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WHEN THE RATIO of fofenf to sensible heof is high the surface cooler con bo supplemented by dehumidifyinp the oir chemfcolly before It enters the cooling coil Heat-Tmisfer Coefficient Vs Face Velocltjr Feet Velocity, fpm 350 400 450 SOO 550 600 A, Blu/hr/tq ft/p 5.9 6.8 6.9 7.2 7.8 8.0 the air and the surface according to equation 3 is: 35 - 64.5 (u - u- - 18.9 F The selected coil would have a sur face area given by equation: " 'J-CT&1Z" " fa " M0 "ri where 12 is the over-all coefficient oi heat transfer taken from table above, which correlates A. and face velocity of air stream (or the system under dis cussion. The face velocity limits are those used in practice with the maximum not over GOO (pm. Best design would be 500 fpm, which we will use here. The over-all coefficients are for wet surfaces with moisture condensation that suits condition*. Required face area using a face velocity of 500 fpm Is*. ' 5T-8J>""1 Cooling-Surface Depth. A coil hav ing about 8 sq ft face ares with a lim iting face velocity of 600 fpm satisfies the Job requirements. In addition, the coil's shspe (number of rows deep) affects the dehuraidifylng efficiency of the system. As the depth of cooling surface increases more dehuraldification is obtained with a greater slope of line l to 2 in Fig. 8. Various combinations are usually presented in manufac turer's data sheets in multiples of 2, 4, 6 and 8 row-deep colls. Suppose that rating tables are not available, and a surface having the fol lowing characteristics is to be used: tion has a ratio of 38.4 per coil or 768 for two sections deep in the direction of air flow. Because this is less than the required 80 ond the face areas coos in multiples of 2 sq ft final economics! selection is a coll two rows deep with o face area of 8 sq ft Fig. 6 (in Part I) may be checked mathematically if the refrigerant tem perature is calculated directly. The In side area of tire coil may be determined from information at hand: . 8 X 2 X 38.4 w dr V------55------ 62 sq ft The refrigerant temperature if Rello of outside tortus to fea ares.... JS.t Ratio ct ootaido to buMa aurfaca............ 9,t lloat irasaler coefficient, relrtcerant Ida, h, ..................................................... 200 Heat tramfev coefficient, air aide (table abere) Face area (3-eq-fl auJtlplea) The coil, whose characteristics were computed in equations 13 and 14, has a ratio of outside surfsco to face area of 80, but the surface under considera t-M-i 42.1 P This agrees closely with the 45 F pre viously approximated. Here we would choose a condensing unit having a capacity of 135,300 Bta per hr at an evaporator temperature of 43 F, or slightly lower to allow for pressure drop in the suction line. Telltales for Pressure Vessels Many unriaso pressure vessels are subject to corro sion or erosion, or both. Useful life can be extended by highly resistant materials or by thicker metal than needed to withstand working pressure safely. In looking for evidence of corrosion or erosion, examine areas at (1) riveted joints (2) portions of metal that have been cold-worked and (3) heads de signed with a short-knuckle radius where stresses may concentrate. Croovlng points to active corrosion. Corrosion on external surfaces con be seen it area is accessible. Only way to examine inaccessible surfaces is to expose them. If an area's condition looks dan gerous, drill test holes to measure metal thickness. As s precaution against failure, periodic inspection can be supplemented by drilling telltale holes in the metal walL Most effective method is to drill holes into the piste from the surface opposite the one exposed to attack. Then corrosion or erosion opens the hole and allows the vessel's contents to lesk out and worn the attendant. Never drill telltale holes too deep. Leave enough metal in the bottom to withstand working pres sure safely. If there is any danger from leakage through the holes do not drill them. If a leak develops in an unfired pressure vessel do not weld the hole, and put it back in service without thoroughly examining both surfaces. Someone may have drilled a telltale hole to warn of reduced thick ness from corrosion or erosion. -- The Locomotive ''two J00O-KW AUTOMATIC EXTRACTION eondemlng unit. Ihrottl. valve. The turbine-lal.r valve, mo drilled lo pon ? 1m, converted 10 operate olio 01 mixed-ot.isuro unit, by ro- 3000-lb-per.hr cooling tteotn through unit to the cooderaer > ,h. check vol.e In Ihe extraction line with o trip . when turbine l> turning ol toted ipeed but corrylng no load Rebuilt Steam Turbines Modernize This Twenty-Year-Old Paper Plant : To carry increaiod itoam and electric loads at greatest ovor- other unit acting as emergency standby. In its day this plant, one of the most oil economy, two automoticextractlon condensing turbines were progressive industrial power units built, had fully justified its design. ! easily converted to act also os mixed-pressure units. Flexi Growfng Loads. Steam and electrical bility and efficiency over wide load range feature new setup, loads grew with passing time because of higher production and changes In . which Includes a large new noncondensing turbine-generator paper type. Production Increased from .30,000 tons annually in 1928 to 70,000 i tons in 1946. Also, the paper machines > were speeded up, needing more power By O H SUKS, Chief Engineer, Serg Paper Ce and higher-pressure steam in the driers. end R D MiARYKUR, Turbfna Spotted!*, Gonercl Electric Ce At prese.nt, six paper machines use .9000 kw and the largest machine alone takes 3000 kw. Energy requirements often exceed 215,000 kwhr daily. 1928, tre Sorc Paper Co, Mid- with 400-psig 70O-F inlet steam, 2-in. ' Additional boiler and turbine ca4Wswn, Ohio, installed two 5000-kw Hg abs exhaust, automatic extraction pocity were needed, so a study .was*" wadensing automatic-extraction tur- at 20 psig and uncontrolled-extraction made of alternate schemes. Steam at auw-geuetstoT* with three boilers to of small steam quantities at about 80 600 psig was considered, but the gain "Wh power and steam to its mill. At psig. Original plant layout ia shown on was not enough to justify two plant Mesm at 20 psig was used Cot p 72, and the Individual turbine per pressures with Increased design and Paper. This product was largely formance 'curves on p 73. Original operating complications. This probably *fl "h'te paper, needing relatively peak electric load with all six paper would not be true If the original pres power. machines running was 3750 kw. One sure had been 250 psig or less. A new The turbines were built for operation turbine could carry the load with the boiler was installed in 1946 to produce 79 (74) POWER February 1441 ^OWER February 1948 (751 71