William David Lubitz

Bioconversion of crude glycerol by fungi

The production of synthetic glycerol from petrochemical feedstocks has been decreasing in recent years. This is largely due to increasing supplies of crude glycerol derived as a co-product from the oleochemical industry, especially biodiesel production. The price of glycerol is at historic lows, and the supply of crude glycerol is projected to grow faster than its industrial uses. This oversupply is driving the transition from glycerol as a product to glycerol as a precursor for new industrial applications, including its use as a substrate for bioconversion. This article reviews the use of fungi for the bioconversion of crude glycerol to the value-added products 1,2-propanediol, ethanol, single cell oil, specialty polyunsaturated fatty acids, biosurfactants, and organic acids. Information on the impurities of crude glycerol from different industrial processes is also included.

Performance Model of Archimedes Screw Hydro Turbines with Variable Fill Level

AbstractArchimedes screw generators (ASGs) are beginning to be widely adopted at low-head hydro sites in Europe due to their high efficiency, competitive costs, and low environmental impact. ASGs are particularly appropriate for low-head sites. Power is transferred from a water flow to an Archimedes screw by the distribution of static pressure produced by the water volumes between the flights of the screw. Two theoretical models based on quasi-static pressure analysis are developed to predict the performance of ASGs. The first model uses idealized geometry, while the second incorporates the geometric properties of a rotating Archimedes screw, including slope, pitch, and inner and outer diameter. The second model was also formulated to simulate the performance of Archimedes screws operating across a full range of fill levels from empty to overfull. Both models predict that if all friction losses and entry and exit effects are neglected, the Archimedes screw can convert all potential energy in a water flow ...

Archimedes Screws for Microhydro Power Generation

Archimedes screw generators (ASGs) are beginning to be widely adopted at low head hydro sites in Europe, due to high efficiency (greater than 80% in some installations), competitive costs and low environmental impact. Compared to other microhydro generation technologies, ASGs have greatest potential at low head sites (less than about 5 m). The performance of an Archimedes screw used as a generator depends on parameters including screw inner and outer diameter, slope, screw pitch and number of flights, and inlet and outlet conditions, as well as site head and flow. Despite the long history of the Archimedes screw, there is very little on the dynamics of these devices when used for power generation in the English literature. Laboratory tests of small Archimedes screws (approximately 1 W mechanical power) have been conducted to support the design and validation of ASG design tools. This paper reports experimental results examining the relationship between torque, rotation speed and power. The laboratory screw maintained reasonable efficiency over wide ranges of operating conditions, although distinct efficiency peaks were found to occur. The cause of changes in power output caused by varying the water level at the outlet of the screw were attributed primarily to the corresponding variation in head, and dynamic limiting of screw rotation speed causing corresponding limits in volume flow through the screw. Test results were qualitatively consistent with data from a prototype ASG installed by Greenbug Energy in southern Ontario, Canada, and recent data reported from European laboratory tests and commercial installations.Copyright

Power Law Extrapolation of Wind Measurements for Predicting Wind Energy Production

This study investigates the level of uncertainty that would be expected if anemometer data from a short tower (less than 40 meters) was used to predict wind speeds and power production at typical utility-scale wind turbine hub-heights. Data from five tall towers was used to predict wind speeds at levels above 70 m based on anemometer data from levels below 40 meters. 1/7 power law, two level power law fit, and hybrids of these methods were applied. Predicted wind speeds were compared to the measured wind speeds at the higher levels to assess the level of error in the predictions. Accuracy of predicting upper level winds varied considerably between sites. Predicting this accuracy at a site without upper level wind measurements or prior knowledge of the upper level wind climate is very difficult, and significant uncertainty in the predicted results must be accepted.

Predicting Hub-Height Wind Speed for Small Wind Turbine Performance Evaluation Using Tower-Mounted Cup Anemometers

Industry standards for small wind turbine (SWT) performance evaluation require estimating hub-height wind speed using either a spatially offset meteorological mast or a cup anemometer extending from a lower elevation on the turbine tower. This paper investigates the use of vertical extrapolation to reduce the uncertainty associated with tower-mounted anemometer wind speed measurements. An experimental study has been performed involving a Bergey XL.1 SWT collocated with a meteorological mast. Results indicate that power law extrapolation can significantly reduce the uncertainty of hub-height wind speed predictions, especially if concurrent wind speed measurements are available at multiple elevations. Best practice methods have been provided. To identify the upper limit of anemometer placement, a porous disk wind tunnel test has been performed and compared with three-dimensional wind speed measurements obtained experimentally. To remain outside the rotors region of influence, it is recommended that the topmost anemometer is positioned one rotor diameter below hub-height.

Effect of Roof Slope on a Building -Mounted Wind Turbine

Knowledge of the wind climate above peaked roofs is necessary to determine whether instal ling small wind turbines on low -rise peaked roof buildings is feasible. There is little published data available documenting how wind speeds above peaked roofs vary relative to a reference open field condition. The wind characteristics at a representative peaked roof barn in southern Ontario, Canada were investigated to help address this need. The barn was simulated using a boundary layer wind tunnel, and the commercial code Fluent. Field measurements at the barn were collected using sonic anemometers and c ompared to the simulation results. Wind speed amplification was confined to a region immediately above the roof and was relatively low for wind energy purposes. It was found that with Fluent, renormalization group (RNG) k -epsilon turbulence closure predict ed winds above the roof peak better than standard k -epsilon. Simulation of buildings with a range of roof slopes found that moderately sloped roofs appear to offer a better combination of wind speed amplification and low turbulence levels at the roof peak, compared to either flat or very steep roofs. Considering only wind -related factors, the placing of very small micro -wind turbines on roof peaks may be warranted. However, if sufficient space is available, placing small turbines on a tower, rather than on the peaked roof of a low -rise building, will usually be the best approach.

Wind environment at a roof-mounted wind turbine on a peaked roof building

Knowledge of the wind resource above peaked roofs is necessary to determine whether installing small wind turbines on low-rise peaked roof buildings is feasible. The wind characteristics at a representative peaked roof barn in southern Ontario, Canada were investigated using a boundary layer wind tunnel and computational fluid dynamics. Field measurements at the barn were collected using sonic anemometers and compared with the simulation results. Wind speed amplification was confined to a region immediately above the roof and was relatively low for wind energy purposes. The presence of nearby trees or buildings adversely impacted wind speed amplification. Considering only wind-related factors, the placing of micro-wind turbines on roof peaks may be warranted. However, if sufficient space is available, it is recommended to place small turbines on a tower rather than on the peaked roof of a low-rise building.

BEM Simulation and Performance Analysis of a Small Wind Turbine Rotor

The blade element momentum (BEM) method is a popular tool for predicting the performance of wind turbine rotors. This study investigated the impact of including factors such as tip loss, hub loss and drag coefficients in BEM simulations of a Bergey XL.1 small wind turbine. The Bergey XL.1 has constant chord, untwisted blades that are challenging to simulate owing to the large variation in angle of attack along the blade during operation. Methods of including post-stall airfoil characteristics, and three wake approaches (Buhl, Glauert and Wilson-Walker) were also examined. BEM simulations were consistent with test data from a Bergey XL.1 collected using a vehicle-based platform. Including tip losses, drag coefficients and wake effects in the BEM simulation had a significant impact on predicted performance, while the effect of including hub loss was negligible. The results illustrate that BEM methods can predict the performance of small wind turbine rotors.

Experimental Validation of Gap Leakage Flow Models in Archimedes Screw Generators

Archimedes screw generators (ASGs) are a form of microhydro power generation that is increasingly being adopted as an alternative renewable energy source. ASGs operate efficiently, even as head approaches zero. A small gap must always exist between the trough and edge of the rotating screw flights to allow screw rotation. This leads to two categories of flow within the screw: the primary flow remains between the helical flights and causes screw rotation, while a secondary leakage flow occurs through the gaps at the screw edges. A high gap leakage flow reduces efficiency because this flow effectively bypasses the working parts of the screw and is lost. An accurate gap leakage model is an essential component of any ASG design model. Current gap leakage models are based on experience with Archimedes screw pumps or are derived from models assuming quasi-static flow through an opening. This experimental study measured the actual leakage flow in an operating laboratory-scale ASG. The fill heights within the buckets were measured using high-speed photography and used to determine bucket volume and therefore non-gap flow. The gap flow is determined based on the difference between the measured total flow through the system and the computed non-gap flow based on the measured fill height and screw speed. The uncertainty of the gap flow is relatively high, since it is calculated based on the difference between two variables with similar magnitude, one of which is calculated based on other measurements. The existing gap flow models did not accurately predict the experimental results. Gap flow was found to be dependent on screw rotation speed, with highest gap flows occurring at intermediate screw rotation speeds. Gap flow reduces to zero as screw rotation speed approaches the maximum possible speed. There is significant uncertainty in the existing gap flow models, and gap flow models constitute one of the largest sources of uncertainty when modeling the performance of ASGs.

Investigation of Wake Effects on the Energy Production of Small Wind Turbines

This paper examines the impact of natural and man-made obstructions on local wind conditions and the performance of small wind turbines when impacted by wake effects. The rural site used for this research contains three Skystream 3.7 turbines in close proximity to each other and several buildings. A 13 m meteorological tower with wind speed and direction sensors was installed in a nearby open area. An empirical analysis was conducted to provide a comparison of turbine performance and measured wind speed for each turbine as a function of localized disturbances caused by turbine placement. Turbine proximity to nearby buildings was observed to cause an overall reduction in power production, although cases of apparent wind speed-up induced by the buildings, and increased relative power output, were also observed. A reduction in wind turbine power output due to the wake of an adjacent turbine was observed. Overall, the turbine closest to the buildings produced about 10% less energy during the measurement period than the most distant turbine. This study confirmed the importance of careful micrositing of small wind turbines, and the complexity of the flow field near buildings and wind turbines.