Document bBBbnG8b7JdXeXNxLLzwMDEyO

Variation of friction factor with Rey nolds number, and roughness is now reliably known for the whole range of numbers generally encountered In in dustry- Surprisingly, at higher Rey nolds numbers the friction (actor be comes a constant, independent of the Reynolds number and a function of the relative roughness only: 1m 1 ' [1.74 + 2 log tfky (8) Limits of applicability for this formula when applied to air at atmoipherlo pressure and temperature are given In Table I. Instead of using the relative roughness k/r. Its reciprocal, the rela tive smoothness r/A, U used for con venience. Relationship of equation (6) and pipe diameters is shown in Fig. 3. Finding Design Constants. Cos veloci ties in exhaust systems usually range from 25 to 80 fps. Higher velocities often cause pressure drops to become so large that single-stage fans can not maintain desired deliveries. Lower velocities are not desirable either, be cause they increase duet site unneces sarily and dust particles settle out, ad hering to the duet walls. As shown in Table I the friction factors computed from equation (6) can He used for all velocities generally encountered in fanpowered systems. Greatest possible error that may oc cur at lower velocities is small in view of other uncertainties, especially the fact that the relative roughness of the pipe is usually not known accurately. Pipe relative roughness, k(r, on which the friction factor depends, can not very well be determined by meas uring the surface projections A and dividing their mean value by radius r. It is most- reliably obtained by finding first the friction factor from lest data on high velocity flow, that Is, for Rey nolds numbers greater than R, in Table l. Unfortunately, very few such testa are known and usually pertinent facts, such as the kind and number ot pipe joints used and information regarding other conditions which influence the pressure drop, are lacking. The calculating chart, Fig. 4, based on equations (4) and (6) helps to quickly the pressure drop in a pi^ length of one diameter when temper.") ature, velocity and relative tmoothnesjl of pipe are known, it shows readil^ the great variation in pressure drop', with the pipe-surface condition and the' utter uselessness of nny pressure-drop] calculation if pipe roughness is u,| known. * Available information indicates that' absolute roughness rather than rl*j live roughness is about the same iorjl various pipe diameters. For round sheet-1 metal ducts, such os fan systems use,y an absolute roughness of .0.015 appeanjl to be a fair mean value. || A concerted effort by all those coo',] earned with designing end insuUi&|:| air-duct and piping systems is needed] to make available more reliable fiov I date than are obtainable today. With easily made pressurtsdrop readings ci` existing systems and the use of Fig. 3 and 4, roughness factors can be found for ducts of given diameters, material^ end kinds and numbers of joints. Australian Plant Of Advanced Design ELECTRICITY comes Into tha plant at 34,500 v; Is stappsd down to 4140 v In tha two 5000-kva transformer# comprising tha main substation alongside tha powerhouse building, above STEAM Is supplied by two 45,000-lb-per-hr oil-fired Integral-furnace bolters. Approximately' 60% of ateum generated la used for proeeaa operations Power for Plastics Production Power services play a major rofc in the complex end closely controlled processes of iaminoted-plostics manu facture ot General Electric's new plant at Coshocton, Ohio, where everything is made, from gears and bearings to in sulators and refrigerator door panels. The single-story plant and the 2-itory and basement office building enclose more than 300,000 sq ft of floor spoce. Here, engineers of the Austin Co, which handled.design and construction, have combined many -new types of building msterial and equipment to insure pro duction efficiency. Electrical Equipment. Purchased elec tricity enters through two 5000-kva 34,500/4160-v transformers supplying four 1000-kva unit substations inside the manufacturing plant, and two 750-kva substations in boilerhouse and varnish building. These deliver 480-v 3-phase current to an overhead-bus distribution system embracing nearly half a milo of plug-in and feeder lines. All smaller transformers are mounted on mezzanines suspended from roof trusses. Varnish house has expJoeionproof equipment Collars. Boilerhouse at northeast corner of site contains two oil-fired Integral-furnace boiiert rated at 45,000 lb per hr. These supply steam lor the many process uses and to unit heat ers for winter heating. Air Conditioning. Certain process areas, where controlled conditions are important, employ air conditioning and special wall construction. These walls consist of 4 in. of outside common brick, backed by 2 in. of foam-glass insulation, 4 in. hollow tile, and 4 in. glazed tile. Air-conditioning equip ment, to maintain 70-F dry bulb end 35% relative humidity, is located on suspended mezzanine platforms. Sypnky County Council's bsw Pynnont B power station will use tha highest steam pressure and temperature in Australia, 1200 pslg and 925 F. Now under construction, the plant will ulti mately house four generators arranged os the unit system, with steam and feedwater mains interconnected. Boiler' plant will have 430,000-lb-perhr radiant-type waterwell units with dry-ash bottoms. Economizers and air preheaters are being provided. The steam generators will feed 5-cyllnder impulse-type 50,000-kw 3000-rpm tur bines driving Spbase 33,000-v S0-cycle alternators. The plant will be pulvertzed-eoal fired, with fuel delivered by ralL English firms are supplying most of the principal plant equipment 44 112) POWER January or pumps and the accumulator fn the back| eund maintain 3000-psl pressure for molding presses, m* r Pumps In background serve the 600-pal system AIR-CONDITIONING equipment serves several controlledconditions arses where laminating stock Is stored and built up for pressing. Total refrigeration toad la 168 ton* fOWER January 1948 (33| 45