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This paper characterizes the state-of-the-art in desiccant dehumidifiers,the key component of desiccant cooling systems. The experimental data are providing industry and end users with independent performance evaluation and assessing the energy savings potential of the technology. As regenerated desiccant dehumidifiers become more widely applied across the country, the motivation has developed to extend sea level engineering data to higher altitude,lower pressure locations. This paper describes a small experiment to conduct heat/mass transfer and fluid dynamic performance evaluations over a range of atmospheric pressures. It evaluates performance and energy efficiency using several figures of merit, including moisture removal capacity normalized by airflow rate (MRC/Q, analogous to grain depression,.GPP), wheel pressure drop dpM), and the energy consumption parameter regeneration specific heat input (RSHI).

Steady-state tests were conducted on a core sample from commercially available dehumidifier wheel, and results were compared at 1.00 atm and 0.84 atm. Tests were conducted with 50/50 wheel face split and balanced air mass flows. Data are presented for face velocities of 300 sfpm, 600 sfpm, and 800 sfpm and humidities between 80 gr/lb and 160 gr/lb. Process inlet air temperature was fixed at 86°F. Regeneration inlet temperature was held constant at 190°F. Regeneration inlet humidity was set equal to process inlet grains for all tests. Matrix rotational speed was fixed at a value optimized for the full-scale equipment over the range of face velocities studied.

Steady-state tests show that for this matrix,under specific test conditions,essentially exact agreement in grain depression is achieved between 1.00 atm and 0.84 atm when inlet grains and air mass flow rates are matched. They also confirm that matrix pressure drops correlate to actual face velocity. These heat/mass transfer and fluid dynamic results support fully developed laminar flow theory. Specifically, to extend dehumidification data to different altitudes, match number of transfer units (NTU)and convective transfer coefficients. Matching NTU requires the air mass flow rates and wheel speeds to be the same,and the convective mass transfer coefficient that remains constant with pressure and velocity is based on absolute humidity or humidity ratio as a surrogate.

Units: I-P

Citation: Symposium, ASHRAE Transactions, vol. 108, pt. 2