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.

Synthesis and electrochemical performances of LiCoO_2 recycled from the incisors bound of Li-ion batteries

A new LiCoO2 recovery technology for Li-ion batteries was studied in this paper. LiCoO2 was peeled from the Al foil with dimethyl acetamide （DMAC）, and then polyvinylidene fluoride （PVDF） and carbon powders in the active material were eliminated by high temperature calcining. Subsequently, Li2CO3, LiOH-H20 and LiAc-2H2O were added into the recycled powders to adjust the Li/Co molar ratio to 1.00. The new LiCoO2 was obtained by calcining the mixture at 850℃ for 12 h in air. The structure and morphology of the recycled powders and resulting samples were studied by XRD and SEM techniques, respectively. The layered structure of LiCoO2 synthesized by adding Li2CO3 is the best, and it is found to have the best characteristics as a cathode material in terms of charge-discharge capacity and cycling performance. The first discharge capacity is 160 mAh·g^-1 between 3.0-4.3 V. The discharge capacity after cycling for 50 times is still 145.2 mAh·g^-1.

Thermal performance analysis of advanced partial gasification combined cycle

This paper presents the thermodynamic performance analysis and comparison of four kinds of advanced pressurized fluidized bed combustion combined cycle (APFBC-CC) system schemes, two based on pressurized fluidized bed (PFB) combustion and the other two based on atmospheric circulating fluidized bed (CFB) combustion. The results show that the first scheme avoids high temperature gas filter, but has the lower cycle efficiency and syngas heating value. The second scheme can gain the highest cycle efficiency, however it is better to now lower the filter operating temperature. The third and fourth schemes, based on CFB, have lower efficiencies than the second one. But the fourth one, with preheating air/steam for gasification, can obtain the highest heating value of syngas and gain higher efficiency than the third one.

Effect of SAP on Properties of High Performance Concrete under Marine Wetting and Drying Cycles

The internal curing effect of superabsorbent polymer(SAP) on the properties of high performance concrete(HPC) under marine wetting and drying cycles(WD cycles) was investigated. Compressive strength, hydration and chloride migration were experimentally investigated and the results were evaluated by compasison with those under fresh water curing(FW). Water absorption and porosity were also evaluated only under WD cycles. The results showed the important influence of wetting and drying cycles on the properties of SAP modified HPC properties. Carefully designed, SAP minimized the long-term compressive strength of HPC under marine WD cycles. The hydration rate was faster in the initial curing, but became lower as compared with that cured in FW. In addition, SAP improved the long-term water absorption resistance and chloride migration resistance of HPC under marine WD cycles. The examination of the porosity showed a lower increase of the volume of capillary pores in SAP modified HPC under long term WD cycles compared with that without SAP. Therefore, internal curing by SAP could improve the durability properties of HPC under marine WD cycles.

Effect of yttrium and calcium additions on electrochemical behaviors and discharge performance of AZ80 anodes for Mg-air battery

The effects of yttrium(Y)and yttrium+calcium(Y+Ca)additions on the electrochemical properties and discharge performance of the as-extruded Mg−8Al−0.5Zn−0.2Mn(AZ80)anodes for Mg−air batteries were investigated.The results show that the addition of 0.2 wt.%Y increased the corrosion resistance and discharge activity of AZ80 anode.This was attributed to the fine and sphericalβ-Mg_17)Al_(12) phases dispersing evenly in AZ80+0.2Y alloy,which suppressed the localized corrosion and severe“chunk effect”,and facilitated the rapid activation ofα-Mg.Combinative addition of 0.2 wt.%Y and 0.15 wt.%Ca generated grain refinement and a reduction of theβ-Mg_17)Al_(12) phase,resulting in a further enhancement in discharge voltage.However,the incorporation of Ca in Mg_17)Al_(12) and Al_(2)Y compounds compromised the corrosion resistance and anodic efficiency of AZ80+0.2Y+0.15Ca anode.Consequently,AZ80+0.2Y anode exhibited excellent overall discharge performance,with the peak discharge capacity and anodic efficiency of 1525 mA·h·g^(−1) and 67%at 80 mA/cm^(2),13%and 14%higher than those of AZ80 anode,respectively.

Mechanical performances and microstructural characteristics of reactive MgO-carbonated silt subjected to freezing-thawing cycles

The characteristics of reactive magnesia(MgO)-carbonated silt in respect to long-term stability have not been well understood in severely cold climate despite the usage of reactive MgO in enhancing the engineering performances.Under the binder content of 15%and initial water content of 25%,MgO-admixed silt specimens were carbonized for 3 h and 6 h and then subjected to different numbers of freezingthawing(F-T)cycles.After different F-T cycles,the physico-mechanical properties of MgO-carbonated silt were analyzed in comparison with Portland cement(PC)-stabilized silt through physical and unconfined compression tests.Besides,a series of micro tests on MgO-carbonated specimens was performed including X-ray diffraction(XRD),scanning electron microscopy(SEM)and mercury intrusion porosimetry(MIP)tests.The results demonstrate that both mass change ratio and moisture content of carbonated/stabilized silt decrease,and these values of MgO-carbonated silt are significantly lower while the density is higher compared to PC-stabilized silt.The strengths and moduli of MgO-carbonated silt are still two times higher than those of PC-stabilized specimens and the strength change ratio of keeps above0.8 after F-T cycles.There is no visible transformation between nesquehonite and dypingite/hydromagnesite,although the XRD peaks of nesquehonite decrease and the bonding and filling effects weaken slightly.After 6 and 10 F-T cycles,the pore-size characteristics changed from a unimodal distribution to a three-peak and bimodal distribution,respectively.The total,macro and large pore volumes increase obviously while the medium and small pore volumes decrease except for intra-aggregate pore.The findings show better F-T durability of MgO-carbonated silt,which would be helpful for facilitating the application of MgO carbonation in the soil treatment.

Dynamic Multi-Physics Behaviors and Performance Loss of Cylindrical Batteries Upon Low-Velocity Impact Loading

In challenging operational environments,Lithium-ion batteries(LIBs)inevitably experience mechanical stresses,including impacts and extrusion,which can lead to battery damage,failure,and even the occurrence of fire and explosion incidents.Consequently,it is imperative to investigate the safety performance of LIBs under mechanical loads.This study is grounded in a more realistic coupling scenario consisting of electrochemical cycling and low-velocity impact.We systematically and experimentally uncovered the mechanical,electrochemical,and thermal responses,damage behavior,and corresponding mechanisms under various conditions.Our study demonstrates that higher impact energy results in increased structural stiffness,maximum temperature,and maximum voltage drop.Furthermore,heightened impact energy significantly influences the electrical resistance parameters within the internal resistance.We also examined the effects of State of Charge(SOC)and C-rates.The methodology and experimental findings will offer insights for enhancing the safety design,conducting risk assessments,and enabling the cascading utilization of energy storage systems based on LIBs.

Performance of pulsed plasma thruster at low discharge energy

As the size of satellites scales down, low-power and compact propulsion systems such as the pulsed plasma thruster(PPT) are needed for stabilizing these miniature satellites in orbit. Most PPT systems are operated at 2 J or more of discharge energy. In this work, the performance of a PPT with a side-fed, tongue-flared electrode configuration operated within a lower discharge energy range of 0.5-2.5 J has been investigated. Ablation and charring of the polytetrafluoroethylene propellant surface were analyzed through field-effect scanning electron microscopy imaging and energy-dispersive X-ray spectroscopy. When the discharge energy fell below 2 J, inconsistencies occurred in the specific impulse and the thrust efficiency due to the measurement of the low mass bit. At energy ≥2 J, the performance parameters are compared with other PPT systems of similar configuration and discussed in depth.

KOH-assisted aqueous synthesis of ZIF-67 with high-yield and its derived cobalt selenide/carbon composites for high-performance Li-ion batteries

To solve the environmental pollution and low yield during the sythesis of zeolitic imidazolate frameworks(ZIFs)and their derived materials,a KOH-assisted aqueous strategy is proposed to synthesize cobalt zeolitic imidazolate framework(ZIF-67)polyhedrons,which are used as precursors to prepare cobalt selenide/carbon composites with different crystal phases(Co_(0.85)Se,CoSe_2).When evaluated as anode material for lithium ion batteries,Co_(0.85)Se/C composites deliver a reversible capacity of 758.7 m A·h·g^(-1)with a capacity retention rate of 90.5%at 1.0 A·g^(-1)after 500 cycles,and the superior rate capability is 620 m A·h·g^(-1)at 2.0 A·g^(-1).The addition of KOH accelerates the production of ZIF-67 crystals by boosting deprotonation of dimethylimidazole,resulting in rapid growth and structures transition from two-dimensional to three-dimensional of ZIF-67 in aqueous solution,which greatly promotes the application of MOFs in the field of energy storage and conversion.

Improved Diurnal Cycle of Precipitation on Land in a Global Non-Hydrostatic Model Using a Revised NSAS Deep Convective Scheme

In relatively coarse-resolution atmospheric models,cumulus parameterization helps account for the effect of subgridscale convection,which produces supplemental rainfall to the grid-scale precipitation and impacts the diurnal cycle of precipitation.In this study,the diurnal cycle of precipitation was studied using the new simplified Arakawa-Schubert scheme in a global non-hydrostatic atmospheric model,i.e.,the Yin-Yang-grid Unified Model for the Atmosphere.Two new diagnostic closures and a convective trigger function were suggested to emphasize the job of the cloud work function corresponding to the free tropospheric large-scale forcing.Numerical results of the 0.25-degree model in 3-month batched real-case simulations revealed an improvement in the diurnal precipitation variation by using a revised trigger function with an enhanced dynamical constraint on the convective initiation and a suitable threshold of the trigger.By reducing the occurrence of convection during peak solar radiation hours,the revised scheme was shown to be effective in delaying the appearance of early-afternoon rainfall peaks over most land areas and accentuating the nocturnal peaks that were wrongly concealed by the more substantial afternoon peak.In addition,the revised scheme enhanced the simulation capability of the precipitation probability density function,such as increasing the extremely low-and high-intensity precipitation events and decreasing small and moderate rainfall events,which contributed to the reduction of precipitation bias over mid-latitude and tropical land areas.

Analysis of the Gas Puffing Performance for Improving the Repeatability of Ohmic Discharges in the SUNIST Spherical Tokamak

The gas puffing performance plays a key role in repeatable discharges in the Sino- UNited Spherical Tokamak （SUNIST） experiments. In this paper, temporal evolution of the gas pressure in the vacuum vessel and the dependence of the repeatability of plasma discharges on different timing arrangements between the gas puffing pulse and the Ohmic field have been experimentally investigated. The results show that, after a fast rising phase, the gas pressure becomes quasi-stationary. In the regime of the discharges being started up when the gas pressure has already reached the quasi-stationary state for about 37 ms, an improved repeatability of the plasma discharges is achieved.

Performance comparison and analysis of a combined power and cooling system based on organic Rankine cycle

A novel power and cooling system combined system which coupled organic Rankine cycle(ORC) with vapor compression refrigeration cycle(VCRC) was proposed. R245 fa and butane were selected as the working fluid for the power and refrigeration cycle, respectively. A performance comparison and analysis for the combined system was presented. The results show that dual-pressure ORC-VCRC system can achieve an increase of 7.1% in thermal efficiency and 6.7% in exergy efficiency than that of basic ORC-VCRC. Intermediate pressure is a key parameter to both net power and exergy efficiency of dual-pressure ORC-VCRC system. Combined system can produce maximum net power and exergy efficiency at 0.85 MPa for intermediate pressure and 2.4 MPa for high pressure, respectively. However, superheated temperature at expander inlet has little impact on the two indicators. It can achieve higher overall COP, net power and exergy efficiency at smaller difference between condensation temperature and evaporation temperature of VCRC.

Thermodynamic Comparison Analysis on CO_2 Transcritical Reverse Cycles with IHX or Expander

To improve the coefficient of performance （COP） of CO2 transcritical reverse cycle and determine the most efficient cycle, comparison analysis on （single-and） two-stage CO2 transcritical cycles with internal heat exchanger （IHX） or expander is presented adopting the principle of thermodynamics. Results indicate that the COP of four cycles,namely single-stage compression with IHX （SI）, single-stage compression with expander （SE）, two-stage compression with IHX （TI） and two-stage compression with expander （TE）, can be ranged as TE>SE>TI>SI. It presents that adopting an expander to recover expansion power is the primary method to improve the COP of CO2 transcritical reverse cycle if the efficiency of the expander is up to a certain value. Under supposed operating condition, where the outlet temperature of gas cooler is 35 ℃ and the evaporating temperature is 5 ℃, the COP of TE cycle is about 4200 higher than that of SI cycle when the expander efficiency is 0.6 and the degree of superheat of IHX is 15 ℃. Therefore TE cycle is the most recommendatory one and it is better to adopt TE in those high-cooling capacity systems because its technology cost will be higher.

Performance of Gas-Steam Combined Cycle Cogeneration Units Influenced by Heating Network Terminal Steam Parameters

The determination of source-side extracted heating parameters is of great significance to the economic operation of cogeneration systems.This paper investigated the coupling performance of a cogeneration heating and power system multidimensionally based on the operating characteristics of the cogeneration units,the hydraulic and thermodynamic characteristics of the heating network,and the energy loads.Taking a steam network supported by a gas-steam combined cycle cogeneration system as the research case,the interaction effect among the source-side prime movers,the heating networks,and the terminal demand thermal parameters were investigated based on the designed values,the plant testing data,and the validated simulation.The operating maps of the gas-steam combined cycle cogeneration units were obtained using THERMOFLEX,and the minimum source-side steam parameters of the steam network were solved using an inverse solution procedure based on the hydro-thermodynamic coupling model.The cogeneration operating maps indicate that the available operating domain considerably narrows with the rise of the extraction steam pressure and flow rate.The heating network inverse solution demonstrates that the source-side steam pressure and temperature can be optimized from the originally designed 1.11 MPa and 238.8°C to 1.074 MPa and 191.15°C,respectively.Under the operating strategy with the minimum source-side heating parameters,the power peak regulation depth remarkably increases to 18.30%whereas the comprehensive thermal efficiency decreases.The operation under the minimum source-side heating steam parameters can be superior to the originally designed one in the economy at a higher price of the heating steam.At a fuel price of$0.38/kg and the power to fuel price of 0.18 kg/(kW·h),the critical price ratio of heating steam to fuel is 119.1 kg/t.The influence of the power-fuel price ratio on the economic deviation appears relatively weak.

Optimization and Performance Comparison of Hairpin?Winding PMSM for Electric Vehicles Under Drive Cycle

Aiming at the problem of large AC copper loss caused by skin effects and proximity effects,and low efficiency at high speed of the hairpin-winding permanent magnet synchronous motor(PMSM)for electric vehicles(EVs),this paper firstly established the electromagnetic analytical model of the hairpin winding to calculate AC resistance.And the finite element model(FEM)of the hairpin-winding driving motor is established to calculate the AC characteristic of the hairpin winding at different speeds and temperatures.Then,combining modified particle swarm optimization(MPSO)and FEM,a 60 k W hairpin-winding PMSM is optimized under driving cycle conditions,and the electromagnetic performance and heat dissipation performance are compared with that of the traditional strand-winding motor.Finally,a prototype is made and an experimental platform is built to test the efficiency Map and temperature rise of the hairpin-winding motor over the whole speed range and verify the accuracy of the proposed optimization design method.The results show that the hairpin-winding PMSM not only has higher slot filling rate,high?efficiency range and power density,but also has better heat dissipation performance,which is suitable for application in the field of electric vehicles.

Analysis of Medical Waste Incinerator Performance Based on Fuel Consumption and Cycle Times

A detailed assessment of an incinerator based on fuel consumption and cycle time data is presented in this paper. The study was conducted at Temeke district hospital for 22 months consecutively covering 654 days of daily data collection on fuel consumption and cycle times. The composition for the medical waste incinerated varied between 15% and 35% for sharps waste and between 65% and 85% for other waste, with mean values of 25% and 75%, respectively. The results revealed poor performance of the incinerator due to higher fuel consumption (above 30 L/cycle). The incineration cycle times were observed to range between 2 and 4 hours, all of which were too high for the loading rates observed (55 - 214 kg). A strong dependency of diesel oil consumption on cycle time was observed due to lack of temperature control leading to continuous fuel flow into the burners. The incineration capacity was very low compared to other incinerators in terms of tons per year. This paper gives an insight on the factors affecting incinerator performance assessed based on diesel oil consumption and cycle times. It can be generalized that the incinerator performance was poor due to several factors ranging from poor incinerator design, operator skills, waste management practices, waste storage practices, etc. The hospital was advised to install a new incinerator with short incineration cycle time (30 - 40 minutes) and lower fuel consumption (10 L/cycle) at a loading rate of 200 kg/cycle.

Structure Evolution and Electrochemical Performance of Al_2O_3-coated LiNi_(0.4)Co_(0.2)Mn_(0.4)O_2 During Charge-discharge Cycling

Several lithium-ion batteries of 18650-type were assembled with pristine or Al2O3-coated LiNi0.4Co0.2Mn0.4O2（NCM） as cathode material and mesocarbon microbeads（MCMB） as anode material.The cycling performance of the batteries was examined under 25 °C at a 2C rate within a potential range of 2.75―4.20 V.The changes of the crystal structure,the lattice parameter,the mean crystallite size,and the mean micro-strain of pristine NCM and Al2O3-coated NCM during the charge-discharge cycling were determined by X-ray diffraction（XRD）.The results indicate that the bulk structure of Al2O3-coated NCM is more stable than that of pristine NCM,which leads to the better cycling performance of Al2O3-coated NCM compared to that of pristine NCM.

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%.

Thermodynamic and Techno-economic Analysis of a Triple-pressure Organic Rankine Cycle: Comparison with Dual-pressure and Single-pressure ORCs

Investigation of a triple-pressure organic Rankine cycle(TPORC) using geothermal energy for power generation with the net power output of the TPORC analyzed by varying the evaporation pressures, pinch temperature differences(tpp) and degrees of superheat(tsup) aimed to find the optimum operation conditions of the system. The thermodynamic performance of the TPORC was compared with a dual-pressure organic Rankine cycle(DPORC) and a single-pressure ORC(SPORC) for geofluid temperatures ranging from 100°C to 200°C, with particular reference to the utilization of a hot dry rock(HDR) geothermal resource. Thermodynamic performances of the TPORC system using eight different organic working fluids have also been investigated in terms of the net power outputs. Results show that a higher geofluid mass flow rate can make a considerable contribution to shortening the payback period(PBP) as well as to decreasing the levelized electricity cost(LEC), especially when the geofluid temperature is low. For the temperature range investigated, the order from high to low based on thermodynamic and techno-economic performances is found to be TPORC > DPORC > SPORC. In terms of using geothermal resources within the given temperatures range(100°C–200°C), the TPORC system can be a better choice for geothermal power generation so long as the wellhead geofluid temperature is between 140°C and 180°C.

Energy and Life Cycle Assessment of Zinc/Water Nanofluid Based Photovoltaic Thermal System

Cooling the PV surface in a Photovoltaic Thermal system is a pivotal operational aspect to be taken into account to achieve optimized values of performance parameters in a Photovoltaic Thermal System.The experimental design used in this study facilitates the flow of varying concentrations of Zn-water nanofluid in serpentine copper tubing installed at the rear of the PV panel thereby preventing the PV surface temperature from increasing beyond the threshold value at which a decrease in electrical efficiency starts to occur.This fusion of solar thermal with PV devices leads to better electrical and thermal efficiency values resulting in decreased cell degradation over time and maximization of the lifespan of the PV module and the energy output from the PV system.Due to the superior thermal heat properties of nanofluids,their usage in such systems has become increasingly widespread.Life cycle metrics which include Energy Payback period,Energy Production Factor and life cycle conversion efficiency were evaluated for the PVT system by exhaustively chalking fundamental parameters such as embodied energy of the PVT setup and the total energy output from the PVT system.This research aims to be a major milestone in the evolutionary journey of Photovoltaic Thermal modules by guiding the engineers working on the theory,design and implementation of PVT systems towards its economic feasibility,environmental impact and energy sustainability.