ChBE Name________________________________________________________________________________ 2100 Homework #7 Due Wed., Oct. 26 Please follow the homework guidelines outlined in the syllabus. Sign the Honor Code and use this page as a coversheet for your solutions.
Honor Code: I commit to uphold the ideals of honor and integrity by refusing to betray the trust bestowed upon me as a member of the Georgia Tech community. _______________________________________ Signature 1. A sample of oxygen is subjected to an absolute pressure of 2.4 atm. If the specific internal energy of the sample at 310 K is 5700 J/mol relative to a known reference state, what is the specific enthalpy of the oxygen relative to that reference state? 2. A weight is added to a piston so that the volume of the gas inside the container is reduced from 2.5 L to 1.0 L at a constant temperature. How must heat do you need to add to the system if you want to increase the volume back to 2.5 L at this new pressure. List your assumptions. 3. Define a system and simplify the open-system energy balance for each of the following cases. State when possible whether nonzero heat and shaft work terms are positive or negative. a. Crude oil is pumped through a cros-country pipeline. The pipe inlet is 200 m higher than the outlet, the pipe diameter is constant, and the pump is located near the midpoint of the pipeline. Energy dissipated by friction in the line is transferred through the wall as heat. b. A chemical reaction takes place in a continuous reactor that contains no moving parts. Kinetic and potential energy changes from inlet to outlet are negligible. c. A liquid stream flows through a heat exchanger in which it is heated from 25C to 80C. The inlet and outlet pipes have the same diameter, and there is no change in elevation between these points. d. Water passes through the sluice gate a of dam and falls on a turbine rotor, which turns a shaft connected to a generator. The fluid velocity on both sides of the dam is negligible, and the water undergoes insignificant pressure and temperature changes between the inlet and the outlet. e. The heart pumps blood in through the arterial side at 100 mmHg and out through the venous side at 0 mmHg. Energy transfers from the blood to the heart as heat as nutrients are absorbed and used. 4. Saturated steam at a gauge pressure of 2 bar is to be used to heat a stream of ethane. The ethane enters a heat exchanger at 16C and 1.5 bar gauge at a rate of 795 m3/min and is heated at a constant pressure to 93C. The steam condenses and leaves the exchanger as a liquid at 27C. Use Perry's to determine the specific enthalpy of ethane at the appropriate temperatures.
a. How much energy (kW) must be transferred to the ethane to heat it from 16C to 93C? b. Assuming that all the energy transferred from the steam goes to heat the ethane, at what rate in m3/s must steam be supplied to the exchanger? If the assumption is incorrect, would the calculated value be too high or too low? 5. Jets of high speed steam are used in spray cleaning. Steam at 15 bar with 150C of superheat is fed to a well-insulated valve at a rate of 1.0 kg/s. As the steam passes through the valve, its pressure drops to one bar. The outlet stream may be totally vapor or a mixture of vapor and liquid. Kinetic and potential energy changes may be neglected. a. Draw and label a flowchart, assuming that both liquid and vapor are emerging from the valve. b. Write and energy balance and use it to determine the total flow rate of enthalpy in the outlet stream. Then determine whether the outlet stream is in fact a mixture of liquid and vapor or whether it is pure vapor. Explain your reasoning. c. What is the temperature of the outlet stream?