Continuum approach to evaluate humidity transportation by an Earth to Air Energy Exchanger

Smaël Magloire Elombo Motoula, Landry Jean Pierre Gomat, Jian Lin and M’passi Mabiala, Bernard

Renewable and Sustainable Energy Reviews, 2022, vol. 165, issue C

Abstract: The efficiency of an Earth to Air Energy Exchanger is evaluated for the transport of outdoor air moisture by the simplified analytical method implemented in the previous paper for the transport of dry air temperature. The approach was to establish and solve analytically the diffusion equation of the air’s mixing ratio in the exchanger. The variation of the saturated air mixing ratio is observed even in the horizontal tubes. The theoretical results indicate that the extreme limits of the mixing ratio of saturated air that the exchanger can reach are ϖs(Tm)=0.00967601 g/g in the vertical part and ϖs(Tmsol)=0.0123178 g/g in the horizontal part. The analysis showed a better understanding of the process. Numerical results of the moisture assessment are plotted against the experimental results. These results conclude that the vertical part has a significant contribution of about three per cent (3%) to the overall efficiency of the device, while it represents less than five per cent (5%) of the length of the whole system. The change in the humid air’s mixing ratio is determined by calculating the mass flux between the humid air and the inner surface of the tubes. To calculate the energy transfer coefficient, the condensate velocity flow was evaluated under humid air flow conditions so that Ul<0.00138m/s; indicating a fringe thickness of the water condensate film such that dl<1.15⋅10−4 m. Considering Ul=0.0004m/s, the present work achieves 98% of the experimental results. This approach could be effectively used for vertical tubes for medium and deep geothermal energy.

Keywords: Earth to Air Energy Exchanger; Film condensation; Mixing ratio; Continuum approach (search for similar items in EconPapers)
Date: 2022
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DOI: 10.1016/j.rser.2022.112562

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