新型利用极低品位热吸收/跨临界循环复合制冷系统研究

An absorption refrigeration system has advantages of utilizing low-grade thermal energy; however, now, absorption refrigeration techonologies encounter interesting challenges to lower its minimum actuating temperatures and achieve more efficient cooling. Although a newly developed absorption/compression refrigeration hybrid system can achieve efficient cooling by utlilizing thermal energy at rather low temperatures,currently, it is still very difficult to achieve efficient cooling by utlizing ultra low-grade thermal energy at lower temperatures. Accordingly, newly developed absorption/cmpression refrigeration hybrid technologies just partially overcome such challeneges. Besides, as a class of new cycles, transcritical cycles show more excellent characteristics than those of conventional compression cycles. It has been proved that transcritical cycles can work well under a very wide operation temperatures. And hence, a transcritical cycle is used to combine with an absorption refrigeration cycle in this proposal, thus, aiming at achieving efficient cooling by utilizing ultra low-grade thermal energy, a novel absorption/transcritical cycle hybrid refrigeration system is proposed. This new system is composed of an absorption refrigeration subsystem and a transcritical heat pump subsystem, and it can achieve efficient cooling of 5℃～7℃ by utilizing ultra low-grade thermal energy of 50～60℃. The simple theoretical calculation results also show it can get a COP value 25～35% higher than that of a conventional one. Furthermore, its minimum actuating temperatures of thermal energy is reduced about 15～25℃. We will pay great attention on the complex phenomenons of energy coupling and conversion in this new system, and finally, hope to ahieve its energy coupling mechanism and cooling mechanism to utilize ultra low-grade thermal energy.

吸收制冷技术具有利用低品位热制冷的优点，也面临着降低最低驱动热源温度以利用更低品位热能有效制冷的有力挑战。现在，新发展的吸收/压缩复合制冷技术已能较好地解决利用温度比较低的热能有效制冷的问题，但是，仍然无法解决利用温度更低的极低品位热有效制冷的难题。跨临界循环作为一类新循环，相较于常规压缩制冷（热泵）循环具有在比较宽广的温度范围内高效工作的优点。本项目把跨临界循环应用于吸收制冷，提出了由吸收制冷子系统与跨临界热泵子系统构成的可以有效利用极低品位热制冷的新型复合制冷系统。初步的理论计算结果表明新系统能利用50～60℃极低品位热获得5℃～7℃制冷，COP可较常规吸收制冷技术提高约25～35%并且其驱动热源的最低温度可以降低约15～25℃。项目拟着重研究新系统中吸收制冷子系统与跨临界热泵子系统之间比较复杂的能量耦合与转换现象，以厘清其能量耦合机理以及利用极低品位热有效制冷的工作机理。

吸收制冷技术具有利用低品位热制冷的优点，也面临着降低最低驱动热源温度以利用更低品位热能有效制冷的有力挑战。当前，新发展的吸收/压缩复合制冷技术已能较好地解决利用温度比较低的热能有效制冷的问题，但是，仍然无法解决利用温度更低的极低品位热有效制冷的难题。跨临界循环作为一类新制冷（热泵）循环，相较于常规压缩制冷（热泵）循具有在比较宽广的温度范围内高效工作的优点。本项目把跨临界循环应用于吸收制冷，提出了一类吸收/跨临界复合制冷新系统，较为深入地研究了新系统中吸收制冷子系统与跨临界热泵子系统之间比较复杂的能量耦合与转换现象，厘清了其能量耦合机理以及利用极低品位热有效制冷的工作机理。通过研究发现：.（1）新系统可以利用40～55℃极低品位热的获得有效制冷；.（2）发展了一套较为全面评价吸收/跨临界复合制冷系统性能的指标，包括表征输入的低品位热制冷效果的COPnet和表征输入的机械功产生的制冷效果的COPmt；.（3）发展了一套较为可靠的吸收/跨临界复合制冷系统的数学物理模型，平均偏差约为8 %；.（4）分析了在不同工况下影响新型复合制冷系统的主要影响因素并明确了新系统的工作机理，即吸收制冷子系统与跨临界子系统之间的能量耦合机理;.（5）研究表明在大部分工况下，新型复合制冷系统的性能较传统两级吸收式制冷系统的性能可以提高约10%~50%；.（6）新型吸收/跨临界复合制冷系统大大地提高了跨临界子系统的能量转换效率，可较常规跨临界子系统的性能提高约50%。