Fluid flow in thermal storage containers
A thermal-storage container used in thermal systems to exchange heat by fluid flow though phase-changing material disposed inside the thermal-storage container, including a thermal-storage container housing, a fluid inlet and a fluid outlet, and one or more capsules containing the phase-change material, and defining a plurality of passages configured to direct the flow of the fluid at different portions inside the housing, wherein an actual fluid flow length from the fluid inlet to the fluid outlet is longer than a direct length measured between the fluid inlet and the fluid outlet through all sections through which the fluid flows. Related apparatus and methods are also described.
1. A thermal-storage container used in thermal systems to exchange heat by fluid flow though phase-changing material disposed inside the thermal-storage container, comprising:
a thermal-storage container housing;
a fluid inlet and a fluid outlet, to allow fluid flow in a general direction of a longitudinal axis of the thermal-storage container, the container having, along the longitudinal axis, an upstream portion followed by a downstream portion; and
capsules containing the phase-change material, each capsule having two heat exchanging surfaces with a surface area larger than all other faces of the capsule, the capsules defining a plurality of passages between the capsules, the passages configured to direct the flow of the fluid at different portions inside the housing,
wherein one or more of the capsules in the upstream portion of the thermal storage container are oriented such that the two heat-exchanging surfaces are vertical and in parallel to the longitudinal axis of the container and one or more capsules in an adjacent downstream portion of the thermal storage container are oriented such that the two heat-exchanging surfaces are horizontal and in parallel to the longitudinal axis of the container.
2. The thermal-storage container according to claim 1 , wherein an actual fluid flow length through the thermal-storage container is longer than twice a straight line length measured between the fluid inlet and the fluid outlet through all sections through which the fluid flows.
3. The thermal-storage container of claim 1 , wherein the thermal-storage container comprises one or more turbulators.
4. The thermal-storage container of claim 1 , wherein said capsule comprises a quartz nucleating agent.
5. The thermal-storage container of claim 1 , wherein the capsules arranged within the thermal-storage container have a combination of concave and convex outlines, defining gaps between contours of the capsules.
6. The thermal-storage container of claim 1 , wherein the capsules contain metal strips, and wherein a length of a metal strip is longer than a width of the capsule.
7. The thermal-storage container according to claim 1 , having a ratio between an average flow cross section area along a flow path in the thermal-storage container and a total heat exchange area of all the capsules in the thermal-storage container between 4.5×10 −5 -45×10 −5 .
8. The thermal-storage container according to claim 1 , having a ratio between an average flow cross section area along a flow path in the thermal-storage container and a total heat exchange area of all the capsules in the thermal-storage container between 1×10 −5 -100×10 −5 .
9. The thermal-storage container according to claim 1 , having a gamma ratio greater than 150 cm/cm 2 , wherein the gamma ratio is defined as a ratio between a linear length in centimeters (cm) of a heat transfer fluid flow path and a free flow cross area per capsule in cm 2 .
10. The thermal-storage container of claim 1 , wherein said capsules comprise at least one surface having protrusions adapted to increase a turbulence of flow of the fluid.
11. The thermal-storage container of claim 1 , wherein:
the thermal-storage container is rectangular, wherein
a ratio of length to width of the thermal-storage container is in a range of 4 to 50; or
a ratio of a width to height of the thermal-storage container is in a range of 0.5 to 4.
12. The thermal-storage container of claim 1 , wherein one or more capsules in the upstream portion are positioned within the thermal-storage container transversely to one or more capsules in the downstream portion.
13. The thermal-storage container of claim 1 wherein:
said thermal-storage container further comprises a plurality of spacers inserted between said capsules;
said spacers to ensure fluid flow of said fluid through said thermal-storage container; and
said spacers to cause turbulent flow when a gap between said capsules increases when said phase-change material melts.
14. A structure comprising a thermal energy storage system comprising at least one thermal-storage container according to claim 1 , built into said structure, wherein:
the structure is selected from a group consisting of:
a wall;
a floor; and
a roof.
15. A method for exchanging heat by fluid flowing through thermal-storage container, the container having, along a longitudinal axis, an upstream portion followed by a downstream portion, the method comprising:
inserting the fluid into the thermal-storage container, via a fluid inlet;
allowing the fluid to flow in a general direction of the longitudinal axis of the thermal-storage container;
allowing heat exchange between the fluid and phase-changing material inside capsules, each capsule having two heat-exchanging surfaces with a surface area larger than all other faces of the capsule, in the thermal-storage container;
and
outputting the fluid from the thermal-storage container, via a fluid outlet;
wherein the method further comprises orienting one or more of the capsules in the upstream portion of the thermal storage container such that the two heat-exchanging surfaces are vertical and in parallel to the longitudinal axis of the container and orienting one or more capsules in an adjacent downstream portion of the thermal storage container such that the two heat-exchanging surfaces are horizontal and in parallel to the longitudinal axis of the container.
16. The method according to claim 15 , wherein the actual fluid flow length from the fluid inlet to the fluid outlet through the thermal storage container is more than two times longer than a direct length measured between the fluid inlet and the fluid outlet.
17. The method according to claim 15 , wherein a flow direction of the fluid is modified by at least 30° to a longitudinal axis of the thermal-storage container by changing the orientation of one or more capsules relative to the longitudinal axis of the thermal-storage container.
18. The method according to claim 15 and further comprising generating a turbulent flow on a heat-exchanging surface of a capsule.
19. The method according to claim 15 , wherein a flow of the fluid is modified, alternating flow between turbulent flow and meandering flow within the thermal-storage container.