Process and Reactor for Heating at Least One Fluid by Magnetic Induction

Abstract

Provided is a process for heating at least one fluid by magnetic induction using at least one metal as a heat transfer medium. The metal is incorporated into the fluid to be heated as a packed bed. A high frequency alternating magnetic field (AC-field) of at least 50 kHz is applied for generating heat in at least a (thin) interfacial layer of the metal and the generated heat is subsequently transferred to the fluid to be heated.

Claims

1. A process for heating at least one fluid by magnetic induction using at least one metal as heat transfer medium, wherein the metal is incorporated into the fluid to be heated as a packed bed, and wherein a high frequency alternating magnetic field (AC-field) of at least 50 kHz is applied for generating heat in at least a layer of the metal and the generated heat is subsequently transferred to the fluid to be heated.

2. The process according to claim 1, wherein the fluid to be heated is a fluid food, in particular a beverage, like milk or juice, or a fluid used in the chemical industry, pharmaceutical industry or biotech industry.

3. The process according to claim 1, wherein the metal comprises spheres with an average diameter between 0.1 and 10 mm, preferably between 0.5 and 8 mm, and more preferably between 1 and 4 mm.

4. The process according to claim 1, wherein the metal comprises ferritic steel, in particular a chemically inert ferritic steel with a high chromium and low carbon content, with high magnetic permeability and low electrical conductivity.

5. The process according to claim 1, wherein the metal is coated for preventing oxidation and electrical insulation.

6. The process according claim 1, wherein the particle packed bed comprises of metallic particles intermixed with inductively inert particles for providing electrical insulation between metallic particles.

7. The process according to claim 1, wherein packed the particle packed bed comprises metallic particles that are intermixed with inert particles or are embedded into inert particles.

8. The process according to claim 1, wherein the packed bed of the at least one material is at least one flat packed bed, a cone-like shaped packed bed or a hollow diamond-like shaped packed bed.

9. The process according to claim 1, wherein the flow velocity of the fluid through the packed bed is 1-10 cm/s, preferably 3-8 cm/s, more preferably 5 cm/s.

10. The process according to claim 1, wherein the fluid is heated to a temperature between 80 and 200° C., preferably between 90 and 180° C., more preferably between 95 and 160° C.

11. The process according to claim 1, wherein the residence time of the fluid is between 10 ms and 1 s, preferably 10 ms and 100 ms, when passing the packed bed.

12. The process according to claim 1, wherein the alternating magnetic field is applied by using at least one induction coil with a coil number of 3-25, preferably 5-10.

13. A reactor for heating at least one fluid in a process according to claim 1 comprising at least one packed bed of at least one metal as heat transfer medium and at least one alternating magnetic field source associated with the reactor for inductive heating of the at least one metal in the packed bed.

14. The reactor according to claim 13, wherein the reactor casing is made of material inert to magnetic induction, such as glass, ceramics, plastics, in order to selectively heat the metallic heat transfer medium.

15. The reactor according to claim 13, wherein the magnetic source is an induction coil surrounding the outer side of the reactor.

16. The reactor according to claim 13, wherein a centered metallic rod or wire is provided for forming a narrow gap between the tube inner wall.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The solution will be explained in the following in more detail with reference to the figures.

[0028] FIGS. 1 and 2 show a schematic views of surface magnetization and fluid heating ability of a packed bed (PB) according to the solution.

DESCRIPTION OF THE INVENTION

[0029] FIGS. 1 and 2 (parts a-j) illustrates various embodiments of a PB according to the solution. A PB of ferritic metal spheres in a tubular reactor (one eighth section) are heated inductively from an alternating (50 kHz) electrical current (1.5 kA) through the surrounding coil (8 turns).

[0030] FIGS. 1 and 2 show computed magnetization of a flat (FIG. 1 part a), cone-like (FIG. 1 part b), hollow diamond-like (FIG. 1 part c), a random intermixed (with inert particles) (FIG. 2 part g), and an embedded (in inert particles) (FIG. 2 part i). Increasing PB thickness is ineffective due to magnetization mostly being confined to the external interface as indicted by black arrows in FIG. 1 part a. Magnetization is more homogeneously distributed for antenna-like PB (FIG. 1 parts b and c). A fluid (water) flowing (5 cm s.sup.−1, yellow arrow) through the PB is heated. Temperature maps of a cross-section are shown in FIG. 1 parts d, e, f, and FIG. 2 parts h and j. Homogeneity and magnitude of fluid temperature depends on PB morphology.

[0031] Increasing the specific surface area of the inductively heated metal, such as by opting for a porous structure (e.g., PB), is an intuitive approach for increasing the heat exchange area. However, inductive heating of the pore interfaces within the metal is not effective for non-isolated and touching PB building blocks due to exponential decay of the internal magnetic field strength (Zinn, S., Semiantin, S. L., Harry, I. L. & Jeffress, R. D. Elements of Induction Heating: Design, Control, and Applications. Carnes Publication Services Inc., 1988) (see FIG. 1 part a). Thick PB structures exhibit no benefit over thin ones. On the contrary, they prolong high-temperature residence time and increase pressure drop.

[0032] Realizing high-specific surface area with small particles also exhibits worse heating performance than larger ones due to inferior ability to confine the magnetic field into the particle. A more viable approach for increasing sought high interfacial area is by enhancing particle surface roughness.

[0033] In order to achieve high temperatures (FIG. 1 parts d, e f, and FIG. 2 parts h and j without local overheating, operation of inductively heated reactor must allow high fluid flow rate and rapid transfer and distribution of thermal energy. The latter is achieved with high Reynold's numbers and short heat transfer distances, or more explicitly, turbulent flow in narrow channels. Here, a tubular reactor like in Duquenne et al. is investigated (FIG. 1 parts a, b, c, and FIG. 2 parts g and i). The reactor tube composition must be inert to magnetic induction (e.g., quartz glass, ceramics, plastics), in order to selectively heat the metallic heat transfer medium. This assembly exhibits the greatest exerted magnetic field strength at the inner wall of the tube because of its decay towards the coil axis. Correspondingly, homogeneous liquid heating (i.e. temperature and residence time) requires either deflection of the magnetic field towards the tube axis or restriction of fluid flow in the tube to a narrow gap concentric to the coil. An antenna-like shape of the PB (FIG. 1 parts b and c) enables the former because of its ability to function as flux guide (Kondo, T. & Itozaki, H. Physica C 392-396, 1401-1405, 2003). Computational results suggest effectivity in regards to fluid temperature homogeneity and magnitude (FIG. 1 parts d, e, f, and FIG. 2 parts h and j). A centered metallic rod or wire can form a narrow gap between the tube inner wall.