Thermal conductivity gages

In these gages, a wire inside the gas whose pressure is to be measured, is electrically heated by a constant power (see Fig. 1.29). As the gas density decreases, the heat loss from the filament to the envelope walls decreases and hence the filament temperature increases (not linearly). The temperature (200-300°C) is read by a thermocouple in thermal contact with the wire. 

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Nitrogen adsorption in the submonolayer region (and hence at very low equilibrium pressures) was determined with the same apparatus but a transistor-type thermal conductivity gage (24) was used for pressure determination. As with the higher pressure runs, equilibrium was checked by taking desorption points at the very lowest pressures several hours were required to reach equilibrium. Where important, the measured pressure was corrected for the thermal transpiration effect. 

Hydrogen at 500 kPa (gage) and Tb = 40° C flows with V = 60 m/s in an insulated tube of square cross section (Fig 6P-1). Electrical energy = 0.5 MW/zn3 is dissipated within the tube1-1 The thermal conductivity of the tube walls is k = 350 W/m-K. Compute (a) the increase of the bulk hydrogen temperature per unit length of pipe, (b) the inner surface temperature of the tube walls, and (c) the outer surface temperature of the tube walls. 

C848- 76. Young s mouutus was also determined at room temperature by strain gaging a four-point bend specimen. Thermal expansion was measured as a function of temperature with a differential transformer. Thermal conductivity and specific heat were determined as a function of temperature via the laser flash method. ... 

The first design of a plasma torch was given in 1957 by Gage who used a direct current arc struck between a cathode rod and a nozzle anode. Forced gas flow extended the arc in the anode nozzle which was strongly cooled. A thermal arc pinch effect was produced by the joint action of the cold wall arc channel and the cold gas sheet around a very high temperature conducting core (the arc coliunn). 

Figure 17.4 Process flow used to fabricate the prototype ultrasonic transducers (a) a silicon (Si) wafer is micromachined to create an array of holes with diameters between 0.75 and 2.00 mm, after which the wafer is then thermally oxidized to grow a 1.5 pm thick S1O2 layer (b) the wafer is then diced into 1 cm wide square die (c) the die is laid flat onto a piece of free-standing F DF film in a jig (the die is now viewed in cross-section through the hole) (d) the die and PVDF film are clamped into the jig against an O-ring forming an air-tight seal, and air pressure is applied to the face of the PVDF film to deflect it into the desired spherical shape (e) finally, conductive epoxy is injected into the hole and a 30 gage wire is potted into the epoxy the air pressure is maintained until the epoxy cures, then the transducer chip is removed from the jig.

A light conducting polymeric material with A d = 11% may be obtained by impregnation of the polymer with microcavities by a resin (the refractive index of which is much higher than that of the matrix polymer) [44], and with further thermal curing. The initial polymer with microcavities is obtained by UV-radiation of a mixture of the polymer and the monomer (for example, PMMA-MMA, i.e. components identical in chemical structure) through a hollow gage. 

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