Laminar flow reactor (LFR) is a type of chemical
reactor that uses laminar flow to control reaction
rate, and/or reaction distribution. LFR is generally a long tube with
constant diameter that is kept at constant temperature. Reactants are injected
at one end and products are collected and monitored at the other. Laminar flow
reactors are often used to study an isolated elementary reaction or multi-step reaction mechanism.
Overview
Laminar Flow Reactor employs the characteristics of laminar
flow to achieve various research purposes. For instance, LFRs can be used
to study fluid dynamics in chemical
reactions, or they can be utilized to generate special chemical structures
such as carbon nanotubes. One feature of the LFR is that
the residence
time (The time interval during which the chemicals stay in the reactor) of
the chemicals in the reactor can be varied by either changing the distance
between the reactant input point and the point at which the product/sample is
taken, or by adjusting the velocity of the gas/fluid. Therefore the benefit of
a laminar flow reactor is that the different factors that may affect a reaction
can be easily controlled and adjusted throughout an experiment.
Means of Analyzing Reactants in LFR
Means of analyzing the reaction include using a probe that
enters into the reactor; or more accurately, sometimes one can utilize
non-intrusive optical methods (e.g. use spectrometer
to identify and analyze contents) to study reactions in the reactor. Moreover,
taking the entire sample of the gas/fluid at the end of the reactor and
collecting data may be useful as well. Using methods mentioned
above, various data such as concentration, flow
velocity and etc. can be monitored and analyzed.
Flow Velocity in LFR
Fluids or gases with controlled velocity pass through a
laminar flow reactor in a fashion of laminar flow.
That is, streams of fluids or gases slide over each other like cards. When
analyzing fluids with same the viscosity ("thickness" or "stickiness")
but different velocity, fluids is typically characterized into two types of
flows: laminar
flow and turbulent flow. Compared to turbulent flow, laminar
flow tends to have a lower velocity and is generally at a lower Reynolds
number. Turbulent flow, on the other hand, is irregular and travels at a
higher speed. Therefore the flow velocity of a turbulent flow on one cross
section is often assumed to be constant, or "flat". The
"non-flat" flow velocity of laminar flow helps explain the mechanism
of a LFR. For the fluid/gas moving of a LFR, the velocity near the center of
the pipe is higher than the fluids near the wall of the pipe. Thus, the
velocity distribution of the reactants tends to decrease from the center to the
wall.
Residence Time Distribution(RTD)
The velocity near the center of the pipe is higher than the
fluids near the wall of the pipe. Thus, the velocity distribution of the
reactants tends to be higher in the center and lower on the side. Consider
fluid being pumped through a LFR at constant velocity from the inlet, and the
concentration of the fluid is monitored at the outlet. The graph of the
residence time distribution should look like a negative slope with positive
concavity. And the graph is modeled by the function: E(t)=0 if t is smaller
than τ/2; E(t)=τ^2/2t^3 if t is greater than or equal to τ/2. Notice that the
graph has the τ value of zero initially, this is simply because it takes
sometime for the substance to travel through the reactor. When the material is
starting to reach the outlet, the concentration drastically increases, and it
gradually decreases as time proceeds.
Characteristics
The laminar flows inside of a LFR has the unique
characteristic of flowing in a parallel fashion without disturbing one another.
The velocity of the fluid or gas will naturally decrease as it gets closer to
the wall and farther from the center. Therefore the reactants have a decreasing
residence
time in the LFR from the center to the side. A gradually decreasing
residence time gives researchers a clear layout of the reaction at different
times. Besides, when studying reactions in LFR, radial gradients in velocity,
composition and temperature are significant.In other words, in other reactors
where laminar flow is not significant, for instance, in a plug
flow reactor, velocity of the object is assumed to be the same on one cross
section since the flows are mostly turbulent. In a laminar flow reactor,
velocity is significantly different at various points on the same cross
section. Therefore the velocity differences throughout the reactor need to be
taken into consideration when working with a LFR.
Research
Various researches pertaining to the modeling of LFR and
formations of substances within a LFR have been done over the past decades. For
instance, the formation of Single-walled carbon nanotube was investigated in a
LFR. As another example, conversion from methane to higher hydrocarbons have
been studied in a laminar flow reactor.
SUBSCRIBERS - ( LINKS) :FOLLOW / REF / 2 /
findleverage.blogspot.com
Krkz77@yahoo.com
+234-81-83195664
No comments:
Post a Comment