太阳能多喷射器制冷系统分析研究

发布时间：2018-09-12 20:15

【摘要】：随着能源危机和环境污染等问题的加剧，以太阳能为热源的喷射制冷系统受到了广泛的关注，太阳能喷射制冷是一种节能环保制冷方式，其运行费用低、地域限制小，能够缓解能源紧缺现状、解决环境污染问题。然而，常规太阳能喷射制冷系统一般只设置单个结构固定的喷射器，从而系统运行工况将到限制，在最佳工况范围外，系统性能往往较低。鉴于此，本文针对一种太阳能驱动的多个喷射器制冷系统进行计算分析，通过对喷射器的切换运行，以实现系统的持续高效运行。首先利用气体动力学函数，结合喷射器内部的热力学状况，对喷射器进行了分析，建立了喷射器的计算模型，，研究了系统运行工况对喷射系数的影响、制冷剂对太阳能喷射系统的影响，以及设置多个喷射器的太阳能喷射制冷系统的性能，并通计算比较，给出了最优的喷射器设置方案。研究表明：（1）在喷射器结构设计时，确定混合室出口截面混合流体的最优折算质量速度，对结构的优化至关重要；对于结构参数给定的喷射器，系统运行工况直接影响到喷射器内部流体流动的状况，临界背压随发生温度和蒸发温度的增大而增大,当喷射器处于极限状态下运行，喷射系数较高。例如Tg=75℃，Tc=35℃，Te=10℃时，喷射系数可达到0.31；（2）建立了喷射器性能计算程序，并验证了模型的正确性，在此基础上，对制冷剂R134a、R236fa和RC318等三种工质的喷射器运行性能进行了研究，研究表明：当选择R134a为制冷剂时，系统性能较好，并且所设计的喷射器结构尺寸最小，适用于设置多个喷射器的太阳能喷射制冷系统。当Tg=85℃，Tc=35℃，Te=10℃时，系统COP可以达到0.25；对应制冷量4kW所需的喷嘴喉部直径、喷嘴出口截面直径和混合室直径分别为：0.3075mm、0.4089mm和0.6179mm；（3）为了保证系统的持续高效运行，针对喷射器的数量设计不同的方案。考虑到太阳能辐射值的改变会直接影响集热热水的温度等，本文采用了基于发生温度分区的喷射器个数设置比较方案，分别对系统性能做了研究，并加以对比，结果表明：方案2设置三个喷射器时系统运行的性能最佳。除了个别发生温度外，方案2和方案3的COP相对偏差都在±10%之内，两者的绝对误差数值很小。设置三个喷射器时，在发生温度70℃至85℃的范围内，系统COP维持在0.2以上，最高值能够达到0.288，在保持系统良好性能的同时，减少了喷射器的数量。
[Abstract]:With the aggravation of energy crisis and environmental pollution, the ejector refrigeration system with solar energy as heat source has been widely concerned. Solar energy ejector refrigeration is a kind of energy-saving and environmental protection refrigeration method. It has low operating costs and small geographical restrictions. It can alleviate the energy shortage and solve environmental pollution problems. In general, the system only has a single ejector with fixed structure, so the operating conditions of the system will be limited, and the system performance is often low outside the optimal operating conditions. That's ok.
Firstly, the ejector is analyzed by using the gas dynamics function and the thermodynamic condition of the ejector. The calculation model of the ejector is established. The influence of the operating condition of the system on the ejection coefficient, the influence of refrigerant on the solar ejection system and the performance of the solar ejection refrigeration system with multiple ejectors are studied. Through comparison and calculation, the optimal ejector setup scheme is given.
(1) In the design of the ejector structure, it is very important to determine the optimal converted mass velocity of the mixing fluid at the outlet section of the mixing chamber for the optimization of the structure; for the ejector with given structural parameters, the operating conditions of the system directly affect the flow of the fluid in the ejector, and the critical back pressure increases with the increase of the occurrence temperature and the evaporation temperature. When the ejector runs in the limit state, the ejection coefficient is high. For example, when Tg = 75, Tc = 35, Te = 10, the ejection coefficient can reach 0.31.
(2) The ejector performance calculation program is established and the correctness of the model is verified. On this basis, the ejector performance of refrigerant R134a, R236fa and RC318 is studied. The results show that when R134a is chosen as refrigerant, the system performance is better, and the designed ejector has the smallest dimension, which is suitable for setting. The COP of the solar ejector refrigeration system with multiple ejectors can reach 0.25 when Tg = 85, Tc = 35, Te = 10, and the throat diameter of the nozzle, the cross-section diameter of the nozzle outlet and the diameter of the mixing chamber are 0.3075 mm, 0.4089mm and 0.6179 mm respectively.
(3) In order to ensure the continuous and efficient operation of the system, different schemes are designed for the number of ejectors. Considering that the change of solar radiation value will directly affect the temperature of hot water, this paper adopts the comparison scheme of the number of ejectors based on the occurrence of temperature zones, and studies the performance of the system, and compares the results. The results show that the performance of the system is the best when three ejectors are set up in scheme 2. The relative deviations of COP of scheme 2 and scheme 3 are all within (+10%) except for the individual occurrence temperature, and the absolute deviations of the two are very small. .288, while maintaining good system performance, it reduces the number of ejectors.
【学位授予单位】：中原工学院
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TB657

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