Heat Flux and Effectiveness in Bubble Colum Dehumidifiers for HDH Desalination
Humidification-dehumidification is a promising technology for decentralized, small-scale desalination, but high energy consumption and large dehumidifier size are disadvantages. Direct-contact dehumidification in bubble columns has previously been shown to decrease dehumidifier volume by an order of...
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| Format: | Article |
| Language: | en_US |
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International Desalination Association
2014
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| Online Access: | http://hdl.handle.net/1721.1/87600 https://orcid.org/0000-0002-2901-0638 https://orcid.org/0000-0002-0606-713X |
| _version_ | 1826217457926275072 |
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| author | Tow, Emily W. Lienhard, John H. |
| author2 | Massachusetts Institute of Technology. Department of Mechanical Engineering |
| author_facet | Massachusetts Institute of Technology. Department of Mechanical Engineering Tow, Emily W. Lienhard, John H. |
| author_sort | Tow, Emily W. |
| collection | MIT |
| description | Humidification-dehumidification is a promising technology for decentralized, small-scale desalination, but high energy consumption and large dehumidifier size are disadvantages. Direct-contact dehumidification in bubble columns has previously been shown to decrease dehumidifier volume by an order of magnitude. In a bubble column dehumidifier, warm, moist air is bubbled though a column of fresh water cooled by heat exchange with seawater feed. The concentration gradient from the warm bubble center to the cool bubble surface drives radial mass diffusion, and water vapor condenses on the surface of the bubble. In this paper, a parallel-flow effectiveness is defined to complement heat flux when assessing the performance of a single-stage bubble column dehumidifier. A bubble column dehumidifier is tested using significantly smaller cooling coils than those tested in previous work. Experimental results are presented in terms of heat flux and effectiveness in order to better understand the factors influencing bubble column dehumidifier performance. It is found that the heat flux can be raised dramatically by reducing the coil area, but that this gain is accompanied by a loss of effectiveness. Increasing air temperature leads to increased heat flux but decreased effectiveness. Because the gas-side pressure drop increases with increasing column liquid height, significantly lower column liquid heights are tested than those used in previous work. The critical liquid height is found to be below 4 cm for the sparger and flow rate tested. Additional heat transfer in the air gap is explored, but found to be minimal for well-designed columns with low temperature pinch. These findings will inform the design of bubble column dehumidifiers for high heat recovery and low capital cost. |
| first_indexed | 2024-09-23T17:04:17Z |
| format | Article |
| id | mit-1721.1/87600 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T17:04:17Z |
| publishDate | 2014 |
| publisher | International Desalination Association |
| record_format | dspace |
| spelling | mit-1721.1/876002022-09-29T23:26:55Z Heat Flux and Effectiveness in Bubble Colum Dehumidifiers for HDH Desalination Tow, Emily W. Lienhard, John H. Massachusetts Institute of Technology. Department of Mechanical Engineering Lienhard, John H. Tow, Emily W. Lienhard, John H. Humidification-dehumidification is a promising technology for decentralized, small-scale desalination, but high energy consumption and large dehumidifier size are disadvantages. Direct-contact dehumidification in bubble columns has previously been shown to decrease dehumidifier volume by an order of magnitude. In a bubble column dehumidifier, warm, moist air is bubbled though a column of fresh water cooled by heat exchange with seawater feed. The concentration gradient from the warm bubble center to the cool bubble surface drives radial mass diffusion, and water vapor condenses on the surface of the bubble. In this paper, a parallel-flow effectiveness is defined to complement heat flux when assessing the performance of a single-stage bubble column dehumidifier. A bubble column dehumidifier is tested using significantly smaller cooling coils than those tested in previous work. Experimental results are presented in terms of heat flux and effectiveness in order to better understand the factors influencing bubble column dehumidifier performance. It is found that the heat flux can be raised dramatically by reducing the coil area, but that this gain is accompanied by a loss of effectiveness. Increasing air temperature leads to increased heat flux but decreased effectiveness. Because the gas-side pressure drop increases with increasing column liquid height, significantly lower column liquid heights are tested than those used in previous work. The critical liquid height is found to be below 4 cm for the sparger and flow rate tested. Additional heat transfer in the air gap is explored, but found to be minimal for well-designed columns with low temperature pinch. These findings will inform the design of bubble column dehumidifiers for high heat recovery and low capital cost. Center for Clean Water and Clean Energy at MIT and KFUPM Massachusetts Institute of Technology (Pappalardo Fellowship) Massachusetts Institute of Technology (Fort and Beth Flowers Family Fellowship) National Science Foundation (U.S.) (Graduate Research Fellowship Program under Grant No. 1122374) 2014-06-02T15:53:10Z 2014-06-02T15:53:10Z 2013-10 Article http://purl.org/eprint/type/ConferencePaper IDAWC/TIAN13 - 121 http://hdl.handle.net/1721.1/87600 Tow, Emily W. and John H. Lienhard. "Heat Flux and Effectiveness in Bubble Colum Dehumidifiers for HDH Desalination." in IDA World Congress on Desalination and Water Reuse: Desalination: a Promise for the future, Oct. 20-25, 2013, Tianjin, China. 14 pp. https://orcid.org/0000-0002-2901-0638 https://orcid.org/0000-0002-0606-713X en_US http://comunicacion-aqualia.fcc.es/salaaqualia/wcm/idc/groups/public/documents/document/mdaw/mdy5/~edisp/cscp085486.pdf Proceedings of the IDA World Congress on Desalination and Water Reuse 2013 Creative Commons Attribution-Noncommercial-Share Alike http://creativecommons.org/licenses/by-nc-sa/4.0/ application/pdf International Desalination Association Prof. Lienhard via Angie Locknar |
| spellingShingle | Tow, Emily W. Lienhard, John H. Heat Flux and Effectiveness in Bubble Colum Dehumidifiers for HDH Desalination |
| title | Heat Flux and Effectiveness in Bubble Colum Dehumidifiers for HDH Desalination |
| title_full | Heat Flux and Effectiveness in Bubble Colum Dehumidifiers for HDH Desalination |
| title_fullStr | Heat Flux and Effectiveness in Bubble Colum Dehumidifiers for HDH Desalination |
| title_full_unstemmed | Heat Flux and Effectiveness in Bubble Colum Dehumidifiers for HDH Desalination |
| title_short | Heat Flux and Effectiveness in Bubble Colum Dehumidifiers for HDH Desalination |
| title_sort | heat flux and effectiveness in bubble colum dehumidifiers for hdh desalination |
| url | http://hdl.handle.net/1721.1/87600 https://orcid.org/0000-0002-2901-0638 https://orcid.org/0000-0002-0606-713X |
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