169,729 research outputs found
A new three-fluid plane membrane contactor for improving energy efficiency of climate control systems
No full textThe 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
Energy saving potential of an innovative membrane contactor hybrid system for vehicles’ climate control
No full textIn this paper an innovative Membrane Contactor Hybrid System (MCHS) for automotive air conditioning is presented and its energy needs are evaluated and compared with those of a traditional system for internal combustion engine vehicles and hybrid ones. The proposed system joints a Vapor Compression Cycle (VCC) with a Liquid Desiccant Cycle (LDC) provided with innovative Three-Fluid Membrane Contactors (3F-MCs). These components are crossed by air, liquid desiccant and a third fluid operating as an internal heat source/sink to control the desiccant temperature. The VCC refrigerant undergoes a two-stage compression process: the lower level is used in a conventional evaporator for cooling the air, and the higher level in an absorption 3F-MC to dehumidify the renewal air. A second 3F-MC (desorber) is heated (by means of hot water derived from the vehicle's engine) in order to reconcentrate the desiccant by discharging water vapor to the environment. Air temperatures between 26 and 32 degrees C and relative humidity in the range 40-80% are considered to perform the comparisons between the two systems. Results show that energy savings can exceed 40% in the case of the most severe external conditions
Enhancing the energy efficiency of land vehicles air conditioning units through a new evaporative membrane cooler
No full textLed by the growing need for energy efficiency in the air conditioning systems on land vehicles, this paper proposes an original approach that integrates evaporative cooling technologies into the existing systems. In detail, the new evaporative membrane system adds to the traditional one an auxiliary kit composed of a water reserve, a circulation pump, a heat exchanger, and an innovative capillary crossflow membrane cooler. The evaporation process is used to both pre -cool the air flow to the condenser, thus lowering the refrigerant condensation temperature, and also to supply refreshed water for pre -chilling the renewal air. The proposed architecture is particularly feasible for vehicular applications where a water reservoir already exists or where it is possible to install and maintain one. The designed membrane cooler grants high mass transfer efficiency, compactness (membrane surface -to -volume ratio around 1000 m 2 /m 3 ) and manages high air flow rates while minimizing pressure loss. It is composed by organized layers of polypropylene capillaries where water flows, and plastic spacers for the airflow. First, the vapor and heat transfer mechanisms involved are investigated and the cooler ' s mathematical model is described. Numerical results show that a wet -bulb effectiveness exceeding 0.85 can be reached. Subsequently, an assessment of energy performance indicators for a motorhome application is conducted within the MATLAB (c) Simulink environment. This involves a comparative analysis between the proposed system and the conventional standalone one. The considered contactor has a total membrane area of 8.32 m 2 and handles 1200 m 3 /h of air and 150 kg/h of water. Results indicate that the efficiency ratio and the energy savings of the two systems decrease as the external air humidity increases even though the average energy efficiency ratio of the new system remains significantly higher. Mechanical energy savings are very interesting and decrease as the external air humidity increases: they are about 36 - 38 % within the humidity range [40 - 50 %], 26 - 30 % within the range [50 - 60 %], and 17 - 21 % within the range [60 - 70 %]. The corresponding water consumptions are between 2 kg/h and 6.5 kg/h, and they increase as air humidity decreases. Due to its simple architecture and high performance, this system is very promising in applications for motorhome, city buses, trains, and trucks
Experimental determination of isothermal vapour transfer rates between moist air and a hygroscopic solution through a hydrophobic synthetic membrane
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Prevenzione di danneggiamenti di origine termoigrometrica negli edifici: una ricerca svolta in Liguria
No full textContattore a membrane a tre fluidi perfezionato e impianto integrato di climatizazione ad alta efficienza energetica utilizzante tale contattore
No full textA new three-fluid plane membrane contactor for improving energy efficiency of climate control systems
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Sulle condizioni igrometriche dell’aria in ambienti destinati alla tutela ed alla conservazione di opere d’arte
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