An experimental study of an ejector-boosted transcritical R744 refrigeration system including an exergy analysis

Elbarghthi, Anas F. A.; Hafner, Armin; Banasiak, Krzysztof; Dvořák, Václav

doi:10.1016/j.enconman.2021.114102

Cited by 44 publications

(12 citation statements)

References 40 publications

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“…On the other hand, the heat transfer coefficients of the hot stream supercritical flow were estimated using the correlation proposed by Zendehboudi et al [ 5 ]. The proposed model includes the effect of buoyancy forces by introducing the Grashof number as shown below:

where the subscripts w and m represent the property value close to the surface and its mean value, respectively.…”

Section: Theoretical Analysismentioning

confidence: 99%

“…R744 (denoted as CO 2 ) has been used widely in the refrigeration system due to its good thermophysical properties and is classified as A1 safety level by ASHRAE [ 5 ]. Moreover, the utilization of supercritical R744 overwhelmed the inefficiency problems in refrigeration cycles at high temperatures since it has a low critical temperature [ 6 ].…”

Section: Introductionmentioning

confidence: 99%

“…The low critical temperature anticipates smooth variation in the thermophysical properties, resulting in a stable operation of the PHE. Recently, Elbarghathi et al [ 5 ] presented a transcritical R744 refrigeration cycle that utilizes the supercritical phase of R744 at the gas cooler and the subcritical R744 at the evaporator. In these applications, the supercritical R744 temperature is relatively high and distant from the critical point, making it suitable for use as a heat source for different applications of PHE.…”

Section: Introductionmentioning

confidence: 99%

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Heat Transfer Analysis between R744 and HFOs inside Plate Heat Exchangers

Elbarghthi

Hdaib

Dvořák

2022

Entropy

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Plate heat exchangers (PHE) are used for a wide range of applications, thus utilizing new and unique heat sources is of crucial importance. R744 has a low critical temperature, which makes its thermophysical properties variation smoother than other supercritical fluids. As a result, it can be used as a reliable hot stream for PHE, particularly at high temperatures. The local design approach was constructed via MATLAB integrated with the NIST database for real gases. Recently produced HFOs (R1234yf, R1234ze(E), R1234ze(Z), and R1233zd(E)) were utilized as cold fluids flowing through three phases: Liquid-phase, two-phase, and gas-phase. A two-step study was performed to examine the following parameters: Heat transfer coefficients, pressure drop, and effectiveness. In the first step, these parameters were analyzed with a variable number of plates to determine a suitable number for the next step. Then, the effects of hot stream pressure and cold stream superheating difference were investigated with variable cold channel mass fluxes. For the first step, the results showed insignificant differences in the investigated parameters for the number of plates higher than 40. Meanwhile, the second step showed that increasing the hot stream pressure from 10 to 12 MPa enhanced the two-phase convection coefficients by 17%, 23%, 75%, and 50% for R1234yf, R1234ze(E), R1234ze(Z), and R1233zd(E), respectively. In contrast, increasing the cold stream superheating temperature difference from 5 K to 20 reduced the two-phase convection coefficients by 14%, 16%, 53%, and 26% for R1234yf, R1234ze(E), R1234ze(Z), and R1233zd(E), respectively. Therefore, the R744 is suitable for PHE as a driving heat source, particularly at higher R744 inlet pressure and low cold stream superheating difference.

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where the subscripts w and m represent the property value close to the surface and its mean value, respectively.…”

Section: Theoretical Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Heat Transfer Analysis between R744 and HFOs inside Plate Heat Exchangers

Elbarghthi

Hdaib

Dvořák

2022

Entropy

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“…Dahmani et al [16] studied the ejector refrigeration system, they found that more than half of the destruction in the ejector refrigeration system using R134a occurred in the ejector. Elbarghthi et al [17] tested and analyzed the CO2 transcritical ejector refrigeration system, evaluated the system parameters under different operating conditions, such as gas cooler pressure, outlet temperature of gas cooler, evaporation temperature and receiver. The experiment shows that with the increase of gas cooler pressure, the exergy destruction of the system gradually increases.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the ejector two-stage compression refrigeration cycle with work performance from energy, conventional exergy and advanced exergy perspectives

Xie

Yang

Zhu

et al. 2022

Preprint

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Low temperature cold chain is the top priority of logistics development at this stage. CO2 (carbon dioxide) refrigeration system is widely used. However, the low efficiency of CO2 refrigeration system is the biggest obstacle to its development. In this research work, a novel trans-critical CO2 refrigeration cycle with ejector for cryogenic storage is proposed. The energy and traditional exergy model of the system are established, and the advanced exergy model is established based on the traditional exergy model, and the actual performance of the system is analyzed. The results show that the exergy destruction of each component of the ejector is the largest in the system, and the optimization potential is the highest in both traditional and advanced exergy models. After studying the influence of main parameters in the system cycle on the system performance and performance, it is found that there is an optimum intermediate pressure and gas cooler pressure in the system to maximize the system performance and efficiency. According to the influence of the change of system parameters on the system, it is found that the outlet temperature of gas cooler has the greatest influence on the optimization of ejector.

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“…Elbarghthi et al implemented an extensive experimental study that used a small ejector throat to analyze the ejector performance under the subcritical and supercritical regions of operations [ 22 ]. The result revealed a high ejector efficiency that could allow 36.9% of the available work rate to be recovered and reach 23% of exergy efficiency at a high exit gas cooler temperature.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of Various Ejector Profiles on CO2 Transcritical Refrigeration System Performance

Elbarghthi

Dvořák

2022

Entropy

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This study examines the potential impact of the different ejector profiles on the CO2 transcritical cooling system to highlight the contribution of the multi-ejector in the system performance improvement. The research compares the implementation of an ejector-boosted CO2 refrigeration system over the second-generation layout at a motive flow temperature of 35 °C and discharge pressure of 90 bar to account for the transcritical operation mode. The result revealed a significant energy saving by reducing the input power to the maximum of 8.77% when the ejector was activated. Furthermore, the multi-ejector block could recover up to 25.4% of the expansion work losses acquired by both ejector combinations VEJ1+2. In addition, the behavior of the multi-ejector geometries and operation conditions greatly influence the system exergy destruction. The analysis shows a remarkable lack of exergy destruction during the expansion process by deploying the ejector in parallel with the HPV.

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An experimental study of an ejector-boosted transcritical R744 refrigeration system including an exergy analysis

Cited by 44 publications

References 40 publications

Heat Transfer Analysis between R744 and HFOs inside Plate Heat Exchangers

Heat Transfer Analysis between R744 and HFOs inside Plate Heat Exchangers

Evaluation of the ejector two-stage compression refrigeration cycle with work performance from energy, conventional exergy and advanced exergy perspectives

Evaluation of Various Ejector Profiles on CO2 Transcritical Refrigeration System Performance

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