Refrigeration Coefficient Of Performance Research Articles

Thermodynamic analyses of an innovative system combined dehumidification, cooling and heating driven by solar energy

For the sake of improving the utilization of solar energy in hot summer and cold winter areas of China, an innovative system combined liquid dehumidification with absorption refrigeration driven by solar energy is proposed in this paper. Solar energy is applied to three subsystems in a cascade utilization approach. Energy, exergy, and dehumidification performances of the system in three typical seasons of hot summer and cold winter areas in China are analyzed and compared. The key parameters including solar radiation intensity, ambient temperature, segment temperature and air relative humidity are investigated to obtain the optimization design of the proposed system. The objective indicators, including dehumidification coefficient of performance, refrigeration coefficient of performance, exergy efficiency, moisture removal rate, humidity efficiency, cooling capacity and heating capacity are discussed, respectively. The results show that, as the ambient temperature and solar radiation intensity increase, the dehumidification coefficient of performance (COPD) declines but the refrigeration coefficient of performance (COPR) rises. The COPD in rainy season is increased by 33.66 % and 50.15 % respectively, compared with that in cooling season and heating season. But the COPR in cooling season is 35.32 % higher than that in rainy season. The minimum of COPD reaches 1.31 at 12 noon. The maximum of COPR in the proposed system is 0.95. The exergy efficiency of the proposed system is improved by combining the liquid dehumidification subsystem and absorption refrigeration subsystem, with the maximum reaching 16.64 %. The proposed system shows better dehumidification performance in rainy season, and the maximum moisture removal rate and humidity efficiency in the proposed system are 27.98 g/kg and 0.83. The proposed system is also used for cooling and heating, with the highest cooling capacity and heating capacity achieving 217.31 kW and 36.58 kW, respectively. The obtained results state that the proposed system has excellent performance for dehumidification, cooling, and heating in hot summer and cold winter areas of China.

Dynamic thermal modeling of the refrigerated liquified CO2 tanker in carbon capture, utilization, and storage chain: A truck transport case study

Proper estimation of the energy consumption of tanker-based methods for the storage and transport of liquified CO2 gas is a major concern in the techno-economic analysis and selection between the existing technologies within the carbon capture, utilization, and storage (CCUS) chain. In this study, the dynamic thermal modeling of a liquified CO2 insulated-body tanker truck equipped with a refrigeration unit is presented to simulate the transient thermal performance of the tanker truck during a typical long-distance delivery mission. The main purpose of this research is to provide a more precise estimation of the heat leak quantity to the tanker, pressure build-up, and the refrigeration cooling demand and energy consumption. A two-way coupled set of unsteady-state differential equations are established on the participating elements included in the non-equilibrium thermal system of the tanker and refrigeration unit. The dynamic variations of ambient condition parameters, including the ambient temperature, solar radiation levels, degree of cloudiness, and wind velocity are incorporated into the model based on the annual average meteorological data in three modes of ambient conditions: the warmest week, a moderate week, and the coldest week of the year. The computational fluid dynamic (CFD) modeling of the liquid and gas phase CO2 inside the vessel is also implemented in order to determine the required heat transfer coefficients used in the model. According to the modeling results, the average vessel inward heat leak changes from 11.08 W/m2 in the warmest week of the year to 8.18 W/m2 and 5.11 W/m2 for a moderate and the coldest week, respectively, with 26.17 % and 53.88 % decrease. On the other hand, the refrigeration coefficient of performance (COP) is improved from 1.10 in the warmest week to 1.23 and 1.36 in a moderate and the coldest week, respectively, by 11.82 % and 23.63 % increase. As a measure of energy consumption of the refrigerated CO2 tanker truck at different ambient conditions, the average compressor power consumption changes from 56 W/m3CO2 in the warmest week of the year to 41 W/m3CO2 and 28 W/m3CO2 in a moderate and the coldest week, respectively, with 26.78 % and 50.00 % decrease. The novel modeling approach proposed in this study could also be used to study various design aspects of the refrigerated CO2 transport and storage tankers.

Experimental Realization of a Quantum Refrigerator Driven by Indefinite Causal Orders.

Indefinite causal order (ICO) is playing a key role in recent quantum technologies. Here, we experimentally study quantum thermodynamics driven by ICO on nuclear spins using the nuclear magnetic resonance system. We realize the ICO of two thermalizing channels to exhibit how the mechanism works, and show that the working substance can be cooled or heated albeit it undergoes thermal contacts with reservoirs of the same temperature. Moreover, we construct a single cycle of the ICO refrigerator based on the Maxwell's demon mechanism, and evaluate its performance by measuring the work consumption and the heat energy extracted from the low-temperature reservoir. Unlike classical refrigerators in which the coefficient of performance (COP) is perversely higher the closer the temperature of the high-temperature and low-temperature reservoirs are to each other, the ICO refrigerator's COP is always bounded to small values due to the nonunit success probability in projecting the ancillary qubit to the preferable subspace. To enhance the COP, we propose and experimentally demonstrate a general framework based on the density matrix exponentiation (DME) approach, as an extension to the ICO refrigeration. The COP is observed to be enhanced by more than 3 times with the DME approach. Our Letter demonstrates a new way for nonclassical heat exchange, and paves the way towards construction of quantum refrigerators on a quantum system.

A case study on experimental and statistical analysis of energy consumption of domestic refrigerator

This paper presents the energy consumption analysis of the refrigerator and the effect of the condenser on it. According to the Bureau of Energy Efficiency (BEE), India, the energy efficiency of electric appliances is the key parameter for testing their performance before domestic use. For energy consumption analyses, the experimentation was conducted on the domestic refrigerator (165 L) top-mounted evaporator by retrofitting the refrigerator with an Elliptical Helical Coil Condenser (EHCC) and existing refrigerator with a Straight Tube Condenser (STC). Box-Behnken Design (BBD) is very significant in determining the significant factor and reducing the number of experiments. BBD has been performed to analyze the significance of factors ambient temperature, fresh food compartment temperature and the heat load in energy consumption, and the Coefficient of Performance (COP) of a refrigerator. The heat load and the ambient temperature are both very significant in determining the refrigerator's energy consumption. The most important thing is to increase the liquid content in the charge before it is supplied to the evaporator to extract more amount of heat to increase the cooling effect. The ANOVA (Analysis of Variance) results show that the ambient temperature and the heat load were more significant in increasing energy consumption and decreasing the COP and vice versa. The results of ANOVA and the experiment are very close; the R2 value 0.995 precisely matches the R2 adj. value 0.994. The statistical analysis using the Box-Behnken design produces a good fitting of the modeled and experimental data set. The present study aims to examine the effects of said factors and the condenser on the domestic refrigerator's energy consumption and COP. The study exhibits some enhancement in the COP to 2.59 contrary to 2.45 and energy consumption reduced to 1191 Wh from 1755 Wh during the trial of 24 h.

Evaporator Frosting in Refrigerating Appliances: Fundamentals and Applications

Modern refrigerators are equipped with fan-supplied evaporators often tailor-made to mitigate the impacts of frost accretion, not only in terms of frost blocking, which depletes the cooling capacity and therefore the refrigerator coefficient of performance (COP), but also to allow optimal defrosting, thereby avoiding the undesired consequences of condensate retention and additional thermal loads. Evaporator design for frosting conditions can be done either empirically through trial-and-error approaches or using simulation models suitable to predict the distribution of the frost mass along the finned coil. Albeit the former is mandatory for robustness verification prior to product approval, it has been advocated that the latter speeds up the design process and reduces the costs of the engineering undertaking. Therefore, this article is aimed at summarizing the required foundations for the design of efficient evaporators and defrosting systems with minimized performance impacts due to frosting. The thermodynamics, and the heat and mass transfer principles involved in the frost nucleation, growth, and densification phenomena are presented. The thermophysical properties of frost, such as density and thermal conductivity, are discussed, and their relationship with refrigeration operating conditions are established. A first-principles model is presented to predict the growth of the frost layer on the evaporator surface as a function of geometric and operating conditions. The relation between the microscopic properties of frost and their macroscopic effects on the evaporator thermo-hydraulic performance is established and confirmed with experimental evidence. Furthermore, different defrost strategies are compared, and the concept of optimal defrost is formulated. Finally, the results are used to analyze the efficiency of the defrost operation based on the net cooling capacity of the refrigeration system for different duty cycles and evaporator geometries.

Construction and characterization of a solar refrigeration system based on nano-graphene

In this present work, we designed and fabricated a solar refrigeration system with increase in its performance compared to present refrigeration system by using different components (solar cell and Peltier module). The construction of the Peltier module was done using nano-graphene composite and its thermoelectric property was utilized for making the hot and cold junctions. A graphene composite material monolith was synthesized using solid state fabrication techniques and this constituted the junction of the Peltier module. A maximum coefficient of performance (COP) of 8.86 was achieved. ZT factor of graphene composite thermoelectric material can be further increased through modification in processing techniques and defect engineering. This will in turn increase the refrigeration COP further.

Thermodynamic Performance Investigation of a Small-Scale Solar Compression-Assisted Multi-Ejector Indoor Air Conditioning System for Hot Climate Conditions

In year-round hot climatic conditions, conventional air conditioning systems consume significant amounts of electricity primarily generated by conventional power plants. A compression-assisted, multi-ejector space cooling system driven by low-grade solar thermal energy is investigated in terms of energy and exergy performance, using a real gas property-based ejector model for a 36 kW-scale air conditioning application, exposed to annually high outdoor temperatures (i.e., up to 42 °C), for four working fluids (R11, R141b, R245fa, R600a). Using R245fa, the multi-ejector system effectively triples the operating condenser temperature range of a single ejector system to cover the range of annual outdoor conditions, while compression boosting reduces the generator heat input requirement and improves the overall refrigeration coefficient of performance (COP) by factors of ~3–8 at medium- to high-bound condenser temperatures, relative to simple ejector cycles. The system solar fraction varies from ~0.2 to 0.9 in summer and winter, respectively, with annual average mechanical and overall COPs of 24.5 and 0.21, respectively. Exergy destruction primarily takes place in the ejector assembly, but ejector exergy efficiency improves with compression boosting. The system could reduce annual electric cooling loads by over 40% compared with a conventional local split air conditioner, with corresponding savings in electricity expenditure and GHG emissions.

Preliminary investigation on pilot-scale photovoltaic-driven cold storage with ice thermal storage based on vapor compression refrigeration cycle

This work built a PV driven cold storage with ice thermal storage based on vapor compression refrigeration, where the compressor power was 4.41 kW. The system was designed in two modes of driving by utility electricity or PV array, and was expected to operate continuously via cascade evaporation in the cold storage. The hourly and daily performance was analyzed and compared between the two modes. The results indicate that the system driven by the stable utility electricity obtains the hourly refrigeration and system coefficient of performance (COP) between 1.02–5.73 and 0.85–4.58, respectively. The daily average refrigeration COP is between 2.75 and 3.02, and the daily average system COP is between 2.27 and 2.46; the highest daily cumulative ice mass reaches 178.45 kg. For the system driven by the PV array, the most daily ice mass of 144.10 kg is obtained with the PV capacity of 5.4 kW and the highest cumulative solar insolation of 20.41 MJ/m2, of which the daily refrigeration and system COP are 1.33 and 0.19, respectively. The characteristics of the ice thermal storage gives that the stored ice of 88.5 kg could sustain the cold storage temperature below 5 °C for about 11 h. Results show a positive trend indicating that this system could be a viable alternative for developing chain logistics service.

Thermal modelling of PVT-CPC integrated vapour absorption refrigeration system

In this paper, the single effect vapour absorption refrigeration (VAR) system is integrated with fully covered semi-transparent photovoltaic thermal-compound parabolic concentrator (PVT-CPC) collector. The thermal model of this integrated system has been obtained under constant mass flow rate mode of the collector. The thermal model is based on the basic energy balance of each component of the integrated system in terms of design and climatic parameters. Also, solar coefficient of performance (SCOP), refrigeration coefficient of performance (RCOP) and exergy coefficient of performance (ECOP) have been evaluated for the proposed integrated system. The numerical simulation have been performed for the climatic conditions of capital city of INDIA (i.e. New Delhi) with the help of MATLAB R2015a. From the results and discussion, it is found that PVT-CPC integrated with VAR system is most suitable for the self-sustained operation up to five hours for a typical day of summer month of New Delhi.

Performance Analyses of Photovoltaic Thermal Integrated Concentrator Collector Combined With Single Effect Absorption Cooling Cycle: Constant Flow Rate Mode

Abstract In the present communication, performance analyses of interconnected N number of fully covered semitransparent photovoltaic thermal integrated concentrator collectors combined with single effect vapor absorption refrigeration system have been carried out. The proposed system was analyzed under the constant mass flowrate of collectors’ fluid. Mathematical expressions have also been derived for generator temperature of the absorption unit as a function of both design and operating parameters. Further, simulations have been performed for a typical day of May month of New Delhi climatic conditions. Performance parameters have been evaluated such as collector exit temperature, generator inlet temperature, electrical power output, electrical efficiency, overall thermal energy gain, instantaneous thermal efficiency, overall exergy gain and coefficient of performance of the absorption system. The simulation code has been written in matlab. From the present analyses, the following salient conclusions have been drawn: Operating generator temperature of the absorption system is suitable for five number of photovoltaic thermal-integrated parabolic concentrator collector connected in series. The proposed system will continue operating for 5 h during May month in New Delhi climate conditions. The maximum solar coefficient of performance, refrigeration coefficient of performance, and exergy coefficient of performance are reported as 0.1551, 0.8344, and 0.2697, respectively, for the proposed novel system under given design and operating conditions. Additionally, the effects of other design parameters of this novel system have also been investigated.

Experimental Investigation of a Vapour Compression Refrigeration System with 15nm TiO2-R600a Nano-Refrigerant as the Working Fluid

Nanofluids are being considered as an efficient heat transfer fluid in various thermal applications. In this work, an experimental study was conducted on TiO2 nanoparticle mixed with R600a as the working fluid. TiO2-R600a nano-refrigerant was used in a domestic refrigerator with little system reconstruction. The refrigerator performance was then investigated using test parameters including: Pull down test, specific compressor work-input, refrigeration effect and coefficient of performance (COP) using steady state analysis. The results indicate that TiO2-R600a nano-refrigerant works efficiently and safely in the refrigerator and the performance was better than the pure R600a system. Overall, 0.1g TiO2 in 40g R600a nano-refrigerant mixture had the highest refrigeration effect and COP and gave the least specific compressor work-input within the test rig.

Reduction of real gas losses with a DC flow in the regenerator of the refrigeration cycle

Improving efficiency is an enduring effort for all refrigeration cycles. Real gases cause “intrinsic” heat losses in the regenerator and degrade the coefficient of performance (COP) of the regenerator of the refrigeration cycle. Previous experimental and numerical studies found that the COP of the regenerative refrigerator can be improved by imposing a direct-current (DC) flow, and the liquefaction rate can be improved by several times when the gas is precooled by the regenerator that works down to the temperatures close to or below the critical point. However, the working mechanism of such improvements has not been fully explored. In this paper, the working mechanism of imposing a DC flow on the regenerator working with a real gas is revealed based on thermodynamic analyses. The theoretical value of the DC flow and its influence on the COP of the regenerator are analyzed. The results show that the COP of the regenerator can be improved by over 10 times with a DC flow. An even higher relative Carnot COP of around 80% is possible to obtain in some specific temperature ranges. The enthalpy loss and the entropy loss of this approach has been estimated. This approach provides a potential way to improve the refrigeration COP and the liquefaction rate significantly. Measured liquefaction results found in the relevant literature have been analyzed to demonstrate the effectiveness of this approach.

Analysis on innovative resorption cycle for power and refrigeration cogeneration

A novel resorption cycle with internal heat recovery process is proposed, which is expected to further explore potentials of power and refrigeration cogeneration. Two sets of basic resorption refrigeration cycles are adopted, which are integrated with turbine/expander to realize quasi-continuous output in both half cycles. An improved cogeneration efficiency could be obtained with safety feature. Different ammonia composite sorbents with better heat and mass transfer performance are selected to investigate the overall performance when heat source temperature is in the range from 200 °C to 360 °C. It is indicated that energy efficiency for power generation is able to reach up to 0.263 at 360 °C heat source temperature while refrigeration coefficient of performance could achieve up to 1.31 at 200 °C heat source temperature. The optimal total exergy efficiency of novel resorption cogeneration cycle is as high as 0.74 by using working pair of FeCl2-CaCl2-BaCl2 at 240 °C heat source temperature. Compared with other sorption cycles for power and refrigeration cogeneration at similar heat source temperatures, the proposed resorption cycle exhibits the highest exergy efficiency, which is about 30% higher than that of water-ammonia sorption cogeneration cycle, and twice higher than that of basic resorption cogeneration cycle.

Implications of Coupling in Quantum Thermodynamic Machines

We study coupled quantum systems as the working media of thermodynamic machines. Under a suitable phase-space transformation, the coupled systems can be expressed as a composition of independent subsystems. We find that for the coupled systems, the figures of merit, that is the efficiency for engine and the coefficient of performance for refrigerator, are bounded (both from above and from below) by the corresponding figures of merit of the independent subsystems. We also show that the optimum work extractable from a coupled system is upper bounded by the optimum work obtained from the uncoupled system, thereby showing that the quantum correlations do not help in optimal work extraction. Further, we study two explicit examples; coupled spin- 1 / 2 systems and coupled quantum oscillators with analogous interactions. Interestingly, for particular kind of interactions, the efficiency of the coupled oscillators outperforms that of the coupled spin- 1 / 2 systems when they work as heat engines. However, for the same interaction, the coefficient of performance behaves in a reverse manner, while the systems work as the refrigerator. Thus, the same coupling can cause opposite effects in the figures of merit of heat engine and refrigerator.

Numerical estimation of energy efficiency in cryogenic chamber with various methods of ventilation and location of test object

Various industries, including automobiles, wind power, railroads, airlines, and defense, have their own individual low-temperature test specifications. Since the performance of a test object has to be evaluated after cooling in a climate-controlled chamber, the process consumes an enormous amount of energy and a long time is needed to cool the object. Reducing energy consumption and increasing the cooling rate would offer a huge environmental and economic benefit. This study analyzed the cooling rate and energy consumption of a cryogenic chamber in terms of the ventilation methods and locations of test objects through computational fluid dynamics analysis. In order to calculate energy consumption, the study fixed the compressor power of the refrigerator and created an energy model in the form of a user-defined function that considered changes in the outlet mass flow and refrigerator coefficient of performance according to changes in outlet temperatures within the chamber; this model is used for numerical analysis. The chamber used for the upper air supply and lower exhaust method (Case A) demonstrated a faster cooling rate by 0%–32% compared to the upper air supply and lower exhaust on the opposite face method (Case B) and the upper air supply and central exhaust on the opposite face method (Case F). Case A generally consumed less energy during cooling, whereas Case F consumed the least amount of energy for 4–6 out of the 12 test object locations. Cases A, B, and F demonstrated the highest cooling rates and the lowest energy consumptions when the test object was located at P5 or P11 opposite of the air supply. The cooling rate of the test object and energy consumption should be considered in the ventilation design of a cryogenic test chamber. In the case of a pre-installed chamber, a proper location should be selected for cooling the test object for fast cooling according to the chamber ventilation method.

Thermodynamic analysis on a modified ejector expansion refrigeration cycle with zeotropic mixture (R290/R600a) for freezers

This study presents a modified ejector expansion cycle with zeotropic mixtures (R290/R600a) for freezers, in which an ejector and a phase-separator are employed to enhance the cycle performance. Energetic and exergetic methods are used to theoretically investigate the system operating characteristics. In addition, comparative research among the modified cycle, conventional ejector expansion cycle and basic throttling cycle is carried out. The results demonstrate that the modified cycle exhibits higher refrigeration COP (coefficient of performance), volumetric refrigeration capacity and system exergy efficiency than conventional ejector expansion cycle and basic throttling cycle. Under the given operation conditions, the system performance improvements of the modified cycle in terms of the COP, refrigeration capacity and system exergy efficiency over the basic throttling cycle could reach about 56.0%, 4.5% and 77.7%, respectively. The performance characteristics of the proposed cycle show its potential practical advantages in freezer applications.

Analysis of Humidified Air Circulation Over the Air Cooled Condenser of Vapour Compression Refrigeration System with Eco Friendly Refrigerants

The performance behavior of vapour compression refrigeration system (VCRS) has been examined in two modes of operation namely atmospheric air circulation (AAC) and humidified air circulation (HAC) over the condensing coil at different loading conditions in the evaporator. This experimental work is carried out by using the refrigerant mixture of R290 and R600a which are eco friendly refrigerants as compared to conventional refrigerants like R12 and R134a. Humidifier unit is assembled with the existing VCRS and the mass flow rate of water supplied is maintained about 1.08 lit/sec. The various performance parameters like coefficient of performance (COP), refrigeration effect, heat rejection in the condenser and power input to the compressor are measured experimentally at different loads in the evaporator. The experimental results of the proposed investigation shows that 19.1% reduction in compressor power consumption and progressive increase in refrigeration effect & COP. COP of HAC mode is about 26.88% higher than AAC mode at 75% loading conditions.

Solar Powered Cascading Cogeneration Cycle with ORC and Adsorption Technology for Electricity and Refrigeration

As a renewable source, solar energy has received more and more attention in recent years. Solar energy can readily provide heat efficiently within the temperature range of 70–100°C. For the utilization of this energy source, a cascading cycle was designed and was discussed. An organic Rankine cycle (ORC) and an adsorption refrigeration cycle were combined to provide the first- and second-stage energy conversion cycle, respectively. In the analysis, R600 was used as the working fluid for the ORC and a silica gel–water working pair was analyzed for the adsorption refrigeration cycle. The energy efficiency for electrical generation and refrigeration, as well as the exergy efficiency of the cascading cycle, was assessed. For an environmental temperature of 30°C and a refrigeration temperature of 12°C, the results showed that typically 1 kW of electricity and 6.3 kW of refrigeration could be generated from approximately 15 kW heating power. The electricity generation efficiency was between 0.1 and 0.15, while the refrigeration coefficient of performance was approximately 0.8. The exergy efficiency was found to be between 0.84 and 0.89 and between 0.32 and 0.46 for the single ORC and adsorption refrigeration cycle, respectively. The overall exergy efficiency was between 0.56 and 0.74.

Effect of evaporator temperature on vapor compression refrigeration system

This paper presents a comparable evaluation of R600a (isobutane), R290 (propane), R134a, R22, for R410A, and R32 an optimized finned-tube evaporator, and analyzes the evaporator effect on the system coefficient of performance (COP). Results concerning the response of a refrigeration system simulation software to an increase in the amount of oil flowing with the refrigerant are presented. It is shown that there is optima of the apparent overheat value, for which either the exchanged heat or the refrigeration coefficient of performance (COP) is maximized: consequently, it is not possible to optimize both the refrigeration COP and the evaporator effect. The obtained evaporator optimization results were incorporated in a conventional analysis of the vapor compression system. For a theoretical cycle analysis without accounting for evaporator effects, the COP spread for the studied refrigerants was as high as 11.7%. For cycle simulations including evaporator effects, the COP of R290 was better than that of R22 by up to 3.5%, while the remaining refrigerants performed approximately within a 2% COP band of the R22 baseline for the two condensing temperatures considered.

The performance evaluation of a micro/nano-scaled cooler working with an ideal Bose gas

Based on the size effect of a confined ideal Bose gas, the design concept of a quantum cooler is originally put forward. The cooler consists of two long tubes with the same length but different sizes of cross section, which are filled up with the ideal Bose gas, and is operated between two heat reservoirs. Expressions for the refrigeration rate and coefficient of performance (COP) of the cooler are derived. The effects of the size effect on the refrigeration rate and COP are discussed. The general performance characteristics of the cooler are revealed.