US2029450A - Heat exchanger - Google Patents

Description

I Feb. 4, 1936. I H, c TRUELSEN 2,029,450

HEAT EXCHANGER Filed Dec. 3, 1932 2 Sheets-Sheet 1 Feb. 4, 1936.

H. c. TRUELSEN HEAT EXCHANGER Filed Dec. 3, 1932 /MM M 2 Sheets-Sheet 2 P atented Feb. 4, 1936 UNITED STATES PATENT OFFICE HEAT EXCHANGEE Heinrich Christian Truelsen,

Crefeld, Germany,

assignor to the firm Liesen & 00., Crei'eld, Germany 7 Claims.

This invention relates to a heat exchanger .consisting of tubular elements arranged in groups, which may be used as an air-heater or as a pre-heater for boiler feed water (economizer), for utilizing the heat contained in furnace gases for pre-heating combustion air or feed water.

By means of such a heat exchanger the waste gases from Diesel engines may be utilized for heating and drying purposes. Apparatus of this type can beused in the chemical industry for heat exchange between two gases, for example,

sulphur-dioxide and sulphur-trioxide in the manufacture of sulphuric acid. The object of the invention is to provide a heat exchanger having high thermic efl'iciency and weight and space requirements considerably inferior to those of prior'installations, whereby the manufacturing costs are much reduced.

Air heaters and pre-heaters for boiler feed water arranged in the path of the waste gases of a furnace are already known. They consist of a number of tubular elements arranged in groups and having smooth walls. In smooth tubes of air-heaters, the wall of which is situated between two heat-exchanging gases, stagnatingboundary layers of the gases are formed, on the inner side and on the outer side of the tubes extending concentrically to the tube wall. These stagnating boundary layers exert an insulating eflfect upon the heating gases as well as upon the air to be heated whereby the heat transmission is greatly impeded. Asimilar phenomenon occurs on the side of the heating gases in pre-heaters for boiler feed water having smooth walled tubes. To avoid this shortcoming it has been proposed to provide ribs on the outer side of the tubes of air-heaters and pre-heaters, in order to enlarge the heat exchanging surfaces.- It,

has been also proposed, to arrange ribs in air heaters on the outer surface and on the inner surface of the tube in order to increase the heat exchanging surfaces, and also the flowing speed of the air. In this arrangement insulating boundary layers are, however, still formed on the gas side and prevent the best possible utilization of the heat contained in the heating gases.

In the heat exchanger according to the invention the tubular elements have needle-like projections on one side or on both sides of the tube wall, which produce eddy currents in the flow of the heat exchanging gases and thereby prevent the formation of stagnating boundary layers, so

that the heat exchange is increased to a multithe needles are preferably arranged both on the inner side and on the outer side of the tubes, but

in pre-heaters for boiler feed water only on the as side in order not to increase excessively the resistance to the flow of water. Flowing water has not the tendency of a gas to form insulating boundary layers and has a higher heat transmission coeflicient than gas. Stoves for heating rooms have beenalready lmown having a device in the charging door for supplying pre- 1 heated secondary combustion air. This device consisted of several chambers projecting into the charging shaft mounted one behind the other, the inner wall of the chambers being provided with needles. These needles provided 15 only on one .side serve, however, merely for enlarging the heat transmitting surface.

In the heater according to the invention eddy currents are produced by the needles of the airheater on both sides of the tube wall and in 20 pre-heaters for boiler feed water on the heat absorbing side, said eddy currents preventing the production of insulating boundary layers along the surfaces of the heat passage. For this purpose it is also necessary, that the distance be- 25 tween the needles should be within certain limits, an average spacing of 20 mms. or less having been found to be most favorable. By the formation ofeddy currents the deposition of soot and flue ash on the needles is also considerably re- 0 duced. If the heating gas is conducted from above to below only the top surface of the needles is covered, after a longer period, with a narrow soot strip the rest of the surface remaining clean. 5

It is advisable, to use in air heaters needle like projections adapted to the specific heats of the heat exchanging gases on both sides of the tube wall. These projections may be of similar or of different lengths, so that the heat ab- 40 sorption on one side of the wall is equal to the heat radiation on the other side'of same.

- The tubular elements of the air heaters according to the invention have box-like enlargements at the ends, said enlargements, known 45 per se, being fitted with mutually abutting flanges and packing inserts. Each box-like enlargement has a flange-like, fashioned rim, which, when the tubular elements are united, bears tightly against the corresponding rim of the adjacent enlarge- 5 ment, a groove designed to receive a packing insert being arranged beside the outer side of this rectly inserted between the end flanges of the tubular elements arranged by the side and on top of each. other. Consequently, these packing inserts have been exposed to the destructive infiuence of the heating gases. This danger is eliminated according to the principles of the present invention; by providing box-like enlargements having flange-like rims at the ends of the tubular elements. These rims are tightly fitted to each other and a groove for packing is provided between them in which the packing is protected against the detrimental influence of the heating gases.

In order to impart to the heating elements of pre-heaters for bofler feed water a high resistance against internal over-pressure, cylindrical tubes situated the one'above the other are united in one cast body. In this case the needles are preferably cast on ribs, which in turn, form one cast body with the heating elements. The tubes united in one cast body extend either up to their ends parallel, the one at the side of the other or they merge at each end into a common discharge tube. In the last mentioned form of construction the well known single passage return bends may be used for connecting the several heating elements, whereas the first mentioned arrangement requires the employment of single passage return bends with two concentric channels extending along a semi-circle. It' :is also possible to employ as heating elements smooth cast or forged iron tubes on which the cast iron rings having radially projecting nee- "dles are fitted at cold or hot state. It may be further mentioned that all the devices of the kind described may be used in similar manner for cooling purposes in condensers, ice machines and the like.

Several embodiments of the invention are i1- lustrated by way of example in the accompanying drawings in which:

Fig. 1 shows in side elevation a heatexchanger tionof a modified embodiment of the invention;

Fig. 8 depicts a cross section taken on the line 8-8 of Fig. 7;

Fig. 9 shows a longitudinal section, somewhat fragmentary, of a connecting piece for a heating element according to the invention.

The heat exchanger, which is, for instance, built as an air heater into a shaft a through which the flue gases flow in the direction of the arrow :c, consists of two groups of tubes b and .0 each of which is composed of parallel tubular elements d. To the one end of the air heater the pressure tube e of a fan I. supplying to the heater the air to be heated, is connected to the lower group of heating tubes b, the discharge pipe g for discharging the heated air being connected on the same side of the air-heater to the upper group of heating tubes c. The opposite and faces of the groups band 0 are-connected the one to the other by a chamber h. The air to be heated is therefore conducted in cross or transverse flow relative to the flue gases. The apparatus may however be constructed so that the air to be heated is conducted in the same direction or in counter flow to the heating gases.

In order to facilitate the uniting of the tubes at to form groups. the tube ends have box-like enlargements i of rectangular or square shape. The enlargements i may be three cornered or the heat contained in the waste gases, the tubes d have needle-like projections m, n on each side of their walls to ensure a goodheat transmission. The needles m, 11 may be either of the same length or of diiferent lengths according to the temperature of the outflowing flue gases and to the nowing speed of the air to be heated.

The tubes d as shown in Fig. 4 areof fiat. oval cross section with two long-stretched parallel sides and rounded ends. Owing to this construction it is possible to give to the needle-like projections during the casting a mutual parallel position.

By the rounded edges of the'tubes d the resistance against flow opposed'to the waste gases by these tubes, is decreased in a considerable measure.

The enlargements i have on the outer side a circumferential raised rim 0, which is ground perfectly plane and at the side of which a cir-' cumierential groove :1 is arranged designed to hold a packing insert (1 of asbestos or similar material. During the tightening of the screws 1 the adjacent rims o of two tube elements are tightly pressed the one against the other. The packing insert q is consequently strongly compressed and partly pressed into the narrow gap existingnbetween two enlargements i. on the one hand a good packing is obtained in this manner and on the other hand it is attained that the construction height of each tube group can be accurately determined. The packing inserts q are perfectly protected by the rims 0 against the destructive influences of the heating gases.

The heating element shown in Figs. 5 and 6 is principally designed to serve in pre-heaters for boiler feed water. Itconsists of a cast body r comprising two cylindrical tubes 8 and t situated the one above the other and separated by 'a horizontal partition u. The two tubes sand t merge at each end into a common tubular end :2. Connecting flanges w are cast on the ends of the cast bodies r adapted to receive a packing insert and having a circumferential groove 11. On

' the cast bodies 1: ribs 2 are cast, which have on both sides parallel needles iii. The needles iii might be cast directly on the heating elements 1', but the arrangement of the ribs allows to accommodate on approximately the same space a. greater number of needles. For technical reasons and with regard to resistance it is advisable, to provide the ribs t as the needles are all of the same length.

The needles I ii in combination with the ribs permit the obtaining of a very intensive heat utilization and high thermlc efiiciency with the economizer. Consequently, with the same efficiency, a saving of space-0f.ab0ut65%, a reduction of weight by 30 to 40% and a reduction of manufacturing cost of about 40% are obtained in comparison withthe conventional installaequal inner cross section. Owing to the fact that the individual tubes' tions.

The combination of several tubes in one cast body has the following advantage. A single tube, the cross sectional area ofwhich is as great as the total cross section of the two tubes 8, 1!, must have a correspondingly larger diameter. The

larger the diameter ,of the'tube is, the less is its strength against excessive intemal pressure. Consequently, the tubes in the arrangement according to the invention can be submitted to a much higher pressure than a single tube of merge at the ends into common tubular flanged ends a the commonly used single passage return bends can be utilized for connecting the heating element. This increases the security of service since only a small'number of flanges and packings are required.

In some cases it is preferred to use tubular elements of circular cross section. A modified embodiment of .the' present invention employing such tubular elements is illustrated in Figs. 7 and 8. As appears from the drawings, a cast iron ring I is shrunk on a smooth tube H of cast iron or forged iron, the said ring being provided with radial needles I0.

. I claim:- i

4 l. A heat exchanger arranged in a furnace or other source of heat in the path of the waste gases, comprising in combination heating elements, united in groups, ribs on said heating elements forming one cast-piece with their heating element, and needles cast on said ribs.

2. A heat exchanger adaptedto be located in the path of heated fluids, comprising heating elements and needles projecting from ring-like reinforcements integral with the walls of the said elements laterally to the path of said fluids adapted to create eddy currents in the flow of said fluid whereby the formation of insulating boundry layers is prevented. I 3. A heat exchanger adapted to be located in the path of heated fluids, comprising heating elements and needles integral therewith projecting from ring-like reinforcements integral with the walls of said elements. laterally to the path of said fluids.

4. A heat exchanger adapted to be located in the path of heated fluids, comprising heating elements adapted to be arranged in groups and needies integral therewith projecting from ring-like reinforcements integral with the walls of said elements laterally to the path of said fluids.

5. A heat exchanger adapted to. be located in the path of heating fluids, comprising tubular heating elements arranged in groups, .cast rings shrunk on said elements and needles integral with said rings projecting therefrom at an angle to the path of said fluids adapted to create eddy currents in the flow of said fluid whereby the formation of insulating boundary layers is prevented.

6. On a heat exchanger located in the path of heated fluids including tubular heating elements adapted to be arranged in groups, the improvement which comprises concentric rings surrounding said elements and needles integral with said rings projecting radially at an angle to the path of said fluids, said needles being arranged sufliciently close together to produce eddy currents in the flowing fluid whereby the insulating boundary layers of said fluid are dissipated.

7. In a heat exchanger, the combination which comprises tubular heating elements adapted to be located in the path of heating fluids, reinforced portions on the walls-of said heating elements, and needles integral with said reinforced portions projecting from each'side of said walls..

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