Structure And Performance Study On Gravity Recirculation Evaporator

Gravity-fed recycle evaporator realizes super feeding liquid for evaporator by thermal-siphon role. Super feeding liquid for evaporator can increase the flow rate of the refrigerant and the degree of wetting of refrigerant side, improving the heat-transfer coefficient of evaporator. In gravity-fed recycle refrigeration system, the heat exchange efficiency of a evaporator with sure structure is decided by recycle quantity of evaporator. Recycle quantity is connected with the type of refrigerant, evaporation temperature, liquid pressure head, and heat input of refrigerant pipe(thermal-siphon power). This project focuses on the influence that the process layout of refrigerant pipe do to the heat input of refrigerant pipe when the evaporator under different cooling temperature corresponding to the circulation ratio.This subject focuses on the characteristics of refrigeration which can recycle in the gravity-fed recycle evaporator. Two-phase flow analysis in the gravity-fed cooling system is analyzed by using the resistance balance, and the model of evaporator’s heat transmission is established. Optimizing the process of in-line evaporator and the cross line of evaporator ①② separately. Comparing the different feed liquid height by the theoretical calculation and then getting the best feed liquid height. Setting up the experimental platform of gravity-fed recycle refrigeration system under this best feed liquid height and researching two kinds of evaporators in experiment before and after optimization.The calculation results of the model have showed that the process layout has a great influence on the performance of recycling evaporator. The air temperature every loop of refrigerant touches in the evaporator before optimization is falling on the direction of airflow. That is to say, following the sequence from 1 to 4 columns, the first column are exposed to the highest air temperature, 2,3,4 columns falling in turn, and column 4 are exposed to the lowest air temperature. When the evaporation temperature is the same, four nest of tubes assigned to the different temperature,(t1-t0)、3(t1-t2)/4-t01、2(t1-t2)/4-t01、(t1-t2)/4-t01 respectively, and the temperature difference of heat transfer is(10 t1 t2-6-7 t01) in average; in terms of enlarging the refrigerating capacity of evaporator after improvement, and on the basis of ensuring the length of evaporating pipes on four parallel branches are equal and keeping the pipelines which cascade in every branch ascending, then the average temperature that every branch touches is(t1-t2)/4-t02. So we can ensure that four refrigerant sides in parallel have both the same n value and Δt value, at the same time comparing the temperature difference of heat transfer △t1 and △t2 of which evaporator separately before and after optimization, distinctly the ratio is greater than one. That is the evaporation temperature of evaporator before optimization is lower than that of the optimized evaporator.Setting up the experimental rig of gravity-fed recycle system and researching the evaporator of the design. The research results have showed that the optimized evaporator draw a higher heat exchange amount per unit area. The refrigerating capacity of evaporator ① increases 60.3% and 44.1% at the room temperature-25 and ℃-20℃, the COP increases 16.67% and 11.49%.The experiment of evaporator ②has further verified that this optimization of flow path also have a good effect on the cross line of evaporator. The heat-transfer coefficient of the optimized evaporator has increased 15.57%~22.77% than that of evaporator before optimization and increased 86.59%~138.22% than that of direct expansion refrigeration system. The highest increases of the refrigerating capacity and COP separately are 21.24%、55.49%.