Magnetic and magnetocaloric effect of Er_(20)Ho_(20)Dy_(20)Cu_(20)Ni_(20)high-entropy metallic glass

Er_(20)Ho_(20)Dy_(20)Cu_(20)Ni_(20)high-entropy metallic glass exhibited excellent magnetic refrigeration material with a wide temperature range and high refrigeration capacity(RC)was reported.Er_(20)Ho_(20)Dy_(20)Cu_(20)Ni_(20)high-entropy metallic glass was observed with typical spin glass behavior around 15.5 K.In addition,we find that the magnetic entropy change(-△S_(M))originates from the sample undergoing a ferromagnetic(FM)to paramagnetic(PM)transition around 20 K.Under a field change from 0 T to 7 T,the value of maximum magnetic entropy change(-△S_(M)^(max))reaches 12.5 J/kg·K,and the corresponding value of RC reaches 487.7 J/kg in the temperature range from 6 K to 60 K.The large RC and wide temperature range make the Er_(20)Ho_(20)Dy_(20)Cu_(20)Ni_(20)high-entropy metallic glass be a promising material for application in magnetic refrigerators.

Development of 400-μW cryogen-free dilution refrigerators for quantum experiments

We have successfully developed cryogen-free dilution refrigerators with medium cooling power that can be applied to quantum experiments. Breakthroughs have been made in some key technologies and components of heat switches and dilution units. Our prototype has been running continuously and stably for more than 100 hours below 10 m K, with a minimum temperature of 7.6 m K and a cooling power of 450 μW at 100 m K. At the same time, we have also made progress in the application of dilution refrigerators, such as quantum computing, low-temperature detector, and magnet integration. These indicators and test results indicate good prospects for application in physics, astronomy, and quantum information.

Intermodal Competition: Cargo Airships versus Long-Haul Trucking for Perishable Commodities

Intermodal competition changes with changes in technology, economics, and environmental concerns. Trucks and airships are generally considered not to be competitors, but this depends on the distance of haul. The tonne-kilometer cost of trucking rises much more quickly with distance than it does the cost of a cargo airship. At some distance, the two modes are direct substitutes. The costs of the Mexico-Canada refrigerated truck supply chain are compared with the costs of a 100t-lift, electrically-powered airship. The flight characteristics of the Hindenburg Zeppelin are used as a model for a modern cargo airship. The supply chain cost of trucking tomatoes is used to test the theorical proposition. The cost difference works out to about US10￠/kg (5￠/lb) advantage for trucking Mexican tomatoes to Canada. However, this cost disadvantage of the airship could be made up by their vibrationless ride, better air circulation and one-day service versus four days by truck. This alternative form of transportation could have a positive impact on worldwide north-south distribution of food. Airships can overcome trade barriers and distance to open new markets for perishable food exports. In addition, they would reduce the carbon emissions of transport. Canada imports 160,000 refrigerated truckloads of fruits and vegetables by from the southern US and Mexico. With an average driving distance of 3,000 km, these trucks emit 606,000 MT of CO2 annually. Airships powered by hydrogen fuel cells would have zero-carbon emissions. Markets are not yet incorporating the environmental advantage of airships in any freight comparison, but inevitably this will be important.

A Review on Technologies for the Use of CO2 as a Working Fluid in Refrigeration and Power Cycles

The use of carbon dioxide as a working fluid has been the subject of extensive studies in recent years, particularly in the field of refrigeration where it is at the heart of research to replace CFC and HCFC. Its thermodynamic properties make it a fluid of choice in the efficient use of energy at low and medium temperatures in engine cycles. However, the performance of transcritical CO2 cycles weakens under high temperature and pressure conditions, especially in refrigeration systems;On the other hand, this disadvantage becomes rather interesting in engine cycles where CO2 can be used as an alternative to the organic working fluid in small and medium-sized electrical systems for low quality or waste heat sources. In order to improve the performance of systems operating with CO2 in the field of refrigeration and electricity production, research has made it possible to develop several concepts, of which this article deals with a review of the state of the art, followed by analyzes in-depth and critical of the various developments to the most recent modifications in these fields. Detailed discussions on the performance and technical characteristics of the different evolutions are also highlighted as well as the factors affecting the overall performance of the systems studied. Finally, perspectives on the future development of the use of CO2 in these different cycles are presented.

Cooling High Power Dissipating Artificial Intelligence (AI) Chips Using Refrigerant

High power dissipating artificial intelligence (AI) chips require significant cooling to operate at maximum performance. Current trends regarding the integration of AI, as well as the power/cooling demands of high-performing server systems pose an immense thermal challenge for cooling. The use of refrigerants as a direct-to-chip cooling method is investigated as a potential cooling solution for cooling AI chips. Using a vapor compression refrigeration system (VCRS), the coolant temperature will be sub-ambient thereby increasing the total cooling capacity. Coupled with the implementation of a direct-to-chip boiler, using refrigerants to cool AI server systems can materialize as a potential solution for current AI server cooling demands. In this study, a comparison of 8 different refrigerants: R-134a, R-153a, R-717, R-508B, R-22, R-12, R-410a, and R-1234yf is analyzed for optimal performance. A control theoretical VCRS model is created to assess variable refrigerants under the same operational conditions. From this model, the coefficient of performance (COP), required mass flow rate of refrigerant, work required by the compressor, and overall heat transfer coefficient is determined for all 8 refrigerants. Lastly, a comprehensive analysis is provided to determine the most optimal refrigerants for cooling applications. R-717, commonly known as Ammonia, was found to have the highest COP value thus proving to be the optimal refrigerant for cooling AI chips and high-performing server applications.

Entropy Assessment on Environmental Influence of Condense Heat in Recovery System in Air-Conditioning Refrigerating Machine

This paper presented an entropy evaluation method for the influences of condense heat recovery system on the environment.Aiming at the damage of the condense heat to the environment,an entropy of resource loss and an emission entropy from the condense heat recovery system in the air conditioning refrigerating machine were introduced.For the evaluation of the entropies,we developed a new algorithm for the parameter identification,called the composite influence coefficient,based on the Least Squares Support Vector Machine method.By simulation,the numerical experiments shows that the Least Squares Support Vector Machine method is one of the powerful methods for the parameter identification to compute the damage entropy of the condense heat,with the largest training error being-0.025(the relative error being-3.56%),and the biggest test error being 0.015(the relative error being 2.5%).

Thermodynamical Evaluation on Magnetocaloric Effect of Magnetic Refrigerating Materials Near Room Temperature

The relationship between isothermal magnetic entropy change DELTA S andadiabatic temperature change DELTA T_(ad) was deduced according to the principles of thermodynamics.The MCE and the engineering application were discussed for Gd and several new kinds of magneticrefrigerating materials near room temperature, Gd_5Si_2Ge_2, MnFeP_(0.45)As_(0.55) and LaFe_(11.2)Co_(0.7)Si_(1.1). Isothermal entropy change is proportional to adiabatic temperature change with afactor of T/C (T is temperature, C is heat capacity). When the comparison of magnetacoloric effectis made for two different materials, we should consider isothermal entropy change as well asadiabatic temperature change.

Study on the Irreversible Thermodynamics of a Marine Engine Exhaust-powered Adsorption Refrigerating System

This study investigates the heat and mass transfer mechanism of a marine engifie exhaust-powered adsorption refrigerating system by using irreversible thermodynamics. The equations of entropy-production rate and the linear phenomenological equations of thermodynamic flux and force are established. The conventional experimental facilities of unit tube are developed and the phenomenological coefficients are obtained by fitting the experimental data. It is concluded that the thermodynamic process in the adsorbent bed is determined by the coupling effect of the heat and mass transfer; furthermore, the mass transfer is determined by the heat transfer. Taking some measures to increase heat transfer can improve the performance of the adsorption refrigerating system. The conclusions presented in this paper may be of value to the engineering applications of the system.

Shengzhou Pushiar Refrigerating Machine Company

Our company is a member of China Refrigerating Air Conditioner Industry Association, and Shanghai Refrigerating Air Conditioner Machinery Industry Association as well. In addition, it is also a member of China Washing Machinery Garment Machinery.

Economy of Energy during Refrigerating Machine Operation

Idealized cycles of refrigerating machines with adiabatic and isothermal compression of refrigerant vapor were investigated. Energetic characteristics of cycles： specific mass and volume cooling capacity q0 and qv, work of compression 1, refrigerating coefficient of performance e and power N for drive of compressor were compared. These characteristics were calculated for eight refrigerants at temperature of their condensation 30 ℃ and temperatures of boiling -15℃ and -30 ℃. The calculations show that the use of isothermal compression of refrigerant vapor ensures economy of energy during refrigerating machine operation.

Magnetocaloric properties of phenolic resin bonded La(Fe,Si)13-based plates and its use in a hybrid magnetic refrigerator

We present a simple hot press-based method for processing La(Fe,Si)13-based compounds consisting of La–Fe–Co–Si–C particles and phenolic resin. The magnetic entropy change △S per unit mass for the La Fe_(10.87)Co_(0.63)Si_(1.5)C_(0.2)/phenolic resin compounds have nearly the same magnitude with the base materials. With the content of phenolic resin of 5.0 wt%, the compound conductivity is 3.13 W·m^(-1)·K^(-1). In order to measure the cooling performance of La(Fe,Si)13-based compounds,the La(Fe_(11.6-x)Co_(x))Si_(1.4)C_(0.15)(x =0.60, 0.65, 0.75, 0.80, 0.85)/phenolic resin compounds were pressed into thin plates and tested in a hybrid refrigerator that combines the active magnetic refrigeration effect with the Stirling cycle refrigeration effect. The test results showed that a maximum cooling power of 41 W was achieved over a temperature span of 30 K.

Effect of Refrigerant on the Performance of a C3/MRC Liquefaction Process

The Mixed Refrigerant(MR)component is an important factor influencing the performances of natural gas lique-faction processes.However,there is a lack of systematic research about the utilization of propane pre-cooled(C3/MRC).In this paper,this mixed refrigerant cycle liquefaction process is simulated using the HYSYS software and the main influential parameters involved in the process are varied to analyze their influence on the liquefaction rate and power consumption.The results show that an effective way for lowering the power consumption of the compressor consists of reducing the flow through the compressor through optimization of the percentage of mixed refrigerant.The power consumption of the compressor in the hybrid refrigeration process is affected by both flow and pressure ratios.Its specific power consumption can be reduced by increasing the flow and decreasing the pressure ratio at the same time.The increase in refrigerant pressure at the high-pressure end can significantly mitigate the energy loss of the heat exchanger and compressor.

Analysis of a Water-Cooled Unit under Different Loads

In order to ensure the safe operation of the compressors used in water chillers,in the present study some interlock protections have been added to the related design.These include a low pressure protection,a high pressure protection,an exhaust temperature protection and a differential pressure protection.Some tests have been conducted by tuning the saturation suction and exhaust temperatures of the compressor through adjustment of the cold source outlet temperature and the ambient temperature.The results show that the ambient temperature increases with decreasing device load and increasing fan speed under the same saturated suction temperature;the device refrigerating capacity steps up with augmenting load and dropping saturation exhaust temperature,while it is not greatly affected by the fan speed.Moreover,the Energy efficiency ratio(COP)decreases with the rise of the saturation exhaust temperature.This parameter is not affected much by the device load and fan speed at high saturation exhaust temperature,while it improves on increasing the device load and decreasing the fan speed at low saturation exhaust temperature.

A Systematic Review of Thermoelectric Peltier Devices: Applications and Limitations

Conventional refrigeration processes release ammonia and freon into the atmosphere,which results in global warming.These problems may be overcome by using thermoelectric modules because of the absence of coolants or refrigerants in these systems.However,the cooling performances of such modules are relatively small in comparison to those of conventional refrigerators.In this paper,the working principles of thermoelectric modules are discussed together with a review of different relevant aspects,namely:the thermoelectric materials,and their mechanical properties used to build thermoelectric devices,different types of thermoelectric devices available on the market,mathematical modeling of thermoelectric materials,and various applications of thermoelectric materials in different fields.

Effect of an Internal Heat Exchanger on the Performances of a Double Evaporator Ejector Refrigeration Cycle

A theoretical investigation is presented about a double evaporator ejector refrigeration cycle(DEERC).Special attention is paid to take into account the influence of the sub-cooling and superheating effects induced by an internal heat exchanger(IHX).The ejector is introduced into the baseline cycle in order to mitigate the throttling process losses and increase the compressor suction pressure.Moreover,the IHX has the structure of a concentric counter-flow type heat exchanger and is intentionally used to ensure that the fluid at the compressor inlet is vapor.To assess accurately the influence of the IHX on the DEERC performance,a mathematical model is derived in the frame of the dominant one-dimensional theory for ejectors.The model also accounts for the friction effect in the ejector mixing section.The equations of this model are solved using an Engineering Equation Solver(EES)for different fluids.These are:R134a as baseline fluid and other environment friendly refrigerants used for comparison,namely,R1234yf,R1234ze,R600,R600a,R290,R717 and R1270.The simulation results show that the DEERC with an IHX can achieve COP(the coefficient of performance)improvements from 5.2 until 10%.

Structure, magnetism and magnetocaloric effects in Er_(5)Si_(3)B_(x)(x=0.3,0.6) compounds

We investigate the structure, magnetic properties, magnetic phase transitions and magnetocaloric effects(MCEs) of Er5Si3Bx(x=0.3,0.6) compounds. The Er5Si3Bx(x = 0.3, 0.6) compounds crystalize in a Mn5Si3type hexagonal structure(space group: P63/cm) and exhibit a successive complicated magnetic phase transition. The extensive magnetic phase transitions contribute to the broad temperature range of MCEs exhibiting in Er_(5)Si_(3)B_(x)(x=0.3,0.6) compounds, with maximum magnetic entropy change(-ΔSM_(max)) and refrigeration capacity of 10.2 J·kg^(-1)·K^(-1), 356.3 J/kg and 11.5 J·kg^(-1)·K^(-1),393.3 J/kg under varying magnetic fields 0–5 T, respectively. Remarkably, the δTFWHMvalues(the temperature range corresponding to 1/2×|-ΔSM_(max)|) of Er5Si3Bx(x=0.3,0.6) compounds were up to 41.8 K and 39.6 K, respectively. Thus, the present work provides a potential magnetic refrigeration material with a broad temperature range MCEs for applications in cryogenic magnetic refrigerators.

Performance optimization on finite-time quantum Carnot engines and refrigerators based on spin-1/2 systems driven by a squeezed reservoir

We investigate the finite-time performance of a quantum endoreversible Carnot engine cycle and its inverse operation-Carnot refrigeration cycle,employing a spin-1/2 system as the working substance.The thermal machine is alternatively driven by a hot boson bath of inverse temperatureβ_(h)and a cold boson bath at inverse temperatureβ_(c)(>βh).While for the engine model the hot bath is constructed to be squeezed,in the refrigeration cycle the cold bath is established to be squeezed,with squeezing parameter r.We obtain the analytical expressions for both efficiency and power in heat engines and for coefficient of performance and cooling rate in refrigerators.We find that,in the high-temperature limit,the efficiency at maximum power is bounded by the analytical valueη_(+)=√sech(2r)(1-η_(C)),and the coefficient of performance at the maximum figure of merit is limited byε_(+)=√sech(2r)(1+ε_(C))/sech(2r)(1+ε_(C))-εC)-1,whereη_(C)=1-β_(h)/β_(c)andε_(C)=β_(h)/(β_(c)-β_(h))are the respective Carnot values of the engines and refrigerators.These analytical results are identical to those obtained from the Carnot engines based on harmonic systems,indicating that the efficiency at maximum power and coefficient at maximum figure of merit are independent of the working substance.

Performance Analysis of a Solar Continuous Adsorption Refrigeration System

A study is conducted on the performances of a solar powered continuous-adsorption refrigerator considering two particular days as references cases,namely,the summer solstice(June 21st)and the autumn equinox(September 21st).The cooling capacity,system performance coefficient and the daily rate of available cooling energy are assessed.The main goal is to compare the performances of a solar adsorption chiller equipped with a hot water tank(HWT)with an equivalent system relying on solar collectors with no heat storage module.The daily cooling rates for the solar refrigerator are found to be 102.4 kWh and 74.3 kWh,respectively,on June 21st and on September 21st,using a total collector’s area of 43.47 m2.The corresponding values for the adsorption chiller equipped with a hot water tank of 2 m3(and using a total collector’s area of 72.45 m2),are 127.1 kWh and 106.13 kWh,respectively.

Establishment of a Model for the Calculation of the COP of a Solar Adsorption Refrigerator

This paper deals with the evaluation of the Coefficient of Performance (COP) of solar adsorption refrigeration. In the literature, simulation models to predict the thermal behaviour and the coefficient of performance of these systems are uncommon. This is why we suggest a model to simulate the operation of the machine in a typical hot and dry climate of the city of Ouagadougou. The objective is to provide a model for calculating the COP from the measurement of the ambient temperature and the irradiation of a given site. Starting from mathematical modelling, a resolution and simulation were made with COMSOL software based on the Dubinin-Astakhov adsorption model, the heat transfer balance equations, and the Linear Driving Force (LDF) model to describe the thermal behaviour of the system. A one-week measurement sequence on the adsorption solar refrigerator at the Albert Schweitzer Ecological Centre (CEAS) validated the numerical results. The measurement shows that for the days with high sunshine, the temperature of the reaction medium reaches 110°C, and the pressure reaches 500 mbar. This leads to a production of cold that allows it to reach the temperature of -5°C at the evaporator. Under these conditions, the COP is worth 14%. These results are obtained both by numerical simulation using the COMSOL 5.1 software and after a measurement session on the solar refrigerator available to the CEAS. We obtained an experimental and theoretical coefficient of performance varying between 9% and 14% with a difference of between 0% and 3%. We conclude that our model is suitable to estimate the COP of any device based on its thermal properties, the ambient temperature and the irradiation of a given site.