The present invention relates to heating and cooling apparatus, and in particular but not exclusively to bench top heating and cooling plates and columns on which an object to be heated or cooled is supported thereon.

There are a number of commercial products available that can provide hot and cold operating conditions. These generally fall into two categories. The first category use Peltier elements. These electric elements are inefficient and use a lot of electricity. In addition to being expensive to run, Peltier device based coolers are usually bulky as it is necessary to house large, low voltage, high current, units to supply the power required for the Peltier elements. Some Peltier devices also require water cooling.

Oil circulators form the second category of heater/coolers. They are bulky, have slow response times, and require pipe connections to the object being either heated or cooled. The response time can be improved by using powerful refrigeration systems though these are expensive.

US 6324857 relates to a temperature controlled bath with both heating and cooling elements (20, 8) submerged within the bath fluid (3). Control of the cooling function is achieved by regulating an expansion valve (7) which controls refrigerant flow through the cooling element (8). The expansion valve is connected to a control line (9) containing a liquid. Regulation of the expansion valve is achieved by varying the temperature of the liquid within the control line using a heater (13) and refrigerant. The refrigerant is either passed through the cooling element (8) or has been introduced via a bypass line (16) downstream of the cooling element. The resulting contraction or expansion of the fluid acts to open or close the expansion valve.

US6938432 relates to a cooling apparatus in which the degree of cooling is achieved by regulating a valve (10). The evaporator maybe incorporated into a plate (15) provided with a temperature sensor (22) linked to the regulating valve (10). The refrigerant flow into the cooling element is also regulated by a further valve (5) to ensure that the refrigerant remains as a gas liquid mixture whilst in and downstream of the evaporator. This is to ensure that the temperature of the refrigerant is uniform throughout the evaporator so there is no variation of temperature across the plate. The apparatus is provided with a heater (11) downstream of the evaporator to ensure all refrigerant is in the gas phase before it reaches the compressor (2). The plate is provided with a separate heater (19) used to warm and dry the plate after a cycle of operation.

The present invention was conceived to provide an efficient, fast thermal response device which could act to heat and/or cool an object through a wide range of operating temperatures (e.g. 250 degrees centigrade down to -150 degrees centigrade) extending both above and below ambient, and in particular to provide precise temperature control of an object at sub ambient temperatures. According to the Invention there is provided heating and cooling apparatus comprising: a surface for supporting an object to be heated or cooled; a heater having a heating element to heat the surface; a vapour compression refrigeration system comprising an evaporator through which a refrigerant flows to cool the surface; means to sense the temperature of the surface and/or the object, and the temperature of at least one of the heating element and the evaporator, and to output signals indicative of these temperatures; a control means to receive the output signals and in response thereto to control operation of the heater and refrigeration system together in order to control the temperature of the surface ; and wherein the heater element is positioned substantially at the exit of a capillary/expansion valve forming part of the vapour compression refrigeration system to provide thermal energy to the refrigerant as it enters the evaporator.. The invention provides convenience as the surface, which may take the form of a plate, can be used directly to support an object and control its temperature precisely through a wide range of temperatures without the need for complex oil baths/circulator connections and the like. Use of the invention enables a device which is compact in size compared to a Peltier device or an oil circulator.

The use of a plate additionally allows other sensing equipment to be easily incorporated allowing the user to measure the influence of temperature to other physical properties of the object.

In a preferred embodiment, the control unit is capable of operating both the compressor and the heating element simultaneously, though a similar benefit may be achieved by switching between the two in quick succession.

In order to achieve a target temperature, the control means typically measures the actual temperature of the surface and the change in rate of the actual temperature, and in response adjusts the power to the heater and cooling system.

The above measurements alone make it hard to provide precise control of the actual temperature of the surface or rate of change of surface temperature because a change in the power provided to either the heater and cooling system does not necessarily produce a proportional response.

By sensing the temperature of both the surface/object, and the heating element/evaporator, more accurate control of the temperature of the surface/object can be achieved. In the most preferred embodiment, the temperature of both the heating element and evaporator are measured. It is preferred that a thermally conducting path exists between the surface, heating element and evaporator. When thermal energy is transferred between these elements primarily through conduction, thermal energy is transferred more quickly, leading to a faster response time as compared with using an immediate fluid to transfer heat between the heating element/evaporator and the object.

A consequence of a faster response time is better control of monitoring processes which require a change in the rate of heating or cooling. Experimentation has indicated that apparatus according to the invention is able to provide control within 0.1 degree C over a wide a range of temperatures both above and below ambient. Examples of processes where the rate is critically important include: solubility, crystallisation, surface diffusion, gas absorption and chemical reaction processes.

The thermally conducting path may be provided through a bridging medium comprising a material having a high thermal conductivity, e.g. of copper or aluminium. For example in one embodiment this bridge could be provided by a casing - housing the heater element and evaporator and defining the surface. Alternatively at least two of the heater, the evaporator and the surface are in direct physical contact with one another, and favourably that the third is in direct physical contact with at least one of the other two. It is most preferred that each of the evaporator, heating element and surface are in contact with the other two. This ensures that thermal energy between all three is transferred as quickly as possible.

It has hitherto been difficult to accurately control the temperature of a plate at sub ambient temperatures because the refrigerant provides a large and instantaneously cooling impact.

This problem has been ameliorated by positioning the heating element to provide thermal energy to the refrigerant flowing through an upstream portion of the evaporator, adjacent the entrance of the evaporator, i.e. the exit of the expansion valve where evaporation first takes place. In this way the heat from the heating element can be used to quickly offset the cooling generated by the evaporated refrigerant. It is preferred that the control means is arranged to vary the speed of a compressor forming part of the vapour compression refrigeration system in order to control the flow of the refrigerant through the evaporator. This may be achieved by providing a compressor powered by a direct current source, and that the control means can vary the current to the compressor to control its speed. This is advantageous over a system in which the compressor is either in an off or on state, and switched between these states as it provides greater control over the rate of flow of refrigerant, and thus control of the cooling effect of the system. This is because there is usually a significant time lag between turning a compressor on and it being effective at pumping refrigerant around the cooling system.

In a preferred embodiment the apparatus comprises a heating/cooling plate, the surface being defined by the plate. In an alternative preferred embodiment, the surface is defined by a column. Where the surface is defined by a column, the apparatus may comprise a further heater arranged substantially at one end of the column, and controlled by the control means in order to provide a temperature gradient across the length of the column. In certain preferred embodiments, the apparatus may further comprise a rotatable magnetic stirring mechanism which can be used when the object to be heated includes a liquid. Typically this would be housed under the surface and operable with a magnetised or magnetisable stirring element placed within the liquid. Expected uses for the invention include but are not limited to: chemical, medical, food and technology sectors.

The invention is described by way of example with reference to the following figures in which:

Figure 1 is a part exploded perspective view of a heating and cooling plate; Figure 2 is a schematic of the heating and cooling plate of Figure 1 ;

Figure 3 is a part exploded perspective view of a heating and cooling column; Figure 4 is a schematic of the heating and cooling column of Figure 3;

Figure 5 is a schematic illustrating an alternative embodiment of a heating and cooling plate in which the capillary is replaced with a variable valve; Figure 6 is a schematic illustrating a further embodiment of a heating and cooling plate comprising a bypass line for refrigerant in order to lower the temperature of refrigerant entering the compressor; and

Figure 7 is a schematic illustrating a further embodiment in which the system comprises a heat exchanger downstream of the evaporator in order to lower the temperature of refrigerant before it enters the compressor.

Referring to Figures 1 & 2 there is shown a heating and cooling plate comprising a housing I, an insulation plate 2, a cylinder 3 which supports a plate 4 onto which an object (e.g. a beaker of liquid) to be heated or cooled can be placed. The plate 4 comprises a material with high thermal conductivity such as copper or aluminium. Within the cylinder 3 and directly below the plate 4 is an electrical heating element 5 and a refrigeration coil 6. The refrigeration element 6 is arranged to be in direct physical contact with the heating element 5. The refrigeration element is formed as a coil nested in a space formed within the arcuate heating element 5. The heating element 5 and refrigeration coil 6 are positioned such that the heating element 5 runs substantially alongside the outermost coil 6, so that they are in direct physical contact. The refrigeration element 6 and heating element 5 are arranged within the cylinder 3 such that when the plate 4 is mounted onto the cylinder 3 it is substantially in physical contact with both the refrigeration coil 6 and heating element 5. The refrigeration coil 6 forms part of a closed vapour compression refrigeration system which also comprises a compressor 7 for compressing gaseous refrigerant flowing from the refrigeration coil 6, a condenser 8 for condensing compressed refrigerant from the compressor 7, a capillary 9 for controlling the flow of liquid refrigerant into the wider refrigeration coil 6. Refrigerant entering the coil 6 evaporates (fully or partially) before flowing back to the compressor 7. The evaporation of the refrigerant provides the cooling effect of the cooling coil 6.

More precise control of the temperature of the plate is found when the heating element is arranged to heat the refrigerant as it flows through an upstream portion of the cooling coil and in particular at or near the exit of the capillary.

Within 25mm from the exit of the capillary running for throughout the length Purposeful direct heating of the refrigerant allows the temperature of the plate 4 to be more precisely controlled, in particular it allows more precise control of the heating and cooling of plate 4 through temperatures including those below ambient over a refrigeration system alone. An example of a suitable compressor 7 is a rolling piston rotary gas compressor or a miniature rotary compressor as provided by Aspen Compressor, LLC. The compressor 7 is powered by direct current. Its speed is controlled by a control unit 11 (see below) by varying the magnitude of the direct current supplied to it. This is used to vary the flow rate of refrigerant through the system and thus control the cooling power of the refrigeration system.

Also within cylinder 3, there is provided a rotatable magnet means 10 for use as part of a magnetic stirrer. The rotating magnetic means is located in position central and below the plate 4, at the centre of the cooling coil 6.

The apparatus further comprises a control unit 11 (shown schematically in Figure 3) comprising a processor and associated circuitry. An example of a suitable unit is the Eurotherm Nanodac Recorder/Controller supplied by Eurotherm Ltd (UK). The control unit 11 typically also includes a user interface 11A in order that the control unit 11 can be programmed with conditions for heating/cooling operations, examples of input data may include the target temperature(s), time to hold at a target temperature, and the rate of temperature change (gradients between target temperatures).

The apparatus also includes a temperature sensor 12A for sensing the temperature of the heating element 5; a temperature sensor 12B for sensing the temperature of the cooling element 6; and a temperature sensor 12C for sensing the temperature of the plate 4. Temperature sensors 12A, 12B and 12C, which may be resistance thermometers, produce output signals indicative of the respective temperatures measured; these outputs are received by the control unit 11. The control unit 11 is programmed, using techniques familiar to persons skilled in the art, e.g. PID or CASCADE, to control the temperature of the plate 4 in view of specific conditions of a heating/cooling operation and in response to the output signals received from the temperature sensors 12A, 12B. The control 11 can use one or more of a number of operating methods. In one method the control unit 11 can vary the current through the heating element 5 only, to increase or decrease the thermal energy provided by it. In a second method, it can vary the current to the compressor 7 only, in order to vary the cooling power of the refrigeration element 6. In a third method it controls the current to both the heater element 5 and the compressor 7 together which may preferably be simultaneous. This latter method is particularly effective where it is wished to vary the temperature of the plate precisely or to gradient the temperature of the plate 4 with time. Because a thermally conductive path exists between each of the heating element 5, cooling element 6 and plate 7, thermal energy is transferred to/from the plate very quickly. And because the heating element is located adjacent the exit of the capillary 9, any change in the latent heat from the evaporating refrigerant can, if needed, be offset very quickly. A second embodiment is illustrated in Figures 3 & 4 in which like components are given corresponding numbering. The plate 4 is replace by a cylinder or column 4A and the cooling element 6A is formed as a helix nested so as to run alongside and contact the inner wall of the cylinder 4A. A heating jacket 5A is arranged substantially around a portion of the cooling element 6A at or adjacent the exit of the capillary 9 in order to heat refrigerant as it enters the cooling element 6A.

This embodiment also comprises a second heater element 5B which is arranged within the cylinder substantially at one end thereof (in this case the top end).

In use a conduit (not shown) for carrying a fluid to be heated or cooled is positioned (e.g. wrapped) around the outer surface of cylinder 4A. The temperature of the outer surface of the cylinder 4A is controlled and varied as before by adjusting the power to the compressor 7 and/or heating element 5 A; this is controlled by the control unit 11. Heating element 5B can be used where it is desired to provide a temperature profile across the height of the cylinder 4A; when in operation the upper portion will be heated by the heater 5B, whilst the lower portion will remain cooled by cooling element 6B. Varying the power to heating elements 5A, 5B and compressor 7 can be used to vary the temperature profile across the height of the cylinder 4A.

Figure 5 illustrates an alternative embodiment which is identical to Figure 2 other than the capillary 9 is replaced by a variable valve 15. This may be opened and closed, if necessary to further control the rate of refrigerant flow through the system. Similarly a variable valve may be used in place of the capillary 9 in the embodiment of Figure 3. In a further embodiment not shown, the control unit 11 may be arranged to control the variable valve 15 instead of the compressor 7. In one method, control of the variable valve is achieved using a fixed voltage and a control signal from control unit 11.

Figure 6 illustrates a further alternative embodiment provided with a by-pass line 16 which incorporates a capillary or variable valve 16A. The function of the by-pass line is to divert a portion of liquid refrigerant passed the refrigeration element 6, and to reintroduce the liquid refrigerant into the conduit between the cooling element 6 and the compressor 7. Once exiting the capillary 16A the refrigerant evaporates thereby reducing the temperature of refrigerant flowing to the compressor 7. This feature is thought to be of use when refrigerant in the cooling element may be heated to a temperature that could damage the compressor 7. This may occur when the refrigeration system is being used to cool down the plate from a high temperature.

Figure 7 illustrates a further alternative in which the temperature of refrigerant flowing to the compressor is cooled by passing it through a second heat exchanger 14 subsequent to flowing through the refrigeration element 6.

Other variations to the above examples are envisaged which fall within the scope of the appended claims. For example, the support and housing for the heating element and refrigeration element take forms other than cylindrical.

The refrigeration element may be shaped other than as a coil. The heating element make be shaped other than arcuate so long as it is arranged to run alongside a portion of the refrigeration element.

Although the heating element and refrigeration elements are shown as tubes with substantially circular cross sections, the element may be formed such that a portion of the surface in contact with the plate 4 and or heating element 5 is planar or flattened. This enables a larger contact area with the surface than an element with a generally circular cross section.

The surface may be provided by forms other than a plate or cylinder, including but not limited to cuboidal, prism shaped and ovoid.

The apparatus may comprise multiple closed looped vapour compression refrigeration systems, preferably arranged to work in a cascade in order to achieve lower maximum operating temperatures. The arrangement of cascade systems is well known in the art.

The surface may be formed from a flexible material. For example the surface may be defined from a sheet of flexible material such as silicone, or from a woven or matted material or fibrous material such as glass fibre.

It may be possible to omit one of the temperature sensors associated with either the heating element or the cooling element so long as a good thermal contact exists between them.