Abstract:
The invention provides drying apparatus including a first chamber for receiving articles to be dried and having an outlet, a second chamber having an outlet, and a fan having a fan inlet and a fan outlet, the fan inlet communicating with the outlet of the first chamber and the fan outlet communicating with the second chamber. The apparatus further includes a vacuum pump communicating with the outlet of the second chamber so that transfer of thermal energy can take place between the first and second chambers. The invention also provides a method of drying including placing articles into a first chamber, evacuating a significant proportion of the air from the first chamber and from a second chamber, evacuating water vapor from the first chamber to the second chamber, allowing the water vapor to condense in the second chamber, and transferring thermal energy from the second chamber to the first chamber.

Description:
FIELD OF THE INVENTION 
     The invention relates to drying apparatus and to a method of drying articles. Particularly, but not exclusively, the invention relates to domestic drying apparatus for drying laundry articles or kitchenware and crockery and to a method suitable for use in a domestic environment. 
     BACKGROUND OF THE INVENTION 
     Conventional methods of drying laundry articles involve tumbling the articles in a drum whilst a warm airstream is passed therethrough. The water trapped in the articles evaporates into the warm airstream and is carried out of the drum therewith. The water vapour is either released into the atmosphere or condensed out of the airstream and collected to be drained off. Conventional methods of drying articles in a dishwasher device also involve passing heated air over the articles to cause evaporation of the water lying on the articles and removing the water vapour with the airstream. The disadvantages of these methods include the fact that the articles to be dried are often subjected to high temperatures if a particularly fast drying time is required. In the case of clothes dryers, this can damage the fabric and, in the case of dishwashers, the crockery becomes too hot to handle as soon as the washing and drying cycle has finished. 
     It is a well known principle that water will boil at a temperature lower than 100° C. if the pressure in the vessel in which it is contained is reduced below atmospheric. Proposals for drying laundry articles based on this principle have been put forward but, to date, none has been found to be sufficiently effective to form the basis for a commercially-viable drying apparatus. The principal reason for this is that the vacuum pump by means of which the chamber containing the articles to be dried is evacuated is required to deliver very high flow rates, in order to be able to evacuate the evaporating water vapour, and to develop a high pressure drop thereacross. Such components, whilst available on the market, are prohibitively expensive for use in the context of domestic apparatus. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide drying apparatus capable of operating on the principle of reduced pressure so as to evaporate water vapour from articles at a temperature lower than 100° C. and which is more cost-effective than previously proposed arrangements. It is another object of the invention to provide drying apparatus which is suitable for use in the domestic environment. It is a further object of the invention to provide a method of drying articles based on the principle of reduced pressure so as to evaporate water vapour from articles at a temperature lower than 100° C. which is more cost-effective than previously proposed methods. It is a still further object of the invention to provide a method of drying articles which is suitable for use in the domestic environment. 
     The invention provides drying apparatus comprising a first chamber for receiving articles to be dried and having an outlet, a second chamber having an outlet, and a fan having a fin inlet and a fan outlet, the fan inlet communicating with the outlet of the first chamber and the fan outlet communicating with the second chamber, the apparatus further comprising a vacuum pump communicating with the outlet of the second chamber, the arrangement being such that transfer of thermal energy can take place between the first and second chambers and means are provided for causing forced circulation of water vapour contained within the first chamber. 
     The arrangement provided avoids the need to provide a vacuum pump capable of developing a high pressure drop and delivering a high flow rate. Essentially, the arrangement allows the first and second chambers to be evacuated after which the water vapour evaporated in the first chamber is condensed in the second chamber without being passed through the vacuum pump. Hence the vacuum pump is required to deliver only a relatively small volume of gas. As such, the cost of the components is kept to a minimum. 
     The arrangement also takes advantage of the fact that, when the water evaporates in the first chamber, it absorbs energy which, in the absence of any input of energy, causes a drop in temperature. Similarly, when the water vapour condenses in the second chamber, it releases energy. However, if the temperature in the first chamber drops significantly, the pressure reduction therein will need to be greater to ensure that the water in the articles is evaporated. Thus, the transfer of thermal energy from the second chamber to the first chamber maintains the temperature in the first chamber and allows the pressure in both chambers to be maintained at an achievable value without reducing the rate at which water can be evaporated in the first chamber. 
     An advantage provided by the invention, when used in the field of clothes dryers, is that effective drying can be carried out relatively quickly without subjecting the articles to be dried to excessively high temperatures. When used in the field of dishwashers, a similar advantage is that, at the end of the washing and drying process, the crockery and kitchenware are at a temperature which is not too hot to be handled immediately. 
     In a preferred arrangement, the first and second chambers have at least one common wall, with the or each common wall being thermally conductive. If the common wall is thermally conductive, it will remain at a lower temperature than the second chamber and so provide a surface on which the water vapour will readily condense. Also, the latent heat of condensation will then pass through the thermally conductive wall into the first chamber to maintain the temperature therein and so encourage the water therein to evaporate from the articles. This increases the efficiency of the apparatus as a whole. 
     Preferably, the first chamber is located partially, more preferably wholly, inside the second chamber. Such an arrangement maximises the area of the common wall available to the water vapour for condensation purposes. 
     It is also preferable, at least for applications in the laundry field, if the first chamber is mounted so as to be rotatable about an axis and means are provided for causing the first chamber to rotate about the axis. In an alternative embodiment, the first chamber may comprise an outer housing and an inner drum, with the outer housing being held stationary with respect to the second chamber and the inner drum being mounted so as to be rotatable with respect to the outer housing. In either case, the articles (which will be articles of laundry) can be tumbled within the first chamber so that different portions of the articles are caused to come into contact with the chamber or drum during the drying process. This reduces the risk of the articles being dried in some places and not others. 
     The alternative embodiment mentioned above can also include at least one vane or blade for causing circulation of air or water vapour within the first chamber when the drum is caused to rotate. This encourages the water vapour to pass across and through the articles to be dried and maximises evaporation of the water within the first chamber. 
     It is preferred that the apparatus is a clothes dryer or a dishwasher. 
     The invention also provides a method of drying articles comprising the steps of:
         (a) placing the articles into a first chamber;   (b) evacuating a significant proportion of the air from the first chamber and from a second chamber;   (c) evacuating water vapour from the first chamber to the second chamber;   (d) allowing the water vapour to condense in the second chamber;   (e) transferring thermal energy from the second chamber to the first chamber; and   (f) causing forced circulation of the air and/or water vapour contained within the first chamber.       

     By transferring thermal energy from the second chamber to the first chamber, the method minimises energy consumption whilst maximising water evaporation in the first chamber. The power consumption required to operate the vacuum pump is also minimised. 
     In a preferred embodiment, the articles are tumbled or otherwise agitated during at least part of the drying process. This maximises the area of contact of the articles with a surface which is at a relatively high temperature and thus reduces the risk of areas of the articles remaining wet or damp. 
     Preferably, the air and/or water vapour in the first chamber is forced to circulate therein, more preferably through the articles themselves, so as to improve the removal, by evaporation, of water which might otherwise remain trapped within the articles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, wherein: 
         FIG. 1  is a schematic side sectional view through a first embodiment of the invention; 
         FIG. 2  is a schematic side sectional view through a second embodiment of the invention; 
         FIG. 3   a  is a schematic side sectional view through a third embodiment of the invention; 
         FIG. 3   b  is a transverse sectional view of the embodiment shown in  FIG. 3   a  taken along the line III—III; 
         FIG. 4   a  is a schematic side sectional view through a fourth embodiment of the invention; and 
         FIG. 4   b  is a transverse sectional view of the embodiment shown in  FIG. 4   a  taken along the line IV—IV. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A first embodiment of the invention is illustrated in FIG.  1 . In  FIG. 1 , the drying apparatus according to the invention takes the form of a dishwasher  10 . The dishwasher  10  comprises an outer casing  12  having an upper wall  12   a , side walls  12   b  and a base  12   c . Suspended between the side walls  12   b  and sealingly attached thereto, is a tray  14  which is inclined downwardly towards an outlet  16 . The outlet  16  is connected to a discharge pipe  18  which leads out of the dishwasher  10  and includes means (not shown) for connecting the discharge pipe  18  to a suitable drain for removing waste water from the dishwasher  10 . A pump  20  and a one-way, non-return valve  22  are arranged between the outlet  16  and the discharge pipe  18  for reasons which will be explained below. The pump  20  and the non-return valve  22  are located and housed in a lower chamber  24  delimited by the tray  14 , the base  12   c  and the lower portions of the side walls  12   b.    
     An upper chamber  26  is delimited by the tray  14 , the upper wall  12   a  and the upper portions of the side walls  12   b . This upper chamber  26  is manufactured so as to be substantially airtight. Appropriate manufacturing and sealing techniques will be apparent to a skilled reader. A first outlet  28   a  communicates with the interior of the upper chamber  26  and leads to a vacuum pump  30  of the type which is capable of developing a relatively high pressure drop (say, 70-90 kPa) and delivering a relatively low flow rate (say, 0.5-1.0 l/s). A second outlet  28   b  also communicates with the interior of the upper chamber  26  and incorporates a valve  31  which allows the second outlet  28   b  to be closed or opened as required. The first and second outlets  28   a ,  28   b  each lead, beyond the vacuum pump  30  or the valve  31 , to an appropriate location for discharging evacuated air from the dishwasher  10 . It is envisaged that this location could be simply to atmosphere. 
     Located inside the upper chamber  26  is an inner chamber  32 . The inner chamber  32  is sealed in an airtight manner from the upper chamber  26 . The inner chamber  32  houses various items of racking  34  adapted and arranged to receive items of kitchenware and crockery  36  to be washed and dried by the dishwasher  10 . The inner chamber  32  has an outlet  38  connected directly to the inlet of a blower  40 . The blower  40  is connected to a motor  42  for driving the blower  40 . The blower  40  is of a type which is capable of passing a relatively high volume of air per second (say, 12-45 l/s) and discharges directly into the upper chamber  26 . A heater  44  is located in the inner chamber  32  immediately beneath, or directly in contact with, the lowermost racking item  34  for purposes which will be described below. 
     The inner chamber  32  is located wholly within the upper chamber  26 . Hence, the walls of the inner chamber  32  form the innermost boundaries of the upper chamber  26 . The walls of the inner chamber  32  are thus common to both the inner chamber  32  and the upper chamber  26 . The walls of the inner chamber  32  are made from a suitable metal or other thermally-conductive material. 
     It will be understood that the dishwasher  10  will further comprise known components required for effecting a washing action. The components described above are required in order to effect drying of the kitchenware and crockery  36  which have previously been washed in the dishwasher  10 . However, further description of the components required to carry out the washing process will not be described any further here. 
     The drying operation of the dishwasher  10  will now be described. Following the completion of the washing cycle, a significant quantity of water will remain inside the inner chamber  32 , particularly on the surfaces of the kitchenware and crockery  36 . The temperature of the contents of the inner chamber  26  is likely to be in the region of 20° C. A drying process is required in order to complete the washing and drying process. In order to achieve this, the blower  40  is operated so as to draw air from the inner chamber  32  into the upper chamber  26  at a relatively high rate. The valve  31  is also opened so that the air in the upper chamber  26  is emitted from the dishwasher  10 . This occurs as a result of the increase in pressure in the upper chamber  26  which inevitably. occurs when air is drawn from the inner chamber  32  by the blower  40  and passed to the upper chamber  26 . When a significant proportion of the air in the inner chamber  32  has been removed therefrom by the blower  40 , the valve  31  is closed. If desired, the blower  40  can be turned off so that the pressures within the inner and upper chambers  32 ,  26  can be allowed to equalise. The blower  40  is then reactivated and the valve  31  opened again so as to allow more air to be expelled from the upper chamber  26 . This process can be repeated several times if desired. At the end of this process, the valve  31  is closed, and the vacuum pump  30  is activated so as to evacuate the upper chamber  26  to a pressure which is significantly lower than atmospheric. By this method, a pressure of around 10 kPa should be achievable within the inner chamber  32  in a relatively short space of time. The water contained within the inner chamber  32  will remain in liquid form at this pressure and at a temperature of around 20° C. 
     Once the desired reduced pressure has been achieved, the heater  44  is turned on. This causes the temperature inside the inner chamber  32  to rise which, in turn, causes the water to evaporate at a temperature which is much lower than 100° C. The temperature at which the water begins to boil will depend upon the pressure of the air inside the inner chamber  32 . In the embodiment, it is envisaged that the temperature inside the inner chamber  32  will be raised to around 50° C. As the water in the inner chamber  32  begins to evaporate, the blower  40  removes the water vapour from the inner chamber  32  and transfers it to the upper chamber  26 . However, the transfer of the water vapour from the inner chamber  32  to the upper chamber  26 , which is at a higher pressure than the inner chamber  32 , encourages condensation of the water vapour. The water vapour thus condenses on the walls of the inner chamber  32 . 
     It will be understood that, when the water evaporates in the inner chamber  32 , it absorbs energy and the tendency will be for the temperature inside the inner chamber  32  to drop below the desired temperature of 50° C. Also, as the water vapour condenses in the upper chamber  26 , its latent heat of condensation is given out, thus causing a rise in temperature in the upper chamber  26 . In the steady state, therefore, the temperature of the water vapour in the upper chamber  26  will be greater than the temperature in the inner chamber  32  and there will be a temperature differential across the walls of the inner chamber  32 , which are in fact common to both chambers  26 , 32 . This allows thermal energy to pass back through the walls of the inner chamber  32  from the upper chamber  26  into the inner chamber. This transfer of thermal energy helps to prevent the temperature inside the inner chamber  32  from dropping to a very low temperature without the continued application of heat from the heater  44 . If no heat were transferred into the inner chamber  32 , the temperature would drop back to a comparatively low value (say, 20° C) and there would be no further evaporation of water at the selected pressure inside the inner chamber  32 . A further reduction in the pressure inside the inner chamber  32  would be required if any further evaporation were to take place. If the pressure drop requirements are too great, then the vacuum pump  30  will need to be capable of developing a very high vacuum and apparatus of this sort is generally very expensive. 
     In the steady state, therefore, the blower  40  and vacuum pump  30  are operating, the valve  31  is closed and the heater  44  is either off or activated on a very low output. The pressure inside the inner chamber  32  will be lower than that in the upper chamber  26  and the temperature inside the inner chamber  32  will be lower than that in the upper chamber  36 . There will be a temperature differential across the walls of the inner chamber  32 . In one example of the apparatus illustrated above, the estimated steady-state pressure inside the inner chamber  32  is approximately 12-14 kPa and the temperature therein will be approximately 50° C. In the upper chamber  26 , the pressure will be approximately 20-25 kPa and the temperature will be approximately 60-65° C. In the inner chamber  32 , whilst liquid water remains therein, water will continue to evaporate and the water vapour will be extracted therefrom and passed to the upper chamber  26 . The water vapour will condense on the walls of the inner chamber  32 , from where it will fall onto the tray  14  and be collected at the outlet  16 . At the end of the washing(ringing cycle, the pump  20  is operated in order to remove the condensed water from the dishwasher  10 . If required, the condensed water can be stored for use in a subsequent dishwashing cycle. 
     A second embodiment of apparatus according to the invention is illustrated in FIG.  2 . In this embodiment, the apparatus takes the form of a tumble dryer or clothes dryer  100 . The clothes dryer  100  has an outer casing  112  which may be generally cylindrical in shape. The outer casing  112  has a cylindrical wall  112   a , a rear wall  112   b  and a door  112   c  arranged opposite the rear wall  112   b . The door  112   c  is hinged so as to be openable so as to allow access to the interior of the clothes dryer  100 . Appropriate seals are provided around the door  112   c  in order to allow the interior of the clothes dryer  100  to be evacuated as will be described below. The lower portion of the cylindrical wall  112   a  is shaped in the manner of a sump  114  and inclined towards an outlet  116 . As described above, the outlet  116  is connected to a discharge pipe  118  with a pump  120  located therebetween and a one-way, non-return valve  119  located in the discharge pipe  118 . 
     An outer chamber  126  is defined and delimited by the outer casing  112 . An outlet  128  communicates with the outer chamber  126  and with a one-way, non-return valve  129  and a vacuum pump  130  located in the outlet  128 . A spur outlet  128   a  communicates with the outlet  128  and has a valve  131  located therein. As before, both the outlet  128  And the spur outlet  128   a  lead to a location (not shown) at which air evacuated from the clothes dryer  100  can be safely and easily released, eg. into the atmosphere. Inside the outer chamber, a cylindrical inner chamber  132  is provided. The inner chamber  132  has a cylindrical wall  132   a , a rear wall  132   b  and a door  132   c  located opposite the rear wall  132   b . Seals are provided around the door  132   c  which will allow the inner chamber  132  to be evacuated to a pressure lower than that of the outer chamber  126 . The inner chamber  132  is located within the outer chamber  126  so that the doors  112   c ,  132   c  are substantially aligned This allows both doors  112   c ,  132   c  to be opened in order to allow articles of laundry to be introduced to the interior of the inner chamber  132  so that the drying process can be carried out. 
     Mounted on the rear wall  132   b  of the inner chamber  132  are a plurality of blowers  140  and motors  142 . The blowers  140  and motors  142  are equispaced about the axis  136  so that the mass of these components is balanced. Apertures  138  are provided in the rear wall  132   b  adjacent each blower  140 . The apertures  138  form outlets from the inner chamber  132  so that water vapour can be evacuated from the inner chamber  132  and transferred into the outer chamber  126  via the blowers  140 . Each blower  140  discharges water vapour directly into the outer chamber  126 . Also provided on the cylindrical wall  132   a  is a heating element  144 , preferably in the form of a film heater wrapped around the cylindrical wall  132   a , appropriate insulation (not shown) being provided if required. 
     The inner chamber  132  is supported on a shaft  134  which, in turn, is rotably mounted, by means of bearings  134   a , on the rear wall  112   b  of the outer casing  112 . A motor  134   b  is provided so that when the motor  134   b  is activated, the inner chamber  132  is caused to rotate about its longitudinal axis  136 . The axis  136  may be, but need not be, coincident with the longitudinal axis of the cylindrical wall  112   a  of the outer casing  112 . 
     It will be appreciated that an appropriate electrical connection will need to be provided to the motors  142  so as to allow the inner chamber  132  to rotate about the axis  136 . An electrical connection to the heating element  144  will also be required. Such rotatable connections are available but can be replaced, if desired, by other arrangements by means of which water vapour can be evacuated from the inner chamber  132  into the outer chamber  126  whilst the inner chamber  132  is rotating about the axis  136 . 
     The clothes dryer  100  described above operates as follows. Articles of laundry requiring to be dried are introduced to the interior of the inner chamber  132  via the doors  112   c ,  132   c . Thereafter, the doors  132   c ,  112   c  are closed. The blowers  140  are then operated with the valve  128   a  open so as to evacuate air from the inner chamber  132  into the outer chamber  126  and thence to atmosphere. When the majority of the air has been evacuated from the inner chamber  132 , the valve  131  is closed and the vacuum pump  130  is operated so as to evacuate the outer chamber  126  to a pressure of between 20 and 25 kPa. The heater  144  is then turned on so as to raise the temperature of the contents of the inner chamber  132 . As the temperature of the contents of the inner chamber  132  is being raised, the motor  134   b  is operated so as to cause the inner chamber  132  to rotate about the axis  136 . If the speed of rotation is above that at which the laundry articles are held against the cylindrical wall  132   a  of the inner chamber  132 , heat will be readily and easily passed from the cylindrical wall  132   a  to the laundry articles. At a speed lower than that at which the laundry articles will remain held against the cylindrical wall  132   a , the laundry articles will be tumbled inside the inner chamber  132 . This maximises the opportunity for the water droplets trapped within the laundry articles to be released into the low pressure atmosphere within the inner chamber  132 . Periods of rotation at a speed which causes tumbling or redistribution of the laundry articles inside the inner chamber  132 , ideally no more than 50 rpm, can be alternated with periods of rotation at a higher speed whilst the temperature of the contents of the inner chamber  132  is increased to the desired temperature. 
     Water droplets trapped within the fibres of the laundry articles will begin to evaporate inside the inner chamber  132  as the temperature within the inner chamber  132  increases. The temperature at which the water droplets will evaporate will depend upon the pressure inside the inner chamber  132 . Spinning the inner chamber  132  at a high speed can also help to extract water from the laundry articles. The blowers  140  remain activated as the water evaporates so as to move the water vapour from the inner chamber  132  into the outer chamber  126 . The compression of the water vapour as it passes through the blowers  140  and enters the outer chamber  126  encourages condensation on the walls of the inner chamber  132 . The condensed water collects in the sump  114  and is discharged through the outlet  116  and discharge pipe  118  by way of the pump  120 . 
     The cylindrical wall  132   a  of the inner chamber  132  is manufactured from a thermally-conductive material so that, as previously, at least some of the latent heat of condensation given off by the condensing water vapour is transferred through the cylindrical wall  132   a  into the inner chamber  132 . This heat energy is passed to the laundry articles in the inner chamber  132 . Continued rotation of the inner chamber  132  discourages localised warming and also allows water to be evaporated from all areas of the laundry articles. In this way, different areas of the laundry articles come into contact with the warmed cylindrical wall  132   a  of the inner chamber  132  at different times. 
     A particular advantage of the arrangement illustrated above is that of being able to detect when the drying process is complete. Whilst water remains present in the inner chamber  132 , the water will continue to evaporate in an ongoing manner. Hence, although the blowers  140  continue to remove water vapour from the inner chamber  132 , the pressure therein will remain relatively constant. However, once substantially all of the water has evaporated, continued operation of the blowers  140  will cause a reduction in the pressure inside the inner chamber  132 . A simple pressure detector  146  located inside the inner chamber  132  can therefore be used to give an indication that the drying process is essentially complete. Alternatively, a sensor (not shown) can be provided to detect a significant increase in the speed of the blower  140  and/or a reduction in the power absorbed by the blower  140 . This can also be used to provide An indication that the drying process is complete. 
     The third embodiment illustrated in the drawings is a variation on the second embodiment illustrated in FIG.  2 .  FIG. 3   a  is a schematic side view of the third embodiment, similar to the side view shown in  FIG. 2 , and  FIG. 3   b  is a sectional view through the apparatus shown in  FIG. 3   a.    
     The outer chamber of the clothes dryer  200  illustrated in  FIGS. 3   a  and  3   b  is very similar to that shown in FIG.  2  and described above. Hence, the clothes dryer  200  has an outer casing  212  having a cylindrical wall  212   a , a rear wall  212   b  and a door  212   c  located opposite the rear wall  212   b . As before, the door  212   c  is sealed in an airtight manner against the remainder of the outer casing  212  when it is closed. The outer casing  212  has a sump  214  in the lower region thereof, which sump  214  has an outlet  216  leading to a discharge pipe  218  via a pump  220 . The outer casing  212  delimits the outer chamber  226  which communicates with an outlet  228  leading to a vacuum pump  230  and a spur outlet  228   a  incorporating a valve  231 . Thus far, the features of the clothes dryer  200  are the same as the corresponding features of the clothes dryer  100  illustrated in FIG.  2 . 
     The clothes dryer  200  also has an inner chamber  232  located inside the outer chamber  226 . However, in contrast to the rotatable inner chamber  132  of the clothes dryer  100 , the inner chamber  232  of the present embodiment is rigidly mounted inside the outer chamber  226 . The inner chamber  232  has a cylindrical wall  232   a , a rear wall  232   b  and a door  232   c  located remote from the rear wall  232   b . As before, the door  232   c  is sealed against the remainder of the inner chamber  232  in an airtight manner when it is closed. A blower  240  is mounted close to the rear wall  232   b  of the inner chamber  232 . A motor  242  is provided in order to power the blower  240 . A conduit  238  leads from the rear wall  232   b  to the blower  240  for carrying gas (water vapour) from the interior of the inner chamber  232  to the blower  240  when the motor  242  is activated. The outlet of the blower  240  leads to a three way valve  243  which is able to direct gas leaving the blower  240  along one of two passageways. The first passageway  243   a  opens into the outer chamber  226 . The second passageway  243   b  leads back into the inner chamber  232  and has a heating element  244  coiled thereabout. The heating element  244  can be used to warm the gas passing along the second passageway  243   b.    
     Mounted inside the inner chamber  232  is a rotatable drum  250 . The drum  250  has a perforated cylindrical wall  252   a  and a circular rear wall  252   b  which can also be perforated if desired. An inwardly extending lip  252   c  surrounds the edge of the cylindrical wall  252   a  on the side remote from the rear wall  252   b . The drum  250  is located inside the inner chamber  232  so that the opening defined by the lip  252   c  is substantially in line with the door  232   c  of the inner chamber  232 . 
     A shaft  234  is rigidly attached to the rear wall  252   b  of the drum  250 . The shaft  234  is rotatably mounted by way of bearings  234   a  on the rear wall  232   b  of the inner chamber  232 . A motor  234   b  is provided to enable the drum  250  to be rotated about the axis  236 . The axis  236  is coincident with the longitudinal axis of the drum  250  and preferably also coincident with the longitudinal axis of the inner chamber  232 . 
     As has been previously mentioned, the cylindrical wall  252   a  of the drum  250  is perforated. The perforations are sufficiently small to retain the laundry items to be dried inside the drum  250 . The lip  252   c  also assists in retaining the laundry articles in the interior of the drum  250  when it is rotated about the axis  236  on actuation of the motor  234   b . The door  323   c  is located and arranged so as to retain the laundry articles inside the drum  250 . 
     A plurality of vanes  254  are arranged on the external surface of the cylindrical wall  252   a  of the drum  250 . The vanes  254  extend axially along the length of the drum  250 , parallel to the axis  236 . As can be seen in  FIG. 3   b , each vane  254  is curved in profile. As the drum  250  is caused to rotate the vanes  254  bring about forced circulation of the water vapour present within the inner chamber  232  and it is preferred that their shape and profile will be selected so as to effect good circulation within the inner chamber  232 . 
     In operation, as before, the laundry articles to be dried are placed inside the drum  250 . The doors  212   c  and  232   c  are used to achieve this. Once the doors  212 ,  232   c  have been closed, the blower  240  is activated so as to remove air from the interior of the inner chamber  232 , In order to achieve this, the three way valve  243  is set so as to pass the incoming air along the first passageway  243   a , ie the air is removed from the inner chamber  232  and passed into the outer-chamber  226 . The valve  231  is open to allow the air removed from the inner chamber  232  to be discharged from the dryer  200 . Once the majority of the air has been removed from the inner chamber  232  in this way, the valve  231  is closed and the vacuum pump  230  is actuated so that the outer chamber  226  and the inner chamber  232  are both evacuated. 
     At this stage, the three way valve  243  is switched to a position in which gas leaving the blower  240  is directed along the second passageway  243   b  and the heating element  244  is turned on. The gas now moved by the blower  240  will simply be circulated through the blower and along the second passageway  243   b , thus causing the said gas to be warmed by the heating element  244 . The temperature of the contents of the inner chamber  232  thus rises and the water contained within the inner chamber  232  will, at a temperature dependent upon the pressure within the inner chamber  232 , begin to evaporate. When the desired temperature of the inner chamber  232  has been reached, the three way valve  243  is returned to the position in which water vapour leaving the blower  240  is passed to the outer chamber  226 . Hence the blower  240  will remove the water vapour from the inner chamber  232  to the outer chamber  226 . Because of the inevitable temperature difference between the inner chamber  232  and the outer chamber  226 , the water vapour condenses in the outer chamber  226 , most probably on the outer wall of the inner chamber  232 , giving out the latent heat of condensation as condensation takes place and causing the wall of the inner chamber  232  to become warmed. The condensed water will collect in the sump  214  and be removed therefrom via the outlet  216  and the discharge pipe  218  using the pump  220 . 
     In order to ensure that all parts of the laundry articles are exposed to air and water vapour during this process, the drum  250  in which the laundry articles are contained is rotated about the axis  236 . This is brought about by actuation of the motor  234   b  which causes rotation of the shaft  234  and thus rotation of the drum  250 . The speed of rotation of the drum  250  is such that the laundry articles perform a tumbling action inside the drum  250 . 
     In order to further enhance the ability of the above-described apparatus to remove all water droplets from the laundry articles, means are provided for forcing the water vapour, and any remaining air, contained within the inner chamber  232  to circulate. This is achieved by the presence of the vanes  254  on the external surface of the drum  250 . Rotation of the drum  250 , and therefore of the vanes  254 , causes movement of the air and water vapour in a radial then axial, direction between the drum  250  and the cylindrical wall  232   a  of the inner chamber  232 . This in turn forces the air and water vapour to circulate to the interior of the drum  250  and, having no other exit route, the air and water vapour then passes through the laundry articles contained within the drum  250  and out of the drum  250  through the perforations in the cylindrical wall  252   a . At this stage, it is advantageous if the drum  250  is rotated about the axis  236  at a speed which forces the laundry articles to be held against the cylindrical wall  252   a . This enhances the evaporation of water droplets retained within the textile articles because, as will be appreciated, the circulating air and water vapour will be warmed as it passes alongside the cylindrical wall  232   a  of the inner chamber  232  and the circulation of the air and water vapour causes the transfer of thermal energy from the cylindrical wall  232   a  into the textile articles which are to be dried, The presence of the vanes  254  along the length of the drum  250  has the advantage that the air and water vapour is forced to flow more uniformly through the laundry articles than if it were simply blown into the interior of the drum  250  from outside and allowed to follow the path of least resistance through the fabric. 
       FIGS. 4   a  and  4   b  illustrate a fourth embodiment of the invention. In this embodiment, the drying apparatus is, once again, a clothes dryer  300  having an outer casing  312 . The outer casing  312  consists of a generally cylindrical wall  312   a , a rear wall  312   b  and a door  312   c  located opposite the rear wall  312   b . As in previous embodiments, the cylindrical wall  312   a  is shaped so that a sump  314  is formed in the lower region of the outer casing  312 . An outlet  316  is provided at the lowest point of the sump  314  so that condensed water can be passed to a discharge pipe  318  via a pump  320  and a non-return valve  322 . The outer casing  312  delimits an outer chamber  326  which has an outlet  328  incorporating a vacuum pump  330 , similar to the arrangements described above. 
     An inner chamber  332  is arranged wholly within the outer chamber  326 . The inner chamber  332  is generally cylindrical in shape and has a substantially cylindrical wall  332   a , a rear wall  332   b  and a door  332   c  located opposite the rear wall  332   b . As previously, the doors  312   c ,  332   c  are aligned so as to allow laundry articles to be introduced to the interior of the inner chamber  332 . The cylindrical wall  332   a  is perforated for reasons which will be described below. The inner chamber  332  is mounted on a shaft  334  via bearings  334   a . A motor  334   b  is provided so as to allow the inner chamber  332  to be rotated about the axis  336 . 
     A fan array  340  is provided radially outwardly of the inner chamber  332 . The fan array  340  comprises a multiplicity of vanes  354  which extend parallel to the longitudinal axis  336  of the inner chamber  332 . A plurality of dividing walls  356  are provided at intervals along the length of the vanes  354  for reasons which will be described below. A support wall  340   a  is provided at one end of the fan array  340  to allow the fan array  340  to be supported via bearings  344  about the shaft  334 . A second motor  342  is provided to enable the fan array  340  to be rotated at relatively high speed about the axis  336 . As can be seen from  FIG. 4   b , the vanes  354  are concave in profile. 
     The operation of the clothes dryer  300  is similar to that of those described above. In order to evacuate air from the interior of the inner chamber  332 , the fan array  340  is rotated at high speed (for example 2,000 rpm). This creates a low pressure immediately outside the cylindrical wall  332   a  of the inner chamber  332 . Air thus passes through the perforations in the cylindrical wall  332   a  and is expelled from the outer chamber  326  via the outlet  328 . The fan array  340  speeds up as air is expelled from the outer chamber  326 . The vacuum pump  330  is then operated in order to evacuate the inner and outer chambers  332 ,  326  until the pressure in the inner chamber  332  has been reduced to a value of 12-14 kPa. 
     During the drying process, the inner chamber  332  is rotated about the shaft  334  at speeds which will allow tumbling of the laundry articles inside the inner chamber  332  or at speeds which will hold the laundry articles against the cylindrical wall  332   a . Most preferably, periods of rotation at different speeds will be provided sequentially as has been outlined above. Meanwhile, the fan array  340  continues to rotate at a relatively high speed (of the order of 10,000 rpm) in order to draw air and water vapour from the interior of the inner chamber  332  through the perforations in the cylindrical wall  332   a  and into the outer chamber  326 . The water vapour condenses in the outer chamber  326 , collects in the sump  314  and, at an appropriate time, is discharged through the outlet  316  and the discharge pipe  318 . The dividing wails  356  arranged along the length of the vanes  354  help to ensure that the flow of water vapour from the inner chamber  332  to the outer chamber  326  is spread reasonably uniformly along the cylindrical wall  332   a  of the inner chamber  332 . 
     Means for heating the contents of the inner chamber  332  have been omitted from  FIGS. 4   a  and  4   b  for the sake of clarity. However, it will be understood that some form of heating means may be required in order to ensure that the water contained within the inner chamber  332  will evaporate. 
     In order to allow heat energy to be transferred from the outer chamber  326  back into the inner chamber  332 , part of the air/water vapour mixture pumped into the outer chamber  326  by the fan array  340  is allowed to circulate back into the inner chamber  332 . This recirculated gas is at an elevated temperature because of the fact that the latent heat of condensation is given off by the condensing water vapour in the outer chamber  326 . The recirculation is facilitated by the previously mentioned perforations in the cylindrical wall  332   a . Part of the heat carried by the recirculated gas is transferred into the water still remaining in the laundry articles located within the inner chamber  332 , which facilitates continued drying by causing evaporation of the said water in the inner chamber  332 . The ratio of air to water vapour present in the recirculated gas, and/or the ratio of recirculated gas to condensed water vapour, can be adjusted so as to optimise the drying performance of the clothes dryer  300 . In order to regulate the amount of recirculated gas, an adjustable valve can be provided in a single aperture in the cylindrical wall  332   a  in place of the previously mentioned perforations. The amount of air remaining in the clothes dryer  300  can be adjusted by operating the vacuum pump  330  for different periods of time during the drying process. This in turn will affect the air to water vapour ratio within the recirculated gas. 
     It will be appreciated that the invention is not intended to be limited to the precise details of the embodiments described above. Firstly, the invention is not intended to be limited to use in dishwashers and tumble dryers. Other uses will be apparent to a skilled reader. Secondly, the heaters described above need not be positioned as illustrated but any arrangement which will effect the heating of the interior of the respective inner chamber will suffice. In a further variation, particularly relevant to the embodiments illustrated in  FIGS. 2 and 3 , the doors of the inner and outer chambers can be integrated into a single, or interconnected, door assembly. Also, different valve arrangements are possible, particularly in respect of the means for emptying the apparatus. For example, the pump in the discharge pipe can be dispensed with if the vacuum pump can be arranged to provide an excess pressure in the outer or upper chamber. In such an arrangement, a spool valve may be provided in association with the vacuum pump to pressurise the apparatus and so force the collected condensed Water out through the discharge pipe when the valve therein is opened. Furthermore, the illustrative temperatures and pressures are not to be regarded as limitative. Further modifications and variations will be apparent to a skilled reader.