Appartus for high‐resolution surface tension measurement

We describe an apparatus for measuring surface tension of insulating liquids by capacitive sensing of capillary rise. Two guarded coaxial capacitors with different gap widths are connected to permit liquid to flow between them. The higher capillary rise in the narrow‐gap capacitor is balanced by a dc voltage applied to the wide capacitor by a servosystem. In a measurements of the surface tension of liquid helium we obtain a resolution of 1 part in 105. The technique is well suited for automated measurements of small changes in surface tension.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70480/2/RSINAK-49-1-94-1.pd

Digitally programmable ratio transformer bridge

We describe a digitally programmable impedance bridge, used here for low‐temperature resistance thermometry, and a compatible digital programming and data logging interface. The bridge employs a commercial programmable ratio transformer to achieve high resolution with minimum circuit complexity. We measure the ratio of the resistances of a carbon thermometer and a fixed reference resistor, both near 2 K, with a resolution limited by Johnson noise in the resistors. The bridge circuit described here is suitable for a variety of programmable or self‐balancing impedance measurements.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71154/2/RSINAK-46-12-1653-1.pd

High Performance and Sub-Ambient Silicon Microchannel Cooling

ABSTRACT High performance single-phase Si microchannel coolers have been designed and characterized in single chip modules in a laboratory environment using either water at 22 0 C or a fluorinated fluid at temperatures between 20 and -40 0 C as the coolant. Compared to our previous work, key performance improvements were achieved through reduced channel pitch (from 75 to 60 microns), thinned channel bases (from 425 to 200 microns of Si), improved thermal interface materials, and a thinned thermal test chip (from 725 to 400 microns of Si). With multiple heat exchanger zones and 60 micron pitch microchannels with a water flow rate of 1.25 lpm, an average unit thermal resistance of 15.9 C-mm