基于喷射器-超声波的风冷单效绝热吸收制冷循环研究

Absorption refrigerator is known of using low-grade heat energy and consuming less mechanical energy, yet its air-cooled difficulty remains unsolved. Adiabatic absorption has been proposed as a solution to the problem. Utilizing the conventional adiabatic absorber will cause much higher solution recirculation ratio and greater recirculation pump energy consumption of absorption refrigeratior. To solve these problems, an injector, which can promote pressure and strengthen absorption ability and an ultrasonic transducer which can atomize solution are introduced to a single effect absorption refrigeration cycle. Specifically, a single effect adiabatic absorption refrigeration cycle using ejector and ultrasonic wave is proposed by using ejector to promote adiabatic absorption pressure, and using ultrasonic atomozation to increase mass transfer space and time during absorption process. The novel cycle is studied theoretically and experimentally. The research particularly focuses on coupling mechanism of two phase flow heat and mass transfer, and adiabatic absorption in ejector and dynamic behavior mechanism of adiabatic absorption process of vacuum ultrasonic atomization droplets in absorber in order to solve the problem of air-cooled difficulty of absorption cycle and significantly improve coefficient of performance which will expand the application scope of the single effect absorption refrigerator. Our researches can provide a better understanding of adiabatic absorption mechanism and refine the theory of absorption refrigeration cycle.

吸收制冷机具有利用低品位热能、机械能消耗少的优点，但面临机组风冷化难题。绝热吸收是实现其风冷化的技术之一，但现有绝热吸收器仍存在溶液再循环倍率过高和再循环泵能耗大问题。本项目结合喷射器增压增效和超声绝热雾化优点，提出将喷射器与超声波技术应用于单效吸收制冷循环，即利用溴化锂溶液在喷射器内实现水蒸气绝热吸收增压过程，并利用超声波在绝热吸收器内的真空雾化增大吸收传质过程空间和时间，从而构建一种基于喷射器-超声波的单效绝热吸收制冷循环。本项目从理论和实验两个方面对所提出的新循环进行详细研究，尤其对喷射器内气液两相流动的传热、传质、绝热吸收耦合机理以及吸收器内超声波真空超声雾化液滴的绝热吸收过程动态行为机理这两个关键科学问题进行深入研究，以期解决吸收制冷循环风冷化问题和制冷效率显著提升，从而拓展单效吸收制冷机应用范围。研究成果丰富并发展溶液绝热吸收过程的理论，还为完善吸收制冷循环的科学理论做出贡献。

太阳能吸收式制冷系统以其节能、环保、低噪等优点，在工业、商业和民用空调领域得到了广泛的应用。针对传统吸收制冷系统存在的能效低、体积大、易结晶、风冷化困难、制作工艺高等问题，从分别增强吸收式制冷系统内发生器的传热效率以及吸收器的吸收效率的角度出发，将喷射器和绝热吸收器一体化设计，以期实现吸收过程的传热传质分段强化，回收高压溶液的节流损失和再循环溶液的余压，进一步增强吸收效果。根据超声空化特性，将超声波振子设置于发生器底部壁面，以期提高发生器内溶液蒸发沸腾过程的发生效率。主要研究内容和结论如下：（1）构建绝热吸收/喷射复合制冷循环的热力学模型，探讨了环境温度、发生温度、蒸发温度及喷射比对新循环制冷性能的影响，并与传统水冷式非绝热吸收/喷射复合制冷循环和传统风冷式单效绝热吸收制冷循环的热力性能进行对比。结果表明，喷射器和绝热吸收器的一体化设计显著的改善了极端条件下新循环的性能，新循环的COP较传统水冷式非绝热吸收/喷射复合制冷循环和传统风冷式单效绝热吸收制冷循环分别提高了10.67%和6.41%；（2）开展空化气泡运动机理研究，建立了气泡动力学方程，研究了超声频率、环境压力、声压幅值和初始半径等参数对溶液空化特性的影响。结果表明，总声强一定时，气泡最大半径随着振子数量的增加而增大。当总声强为1 W/cm2，超声振子的数量为24至25时，空化气泡最大半径增加率不超过1%，单振子作用下的真空发生器中的溶液更易进行稳态空化，而多振子作用下的真空发生器中的溶液更易产生瞬态空化；（3）进行超声雾化发生器的理论研究，提出了一种新型超声雾化发生器。结果表明，超声雾化技术应用于发生器，在消耗微小能量的前提下可获得更高的系统能效，新型发生器的吸收式制冷系统的制冷量和制冷系数分别较传统发生器提高了33.21%和31.33%；（4）搭建超声波强化溴化锂水溶液发生过程的实验装置，为超声波理论模型的建立与研究提供实验数据支撑。