Jet ejectors of excellept efficiency have been developed by Ingersoll-Rand, Croll-Reynolds, Schutte & Koerting, and other advertisers in these pages, for a large variety of uses in the condensation of vapors and the production of high vacua. The device is so simple that stock ejectors are available for almost any capacity or back pressure, and nearly top economy is thus provided in all applications. Capacity of an ejector is usually expressed on a weight basis in pounds per hour, rather than in cubic feet per minute. For all applications where very low pressures are required or where the vapor handled contains noncondensable gas, the practice is to use two or three ejectors in series, with precondensation and also interstage coaling or condensing when required. One line of ejectors is designed for capacity load a t 4 inches of mercury absolute suction pressure. If operated a t the same steam pressure to produce 2 inches of mercury absolute suction pressure, the capacity falls to 21% of design capacity a t 4 inches of mercury absolute pressure, but 200y0 of capacity operation can be obtained if the suction pressure is raised to 7.7 inches of mercury absolute. When three suitably designed ejectors are used in series, the set will move 25% of rated capacity at 0.2 inch of mercury absolute pressure, 100~o a t 0.5inch, and 225y0of capacity a t 1.5 inches. This wide range of usefulness is indicative of the importance of these lowcost stationary devices. Compression of waste or exhaust steam from a low pressure to a pressure two or three times higher can be carried out by noncondeqsing jet ejectors. Steam a t considerably higher pressure than the discharge pressure must be supplied to the nozzle, and the economy of use is somewhat poor. The thermal efficiency is relatively high because all the steam used in the nozzle as well as the steam compressed is available a t the higher pressure. Because the capacity of ejectors is usually expressed on a weight basis, one seldom realizes the enormous volume of vapor these small devices can handle. It is so large that a jet-propelled pump or compressor is often used to cool, or refrigerate water by self-evaporation. By placing a jet ejector suction chamber on a baffled tank containing water and then evacuating the water vapor a t 1or 2 inches mercury pressure absolute, the water in the tank is cooled by evaporation. By admitting ordinary temperature water a t the proper rate and pumping out the cooled water, a continuous supply of water at temperatures as low as 38’ F. can be obtained. The vaporization of about 1 %of the water in the tank cools the remainder 10’ F. This type of equipment is light in weight and compact in size, and operates without vibration or noise. Steam and water are the only costs of operation, a8 maintenance is negligible and there is no refrigerant to handle or replace. Numerous inventors and hundreds of inventions were offered to win the first World War; but we seemed to possess more common sense back in those days, and no one dreamed that a Technical Mobilization Act was needed to handle the problems. Instead it was realized that the situation required only a small competent group to interview and appraise the inventions. The main problem was to direct inventors to a group suitably trained to evaluate the proposal. The money required came from a fund known as Armaments (Continued on page 80)
GENERAL misconception has been prevalent lately that jet propulsion is new, one of the marvels of the present war. A strenuous bit of travel recently showed the writer that many well informed people are overlooking the historical facts and timing connected with hundreds of useful applications of jetpropelled devices. The Pullman smoking-room experts, even those mechanically inclined, invariably gave the impression that jet-propelled devices are the latest and most wonderful inventions ever produced by the supercreative German mind. It is this last interpretation, as much as the error in timing, which has inspired this article. A short but inclusive search failed to reveal just when the first “injector” was used t o pump feed water into a steam boiler, but they were in common use on locomotives in 1881. This simple light-weight device then, as today, received steam from the boiler it was feeding, discharged this steam through a jet, and imparted to the feed water sufficient velocity to force it into the boiler against the working pressure. The use of jet energy for many simple purposes is certainly over one hundred years old. During this period the development and application of jets have led to such uses as pumping, circulating, compressing, evaluating, agitating, mixing, and refrigerating. Design improvements ‘have greatly increased the efficiency of operation without increasing the number or complication of the parts required. A typical jet ejector consists of three pieces, with two gaskets and the necessary bolts to join the steam nozzle, the suction chamber, and the diffuser throat. Since there are no moving parts, maintenance is very low and efficiency of operation is maximum throughout the life of the equipment. The pressure on the steam or other fluid used in the jet should ordinarily be higher than the discharge pressure a t the diffuser throat. I n jet devices the amount of steam used is sometimes rather high, but in many applications the thermal efficiency is nearly 100%. This is especially true when a steam jet agitator is used in a tank of liquid to be heated. An interesting example of jet power applied to circulation was demonstrated about 1927 in a European synthetic ammonia process. A characteristic of most processes is the “circulating loop” at the end of the purification train. Because only one fifth to one sixth of the gas is converted to ammonia a t each contact with the catalyst, it is necessary to condense out the ammonia, renew the gas volume, and return the mixture to the catalyst. A one-stage circulating compressor is used in m e t processes to maintain even uniform flow of gas in the loop. One process uses an injector to produce the desired circulation, with somewhat questionable results. The purified make-up gas, representing a t least one fifth the total gas volume in circulation, is compressed to 950 atmospheres; a t this pressure it is used in the primary nozzle of a jet ejector with the suction chamber and diffusor dischaTge a t 600 atmospheres pressure connected into the circulating loop. The circulating compressor would cost about five or six times the cost of this ejector, but the increase in size of the main compressors and driving engines, and the difficulty of operating the entire purification train a t different pressures from 800 to 950 atmospheres makes this proress unattractive, even though it is leas expensive to install.
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and Fortifications-C. The work could have been exceedingly interesting but for certain patterns of human nature which were encountered at once. History seldom records the acceptance of adverse decisions by inventors of dream gadgets no matter how fair and accurate they may be. This was particularly true of the many inventors of “electrical death ray” devices, which were considered so important they could not be patented and so powerful whole populations could be killed in a few minutes. The disagreeableness usually started when one inquired about the degree of immunity for the operator or just what tests had actually been made and the number of people killed by coroner’s count. It was astounding to witness the impatience of the inventors over the least criticism of their unproved statements. Second only to the “electrical death ray” were the numerous rocket devices, including rocket-propelled airplanes. Into this Tommy Tinker atmosphere came Farley G. Clark to propose the development of jet-propelled military planes. As chief engineer of the Toronto Power Company, a large Canadian firm a t Niagara Falls, his able, technical appeal for the development of jet-propelled military planes was refreshingly scientific. Based upon memory only, his rough specification appears strikingly like the jet applications being tried today. Clark proposed a plane of conventional design, without a motor and driven only by fuel burned under forced combustion, with the products passing t,hrough a jet whose reaction against atmospheric resistance would drive the plane. Clark admitted his studies were preliminary, but he had figures to show that the required energy was there. He made no extravagant claims for fuel consumption, but took reasonable credit for the small weight and total absence of drag of jets against the weight and front resistance of airplane motor and propeller of those days. His most logical and important argument for the adoption of jet-propelled planes was based on sound economic engineering. Why put a motor with severe vibration characteristics into a plane, a t a cost of 12,000 to 14,000man-hours and $50,000 to $60,000when its useful combat life might be 10, 8, or even fewer air-hours, just to obtain a little fuel economy. This was an early lesson in the peculiar economics of military machines which might have borne valuable fruit except that it had a powerful competitor. Wide publicity combined with complete mystery already surrounded the most glamorous Liberty motor being designed beyond locked doors, and the jet propulsion theory was filed. A valuable development of jet energy has been successfully applied to hydroelectric installations by Oscar G. Thurlow, formerly chief engineer of the Alabama Power Company. I n most hydroelectric plants the water turbine is placed some several feet above the mean water level below the dam, and this distance is filled in with the discharge draft tube. The pull of the water in the draft tube together with the improved flow characteristics due to this tube make the fall below the wheel quite as effective as the head above the wheel in normal operation. When flood waters occur, all this changes. The water due to the flood volume backs up below the dam and greatly decreases the effective useful head. There is too much water everywhere. By means of several jets properly placed near the discharge tubes of the turbines, this troublesome excess watdr is put to work. Some of the useless flood water is taken from the high level above the dam and discharged through these jets, where the energy in the jets is used t o pump water away from the discharge of the turbines. This gives the effect of lowering the level of the “tail water”. When in operation these jets tend to restore the maximum difference in level between the height of water above and below the dam. This jet application has recovered a large amount of energy which would otherwise be lost and has won honors from The Franklin Institute for Thurlow. w)
