US2528623A - Low-temperature heater for heating air - Google Patents

Description

Nov. 7, 1950 P. G. VICARD Q 2,528,523

LOW-TEMPERATURE HEATER FOR HEATING AIR Filed.July 10, 1947 ummnmuuu unmmmmm llllllllllllllllll Patented Nov. 7, 1950 OFFICE LOW-TEMPERATURE HEATER FOR HEATING AIR Pierre Georges Vicard, Lyon, France Application July 10, 1947, Serial No. 760,056

. In France April 11, 1941 Section 1, Public Law 690, August 8, 1946 Patent expires April 11, 1961 4 Claims.

The present invention relates to low temperature heaters and has among its objects the provisions of simple construction and particularly economical utilization of the heat developed in the combustion chamber of such heaters.

The improvement essentially consists in arranging the flow of the combustion gases in such a manner that the same are first discharged from the combustion chamber into a primary heat exchanger, whereupon they pass for reheating around the combustion chamber in a passage formed between the double walls thereof, and thereafter the gases pass through a secondary heat exchanger and are then expelled in cooled state to the outside, normally by suction of a suitable fan.

' The novel features which I consider as characteristic for my invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection withthe accompanying drawings, in which:

The figure presents a sectional View, in schematic, of one embodiment of my invention.

A low temperature heater is illustrated in the drawing, comprising a hollow heating element made of refractory material and having on its interior a combustion chamber a. surrounded by double walls anddimensioned and equipped in accordance with the type of fuel used, which may be of solid, liquid or gaseous substance. A primary heat exchanger b is located adjacent to the exterior of the combustion chamber a-and is made of a metal of high thermal conductivity andcomprises tubes which are smooth on the inside and provided with fins on the outside; said g from the exteriorlof the heating element.

A secondary heat exchanger d, similar to the primary heat exchanger b, is located near the same and comprises tubes having a smooth surface on the interior and integral fins on the exterior; said tubes are connected with one end to the conduit for providing continuous communication therewith and are connected with the other end to a waste gas collector e. A fan i is provided adjacent to the waste gas collector e and arranged to provide an induced draught for the entire path of fumes for removing the combustion gases from the collector for discharge into a chimney.

Furthermore, the device comprises a shaft 9 housing the two heat exchangers b and d and adapted to direct over these exchangers a stream of cool air to be heated.

The operation of my device is as follows:

Owing to the reduced pressure provided by the action of the fan I, the gases are forced through the primary heat exchanger b .where their heat is given off, heating the cold air surrounding them. Thereafter, they arrive in a fairly cool state in the passage 0, adjacent to the combustion chamber a, and bypassing through the passage they absorb heat developed in the combustion chamber a. After being thus reheated, the gases flow through the tubes of the secondary heat exchanger d, therein giving off their heat, and are finally discharged through the chimney by fan action. I

Cool air is directed into the device by the duct g and is heated while passing over the exterior surface of the tubes of the two heat exchangers which areprovidedwith fins, as already setforth above, for increasing the exterior surface area and thereby promoting the rate of heat transmission.

The heat exchange occurs under particular conditions specified below. Only a portion'of the heat developed by combustion is taken along by the gases which transmit it by means of the primary heat exchanger 1) to the air to be heated; the other portion of the heat is absorbed by the walls of the combustion chamber which transmit it to the gases directed through the passage 0 therein, and is finally used to heat the air by means of the second heat exchanger d.

It is therefore possible to have a combustion chamber of high temperature, and to reduce excess air of combustion to a practically negligible value resulting in a high degree of efficiency of Combustion. Since on the other hand, the heat of combustion is in fact completely passed along to the cool air by the heat exchangers, the overall efiiciency of the heater is very high.

The rate of transfer. of heat between the hot gases and the heat exchangers, as well as that between the exchangers and the cold air, is proportional to the product of the surface area of heat transmission and the difference of temperature levels.

Transfer of heat between the hot gases and the heat exchangers takes place along the relatively small inner smooth surface of the tubes; hence the difference in temperature should be great. On the other hand, as the transfer of heat between the heat exchangers and the cold air takes. place along the outer surface of the tubes provided with fins and consequently relatively large, the difference in temperature may therefore be small. In view of the high thermal conductivity ooefficient of the metal from which the tubes are I made, it is possible, for practical purposes, to disregard the difference of temperature between the At the at a low cost by using commercial metals which are inexpensive and easily available.

The. heater may also be used without fan at a lower rate with natural draught action.

It will be understood that each of the elements described above, or two or more together, may also find. a, useful-application in other types of improvements, in low temperature heaters, differing from the types described above.

WhileI have illustrated and described the in.- vention as embodied in low temperature heaters, I do notintend. to. be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of my invention.

Without further analysis, the foregoing will so fully reveal the gist of my invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute. essential characteristics of the generic or specific aspects of this invention, and, therefore such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What. I claim as new and desire to secure by Letters Patent is:

1., In a low temperature heater, a heating element having on the interior a. chamber for fuel combustion and a passage around the same separated therefrom by a heat conductive wall surrounding said chamber; and a plurality of exposedheat exchangers each including a tube having a smooth interior surface and carrying fins on the exterior surface for providing a large surface area, and, each arranged so as to conduct gases through its interior and so as to be surrounded by the cool air to. be heated and to heat 4 with one end to said chamber and with its other end to one end of said passage for receiving combustion gases developed in said chamber and emanating therefrom at elevated temperatures and for conducting them to said passage, and another of said heat exchangers connected to the other end of said passage for conducting gases therefrom, said passage thus connecting said heat exchangers and adapted to conduct gases therebetween and adjacent to said heat conductive wall surrounding said chamber for causing, the gases to be reheated.

2. In a low temperature heater for heating air, a heating element having on the interior a chamvberfor fuel combustion and a passage around the same separated therefrom by a heat conductive wall surrounding said chamber, a plurality of heat fins-onthe exterior surfaces for providing large,

surface areas and each arranged to conduct gases through its interior and each surrounded by the cool. air to be heated; one of said heat exchangers connected with one end to said chamber and with its other end to one end of said passage for receiving combustion gases developed in said chamber and emanating therefrom at elevated temperatures and for conducting them to said passage; another of said heat exchangers connected to the other end of said passage for conducting gases therefrom, said passage thus connecting said heat exchan ers and adapted to conduct gases therebetween and adjacent: to said heat conductive wall surrounding said chamber for causing the gases to be reheated, and means arranged to admit the cold air to be heated. and to direct the same towards the exterior surface of said heat exchangers.

3. In a. low temperature heater for heating air, a heating element having on the interior a chamber for fuel combustion, and a passage around the same separated therefrom by a heat conductive wall, surrounding said chamber; and a plurality of exposed heat exchangers each arranged so as to conduct gases through its interior and so as .to besurrounded by the cool air to be heated and. to heat the same, one of said heat exchangers connected with one end to said chamber and with its other end to. one end of said passage for receiving combustion gases developed in said chamber and emanating therefrom at elevated temperatures and for conducting them to said passage, and another of said heat. exchangers connected to the other end of said passage for conducting gases therefrom, said passage thus connecting said heat exchangers and adapted to conduct gases therebetween, and adjacent tosaid heat conductive wall surrounding said chamber for causing the gases to be reheated.

4. In a low temperature heater for heating air, a heating element having on the interior a. chamber for fuel combustion and a passage around the same separated therefrom by a heat conductive wall surrounding said chamber, a plurality of heat exchangers each arranged to conduct gases through its interior and each surrounded by the cool air to be heated; one of said heat exchangers connected with one end to said chamber and with its other" end to one end of said passage for-receiving combustion gases developed in said chamber and emanating therefrom at elevated temperatures and for conducting them to said-passage; anotherof said heat exchangers connected to the; other end of: said passage for conducting gases therefrom, said passage thus connecting said heat exchangers and adapted to conduct gases therebetween and adjacent to said heat conductive wall surrounding said chamber for causing the gases to be reheated; and means arranged to admit the cold air to be heated and to direct the same towards the exterior surface of said heat exchangers.

PIERRE GEORGES VICARD.

REFERENCES CITED The following references are of record in the file of this patent:

Number 0 Number 6 UNITED STATES PATENTS Name Date Evans Apr. 25, 1893 Keller Dec. 10, 1940 Nelson Sept. 2, 1941 Gygi July 10, 1945 FOREIGN PATENTS Country Date Switzerland T Sept. 1, 1944

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