Study On Performance Of Steam Jet Refrigeration System For Low Grade Waste Heat Utilization

With the proposal and continuous promotion of the major strategic goal of "carbon neutralization and carbon peak",more and more attention has been paid to energy conservation and full utilization.In particular,industrial energy consumption accounts for a large proportion of China’s total energy consumption,and the amount of waste heat discharged is huge.Based on the recovery and utilization of medium and high grade waste heat,if the low grade waste heat below 200 ℃ can be further utilized,it is of great significance for systematic energy conservation,efficiency improvement and carbon reduction.The water vapor jet refrigeration system can realize the preparation of low temperature chilled water through the ejector driven by low grade waste heat steam.The system adopts water,an environment-friendly natural working medium with simple structure and very low power consumption,which has natural advantages unmatched by other refrigeration systems.In order to improve the energy efficiency of water vapor jet refrigeration system and broaden its working range and application scope,this thesis establishes the simulation calculation model and entransy loss analysis model of water vapor jet refrigeration system,designs and builds a small water vapor jet refrigeration system prototype and experimental system,and analyzes the working steam mass flow,ejector steam mass flow.The variation law of injection coefficient and system refrigeration performance are compared and analyzed,and the variation law and distribution of entransy loss of the system under variable working conditions are discussed and studied,so as to provide theoretical guidance for the design and performance improvement of water vapor injection refrigeration system driven by low grade waste heat.The main contents are as follows:(1)The simulation calculation model of steam jet refrigeration system for the utilization of low grade waste heat is constructed,and the influence and variation law of different generation temperature,evaporation temperature,condensation temperature and other parameters on the performance of working steam mass flow,system refrigeration capacity,injection coefficient and so on are studied.It is found that the working steam quality decreases with the increase of the generation temperature,the injection coefficient increases first and then decreases,and the refrigeration capacity of the system increases with the increase of the generation temperature.When the generation temperature exceeds the design value,the upward trend slows down.As the evaporation temperature rises from 2℃ to 22℃,the quality of working steam continues to decline and the refrigeration capacity of the system continues to rise.When the generation temperature is 140℃ and the condensation temperature is 26 ℃,the refrigeration capacity of the system reaches6.56 kw,an increase of 59.6%.It is found that there is a critical condensation temperature,before this temperature,the refrigeration capacity of the system is hardly affected by the condensation temperature.After exceeding this temperature,the refrigeration capacity of the system decreases rapidly with the increase of the condensation temperature.(2)The analysis model of entransy loss of steam jet refrigeration system for the utilization of low grade waste heat is established,and the variation trend and weight distribution law of entransy loss rate of each component and system under different generation temperature,evaporation temperature and condensation temperature are analyzed.The entransy loss rate increased first and then remained unchanged,and the entransy loss rate of condenser increased first and then decreased.With the increase of evaporation temperature,when the condensation temperature is 24℃,26℃ and 28℃,the corresponding fire product loss rate of ejector decreases by 49%,44.6% and 45.31% respectively,the fire product loss rate of evaporator decreases by1.6 times,1.7 times and 2.0 times respectively,the fire product loss rate of condenser decreases by 35.5%,34.6% and 34.4% respectively,and the fire product loss rate of system decreases by 69.3%,57.8% and 50.5% respectively.With the increase of condensation temperature,the entransy loss rate of ejector,condenser and system continues to rise,and the entransy loss of evaporator first remains unchanged and then decreases rapidly.Under different generation temperature,evaporation temperature and condensation temperature,the proportion of entransy loss of ejector in the system is the largest,followed by cooling water and chilled water pipes.Condenser and evaporator have little impact on the entransy loss of the system.(3)The steam jet refrigeration system and its main components for the utilization of low grade waste heat are designed,and the experimental platform is built to verify the thermal characteristics of the system under different working conditions.Complete the design calculation and selection of the main components of the steam injection refrigeration system,determine the structural dimensions of the nozzle and diffuser of the ejector,as well as the design of the evaporator,condenser and storage tank.On this basis,through simulation and experimental research,it is obtained that with the increase of the generation temperature,the mass flow of the injected steam,the injection coefficient and the cop of the system increase first and then decrease;With the rise of evaporation temperature,all three show an upward trend.When the generation temperature is 140℃ and the condensation temperature is 26 ℃,the experimental results show that the mass of ejected steam increases by1.5 times,the injection coefficient increases by 25%,and the cop of the system increases by nearly 1.4 times;Both simulation results and experimental results show that the generation temperature is 140℃,the evaporation temperature is 10℃,and the mass flow of ejector steam,injection coefficient and system COP are almost a fixed value before 24℃.Then,with the increase of condensation temperature,they all decrease rapidly.The experimental results show that when the condensation temperature rises from 24℃ to 30℃,the mass flow of ejector steam decreases by2.51kg/h,the ejector coefficient decreases by 0.37 and the system cop decreases by 0.32.