Document 3ek3wB9q6naBMjoQjy0BjmDy3

1160 CHAPTER 47 1957 Guide Step S: The pick-up of moisture per pound for the total air circulated is = 0.0051 lb. 0.0280 -- 0.0051 = 0.0229 lb moisture per lb of air for the supply air. Assuming an existing wet-bulb of 100 F, the supply air dry-bulb will be 182 F. The mixture of recirculated air at 160 F dry-bulb and 100 F wet-bulb, with outside air at 80 F dry-bulb and 72 F dew-point, will be at approximately 120 F dry-bulb and 89 F wet-bulb. Step 6: The heat required may be determined from Equation 26 by substitution of the following values: N = 307 X 60 = 18420 lb of air per hr; S = 900 lb; c = 24 + 0.45^-'--) = 0.251; t\ = 80 F; h = 160 F; t/ = 100 F; X = 1100 (approx.); W = 0.005 lb; Si = 0.22. Q = 18420 (0.251) (160 - 80) + 18420 (110 + 160 - 100) (0.028 - 0.0168) + 900 (100 - 80) (0.22 + 0.005) + Q, = 609,000 Btu per hr -f <2TM The heat input requirement is therefore 609,000 Btu per hr plus radiation and con vection losses (Q,c) which may be computed from the known construction of the dryer surfaces and the heat transfer coefficients. Summer conditions were used in Example 1 in order to obtain the maximum heat requirement which would be the case, except under the unusual condition where radi ation and conduction losses are a large percentage ef the total. In winter it is usually possible to take advantage of drier makeup air, and either speed up the process or operate at a lower dry-bulb temperature. Controls for the system selected for Example 1 would consist of a thermo stat in the main return air duct controlling the heat input to maintain constant dry-bulb temperature. A wet-bulb controller in the return cir culating duct would maintain constant desired wet-bulb temperature by simultaneous positioning of three sets of dampers in the makeup air, the exhaust air and the recirculated air ducts. REFERENCES 1 Drying, by W. R. Marshall, Jr. and S. J. Friedman, Perry's Chemical Engineers' Handbook, McGraw-Hill Book Co., Inc., New York, 3rd Edition, 1950. Indicated material supplied by W. R. Marshall, Jr. and S. J. Friedman, authors of theSectioD on Drying m the Third Edition of the Chemical Engineers' Handbook. Permis sion to use this materia) has been kindly granted to The Guide by the Editor, John H. Perry, and by McGraw-Hill Book Company, publishers of the Chemical En*gTinheeerDs'ryHinagndobfoFooko.ds, by W. R. Marshall, Jr. (Heating, Piping and Air Condition ing, September to December, 1942, and November and December, 1943). * Drying Materials in Trays, by C. B. Shepherd, C. Hadlock and R. C. Brewer (In4dDursytriniagl aonfdSEonlidgsinebeyriTnghrCouhgemh-iCstirryc,uAlaptiroiln,, 1b9y38W). . R. Marshall, Jr. and O. A. Hougen (Transactions, American Institute of Chemical Engineers, 1942). 1 Heat, Mass and Momentum Transfer in the Flow of Gases through Granular Solids, by B W. Gamson, G. Thodos and O. A. Hougen (Transactions, American Ins'MtituatsesoTfrCanhesmfeircainl EthneginFeloewrs,o1f9G43a)s.es through.Granular Solids Extended to Low Modified Reynolds Numbers, by C. R. Wilke and O. A. Hougen (Transactions, Ameri can1 LInimstiittauttieonosf Cohf DemifficuaslioEnngEinqeueartsio, n1s94in5).Drying, by O. A. Hougen, H. J. McCauley and W. R. Marshall (Transactions, American Institute of Chemical Engineers, 1940). * What the Air Conditioning Engineer Should Know About Drying (Healing and VenStiplartainygD, Dryeincegm, bbeyr,B1e9n42B).. Fogler and Robert V. Kleinschmidt (Industrial and En"ginAeneIrnintrgodCuhcetmioisntrtyo, CDoencveemcbtieorn, D19r3y8in).g and Drying Calculations, by V. P. Victor (Beating and Ventilating, Vol. 41, Dec. 1944, p. 67). CHAPTER 48 TRANSPORTATION AIR CONDITIONING Railway Passenger Car Air Conditioning; Streetcar and Trolley Coach Heating and Ventilating; Passenger Bus Air Conditioning; Automobile Air Conditioning; Aircraft Air Conditioning; Ship Air Conditioning, Heating and Venti lating, Air Conditioned Space Treatment, Systems and Controls THE principles of air conditioning applying to stores, restaurants, hos pitals, theaters, and homes are applicable to railway passenger cars, passenger buses, automobiles, streetcars, trolley coaches, airplanes and ships. However, equipment used for mobile applications differs from thatused for stationary purposes in that it must meet additional requirements. Equipment must be compact, accessible for quick inspection and servicing, light-weight and unaffected by vibration and impact. Freedom from vi bration which could be transmitted to supporting vehicle and thus to pas sengers, is essential. RAILWAY PASSENGER CAR AIR CONDITIONING The railway passenger car represents a very difficult air conditioning problem. Space is strictly limited so that all equipment and ducts must be reduced to minimum size. Electric power supply and water supply also are limited. All equipment must withstand severe vibration and shock, and must be very reliable since servicing points are frequently far apart. During the heating season it is necessary to heat conventional cars with steam from the locomotive at pressures that may vary from 250 psig to only 5 or 10 psig on the last car in long trains. Passengers in window seats must sit only a few inches from cold outside walls and windows, and must also be very close to standing radiation installed along sides of cars. Sud den changes in load may be caused by changes in sun, wind, or train move ment. Even in coldest weather, outside doors must be opened frequently. During the cooling season, the problem is further complicated by a high concentrated internal load due to the passengers. Also, air distribution problems are increased by low ceilings and short air throws. Heating The heating of passenger cars is accomplished by using a split system consisting of an overhead air circulating system with heating and cooling coils, and standing radiation (floor heat) along car sides. The floor heaters, which usually consist of finned tubing, may be made more efficient by using covers designed to increase gravity air circulation, and to direct the warm air from finned heating surface along cold outside walls and car windows. In some new cars, wall convector panels are used and extend the full length of the car, with air intakes along the floor and outlets at win dow sill height and at window head height in dead-light panels. The heated panel protects passengers from cold outside walls, and the chimney effect of the panel duct increases air flow and improves heating surface efficiency. Floor heat is supplied by introducing steam into an inner tube within a finned tube or by means of a separate steam-to-liquid heat exchanger. 1161