Process Intensification and Green Processing Using Cavitational Reactors - Process Intensification for Green Chemistry - page 204

P2

CW out

BYE PASS
LINE

C W in

P1

TANK

V2 V3

V1 CENTRIFUGAL

PUMP

P1, P2- Pressure gauge

V1,V2,V3 - CONTROL VALVES

Figure 7.5 Schematic representation of hydrodynamic cavitation setup based on a flow loop
housing a cavitation chamber. Reprinted from [ref 7] # 2008, with permission from Elsevier.

flexibility in terms of the operating (control of inlet pressure, inlet flow rate, temperature)
and geometric conditions (different arrangements of holes on the orifice plates). Depending
on the type of application and the requirements, geometry and operating conditions can be
selected in the hydrodynamic cavitation reactor to maximize the cavitational effects at
minimum possible energy consumption. Sampathkumar and Moholkar [22] recently put
forth a conceptual design for a novel hydrodynamic cavitation reactor that uses a
converging-diverging nozzle to create the pressure variation in the flow required to drive
bubble motion, instead of orifice plates. The cavitation bubbles or nuclei are introduced in
the water flow externally, upstream of the nozzle, using a sparger. Different gases can be
used for the introduction of the bubbles. The size of the gas distributor (usually a glass frit),
the flow rate of the gas and the pressure of gas in the reservoir (or source) from which the
gas is withdrawn can be controlled to determine the initial size of the cavitational nuclei
and the gaseous composition of the cavity, which significantly affects the resultant
cavitational intensity. The aim should be to generate the smallest size of nuclei possible
in order to maximize the intensity and hence the net cavitational effects.

7.4 Mathematical Modelling

Modelling of cavitational reactors can aid in efficient design and subsequent operation of
large-scale reactors. Two aspects of modelling - the bubble dynamics and pressure field
distributions in the reactor - are very important for efficient design. The bubble dynamics
analysis gives an idea of the cavitational intensity, while theoretical modelling for pressure
field distributions can aid in obtaining uniform cavitational activity distribution. It is not
possible to cover the detailed mathematical modelling aspects given the focus of the topic,
but some basic discussion has been offered to aid better understanding.