Experimental Evaluation of a Novel Tube Bundle Solar Driven Liquid Desiccant Regenerator
Abstract
A novel design of an internally heated tube-bundle heat and mass exchanger is presented and experimentally examined in this paper. The main focus for the design of the regenerator was to avoid carryover of the lithium chloride solution (LiCl-H2O) to the regenerator air-stream. Furthermore, an important aim was to realize an improved heat and mass transfer coefficients, as well as higher chemical, physical, and thermal stability of the construction and to reach an even wettability and maximum uniform distribution of the liquid desiccant in the regenerator. The presented regenerator is the core of a demonstration plant of a liquid desiccant system that will be used for drying hay bales. The system will be installed in an agricultural domain in North Hessen, Germany. The liquid desiccant regenerator is made of copper pipes, protected from the corrosive medium, the LiCl- solution, with a thin powder coating layer. The copper tubes are covered with textile sleeves. The total exposed surface area of the regenerator is about 4 m2. The air stream and the LiCl solution flow are arranged in a cross flow configuration. The regenerator is tested in the laboratory at Kassel University. Four test sequences each with three experiments were performed by varying one of the inlet parameters in each test sequence. The moisture removal rate is studied as a function of desiccant mass flow rate, desiccant inlet temperature, heating-water inlet temperature and air inlet temperature. It is found that the moisture removal rate increases with increasing desiccant flow rate, desiccant inlet temperature and heating-water inlet temperature. Also, increasing the air inlet temperature has only a small effect on the increment of the moisture removal rate; this raises the question about the viability of preheating the regeneration air before coming in contact with diluted desiccant solution especially if the regenerator is internally heated. The diluted desiccant solution could be re-concentrated by using heating water with a temperature of 50 °C. Furthermore, an increase in the concentration of the LiCl-solution by 4% is observed when the inlet heating- water temperature is 70 °C.
Keywords
Liquid desiccant, Tube-bundle, Regenerator, Heat and mass exchanger, Drying.