Heat exchanger

The disclosure relates to a heat exchanger including an evaporator with a pair of base plates, each base plate having a first surface with channels extending from a manifold at a first end of the evaporator to a manifold at a second end of the evaporator, some of the channels are embedded into the base plate and some of the channels are arranged outside of base plate, a condenser with channels extending from a manifold at a first end of the condenser to a manifold at a second end of the condenser, at least one riser pipe and at least one return pipe.

This application claims priority under 35 U.S.C. §119 to European Patent Application No. 11180185.8 filed in Europe on Sep. 6, 2011, the entire content of which is hereby incorporated by reference in its entirety.

FIELD

The present disclosure relates to a heat exchanger and for example, to a heat exchanger for use in cooling electronic apparatuses.

BACKGROUND INFORMATION

A known heat exchanger has evaporator channels and condenser channels extending between a first and a second end of the heat exchanger. The opposite ends of the heat exchanger are provided with connecting parts that provide fluid paths between the evaporator channels and the condenser channels. A first heat transfer element is arranged in a vicinity of the first end of the heat exchanger for transferring heat load to a fluid in the evaporator channels. Similarly, a second heat transfer element is arranged in a vicinity of the second end of the heat exchanger for transferring heat load from a fluid in the condenser channels to the surroundings.

The above-described heat exchanger can be efficient in cooling down, for example, power electronics attached to the first heat transfer element. Due to a thermosyphon type construction, cooling can be achieved without needing a pumping unit.

However, the channels of the heat exchanger can be vulnerable to external damage where a fluid leak may occur, which in turn can lead to damage due to absence of cooling. Additionally it can be difficult to ensure even distribution of the fluid both in the condenser and in the evaporator.

SUMMARY

A heat exchanger is disclosed comprising an evaporator for receiving a heat load and the evaporator comprises a pair of base plates each base plate having a first surface with channels extending from a manifold at a first end of the evaporator to a manifold at a second end of the evaporator, some of the channels are embedded into the base plate and some of the channels are arranged outside of said base plate. The pair of base plates of the evaporator are arranged with their respective first surfaces towards each other. A condenser for passing a heat load to surroundings, the condenser comprising channels extending from a manifold at a first end of the condenser to a manifold at a second end of the condenser, pipes connecting the evaporator and condenser to each other in order to pass fluid between the evaporator and condenser. At least one riser pipe connecting the manifold at the second end of the evaporator to the manifold at the second end of the condenser and at least one return pipe connecting the manifold at the first end of the condenser to the manifold at the first end of the evaporator.

DETAILED DESCRIPTION

The use of a pair of base plates with channels on a respective first surface such that the first surfaces of the plates are turned to face each other, can result in a heat exchanger with an evaporator that is mechanically well protected against external shocks. Due to the connections between the evaporator and the condenser, uniform fluid distribution and a good thermal efficiency can be obtained.

FIGS. 1 to 5illustrate a first exemplary embodiment of a heat exchanger1according to the disclosure. The heat exchanger includes an evaporator2for receiving a heat load and for passing the heat load into fluid in channels of the evaporator2. The fluid is forwarded to a condenser3, from where the heat load of the fluid is passed to the surroundings of the condenser3. The fluid is then returned from the condenser3to the evaporator2.

FIGS. 2 and 3illustrate details of the evaporator2. The evaporator2includes two base plates4and5with first surfaces6turned towards each other. Such an arrangement can be utilized for cooling down electronic components attached to the base plates4and5, for example, in which case the heat exchanger1can be utilized in an electronic device like a frequency converter or an inverter. The first surface6of both base plates can be provided with channels7and8extending from a manifold9at a first end of the evaporator2to a manifold10at a second end of the evaporator2. Some of the channels7can be embedded into the base plates4and5to provide evaporation channels, while the remaining channels8can be located outside of the base plates4and5to provide a return path for non-vaporized liquid that comes out of the evaporation channels7. In the illustrated example (FIG. 1), the second end (with manifold10) of the evaporator2can be located at a higher level than the first end (with manifold9) of the evaporator.

In the illustrated example, the channels7and8can be arranged into pipes whose internal and external walls separate the channels7and8from each other. In this example the channels can be located within a plurality of MPE (Multi Port Extruded) pipes that are arranged partly into parallel grooves manufactured into the surfaces of the base plates4and5.

The channels7and8can be of a capillary dimension. In this context “capillary dimension” can refer to channels that are capillary-sized, which means that they have a size small enough for bubbles to grow uniquely in a longitudinal direction (in other words in the longitudinal direction of the channel as opposed to the radial direction) and thereby create a so called bubble lift effect by pushing the liquid. The diameter of a channel or tube which is considered capillary depends on the fluid or refrigerant that is used (boiling) inside. The following formula, for instance, can be used to evaluate a suitable diameter: D=(sigma/(g*(rhol−rhov)))^0.5, wherein sigma is the surface tension, g the acceleration of gravity, rhov the vapour density and rhol the liquid density. This formula gives values from 1 to 3 mm for R134a (Tetrafluoroethane), R145fa and R1234ze (Tetrafluoropropene), which are examples of the fluids suitable for use in the heat exchanger illustrated in the figures.

The first and second ends of the evaporator can be provided with manifolds9and10which connect the channels7and8of the evaporator to each other. InFIG. 4, the manifold10of the second end of the evaporator2is illustrated in more detail. A similar manifold9can also be employed in the first end of the evaporator. In the illustrated example, the manifold10can include two separate tubes11and12, each connecting the channels7,8of one base plate4and5to each other. The tubes11and12have a diameter roughly equivalent to the depth of the MPE pipes containing the channels7and8, and the tubes provide a path for each of the two rows of MPE pipes. In order to provide efficient fluid circulation and an even fluid distribution, the tubes11and12can be connected to each other by communication ports13allowing fluid communication between the tubes11and12. Ideally, the communication ports13are as evenly distributed as possible and there should be as many communication ports13as possible.

Instead of the illustrated manifolds, it is possible to utilize manifolds including one piece, which contains the functionality of parts11,12and13. The manifold allows liquid and/or vapor to come/go from/to channels7,8and to/from riser pipe14and return pipe18. The manifold creates a path for liquid to go back in the channels of the MPE tubes and it also creates a path for vapor to go to pipes14.

FIG. 4also illustrates the attachment of a riser pipe14to the second manifold10of the evaporator2. Due to the ports13allowing fluid communication between the tubes11and12, it can be sufficient to have only one riser pipe interconnecting the manifold10at the second end (upper end in the figures) of the evaporator2with the manifold16at the second end (upper end in the figures) of the condenser3. However, in order to provide a more efficient solution, two riser pipes can be connected between the manifold10at the second end of the evaporator and the manifold16at the second end of the condenser, as illustrated inFIG. 1. Manifolds10and16and the riser pipes14create a path for gas to proceed from the evaporator2to the condenser3.

The condenser3includes channels17extending from a manifold15at a first end of the condenser3to a manifold16at a second end of the condenser3, as illustrated inFIG. 5, for instance. The channels of the condenser17can be of capillary dimension, however, this is not necessary in all embodiments. In the illustrated example ofFIG. 1, the second end of the condenser3can be located at a higher level than the first end of the condenser, and additionally, the first end of the condenser can be located at a higher level than the second end of the evaporator.

In the illustrated example, the condenser and evaporator create a tilt angle. In order for the system to work with gravity and vapor without any pumps the condenser should be located above the evaporator. Otherwise the location of the condenser and evaporator is free. Length and the form of the pipes14,18vary accordingly.

The condenser3can be implemented by using a plurality of parallel pipes, such as MPE pipes (arranged in similar rows as illustrated inFIG. 3), whose internal and external walls separate the channels17from each other. In the illustrated example, the condenser3has been implemented to include two rows19of such pipes, and the outer walls of the pipes of each row are interconnected by fins in order to efficiently conduct heat into an air flow passing between the channels17on its way through the condenser3. Consequently, fluid introduced into the manifold16at the second end of the condenser3is cooled with air or other gas going through the condenser, while the fluid flows to the manifold15at the first end of the condenser3via the channels17. The manifolds15and16may be implemented in the same way as illustrated inFIG. 4, for example, as two separate tubes connected to each other by communication ports.

Instead of having air or another suitable gas flowing between the channels17of the condenser, the heat exchanger can be of liquid to liquid type, in which case a fluid flows between the channels. A liquid cooled condenser is previously known from EP-A1-2282624, for example.

The manifold15located at the first end (lower end in the figures) of the condenser3is connected with a return pipe18to the manifold9at the first end (lower end in the figures) of the evaporator2. Due to the communication ports allowing fluid communication between the tubes of the manifolds9and15, a single return pipe18can be sufficient. However, in order to provide a more efficient solution, two return pipes18can be connected between the manifold15at the first end of the condenser3and the manifold9at the first end of the evaporator, as illustrated inFIG. 1. Manifolds9and15and the pipes18create a path for liquid to go back from the condenser to the evaporator.

FIG. 6illustrates the principle of a two-phase thermosyphon. The heat exchanger illustrated inFIG. 1may operate according to this principle.

The fluid contained in the channel is heated at the evaporator20in order to cause vapour to proceed via the manifold21to the condenser22. At the condenser the heat load is passed to the surroundings and liquid produced due to this is returned via the second manifold23to the evaporator20.

In the illustrated example, the heat exchanger has been made for example, from aluminium. All parts can be cut, milled, bended and/or extruded. The evaporator and the condenser has been manufactured separately with a brazing process. Pipes14and18are attached to evaporator and condenser by welding. However, it should be observed that many variants exists.

The material can be other than aluminum. For example, copper can be used. However, also other materials can be used and different material can be used in different parts. Materials suitable for use can have good thermal conductivity.

The parts can be manufactured with many different manufacturing processes and the assembly can be done differently than with brazing and welding. Depending on the manufacturing and assembly processes the number of parts can be different than in the illustrated example.

In the illustrated example the main shape of pipes and channels is round. Naturally the shape can also be different depending on the manufacturing process.

It is to be understood that the above description and the accompanying figures are only intended to illustrate the present disclosure. It will be obvious to a person skilled in the art that the disclosure can be varied and modified without departing from the scope of the disclosure.