Review:
Exam 4- Material & Energy Balances, Engr. Economics
Supplemental Instruction
IowaStateUniversity / Leader: / Becca
Course: / ChE 160
Instructor: / Heinen/Haman
Date: / 04/24/2016

Resources

  • Elementary Principles of Chemical Processes by Felder and Rousseau (ChE 210 book)
  • LearnChemE by University of Colorado-Boulder on YouTube
  • Chapters 8 and 9 from Eide Textbook

Study strategies

  • Really understand the basics and go from there
  • Look at the SI worksheets posted
  • Redraw graphs and figures
  • Rewrite notes
  • Reword ideas and principles
  • Write out steps to problem solving
  • Talk about notes and concepts with a friend
  • Make your own example problems
  • Write a reference sheet with all study information to review right before
  • Make your 3”x5” note card

Notes from Becca

  • Read through Exam 4 information on Blackboard
  • You should be able to finish the entire exam in 50 min
  • Strategize—start with the easy problems first to knock them out or hard problems first
  • PRACTICE TIMING WITH MATERIAL BALANCES!
  • If you don’t know, skip it and come back
  • Show your work! Partial credit is better than no credit

PRACTICE EXAM (Note: adapted from Dr. Heinen’s practice exam format.)

Short Answer:

Write the simplified closed- or open-system energy balance equation for each of the specified systems in each of the following cases. What are the un-simplified versions of the closed and open energy balance equations? Is the process open or closed?

  1. Steam enters a rotary turbine and turns a shaft connected to a generator. The inlet and outlet steam ports are the same height. Some energy is transferred to the surroundings as heat. SYSTEM = steam
  1. A liquid stream flows through a heat exchanger in which it is heated from 25 °C to 80 °C. The inlet and outlet pipes have the same diameter, and there is no change in elevation between these points. SYSTEM = liquid
  1. Water passes through a gate of a 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 outlet. SYSTEM = water
  1. 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. SYSTEM = reactants & products
  1. An endothermic reaction takes place in a closed, adiabatic reactor. SYSTEM = reactants & products

Calculate the semi-annual payment of a $40,000 loan to be paid over 5 years at an annual interest rate of 3.5%.

Problem Solving

Problem solutions must be presented professionally to receive full credit, including the given/find/assume/solution format. Diagrams are required. How long will it take to draw diagrams? Plan accordingly!

A stream of a solvent and a mineral enter a separation process at 12 lbm/s. The separation process removes 8 lbm/s pure solvent from the stream. The rest of the material leaves in another stream headed toward a boiler where solvent is boiled off to get 1.1 lbm/s of a 95% mineral powder. Create a diagram and mass balance for this system. What is the composition of the entering stream?

In your process, saturated steam at a pressure of 5.0 bar is used to heat a stream of ethylene. The ethylene enters the heat exchanger at 27°C and 1.0 bar at a rate of 520 kg/min and is heated at constant pressure to 52°C. The steam condenses and leaves the heat exchanger as a liquid at 30°C. How much energy (kW) must be transferred to the ethylene to heat it from 27°C to 52°C? If the energy transfer is 90% efficient, what mass flow rate of steam must be supplied?

Component / Phase / Temperature / Pressure / Enthalpy
Steam / Saturated / 151.8°C / 5.0 bar / 2747.5 kJ/kg
Liquid / 30°C / 0.0424 bar / 125.7 kJ/kg
Ethylene / Gas / 27°C / 1.0 bar / 460.5 kJ/kg
Gas / 52°C / 1.0 bar / 526.8 kJ/kg

You are looking at two different distillation columns for your process. Column 1 costs $90,000 and is expected to last 20 years. Annual maintenance and operation costs are $4,100, and the salvage value in 20 years is estimated to be $6,000. Column 2 costs $70,000 and is estimated to last 20 years. Annual maintenance and operation costs are $7,000, and the salvage value in 20 years is estimated to be $2,500. Calculate the equivalent uniform annual cost of each column assuming a 7.0% annual interest rate. Which purchase is best?Don’t forget to draw cash flow diagrams!

After all of that, what should you put on your 3”x5” note card to bring into the exam?

What topics should you spend more time studying?

Are there any study strategies that have worked well for you?

GOOD LUCK! YOU WILL DO GREAT! 