Experimental and Numerical Investigation of Solar Powered Solid Desiccant Dehumidifier

In many parts of India, hot and humid conditions are present. In such an environment, the dry air is essential for domestic and industrial purposes. The dry air is produced by using the simple vapour compression system but it leads to environmental issues. The various solid desiccants like silica gel, activated alumina and activated charcoal are used to produce the dry air. This method has low operating and maintenance cost and is environment friendly. Also, these desiccants perform very well in high humid regions and are easily regenerated in tropical conditions of India.

Detailed review of the literature on solar assisted desiccant dehumidification system revealed many interesting possibilities. The studies show that solid desiccant dehumidifier can be easily regenerated when the evacuated tube solar air collector is attached to it. The main stress has been laid on the mathematical modeling of desiccant wheel for various designs, which helped in finding the suitable desiccant wheel design that can be regenerated at low temperature.

The experimental investigation of one ended normal evacuated tube solar air collector has been carried out for producing the hot air under the Indian climatic conditions. To enhance the outlet temperature, copper coil and reflectors have been used. Both the configurations, parallel flow and counter flow are examined experimentally by changing the position of blower. It has been found that the setup operated more efficiently at high air flow rate in counter flow when both the reflectors and copper coil were used.

The hot air produced from evacuated tube solar air collector has been used to regenerate the various solid desiccants like silica gel, activated alumina and activated charcoal and their comparative performances have been evaluated. The regeneration performance is greatly affected by the regeneration temperature and it also depends on the initial moisture content, regeneration air moisture at inlet, temperature of the desiccant and the flow rate of regeneration air. On comparing the performance of desiccants at different air flow rates, it has been found that evacuated tube solar air collector regenerates these desiccants properly and the regeneration performance of silica gel is better as compared to activated alumina and activated charcoal. For air dehumidification, silica gel is also a vi better adsorbent as compared to activated alumina and activated charcoal for humid climatic conditions of India.

Experimental studies have been carried out on solar powered desiccant wheel for producing the dry air in Indian climatic conditions. The regeneration and adsorption processes have been taken into account for this setup. The regeneration performance and adsorption performance are affected by the regeneration temperature, rotational speed of desiccant wheel, air flow rate and ambient conditions. Regeneration temperature directly affects the effectiveness of the desiccant wheel.

Experimental results obtained from solar powered desiccant wheel for the moisture removal process have been compared with simulation results of mathematical model at same operating and design parameters. Simulation results are also validated with the experimental data of Kodama PhD thesis (1995).

A mathematical model has been used to estimate the optimum design parameters of a desiccant wheel for reducing its weight and size. This model has been used to conduct a comparative performance analysis in both the directions of rotation (clockwise and anticlockwise) of desiccant wheel with purge sector and it has been found that the anticlockwise direction gave better results than clockwise direction for all the cases.

This model has also been used to compare the performances of two sector and four sector desiccant wheels. It has been found that the maximum relative moisture removal efficiency of both, the two sector and four sector is same but in two sector, it has been obtained at twice the rph of a four sector. This model has also been used to analyze the performance of two sector desiccant wheel with heated and cooled purge at different regeneration temperatures and it has been found that at low rph, the desiccant system with a higher purge angle and lower regeneration angle performed better as compared to a lower purge angle and higher regeneration angle.

It has been concluded from the present work that the solar powered solid desiccant dehumidifier operated well in hot and humid climatic conditions of India and can be a viable alternative to the conventional heater. This system can also be effectively used for industrial and domestic purposes.