HEAT EXCHANGER DEVICE COMPRISING A PHASE-CHANGE MATERIAL

Abstract

Heat exchanger device comprising a tubing for receiving and delivering a heat transfer fluid; a phase-change material, PCM, encompassing said tubing; a plurality of cells receiving the phase-change material, PCM, such that the flow of the heat transfer fluid in said tubing causes each cell PCM to change phase gradually in the direction of the inlet to the outlet. The cells may be closed cells or open cells, the tubing may comprise fins and the exchanger may comprise an external tank for containing the PCM. The heat exchanger may comprise a second tubing for receiving and delivering a second heat transfer fluid, wherein the second tubing is connected to the PCM cells and/or to the fins of the first tubing, such that heat is transferred between the first tubing and the second tubing as each cell PCM gradually changes phase.

Claims

1. A heat exchanger device comprising: a tubing comprising an inlet and an outlet, for respectively receiving and delivering a heat transfer fluid; a phase-change material (“POCM”) in contact with said tubing; and a plurality of heat-exchanging fins connected to said tubing, arranged to define a plurality of cells receiving the PCM between adjacent said fins, wherein the PCM is contained in said plurality of cells arranged such that the flow of the heat transfer fluid in said tubing causes each cell PCM to change phase sequentially in the direction of the inlet to the outlet, wherein the thickness of each changing phase PCM cell, the thickness being the distance between adjacent heat-exchanging fins, is sufficiently thin such that the the PCM in said PCM cell changes phase at the same time.

2. The heat exchanger device according to claim 1, wherein said heat-exchanging fins are connected to, and extend from, said tubing.

3. The heat exchanger device according to claim 1, wherein the cells are open cells and the heat exchanger comprises an external tank for containing the PCM.

4. The heat exchanger device according to claim 1, wherein the cell thickness tapers away from the tubing.

5. The heat exchanger device according to claim 1, wherein the transversal profile of each heat-exchanging fin is curved or bent towards an adjacent fin as each fin extends from the tubing.

6. The heat exchanger device according to claim 1 wherein the PCM cells are arranged as stacked rows, and the tubing is ‘S’-shaped going through stacked rows of PCM cells.

7. The heat exchanger device according to claim 1, further comprising a second tubing for respectively receiving and delivering a second heat transfer liquid, wherein the second tubing is in contact with the PCM, such that heat is transferred between the first tubing and the second tubing as the PCM changes phase gradually in the direction of the inlet to the outlet.

8. The heat exchanger device according to claim 7, wherein heat is transferred between the first tubing and the second tubing as each cell PCM changes phase sequentially.

9. The heat exchanger device according to claim 1, further comprising a second tubing for respectively receiving and delivering a second heat transfer fluid, wherein the second tubing is connected to the fins of the first tubing, such that heat is transferred between the first tubing and the second tubing as the PCM changes phase gradually in the direction of the inlet to the outlet.

10. The heat exchanger device according to claim 9, wherein heat is transferred between the first tubing and the second tubing as each cell PCM changes phase sequentially.

11. The heat exchanger device according to claim 7, wherein the PCM cells are arranged as stacked rows, and the first and second tubing are ‘S’-shaped going through stacked rows of PCM cells.

12. The heat exchanger device according to claim 1, previous claims, wherein the fin thickness tapers away from the tubing.

13. The heat exchanger device according to claim 1, wherein the PCM cells are stacked in one or more rows.

14. The heat exchanger according to claim 1, further comprising a hot water distribution point, in particular the hot water distribution point is an electric water heater or a gas water heater.

15. A heat exchanger system comprising: two or more of the heat exchanger devices according to claim 1, wherein said heat exchanger devices are coupled in parallel, are coupled in series, or are coupled in series and parallel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The following figures provide preferred embodiments for illustrating the description and should not be seen as limiting the scope of invention.

[0061] FIG. 1: Schematic representation of an embodiment of the device (cut view) with insulated tank, heat exchanger fins and tubing, and a PCM bath in open cells zones.

[0062] FIG. 2: Schematic representation of an embodiment of different PCM zones, showing the PCM melting or solidifying depending on the temperature of the inlet operating fluid and the PCM phase change temperature. PCM phase changing is occurring in a segment of the exchanger resulting in a constant temperature outlet and constant heat transfer.

[0063] FIG. 3: Schematic representation of embodiments with different possible fin geometries.

[0064] FIG. 4: Schematic representation of the fins showing the variation of fin thickness and the variation of the PCM layer thickness between fins.

[0065] FIG. 5: Schematic representation of a domestic hot water distribution network in a building with centralized heating system and temperature correction devices installed in specific points to passively correct the response time of the hot water in each consumption point.

[0066] FIG. 6: Schematic representation of embodiments with different possible heat exchanger concepts based in macro-encapsulated PCM.

[0067] FIG. 7: Schematic representation of embodiments with different possible heat exchanger concepts based in plates disposed in parallel.

DETAILED DESCRIPTION

[0068] FIG. 1 shows a schematic representation of an embodiment of the device (cut view) with insulated tank 101, heat exchanger fins 102 and tubing 103, and a PCM bath in open cells zones 104.

[0069] FIG. 2 shows a schematic representation of an embodiment of the device (schematic view) with insulated tank 101, heat exchanger fins 102 and tubing 103, and a PCM bath in open cells zones 104. The different PCM zones are represented, showing the PCM melting or solidifying depending on the temperature of the inlet operating fluid and the PCM phase change temperature. PCM phase changing is occurring in a segment of the exchanger resulting in a constant temperature outlet and constant heat transfer.

[0070] A part of the PCM zones 104a have already changed phase, another part of the PCM zones 104b are changing phase, and finally another part of the PCM zones 104c have not yet changed phase.

[0071] FIG. 3 shows a schematic representation of embodiments with different possible fin geometries.

[0072] FIG. 4 shows a schematic representation of the fins showing the variation of fin thickness and the variation of the PCM layer thickness between fins. The detailed representation of the fins shows specifically (i) the variation of the fin thickness (f1, f2) and (ii) the variation of the PCM layer thickness between fins (m1, m2).

[0073] FIG. 5 shows a schematic representation of a building's domestic hot water distribution network with centralized heating 501, passive temperature correction devices 502, 504-507 and consumption points of domestic hot water 503. The temperature correction devices are based in the disclosed heat exchanger but once applied in a distribution network there are additional concerns, like the pressure loss, that must be addressed as is well known in the art by specifying adequate pipe sizes and flows. The network optimization based in the consumption profiles in each consumption point and the location and capacity of each temperature correction devices results in a simplified network that responds equally to the specific needs of the building.

[0074] FIG. 6 shows a schematic representation of embodiments with different possible heat exchanger (FIG. 6a, 6b, 6c) concepts based in encapsulated PCM 602 where the PCM is constrain within a container or capsule 601. The detailed representation of the encapsulated PCM shows specifically (a) tubes or spheres for encapsulation of the PCM for interstitial flow of the operating fluid (b) parallel plates with encapsulated PCM for parallel flow of the operating fluid and (c) parallel plates with encapsulated PCM for perpendicular meandering flow of the operating fluid.

[0075] FIG. 7 shows schematic representation of embodiments with different possible heat exchanger concepts based in plates disposed in parallel, i.e. embodiments similar to the embodiment of FIG. 6(b) for parallel flow of the operating fluid along the PCM-containing plates where the PCM 702 is constrained between parallel plates 701—the plates maybe optionally flat. The detailed representation of the parallel plates shows in particular (a) parallel flat plates with PCM and the operating fluid zones (b) parallel plates with fins embedded in the PCM zone or/and in the operating fluid zone for higher contact area and (c) corrugated parallel plates separating alternating PCM and operating fluid zones.

[0076] An important preferred aspect in the thermal power of the presented device is the geometry of the fins. As shown in FIGS. 3 and 4, several parameters may be taken into account in the design, such as: (i) the fin shape, (ii) the PCM thickness between fins and (iii) the fin thickness. The heat exchange optimization using the mentioned variables is driven by the temperature variation along the fins. Their capacity to conduct the energy from/to a PCM with low thermal conductivity, preserving the phase change concentrated a specific zone of the heat exchanger, is highly dependent on those parameters.

[0077] By having a decreasing fin thickness as the fins distance themselves from the tubing, this allows a more uniform thermal exchange for each PCM zone. This is also beneficial to the overall objective of having individual PCM zones change phase sequentially but also uniformly and as a whole for each zone.

[0078] By having a decreasing width of the PCM zone as the distance increases from the tubing, this also allows a more uniform thermal exchange for each PCM zone, also facilitating that each individual PCM zone changes phase uniformly and as a whole.

[0079] Concerning the design of the heat exchanger, and in order to ensure a constant outlet temperature and power of the heat exchanger, several parameters are accounted for. These parameters are related with (i) the interface between the operating fluid and the inner surface of the tubing, (ii) the heat conduction through the heat exchanger and (iii) the heat transfer between the heat exchanger and the PCM.

[0080] The parameters related with the interface operating fluid/surface of the tubing includes the section area and geometry of the tubing, surface roughness, flow rate and properties of the operating fluid. The turbulence of the flow is affected by these parameters and consequently the thermal convention in the inner surface of the tubing will depend on each of these parameters.

[0081] The heat conduction along the heat exchanger depends on the material and geometrical properties. The temperature distribution, in turn, affects the heat transfer between the heat exchanger and the PCM.

[0082] The geometry of the heat exchanger influences the local ratio between the PCM volume and the interface area PCM/heat exchanger and the temperature differential between the fin and the PCM decreases when moving away from the tubing. Considering that the heat transfer is directly proportional to the temperature differential less energy is transmitted to the fin in a zone away from the tube. Therefore, in zones away from the tubing a lower ratio volume of PCM/area of interface will ensure a constant heat transfer. Thus, the totality of PCM around a specific zone of the heat exchanger can change phase at the same time. The described heat exchanger design in particular intends to compensate the low conduction properties of the PCM in order to use all the latent energy stored.

[0083] In an embodiment, where the PCM material is arranged such that the flow of the heat transfer fluid in said tubing causes the PCM to change phase, wherein said PCM phase changing is limited to a part of the heat exchanger device, wherein said part moves gradually in the direction of the inlet to the outlet, the thickness of the PCM part changing phase is sufficiently thin such that the totality of the PCM in said PCM part can change phase at the same time—the thickness being the distance between adjacent heat-exchanging fins or heat-exchanging plates.

[0084] In particular, the totality of a PCM part extending between adjacent heat-exchanging fins or heat-exchanging plates can change phase at the same time.

[0085] In an illustrative embodiment, a heat exchanger with a heating power of 14 kW able to heat a water flow of 8 litters per minute from 15° C. to 40° C. consisting on a sequence of copper fins 0.3 mm thick with an individual contact area (PCM-fin) of 4.800 mm.sup.2 providing a ratio volume/contact area of 1.5 mm.sup.3/mm.sup.2 in zones close to the tubing and 0.6 mm.sup.3/mm.sup.2 in zones with distance higher than 6 mm from the tubing centre.

[0086] In an illustrative embodiment, the disclosure heat exchanger device can be used to correct the temperature of an operating fluid in whole distribution network, see for example FIG. 5. The device can be installed in delivery 503 or intermediate 502, 504-508 points providing a global correction of the different segments of the circuits benefiting from the sequential arrangement where one intermediate point can provide temperature correction for whole the downstream network.

[0087] In an embodiment, an association of devices can be used in the network to correct the temperature of several delivery points in different locations in a parallel 502, 506, 507 and/or serial arrangement 502, 504, 505, see for example FIG. 5. The capacity and power of each device is calculated according to the specifications of the network.

[0088] In an embodiment, the devices to install in intermediate points can consist in a heat exchanger incorporating encapsulated PCMs. In this embodiment, the pressure drop at this point can be reduced and therefore the delivery pressure and flow in all downstream points can be nearly constant.

[0089] The disclosure should not be seen in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof.

[0090] The above described embodiments are combinable.

[0091] The following claims further set out particular embodiments of the disclosure.