GB2099118A

GB2099118A - Fluid heating device

Info

Publication number: GB2099118A
Application number: GB8210473A
Authority: GB
Original assignee: Murata Manufacturing Co Ltd
Current assignee: Murata Manufacturing Co Ltd
Priority date: 1981-04-10
Filing date: 1982-04-08
Publication date: 1982-12-01
Also published as: FR2503846B1; FR2503846A1; IT1157954B; IT8267483A0; DE3213619A1; GB2099118B; DE3213619C2; JPS57170481A; IT8267483A1

Abstract

A fluid heating device which includes a positive temperature coefficient thermistor element 22 having first and second main heating surfaces at its opposite faces, and multi-passage tubes (23), 24 each made of metallic material having a favorable heat conductivity and arranged to first pass along the first main heating surface and subsequently pass along the second main heating surface of the thermistor element so as to cause fluid to flow through the multi-passages formed in the multi-passage tubes, and thus, the fluid flowing through the multi- passages is first heated by heat of the first main heating surface and further heated by heat of the second main heating surface. <IMAGE>

Description

SPECIFICATION Fluid heating device The present invention generally relates to a heating device and more particularly, to a fluid heating device for use, for example, in a percolator or drip type coffee maker and the like for heating water.

Generally, a drip type coffee maker has a construction as shown in Fig. 1, in which water F contained in a water tank 1 is introduced into a water heating container 9 through a water pouring pipe 5 connected between the tank 1 and the container 9 and provided with a pipe junction 2 and a check valve 3, and is heated by a heater 4 provided for the water heating container 9 so as to be raised in its temperature. The water F in the container 9 thus heated is brought into a boiling state or state just before boiling, with a consequent increase of inner pressure within said container 9, and thus, urged to be discharged out of the water heating container 9 through the water pouring pipe 5 or a hot water discharge pipe 6 extending from the container 9 towards a filter basket 7 mounted on a jug 8.In the above case, since the water pouring pipe 5 is provided with the check valve 3, water F flows in a direction indicated by the arrow A, but it does not flow in a direction of the arrow B, and therefore, water F (hot water) in the water heating container 9 is discharged outside the container 9 only through the hot water discharge pipe 6.

Upon discharge of water F (hot water) in the above described manner, the inner pressure of the water heating container 9 is lowered, and by the water pressure of water F accommodated in the water tank 1, water F is again poured into the container 9 through the pipe 5. Subsequently, the pouring of water F into the container 9 and discharge thereof out of said container 9 are intermittently repeated, and water F (hot water) intermittently discharged through the hot water discharge pipe 6 is dripped into the filter basket 7 so as to be collected in the jug 8 through coffee powder or ground coffee (not shown) accommodated in the filter basket 7 in a known manner.

Conventionally, in the drip type coffee maker as described so far, for the heating device including the water heating container 9 and the heater 4, there has been proposed, for example, an arrangement as shown in Figs. 2(a) and 2(b), which includes a U-shaped base 10 of aluminum diecast material formed therein with two grooves (not particularly shown) conforming in shape to the configuration of the base 10, a water pipe 11 of aluminum or stainless steel, etc. and a heater pipe 1 2 prepared by inserting a resistant wire such as a nichrome wire or the like into a pipe made, for example, of stainless steel or Inconel (name used in trade and manufactured by Henry Wiggins Co., U.S.A.) with subsequent filling of insulating material into the pipe, which pipes 11 and 1 2 are respectively fitted into said two grooves under pressure, and a thermostat 1 3 provided at approximately a central portion of the base 10 for controlling the temperature of the heater pipe 12.

The known heating device for the drip type coffee maker as described above, however, has drawbacks as follows.

(i) Since the entire peripheral surface of the heater pipe 12 is not necessarily in close contact with the base 10, and moreover, the heater pipe 12 forced into the base 10 under pressure gives rise to a large contact heat resistance between the heater pipe 12 and the base 10, heat conductivity from the heater pipe 12 towards the base 10 is not favorably effected.

(ii) With respect to the water pipe 11 and the base 10 also, heat transfer from the base 10 towards the water pipe 11 is not favorably effected, either.

(iii) In addition to the drawbacks as described in the above items (i) and (ii), since the base 10 itself has a heat resistance, thermal efficiency is low owing to poor thermal coupling between the heater pipe 12 and the water pipe 11.

(iv) Since the resistant wire such as the nichrome wire or the like is employed, temperature adjusting switch means such as the temperature control thermostat 13 and the like is required, and thus, noises tend to be produced, with a large rippling or fluctuation in the temperature, while the time required for completion of heating the necessary amount of water is undesirably increased.

(v) For increasing the contact area between the water pipe 11 and the base 10, the number of curved or bent portions of the water pipe 11 may be increased, but in the above case, precise bending processing of the water pipe 11 is required, and even when the fitting groove is formed in the base 10 in conformity with the bendings of the water pipe 11, it is still very difficult to achieve a sufficient thermal contact between the water pipe 11 and the base 10, due to deviations etc. in the contact during fitting.

Accordingly, an essential object of the present invention is to provide a fluid heating device, for use, for example, in a drip type coffee maker and the like, which is so arranged that, by providing fluid passages made of metal with a good heat conduction and arranged to pass from one main heating surface of a flat plate-like positive temperature coefficient thermistor towards the other main heating surface thereof, the fluid is further heated by heat from the other main heating surface after having been heated by the heat of the one main surface of the positive temperature coefficient thermistor for improving heating efficiency of the fluid through direct heating of the fluid passages by said thermistor, while the temperature control switch or the like is dispensed with, through utilization of a self temperature control characteristics possessed by said positive temperature coefficient thermistor.

Another important object of the present invention is to provide a fluid heating device of the above described type which is simple in construction and stable in functioning at high reliability, and can be readily produced at low cost.

In accomplishing these and other objects, according to one preferred embodiment of the present invention, there is provided a fluid heating device which includes a positive temperature coefficient thermistor element of a flat plate-like configuration having first and second main heating surfaces at its opposite faces, and multipassage tubes each made of metallic material having a favorable heat conductivity and arranged to first pass along the first main heating surface and to subsequently pass along the second main heating surface of the positive temperature coefficient thermistor element so as to cause fluid to flow through the multi-passages formed in the multi-passage tubes, and thus, the fluid flowing through the multi-passages is first heated by heat produced by the first main heating surface and further heated by heat produced by the second main heating surface of the positive temperature coefficient thermistor element.

By the arrangement according to the present invention as described above, an improved fluid heating device has been advantageously presented, with substantial elimination of disadvantages inherent in the conventional fluid heating devices of this kind.

These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which: Fig. 1 is a schematic side sectionai view of a percolator or drip type coffee maker to which a fluid heating device according to the present invention may be applied (already referred to), Fig. 2(a) is a schematic top plan view partly in section of a conventional water heating device employed in the coffee maker of Fig. 1 (already referred to), Fig. 2(b) is a cross section taken along the line llb-llb in Fig. 2(a) (already referred to), Fig. 3 is a perspective view showing a general construction of a fluid heating device according to one preferred embodiment of the present invention, Fig. 4 is a perspective exploded view of a heating unit employed in the fluid heating device of Fig. 3, Fig. 5 is a perspective view of a multi-passage tube employed in the fluid heating device of Fig.

3, Fig. 6 is a top plan view of the multi-passage tube of Fig. 5, to which a water feed pipe and a water discharge pipe are attached, Fig. 7(a) is a perspective view of a metal fitting employed in the fluid heating device of Fig. 3, Fig. 7(b) is a perspective view of a plate spring engageable with the metal fitting of Fig. 7(a) to constitute binding means and employed in the fluid heating device of Fig. 3, Figs. 8(a) and 8(b) are schematic diagrams explanatory of temperature distributions in the multi-passage tubes employed in the fluid heating device of Fig. 3, Fig. 9 is a view similar to Fig. 3, which particularly shows a modification thereof, Figs. 10(a) and 10(b) are schematic diagrams showing configurations of the multi-passage tubes which may be employed in the modified fluid heating device of Fig. 9, Fig. 11 is a perspective exploded view showing another modification of the metal fitting employed in the fluid heating device of Fig. 3 or 9, Fig. 12 is a view similar to Fig. 11, which particularly shows a further modification thereof, Fig. 13 is also a view similar to Fig. 11, which particularly shows a still further modification thereof, Figs. 14(a) and 14(b) are schematic diagrams explanatory of another modification of the metal fitting of Fig. 13, Fig. 1 5 is a side elevational view, partly in section, of a fluid heating device according to another embodiment of the present invention, Fig. 1 6 is a perspective view showing, on an enlarged scale, a pipe member to be employed in the fluid heating device of Fig.15, and Figs. 1 7(a) and 17(b) are schematic diagrams showing still further modifications in which directions of water passing over the upper and lower main heating surfaces of the positive temperature coefficient thermistors are arranged to cross each other.

Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout several views of the accompanying drawings.

Referring now to the drawings, there is shown in Fig. 3, a fluid heating unit H1 according to one preferred embodiment of the present invention, which generally includes a heating unit 21 having a positive temperature coefficient thermistor element 22 of plate-like configuration, multipassage tubes 23 and 24 each having a large number of passages or through-holes 53 (Fig. 5) formed therein as water passages and provided in contact with the opposite surfaces of the heating unit 21, and a metal fitting 25 of a generally Ushaped cross section disposed to surround the multi-passage tubes 23 and 24 so as to hold the heating unit 21 between the tubes 23 and 24 as binding means in cooperation with a plate spring 26 which is engageable with opposite side walls of the metal fitting 25 in a manner to be described later.

Referring to Fig. 4, the heating unit 21 as described above further includes the positive temperature coefficient thermistor element 22, an insulating spacer 27 disposed below said thermistor element 22, terminal plates 28 and 29 for holding the thermistor 22 and the insulating spacer 27 therebetween, and insulating ceramic plates 30 and 31 respectively provided to further hold the terminal plates 28 and 29 therebetween.

For assembly, the positive temperature coefficient thermistor element 22 which is prepared by sintering a positive temperature coefficient thermistor material into the plate-like configuration and forming electrode layers 22a and 22b on the opposite surfaces thereof, is fitted into a rectangular opening 32 formed in the insulating spacer 27 and corresponding in its external shape to that of the thermistor element 22, and the insulating ceramic plate 30 is piled upon the terminal plate 28 disposed over the electrode layer 22a, while the insulating ceramic plate 31 is applied onto the terminal plate 29 laid on the electrode layer 22b.

The raised portions or protrusions 33 and 34 provided at opposite side edges of the terminal plate 28 are arranged to be fitted into corresponding slits 35 and 36 formed in the insulating spacer 27 so as to be folded at their distal ends for preventing positional deviation of the terminal plate 28, while raised portions 37 and 38 provided at opposite side edges of the terminal plate 29 are also fitted into corresponding slits 39 and 40 formed in the insulating spacer 27 so as to be folded at the distal ends thereof for prevention of positional deviation of said terminal plate 29.

The terminal plates 28 and 29 are further formed with projections or lugs 41 and 42, and 43 and 44 respectively for connecting lead wires (not shown) thereto, and in positions corresponding to these lugs 41 and 42 and 43 and 44, the insulating spacer 27 is formed with projections 45 and 46, while the insulating ceramic plates 30 and 31 are respectively provided with projections 47 and 48, and 49 and 50 as shown. It is to be noted that either one set of the lugs 41 and 42, and 43 and 44 provided on the terminal plates 28 and 29 may be omitted for simplification of the construction depending on necessity.

On the other hand, the multi-passage tubes 23 and 24 referred to earlier each have a structure as shown in Fig. 5.

More specifically, each of the multi-passage tubes 23 and 24 made of metallic material having a good heat conductivity such as aluminum, copper or the like may be produced, for example, by an extrusion process, and is formed with a large number of bores or through-holes 53 as water passages communicating from its one side face 51 to the other side face 52. To the one side face 51 and the other side face 52 of each of the multi-passage tubes 23 and 24, a water feed pipe 54 and a water discharge pipe 55 (Fig. 6) are fixed in the manner as described hereinbelow.

The water feed pipe 54 and the water discharge pipe 55 are each cut out at predetermined portions thereof to receive therein the one side face 51 and the other side face 52 of the multi-passage tube 23 or 24, and are secured to said tube 23 or 24 by a method such as brazing, etc.

It should be noted that the fixing of the water feed pipe 54 and water discharge pipe 55 may be effected, for example, by the known vacuum brazing method with the use of a brazing material, and in the above practice, a large number of the water feed pipes 54 and water discharge pipes 55 may be brazed efficiently at one time.

As shown in Fig. 6, one end 54a of the water feed pipe 54 and also, one end 55a of the water discharge pipe 55 are respectively sealed by brazing after having been crushed, and thus, water introduced into the water feed pipe 54 as indicated by the arrow A0 flows through the passages 53 in the multi-passage tube 23 (or 24).

as shown by the arrows Al, and is discharged from the water discharge pipe 55 as indicated by the arrow A2.

Between the two multi-passage tubes 23 and 24 having the constructions as described above the heating unit 21 is disposed as shown in Fig. 3, with the heating unit 21 and the multi-passage tubes 23 and 24 being combined into one unit by the metal fitting 25 and the plate spring 26 for the binding means which are described in more detaii hereinbelow.

Referring further to Figs. 7(a) and 7(b), the metal fitting 25 is prepared by folding a resilient metallic plate of a predetermined width into a generally U-shape as shown in Fig. 7(a), and opposite side walls 56 and 57 of said metal fitting 25 are respectively formed with openings or slits S each having lower portions with a width WO for receiving therein the projections 45, 47 and 49, and 46, 48 and 50 with a corresponding width W, of the insulating spacer 27 and insulating ceramic plates 30 and 31 for the heating unit 21, and upper portions with a width W1 for receiving therein base portions 60 and 61 formed at opposite ends 58 and 59 of the plate spring 26 (Fig. 7(b)), and also, intermediate slits 56a and 57a with a width W2 for receiving therein said opposite ends 58 and 59 of the plate spring 26.

It is preferable that the widths W, WO, W1 and W2 should be set in such a relation as W < W0, W0 < W2, and W1 < W2, and that folded portions 62 and 63 of the metal fitting 25 should be rounded to have a predetermined small radius as shown in Fig. 7(a) so that the metal fitting 25 may be brought uniformly into pressure contact with the corresponding surface of the multi-passage tube 24.

Meanwhile, as shown in Fig. 7(b), the plate spring 26 is formed by bending upwardly a spring material in a plate-like configuration, at two positions adjacent to the opposite edges thereof, while its opposite end portions 58 and 59 are reduced in the width as compared with other portions, with said end portions 58 and 59 being further notched to provide the base portions 60 and 61 described earlier.

For assembly, the multi-passage tubes 23 and 24 holding the heating unit 21 therebetween are fitted into between the side walls 56 and 57 of the metal fitting 25, and thereafter, the opposite end portions 58 and 59 of the plate spring 26 are respectively fitted into the slits 56a and 57a of the side walls 56 and 57 of the metal fitting 25 so as to securely hold the heating unit 21 and multipassage tubes 23 and 24 between the metal fitting 25 and the plate spring 26 by the spring force of the plate spring 26 as illustrated in Fig. 3.

The open end of the water discharge pipe 55 for the multi-passage tube 24 and the open end of the water feed pipe 54 of the other multi-passage water tube 23 are connected to each other by a pipe or tube not particularly shown.

With the heating device H1 described so far and having the construction as shown in Fig. 3 being applied to a water heater, for example, of the coffee maker as shown in Fig. 1, upon pouring water F into the open end of the water feed pipe 54 for the multi-passage tube 24 in the direction of the arrow B0 in Fig. 3, the water F flows through the passages 53 (Fig. 5) of the multipassage tube 24, and in the course before reaching the water discharge pipe 55, is raised in its temperature by the heat imparted to .he multi passage tube 24 by the positive temperature coefficient thermistor 22.

Meanwhile, water F discharged from the water discharge pipe 55 for the multi-passage tube 24 is introduced into the passages 53 (Fig. 5) of the other multi-passage tube 23 as indicated by the arrow B 1, through the water feed pipe 54 therefor, and before reaching the water discharge pipe 55 for the tube 23, is further heated by the heat imparted to the multi-passage tube 23 by the positive temperature coefficient thermistor 22 so as to be discharged through said discharge pipe 55 in the state of boiling or immediately before boiling as shown by the arrow B2.

Accordingly, if the above water discharge pipe 55 for the multi-passage tube 23 is arranged to be connected to the hot water discharge pipe 6 of the drip type coffee maker of Fig. 1, hot water in the state of boiling or immediately before boiling is to be dripped from said pipe 6 into the filter basket 7.

It is to be noted here that the directions of flow of water F flowing through the water passages 53 for the multi-passage tubes 23 and 24 should preferably be arranged in opposite directions to each other along the upper and lower main heating surfaces of the positive temperature coefficient thermistor 22 as described earlier.By the above arrangement, as shown in a diagram of Fig. 8(a) schematically illustrating temperature distributions for the multi-passage tubes 23 and 24, temperature of the upper main heating surface confronting a low temperature portion of the lower main heating surface of the thermistor 22 is raised, while, on the contrary, the temperature of the upper main heating surface corresponding to a high temperature portion of the lower main heating surface of the thermistor 22 is lowered, and thus, thermal stress in the positive temperature coefficient thermistor element 22 is advantageously reduced.

On the other hand, as shown in Fig. 8(b), if the water F flowing through the water passages 53 of the multi-passage tubes 23 and 24 is directed in the same direction along the upper and lower sides of the positive temperature coefficient thermistor 22, said thermistor 22 is subjected to a large thermal stress, with a consequent reduction in efficiency of the water heater.

Referring now to Fig. 9, there is shown a modification of the fluid heating device H1 of Fig.

3. In the modified heating device H2 in Fig. 9, the two multi-passage tubes 23 and 24 described as employed in the arrangement of Fig. 3 is replaced by a multi-passage tube 70 prepared, for example, by an extrustion process and folded, at its approximately central portion, into a U-shape, with the water discharge pipes 55 for the multipassage tube 24 and the water feed pipe 54 for the multi-passage tube 23 in the arrangement of Fig. 3 being omitted at one side of the heating device H2.

By the above arrangement of Fig. 9, procedures for processing and mounting the water discharge pipe 55 for the tube 24 and the water supply pipe 54 for the tube 23 required in the arrangement of Fig. 3 may be advantageously eliminated for reduction of cOst for the water heater.

It is to be noted here that, if it is intended to reduce a distance x (= thickness of the heating unit 21) in the folded multi-passage tube 70 shown in Fig. 1 0(a), in the case where half of a difference between the thickness T of the multipassage tube 70 and the outer diameter t of the water feed pipe 54 and water discharge pipe 55 as represented by (t-T)/2 is larger, for example, than x/2, the centers of the water feed pipe 54 and water discharge pipe 55 should preferably be.

deviated by a distance y (Fig. 10(a)). Meanwhile, when the distance x in the folded tube 70 and the thickness T thereof is in the relation as x < T, the water passages (not particularly shown) in the multi-passage tube 70 are subjected to a large deformation if said tube 70 is bent in the manner as shown in Fig. 10(a), with a possibility that these water passages are blocked.

In the case as described above, it may be so arranged that, as shown in Fig. 10(b), the multipassage tube 70 is bent with a radius of curvature R larger than x/2 as referred to above so as to present a configuration as shown in dotted lines in Fig. 9. By the above arrangement, the multipassage tube 70 is caused to contact, under uniform pressure, the upper and lower main heating surfaces of the thermistor 22 for the heating unit 21 in a direction perpendicular thereto.

Referring to Figs. 11 through 13, there are shown modifications of the metal fitting 25 and the plate spring 26 described as employed in the embodiments of Figs. 3 and 9.

In the modification of Fig.11, the metal fixture includes a metal fitting 72 folded into a generally U-shape and formed, in opposite side walls thereof, with notches 73 and 74, a plate member 75, and a wire spring 71 of a U-configuration as shown. For application, the wire spring 71 is engaged with the corresponding notches 73 and 74 of the metal fitting 72 so that the heating unit 21 and the muiti-passage tubes 23 and 24 (Fig.

3) orthe heating unit 21 and the folded multipassage tube 70 (Fig. 9) are held between the plate member 75 and the metal fitting 72 into one unit by the spring force of the wire spring 71.

In the above case, the plate member 75 may be dispensed with, depending on necessity.

Meanwhile, in the modification of Fig. 12, a spring portion 26B equivalent to the plate spring 26 in Figs. 3 and 9 is integrally formed with one edge of the metal fitting 25B for simplification in structure and manufacturing process, although the functions and effects thereof are generally similar to those in the combination of the plate spring 26 and metal fitting 25 of Figs. 3 and 9.

Furthermore, in the modification of Fig.13, the metal fixture includes an upper metal fitting 82 of a generally U-shape having inwardly bent portions 81 at end portions of its opposite side walls, and a lower metal fitting 84 of a similar U-shape also having corresponding outwardly bent portions 83 at end portions of opposite side walls thereof. For application, the metal fittings 82 and 84 are applied onto the combination of the heating unit 21 and the multi-passage tubes 23 and 24 (Fig.

3) or the combination of the heating unit 21 and the multi-passage tube 70 (Fig. 9) from upper and lower sides thereof for securing the combination in one unit by engaging the bent portions 81 and 83 of the metal fittings 82 and 84 with each other through a single operation.

The metal fixture of Fig. 13 may further be modified as shown in Fig. 14(a) and 14(b).

In the modification of Fig. 14(a), the upper metal fitting 82' is formed, at end portions of its side walls, with bent portions 81' and 81" directed in the same direction, while the lower metal fitting 84' is also provided at end portions of its side walls, corresponding bent portions 83' and 83" directed in the same direction to each other, but in a direction opposite to that of the bent portions 81' and 81" of the upper metal fitting 82'.For assembly, the upper and lower metal fittings 82' and 84' are fitted onto the combination of the heating unit 21 and tubes 23 and 24 (Fig. 3) or the combination of the heating unit 21 and the tube 70 (Fig. 9) from the upper and lower sides of the combination for fixing said combination into one unit by inserting pins 58 between the bent portions 81' and 83' and 81" and 83".

It is to be noted here that, although not particularly shown, the heating unit 21 and the multi-passage tubes 23 and 24 or the heating unit 21 and the multi-passage tube 70 may be secured into one unit also by screws and nuts, etc., or through caulking or staking and the like instead of employing the metal fittings or fixtures described so far.

Referring to Fig.15, there is shown another embodiment according to the present invention.

The fluid heating device H3 in Fig. 1 5 includes metallic pipes 90 made of a metal having a favorable heat conductivity and each bent or folded at several points in a zigzag manner as shown in Fig. 16, two equalizing plates 91 on which said metallic pipes 90 are secured by means, of brazing, etc., and the positive temperature coefficient thermistor element 22 sandwiched between the equalizing plates 91 and secured thereat by combining the plates 91 with screws 92 and nuts 93.In the above arrangement in which water is arranged to flow through the metallic pipes 90 along the upper and lower surfaces of the thermistor element 22, the procedures for mounting the water feed pipe 54 and water discharge pipe 55 as required when the multi-passage tubes 23 and 24 (Fig. 3) or the multi-passage tube 70 are employed, may be dispensed with, while the amount of water to be heated may be altered or adjusted by varying the diameter of the metallic pipes 90, and thus, alterations in the specifications and design of the heating device can be markedly facilitated.

It should be noted here that although the present invention has been described so far with reference to the fundamental embodiments therefor, the concept of the present invention is not limited to the foregoing embodiments alone, but may further be altered or modified in various ways within the scope. For example, the multipassage tubes 23 and 24 or the multi-passage tube 70 described as formed by the extrusion method in the foregoing embodiments may be replaced by those formed by a so-called roll-bond process in which, with bonding portions and nonbonding portions being provided during bonding between the metallic plates of different thicknesses made of aluminum or the like, the passages are formed therein by injecting air, oil, etc., under pressure through side sections of the non-bonding portions so as to cause the metallic plate with a smaller thickness to expand.

It is also to be noted that the directions of flow of water passing along the upper and lower main heating surfaces of the positive temperature coefficient thermistor element 22 may be arranged to cross at right angles with each other on the upper and lower portions of said thermistor element 22 as shown in Fig. 17(a) or 17(b).

It should be further noted that the present invention is not limited in its application to the drip type coffee maker alone, but may also be readily applied, for example, to an instantaneous water heater, and a heating device for heating fluids such as water, oil or refrigerant, etc.

As is clear from the foregoing description, according to the present invention, since it is so arranged that fluid is adapted to be heated by the positive temperature coefficient thermistor element by causing the fluid to flow through passages passing from one main heating surface to the other main heating surface of said thermistor element in the plate-like configuration, temperature adjusting devices such as a thermostat, etc. may be advantageously dispensed with, owing to the self-temperature control function possessed by the positive temperature coefficient thermistor element for appreciable reduction in cost for the fluid heating device, with simultaneous elimination of noise generation, and reduction of temperature pulsation in the fluid to be heated.

Meanwhile, since the positive temperature coefficient thermistor element may be subjected to a flat lapping or polishing process, thermal resistance between the fluid and the thermistor element can be markedly reduced as compared with the conventional practice in which the resistant wire pipe is employed, and thus, a fluid heating device having favorable thermal efficiency and thermal response, etc. may be presented.

Furthermore, owing to the positive resistance temperature characteristics possessed by the positive temperature coefficient thermistor, the fluid heating device of the present invention is capable of heating the fluid upon starting of power supply without any loss, thus resulting in a marked reduction of the total heating time for heating the fluid, while, due to the fact that the power consumption is controlled depending on the magnitude of loads, extremely favorable energy efficiency may be achieved.

Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be noted here that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as included therein.

Claims

1. A fluid heating device which comprises a positive temperature coefficient thermistor element of a flat plate-like configuration having first and second main heating surfaces at opposite faces thereof, and fluid passage means made of metallic material having a favorable heat conductivity and arranged to first pass along said first main heating surface and to subsequently pass along said second main heating surface of said positive temperature coefficient thermistor element so as to cause fluid to be heated, to flow through said fluid passage means, whereby the fluid flowing through said fluid passage means, is first heated by heat produced by said first main heating surface and further heated by heat produced by said second main heating surface of said positive temperature coefficient thermistor element.

2. A fluid heating device as claimed in Claim 1, wherein said positive temperature coefficient thermistor element constitutes a heating unit together with plate members arranged to contact said first and second main heating surfaces of said thermistor element and said fluid passage means.

3. A fluid heating device as claimed in Claim 2, wherein said fluid passage means is of tube means having a plurality of fluid passages formed therein and so disposed as to receive heat from said first and second main heating surfaces and provided with a fluid supply port and a fluid discharge port communicated with said fluid passages.

4. A fluid heating device as claimed in Claim 3, wherein said tube means includes a first multipassage tube and a second multi-passage tube made of metallic material of a favorable heat conductivity and respectively provided along said first and second main heating surfaces of said positive temperature coefficient thermistor element.

5. A fluid heating device as claimed in Claim 3, wherein said tube means is a multi-passage tube member made of metallic material of a favourable heat conductivity and formed into a configuration of U-shaped cross section so as to be disposed along said first and second main heating surfaces of said positive temperature coefficient thermistor element.

6. A fluid heating device as claimed in Claim 3, wherein said tube means includes a first and second pipe members made of metallic material of a favorable heat conductivity and bent into a zigzag configuration, and respectively provided along said first and second main heating surfaces of said positive temperature coefficient thermistor element.

7. A fluid heating device as claimed in Claim 2, wherein the fluid flowing through said fluid passages along said first and second main heating surfaces of said positive temperature coefficient thermistor element is directed in directions opposite to each other.

8. A fluid heating device as claimed in Claim 2, wherein the fluid flowing through said fluid passages along said first and second main heating surfaces of said positive temperature coefficient thermistor element is directed in directions intersecting at right angles with each other.

9. A fluid heating device as claimed in Claim 2, wherein said heating unit and said fluid passage means are combined into one unit by binding means so as to constitute said fluid heating device.

1 0. A fluid heating device as claimed in Claim 9, wherein said binding means includes a metal fitting receiving therein said heating unit and said fluid passage means, and a spring member engageable with said metal fitting so as to combine said heating unit and said fluid passage means into one unit.

11. A fluid heating device as claimed in Claim 9, wherein said binding means includes a metal fitting receiving therein said heating unit and said fluid passage means, a plate member, and a wire spring member engageable with said metal fitting so as to combine said heating unit and said fluid passage means into one unit through said plate member.

12. A fluid heating device as claimed in Claim 9, wherein said binding means is a metal fitting having a receiving portion for receiving therein said heating unit and said fluid passage means, and a spring portion acting as a plate spring and engageable with said receiving portion so as to combine said heating unit and said fluid passage means into one unit.

13. A fluid heating device as claimed in Claim 9, wherein said binding means includes a metal fixture having a first metal fitting and a second metal fitting holding said heating unit and said fluid passage means therebetween, and engageable with each other at opposite edge portions thereof so as to combine said heating unit and said fluid passage means into one unit.

14. A fluid heating device as claimed in Claim 13, wherein said opposite edge portions of said first and second metal fittings are arranged to be engaged with each other through pin members.

1 5. A fluid heating device as claimed in Claim 9, wherein said binding means includes set screws extending through said plate members on which said fluid passage means is secured, and engaged with corresponding nuts so as to combine said heating unit and fluid passage means into one unit.

1 6. A fluid heating device as claimed in Claim 15, wherein said plate members are equalizing plates, said fluid passage means includes metallic pipe members having a favorable heat conductivity and each bent at a plurality of places thereof in a zigzag manner so as to be fixed onto said equalizing plates.

1 7. A fluid heating device, as hereinbefore described, with reference to, and as shown in, the accompanying drawings 1 and 3 to 1 7.