Process for producing a magnetocaloric composite material and a corresponding heat exchanger

Abstract

A process is disclosed for producing a magnetocaloric composite material for a heat exchanger. The process comprises the following steps: Providing (S110) a plurality of particles (110) of a magnetocaloric material in a shaped body (200) and immersing the plurality of particles (110) present in the shaped body (200) into a bath in order to coat the particles by a chemical reaction and bond them to one another.

Claims

1. A process for producing a magnetocaloric composite material for a heat exchanger, with the following steps: providing a plurality of particles of a magnetocaloric material in a shaped body; immersing the plurality of particles present in the shaped body into a liquid bath the immersing step coating the particles in the liquid bath through a chemical metal coating, the coating serving to bond the plurality of particles to one another using the coating so as to form the magnetocaloric composite material.

2. The process according to claim 1, wherein the particles are pretreated with at least one of the following steps: pretreating with a sodium hydroxide solution, pretreating with a sulfuric acid, pretreating with a hydrochloric acid, wherein ethanol and/or water are used to rinse between each step.

3. The process according to claim 1, wherein the plurality of particles are pretreated in N-Methyl-2-pyrrolidone for at least one hour.

4. The process according to claim 1, wherein the liquid bath comprises at least one of the following substances: ammonium chloride, sodium citrate, nickel(II) chloride or other metal ions, in particular made of compounds with chromium or zinc and water, and wherein the process also comprises heating the bath to more than 50° C. or roughly 60° C.

5. The process according to claim 1, wherein ammoniac and then sodium phosphinate are also added to the liquid bath.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The exemplary embodiments of the present invention will be better understood on the basis of the following detailed description and the accompanying drawings of the different exemplary embodiments, which should not, however, be understood such that they limit the disclosure to the specific embodiments, but rather merely serve as clarification and for understanding.

(2) FIG. 1 shows a flow diagram of a process according to an exemplary embodiment of the present invention.

(3) FIG. 2 shows a magnetocaloric composite material according to the production using the process according to the invention.

(4) FIG. 3 shows a temperature profile of a heat exchanger during remagnetizations.

(5) FIG. 4 shows a heat exchanger with a shaped body, which is used for production according to exemplary embodiments.

DETAILED DESCRIPTION

(6) FIG. 1 shows a flow diagram of a process for producing a magnetocaloric composite material for a heat exchanger. The process comprises the steps: providing S110 a plurality of particles of a magnetocaloric material in a shaped body; and immersing S120 the plurality of particles present in the shaped body into a bath in order to coat the particles by a chemical reaction and bond them to one another.

(7) The bath can in particular be a nickel bath. However, the invention should not be limited to a nickel bath. The production process can, however, have one or a plurality of the following optional steps/materials: 1. The particles can be pretreated with sodium hydroxide solution (NaOH), sulfuric acid (H.sub.2SO.sub.4) and hydrochloric acid (HCl) (ethanol (C.sub.2H60) and water (H.sub.2O) can be used to rinse repeatedly between each step). An additional pretreatment can be carried out for a few hours in N-Methyl-2-pyrrolidone to remove polymer residues. 2. The exemplary nickel bath can be mixed from nickel(II)-chloride (NiCl.sub.2), ammonium chloride (NH.sub.4C1), sodium citrate (Na.sub.3C6H.sub.5O.sub.7) and water (H.sub.2O) and heated to approx. 60° C. 3. Ammoniac (NH.sub.3) and then sodium phosphinate (NaH.sub.2PO.sub.2) can be added. 4. Pretreated particles can then be exposed to the exemplary nickel bath.

(8) The magnetocaloric particles 110 can be bonded into a porous structure by the chemical reaction of the particle surface of the magnetocaloric particles 110 with the exemplary nickel solution (nickel bath). At the same time, a full or uniform coating of each particle is ensured by this reaction, said particles are therefore protected from all chemical attacks. Additionally, there are no toxic components contained such that the magnetocaloric composite material is suitable for many usage purposes.

(9) FIG. 2 shows, by way of example, a magnetocaloric composite material produced with a plurality of magnetocaloric particles 110 which have a nickel coating 120 (or other metal surface) due to immersing into the exemplary nickel bath, said nickel coating at the same time serves to bond the plurality of particles 110. As a result of this process, a plurality of cavities 130 are present between the nickel-plated particles 110 which can serve to pump a liquid such as for example water through and generate a heat exchanger as a result. Thus, for example the magnetocaloric material can be heated by applying the magnetic field and then a liquid such as water can be pumped through which absorbs the heat. Then, cooling takes place by a demagnetization step. The cooling generated as a result can in turn be absorbed by water and then channeled on to the medium to be cooled.

(10) La(Fe,Mn,Si)13H heat exchangers have proven particularly effective for the potential application of magnetocaloric materials in cooling systems owing to their excellent property profile. However, the invention should not be limited to the material used. Further materials would be e.g. gadolinium, Fe2P or Ni—Mn—In Heusler compounds.

(11) FIG. 3 shows, by way of example, a temperature profile from demonstrator measurements of identically-constructed heat exchangers. The graph 210 shows the heat exchanger according to the invention based on nickel-plated particles, the graph 220 shows the

(12) heat profile based on a polymer bond and the graph 230 shows the heat profile based on a pebble bed (without bonding). The difference between each of the two graphs shows the temperature difference that can be reached between the magnetized and demagnetized shape. It is clearly apparent that a greater temperature difference is reachable by the nickel plating than for example by the polymer bond of the magnetocaloric particles. Owing to the increased heat transfer, the saturation is significantly more quickly reached in the exemplary embodiments of the present invention (graph 20). At the same time, a higher temperature difference is generated. Accordingly, the heat exchanger works more efficiently.

(13) FIG. 4 shows the example of a heat exchanger with a shaped body 200 in which the plurality of particles 110 is introduced. After the particles 110 have been introduced in the shaped body 200, they are exposed to an exemplary nickel bath which leads to bonding of the particles.

(14) The structure of the heat exchangers and the bonding of the particles 110 to one another significantly affects the efficiency during dynamic cooling processes, heat conductivity and mechanical and chemical stability. This applies particularly for use in cooling units.

(15) The production process according to the invention offers a series of advantages in comparison to known solutions. Thus, a chemical reaction takes place on particle surfaces during nickel plating with the above-mentioned nickel solution, whereby said particle surfaces are covered with a uniform nickel layer 120 and bonded to one another. The process is comparatively simple and requires only few tools.

(16) The manufacture of heat exchangers of nickel-plated magnetocaloric particles 110 is significantly more cost effective, unlike the conventional, magnetocaloric composite materials, which are based on metal and polymer-bound composites. The substances used for production are available cost-effectively and are non-toxic. The higher mechanical and chemical stability that can be reached guarantees a longer useful period and reuse. The magnetocaloric composite material can in particular be used for magnetic cooling units and cooling systems, but also for characterizing new magnetocaloric materials as heat exchangers.

(17) The features of the invention disclosed in the description, claims and the figures can be essential to achieving the invention both individually and also in any combination.

LIST OF REFERENCE NUMERALS

(18) 110 magnetocaloric particles 120 metal surface layer 130 cavities 210, 220, 230 temperature profiles 200 shaped body