WO1994005846A1

WO1994005846A1 - Heat pump cycle clothes drier

Info

Publication number: WO1994005846A1
Application number: PCT/NZ1993/000073
Authority: WO
Inventors: Ian Campbell Mcgill
Original assignee: Fisher & Paykel Limited
Priority date: 1992-08-27
Filing date: 1993-08-26
Publication date: 1994-03-17
Also published as: AU4764693A

Abstract

A forced air clothes drier which removes water vapour from the air exhausted from the chamber (1). The vapour containing air (A) is passed through one or two compressors (4, 7), a heat exchanger (12) and an expansion means (8) as the working fluid in a heat pump/refrigeration cycle. The condensed water vapour is drawn off at the expansion means. The cycle is preferably closed and the dry air (G) leaving the expansion means is returned to the drying chamber. The expansion means may be a turbine (8) mechanically coupled to one of the compressors (7) to improve the efficiency of the drier.

Description

"HEAT PUMP CYCLE CLOTHES DRIER" TECHNICAL FIELD

The present invention relates to clothes driers and in particular but not solely domestic forced air tumble driers. A heat pump/refrigeration cycle is used to dry the air passed through the drier drum.

BACKGROUND ART

Most domestic clothes driers are characterised by the use of electric resistance heating to heat the air used for drying and by their open cycle nature. This latter characteristic leads to problems in the disposal of moisture laden air exhausted from the drier. Electrically heated relatively dry air is blown into the drier drum and moisture released from the clothes being dried is entrained in the air flow and the resultant cooler wet air exhausted from the drier cabinet. In such an open system drier the cool wet air must be exhausted into a space where its deleterious effects are minimal or tolerable. It is sometimes difficult to exhaust this air to the exterior of the building in which the drier is located and there may be no spaces within the building suitable for receiving the cool wet air.

Another problem is the efficiency of driers using electrically heated air.

It is known to use heat pumps to heat air in a variety of applications using standard refrigerants as the working fluid and a refrigerant to air heat exchanger to heat the air. Air cycle refrigerators have been described in GB 2,237,373 and Gigiel, "Is Air a Viable Alternative ReMgeτant?" Australian Refrigeration Air Conditioning and Heating Jan, 1990, and direct cooling by the air used as the working fluid is disclosed.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a forced air clothes drier which will go some way towards overcoming the abovementioned disadvantages by the use of an air-cycle heat pump.

Accordingly in one aspect the invention consists in a method of drying clothes wherein clothes containing moisture are placed in a chamber and air is passed through said chamber characterised in that: a refrigeration cycle including compression, expansion and heat transfer processes is used to heat and pressurise said air,

the air to be heated comprises the working fluid for said cycle and any water vapour entrained in the air in passing through said chamber is condensed in the cycle cooling processes and controllably removed from the cycle. In a second aspect the invention consists in a clothes drier wherein clothes containing moisture are dried in a chamber by a flow of air which is passed through said chamber characterised in that: compression means, expansion means and heat transfer means are arranged to form a refrigeration cycle, said compressor means heats and pressurises air inducted from said chamber, the air admitted into said chamber comprises the working fluid for said cycle, and water vapour entrained in the air which has passed through said chamber is condensed in the heat transfer means and expansion means in the cooling stages of the cycle and controllably removed therefrom.

In a third aspect the invention consists in a clothes drier comprising: a chamber for receiving moisture-containing clothes, a compressor which draws moist air from the chamber and heats and pressurises said air, a heat exchanger having a primary circuit for cooling and a secondary circuit for heating, the inlet of said primary circuit connected to the outlet of said compressor to thereby cool heated air from the compressor, a turbine means connected to the outlet of said primary circuit through which the cooled air is expanded to further cool said air below the dew point temperature of the air to thereby substantially condense out the water content of said air, the outlet of said turbine being connected to the inlet of said secondary circuit to cause the expanded dry air to be heated as it passes through the secondary circuit of said heat exchanger, and the outlet of said secondary circuit being connected to said chamber to discharge heated dry air therein. The invention is based on the concept of introducing a drying chamber in an appropriate part of a refrigeration cycle, where air is the working fluid, condensing water vapour out of the air in the refrigerator cycle cooling stages and controllably removing the condensate from the cycle. The cycle may be essentially closed and the working fluid recirculated or it could be open at a point in the cycle which would allow dry air at approximately ambient temperature to be discharged and ambient air inducted.

BRIEF DESCRIPTION OF DRAWINGS The preferred form of the invention will now be described with reference to the accompanying drawings in which;

Figure 1 shows in diagrammatic form a closed cycle clothes drier incorporating the present invention;

Figure 2 shows the drier cycle of the present invention plotted on a psychrometric chart;

Figure 3 is a temperature-entropy diagram of the drier cycle, Figure 4 shows in diagrammatic form a change to the configuration of the drier depicted in Figure 1 to produce an open cycle drier, and

Figure 5 shows in diagrammatic form a cross section through the preferred form of tumbler drier incorporating the present invention.

MODES FOR CARRYING OUT THE INVENTION

Referring to Figures 1 and 5 a drier drum 1 into which clothes are placed is shown having an air inlet 2 and an air outlet 3. The drier drum 1 is rotated to "tumble" the clothes as is present practice. It will be readily appreciated that what is required is that hot dry air should enter inlet 2 which after passing through the drum and the clothes to be dried will emerge at outlet 3 as cooler moister air. According to the present invention it is proposed to pass the air leaving inlet 3 through a series of thermodynamic processes so that the same air with water vapour removed therefrom can be delivered to inlet 2 in the required hot and dry state. That is, the present invention seeks to provide a drier which does not use electrically energized resistance heating to heat incoming air admitted to the drier drum. The air flow through the system to cause clothes drying is as follows. Moist air at 32°C and 90% relative humidity or a humidity ratio of 27 grams moisture per kg dry air from outlet 3 in condition A (see Figures 2 and 3) is fed through a lint filter

17 to a compressor 4 driven by an electric motor 5. Motor 5 could be the same motor as that which rotates the drier drum although a highly geared drive would then need to be used to couple to the compressor. The compressor 4 could be dispensed with and the motor 5 used to drive compressor 7, but there are advantages in using two stages of compression as will be explained below. Air at the compressor outlet

5 is in state B, that is, increased in temperature by about 7°C. This air then undergoes a second stage of compression in a turbo compressor 7. This compressor is driven by turbine 8. The air at the output 9 of turbo compressor 7 is in state C, that is around 73°C and at a pressure of about 1.9 atmospheres. The compressors 4 and 7 and turbine 8 are preferably of the mixed flow multi-blade type designed to run at speeds between 30,000 to 100,000 r.p.m. and motor 5 runs at comparable speeds. High pressure air from the outlet 9 of compressor 7 is passed through a filter or separator 10 to remove lint whereupon it enters the primary side 11 of a heat exchanger 12. The air leaves primary side 11 of the heat exchanger 12 in state D having given up heat and is now at a temperature of 42°C. This air is then passed through a second heat exchanger 13 in which the air is exposed to ambient temperature and leaves the heat exchanger 13 by airline 15 in state E at approximately 35°C. In passing through the ambient heat exchanger 13 at least some water vapour in the air reaches its dew point and water starts to form in the air line

15 (see D to E in Figure 2).

The air in state E is then expanded through turbine 8 thus undergoing a temperature drop and a fall in pressure to one atmosphere. The expansion of the air in turbine 8 rotates the turbine impeller (not shown) which in turn rotates shaft 16 and thus the impeller of the turbo compressor 7. Thus, the enthalpy loss through turbine 8 is converted to useful work at the turbine shaft which is used to power compressor 7 and thereby increase the efficiency of the drier. In leaving the turbine in state F at about 20°C the air humidity ratio has been reduced to about 15 grams moisture per kilogram dry air. Water lost from air line 14 is bled from turbine 8 into a container (not shown). After leaving turbine 8 the air in state F passes through a secondary circuit 14 of heat exchanger 12. In passing through the heat exchanger the dry air increases in temperature from about 20°C to around 60°C, being heated by the air passing through the primary circuit 11. The air at this temperature and at a pressure of one atmosphere (state G) provides the inlet air for the drier drum 1. The air entering the drum has a relative humidity of approximately 12%.

The drier described above has an air flow rate of 50 gls and extracts 0.6 gls water for a work input of approximately 860 watts at realistically obtainable cycle efficiencies. In a variant an open cycle could be used which would still retain many of the advantages already discussed. That is, dry air in state F could be exhausted from the cycle without detriment to the surroundings and ambient air induced into the^'cycle at point 19 as shown in figure 4.

The present invention provides a clothes drier which does not exhaust moist air, while at the same time has good efficiency and can be built to acceptable physical dimensions.

Claims

1. A method of drying clothes wherein clothes containing moisture are placed in a chamber and air is passed through said chamber characterised in that: a refrigeration cycle including compression, expansion and heat transfer processes is used to heat and pressurise said air, the air to be heated comprises the working fluid for said cycle and any water vapour entrained in the air in passing through said chamber is condensed in the cycle cooling processes and controllably removed from the cycle.

2. A method according to claim 1 wherein said cycle is substantially closed and the air recirculated.

3. A method according to claim 1 wherein said cycle is open at a point where the air is dry and approximately at ambient temperature.

4. A method according to any one of the preceding claims wherein the compression process is carried out in two stages, the expansion process produces work and said work is utilised in at least one of the compression stages.

5. A clothes drier wherein clothes containing moisture are dried in a chamber by a flow of air which is passed through said chamber characterised in that: compression means, expansion means and high and low temperature heat transfer means are arranged to form a refrigeration cycle, said compression means heat and pressurise air inducted from said chamber, the air admitted into said chamber comprises the working fluid for said cycle, and water vapour entrained in the air which has passed through said chamber is condensed in the heat transfer means and expansion means in the cooling stages of the cycle and controllably removed therefrom.

6. A clothes drier according to claim 5 wherein said refrigeration cycle is substantially closed and the dry air leaving the expansion means is delivered into the low temperature heat transfer means for subsequent induction into said chamber.

7. A clothes drier according to claim 5 wherein said refrigeration cycle is open between said expansion means and the low temperature heat transfer means.

8. A clothes driver according to any one of the preceding claims wherein said expansion means produces work and said work is utilised by said compression means.

9. A clothes drier comprising: a chamber for receiving moisture containing clothes, a compressor which draws moist air from the chamber and heats and pressurises said air, a heat exchanger having a primary circuit for cooling and a secondary circuit for heating, the inlet of said primary circuit connected to the outlet of said compressor to thereby cool heated air from the compressor, a turbine means connected to the outlet of said primary circuit through which the cooled air is expanded to further cool said air below the dew point temperature of the air to thereby substantially condense out the water content of said air, the outlet of said turbine being connected to the inlet of said secondary circuit to cause the expanded dry air to be heated as it passes through the secondary circuit of said heat exchanger, and the outlet of said secondary circuit being connected to said container to discharge heated dry air therein.

10. A clothes drier comprising: a chamber for receiving moisture-containing clothes, a compressor which draws moist air from the chamber and heats and pressurises said air, a heat exchanger having a primary circuit for cooling and a secondary circuit for heating, the inlet of said primary circuit connected to the outlet of said compressor to thereby cool heated air from the compressor, a turbine means connected to the outlet of said primary circuit through which the cooled air is expanded to further cool said air below the dew point temperature of the air to thereby substantially condense out the water content of said air, the outlet of said turbine discharging into the environment, the inlet of said secondary circuit open to said environment and the outlet of the secondary circuit being connected to the inlet of said chamber.

11. A clothes drier according to either of claims 9 or 10 wherein a second compressor is coupled to receive the discharge from the first compressor and said second compressor discharges into said heat exchanger primary circuit, and drive means connect the output shaft of said turbine means to the input shaft of said second compressor.

12. A clothes drier according to any one of claims 9 to 11 wherein a second heat exchanger is coupled between the output of the primary circuit of the first heat exchanger and the input of the turbine means, said second heat exchanger configured to transfer heat to ambient environment.