Field of the Invention

The present invention relates to a micro channel heat exchanger that is configured for hydraulic reversibility for evaporator or condenser, which heat exchanger comprises at least one inlet for refrigerant, which heat exchanger comprises at least one outlet for refrigerant, which heat exchanger comprises at least one inlet distribution tube connected to the inlet, and which heat exchanger comprises at least one collection tube for collecting refrigerant. Background of the Invention

Micro channel heat exchangers have been used for condenser coils for several years successfully replacing the well-known fin and tube type heat exchanger in many applications.

Object of the Invention

It is an object of the invention to perform automatic change from condensation into evaporation. A further object of the invention is to achieve effective evaporation in a micro channel evaporator designed for both condensation and evaporation

Description of the Invention

The object may be achieved by a micro channel heat exchanger configured for hy- draulic reversible operation as a evaporator or condenser and comprising at least one inlet for a refrigerant and at least one outlet for the refrigerant, which heat exchanger comprises at least one inlet distribution tube connected to the inlet, and which heat exchanger comprises at least one collection tube for collecting the refrigerant to at least one outlet, where the inlet distribution tube comprises an inner tube connecting the inlet to the inlet distribution tube via a connection operatively configured to change between evaporator operation and condenser operation by at least one valve and so that in condenser operation, the connection is open for flow from the inner tube to the distribution tube. The object can be fulfilled by a heat exchanger as disclosed in the preamble to claim 1 and further modified in that the inlet distribution tube comprises a inner tube, which inner tube is connected to the inlet, which heat exchanger comprises at least one valve, which valve by evaporator operation closes a connection between the inner tube and the outer distribution tube, which valve by condenser operation is open for flow from the inner tube to the distribution tube.

Hereby the possibility to change between two different modes of operation can be achieved. In condenser operation mode there is a traditional mainly open flow through the heat exchanger. The pressure of the refrigerant is relative high because the refrigerant has just left, probably, a compressor. Therefore, when entering the condenser the refrigerant is relatively warm and the pressure is relatively high. By condensing, the refrigerant entering the system will be in a gas form and when it leaves it is converted into a liquid. Therefore, relatively large openings are acceptable in the flow of refrig- erant by condensation. However, in operation as an evaporator, a distribution of the liquid flow is necessary, otherwise if the liquid refrigerant is concentrated in for example only some micro channels, an evaporator will work relatively ineffective. Therefore, it is necessary to distribute the liquid refrigerant into the high number of micro channels in order to achieve a good evaporation.

With a valve mechanism it is possible to change between the two kinds of operation. Different valves can be used, for example it would be possible to use a magnetic valve to perform the change, which valve in operation may be connected to a control system, which in the same way controls the shift from evaporation to condensation. This shift is probably used in heat pumps combined with air condition use of same components. In fact many different valves can be used; manual valves are another example where the hand tool is used to change the valve. An automatic valve will of course be the most effective, as that valve is operating without any external connection. In a preferred embodiment of the invention the inner tube can comprise a number of bleed holes for limiting the flow towards the distribution tube in evaporator operation. Hereby it is achieved that a number of small bleed holes can form jets in different directions from the inner tube into the outer tube. Hereby a distributed evaporation can be performed. In a further preferred embodiment of the invention the valve can be pressure activated.

Hereby it is achieved that the valve works automatically. As there is a change in operation pressure between condensation and evaporation, energy for opening or closing can be picked by the pressure difference.

In a further preferred embodiment of the invention in evaporator mode of operation the valve can be closed and the bleed holes in the wall on the inner tube are configured to form jets directed towards the micro channels. Hereby it can be achieved that jets are directed directly to the inlet of the micro channels. Thus, it is achieved that most of the channels will get a jet of liquid refrigerant which then on its way through the evaporator will evaporate into a gas and keep the inner of the micro channels, and thereby also the outer of the micro channels, at a low temperature and thus achieve very effective operation of the evaporator.

In a further preferred embodiment of the invention the valve can operate against a valve seat formed at the end of the inner tube, which valve is formed by a bellow, which bellow contains a gas. Hereby it is achieved that the bellow will work as an automatic valve actuator. The pressure inside the valve can be selected by the selection of a gas in accordance with the actual pressure and a temperature so that in evaporation mode with low pressure the bellow will expand and close the valve, and in the operation of condenser the higher pressure will perform opening of the valve by compressing the gas inside the bellow.

By reversible or alternating coil hydraulics is understood a configuration that can operate in evaporation or condensation modes and change between the two modes. The following invention is related to hydraulic reversibility for mini / micro channel heat exchangers. A special version of such an exchanger is shown in figure 1.

Micro channel heat exchangers have been used for condenser coils for several years, successfully replacing the well-known fin and tube type heat exchanger in many applications. This is mainly due to their high efficiency, low cost, low weight and low refrigerant charge which made them highly successful in automobile applications. However, using the above type of heat exchanger for evaporators in the HVAC segment has been much more limited. One of the reasons for this is that the heat transfer process for an evaporator is much different from the condensing process. The nature of the condensing process is very much facilitated by the coil geometry, whereas the evaporation process is not. Practices have shown that it is much more difficult to operate an evaporator than a condenser efficiently by using mini channel geometry. Figure 2 shows a cut through of a special coil. The coil has a distributer tube containing jets and is designed for evaporative purpose. The jets are also shown in figure 3. The purpose of the jets is to distribute the coolant evenly into the mini channel geometry which is necessary to facilitate a high efficiency for the process. This construction is associated with a significant pressure drop through the jets. This special geometry is not used in condenser coils as the flow path is reverse and of a nature that does not need any special geometry to be operated. At this time we have no knowledge of mini channel heat exchangers being used for alternating cooling / heat pump operations. The current innovation makes it possible to manufacture a cost efficient multipurpose coil using a simple low cost valve. This valve is shown in figure 4. By using this ap- proach it is now possible to operate the coil as both condenser and evaporator. This can for instance turn out very useful for systems alternating between cooling and heating application, but not limited to split type heat pump and cooling systems for domestic applications. The valve makes it possible to use the jets when the coil operates as an evaporator. In this scenario, the valve is closed forcing refrigerant through the jets. Similarly, the valve makes it possible not to use the jets when the flow is reversed for condenser use. In its simplest form, the bellow valve is pressure operated. The valve might also use a spring or the bellow itself might act as a spring. Also, the bellow might be filled with a gas or it might not. In a preferred embodiment the bellow is filled with a gas which is non-condensable in the operating design window. Now withstanding this, the pressure inside the bellow is fixed at a desired level which is reasonable "constant". In reality it is of course not. The pressure inside the coil is always dominated by the saturation state of the coil. When the coil operates as an evaporator, this pressure is low. It should also be lower than the pressure inside the bellow valve which makes the bellow close the valve forcing the refrigerant through the system of jets. The coil now efficiently operates as an evaporator.

The state with the valve closed is shown in figure 5a. In figure 5b the valve is open and the coil operates as a condenser. Reversing the flow path increases the pressure inside the coil. This higher pressure is higher than the pressure inside the bellow, and the bellow opens the valve. This allows the condensed refrigerant to bypass the jets and enter the tube directly. This is of paramount importance. If the valve was not there, there would be a significant pressure drop through the jets which would facilitate a pressure drop, destroying the possible sub cooled liquid state or even worse make the refrigerant boil compromising the entire system stability as the expansion valve would not function correctly anymore.

The bellow valve is shown in figure 4. The bellow is preferably made in a material with a higher melting point than aluminum. The bellow disk is preferably made from aluminum, possible even clad material. This construction allows the bellow to be soldered into the system with the rest of the construction when it runs through the furnace. The bellow valve should be made in such a way that it can be charged with gas either prior to being soldered into the construction or after the soldering process. In the case where it is charged after being soldered into the construction, it should pref- erably have an opening in the disk with a capillary charging tube, a ball type charging facility or similar. The latter construction enables high design flexibility as the pressure inside the bellow to be calibrated for many different design temperatures by means of a very simple gas charging mechanism. Figure 6 shows schematics of the system. Both coils are of this special alternating type and these are similar for the current construction. The function on the left is reversed compared to the function on the right. Connecting the coils is very easy and needs no additional tubing. Description of the Drawings

Figure 1 shows one possible embodiment for a heat exchanger 2.

Figure 2 shows the same embodiment for a heat exchanger as figure 1 but in a sectional view.

Figure 3 shows an end sectional view of the heat exchanger 2.

Figure 4 shows a bellow forming an actuator for the valve. Figure 5a shows an enlarged sectional view of the valve mechanism placed inside a distribution tube and figure 5b shows the same embodiment but in the other way of operation.

Figures 6 and 7 disclose, for example, an air condition system having different modes of operation.

Detailed Description of the Invention

Figure 1 shows one possible embodiment for a heat exchanger 2. This heat exchanger comprises an inlet 4 and an outlet 6. A lower distribution tube 8 is indicated as well as a colleting tube 10. A number of micro channels 20 are connected between the lower distribution tube 8 and the upper colleting tube 10. The micro channels have a large surface and therefore, a relative good heat transmission is performed to the surrounding air.

Figure 2 shows the same embodiment for a heat exchanger as figure 1 but in a sec- tional view, where the inner part of the heat exchanger is disclosed. The inlet 4 is connected to a tube 12 and it is clearly indicated that micro channels 20 are connecting the distribution tube 8 with the collecting tube 10. The inner tube 12 ends in valve 14 which is pressure activated, which valve 14 is adapted to close the connection between the distribution tube 8 and the inner tube 12. Figure 3 shows an end sectional view of the heat exchanger 2. The distribution tube 8 is indicated and it is clear that micro channels 20 are connected to the distribution tube 8. The inner tube 12 comprises bleed holes 16, which bleed holes 16 are forming jets directed towards the micro channels 20.

Hereby it can be achieved that in evaporation mode a highly effective distribution of refrigerant to the different micro channels 20 will be performed. This will increase the efficiency of the evaporator. Figure 4 shows a bellow 24 forming an actuator for the valve 14.

Figure 5a shows an enlarged sectional view of the valve mechanism placed inside a distribution tube 8. The valve 14, formed by a bellow 24, is closing the inner tube 12. Herby is the refrigerant forced to be distributed in form of jets through the bleed holes 16. With the bellow 24 in a closed situation the pressure in the evaporator will be relative low because the evaporator will probably be connected to the suction side of a compressor.

Figure 5b shows the same embodiment but in the other way of operation, probably as a condensation unit. In this situation, the bellow 24 will be subjected to a higher pressure as the condensation unit is connected to the pressure side of a compressor. This increasing pressure will open the valve 14 by compressing the bellow 24. Because the bellow now has opened the valve, it is possible to see a valve seat 22. Which valve seat is formed at the end of the inner tube 12.

Figures 6 and 7 disclose, for example, an air condition system having different modes of operation. A compressor 104 has a suction side 106 and a pressure side 108. Both suction side 106 and pressure side 108 are connected to a shifting valve 110. This is a so-called cross over valve, which contains the flow of the refrigerant. In the situation indicated in figure 6 the pressure side 108 is connected through the valve 1 10 into the line 112. This line 112 leads to a condenser 114. A flow restriction such as an expansion valve 116 reduces the pressure before the flow enters an evaporator 118. From the evaporator the gas will flow through line 120 and once again through the valve 110 into the suction line 106. In figure 7 the valve 110 is in its opposite position. Hereby, the previous condenser 114 is now changed into an evaporator. The flow direction is different due to the change of the valve 110.

Thus, simply by one change of a valve 110 the possibility to change the cooling system from air condition into heat pump operation mode is achieved.