Browsing by Author "Sian, Rony A."

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A generalized log-linear poisson-modeled correlation to predict the optimal heat rejection pressure of transcritical CO2 systems
(2018-01-01)
Sian, Rony A.
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Wang, Chi-Chuan
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機械工程學系
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Department of Mechanical Engineering
In this study, a comprehensive literature survey of all the experimental data available in literature regarding optimal heat rejection pressure on transcritical carbon dioxide systems is carried out. Based on the phenomenological analysis and quantitative assessment of the data, a Poisson regression analysis is performed and a new dimensionless correlation to predict the optimal heat rejection pressure is developed. The influences of relevant parameters on heat rejection pressure, such as ambient temperature and temperature at the gas cooler are taken into account in the correlation development. The proposed correlation is tested against experimental measurements and is further validated by comparison to all existing experimental data collected from literature. Additionally, the predictive ability of the newly proposed correlation is discussed, tested against experimental data found in literature and compared with existing correlations. Upon comparison with existing correlations, the new generalized dimensionless correlation proposed in this study predicts the optimal heat rejection pressure with an average deviation of 1.31% and a standard deviation of 4.26 bar. Thus, becoming the most accurate correlation up to date, yet providing a much wider range of temperature applicability than the correlations currently available in literature.
A rationally based model applicable for heat pump tumble dryer
(2019-04-26)
Lee, Bing-Hung
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Sian, Rony A.
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Wang, Chi-Chuan
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機械工程學系
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Department of Mechanical Engineering
The present study proposes a rationally based heat pump clothes dryer model which is capable of handling transient behaviors of both air-side and refrigerant side. The model can take into account the geometrical variation of the heat exchangers. Yet the proposed model is free from extra constraints that were normally imposed by previous studies. The simulation shows that there exist three stages in a typical drying process, including a preheat stage, followed by a constant evaporation stage, and finally a falling drying rate period. The calculation indicates that the variation of the clothes temperature and the system suction/discharge pressure show an appreciable rise in the first stage, remain nearly unchanged at the second stage, and increase again at the final stage of drying process. Also, the corresponding maximum specific moisture extraction rate (SMER) peaks at the end of the second stage while the corresponding coefficient of performance (COP) drops continuously. The simulation also indicates that increasing the air volumetric flowrate yields a lower discharge/suction pressure, a higher COP value, and a shorter drying time. The results also suggested that a good strategy to maximize COP is initiated by a low volumetric rate during the preheat stage, increasing it during the second stage and lowering it to an intermediate flowrate at the end of the drying period. Increasing heat exchanger size, either by increasing heat exchanger width or the number of tube row, results in a lower suction/discharge pressure and a shorter drying time. Although both approaches adopt larger surface area to promote overall performance, it is found that increasing the width of heat exchanger yields more effective results.
Comparative study for CO2 and R-134a heat pump tumble dryer - A rational approach
(2019-10-01)
Sian, Rony A.
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Wang, Chi-Chuan
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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.
Constraints-free modeling and experimental validation of a transcritical CO2 system for medium and large scale applications
(2017-09-01)
Sian, Rony A.
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Wang, Chi-Chuan
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機械工程學系
;
Department of Mechanical Engineering
A constraints-free transcritical CO2 heat pump model for medium and large system applications is proposed and validated through experimental measurements. The model features five components, namely: compressor, chevron-type plate heat exchanger as gas cooler, expansion valve, fin-and-tube evaporator and chevron-type plate internal heat exchanger. Unlike existing models, the proposed model takes into account the detailed geometric characteristics of each component at a wide range of operating conditions without imposing any constraints, such as constant temperatures and pressures. Parametric studies regarding the influence of relevant operating and design parameters, such as ambient temperature, water inlet temperature and chevron inclination angle are conducted and a brief discussion on pressure optimization regarding the influence of compressor speed, expansion valve openness and number of plates at the internal heat exchanger is carried out. Comparison between the experiments and simulations showed that the model accurately reflects the actual system with a maximum error of 9.6% and 3.9% for the coefficient of performance and heating capacity, respectively. The parametric examinations are thoroughly compared to results published in literatures. In essence, the results showed that the COP and the heating capacity simultaneously increase with dry bulb temperature and chevron inclination angle, reaching a maximum at about 70, while the effects of water inlet temperature are more significant and opposite to that of dry bulb temperature. (C) 2017 Elsevier Ltd. All rights reserved.