CHEG 3300 – Mass Transfer-Mechanistic Engineering Approach to Improve Mass Transfer in Unit Operations


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Project Work (CHEG 3300 – Mass Transfer)
Mechanistic Engineering Approach to Improve
Mass Transfer in Unit Operations
Submission due dates: March 13 and April 21
Project Description
A chemical engineer has a task to enhance the hydrodynamic and mass transfer rate in the fluid by
developing a mechanistic engineering approach to vary the physical properties of the fluid,
intensify the absorption and diffusion process. One of the approaches could be incorporating
nanofluids or nanoparticles to enhance the performance of gas absorption systems. The principal
advantages of using nanoscopic fluids or nanoparticles are: (a) amount of chemical absorbents can
be decreased (b) tower or column height can be reduced, both by achieving larger mass transfer
coefficients with nanoscopic fluids or particles. The major objective of this project work is to
propose a comprehensive mass transfer model to enhance the mass transfer rate either in a packed
bed column or a plate column.
Investigate how to enhance the gas side mass transfer coefficient. Thoroughly investigate various
operating conditions by specifying the characteristic parameters of the system in the first step.
Consider a laminar flow for both the compressible gas and incompressible fluid. The effects of
pressure and concentration on the physical properties of the gas phase must be studied. It is
important in the first step to achieve the equilibrium state for the interacting components.
Investigate the transport properties such as molecular diffusion to achieve the state. Thoroughly
study the thermodynamics in the solution and how to accomplish the equilibrium steady states by
sequentially investigating the properties of the system, variables, parameters to be evaluated and
their corresponding boundary conditions to understand the contributions, limitations of latent heat
and sensible heat combined with hydrodynamic properties to maintain the equilibrium throughout
the column height.
Mass transfer coefficients can be influenced by the forces acting on the Brownian motions of the
nanoparticles. The direction of flow must be towards the interface. Your approach should be
directed towards increasing the mass transfer coefficients in the column resulting in larger
diffusion flux of the gas into the liquid phase. Consider the residence time distribution in the
column. For example, an increase in the gas flow rate reduces the residence time. Mass transfer
rate can be enhanced because of the large reaction rate. Facilitating larger liquid velocity closer to
the gas-liquid interface is another phenomenon that can enhance the mass transfer rate. Overall,
liquid flow rate plays an important role in the column performance.
Natural convection heat transfer of nanofluids can be considered. You should study the
advantages of using nanofluids compared to conventional micro fluids and how the volume
fraction of nanofluids has an advantage over the micro fluids. Study the heat conductivity
coefficient, enthalpy changes that limit the enhancement heat transfer of nano and micro fluids.
For example when compared to water, nanofluids deteriorate the convection heat transfer
(determined by the volume fraction). Also please note that the heat conductivity coefficient cannot
compensate for the increasing viscosity of the nanofluid. A continuity equation combined with
momentum equation (relating the above behavior) can be evaluated in terms of thermal
conductivity, specific heat and temperature of mixed nanofluid. Enhancement heat transfer can be
accomplished at high temperature differences. The driving force initially is derived from the
temperature difference. Adding nanoparticles not only increases the heat conductivity but also
increases the viscosity of the fluid which creates the viscous forces for the natural convection heat
transfer. At low temperatures, viscous forces play a major role for heat conduction. Therefore the
heat transfer performances at lower temperatures will be worse than the higher temperatures. You
also need to study on how to increase the collisions between these nanoparticles to increase
convection heat and mass transfer. Please note: (a) driving forces increase with temperature
difference (b) dynamic equilibrium in an equilibrium process can be at steady state, but a steady
state need not be in equilibrium in the irreversible process.
Assumptions: Assume that the mixed nanofluid is a continuous medium. There is no motion slip
between nanoparticles and fluids. But there should be thermal equilibrium between nanoparticles
and the mixed fluid. Neglect the effects of column shape, type of material and any presence of
rotating magnetic fields. Assume that the liquid phase composed of nanofluids is a homogeneous
continuous medium. Use fluid mechanics and hydraulic concepts to explain the hydrodynamic
behavior of the column. The liquid and gas flow counter currently in the column. The same
approach can be generalized for the entire column. In its standard state, the enthalpy change of
formation of any element has to be zero. (Note: Enthalpy is proportional to temperature change
or temperature gradient, only in an adiabatic process. An isothermal process will have enthalpy
change). The system has to be in dynamic equilibrium to achieve steady state.
Propose a continuity equation which captures the above phenomena mentioned for an
incompressible liquid phase and a compressible gas phase.
1. Assuming laminar flow, propose an equation of motion for the gas phase.
2. What can be the species continuity equations for liquid and gas phases in the column (nonconductive
systems)?
3. How do we derive the driving force for the overall mass diffusion flux? Use Fick’s law
combined with flow factors of the fluid.
4. Propose a gas phase and a liquid phase mass transfer model which explains the overall
phenomenon at the interface.
Target Assessment Dates:
A. By Monday, March 13, submit the outline/proposal (3-4 pages) for 50% grade:
 A conceptual model of the proposed system …………….. (15 points).
 Proposed approach defining ……………….(20 points)
o variables
o parameters and
o boundaries or limitations
 Conditions leading to interfacial thermal equilibrium (steady state) ….(15 points)
B. By Friday, April 21, submit the following full project report (8-10 pages including the
previous proposal of March 13) for 50% grade:
 Questions 1-4 mentioned above.
Project Write-Up Structure (valid only for the final report of April 21):
• Problem Statement ………………………………………………..(5 points)
• Task Identified (Include the proposal outline of Mar 13 here)….(5 points)
• Parameters Selected …………………………………………………(5 points)
• Background ……….…………………………………………………(5 points)
• Approach …………………………………………………………..(10 points)
• Description …………………………………………………………(10 points)
• Conclusion ……….…………………………………………………(5 points)
• References ……………………………………………………………(5 points)

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