Anil Kommareddy

High-resolution global maps of 21st-century forest cover change.

Forests in Flux Forests worldwide are in a state of flux, with accelerating losses in some regions and gains in others. Hansen et al. (p. 850) examined global Landsat data at a 30-meter spatial resolution to characterize forest extent, loss, and gain from 2000 to 2012. Globally, 2.3 million square kilometers of forest were lost during the 12-year study period and 0.8 million square kilometers of new forest were gained. The tropics exhibited both the greatest losses and the greatest gains (through regrowth and plantation), with losses outstripping gains. Landsat data reveals details of forest losses and gains across the globe on an annual basis from 2000 to 2012. Quantification of global forest change has been lacking despite the recognized importance of forest ecosystem services. In this study, Earth observation satellite data were used to map global forest loss (2.3 million square kilometers) and gain (0.8 million square kilometers) from 2000 to 2012 at a spatial resolution of 30 meters. The tropics were the only climate domain to exhibit a trend, with forest loss increasing by 2101 square kilometers per year. Brazil’s well-documented reduction in deforestation was offset by increasing forest loss in Indonesia, Malaysia, Paraguay, Bolivia, Zambia, Angola, and elsewhere. Intensive forestry practiced within subtropical forests resulted in the highest rates of forest change globally. Boreal forest loss due largely to fire and forestry was second to that in the tropics in absolute and proportional terms. These results depict a globally consistent and locally relevant record of forest change.

Study of Light as a parameter in the growth of algae in a Photo-Bio Reactor (PBR)

A photo-bio Reactor is a system that provides an artificial environment for photosynthetic organisms (Algae) to perform a chemical conversion. Light is an important parameter in a photosynthetic process. Light is emitted both in visible and invisible wavelengths. Each wavelength is associated with particular quantum energy. Like all living things algae is favorable to certain wavelengths in the light spectrum. Certain wavelengths of light are converted into useful energy in the process of photosynthesis. It is important to investigate which wavelengths are important for the growth of algae in the PBR for achieving high yields. Different types of light sources with different spectrum were chosen for further experimentation. Time, light intensity and the algae antenna also control the photosynthesis process. Excess light even in the appropriate wavelengths will be converted in to heat and not used for photosynthesis. Light with wavelengths between 600-700nm is the most efficient for photosynthesis. Light emitting diodes (LEDs) with a peak weavelength of 643nm are the most cost effective light source if operation of the PBR is 1 year or more.

Analysis of Currents and Mixing in a modified Bubble Column Reactor

A modified bubble column reactor to be used as Photobioreactor (PBR) is studied. PBRs are used to grow photosynthetic microalgae, which depend on light, nutrients and carbon dioxide for their growth. Carbon dioxide availability is dependents up on the amount of volumetric mass transfer taking place in the reactor. Bubble columns are known for high mass transfer rates, modifications to the existing bubble columns shows to increase the volumetric mass transfer in the system. The major modifications that are incorporated in the present PBR are rectangular flat walled columns and porous membrane for gas dispersion. Based on the previous work done in the area, hydrodynamics of bubble columns are influence by superficial gas velocity, gas holdup, bubble diameter, column geometry, use of antifoaming material and pressure. By using porous membrane, volumetric gas transfer was shown to improve over spared systems. Due to the interdependence of the factors influencing hydrodynamics, computational fluid dynamics (CFD) simulations based on eulerian equations are needed. Further CFD simulations are needed to understand liquid current flows and mixing.

Demonstration of Percent Tree Cover Mapping Using Landsat Analysis Ready Data (ARD) and Sensitivity with Respect to Landsat ARD Processing Level

The recently available Landsat Analysis Ready Data (ARD) are provided as top of atmosphere (TOA) and atmospherically corrected (surface) reflectance tiled products and are designed to make the U.S. Landsat archive for the United States straightforward to use. In this study, the utility of ARD for 30 m percent tree cover mapping is demonstrated and the impact of different ARD processing levels on mapping accuracy examined. Five years of Landsat 5 and 7 ARD over 12 tiles encompassing Washington State are considered using an established bagged regression tree methodology and training data derived from Goddard LiDAR Hyperspectral & Thermal Imager (G-LiHT) data. Sensitivity to the amount of training data is examined with increasing mapping accuracy observed as more training data are used. Four processing levels of ARD are considered independently and the mapped results are compared: (i) TOA ARD; (ii) surface ARD; (iii) bidirectional reflectance distribution function (BRDF) adjusted atmospherically corrected ARD; and (iv) weekly composited BRDF adjusted atmospherically corrected ARD. The atmospherically corrected ARD provide marginally the highest mapping accuracies, although accuracy differences are negligible among the four (≤0.07% RMSE) when modest amounts of training data are used. The TOA ARD provide the most accurate maps compared to the other input data when only small amounts of training data are used, and the least accurate maps otherwise. The results are illustrated and the implications discussed.

Investigation of Bubble and Fluid Flow Patterns Within a Column Photobioreactor

This research study investigates bubble and liquid circulation patterns in a vertical column photobioreactor (PBR) both experimentally as well as computationally using computational fluid dynamics (CFD). Dispersed gas-liquid flow in the rectangular bubble column PBR are modeled using Eulerian-Lagrangian approach. A low Reynolds number k-epsilon CFD model is used to describe the flow pattern near the wall. A flat surface bubble column PBR is used to achieve sufficient light penetration into the system. Bubble size distribution measurements were completed using a high-speed digital camera. Operating parameters, bubble flow patterns, and internal hydrodynamics of a bubble column reactor were studied, and the numerical simulations presented for the hydrodynamics in a bubble column PBR account for bubble phenomena that have not been sufficiently accounted for in previous research. Bubble size and shape affect the hydrodynamics as does bubble interaction with other bubbles (multiple bubbles in a flow versus single bubbles and wall effects on bubble(s) that are not symmetrical or bubbles not centered on the reactor cross-section). Understanding the bubble movement patterns will aid in predicting other design parameters like mass transfer (bubble to liquid and liquid to bubble), heat transfer (within the PBR and between the PBR and environment surrounding the PBR), and interaction forces inside the PBR. The computational results are validated with experimental data and from current literature.

Computational and Experimental Investigation of Bubble Circulation Patterns Within a Column Photobioreactor

This research project investigates bubble and liquid circulation patterns in a vertical column photobioreactor (PBR) both experimentally as well as computationally using Computational Fluid Dynamics (CFD). Dispersed gas–liquid flow in the rectangular bubble column PBR are modeled using Eulerian–Lagrangian approach. A low Reynolds number k–e CFD model is used to describe the flow pattern near the wall. Bubble size distribution measurements are carried out using a high-speed digital camera. A flat surface bubble column PBR is used to achieve sufficient light penetration into the system. Carbon dioxide, which is necessary for photosynthetic microalgae growth, is added to the sparged air. The results are validated with experimental data and from current literature. Design parameters, bubble flow pattern and internal hydrodynamics of a bubble column reactor were studied and the numerical simulations presented for the hydrodynamics in a bubble column PBR account for bubble phenomena that have not been sufficiently accounted for in previous research. Bubble size and shape affect the hydrodynamics as does bubble interaction with other bubbles (multiple bubbles in a flow versus single bubbles and wall effects on bubble(s) which are not symmetrical or bubbles not centered on the reactor cross-section). Understanding the bubble movement patterns will aid in predicting other design parameters like mass transfer (bubble to liquid and liquid to bubble), heat transfer (within the PBR and between the PBR and environment surrounding the PBR), and interaction forces inside the PBR.Copyright

Design and construction of light guides for efficient transfer of light in to a dense algal culture in a Photo-Bio Reactor (PBR)

A photo-bio Reactor is a system that provides an artificial environment for photosynthetic organisms (Algae) to perform a chemical conversion. The conversion process of interest is the conversion of air and liquid pollutants from livestock housing to algal biomass. Light is an important parameter for the growth of algae. The walls of the PBR are made of acrylic material. The light is fed to the system through the sidewalls of PBR. The first proto-type built and tested in summer 1998 at South Dakota Sate University (SDSU) showed that light penetration in the growth medium is an important factor to achieve high yield. It is also noted that as the algae starts growing, its density in the growth medium increases and obstructs the light penetration in to growth medium. Acrylic rods were used as light guides to enhance light transmission into the dense (opaque) algae medium solution. Different types of light guides were designed and test results are presented. It was found that light guide light transmission improved from 57% to 97% when the guide is saw cut and ends smoothed by belt grinder compared to a guide which is saw cut and ends smoothened lathe. Better distribution of light was obtained when a cone shaped with an angle of 60 ° at the center on one side of the guide is cut. Transmission characteristics of light guide from air to acrylic rod, acrylic rod to air and acrylic to water interfaces are discussed their performances is compared with test results.

Computational and Experimental Investigation of Heat Transfer Within a Column Photobioreactor

The goal of this research is to investigate heat transfer effects of two phase gas-liquid flows in a column photobioreactor (PBR) experimentally as well as computationally using Computational Fluid Dynamics (CFD). The authors have completed a preliminary study on bubble formation, rise and resulting circulation patterns using lab-scale experiments and CFD simulations. This study extends on this previous work by investigating the relationships of bubble drag coefficient and bubble Reynolds number with superficial gas velocity and a study of heat transfer within the PBR. It is hypothesized that a greater understanding the bubble movement patterns will aid in predicting heat transfer rates within the PBR. Dispersed gas–liquid flow in the rectangular column PBR are modeled using the Eulerian–Lagrangian approach. The heat transfer process has been considered for the case of a steady state three dimensional PBR. A low Reynolds number k–epsilon CFD model is used for the description of flow pattern near the wall. The velocity profiles and eddy diffusivity obtained by the model are utilized to predict heat transfer coefficients for different superficial gas velocities. The information on heat transfer effects between cooling or heating surfaces and a gas-liquid dispersed bed is essential for designing a PBR. Carbon dioxide, which is necessary for photosynthetic microalgae growth, is added to the system. Bubble size distribution measurements are carried out using a high-speed digital camera. The main interaction forces, i.e. the drag force, the added mass force, and lift force are considered. Heat transfer and internal hydrodynamics of a column reactor are studied and the numerical simulations results are presented for heat transfer and hydrodynamics in column PBRs. The results are validated with experimental data and with data from current literature.Copyright

Review of Flow Patterns in a Column Reactor for Photobioreactor Application

Photobioreactors (PBRs) and chemical reactors are often vertical columns with either circular or rectangular cross sections. The reactors are frequently referred to as column reactors and are treated as if they perform in the same manner. The reactors can have two different types of flow established in them regardless of cross sectional shape depending on the saprger/diffuser type and location within the reactor. The flow patterns in the reactors are induced by gas that is bubbled into the reactor volume usually near the bottom of the reactor. When the gas bubbles rise up through the reactor in a plug flow fashion, most of the mixing is in the radial direction which tends to make the reactor liquid and gas more homogeneous across the width of the reactor. The gas bubbles in the reactor may not move up through the reactor in a plug flow fashion, but may instead move vertically up through a portion of the reactor cross-section. This will establish a column of bubbles and liquid rising from the bottom of the reactor up to the surface and, in turn, induce a column(s) of liquid moving downward from the top of the reactor to the bottom. This behavior is similar to an air lift reactor which generally has walls physically dividing the upward (riser) and downward (down comer) flows. Without physical separation of the flows, the percent of cross sectional area of the reactor acting as the riser and down comer is established by the gas flow rate through the reactor, reactor cross sectional area, and the reactor volume. Velocity of flow(s) in the reactors is often based on the superficial gas velocity, which is the incoming gas flow rate divided by the gross cross sectional area of the reactor volume. This parameter may not relate to the two flows in the same manner. The two different flow patterns will be discussed in relation to superficial gas velocity, light in a PBR, chemical reactions in the reactor, and riser and down comer size.Copyright

Experimental Determination of Pressure Loss Through Porous Membranes

Air with carbon dioxide is bubbled through Photobioreactors (PBRs) to add carbon dioxide to the reactor medium, remove oxygen, and mix the medium. Most PBR systems use various types of spargers/diffusers that consist of straight or curved tubes with perforation in them to inject air into the PBR reactor volume. A possible novel approach to introducing air into the PBR reactor volume is to use a plenum under the PBR reactor volume in conjunction with a porous membrane that separates the air in the plenum from the liquid medium in the reactor volume. The resistance offered by the porous membrane and the liquid in the reactor volume to air flow needs to be established so that power requirements to provide the desired air flow through the PBR can be determined. Four types of porous membranes were tested: 1)Sintered High Density Polyethylene HDPE 1.59 mm thick with 15–45 μm pore size, 2) Sintered HDPE 0.79 mm thick with 20μm pore size, 3) Genpore black plastic sheet with 45 μm pore size, and 4) Porex 7896 HDPE with pore size of 35 μm). Specimens were tested in a 76.2 mm inside diameter reactor with a depth of 304.8mm and a 76.2 mm plenum depth. Water was used as the reactor medium and the depth was varied between 0 and 228.6 mm. Results showed that the Porex 7896 membrane had little resistance to air flow when the water depth was 0.0mm (1–22 Pa), 1–200 Pa for the Genpore plastic sheet, 1200–1400Pa for the Porex with 20μm pores, and 1100–2500 Pa for the Porex with the 15–45 μm pore sizes for superficial air velocities between 0.00345 m/s to 0.0242 m/s. Water depth was then increased to 228.6 mm in 25.4 mm increments and tested with the same air flow rates. The addition of water significantly increased the resistance to air flow for all membranes (highest being 4200 Pa). Least square correlations for the membranes using water depth and superficial air velocity indicate that resistance to air flow of the membranes was linear with superficial velocity but parabolic with water depth.Copyright