A digital twin-based integrated optimization strategy for cascade refrigeration systems to boost energy efficiency

Applications of dual-evaporator refrigeration systems have recently gained much attention both in academia and industry due to their multiple benefits. In this study, a comprehensive thermodynamic and economic analysis is conducted to evaluate the potential of using several environmentally friendly refrigerant couples and identifies the most suitable one yielding the best economic results. To achieve this goal, a detailed parametric study is conducted, and an optimization process is performed using a particle swarm optimization (PSO) approach to minimize the unit production cost of cooling (UPCC) of the cascade refrigeration system. The results showed that among all selected 18 refrigerant pairs and for all ranges of examined operating parameters, the R170-R161 pair and R1150-R1234yf pair are identified as the best and worst pairs, respectively, from both thermodynamic and economic viewpoints. The results also confirm that R170-R161 pair has an improvement over R717-R744, used as a typical refrigerant pair of cascade refrigeration cycles. For a base case analysis, the COP of R170-R161 and R1150-R1234yf pairs is determined as 1.727 and 1.552, respectively, while their UPCC is found to be $0.395/ton-hr and $0.419/ton-hr, respectively, showing the influence of proper selection of refrigerant pairs on the cascade cycle’s performance. Overall, this study offers a useful thermodynamic and economic insight regarding the selection of proper refrigerant pairs for a dual-evaporator cascade vapor compression refrigeration system.

The refrigeration system is one of the most important and critical utility systems in the chemical and petrochemical industries. The traditional cascade refrigeration system (CRS) has been used for decades in ethylene plants. However, the mixed refrigerant system (MRS) with higher energy efficiency and less capital expenses than CRS has not widely been applied in ethylene plants. In this paper, a general methodology has been proposed for the synthesis of a tertiary refrigerant of MRS containing a mixture of methane, ethylene and propylene that can satisfy all the cooling/heating refrigeration that the traditional ethylene–propylene CRS serves in an ethylene plant. The exergy-temperature chart combined with the exergy analysis is presented to analyze comprehensively the thermodynamic nature of both CRS and MRS. Furthermore, the comparison of economic performances of these two different systems is also conducted. The efficacy of the developed MRS methodology has been demonstrated by a case study, where the ...

Several media report highlight on that the pharmaceutical companies require ultra-low temperatures -80°C to transport and store its COVID-19 vaccines. This research presents the thermodynamic analysis on cascade refrigeration system (CRS) with several refrigerant pairs which are R32/R170, R123/R170, R134a/R170, R404A/R170, R407c/R170, R410/R170, and the hydrocarbon (HC) refrigerant pair Propane/Ethane, namely R290/R170. Besides, the results of R22/R170 pair, which is not recommended to be used due to phase out of R22 as per Montréal Protocol, are included as base case to compare the novel hydrocarbon pairs in CRS and the old trend of refrigerant pairs. Thermodynamic properties of all these pairs were investigated and compared under different intermediate temperature used in CRS heat exchanger, which thermally connected both the Low and High temperature cycles (LTC) and (HTC). By applying the first law of thermodynamics, the coefficients of performance (COPs) and the specific power consumptions (SPC) in kW/TR are presented and compared. In addition, by applying the second law of thermodynamics the exergetic efficiencies were estimated. The results reveal the promising opportunity of using the HC pair (R290/R170). The minimum SPC in kW/TR is recorded for the pair R123/R170. One the other hand, the highest exegetic efficiency values are observed to be 40%, 38%, and 35% for the pairs R123/R170, R290/R170, and R134/R170, respectively. This research concludes that the HC pair (R290/R170) is highly recommended for CRS applications either to transport the COVID-19 or store it in cold storage rooms in hospitals and clinics. All precautionary measures should be carefully applied in design and operation of HC pair (R290/R170) due to its flammability hazard.

Experimental evaluation of low-GWP refrigerants R513A, R1234yf and R436A as alternatives for R134a in a cascade refrigeration cycle with R744

The cascade refrigeration system with two-stage compression (CRST) with R1150/R717 as the refrigerant group was studied to replace the three-stage cascade refrigeration system (TCRS) with R1150/R41/R717 as the refrigerant group, aiming to improve the operational efficiency of the industrial refrigeration system in the temperature range of −120°C to −80°C. This paper selected typical cities in five major climatic zones in China to analyze the coefficient of performance (COP), annual total power consumption, and seasonal energy efficiency ratio (SEER) of CRST and TCRS under different climatic conditions based on compressor discharge temperature, compressor input power, COP, and thermodynamic perfectibility. According to the results, the compressor input power of CRST is 1.45–1.61 kW lower than that of TCRS. CRST improved by 7.0%–11.7% in terms of COP and thermodynamic perfectibility. The seasonal performance analysis compared the CRST and TCRS operating in five different climate zones; the SEER of CRST increased by 26.3%–29.2%. CRST has a significant energy-saving effect, with an annual total power consumption of 8.6%–10.2% lower than that of TCRS. Finally, in the evaporation temperature range of −120°C to −80°C, the technical scheme of using CRST to replace TCRS in different climate zones is entirely feasible.

Thermodynamic and economic performance comparison between reverse Brayton cycles and cascade refrigeration cycles with eco-friendly refrigerants

Coupling Refrigeration System Synthesis and Heat Exchanger Network Design

A comprehensive exergy-based evaluation on cascade absorption-compression refrigeration system for low temperature applications - exergy, exergoeconomic, and exergoenvironmental assessments

Ultra-low temperature chillers have seen increasing demand with the advancement of semiconductor technology. Mixed refrigerant (MR) cascade refrigeration systems (CRSs) are widely utilized for their stability and high cooling performance at low temperatures. Extensive research has been conducted on optimizing MR, which has a significant impact on CRS performance. However, most previous studies have either fixed the system pressure or used the refrigeration effect as the sole performance indicator. This did not account for the potential of achieving higher performance with an optimal MR composition at the same target temperature. In this study, a detailed parametric analysis was performed to investigate how the mass fractions of high-, mid-, and low boiling point refrigerants affect the coefficient of performance (COP) and exergy in ultra-low temperature CRSs without fixing the suction pressure. The analysis revealed that at the point of maximum COP, the refrigeration effect was relatively low, highlighting the limitations of using the refrigeration effect alone as a performance indicator. Additionally, COP was found to inversely correlate with total exergy destruction. As cascade temperature increases, COP tends to decrease, emphasizing the need for appropriate cascade temperature selection for MR CRS performance. This study introduces a novel approach to optimizing MR composition under various operating conditions, contributing to the advancement of ultra-low temperature CRSs.

Energy, environmental, and economic analysis of novel R744/R290 cascade refrigeration systems designed for warm ambient conditions utilizing ejector

Comparative analysis of thermodynamic performance of a cascade refrigeration system for refrigerant couples R41/R404A and R23/R404A

A Cascade refrigeration system using mixture of carbon dioxide and hydrocarbons for low temperature applications

This work focuses on the thermodynamic behaviour of the humid air from a refrigerated space as the working fluid of a cascade refrigeration system with an inverse Brayton cycle as the bottom sub-cycle. The integration of this technology with a conventional NH3 compression cycle for a cold store application overcomes some of their respective drawbacks. The cold heat exchanger is replaced by an inlet port delivering the cold air from the turbine and the heat load due to the air fan is therefore eliminated. The effect of temperature and pressure drop within the turbine brings the fluid to the vapour content saturation and ice formation. In this study, the fluid’s transformation is analyzed as a series of equilibrium states for a realistic estimation of the outlet air conditions. Finally, a first screening of the relevant design parameters for an overall system optimization is presented, showing that the efficiency gap of the Brayton cycle can be reduced in this cascade configuration.

The paper analyzes electric energy consumption of three different refrigeration installations: cascade refrigeration system with R134a in the high temperature circuit and CO2 in the low temperature circuit, single stage refrigeration system operating with R404A and two-stage transcritical CO2 system. The indirect impact of the refrigeration system on global warming through electric energy consumption was examined. Thermodynamic cycles of these installations have been described and models have been developed to analyze the electric energy consumption required to drive the compressor as the largest consumer, for the cooling capacity of the evaporator 5,7 kW at evaporation temperature -30 °C for meteorological 2017, in the city of Belgrade. As a basis for comparative analysis, the existing cascade refrigeration system, which is located in the Laboratory for Thermal Science at the Faculty of Mechanical Engineering in Belgrade, was selected.

The cascade refrigeration systems (CRS) used in hypermarkets and supermarkets, which are used by many people, have been employing R744 for the low-temperature cycle (LTC) and R404A for the high-temperature cycle (HTC) due to environmental and public safety issues. However, the use of R404A is limited due to its high GWP, and therefore research on alternative refrigerants is necessary. Nevertheless, there is no detailed study in the literature that compares and analyzes the three refrigerants for practical design by applying R744 for LTC and R404A, R448A, and R449A for HTC in CRS. Therefore, this study aims to provide data for the practical detailed design of an alternative system to R744/R404A CRS. Under standard conditions, we analyzed how the exergy destruction rate (EDR) and exergy efficiency (EE) of the system and the EDR of each component change when the important factors affecting CRS (degree of superheating (DSH), degree of subcooling (DSC), and internal heat exchanger (IHX) efficiency of HTC, DSH of LTC, condensation temperature (CT), evaporation temperature (ET), cascade evaporation temperature (CET), and temperature difference of CHX) are varied over a wide range. The main conclusions are as follows. (1) Under the given constant conditions, the smallest change in system EDR based on R448A is DSH of HTC (decreased by 0.07–0.1 kW), followed by IHX of HTC (decreased by 0.12–0.3 kW), DSH of LTC (increased by 0.19–0.25 kW), DSC of HTC (decreased by 0.59–0.69 kW), temperature difference of CHX (increased by 1.57–1.83 kW), CET (decreased and then increased by 0.67–4.43 kW), CT (increased by 1.49–3.9 kW), ET (decreased by 2.39–4.61 kW). (2) The highest change rate of system EE based on R448A is CET (increased and then decreased by 1.38–8.28%), followed by temperature difference of CHX (decreased by 2.96–3.16%), ET (increased and then decreased by 0.63–2.75%), DSC of HTC (increased by 1.26–1.34%), CT (increased and then decreased by 0.24–1.12%), IHX of HTC (increased by 0.11–1.02%), DSH of LTC (decreased by 0.35–0.49%), and DSH of HTC (increased by 0.14–0.19%).