) ? 4. (8 points, This problem was on the 2010 Midterm 1) We have a ﬂow system with three inlets and one outlet. The gases we are using have c P ( A ) = 1 . 78 kJ kg K and c P ( B ) = 2 . 38 kJ kg K . In inlets 1 and 2 gas A enters with 1 kg/min each, in inlet 3 gas B enters with 2 kg/min. (Steady state) (a) What is the ﬂow rate in the outlet. (b) Assume only inlets 1 and 2 are open and the gases enter with 340 K in inlet 1 and 360 K in inlet 2 what is the outlet temperature? (c) Inlet 3 is opened and the gas enters with 333 K (rest as in part b), what is now the outlet temperature? (d) In the system of part c we have now heat loss of . Q = 1 . 6 kW and we add stirring to improve mixing with . W = 750 W. What is now the outlet temperature?...
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