【摘要】：隨著能源危機和環(huán)境污染等問題的加劇，以太陽能為熱源的噴射制冷系統(tǒng)受到了廣泛的關(guān)注，太陽能噴射制冷是一種節(jié)能環(huán)保制冷方式，其運行費用低、地域限制小，能夠緩解能源緊缺現(xiàn)狀、解決環(huán)境污染問題。然而，常規(guī)太陽能噴射制冷系統(tǒng)一般只設(shè)置單個結(jié)構(gòu)固定的噴射器，從而系統(tǒng)運行工況將到限制，在最佳工況范圍外，系統(tǒng)性能往往較低。鑒于此，本文針對一種太陽能驅(qū)動的多個噴射器制冷系統(tǒng)進行計算分析，通過對噴射器的切換運行，以實現(xiàn)系統(tǒng)的持續(xù)高效運行。 首先利用氣體動力學函數(shù)，結(jié)合噴射器內(nèi)部的熱力學狀況，對噴射器進行了分析，建立了噴射器的計算模型，，研究了系統(tǒng)運行工況對噴射系數(shù)的影響、制冷劑對太陽能噴射系統(tǒng)的影響，以及設(shè)置多個噴射器的太陽能噴射制冷系統(tǒng)的性能，并通計算比較，給出了最優(yōu)的噴射器設(shè)置方案。研究表明： （1）在噴射器結(jié)構(gòu)設(shè)計時，確定混合室出口截面混合流體的最優(yōu)折算質(zhì)量速度，對結(jié)構(gòu)的優(yōu)化至關(guān)重要；對于結(jié)構(gòu)參數(shù)給定的噴射器，系統(tǒng)運行工況直接影響到噴射器內(nèi)部流體流動的狀況，臨界背壓隨發(fā)生溫度和蒸發(fā)溫度的增大而增大,當噴射器處于極限狀態(tài)下運行，噴射系數(shù)較高。例如Tg=75℃，Tc=35℃，Te=10℃時，噴射系數(shù)可達到0.31； （2）建立了噴射器性能計算程序，并驗證了模型的正確性，在此基礎(chǔ)上，對制冷劑R134a、R236fa和RC318等三種工質(zhì)的噴射器運行性能進行了研究，研究表明：當選擇R134a為制冷劑時，系統(tǒng)性能較好，并且所設(shè)計的噴射器結(jié)構(gòu)尺寸最小，適用于設(shè)置多個噴射器的太陽能噴射制冷系統(tǒng)。當Tg=85℃，Tc=35℃，Te=10℃時，系統(tǒng)COP可以達到0.25；對應制冷量4kW所需的噴嘴喉部直徑、噴嘴出口截面直徑和混合室直徑分別為：0.3075mm、0.4089mm和0.6179mm； （3）為了保證系統(tǒng)的持續(xù)高效運行，針對噴射器的數(shù)量設(shè)計不同的方案�？紤]到太陽能輻射值的改變會直接影響集熱熱水的溫度等，本文采用了基于發(fā)生溫度分區(qū)的噴射器個數(shù)設(shè)置比較方案，分別對系統(tǒng)性能做了研究，并加以對比，結(jié)果表明：方案2設(shè)置三個噴射器時系統(tǒng)運行的性能最佳。除了個別發(fā)生溫度外，方案2和方案3的COP相對偏差都在±10%之內(nèi)，兩者的絕對誤差數(shù)值很小。設(shè)置三個噴射器時，在發(fā)生溫度70℃至85℃的范圍內(nèi)，系統(tǒng)COP維持在0.2以上，最高值能夠達到0.288，在保持系統(tǒng)良好性能的同時，減少了噴射器的數(shù)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.
【學位授予單位】：中原工學院
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TB657

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