Operation Teapot, Project 8.4E Air Temperature Measurements Over Several Surfaces

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BEST AVAILABLE COPY Defense Technical Information Center DEFENSE LOGISTICS AGENCY Cameron Station • Alexandria, Virginia 22314 BEST AVAILABLE COPY

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AIR TEMPERATURE MEASUREMENTS OVER SEVERAL SURFACES HEADQUARTERS FIEID COMMAND. ARMED FORCES SPEClAt WEAPONS PROJECT SANDIA BASE. AIBUOUERQUE. NEW MEXICO APPROVED FOR open rDRUCATTOIT. BEST AVAILABLE COPY

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BEST AVAILABLE COPY This document consists of 42 pages No. 230 of 235 copies. Series A OPERATION TEAPOT PROJECT 8,4e Report to the Test Director AIR TEMPERATURE MEASUREMENTS OVER SEVERAL SURFACES San Prancisco, Califomla BEST AVAILABLE COPY

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SUMMARY OF SHOT DATA, OPERATION TEAPOT h^Ot Code Name Dale Tima* Area Type Longitude of 1 Waap 16 Kebruarjr 1200 T-T-4T 762-fi Air it jin ti 14 Zucchini 16 May 0500 T-7-la 600-ft Tower e 2 t Actual aero point 38 feet north. 428 feet weat of T- 7-4. t Actual aero point 64 feet north, 62 foet aeat of T—7-4. I Actual aero point 36 feel eouth. 397 feet weat of T-6.

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BEST AVAILABLE COPY Preshock air-teciperature neaeureaients in the vicinity of a nuc lear detonation are reported. Although no data were obtained for close-in stations over water, asphalt, and desert, somewhat interest ing but unusual results were obtained for stations of simulated, terrain such as plots of ivy plants, fir boughs, wood, and concrete. The maximum sir temperatures above ambient were found to be in excess of 1,500°C over all plots. Furthermore, an increase in maxi mum air temperatures with elevation was found over all plots. Results of supporting high speed photographic coverage and gas analysis of air above irradiated plots are reported. An attempt to explain the results is given despite the lack of sufficient data.

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Thifl report present# the final results of one of the 56 projects comprise lag the Military Effects Program of Operation Teapot, which Included 14 test detonations at the Nevada Test Site in 1955* For overall Teapot military-effects information, the reader is re ferred to "Sumiary Report of the Technical Director. Military Effects Program,* VT-1153, which includes the following: (1) a description of each detonation including yield, aero-point environment, typo of device, ambient atmospheric conditions, etc*; (2) a discussion of project results; (3) a tnaaaary of the objectives and results of each project; and (4) a listing of project reports for the Military Effects Program, The help of the following i# gratefully acknowledged: A. L. Creig who contributed in a major way in the planning and who provided much of the help In assembly and calibration of the HiVats; F. Sauer and S. Scesa for many helpful discussions; and W. B. Plum, Project Officer, who was a source of constant encourage

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BEST AVAILABLE COPY 1.2 Background and History. ..................................................................... 7 2.1 Basic Considerations in Air Temperature Measurements. . . 9 2.2 Description of HiVat and Associated Equipoent........................... 9 4.2.1 Water Line Station..................................................................... 19 4.2.2 Asphalt Line Station.............................. 19 4.2.5 Ga* Semples from Irradiated Plots..................... 27 CHAPTER 5 DISCUSSION OF KESUITS........................................................................ 37 CHAPTER 6 CONCLUSIONS AND KECOMMENIATIONS.................................................... 39 4.1 Results of Analysis of Gas Samples in Volume Per 2.1 Cocporjents of HiVatandHiVat Mount................................................ 10 BEST AVAILABLE COPY

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BEST AVAILABLE COPY 2.2 Reaponoe of HiVat as FunctionofFlow Rato at 2*3 Temperature Profile Along a Meaeter of Air Stream 3.1 Schematic Layout of Stations onFrenchmanFiat...........................16 4.1 Air Temperature Above Ambient at 1/2 ft Elevation 4.2 Air Temperature Above Ambient at 1 l/2 ft Elevation 4.3 Air Temperature Above Ambient at 3 ft Elevation 4.4 Air Temperature Above Ambient at 6 and 10 ft Elevation, 4.5 Air Temperature Above Ambient Over Concrete Plot.... 23 4.6 Air Temperature Above Ambient Over Ivy Plot.............................. 24 4.7 Air Temperature Above Ambient Over Fir Bough Plot • • • • 25 4.8 Air Temperature Above Ambient Over Wood Plot............................ 26 4.9 Photographic Sequence over Sirface at2,000 ft 4.10 Photographic Sequence over Surface at 2,000 ft 4.11 Photographic Sequence over Concrete Surface ....... 32 4.12 Photographic Sequence over Fir BoughPlot ..................................34 4.13 Photographic Sequence over Ivy Plot............................................ 35 4.14 Photographic Sequence over Wood Plot..........................................36 BEST AVAILABLE COPY

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BEST AVAILABLE COPY This project vas to obtain air-temperature data, Its temporal history, and spatial distribution over simulated and natural ground coverings In the vicinity of a nuclear detonation prior to shock arrival. These measurements were then to be correlated with soundvelocity and air-blast measurements to provide some Insight as to the origin and the mechanism of the formation of a precursor, In view of the suspected importance of the latter in causing anomalous air blasts associated with shock arrival. From a military tactical and operational viewpoint, it is important that a better understanding of the precursor be obtained, in order to provide a realistic basis for predicting the effects of nuclear detonations. 1.2 BACKGROUND AND HISTORY Under certain conditions in nuclear detonations, a precursor pressure wave is formed which develops prior to shock arrival and considerably modifies the intensity of the air blast. Also, a layer of very highly heated air forms above the ground prior to shock arrival which has been related to the formation of the precursor. The first most extensive air-tenperature measurements prior to shock arrival in the vicinity of nuclear detonations were made in Operation Tumbler (Reference l). These ware made in c on junction with air-blast measurements in order to establish any correlation which may exist between these parameters. Fine-wire aspirated thermocouples and resistance thermometers, as well as sonic-velocity methods, were used, all being mounted at various heights on 50-foot towers. The latter was stationed at several distances from ground zero. In general, extremely high tenrptiatures were obtained (in some cases in excess of 1,000°C) for the air just above ground level up to a height of a "^ew feet. Furthermore, the air temperature decreased rapidly with height, with the result that above 10 feet the temperature increase above ambient was relatively small. The observed heated layer of air may well provide one of the necessary conditions for the development of the precursor. Although no definite conclusion could be made about the mechanism of formation of the heated _.aycr of air, it was the opinion that much of the heating was due to rapid convecti/e heat transfer between presbock dust and the turbulent air (Reference 2). One of the conditions important to the formation cf the heated layer of air is the nature rnd characteristics of the underlying terrain in the vicinity of a nuclear detonation. It is clear that the latter would be important, especially if it played a major role in controlling the heat-transport mechanism. For example, preshock BEST AVAILABLE COPY

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BEST AVAILABLE COPY sonic velocity measurements (Reference 3) made by the Naval Electronics Laboratory (NEL) over an area covered by fir boughs appeared to give anomalously high results in Operation Up shot-Knothole. Furthermore, in the laboratory at the Naval Radiological Defense Laboratory (NRDL), the irradiation of organic sample a with a simulated pulse of thermal radiation resulted in very-fine, high-speed flaming Jets arising over the irradiated surface. It is thus possible to attribute much of the observed heating of the air in the field to a process such as that observed in the laboratory for comparably irradiated surfaces. In view of the possible importance of the nature of terrain in precursor formation, air temperature measurements over a variety of simulated teirains would he highly desirable. Such measurements as these should then be correlated with those of air blast. It would be also helpful to determine the nature and amount of gaseous emanations arising from the irradiated plots of simulated terrain. BEST AVAILABLE COPY

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BEST AVAILABLE COPY There have been a number of air and gas-temperature measuring techniques developed, come of which are described in Referer:e 4. Most of these devices were designed for temperature measurements of gases at constant or relatively slow-changing temperatures. For the measurement of preshock air temperatures in the vicinity of nuclear detonations, certain stringent requirements must be met in selecting and designing air-temperature measuring devices. Thus, it is desirable to use an instrument with a time constant of the order of 50 msec or less, with an adequate sensitivity over a wide range in temperature (ambient to about 2,000°C), and of simple design yet rugged enough to withstand rough handling in field installations. Ihe selection of the method of measuring air temperature was, therefore, based on the above considerations as well as on the experience gained with that used in Operation Tumbler; namely, thermocouple cr HiVat). Although in principle the design chosen vas similar to that used previously, a number of modifications were made as will be described below. 2.2 HIVAT AND ASSOCIATED EQUIPMENT The final design of the HiVat is shown in Figure 2.1, which Rh0.io thermocouple. T. was used, the Junction being placed on tHfi' axis of pyrex glass tubes I and 0. the air inlet and outlet tubes respectively. Tube I consisted of a piece of S-ran outside diameter and 1-ram thick-wall pyrex glass tubing fused on to that of a 6-mm outside diameter and 1-rnn thick-wall tube, the overall length being about 1 3/4 inches. Tube 0 was thesame as the latter half, being about 7/8 inches long. Thermacnple T vas mounted on a very thin disk of mica, M. 1 l/4 inches In diameter, which had a hole cut out at its center about 3/l6 inch diameter and held in place (with the thermocouple Junction centered in the hole) by means of a small amount of cement. The Pt wire of the couple was cemented on one face of the mica disk while the Ptg.qo^Q^O w^re waa cemented on the opposite face. Thus, electrical contact of each wire vas made with brass cylinders and Co when placed face-to-face against the mica disk as shown, at "the same time the latter electrically insulating Ci from C2* Because of the relatively large masses of C^ and Co, they both^served as cold, or reference, Junctlora for the thermo couple, Tubes I and 0 were inserted in the 1/4-inch diameter holes BEST AVAILABLE COPY

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BEST AVAILABLE COPY drilled throufjh the axes of and respectively, tube I being held in place with an asbestos padding, A, and 0 with sealing wax, W. Screws and S^ served not only to rigidly hold Cj and C£ together but also as binuing posts for maxing connections to the external circuit. Fiber washersvere used to insulate and from C-, and Cp* respectively. Note that Cp is threaded for making connections with UC fittings leading to the aspirating system. The HiVat is thus mounted in an aluminum holder H and held in place by the fiber bushings and and screws and 3^. The diameter of H was such that it could easily fit into a 2-inch pipe. The HiVats were removed from the holder when tested and calibrated in laboratory by carefully’Welding the ends of the two wires using a email oxygen blowpipe burner. The performance of these thermocouples BEST AVAILABLE COPY

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BEST AVAILABLE COPY was compared to that purchased from Balter and Company, Inc. They were found to give an almost identical teaperature-versus-millivolt 2-3 CALIBRATION OF HIVAT In order to determine the reproducibility cud accuracy of the HiVat, the following experiments were carried out in the laboratory. The results of these experiments therefore provided the basis of any corrections which should be applied to the measured temperatures in the field. In all these laboratory experiments, a Lindberg muffle furnace was used as the source of heated air. In sampling the latter from the oven. It was extremely important that none of the colder ambient air outside the furnace be entrained. The heated air was thus drawn through the HiVat by means of a compressed air aspirator, the sampling being controlled by an on-off solenoid valve. A hollow transite cylinder, inserted and sealed in a small port in the furnace, provided a convenient means for sampling the heated air. Thus, a cylinder so thas its junction was about 1/8 inch from the inlet end, Figure 2.2 Response of HiVat as Function of Flow at Various Air Temperatures. BEST AVAILABLE COPY

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BEST AVAILABLE COPY I, of the HiVat. The thermocouple response was measured hy means of Inasmuch as the performance of the HiVat is determined to a large extent by the effective convective heat transfer between the heated air and thermocouple, the response of the HiVat vas measured as a function of air velocity or flow rate. The results are shown in Figure 2.2. Evidently, the HiVat response was independent of flow rate above 0.5 to 0.6 ft^/nin. Therefore, it vas decided to use flow rates between 0.6 and 0.7 ft^/min in all experiments and in the In order to determine the degree of precision required in centering the Junction of the thermoc'-uple in the HiVat, the air temperature profile was obtained by measuring the temperature at various points along two perpendicular diameters of the circular cross section of the stream of air in the region of the HiVat thermocouple. Although these measurements could not be made with precision, the results obtained appeared to be reasonably indicative, as shown in Figure 2.3» It is to be noted that the temperature profile vac symmetric and fairly flat near the center of the stream. Figure 2.3 Temperature profile along a diameter of ulr stream passing thermocouple in HiVat. Origin of abscissa represents center of air stream. Temperature profile along a diameter perpendicular to the above gives identical curve, hence profile oyum,*trie about origin. Air temperature at center about 510°c.t -1 0 Thus, it was assumed that the air temperature in the moving stream vas sensibly constant within a region at least 1 mm in diameter about the center of the stream. Although it vas found that the response of the laboratory-fabri cated thermocouples vas the same as calibrated standard Pt - Pto qq KbQ^Q thermocouples, it was felt that a further check on the cali bration would be desirable. This was accomplished by determining the induing point of 1-mll diameter aluminum and gold vires with the HiVats, Thus, on c of these vires was mounted in the HiVat parallel to the themocouple and close enough so that both were within the region of constant temperature in the center of the air flow. Then, by increasing the air teinperature, which was measured by the HiVat, the point at which the aluminum or gold wire melted was noted. Hie results are shewn in Table 2.1. The agreement between the accepted melting points and those measured in this experiment is remarkably good. In fact, the deviation from the accepted melting point for both aluminum and gold can be reasonably accounted for by calculating the heat conduction losses (assuming radiation losses small) along the vires To obtain some measure of the response time of the HiVat to a BEST AVAILABLE COPY

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BEST AVAILABLE COPY Buddea increase in air temperature froa ambient to about 1,0Q0°C, a was found that a conservative estimate of the response time was some thing less than 50 msec. However, it was felt that this was probably the response time of the solenoid valve used to control the sudden input of heated air into the HiVat and that …