Results 1 - 10 of 19
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[en] Highlights: • An ejector-assisted loop heat pipe with a flat evaporator (ELHP) is proposed. • The ejector is used to remove the generated vapor in the CC due to the heat leak. • Performances of the ELHP and basic loop heat pipe (BLHP) are compared. • Comparisons show that operating temperature of the ELHP is lower than that of the BLHP. • Compared with the BLHP, the condenser length of ELHP can be decreased significantly. - Abstract: This paper proposes an ejector-assisted copper–water loop heat pipe with a flat evaporator (ELHP) for applications in electronic cooling. In the ELHP, the ejector is used to remove the generated vapor in the compensation chamber due to heat leaks through the wick, which could eliminate the need for the subcooling liquid supplied to the compensation chamber and improve the loop heat pipe performances. The steady-state performance of ELHP is simulated based on an established mathematical model and compared with the basic loop heat pipe with a flat evaporator (BLHP). The simulation results show that the operating temperature of the ELHP can be lower than that of the BLHP under the same heat load condition. Since the working fluid subcooling zone in the ELHP condenser is not required, the total length of the pipe-in-pipe type condenser also can be decreased by 24.4–34.8% when compared with that of the BLHP under given operating conditions. In addition, the effects of the thickness of the wick, the total length of the condenser, the inner diameter of the vapor line and the mass flow rate and inlet temperature of the cooling water on the performances of the ELHP are also evaluated in this study. These simulation results indicate that the ELHP can achieve a better performance than BLHP, which could be beneficial to the applications in electronic cooling.
[en] This paper presents an experimental investigation on a NERC (novel ejector enhanced refrigeration cycle) applied in the domestic refrigerator-freezer (BCD-249). Experimental studies were conducted to validate the NERC system feasibility in a practical NERC based refrigerator-freezer prototype. The system performances of energy consumption, ejector pressure lift ratio and compressor power were compared under different combinations of system configuration parameters. The results showed that the NERC system could effectively reduce the thermodynamic losses in the throttle processing. The minimum energy consumption of 0.520 kWh 24 h"−"1 was obtained for the NERC prototype, indicating 5.45% energy consumption reduction compared with the conventional domestic refrigerator-freezer. Furthermore, the effects of system configuration parameters including the refrigerant charge amount, the compressor displacement and the length of capillary tube were investigated. This study aims at providing deep insight into ejector-expansion technology applied in domestic refrigerator-freezers. - Highlights: • A NERC (novel ejector enhanced refrigeration cycle) was experimentally studied. • 73 experimental data points with different system configuration were acquired. • Energy consumption could be reduced with optimum system configuration. • 5.45% energy consumption reduction is obtained compared with the conventional system.
[en] Highlights: • The two-phase driven ejector performance was experimentally studied. • Effects of operational and geometric parameters for the ejector were examined. • The ejector performance was strongly affected by those parameters. • Maximum ejector efficiency could be obtained with proper parameters. - Abstract: This paper presents an experimental investigation on two-phase driven ejector performance characteristics in a novel ejector enhanced refrigeration system (NERC). An experimental setup using refrigerant R600a is designed and built based on the NERC system. In the experimental setup, the ejector uses two-phase refrigerant coming from the high-temperature evaporator as the primary fluid. The experiments are carried out to examine the influences of the main operational and geometric parameters, including the primary fluid pressure, the secondary fluid pressure, the NXP and the nozzle throat diameter. The results show that the entrainment ratio, the pressure lift ratio and the overall ejector efficiency of the two-phase driven ejector are strongly affected by those parameters. Additionally, the effect of the quality of the two-phase primary fluid is also experimentally investigated. The meaningful results obtained here may serve as good guidelines for further improving the two-phase driven ejector performance and providing promising use of the two-phase driven ejector in the ejector-expansion technology.
[en] Highlights: • A modified direct expansion solar-assisted heat pump water heater is investigated. • An additional air source evaporator is used in parallel way in the M-DX-SHPWH system. • The M-DX-SHPWH system displays a higher performance at the low solar radiation. • Effects of solar radiation and air temperature on the performance are discussed. - Abstract: This paper investigated a combined solar/air dual source heat pump water heater system for domestic water heating application. In the dual source system, an additional air source evaporator is introduced in parallel way based on a conventional direct expansion solar-assisted heat pump water heaters (DX-SHPWH) system, which can improve the performance of the DX-SHPWH system at a low solar radiation. In the present study, a dynamic mathematical model based on zoned lump parameter approach is developed to simulate the performance of the system (i.e. a modified DX-SHPWH (M-DX-SHPWH) system). Using the model, the performance of M-DX-SHPWH system is evaluated and then compared with that of the conventional DX-SHPWH system. The simulation results show the M-DX-SHPWH system has a better performance than that of the conventional DX-SHPWH system. At a low solar radiation of 100 W/m"2, the heating time of the M-DX-SHPWH decreases by 19.8% compared to the DX-SHPWH when water temperature reaches 55 °C. Meanwhile, the COP on average increases by 14.1%. In addition, the refrigerant mass flow rate distribution in the air source evaporator and the solar collector of the system, the allocation between the air source evaporator and the solar collector areas and effects of solar radiation and ambient air temperature on the system performance are discussed.
[en] Highlights: • 3.0 °C temperature enhancement experimentally demonstrated on a realistic TEC. • There exists an optimum initial steady current for maximum temperature enhancement. • Temperature enhancement continuously obtained in continuous pulse experiment. • Temperature increment in continuous pulses is similar to first-order step response. • Different cooling loads lead to different initial temperatures but similar trends. - Abstract: This paper presents an experimental investigation on cooling characteristics of a realistic thermoelectric module (TEM) that operates under single and continuous square current pulse. The experimental system is built and the related study is performed. A cooling temperature enhancement of 3.0 °C relative to steady current operation on a realistic TEM is demonstrated. Further experimental data reveal that there exists an optimum initial steady current which provides the maximum cooling temperature enhancement in the current pulse operation. In addition, the value of the supercooling and the temperature overshoot always stay close. Moreover, continuous temperature enhancement in each current pulse is achieved on a realistic TEM operated with continuous current pulses. Cooling temperature in each current pulse shows an increasing trend similar to that of a first order step response. The cooling characteristics under different cooling loads are quite similar, except for the different initial temperatures.
[en] Highlights: • Optimization of a thermoelectric cooler system is presented. • The total heat transfer area of heat exchangers is considered as a constraint. • The best performances are characterized by different optimal area allocation ratios. • Optimal area allocation ratios are mainly affected by hot side thermal conductance. - Abstract: In this paper, the theoretical analyses are conducted to explore the optimization problems of thermoelectric cooler (TEC) systems applied in electronic cooling. The study mainly focuses on the optimal heat exchanger configuration of a TEC system. The effects of total heat transfer area allocation ratio, thermal conductance of the TEC hot and cold side and TEM element material properties on the cooling performance of the TEC are investigated in detailed based on the developed mathematical model. The analysis results indicate that the highest coefficient of performance (COP), highest heat flux pumping capability of the TEC and lowest cold side temperature can be achieved by selecting an optimal heat transfer area allocation ratio. The optimal heat transfer area allocation ratio mainly depends on the relevant objective functions, the hot and cold side thermal conductance, total heat exchanger size and the TEM element material properties. These results reveal that the heat transfer area allocation ratio is an applicable characteristic of optimum design for TEC systems. It is hoped that the considerations and analysis results may provide guides for the design and application of practical thermoelectric cooler system in electronic cooling
[en] Highlights: • An integrated two-stage thermoelectric module using dual power sources is studied. • The cooling capacity and COP can reach their maximum at respective optimal currents. • The maximum cooling capacity rises with increasing leg length allocation ratio. • In the case of Q_c_,_m_a_x, an optimum leg length allocation ratio can achieve an optimum COP. - Abstract: This paper presents an integrated two-stage cascaded thermoelectric module (TTEM) operating with dual power source. The integrated TTEM contains two stages of thermocouples with identical semiconductor cross-sectional area but different leg lengths. An analytical model for the TTEM is developed, and the influences of the key parameters are theoretically investigated. The obtained results indicate that optimum two stage currents combination can maximize both the cooling capacity and coefficient of performance (COP). Furthermore, the leg length allocation ratio for the two stages affects the maximum cooling capacity significantly. Larger leg length proportion of the colder stage may effectively contribute to the improvement in maximum cooling capacity. In addition, there exists an optimum leg length allocation ratio to obtain the corresponding optimum COP when the two stage currents are set to achieve the maximum cooling capacity of the TTEM. However, the total leg length has no effect on the corresponding optimum COP
[en] Highlights: • Double ejectors are applied in a two-stage transcritical CO2 heat pump cycle. • The performance of the new cycle with double ejectors is evaluated theoretically. • The new cycle exhibits higher performance compared to the basic two-stage cycle. • The heating COP can be increased by 10.5–30.6% under given operation conditions. - Abstract: In this study, two ejectors are proposed as expansion devices for a two-stage transcritical CO2 heat pump cycle to enhance the cycle performance. The two ejectors are arranged at the low- and high-pressure stages, respectively, to recover more available expansion work, and significantly reduce the throttling loss at each stage. The performance of the improved two-stage cycle is evaluated by using the developed mathematical model, and then compared with those of the basic two-stage cycle with a flash tank. The simulation results show that the improved two-stage cycle exhibits higher heating COP and volumetric heating capacity compared to the basic two-stage cycle. By further incorporating an internal heat exchanger, the heating COP can be increased by 10.5–30.6% above that of the baseline cycle when the subcooling degree varied from 0 to 15 °C under given operation conditions of −15 °C evaporating temperature, 10 MPa gas cooler pressure and 35 °C outlet temperature. Additionally, the effects of the gas cooler pressure and intermediate pressure on the maximal heating COP are also discussed
[en] Highlights: • A novel dual-nozzle ejector enhanced refrigeration cycle is proposed. • The novel cycle is evaluated by using the developed mathematical model. • The results show the performances of the novel cycle could be significantly improved. • The novel cycle shows its promise in household refrigerator-freezers applications. - Abstract: In this study, a novel dual-nozzle ejector enhanced refrigeration cycle is presented for dual evaporator household refrigerator-freezers. The proposed ejector equipped with two nozzles can efficiently recover the expansion work from cycle throttling processes and enhance cycle performances. The performances of the novel cycle are evaluated by using the developed mathematical model, and then compared with that of the conventional ejector enhanced refrigeration cycle and basic vapor-compression refrigeration cycle. The simulation results show that for the given operating conditions, the coefficient of performance (COP) of the novel cycle using refrigerant R134a is improved by 22.9–50.8% compared with that of the basic vapor-compression refrigeration cycle, and the COP improvement is 10.5–30.8% larger than that of the conventional ejector enhanced refrigeration cycle. The further simulation results of the novel cycle using refrigerant R600a indicate that the cycle COP and volumetric refrigeration capacity could be significantly improved
[en] Highlights: • A new ejector enhanced auto-cascade refrigeration cycle using R134a/R23 is proposed. • The performance of new and basic cycles is compared by simulation method. • The new cycle outperforms the basic cycle in both energetic and exergy aspects. • Both cycles have optimum mixture compositions to obtain optimal performance. - Abstract: A new ejector enhanced auto-cascade refrigeration cycle using R134a/R23 refrigerant mixture is proposed in this paper. In the new cycle, an ejector is used to recover part of the work that would otherwise be lost in the throttling processes. The performance comparison between the new cycle and a basic auto-cascade refrigeration cycle is carried out based on the first and second laws of thermodynamics. The simulation results show that both the coefficient of performance and exergy efficiency of the new cycle can be improved by 8.42–18.02% compared with those of the basic cycle at the same operation conditions as the ejector has achieved pressure lift ratios of 1.12–1.23. It is found that in the new cycle, the highest exergy destruction occurs in the compressor followed by the condenser, cascade condenser, expansion valve, ejector and evaporator. The effect of some main parameters on the cycle performance is further investigated. The results show that for the new cycle, the achieved performance improvement over the basic cycle is also dependent on the mixture composition and the vapor quality at the condenser outlet. The coefficient of performance improvement of the new cycle over the basic cycle degrades with increasing vapor quality. In addition, there exists an optimum mixture composition to obtain the maximum coefficient of performance for the new cycle when other operation conditions are given. The optimum mixture composition of both cycles may be fixed at about 0.5 under the given evaporating temperature.