US3244860A

US3244860A - Heaters for gases

Info

Publication number: US3244860A
Application number: US261696A
Authority: US
Inventors: Lindley Bryan Charles
Original assignee: CA Parsons and Co Ltd
Current assignee: CA Parsons and Co Ltd
Priority date: 1962-04-26
Filing date: 1963-02-28
Publication date: 1966-04-05
Anticipated expiration: 1983-04-05
Also published as: GB992916A

Description

April 1966 B. c. LINDLEY 3,244,860

HEATERS FOR GASES 2 Sheets-Sheet 1 Filed Feb. 28, 1963 B. C. LINDLEY HEATERS FOR GASES April 5, 1966 2 Sheets-Sheet 2 Filed Feb. 28, 1965 United States Patent 3,244,860 HEATERS FOR GASES Bryan Charles Lindley, Newcastie-upon-Tyne, Nor-thumberland, England, assignor to C. A. Parsons & Company Limited Filed Feb. 28, 1963, Ser. No. 261,696 Claims priority, application Great Britain, Apr. 26, 1962, 16,043/62 3 Claims. (Cl. 219-374) This invention relates to heaters for gases, and is particularly applicable to systems in which it is necessary to keep the pressure drop at a minimum and the tolerable pressure drop across the heater is such that turbulent flow of gas through the heater is not permissible, it can however be used in turbulent flow conditions, in other words, whilst the heater is particularly suitable for systems where it is necessary to keep pressure drop at a minimum or the pressure drop is such that turbulent fiow is not permitted the heater can be used under conditions where flow conditions are turbulent.

The object of the present invention is to provide a heater for gases which is relatively simple and inexpensive to make and which has good heat transfer properties with a minimum of pressure loss.

The invention consists in a heater for gases comprising a casing and a metal electrical resistance heating element within the casing, the element being of metal mesh strips orientated so that they are parallel or substantially parallel to the axis of the heater.

The invention also consists in a heater in accordance with the preceding paragraph in which several of said elements are arranged one Within the other in spaced relation in the casing and connected electrically in parallel.

The invention also consists in a heater in accordance with either of the preceding paragraphs in which the strips are tilted so as to be parallel to the direction of gas flow at entry to the mesh or through the elements.

The invention also consists in a heater substantially as described below with reference to the accompanying drawings in which:

FIGURE 1 is a longitudinal section through a heater for inert gases used in magneto-hydrodynamic apparatus in accordance with one form of the invention;

FIGURE 2 is a section on line A-A of FIGURE 1;

FIGURE 3 is a section on line B-B of FIGURE 1;

FIGURE 4 is a fragmentary plan view showing the expanded metal mesh utilized for a heating element; and

FIGURE 5 is a sectional view taken substantially on the line 5-5 of FIGURE 4.

In carrying the invention into eifect in the form illustrated by way of example, the heater consists of a casing 1 enclosing a metal mesh electrical resistance heating element 2. The element 2 has metal mesh strips 2a which extend parallel or substantially parallel to the axis XX of the heater. In the form shown several are arranged one within the other but in spaced relation as shown in FIGURE 2 and are connected electrically in parallel. As alternatives to the hexagonal arrangement shown the elements may, for example, be arranged as concentric cylinders or as a spiral.

The elements are held in terminal blocks 3, 4 at each end thereof and power is supplied via block 3, through connections 5 and block 4 through connections 6. The latter may be flexible to allow for expansion of the elements.

The gas to be heated is directed into the outer part of the space in casing 1 containing the element and flows 3,244,860 Patented Apr. 5, 1966 ice radially inwards to a central space 1a which communicates with an outlet duct 7.

One way of conducting the gas to the space surrounding the element is illustrated in FIGURES 1 and 3. Gas enters inlet 8 which for part of its length surrounds outlet 7 and then flows through radial holes in terminal block 3 to enter the said space.

The whole element assembly may be surrounded by one or more radiation shields and gas flow distributors 10 with openings 10 therein for the passage of gas. These openings 10' can be graded in size so as to cause the gas to be equally distributed along the length of the element. The shield 10 is spaced outwardly of the outermost heating element 2 and inwardly from the sidewall of the casing 1, as clearly shown in FIG. 1 to reduce radiation from the outermost heating element to the sidewall of the casing.

At the right hand end of theelement assembly in FIGURE 1 is a gas baflle 11 which prevents hot gas reaching terminal block 4 and helps direct the gas into outlet 7. A radiation shield may be provided for terminal block 3 if so desired.

The elements may, for example, be of aluminium, stainless steel, nickel-chromium alloy, or a tantalumtungsten alloy, depending on the temperature of gas required; the latter material, for example, would enable chemically inert gases, such as helium, neon, argon, or the like, to be heated to temperatures as high as 2400 C. The casing may, for example, be made from aluminium, mild steel or stainless steel, depending on requirements.

The mesh presents a large surface area for heat transfer within the given space and the pressure loss through the mesh is low; the pressure loss may be substantially reduced Without much loss in heat transfer properties by arranging that the metal sections forming the expanded mesh provide walls 12, as shown in FIGS. 4 and 5, which are parallel to the direction of gas flow at entry to the mesh, or through the elements as shown by the arrow in FIG. 5. Advantage may be taken of natural convection flow by arranging the heater vertically with the right hand side (in FIGURE 1) lowermost.

Heaters of the kind described may be used with space heating apparatus or air-conditioning apparatus. They may also be used in magneto-hydrodynamic apparatus for the direct generation of electricity.

I claim:

1. An electrical heater for gases, said heater compris ing a hollow closed casing, a plurality of tubular electrical heating elements supported in the casing in spaced relation to the walls thereof and disposed one within the other in spaced concentric relationship, means electrically connecting said elements in parallel, said elements being formed of metal mesh to provide passages therethrough for a gas to be heated, gas inlet and outlet means connected to the casing, means within said casing providing a path for gas fiow within the casing through the passages in said elements in a generally radial direction between said inlet and outlet means, a radiation shield disposed within said casing surrounding said elements and spaced outwardly of the outermost heating elements and inwardly from the casing side wall to reduce radiation of heat from said outermost element to the side wall of the casing, said shield being disposed in the path of gas flow between said inlet and outlet means to direct the flow of gas substantially longitudinally of said elements, said shield having gas flow openings spaced longitudinally thereof and graded in size to cause the gas to be substantially equally distributed along the length of the heating elements.

'3 L9 2. An electrical heater as defined in claim 1, in which said heating elements are provided by an expanded metal mesh and with the walls of the passages through said heating elements being disposed obliquely to a plane perpendicular to the common axis of said elements, whereby the gas flow through said passages is in a generally radial direction but oblique to the common axis of said elements. 3. An electrical heater as defined in claim 2, in which said heating elements are progressively displaced axially of said casing, the innermost element of a pair of adjacent elements being displaced further in the direction of oblique gas flow than the outermost element of said pair, said gas flow through said elements being inwardly from the outermost element to the innermost element.

References Cited by the Examiner UNITED STATES PATENTS 2,658,742 11/ 1953 Suter et a1. 2,797,297 6/1957 Nihlen 219-280 2,837,623 6/1958 Judson et al 219-381 3,016,693 1/1962 Jack et a1 219378 X FOREIGN PATENTS 717,612 10/1954 Great Britain. 7 745,031 2/ 1956 Great Britain.

ANTHONY BARTIS, Acting Primary Examiner.

RICHARD M. WOOD, Examiner.

Claims

1. AN ELECTRICAL HEATER FOR GASES, SAID HEATER COMPRISING A HOLLOW CLOSED CASING, A PLURALITY OF TUBULAR ELECTRAICAL HEATING ELEMENTS SUPPORTED IN THE CASING IN SPACED RELATION TO THE WALLS THEREOF AND DISPOSED ONE WITHIN THE OTHER IN SPACED CONCENTRIC RELATIONSHIP, MEANS ELECTRICALLY CONNECTING SAID ELEMENTS IN PARALLEL, SAID ELEMENTS BEING FORMED OF METAL MESH TO PROVIDE PASSAGES THERETHROUGH FOR A GAS TO BE HEATED, GAS INLET AND OUTLET MEANS CONNECTED TO THE CASING, MEANS WITHIN SAID CASING PROVIDING A PATH FOR GAS FLOW WITHIN THE CASING THROUGH THE PASSAGES IN SAID ELEMENTS IN A GENERALLY RADIAL DIRECTION BETWEEN SAID INLET AND OUTLET MEANS, A RADIATION SHIELD DISPOSED WITHIN SAID CASING SURROUNDING SAID ELEMENTS AND SPACED OUTWARDLY OF THE OUTERMOST HEATING ELEMENTS AND INWARDLY FROM THE CASING SIDE WALL TO REDUCE REDIATION OF HEAT FROM SAID OUTERMOST ELEMENT TO THE SIDE WALL OF THE CASING, SAID SHIELD BEING DISPOSED IN THE PATH OF GAS FLOW BETWEEN SAID INLET AND OUTLET MEANS TO DIRECT THE FLOW OF GAS SUBSTANTIALLY LONGITUDINALLY OF SAID ELEMENTS, SAID SHIELD HAVING GAS FLOW OPENINGS SPACED LONGITUDINALLY THEREOF AND GRADED IN SIZE TO CAUSE THE GAS TO BE SUBSTANTIALLY EQUALLY DISTRIBUTED ALONG THE LENGTH OF THE HEATING ELEMENTS.