|Four Axis Measurement Table
The four-axis measurement table uses four computer-controlled stepper motors to position a sensor and test piece so that high resolution surface profiles can be measured. The sensor can be moved in the X-Y-Z directions. The test piece can be rotated. In this way, the sensor can be brought in perpenicularly to any part of the test blade.
The naphthalene blade has two metal rims at its top and bottom, with naphthalene on the surface between the rims. The rims serve as non-subliming reference surfaces. A typical measurement procedure would start by locating the reference surface at one end, and then scanning up the blade to the second refence surface. We record the local surface elevation relative to the two reference edges both before and after the blade is exposed to flow in the wind tunnel. The difference in the before and after surface elevations will give us the local mass loss and ultimately the mass transfer coefficient.
Using this system we can make approximately 2500 surface elevation measurements in an hour. The high data density of the naphthalene technique is one of its strongest advantages.