AU706134B2 - Drier - Google Patents

Description

PcTAU9 6 0 0 8 I 1 RECEIVED 2 9 APR I97

DRIER

FIELD OF THE INVENTION THIS INVENTION relates to a drier and is more specifically concerned with improving the performance and efficiency of a domestic tumble drier, without greatly increasing its cost.

STATE OF THE ART The conventional domestic tumble drier has a casing containing an axially-horizontal drum in which the clothes to be dried are tumbled over one another by rotation of the drum. A heating element, usually located behind a perforated rear wall of the drum, is arranged in an air path along which ambient air is driven into the drum interior. The heated air in the drum extracts the moisture from the clothes and is usually vented to atmosphere by way of the front of the drum. Other designs of tumble drier draw in air from the interior of the casing by way of perforations in the front of the drum which is heated by a surrounding coil heater. Moisture vaporising from the clothes inside the drum is carried by the air through a filter at the back of the drum and is exhausted to atmosphere by way of an outlet behind the drum.

In some dwellings, there is no provision for venting the hot humid air from a tumble drier to atmosphere. It is then discharged back into the dwelling. This may cause problems if the dew point of the air in the dwelling is raised above the temperature of its walls or windows. In these circumstances, the moisture in the air condenses on the walls and windows. This is not only unsightly, it can cause mould damage on walls, and water runs on the windows.

Attempts have been made to remove some of the moisture from the hot humid air before it leaves a domestic tumble drier. One approach adopted for achieving this, is to pass the hot humid air through a heat exchanger which is usually of a cross-flow, tubular type.

The outside of the heat exchanger is provided with fins and a fan-driven motor is incorporated into the casing to blow ambient air over the external finned surfaces of the heat exchanger to cool it. The hot humid air leaving the drum is cooled by passage through the heat exchanger and some of the water vapour in the air condenses and is rom the heat exchanger into a condensate collector. The humid air, now cooled c\'RAL 1- NT AMENDED 8HE

IPEA/AU

Ocr'ATT i 6 10 0 8 1 1 2 to a temperature closer to the room temperature and having a reduced moisture content, is re-heated and then re-circulated through the drum. It is inevitable with such an arrangement that the fan used to cool the cross-flow condensing heat exchanger increases the running costs of the machine.

Domestic tumble driers using re-circulation of the air to achieve drying and operating on the above principle, are described in British Patent Application No. 2109520, German Patent No. 4009102A1 and British Patent Application No. 2082741.

A further disadvantage is that the installation of moulded plastics ducting inside the casing to convey the hot humid air from the drum to the heat exchanger and then to atmosphere, represents a substantial cost item and increases the resistance to air-flow through the tumble drier. Further increased running costs are thus incurred.

OBJECT OF THE INVENTION The object of this invention is to improve the efficiency of operation of a tumble drier by reducing its running costs.

THE INVENTION In accordance with the broadest aspect of this invention, a domestic tumble drier including: an isolating heat exchanger having separate primary and secondary air-flow circuits each extending between its own inlet and outlet openings; first means for passing approximately the same quantity of air per minute through the primary and secondary circuits of the heat exchanger; second means for conveying ambient cold air along a path which extends, in turn, through the primary circuit of the heat exchanger, a rotatable tumbler drum in which drying of the clothes takes place, and the "econda-ry circuit of the heat exchanger, before the air is discharged to atmosphere; and, a heater operable to either heat the air before it enters the drum or to heat the drum itself so that the moisture in the clothes is converted into water vapour in the drum; in which tumble drier the casing has two spaced parallel front walls forming a compartment therebetween which is closed by an access door mounted on the outer front wall and located in a central region of the compartment so that, when the door is opened, it gives access to the interior of the drum for loading clothes therein; the door having means for venting hot moist air from the drum interior radially outwards into the compartment which conveys the hot moist air to the isolating heat exchanger.

3T O« AMENDED SHEET I P ~VAAU 'C!AU jI/ RECEIVED 25;+ 3 The heater may be an electrical heater or a gas heater.

PREFERRED FEATURES OF THE INVENTION The energy required to operate the tumble drier of the invention is substantially reduced as the heat exchanger operates to transfer to the dry air passing through its primary circuit, much of the heat contained in the hot moist air passing through its secondary circuit. This reduction in energy used to operate the tumble drier is reflected in an enhanced efficiency of operation.

Suitable means are provided for removing some of the water vapour from the air stream leaving the drum. Such water vapour may be condensed in the isolating heat exchanger and drained continuously from it to a condensate collector. However, it is preferred to pass the cooled humid air leaving the secondary circuit of the heat exchanger through a second heat exchanger, suitably of elongated counterflow type, and in which final cooling of the humid air takes place before it is discharged to atmosphere. Such cooling is preferably effected by passing the incoming ambient air through the second heat exchanger before it is supplied to the isolating heat exchanger. Condensate collecting in the condenser is then passed to a condensate collector.

The preferred construction of heat exchanger is one comprising a set of parallel plates having ribs pressed out of them and equipped with drainage holes for allowing condensate to be removed from it. Such a heat exchanger is described in detail in my co-pending patent application No. PN 6979 filed in Australia on 4th December 1995 and now the subject of PCT International Patent Application No. PCT/AU96/00731 having the international filing date of 1 5th November 1996.

In one form of tumble drier, the hot moist air passes from the front of the drum through a filter to the compartment provided by the cavity formed between the two parallel front walls of the tumble drier. This compartment guides the hot humid air to a second cavity formed between a second pair of spaced parallel walls arranged either at one of the sides, or above, or beneath the tumble drier, and the isolating heat exchanger may be located in this second cavity. The air-flow to and from the primary and secondary circuits of the heat exchanger may be guided by partitioning erected in the cavity. Such 30 an arrangement has the advantage that it avoids the need of expensive plastics mouldings to guide the air to and from the heat exchanger. Where a separate condenser is used, this may be located in the second cavity.

AMENDED

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WO 97/23680 PCT/AU96/00811 4 In one arrangement heat dissipation of the heater is controlled electronically to maintain a desired temperature difference between the inlets of the primary and secondary circuits of the isolating heat exchanger. The advantage of operating the heater in this way, is that the thermal efficiency of the heat exchanger is at a maximum when a particular temperature difference occurs between the input temperatures of the primary and secondary air. This is particularly so when the isolating heat exchanger of substantially counterflow type and as all-metal construction is used.

INTRODUCTION TO THE DRAWINGS The invention will now be described in more detail, by way of examples, with reference to the accompanying drawings, in which:- IN THE DRAWINGS FIGURE 1 is a simplified diagrammatic side view of a first embodiment of tumble drier; FIGURE 2 is a diagrammatic perspective view of the working parts of a second form of tumble drier; FIGURE 3 is a diagrammatic side view of a tumble drier using the component parts arranged generally as illustrated in Figure 2; FIGURE 4 is diagrammatic plan view of some of the component part of the tumble drier of Figure 3, as would be seen when viewed along the line and in the direction indicated by the arrows VI -VI in Figure 3; FIGURE 5 is diagrammatic side view of the working parts of a third form of tumble drier; and, FIGURE 6 is a front view of the tumble drier of Figure 5 as viewed in the direction and along the line indicated by the arrows YIU VII in Figure DESCRIPTIQN OF THE FIRST EMBODIMENT The tumble drier shown in Figure 1 has a parallelepiped casing 1 having a cylindrical cowl 2 extending inwardly from its rear wall shown on the left-hand side of Figure 1.

WO 97/23680 PCT/AU96/00811 The cavity of the cowl contains an electrical heating element 3 and accommodates a rearend portion of a cylindrical tumble drier drum 4 which is rotatable about a horizontal axis X-X by a belt drive 5 driven by an output drive pulley of an electric motor 7. The drum 4 has a perforated rear wall 6.

The front-end portion of the drum 4 is of a curved re-entrant shape 8 surrounding a circular opening 9. During operation of the tumbler drier, the opening 9 closely surrounds an inner end of a door 10 which is hinged to the front wall of the casing 1 and has an outwardly flared wall 12. The inner end of the wall 12 opens into the interior of the drum and the outer end of the wall 12 is closed by a transparent, dished window The inner end of the wall 12 is spanned by a porous filter 13 on which lint collects during usage of the tumble driver. Hot humid air leaves the interior of the drum 4 by way of the filter 13, as shown by the arrows. This air enters an interior cavity 14 of the wall 12 which is provided with a ring of rectangular ports 15 opening into the interior of a circular manifold 16 of channel-shaped cross-section. The hot humid air is supplied by the manifold 16 to a duct 17 which extends to a fan 18 associated with a secondary circuit of an isolating heat exchanger 19. This is constructed from a set of vertical metal plates having ribs stamped out of them as described in my co-pending PCT patent application mentioned above.

The heat exchanger 19 has a primary circuit 31 which, as shown by the dotted arrowed flow path, is substantially in counterflow through most of its length with the secondary circuit The hot humid air driven into the secondary circuit of the heat exchanger by the fan 18, delivers much of its heat to the primary circuit 31 before leaving by way of an outlet 21 which is connected by ducting 22 to the interior of a tube condenser 24. The tube condenser is of extended length and contains a finned tube through which cooling ambient air is passed in the direction of the broken arrow 34. As is apparently from the drawing, the humid air entering the condenser 24 by way of an entry 23, travels in counterflow to the cooling air 34 and is thus cooled so that much of the moisture contained in it condenses and travels through an outlet pipe 28 to a condensate collector 27. A second outlet pipe 29 leads from the heat exchanger 19 to the collector 27 and drains away any condensation which forms in the heat exchanger.

WO 97/23680 PCT/AU96/00811 6 The humid air, which is now cooled almost to room temperature, leaves the condenser 24 by way of an outlet 26 and is supplied to an exhaust opening 41 in the rear wall of the casing 1.

Ambient air from inside the casing is drawn through the condenser 24 by a fan disposed at the inlet end of the secondary circuit of the heat exchanger 19. This dry ambient air flows along the path 34 in the condenser 24 and maintains it cool enough to condense moisture from the humid warm air leaving the heat exchanger 19.

The air from the fan 30 is driven around a secondary circuit 31 of the heat exchanger and is thereby pre-heated before discharging by way of an outlet 37 and a duct 36 leading, as shown by the broken arrows, to an inlet 42 of the cylindrical cowl 2. The air flows through the interior cavity 38 of the cowl 2 and through the heater before passing into the interior of the drum 4 by way of the perforated rear wall 6.

The temperature of the air supplied to the primary and secondary circuits of the heat exchanger 19 is continuously monitored by a comparator 43 which sends a signal to a controller 44 in accordance with the difference between the two air temperatures being monitored. The controller 44 adjusts an electrical gating switch 45 connected in an electrical supply circuit 46 leading to the heater 3. The heat dissipation of the heater 3 is thus controlled by the comparator 43. The electrical heater may be replaced by a gas heater if required.

OPERATION OF FIRST EMBODIMENT To use the tumble drier the front door 10 is opened and swung back about its hinge against the casing to expose the filter 13. Any lint which may have collected on the filter from the previous use of the tumble drier, can be readily stripped off it.

Clothes to be dried are passed through the door opening into the interior of the drum 4 by way of the aperture 9. The door 10 is then closed so that it assumes the position as shown in Figure 1. On starting the tumble drier the heater 3 is energised to provide the interior of the drum with hot air. This absorbs moisture from the tumbling clothes and passes out of the drum 4 by way of the cavity 14 in the door 10. The hot humid air exhausts from the door cavity 14 by way of the ports 15 and the manifold 16, and is drawn through the ducting 17 by the fan 18 so that it flows through the primary circuit of the heat exchanger 19.

WO 97/23680 PCT/AU96/00811 7 Dry ambient air from the casing 1 is sucked through the condenser 24 by the fan 30 and is passed through the secondary circuit 31 of the heat exchanger 19 where it extracts heat from the hot humid air passing through the primary circuit 20. Any condensation produced in the primary circuit 20 is discharged by way of the pipe 29 to the condensate collector 27. The pre-heated dry air from the secondary circuit 31 flows to the cavity 38 of the cowl 2 where it is heated and passed into the interior of the drum 4 to continue the drying process.

The cooled humid air from the primary circuit of the heat exchanger 19 is further cooled by passage through the condenser 24 and is discharged almost at room temperature through the exhaust 41 at the rear of the casing 1. Condensation formed in the condenser 24 is passed to the condensate collector by way of the pipe 28. Periodically the condensate collector 27 may be removed from the casing and emptied. Alternatively, it may be provided with an outlet leading to a drain.

The two fans 18 and 30 associated with the heat exchanger 19 are driven by a common motor and have the same characteristics so that approximately the same volume of air is driven through the primary and the secondary circuits of the heat exchanger. The temperatures of this air is continuously monitored by the comparator 43 and the heat dissipation of the heater 33 is controlled by the gating switch 45 to maintain the temperature difference of the air entering the primary and secondary circuits of the heat exchanger 19 substantially at a predetermined value at which the thermal efficiency of the heat exchanger 19 is optimised.

DESCRIPTION OF SECOND EMBODIMENT Figure 2 shows principal parts of a condensing tumble drier arranged in a different layout to that shown in Figure 1. Corresponding parts of the tumble drier have similar references but these are in the one-hundred series.

Tumble drying occurs in a drum 104 rotated about a horizontal axis by a belt drive 105 form a pulley of a motor 107.

In this embodiment, the isolating heat exchanger 119 is arranged horizontally above the drum 104 in a separate compartment. The hot humid air from the drum 104 follows the path shown by full arrows and leading from the front of the drum 104 to an input fan 118 WO 97/23680 PCT/AU96/00811 8 associated with the heat exchanger 119. It then follows the full arrowed path which leads out of the back of the heat exchanger 119 and into the condenser 124 which is arranged behind the heat exchanger 119.

Dry air is supplied by the fan 130 to the secondary circuit 131 of the heat exchanger 119 and, after flowing in counterflow to the hot humid air passing along path 120, leaves the back of the heat exchanger 119 and is supplied through an inlet 142 to the circular cavity of the cowl 102 which contains the perforated rear end of the drum 104 and the heater.

The dry air for the fan 130 is drawn in by way of the condenser 124 as shown by the broken arrows. A drain pipe 128 feeds condensation collected in the condenser and any condensation which also forms in the heat exchanger 119 downwardly to a condensate collector 127.

The physical layout of the principal parts of the second embodiment of tumble drier in its casing, will now be explained in more detail with reference to Figures 3 and 4.

The casing 101 of the tumble drier has two, parallel, spaced front walls 150, 151. The hinged door 110 has its flared wall 112 sealing against respective openings formed in the walls 150,151 so that the rectangular ports 115 in the flared wall 112 discharge hot humid air from the door cavity 114 into the space between the two walls 150, 151. This hot humid air enters the cavity 114 by way of the filter 113.

The cavity between the two walls is closed at its lower end and opens, at its upper end, into a channel 152 which is formed to one side of a second cavity formed between two, spaced, parallel top walls 153, 154 of the casing 101.

The space between the two walls 153, 154 provides a compartment in which the horizontal heat exchange stack 119 is located. The channel 152 carries the hot humid air from the cavity 156 (see figure 4) to the motor-driven inlet fan 118 of the heat exchanger stack 119. A partition plate 157 ensures that the hot humid air from the front cavity 156 can only flow through the channel 152 which leads to the fan 11 8.

WO 97/23680 PCT/AU96/00811 9 After passing through the heat exchanger 119, the cooled humid air flows to the condenser 124 which is arranged in the compartment between the parallel top walls 153,154, immediately behind the heat exchanger 119.

Ambient dry air is drawn into the casing 101 an inlet 158. The dry air is sucked through the condenser 124 to cool it, by the fan 130. The path of the dry air is denoted by broken arrows and it will be observed that it travels substantially in counterflow to the humid air in the condenser 124 and the heat exchanger 119. The dry air is thus prewarmed before passing through the duct 160 to the interior cavity of the cowl 102. Here is it heated by the heater 103 before entering the rear of the drum 104 by way of the perforated back wall 106.

The heat exchanger 119 is slightly tilted towards one corner so that any condensation accumulating on its plates flows to this corner where it passes down through weep holes (not shown) leading to the condensate outlet pipe 128. This carries condensate downwardly to the condensate collector 127 located beneath the drum 104 as shown in Figure 3.

A filter 113 is located inside the door 110 and can be cleaned when the door is opened.

An advantage of the construction of the tumble drier shown in Figures 2, 3 and 4, is that the path followed by hot humid air from the interior of the drum to the heat exchanger 119, is not confined to a tortuous path provided by expensive plastics mouldings.

Instead, it follows a path of relatively large cross-section at area defined between flat plates which are easily fabricated and form the twin top walls and twin front walls of the casing 101. There is thus less resistance in the air-flow path and the cost of fabricating the tumble drier is diminished as the use of expensive plastics mouldings is largely avoided.

The electrical heater may be replaced by a gas heater if desired.

DESCRIPTION OF THIRD EMBODIMENT Figures 5 and 6 correspond to Figures 3 and 4 and show a third embodiment of condensing tumble drier in which parts corresponding to those of the second embodiment are correspondingly numbered, except that the numbers in this case lie in the two hundred or series.

WO 97/23680 PCT/AU96/00811 In the third embodiment, the isolating heat exchanger 219 is arranged in a vertical compartment 280 provided between two spaced parallel side walls 261, 262 provided to one side of the horizontal drum 204.

As with the previous embodiment, a cavity 256 is formed between the two front walls 251 and 256 of the tumble drier, and the door 210 is hinged at one side to the outer front wall 250.

The front end of the side compartment 280 containing the heat exchanger 219, is closed by a plate 264 as shown in figure 5, so that hot humid air from the front compartment 256 flows into an upper horizontal channel 266 extending horizontally directly beneath the top wall of the casing. Partition plates 267, 268 ensure that the hot humid air can only enter the fan 218 of the heat exchanger 219. This fan is located at the back of the channel 266.

The hot humid air follows the path shown by the continuous arrows in Figures 5 and 6 and leaves the heat exchanger 219 by way of a duct 270 which leads into the condenser 224 which is located behind the heat exchanger 219. A further duct 271 carries the cooled humid air from the condenser to the outlet 241 in the rear of the casing 201.

Ambient dry air from outside the casing is drawn into the compartment 264 by the fan 230, by way of the condenser 224, as indicated by the path shown by broken arrows.

After travelling in counterflow to the hot humid air in the heat exchanger 219, the preheated air passes through a duct 260 which extends rearwardly and horizontally to convey the pre-heated air to the cavity of the cylindrical cowl 202 in which the perforated rear end of the rotating tumbler drum 204 is located. This pre-heated air is further heated by a heating element 203 before entering the drum 204 by way of its perforated rear wall.

In this third embodiment, the heat exchanger 119 is tilted slightly downwards at its front end so that any condensation formed within it can flow downwardly from the lower front end by way of the pipe 229 to the condensate collector 227. This slight tilt is too small to be shown in the figures.

WO 97/23680 PCT/AU96/00811 11 As with the previous embodiment, the condensing tumbler drier has few air flow paths of restricted cross-section and does not require the use of expensive plastics mouldings such as are necessary with currently available tumble driers of the condensing type.

All of the embodiments of the invention are more economical in their operation than currently available tumbler driers, as much of the heat used to dry the clothes in the drum is recovered in the heat exchanger and condenser and used to pre-heat the dry air supplied to the drum.

As with earlier embodiments, a gas heater may be used instead of an electrical heater.

VARIATIONS TO THE INVENTION The principal feature of importance of the invention is the ability to recover heat which would otherwise be lost from the tumble drier, in the heat exchanger. It is not essential that the tumble drier also condenses water vapour from the hot humid air leaving the tumbler drum, although this is obviously an advantage when the tumbler drier is to be used in dwellings having no facilities for venting the cooled humid air to atmosphere.

However, the use of a separate condenser and condensate collector is advisable because a higher proportion of the water content of the air leaving the drier is recovered, and when drying is being carried out in humid ambient conditions, there is always the risk of condensation occurring in the counterflow heat exchanger used to pre-heat the air fed to the drum of the drier. However it is stressed that the use of the incoming dry air to the condense moisture out of the hot humid air, is a less important feature of the tumble drier of the invention than its ability to be constructed and operated more economically than currently available tumble driers of equivalent drying capacity.

In all of the above embodiments the two fans associated with respective flow paths through the isolating heat exchanger preferably have similar characteristics and are driven at substantially the same speed by a single electric motor.

Claims (7)

1. A domestic tumble drier including: an isolating heat exchanger having separate primary and secondary air-flow circuits each extending between its own inlet and outlet openings; first means for passing approximately the same quantity of air per minute through the primary and secondary circuits of the heat exchanger; second means for conveying ambient cold air along a path which extends, in turn, through the primary circuit of the heat exchanger, a rotatable tumbler drum in which drying of the clothes takes place, and the seconarycircuit of the heat exchanger, before the air is discharged to atmosphere; and, a heater operable to either heat the air before it enters the drum or to heat the drum itself so that the moisture in the clothes is converted into water vapour in the drum; in which tumble drier the casing has two spaced parallel front walls forming a compartment there- between which is closed by an access door mounted on the outer front wall and located in a central region of the compartment so that, when the door is opened, it gives access to the interior of the drum for loading clothes therein; the door having means for venting hot moist air from the drum interior radially outwards into the compartment which conveys the hot moist air to the isolating heat exchanger. a. A tumble drier as claimed in claim 1, in which a counterflow condensing heat exchanger is arranged to condense water vapour from the warm humid air leaving the isolating heat exchanger.

3. A tumble drier as claimed in claim 1, or claim 2, including a removable condensate collector connected to hold condensation accumulated during operation of the tumble drier.

4. A tumble drier as claimed in any one of the preceding claims, in which the access door has provision for holding a filter for removing linter entrained in hot humid air leaving the drum, and the door has a cylindrical wall portion providing internally a cavity which communicates with the interior of the drum by way of the filter, and communicates with the surrounding compartment formed between the two front walls by way of a ring of ports through which hot humid air from the cavity is discharged radially into the compartment. ~STy F AMENDED SHE-, IPEA/AU PCTt 6 0 0 8 1 13 A tumble drier as claimed in claim 4, in which a second pair of spaced parallel walls extending perpendicularly of the plane of the front walls provides a compartment at one side of the tumble drier, and the heat exchanger is located between the second pair of walls.

6. A tumble drier as claimed in claim 4, in which the second pair of spaced parallel walls defined a horizontal top compartment to the casing, and the heat exchanger is located substantially horizontally within the top compartment and is slightly tilted to drain condensate towards one lower corner.

7. A tumble drier as claimed in claim 5 or claim 6, in which the isolating heat exchanger has its primary and secondary circuits arranged substantially in counterflow and is provided with means for allowing condensation formed in it to drain downwardly to a condensate collector.

8. A tumble drier as claimed in any one of the preceding claims, in which the two separate circuits through the isolating heat exchanger have respective associated fans having similar characteristics and which are driven by a common motor at substantially the same speed.

9. A tumble drier as claimed in claim 5 or claim 6 or either of claims 7 and 8 when dependant thereon, in which partitions are used to provide channels for conveying hot humid air from the tumble drier to the inlet of the primary circuit of the heat exchanger. AMENDED SHEET IPEA/AU