A method for estimating above-ground biomass in Phragmites stands

The method involves measuring the shoot height distribution of the Phragmites australis population. Shoot height is transformed to shoot dryweight by means of an empirical model. Summing the converted dry weight of all the shoots gives an approximation of the yield

Steady state optimization of a PEM fuel cell system operational parameters

The PEMFCs systems are seen as a likely fuel cell choice for the automotive applications. Automotive applications lead to variable power operation. The architectures typically adopted are load following or fuel cell-battery hybrid systems. This article studies a control strategy of the operating conditions for the variable power configuration, typical in a load following applications. In most of the existing applications, the operating conditions are fixed to the nominal values. Typically, the temperature is set to 70°C, the air stoichiometry ratio is set to 2, the cell voltage is set to 0.6V, operating at ambient pressure (1 atm). Fuel cells have a wide power density range. At steady state conditions for fixed operating variables it is possible to change the produced power by changing the load current. The proposed control strategy is obtained by numerical optimization. The optimization process uses a zero dimensional fuel cell mathematical model, taking into account also the losses related to the air compressor system and the balance of plant. The power loss in the intake air compressor system is a critical factor because it can reach values as high as 25% of the total stack power. The numerical optimization is performed in order to maximize the energy conversion efficiency at desired power density by optimizing the operating conditions such as temperature, pressure, air stoichiometry ratio and load current. The optimization algorithm is an exhaustive discrete optimal search. Each variable has a fixed range and fixed number of values. Variables are i,?,T,p and Power. For each set of operating points, voltage and the stack power are computed. The power consumed by the air compressor is subtracted from the stack power subsequently. The optimization algorithm can also run in on-line control scheme. The results of the optimization process are curves that show values of the optimum operating variables as a function of the net power. The parameters of the fuel cell model correspond to the characteristics of the GORE Primea Series. 56 MEAs. The power of the fuel cell PEM stack corresponds to a 1 kW, 20 cells, 200cm2. The air compressor model corresponds to the Thomas Industries, Inc., diaphragm pump, 2.4atm gauge. The numerical optimization of the system and the data management is performed using LabVIEWr by National Instruments