Carbon Dioxide Refrigeration Research Articles

A Preliminary Study of a Prototype Cryoablation Needle on Porcine Livers for Pancreatic Cancer Treatment.

Background and Aims: Despite its relatively low incidence rate compared to others, pancreatic cancer has a poor prognosis owing to its late detection and poor response to systemic chemotherapy. Because the effectiveness of chemotherapy is still restricted, the need for locoregional treatment is increasing. Cryoablation is an effective and minimally invasive treatment for some cancers, but its efficiency in pancreatic cancer is limited. Despite recent reports about promising outcomes, the optimal method and conditions of treatment are not known. In this preliminary study, we aimed to develop a cryoablation needle which can control the ablated area considering application through endoscopic ultrasonography. Methods: Here, we used a novel cryoneedle cooling system which can adjust the ablation range based on a liquid carbon dioxide refrigerant. Applied to the livers of swine, the cryoablation needle rapidly reached -60 °C within 30 s and cryoablation was performed for approximately 240 s. Based on the distance and depth, we collected real-time temperature data during the procedure. To compare the extent of cell death over time, tissue samples were collected hourly from 3 to 6 h after the procedure. Results: Approximately 4-5 mm of tissue was ablated via cryoablation, and cell death progressed over time after cryoablation. Moreover, the ablated lesions could be regulated using an insulating agent on the needle. Conclusions: This preliminary study on a novel surgical cooling needle system compatible with endoscopic ultrasound for cryoablation-based pancreatic cancer treatment confirmed the efficacy of cryoablation and identified the conditions necessary to induce necrosis. Additionally, this study evaluated the effectiveness of the insulation component of the system in protecting normal cells and assessed the extent of necrosis over time after the procedure.

Tribological performance of lubricating oils with iron tribopairs under elevated temperature and pressure in carbon dioxide refrigerant

Recent interest in carbon dioxide-based refrigeration has increased. Despite the positive environmental impacts, carbon dioxide makes a complex refrigerant due to elevated pressures and temperatures inside the compressor and the reactivity of CO2 with the lubricant. Tribological experiments were performed using synthetic oils paired with ductile iron tribo-pairs under high pressure CO2. The three lubricants investigated were PAG (Polyalkylene Glycol) and two POE (Polyolester) oils of different viscosities. Elevated temperatures resulted in higher unstable COF for POE and quicker corrosion and degradation of the tribolayer on the surface. In the case of POE, corrosion is significant in causing unstable COF performance at higher temperatures as the ester groups in POE result in more reactivity with the iron surface.

A new multi‐objective optimization of refrigeration cycles (Case study: “Optimization of transcritical carbon dioxide cycle”)

AbstractFor store and maintain products, ingredients, and other perishables at a safe temperature, there is a growing need for low‐temperature refrigeration systems. In this study, a new multi‐objective exergetic criterion is proposed for the optimization of refrigeration cycles, the conventional coefficient of performance (COP) maximization method results in high evaporator temperature, which is in contrast with the philosophy of the invention and design of refrigeration cycles. Thus, it is not a suitable platform for comparing different refrigeration cycles. This research aims to define a practical performance analysis parameter for designing and comparing refrigeration cycles. The novelty of this research is incorporating the impact of evaporator temperature into the COP concept. A performance comparison of the multi‐objective optimization is drawn with that of the maximum COP state on a transcritical carbon dioxide refrigeration cycle. According to the comparison, the evaporator temperature at the optimal state of multi‐objective exergetic optimization was 44 K lower than that of the maximum COP state, which demonstrates the excellent performance of the method. The results of the new multi‐objective exergetic optimization can be used to design low‐temperature evaporation refrigeration cycles. In the end, the flowchart of the suggested performance optimization is presented. Exergy of power at the optimal point of exergetic optimization is about 77% higher than the maximum COP. A comparison of the results obtained from maximum performance coefficient with optimal point of exergetic optimization suggests that the performance coefficient at optimum state of exergetic optimization is about 58% lower than the maximum COP.

Synergetic characteristic of a novel thermally-driven CCHP system based on supercritical and transcritical CO2 cycles

A novel poly-generation system is proposed based on supercritical carbon dioxide (SCO2) Brayton cycle and transcritical carbon dioxide (TCO2) refrigeration cycle to meet the seasonal energy demand in buildings. The thermodynamic model of the combined cooling, heating and power (CCHP) system was constructed based on the laws of thermodynamics, and seasonal operation modes were also analyzed. The Techno-economic performance of CCHP system was analyzed and compared with the single output systems and organic working fluids. The results show that the temperature of the turbine inlet in SCO2 cycle should be close to the heat source temperature and the temperature of the condenser outlet should be close to the critical temperature. The optimal pressure of the condenser outlet for coefficient of performance is about 9.3 MPa, while it is 8.6 MPa for power generation. The optimum thermodynamic and economic performance cannot be achieved simultaneously. The power generation of CO2 is 13.13% worse than that of organic working fluids and coefficient of performance of former is worse than that of latter. As the manufacturing cost goes down over time, the CCHP system based on CO2 will further improve its economic performance in the future.

Optimization and Analysis of an Integrated Liquefaction Process for Hydrogen and Natural Gas Utilizing Mixed Refrigerant Pre-Cooling

Liquefying hydrogen is an efficient way to store and transport hydrogen. However, the hydrogen liquefaction process is energy intensive. Therefore, an integrated liquefaction process of hydrogen and natural gas utilizing the mixed refrigerant cycle and the hydrogen Claude cycle is proposed. The process not only couples a steam methane reforming process to produce hydrogen and a carbon dioxide refrigeration cycle to assist in pre-cooling, but also employs a solar energy absorption refrigeration system to enhance energy efficiency. The proposed process is simulated and optimized using HYSYS and the particle swarm optimization algorithm, and energy, exergy, and economic analyses are performed. The energy analysis shows that the specific energy consumption of the proposed process is 5.2201 kWh/kg, a reduction of 10.67% compared to the base case. The exergy loss and exergy efficiency are 64,904 kW and 62.21%, which are 13.63% and 6.63% lower than the base case, respectively. The economic analysis shows that the total annualized cost of the process is USD 28.6 million per year. The proposed integrated liquefaction process not only realizes the high efficiency of energy utilization but also follows the development trend of integrated energy systems.

Thermodynamic investigation of a centrifugal reverse Brayton cycle for refrigeration in air conditioning filed

The reverse Brayton cycle (RBC) is known to exhibit a lower coefficient of performance (COP) when compared to conventional vapor-compression refrigeration systems. To tackle this issue, this study proposes a centrifugal reverse Brayton cycle (CRBC) that features a rotating heat exchanger, which utilizes the conversion mechanism between equal potential energy and pressure energy to enhance system performance. The findings indicate that the COP of the CRBC is roughly inversely proportional to the working fluid density, making CO2 a more suitable option for CRBC systems than conventional working fluids. We propose three different cycles for the CRBC system: the diamond cycle, trapezoid cycle, and rectangle cycle. From both technical and operational perspectives, the trapezoid cycle appears to be the preferred choice for CRBC. When the isentropic efficiency of the CRBC system exceeds 95%, its coefficient of performance (COP) ranges from 5.31 to 5.7, whereas the COP of transcritical carbon dioxide refrigeration cycle (tCO2), air RBC, and CO2 RBC are around 4.3, 1.9, and 0.79, respectively. This suggests that the performance of the CRBC system surpasses that of RBC by a significant margin, while achieving comparable performance to conventional vapor compression refrigeration systems. Moreover, the dimensionless power reflecting the installation capacity requirements for CRBC, tCO2, air RBC and CO2 RBC are around 0.2, 0.35, 5.3 and 1.9, respectively. This indicates that the compressor/expander capacity demand for system CRBC approaches the thermodynamic minimum.

Performance analysis of a new mechanical superheat coupled-orc refrigeration system with thermoelectric conversion

This paper proposes a new refrigeration and energy conversion system, namely Expander Mechanical Overheating-Organic Rankine Cycle (EMO-ORC) system. Compared with the existing carbon dioxide (R744) refrigeration system, the new system can not only improve the coefficient of performance (COP) of the system and reduce the discharge pressure, but also effectively recover the waste heat of the system, and convert it into electrical energy. Simulation were conducted to compare its system performance with R744 refrigeration system (with heat exchanger), at the same time, the effect of different factors on the performance of new system is analyzed. The results demonstrate that, at the same evaporation temperature and gas cooler outlet temperature, compared with the system (with heat exchanger), the COP of the new system increased by 8.2% and 8.9% on average, respectively. And the discharge pressure decreased by 0.88% and 0.79%, respectively. In the given superheat degree range, compared with the system(with heat exchanger), the COP of the new system is increased by 4.5% on average, and increased by 10.2% at the highest level. Under the most given working conditions, the cooling capacity of new system is higher than that of the system (with heat exchanger), and the power consumption is lower than that of the system (with heat exchanger). In the new system, the narrow point temperature difference and the outlet temperature of the first stage gas cooler have a greater impact on the COP, with the increase of both, the COP of the new system increases by 5.6% and decreases by13.7%, respectively.

Improvement design and performance assessment of combined cooling and power system using CO2 for waste heat recovery

Waste heat recovery (WHR) is an efficient approach to reducing fossil fuel consumptions and carbon dioxide emissions. In shipboards, gas turbine exhaust can be recovered to simultaneously produce power and cooling for meeting the actual need of marine. The supercritical carbon dioxide (sCO2) power cycles and transcritical carbon dioxide (tCO2) refrigeration cycles have many advantages of compact layout, high efficiency, and environmentally friendly property. Accordingly, combined cooling and power systems (CCPs) integrating sCO2 power cycle with tCO2 refrigeration cycle are considered as competitive and promising WHR systems. However, a large space is still left for CCP to improve its overall performance. In this study, a novel CCP is proposed based on two traditional CCPs. Mathematical models are developed based on the software MATLAB to conduct quantitative parametric analyses, three-objective optimizations and exergy analyses on these systems. The results indicate that compared with two traditional systems, the proposed system can enhance net power output by 40.185% and 35.743% while obtaining a comparable refrigeration capacity and total product unit cost. Exergy analysis indicates that the maximum exergy destructions occur in recuperators and cooler, and the proposed system can significantly reduce exergy destructions in these components compared with two traditional systems.

Performance evaluation of trans-critical carbon dioxide refrigeration system integrated with porous internal heat exchange

Performance evaluation of trans-critical carbon dioxide refrigeration system integrated with porous internal heat exchange

Blade design and analysis of centrifugal compressors for the transcritical carbon dioxide refrigeration cycle

The compressor is one important component in the transcritical CO2 (carbon dioxide) refrigeration cycle. The CO2 compressor has a small volume at the same refrigeration capacity because its refrigeration capacity per unit volume is large. The radial compressor often used in the CO2 refrigeration cycle has complex internal flow and difficult blade modeling. The paper presented a new centrifugal compressor with radial flow, whose blades are straight and easy to process. Taking a single stage compressor blade for example, the effects of the velocity coefficient, energy head coefficient, rotational speed of the moving blade, blade height, inlet radius and radial distance of the blade on the efficiency and pressure ratio were studied. According to the conclusions, the paper designed and simulated the blades of two compressors of the transcritical CO2 two-stage refrigeration cycle. Simulation result showed that the efficiencies of the two compressors were respectively 84.97% and 87.23%.

Energy, Exergy, and Economic (3E) Analysis of Transcritical Carbon Dioxide Refrigeration System Based on ORC System

This paper used the energy, exergy, and economic analysis of a carbon dioxide (CO2) transcritical two-stage compression system based on organic Rankine cycle (ORC) waste heat recovery technology. When the intermediate pressure and high-pressure compressor outlet pressure were changed, respectively, this study simulated the change in system energy efficiency by adding the ORC for waste heat recovery, calculated the ratio of exergy loss of each component, and performed an economic analysis of the coupled system. The results show that adding waste heat recovery can effectively increase the energy efficiency of the system, and among all components, the heat exchanger had the largest exergy loss, while the evaporator had the highest capital investment and maintenance costs.

An Improved Geometric Theoretical Model and Throughflow Prediction Method for a CO2 Scroll Compressor of Automotive Air Conditioning System

The scroll-type compressor is the core component of the refrigeration system using the natural refrigerant carbon dioxide. An accurate scroll geometric theoretical model is essential for evaluating and enhancing compressor performance. The present paper proposed and validated an improved geometric theoretical model of a scroll compressor. A vector triangle method-based general piecewise function describes precisely the volume variation of the working chambers, based on which the transient throughflow modeling and performance evaluation of a carbon dioxide scroll compressor were conducted. The mechanisms and influencing factors of the suction precompression and the asymmetry discharging were analyzed. The results indicate that the strength of the suction precompression is mainly influenced by the suction vacuum under different rotating speeds, partly associated with the tangential leakage under low rotating speeds. The increasing initial suction pressure contributes to the linear raising of the pressure difference between suction initial and ending pressures, decreasing the precompression extension slightly. The variation of the discharge throughflow areas of two symmetric discharge chambers dominates the pressure asymmetry, which is gradually eliminated by the overlapping throughflow area. Compared with the circular discharge structure, the waist-shape port reduces the pressure asymmetry degree and shortens its duration.

Impact of a thermoelectric subcooler heat exchanger on a carbon dioxide transcritical refrigeration facility

To improve the performance of vapour compression refrigeration cycles, the inclusion of a thermoelectric subcooler for low-medium power units has been the focus of recent studies due to its robustness, compactness and simplicity of operation. In thermoelectric systems, it has been demonstrated that the heat exchangers used in the hot and cold side of the thermoelectric modules have a critical impact in the performance of the system. This influence has not yet been studied for thermoelectric subcooling systems in vapour compression cycles. This work, for the first time, evaluates the impact that the heat exchangers of a thermoelectric subcooler, included in a transcritical carbon dioxide refrigeration cycle, have, in the performance of the refrigeration cycle. The influence is quantified in terms of: optimum working conditions, coefficient of performance and cooling capacity. The results show that, through an optimization of the heat exchangers of the thermoelectric subcooler, the performance improvements on the coefficient of performance using this technology are boosted from 11.96 to 14.75 % and the upgrade in the cooling capacity of the system rises from 21.4 to 26.3 %. Moreover, the optimum gas-cooler working pressure of the system is reduced and the optimum voltage supplied to the thermoelectric modules increases.

Performance assessment of an experimental CO[formula omitted] transcritical refrigeration plant working with a thermoelectric subcooler in combination with an internal heat exchanger

Regulations in the refrigeration sector are forcing the transition to low global warming potential fluids such as carbon dioxide in order to decrease direct greenhouse gases emissions. Several technologies have arisen over the past years to compensate the low performance of the transcritical carbon dioxide vapour compression cycle at high ambient temperatures. For low–medium power units, the inclusion of a thermoelectric subcooler or an internal heat exchanger have been proven as effective solutions for enhancing the coefficient of performance. However, the combination of a thermoelectric subcooler and an internal heat exchanger working simultaneously is yet to be explored theoretically or experimentally. This work presents, for the first time, an experimental transcritical carbon dioxide refrigeration facility that works simultaneously with a thermoelectric subcooler and with an internal heat exchanger in order to boost the cooling capacity and coefficient of performance of the refrigeration system. The experimental tests report improvements at optimum working conditions of 22.4% in the coefficient of performance and an enhancement in the cooling capacity of 22.5%. The 22.4% increase in coefficient of performance would result in a decrease of energy consumption along a reduction of the greenhouse gases emissions. The proposed combination of a thermoelectric subcooler and an internal heat exchanger outperforms each of the technologies on their own and presents itself as a great controllable solution to boost the performance and reduce the greenhouse gasses emissions of transcritical carbon dioxide refrigeration cycles.

Experimental evaluation of a transcritical CO[formula omitted] refrigeration facility working with an internal heat exchanger and a thermoelectric subcooler: Performance assessment and comparative

The use of carbon dioxide in transcritical state has become one of the most used solutions to comply with the F-Gas directive and reduce greenhouse gases emissions from refrigeration systems at high ambient temperatures. For low-medium power units, the commonly used solutions to improve the efficiency such as the ejector, multiple compressor arrangements, mechanical subcooler, etc., add complexity and increase the cost of the refrigeration facility, which is not ideal for small units. In this low-medium power range, two technologies stand out to increase the performance of a carbon dioxide transcritical cycle: the internal heat exchanger and the thermoelectric subcooler. This study brings a complete research in which both solutions have been tested in the same experimental transcritical carbon dioxide refrigeration facility under the same working conditions. It focuses on the real performance of both systems and discusses the strengths and weaknesses of using an internal heat exchanger or a thermoelectric subcooler. The results show that the thermoelectric subcooler outperforms the internal heat exchanger in both the coefficient of performance and the cooling capacity while also being a more controllable and flexible solution.

Experimental study on improved performance of an automotive CO2 air conditioning system with an evaporative gas cooler

A well-known challenge in the application of carbon dioxide (CO2) refrigerant for vehicles is the great energy efficiency attenuation in hot climates. In attempting to solve this problem, a novel design integrating evaporative cooling with automotive CO2 air conditioning system, where water was sprayed to the gas cooler, was introduced and experimentally investigated in present work. Results illustrate that with this design the CO2 temperature leaving gas cooler could be reduced to a lower level or even below the outdoor air temperature, thus inducing a significant performance improvement. A coefficient of performance (COP) enhancement percentage of 42.4% was achieved at 35°C outdoor condition. This percentage was increased up to 52.9% when outdoor air temperature increased to 45°C. With the decreased outdoor air velocity and the decreased outdoor air humidity, the merit of this design was more significant. These indicate that the evaporative gas cooler is a promising technology to alleviate the problem of performance deterioration in hot and dry weather conditions. A reduced spray water temperature could not cause a significant change in the COP enhancement. This may be attributed to that the sensible heat during droplet heat-up period was negligible compared to the latent heat of droplet evaporation. When the surface position of gas cooler chosen to be sprayed was moved from CO2 inlet to CO2 outlet, the COP enhancement increased, which suggests that water should be sprayed to the area where wall temperature is low.

Corrigendum for “Effect of using a porous gas cooler on the performance of trans‐critical carbon dioxide refrigeration cycle”

Corrigendum for “Effect of using a porous gas cooler on the performance of trans‐critical carbon dioxide refrigeration cycle”

Effect of using a porous gas cooler on the performance of trans‐critical carbon dioxide refrigeration cycle

AbstractUsing porous gas coolers is a novel method that can be used to enhance performance parameters in the trans‐critical carbon dioxide refrigeration cycle. The behavior of trans‐critical carbon dioxide and the effect of using porous gas coolers in refrigeration systems are researched in this experimental study. Cycle coefficient of performance, heat rejection rate, evaporator cooling capacity, evaporator cooling capacity enhancement factor, coefficient of performance enhancement factor, power consumption per ton of refrigeration, and pressure drop were investigated as functions of gas cooler outlet temperature, gas cooler porosity, gas cooler pressure ratio, and air ambient temperature. Porosities of 100% (empty gas cooler; no steel balls are used during this test), 48%, 40%, and 34% were considered. Experiments were conducted at 4°C evaporating temperature and 5°C superheat. Evaporator cooling capacity and evaporator cooling capacity enhancement factor are increased by about 103% and 35.4% when reducing gas cooler outlet temperature and porosity up to 36°C and 34%, respectively. Results of this study showed that cycle coefficient of performance, coefficient of performance enhancement factor, and gas cooler heat rejection rate can be increased up to 94.4%, 55.8%, and 85.5%, respectively when reducing gas cooler porosity and gas cooler outlet temperature up to 34% and 36°C. Increasing the gas‐cooler pressure ratio up to 1.341 and reducing gas cooler porosity up to 34% resulted in an increase of about 76.2% in the coefficient of performance. A decrease in power consumption per ton of refrigeration by about 43.9% is recorded when decreasing gas cooler inlet pressure and porosity up to 84 bars and 34%, respectively. Experiments revealed that a decrease in pressure drop of about 43.7% can be achieved by increasing gas cooler outlet temperature up to 52.1°C and keeping gas cooler porosity at 34%. The cycle coefficient of performance can be increased by decreasing air outside ambient temperature.

Experimental investigation of a novel cascade refrigeration system with a CO2 sublimation cycle as the lower stage

• A cascade system with a CO 2 sublimation cycle in the lower stage is experimentally investigated. • Continuous operation below the triple pressure of CO 2 has been realized. • The transient behaviors and blocking issues as an example case are discussed. • In addition, HFE 7500 is used as carrier-fluid to reduce the blockages. • The performance of the system both with and without the carrier-fluid is investigated at different sublimation temperatures. • Optimization potentials of the system are analyzed. Some studies in recent years have shown the possibility of extending the application temperature of the natural refrigerant carbon dioxide (CO 2 ) below its triple point. Thus, CO 2 could be a potential alternative refrigerant for R-23 in ultralow-temperature (ULT) refrigeration systems. This paper introduces a special cascade system, whose lower stage can be switched between a CO 2 sublimation cycle and a conventional R-23 cycle, so that both cycles can be compared directly under the same ambient conditions. The sublimation system features a unique sublimation heat exchanger, which allows the operation with an extra carrier fluid in order to improve the heat transfer and reduce the blockage by solid CO 2 . In this study, experiments were carried out using HFE-7500 as the carrier fluid (“wet sublimation”) as well as without the carrier fluid (“dry” sublimation). The system was able to be operated continuously in both operating mode. A refrigerating capacity of 600 W was achieved at a sublimation temperature of -79°C. The transient behavior and blocking issues of the system are discussed. The efficiency of the sublimation system during stable operations are compared with the result of the reference R-23 system. It shows that there is still large potential for improvement on the system performance of the CO 2 sublimation system.

Energy and Exergy Analysis of Transcritical Carbon Dioxide Refrigeration Cycle

The effects of conventional refrigerants on ozone layer and its effect on global warming are known. Refrigerants based on chlorofluorocarbons (CFC) and hydrochlorofluorocarbons (HCFCs) have been used in refrigeration systems for a long time and are still being used. Instead of these refrigerants, the use of natural refrigerants which are much less harmful to the environment, has been given importance. Carbon dioxide is the first that comes to mind among these fluids. In this study, energy and exergy analysis of transcritical carbon dioxide refrigeration cycle examined as theoretically. Energy and exergy analysis were made for different evaporator temperatures and outlet temperatures from gas cooler. Exergy losses of each component of the transcritical carbon dioxide refrigeration cycle were determined. In addition, the first and second law efficiencies of the refrigeration cycle were determined. When the evaporator temperature is -5 oC and the outlet temperature from the gas cooler is 20 oC, the highest exergy efficiency value was determined as 41.19 in this study.