Browsing by Author "Yu, Pei-Yu"

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Performance evaluation of a tube-in-tube CO2 gas cooler used in a heat pump water heater
(2014-04-01)
Yu, Pei-Yu
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Lin, Wei-Keng
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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, investigation of the performance of a tube-in-tube counter-flow water-cooled CO2 gas cooler operating above and near critical pressure is presented using a heat pump water heater with CO2 flowing in the annulus side. A tube-in-tube heat exchanger model applicable for supercritical fluid CO2 and water was also developed and validated. The measured total heat transfer capacity ranged from 1.31 to 4.06 kW at various test conditions. The calculations show good agreement with the experimental results. The results demonstrate that the variation of CO2 temperature tends to show very slow decreasing near the pseudo-critical region when compared to the inlet region. Yet this phenomenon becomes more pronounced as the inlet pressure is close to the critical pressure (73.8 bar). The calculation also reveals a peculiar phenomenon that the local heat transfer rate of the heat exchanger peaks within the heat exchanger near the pseudo critical region due to the drastic rise of specific heat (C-p value). (C) 2014 Elsevier Inc. All rights reserved.
Performance of a tube-in-tube CO2 gas cooler
(2012-11-01)
Yu, Pei-Yu
;
Lin, Kai-Hsiang
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Lin, Wei-Keng
;
Wang, Chi-Chuan
;
機械工程學系
In this study, a tube-in-tube heat exchanger model applicable to supercritical CO2 and water was developed. The developed model is first validated with some existing measurements. Normally, the variation of the heat transfer rate for a constant-property working fluid shows a monotonic decrease from the inlet of minimum heat capacity flow rate (C-min). By contrast, the CO2 may present a local minimum and a local maximum along the length of the heat exchanger, provided CO2 passes through the pseudo-critical temperature, and this phenomenon becomes more and more pronounced when the pressure is close to the critical pressure. In contrast, it is possible for a local maximum heat transfer rate to occur near the inlet of C-min even when the CO2 does not pass through the pseudo-critical point. This happens when C-min is on the water side and the property variation of CO2 is taken into account. The calculation also shows that the effect of the inlet pressure on the variation of the CO2 temperature is not as apparent as the effect of the inlet pressure on the heat transfer rate, even when there is a significant change in the overall heat transfer coefficient, implying that the heat transfer characteristics of CO2 near the pseudo-critical region is similar to normal refrigerants, which show an invariant temperature at the condensation point. Hence, it would be beneficial to extend the influence of the pseudo-critical region when taking the heat transfer augmentation into consideration. (C) 2012 Elsevier Ltd and IIR. All rights reserved.
Robust BDCM sensorless control with position-dependent load torque
(2007)
Huang, Chih-Kai
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Yu, Pei-Yu
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Chen, Hung-Chi
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交大名義發表
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National Chiao Tung University
This paper presents the robust sensorless operation for brushless DC motors (BDCMs) loaded by the position-dependent load where the load torque is a function of the rotor angle (not electrical angle). Without any position sensor, the reliable position signals are generated from the motor terminal voltages through sensorless circuits. In order to reduce the speed variations especially in the low speed, an additional gain to adjust output voltage is included in the speed loop to compensate the repetitive position-dependent load. In first, the effects of position-dependent load on the speed variations and the commutation intervals are studied. It shows that we can estimate the position-dependent load from the commutation intervals. Then, we introduce the used sensorless scheme based on sensing terminal voltage. Finally, some simulated results have been given to demonstrate the robust performance of the proposed sensorless control for the position-dependent loads.