Carnot COP Research Articles

Anisotropy of elastocaloric cooling effect in equal atomic ratio NiTi alloy with crystallographic texture

The influence of anisotropy induced by the crystallographic texture on the elastocaloric cooling effect of rolled NiTi alloy was investigated. Cyclic tensile tests were conducted along various directions angles (θ) between the rolling direction (RD) and the transverse direction (TD). The results demonstrated that the dominant texture component of the material were {110}<110> and {001}<110>. With the presence of texture component {110}<110> and {001}<110>, the elastocaloric cooling effect of rolled NiTi alloy presented unusual anisotropy. The adiabatic temperature change ΔTadi is maximum in the θ = 0° direction (//RD) and minimum in the θ = 90° (//TD)direction. The material coefficient of performance COPmat and Carnot COP were also analyzed and evaluated. The maximum COPmat and Carnot COP obtained were 26.5 and 67%, respectively, indicating a remarkable balance between cooling capacity and efficiency. The present research shed light on optimizing the elastocaloric cooling effect by introducing crystallographic texture characteristic in rolled NiTi alloy.

Experimental performance analysis of a biogas energy assisted hybrid milk cooling system

Biogas energy assisted hybrid milk cooling system was investigated experimentally, in this study. The system operated in a cycle. Primarily, biogas was obtained from the residues of animals in the farm environment and an internal combustion gas engine is started with this gas. Then, the gas engine provided the power required for the compressor of the cooling system to operate. The main purpose of the study was to encounter the energy required for milk cooling only from the biomass potential of animal wastes and in this way, it was to bring a system with high energy efficiency for milk cooling process to the literature and industry. In experiments, 150 liters of milk in the first milking and 300 liters of milk in the last milking were cooled. It was determined that the energy consumption in the first and last milking is 2.29 kWh and 2.54 kWh. The results revealed that this developed system was 45.61% and 41.61% more advantageous for first and last milking, respectively, compared to conventional milk cooling systems in terms of energy consumption. When the system compared to other alternative energy source assisted milk cooling technologies with similar milk cooling capacity, It was observed that 14.55% and 24.40% more efficient with regards to energy consumption for the first and last milking. Additionally, experimental and Carnot COP values of the cooling system were determined as 4.29 and 8.26, respectively. These data revealed that the hybrid system had a higher performance of 38.4% compared to other milk cooling techniques.

Second order cyclic analysis of counter flow pulse tube refrigerator

Stirling machines are ecologically propitious refrigeration devices that utilize natural gases like helium, nitrogen, or air. Stirling machines are active refrigerators that should be designed with minimal vibrations and durability in order to fulfil current and future commercial de-mands and requirements. The present paper deals with the modification of the inertance pulse tube refrigerator in which the reservoir is eliminated and replaced with another pulse tube refrigerator. These two pulse tube refrigerators are operated at 180 degrees out of phase, called counter-flow pulse tube refrigerators (CFPTR). The second-order cyclic analysis approach is used to develop a mathematical model for evaluating the performance of CFPTR. This paper describes a modified second-order cyclic approach in detail. The performance of CFPTR is evaluated by estimating the ideal refrigerating effect, ideal power input, and losses individual-ly, yielding net power input and net refrigerating effect. The net refrigerating effect of 30.88W at 70K is obtained with the percentage of Carnot COP of 13.71. The CFD modeling of CFPTR is used to corroborate the second order cyclic model.

Water Conditioning Refrigeration System Design and Construction for Lobster Cultivation

This research is to determine the cooling burden of the water conditioning system for lobster conditioning, where water must be conditioned to its temperature by its 21°C conditioning. This device uses steam compression systems precisely by utilizing water conditioning systems to condition water to stay awake at a temperature of 21°C. The method used in this study was to determine the volume of the water tank and its cooling capacity by calculating the load load and calculating the heat load through the walls of the water tank and other heat generated. For lobster cultivation, an air conditioning machine with a capacity of 1/2 PK. From the results of testing the tool for 3 hours, the results of system performance at an evaporation temperature of 15.2 °C and a product temperature of 21 °C obtained a Carnot COP of 7.11, an actual COP of 5.87, and an efficiency of 82.55%. This is in accordance with Design Carnot COP 8, actual COP design of 6.7, and design efficiency of 83%.

Simulation study on superposition expansion of belt electrocaloric refrigeration structure

Electrocaloric cooling technology has revived rapidly in recent years due to the discovery of the giant electrocaloric effect. The researches on electrocaloric cooling devices reported in recent years still have the disadvantages of the small adiabatic temperature change and low cooling power. In this work, a belt electrocaloric refrigeration structure was proposed and simulated by the finite element method. The banded electrocaloric material driven by the motor passes through the hot end and the cold end successively in this device, so as to realize continuous cooling. In addition, the adiabatic temperature change and cooling power density can be increased by superimposing the unit model. Numerical study has been performed to analyze the influence of the motion speed and length of the electrocaloric module and the temperature span on refrigeration performance. The results show that the temperature span of the double-layer unit model under adiabatic condition can reach 32.68 K, which is about twice that of the single-layer unit model. When the system is operated at a temperature span of 18 K, a cooling power density of 3.56 W∙cm−2 and a percent of Carnot COP of 28.5 % are achieved for double-layer unit model.

Comparative Assessment of Environment-Friendly Alternative to R134a in Vapour Compression Refrigeration System using Exergy Destruction

The goal of this research is to compare the performance of a vapour compression refrigeration system using R-600a to a similar system having R-134a as a refrigerant. Both refrigerants have no potential to deplete the ozone layer. However, because R-134a is an HCF, its global warming potential is rather strong, whereas R-600a's is nearly none. The two refrigerants' desirable properties are compared. R-600a is a better refrigerant for a vapour compression refrigeration system, according to this comparison. The average values of the required parameters are then presented once a number of trials have been completed. To compare the refrigerants, the coefficient of performance, refrigeration effect, Carnot COP, and second law efficiency were calculated. The findings show that R-600a is a superior refrigerant. The system's primary components' exergy destruction has also been calculated. It demonstrates that the compressor has depleted its maximal exergy. R-600a is a strong alternative to R-134a, which is currently utilized in household refrigerators, according to the analysis.

The Effect of Suction Refrigerant Pressure Changes on the Performance of the Freeze-Drying System

The purpose of this study was to determine the effect of pressure changes on the performance of the freeze-drying refrigeration system. This research method is to vary the suction pressure of 10psi, 20psi, and 30psi on the performance of the freeze dryer cooling system where the type of refrigerant used is R404A with a compressor capacity of 1.5PK. Based on the test of this tool, the performance of the freeze-drying system produces Actual COP values at various pressures of 10psi, 20psi pressure, and 30psi pressure with values of 2.13, 2.44, 2.50, respectively. While the Carnot COP values for the variation of refrigerant suction pressure are 2.77, 3.03, and 3.10, respectively. While the efficiency values for pressure variations are 76.84%, 78.90%, and 82.25% of these values, it can be said that the highest efficiency value is at 30psi pressure. so it can be concluded that the freeze-drying machine that we make will work well at a pressure of 30 psi

Second order cyclic analysis of counter flow pulse tube refrigerator

Stirling machines are ecologically propitious refrigeration devices that utilize natural gases like helium, nitrogen, or air. Stirling machines are active refrigerators that should be designed with minimal vibrations and durability in order to fulfil current and future commercial de-mands and requirements. The present paper deals with the modification of the inertance pulse tube refrigerator in which the reservoir is eliminated and replaced with another pulse tube refrigerator. These two pulse tube refrigerators are operated at 180 degrees out of phase, called counter-flow pulse tube refrigerators (CFPTR). The second-order cyclic analysis approach is used to develop a mathematical model for evaluating the performance of CFPTR. This paper describes a modified second-order cyclic approach in detail. The performance of CFPTR is evaluated by estimating the ideal refrigerating effect, ideal power input, and losses individual-ly, yielding net power input and net refrigerating effect. The net refrigerating effect of 30.88W at 70K is obtained with the percentage of Carnot COP of 13.71. The CFD modeling of CFPTR is used to corroborate the second order cyclic model.

Environmentally-sound: An acoustic-driven heat pump based on phase change

Thermoacoustic technology is a promising approach for environmentally-friendly, low-cost heat pumping. Here, we present experiments demonstrating an acoustic-driven phase-change heat pump, and a theoretical performance analysis. An experimental setup was constructed and tested, employing a binary mixture of an ‘inert’ and a ‘reactive’ component as the working fluid. In such a system, the reactive component undergoes evaporation and condensation as part of the acoustic cycle, resulting in latent heat transfer that augments the overall heat flux. In order to further characterize the performance of such a system, a mathematical model of the thermoacoustic heat pump was employed. Experiments generally demonstrate that a larger cooling power and a higher COP can be obtained with phase change, compared with a classical system. However, this enhancement is only maintained as long as the temperature difference does not exceed a ’critical’ value. Otherwise, the time-averaged mass flux reverses its direction and thereafter carries heat against the heat pumping direction. This critical temperature difference is proportional to the value of the local acoustic impedance. We found that increasing the acoustic impedance by locally enlarging the cross-sectional area of the stack, resulted in better performance and enabled an increased temperature difference. Further, a high concentration of the reactive component is required for efficient operation. For instance, a COP above 40% of the Carnot COP can theoretically be obtained when the heat pump is operated with isopropanol at a concentration of ~0.8, at a temperature difference of 30°C.

A compact standing-wave thermoacoustic refrigerator driven by a rotary drive mechanism

The design, the manufacture and the testing of a novel refrigeration system that is based on the thermoacoustic energy-conversion technology is reported. A 1-D linear acoustic model is specifically developed and carefully implemented in the present device. The system consists of two similar harmonically-oscillating pistons driven by a commercial 1-HP rotary drive mechanism operating at a frequency of 42 Hz -hereby, replacing typical expensive acoustic drivers-, and a thermoacoustic stack within which the energy conversion of sound into heat is taken place. Air at ambient conditions is used as the working gas while the amplitude of the driver's displacement reaches 19 mm. The 30-cm-long stack is a simple porous ceramic material having 100 square channels per square inch. Oscillating-gas pressure and temperature measurements show a maximum temperature span between the stack hot and cold ends of about 27° with an estimated Carnot COP around 11. A corresponding dynamic pressure of 7-kPa-amplitude is recorded (drive ratio of 7%) and found in a good agreement with theoretical prediction. The measured cooling effects at various phase shifts between the motions of the two opposite pistons show qualitative agreement with available theoretical values. However, the system behavior is noted to be clearly non-linear with significant energy loss mechanisms. This work helps understanding the operation principles of thermoacoustic refrigerators and represents a keystone towards developing commercial thermoacoustic refrigerators.

Energy, Exergy and Anergy Analysis of Vertical Split Air Conditioner Under experimental ON-OFF Cycling

A time series analysis can help to observe the behavior of the system and specify the system faults. In addition, it also helps to explain the various energy flows in the system and further aid in reducing the thermodynamic losses. The intelligent supervisory LabVIEW software can monitor the incoming data from the system by using Arduino microcontroller and calculates the important parameters. Energy, exergy, and anergy analysis present in this paper to investigate the system performance as well as its components. To accomplish this, a 4-ton vertical split air conditioner based on vapor compression refrigeration cycle charged with refrigerant R-22 was modified for experimental analysis. The results showed that during 5400 secs of experimental study, the system shut down once by the software for 5 min. The volumetric and isentropic efficiencies of the compressor were 79.85 % and 64.48 % respectively. The maximum entropy generation was due to the compressor of 3.4 W/K while the maximum anergy was due to the condenser of 1.39 kW. The exergy efficiencies of the compressor, condenser, and the evaporator were 73.57, 40.18, and 47.45 % respectively. The system and Carnot COP were 2.53 and 4.9 respectively. The exergy efficiency of the air conditioning system was 48.7 %.&#x0D;

Effect of operation conditions on the second law analysis of a desiccant cooling system

In order to evaluate the potential of a desiccant based evaporative air conditioning system, a second law analysis of the systems was investigated. In this work, a wide range of working parameters that are regeneration temperature from 90°C to 110°C, volume flow rate from 2000m3 to 4000m3 and ambient air conditions which are relative humidity, ambient air temperature and wet-bulb temperature is carried out for performance calculation of the system. It is observed from results that the Carnot COP and the thermal COP of the system varies vice versa during the day. The highest value of Carnot COP and the thermal COP is about 25 and 0.62, respectively. Also, the cooling capacity has significant effect on the second law efficiency. The importance of this study shows that the second law analysis can provide useful information with respect to the theoretical upper limit of the system performance, which cannot be obtained from the first law of thermodynamic analysis alone.

Performance analysis for Feynman's ratchet as a refrigerator with heat leak under different figure of merits

The performance of Feynman's ratchet refrigerator with heat leak has been studied under the maximum COP, maximum cooling rate and maximum χ figure of merits. The χ criterion considers both the COP and cooling rate, which can been seen as a trade-off between COP and cooling rate. Therefore the traditional performance region between maximum cooling rate and maximum COP can be divided into two more specific ones (the region between maximum cooling rate and maximum χ, and the region between maximum χ and maximum COP), which represent two different operating demands. The results shows that the operating parameters such as heat leak, external moment, intrinsic energy potential and the Carnot COP have significant impacts on the performance of the Feynman's ratchet refrigerator. If the parameters are properly chosen, the refrigerator can be controlled to operate within the optimal regimes to fulfill the actual specified demands. Furthermore, for given Carnot COP and heat leak, there exist upper bounds for the maximum value of the maximum COP, maximum cooling rate and maximum χ, respectively.

Development of 1 kW Stirling cryocooler using a linear compressor

Cryogenic cooling systems for HTS electric power devices require a reliable and efficient high-capacity cryocooler. A Striling cryocooler with a linear compressor can be a good candidate. It has advantages of low vibration and long maintenance cycle compared with a kinematic-driven Stirling cryocooler. In this study, we developed a dual-opposed linear compressor of 12 kW electric input power with two 6 kW linear motors. Electrical performance of the fabricated linear compressor is verified by experimental measurement of thrust constant. The developed Stirling cryocooler has a gamma-type configuration. The piston and displacer are supported with a flexure spring. A slit-type heat exchanger is adopted for the cold and warm-end, and the generated heat is rejected by cooling water. In the cooling performance test, waveforms of voltage, current, displacement and pressure are obtained and their amplitude and phase difference are analysed. The developed cryocooler reaches 47.8 K within 23.4 min. with no-load. Heat load tests shows a cooling capacity of 440 W at 78.1 K with 6.45 kW of electric input power and 19.4 of % Carnot COP.

Development of high capacity stirling cryocooler

Abstract Cryogenic cooling system for HTS electric power devices requirea reliable and efficient highs -capacity cryocooler. A Striling cryocooler with a linear compressor can be a good candidate. It has advantages of low vibration and long maintenance cycle compared with a kinematic-driven Stirling cryocooler. In this study, we developed dual-opposed linear compressor of 12 kW electric input power with two 6 kW linear motors. Electrical performance of fabricated linear compressor is verified by experimental measurement of thrust constant. The developed Stirling cryocooler has gamma-type configuration. Piston and displacer are supported with flexure spring. A slit -type heat exchanger is adopted for cold and warm -end, and the generated heat is rejected by cooling water. In cooling performance test, waveforms of voltage, current, displacement and pressure are obtained and their amplitude and phase difference are analysed. Moreover, temperatures of cooling water, housing and l inear motor are recorded and electric power parameters of driving circuit are also obtained. The developed Stirling cryocooler reaches to 47.8 K within 23.4 min. with no -load. From heat load tests, it shows cooling capacity of 440 W at 78.1 K with 6.45 kW of electric input power and 19.4 of % Carnot COP.

Design and modeling of a fluid-based micro-scale electrocaloric refrigeration system

A refrigeration system composed of silicon MEMS cooling elements is designed based on the electrocaloric (EC) effect in a P(VDF–TrFE–CFE) terpolymer, poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) 59.2/33.6/7.2mol%. Each cooling element includes two diaphragm actuators fabricated in the plane of a silicon wafer, which drive a heat transfer fluid back and forth across terpolymer layers that are placed between them. In the EC effect, reversible temperature and entropy changes related to polarization changes appear in a material under the application and removal of an electric field. Finite element simulations are performed to explore the system performance. The effect of the applied electric field is studied, and the time lag between the electric field and the diaphragm motion is found to significantly affect the cooling power. A parametric study of the operating frequency, externally-applied temperature span, and the electric field amplitude are conducted. The results indicate that when the system is operated at a temperature span of 15K, a cooling power density of 3W/cm2 and a percent of Carnot COP of 31% are achieved for one element.

Realistic minimum desorption temperatures and compressor sizing for activated carbon + HFC 134a adsorption coolers

A low thermal diffusivity of adsorption beds induces a large thermal gradient across cylindrical adsorbers used in adsorption cooling cycles. This reduces the concentration difference across which a thermal compressor operates. Slow adsorption kinetics in conjunction with the void volume effect further diminishes throughputs from those adsorption thermal compressors. The problem can be partially alleviated by increasing the desorption temperatures. The theme of this paper is the determination the minimum desorption temperature required for a given set of evaporating/condensing temperatures for an activated carbon + HFC 134a adsorption cooler. The calculation scheme is validated from experimental data. Results from a parametric analysis covering a range of evaporating/condensing/desorption temperatures are presented. It is found that the overall uptake efficiency and Carnot COP characterize these bounds. A design methodology for adsorber sizing is evolved.

Entropic analysis of adsorption open cycles for air conditioning. Part 2: interpretation of experimental data

The full second-law analysis, developed in Part 1 (M. Pons and A. Kodama, Int. J. Energy Res. 2000; 24: 251–262) is applied to experimental results. That approach takes into account the irreversibilities due to the open character of the cycle. Measurements are performed on a solid desiccant cooling unit operated in the ventilation mode. Experimental data permit us to establish the entropy balance of the unit. The results show that the sum of all the considered entropy productions completely explain the difference between the Carnot COP and the actual COP of the unit. The effects of three experimental parameters are investigated: the rotation speed of the dehumidifier (desiccant wheel), the air velocity and the regeneration temperature. Experimental results show that there exists an optimal rotation speed which results from a combination between the different entropy productions in the cycle. When the air velocity is increased, together with an accordingly optimized rotation speed, the cooling capacity increases while the COP decreases due to increases in the entropy productions in the dehumidifier and sensible heat exchanger. Moreover, it appears that the most significant entropy productions take place in the dehumidifier and heating system. In the investigated experimental unit, these two entropy productions have similar magnitudes. However, when the regeneration temperature is increased, the irreversibilities due to mass exchanges with outside air become comparable to these and surely should not be forgotten in a global optimization of the process. The present analysis is a solid basis for reducing the largest entropy productions thus optimizing the process. Copyright © 2000 John Wiley & Sons, Ltd.

The impact of heat exchanger type on the design and performance of optimized thermoacoustic refrigerators

A basic thermoacoustic cooler design was optimized with three different types of heat exchangers to obtain high COP predictions in a 200-W refrigeration application. The heat exchanger designs employed: (1) a parallel array of copper-alloy plates (conduction); (2) a single-pass, single row of finned tubes, with water/ethylene glycol mixtures as the secondary fluids (finned tube); and (3) a parallel array of infinitely conductive plates (ideal). The optimization scheme utilized the Simplex algorithm, and the analysis was performed by DELTAE coupled with an original heat exchanger modeling tool which incorporated conventional straight fin analysis and semiempirical flow correlations. The external cooling and heat rejection temperatures were fixed at 260 and 310 K, for which the Carnot COP is 5.2. The best COP’s resulting from the optimization of around 25 design parameters for each case were approximately 2.0 (conduction), 2.5 (finned tube), and 3.0 (ideal). In the finned tube device, the COP was limited by the cold exchanger secondary fluid properties. The use of a phase change secondary fluid, in conjunction with a heat pipe, for example, may further improve the performance of finned tube heat exchangers. The ideal case performance represents a probable upper limit for the configuration considered.

A comparative thermodynamic study of sorption systems: second law analysis

As a consequence of the phasing out of CFCs, sorption systems appear to be potential candidates to replace vapour compression systems. Amongst sorption systems there exists a choice between several systems, such as liquid absorption, solid adsorption and chemical reaction heat pumps. Nevertheless, few comparative studies between these systems have been undertaken so far. It is the aim of this paper to present such a study based on combined first and second law thermodynamical analysis of the different cycles. Simple entropy generation processes explain why the basic cycles for these systems yield performances much lower than the Carnot efficiency. The possibility of operating regenerative cycles with internal heat recovery and higher efficiencies has also been considered for typical common base conditions. Different entropy generation considerations have been visualised, such as thermal coupling (external/internal), non-uniform temperature component entropy production and other irreversible processes for the COP degradation in these systems. It is found that thermal coupling irreversibilities in solid sorption systems and other internal irreversibilities in liquid sorption systems with solution heat exchanger are dominant in the actual COP degradation with respect to the reversible Carnot COP.