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Subject: search.filters.subject.R134a

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    Comparative study for CO2 and R-134a heat pump tumble dryer - A rational approach
    (2019-10-01)
    Sian, Rony A.
    ;
    Wang, Chi-Chuan
    ;
    機械工程學系
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    Department of Mechanical Engineering
    A comparative study on the performance of CO2 and R-134a for heat pump clothes drying applications is conducted via a rationally based model. The model comprises unique features such as capability of handling transient behaviours of drying process, freedom from extra constraints normally imposed on heat pump drying modelling and accountability for detailed geometry of the major components. Simulations for both R-134a and CO2 system are performed, validated and further compared to experimental data available in literatures with good agreement. In comparison with R-134a, CO2 dryer yields higher drum outlet air and clothes temperatures, up to 15 degrees C and 6 degrees C, respectively. Yet, increments of 13% and 8% in specific moisture extraction rate (SMER) and coefficient of performance (COP) result on 15% reduction of drying time. Additionally, although subsequent parametric comparison studies on the transient performance of both systems revealed similar effect on system performance subject to same geometrical/operational parameter variation, the analyses also further confirm solid prevalence of the CO2 system over that of R-134a, in terms of COP, SMER and drying time. Finally, a brief discussion regarding pinch analysis is carried out, revealing further potential optimization for the CO2 system regarding heat exchangers. (C) 2019 Elsevier Ltd and IIR. All rights reserved.
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    Condensing heat transfer coefficients of R134a in smooth and grooved multiport flat tubes of automotive heat exchanger: An experimental investigation
    (2019-05-01)
    Ammar, Syed Muhammad
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    Abbas, Naseem
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    Abbas, Saleem
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    Ali, Hafiz Muhammad
    ;
    Hussain, Iftikhar
    Condensation heat transfer coefficient of R134a was obtained in multi-port micro channel smooth and grooved flat tubes of automotive heat exchanger. The test consisted of two smooth and one grooved tube. The test range covered mass flux 490-1600 kg/m(2) s, heat flux 5.5-19 kW/m(2) and saturation temperature 51-68 degrees C. Results revealed that condensation heat transfer coefficient increased with an increment of mass flux, vapor quality and decreased with the increase of saturation temperature. The effect of heat flux on heat transfer coefficient was negligible. The grooved tube showed larger heat transfer coefficient than that of smooth tubes. A comparison of the present data of flat tube with existing correlations revealed that the heat transfer coefficient was not reasonably predicted, therefore new correlation was developed for heat transfer coefficient that predicted 86% data within +/- 30% with a mean error of 16%. (C) 2019 Elsevier Ltd. All rights reserved.
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    Solubility measurements of surfactants and dissolution of cytochrome c in 1,1,1,2-tetrafluoroethane modified with organic solvents
    (2007-02-01)
    Li, Jie-Ren
    ;
    Yu, Tiing
    ;
    應用化學系
    ;
    Department of Applied Chemistry
    The solubilities of four surfactants, sodium bis-2-ethylhexyl sulfosuccinate (AOT), cetyltrimethylammonium chloride, didodecyldimethylammonium bromide, and n-dodecyltrimethylammonium chloride in liquid refrigerant 1,1,1,2-tetrafluoroethane (R134a) modified with methanol, ethanol, and 2-propanol were measured. The measurements were performed under 25 and 50 bar at 25 degrees C. The solubility of AOT was as high as 92 mM in R134a with addition of 2% ethanol. Cytochrome c molecules were then verified to be soluble in the AOT-containing and ethanol-modified R134a solution. Accordingly, liquid R134a is suggested as a potential extraction solvent for hydrophilic compounds.