Cascade Cycle Research Articles

Energy and exergy analyses of a solar-driven ejector-cascade heat pump cycle

To improve the performance of an air-source heat pump cycle under low ambient temperature, a solar-driven ejector-cascade heat pump cycle which consists of an ejector sub-cycle and a vapor compression sub-cycle is discussed. Energy and exergy models are developed to conduct analyses on the cascade cycle, in which the ejector sub-cycle takes R134a, R1234yf or R141b as a working fluid and the vapor compression sub-cycle uses R1234yf as a refrigerant. The results indicate that the proposed cycle can significantly improve the thermodynamic performance of the air-source heat pump under low ambient temperature, especially when the ejector sub-cycle employs an R141b ejector. Energy investigation finds that the variation of the thermal coefficient of performance (COPh) exhibits the opposite trend to that of the mechanical coefficient of performance (COPm) as the generation temperature, the intermediate condensation/evaporation temperature or the condensation temperature varies. Exergy analysis indicates that the exergy destructions in the solar collector-generator, the ejector, the compressor and the expansion valve of vapor compression sub-cycle are much larger than those in other components. We hence conclude that decreasing various losses in these components are the key tasks to improve the performance and exergy efficiency of the cascade system.

Comparative investigation and multi objective design optimization of R744/R717, R744/R134a and R744/R1234yf cascade rerfigeration systems

This study aims to make a comparative investigation on performance analysis of cascade refrigeration systems using R744/R717, R744/R134a, and R744/R1234yf refrigerant pairs. Artificial Cooperative Search methaheuristic algorithm is put into practice to obtain the optimal values of eight design parameters including Condenser and evaporator temperature, R744 condensing temperature, temperature difference in the cascade condenser, and amount of subcooling and superheating at the bottom and the top of the cascade cycle. Second law efficiency and total annual cost of the cascade refrigeration system are chosen as design objectives to be optimized individually and concurrently in order to obtain the optimal operating conditions of the system. Single optimization results show that R744/R1234yf system has the lowest operating cost while having the highest second law efficiency compared to other cycle configurations. A set of non-dominated solutions obtained through multi objective Artificial Cooperative Search algorithm is represented in the form of Pareto front and the best result is chosen from the well-reputed decision makers of TOPSIS and LINMAP for each cycle configuration. Multi objective optimization results reveal that design variables of the refrigeration system can create a trade off between problem objectives. A sensitivity analysis is performed to investigate the influences of varying values of design variables upon problem objectives while the system is operated under optimal conditions.

Thermodynamic analysis of a new cascade ORC and transcritical CO2 cycle to recover energy from medium temperature heat source and liquefied natural gas

In this paper, a novel cascade cycle is proposed to recover energy from a medium temperature waste stream and a liquefied natural gas vaporization unit simultaneously. To analyze the system, its performance is compared with a single organic Rankine cycle and a single transcritical carbon dioxide cycle at the same operation conditions. Both energy and exergy analyses are applied to the system. In addition, different working fluids are examined in this study. In order to find the best configuration and working fluid, optimization algorithm is utilized. Results showed that the best performance is for a cascade cycle with Pentane as working fluid for ORC section. Its exergy efficiency is evaluated 13.08%, while the highest exergy efficiency for an ORC and a transcritical CO2 cycle is 12.3% and 11.24%, respectively. This increase in efficiency is because of better thermal match between hot and cold streams in vapor generator and condenser sections. Based on the exergy analysis, the highest rate of exergy destruction in all cycles belongs to the preheater and condenser respectively. Finally, sensitivity analysis showed that in the proposed cascade cycle, ORC’s condenser pressure and pinch temperature of the heat exchanger are the most important parameters which can significantly affect the system performance and their value should be selected carefully.

Venus Lander Electronics Payload Thermal Management Using a Multistage Refrigeration System

This paper presents the analysis and optimization of multistage refrigeration thermal control system for use in cooling electronics payloads on Venus lander missions. The paper outlines the challenges associated with thermal management of electronics in the extreme temperature and pressure environment of Venus. The multistage cascaded vapor compression refrigeration is comprised of a topping cycle using methyl linoleate fatty acid methyl ester with intermediate Supercritical Carbon Dioxide and Transcritical Carbon Dioxide cycles and a bottoming cycle using R-410A refrigerant. Results for analysis optimization of the cascade cycle using MATLAB’s genetic algorithm are presented, which demonstrate the effect of the low-side evaporator pressure on the coefficient of performance of the system. A study of the bottoming working fluid selection shows Ammonia to be a better candidate working fluid for the bottoming cycle than R-410A refrigerant. The paper then presents analysis results for the four-stage cascade refrigeration cycle Ammonia/Supercritical Carbon Dioxide/Transcritical Carbon Dioxide/Methyl Linoleate Fatty Acid Methyl Ester for a refrigeration effect of 100 W with payload at 100°C and a hot-sink temperature of 465°C, lending an optimized total cycle compressor power of approximately 115 W corresponding to a coefficient of performance of 0.87 for the cascade system. The paper presents preliminary design of the heat-rejection system radiator used to interface the cascaded system to the Venus atmosphere.

Enhancement of a Boil-off Gas Re-liquefaction System with Cascade Cycle

Enhancement of a Boil-off Gas Re-liquefaction System with Cascade Cycle

Design and experimental study of an air source heat pump for drying with dual modes of single stage and cascade cycle

The heat pump drying system is a prospect technology for material drying due to its advantages of high efficiency and energy saving. This paper presents a design of an air source heat pump with dual modes for drying. The operation mode changes between a single stage and a cascade cycle to satisfy the heating demand under different ambient temperatures. A prototype of this dual-mode heat pump is developed using R22 and R134a as refrigerants. To verify the feasibility and to investigate the characteristics of this heat pump, an experimental study is carried out. According to the results of this study, the supplying air temperatures satisfied the drying demand (70 °C) when the heat pump operated at its design condition which is an ambient temperature of 0 °C for the cascade cycle and 20 °C for the single stage. With the increase of the ambient temperature, the supplying air temperature, heating capacity and electric power all increased at both operation modes. The difference of electric power between the two modes also increased with the ambient temperature, but the difference of supplying air temperature decreased. Although the variation of compressors’ pressure ratio was small within each mode, the pressure ratio of the high stage’s compressor changes a lot which was about 3.8 for the single stage and 5.5 for the cascade cycle. With the same supplying air temperature, the lines of coefficient of performance (COP) at different modes crossed each other. The COP of single stage was higher after an ambient temperature of 2 °C for the developed heat pump.

Biogas upgrading process via low-temperature CO2 liquefaction and separation

In the field of biogas upgrading, there are five conventional technologies used for CO2 removal, namely, water scrubbing, chemical and physical scrubbing, membranes and Pressure swing adsorption. The present study aims to introduce an additional method for CO2 removal. On this basis, a process of low-temperature CO2 liquefaction and separating from CH4/CO2 mixture is proposed as an alternative to the conventional upgrading technologies. The process simulation is done by Aspen HYSYS software which is a conventional chemical process simulator. In the system, four-stage compression, two low-temperature distillation columns, auxiliary refrigeration cascade cycle, expander and sufficient internal heat recovery are adopted. Installing Expander and internal heat recovery in the process can reduce the total energy penalty by 30%. with avoiding the occurrence of CO2 freeze-out, the process can achieve a reduction of CO2 concentration from 40% (mol) in raw biogas mixture to 2.9% (mol) in the upgraded biogas to meet the specification for pipeline transport or vehicle fuel (typically 2–3% CO2). Moreover, the total energy consumption is only 0.25 kWh/Nm3raw biogas with over 99.9% (mol) CO2 purity captured and produced in liquid form as a by-product for transport. Further studies are performed to show the effect of varying CO2 concentration in the feed and the capacity of the plant on different process variables. It is concluded that the system can serve as a new promising approach for CO2 removal to upgrade biogas with low energy penalty.

Preliminary theoretical analyses of thermal performance and available energy consumption of two-stage cascade cycle heat pump water heater

In this paper, the analysis model of thermal performance and available energy of two-stage cascade cycle heat pump water heater (HPWH) was established. For the first time, the equivalent transformation thermodynamic analysis method and available energy consumption equation were employed to carry out the theoretical analyses of thermal performance and available energy consumption for two-stage cascade cycle HPWH. And the correctness of the analysis approach proposed in this paper was verified by an example. The calculation results showed a significant agreement with the results derived by the first law of thermodynamics and energy conservation law. The available energy analysis of two-stage cascade cycle HPWH clearly revealed the available energy consumption rates for different working processes, including heat transfers of heat exchangers, flow of heat-carrying fluid, working medium cycle, output of hot water, etc. This approach could be conveniently used in the analyses of thermal performance and available energy consumption for actual complex thermal system with irreversible process. This paper provided the theoretical basis for the actual optimization design and operation analysis of cascade type heat pump systems, and furthermore, the results of the calculation instance would also have a certain reference value.

Supercritical CO2 Rankine cycles for waste heat recovery from gas turbine

A supercritical carbon dioxide (S-CO2) Rankine cycle for waste heat recovery (WHR) from a gas turbine can achieve high efficiency despite its simplicity and compactness in comparison to a steam/water cycle. With respect to WHR, it is very important to maximize the net output power by incorporating the utilization efficiency of the waste heat in conjunction with the cycle thermal efficiency. A simple S-CO2 Rankine cycle used for a high-temperature source cannot fully utilize the waste heat because the working fluid is preheated by the recuperator to a high temperature to achieve a high cycle efficiency. To recover the remaining waste heat from a simple cycle, a cascade cycle with a low-temperature (LT) loop can be added to the high-temperature (HT) loop, or a split cycle—in which the flow after the pump is split and preheated by the recuperator and LT heater separately, before the HT heater can be used. This study presents a comparison of three cycles in terms of energy and exergy analyses of their systems. The results show that a split cycle can produce the highest power of the threes systems considered over a wide range of operating conditions. The reasons for this are explained in detail.

Exergoeconomic analysis of cascaded organic power plant for the Port Harcourt climatic zone, Nigeria

AbstractThis paper presents the exergoeconomic analysis of a 100 kW solar driven organic Rankine cycle (ORC) power plant for the Port Harcourt climatic zone, latitude 4.5–5.5°N and longitude 6.5–7.5°E, at an ambient temperature range of 23–31°C. A cascade cycle of R134a and R290 working fluids was considered for the proposed plant. The relationships between thermodynamic properties and characteristics were formulated and numerical solutions obtained in the Microsoft Excel and MATLAB environments for the assessment of the performance of the plant. The size and mass flow rate of water through the flat plate solar collector, mass flow rates, efficiencies, and other relevant parameters of the cycles were determined. The energy and exergy efficiencies of the proposed plant, at the optimal collector operation, are 18.92 and 21.61%, respectively. The total capital investment, levelized cost of energy, payback time and the earning power of the investment were estimated to be 352 US$/kW, 0.0072 US$/kWh, 2 years 7 ...

Thermodynamic analysis of a novel ejector-cascade refrigeration cycles for freezing process applications and air-conditioning

Waste heat from the gas cooler is a form of free energy, which can be utilized to drive an ejector cooling cycle. This paper presents a new CO2 ejector-cascade refrigeration cycle. The effects of important parameters on the thermodynamic performance of the new cycle are theoretically investigated based on energetic and exergetic analyses. Furthermore, the performance comparison of the proposed cycle and conventional cycle is carried out. The theoretical study shows that the new cycle exhibits a reasonable value of COP (coefficient of performance) and system second law efficiency. For the same cooling capacity, the improvements of the maximum COP and second law efficiency could reach 37% and 12%, respectively, over those of the conventional cascade cycle under the given operating conditions and at the optimum gas cooler pressure.

Evaluation thermodynamic perfection of the cogeneration cascade machines cycles

One of the promising trends in the refrigerating engineering is building machines for industrial processes with the simultaneous use of two thermal effects (heat and cold). The fundamental possibility to build machines, operating on a complex reverse thermodynamic cycle with the production of low-grade cold and high-grade heat is considered. Such machines are called heating cascade machines. The synthesis of cyclic machine solutions for various pairs of materials, based on thermodynamic analysis by the “method of cycles” is carried out. The analysis of the supercritical cycle of the upper cascade with R744 by the entropy-cycle method is performed. It is shown that the compound Carnot-Lorenz cycle (“triangular”) should be chosen as the cycle model. The problem of determining the degree of thermodynamic perfection of the cascade cycle, which takes into account the simultaneous production of two thermal effects – cold and heat is solved. An example of the calculation of the machine characteristics under variable input parameters: temperature in the condenser-evaporator and the pressure in the gas cooler is given. The comparison with the characteristics of the cascade machine, operating in the same mode, but with one thermal effect – the production of cold, which showed the benefits of heating cycles is performed. It is proved that, given the simultaneous high temperatures of the heat produced and low temperature of the cold produced in the cascade heating machine, energy performance is quite high. General recommendations – in terms of energy saving, heating cascade units and machines, operating with R744 as a working substance of the upper cascade and the cycle in the supercritical region with the simultaneous heat and cold production should be designed.

Analysis of a novel solar electricity generation system using cascade Rankine cycle and steam screw expander

A novel solar electricity generation system (SEGS) using cascade cycle is proposed. The top and the bottom are steam Rankine cycle (SRC) and organic Rankine cycle (ORC). Particulary, screw expander (SE), which is characterized by good applicability in power conversion with steam–liquid mixture, is employed in the SRC. Steam is generated directly in the parabolic trough collectors (PTC) and expands in the SE. The heat released by steam condensation is used to drive the ORC. This type of SEGS has the advantages of avoidance of superheated steam, moderate operating temperature and pressure, low technical requirements in heat collection and storage, and suitableness for distributed power generation. Simulation of the system performance is conducted on the use of ten ORC fluids. Four hot/cold side temperatures of 473/313K, 473/293K, 523/313K and 523/293K are exemplified. The results indicate the ORC evaporation temperature corresponding to theoretical maximum solar power efficiency fails to provide a pressure ratio (PR) that matches the SE built-in PR. Off-design operation of the SE is recommended for the purpose of higher system efficiency and simpler ORC turbine. Efficiency of 13.68–15.62% for the proposed system can be achieved.

Operational optimisation of centrifugal compressors in multilevel refrigeration cycles

Low-temperature energy systems are processes that require cooling at temperatures below ambient, which are accomplished using refrigeration cycles. Little research has addressed the operational optimisation of refrigeration cycles considering the performance of existing equipment. This work develops a methodology for operational optimisation of refrigerated processes, taking into account existing centrifugal compressors. For the optimisation of multilevel cycles, the evaporation temperatures of each level are varied to find a set of operating conditions that minimise shaft work demand. The optimisation takes into account equipment constraints, including compressors on a common shaft, minimum and maximum allowable inlet flow rates, etc. Two examples are presented; the first represents a three-level refrigeration cycle and the second a cascade cycle. For the two examples, the conditions of the base case are optimised, identifying improvements of around 3% in shaft work demand. In addition, both cycles were also optimised for a range of process cooling demands.

Experimental study of R134a/R410A cascade cycle for variable refrigerant flow heat pump systems

Cascade cycle is widely applied to heat pumps operating at low ambient temperature to overcome problems such as low heating capacity and Coefficient of performance (COP) deterioration A number of researches have been conducted on cascade cycle heat pumps, but most of those studies were focused on system optimization to determine optimal intermediate temperature in air-to-water heat pumps. However, experimental optimization in regard to air and water heating simultaneously using a cascade cycle has been an understudied area. Therefore, we focused on experimental analysis for a cascade system with Variable refrigerant flow (VRF) heat pumps. Experiments were conducted under a variety of operating conditions, such as ambient and water inlet temperature. COP increased up to 16% when water inlet temperature decreased. COP of VRF heat pumps with cascade cycle is three-times higher compared with conventional boilers as well as 17% higher compared to single heat pumps.

ИСПОЛЬЗОВАНИЕ ДИОКСИДА УГЛЕРОДА КАК ЭФФЕКТИВНОГО РАБОЧЕГО ТЕЛА В ХОЛОДИЛЬНЫХ МАШИНАХ: ИСТОРИЯ, НЫНЕШНЕЕ СОСТОЯНИЕ И ПЕРСПЕКТИВЫ

As the working substance vapor compression refrigeration machines (VCRM) and heat pumps (HP) can use different gases. These include not only specifically synthesized chemical compounds, but also natural refrigerants - ammonia, carbon dioxide, hydrocarbons. Described cooling cycles useful for work a carbon dioxide (R744). Discussed subcritical, transcritical, throttle, and throttle-expander cascade cycle in which carbon dioxide used as the low-temperature refrigerant circuit. Attention paid to the analysis of the merits of carbon dioxide cycle, which enabled the compressor of Vorhis. Shows a comparison the characteristics of the throttle cycles at different temperatures cooling, one- and two-stage compression. Is set out short history of creation refrigeration units and heat pumps operating on CO2, indicated their main manufacturers producing equipment, taking into account characteristics of the working substance which be used. The advantages of heating and cooling systems working on carbon dioxide, compared with systems using alternative refrigerants.

Performance evaluation and optimal configuration analysis of a transcritical carbon dioxide/propylene cascade system with vortex tube expander in high-temperature cycle

This paper presents a theoretical investigation on the thermal performance of a natural refrigerant-based cascade refrigeration-heat pump system used to produce both heating and cooling. A parametric evaluation is also presented for carbon dioxide-propylene working pair by varying parameters like evaporating, gas cooler exit temperature, and temperature difference in the cascade heat exchanger of the system. The topping cycle of the system is provided with a vortex tube instead of an expansion valve. The maximum increase in coefficient of performance of the present system is 5.9 % compared to that of the transcritical cascade cycle without vortex tube expander, in the assumed range of operating parameters. The model predicts performance parameters and operating conditions e.g., pressure, enthalpy, temperature, and entropy at different state points. The proposed transcritical model is optimized for overall coefficient of performance, intermediate temperature, and mass flow ratio with the help of multi-linear regression analysis. The influences of main parameters on the optimum design quantities are displayed in tables and figures. The cascade refrigeration-heat pump model with carbon dioxide/propylene as refrigerants is validated by comparing the coefficient of performance values with other reference cascade systems. This study could contribute to the further development and the optimal design of carbon dioxide-propylene cascade refrigeration systems.

Analysis and efficiency enhancement of a boil-off gas reliquefaction system with cascade cycle on board LNG carriers

In this paper, an LNG boil-off gas (BOG) reliquefaction plant operating in accordance with cascade vapor compression cycles, using propylene and ethylene as refrigerants, on board LNG carriers is investigated. As consequence of the analysis results, a new and original design is proposed to reduce power consumption and improve its exergy efficiency. Through energy and exergy analysis, a thermodynamic model is carried out to analyse and evaluate operating conditions as well as to obtain performance values such as the Coefficient of Performance (COP), exergy efficiency, irreversibilities and specific energy consumption. The thermodynamic analysis is performed using the Engineering Equation Solver (EES) software environment. The results of the improved design implemented on the reliquefaction plant for LNG tank conditions of -160.82°C, a plant BOG input temperature of −125°C and 25°C seawater, give COP values of 0.22 and an exergetic efficiency of 37%, such values being 22.22% and 19.35% greater than the original design. The specific energy consumption decreases 14.66% to 0.64kWh per kg/s of natural BOG. The proposal for improving efficiency is founded on BOG cold energy recovery and BOG compression heat rejection with cooling water in the intercoolers.

Experimental evaluation of an internal heat exchanger in a CO2 subcritical refrigeration cycle with gas-cooler

We present the experimental evaluation of an internal heat exchanger or suction-line/liquid-line heat exchanger in a CO2 subcritical refrigeration plant with gas-cooler. The plant, driven by a 1.5 kW CO2 semi hermetic compressor, uses brazed plate heat exchangers as condenser, evaporator and internal heat exchanger, an air finned tube gas-cooler and an electronic expansion valves. The evaluation (77 steady-states) covers evaporating temperatures from −40 to −25 °C and condensing temperatures from −15 to 0 °C, always at the nominal speed of the compressor. Here, the effect of the internal heat exchanger on the main energy parameters is analysed, i.e., cooling capacity, COP and heat rejection at gas-cooler and condenser. Also, the effect of the internal heat exchanger in a cascade cycle is analysed theoretically. It has been concluded that the internal heat exchanger does not improve the performance of the subcritical cycle, but it could improve the energy performance if it is used inside a cascade refrigeration system.

Technical Evaluation of C3-MR and Cascade Cycle on Natural Gas Liquefaction Process

Technical Evaluation of C3-MR and Cascade Cycle on Natural Gas Liquefaction Process