EQUIPMENTt
SwRTs new high thermal flux unit c a n g e n e r a t e a t e m p e r a t u r e of 9 4 0 0 ° F . — h i g h e r than solar furnaces. H e r e , Dr. Francis C. T o d d of S w R I examines the flux unit within t h e pressure vessel. A parabolic mirror is in the b a c k g r o u n d
SwRI Builds High Thermal Flux Unit N A C A sponsors project to study problems of missile re-entry into earth's atmosphere HAT GOES U P must come down, including ballistic missiles. But the question is—how d o you get them back into the earths atmosphere without their disintegrating? Southwest Research Institute m a y find the answer with the help of their new high thermal flux unit. SwRI scientists h o p e to find new materials for ballistic missiles—materials that k e e p their shape and strength w h e n they hit t h e earth's atmosphere at high speeds. Widi the new apparatus, they can study the effects of high energy 68
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concentrations on t h e physical and chemical properties of materials. T h e project is sponsored by t h e N a t i o n a l Advisory Committee for Aeronautics. Ironically, o u t m o d e d trolley cars m a y figure in the solution of this rocket age problem. Resistors u s e d in the e q u i p m e n t came from discarded street cars. • Not the Hottest. T h e unit can generate temperatures of 9400° F., surpassing the upper limit of solar furnaces. It may go as h i g h as 9 7 0 0 ° F . , says Francis C. T o d d , m a n a g e r of SwRI's physical d e p a r t m e n t . Other
units h a v e gone to higher temperatures. However, high temperatures alone are not enough, T o d d points out. The best possible heat flux is required to simulate t h e energy transfer phenomena which occur w h e n a missile reenters the atmosphere. T h e unit has a high intensity arc that comes from carbon electrodes operating in air. This eliminates the need for water stabilization. Power input is 500 k w . However, t h e unit can b e overloaded to 2000 lew. for a minute. Controls are such that a specimen may be subjected to energy from the source for as little as 1 / 3 6 o s e c * Parabolic mirrors direct the energy (radiant light and h e a t ) from d i e arc to the test specimen. T h e specimen rests in a special holder in which pressure a n d gas composition may b e controlled. A pressure vessel, which can withstand pressures to 150 p.s.i., houses the entire unit. H o w long can a material withstand concentrated heat before it melts or vaporizes? SwRI will be able to observe this on samples placed in their unit using a camera that operates at 4000 frames per sec. Thermocouples, which can b e activated for only a fraction of a second to prevent melting, indicate temperature. Samples are also examined with electron microscope and X-ray diffraction techniques. Other features of t h e flux unit: • T h e sample is subjected to p u r e radiation—it is not placed in the arc. • Ionization within the unit can b e m a d e to compare w i t h that in the ionosphere. • T h e unit offers a good comparison with temperatures at high altitudes. • A high degree of current and voltage control allows temperature to b e regulated accurately. • Chemical Processes Too. SwRI will n o t use t h e unit for missile problems alone. T h e Physics D e p a r t m e n t will also use it as a high temperature source for developing new chemical processes. W h e n temperatures fluctuate, competing reactions may occur within a chemical process. The accurate t e m p e r a t u r e control will eliminate these competing reactions, says T o d d . So far SwRI scientists have been busy collecting performance data. T h e next step is basic studies on the effect of t h e r m a l flux on the physical a n d chemical properties of possible missile materials. A pilot model of a larger unit has been m a d e should NACA w a n t to expand its missile research work.
