(A)
Interpretation:
The rate at which heat is added to the toluene in the reboiler
Concept Introduction:
Thesteady state energy balance equation on reboiler (toluene).
Here, time taken is
(A)
Explanation of Solution
Given information:
Mass flow rate of toluene is
80% toluene is heated up to saturated vapor at pressure of 1.1 bar.
Mass flow rate of benzene is
25% benzene is heated up to saturated vapor at pressure of 0.9 bar.
Calculate the heat transfer using steady state energy balance equation on reboiler (toluene).
Rewrite the steady state Equation (1) by neglecting the work done, potential energy, and kinetic energy.
Here, initial molar enthalpy is
Refer the NIST webbook, obtain the enthalpy of saturated liquid and vapor toluene corresponding to pressure of
Calculate final molar flow rate of liquid
Substitute
Substitute
Thus, the rate at which heat is added to the toluene in the reboiler is
(B)
Interpretation:
The flow rate of steam entering the reboiler at pressure of
Concept Introduction:
Write the steady state energy balance equation around the water passing through the reboiler.
Here, mass is
(B)
Explanation of Solution
Given information:
For steam at 1 bar:
For steam at 3 bar:
For steam at 5 bar:
Calculate the heat transfer using steady state energy balance equation on reboiler (toluene).
Rewrite the steady state Equation (4) by neglecting the work done, potential energy, and kinetic energy.
Refer the Appendix table A-1, “Saturated steam-Pressure increments”, obtain the value of initial and final specific enthalpy corresponding to pressure of
Substitute
Thus, the flow rate of steam entering the reboiler at pressure of
Refer the Appendix table A-1, “Saturated steam-Pressure increments”, obtain the value of initial and final specific enthalpy corresponding to pressure of
Substitute
Thus, the flow rate of steam entering the reboiler at pressure of
Refer the Appendix table A-1, “Saturated steam-Pressure increments”, obtain the value of initial and final specific enthalpy corresponding to pressure of
Substitute
Thus, the flow rate of steam entering the reboiler at pressure of
(C)
Interpretation:
Comments on the result of part B, explanation about high pressure steam turbine.
(C)
Explanation of Solution
Here, the mass flow rate is almost equal at different pressures. Though, these estimations do not explain the temperature driving force needed in a heat exchanger.
Referred data from NIST Webbook, the boiling temperature for toluene at pressure of
The high pressure steam has a higher temperature of
While the higher-pressure steam is high cost, the calculations in part (B) do not description for the equipment cost. A higher the temperature dissimilarity between the toluene and steam means faster heat exchange, which means a smaller heat exchanger is required. The exchange between equipment costs and operating costs are typically explained in design courses in the chemical engineering program.
(D)
Interpretation:
Flow rate of water if the water is used as coolant.
Concept Introduction:
Write the steady state energy balance equation for benzene entering and leaving the condenser.
Write the expression to determine the heat capacity of liquid water from Appendix D:
Here, final and initial specific enthalpy is
Write the formula to calculate the constant pressure heat capacity
Here, gas constant is
(D)
Explanation of Solution
Calculate the heat transfer using steady state energy balance equation benzene for entering and leaving the condenser.
Rewrite the steady state Equation (6) by neglecting the work done, potential energy, and kinetic energy.
Refer the NIST webbook, obtain the value of
Substitute
Rewrite the Equation (6).
Therefore the coolant enters the condenser at temperature of
Determine the heat capacity of liquid water from Appendix D:
Calculate the constant pressure heat capacity.
Substitute
Here, molecular weight is
Refer the Appendix table D, “Heat Capacity”, obtain the constant values of constant
Substitute
Substitute
Thus, the flow rate of wateris
(E)
Interpretation:
The flow rate of air
Concept Introduction:
Write the expression to calculate the change in specific enthalpy
Here, constant pressure heat capacity of nitrogen for ideal gas is
Write the expression to calculate the mixture of 0.79% of nitrogen and 0.21% of oxygen of constant pressure heat capacity
Here, gas constant is
(E)
Explanation of Solution
Given information:
Pressure is 1 bar and specific heat capacity is
Calculate the mixture of 0.79% of nitrogen and 0.21% of oxygen of constant pressure heat capacity
Calculate the change in specific enthalpy
Substitute
From Appendix D.1, “Ideal Gas Heat Capacity”, obtain and write the constant values of nitrogen and oxygen as in Table (1).
Name | Formula | A | ||||
Nitrogen | 3.539 | 0.007 | 0.157 | |||
oxygen | 3.630 | 0.658 | ||||
Air | 3.5581 | 0.1437 |
Substitute 3.5581 for A,
Substitute
Thus, the flow rate of air is
(F)
Interpretation:
Suggestion for using water instead of air.
(F)
Explanation of Solution
The mass flow rate of the air is 4 times greater than the mass flow rate of the water, for the equal amount of cooling. Again, these estimations do not account the cost of equipment.
The volume of 5.94 kg of air is orders of magnitude larger than the volume of 1.43 kg of liquid water at ambient pressure, which has implications for the equipment size.
Transfer of heat to liquids is much more efficient compared to heat transfer to low-pressure gases that also effects the size, and therefore the equipment cost of the heat transfer.
Thus, liquid water has the coolant has many benefits regardless of the fact that air free but water isn’t.
Want to see more full solutions like this?
Chapter 3 Solutions
Fundamentals of Chemical Engineering Thermodynamics, SI Edition
- Introduction to Chemical Engineering Thermodynami...Chemical EngineeringISBN:9781259696527Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark SwihartPublisher:McGraw-Hill EducationElementary Principles of Chemical Processes, Bind...Chemical EngineeringISBN:9781118431221Author:Richard M. Felder, Ronald W. Rousseau, Lisa G. BullardPublisher:WILEYElements of Chemical Reaction Engineering (5th Ed...Chemical EngineeringISBN:9780133887518Author:H. Scott FoglerPublisher:Prentice Hall
- Industrial Plastics: Theory and ApplicationsChemical EngineeringISBN:9781285061238Author:Lokensgard, ErikPublisher:Delmar Cengage LearningUnit Operations of Chemical EngineeringChemical EngineeringISBN:9780072848236Author:Warren McCabe, Julian C. Smith, Peter HarriottPublisher:McGraw-Hill Companies, The