WO2014180505A1

WO2014180505A1 - Apparatus for detecting leakage in a cooling system and method of detecting leakage

Info

Publication number: WO2014180505A1
Application number: PCT/EP2013/059653
Authority: WO
Inventors: Tekin Yilmaz; Hudai TUZUN; Riza URTEKIN; Ayse OZBEK
Original assignee: Arcelik Anonim Sirketi
Priority date: 2013-05-08
Filing date: 2013-05-08
Publication date: 2014-11-13

Abstract

The present invention relates to leakage detection apparatus (1) for detecting leakage in a cooling systenn (2) or in a sub-unit of the cooling systenn (2), in particular a refrigerator. The leakage detection apparatus (1) includes an inlet (3) for receiving a pressurized fluid from a supply apparatus (4), an outlet (5) for pressurizing the cooling system (2) or the sub-unit of the cooling system (2) with the fluid received by the inlet (3), a valve (6) fluidly connecting the inlet (3) and the outlet (5) and a pressure sensor (7) for detecting a fluid pressure in the outlet (5). The leakage detection apparatus (1) according to the present invention further comprises a first temperature sensor (9) for detecting a fluid temperature in the outlet (5), a retrievable memory (8) for recording the detected fluid pressure and fluid temperature and a control unit (10) adapted to pressurize the cooling system (2) or the sub-unit of the cooling system (2) to subsequently close the valve (6) and after a settling time, to periodically record a simultaneously detected fluid pressure and fluid temperature into the memory (8).

Description

APPARATUS FOR DETECTING LEAKAGE IN A COOLING SYSTEM AND METHOD OF DETECTING LEAKAGE

The present invention relates to an apparatus for detecting leakage in a cooling system or in a sub-unit of the cooling system, in particular a refrigerator for domestic use, a system using the apparatus for detecting leakage, and a method of detecting leakage.

It is common practice in the field of refrigeration and air-conditioning to test a cooling system or its sub-units for gas tightness prior to charging the cooling system with a refrigerant for a first-time operation. A test for gas tightness may also be necessary to locate one or more leaks for maintenance of the cooling system when the charged refrigerant is lost.

In general, leak tests are devised either to detect the presence of a leak or to locate a leak in a cooling system. Several methods for detecting leaks have been developed. Commonly used techniques for detecting leaks are the pressure decay method and the pressure rise method. These methods work in an opposite manner. In the pressure rise method the cooling system is initially evacuated. Subsequently, the internal pressure is monitored over time. If the cooling system has a part which is not correctly brazed or which has pores, cracks, holes, and the like, then the internal pressure rises. This method has also some disadvantages. A sudden pressure decrease during the evacuation may, for instance, cause stress on the weak parts or even damage the interior parts by cavitation. In the pressure decay method, the cooling system is pressurized with a fluid such as dry air or nitrogen. Subsequently, the internal pressure of the cooling system is monitored over time. If the cooling system has a leak, then the internal pressure drops. However, if there is no leak, then the pressure remains constant.

CN202229890U discloses a leak detection device including a fluid inlet and a fluid outlet which are in fluid communication through a valve, and a pressure meter located on an downstream side of the valve, for measuring a fluid pressure.

In cooling systems, the leaks may have different sizes. A leak with a large size is relatively easy to detect and to locate in comparison to a smaller leak present in a cooling system. In the pressure decay method, a small leak causes the pressure to drop only relatively slowly – which may be difficult to detect. Thus, the sensitivity of the leakage detection depends on the resolution of the pressure sensor and also on the testing time. However, these are important cost factors for manufacturers. On the other hand, test results may be adversely influenced by uncontrollable sources of errors such as instabilities and fluctuations in the cooling system. The reliability and the preciseness of the test results are very important in view of the warranty period of the cooling systems. Longer test periods generally increase reliability of the test results. However, this is not desired.

An objective of the present invention is to provide an apparatus for detecting leakage in a cooling system or in a sub-unit of the cooling system such as a refrigerator, a system having the apparatus for detecting leakage, and a method of detecting leakage which overcome the drawbacks of the above mentioned prior art and enable a reliable, precise, fast, and cost-efficient detection of a leak.

This objective has been achieved by the leakage detection apparatus according to claim 1, the leakage detection system according to claim 8, and the method of leakage detection according to claim 10. The dependent claims define preferred embodiments of the present invention.

The leakage detection apparatus according to the present invention comprises an inlet for receiving a pressurized fluid from a supply apparatus; an outlet for pressurizing a cooling system or a sub-unit of the cooling system with the fluid received by the inlet; a valve fluidly connecting the inlet and the outlet; a pressure sensor for detecting a fluid pressure in the outlet; a first temperature sensor for detecting a fluid temperature in the outlet; a retrievable memory for recording the detected fluid pressure and fluid temperature; and a control unit adapted to pressurize the cooling system or the sub-unit of the cooling system, to close the valve, and after a settling time, to periodically record a simultaneously detected fluid pressure and fluid temperature, into the memory.

By virtue of detecting the fluid temperature, the changes in the fluid pressure which are caused by thermal fluctuations in the cooling system are also implicitly captured and recorded into the memory. Thereby, the recorded data is rendered suitable for virtually eliminating uncontrollable sources of errors such as thermal fluctuations in the cooling system. The recorded data in the memory can be retrieved and analyzed by a remote computerized system in which the leakage detection method of the present invention is installed. The recorded data may be retrieved manually by a portable media or by a wired or wireless bidirectional communication means and transmitted to the computerized system for monitoring and/or analyzing the recorded fluid pressures and fluid temperatures.

In a preferred embodiment, the leakage detection apparatus further comprises a second temperature sensor for detecting an ambient temperature. Thereby, temperature changes in the environment are monitored over time. In this embodiment, the control unit periodically records the ambient temperature simultaneously detected with the fluid pressure and the fluid temperature, into said memory. Thereby, the recorded data is also rendered suitable for virtually eliminating uncontrollable sources of errors such as thermal fluctuations in the cooling system which are induced by changes in the ambient temperature. The recorded data in the memory can be similarly retrieved and monitored and/or analyzed by a remote computerized system.

In another preferred embodiment of the present invention, the control unit of the leakage detection apparatus is equipped to analyze the recorded data itself. The control unit, rectifies the detected fluid pressures by compensating for the changes in the respectively detected fluid temperatures, evaluates a leakage amount of the fluid on the basis of changes in the rectified fluid pressures, and determines whether there is a leak based on the evaluated leakage amount. Thereby, thermal fluctuations in the cooling system are virtually eliminated by rectifying the fluid pressure data.

In yet another preferred embodiment, the control unit finds one or more intervals in which an absolute rate of change in the ambient temperature is less than a threshold rate, preferably less than 5 C° per hour, or more preferably less than 2 C° per hour, and disregards the fluid pressures recorded in the memory which temporally lie outside the one or more intervals found, when evaluating a leakage amount. Thereby, the environmental effects on the cooling system can be further suppressed. Hence, the leakage amount is evaluated by using more reliable pressure data. The leakage detection apparatus may be installed in a cooling or freezing compartment of the cooling system when collecting data to enable thermal isolation from the environment. Thereby, the adverse environmental effects can be even further suppressed.

In the above-mentioned embodiments, any adverse effects on the fluid pressure caused by the heat produced in the leakage detection apparatus itself is also virtually eliminated. However, the analysis may be performed on a remote computerized system to avoid any heat sources disturbing the sensors.

In a further embodiment, the control unit finds one or more intervals in which the rectified fluid pressures strictly or monotonically decrease, and disregards the fluid pressures recorded in the memory which temporally lie outside the one or more intervals, when evaluating a leakage amount. Thereby, pressure regimes which do not have a decay character and which may be caused by an instability in the cooling system are further excluded from the evaluation.

In a still further embodiment, the control unit determines that there is leakage if the evaluated leakage amount accumulated over a respective detection period which is preferably less than 48 hours, more preferably less than 8 hours, still more preferably less than 2 hours, exceeds a threshold leakage rate.

In a still further embodiment, the control unit evaluates a leakage rate of the fluid on the basis of a decay rate of the rectified fluid pressure by a statistical regression technique, and determines that there is a leakage if the evaluated leakage rate exceeds a threshold leakage rate. Thereby, the total detection period can be drastically reduced depending on a level of the statistical significance of the regression.

Additional advantages of the leakage detection apparatus, the leakage detection system, and the method of leakage detection of the present invention will now become apparent with the detailed description of the preferred embodiments with reference to the accompanying drawings in which:

Figure 1 - is a perspective view of a leakage detection system for detecting leakage in a cooling system or in a sub-unit of the cooling system according to a preferred embodiment of the present invention. The solid arrows show fluid paths when pressurizing the cooling system;

Figure 2 - is a flowchart showing steps of a method of detecting leakage in a cooling system or in a sub-unit of the cooling system according to a preferred embodiment of the present invention.

The reference signs appearing on the drawings relate to the following technical features.

Leakage detection apparatus
Cooling system
Inlet
Supply apparatus (nitrogen)
Outlet
Valve
Pressure sensor
Memory
1^st temperature sensor
Control unit
2^nd temperature sensor
Communication means
Computerized system
Leakage detection system
Compressor
Display

Figure 1 shows a leakage detection apparatus (1) for detecting leakage in a cooling system (2) or in a sub-unit of the cooling system (2), in particular a refrigerator. The leakage detection apparatus (1) comprises an inlet (3) for receiving a pressurized fluid from a supply apparatus (4), an outlet (5) for pressurizing the cooling system (2) or the sub-unit of the cooling system (2) with the fluid received by the inlet (3), a valve (6) fluidly connecting the inlet (3) and the outlet (5), and a pressure sensor (7) for detecting a fluid pressure in the outlet (5).

The leakage detection apparatus (1) according to the present invention further comprises a first temperature sensor (9) for detecting a fluid temperature in the outlet (5), a retrievable memory (8) for recording the detected fluid pressure and fluid temperature and a control unit (10) adapted to pressurize the cooling system (2) or the sub-unit of the cooling system (2), to subsequently close the valve (6), and after a settling time, to periodically record a simultaneously detected fluid pressure and fluid temperature, into the memory (8).

The leakage detection apparatus (1) further comprises a second temperature sensor (11) for detecting an ambient temperature. In this embodiment, the control unit (10) is further adapted to periodically record an ambient temperature simultaneously detected with the fluid pressure and the fluid temperature, into said memory (8).

The leakage detection apparatus (1) preferably further comprises a bidirectional wired communication means (12) for sending the recorded fluid pressures and the recorded fluid temperatures to a computerized system (13) for monitoring and/or analysis. Alternatively, the recorded data may be retrieved manually by a portable media or by a wireless bidirectional communication means and transmitted to the computerized system for monitoring and/or analyzing the recorded fluid pressures and fluid temperatures.

The control unit (10) includes a compensation means adapted to rectify the detected fluid pressures by compensating for the changes in the respectively detected fluid temperatures, an evaluation means adapted to evaluate a leakage amount of the fluid on the basis of changes in the rectified fluid pressures and a determination means adapted to determine whether there is a leak based on the evaluated leakage amount.

The evaluation means in the control unit (10) is further adapted to find one or more intervals in which an absolute rate of change in the ambient temperature is less than a threshold rate, and to disregard the fluid pressures recorded in the memory (8) which temporally lie outside the one or more intervals found, when evaluating a leakage amount. The threshold rate is preferably less than 5 °C per hour, or more preferably less than 2 °C per hour.

The evaluation means in the control unit (10) is further adapted to find one or more intervals in which the rectified fluid pressures strictly or monotonically decrease, and to disregard the fluid pressures recorded in the memory (8) which temporally lie outside the one or more intervals, when evaluating a leakage amount.

The determination means of the control unit (10) is further adapted to determine that there is leakage in the cooling system (2) or in the sub-unit of the cooling system (2) if the evaluated leakage amount within a respective detection period exceeds a threshold leakage rate. The threshold leakage rate is preferably in a range of 10 to 12 grams per annum.

The evaluation means in the control unit (10) is further adapted to evaluate a leakage rate of the fluid on the basis of a decay rate of the rectified fluid pressure. The evaluation means applies for example, a statistical regression technique such as an exponential or logarithmic regression to the detected fluid pressures to obtain a decay rate. In this preferred embodiment, the determination means is further adapted to determine that there is a leakage if the evaluated leakage exceeds the threshold leakage rate.

Next, a leakage detection system (14) for detecting leakage in a cooling system (2) or in a sub-unit of the cooling system (2) will be explained with reference to Figure 1.

Figure 1 shows a leakage detection system (14) of the present invention. As shown in Figure 1, the leakage detection system (14) comprises the leakage detection apparatus (1) according to the present invention and a supply apparatus (4) for supplying the leakage detection apparatus (1) with pressurized nitrogen gas.

The supply apparatus (4) as shown in Figure 1, preferably includes a nitrogen generator capable of producing nitrogen enriched dry air by filtering nitrogen from the ambient air through a membrane. As shown in Figure 1, a compressor (15) is used to supply the membrane with pressurized ambient air. Alternatively, a tube containing pressurized nitrogen can be used to supply the leakage detection apparatus (1) with pressurized nitrogen gas.

In the leakage detection system (14) of the present invention, it is also preferable to alternatively use a clogging device for the purpose of supplying the leakage detection apparatus (1) with pressurized nitrogen gas. A clogging device suitable for this purpose is known from WO 2004/059225. The content of this application is herein incorporated by reference into the present application.

Next, a method of detecting leakage in a cooling system (2) or in a sub-unit of the cooling system (2) will be explained with reference to Figure 2.

First, the cooling system (2) is shut down. Any residual refrigerant in the cooling system (2) is maximally recovered. If any parts need to be brazed, the brazing work is completed. It is waited until the brazed parts sufficiently cool down.

As shown in Figure 2, in step 101, the cooling system (2) or the sub-unit of the cooling system (2) is evacuated. In step 102, the cooling system (2) or the sub-unit of the cooling system (2) is pressurized with a fluid such as nitrogen enriched dry air. In step 103 to step 106, the cooling system (2) is pressurized between 4500 mbar to 6000 mbar. In step 104 and step 105, the technician is informed via a display (16) provided on the leakage detection apparatus (1), when the fluid pressure is not within the preferred range. In step 107, the control unit (10) closes the valve (6). The valve (6) is preferably a solenoid valve (6). In step 108, the control unit (10) displays a prompt on the display (16) asking the technician to install the leakage detection apparatus (1) in a freezer compartment or in a cooling compartment of the cooling system (2). After elapse of a settling time the detection and recording phase is initiated.

As shown in Figure 2, in step 109a, the control unit periodically and simultaneously detects a fluid pressure and a fluid temperature of the cooling system (2). The sampling frequency is preferably 60 seconds. The display (16) is preferably a touch screen. The sampling frequency is adjustable over the touch screen. In step 109c, the detected fluid pressure and fluid temperatures are periodically recorded into the memory (8). The detection and recording of the fluid pressure and fluid temperature is periodically continued for a predetermined test duration or until it is determined that there is a leak in the cooling system (2). The determination is done by the control unit (10) of the leakage detection apparatus (1) or a computerized system. In step 110, the recorded data is preferably sent to a computerized system for monitoring and/or analysis. The control unit (10) also keeps a record of the temporal sequence of the recorded data. The control unit (10) has an internal clock.

As shown in Figure 2, in step 109b, preferably an ambient temperature is periodically detected simultaneously with the detection of the fluid pressure and the fluid temperature. In step 109c, the detected ambient temperature is also recorded into said memory (8). The detection and recording of the ambient air temperature is periodically continued a predetermined test duration or until it is determined that there is a leak in the cooling system (2).

As shown in Figure 2, in step 111a, the detected fluid pressures are rectified by compensating for the changes in the respectively detected fluid temperatures. In step 111b, a leakage amount of the fluid on the basis of changes in the rectified fluid pressures is evaluated. In step 111c, it is determined whether there is a leak based on the evaluated leakage amount. The leakage amount is cumulatively evaluated over the test duration.

As shown in Figure 2, in step 112, it is determined that there is leakage in the cooling system (2) or in the sub-unit of the cooling system (2), if the evaluated leakage amount within the respective detection period exceeds a threshold leakage rate. In step 113, the leakage amount and/or rate is displayed.

As shown in Figure 2, in step 111b, preferably, one or more intervals in which an absolute rate of change in the ambient temperature is less than a threshold rate is found, and the fluid pressures recorded in the memory (8) which temporally lie outside the one or more found intervals is disregarded in step 111c when a leakage amount is being evaluated.

Claims

A leakage detection apparatus (1) for detecting leakage in a cooling system (2) or in a sub-unit of the cooling system (2), in particular a refrigerator, comprising,

- an inlet (3) for receiving a pressurized fluid from a supply apparatus (4),

- an outlet (5) for pressurizing the cooling system (2) or the sub-unit of the cooling system (2) with the fluid received by the inlet (3),

- a valve (6) fluidly connecting the inlet (3) and the outlet (5) and

- a pressure sensor (7) for detecting a fluid pressure in the outlet (5),

characterized in that

- a first temperature sensor (9) for detecting a fluid temperature in the outlet (5),

- a retrievable memory (8) for recording the detected fluid pressure and the detected fluid temperature and

- a control unit (10) adapted to pressurize the cooling system (2) or the sub-unit of the cooling system (2), to subsequently close the valve (6), and after a settling time, to periodically record a simultaneously detected fluid pressure and fluid temperature into the memory (8).
The leakage detection apparatus (1) according to claim 1, characterized in that further comprising a second temperature sensor (11) for detecting an ambient temperature; and in that the control unit (10) is further adapted to periodically record an ambient temperature simultaneously detected with the fluid pressure and the fluid temperature, into said memory (8).
The leakage detection apparatus (1) according to claim 1 or 2, characterized in that the control unit (10) comprises

- a compensation means adapted to rectify the detected fluid pressures by compensating for the changes in the respectively detected fluid temperatures,

- an evaluation means adapted to evaluate a leakage amount of the fluid on the basis of changes in the rectified fluid pressures and

- a determination means adapted to determine whether there is a leak based on the evaluated leakage amount.
The leakage detection apparatus (1) according to claim 3, characterized in that the evaluation means is further adapted to find one or more intervals in which an absolute rate of change in the ambient temperature is less than a threshold rate, and to disregard the fluid pressures recorded in the memory (8) which temporally lie outside the one or more intervals found, when evaluating a leakage amount.
The leakage detection apparatus (1) according to claim 3 or 4, characterized in that the evaluation means is further adapted to find one or more intervals in which the rectified fluid pressures strictly or monotonically decrease, and to disregard the fluid pressures recorded in the memory (8) which temporally lie outside the one or more intervals, when evaluating a leakage amount.
The leakage detection apparatus (1) according to any one of claims 3 to 5, characterized in that the determination means is further adapted to determine that there is leakage in the cooling system (2) or in the sub-unit of the cooling system (2) if the evaluated leakage amount within a respective detection period exceeds a threshold leakage rate.
The leakage detection apparatus (1) according to any one of claims 3 to 5, characterized in that the evaluation means is further adapted to evaluate a leakage rate of the fluid on the basis of a decay rate of the rectified fluid pressure and the determination means is further adapted to determine that there is a leakage if the evaluated leakage rate exceeds a threshold leakage rate.
A leakage detection system (14) for detecting leakage in a cooling system (2) or in a sub-unit of the cooling system (2) according to any one of the claims 1 to 7, characterized in that the leakage detection apparatus (1) and a supply apparatus (4) for supplying the leakage detection apparatus (1) with pressurized nitrogen gas.
The leakage detection system (14) according to claim 8, characterized in that the supply apparatus (4) includes a nitrogen generator capable of producing nitrogen enriched dry air by filtering nitrogen from the ambient air through a membrane and a compressor (15) for supplying the membrane with pressurized ambient air.
A method of detecting leakage in a cooling system (2) or in a sub-unit of the cooling system (2), comprising the steps of:

- evacuating the cooling system (2) or the sub-unit of the cooling system (2) (101)

- pressurizing the cooling system (2) or the sub-unit of the cooling system (2) with fluid such as nitrogen enriched dry air (102-106),

- periodically and simultaneously detecting, after a settling time, a fluid pressure and a fluid temperature of the cooling system (2) (109a) and

- recording the detected fluid pressure and detected fluid temperatures into a memory (8) (109c).
The method of detecting leakage according to Claim 10, further comprising the steps of:

- periodically detecting an ambient temperature simultaneously with the detection of the fluid pressure and the fluid temperature (109b) and

- recording the detected ambient temperature into said memory (8) (109c).
The method of detecting leakage according to claim 10 or 11, further comprising the steps of:

- rectifying the detected fluid pressures by compensating for the changes in the respectively detected fluid temperatures (111a),

- evaluating a leakage amount of the fluid on the basis of changes in the rectified fluid pressures (111c) and

- determining whether there is a leak based on the evaluated leakage amount (112).
The method of detecting leakage according to claims 11 and 12, further comprising a step of:

- finding, in the evaluation step (111c), one or more intervals in which an absolute rate of change in the ambient temperature is less than a threshold rate, and disregarding the fluid pressures recorded in the memory (8) which temporally lie outside the one or more intervals found, when evaluating a leakage amount (111b).
The method of detecting leakage according to claim 12 or 13, further comprising a step of:

- determining that there is leakage in the cooling system (2) or in the sub-unit of the cooling system (2) if the evaluated leakage amount within a respective detection period exceeds a threshold leakage rate (112).
The method of detecting leakage according to any one of claims 10 to 14, by using the leakage detection apparatus (1), further comprising a step of:

- retaining the leakage detection apparatus (1) in a freezer compartment of the cooling system (2) during the detection and recording (108).