Chapter 4 Flashcards
(21 cards)
What is the law of conservation of mass?
mass can neither be created no destroyed
What is a mass balance or material balance?
Mass balance is a consideration of the input, output, and distribution of a substance between streams in a process or stage.
What is a batch process?
the feed is charged (fed) into a vessel at the beginning of the process and the vessel contents are removed sometime later.
- no mass crosses the system boundaries between the time the feed is charged and the time the product is removed.
What is a continuous process?
the inputs and outputs flow continuously throughout the duration of the process.
ex: pumping a mixture of liquids into a distillation column at a constant rate and steadily withdrawing a product streams from the top and bottom of the column
What is an example of a batch process?
readily adding reactants to a tank and removing the products and unconsumed reactants somtime later when the system has come to equlibrium
What is a semibatch process?
Any process that is neither batch nor continuous
What is an example of a semi batch process?
Allow the contents of a pressurized gas container to escape to the atmopshere; slowly bend several liquids in a tank from which nothing is being withdrawn
What does it mean for a process to be operating at a steady state?
if all the values in a process do not change with time, except possibly for minor fluctuations about constant mean values
What does it mean if a process is operating at a transient or unsteady state?
when any process variables change with time
Which process is typically unsteady state operations?
batch and semi batch
Which process is either steady state or transient?
continuous process
What is the general equation for a balance?
input + generation - output - consumption = accumulation?
What is a differential balance?
balances that indicate what is happening in a system at an instant in time
- this balance is usually applied to a continuous process
- terms are typically a rate
What is an integral balance?
balances that describe what happens between two instants of time
- terms in the equation are an amount (people, gSO2, barrels)
- balance is usually applied to a batch process
What is the simplified equation for a continuous steady state process?
input + generation = output + consumption
What is the accumulation equation for a batch process?
initial input + generation = final output + consumption
What is the purpose of a flow chart?
using boxes and symbols to represent process units (reactors, mixers, separation units) and lines with arrows to represent inputs and outputs
What is the first step for labeling a flow chart?
Write the values and units of all known stream variables at the locations of the streams on the chart
What is the second step for labeling a flow chart?
Assign algebraic symbols to unknown stream variables and write these variable names and their associated units on the chart
What is a degree of freedom analysis?
using a properly drawn flowchart to determine whether you have enough information to solve a given problem
What is the method for a degree of freedom analysis?
Draw and completely label a flowchart, count the unknown variables on the chart, and then count the independent equations relating them, and then subtract the second number from the first.
ex: n unknowns - n independent equations
