A t the present tine, certain qu(UTtit&%iw features of heat pipe behavior ham not i n fact been verifFsd e~rirmantally, though they cas be predicted w i t h mine confideme. A few properties cannot yet m n be fireswith any conviction. Tht anaQsir presented here is an abr%dgemmt of L4-32b6-MS9 "Theory of B a t Pkpes" , and i s intended sirrp;tY'to off'er s a w i n i t i a l orientation i n the quantitative prlncipAes of heat pipes, mB to 8arw us a e t W w for Azrther experinentation, appliuationa, ssd isgrovament of the theory.The advantages-of hea* pipes are best realized when they are long asld thin, that is, take the form of long cylinders or extended t h i n planar ~tnrctuses. For definitesees the discussion here w i l l be confirred to right circular cylinders of 1-e length-to-diameter ratio. . The course of Mdlysie for other ehapes will be evident, though not alwwe straight-forwasd i n detail. As ehawn i n Fig. 1, such a hast p5.pe consf sts of r containing tube of length f with outer radius r an snnulsr capillary structure eatwaked Kith a wetting lsquid, P 'with outer r d l w r,, and a vapor apace of radius rv*
Uranium carbide is found to have the property of high thermionic emission in the observed temperature range from 1400 to 1800°K. The parameters of the Richardson equation which can be used to fit the data are A=7.3×105 amp/cm2 (°K)2 and φ=4.57 v. While these parameters accurately predict the observed saturated currents, it is doubtful that such anomalous values are of theoretical significance within the framework of the Richardson-Dushman derivation. A solid solution form of uranium carbide and zirconium carbide gives substantially the same thermionic emission as uranium carbide, and for other reasons appears to be the more useful emitter. The carbides require no surface preparation or activation schedule for use as emitters.
The operation of a cesium plasma thermocouple is described for a range of hot-junction temperatures from 1600°K to 2600°K and for a range of cesium pressures from 10−5 mm Hg to 2 mm Hg. Electromotive force and short-circuit current data are presented for cells containing three different emitter substances: Ta, ZrC, and (ZrC) (UC). In the range of pressure and temperature variation studied, the observed electromotive forces are between 1 and 4.5 volts. Short-circuit current depends markedly on the current emission properties of the hot electrode. The largest short-circuit current density observed for the (ZrC) (UC) emitter, is 62 amperes per square centimeter.
Some aspects of the performance of a cesium plasma cell with tantalum emitter are evaluated in terms of experimental determinations of the effects of variations in such parameters as cesium vapor pressure, emitter temperature, and emitter-collector separation distance. Experiments relating to the effect of collector serrations and to the feasibility of radiation shielding are described. Voltage-current characteristics are presented for several emitter temperatures and for a wide range of cesium vapor pressure.
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