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JRI Research Team Develops Thermal Battery, a Nested Absorption Refrigerator

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Four students from different Southern California high schools participated in a research project that developed a novel heat pump technology. Heat pumps are devices that move heat from a colder area to a warmer area. Heat pumps are found in many common appliances including refrigerators and air conditioners. Generally speaking, heat pumps must be powered by either electrical power or a high temperature heat source. As a result, they typically use energy as opposed to providing energy.

 

One type of heat pump, the absorption refrigerator, provided a clue to how to generate a heat pump that could be used as a heat source. This technology, first widely used in the mid to late 1800s, uses substances known as desiccants to force water to boil at low pressure. By drawing water vapor from the water, the desiccant forces the remaining water to cool. The cold water can be used for refrigeration or air conditioning.

 

Eventually the desiccant absorbs all the water it can. When this happens, desiccant must be dried out. This is done by heating the desiccant to a high temperature, which boils off the water it has absorbed. The water that is boiled off can be captured and reused. Yet this heating process is what utilizes the energy. The JRI research group has been working to eliminate this requirement.

 

For the past several years ago, the students' Research Mentor has worked to enable the same process using desiccants that are more easily dried than those generally used in absorption refrigeration. However, such desiccants produced limited cooling effect due to their lower absorptive potential. As a result, a redesign of the basic heat pump technology was needed.

 

The students worked for over two years with their Research Mentor, trying many different designs. Each design required the design of a new system, fabrication and assembly of its parts, and careful and rigorous testing. Each design provided more information but a confusing set of experiments in which the basic physics seemed to reverse itself without explanation seemed to stretch on and on.

 SungMin Kim, student leader of the research group, at the ICCE2015 conference.   David Gong, student researcher, at the ICCE2015 conference.

SungMin Kim (student group head) and David Gong at the ICCE 2015 conference.

The breakthrough came when the group realized that a liquid desiccant tends to absorb water vapor at its surface, but it's too dense to enable the water to diffuse throughout the liquid. As a result, the desiccant was absorbing water vapor, but the liquid water was resting at the surface of the liquid desiccant. The water effectively blocked any further absorption. Once this was realized and the design changed so as to solve this problem, the technology began working. The group constructed and characterized several different devices, eventually settling on a modular design. The design was demonstrated to enable heating of more than 42 degrees Celsius (75.6 degrees Farenheit), more than sufficient for refrigeration in most human habitable environments.

Thermal camera image of running three cell thermal battery. 

The group compiled their results in a scientific paper entitled “Entrochemical thermal battery design for atmospheric heat collectors”. The paper was submitted to the 2015 International Conference and Exhibition on Clean Energy sponsored by the International Academy of Energy, Minerals, and Materials. The paper was accepted and the group was invited to Ottawa Canada to present their research results. The students are Sungmin Kim (18) from Beverly Hills High School in Beverly Hills, CA (now attending the University of Southern California and continuing on to Cornell University in 2016); Robert Xu (18) from Arcadia High School in Arcadia, CA (now attending CalPoly San Louis Obispo); Aurpon Gupta of Torrey Pines High School in San Diego, CA (now attending University of California, San Francisco), and David Gong from San Marino High School in San Marino, CA.

 

Since completing this first research effort, Kim, Xu, and Gupta have gone on to university. They are studying environmental engineering, chemical engineering, and computer science, respectively. Gong is continuing to work on applications of the new technology and has successfully partnered with three other students to develop a water heater that is heated using this process. He hopes to be able to develop a prototype device that can deliver hot water to homes and businesses without using electricity or fuel and which is powered entirely from environmental heat.

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