Comparative Analysis of Hydrodynamics Behavior of Microalgae Suspension Flow in Circular, Square and Hexagonal Shape Photo Bioreactors (original) (raw)
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Rajshahi University Journal of Science and Engineering , 2016
In biofuel technology from microalgae, the main optimal factors for microalgae cultivations are light, CO 2 and temperature. As microalgae are photosynthetic microorganisms thus they convert sunlight, water and CO 2 to algal biomass. We consider a two phase flow for CO 2 and Microalgae suspension to understand fluid dynamics phenomena after injecting CO 2 gas inside a tubular Photobioreactor (PBR).The growth rate of the microalgae cell is taken as a function of available sun light at Chittagong University of Engineering & Technology (CUET) in our study. A 20.94m long and 0.025m tubular PBR is considered for the simulation. To observe the microalgae cell growth, we selected the 21 st June for a bright sunny and the longest day of a year. From the simulation after day seven we observed a very slow growth for the microalgae culture. It is noted that the growth related to concentration of microalgae is increased by day length with respect to continuous sunlight. A small fluctuation of shear rate around U-loop area is also found in our simulation which may be caused to reduce the volumetric production due to cell fragility. From the velocity profile we found that, the velocity is generally higher in the middle of the tube gives a parabolic shape of the suspension flow.
The Development of Tubular Photobioreactor for Microalgae Cultivation
ASEAN Journal of Chemical Engineering
In a tubular photobioreactor, microalgae cells obscure one another (Self-shading), leading to the microalgae at the bottom of the tube getting less light. The objective of this research was to design and develop Tubular Photobioreactor with 93.5 liters for microalgae cultivation. The experiments had two steps. The first step was designing the solar receiver by inserting the fin into each tube wall as follows: 12-34, 1-2-3-4, 1234, and 13-24. Then, FLUENT software was used to simulate flow behavior inside the tube by Computational Fluid Dynamics by observing the pressure drop, the amount of energy consumption, and the swirling velocity to select the best fin-type. The best fin-type with the growth rate equation is introduced in the next step to simulate the microalgae's growth and movement using the user-defined function technique. The comparison of a tubular photobioreactor is investigated between fin and without fin by observing biomass production. The results showed that algae...
Journal of Environmental Chemical Engineering, 2021
Appropriate hydrodynamic conditions are crucial in photobioreactors (PBR) in order to prevent sedimentation of microalgal biomass and to ensure the uniform exposure of microalgae cells to light and nutrients. Hydrodynamic conditions are also important to guarantee efficient mass transfer and proper shear stress on the transparent walls of the PBR, which can avoid the formation of undesired biofilm. Numerical simulations based on Computational Fluid Dynamics (CFD) can assist to improve the hydrodynamic design and optimization of PBRs. In this study, CFD was used as a tool to investigate the hydrodynamics of a hybrid horizontal tubular PBR designed for microalgae cultivation and wastewater treatment. The flow regime, average circulation time and shear stress distribution in the tubes were evaluated. To establish the reliability of the simulation study, the CFD model was validated using tracer experimental tests and ultrasonic flow meter measurements. Results showed that the hydrodynamic conditions in the tubes resembled plug flow with small axial dispersion. The simulated velocity profile in the tube corresponded to the analytical velocity profile based on experimental data. Simulations also showed that, even increasing flow velocities, low velocity zones were present in some zones of the PBR. The shear stress distribution in the tubes showed values higher enough to reduce or avoid the formation of biofilm, nevertheless the shear stress value is not sufficient to remove the already formed biofilm. Based on the numerical investigation and practical evaluation, this study demonstrated that CFD is a useful tool to optimize PBR design and operation in order to enhance microalgae production and boost the scale-up of this technology.
Design of a Stacked-layer Tubular Photobioreactor for Microalgae Cultivation
KMUTNB International Journal of Applied Science and Technology, 2015
A tubular photobioreactor is one of the most effective methods of microalgae cultivation because of the high solar receiver area and better biomass productivity. However, the pressure drop along the tubular solar receiver induces a relatively high dead zone. An optimal design is necessary to maximize biomass productivity. In this article, the proposed model can reduce the dead zone by up to 15% under a pressure drop of 106 Pa. To optimize the area requirement, three configurations with different stacking angles of 30, 45, and 60°, are simulated. The optimal 60° stacked-layer model is then connected to an airlift device to demonstrate the complete system. This model can circulate seawater inside the reactor at an average velocity of 0.188 m/s with 0.07 m/s of air inlet velocity. The radial flow can force the microalgae from the inner part of the tube to the outer part and back again throughout the entire stacked section. This turbulence will enhance biomass productivity because the microalgae are moved from the darker interior of the tube to the periphery where they are exposed to solar radiation. The optimal stacked-layer tubular photobioreactor has a slope of 60° with four stacked layers. This modification promotes the circulation of microalgae in both axial and radial directions.
The tolerance to shear stress of Tetraselmis suecica, Isochrysis galbana, Skeletonema costatum, and Chaetoceros muelleri was determined in shear cylinders. The shear tolerance of the microalgae species strongly depends on the strain. I. galbana, S. costatum, and C. muelleri exposed to shear stress between 1.2 and 5.4 Pa resulted in severe cell damage. T. suecica is not sensitive to stresses up to 80 Pa. The possibility to grow these algae in a tubular photobioreactor (PBR) using a centrifugal pump for recirculation of the algae suspension was studied. The shear stresses imposed on the algae in the circulation tubes and at the pressure side of the pump were 0.57 and 1.82 Pa, respectively. The shear stress tolerant T. suecica was successfully cultivated in the PBR. Growth of I. galbana, S. costatum, and C. muelleri in the tubular PBR was not observed, not even at the lowest pumping speed. For the latter shear sensitive strains, the encountered shear stress levels were in the order of magnitude of the determined maximum shear tolerance of the algae. An equation was used to simulate the effect of possible damage of microalgae caused by passages through local high shear zones in centrifugal pumps on the total algae culture in the PBR. This simulation shows that a culture of shear stress sensitive species is bound to collapse after only limited number of passages, confirming the importance of considering shear stress as a process parameter in future design of closed PBRs for microalgal cultivation.
In this study, a two phase flow for CO 2 and Microalgae suspension is considered to understand fluid dynamics phenomena after injecting CO 2 gas inside a tubular Photobioreactor (PBR).The growth rate of the microalgae cell is taken as a function of available sun light at Chittagong University of Engineering & Technology (CUET). The tubular PBR is considered in our study have the radius of 0.025m while the entire length is 20.94m. To observe the growth of microalgae cell we selected the 21 st June for a bright sunny and the longest day of a year. From the simulation after day seven we observed a very slow growth for the microalgae culture and the growth related to concentration of microalgae is increased by day length with respect to continuous sunlight. A small fluctuation of shear rate around U-loop area is also found in our simulation which may be caused to reduce the volumetric production due to cell fragility.
This paper aims to show dynamic behavior of microalgae suspension in a Horizontal Loop Tubular Photobioreactor (HLTP). Two models of a single-phase flow and a two-phase flow have been proposed taking into account the light irradiance. The governing equations describing a single-phase flow are the continuity equation and the Navier-Stokes equation. The viscosity of the microalgae suspension is a function of microalgae cell concentration which varies in time. Using the governing equations of a single-phase flow together with the Cahn-Hiliard mass conservation equation, we can describe the dynamic behavior of a two-phase flow. The results obtained from both models are compared. It is noted that both results are significantly different. In the two-phase flow model, the mass transfer rate and the shear rate are higher than those obtained from the single-phase model.
Numerical investigation of a bubble-column photo-bioreactor design for microalgae cultivation
Biosystems Engineering, 2012
Renewable energy is interesting as a countermeasure for the fossil energy depletion and carbon dioxide reduction. Biodiesel using vegetable oils is one of the most desirable renewable energy because it can be an alternate diesel to petroleum. However, the biodiesel from soybean or corn, etc. can be confronted with food crisis. Microalgae have recently been researched as a new biodiesel source which not only contain high oil lipids with high growth rate but also offer value-added products such as cosmetics, health functional food or pharmacy from the residue. Because pond production system has limitations in unstable weather conditions and insufficient land availability especially in Korea, photo-bioreactors (PBRs) is essential for their cultivation. More so, controlling the suitable environments such as light, nutrients, carbon dioxide, temperature, etc. in the PBR is possible. Despite the availability of PBRs at present, only a few can be practically used for mass production due to some limitations. In this study, computational fluid dynamics (CFD) was used to design an optimum bubble-column PBR for mass production of microalgae. Multi-phase models including bubble movement, meshes and time step independent tests were considered to develop the three-dimensional CFD model. The model was enhanced and validated through Particle Image Velocimetry (PIV) tests. Various types of PBRs were simulated and compared quantitatively with consideration of the microalgae's growth model adaptable for the CFD model and an evaluation method of mixing efficiency in the PBRs has been done. This research can be used as a basic technique for microalgae production on a large scale.
Biosystems Engineering, 2014
Dead zones Turbulence intensity A numerical simulation using computational fluid dynamics (CFD) was utilised to investigate the flow hydrodynamics of cylindrical bubble column type photobioreactors (PBRs) with a 30 l culture medium. To establish the reliability of the simulation study, the CFD model was validated using particle image velocimetry (PIV) computed data under various air flow rates. There were 32 simulation cases for the study comprising two PBR designs, four air flow rates and four nozzle size diameters. Hydrodynamic analyses such as % volume of dead zones, average circulation time and turbulence intensity inside the simulated PBRs were evaluated. Results have shown that the most appropriate PBR for microalgae cultivation was a design with internal baffle and an extended cone-shaped bottom section. In addition, the recommended nozzle diameter was found to be 10 mm and a minimum air flow rate of 0.10 vvm. To eliminate dead zones inside the PBR, the flow rate can be slightly increased but should not exceed 0.15 vvm. Practical evaluation through laboratory experiments has further confirmed the results of the study where the biomass concentration of Chlorella vulgaris from the proposed PBR was significantly higher compared to the standard PBR design. Based on the numerical investigation and practical evaluation, the improved PBR can be seen to be more effective in culturing microalgae particularly for larger scale mass production.
Investigation of Flow Dynamics for a Microalgae Suspension in an Open Pond System
American Journal of Computational Mathematics
In the microalgae based biofuel technology, two main cultivation methods are available such as the Open pond system and the Closed photo bioreactor (PBR). The primary advantages of utilizing open raceway ponds are low production and maintenance cost. Though the open raceway ponds have been adjudged potentially cost effective, so many surrounding issues are involved to produce microalgae at a large scale that could make microalgae fuel cost competitive with the conventional petro oil. Many researchers have been studied so far to increase the efficiency of the cultivation methods without providing a proper mathematical model of flow dynamics inside the open raceway ponds. This paper presents a mathematical model to analyze the flow behavior of an open pond culture focusing the mixing factors by using a paddlewheel while the paddlewheel have its own unique dynamic characteristics. From our simulation we observed that the paddlewheel plays a vital role in mixing and the growth of microalgae. The velocity profiles, shear stress distributions are also studied at different parts of an open pond culture for a microalgae suspension.