Search

Stepped planning hulls are commonly used on fast planning boats and water-based aircraft, but numerical means for simulating their hydrodynamics are rather limited. In this study, a panel method involving hydrodynamic sources has been applied for modeling a stepped planning hull and accounting for water surface deformations in the air-ventilated cavity and surrounding water domain. Parametric calculations have been carried out for a selected hull with variable deadrise angles and at two speed regimes. Results are shown for the boat attitude, lift–drag ratio, and drag components. The variations of the wetted surfaces on two bodies of a stepped hull are also presented and related to variations in hydrodynamic characteristics of the hull.

Despite rising popularity of planing catamarans, numerical methods for predicting their hydrodynamics are rather scarce and incomplete. The hydrodynamic interaction between hulls planing parallel to each other is known to become significant when spacing between hulls is sufficiently small. In the present study, a potential-flow method of hydrodynamic sources is applied for modeling steady hydrodynamic characteristics of twin-hull setups. Parametric calculations are carried out for symmetric hulls in variable speed regimes at different spacings, hull aspect ratio, and deadrise angles. Results are presented for the lift coefficient and center of pressure, and some illustrations are given for the water surface elevations. The lift coefficient is found to increase with smaller spacings and higher aspect ratios at moderate and high Froude numbers.

In a bubble column-based photobioreactor, sparger design and placement govern the bubble size distribution and gas hold-up. These factors in turn influence flow pattern, effective interfacial area, rates of mass and heat transfer, and mixing. Previous computational studies of the hydrodynamic and heat transfer effects within a column photobioreactor for one sparger row have found that bubble Nusselt number and heat transfer coefficient with respect to superficial velocity do not follow any particular pattern. This study evaluates the temperature distribution and heat transfer within a photobioreactor in an effort to explain the earlier study results. Experimental and computational studies will focus on the bubble flow pattern and heat transfer within a rectangular column photobioreactor (33.65 cm long × 30.48 cm wide × 33.97 cm tall) with a single row sparger located either lengthwise or widthwise at the center of the base (27.94 cm long × 1.27 cm wide). Temperature distribution and heat transfer for both sparger positions will be compared. Carbon dioxide, water, light photons, algal cells, and nutrients need to come together continuously for successful algal production, hence mixing of the nutrients, algal cells, and carbon dioxide is essential. Instead of a light source, a heat source is used in the system. Constant electric energy is supplied to the heating pad, which converts the electric energy to thermal energy. Thermocouples are placed inside the PBR to record temperature at 36 different spatial positions. The experimental results are compared with previously developed CFD simulations. The sparger not only effects the aeration inside the PBR, but also creates mixing in the PBR. Proper design and placement of the sparger ensures proper mixing in the PBR. The present study shows the effects bubble movement and flow pattern have on the temperature distribution and how well the simulation predicts the temperature distribution inside a PBR. The present research is a continuum of previous work aimed at pursuing the optimum design of a column PBR which is commercially viable and effective at producing algal biofuels and bioproducts.Copyright © 2013 by ASME

Air with carbon dioxide is often bubbled through photobioreactors (PBR) growing green and blue-green algae to mix the growth medium with the suspended algae. The mixture of bubbles (1) maintains alga, nutrient, and temperature distribution uniformity, (2) removes oxygen from the growth medium produced as a byproduct of photosynthesis, and (3) adds carbon dioxide to the growth medium to replace carbon dioxide consumed in photosynthesis. The air often enters the PBR growth medium as bubbles through a sparger/diffuser located near the bottom of the reactor. The bubbles rise up through the growth medium in the reactor, mix and exchange gases with the growth medium and exit through the top of the reactor. Mixing with bubbles needs to be understood to improve the efficiency of the PBR system. Bubble diameters are need for the understanding of the volumetric mass transfer coefficient in the system. A PBR was tested with flow rates of 2-8 liter/min from the sparger and the bubble sizes are determined using high speed video camera data and image analysis tools in Matlab software. The bubble size distribution spaned from 1 to 3 mm for flow rates of 2 – 8 liter/min. The bubble regime was determined to be homogenous regime.

An important factor in designing photobioreactors is appropriate selection of sparger geometry and placement. The sparger governs the bubble size distribution and gas hold-up. These factors in turn influence flow pattern, effective interfacial area, rates of mass transfer, heat transfer, and mixing. This project investigates the effects of sparger geometry and placement on bubble and fluid flow patterns and convective heat transfer within a column photobioreactor (PBR) using Computational Fluid Dynamics (CFD). Experimental and computational studies have been completed that focused on the hydrodynamics and heat transfer within a rectangular column photobioreactor (34.29 cm long × 15.25 cm wide × 34.29 cm tall) with a single sparger located at the center of its base (33.02 cm × 1.27 cm) running lengthwise. Similar studies have also been completed analyzing a full width sparger on the bottom of the PBR similar to a porous membrane sparger. This study extends previous work by investigating the flow patterns and heat transfer effects due to multiple rows of spargers at different spacings running perpendicular to the length of the PBR. Comparison of hydrodynamic and heat transfer parameters are made for the different types of spargers at different volumetric flow rates. The gas bubbles and the water-based media within the photobioreactor are modeled using the Lagrangian-Eulerian approach. A low Reynolds k-Epsilon turbulence model is used to predict near-wall flow patterns. The main interaction forces between the bubbles and the media, including drag forces, added mass forces, and lift forces, are considered. The overarching goal of this research is to improve PBR designs, thus enhancing microalgae production for biofuel and bioproducts production. It is hypothesized that changing the spacing of the PBR spargers will alter the bubble flow patterns. Despite its importance, optimizing the sparger geometry and placement in PBRs for microalgae production is still largely not understood. In this study, simulation results are presented for various sparger spacings, which can be helpful in designing sparger geometry and placement for maximized microalgae production.Copyright © 2012 by ASME

This project investigates the effects of sparger geometry and placement on bubble and fluid flow patterns and convective heat transfer within a column photobioreactor (PBR) using Computational Fluid Dynamics (CFD). Experimental and computational studies have been completed that focused on the hydrodynamics and heat transfer within a rectangular column photobioreactor (34.29 cm long × 15.25 cm wide × 34.29 cm tall) with a single sparger located at the center of its base (33.02 cm × 1.27 cm) running lengthwise. This study extends previous work by investigating the flow patterns and heat transfer effects due to full bottom sparger or porous sparger. The gas bubbles and the water-based media within the photobioreactor are modeled using the Lagrangian-Eulerian approach. A low Reynolds k-Epsilon turbulence model is used to predict near-wall flow patterns. A flat surface photobioreactor is used to achieve sufficient light penetration into the system. The main interaction forces between the bubbles and the media, including drag forces, added mass forces, and lift forces are considered. The overarching goal of this research is to produce biofuels and bioproducts through the improved design of column PBRs used for microalgae production. An important factor in designing photobioreactors is the appropriate selection of sparger geometry and placement. The sparger governs the bubble size distribution and gas holdup. These factors in turn influence flow pattern, effective interfacial area, rates of mass transfer, heat transfer, and mixing. It is hypothesized that increasing the sparger width will improve uniformity of bubble distribution as well as mixing. Despite its importance, optimizing the sparger geometry and placement in PBRs for microalgae production is still largely not understood. In this study, the simulation’s results are presented for various spargers, which can be helpful in designing appropriate sparger geometry and proper placement for increased microalgae production.Copyright © 2012 by ASME