Study On A Hybrid System Of Open Absorption Heat Pump And Dewpoint Cooler

The world is facing unprecedented challenges of energy security and climate change because of the rising energy demand which is mainly due to the rising heating,drying,and cooling demands in residential as well as the industrial sector.The inefficient systems with less energy utilization rate,emission of a significant amount of waste heat in the environment,increased industrial energy consumption due to the processes,and the industrial spread with time are the main key challenges of the industrial world.Industrial exhausts release a huge amount of latent waste heat in the form of flue gases and at the same time,a significant amount of energy is consumed by the industrial processes of compressed deep air drying.The open absorption technology which exits for decades is being used in the industrial sector for latent heat recovery from moist flue gas and to improve the industrial process through recovered heat.However,the energy utilization is still inefficient and this technology is not mature enough.In this regard,the open absorption technology has been employed in this study to propose novel multifunctional hybrid open absorption systems to utilize the latent waste heat from moist flue gases to supply hot water for heating and to dehumidify the ambient air for industrial or space cooling applications at the expense of any external low grade heat source for regeneration requirement.The process and thermodynamic models of this kind of system are developed to analyze the performance in detail.The effects of important inlet operating parameters are studied on different performance parameters.The theoretical results of the single stage configuration reveal that the system is capable to provide 176.9k W heating capacity at the thermal coefficient of performance of 2.22 with heat recovery efficiency of 87.1% and the cooling capacity of 9.87 k W is achieved at system design specifications.An experimental setup of this single stage system has been developed and detailed experiments have been conducted to validate the theoretical results which has confirmed the accuracy of the model.Similarly,the idea of a multifunctional open absorption system for efficient energy utilization is also presented for the double stage which can overcome the high regeneration temperature requirement of the single stage and operate for low humidity levels.The energy performance comparison of both configurations is conducted and results show that the thermal COP of the double stage system varies from 1.24 to the maximum value of 2.39,while the single stage system can achieve the thermal COP between 1.34-2.54.Furthermore,the double stage multifunctional system can operate for a wider range of operational parameters such as the lower heat source temperature of96.3-159.6℃ and humidity range of 0.054-0.2kg/kg.The lower and wider temperature range,as well as the wider humidity range of the proposed system,make it more suitable for low grade thermal energy utilization and improved latent heat recovery.To deal with the industrial energy consumption to fulfill the deep dry air needs with low humidity level requirements,a novel multifunction open absorption heat pump system with a compressed air dryer is also proposed in this study.This proposed system can not only provide industrial heating through latent heat recovery but also provides deep dried compressed air.This deep dry air with low humidity is important,especially for the textile and fiber industries.The theoretical results of this system revealed that this novel system is capable to provide dehumidified air at low humidity levels of 1.05g/kg by operating at COP of 1.94 at the dryer’s pressure of 600 k Pa and can recover the latent heat from moist gas with the efficiency of 91.95%.The thermal performance of this system is strongly influenced by the compressed air dryer’s pressure such that the 13.2-42.7% preliminary solution regeneration can be covered by the heat recovered from compressed air and the further regeneration requirement can be served by using a heat source of temperature between 113-120℃.This research also studies a new counter-cross flow configuration of dewpoint evaporative coolers.The new dewpoint cooler is more efficient,flexible in air flows and can control the cooling capacity of the system through variable extraction ratio.The more remarkable factor of this dewpoint cooler is that it is provided with two inlet air streams and the extraction ratio of the secondary air can be controlled as compared to the conventional counterflow configurations in which the extraction ratio is unchangeable due to the structure with the single air stream.An experimental setup of this dewpoint cooler has been developed and the experiments have been conducted to validate the theoretical results.The theoretical and experimental results highlight that the new dewpoint cooler has 14.39-33.8% higher dewpoint cooling effectiveness as compared to the conventional counter type.Furthermore,the theoretical model is verified by results obtained from real experiments on the developed prototype.