High precision of measurement of methane potential is important for the economic operation of biogas plants in the future. The biochemical methane potential (BMP) test based on the VDI 4630 protocol is the state-of-the-art method to determine the methane potential in Germany. The coefficient of variation (CV) of methane yield was >10% in several previous inter-laboratory tests. The aim of this work was to investigate the effects of inoculum and the digestion system on the measurement variability. Methane yield and methane percentage of five substrates were investigated in a Hohenheim biogas yield test (D-HBT) by using five inocula, which were used several times in inter- laboratory tests. The same substrates and inocula were also tested in other digestion systems. To control the quality of the inocula, the effect of adding trace elements (TE) and the microbial community was investigated. Adding TE had no influence for the selected, well- supplied inocula and the community composition depended on the source of the inocula. The CV of the specific methane yield was <4.8% by using different inocula in one D-HBT (D-HBT1) and <12.8% by using different digestion systems compared to D-HBT1. Incubation time between 7 and 14 days resulted in a deviation in CV of <4.8%.

Ripe green banana (Musa sp., AAA group, cv. Zhonggang) fruits treated with 1-methylcyclopropene (1-MCP) significantly delayed the peaks of respiration rate and ethylene production but did not reduce the peak height. Mature banana fruits were also treated with 1-MCP for 24 h at 20 C and then exposed to 50 mL/L ethylene or stored at different temperatures to analyse the effects of external added ethylene. Reductions in firmness, titratable acidity (TA) and starch content (SC) of banana fruits were remarkably delayed by 1-MCP treatment. 1-MCP treatment also delayed the increase of total soluble sugar (TSS) and soluble pectin (SP) contents. Soluble solids (SS) content in the 1-MCP-treated fruit remained almost unchanged during the first 10 days of storage at 20 C. No significant differences in TA, TSS, SP and SS levels were observed between the fruit treated with 1-MCP alone and the fruit treated with 1-MCP plus ethylene. The 1-MCP effects on all the parameters related to banana ripening were enhanced by low temperature storage and reduced by high temperature storage.

Cavitating flow around a hydrofoil was simulated using a transport equation-based model with consideration of the influence of noncondensable gases. The cavity length and the pressure distributions on the suction side can be well predicted for stable cavities using the standard renormalization-group (RNG) κ-ε turbulence model with proper noncondensable gas mass fraction. The unstable cavity shedding at lower cavitation numbers was not well predicted by the standard RNG κ-ε turbulence model. A modified RNG κ-ε turbulence model was evaluated by comparing the calculated spatial-temporal pressure distributions on the suction wall with experimental data. The results showed that the predicted cavity growth and shedding cycle and its frequency agree well with the experimental data. However, the pressure increase caused by interaction of the reentrant flow and the cavity interface is overestimated, which caused the time-averaged pressure on the front part of the hydrofoil to be overestimated. The time-averaged pressure on the rear of the hydrofoil was low because the small cavity shedding on the rear part of the cavity was not predicted.

Pressure oscillations caused by vortex rope were measured in the draft tube of a prototype Francis turbine. The three-dimensional, unsteady Reynolds-averaged Navier-Stokes equations with the RNG κ−ϵ turbulence model were solved to model the flow within the entire flow path of the prototype hydraulic unit including the guide vanes, the runner, and the draft tube. The model was able to predict the pressure fluctuations that occur when operating at 67–83% of the optimum opening. The calculated frequencies and amplitudes of the oscillation show reasonable agreement with the experiment data. However, the results at 50% opening were not satisfactory. Pressure oscillations on the runner blades were found to be related to the precession of vortex ropes which caused pressure on the blades to fluctuate with frequencies of −fn+fd (fn is the rotational frequency and fd is vortex procession frequency). The peak-to-peak amplitudes of the pressure oscillations on the blades at the lower load conditions (67% opening) were higher than at higher load conditions (83% opening). Fluctuations on the suction side tended to be stronger than on the pressure side.

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