A graphite resistance heater for a hypersonic wind tunnel using nitrogen: Part I. Description of tunnel and heater

• Published in: International journal of heat and mass transfer 1962, Vol.5 (11), p.1081-1093
• Main Authors: Shreeve, R.P., Lord, W.T., Boersen, S.J., Bogdonoff, S.M.
• Format: Article
• Language: English
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/0017-9310(62)90061-3

A heater system has been developed for a hypersonic wind tunnel which uses nitrogen as the test gas, and operates continuously at Mach numbers up to 20. The system uses a small electrically heated graphite element containing a spiral gas passage. A small pilot hypersonic nitrogen tunnel has been used in the development of the heater system. The tunnel is designed to operate ultimately at a gas stagnation pressure of 10 000 1bf/in 2, but the work described here refers to operation at up to 1000 1bf/in 2 stagnation pressure. This paper is concerned principally with the development of the heater system, and not with the establishment of high Mach number flow in the test section (for which purpose a second hypersonic nitrogen tunnel is being used). The stagnation temperature required to avoid condensation of the nitrogen in the test section at a Mach number of 20 is about 5000°R. The major problems encountered in achieving such a temperature, which is below that at which nitrogen begins to dissociate and so starts to react with graphite, have been caused by chemical reactions involving substances other than pure nitrogen and pure graphite. The purity of the gas supply, the cleanliness of the equipment and the grade of graphite are of the utmost importance. A thin impermeable coating of pyrolytic graphite over the outside of the heater element has been found to prevent the formation of holes in the outer wall, which occurred with uncoated elements. Such coated elements have regularly been used to provide steady gas temperatures up to 5000°R at 1000 1bf/in 2 pressure. (The results are presented in detail in Part II.) Extending operation of the heating system to higher pressures is expected to present only minor problems. Gases other than nitrogen have been successfully used with the present heater and it is further suggested that experience gained with the described system will have application in the design of a similar heater for air as suitable non-oxidizing materials become available. Un système de chauffage a été étudié pour une soufflerie hypersonique continue à azote, fonctionnant à des nombres de Mach allant jusqu'à 20. Ce dispositif utilise un élément de graphite chauffé électriquement et percé d'un trou en spirale pour le passage du gaz. On a utilisé une petite soufflerie pilote à azote pour étudier ce réchauffeur. La soufflerie est prévue pour fonctionner à une pression d'arrêt maximum de 700 kg/cm 2, mais le travail ci-dessous se rapporte à un foncti