Heat and Moisture Transfer in Desiccant Coated Rotary Energy Exchangers: Part II. Validation and Sensitivity Studies: Fid-Bau Portal

Heat and Moisture Transfer in Desiccant Coated Rotary Energy Exchangers: Part II. Validation and Sensitivity Studies

Simonson, Carey J. / Besant, Robert W.

In this paper, results from the numerical model for coupled heat and moisture transfer in rotary energy exchangers, presented in Part I, are compared with experimental data. The agreement between the measured and simulated effectivenesses (sensible, latent, and total energy) is close and within the experimental uncertainty. In addition, the effects of certain assumptions were investigated for sensitivity on the predicted performance of regenerative energy exchangers

The sensitivity results are calculated with a 0.9 m diameter by 0.1 m long aluminum matrix wheel that is coated with a molecular sieve desiccant (20% by mass). The desiccant has a maximum moisture capacity of 20% by mass. The porosity of the wheel is 85% and the normal rotational speed is 20 rpm. The design mass flow rate of air is 0.5 kg/s [1.6 kg/(s·m²)] giving a face velocity of 1.3 m/s. Neglecting thermal and moisture storage in the air is shown to result in errors as large as 2.4% in the predicted effectiveness of a rotary energy exchanger at typical wheel speeds. Including the heat of sorption in the model affects the predicted effectiveness only slightly (<0.5%). However, the predicted effectiveness is greatly affected (up to 48%) by whether the heat of phase change is assumed to remain in the air or in the matrix. Controlling the energy rate of the energy exchanger by controlling wheel speed may be impractical because the sensitivity of each effectiveness to wheel speed differs with each operating condition. The model is also used to show the importance of the entry length and thermal conductivity on the predicted performance of rotary energy exchangers.