Encapsulation of thermal energy storage media
In one embodiment, a method for fabricating a ceramic phase change material capsule includes forming a solid phase change material pellet, coating the pellet with a green ceramic material, and sintering the green ceramic material while on the pellet to form a ceramic outer shell of the capsule.
1. A method for fabricating a ceramic phase change material capsule, the method comprising:
forming a solid phase change material pellet;
coating the pellet with a layer of non-polymeric sacrificial material;
further coating the pellet with a first layer of green ceramic material;
heating the coated pellet to cause the sacrificial material to melt and seep out through pores of the green ceramic material to create a void between the pellet and the green ceramic material;
further coating the pellet with a second layer of green ceramic material; and
sintering the first and second layers of green ceramic material coated on the pellet to form a ceramic outer shell of the capsule.
2. The method of claim 1 , wherein forming a solid phase change material pellet comprises forming the pellet from two or more different phase change materials having different melting points.
3. The method of claim 2 , wherein forming the pellet from two or more different phase change materials comprises forming a first partial pellet from a first phase change material, forming a second partial pellet from a second phase change material, and combining the two partial pellets to form a single whole pellet.
4. The method of claim 1 , wherein heating the coated pellet comprises heating the coated pellet to a temperature of approximately 120 to 150 degrees Celsius.
5. The method of claim 1 , wherein the sacrificial material is palmitic acid.
6. The method of claim 1 , wherein sintering comprises heating the coated pellet to a temperature of approximately 1040 to 1110 degrees Celsius.
7. The method of claim 6 , wherein forming a solid phase change material pellet comprises forming a first partial pellet from a first phase change material, forming a second partial pellet from a second phase change material, and combining the two partial pellets to form a single whole pellet, and wherein the sintering melts the first and second phase change materials so that they mix and form a eutectic phase change material in situ.
8. The method of claim 1 , wherein coating the pellet with a layer of non-polymeric sacrificial material comprises coating the pellet with molten non-polymeric sacrificial material and then allowing the material to cool and solidify on the pellet.
9. The method of claim 1 , further comprising partially sintering the first layer of green ceramic material before further coating the pellet with a second layer of green ceramic material.
10. The method of claim 1 , further comprising, after sintering, subjecting the coated pellet to thermal cycling at an elevated temperature above a melting temperature of a phase change material contained in the pellet but below a temperature at which the sintering is performed.