US2217595A

US2217595A - Electric immersion heater

Info

Publication number: US2217595A
Application number: US256020A
Authority: US
Inventors: John D Morgan; Percy B Levitt
Original assignee: POWER PATENTS CO
Current assignee: POWER PATENTS CO
Priority date: 1939-02-13
Filing date: 1939-02-13
Publication date: 1940-10-08
Anticipated expiration: 1957-10-08

Description

Get. 8, 1940 J D MORGAN ET AL 2,217,595

-ELECTRIC IMMERSION HEATER Filed Feb. 13, 1939 IN EN P E R C sf L 3 1 v 3 ATTORNEY Patented Oct. 8, 1940 PATENT OFFICE ELECTRIC IMJVIERSION HEATER John D. Morgan, South Orange, and Percy B. Levitt, Millburn, N. 3., assignors to Power Patents Company, Hillside, N. 1., a corporation of Maine Application February 13, 1939, Serial No. 256,020

2 Claims.

The present invention relates to electrical heating devices, and more particularly to an electrical heater adapted for immersion in liq-- uid for the purpose of heating the same.

A particular object of the invention is to pro vide an electric immersion heater which is adapted for heating the lubricating oil supply of an airplane to a. predetermined maximum temperature.

With the aforesaid object in view, the present electrical heater has been designed to meet therequirement of an electric heater which shall be compact in size, light in weight, eiilcient in developing and transferring heat to the liquid in II which it is immersed, and of suchconstructlon as to withstand, without injury to its parts, the vibrational and other shocks and jars to which it may be subjected while in use in an airplane oil tank.

3 With the above and other objects and few tures in view, the invention comprises the 1m proved immersion heater which is hereinafter described and more particularly defined by the accompanying claims.

8 The various features of the invention are illustrated by the accompanying drawing, in which:

Fig. 1 is a longitudinal sectional view of a preferred design of heater immersed in a receptacle of oil or other liquid to be heated.

Fig. 2 is a cross sectional view of the heater taken on the line 2-4 of Fig. 1;

Fig. 3 is a cross-sectional view of the heater taken on the line 3-3 of Fig. l;

Fig. 4 is an enlarged longitudinal sectional view of a small portion of the heater illustrating the dielectric coatings for the resistance element.

Referring to the drawing, Fig. 1 illustrates w a heater Ill of the preferred type submerged in oil or other liquid in a tank It having walls It. Since one requisite of the heater is mechanical strength to withstand shocks, it is provided with a strong dielectric refractory core it which pref- 5 erably has the form of a cylindrical tube with a central longitudinal bore It. A preferred refractory material for the construction of this core is a mixture of about equal parts by weight of natural and milleagratn zircon which has been heat bonded by the reaction products supplied by about 6% of the weight of the zircon of orthophosphoric acid.

The heating element consists of a helical coil of wire I! wrapped with many turns about the periphery of core I4 throughout its length. In

order to provide a compact heating device of high heating efficiency, the element is pref erably made of small diameter high temperature resistant alloy having closely spaced turns. A preferred wire is one of about #22#26 gauge 8- made of an alloy of 30-40% chromium, l-8% aluminum, 0 5% cobalt and the balance iron. In order to obtain close spacing of the turns of wire along the length of the core-without short circuiting the wire may be protected before it) wrapping it around the core in constructing the heater, by applying a high voltage heating current thereto in an air or other oxidizing atmosphere, whereby a metal oxide film 26! (Fig. at is built up on the surface of the wire throughout its length. As an additional precaution against short circuiting of current between in dividual turns of the wire coil or hetweeri wire and a metal casing 22 of the heater a low temperature 11 dial coating M is built up on 5 Us. the wire wrapped core and hardened by halting thereon, as a step in the construction. of the heater. The thickness of coating 24 around. the wire coil is preferably only sufficient to insure 9& against shorting to the casing 22. A preferred material for the coating is a mixture of milled grain (under 300 mesh) zircon and 30% natural grain (thru 40 mesh) zircon bonded with 6% P205 and 2% chromic acid. This coat- 30 ing can be hardened by baking at a temperature as low as 600 F.

After wrapping the oxide coated wire ll around the core H and applying and baking the dielectric coating 24. the ends of the coil of wire 85 I8 are connected to lead-in wires 28, and the resulting unit is inserted within the metal casing 2!. Wires 26 are shown extending to a thermostat switch" on the outside of tank 92 through a tubular extension 30 of casing 22. The wires 40 28 are mounted within casing 30 in protective dielectric tubes 32 of porcelain or other suitable refractory; tubes 32 being rigidly centered within the casing by a heat bonded dielectric refractory filling 34 which physically bands the 4;; tubes 32 and casing 30 together. The rei'rae tory shell 34 may preferably be made of the same refractory material employed in the coating 2|, and should be Joined integrally with the coating 24 at the heater end of the tube 30, as 5s illustrated.

After inserting the wire wrapped and coated core in the casing 22 in the position illustrated, the next step in the construction of the heater is to fill the annular space between the inside 55 -of the tank ll.

surface of the casing 22 and the outer surface .gof the coating 24 with a highly heat conductant compactly tamped dielectric powder filling 36. A preferred material for the filling 36 is prepared by first heating finely divided (thru 150 mesh) ferrosilicon powder silicon) in an oxidizing atmosphere to a temperature of 2350" F. while agitating the powder to build up an oxide coating or film on the individual grains. The purpose of thus imparting an oxide coating to the particles is to increase the dielectric properties of the powder-and accordingly this step may be omitted in c ase the coating 24 is thick enough to insure against shorting of current between the resistance coil and casing 22. The powdered ferrosilicon is compactly tamped in the space between casing 22 and coating 24-as by vibrating the unit while introducing the powder. Before sealing the heating unit by welding an end plate 36 to the casing 22, electric current is preferably applied to the wire coil ill in amount sufiicient to thoroughly heat and dry out all parts thereof, including the packed powder filling 36. The sealed casing 22, together with the powder filling 66, is designed to afford a highly heat conductant, corrosion and leak age-proof housing for the resistance coil, with suflieient strength and flexibility to protect all parts of the heater against breakage and injury.

The heating unit is supported within the tank H by being clamped by means of a nut 40 .to a metal cap 42 having threads on its periphery which engage threads in a metal ring 44 which is in turn inserted in a circular aperture in one of the tank walls I2 and may be welded in place. A circular metal plate 46 is tightly fitted in an annular recess formed by shoulders 46 on rearwardly projecting extensions of cap 42; plate 46 forming the base of a housing for the switch 26. The leads 26 are connected through the switch with a cable 50 leading from a source of electric current.

An open ended tubular metal well 52 has its side walls at the open end welded'or otherwise connected by a sealed joint. to the plate 42. The closed end of the well 52 extends into an annular chamber 54 lying between the outer wall of extension 30 of casing 22 and the inner wall of an open ended metal shell 56. The rearward end of shell 56 is threaded to engage threads on an annular forwardly projecting shoulder 56 of cap 42. One or more apertures 60 are provided in the rearward side walls of shell 56, communicably connecting chamber with the interior A plurality of webs 62 extend inward radially from the forward inner wall of shell 56 to form a plurality of longitudinal groove passages 64 for circulation of liquid in a plurality of streams from one end to the other of shell 56 in intimate heat transfer contact with heater casing 22. This construction-permits rapid circulation of the liquid over the heater surface without formation of eddy currents.

The switch 28 is designed for operation as a thermostat switch whereby to limit the maximum temperature to which the liquid in the tank I l is heated. The mechanism for automatically opening the switch to cut oil the supply of current to the heater when the liquid has reached a predetermined temperature may be broadly des ignated as a vapor tension Sylphon. The essential elements of this mechanism consist of a small vapor expansion chamber 66 formed on the switch side of an aperture 68 in plate 46 and lying between the plate and a flexible spring metal disc diaphragm HI; together with a liquid filled metal capsule 12 mounted in well 52 with wardly against an adjustably hinged leaf spring 76, one end of which is hinged to a shoulder of plate 46 by a screw I6. The other end of spring 16 has an aperture or slot through which passes a bolt 60, one end of which is aflixed to the plate 46, while the other end carries a nut 62 which serves as an adjustable shoulder for one end of a coil spring 64. The other end of spring 64 holds leaf spring 16 under adjustable compression out of contact with an actuating pin 66 for the switch 26. Switch 26 is operative to hold a closed circuit connection between the terminals of the cable 50 and the leads 26 for heater III,- while the vapor tension Sylphon operates to open the circuit by forcing spring 16 and pin 66 upwardly against the adjustable tension of spring 84, when the vapor tension in the Sylphon is high enough.

Capsule 12 of the Sylphon unit may be filled with water, alcohol, ether, various alcohol-water mixtures, or other organic or inorganic liquids having boiling points approximating the predetermined maximum temperature to which the oil or other liquid in the tank is to be heated. For example, the capsule of a Sylphon employed with a heater which is designed for keeping lubricating oil at a temperature of -140 F. may be filled with ether.

The invention having been thus described, what is claimed as new is:

1. An electric immersion heater comprising a rigid bonded dielectric refractory core, a helically coiled metal resistance wire surrounding and supported by said core, a thin bonded dielectric heat conductant refractory coating embedding said wire coil, a flexible shock absorbent heat conductant dielectric filling surrounding the bonded refractory coating of the coil, and a sealed tubular metal casing in contact with the outer surface of the flexible dielectric filling and enclosing the element, together with a tubular metal shield disposed in closely spaced relation around the heater casing and having a plurality of radially arranged longitudinal grooves in the inner wall thereof together with side wall apertures for circulation of liquid to be heated in contact with the heater casing.

2. Apparatus as defined in claim 1 in which said flexible dielectric filling between the refractory coated coil and the outer metal casing comprises finely ground ferrosilicon powder each grain of which is coated with an oxide film.

JOHN D. MORGAN. PERCY B. LEVI'I 'I.