Design And Research On Off-design Performance Of A Vertical Falling Film LiBr/H₂O Absorption Heat Transformer

Nowadays, due to the increasingly prominent energy and environment problems, energy-saving and emission reduction technology is more and more important. Absorption heat transformer (AHT) has become the research focus in the past few decades because of its unique advantages in the waste heat utilization field. But the utilization of waste heat is limited by so many factors, such as the parameters of the waste heat resource, environmental factor and so on. So in order to better design and operate Absorption heat transformer system, the simulation and research on the off-design operation of it is necessary.Supported by the National Basic Research Program of China, the Hi-tech Research and Development Program of China, and the National Natural Science Foundation of China, this thesis carries out the simulation and design work on the Absorption heat transformer cycle and components. Based on this work, simulation and deep analyses on the off-design operation of Absorption heat transformer is carried out. Then the key process which seriously affects the off-design performance of the Absorption heat transformer is found out and analyzed in depth. Finally, effective controlling method is proposed to improve the Absorption heat transformer’s off-design performance.To conduct a study on the off-design operation of the Absorption heat transformer, it is necessary to design an unit first. So mathematical model of the Absorption heat transformer cycle is built to design a series connected Absorption heat transformer unit whose output heat capacity is1OkW. Moreover, in order to better analyze the performance of the Absorption heat transformer, some parameters and evaluation criteria are defined and analyzed, such as the ideal coefficient of performance, the exergy efficiency, coefficient of performance coefficient of performance, and the exergy loss ratio. Some derivation and decomposition of the parameters and evaluation criteria are carried out to understand them better and establish connections among them.In order to establish connections between the heat carrier and the cycle working medium, numerical simulation on the LiBr/H2O falling film generation and absorption process outside vertical tube is conducted and, and the average mass flux of vapour per unit area is achieved. Then the primary design of the generator, absorber, condenser and evaporator is carried out, and the structural parameters of the components, such as the number and length of tube, are achieved.Combining with the designed structural parameters and the mathematical model of the falling film process, the mathematical model of the Absorption heat transformer cycle is modified to simulate the off-design operation of the Absorption heat transformer. The effect of the input parameters of the heat resource water and cooling water on the exergy efficiency, coefficient of performance, output heat capacity is simulated and analyzed in depth. The variation of exergy loss distribution in the Absorption heat transformer against the input parameters of the heat resource water and cooling water is simulated and analyzed to find out the key process which seriously affects the exergy efficiency of Absorption heat transformer, then the exergy loss ratio of the key process is analyzed in depth to help to propose a controlling method, which is effective to improve the off-design performance of the Absorption heat transformer.