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Research Papers: Porous Media

Effects of Physical and Sorption Properties of Desiccant Coating on Performance of Energy Wheels

[+] Author and Article Information
Farhad Fathieh

Mem. ASME
Department of Mechanical Engineering,
University of Saskatchewan,
57 Campus Drive,
Saskatoon, SK S7N 5A9, Canada
e-mail: Farhad.Fathieh@usask.ca

Majid Nezakat

Department of Mechanical Engineering,
University of Saskatchewan,
57 Campus Drive,
Saskatoon, SK S7N 5A9, Canada
e-mail: Majid.Nezakat@usask.ca

Richard W. Evitts

Department of Chemical and
Biological Engineering,
University of Saskatchewan,
57 Campus Drive,
Saskatoon, SK S7N 5A9, Canada
e-mail: Richard.Evitts@usask.ca

Carey J. Simonson

Department of Mechanical Engineering,
University of Saskatchewan,
57 Campus Drive,
Saskatoon, SK S7N 5A9, Canada
e-mail: Carey.Simonson@usask.ca

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received April 24, 2016; final manuscript received December 15, 2016; published online February 28, 2017. Assoc. Editor: Ali Khounsary.

J. Heat Transfer 139(6), 062601 (Feb 28, 2017) (14 pages) Paper No: HT-16-1227; doi: 10.1115/1.4035650 History: Received April 24, 2016; Revised December 15, 2016

Desiccant-coated energy wheels are rotary-air-to-air energy exchangers widely used in ventilation systems to reduce the energy consumption required in industrial environments and commercial buildings. In this study, the effects of silica gel microphysical properties, i.e., pore width (Pw), specific surface area (SA), and particle size (dp), on the moisture recovery efficiency (latent effectiveness) of energy wheels are investigated. Three silica gel samples with different particle size and pore width (55 μm–77 Å, 150 μm–63 Å, and 160 μm–115 Å) are selected to coat small-scale energy exchangers. The sorption performance of the exchangers is determined from their normalized humidity response to a step increase in the inlet humidity at different flow rates. The results demonstrate that the transient humidity response is mainly specified by the desiccant pore size distribution, specific surface area, and mass of the coating. The transient analytical model is used to calculate the latent effectiveness (ɛL) of the exchangers from the transient humidity response. It was found that the exchanger coated with the smallest pore width (63 Å) has the highest available surface area and the highest latent effectiveness. With almost the same particle size (dp = 150 μm and 160 μm), the latent effectiveness increases by 5% (at wheel speed 20 rpm and Re = 174) as the pore width reduces from 150 Å to 63 Å. Increasing the particle size from 55 μm to 150 μm with almost the identical pore width (Pw = 63 Å and 77 Å) results in a slight enhancement in the latent effectiveness. ɛL is also calculated for correlated data (Yoon–Nelson model) where the results agree within experimental uncertainty bounds.

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Figures

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Fig. 1

A conceptual view of molecular structure of amorphous silica gel

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Fig. 2

Schematic of the small-scale energy exchanger

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Fig. 3

Schematic of the test facility with the airflow lines, the measurement instrumentation, and the test section

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Fig. 4

IR spectroscopy of the silica gel samples

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Fig. 5

Particle size distribution of silica gel desiccants obtained from particle size analyzer

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Fig. 6

Sorption isotherms for (a) SG55-77, (b) SG150-63, and (c) SG160-115 obtained through N2 gas sorption test at 77 K

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Fig. 7

SEM images of silica gel particles coated on an aluminum substrate

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Fig. 8

Breakthrough curves for water vapor adsorption on the mesoporous silica gels in the small-scale exchangers at different flow rates (ΔRH = 40% and Tair = 23.1 °C)

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Fig. 9

Moisture content in the small-scale exchanger with time during the dehumidification at different flow rates (ΔRH = 40% and Tair = 23.1 °C)

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Fig. 10

Breakthrough curves of water vapor on silica gel-coated exchanger EX160-115 at different flow rates (ΔRH = 40% and Tair = 23.1 °C)

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Fig. 11

Latent effectiveness an equivalent wheel with the matrix coated with the same desiccant particles at different angular speeds and balanced supply and exhaust flow rate

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Fig. 12

The latent effectiveness of tested exchangers obtained by applying DEM on the transient test data and Yoon–Nelson correlated data at different Re numbers and wheel angular speed of ω = 0.5 rpm

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