Patent ID: 12209824

The conventional refrigeration dryer1′ inFIG.1for drying compressed air from a compressor plant comprises a heat exchanger2′ with a housing3′ enclosing an internal cavity and a set of channels, each of the channels in this set passing through the housing3′, the internal cavity and again through the housing3′.

The air to be dried flows in the internal cavity across the channels. Said compressed air to be dried is cooled by sending an initially two-phase cooling agent through the channels. Said initially two-phase cooling agent evaporates as it passes through these channels due to heat exchange with the compressed air in the internal cavity around the channels.

The heat exchanger2′ further comprises an inlet collector4′ with a side inlet5′ for the initially two-phase cooling agent. The inlet collector4′ is hermetically attached to the housing3′ across all inlet orifices of the channels. In this way, the inlet orifices of the channels are in fluid communication with an inlet collector chamber in the inlet collector4′, which inlet collector chamber collects a flow of the initially two-phase cooling agent that enters the inlet collector4′ via the side inlet5′.

The inlet collector chamber may have a distribution pipe, a structured medium or inserts to distribute the initially two-phase cooling agent entering the inlet collector4′ via the side inlet5′ uniformly across the set of channels.

Furthermore, the heat exchanger2′ comprises an outlet collector6′ with an outlet7′ for the initially two-phase cooling agent. The outlet collector6′ is hermetically attached to the housing3′ across all outlet orifices of the channels. In this way, the outlet orifices of the channels are in fluid communication with an outlet collector chamber in the outlet collector6′, which outlet collector chamber collects flows of the initially two-phase cooling agent that enters the outlet collector6′ via the outlet orifices of the channels. The initially two-phase cooling agent can then leave the outlet collector6′ via the outlet7′.

The refrigeration dryer1according to the invention inFIG.2comprises, analogously to the conventional refrigeration dryer1′ inFIG.1, a heat exchanger2with a housing3enclosing an internal cavity and a set of channels, each of the channels in this set passing through the housing3, then the internal cavity and again through the housing3.

An inlet collector4of the heat exchanger2has an inlet5for an initially two-phase cooling agent. In this case, this inlet5is centrally located opposite the inlet orifices of the channels, which in itself ensures a more uniform distribution of a flow of initially two-phase cooling agent entering through said inlet5than would be the case with a side inlet5′ such as in the heat exchanger2′ of the conventional refrigeration dryer1′ inFIG.1.

Similarly, an outlet7of an outlet collector6of the heat exchanger2is centrally located opposite the outlet orifices of the channels, which offers an analogous advantage in comparison with the side outlet7′ such as in the heat exchanger2′ of the conventional refrigeration dryer1′ inFIG.1.

Optionally, the heat exchanger2is also equipped with an intermediate collector8for levelling pressure levels in the set of channels between the inlet collector4and the outlet collector6.

FIG.3ashows the heat exchanger2inFIG.2with an open view of the inlet collector4, andFIG.3bshows the heat exchanger2inFIG.2with an open view of the outlet collector6.

In the inlet collector chamber9first flow-rate distribution means10are disposed which distribute and direct the flow of the initially two-phase cooling agent entering the inlet collector4through the inlet5to the inlet orifices11of the channels12, which channels12pass through the internal cavity enclosed by the housing3of the heat exchanger2and finally exit through the outlet orifices14into the outlet collector6with the outlet7.

FIG.4ashows an isometric view of the inlet collector4with inlet5.

Said inlet5is in this case implemented as an elongated slot of which the dimensions, in a direction perpendicular to said inlet5, are approximately equal to the dimensions of the first flow-rate distribution means10. As a result, when the inlet collector4is produced, the location of the first flow-rate distribution means10is easily accessible after said inlet5has been formed, so that the first flow-rate distribution means10can then be easily formed using a standard machining technique.

FIG.4bshows a view of the inlet collector4inFIG.4aaccording to a direction perpendicular to the inlet5of the inlet collector4, whileFIG.4cshows a view of said inlet collector4inFIG.4aaccording to an intersection A-A inFIG.4b.

Both inlet5and inlet collector chamber9are symmetrical according to a first plane of symmetry B-B and a second plane of symmetry coinciding with the plane of intersection A-A and intersecting this first plane of symmetry B-B.

The first flow-rate distribution means10consist of a single body15comprising two flow-conducting surfaces16which are symmetrical with respect to each other according to the first plane of symmetry B-B and the second plane of symmetry A-A, and which two flow-conducting surfaces16, as seen from the inlet5, incline downward in a first direction R1perpendicular to the first plane of symmetry and/or in a second direction R2perpendicular to the second plane of symmetry.

In this case, the single body15of the first flow-rate distribution means10is implemented with a cross section which, considered in a plane equal or parallel to the plane of intersection A-A, comprises a substantially full and substantially isosceles triangle of which the sides of equal length are formed by the two flow-guide surfaces16.

It would not be excluded in the scope of the invention that alternatively or similarly a cross section, considered in a plane equal or parallel to the intersection plane B-B, would include a substantially full and substantially isosceles triangle of which the sides of equal length were formed by the two flow-conducting surfaces.

It would not be excluded in the scope of the invention that alternatively or similarly a cross-section, considered in a plane equal or parallel to the intersection plane B-B, would include a substantially full and substantially isosceles triangle of which the sides of equal length were formed by the two flow-conducting surfaces.

The inlet orifices11of the channels formed by the set of channels12are arranged in a straight line according to the first direction R1and symmetrically with respect to each other according to the first plane of symmetry B-B.

In the context of the invention, however, it cannot be excluded that the inlet orifices of the set of channels are arranged symmetrically with respect to each other in some other way according to the first plane of symmetry and the second plane of symmetry, for example when the inlet orifices are disposed at a regular distance on concentric circles or when the inlet orifices are positioned according to a pattern corresponding to grid points of a rectangular grid or a hexagonal honeycomb grid.

The single body15of the first flow-rate distribution means10may optionally include a through-hole17having an axis18according to a straight line common to the first plane of symmetry B-B and the second plane of symmetry A-A.

The inlet collector4includes a wall delimiting the inlet collector chamber9, which wall has a surface19facing the inlet collector chamber9that is opposite and substantially parallel to the two flow-conducting surfaces16. This allows a velocity of the initially two-phase cooling agent entering the inlet collector chamber9along inlet5to be maintained, which reduces the likelihood of liquid particles from the initially two-phase cooling agent precipitating against walls delimiting the inlet collector chamber9, whereby these liquid particles remain better dispersed in the initially two-phase cooling agent.

In order to keep the velocity of the initially two-phase cooling agent as high as possible, a dimension of the inlet collector chamber9in a direction common to the first plane of symmetry B-B and the second plane of symmetry A-A is best chosen as small as possible, typically smaller than 2.0 times the diameter D of the channels formed by the set of channels12.

FIG.5ashows an isometric view of the outlet collector6with outlet7.

FIG.5bshows a view of the outlet collector6inFIG.5aaccording to a direction perpendicular to the outlet7of the outlet collector6, whileFIG.5cshows a view of the outlet collector6inFIG.5aaccording to an intersection C-C inFIG.5b.

The outlet collector chamber20has a substantially cuboid shape, where the outlet orifices14of the channels12are in fluid communication with the outlet collector chamber20on a first side of the outlet collector chamber20and where the outlet7is in fluid communication with the outlet collector chamber20on a second side of the outlet collector chamber20opposite the aforementioned first side of the outlet collector chamber20.

To create a uniform outflow of the first initially two-phase cooling agent in the outlet collector chamber20, a perpendicular distance between the aforementioned first side and the aforementioned second side is best chosen large enough, typically minimally 1.0 times the diameter D of the ducts.

FIG.6shows an isometric view of an intermediate collector8according to the invention.

Second flow-rate distribution means21are formed by an internal cavity22in the intermediate collector8configured such that a flow of the initially two-phase cooling agent in a channel in the set of channels12can be at least partially diverted from this channel to and into another channel of the set of channels12. This allows pressure levels in the channels formed by the set of channels12to be equalized.

The inlet collector, outlet collector and intermediate collector described above can be produced in a simple and inexpensive way using a machining technique compared to more advanced techniques such as additive manufacturing.

COMPARATIVE EXAMPLE

As shown inFIG.1, a FD 1010 VSD refrigeration dryer made by Atlas Copco Airpower was used to test a standard eight-row heat exchanger 1629 1926 00 made by AKG Thermotechnik to cool and dehumidify a flow rate of 1010 l/s, 750 l/s and 500 l/s of ambient air at an initial temperature of 25° C., which ambient air is brought to an overpressure of 7 barg and enters the heat exchanger at a temperature of 35° according to the conditions of ISO standard no. 7183 option A1. 7183 option A1.

InFIG.7a distribution is shown of a temperature of dried compressed air around all channels in the housing of the heat exchanger, measured at positions a to i, as a function of the flow rate of ambient air. In this case, the temperature of the dried compressed air is controlled to a setpoint of 3.0° C. according to ISO standard no. 8573-1 class 4 under test conditions of ISO standard no. 8573-3.

This setpoint is represented inFIG.7by a long-dashed line. The distribution of the temperature of dried compressed air is shown asa solid line with circular symbols for an ambient airflow rate of 1010 l/s;a short-dashed line with square symbols for an ambient airflow rate of 750 l/s; anda dotted line with rhombic symbols for an ambient airflow rate of 500 l/s.

In a water separator behind the heat exchanger, two measurements of the LAT are further carried out: a “LAT left” measurement at position j and a “LAT right” measurement at position k.

Finally, the dew point of the compressed air and the evaporation temperature of the initially two-phase cooling agent are determined.

This leads to the following measurement results:

airflow rate1010 l/s750 l/s500 l/sLAT left-LAT right(° C.)2.0, 3.71.8, 3.61.2, 4.0PDP (° C.)3.13.32.8Tevap (° C.)−3.0−2.1−2.1

In this case, two parameters can be identified as performance indicators of the heat exchanger:a maximum value for the temperature difference “ΔTair” between a warmest and a coldest temperature of the dried air around the channels in the housing of the heat exchanger, in this case 9.8° C., 10.0° C. and 11.0° C. for an air flow rate of 1010 l/s, 750 l/s and 500 l/s respectively; anda proximity or approach, which is a temperature difference between the dew point PDP and the evaporation temperature Tevap, in this case 6.1° C., 5.4° C. and 4.9° C. for an air flow rate of 1010 l/s, 750 l/s and 500 l/s respectively.

Due to low temperatures of the dried compressed air at positions d to h, there is a risk that the heat exchanger would partially freeze there if the evaporation temperature of the cooling agent were to be further lowered by a pressure drop of the cooling agent, especially at low air flows. For this reason and because of high temperatures at positions a and b, a desired average temperature for the dried compressed gas of 3° C. cannot be achieved.

Examples 1 to 4

Example 1 differs from the comparative example in that the inlet collector of the heat exchanger is replaced by an inlet collector with first flow-rate distribution means according to the invention as shown inFIG.4a-4c.

FIG.8ashows for Example 1 the distribution of the temperature of dried compressed air around all channels in the housing of the heat exchanger, measured at positions a to i. This distribution is shown as a solid line with triangular symbols. The setpoint of 3.0° C. is represented by a long-dashed line.

Example 2 differs from the comparative example both in that the inlet collector of the heat exchanger is replaced by an inlet collector with first flow-rate distribution means according to the invention as shown inFIG.4a-4c, and in that the outlet collector is replaced by an outlet collector according to the invention as shown inFIG.5a-5c.

FIG.8bshows for Example 2 the distribution of the temperature of dried compressed air around all channels in the housing of the heat exchanger, measured at positions a to i. This distribution is shown as a solid line with triangular symbols. The setpoint of 3.0° C. is represented by a long-dashed line.

In Example 3, in the comparative example, the inlet collector of the heat exchanger is replaced by an inlet collector with first flow-rate distribution means according to the invention as shown inFIG.4a-4c, and an intermediate collector according to the invention as shown inFIG.6is incorporated in the heat exchanger.

FIG.8cshows for example 3 the distribution of the temperature of dried compressed air around all channels in the housing of the heat exchanger, measured at positions a to i. This distribution is shown as a solid line with triangular symbols. The setpoint of 3.0° C. is represented by a long-dashed line.

In Example 4, in the comparative example, the inlet collector of the heat exchanger is replaced by an inlet collector with first flow-rate distribution means according to the invention as shown inFIG.4a-4c, the outlet collector is replaced by an outlet collector according to the invention as shown inFIG.5a-5c, and an intermediate collector according to the invention as shown inFIG.6is incorporated in the heat exchanger.

FIG.8dshows, for Example 4, the distribution of the temperature of dried compressed air around all channels in the housing of the heat exchanger, measured at positions a to i. This distribution is shown as a solid line with triangular symbols. The setpoint of 3.0° C. is represented by a long-dashed line.

This leads to the following measurement results at an airflow rate of 1010 l/s for the various examples 1 to 4:

Example1234LAT left-LAT right(° C.)3.0-3.13.0-3.13.1-3.33.3-3.4PDP (° C.)3.22.83.13.7Tevap (° C.)−1.7−1.6−0.9−0.9

Consequently, the proximity between the dew pressure and the evaporation temperature in examples 1 to 4 is equal to 4.9° C., 4.4° C., 4.0° C. and 4.6° C. respectively.

The maximum value for the temperature difference ‘ΔTair’ for Examples 1 to 4 is equal to 4.4° C., 4.3° C., 3.2° C. and 3.1° C. respectively.

Example 5 and 6

A refrigeration dryer with the heat exchanger according to Example 4 is also tested at low airflow rates: an airflow rate of 750 l/s in Example 5 and an airflow rate of 500 l/s in Example 6.

FIG.9shows for Examples 5 and 6 the distribution of the temperature of dried compressed air around all channels in the housing of the heat exchanger, measured at positions a to i.

The setpoint of 3.0° C. is shown inFIG.9by a long-dashed line. The distribution of the temperature of dried compressed air is shown asa solid line with circular symbols for an ambient airflow rate of 1010 l/s;a short-dashed line with square symbols for an ambient airflow rate of 750 l/s; anda dotted line with rhombic symbols for an ambient airflow rate of 500 l/s.

Measurement results for Examples 5 and 6 are summarized in the table below:

Example456LAT left-LAT right(° C.)3.3-3.43.2-3.31.9-2.1PDP (° C.)3.73.72.4Tevap (° C.)−0.90.90.3Proximity (° C.)4.62.82.1

When the proximities in Examples 4 to 6 are compared with the proximities in the comparative example, it can be concluded that for the same airflow rate the proximities in Examples 4 to 6 are smaller than those in the comparative example. Furthermore, a decrease in the proximity at the low airflow rates in Examples 5 and 6 with respect to the proximity in example 4 is greater than the decrease that occurs at the low airflow rates in the comparative example.

The smaller the proximity, the greater the heat transfer between the initially two-phase cooling agent and the compressed air, and the more energy-efficient the refrigeration dryer operates as a result.

The improved smaller proximities in Examples 4 to 6 can be explained by a more uniform distribution of the temperatures of dried compressed air around all channels in the housing of the heat exchanger, as a result of which said temperatures can be controlled closer to the setpoint of 3.0° C. without running the risk of one of these temperatures becoming too low so that the heat exchanger would freeze up.

The maximum value for the temperature difference ‘ΔTair’ for Examples 5 to 6 is equal to 1.8° C. and 1.1° C. respectively.

The present invention is by no means limited to the embodiments described as examples and shown in the figures, but a heat exchanger according to the invention, an inlet collector and/or an outlet collector for such a heat exchanger, or a refrigeration dryer provided with such a heat exchanger may be implemented in all kinds of variants and/or dimensions without going beyond the scope of protection of the invention according to the claims.