Document YDXJ9NkDnzV44jMeavqNvr8kn

i ll ;U f 1; - These three tables are based S fi li i i&t-.on thoroughly practical con- | siderations of standard Insu- | -4 lotion thickness, heat loss, load J 1 Visi*factor, fixed'charges, fuel cost, 0.3 temperature conditions, oper v11m j II 11 tiating hours and labor costs f JMWtliffl ,400 600 000 1,000 1,200 Haat trantmlatlen, Btu ft* hr per, sq ft, a. INSULATION SURFACE RESISTANCE depends on the rate of unit hoot flow; the 3 resistance decrcoscs with Increasing hoot transmission through Intulotlon surface I 1: Unit Heat Loss lor 85% Magnesia Block Insolation,' fin. Asbestos Cement Finish Vertical Position Difference. F' 100 200 300 400 soo Btork thieknea, in. 1 It 2 21 3 Heat tou. Btu per tq ft per hr per F 1 0.297 0.308 0.320 0.332 0.344 0.216 0.224 0.233 0.242 0,250 0.170 0.176 0.183 - 0.190 0.196 0.140 0.145 0.150 0.156 0.161 0.119 0.1235.0.129 0.1325 0.137 ' tfol surface to sir II: Thickness ol Insulation Recommended as Economical Column number 2 4 5 6 7 8 9 to Hal turjace temperature, F ' /ruuiafion thieknea. in. 180 1 l 1 L 1 l It It 2 2 212 to 266 1 1 1 l l It It 2 2 21 267 to 337 1 1 l It It u 2 2 2t 3 338 to 587 1 1 U It 2 2 2| 2t 3 3 388 to 499 1 n It 2 2 2| 21 3 3 3 500 to 600 U 2 2 21 2) 3 3 3 3 3 Here Is a Quick Way to Find Economical Insulation Thickness III: Column Index (or Table II on Economical Thickness ol Insolation Heat coil, i per i(f Blu 20 25 30 35 40 45 SO 55 60 Beiimaled Annual operation. hr per yr fixed charger. % 8760 7200 6000 5000 15 5 6 7 0 9 9 10 10 10 15 S 6 6 7 e 0 9 9 10 15 4 5 6 6 7 7 8 8 9 15 4 S S 6 7 7 6 9 prepared to aid in selecting the most]] economical thickness of single-layer.! 65% magnesia block insulation, is ten* ported in the following discussion. All the majority -of block insulations uej finished with V4*in. asbestos eemcayj this factor has been taken into account} in the calculations. Hoot-Leu Calculation. Table 1 wsjl calculated' with the following esttbjj lished equations for heat transmission^ . _ I. - t, * x * 4. 1 -ir+-sr+ -- 8760 7200 6000 5000 0760 7200 6000 5000 20 4 6 6 7 7 899 20 4 6 6 7 7 8 8 20 2 3 4 S 6 6 7 7 7 20 2 S 455667 25 3 4 5 6 6 7 7 8 ' 8 25 2 3 4 5 5 6 6 7 7 25 1 2 3 4 5 5 6 6 6 25 2 2 3 4 4 5 S 6 Recommendations by the industry for the economical thickness of 85%. magnesia insulation have ordinarily been based on one factor, range of. operating temperoture; for pipe insula tion, pipe sixes have also been con sidered. These recommendations have rarely taken account of other operating varinblea. To assist in finding the most eco nomical thickness of pipe insulation, a study incorporating tables of economi cal thickness for varying hours of op eration, cost of heat, amortization rate, temperature range and pipe size was prepared by the Magnesia Insulation Manufacturers Association and pub lished by the American Society of Heating and Ventilating Engineers*. A similar study of block insulation. l/i where 9 - heat transmission, Btu per sq ti per hr <1 -- temperature of hot surface of ioiv*3 tlon, F Jj ( - temperature of sir on oool lids % insulation, F di -- thieknea of first material (65% magoeeis block), in. it thickness of second material (asbestos-cement finish), in. Jti -- conductivity of first material at mean temperature, Btu per bt (* aq ft per io. per P f fci - conductivity of second material ri mean temperature, Btu per hr K sq ft per in. per F I e * air-film conductivity, Btu per hr W aq ft per P (/, - heat-tranamiaslon coefficient. Btu per hr per sq ft per F - The curve shows the relationship l*1 Iwccn the surface resistance (1/c) *' total heal transmission. The resist**^ decreases as the beat transmission creases. Values of k% for 65% magnesia wet 90 (476) POWER A119.1t 1V obtained from conductivity testa made by the insulation manufacturers: Conductivity Tarts Mean temperature, F k 100 0.39 300 0.45 SOO 0.51 meat was assumed to be 1.S0 for all mean-temperature values. Intufatioo Thickneii. Cost of apply ing insulation blocks is made up of the following items: (1) B5% mag nesia block Inaulotion (2) hexagonal wire mesh (3) asbestos cement finish () labor. Cost of wire wesh end as bestos-cement finish is independent of block-insulation thickness, so total cost should vary only with labor and block thickness. Consensus of the insulation contract- "I ,ndustry states that theoretically here should be a slight increase fn *c*t of application per sq fl of block ^`h increasing thlekness, but the dlf- ** 10 that using a vari- ,abor hgure Ls not justifiable, erefare, it U assumed that an inu *tion mechanic would apply about e *quare footage per day of 1 t *1 , e ^tT thickness of block from y ? L ft' *kick. Hence, the only cost L a, e the finished installation ii*\ . ? lho C0lt of this bloek insula- fisur* . V* U per board foot. .This ' ' * l% on a 1947 survey amoog insulation contractors In various sec tions of tho country.- All other costs are fixed and need not be considered to establish economical thickness provided the surface is to be insulated at all. The economical thickness results in the smallest sum per year of cost of insulation and cost of beat lost through the Insulation. Exempts: Cost of heat. I per 101 Btu 60 Annual hr of operation 7200 Fixed charge rale, % 20 Boiler steam praaurs. prig 100 8team temperature, F 338 Air temperature, P 75 Annual cost of insulation, g 6.22 X fixed eharge rate X thieknea - 0.22 X 0.20 X i 60.044 per year Cost of heat lost annually TM hr operation X heat cost X l/e X (<i -- U) - 7200 X 2jgr X -31t X - JO.298 per year Similar calculations for other thick nesses result in the following annual costs: Calculations for Other Thicknesses Insulation - Annual costs, t thickness, in. Insulation Heat Total 1 0.044 1U 0,006 2H 0.088 2\i ' 0.110 0.208 0.218 0.170 0.139 0.342 0.284 0.258 0.249 3 0 132 0.110 0.231 The above table shows minimum cost occurs with the 2V4-in. thickness, which is then the economic choice. Table II was calculated on the above basis for conditions varying over the following ranges: Heat cost, 4 per 10* Btu...........20 to 60 Operation, hr per yr...........5000 to 6760 Fixed charges, %........................10 to 25 To use Table ll, first refer to Table III to find the column number corre sponding to the desired hours of op eration, fixed charge rote and heal cost With the column number and initial steam temperature find the economicalthickness in Table II. For the example worked out above. Table III shows that column No. 7 applies. Then in Table II, under column 7 opposite 336 F find the economic thickness of 2% in. STEEL MILL POWER When steel-mill engineers talk power, It's with a capital "P". Jones & Laughlin's new 5-stand tandem mill at the Aliquippa Works, which has rolled strip at 6250 fpm (over 71 miles per hr), takes the output of two huge mg sets rated at 14,200 kw. Designed and built by Mesta Machine Co, ,010 mill has six CE motors with a combined ca pacity of 16,850 hp, which because of special insulation con carry 20,100 hp continuously without overheating. Each of the twin stands has a separate gen erator to supply 3c to its stand and reel motors; with amplidyne control this arrangement makes for ease of operation and fullest possible adjust ment of stand speed. Auquil (940 (479) 91