Status of Enhanced Heat Transfer in Systems With Natural Refrigerants

Global environmental and energy concerns have prompted the heating, ventilating, air-conditioning, and refrigeration industry to revisit the use of natural refrigerants. Nearly all natural refrigerants have superior transport properties as compared with synthetic refrigerants; however, the drawback with natural refrigerants has been their toxicity and flammability with an exception of carbon dioxide. In order to overcome this hurdle, it is essential that enhanced surface methods be developed and introduced to reduce the refrigerant charge in a system. Halocarbon industry has expended enormous amount of time and money in developing the ultrahigh efficiency heat exchangers. This experience and knowledge is available and could be applied in developing the efficient exchangers for natural refrigerant applications. This paper presents an overview of the status of natural refrigerants and the trends in the development of compact and low-charge systems.