US20130333408A1

US20130333408A1 - System for drying and/or cooling an airflow

Info

Publication number: US20130333408A1
Application number: US13/997,027
Authority: US
Inventors: Willem Meijer; Arthur Van Der Lee
Original assignee: OPTIMAIR HOLDING BV
Current assignee: OPTIMAIR HOLDING BV
Priority date: 2010-12-24
Filing date: 2011-12-22
Publication date: 2013-12-19
Also published as: MX2013007406A

Abstract

The invention relates to a system for drying and/or cooling an airflow, comprising: at least one cooling device for cooling an airflow, comprising:—at least one cooling channel with an inflow opening for the airflow for cooling and an outflow opening for the cooled airflow,—at least one evaporating channel separated from the cooling channel by a transfer wall and having an inflow opening which is connected for medium throughflow to the outflow opening of the cooling channel, and an outflow opening, and—means for wetting the side of the transfer wall directed toward the evaporating channel, and a drying device for drying the airflow, comprising:—a drying channel with an inflow opening for the airflow for drying and an outflow opening for the dried air-flow, wherein the outflow opening of the cooling channel of the or a cooling device and/or the outflow opening of the evaporating channel of the or a cooling device is connected for medium throughflow to the inflow opening of the drying device.

Description

The invention relates to a system for drying and/or cooling an airflow, comprising:
at least one cooling device for cooling an airflow, comprising:

- at least one cooling channel with an inflow opening for the airflow for cooling and an outflow opening for the cooled airflow,
- at least one evaporating channel separated from the cooling channel by a transfer wall and having an inflow opening which is connected for medium throughflow to the outflow opening of the cooling channel, and an outflow opening, and
- means for wetting the side of the transfer wall directed toward the evaporating channel, and

a drying device for drying the airflow, comprising:

- a drying channel with an inflow opening for the airflow for drying and an outflow opening for the dried airflow.

Such a cooling device is for instance known from NL-C-1030538. Reference is made to this patent publication for an example of the operation of a cooling device which can be applied in the system according to the present invention. A drying device, for instance known from NL-C-1029822, wherein reference is made to this patent publication for an example of the operation of a drying device which can be applied in the system according to the present invention, is normally arranged upstream of the cooling device so that the airflow is dehumidified before it flows into the cooling device. A warm, moist airflow can in this way be drawn from the area surrounding the system into the inflow opening of the drying channel of the drying device and there dehumidified, after which the airflow is cooled in the cooling device to a cool, dry airflow which can be used for random purposes. This cool, dry airflow can for instance be supplied to a space. It is noted that other types of dryer and cooling device are also suitable for the system according to the invention.
The invention has for its object to provide such a system for drying and/or cooling an airflow, whereby the airflow is dehumidified efficiently, or at least effectively, in the drying device.
For this purpose the system of the type according to the invention stated in the preamble has the feature that the outflow opening of the cooling channel of the cooling device and/or the outflow opening of the evaporating channel of the cooling device is connected for medium throughflow to the inflow opening of the drying device.
It has been found by applicant that the efficiency of a drying device of a moist airflow increases with the relative humidity of the airflow. The airflow coming from the outflow opening of the cooling channel of the cooling device and/or the outflow opening of the evaporating channel of the cooling device usually has a higher relative humidity than the ambient air, whereby the drying device can dry the airflow coming from the cooling device efficiently. The relative humidity of the airflow is increased in the cooling channel in that at a constant absolute humidity of the airflow the temperature of the airflow decreases, this resulting in an increase in the relative humidity. The relative humidity of the airflow is increased in the evaporating channel of the cooling device in that the airflow cools by means of evaporation of the moisture applied to the transfer wall and thereby absorbs heat via the transfer wall from the airflow flowing through the cooling channel. The temperature of the airflow in the evaporating channel will increase due to the heat absorption, whereby this airflow can absorb more moisture. Due to the evaporation of the moisture and the temperature increase both the absolute and the relative humidity of the air in this way increase, and this relative humidity will be higher than the relative humidity of ambient air.
The relative humidity of the airflow in the system according to the invention is therefore increased in the cooling device, after which the airflow is dehumidified in the drying device. The air which is efficiently dehumidified in this manner can for instance be supplied to a space where dry air is desired or, if desired, be used for any random application. The air to be dehumidified can for instance be ambient air, which is for instance drawn into the inflow opening of the cooling channel of the cooling device. Optionally or additionally, the ambient air can also be another random airflow.
The system according to the invention is therefore distinguished from the known system in that it is now precisely the cooling device which is arranged upstream of the drying device instead of downstream. It would seem contradictory to first increase the relative humidity of an airflow before drying it, but according to the invention it is precisely this which increases the efficiency of the drying device. The air which is dried efficiently in this manner can be used for air drying processes or for air cooling processes.
In another embodiment of the system according to the invention the outflow opening of the drying device is connected for medium throughflow to the inflow opening of the cooling channel of the or a cooling device.
The dehumidified air is hereby cooled once again to a cool, dry airflow which can be used as desired. This cool, dry airflow can for instance be supplied to a space.
In an embodiment of the system according to the invention the system comprises two cooling devices, wherein the outflow opening of the drying device is connected for medium throughflow to the inflow opening of the cooling channel of the one cooling device, and wherein the outflow opening of the cooling channel of the other cooling device and/or the outflow opening of the evaporating channel of the other cooling device is connected for medium throughflow to the inflow opening of the drying device.
In another embodiment of the system according to the invention the system comprises a heat exchanger which is connected on the one side for medium throughflow to the outflow opening of the cooling channel of the cooling device and/or the outflow opening of the evaporating channel of the cooling device, and which is connected on the other side for medium throughflow to the inflow opening of the drying device and/or the inflow opening of the cooling channel of the cooling device.
In such a system the cooled airflow is not supplied to a space but brought into heat-transferring contact in the heat exchanger with a heat or cold-transferring medium. The temperature of the cooled airflow will increase here, while the heat or cold-transferring medium will cool. The heat or cold-transferring medium can be a second airflow, for instance ambient air, which is drawn into the heat exchanger, cooled and subsequently supplied to a space. The heat or cold-transferring medium can also be water, which water is cooled in the heat exchanger. This cooled water can for instance be used to cool a building.
The heat exchanger can be any random type of heat exchanger, wherein the flows are in counterflow.
The heat exchanger is for instance connected on the one side for medium throughflow to the outflow opening of the cooling channel of the cooling device and connected on the other side for medium throughflow to the inflow opening of the cooling channel of the cooling device and/or the inflow opening of the drying device, wherein the outflow opening of the cooling channel and/or the outflow opening of the evaporating channel of the cooling device is connected for medium throughflow to the inflow opening of the drying device.
This system has the advantage that the cooled airflow is discharged from the outflow opening of the cooling channel of the cooling device to the heat exchanger, while the airflow from the outflow opening of the evaporating channel of the cooling device, which airflow has a higher temperature than the airflow coming from the cooling channel, is carried to the inflow opening of the drying device.
The system is for instance a closed system in respect of at least the airflow. This has the advantage that the system is independent of the outdoor climate.
In a closed system means can moreover be present for adjusting the air pressure in the system. The value for the air pressure in the system can for instance lie between 0.5 bar—3 bar. The air pressure can particularly be 0.5 bar, 1 bar or 2 bar.
A higher air pressure has the advantage that fewer grams of water per kilogram of air have to be extracted from the airflow than at a lower air pressure in order to cool the air by a determined number of degrees. A lower air pressure has on the other hand the advantage that a lower temperature of the airflow can be achieved at a constant absolute humidity than at a higher pressure. It is therefore possible to opt for a determined air pressure subject to the application of the system.
In a practical embodiment the drying device comprises drying means for drying the airflow. Such drying means are hygroscopic and absorb moisture from the airflow through absorption and/or adsorption. Examples of such drying means are for instance, though not exclusively, silica gel, ammonium nitrate, calcium chloride, carbonyl fluoride, magnesium sulphate, sodium chloride, sodium sulphate, sodium propionate, a (p(AA)) sodium salt.
The drying means are preferably of a type wherein the amount of moisture which the drying means can absorb relative to the dry weight of the drying means increases with a rise in the relative air humidity.
With such drying means the drying device will be able to absorb more moisture from the airflow in efficient manner at a higher relative air humidity than at a lower relative air humidity.
From a determined value of the relative air humidity the amount of moisture which the drying means can absorb relative to the dry weight of the drying means particularly increases at least more or less exponentially with a rise in the relative air humidity.
Determined salts for instance show such a more or less exponential curve from a determined value of the relative air humidity, whereby the moisture absorption of the drying means takes place in highly efficient manner at a high relative air humidity of the airflow above this determined value.

The invention will be further elucidated hereinbelow with reference to figures shown in a drawing, in which:

FIGS. 1-5 show schematically different embodiments of the system according to the invention;

FIGS. 6A-6C show the Mollier diagram at 0.5 bar (FIG. 6A); 1 bar (FIG. 6B); and 2 bar (FIG. 6C); and

FIG. 7 shows schematically the amount of moisture which the drying means can absorb relative to the dry weight as a function of the relative air humidity for silica gel and a sodium salt.

The airflows are designated in the figures with arrows. Where an arrow splits into two or more continuous arrows means that parts of the airflow are separated and these partial airflows flow to different destinations. The flow rate of the different partial airflows and the ratios of different partial airflows can be variable, and in that case be adjusted as desired.
FIG. 1A shows a system for cooling an airflow, comprising a cooling device 1 for cooling an airflow, comprising at least one cooling channel 10 with an inflow opening for the airflow for cooling and an outflow opening for the cooled airflow, at least one evaporating channel 12 separated from cooling channel 10 by a transfer wall 11 and having an inflow opening, which is connected for medium throughflow to the outflow opening of cooling channel 10, and an outflow opening, and means for wetting the side of transfer wall 11 directed toward evaporating channel 12. The system further comprises a drying device 2 for drying the airflow, comprising a drying channel 13 with an inflow opening for the airflow for drying and an outflow opening for the dried airflow.
The air which flows into the inflow opening of cooling channel 10, and the relative humidity of which is increased in cooler 1, can for instance be ambient air. In the system according to FIG. 1A a part of the airflow coming from cooling channel 10 flows to the inflow opening of drying channel 13 and another part flows to the inflow opening of evaporating channel 12. The air with a relative humidity increased by cooling device 1 is dried in drying device 2. This air can for instance be supplied via the outflow opening of drying channel 13 to a space in which dry air is desired.
In a system according to FIG. 1A it is also possible, alternatively or additionally, for the outflow opening of evaporating channel 12 to be connected for medium throughflow to the inflow opening of drying channel 13. At least a part of the warm, moist airflow coming from evaporating channel 12 can hereby be dehumidified in drying device 2.
FIG. 1B shows the system according to FIG. 1A wherein the outflow opening of drying channel 13 of dryer 2 is connected for medium throughflow to the inflow opening of cooling channel 10 of cooler 1, so that a part of the airflow dehumidified in dryer 2 is fed back into the inflow opening of cooling channel 10 of cooling device 1. Because at least a part of the airflow is in this way guided twice through dryer 2, the absolute humidity of the airflow will be lower compared to a system according to FIG. 1A in which the airflow is guided once through dryer 2. This can be advantageous when air with a low absolute humidity is desired.
FIG. 2 shows a system with two coolers 1 a and 1 b. The outflow opening of drying device 2 is connected here for medium throughflow to the inflow opening of cooling channel 10 b of the one cooling device 1 b, wherein the outflow opening of cooling channel 10 a of the other cooling device 1 a is connected for medium throughflow to the inflow opening of drying device 2. In the system according to FIG. 2 a part of the airflow coming from cooling channel 10 a flows into drying device 2 via the inflow opening of drying channel 13 and another part flows into the other cooling device 1 a via the inflow opening of evaporating channel 12 a. It is noted that, alternatively or additionally, the outflow opening of evaporating channel 12 a of the other cooling device 1 a can be connected for medium throughflow to the inflow opening of drying device 2. Ambient air is drawn in here via the inflow opening of cooling channel 10 a of the other cooler 1 a. Cooled air is supplied to a space from the outflow opening of cooling channel 10 b of cooler 1 b.
In FIG. 3A the outflow opening of drying device 2 is connected for medium throughflow to the inflow opening of cooling channel 10 of cooling device 1 and the outflow opening of cooling channel 10 of cooling device 1 is connected for medium throughflow to the inflow opening of drying device 2. The airflow coming from the outflow opening of the cooling channel of cooling device 1 separates into three partial airflows, of which the first partial airflow is guided into drying device 2 and the second partial airflow is supplied to for instance a space, and wherein the third partial airflow is guided into the inlet opening of evaporating channel 12 of cooling device 1. For the purpose of illustration, about ⅓ of the cooled air is for instance supplied to the space, about ⅓ of the cooled air is supplied to dryer 2 and ⅓ of the cooled air is also supplied to evaporating channel 12 of cooler 1, after which the moist airflow is supplied to an area outside the space. These ratios can also be different. It is for instance possible to supply ½ of the cooled air to dryer 2 and ½ to the space and/or to evaporating channel 12. In the system according to FIG. 3A ambient air is drawn into the inflow opening of cooling channel 10 of cooler 1 and mixed with dried air coming from dryer 2 and/or ambient air is drawn into the inflow opening of drying channel 13 of dryer 2, as shown by the broken arrows.
FIG. 3B shows the system of FIG. 3A in which the outflow opening of evaporating channel 12 of cooler 1 is moreover connected for medium throughflow to the inflow opening of drying channel 13 of dryer 2 so that the warm, moist air coming from evaporating channel 12 is dehumidified in dryer 2.
FIG. 4 shows a system with one cooler 1, one dryer 2 and one heat exchanger 3. Heat exchanger 3 is connected on one side here for medium throughflow to the outflow opening of cooling channel 10 of cooling device 1 and connected on the other side for medium throughflow to the inflow opening of drying channel 13 of drying device 2. In the system according to FIG. 4 the cooled airflow is not supplied to a space but brought in a first channel 14 of heat exchanger 3 into heat-transferring contact with a second airflow in a second channel 15 of heat exchanger 3 via a heat-transferring partition wall 16. The temperature of the cooled airflow will increase here, while the second airflow will cool. The second airflow is for instance ambient air which is drawn into heat exchanger 3, cooled and subsequently supplied to a space. Ambient air can further be drawn into the inflow opening of cooling channel 10 of cooler 1 and/or into the inflow opening of drying channel 13 of dryer 2. The airflow coming from the evaporating channel of cooler 1 is discharged to the surrounding area outside the system.
FIGS. 5A and 5B show systems which are closed in respect of at least the airflow and have a cooler 1, a dryer 2 and a heat exchanger 3. Because the airflow remains in the system, the cooling capacity of the system is at least less affected by the climate of the surrounding area. The cooled airflow coming from the outflow opening of cooling channel 10 of cooler 1 is brought in first channel 14 of heat exchanger 3 into heat-transferring contact with the second airflow in second channel 15 of heat exchanger 3 via a heat-transferring partition wall 16, wherein the second airflow is supplied to a space. The airflow coming from evaporating channel 12 of cooler 1 is guided to the inflow opening of drying channel 13 of dryer 2. In the system according to FIG. 5A the airflow coming from evaporating channel 12 is mixed with the airflow coming from first channel 14 of heat exchanger 3. In the system according to FIG. 5B the airflow coming from first channel 14 of heat exchanger 3 is guided to the inflow opening of cooling channel 10 of cooler 1. As shown by the broken arrow, in the systems according to FIGS. 5A and 5B a part of the cooled airflow coming from cooling channel 10 of cooler 1 can be guided to the inlet opening of drying channel 13 of dryer 2. It is noted that an airflow for regeneration of dryer 2 and/or the second airflow flowing through second channel 15 of heat exchanger 3 can optionally be located in closed or open systems.
The distribution of the airflows can otherwise be adjusted as desired. In FIGS. 5A and 5B it is thus possible for about ⅓-⅔ of the airflow coming from evaporating channel 12 of cooler 1 to be guided to the inflow opening of dryer 2 and for about ⅓-⅔ of the cooled airflow coming from the outflow opening of cooling channel 10 of cooler 1 to be guided to heat exchanger 3.
It may also be the case that a part of the cooled airflow coming from the outflow opening of cooling channel 10 of cooler 1 is mixed with the airflow coming from evaporating channel 12 of cooler 1, and that this mixture is guided to dryer 2. The amount of moisture to be dried in grams per kg of air is thus reduced, and due to the drying the rise in the temperature of the airflow is relatively lower than if only the warm, moist airflow coming from evaporating channel 12 is guided to dryer 2.
The Mollier diagrams of FIGS. 6A-6C show that at an air pressure of 2 bar (FIG. 6C) less water, expressed in g water/kg air, has to be extracted from the airflow in order to reach a determined temperature of the airflow than at an air pressure of 1 bar (FIG. 6B) or 0.5 bar (6A). FIGS. 6A-6C further show that at a constant absolute humidity an absolute lower temperature can be reached at an air pressure of 0.5 bar (FIG. 6A) than at 1 bar (FIG. 6B) or 2 bar (FIG. 6C).
FIG. 7 shows for silica gel and a sodium salt the amount of moisture which the drying means can absorb in relation to the dry weight (Δm) as a function of the relative air humidity (RH). This shows that in the case of a sodium salt the amount of moisture which can be absorbed increases more or less exponentially, or at least progressively, from a relative air humidity of about 50%. A sodium salt therefore absorbs moisture from the air efficiently when the airflow has a relative air humidity of between 50% and 100%, wherein 90% air humidity is a practical value. Because the amount of moisture a sodium salt can absorb increases exponentially from a relative air humidity of about 50% to a relative air humidity of about 100%, the relative air humidity is preferably as high as possible.
The invention is not limited to the shown embodiments, but also extends to variants within the scope of the appended claims.
The stated and shown ratios of the airflows serve only for the purpose of illustration and should in no way be interpreted as being limitative.

Claims

1. A system for drying and/or cooling an airflow, comprising:

at least one cooling device for cooling an airflow, comprising:

at least one cooling channel with an inflow opening for the airflow for cooling and an outflow opening for the cooled airflow,

at least one evaporating channel separated from the cooling channel by a transfer wall and having an inflow opening which is connected for medium throughflow to the outflow opening of the cooling channel, and an outflow opening, and

means for wetting the side of the transfer wall directed toward the evaporating channel, and

a drying device for drying the airflow, comprising:

a drying channel with an inflow opening for the airflow for drying and an outflow opening for the dried airflow,

characterized in that

the outflow opening of the cooling channel of the cooling device and/or the outflow opening of the evaporating channel of the cooling device is connected for medium throughflow to the inflow opening of the drying device.

2. The system as claimed in claim 1, wherein the outflow opening of the drying device is connected for medium throughflow to the inflow opening of the cooling channel of the or a cooling device.

3. The system as claimed in claim 1, comprising two cooling devices, wherein the outflow opening of the drying device is connected for medium throughflow to the inflow opening of the cooling channel of the one cooling device, and wherein the outflow opening of the cooling channel of the other cooling device and/or the outflow opening of the evaporating channel of the other cooling device is connected for medium throughflow to the inflow opening of the drying device.

4. The system as claimed in claim 1, comprising a heat exchanger which is connected on the one side for medium throughflow to the outflow opening of the cooling channel of the cooling device and/or the outflow opening of the evaporating channel of the cooling device, and which is connected on the other side for medium throughflow to the inflow opening of the drying device and/or the inflow opening of the cooling channel of the cooling device.

5. The system as claimed in claim 4, wherein the heat exchanger is connected on the one side for medium throughflow to the outflow opening of the cooling channel of the cooling device and connected on the other side for medium throughflow to the inflow opening of the cooling channel of the cooling device and/or the inflow opening of the drying device, and wherein the outflow opening of the cooling channel and/or the outflow opening of the evaporating channel of the cooling device is connected for medium throughflow to the inflow opening of the drying device.

6. The system as claimed in claim 5, wherein the system is a closed system in respect of at least the airflow.

7. The system as claimed in claim 6, wherein the value for the air pressure in the system is between 0.5 bar-3 bar.

8. The system as claimed in claim 1, wherein the drying device comprises drying means for drying the airflow.

9. The system as claimed in claim 8, wherein the amount of moisture which the drying means can absorb relative to the dry weight of the drying means increases with a rise in the relative air humidity.

10. The system as claimed in claim 9, wherein from a determined value of the relative air humidity the amount of moisture which the drying means can absorb relative to the dry weight of the drying means increases at least more or less exponentially with a rise in the relative air humidity.