Ph. Rudolf von Rohr

Encapsulation of abrasive particles by plasma CVD

A new abrasive material for high-temperature cutting processes has been designed, which combines hardness and chemical stability, by encapsulating hard particles (SiC) with an inert metal oxide film (alumina). Using a circulating fluidised bed reactor system and the plasma chemical vapour deposition (CVD) technique, the coating is very uniform and it can be combined with a subsequent surface treatment for improved adhesion to the bonding matrix. A barrier layer thickness of 1 μm is sufficient to stabilize the particles in a Ni-alloy matrix at 1000 °C. Partial film removal by attrition during the film deposition process causes local dissolution at the edges.

Calibration of a Gardon Sensor in a High-Temperature High Heat Flux Stagnation Facility

A calibration methodology developed for custom-made heat flux sensors used for the investigation of hydrothermal spallation drilling is presented. An air jet stagnation convection calibration system allowing independent control of jet velocity and temperature, cooling water flow and temperature, stand off distance, and nozzle diameter was built. A thermopile device was used as reference heat flux sensor. Air jets with velocities up to 400 m/s, exit temperatures of 760°C, and heat fluxes up to 0.6 MW/m2 can be reached. The standard deviation of a reference heat flux measurement is below 2%, and overall uncertainty achieved is less than 5.5%.

Bubble Bed Aeration for Animal Cell Cultures

Aeration problems have been entitled many times to be responsible for low production rates of animal cell cultures. Although the oxygen requirements of animal cells are relatively low, the cells are extremely sensitive to interaction with gas bubbles. Aunins and Henzler [1] related the cell damage under normal culture conditions almost completely to the introduction, dispersion, and disengagement of gas bubbles. Although cells can be damaged by fluid agitation, the turbulent shear stresses necessary to give significant death rates are relatively high (0.1 to 1 N/m2).