STEAM CONDENSATION Effect of Tube Position H. T. QUIGG,' WILLIAM C. MOYER,a AND R. L. HUNTINGTON University of Oklahoma, Norman, Okla.
Over-all coefficients were obtained o n a single-tube steam condenser placed in several positions (horizontal, 45", and vertical). The nature of the different types of condensation was observed through a Pyrex glass jacket enclosing the steam space. The Reynolds numbers in consistent units for the cooling water, D u p / p , varied from 3,000 t o 50,000 and for the steam condensate, 4r/p, (with the tube in the 45" and vertical positions) from 200 t o 1500. A t the slower flow rates the effect of tube position is negligible, but a t the higher Reynolds numbers the over-all coefficients for the 45" and hori-
J
zontal tube positions were approximately 25 to 50 per cent higher, respectively, than the corresponding ones for the vertical position. By graphical analysis the individual film coefficients for the water film were found t o vary from 200 t o 3800 B.t. u./hour/square foot/ O F.,depending largely upon water velocity ; the condensing steam films were 795, 1060, and 1370 for the vertical, 45", and horizontal positions, respectively. The ratio of the areas covered by dropwise condensation of steam t o those of film condensation was about 1 t o 4 for the horizontal tube and 1 t o 9 for the vertical tube position.
In order to eliminate chances for accumulative errors resulting from such causes as gradual scale formation runs were made at random both for different water rates and the several tube positions. Preliminary (or trial) runs were made over a period of a week to allow a thin coating of rust to build up on the exterior of the tube. Because of the unusual softness of the water supply, it was unnecessary to clean the inside of the tube during the entire period of occasional operation from February to June, 1937. The tube was placed in three different positionshorizontal, 45", and vertical. In each position the steam and cooling water were flowed countercurrently, and for the horizontal and vertical positions, parallel flow as well as countercurrent. In a11 of the 45' and vertical runs, the steam flowed downward.
URGENSEN and Montillon (6) worked extensively on the determination of steam and water film coefficients
on a condenser tube placed a t various angles from the horizontal to the vertical. Their condenser tube was enclosed in an iron jacket, however, so that no qualitative data were obtained on the nature of the condensing steam film. Other investigators (1-4, 8) recently reported results on the Condensation of steam and other vapors. in a glass-jacketed apparatus but in most instances for one tube position only. This investigation was undertaken, therefore, to obtain (a) qualitative information on the nature of the condensation of the steam in the several tube positions, and ( b ) quantitative data on over-all coefficients from which the individual films might be estimated by graphical methods.
Experimental Procedure The apparatus is shown in Figure 1, with the Pyrex-jacketed tube in a 45" angle from the horizontal: The condenser tube consisted of 0.622-inch i. d. and 0.84inch 0. d. standard half-inch wrought-iron pipe, 4 feet 9 inches in length. The Pyrex jacket was 2.25 inches i. d. and 2.75 inches 0. d. Steam from the university powerhouse was admitted to the glass jacket through two openings in the glass tee at one end of the jacket. The cooling water, obtained from the mains, had a hardness of only 50 to 75 parts per million and was practically free of scale-forming constituents. The data were obtained during 15-30 minute periods during which fairly steady operating conditions were maintained, as evidenced by the fact that the water rate was constant within *2 per cent a n t the temperature of the outlet water did not vary over * L O F. The temperature readings included the inlet and outlet cooling water, the saturated steam, and the steam condensate at the steam outlet. 1
Present address, Phillips Petroleum Company, Bartlesville, Okla. Texas.
* Present address, Texas Company, Port Arthur,
FIGURE 1. APPARATUSSET-UPWITH TUBEIN 45' POSITION 1047
INDUSTRIAL AND ENGINEERING CHEMISTRY
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VOL. 30, NO. 9
FROM STEAM TO WATER IN HALF-INCH WROUGHT-IRON PIPE (HORIZONTAL TUBE,PARALLEL FLOW) TABLEI. HEATTRANSMISSION
Run NO.
Duration of Run HT.
Steam Temp., ta
F.
-Water In, ti
F.
Tem
8bT ta
A?. Temp., Condensate Difference. Temp., t Atrtv.
F.
O
F.
January 19, 1937
0.207 0.385 0.231
210.0 210.0 210.0
61.5 62.8 64.0
95.0 108.8 99.5
4 5 6 7 8 9 10 11 12 13 14 15 16
0.1013 0.2040 0.3248 0.1375 0.2455 0.0833 0.0833 0,1485 0,1458 0.1846 0.1750 0.3260 0.1596
209.50 209.60 209.63 209.45 209.60 209.40 209.40 209.40 209.50 209.50 209.50 209.60 209.65
65.00 63.00 61.25 62.00 61.50 62.50 64.50 64.00 64.00 63.25 62.00 61.75 61.60
85.75 96.25 110.00 89.00 112.50 81.50 83.00 91.50 96.00 99.75 106.00 137.75 118.15
17 18 19 20 21 22 23 24
0.267 0.285 0.0925 0.1375 0,1496 0.1790 0,1900 9.1500
210.2 210.3 210.1 210.2 210.2 210.3 210.3 210.3
64.75 64.25 65.00 64.5 64.25 63.75 63.0 63.0
134.8 152.5 82.75 88.25 96.25 108.25 126.5 117.5
25 26 27 28 29
0.0917 0,1085 0.1834 0.3441 0.1029
210.1 210.1 210.1 210.2 210.0
65.0 65.0 65.0 64.25 64.0
84.5 87.5 96.0 115.5 85.5
92 93 94 95 96 97 98 99 100
0.0848 0.2610 0.0680 0,1140 0.0848 0.0848 0.1180 0.0918 0.1167
212.2 211.2 211.2 210.5 210.0 210.0 210.1 210.0 210.35
67.0 67.25 68.0 67.5 67.5 67.5 68.0 67.0 68.0
80.5 120.5 141.0 93.5 85.0 84.5 101.0 89.5 155.5
1 2 3
... ... ...
Water
Water per Hr.
Linear Velocity
Lb.
Ft./sec.
1935 1040 1732
Over-all Calcd. Heat Transfer Water Film Coefficient, Coefficient, U hw
4.17 2.24 3.735
474.0 372.5 462.0
1148.0 695.0 1048.0
3945.0 1960.0 923.5 2090.0 815.0 4803.0 4803.0 2694.0 2054.0 1625.0 1142.0 306.5 626.0
8.510 4.220 1,990 6.275 1.758 10.350 10.350 5.810 4.440 3.500 2.461 0.662 1.350
592.0 488.0 354.0 564,O 328.0 636.0 626.0 544.0 490.0 446.0 386.0 212.0 289.0
2025.0 1150.0 635.0 1582.0 573.0 2366.0 2366.0 1490.0 1203.0 995.0 749.0 262,O 456.0
281.0 175.5 4325.0 2910.0 2000.0 1118.0 394.2 666.0
0,606 0.378 9.330 6.275 4.32 2.41 0.85 1.435
180.0 155.5 550.0 495.0 470.0 384.0 215.9 299.0
244.0 167.0 2180.0 1580.0 1177.0 735.0 321.0 487.0
4360.0 3690.0 2180.0 871.0 4175.0
9.40 7.95 4.70 1.88 9.02
602.0 596.0 501.0 361.0 639.0
2195.0 1920.0 1260.0 604.0 2120.0
4720.0 760.0 368.0 2630.0 4720.0 4720.0 1695.0 3270.0 240.0
10.3 1.65 0.792 5.68 10.3 10.3 3.66 7.05 0.518
441.0 321.0 246.5 506.0 593.0 575.0 430.0 535.0 219.0
2360.0 543.0 302.0 1460.0 2360.0 2360.0 1023.0 1740.0 215.0
F'ebruarv ~. -
6. . 1937 199.5 133.5 128.9 202.0 122.8 203,O 133.5 201.5 121.1 202.8 202.0 137.2 135.5 202.3 131.5 202.5 202.0 128.6 127.1 202.0 124.5 202.5 200.5 105.2 118.1 202.5 February 9, 1937 186.5 106.9 95.4 190.5 135.5 193.5 133.3 194.5 130.1 201.0 123.8 202.0 111.0 199.0 116.3 200.0 February 11, 1937 194.5 135.3 198.5 133.8 199.0 129.1 200.0 118.5 198.0 135.0 M a y 1, 1937 190.0 138.5 201.5 119.0 202.0 104.0 199.0 129.5 189.0 133,5 199.5 133.7 200.0 125.0 200.0 131.5 198.5 91.6
The original data are presented in Tables I and 11. I n Figure 2A the horizontal runs, both parallel and countercurrent, are shown with the over-all coefficients in their relation to water velocity through the condenser tube. Although the points are somewhat erratic for the higher velocity runs, there is no appreciable difference between the coefficients for parallel and for countercurrent flow. The condensing steam appeared to be about 75 to 85 per cent filmwise. The film was noticeably thicker on the bottom of the tube where large drops formed before they fell from the underside surface. These drops were swept along with the steam for some distance from the steam inlet, with the result that the condensate fell from the tube a t intervals of 8 to 10 inches near the steam inlet; however, the drops became progressively more numerous toward the steam outlet with only 0.3-0.6 inch spacing between the falling drops. The condensate temperature fell below 190" F. on only one run. This slight reduction in the temperature of the condensate below the steam temperature shows that the steam fdm does not long remain in contact with the cold condenser tube in horizontal flow.
The condensation for the vertical runs was approximately 90 to 95 per cent filmwise and 5 to 10 per cent dropwise. I n previous work done in these laboratories (IO),similar condensation was observed. The dropwise condensation took place near the upper end of the tube, where the drops apparently stuck to the surface for some time before they broke loose. Toward the lower part of the tube, the film became so heavy that i t appeared to consist of rivulets covering the tube with vaxying degrees of thickness. It is interesting to observe how much lower the temperatures were for the condensate from the vertical tube than for the horizontal position. Whereas 186" F. was the lowest for the condensate from the horizontal tube, 114' F. was obtained on one of the high-velocity runs on the vertical tube, with many temperatures as low as 130" to 150" F. for the condensate with the tube in the latter position. These lower temperatures indicate that the condensing steam fYm is much thicker for the vertical tube, and consequently the steam film coefficient may be expected to be much lower than the corresponding coefficientfor a horizontal tube.
Vertical Tube Position
Comparison of Tube Positions
The parallel and countercurrent runs for the tube in its vertical position are compared in Figure 2B. The coefficients for the vertical parallel runs (water and steam both flowing downward) are from 2 to 10 per cent higher than the countercurrent runs (water upward and steam downward). This difference may be explained from the fact that more turbulence probably resulted in the downward flow of water against the opposing convection currents, and thus caused a thinner water film and a higher over-all coefficient. Jurgensen and Montillon (6) observed a somewhat similar difference in the coefficients for these two types of flow.
The countercurrent runs for the horizontal, 45", and vertical positions are compared in Figure 2C. The over-all coefficients diverge markedly with increasing flow rates. At a water velocity of 10 feet per second the over-all coefficients for the horizontal position are 47 per cent higher than for the vertical tube. The coefficients for the 45" position fall about halfway between the horizontal and the vertical. In the 45" angle runs no drops of condensate fell from the condenser tube during any of the runs; however, the liquid layer was noticeably thicker on the lower side of the tube. The temperature of the condensate varied between 144" and
SEPTEMBER, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
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FIGURE2. OVER-ALLCOEFFICIENTS A . Horizontal runs, parallel and countercurrent flow; Reynolds numbers, 3,000 t o 50,000 for cooling water B . Vertical runs parallel and countercurrent flowReynolds numbers,’ 3,000 to 50,000 for cooling water; 19d to 1510 for steam condensate C. Comparieon of runs for tube in horizontal, 4 5 O , and vertical positions
162’ F. as it left the tube, as shown in the last section of Table 11. These condensate temperatures are intermediate between the condensates coming from the horizlontal and vertical tubes. The range of Reynolds numbers for the water varied from 3,000 to 50,000, and for the condensing steam from 100 to 1500 all based on consistent units.
Graphical Analysis of Film Coefficients Although Lucke (7) is understood to have been the originator of the method, Wilson (11) was the first to apply this graphical analysis of the over-all coefficient in order to evaluate the variable film. I n using this method, it is assumed
that the resistance of the tube wall plus the resistance of the steam film is constant for each tube position. The data in Figure 3 fall to a large extent on straight lines which are based on the following relation:
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VOL. 30, NO. 9 1
TABLE 11. DATAFOR VARIOUSTUBEPOSITIONS Run No.
Duration of Run
HT.
Steam Temp.,
-Water
ta
tl
O
F.
In,
Temp., out,
Condensate Av. Temp. Temp., Difference,
t2
Atav.
t4
Water Over-all Calcd. Linear Heat Transfer Water Film
Water per Hr.
' F.
Velocity
Lb. Horizontal Tube, Countercurrent Flow. Februarv. 13.. 1937
O
F
F.
10.34 2.35 5.0 7.49 0.98 0.228 0.709 7.05 1,568 0,401 9.41 6.46 4.10 8.18
622 392 514 580 247 121 206 572 326.5 173 62 1 564 490 603
3780 858 1825 2730 358 112.4 258.2 2575 572.5 146.4 3440 2360 1496 2985
4.78 9.00 0.40 1.35 3.53 5.97 2.30 8.08 0.89 0.535 7.59
398 463 227 267 367 414 323 460 216 195.3 445
1490 2463 204 540 1170 1780 828 2262 387 277 2151
hw
209.7 209.8 209.8 209.8 210.0 210.0 210.0 209.8 210.0 210.0 209.8 209.95 210.0 209.9
68 69 70 71 72 73 74 75 76 77 78
0.1351 0.9590 0.1612 0.1195 0.1832 0.1444 0.1875 0,1070 0.1209 0,1209 0.1136
211..8 210.2 210.8 211.4 212.0 212.3 211.8 210.2 211.0 210.8 210.3
44 45 46 47 48 49 50 51 52
0'. 0847 0.2705 0.2567 0.2430 0.2690 0.1376 0.0973 0.1526 0.1250
211.3 209.65 214.75 210.15 209.4 209.5 209.7 209.4 209.4
10.16 3.18 3.455 0.443 2.40 4.71 1.662 5.66 6.90
436 170.3 345 162.5 315 381 281 395.5 406
2582 1078 1145 222 856 1466 638 1695 1992
53 54 55 56 57 58 59 60 61 62 83 64 65 66 67
0.1208 0.2900 0.2192 0.4125 0.1735 0.0862 0.1221 0.1361 0.0986 0,1222 0.1042 0.0945 0,0973 0.1042 0.0945
210.15 210.15 214.5 210,75 210.2 210.0 210.0 210.0 210.15 209.8 209.8 209.8 209,8 209,8 209.8
7.14 2.23 3.44 0.268 0.311 9.99 7.05 4.75 1.09 8.23 8.28 9.13 6.65 6.21 9.14
447.5 304.0 344.0 115.0 112.5 438.0 406.0 377.0 249.9 406.0 408.0 417.0 398.0 403.5 418.0
2044 808 1149 148 168 2680 2070 1476 456 2300 2290 2495 1935 1831 2498
79
0.0918 0.2610 0.2235 0.1084 0.1055 0.1515 0.1958 0.1291 0.1488 0.0944 0.1178 0.1445 0.1235
209.8 210.2 210.15 210.0 210.0 210,15 210.4 210,4 212.3 210.0 210.0 210.0 210.1
9.38 2.48 0.965 7.85 6.13 1.42 0.551 0.417 2.90 9.14 7.34 4.47 3.49
497 380 253 480 475 293 177 183.1 388 530 504 , 434 404
2520.0 872.0 408.0 344.0 1800.0 553.0 260.0 209 5 987.0 2470.0 2070.0 1390.0 955.0
45' Angle Tube, Countercurl mt Flow, April 24, 1937 67.5 83.5 144.0 134.1 4360 , 67.5 109,o 161.0 120.5 1150 67.5 130,5 162.5 106.8 448 146.0 66.75 85.0 134.2 3685 67.5 90.25 153.0 130.5 2843 158.5 67.5 120.5 114.3 660 67.25 141.0 162.0 102.0 256 91.2 193.5 161.0 67.0 157,O 160.5 67.0 104.75 125.4 1345 145.5 67.0 83.8 134.5 4240 149.5 67.0 87.0 135.0 3400 149.5 67.0 95.0 128.5 2075 152.0 67.0 100.0 126.1 1620
-$ -- R~ + R~ + & where U = over-all coefficient, B. t. u./hr./sq. ft./' F. 1/U = over-all resistance R1 = resistance of tube wall Rz = resistance of steam film V = linear velocity of water in tube, ft./sec. l / b = constant or slope of line
RI is calculated to be 0.00042. The intercept on the l / U axis represents R1 Rz. For the horizontal, 45", and vertical positions Rz (steam film resistance) is 0.00073, 0.00094 and 0.00126, respectively. The corresponding film coefficients, or the reciprocals of the resistances, are 1370, 1060, and 795 B. t. u./hour/square foot of outer tube surface/" F. temperature difference. The water film coefficient is bVQes or the reciprocal of the resistance, l/bV0a8. The water film coefficients vary from 215 to 3780 for horizontal flow, from 209.5 to 2520 for the 45" position, and from 148 to 2680 for the vertical position, all based on outside tube surface.
+
135 4800 121.8 1090 131 2321 135 3475, 109.1 454 91.6 105.9 329 108.2 134.4 3272 114.6 728 94.5 186 134.6 4360 132.6 3000 128.8 1910 134.5 3890 March 20, 1937
Coefficient,
U
0.0834 0.1834 0.1291 0.1151 0.2221 0.4720 0.1820 0.1221 0.2745 0.2692 0.0916 0.1333 0.1570 0.1055
so
83.25 203 109.5 205.5 93.25 203 86.5 203 124,5 206 173.0 205,5 133.5 205.5 87.5 204 116.5 204.5 154.25 205.5 85.0 202.5 90.0 203 98.0 203 85.75 202 Vertical Tube, Parallel Flow.
Coefficient,
Ft./sec.
30 31 32 33 34 35 36 37 38 39 40 41 42 43
81 82 83 84 85 86 87 88 89 90 91
65.0 63.75 63.0 63.0 62.5 63.75 62.75 63.0 62.75 62.5 65.0 64.0 63.5 64.0
a
Film Thickness for Vertical Tube Runs The theoretical film thicknesses of the steam films were calculated from the Nusselt equation (9) : M =
(%)"8
where M
= thickness of film, f t . J? = mass rate of flow per unit of tube periphery,
lb./hr./ft. viscosity at av. temp. of film, lb./hr./ft. = 2.42 X centipoises = density, lb./cu. f t . = acceleration due to gravity, 4.18 X lo8 ft./hr./hr.
p = p
g
This equation assumes a film of uniform thickness not subject to ripples or other irregularities. Kirkbride (6) made measurements of the thickness of oil and water films by means of a micrometer. In this investigation a micrometer with an accuracy of 0.001 inch was clamped onto the Pyrex jacket. A sharp-pointed
SEPTEMBER, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
1051
The theoretical average film thickness for several representative runs are also shown in Figure 4. That the measured thickness should prove to be much greater than the theoretical is due to the fact that the micrometer recorded the maximum thickness of the rivulets as they trickled down the tube wall in irregular paths.
Acknowledgment The authors wish to express their appreciation to M. R. Dean and N. Dunten for the assistance they gave by making some preliminary tests of a similar nature.
Literature Cited Baker, E. M., and Mueller, A. C., IND. ENO. CHEM.,29, 1067 (1937). Drew, T. B., Hottel, H. C . , and McAdams, W. H., Trans. Am. Inst. Chem. Engrs., 27, 271 (1936). Jakob, Max, Mech. Engr., 58, 643 (1936). Jeffrey, J. C., and Moynihan, J. R., Ibid., 55,751 (1935). Jurgensen, D.F.,Jr., and Montillon, G . H., IND.ENG.CHEM., 27,1466 (1935). Kirkbride, C. G., Ibid., 26, 425 (1934). Lucke, C. E.,i n McAdams’ “Heat Transmission,” p. 265, New York. McGraw-Hill Book Co.. 1933. Nagle, W. M., and Drew, T. B., Trans. Am. Inst. Chem. Engrs., 30, 217 (1933-34). Nuaselt, W., 2. Ver. deut. Ing., 60,541 (1916). Patterson, W. C., Weiland. J. H., Reeburgh. S. L., King. R. A.. and Huntington, R. L., Trans. Am. Socy Inst. Chem.-Engrs.; 33, 216 (1937). Wilson, E. E., Trans. Am. SOC.Mech. Engrs., 37,47 (1915).
0
FIGURE;4. MEASURED AND CALCULATED STEAMFILM
THICKNESS AS A FUNCTION OF Re INQ
FILM
= 4r/p FOR CONDENS-
extension, reaching into the steam jacket, made i t possible to observe the contact of the point with the steam film, a t which point a n initial reading was made. When the point was moved inward a low-voltage electric circuit indicated its contact with the iron tube wall. Figure 4 shows the results of measuring the steam film thickness a t three positions on the vertical tube and a t different flow rates. The position on the tube has a greater effect on the film thickness than the flow rate. With increasing steam rates the film became thinner near the top of the tube where the steam entered. At the lower positions on the tube the thickness of the film tends to increase slightly with the higher flow rates.
RECEIVEDApril 26, 1938. Presented before the Division of Petroleum Chemistry a t the 95th Meeting of the American Chemical Society, Dallas, Texas, April 18 t o 22, 1938. The d a t a of this paper are the results of work done by H. T. Quigg and W. C. Moyer in 1937 for their undergraduate theses i n chemical engineering a t t h e University of Oklahoma.
DEHYDROPOLYMERIZATION
OF ETHYLENE V. I. KOMAREWSKY AND N. BALAI Laboratory of Universal Oil Products Company at Armour Institute of Technology, Chicago, Ill.
By subjecting ethylene to catalytic polymerization in the presence of a polymerizing (phosphoric acid) and dehydrogenating catalyst, a directed conjunct polymerization takes place with increased formation of aromatic hydrocarbons. By subjecting ethylene to a thermal polymerization (no polymerization catalyst) in the presence of a dehydrogenating catalyst (nickel), aromatic hydrocarbons are formed. Both reactions might be called “dehydropolyrnerization.” These facts prove the correctness of the mechanism of ethylene polymerization suggested by Ipatieff and Pines.
I
N AN ARTICLE on the polymerization of ethylene in the
presence of phosphoric acid catalyst, Ipatieff and Pines ( I ) made the imDortant observation that the lirruid - Dolvmers . formed containeh olefinic, paraffinic, naphthenic, a n i aromatic hydrocarbons. The formation of these hydrocarbons was explained by the following successive reactions: 1. Polymerization of olefins. 2. Cyclization of olefins to naphthenes. 3. Dehydrogenation of naphthenes to aromatics. 4. Hydrogenation of olefins (formed according t o reaction 1) by hydrogen (evolved according to reaction 3) ;this hydrogenation results in the formation of paraffinic hydrocarbons.
This type of polymerization, where different types of hydrocarbons are formed, has been named “conjunct polymeriation” (2). If this mechanism is correct, i t might be possible to influence these successive reactions by directing them in some particular way. Of most practical interest would be the step whereby the naphthene dehydrogenation is increased in order to produce a larger amount of aromatics in the product. It is clear from the scheme presented above that the increased dehydrogenation will be followed by an increased formation of paraffin hydrocarbons which, according to the observation of the same authors, will be mostly of the is0 structure. Therefore a polymer with better motor properties might be produced by such directed conjunct polymerization.
