Performance Of Refrigeration Cycle Research Articles

Development of an Integrated Structure for the Tri-Generation of Power, Liquid Carbon Dioxide, and Medium Pressure Steam Using a Molten Carbonate Fuel Cell, a Dual Pressure Linde-Hampson Liquefaction Plant, and a Heat Recovery Steam Generator

Due to the increase in energy consumption and energy prices, the reduction in fossil fuel resources, and increasing concerns about global warming and environmental issues, it is necessary to develop more efficient energy conversion systems with low environmental impacts. Utilizing fuel cells in the combined process is a method of refrigeration and electricity simultaneous production with a high efficiency and low pollution. In this study, a combined process for the tri-generation of electricity, medium pressure steam, and liquid carbon dioxide by utilizing a molten carbonate fuel cell, a dual pressure Linde-Hampson liquefaction plant and a heat recovery steam generator is developed. This combined process produces 65.53 MW of electricity, 27.8 kg/s of medium pressure steam, and 142.9 kg/s of liquid carbon dioxide. One of the methods of long-term energy storage involves the use of a carbon dioxide liquefaction system. Some of the generated electricity is used in industrial and residential areas and the rest is used for storage as liquid carbon dioxide. Liquid carbon dioxide can be used for peak shavings in buildings. The waste heat from the Linde-Hampson liquefaction plant is used to produce the fuel cell inlet steam. Moreover, the exhaust heat of the fuel cell and gas turbine would be used to produce the medium pressure steam. The total efficiency of this combined process and the coefficient of performance of the refrigeration plant are 82.21% and 1.866, respectively. The exergy analysis of this combined process reveals that the exergy efficiency and the total exergy destruction are 73.18% and 102.7 MW, respectively. The highest rate of exergy destruction in the hybrid process equipment belongs to the fuel cell (37.72%), the HX6 heat exchanger (8.036%), and the HX7 heat exchanger (6.578%). The results of the sensitivity analysis show that an increase in the exit pressure of the V1 valve by 13.33% would result in an increase in the refrigeration energy by 2.151% and a reduction in the refrigeration cycle performance by 9.654%. Moreover, by increasing the inlet fuel to the fuel cell, the thermal efficiency of the whole combined process rises by 18.09%, and the whole exergy efficiency declines by 12.95%.

Experimental Analysis of Refrigeration Ejector System by using Different Organic Refrigerants

This paper presents the experimental analysis performed on ejectors to optimize operating conditions like evaporator temperature, condenser temperature and generator temperature. Using the environmentally friendly working fluid R134a, R152a, R600a, R717 (Ammonia). Parametric analysis was performed to review the effect of blending chamber geometry on ejector performance which has direct impact on coefficient of performance of ejector refrigeration cycles. Results show that operating conditions and thus the effect of the deflection of the primary flow on the secondary flow is set. CFD simulations was performed to identify optimum geometry and optimum operating condition

Thermodynamic analysis and parametric optimization of ejector heat pump integrated with organic Rankine cycle combined cooling, heating and power system using zeotropic mixtures

Schematic diagram of ejector heat pump integrated with organic Rankine cycle combined cooling, heating and power (ORC-CCHP) system and mass fractions of (R141b/R134a) in ORC and heat pump loop, merits: great temperature glides in the high-temperature evaporator and high-temperature condenser, beneficial to generate plentiful refrigeration capacity in the heat pump loop. • Comprehensive thermal efficiency is proposed to achieve energy utilization potential substantially. • Mass fractions of zeotropic mixture, generator temperature and entrainment ratio are optimized. • R141b/R134a(55%/45%) achieves optimum mass fractions in ORC and heat pump loop. • Comparative analysis of basic ORCs, ORC with post ejector, ORC with ejector heat pump, EORC is conducted. • Ejector heat pump integrated with ORC-CCHP system is thermodynamiclly feasible and economically attractive. To improve the coefficient of performance ( COP ) of ejector refrigeration cycle (ERC), a novel ejector heat pump integrated with organic Rankine cycle combined cooling, heating and power system (ORC-CCHP) using zeotropic mixtures is established in this study. The comprehensive thermal efficiency is proposed considering exergy efficiency and heat recovery efficiency simultaneously. Results show that the entrainment ratio can be determined with the objective of exergy efficiency, while generator temperature and mass fraction of zeotropic mixture are optimized with the comprehensive thermal efficiency. With the optimized entrainment ratio of 0.2 and generator temperature of 351.15 K, R141b/R134a (55%/45%) achieves the power efficiency of 4.21%, refrigeration efficiency of 14.6% and COP of 1.12, which are considerably higher than those of pure R141b or R134a. Meanwhile, R141b/R134a with optimum mass fractions in ORC and heat pump loop can generate plentiful refrigeration capacity, great temperature glides in the high-temperature evaporator and high-temperature condenser. The comparative analysis of basic ORCs, ORC with post ejector, ORC with ejector heat pump, ORC combined with ejector (EORC) is carried out. The ejector heat pump integrated with ORC-CCHP system is thermodynamically feasible and economically attractive, thanks to optimized system parameters and optimum compositions of zeotropic mixture, giving support of new applications of ERC coupled with positive and reverse Carnot cycles.

Thermodynamic analysis of a novel solar-driven booster-assisted ejector refrigeration cycle

This paper presents a subcooling booster-assisted ejector refrigeration cycle (SBERC) for refrigeration applications in the field of solar-driven air conditioning. The innovation is that a subcooler and IHX is introduced to enhance the ejector refrigeration cycle performance effectively. In the SBERC, the refrigerant at the generator outlet is in a two-phase state. Energy and exergy analyses are conducted on two basic cycles and the novel cycle using environmentally friendly refrigerant R1234ze(E). Compared with two basic cycles, the COPt of the novel cycle is increased by 51.1% and 20.5%, respectively; the exergy efficiency ηex is increased by 38.2% and 15.1%, respectively, under a typical working condition. Under all given working conditions, the cooling performance of the novel cycle is better than that of two booster-assisted ejector refrigeration cycles. The results also indicate that the novel cycle obtains higher exergy efficiency, and requires less solar energy input than two basic cycles when solar radiation intensity ranges from 600 to 1000 W/m2. Besides, the performance coefficient of the novel cycle reached a maximum value when the refrigerant vapor quality at the generator outlet is about 0.73 under a typical working condition, and the higher effectiveness IHX and subcooler bring better cycle performance.

Pool boiling heat transfer coefficient of dimethyl ether and its azeotropic ternary mixtures

Dimethyl ether (DME) is a popular medium widely used in industrial applications. Being highly flammable substance, only recently it has again found commercial use as a primary working fluid in cooling and heating systems. Known as refrigerant RE170, it is now considered to be one of the potential natural refrigerants of the future due to minimal Global Warming Potential and zero Ozone Depletion Potential.Two novel azeotropic ternary mixtures of RE170/R1234yf/R152a were developed in order to improve cooling capacity and performance of a dimethyl ether refrigeration cycle. The mass ratios were purposefully selected to offer high cycle efficiency COP, high specific cooling capacity qe, small specific volume of vapour, reduced compressor power requirements, and the smallest possible temperature glide.The mixtures were subjected to experimental analysis in order to establish to what degree the added fluids (R1234yf and R152a) influence boiling and heat transfer performance. Boiling curves and heat transfer coefficients were determined experimentally and compared with the values obtained for pure RE170. Finally, several known heat transfer coefficient correlations (suitable for both hydrocarbons and synthetic refrigerants) were applied to the resulting data and evaluated for accuracy by evaluation of MAPE. The Cooper correlation was the most accurate for for ternary mixtures of dimethyl ether in the broadest range of temperatures, heat fluxes, and compositions (MAPE between 3.5-19.8). In order to improve the accuracy even further, the original Cooper correlation was modified with the acentric factor and the molecular mass power factor was optimised for modern chloride-less refrigerants. Resulting equation, when applied to ternary mixtures, returns errors below 5% in the entire range of experimental data.

The effect of thermal hysteresis on the performance of a regenerative Ericsson refrigeration cycle with MnFe-based composite material

MnFe-based magnetocaloric materials exist a giant magnetocaloric effect so that they can be used as the working substance for room-temperature magnetic refrigeration. But there are two key problems to be solved before employing them as the working substance: one is that for single MnFe-based material, its giant magnetocaloric effect only arise in a small temperature range and the other is that these materials exist generally thermal hysteresis. For these reasons, a novel composite material based on MnFe-based materials is designed optimally, and a regenerative Ericsson refrigeration cycle using the composite material as the working substance is established. Furthermore, the performance of the refrigeration cycle with the composite is analyzed and evaluated. The influences of thermal hysteresis on main thermodynamic parameters of the refrigeration cycle are revealed by numerical calculation. The research results can provide some significant guidances for the parametric design and performance improvement of room-temperature magnetic refrigerators.

A Novel Technique for Improving the Performance of Ammonia Absorption Refrigeration Cycle

The world is now living in an energy crisis. Refrigeration and air-conditioning systems have become the basics of daily life in various fields and accordingly, it cannot be dispensed. Refrigeration machines and air-conditioning systems are the most energy-consuming systems, independent on the application whether it is domestic, commercial, industrial or medical. Therefore, using cooling systems which are powered by thermal energy, e.g., solar energy, can save a lot of electrical energy. Absorption refrigeration system is an example of a refrigeration system powered by heat energy. However, the system problem here is that it has low coefficient of performance (COP). The objective of this research is to improve the COP of the ammonia absorption cycle. This is done in the absorber unit by improving the absorption of the refrigerant ammonia into the ammonia–water solution. The absorption efficiency is improved by using (1) a stirrer pump to improve mixing, (2) sprayers to increase the contact area between ammonia and ammonia–water solution and (3) continuous cooling of the solution during the absorption process via an external heat exchanger. The COP of the ammonia absorption cycle has increased from 0.48 to 0.715, i.e., by 49%. This is due to the improvement of the absorption of the ammonia into the ammonia–water solution.

Exergetic Investigation of the Effects of Superheating and Subcooling on Performance of a Vapor Compression Refrigeration Cycle

The aim of this study is to investigate the effects of superheating and subcooling values on the cooling performance of a vapor compression refrigeration cycle. For this purpose, a refrigeration cycle with cooling capacity of 8 kW using R404A was examined by changing superheating and subcooling values. Energy, exergy and entropy balances were applied for evaporation and condensation temperatures of 0℃ and 45℃, respectively. In order to evaluate the performance of the refrigeration cycle, coefficient of performance (COP) for cooling, the amount of energy transfer, rate of exergy destruction and rational exergy efficiency of the all components (evaporator, compressor, condenser and expansion valve) and the whole system were determined.

Experimental validation of new approach for waste heat recovery from combustion engine for cooling and heating demands from combustion engine for maritime applications

Abstract Waste heat recovery is one of the crucial and fundamental issue of energy management related with energy efficiency improvement, fuel savings, and reduction of greenhouse gases emissions. The paper provides with the experimentation of the prototype heat recovery system dedicated to the small and mid-sized maritime combustion engines of the nominal load of 100–250 kW. The waste heat recovery system is covering the innovative low-pressure steam indirect heat transfer subsystem. The recovered heat is consumed by a heating system and a prototype heat driven ejector refrigeration cycle operating with environmentally safe refrigerant. It was demonstrated that the refrigeration system produces up to 30 kW of cold by consuming 75 kW of heat gathered from flue gases. This is the first prototype of the compact heat driven refrigeration system for marine applications. The waste heat recovery system additionally provides with approximately 60 kW heat recovered from water jacked cooling of the engine block which is used for heating capacity dedicated for tap water and space heating purposes. This covers almost all small and mid-sized vessels needs for thermal energy. The prototype design has been approved by two independent maritime classification societies.

Accurate and Model-Free Control Function for a Single Stage Transcritical Refrigerator Cycle.

Transcritical cycles are a successful and probed system in engineering practices, particularly in refrigeration. Therefore, their optimization is a critical factor in the design, control, and operation in order to maximize the coefficient of performance (COP) and to find the optimal pressure operating conditions. Often, this labor is faced using empirically based correlations, which are limited by their origin and the configuration of the cycle. In this regard, this work is devoted to the development of a rigorous and general framework in order to characterize the behavior and performance of a simple transcritical refrigeration cycle. An accurate mathematical expression for the COP depending on the compressor efficiency and the properties of the working fluid is presented. The expression proposed has no approximations and is relevant to any model depending on the Helmholtz variable group, being easy to combine with any equation of state (EOS), regardless of its complexity. From this expression, it is possible to derive a simple control function for transcritical refrigeration cycles. As an example, the expression is combined with the Span–Wagner EOS, presenting a comprehensive application for a transcritical cycle using CO2 and N2O as working fluids.

Experimental investigation of closed loop spray cooling with micro- and hybrid micro-/nano-engineered surfaces

With the urgent demands of ultra-high heat flux cooling technology, enhancement of spray cooling by surface structure as an effective thermal management method has drawn increasing attention. Combining micro- and nano-structures is a promising way to improve spray cooling but only a few attempts have been made, especially in an application oriented closed loop system. Here, spray cooling heat transfer of flat, rough, micro-structured and hybrid micro-/nano-structured surfaces are experimentally investigated in a closed loop spray cooling system based on R134a refrigeration cycle. The results show that compared with the flat surface, the rough heating surface, micro-structured surfaces and hybrid micro-/nano- engineered structures can increase the critical heat flux (CHF) by 15%, 42% and 59%, and heat transfer coefficient (HTC) of spray cooling system by 14%, 28% and 42%, respectively. The optimum characteristic size of micro structure is 200 μm, which corresponds to the mean droplet diameter. By combining this micro structure with irregular ZnO nanowires, the maximum CHF, HTC and system efficiency are obtained as 180 W/cm2, 30 kW/m2K and 29.4%. The system combines the advantages of high cooling performance of spray cooling and the stable operation of refrigeration cycle. With closed loop experiments, the heat transfer enhancement by micro- and hybrid micro-/nano-structures is validated, and parametric influences as well as corresponding mechanisms are analyzed, which provide insights to guide industrial applications, and facilitate interdisciplinary study between advanced engineering materials and heat transfer to help expanding the frontier of spray cooling.

Dynamic performance analysis of inverter-driven split air conditioner

Abstract Variable speed technology has a great potential for improving energy efficiency and performance of vapor compression refrigeration cycle. Therefore, the study of dynamic characteristics of the refrigeration cycle using this new technology becomes essential. This study experimentally investigates the dynamic behavior of a split R-410A air conditioner comprising variable speed compressor, variable speed condenser fan, three speed evaporator fan and electronic expansion valve. The characteristics of the conditioner have been presented during the startup and shutdown periods. Furthermore, the effect of changing evaporator fan speed during the running of the conditioner has been illustrated and discussed. The influence of evaporator and condenser inlet air temperatures on the power consumption and coefficient of performance of the conditioner has also been investigated. The experimental results show that increasing the condenser entering air temperature by 7 °C, the power consumption has been increased by 18% and the coefficient of performance decreased by 15%.

The effect of stage number on the performance of a vapor compression refrigeration cycle using refrigerant R32

In the refrigerant cycle of Air-Conditioning (AC) unit the mainly used cycle is vapor compression cycle. The performance of the refrigerant, named as Coefficient of Performance (COP), need to be improved by using modification. The modification by using multi stage is one of the potential solutions. In the present study, the effect of number of stage to the performance will be explored. A simple vapor compression cycle that is typically used in the AC unit is taken into study. IN the cycle the refrigerant is difluoromethane R32. Three different stages are examined, they are single stage, two-stages, and three stages. The numerical analyses are carried out using commercial Aspen One software. The COP, mass flow rate of the refrigerant and compressor power will be discussed. The result shows that increasing the number of stages related to increasing the COP.

Performance of ejector refrigeration cycle based on solar energy working with various refrigerants

The refrigerator unit based on electrically driven vapor compression technology consumes high energy, associated with high cost and loss of ecosystem. Recently, solar thermal energy emerges as a key research area and introducing it in refrigerator application has happened extremely fast. Solar thermal refrigeration systems based on ejector compression technology are thriving because of its utilization of low-grade energy sources, straight forward design, non-moving parts, lower maintenance costs, and durability. In this present work, the performance of a solar ejector refrigeration system (ERS) is calculated analytically using one-dimensional model. The performance parameters are calculated with the assumption that both the condensation and evaporation processes occur along the saturation line. Initially, the influence of the ejector area ratio, generator temperature, condenser temperature, and evaporator temperature on the performance of the ERS is analyzed in critical mode with water (R718) as the working fluid. The analysis shows that the coefficient of performance increases more than two times on increasing the ejector area ratio from 6.4 to 12.8. The results also show that a higher coefficient of performance (COP) is obtained at a higher ejector area ratio. The COP is found to be inversely related to the generator temperature, meanwhile the coefficient of performance increase more than 74% on increasing the refrigeration temperature from Tc = 8 °C to Tc = 15 °C. Then, the performance of ERS is obtained at the subcritical conditions at varying generator temperatures. At subcritical mode, COP is found to be directly proportional to the generator temperature, and the highest COP occurs at an optimum generator temperature. The performance of the ERS with various refrigerants as R717, R718, R245fa, R123, R141b, and R365fa is calculated at the critical mode. With refrigerant R717, the system shows higher performance as well as a cooling effect than other refrigerants. However, most environmental benign refrigerant R718 shows comparatively low performance, but it is found that R718 produces a significant cooling effect than other refrigerants excluding R717 refrigerant.

A novel approach for energy and mass transfer characteristics in wet cooling towers associated with vapor-compression air conditioning system by using MgO and TiO2 based H2O nanofluids

In hot weather, the performance attributes of the refrigeration cycles associated with cooling towers drop pointedly, and thus, the energy consumption excesses in addition to more troubles start to occur. Improve the cooling tower performance before the cooled fluid enters the condenser of the vapor compression air conditioning system (VCACS) can enhance the refrigeration cycle performance, lowering operating and maintenance cost, conserve the environment, and consequently save consumed energy. In this research, the experimental work on the performance-enhancing of a central air-conditioning utilizing cooling tower is presented under an enormous range of design and operating conditions. The purpose is to investigate the trace of several design parameters such as; nanoparticle concentration ratios, nanoparticle type, filling type, filling sheet spacing and sprayer angle whereas the operation parameters as; working fluid flow rate and air velocity on the performance characteristics for the VCACS. Two nanomaterial types being contemplated are MgO and TiO2 at varied concentrations of 0.1, 0.5, and 1.0% wt. It is found that the using of spiral sprayer with a spray angle of 90° had an effect of 106% and a 76.5% increase on the cooling tower effectiveness in comparing with a spray angle of 30°, and 150°, respectively. The maximum overall system performance index is observed at PVC fill, β = 12 mm, a nanoparticle of MgO based water, φ = 1%, and θ = 90°. Correlations of Ka.VP/ṁf and ε are predicted with its deviations using DataFit software based on the obtained experimental data.

Investigating the effect of using nanofluids on the performance of a double-effect absorption refrigeration cycle combined with a solar collector

In this article, the performance of a double-effect LiBr-H2O absorption refrigeration cycle is studied and is improved by applying solar energy and utilizing nanofluids. A trough collector is used to preheat the working fluid before entering the generator of the cycle. In addition, four different nanofluids are considered as the heat transfer fluid of the collector: Al2O3, Ag, Cu, and CuO. The effects of using nanofluids on the outlet temperature of the heat transfer fluid, the temperature of the working fluid entering the generator, the heat produced by the generator, and COP of the cycle are studied. Different concentrations of the nanoparticles from 0 to 2.5% are considered for the nanofluids. The results indicate that in all the concentrations, Ag nanoparticles will have a better performance comparing to the other types. Furthermore, it was concluded that the higher concentrations of the nanoparticles and along with it the higher inlet temperature of the generator will decrease the generator heat production rate up to 4%. Moreover, considering the constant cooling capacity of the cycle, usage of the Ag nanoparticles in the concentration of 2.5% increases the value of COP up to 3.9%, with respect to the pure water.

Thermodynamic Performance of a Double-Effect Absorption Refrigeration Cycle Based on a Ternary Working Pair: Lithium Bromide + Ionic Liquids + Water

For an absorption cycle, a ternary working pair LiBr–[BMIM]Cl(2.5:1)/H2O was proposed as a new working pair to replace LiBr/H2O. The thermodynamic properties including specific heat capacity, specific enthalpy, density, and viscosity were systematically measured and fitted by the least-squares method. The thermodynamic performance of a double-effect absorption refrigeration cycle based on LiBr–[BMIM]Cl(2.5:1)/H2O was investigated under different refrigeration temperatures from 5 °C to 12 °C. Results showed that the ternary working pair LiBr–[BMIM]Cl(2.5:1)/H2O had advantages in the operating temperature range and corrosivity. Compared with LiBr/H2O, the operating temperature range was 20 °C larger, and the corrosion rates of carbon steel and copper were reduced by more than 50% at 453.15 K. However, the double-effect absorption refrigeration cycle with LiBr–[BMIM]Cl(2.5:1)/H2O achieved a coefficient of performance (COPc) from 1.09 to 1.46 and an exergetic coefficient of performance (ECOPc) from 0.244 to 0.238, which were smaller than those based on LiBr/H2O due to the higher generation temperature and larger flow ratio.

Performance analysis of R1234yf/ionic liquid working fluids for single-effect and compression-assisted absorption refrigeration systems

Due to the disadvantages of conventional working pairs (NH3/H2O and H2O/LiBr) in the absorption-refrigeration cycles, 2,3,3,3-Tetrafluoroprop-1-ene(R1234yf)/ionic liquid (IL), which possessed of remarkable properties, has received more and more attention. In this work, the thermodynamic performance of single-effect and compression-assisted absorption refrigeration cycles were analyzed using R1234yf as refrigerant and ILs (including [emim][BF4], [hmim][BF4], [omim][BF4], [hmim][Tf2N], [hmim][PF6] and [hmim][TfO]) as absorbent, the thermodynamic properties of working pairs was estimated by the NRTL model. The effects of generation, evaporation, condensation and absorption temperature as well as compression ratio on the cooling performance and circulation ratio were studied in various working conditions. Compared to the single-effect cycle, the compression-assisted cycle effectively improves the cooling performance, reduces the circulation ratio and extends the operation range of generation, evaporation and absorption temperatures. At the same working condition, [hmim][Tf2N] performs the best while [emim][BF4] has the lowest COP, the cooling performance of [hmim][BF4], [omim][BF4], [hmim][TfO] and [hmim][PF6] is similar.

A numerical contrast on the adjustable and fixed transcritical CO2 ejector using exergy flux distribution analysis

An adjustable ejector with a needle is deemed as an effective device to improve the performance of the transcritical CO2 refrigeration cycle with a wide operating conditions. In this paper, a homogeneous CFD model is built up to compare the performance of the adjustable and fixed ejectors with the same key structural sizes. By validating the numerical results with the experimental data, the k-ε RNG and k-ε Realizable are considered to predict the performance of the CO2 ejector well. Furthermore, an exergy analysis model is proposed to obtain the exergy fluxes of the primary and secondary flows are obtained, respectively. The results discover that the main exergy transfer (interaction between the primary and secondary flows) locates in the suction chamber. Meanwhile, the higher exergy loss is observed in the suction chamber of the adjustable ejector due to flow separation along the needle and higher viscous dissipation of oblique shock wave, which results in 5%–11% lower entrainment ratio than that of the fixed ejector. However, the higher velocity in the fixed ejector results in higher friction of the wall and more intense flow separation in the diffuser which causes higher exergy loss in the mixer and diffuser. Accordingly, the exergy efficiency of the adjustable ejector is only 0.5% lower than that of the fixed ejector. In spite of the special case in this paper, the adjustable ejector is considered to be able to achieve a similar exergy efficiency with the fixed ejector.

Performance of a new two-stage transcritical CO2 refrigeration cycle with two ejectors

The present study describes a new two-stage transcritical CO2 refrigeration cycle with two ejectors (NERC). At this studied cycle (NERC), vapor compression is performed in two stages and each vapor compression line includes separate ejector. Thermodynamic and exergetic analysis of the proposed cycle are performed using Engineering Equation Solver (EES) software. The new cycle (NERC) is compared with a conventional cycle. It is found that depended on conditions the new cycle (NERC) improves the COP from 20% to 80% compared to the conventional cycle. The effects of main cycle parameters i.e. the high-side pressure of a compressor (discharge pressure), intermediate pressure, the outlet temperature of gas cooler and evaporator temperature on COP are studied.