Abstract
The objective of this study is to investigate the changes of the performance of a hot water absorption chiller as influenced by the characteristics of the heating tubes inserted in its regenerator. The absorption chiller is generally composed of four major components: evaporator, condenser, absorber, and regenerator. Among these components, the regenerator is responsible for the separation of the mixed liquid absorbent and refrigerant, and returning the refrigerant to its role.
The absorbent and the refrigerant flowing inside the regenerator were LiBr and water, respectively. The experiments were done based on a 55% absorbent concentration.
Basically, the methods of operation in the regenerator and the absorber are flooded method and falling film method, respectively. In the flooded method, the heating tubes are immersed in the liquid absorbent to heat and boil the absorbent. On the other hand in the falling film method, the absorbent that is heated by the heat source flows inside the tubes, goes to a tray, and flows down above the heating tubes. Heat transfer occurs when the flowing absorbent is in contact with every heating tube. With this, the water refrigerant that is mixed with the absorbent is evaporated and results to its regeneration.
In this study, the falling film method was used and the thermal characteristics of the heating tubes were investigated. Hot water heat source was flowing inside the tubes and liquid absorbent was flowing down on the outside of the tubes. Four types of tubes were used. These were bare tubes, notched tubes, NF tubes, and endcross tubes.
In the experiments, the inlet and outlet temperatures of the absorbent and the inlet and outlet temperatures of the refrigerant in the generator were measured. Also, the pressure of the generator and the flow rate of the refrigerant and the absorbent were measured. A Labview program was used for the measurements.
Tests were conducted on the various heating tubes using the same experimental conditions. The values of the overall heat transfer coefficient were determined. With this, the type of heating tubes that resulted to the improvement of the performance of the absorption chiller can be identified. For each type of heating tubes, the heat transfer rate on the water side and the overall transfer coefficient were measured. Also, the local heat transfer coefficient inside the tubes were determined.
Also on the liquid absorbent side, the heat transfer coefficient, the heat transfer rate, etc. were determined. The effects and the characteristics of the absorbent as influenced by the fluid film velocity were identified and compared.