GB1603878A

GB1603878A - Device for heating-up fluids

Info

Publication number: GB1603878A
Application number: GB17523/78A
Authority: GB
Original assignee: SENTRAS AG
Current assignee: SENTRAS AG
Priority date: 1977-05-04
Filing date: 1978-05-03
Publication date: 1981-12-02
Also published as: CH638299A5; SE7805096L; ATA307478A; JPS5413056A; FR2389858A1; AT361950B; FR2389858B1; DE2719958A1

Abstract

The device has a chamber (2) in which there is or are arranged for the fluid a skeleton-like material (1) or suspended, spatially distributed, fine particles. Furthermore, an artificial radiation source (4, 5) whose radiation heats the skeleton-like material is arranged inside or outside the chamber. Due to this arrangement, transport of heat by conduction to the surfaces around which flow takes place is no longer required and an additional heat transfer resistance is eliminated. Due to the large surface of the spatial structure or the suspended particles, convective heat transfer to the fluid takes place at small temperature differences. The device can be integrated into a recuperative heat exchanger. In order to achieve chemical reactions, the spatial structure which absorbs the radiation can have a surface refined by heat treatment and/or a catalytic effect. <IMAGE>

Description

(54) A DEVICE FOR HEATING-UP FLUIDS (71) We, SENTRAS AG, a Swiss company of Rebmatt 3 CH-6317 Oberwil, Switzerland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a device for heating up fluids, that is to say gases or liquids, by the fluid going round or up against faces from which the heat goes into the fluid.

A large number of devices of this kind have been put forward in the past as for example heat-exchangers as automobile radiators, oil coolers and liquid heaters, in the case of which, for increasing the uptake of heat by a fluid the faces over which the fluid goes are made as great as possible in size, for.example by the use of ribs or the like.

In the German specification (Offenlegungs schrift 1,962,488 the heat exchange face is to be made greater in size by the use of metallized foam. However a shortcoming in all systems put forward so far is that the heat is to be transported to the faces, round which the fluid goes, by thermal conductivity. If such thermal conductivity is not or not fully effected, the increased size of the faces does not make for any increase in the exchange of heat and instead only makes it harder for the fluid to go through the system.

So one purpose of the invention is that of increasing heat exchange to fluids and more particularly that of making possible a higher efficiency without making the apparatus more complex.

According to the present invention there is provided a device for heating-up fluids in a vessel to which heat is applied, characterised in that there is arranged within the vessel a material with a spatial distribution in the form of non-cohering fine particles or skeleton-like cohering fine particles, which forms a spatial structure, and an energy source that heats the material primarily by electromagnetic radiation via a free space between said material and said source.

In this case it is no longer necessary for the heat to be transported by thermal conductivity to the faces round or over which the fluid is in motion and in fact the skeleton-like material or the small particles take up the heat energy in the form of radiation energy through their surface and are then able to give up the energy at the same position to the fluid by convection. There is nothing to get in the way of heat exchange and further there is not the limitation that heat energy has to be transported through the material to the faces over or round which the fluid is in motion.

For solar collectors designed for making use of the heat of radiation of the sun for use of the heat in it, more particularly for heating purposes, there has been a suggestion in the past to make use of a skeleton-like mat serial, which has a heat carrier, more particularly water, going round it. However so far no attempt has been made to make use of this idea for uptake of the radiation-heat by a fluid for heat exchange apparatus, for example continuous current heaters or reaction columns for the chemical industry. In such cases control of the gases or liquids is to be readily possible and they are to be heated up without overheating at certain points or they are to be heated up to certain reaction temperatures able to be exactly controlled.

For making the best possible use of the radiation energy the skeleton-like material or the small particles, now referred to as absorbers as well because of their function, are to have the highest possible absorption coefficient for the radiation. In an earlier suggestion the absorber face was specially painted for this purpose. The increase in effect produced by this step are however limited and furthermore signs of aging and dirt quickly lead to less good effects. If on the other hand as in the present invention the absorber is made up of the skeleton-like material or the small particles, reflection a number of times within the material or between the particles is able to lead to a generally complete absorption, as is a noted fact.

In a way similar to a black box, in which radiation goes in through a small opening and after reflection a number of times at the wall is lastly completely absorbed, the absorption coefficient for the material face does not have to be particularly large, because the energy amount, reflected each time, of the radiation taken in by the threedimensional structure or between the particles is absorbed at the next reflections which take place. In this respect changes in the surface generally do not have any effect.

Finally despite a large total surface area of the skeleton-like material or the fine parts and the resulting large heat transfer surface the mass of the absorber can be kept very small so that the heat capacity and therefore the thermal inertia can also be very small. In the case of the use of a heat carrier which also has a very low thermal inertia, that is to say more especially gaseous heat carriers, the temperature of the system quickly responds to the incident radiant energy.

The skeleton-like material with an open three-dimensional structure can be provided in various different forms. For many cases of application with a medium temperature range the skeleton-like material consists, in accordance with a further development of the invention, of reticulate foam material.

Such a material can for example be polyurethane, polyvinyl chloride, polyethylene and similar plastics in the form of a hard foam, in the case of which the walls of the carriers or pores are destroyed by subsequent treatment or during the foaming operation and only a skeleton of material is left. The effective surface area of such material is extraordinary large, for example per millimeter of thickness of the material it is three to five times the projected surface area so that a transfer of heat with only very small temperature differences is possible.

The structure of the material furthermore ensures an intensive mixing of the heat carrier and a heat transfer with minimum temperature differences. The material filling coefficient of reticulate foam material is very small and for example only three percent of the total volume is occupied by the material itself. Therefore the specific heat and accordingly the thermal inertia of the reticulate material, expressed in terms of the overall volume, are also small.

The pore size of the reticulate material can be selected in accordance with the specific purpose of application. Conven tionalvues for a medium pore size lie between 80 ppi (pores per inch) and 5 ppi. Having regard to the pressure drop of the heat carrier passing through the material the pores are preferably selected so as to be comparatively large, for example between 5 and 20 ppi in the case of a system in which air flows through the material. The optimum pore size for the respective application furthermore depends upon the refractive index of the heat carrier and the layer thickness. In the case of a system in which air flows through the material the pore size is selected for a specific layer thickness to be just such that the material is no longer transparent. In this case the whole incident radiation will be absorbed completely after multiple reflection in the absorbing material.

In lieu of reticulate foam material the skeleton-like material can, in accordance with a further development of the invention, also be a fibrous body or a threedimensional network in the form of a felt, batt, knitted mesh, woven fabric or ball of filaments, strips or wires.

The fibers, filaments or strips can be or organic or inorganic materials. For higher temperatures metal can specifically be considered.

Finally in accordance with a further development of the invention the skeletonlike material consists of a three-dimensional arrangement of filaments, strips or wires which at least in groups and/or at least in certain areas are arranged parallel with a spacing between them. Such a material can for example comprise helices, sieve-like structures, grids of staggered wires or also wreath-like structures or also festoons in the case of which the filaments strips or wires project radially from the axis of the festoon.

In all cases of such skeleton-like materials the layer thickness of the absorber is to be so selected having regard to the spacing and the dimensions of the elements of the material that direct passage of the radiation through the structure cannot occur but on the other hand the total incident radiant energy is trapped by multiple reflections.

It is not necessary for the mean pore size or the mean spacing between the elements of the skeleton-like material to be constant and instead in accordance with a still further development of the invention an improved absorption of the radiant energy can be ensured if the interstices of the skeletonlike material change in the direction of incidence of the radiation. For example in the case of the use of reticulate foam material layers with a decreasing pore size can be employed.

In the case of the use of small solid particles or in the form of liquid drops it is to be seen, as is the case with skeleton-like material, that the working face is very great, so that heat exchange with only small temperature changes is possible. Furthermore the degree to which the space is taken up, that is to say that part of the volume taken up by the small particles in the liquid, and for this reason the specific heat and the thermal inertia are able to be kept small. The parti cles may be stationary in a system or it is possible for them to be mixed with the liquid before it goes into the chamber or the radiation zone of the chamber, and then they are able to be separated from it again. The size and form of the particles is to be selected with a view to the case of use in hand and the conditions coming into question. However generally solution of the particles in the fluid is not desired. The form of the particles is dependent on the ways of making them. It is possible to make use of small balls, small crystals and other forms. Furthermore the selection of the particles is dependent on any reaction planned with respect to the material used as well. For the selection of the size it is to be noted that the diameter of the particles is to be greater than the wavelength of the radiation to be absorbed.

This furthermore makes it possible to have a certain chance of selection (or selectivity) with respect to the wavelength of the radiation to be absorbed. If the particles are in comparison great in size and generally the whole radiation spectrum is absorbed by them, chemical processing of the particles may be used to make a selection of the wavelength. Such a treatment has the same purpose as vapor-coating of faces with quarter-wavelength layers.

As an example for small particles in a fluid, that is to say in a current of gas or liquid, the following materials may be given: metal dusts, inorganic and organic powders, flakes, spherulets of plastics, small fibers of inorganic or organic material.

As an example, particles of soot having a radius of 800 in a layer of 1 cm thickness absorb approximately 99% of the radiant energy of a source having a temperature of 2000 K, when 10'2 particles per cm3 are present, and approximately 40% when there are 1010 particles per cm present. When there are particles of 50 A radius, the corresponding concentrations are approxi- mately 1016 and 10'4 particles per cm , resp.

As powder-like materials compositions, f.e. V2OS, Al203, Si 03, K20, Ni, Pt can be used, which also have catalytic effects. If only a heating effect is intended, powder of stainless steel oxide can be used.

For making the best possible use of radiation in a further form of the invention in which the radiation source is placed outside the chamber the chamber walls, which are transparent to radiation, are made nonreflecting for the frequency range of the radiation coming into question, for example by a generally used method of vapor-coating with quarter-wavelength layers with the desired selection of the refractive index. For increasing heat insulation of the chamber, on the other hand, its walls can be made mirror-faced for the frequency range of the natural radiation of the absorber.

As is the case with the small particles it is possible as well for the skeleton-like material to be made non-reflecting by faceprocessing. Such processing may be limited to the top layer (which is responsible for the reflecting effect seen on looking at the absorber). It is in fact only in this case that a loss is produced by single reflection of the radiation from outside back into the space.

In the deeper layers, on the other hand, the rays are kept in as in a black box in the same way, not being important if the face has been processed or not.

In particluar in the case of the use of a reaction vessel it is possible to make use of a further development of the invention in which the skeleton-like material or the small particles are covered with a catalyst or made up of a catalyst. As a skeleton-like material it is for this purpose possible to use for example a mesh or fabnc of platinum wires.

The catalyst may furthermore be in the form of a powder or in the form of a coating on the skeleton-like material. In this manner chemical reactions may be effected, as for example thermal splitting or cleavage of NO2 into NO under the effect of the radiation. The size-distribution and make-up of the fine particles or drops may be such that a part or a sort is only used for heating up the fluid and the rest is used for making possible a certain chemical reaction. In the case of the use of skeleton-like material the pore size may be changed in any desired manner for the same purpose or different material may be placed in different parts of the reaction chamber. In a further development of the invention it is possible for the chamber to be part of a recuperative heat exchanger in such a way that the fluid coming in gives up part of its heat to the fluid going in with the outcome that the energy to be used is able to be decreased. An example of this is the burning of solvents in air coming out of the apparatus, the concentration of the solvent vapors changing to a very great degree.

If then in times in which there is a very low concentration the reaction heat is not enough for making certain that burning goes on all the time, in a radiation zone in the invention the energy necessary for keeping up to the reaction temperature may be quickly put in. The energy balance is made better by the heat exchanger because the incoming waste air current is heated up by the heat of reaction.

The invention will now be described by way of example with reference to embodiments in conjunction with the figures of the accompanying drawings in which: Figures 1 and 2 show a continuous flow heater as one embodiment of the invention in two views, Figures 3 and 4 show two embodiments for reaction vessels in accordance with the invention, which can be used in industrial processes, Figures 5 and 6 show respectively two sectional views on the section stations A-A of Figure 6 and B-B of Figure 5 of a tubular device of the invention.

The continuous flow heater shown in Figures 1 and 2 has a continuous flow chamber for the heat medium to be heated, as indicated diagrammatically by arrows. The interior of the chamber is filled with an absorber material 1, which has an open three-dimensional structure that is to say a spatial distribution. In the embodiment shown it is a question of reticulate foam material. In the interior of the material 1 infrared sources 4 are arranged to give electromagnetic radiation across free space and which each have an electrically heated helical filament 5 and which in accordance with the filament temperature to be used can be evacuated or filled with halogen. Electrical leads 6 pass to a current supply, not shown.

The container walls 2 have a mirror coating which is effective for all wavelengths so that no losses owing to radiation to the outside can occur.

The temperature of the heat carrier flowing through the continuous flow heater can be set extraordinarily rapidly and precisely by regulation of the infrared source 4. The continuous flow heater is therefore very suitable as a temperature regulating component.

In Figures 3 and 4 a container is shown in the form of two parallel tubes, which at both ends are connected with unions 8, comprises an absorber material 1 in accordance with the invention. An endpiece 9 serves to hold the material 1 in position. Between the two tubes 23 there are one (Figure 3) or three (Figure 4) electromagnetic radiation sources ,which heat-up the flowing medium primarily by electromagnetic radiation across free space through the agency of the absorber material 1. Lead through arrangements 7 comprise the electrical leads 6 for the radiation source 5.

In the case of the two embodiments of figures 3 and 4 a concentric arrangement can be adopted in such a manner that the absorber material 1 is arranged in the form of a hollow cylinder in a suitable shaped vessel, which then contains the electromagnetic radiation source in the interior.

The container walls 24, adjacent to the infrared sources, are again provided with an anti-reflective coating effective as regards infrared radiation, while the outer walls 25 are given a mirror coating effective for all wavelengths in order to avoid losses.

In Figures 5 and 6 in a tube 26 as an absorber is arranged a skeleton-like material. Several infrared sources 4 are provided, with reflectors 10 to concentrate their radiation on the material 1 in the tube 26 and as a result it is possible to achieve a high energy density in the material 1 and therefore a rapid, easily regulated and effective heating up of the medium flowing through the tube 26.

WHAT WE CLAIM IS: 1. A device for heating-up fluids in a vessel to which heat is applied, characterised in that there is arranged within the vessel a material with a spatial distribution in the form of non-cohering fine particles or skeleton-like cohering fine particles, which forms a spatial structure, and an energy source that heats the material primarily by electromagnetic radiation via a free space between said material and said source.

2. The device according to claim 1, wherein the skeleton-like material consists of reticulate foam material.

3. The device according to claim 1, wherein the skeleton-like material is a fibrous body.

4. The device according to claim 1, wherein the skeleton-like material is a three-dimensional network in the form of entangled or felted fibres, a knitted fabric a woven fabric or a ball of fibres, strips or wires.

5. The device according to claim 1, wherein the skeleton-like material consists of a three-dimensional arrangement of filaments, strips or wires which at least in groups and/or at least in certain areas are arranged parallel with a spacing between them.

6. The device according to any one of the preceding claims, the interstices vary in the direction of incidence of the radiation.

7. The device according to any one of claims 16, distribution of the small particles is effected by swirling round in a chamber.

8. The device according to claim 7, the small particles are kept in suspension in the chamber.

9. The device according to claim 7, wherein the size-distribution of the particles is made on the lines of a certain selection.

10. The device according to claim 7 wherein the chamber is made as a continuous current chamber for the fluid and at its inlet opening an intake part is placed for the particles.

11. The device according to claim 10, wherein the continuous current chamber has at its outlet opening for the fluid a separating unit for getting back the particles from the fluid.

12. The device according to any one of the preceding claims, wherein the walls of the vessel or chamber are made nonreflecting for a certain frequency range of radiation.

13. The device according to any one of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. invention, which can be used in industrial processes, Figures 5 and 6 show respectively two sectional views on the section stations A-A of Figure 6 and B-B of Figure 5 of a tubular device of the invention. The continuous flow heater shown in Figures 1 and 2 has a continuous flow chamber for the heat medium to be heated, as indicated diagrammatically by arrows. The interior of the chamber is filled with an absorber material 1, which has an open three-dimensional structure that is to say a spatial distribution. In the embodiment shown it is a question of reticulate foam material. In the interior of the material 1 infrared sources 4 are arranged to give electromagnetic radiation across free space and which each have an electrically heated helical filament 5 and which in accordance with the filament temperature to be used can be evacuated or filled with halogen. Electrical leads 6 pass to a current supply, not shown. The container walls 2 have a mirror coating which is effective for all wavelengths so that no losses owing to radiation to the outside can occur. The temperature of the heat carrier flowing through the continuous flow heater can be set extraordinarily rapidly and precisely by regulation of the infrared source 4. The continuous flow heater is therefore very suitable as a temperature regulating component. In Figures 3 and 4 a container is shown in the form of two parallel tubes, which at both ends are connected with unions 8, comprises an absorber material 1 in accordance with the invention. An endpiece 9 serves to hold the material 1 in position. Between the two tubes 23 there are one (Figure 3) or three (Figure 4) electromagnetic radiation sources ,which heat-up the flowing medium primarily by electromagnetic radiation across free space through the agency of the absorber material 1. Lead through arrangements 7 comprise the electrical leads 6 for the radiation source 5. In the case of the two embodiments of figures 3 and 4 a concentric arrangement can be adopted in such a manner that the absorber material 1 is arranged in the form of a hollow cylinder in a suitable shaped vessel, which then contains the electromagnetic radiation source in the interior. The container walls 24, adjacent to the infrared sources, are again provided with an anti-reflective coating effective as regards infrared radiation, while the outer walls 25 are given a mirror coating effective for all wavelengths in order to avoid losses. In Figures 5 and 6 in a tube 26 as an absorber is arranged a skeleton-like material. Several infrared sources 4 are provided, with reflectors 10 to concentrate their radiation on the material 1 in the tube 26 and as a result it is possible to achieve a high energy density in the material 1 and therefore a rapid, easily regulated and effective heating up of the medium flowing through the tube 26. WHAT WE CLAIM IS:

1. A device for heating-up fluids in a vessel to which heat is applied, characterised in that there is arranged within the vessel a material with a spatial distribution in the form of non-cohering fine particles or skeleton-like cohering fine particles, which forms a spatial structure, and an energy source that heats the material primarily by electromagnetic radiation via a free space between said material and said source.

13. The device according to any one of

the preceding claims wherein the walls of the vessel or chamber are mirrored for the frequency range of the radiation of the skeleton-like material or of the small particles.

14. The device according to any one of the preceding claims, wherein the skeletonlike material or the small particles are coated with a catalyst or made of a catalyst.

15. The device according to any one of the preceding claims, wherein the skeletonlike material or the fine particles have a processed face.

16. The device according to any one of the preceding claims, wherein the vessel or chamber is a part of a recuperative heat exchanger so that the outgoing fluid gives up part of its heat to the incoming fluid.

17. A device constructed and arranged substantially as herein described and as shown in Figures 1 and 2 of the accompanying drawings.

18. A device constructed and arranged substantially as herein described and as shown in Figures 3 and 4 of the accompanying drawings.

19. A device constructed and arranged substantially as herein described and as shown in Figures 5 and 6 of the accompanying drawings.