US 2279548 A
Description (OCR text may contain errors)
April 14, 1942. E. G. BAILEY 2,279,548
LIQUID vAPoRIzING TUBE Filed June 11, 195s 3 Sheets-sheet 2 INVENT OR.
Apri-1 14, 1942. Y @may 2279.548*
LIQUID vAPoRIzVING TUBE INVENTOR Ervin aviley' l ATTORNEY.
Filed Junen, 193s'. s sheets-sheet 3'" I v Patented Apr. 14, i942 UNITED STATES PATENT OEI-ICE l l LIQUID VAPORIZING TUBE Ervin G. Bailey, Easton, Pa., assigner to The Babcock & Wilcox Company, Newark, N. J., a corporation of New yJersey Application June 11, 193s, serialize. 213,130
steam generating tubes of a steam generator which in view of their location relative to the furnace normally absorb heat at relatively high rates. i x
In the operation of a water tube steam boiler, for example, it is essential to operation that water flow through the inside of each steam generating tube while heat is being received by the tube on its outer face. Steam is formed in the water inside of the tube, and at successively ,greater distances along its length there 4will be an increasing fraction of the flowing uid in the form of steam and a decreasing fraction in the form of water, depending upon the rate of heatl absorption. When steam flows with water inside' of a tube it may have any one of several different physical relations with the water. The steam may be uniformly distributed in the ,form of small bubbles inthe flowing water, the bubbles originating on the tube inner wall surface and being detached therefrom by various local forces, or in the form of large bubbles more or less uniformly distributed, or in the form of segregated steam and watermasses alternating along the tube length or in other forms. When the `vo1 umetric ratio of steam to water is quiteV large the water may be more or less uniformly distributed through the steam as a fog or mist, or as a nlm on the inside of the tube wall, or as a more or' less segregated parallel stream. Such a film or layer of water may be uniformly distributed around the tube circumference at `any given cross-section of the tube, or over only a part of the tubeinner wall surface. Under the latter condition the part of the inner wall surface notv in contact with the water will be dry, while the part that is in contact will be wet.
It is well known that the wall metal temperature of a steam boiler water tubewill not Arise,
- through the metal of the tube wall due to the contact of hot gases or radiation from the furnace. It is also well known that when any part of the inner wall surface of a tube is dry that portion of the tube wall will tend to overheat and be damaged even with moderate heat transfer rates, in spite ofthe fact that other wall' parts adjacent toit, either circumferentially or longitudinally, may be at safe temperatures with even higher heat transfer rates because of local wetness of those wall parts. This fact limits the average heat transfer rate and the generating capacity of the whole tube. `This limitation becomes most severe if the heat transfer rate varies circumferentially of a tube that is not internally wet over its whole circumference and the more intense heating is applied to the dry portion of the tube wall. i
The main object of my invention ,is the provision of an improved construction of a tubular vapor generating element which is characterized by simple and effective means lfor insuring substantially uniform circumferential distribution of the `liquid in a liquid-vapor stream flowing therethrough over the inner wall vsurface of thel vapor generating element irrespective of the position of the tube and without requiring any, distortion of the tube or substantial weakening` of `the tube wall and without 'materially increasing its-cost of manufacture or installation. A further and' more specic object is an improved wall construction of a steam generating tube of cir-I cular cross-section ofthe character described which is adapted for'use in parts of the steam generator where the enclosed fluid has a vhigh ratio of steam to Water by volume andv the tube is mainly heated over only part of its circumferential area. y.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a partA of this specification. Fora better understanding of the invention, its ,opnzrating advantages and specific objectsattained vby itspusve, reference should be had to the accompanying drawings and descriptive matter inwliich I have. illustrated and described a preferred embodiment of my invention. y
0f the drawings: l .n
Fig. 1 is a transverse section of a vapor gen.- erating tube Aconstructed in accordance with my invention;
Fig. 2 Vis a view oa portion of the-wall of the tube shown in Fig. 1 ,magnified twenty times;
Fig. 3 is a developed view of the inner wall surface of the tube shown in Fig. 1
'is a-sectional elevation of a forced dow steam generator in which the invention is adaptcirculation steam 'generator adapted to incorporate the invention, and
Fig. 6 is a somewhat diagrammatic view of a tube coil constructed in accordance with the invention.
In accordance with my invention, the tubular vapor generating element is formed of suitable carbon or alloy steel tubing of circular crosssection having a smooth outer wall surface Il, although studs or other forms of extended surface may be applied thereto if desired provided that the inner wall surface is not distorted in The inner wall surface II of the tube is formed throughout its length, or a predetermined portion thereof, with a circumferentially arranged series of slightly separated parallel-continuous grooves I2 of helical form, preferably formed by riding the tube with relatively shallow grooves of approximately rectangular cross-section having a relatively -high pitch. With this formation lthe grooves will be separated by lands I3, the sides of which dedne the adjacent sides of the adjoining grooves.
- By way of example and not of limitation, the tube shown is of 11/2" O. D. with a wall thickness of .125 and the riding having helical grooves .0375" in width and .015" depth,` adjacent grooves being separated by lands .025" in width.
The riding consists of 53 grooves and lands arranged `witha pitch of 7%", which when developed as shown in Fig. 3, will have a base angle a of approximately 60.
The tube specidcally described is especially designed for use as a wall tube in the upper wall portion and burner throat of the furnace of a forced dow high pressure steam generator having small liquid and heat storage capacity, such as illustrated in Fig. 4 and disclosed in my. pending application Serial No. 113,060, dled November 27, 1936. Y
The rided tubes of my invention are also adapted for effective use in natural circulation steam generators, such as shown in Fig. and disclosed in a pending application of R. Shellenberger, Serial No. 137,158, died April 16, 1937,
and other forms of .vapor generators, where the o vapor generating tube conditions render the use of rided tubes desirable in all or a portion of the vapor generating,V section thereof.
In the installation of rided steam generating tubes of the character'described in a water tube steam boiler, such tubes will be located in the part or parts of the circulation system where thev duid stream has a high ratio of steam to water by volume. By a high volumetric ratio of steam to water, I have in mind a steam fraction of at least 75% of the duid stream and usually 'substantially greater. My invention'will be foundhighly effective even when the volume of water flowing through a rided tube is only sudicient to partly dll the wall grooves I2.
In the operation of a water tubeboiler with rided tubes, the outer layer of the dowing duid cause a circumferential motion in at least part of it. When the ratio of steam to water by volume has become high enough the water that might otherwise fail to be uniformly'distributed circumferentially and dow along the bottom of a horizontal tube or the outside of a bend in a tube, for example, will be caught by the riding that would cause damage by overheating if plain tubes were substituted.
In cases where the unevaporized water is small .in amount and would tend to flow along the bottom of a horizontally arranged plain tube, one
side of which is subjected to more intense heating, in a rided tube similarly arranged the riding would cause the bottom stream of water to be lifted and to sweep the highly heated side. 4In such cases it is desirable that the riding be left or right-handed according to in which direction the lifting of the water from the bottom would be least, i. e., the riding should be arranged so that the rotary movement of the water will be in the direction from the bottom toward the heated side. Where tubes are arranged in coils consisting of parallel tube legs with opposite reverse bends at oppom'te ends; the tube legs can be advantageouslyformed, as shown in Fig. 6, by tubes rided alternately left and right-handed to secure proper distribution of the liquid after dowing through the reverse bends.
, The use of the tube wall construction described for the/high temperature generating section of a vapor generator will substantially increase its operating capacity in cases where the use of is dedected by the riding in such a way as to plain tubes in this location necessitated operation at reduced capacity for high availability and economic maintenance. It has also been found that riding of the character described edects a decrease in the pressure drop through the tube at high mass dow rates of the duid stream, as compared to that in plain tubes. The character of riding particularly adapted for the most effective use of the invention docs not decrease the dow area of the tube, or materially weaken the tube wall.
While in accordance with the provisions of the statutes I have illustrated and described herein the best form of the invention now known to me, those skilled in the art will -understand that changes may be made in the form of the tube disclosed without departing from the spirit of the invention covered by my claims, and that my invention may sometimes be used to advantage over only a portion of the tube wall area.
l. A vapor generating tube coil consisting a series of side-by-side tubes of circular crosssection serially connected at their opposite ends by reverse bends, adjacent tubes having their inner wall surfaces lternately rided in opposite dlrections.
2.- As a new article of manufacture, a vapor generating tube for conducting a vaporizable liquid and its vapor having a circular cross-section and a series of shallow helical grooves formed in its internal wall surface and uniformly spaced circumferentially of the tube, said grooves being constructed of a size and shape providing an unobstructeddow area at least of the total dow area of the tube and a tube internal surface 3. As a new article of manufacture, a vapor generating tubev for conducting a vaporizable liquid and its vapor having a circular cross-section and a multiplicity of continuous helical grooves` *l liquid volumetric ratio having a circular crosssection and its internal wall surface formed in a multiplicity of alternating continuous helical grooves and lands of a relatively high uniform pitch and uniformly spaced circumferentially of the tube, said grooves and lands being constructed of a size and shape providing an unobstructed tube flow area at least 90% of its total flow area, a groove depth not more than of the maximum internal tube radius, and a tube internal surface area not more than twice the internal surface area of an ungrooved tube of the same maximum internal diameter.
5. In a vapor generator, a substantially horizontal vapor generating tube of circular crosssection arranged to receive heat mainly. on one side thereof and normally conducting a vaporizg able liquid and its vapor, said vapor generating tube having its internal wall surfacev formed in a series of shallow helical grooves pitched in a direction tending to cause liquid in the bottom of .the tube to be lifted along the highly heated side of the tube and uniformly spaced circumferentially of the tube. and said grooves being constructed of a size and shape providing an unobstructed flow area of the tube at least 90%l of its total now area.
6. In a vapor generator, a furnace, a substan" tially horizontal vapor generating furnace wall tube of circular cross-section arranged to receive heat mainly on one side thereof at relatively high rates of heat absorption and normally conducting a vaporizable liquid and its vapor in a high vapor-liquid volumetric ratio, said furnace wall tube having its internal wall surface formed in a multiplicity of shallow helical grooves of uniform pitch in a direction tending to cause liquid in the bottom of the tube to be lifted along the highly heated side of the tube and uniformly spaced circonstructed of a size ands'hape providing an unobstructed tube flow area at least 90% of its total ow area, a groove depth not more than 10% -of the maximum internal tube radius, and a tube internal surface area not more than twice the internal .,surfacearea of an ungrooved tube of the same maximum internal diameter.
7. In a vapor generator, a vapor generating tube of circular cross-section arranged to receive heat at relatively high rates of heat absorption and normally conducting a vaporizable liquid and its vaporin a high vapor-liquid volumetric ratio,
said vapor generating tube having its internal wall surface formed in a multiplicity of shallow helical grooves of uniforml pitch and uniformly 'spacedcircumferentially of the tube, said grooves providing an unobstructed tube flow area atv least of the total ow area, and a tube internal surface area not more than twice the internal surface area of an ungrooved tube of the same maximum internal diameter.
8. In'a vapor generator, a furnace, a vapor generating furnacewall tube of circular crosssection arranged to receive heat from said furnace at relatively high rates of heat absorption and normally conducting a high velocity stream of a vaporizable liquid and its vapor in a high vapor-liquid volumetric ratio, said vapor generating furnace wall tube having its internal wall surface formed in a multiplicity of alternating continuous helical grooves and lands of relatively high uniform pitch and uniformly spaced circumferentially of the tube, said grooves and lands providing an unobstructed tube flow area at leastv 90% of its total flow area, and a tube internal surface area not more than twice the `internal surface area of an ungrooved tube of the same maximum internal diameter.
9. In avapor generator, a vapor generating. tube of circular cross-section arranged to receive heat mainly on one side thereof and normally conducting a high velocity stream of a Vaporizable liquid and its vapor in a high vapor-liquid volumetric ratio, the internal wall surface of said tube having a multiplicity of continuous. shallow than twice the internal surface area of an uncumferentially of the tube, said grooves being grooved tube of the salme maximum vinternal diameter.
ERVIN G. BAILEY.