The worldwide growing interest in improving the energy efficiency of climate control systems has led the research towards the study of innovative plant components. Promising components seem to be combined membrane contactors (CMCs), which can exchange both sensible and latent heat with the process air [1-4]. In a CMC, vapour and heat transfers take place between air and a liquid phase (water/desiccant solution) through a membrane that is permeable only to vapour. The absorption/desorption of vapour by the liquid phase acts as a latent heat source that leads to a downstream temperature variation in the liquid and, thus, to a reduction in the overall mass transfer potential. To minimize this effect allowing for an enhancement of the contactor performance, a third fluid undergoing a phase change can be used as a thermal reservoir (three-fluid CMC). In a very recent paper [5], the Authors have studied numerically and experimentally the behavior of a prototype three-fluid CMC employing microporous polypropylene (PP) capillaries. The results obtained suggested that an improved CMC with thinner membranes and denser packing could yield much better performances enlarging application potentialities in different fields. In the present paper, an innovative three-fluid CMC with thin plane membranes, that can be assembled by modifying commercially available components (aluminum evaporators), is proposed and its heat and mass transfer performance is numerically investigated. The study takes into account experimental data obtained at the University of Genoa [6] with reference to the air-side mass transfer, which greatly affects the overall mass transfer resistance. Meanwhile, a CMC prototype is on the way to be assembled at the University of Genoa. In the Figure, a sketch of the repetitive module considered in the numerical model is shown. Preliminary results obtained by means of a finite volume numerical code written in the Matlab environment (©Mathworks, Inc.) are presented. The main advantages of this membrane geometry with respect to the capillaries considered in Ref. [5] are: a simpler and cheaper practical feasibility; higher values of Nusselt and Sherwood numbers, for given head losses; a higher overall compactness of the CMC. The vapour transfer rate allowed by the CMC will be discussed in comparison with previous theoretical and experimental results presented in Ref. [5]. Potential applications of CMC components are presented, from indoor air quality dehumidification/humidification processes in refrigeration systems to summer building refreshing. References [1] Isetti C., Nannei E., Orlandini B., Capannelli G., Bottino A., Sensible and Latent Heat Exchangers to Improve Energy Efficiency of AC Systems, 4th European Workshop on Mobile Air Conditioning and Vehicle Thermal Systems, Turin, Italy, December 1–2, 2011. [2] Jia C.X., Dai Y.J., Wu J.Y., Wang R.Z., Analysis on a Hybrid Desiccant Air-Conditioning System, Applied Thermal Engineering 2006; 26: 2393–2400. [3] Zhang L., Heat and Mass Transfer in a Randomly Packed Hollow Fiber Membrane Module: A Fractal Model Approach, International Journal of Heat Mass Transfer 2011; 54: 2921–2931. [4] Isetti C., Nannei E., Capannelli G., Bottino A., Contactor Module with Hydrophobic Capillary Membrane Integrated in a Heat Exchanger and Hybrid Plant for the Dehumidification/Conditioning of Air, International Application published under the Patent Cooperation Treaty (PCT) WO 2012/042553 A1. [5] Isetti C., Nannei E., Orlandini B., Three-fluid membrane contactors for improving the energy efficiency of refrigeration and air-handling systems, International Journal of Ambient Energy 2013; DOI:10.1080/01430750.2012.755905. [6] Orlandini B., Studio sperimentale e teorico su scambiatori a membrana per il controllo delle condizioni microclimatiche interne, PhD Thesis, University of Genoa, 2011.
A new three-fluid plane membrane contactor for improving energy efficiency of climate control systems
LAZZARI, STEFANO
2013
Abstract
The worldwide growing interest in improving the energy efficiency of climate control systems has led the research towards the study of innovative plant components. Promising components seem to be combined membrane contactors (CMCs), which can exchange both sensible and latent heat with the process air [1-4]. In a CMC, vapour and heat transfers take place between air and a liquid phase (water/desiccant solution) through a membrane that is permeable only to vapour. The absorption/desorption of vapour by the liquid phase acts as a latent heat source that leads to a downstream temperature variation in the liquid and, thus, to a reduction in the overall mass transfer potential. To minimize this effect allowing for an enhancement of the contactor performance, a third fluid undergoing a phase change can be used as a thermal reservoir (three-fluid CMC). In a very recent paper [5], the Authors have studied numerically and experimentally the behavior of a prototype three-fluid CMC employing microporous polypropylene (PP) capillaries. The results obtained suggested that an improved CMC with thinner membranes and denser packing could yield much better performances enlarging application potentialities in different fields. In the present paper, an innovative three-fluid CMC with thin plane membranes, that can be assembled by modifying commercially available components (aluminum evaporators), is proposed and its heat and mass transfer performance is numerically investigated. The study takes into account experimental data obtained at the University of Genoa [6] with reference to the air-side mass transfer, which greatly affects the overall mass transfer resistance. Meanwhile, a CMC prototype is on the way to be assembled at the University of Genoa. In the Figure, a sketch of the repetitive module considered in the numerical model is shown. Preliminary results obtained by means of a finite volume numerical code written in the Matlab environment (©Mathworks, Inc.) are presented. The main advantages of this membrane geometry with respect to the capillaries considered in Ref. [5] are: a simpler and cheaper practical feasibility; higher values of Nusselt and Sherwood numbers, for given head losses; a higher overall compactness of the CMC. The vapour transfer rate allowed by the CMC will be discussed in comparison with previous theoretical and experimental results presented in Ref. [5]. Potential applications of CMC components are presented, from indoor air quality dehumidification/humidification processes in refrigeration systems to summer building refreshing. References [1] Isetti C., Nannei E., Orlandini B., Capannelli G., Bottino A., Sensible and Latent Heat Exchangers to Improve Energy Efficiency of AC Systems, 4th European Workshop on Mobile Air Conditioning and Vehicle Thermal Systems, Turin, Italy, December 1–2, 2011. [2] Jia C.X., Dai Y.J., Wu J.Y., Wang R.Z., Analysis on a Hybrid Desiccant Air-Conditioning System, Applied Thermal Engineering 2006; 26: 2393–2400. [3] Zhang L., Heat and Mass Transfer in a Randomly Packed Hollow Fiber Membrane Module: A Fractal Model Approach, International Journal of Heat Mass Transfer 2011; 54: 2921–2931. [4] Isetti C., Nannei E., Capannelli G., Bottino A., Contactor Module with Hydrophobic Capillary Membrane Integrated in a Heat Exchanger and Hybrid Plant for the Dehumidification/Conditioning of Air, International Application published under the Patent Cooperation Treaty (PCT) WO 2012/042553 A1. [5] Isetti C., Nannei E., Orlandini B., Three-fluid membrane contactors for improving the energy efficiency of refrigeration and air-handling systems, International Journal of Ambient Energy 2013; DOI:10.1080/01430750.2012.755905. [6] Orlandini B., Studio sperimentale e teorico su scambiatori a membrana per il controllo delle condizioni microclimatiche interne, PhD Thesis, University of Genoa, 2011.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
