IL109468A - Inductive heater for the uniform heating of liquid - Google Patents

Description

INDUCTIVE HEATER FOR THE UNIFORM HEATING OF LIQU CHEN LIQUID HEATER LTD.

C: 1051B INDUCTIVE HEATER FOR THE UNIFORM HEATING OF LIQUID FIELD OF THE INVENTION The present invention relates to an inductive heater for uniform heating of liquids, more particularly, for pasteurization of edible liquids such as milk, dairy products, juice, wine, etc. The invention is a modification of the invention described and claimed in Israel Patent Specification No. 108339 filed on January 1994 (hereinafter "the main patent").

BACKGROUND OF THE INVENTION Inductive heaters are well known and widely used in various fields of technology. A conventional inductive heater comprises a transformer provided with a primary coil connected to an electric power source, and with a secondary coil having an electric resistance and acting as a heating element. A secondary coil of this type creates overheated areas of media placed near the coil, whereas volumes of the same media distanced from the coil are usually underheated. Therefore, the conventional inductive heater can be used for heating directly the media surrounding its secondary coil only when the temperature gradient occurring in the media is not a critical parameter in the specific application.

In some cases, however, it is very important to achieve relatively low and uniform temperatures over a large heating surface; for example, such a requirement is important for pasteurization of milk, juice, wine, etc., and for domestic air heaters.

The apparatus used presently for pasteurization utilize non-inductive heat exchangers having two separate circuits for conveying, respectively, an intermediate overheated media and a liquid to be heated up to the required temperature. More particularly, overheated vapor ( the so called first media), which is used as a heat source, is conveyed along the metal conduit of the heat exchanger thus heating its walls which then transfer the heat to the liquid to be heated (the so called second media). The two-circuit exchangers, herein described, are complex, bulky and expensive. Moreover, they are characterized by high thermal inertia, which renders rapid and accurate adjustment of the temperature of the second media impossible. It should be also noted, that the conduits must be daily serviced and cleaned in a time consuming process.

The main patent 108339 describes an inductive heater for direct heating of fluids, which resolves some of the problems mentioned above. It comprises a transformer, provided with a primary coil connected to a power source, and at least one short circuited member generating and radiating heat directly to a fluid and acting as a secondary coil. This heating member has a cross-section in the form of a single closed loop embracing the core of the transformer. The above mentioned patent application comprises a description of several modifications of the device, which are intended for heating gases and liquids. In one of the described embodiments for heating liquids the heating member is made in the form of a bent pipe section embracing the transformer's core, so that the ends of this pipe section are left open for conveying the liquid therethrough, and short-circuited. The inductive electric current generated in the pipe section uniformly heats the surface of its walls. It should be noted, that in the above system the temperature of the heating member may be easily regulated by controlling the current. The liquid passes through the pipe and is directly heated by its walls.

The described device has some specific disadvantages, which are especially noticeable in the applications related to the food industry. For example, rinsing and sterilizing the bent pipe section mounted on the transformer is extremely difficult. It is also known, that the liquid passing laminarly through the tube portion having a circular cross section, will always be heated more close to the walls of the tube, and less along its central axis. Thus when using the described device for pasteurization of food products requiring uniform heating, one can not achieve the most desirable thermal conditions.

OBJECT OF THE INVENTION The object of the present invention is to provide an inductive heater for pasteurization of edible liquids overcoming the above mentioned disadvantages.

SUMMARY OF THE INVENTION The object defined above is achieved by the present invention which provides an inductive heater for uniform heating of a liquid throughout its volume, comprising a transformer and at least one short circuited secondary coil constituting a heating member adapted to heat the liquid by direct heat exchange throughout its surface; said heating member being in the form of a curved pipe serving for conveying the liquid therethrough and surrounding the core of said transformer in such a manner that the ends of the curved pipe are short circuited; said curved pipe comprising at least one detachable portion, so as to facilitate cleaning of said pipe when said detachable portion is removed.

According to one embodiment of the invention, said curved pipe is a U-shaped assembly comprising two detachable parts: the first part being a curved pipe portion of the U-shaped assembly, and the second part comprising a pair of linear parallel pipe portions of said U-shaped assembly, being short circuited by a shunting spacer located between one pair of adjacent ends of said two linear parallel pipe portions; the opposite pair of their ends being adapted for coupling with said curved pipe portion.

In this embodiment the inductive heating current passes along all the U-shaped assembly and is short circuited via the shunting spacer. It should be noted that in this modification the two detachable parts of the U-shaped assembly must not create an excessive resistance at their coupling areas. It may be achieved by introducing between them O-rings manufactured from a non-toxic conductive material. The U-shaped assembly constructed according to this embodiment can be rinsed and cleaned when disassembled, and then, after being assembled, sterilized by overheating using a powerful inductive electric current.

According to another embodiment of the invention, said second part of the U-shaped assembly comprises an additional shunting spacer located between the opposite pair of adjacent ends of said two linear pipe portions so that said second part has the form of a rectangular frame.

In this embodiment the inductive heating current is short circuited through the two linear pipe portions and a pair of shunting spacers. It means that in this case the curved porion of the U-shaped assembly practically does not participate in the heating process of the liquid and serves only for transferring thereof from one linear portion to another and for simultaneous mixing the liquid. The curved portion of such U-shaped assembly may be interconnected with the linear portions thereof by the aid of O-rings made of an insulating non-toxic rubber-like material allowed for use in the food industry. This embodiment differs from the earlier described one also by the manner of sterilization of the U-shaped assembly, namely: its "linear" portion is adapted to be sterilized by a powerful electric current, and the detached curved portion must be sterilized separately.

In order to improve the uniformity of pasteurization, the following means are suggested to decrease the temperature gradient inside the pipe assembly and increase the turbulency of the liquid flow thereinside. At least the linear pipe portions may be provided with removable and washable inner inserts, having the thermal inertia equal or less then that of the pipes, lest the time necessary for thermoregulation of the inductive heater rise.

According to one embodiment of the invention said inserts are in the form of balls having a diameter which is at least half of the inner diameter of said linear pipe portions, and being distributed therealong in one layer so as to be in contact with each other. Such balls could be removed from the pipe sections for rinsing and sterilization, and returned thereinto after these operations are completed.

In accordance with another embodiment of the invention the linear pipe portions of the U-shaped assembly are each provided with a removable tubular insert adapted to be coaxially maintained inside said pipe portion so as to form an annular passage for the liquid therebetween.

The tubular insert may consist of a hollowed cylindrical body (either conductive or not) provided at its closed ends with annular tips having outwardly projecting pins (preferably non-conducting), said pins serve for maintaining the tubular insert inside the pipe portion.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is further described with the reference to the following non-limiting drawings, where: Fig. 1A is a schematic cross-sectional view of the device according to the invention; the cross-section is made across its tubular heating element.

Fig. IB is a cross-sectional view of the device shown in Fig.l A along line "B-B", i.e. along the tubular U-shaped heating element.

Fig. 2 is an enlarged longitudinal cross sectional view of a linear portion of the tubular heating element along line C-C in Fig.l, according to one embodiment of the invention.

Fig. 3 is an enlarged partial longitudinal cross sectional view of a linear portion of the tubular heating element along line C-C in Fig.l, according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1A and IB illustrate an inductive device 10 for heating liquids which comprises a transformer core 12 having a primary coil 14 and a secondary short circuited element in the form of a curved U-shaped pipe 16, acting as a secondary short-circuited coil. The U-shaped pipe 16 is assembled from a pair of parallel linear pipe sections 17, 19, and one curved pipe section 18 adapted to be removably attached to the linear sections 17 and 19 as it is shown in the drawing. The free ends of the pipe sections 17 and 19 serve as an inlet and an outlet for pumping a liquid through the U-shaped assembly 16. The assembly 16 is short circuited via shunting spacers 20 and 21 which form a rigid construction with the pipe sections 17 and 19. In this embodiment the curved section 18 is coupled with the linear pipe sections by isolating O-rings 13 and serves only for transferring the liquid to be pasteurized from the pipe section 17 to the pipe section 19, and mixing it simultaneously.

This construction is simple to manufacture, to assemble and disassemble, and consequently, it is easy to rinse and sterilize after a pasteurization cycle. More particularly, before starting another cycle (for example, for pasteurizing another product), the construction comprising the pipe sections 17 and 19 may be disconnected from the curved pipe section 18, rinsed well and then sterilized by overheating using a high power electric current. The curved section 18 can be washed and sterilized separately.

In another embodiment of the device the curved section 18 may also serve for heating the liquid passing therethrough. In this second embodiment the shunt 21 is absent, and the O-rings 13 should be made of a conducting non-toxic material which does not create excessive resistance between the pipe sections.

Fig. 2 illustrates one of the techniques enabling to improve the uniformity of the temperatures over the radial cross-section of the pipe section 17 or 19 during the process of heating the liquid thereinside. The pipe 17 (or 19) contains removable and washable metal balls 22, having a diameter which is at least half of the inner diameter of the pipe sections, and being distributed along the pipe in one layer. The balls 22 preferably have equal or lower thermal inertia than the pipe sections. If the thermal inertia of the balls 22 is lower or equal to that of the pipe portions, the balls will reach the predetermined temperature at a time interval not greater than the time needed to heat the pipes ( for instance, before starting a pasteurization cycle), and when the final temperature is reached, the balls will act thermally as part of the pipe.

As it was mentioned above, the balls 22 have such a diameter as to be distributed along the pipe in one layer only and in contact with each other. This layer of the balls diminishes the actual inner diameter of the pipe, simultaneously increasing the turbulency of the liquid flow therethrough. Both these factors result in a more uniform heating of the liquid.

Fig. 3 illustrates another technique for increasing the uniformity of the heating.

There is provided a pair of inner tubular inserts 24 ( one of them is shown in the illustration) adapted to be introduced into the linear pipe sections 17 and 19 ( only the section 17 is shown) so as to leave there annular passages 25 for the liquid flow. In this particular case the insert 24 is made in the form of a hollowed tube 26 provided at both its closed ends with annular tips having a plurality of outwardly protruded radial pins 28 which serve for maintaining the tube 26 at a substantially central position inside the pipe 17. The pipe 19 is also provided with the analogous insert. The insert 24 is supposed to have the thermal inertia being equal or less than that of the pipe sections, so that it will not require more time to be heated than the pipes, when preheating the device before starting a pasteurization cycle. The liquid flowing via the pipe sections 17 and 19 passes through the annular gap 25 having a cross section smaller than the cross section of the pipe 17 (19), which fact results in a turbulent liquid flow in this gap. Both of these two factors, i.e. the diminished layer of the liquid to be heated, and the turbulent liquid flow will bring the uniformity of heating of this liquid to increase. As it was mentioned above, this parameter is the most important one to the pasteurization process. On the other hand, the simplicity of the described device for pasteurization and its ability to be easily assembled, disassembled, rinsed and sterilized make it useful for pasteurization of a wide variety of liquid products, and effective for a wide scope of enterprises (both large and small) which are active in this field.

Claims (8)

1. An inductive heater for uniform heating of a liquid throughout its volume, comprising: a transformer, having at least one short-circuited secondary coil consisting of a substantially U-shaped pipe having a curved pipe portion surrounding the core of said transformer and being short-circuited at its open ends, and a pair of linear parallel pipe portions; said pipe portions serving for conveying the liquid therethrough and heating it uniformly by direct heat exchange throughout its surface, characterized in that said pipe portions comprises at least one detachable part, which can _be dismounted so as to facilitate cleaning of said pipe portions ; and an inner removable and washable turbulence means placed in the pipe so as to increase turbulence of the liquid flow, thus preventing some portions of the liquid from getting much hotter than others.

2. An inductive heater according to claim 1 , wherein said turbulence means comprises balls of at least half of the inner diameter of said U-shaped pipe.

3. An inductive heater according to claim 1 , wherein said turbulence means comprises a pair of tubular inserts, each of them being adapted to be coaxially maintained inside said linear pipe portions so as to form an annular passage for the liquid therebetween.

4. An inductive heater according to claim 3 wherein said linear portions of said U-shaped pipe are short-circuited by an additional shunting spacer located at or adjacent their ends adapted for coupling with said curved pipe portion.

5. An inductive heater according to claim 1 , wherein said curved pipe portion is detachable and said linear portions are short-circuited at or adjacent to their free ends utilizing a shunting spacer.

6. An inductive heater according to claim 1 , wherein said turbulence means has a thermal inertia equal to or less than that of said pipe and serves both for decreasing the temperature gradient inside said pipe and increasing the turbulency of the liquid flow thereinside.

7. An inductive heater according to claim 6, wherein said turbulence means is provided in the linear pipe portions only.

8. An inductive heater according to claims 6, 7, wherein said turbulence means is provided as said balls being distributed therealong in one layer so as to be in contact with each other. For the Aoplicant