Generation of Microbubbles through Single Loop and Double Loop Fluid Oscillator for Photobioreactor Aeration
Corresponding email: nasruddin@eng.ui.ac.id
Published at : 29 Nov 2019
Volume : IJtech
Vol 10, No 7 (2019)
DOI : https://doi.org/10.14716/ijtech.v10i7.3691
Rizaldi, M.I., Rahman, A., Deendarlianto., Prihantini, N.B., Nasruddin., 2019. Generation of Microbubbles through Single Loop and Double Loop Fluid Oscillator for Photobioreactor Aeration . International Journal of Technology. Volume 10(7), pp. 1446-1452
| Muhammad Ilham Rizaldi | Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia |
| Arif Rahman | Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia |
| Deendarlianto | Department of Mechanical and Industrial Engineering, Faculty of Engineering, Universitas Gadjah Mada, Yogyakarta 55281, Indonesia |
| Nining Betawati Prihantini | Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia |
| Nasruddin | Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia |
Microbubbles are known for their many
applications. Recently there has been new findings regarding the growth
of susceptible microalgae through microbubble aeration. There are three methods
used to generate microbubbles for this microalgae strain. Unfortunately, for some
methods, the cost of generating microbubbles
is still high. However, fluidic oscillators
can be used to produce microbubbles at a
reasonable cost. There are two types of fluid oscillators: single loop and double loop. This study
determined the bubble size produced with these oscillators. Bubble size data
was recorded using a high-speed camera at air flow rates of 6 LPM, 9 LPM, 12 LPM, and 15
LPM, and utilized 10 µm microporous shafts as the diffuser. The data were processed using ImageJ software. The results showed that the size of
the bubble using a single loop fluid oscillator was smaller than that of the
double loop fluid oscillator. The smallest bubble size was obtained in a single loop fluid oscillator
with an airflow of 6 LPM.
Fluid oscillator; Microbubble; Photobioreactor
The issues related
to increased energy demand, environmental pollution and depletion of fossil
fuels are considered very urgent: renewable and alternative fuels must replace
fossil fuels while maintaining fresh air and
ensuring energy security (Pham et al., 2018). Biodiesel
is an alternative fuel that contains long chain fatty acids known as mono alkyl
esters. It is predominantly a
renewable, clean-burning fuel that is environmentally friendly, nontoxic, and
free from harmful sulphur (Hidayat et al., 2018). The application of microalgae to
biodiesel production has great potential: it has gained attention
because it can produce oil in the cells
of its body. The oil content in microalgae ranges from 20–50% and microalgae
can exceed 80% of the weight of dry biomass (Rahman et al., 2019).
A
lot of microalgae biomass can be cultivated by using photobioreactors. Using
this method, microalgae conduct photosynthesis as they would in their natural
habitat. The process of photosynthesis requires light and carbon dioxide as energy sources for the growth of
microalgae. During
the process of photosynthesis in photobioreactors, microalgae absorbs the content of
A microbubble isdefined as a bubble
with a diameter ofless than one millimeter (50–200 µm) (Juwana
et al., 2019;Deendarlianto et al., 2015). Microbubbles have advantages across many applications due to their bubble size. For example, they have been used in wastewater treatment (Rehman
et al., 2015;Budhijanto et al.), biomolecular separation (Lye
et al., 2001) and microorganism aeration (Hanotu
et al., 2016). Their small size yields
advantages, such as higher surface to volume ratio, which provide higher mass transfer rates.
Another advantage of
microbubbles is slow
rise velocity, which allows more
substances to dissolve
in the medium due to its residence time (Zheng
et al., 2018).
Microbubbles
have
unique characteristics,
such as high gas dissolution, low rising velocity, and high interfacial area (Deendarlianto
et al., 2015). Recently, there has been a special
case regarding the growth of susceptible microalgae strains using microbubbles.
One method of generating microbubbles
uses
pumped water; however, this cannot be used to breed micro algae because it creates circulation. As a result, the strain would experience high shear stress due to the pumping action and would eventually
decease. The only way to develop microbubbles without creating circulation
involves pumping air
through sparger in
photobioreactor, and there
are three methods of achieving
this. The most common method uses compressed air, which flows
through a specifically designed nozzle to generate small bubbles based on the
cavitation principle. The second method uses ultrasonic sound waves to oscillate a needle tip
following air coming through the water chamber, thus creating a continuous
stream of tiny bubbles (Makuta
et al., 2005). Unfortunately, both methods require high energy
densities; this makes the operational cost of a photobioreactor quite high (Zimmerman
et al., 2008). One possible low-cost method
involves microbubble generation by oscillating the airflow using mechanical
vibration. The bubbles
generated will break off
at a size that is close to the diameter of the hemisphericalcap.
A fluidic oscillator is a no moving part jet actuator
that is able to oscillate airflow because of its special geometry. It has a low cost because it is easy to manufacture using the CNC (Computer Numerical Control) machining process and does not need
frequent maintenance. There have been many reviews about the characteristics of
fluidic oscillators. The most common types of fluidic oscillators are the
double loop fluid oscillator and the single loop fluid oscillator, created by Warren and Spyropoulos (Warren,
1964;Spyropoulos, 1964). Recently, Tesar has made a modified model using both types that can achieve an oscillation frequency up to ~200 Hz (Tesa? et al.,
2013;Zimmerman et al., 2011). However, no reviews have comprehensively studied bubble
generation through fluidic oscillators using a microporous sparger as a diffuser.
This study will investigate the bubble size produced by fluidic
oscillators effectively.
In conclusion, airflow affects the characteristics of bubble size: a higher airflow results in more bubbles with larger diameters and the uneven
distribution of
bubble sizes formed along the microporous sparger. This phenomenon occurred due to the conjunction of bubbles
that had been formed
earlier. Otherwise, the bubbles formed would be smaller and more evenly
distributed. Single loop fluidic oscillators can generate smaller bubbles than
double loop fluidic oscillators based on this research data.
The authors would like to thank the Ministry of
Research, Technology and Higher Education of Republik Indonesia (KEMENRISTEK-DIKTI RI) for funding this
research for the Masters program
toward a Doctorate for Superior Bachelor (PMDSU) 2019 with contract number
NKB-1862/UN2.R3.1/HKP.05.00/2019.
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