Caloric Systems for Cooling, Heating, and Work

全球对空间制冷、供暖、制冷和储热等热服务的需求约占全球能源消耗的40%-50%。根据劳伦斯伯克利国家实验室最近的一项研究，到2030年，世界上可能会增加7亿台空调，到2050年，可能会增加16亿台。这只是新的需求如何导致额外的发电量和温室气体排放的一个例子，“就像世界上增加了几个新的国家一样”。目前的供暖和制冷技术已经成熟，但使用的工质存在臭氧消耗、全球变暖和安全问题。全球正在努力将替代技术商业化，使用固体材料的新循环已被确定为有希望的替代材料。热量材料是具有一种或多种可逆工作模式的固体物质，其主要有序性模式定义。例子包括磁热(MC磁序)、弹性热学(EC结构序)和电热学(EC电序)。具有多个工作模式的材料是多热量的。特别令人感兴趣的是，材料表现出一级相变，提供了随着温度和外加磁场的巨大变化的熵。在实践中，热能材料的使用类似于蒸汽压缩系统，在该系统中，绝热功输入导致可逆的温度变化。在供暖或制冷系统中使用热能材料的挑战之一是可逆温度变化的幅度，以及响应显著的温度范围。为了克服这一点，活性热量再生器(ACR)在分层再生器结构中使用一种或多种材料，从而产生级联循环。实际上，热量从一个位置或材料泵送到下一个位置或材料，跨越所需的温度范围。许多热能材料都存在类似的问题，即温度和电场对热能的响应有限，这表明需要一个ACR循环。本研究计划的目标是开发高效的热能转换系统。讨论了三个领域：(1)发展我们对热量热力学的理解，(2)确定能够实现高性能的工艺，(3)开发具有成本效益的高效设备。

Global demand for thermal services including space cooling, heating, refrigeration, and thermal storage is responsible for approximately 40-50% of global energy consumption. According to a recent study from Lawrence Berkeley National Laboratory, the world may see an additional 700 million air conditioners by 2030, and 1.6 billion of them by 2050. This is but one example of how new demands can result in additional electricity generation and GHG emissions “like adding several new countries to the world.” Current technologies for heating and cooling are mature, but use working fluids with ozone depletion, global warming, and safety concerns. A global effort is underway to commercialize replacement technologies new cycles using solid materials have been identified as promising alternatives.Caloric materials are solid substances with one or more reversible work modes defined by their dominant ordering mode. Examples include magnetocaloric (MC magnetic order), elastocalorics (eC structural order), and electrocalorics (EC electrical order). Materials with more than one work mode are multicaloric. Of particular interest are materials exhibiting first order phase transformations providing large changes in entropy with temperature and applied field. In practice, the use of caloric materials is analogous to vapour-compression systems where adiabatic work input results in a reversible temperature change. One of the challenges of using caloric materials in heating or cooling systems is the magnitude of the reversible temperature change, and the temperature range over which the response is significant. To overcome this, an active caloric regenerator (ACR) uses one or more materials in a layered regenerator structure so that a cascade of cycles is created. In effect, heat is pumped from one location, or material, to the next, across a desired temperature span. Many caloric materials suffer from similar problems of limited caloric response with respect to temperature and field suggesting the need for an ACR cycle.The objective of this research program is to develop efficient caloric systems for energy conversion. Three areas are addressed: (1) developing our understanding of caloric thermodynamics, (2) determining the processes which enable high performance, (3) developing efficient devices that are cost effective.