Ilarch, 1932
I N D U S T R I A L A N D E K G I N E E H I N G C H E M I ST R 1
production of cuts from their bulletins: the Builders Iron Foundry, makers of Venturi meters and the shunt meter; the Brown Instrument Company; the Foxboro Company, the Bailey Meter Company, and the Republic Flow Meters Company, makers of orifice and related meters; the Metric Metal Works of the American Meter Company, makers of orifice and diaphragm displacement meters; Cutler-Hammer, Inc., makers of the Thomas meter; The Roots-ConnersvilleWilbraham Division of International-Stacey Corporation. makers of rotary displacement meters; Schutte & Koerting Co., makers of the Rotameter; and the New Jersey Meter Company, makers of the Tool-om-eter. The reports of the A. S. M. E. Special Research Committee on Fluid Meters have also been of great assistance. BIBLIOGRAPHY GEKERAL (1) Am. Soc. Mech. Eng., Rept. of Special Research Committee on Fluid Meters, Parts I and 11, 1931.
213
( 2 ) Bean, Benesh, and Buckingham. Bur. Standards J . Research,
7, 93-144 (1931). (3) Brenner, E . C., Gas Age-Record, 51, 503-4 (1923). (4) Bur. Standards, Circ. 309 (1926). (5) Turner and Winship, Chem. M e t . Eng., 30, 633 (1924). DIFFERENTIALPRESSURE METERS (1) Am. Meter Co., Bull. E-2, 1931. (2) Bean, Buckingham, and Murphy, Bur. Standards, Research Paper 49 (1929). ( 3 ) Beitler and Bucher, Trans. Am. SOC.Mech. Eng., Hydraulics, 52 (7a), 77-87 (1930). (4) Foxboro Co., "Principles and Practice of Flow Meter E n d neering-The Orifice Meter for Gas and Liquid Measurement," 1930. ( 5 ) Smith, Trans. Am. SOC.Mech. Eiig., Hydraulics, 52(7b), 89109 (1930). (6) Spitaglass, J. M., Mech. Eng., 45, 342-8 (1923). (7) Spitzglass, J . M., Iron Steel Eng., 7, 217-20 (1930). (8) Witte, R., Z. Ver. deut. Ing.,72, 1493-1502 (1928). DISPLACEMEST METERS (1) Am. Meter Co., Handbook E-4. 1930 RECEIVEDNovember 30, 1931
Heat Transmission to Oil Flowing in Pipes Effect of Tube Length T. K. SHERWOOD, D. D. KILEY,AND G. :E. MANGSEN, Worcester Polytechnic Institute, Worcester, Mass. turbulent motion. Four lengths HE coefficient of h e a t Data are reported on heating a light hydroof pipe were used, the ratio of transfer between a tube carbon oil flowing in both viscous and turbuleni length to diameter T being varied a n d a fluid flowing flow through each of several horizontal lengths from 59 to 224. A sharp contracthrough i t has been assumed to of 0.593-inch i. d. copper tube. Heat was tion from a 1.44-inch hard-rubbe influenced in two quite differsupplied by steam condensing outside the tube; ber approach pipe t o the 0.593ent Fays by the length of the inch internal diameter test pipe tube. Various German writers oil rate, steam temperature, and inlet and outlet was designed to simulate turbuhave discussed a heat-penrtraoil temperatures are recorded. .A mechanical lence conditions a t the entrance tion effect, or increased difficulty stirrer was used to m i x the oil thoroughly before t o a tube held in the tube sheets of heat inflow to the fluid core as its outlet temperature. measuring of a large condenser or tubular the fluid moves along the tube. I n the turbulent-flow region, the data are well exchanger. In spite of this conThe fluid near the tube wall betraction and consequent probcomes heated (or cooled) nearly correlated by the method of plotting of Morris able turbulence a t the inlet, the to the tube temperature, and the and M'hitman, although this method is unsatisdata were found to fall, within rate of heat flow per degree diffactory in the viscous region. I n the aiscousthe accuracy of the work, on a ference, between the temperature jlow region the data are well correlated by the single line when plotted in the of the tube and the mean temmethod of plotting of Drew, Hogan, and iWcusual ways. It was concluded perature of the fluid, would be that, for water in turbulent flow, e x p e c t e d to be d e c r e a s e d . Adams, whose empirical curve is substantiated the effect of tube length on thf Graetz (5') has derived a theoreti.for tube lengths greater than about 100 diamerate of heat flow is negligible. cal relation for viscous flow which ters. As the oil velocity is increased, the obIn the well-known work oi indicates a considerable effect of served sudden rise of the outlet temperature of the Morris and Whitman (6)on heattube length on the fluid-temperaoil indicates a critical value of the Reynolds ing and cooling oils, only one ture rise per unit length of pipe. pipe was used, and consequently For turbulent flow, the rate of number which compares well with the accepted no information was gained as to heat transfer might be expected ralues for isothermal flow. the possible effect of tube length to be influenced by the turbuor end effects. Recently Drew, lence normally present a t the tube inlet, followkg a contraction or elbow in the line. Since Hogan, and McAdams (2)have suggested a method of correlathe effect of this turbulence in improving heat transmission is tion of viscous-flow data, based on the Graetz theoretical equaprobably concentrated over the first few diameters of the tube, tion mentioned above. These authors plot (tz - t J / ( T w - tl) the average rate of heat flow for the pipe as a whole should be a vs. Wc/kL, using the data of two investigators on heating a function of the tube length. This effect has been discussed by light Velocite B oil. The first group is the ratio of the temperature rise to theinitial temperature difference; and in the second McAdams and Frost (j)who , proposed a factor 1 by group W represents the weight rate of flow, c the specific heat, '7') which the coefficient should be multiplied. r represents the k the thermal conductivity, and L the heated length of the ratio of tube length to diameter. tube. The slope of the line representing the Graetz theoA previous article (4) describes the results of a study of the retical relation is negative and numerically much less than effect of tube length on heat transfer to water flowing in unity; an appreciable effect of tube length on the temperature
T
(+
274
INDUSTRIAL AND E S G I N E E R I N G
rise per unit length is consequently indicated. The data plotted indicated a similar line, although falling considerably above the theoretical curve. The data reported, however, were obtained using tube lengths of 55 and 59 inches, respectively, and consequently throw little light on the validity of the effect of tube length indicated by the Graetz relation.
CHEMISTRY
Vol. 24, No. 3
thermometers, reading t o 0.1 " and carefully calibrated against each other, were used a t the oil inlet and outlet. With each tube length, blanks were run with no oil flowing t o determine the rate of heat loss from the apparatus. The inside of the test tube m s cleaned frequently with a stiff brush to prevent the formation of dirt or scum.
7.
PHYSICAL PROPERTIES OF THE OIL
51
The hydrocarbon oil used was described by the manufacturer as a light asphaltic-base heat-transfer oil. Its specific gravity, as determined by a Pllohr-Westphal balance, was 0.923 a t 15" C. X standard Saybolt viscometer nas used to determine its viscosity-temperature curve, the coordinates of which are given in Table I. Its thermal conductivity expressed as R.t. u. per hour per square foot per " F. per foot was (8) 0.0765 at 30" C. (86" F.), 0.0755 a t 75" C. (167" F.), and 0.0748 a t 100" C. (212" F.). A constant value of 0.076 was used in the calculations.
48
3,
21
IC
E 4
T4BLE I.
VISCOSITY O F
3
TEIIPER~TZRE 7
" C .1
400
600
1000
2000
4000 6000
loo00
20000
40000
FIGURE 1. DAT4 PLOTTED, USINGCOORDIVATES OF J ~ O R R I S
18 3 26 5 33 3 39 4 44.1
Kinematic
Centtpo'ers
F. 65 i9 92 103 111
OIL
VISCOSITl
0 8 0 0
5
Grams/ec. i2 0 44 0 31 5 24 0 18 8
.Ibsolute Puunds/(houra) fieel)
161 9s
70 2 53 5 41 9
AND w H I T M 4 \
The present article describes the results of euperiments on heating oil in both the viscous and turbulent regions, using four lengths of 0.593-inch i. d. copper tube. The oil used was a light heat-transfer oil, and the apparatus was slightly modified from that used by Lawrence and Sherwood (6).
APPAB ATU s The apparatus consisted of the double-pipe heater under test, an outlet mixing chamber with stirrer, a double-pipe cooler, receiving tanks, circulating pump, and the usual accessories. The test section was supported in small tube sheets held in a standard 4-inch steel jacket, forming the steam space. The oil approached the tube sheet a t the inlet end through a 1.44-inch i. d. hard-rubber pipe, the section contracting a t the ferrule t o the 0.593-inch i. d ,0.75-incho. d., copper test section. ilt the outlet end the section expanded from that of the copper tube to a short section of standard 4inch steel pipe in which was placed the thermometer indicating the temperature of the oil at the outlet. Between the outlet of the test tube and this thermometer was inrerted a stirrer driven by a small electric motor, ensuring thorough mixing of the oil before measuring its average temperature. The zinc blade of the stirrer was 3l/2 X 2 inches, attached to a shaft passing through a packing gland in the wall of tlie 4-inch pipe. S o attempt was made to measure the surface teinperature of the copper tube, for the reason that, in heating oil with qteam, the steam-side resistance is but a small fraction of the ovec-all resistance t o heat flow, and may be estimated nith sufficient precision. The weight rate-of-flow of oil wac obtained by direct measurement in every run, using a Stopwatch to measure the time required to collect from 1 t o 2 gallon
