GB2107042A

GB2107042A - Apparatus for controlling the temperature of a fluid

Info

Publication number: GB2107042A
Application number: GB08129331A
Authority: GB
Inventors: Reginald Arthur Lodge
Original assignee: Oxy Metal Industries Corp
Current assignee: Oxy Metal Industries Corp
Priority date: 1981-09-29
Filing date: 1981-09-29
Publication date: 1983-04-20
Also published as: NL8203787A; ES8400614A1; JPS5869331A; GB2107042B; ES516032A0; FR2513776A1; DE3233577A1

Abstract

Apparatus for controlling the temperature in a fluid which comprises an agitator 13 which both agitates and heats the fluid. The heating is achieved by means of electric heater elements within the agitator blades. The apparatus is particularly for use in an air circulatory oven. <IMAGE>

Description

SPECIFICATION Apparatus for controlling the temperature of a fluid The present invention relates to apparatus for controlling the temperature of a fluid for example, a fluid which is kept in a state of agitation.

Two of the disadvantages of known apparatus for performing these functions is that it is frequently difficult to achieve good heat transfer to/from the fluid and also difficult to achieve a truely even temperature throughout the fluid with a result that hot-spots may occur.

It is an object of the present invention to provide apparatus for fluid temperature control which is compact and in which heat is transferred more efficiently while at the same time achieving a substantially even temperature distribution.

According to the invention, apparatus for controlling the temperature of a fluid, comprises an agitator arranged to agitate the fluid, the agitator having heating or cooling means arranged to effect the heat exchange with the fluid through the surface of the agitator.

The fluid, which may be a gas, liquid orfluidised solid, may have its temperature controlled by being heated, cooled or maintained at a constant temperature.

Using such apparatus it may be possible to achieve an even temperature distribution throughout the fluid at high efficient heat exchange rates since the heat dissipation per unit area of heater may be higher. Thus the radiation area may be reduced and a smaller heat source used. Also, the substantially total heat transfer to the moving fluid results in the virtual elimination of hot-spots, while the absence of heating/cooling banks can result in a reduction in the pressure drop across the apparatus. Furthermore, in applications where directional control of heated fluid is desired, this may be achieved more easily using apparatus in accordance with the invention.

Finally, such a construction may be compact and also economical to operate.

Preferably the agitator is a fan for circulating a gas, and preferably, the fan has blades which include electrical heating elements. In such a case, the fluid may be compressed adjacent the blades resulting in improved heat transfer.

Heating elements may be connected to an external electricity supply or may be connected to a generator driven by a motor for the fan. In the latter case, the heater may work only when the impeller is rotating so that the apparatus will effectively be self-protecting or fail-safe.

Alternatively the agitator may be an impeller or some other stirrer for a liquid.

The agitator may be provided, in place of electrical heating elements, with channels for a heat exchange medium which may effect heating or cooling.

Thus the invention may be applied to fans in ovens, stirrers in liquid tanks, air conditioning plants, driers, e.g. domestic hair driers and mobile heaters and coolers.

In the case of ovens, an oven preferably comprises a housing in combination with an agitator as described above, the agitator being within the housing and being driven by a motor outside the housing.

In known ovens having an air circulation fan, the heat is supplied by means of standard heating elements in the oven, frequently in the oven walls, however, in the preferred oven construction, the heat transfer may be more efficient and the possibility of hot-spots minimised.

The oven may include an inner chamber spaced from the outer housing, the agitator being located in the space and arranged to draw gas from within the inner chamber, to effect heat exchange with the gas and to circulate the gas back into the inner chamber.

Apparatus in accordance with the invention may also show a number of economic advantages.

Thus use of a single unit to achieve movement and temperature control of the fluid means that such'a system may be cheaper and also smaller thus saving space and minimising weight. Also, the power consumption may be reduced. Further, standardisation may be easier which may reduce costs and also may make maintenance easier, and render the use of standby units financially viable.

Economic savings may also be made when built-in power transformation is employed.

The invention may be carried into practice in various ways and one embodiment will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic vertical section through the right-hand half of a fan assembly; and Figure 2 is a diagrammatic vertical section through an air circulatory oven incorporating a fan assembly as shown in Figure 1.

The assembly shown in Figure 1 comprises an electric motor 11 with a hollow drive shaft 12 having a fan 13 mounted at the lower end. The motor 11 is supplied through a slip ring arrangement 14 and is connected to a heat insulation plug 1 5 by means of a plate 1 6 which carries a lifting handle 17.

The shaft 12 rotates in the motor 11 by means of a plain bearing 1 8 and carries a heat dissipation plate 1 9 which extends radially between the motor 11 and the insulation plug 1 5.

The fan 13 comprises six fins 21 only one of which is shown. Each fin 21 carries a blade 22 which includes an electrical heating element shown diagrammatically by broken line 23. In the present embodiment, the blades 22 are formed of CHROMALOX (Registered Trade Mark). The heating element 23 is supplied with current via heat resistant cables 24 connected to the same supply as the motor 11. In the present embodiment the cables are of PYROTENEX (Registered Trade Mark). The amount of heat which travels back to the motor 11 via the shaft 12 is reduced to an acceptable level by the dissipation plate 1 9.

Figure 2 shows the assembly of Figure 1 incorporated in an air circulatory oven, which in this instance is a low temperature annealing furnace which operates at up to 7000 C.

The oven comprises an outer housing 31, including two layers of refractory material for heat insulation, and an inner chamber 32 made from 18/8 stainless steel. The housing 31 has an aperture in its top wall which houses the insulation plug 1 5. This locates the motor 11 and fan 1 3 in position with the motor 11 outside and above the housing 31, and the fan 13 inside the housing 31 but above the chamber 32. The oven stands on legs 33, two of which are shown.

The chamber 32 is attached to the housing 31 and is spaced from it on all sides leaving a space 34. The chamber 32 has an opening 35 in its upper surface immediately beneath the fan 13, while its base is in the form of a screen 36.

In operation, power is supplied to the motor 11 and the heating elements 23 in the blades 22. As the fan 1 3 rotates, therefore, the blades 22 heat the air which immediately surrounds them and moves this air outwards and downwards in the direction of arrows A in the space 34 between the chamber 32 and the housing 31. To replace this heated air, air is drawn up through the inner chamber 32 in the direction of arrows B, and through the aperture 35. This latter air is then replaced by the earlier heated air which travels through the space 34 and into the chamber 32 via the screen 36. Thus it will be seen that the air in the oven is heated and circulated by the fan 13, so heating the oven and any contents within the chamber 32.

Although not shown, there may be baffles located in the space 34 to achieve the desired air flow pattern. Furthermore, there is a control system (not shown) associated with the oven which comprises a number of temperature sensors at various positions within the oven connected to a controller. The controller adjusts the power supply to the motor 11 and to the heating elements 23 in dependence upon the desired temperature and the temperatures sensed by the sensors, so that the degree of circulation and the amount of heat supplied can each be increased or decreased to achieve an even temperature distribution at the desired level.

Whilst it is preferred that the heating or cooling means should be located within the agitator e.g. in the blades of a fan type agitator, it will be appreciated that the heating or cooling means may form part of the surface of the agitator. The heating or cooling means may alternatively be located on the surface of the agitator thus affording part of the surface of the agitator through which the heat exchange occurs.

Both CHRONALOX and PYROTENEX referred to above are proprietory materials and comprise a heating element within a heat-resistant sheath, with an insulating material such as mica in between.

Claims

1. Apparatus for controlling the temperature of a fluid, comprising an agitator arranged to agitate the fluid, the agitator having heating or cooling means arranged to effect heat exchange with the fluid through the surface of the agitator.

2. Apparatus as claimed in Claim 1 in which the agitator is a fan for circulating a gas.

3. Apparatus as claimed in Claim 2 in which the fan has blades which include electrical heating elements.

4. Apparatus as claimed in Claim 3 in which the elements are connected to an external electricity supply.

5. Apparatus as claimed in Claim 3 in which the elements are connected to a generator driven by a motor for the fan.

6. Apparatus for controlling the temperature of a fluid constructed and arranged substantially as herein specifically described with reference to and as shown in Figure 1 of the accompanying drawings.

7. An oven comprising an outer housing in combination with an agitator as claimed in any of Claims 2 to 6, the agitator being within the housing and being driven by a motor outside the housing.

8. An oven as claimed in Claim 7 further including an inner chamber spaced from the outer housing, the agitator being located in the space and arranged to draw gas from within the inner chamber, to effect heat exchange with the gas and to circulate the gas back into the inner chamber.

9. An air circulatory oven constructed and arranged substantially as herein specifically described with reference to and as shown in the accompanying drawings.