WO2010104431A1

WO2010104431A1 - Heat transfer arrangement in a radio network node

Info

Publication number: WO2010104431A1
Application number: PCT/SE2009/050255
Authority: WO
Inventors: Fredrik Jonsson
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2009-03-12
Filing date: 2009-03-12
Publication date: 2010-09-16

Abstract

A heat transfer arrangement (220) in a radio network node (200) is provided. The arrangement comprises an evaporator (222) adapted to extract heat from a first (location 210) and to evaporate a refrigerant in the evaporator (222), a condenser (224) outside the first location (210) remote from the evaporator (222) adapted to condense the evaporated refrigerant. The arrangement (220) further comprises a refrigerant circuit (226) comprising means (226a, 226b) adapted to lead the evaporated refrigerant from the evaporator (222) to the condenser (224) and means adapted to lead the condensed refrigerant from the condenser to the evaporator. The heat transfer arrangement (220) further comprises a temperature-sensitive valve (230) comprising a bi-metal member (232a, 232b). The bi-metal member is adapted to sense the temperature of the refrigerant and is arranged to open and/or close the temperature sensitive valve (230) such that the refrigerant flow (228) through the refrigerant circuit (226) is controlled in response to the refrigerant temperature.

Description

HEAT TRANSFER ARRANGEMENT IN A RADIO NETWORK NODE

TECHNICAL FIELD

The present invention relates to a heat transfer arrangement in a radio network node. More particular, the present invention relates to a temperature sensitive valve for controlling a refrigerant flow in the heat transfer arrangement.

BACKGROUND

Generally, a modern radio communication system comprises a radio access network and a number of communication devices. The radio access network is built up of several nodes, in particular, radio base stations. The primary task of a radio base station is to send and receive information to/from the communication devices within a cell served by the radio base station, In many cases, the base station is run 24 hours a day. Therefore, it is of particular interest and importance to ensure that the base station is operable predictably and reliably. The radio base station comprises an electronic component housing. Inside the electronic component housing there are arranged electronic components and circuitry for performing different tasks of the radio base station. For example, the circuitry may comprise a power control unit, a radio unit, comprising a radio amplifier, and a filtering unit for performing corresponding tasks.

Heat generated in the circuitry of the base station, in particular the radio unit, may not always dissipate naturally to a sufficiently high degree. Instead, heat is accumulated in the circuitry and temperature of the circuitry increases. The increased temperature of the circuitry may impair the performance of circuitry within the radio base station, e.g. the circuitry within the radio base station may fail. Consequently, unpredicted interruptions in operation of the base station may occur.

Radio network nodes are normally equipped with some kind of climate system. Some electronic component housings need to be cooled due to the heat generated by the electronic equipment inside the housing. A cooling fan directing air through the housing is sufficient for some applications and/or under certain operating conditions. For other applications and/or under other operating conditions a heat transfer system utilizing a refrigerant, which evaporates in an evaporator and condenses in a condenser, might be required. Such a heat transfer system comprises a thermosiphon. The evaporator would be arranged to use heat from the electronic components to evaporate the refrigerant and in this way cool the electronic components. However, under certain conditions it is not desirable to cool the electronic component housing as it could lead to a too low temperature inside the electronic component housing, which also could harm the electronic components and circuitry inside the electronic component housing. At low external ambient temperatures, the heating which arises naturally from the electronic equipment is sometimes insufficient to keep the internal temperature sufficiently high. In some applications, a heater is therefore arranged for warming up the air within the enclosure.

Externally mounted enclosures for mobile radio base stations potentially experience a wide range of ambient temperatures. One problem that can occur is that cold ambient air is pushed through the external side of the climate system due to wind leading to undesired cooling of the system. In some cases the heat generated by the network node equipment and the heater is transferred to the ambient air due to this situation and the network node is too cool to work properly.

Prior art solutions to the above problem may typically involve external mechanical arrangements on the external side of the climate system such that less air is pushed through the external part of the climate system due to wind load. A further prior art solution is to arrange a by-pass route inside the enclosure housing the electronic equipment such that at certain low temperatures the internal air would not pass over the internal part of the climate system but in an alternative route resulting in that heat is not transferred from the internal air. However, both the above solutions occupy precious space in the radio base station and higher design and production costs are also to be expected. In a still further prior art solution, an electric valve may be introduced in the climate system such that the circulation of refrigerant is stopped at low temperatures. A drawback with this solution is that it requires a power supply to the valve as well as some control signals for when the valve shall open and close which makes this solution expensive as well as less reliable in running. SUMMARY

An object of the present invention is to alleviate at least some of the above disadvantages and provide an improved heat transfer arrangement in a radio network node.

According to an aspect of the invention, the object is achieved by a heat transfer arrangement in a radio network node. The arrangement comprises an evaporator adapted to extract heat from a first location and to evaporate a refrigerant in the evaporator, a condenser outside the first location remote from the evaporator adapted to condense the evaporated refrigerant. The arrangement further comprises a refrigerant circuit comprising means adapted to lead the evaporated refrigerant from the evaporator to the condenser and means adapted to lead the condensed refrigerant from the condenser to the evaporator. The heat transfer arrangement further comprises a temperature-sensitive valve comprising a bi-metal member. The bi-metal member is adapted to sense the temperature of the refrigerant and is arranged to open and/or close the temperature sensitive valve such that the refrigerant flow through the refrigerant circuit is controlled in response to the refrigerant temperature.

An advantage with the present invention is that the temperature sensitive valve comprising a bi-metal member is working without any external source of energy or control signals arrangement. A further advantage is that the solution is cost effective. Hence, an improved heat transfer arrangement in a radio network node is provided in accordance with the object of the invention.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. Those skilled in the art realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention, as defined by the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects of the invention, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:

Fig. 1 schematically illustrates a heat transfer arrangement in a radio network node according to the present invention,

Fig. 2a and 2b illustrates an embodiment of a temperature sensitive valve comprising a bi-metal member, and

Fig. 3a and 3b illustrates another embodiment of a temperature sensitive valve comprising a bi-metal member.

DETAILED DESCRIPTION

The present invention will now be described more fully with reference to the accompanying drawings, in which example embodiments are shown. However, this invention should not be construed as limited to the embodiments set forth herein. Disclosed features of example embodiments may be combined as readily understood by one of ordinary skill in the art to which this invention belongs. Like numbers refer to like elements throughout.

As used herein, the term "comprising" or "comprises" is open-ended, and includes one or more stated features, elements, steps, components or functions but does not preclude the presence or addition of one or more other features, elements, steps, components, functions or groups thereof.

Well-known functions or constructions may not be described in detail for brevity and/or clarity.

Fig. 1 illustrates a heat transfer arrangement 220 in a radio network node 200. The radio network node is only schematically illustrated with a box and comprises an electronic equipment housing 210 for holding electronic equipment 212. In example embodiments the electronic equipment housing 210 may be a radio base station and the electronic equipment 212 may be part of devices and electric components associated with such a radio base station, e.g. a radio unit. The heat transfer arrangement 220 is adapted to cool the electronic equipment 212 and comprises an evaporator 222 adapted to extract heat from the electronic equipment housing 210 and to evaporate a refrigerant in the evaporator 222. The refrigerant fluid is held and circulated in a refrigerant circuit 226. The refrigerant circuit comprises means 226a for transporting the refrigerant from the evaporator 222 to a condenser 224, and means 226b for transporting the refrigerant from the condenser 224 to the evaporator 222, said means 226 a and 226 b allowing a refrigerant flow 228 in the refrigerant circuit 226. Further, in the refrigerant circuit 226 the condenser 224 is arranged remote from the evaporator 222 and outside the electronic equipment housing 210. The condenser 224 emits heat to the surroundings outside the electronic equipment housing 210. The location outside the housing may be in contact with the ambient air. The means for transporting the refrigerant may comprise of a first conduit 226a connecting the evaporator 222 with the condenser 224 and a second conduit 226b connecting the condenser 224 with the evaporator 222. The heat transfer arrangement 220 described in relation to Figure 1 may be a thermosiphon.

The heat transfer arrangement 220 further comprises a temperature sensitive valve 230 for controlling the refrigerant flow 228 in the refrigerant circuit 226. The temperature sensitive valve 230 comprises a bi-metal member 232a, 232b which is described in more detail in relation to Figures 2a-2b and 3a-3b. The valve 230 may open and/or close the refrigerant circuit 226. When the valve 230 is closed no circulation or only a negligible circulation, is allowed in the refrigerant circuit 226 which means that no, or only a negligible, heat transfer takes place. When the valve 230 is open, a restricted flow or unrestricted flow is allowed and heat from within the electronic equipment housing 210 is transferred to outside the housing. In case of a restricted refrigerant flow 228, the flow is slowed down in the refrigerant circuit 226. In this way no heat or much less heat is transferred from the evaporator 222 to the condenser 224 of the heat transfer arrangement. The temperature sensitive valve 230 may be arranged in the first conduit 226a adapted to lead the evaporated refrigerant from the evaporator 222 to the condenser 224. In an embodiment, the temperature sensitive valve 230 may be arranged within the evaporator 222. The heat transfer arrangement 220 comprising a temperature sensitive valve 230 with a bi-metal member 232a, 232b may be constructed without any moving parts in contact with air. This makes the arrangement reliable as the risk of corrosion to parts of the valve is minimized.

A bi-metal refers to an object that is composed of two separate metals joined together. Instead of being a mixture of two or more metals, like alloys, bi-metallic objects have layers of different metals. A commonly used combination of metals is steel and copper.

The bi-metal member 232a, 232b may convert a temperature change in its environment into mechanical displacement. The reason for this is that the material comprises two strips of different metals which expand at different rates as they are subjected to heat. The two strips are joined together throughout their length either by riveting, brazing or welding. The different thermal expansion of the two materials forces a flat strip of bi- metal to bend one way if heated, and in the opposite direction if cooled below its normal temperature. The metal having the higher thermal expansion coefficient is on the outer side of the curve as the strip is subjected to heat.

The bi-metal member may be used in its flat form232a, i.e. a bi-metal strips or discs, as well as wrapped into a coil 232b. A coiled bi-metal strip gives an improved sensitivity due to its greater length. The temperature sensitive valve comprising a bi-metal member may be designed to have any desired opening and closing temperatures. By altering the size, shape and composition of the bi-metal member different temperatures for opening and/or closing the valve may be achieved.

Figures 2a and 2b discloses an embodiment of the temperature sensitive valve 230 in which the bi-metal member 232a may be directly arranged to open and close the temperature sensitive valve 230 as a response to a temperature change in the environment of the bi-metal member 232a. The bi-metal member 232a is adapted to move between a first configuration closing the refrigerant circuit 226 and a second configuration opening the refrigerant circuit 226 in response to a refrigerant temperature sensed by the bi-metal member 232a. In this embodiment, the bi-metal member 232a has the form of an elongated piece of bi-metal, i.e. a bi-metal strip. The bi-metal strip 232a is arranged in the valve 230 in front of the valve outlet 238. In Figure 2a the temperature sensitive valve 230 is closed and the bi-metal strip 232a has a first straight configuration. The valve outlet 238 is shut off by the straight bi-metal strip 232a. Refrigerant from the evaporator 222 is in contact with the valve 230 through valve inlet 236. At a certain threshold temperature the bi-metal member 232a adopts a second configuration which is that of a bent bi-metal strip shown in Figure 2b. The second configuration covers a range of configurations from a slight bend of the bi-metal strip 232a allowing a restricted flow 228 in the refrigerant circuit 226 to a full bend of the bi-metal strip allowing an unrestricted flow 228 in the refrigerant circuit 226. In Figure 2b the valve 230 is open and refrigerant may pass out through the valve outlet 238 into the refrigerant circuit 226.

Another embodiment of the temperature sensitive valve 230 is shown in Figures 3a-3b. Here the bi-metal member 232b is indirectly involved in opening and closing the temperature sensitive valve 230. The bi-metal member 232b is connected to a plate member 234, which plate member 234 is adapted to control the refrigerant flow 228 as a response to a refrigerant temperature sensed by the bi-metal member 232b. The plate member 234 may have rectangular shape with an opening 235 or aperture in one of its ends. When the valve 230 is closed, the plate member 234 covers the valve outlet 238 and no refrigerant may pass out to the circuit 226. In this embodiment, the bi-metal member 232b may be a coiled bi-meta! strip. When the refrigerant temperature increases, the coiled piece of bi-metal 234b increases its length and the plate member 234 is moved upwards, see Figure 3b. The aperture 235, or at least parts of it, is now in front of the valve opening 238 and refrigerant may pass out into the refrigerant circuit 226. An advantage with this embodiment is that a coiled bi-metal strip has an increased sensitivity to temperature changes due to its length.

In Figure 2a and 3a there is no circulation of refrigerant in the refrigerant circuit 226. Any heat generated by the electronic equipment 212 will remain within the housing 210. The temperature-sensitive valve 230 is adapted to be closed at refrigerant temperatures being equal to or less than approximately 5 degrees Celsius.

In operational mode, the heat transfer arrangement 220 is adapted to transfer heat from a first location, i.e. from inside the electronic equipment housing 210 to outside the electronic equipment housing 210 to maintain an acceptable temperature inside the housing. This is important in order to protect the electronic equipment 212 from harmful temperatures. The refrigerant inside the refrigerant circuit 226 is evaporated in the evaporator 222. When the refrigerant reaches the condenser 224 it condenses.

In a first situation, when the electronic equipment 212 inside the electronic equipment housing 210 generates heat to such an extent that the inside of the electronic equipment housing 210 requires cooling, the temperature sensitive valve 230 is opened to allow unrestricted flow 228 in the refrigerant circuit 226. In an embodiment, this first situation may occur at temperatures in the electronic equipment housing of approximately 20 degrees Celsius or more.

In a second situation, e.g. when ambient temperature has fallen or due to strong winds, a desired temperature may be maintained inside the electronic equipment housing 210 by means of a restricted flow 228 in the refrigerant circuit 226. A restricted flow in the refrigerant circuit 226 gives a moderate cooling efficiency. In an embodiment, this second situation may occur at temperatures in the electronic equipment housing 210 in the range of +5⁰C to +2O⁰C.

In a third situation, e.g. when ambient temperature has fallen further, a desired temperature may be maintained inside the electronic component housing without the aid of the heat transfer arrangement 220. Accordingly, the temperature sensitive valve 230 is closed and the refrigerant flow 228 in the refrigerant circuit 226 is stopped or is only a negligible flow. The heat transfer from the electronic equipment housing 210 to the environment outside the housing is reduced to a minimum.

Even though the invention has been described with reference to example embodiments, many different alterations, modifications and the like will become apparent for those skilled in the art. The plate member 234 may for instance have any suitable geometrical form and the aperture 235 may comprise several apertures of different sizes and forms. Further, the form of the bi-metal strip may instead be in the form of a bi-metal disc.

Therefore, it is to be understood that the foregoing is illustrative of various example embodiments and is not to be limited to the specific embodiments disclosed and that modifications to the disclosed embodiments, combinations of features of disclosed embodiments as well as other embodiments are intended to be included within the scope of the appended claims.

Claims

1. A heat transfer arrangement (220) in a radio network node (200), the arrangement (220) comprising

- an evaporator (222) adapted to extract heat from a first location (210) and to evaporate a refrigerant in the evaporator (222),

- a condenser (224) outside the first location (210) remote from the evaporator (222) adapted to condense the evaporated refrigerant,

- a refrigerant circuit (226) comprising means (226a) adapted to lead the evaporated refrigerant from the evaporator (222) to the condenser (224) and means (226b) adapted to lead the condensed refrigerant from the condenser (224) to the evaporator (222), characterised in that the heat transfer arrangement (220) further comprises a temperature-sensitive valve (230) comprising a bi-metal member (232a, 232b), said bi-metal member (232a, 232b) is adapted to sense the temperature of the refrigerant and is arranged to open and/or close the temperature sensitive valve (230) such that the refrigerant flow (228) through the refrigerant circuit (226) is controlled in response to the refrigerant temperature.

2. A heat transfer arrangement (220) according to claim 1 , wherein the bi-metal member (232a) is adapted to move between a first configuration closing the refrigerant circuit (226) and a second configuration opening the refrigerant circuit

(226) in response to a refrigerant temperature sensed by the bi-metal member (232a).

3. A heat transfer arrangement (220) according to claim 2, wherein the first configuration of the bi-metal member (232a) is that of a straight bi-metal strip.

4. A heat transfer arrangement (220) according to claim 2, wherein the second configuration of the bi-metal member (232a) is that of a bent bi-metal strip.

5. A heat transfer arrangement (220) according to claim 4, wherein the second configuration covers a range of configurations from a slight bend of the bi-metal strip (232a) allowing a restricted flow (228) in the refrigerant circuit (226) to a full bend of the bi-metal strip (232a) allowing an unrestricted flow (228) in the refrigerant circuit (226).

6. A heat transfer arrangement (220) according to claim 1 , wherein the bi-metal member (232b) is connected to a plate member (234), which plate member (234) is adapted to control the refrigerant flow (228) as a response to a refrigerant temperature sensed by the bi-metal member (232b).

7. A heat transfer arrangement (220) according to claim 6, wherein the bi-metal member (232b) is a coiled bi-metal strip.

8. A heat transfer arrangement (220) according to any of claims 2-6, wherein the temperature-sensitive valve (230) is adapted to be closed at refrigerant temperatures being equal to or less than approximately 5⁰C.

9. A heat transfer arrangement (220) according to any of claims 2-7, wherein the temperature-sensitive valve (230) is adapted to be open and allow a restricted flow (228) in the refrigerant circuit (226) at refrigerant temperatures in the ranges 5⁰C to 2O⁰C.

10. A heat transfer arrangement (220) according to any of claims 1-7, wherein the temperature-sensitive valve (230) is adapted to be open and allow an unrestricted flow (228) in the refrigerant circuit (226) at refrigerant temperatures being higher than approximately 2O⁰C.

11. A heat transfer arrangement (220) according to any of claims 1-10, wherein the means (226a, 226b) adapted to lead the refrigerant to or from the condenser are first (226a) and second (226b) conduits.

12. A heat transfer arrangement (220) according to claim 11 , wherein the temperature sensitive valve (230) is arranged in the first conduit (226a) adapted to lead the evaporated refrigerant from the evaporator (222) to the condenser (224).

13. A heat transfer arrangement (220) according to any of the preceding claims, wherein the radio network node (200) is a radio base station.