Thermal modelling and optimization of low-grade waste heat driven ejector refrigeration system incorporating a direct ejector model

Riaz, Fahid; Lee, Poh Seng; Chou, S.K.

doi:10.1016/j.applthermaleng.2019.114710

Cited by 37 publications

(23 citation statements)

References 33 publications

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“…This model has been validated with published data from experimental and simulation works. The details of this new analytical model of ejector can be found in F. Riaz et al [40]. Since there are thermodynamic irreversibilities within the ejector due to high-speed mixing and the compression shock, the pressure drop cannot be neglected as it is quite significant.…”

Section: Ejectors As Thermal Compressormentioning

confidence: 99%

“…The used ejector model incorporates the pressure drop by taking the isentropic efficiencies into the consideration. The ejector modelling details have been published in our previous paper which has been cited in F. Riaz et al [40] where the details of thermodynamic states inside the ejector have been discussed in detail along with the T-s diagram. Additionally, the ejector efficiencies have been calculated based on the optimized CFD based design obtained with ANSYS-FLUENT simulations.…”

Section: Ejectors As Thermal Compressormentioning

confidence: 99%

“…For the validation, an EES model of the proposed system is developed so that the simulation results of the EBSILON model can be compared with the EES model. The details of modelling of a thermodynamic system and its integration with the developed ejector model can be found in the reference F. Riaz et al [40]. For validation, both EES and EBSILON models have been simulated for the same working conditions as discussed in the section of EBSILON modelling.…”

Section: Validation Of Ebsilon Model With Ees Modelmentioning

confidence: 99%

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Energy Analysis of a Novel Ejector-Compressor Cooling Cycle Driven by Electricity and Heat (Waste Heat or Solar Energy)

et al. 2020

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Low-grade heat is abundantly available as solar thermal energy and as industrial waste heat. Non concentrating solar collectors can provide heat with temperatures 75–100 °C. In this paper, a new system is proposed and analyzed which enhances the electrical coefficient of performance (COP) of vapour compression cycle (VCC) by incorporating low-temperature heat-driven ejectors. This novel system, ejector enhanced vapour compression refrigeration cycle (EEVCRC), significantly increases the electrical COP of the system while utilizing abundantly available low-temperature solar or waste heat (below 100 °C). This system uses two ejectors in an innovative way such that the higher-pressure ejector is used at the downstream of the electrically driven compressor to help reduce the delivery pressure for the electrical compressor. The lower pressure ejector is used to reduce the quality of wet vapour at the entrance of the evaporator. This system has been modelled in Engineering Equation Solver (EES) and its performance is theoretically compared with conventional VCC, enhanced ejector refrigeration system (EERS), and ejection-compression system (ECS). The proposed EEVCRC gives better electrical COP as compared to all the three systems. The parametric study has been conducted and it is found that the COP of the proposed system increases exponentially at lower condensation temperature and higher evaporator temperature. At 50 °C condenser temperature, the electrical COP of EEVCRC is 50% higher than conventional VCC while at 35 °C, the electrical COP of EEVCRC is 90% higher than conventional VCC. For the higher temperature heat source, and hence the higher generator temperatures, the electrical COP of EEVCRC increases linearly while there is no increase in the electrical COP for ECS. The better global COP indicates that a small solar collector will be needed if this system is driven by solar thermal energy. It is found that by using the second ejector at the upstream of the electrical compressor, the electrical COP is increased by 49.2% as compared to a single ejector system.

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Section: Ejectors As Thermal Compressormentioning

confidence: 99%

Section: Ejectors As Thermal Compressormentioning

confidence: 99%

Section: Validation Of Ebsilon Model With Ees Modelmentioning

confidence: 99%

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Energy Analysis of a Novel Ejector-Compressor Cooling Cycle Driven by Electricity and Heat (Waste Heat or Solar Energy)

et al. 2020

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“…Although in most industries compressors have conventionally been employed to pressurize gas, it still has many weaknesses of high cost, high electric energy consumption, and complicated maintenance. Today, when energy consumption is rapidly increasing, energy‐saving and consumption reduction are the inevitable development trends 1 . Therefore, it is indispensable to find a more economical and lower energy consumption pressurization device to replace the compressor.…”

Section: Introductionmentioning

confidence: 99%

Design and numerical investigation of ejector for gas pressurization

Wang

Li³

et al. 2021

Asia-Pacific J Chem Eng

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Compared with the compressor, the ejector is a novel cost‐effective device to pressurize gas. Taking the regeneration natural gas pressurization process in the molecular sieve dehydration system as an example, it is first proposed to replace the compressor with an ejector to accomplish the pressurized recovery of low‐pressure regeneration natural gas. The numerical simulation method has been validated, and its results agree well with published experimental results. The simulation results indicate that the ejector designed with one‐dimensional theory can achieve the low‐pressure gas pressurization. Besides, the influence of operating parameters and structural parameters on the ejector performance is also investigated. As the discharged pressure increases, the entrainment ratio gradually decreases, but the pressure ratio rises linearly. With the increase of the induced flow pressure, the ejector pressurization range reduces. Under different discharged pressure, the entrainment ratio presents three different trends when the primary flow pressure enhances. Also, a larger nozzle exit diameter will cause the shock wave phenomenon, which is not conducive to the ejector performance, so there is an optimal nozzle exit diameter for the ejector. The length of the constant‐area mixing chamber has seldom effect on the pressure ratio. The optimal value of the NXP for entrainment ratio is equal to (0.5–1.0)d2. In conclusion, the research provides a new gas pressurization approach and a much better understanding of the gas flow and mixing process within the ejector.

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“…More than 60% of the energy produced by fossil fuels is dissipated as wasted heat, from which more than 50% is low-grade heat energy with temperatures lying lower than 275 • C [1][2][3]. Low-grade heat is also available from green energy resources like geothermal [4] and solar energy [5]; hence, utilizing low-temperature thermal energy leads to an increased thermal efficiency [6] and in the percentage of green energy [7]. Buildings, primarily for HVAC, consume about 40% of the world's primary energy and are responsible for about one-third of global CO2 emissions [8].…”

Section: Introductionmentioning

confidence: 99%

Direct Analytical Modeling for Optimal, On-Design Performance of Ejector for Simulating Heat-Driven Systems

et al. 2021

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This paper describes an ejector model for the prediction of on-design performance under available conditions. This is a direct method of calculating the optimal ejector performance (entrainment ratio or ER) without the need for iterative methods, which have been conventionally used. The values of three ejector efficiencies used to account for losses in the ejector are calculated by using a systematic approach (by employing CFD analysis) rather than the hit and trial method. Both experimental and analytical data from literature are used to validate the presented analytical model with good agreement for on-design performance. R245fa working fluid has been used for low-grade heat applications, and Engineering Equation Solver (EES) has been employed for simulating the proposed model. The presented model is suitable for integration with any thermal system model and its optimization because of its direct, non-iterative methodology. This model is a non-dimensional model and therefore requires no geometrical dimensions to be able to calculate ejector performance. The model has been validated against various experimental results, and the model is employed to generate the ejector performance curves for R245fa working fluid. In addition, system simulation results of the ejector refrigeration system (ERS) and combined cooling and power (CCP) system have been produced by using the proposed analytical model.

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Thermal modelling and optimization of low-grade waste heat driven ejector refrigeration system incorporating a direct ejector model

Cited by 37 publications

References 33 publications

Energy Analysis of a Novel Ejector-Compressor Cooling Cycle Driven by Electricity and Heat (Waste Heat or Solar Energy)

Energy Analysis of a Novel Ejector-Compressor Cooling Cycle Driven by Electricity and Heat (Waste Heat or Solar Energy)

Design and numerical investigation of ejector for gas pressurization

Direct Analytical Modeling for Optimal, On-Design Performance of Ejector for Simulating Heat-Driven Systems

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