rules of thumb - for heat exchanger

							:It exchangers . Take true countercurrent flow in a shell-and-tube. ex• 1ger as the basis for comparison. Standard tubes are 3/4-in.-O.D., I-in. triangular spacing, ;long; a shell 1 ft dia. accommodates 100 ft2; 2 ft di_a.,450 3' ft dia.; 1,~QQ:.f.t~ (") > ' <;;; 01"1';;" i:}~l\ .1 \. ",':, i Tubesideis for corrosive, fouling, scaling and high~ure fluias. Shellside is for viscous and condensing fluids. Pressure dropl' are li,8sifor boiling liqJids, and 3-9 psi tther services~ JO .;. LJ k fa :?{1 ••6? JE Minimum temperature-approach is ArE with normal . f rnts, 10"F or less- with refrigerants. 1...'",(, J "', '1 3_'· '(8

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s, Btu/(h)(ft2)("F): water-to-liquid, 150; 'condensers, 150; i-to-liquid, 50; liquid-to-gas, 5; gas-to-gas; 5; reboiler, e 8'orthe maximum flux in rebailers, use 10,000. s Jouble-pipe exchangers are competitive at duties re- ,t IlglQQ::~QQJt2. ~~. '2.':;; ~ I tl.S HL. ,\ 4«;~' q Compact (plate or finned-tube) exchangers have 350 ft2_~,; rface area/ft3 of volume, and about four times the heat if] fer per cubic foot of shell-and-tube units. i~ Plate-and-frame exchangers are suited to sanitary ser~ 0 and, in stainless steel, are 25-50% cheape1:'"'than shellIIbe units. p For air coolers: tubes are 0.75-1.00 in. O.D.; total finned d ce is 15-20 ft2/ft2 of bare surface; the overall heatfer coefficient, U, = SO-100 Btu/(h)(ft2 bare surfar: ); fan power-input is 2-5 hp/(million Btu)(h); the ap- 5; h is 50" or more. dl For fired heaters: Radiant rate is 12,000 Btu/(h)(ft2); III ction rate, 4,000 Btu/(h)(ft2); cold-oil~tube velocity, 6 :hermal efficiency, 70-75%; fiuegas temperature, 250- c( above feed inlet; stack-gas temperature 650-950°F. al lximately equal heat transfer occurs in both sections. in