Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture (USDA). USDA is an equal opportunity provider and employer. Mass, energy, and exergy balances are analyzed for bio-oil production in a bench-scale fast pyrolysis system developed by the USDA's Agricultural Research Sen'ice (ARS) for the processing of commodity crops to fuel intermediates. Because mass balance closure is difficult to achieve due, in part, to the system's small size and complexity a linear programming optimization model is developed to improve closure of elemental balances without losing the overall representation of the pyrolysis products. The model results provide an opportunity to analyze true energy and exergy balances for the system. While energy comparisons are based on heating values, exergy flows are computed using statistical relationships and other standard techniques. Comparisons were made for a variety of biomass feedstocks including energy crops and various byproducts of agriculture and bioenergy industiy. The mass model allows for proper accounting of sources of mass loss and suggestions for improved system performance. Energy recovery and exergetic efficiency are compared for a variety of pyrolysis product utilization scenarios including use of biochar and noncondensable gases as heat sources. Exergetic efficiencies show high potential for energy utilization when all the pyrolysis product streams can be recycled to recuperate their internal energy. The exergy analysis can be beneficial to developing exergetic life cycle assessments (ELCA) for the fast pyrolysis process as sustainable technology for advanced biofuels production.

Mass balance closure and exergetic efficiency is evaluated for a bench scale fast pyrolysis system. The USDA Agricultural Research Service (ARS) has developed this system for processing energy crops and agricultural residues for bio-oil (pyrolysis oil or pyrolysis liquids) production. Mass balance closure cannot be achieved due to the system size and complexity of inputs and outputs. A linear programming optimization model is developed to use the experimental data to achieve improved closure of elemental balances without losing the overall representation of the pyrolysis products. Having improved the mass balance, it is then possible to evaluate the exergy of the system. Exergy flows are computed using statistical relationships and other standard techniques. Computational details and results are discussed for switchgrass, a typical candidate biomass. Solutions for the minimum and maximum bio-oil outputs were generated. These particular results indicated that bio-oil accounted for approximately 10% of the loss mass. Considering all products as useful, the exergy destruction is approximately 20%. If the bio-oil alone is considered useful, the exergy destruction is about 40%. Further exercise of the model can be useful in evaluating mass losses and exergy for other feedstock and experimental runs.

The interface between intersecting microfluidic flows is investigated experimentally. Two microchannel configurations are studied. Each configuration has a main channel and an intersecting daughter channel. The channel cross sections are equal and square with the intersection either at 90 or 45 degrees. Flow visualization is achieved using confocal fluorescence microscopy. The flow interface is examined for equal and unequal viscosities and a range of Reynolds numbers. Viscosity differences and Reynolds numbers influence the three-dimensional nature of the interface. As the Reynolds number increases, the increased flow inertia produces curvature in the interface surface perpendicular to the flow. Curvature is also evident in flows with unequal viscosities. The interface location at fixed flow ratios is independent of the Reynolds number, but varies significantly with unequal viscosity ratios. Viscosity and Reynolds number effects are similar in both the 45 and 90 degree configurations.