Energy consumption for heating and cooling is a major part of global energy use and is still increasing rapidly. Adsorption-driven refrigeration has emerged as a promising and more energetically efficient alternative to the traditional vapor-compression systems, as it can efficiently utilize lower-grade thermal energy such as solar energy to replace electricity. The key driving force of this process is the adsorption equilibrium of the refrigerant in an adsorbent material. Therefore, the choice of adsorbent/refrigerant working pair is critical to the performance of the system. Metal-organic frameworks (MOFs), with large surface areas and tunable chemical environments, have the potential to be excellent adsorbent materials, while ethanol, which has large latent heat, low toxicity and low cost, is a good refrigerant. In this work, we used combined experimental and computational approaches to gain better understanding of the underlying thermodynamics in the adsorption cooling system. We chose a series of MOFs with similar building blocks but diverse topologies and estimated their performance as adsorption coolers by performing experiments and simulations on ethanol adsorption. Experiments and simulations agreed well on the adsorption isotherms, and molecular-level insights into the adsorption thermodynamics were also gained from the atomistic simulations. We established structure-property relationships between the topologies of the MOFs and their ethanol working capacities under different working conditions that can be used as design rules. Based on this, we identified an optimal MOF for this application, and our experiments and simulations both showed superior cooling capacity for this MOF, which verified our design rules.

Thermodynamics of ethanol adsorption in metal-organic frameworks: Effects of material topology and design rules for adsorption cooling applications

2019 Spring National Meeting

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