Thermal storage system using encapsulated phase change materials in LED lamps
A phase change material (PCM) is used as thermal storage for lighting systems. The PCM is placed in a thermally conductive container in close contact with the lighting system. As the PCM absorbs heat, it changes from a solid to a liquid state, but the temperature of the PCM is clamped at its melting point temperature. For LED-based systems, the PCM is selected to have a melting point such that the junction temperatures of the LEDs in the system are maintained at approximately their optimum operating temperature inside the lighting system housing. Because the thermal conductivity of the molten PCM is poor, a low thermal resistance heat flow path is provided from the PCM to the container.
1. A thermal storage system for a lighting system, comprising:
a phase change material (PCM) having a melting point temperature, the PCM being formed in pellets that are pelletized by encapsulating PCM in a high thermal conductivity material;
a plurality of pouches wherein the PCM is disposed; and
a container holding the plurality of pouches wherein the PCM is disposed, wherein the container is thermally conductive, sealed, and structurally arranged for thermal coupling to the lighting system.
2. The thermal storage system of claim 1 wherein the PCM is combined with a nucleating agent and/or a stabilizing agent.
3. A thermal storage system as recited in claim 1 , wherein the pellets are partially filled with PCM.
4. A thermal storage system as recited in claim 1 further include a spring loading system disposed in the container, and wherein the plurality of pouches are preloaded against a surface of the container using the spring system.
5. A lighting system for providing illumination, the lighting system comprising:
a housing including the following components:
a lamp disposed within the housing, the lamp including a plurality of light emitting diodes (LEDs) and a lens, the plurality of LEDs having an optimum operating temperature;
a container disposed within the housing, the container including pelletized phase change material (PCM) disposed in a plurality of pouches, the container being made of a non-corrosive thermally conductive material, the pelletized phase change material pellitized by encapsulating PCM in a high thermal conductivity material;
a structure thermally coupling the lamp to the container;
wherein the container and the PCM material and mass are selected according to thermal properties of the lighting system to effectively clamp operating temperature of the plurality of the LEDs to about the optimum operating temperature within a fixed duty cycle for the cyclical application.
6. A lighting system as recited in claim 5 , further comprising a convective cooling element, wherein heat retained within the PCM during operation of the lighting system is useful for driving heat dissipation via the convective cooling element when the lighting system is not in operation.
7. A lighting system as recited in claim 5 , wherein the PCM pellets are spherical having a diameter ranging from about 0.1 microns to about 1.0 microns.
8. A lighting system as recited in claim 5 , wherein the encapsulating material is metallic and applied with a thickness of 0.1 microns or thinner.