Discharge Temperature Research Articles

Influence of Different Factors on Preparation of Carbon Nanotubes by Arc Discharge Method

This passage summarizes the research status of carbon nanotubes and the future development trends. It introduces the preparation techniques of carbon nanotubes, covering both the basic theoretical foundations and practical approaches. The influences of key factors such as discharge atmosphere, catalysts, and temperature on the preparation efficiency and quality of the arc discharge method are thoroughly analyzed. Through a systematic summary and comparison of relevant domestic and international research, the paper reveals several current technological hot spots and difficulties that need to be addressed. Moreover, the essay prospects the future development of carbon nanotubes, highlighting their wide-ranging application potential in global innovation and sustainable development. It is evident that carbon nanotubes hold promising prospects across diverse fields, including electronics, energy storage, composite materials, and environmental technologies, which will play an essential role in meeting future challenges and driving technological advancements.

Abnormal temperature rise and discharge characteristics of decay-like composite insulators

Abstract In recent years, there have been multiple incidents of fracture faults caused by the deterioration of composite insulators in China, seriously threatening the safe operation of the power system. This article takes a 500 kV decay-like composite insulator collected from the operation site as the research object, conducts visual inspection and analysis of its shed and core rod degradation status, and tests its infrared temperature rise and ultraviolet discharge distribution under power frequency operating voltage and related electrical parameters. Finally, an electric thermal coupling finite element model is established to analyze its discharge and tem-perature rise mechanism. The research results found that the infrared temperature rise characteristics and ultraviolet discharge characteristics of decay-like composite insulators can reflect their degradation status. As the testing distance increases, the measured infrared temperature rise gradually decreases. The distortion of dielectric parameters and the decrease in insulation resistance have caused partial discharge and abnormal temperature rise of decay-like insulators. In addition, compared to ultraviolet imaging detection, infrared temperature measurement can better reflect the internal defects of decay-like composite insulators and is less susceptible to interference from unrelated discharges around them.

Evaluating case definitions of respiratory disease in dairy calves: a scoping review.

Bovine respiratory disease (BRD) is one of the most common diseases observed in dairy calves in both the pre- and post-weaning periods. Despite its common occurrence, there has been no formal synthesis (e.g., scoping review) of the scientific literature surrounding diagnosing BRD in dairy calves. As such, the objective of this scoping review was to describe what case definitions for diagnosing BRD in dairy calves have been used in research. An initial search of peer-reviewed journals and the gray literature yielded 12,001 unique articles, of which 307 records containing 358 case definitions were included. Seven categories of diagnostic methods were used to categorize case definitions: (1) clinical scoring systems alone were the most used diagnostic method (n = 148, 41%) followed by (4) physical exam parameters alone (i.e., the study did not provide a detailed description of how the calf was assessed for each component of the physical exam [i.e., no description or scoring options reported]), n = 91, 25%), (5) physical exam parameters in combination with other diagnostic methods (n = 40, 11%), (6) thoracic ultrasound alone (n = 31, 9%), (2) clinical scoring system in combination with other diagnostic methods (n = 23, 7%), (3) clinical scoring system in combination with thoracic ultrasound (n = 10, 3%), and (7) other diagnostic methods (n = 15, 4%). Only 2-thirds of publications provided a citation for their case definition (n = 230, 64%), of which the Wisconsin clinical scoring system was most referenced (n = 100, 43%), followed by the California clinical scoring system (n = 19, 8%). An attempt was made to compare entire case definitions within each diagnostic method; however, they displayed substantial diversity which limited the ability to compare them at this level. Instead, counts of individual factors within each case definition (e.g., individual clinical signs) were reported for each diagnostic method. From all case definitions across the 7 diagnostic method categories (n = 358), common factors assessed included cough (n = 224, 63%), nasal discharge (n = 213, 60%), and body temperature (n = 142, 54%). Across all case definitions, additional parameters such as validity were frequently not reported - only 4 (1.1%) were referred to as validated, 9 (2.5%) were being validated in the study, and 28 (7.8%) modified existing case definitions. Additionally, assessment of severity of disease when present (e.g., mild, moderate or severe) was frequently not reported (n = 336, 93.9%). Further, 106 (29.0%) reported assessments of accuracy, 66 (18.4%) of which were reports of qualitative oversight (e.g., training of assessors) and 40 (11.1%) of which were related to a quantitative assessment of accuracy (e.g., sensitivity and specificity). Parameters surrounding conducting the assessment were also extracted, for example how often (most common: at least daily, n = 120, 33.5%) and who conducted it (most common: information not reported, n = 144, 40.2%). The findings of this scoping review highlighted the need for a validated, standardized set of criteria for BRD diagnosis in dairy calves, achievable through following the methodology of developing a core outcome set.

Experimental Investigation of Temperature Homogeneity and Peak Temperature in a Battery Pack of Cylindrical Li-ion Cells Under Free and Forced Convection

Electrical vehicles (EVs) are emerging as a suitable replacement for conventional IC engine-based automobiles because of their environmental friendliness. An EV is powered by a rechargeable battery pack usually made of Lithium-ion batteries and these batteries generate heat during their operation cycle due to exothermic reactions and ohmic effect. Thermal management of batteries is important for their safe operation and optimum lifespan. In this paper, a comparative analysis of temperature homogeneity, peak temperature and average temperature of battery pack is presented between free and forced convection-based Battery Thermal Management System (BTMS). Cells that are at higher temperature than average temperature of battery pack are more liable to fail earlier as compared to other cells of pack. Present research focuses on finding such critical cells in a battery pack consisting of twelve lithium-ion batteries. The battery pack is discharged at three different rates: 1C, 2C and 3C, and temperature of each cell is measured at regular intervals during the discharge process. The experimental results from present study revealed that free convection is better at maintaining temperature homogeneity, but peak temperatures were above 50 ̊C. Forced convection based BTMS was able to keep peak temperatures below 50˚C at 1C discharge rate but temperature homogeneity was not maintained within ideal limits of 5˚C. At higher discharge rates, the performance of both free convection and forced convection based BTMS is not within acceptable limits. Critical cells were identified to get better insight into limitations of conventional cooling systems so that better layout of battery module and better alternative methods of battery pack cooling can be developed.

Performance study of oil-injection hermetic CO2 scroll compressor for automotive air conditioning system.

An oil-injection CO2 scroll compressor prototype and relative simulation model are developed for automotive Air Conditioning. The effects of oil to refrigerant mass ratio on the compressor performance are studied theoretically and experimentally. The results show that oil-injection is an effective way to improve the volumetric and indicated efficiencies, and reduce discharge temperature. The optimal oil-injection quantity varies at different conditions, and it decreases from 7.9% to 6.3% at fixed discharge pressure 10MPa when the suction pressure increases from 4.5MPa to 5MPa. Similar linear relationships are found and the different slopes of the line are exhibited at fixed suction and discharge pressure separately. Numerical results show that oil-injection has little influence on pressure in working chamber during suction and discharge process, but it can slow up the rising of pressure in compression process and reduce the salient of pressure at the end of compression process.

Research on the performance of ultra-low temperature cascade refrigeration system based on low GWP refrigerants

The EU Security Council and Parliament have tentatively agreed to ban fluorinated gases with a global warming potential (GWP) higher than 150 in split air conditioners and heat pumps from 2027. This will further motivate the refrigeration industry to accelerate the search for refrigerants with low GWP and zero ozone depletion potential (ODP). At present, research into low GWP refrigerants for cascade systems is limited, focusing mainly on single refrigerant substitutes without comprehensive comparisons and lax GWP restrictions. In this study, the cascade refrigeration cycle (CRS) system is established to meet the demand of −100 to −50 °C. The GWP of the refrigerants is strictly controlled below 150, and a comprehensive screening of the four generations of refrigerants is carried out to identify refrigerant pairs that meet environmental and refrigeration requirements. The relationship between the high-temperature cycle (HTC) evaporation temperature and the optimal coefficient of performance (COP) is determined, and the effects of the low-temperature cycle (LTC) evaporation temperature Te concerning with mass flow rate, discharge temperature of compressor, compressor power consumption, exergy destruction, and exergy efficiency are analyzed in detail. The thermodynamically superior refrigerant pairs are identified by comparison with several conventional refrigerant pairs. The results show that when Te > −67 °C, R170/R600a is preferred, and when Te ≤ −67 °C, R170/R1270 is preferred. In the temperature range of −100 ∼ −50 °C, R170/R1270 is the better refrigerant pair, which can improve the performance by 6.39–13.11 % than traditional refrigerant pairs. Finally, the exergy destruction analysis of CRS components is carried out, which provides a reference for refrigerant selection and system optimization of CRS in the field of ULT.

Low-temperature reduction of NOx with NH3 using a hybrid system of non-thermal plasma-LaMn0.9CO0.1O3 perovskite nanocatalyst

The catalytic reduction of NOx at low temperatures presents a significant challenge, which can potentially be overcome by integrating plasma into the process. Porous perovskites emerge as promising catalysts for plasma-assisted NOx removal. In this study, perovskite catalysts LaMnO3 and LaMn0.9Co0.1O3 were synthesized using the auto-combustion sol-gel method with different fuels and subsequently evaluated for their efficiency in plasma-catalytic NOx removal in the presence of NH3. Analyses including XRD, BET, FESEM, TEM, FTIR, DRS, and TGA indicated that while the samples exhibited similar crystal sizes, they displayed varying levels of defects. Notably, the LaMn0.9Co0.1O3 catalyst synthesized with citric acid as the fuel (designated as LMC-Ci) demonstrated a highly porous and homogenous network structure, characterized by cubic-spherical particles measuring 20–30 nm, as corroborated by the XRD data. The co-substitution of cobalt in LaMnO3 enhanced light absorption, enabling the catalyst to effectively utilize ultraviolet photons produced by the plasma. Among the evaluated catalysts, LMC-Ci achieved the highest activity, resulting in a 98 % removal rate of NOx. The study further examined the influence of operational parameters, including discharge time, temperature, space velocity, and specific input energy, on the performance of the selected catalyst, revealing that plasma presence significantly reduced the operating temperature to 80 °C.

Comparative analysis of a modified cascade refrigeration cycle including an auto-cascade refrigeration cycle using different zeotropic refrigerant mixtures for reducing the environmental impact

The two primary challenges in auto-cascade refrigeration (ACR) cycles are high compressor discharge temperatures and low efficiency at ultra-low temperatures. This study proposes a modified cascade refrigeration cycle (MCR) combined with an ACR cycle for cooling to –60 ℃. The innovative aspect of this work is to improve the ACR performance with simpler designs without increasing the system complexity, contrary to the common trend. For the high-temperature cycle (HTC), a dual evaporator refrigeration cycle with R1234yf is used while an ACR cycle is used for the low-temperature cycle (LTC). Environmentally friendly refrigerant mixtures, such as R170/R290, R170/R600a, and R170/R600, were analyzed using energy, exergy, and exergoeconomic methods. The results show that compared to R23/R134a, the R170/R600 significantly improves the performance of the MCR by increasing the COP and exergy efficiency by 24.0 %, and reducing the exergy destruction by 26 %, unit cooling cost by 11.2 %, and total investment cost by 9.7 %. Moreover, when compared with theoretical studies COP improvements range from 38.7 % to 94.1 %, demonstrating the importance and superiority of the system proposed in this study.

Fishway assessment and monitoring for endemic migratory fish using multiple techniques in high-altitude river systems: A case study from the Yarlung Zangbo River, Southeastern Tibetan Plateau

The Yarlung Zangbo River (YZR) on the Tibetan Plateau is a prime hotspot for hydropower development in China, yet this inevitably poses risks to river connectivity and the survival of its unique endemic fish species. Fishway installations are often adopted to mitigate the impacts on fish, but their effectiveness especially in high-altitude regions remains inadequately studied. Our study offers the first comprehensive evaluation of a fishway installed on a primary tributary of the YZR from 2019 to 2021, using multiple methods including fish sampling, video monitoring, hydroacoustic detection, and passive integrated transponder telemetry technology. The below-dam fish community was dominated by cold-water rheophilic Schizopygopsinae, Schizothoracinae, and Nemacheilidae. Fish movements exhibited distinct seasonal and diel patterns, with activity rising in April and peaking in May. Approximately 75.0 % of fish movements within the fishway were recorded during daytime (7:00–19:00), whereas the fish assemblage near the fishway entrance primarily occurred during nighttime (20:00–6:00). Telemetric trials on five endemic species revealed upstream- and downstream passage efficiencies of 31.0 % and 61.7 %, respectively. Passage efficiency, transit time, and speed varied substantially among species and individuals, primarily affected by environmental factors such as fishway discharge and water temperature. Our findings provide the essential information on fish behavior and movement patterns for designing more effective fishways in plateau regions and underscore the importance of continuous monitoring and evaluation to optimize fishway performance, ensuring that the conservation of endemic fish species is achieved successfully amid expanding hydropower development in the region.

Post 80% Cycling of Li-Ion Cells, an Update on a Seven Year Cycling Study of Diverse Lithium-Ion Battery Chemistries

Li-ion batteries are increasingly being used in various sectors, including consumer electronics, electric vehicles (EVs), and grid energy storage, as critical components in modern infrastructure. Convention for the EV market dictated that 80% of the initial capacity of the battery represented the end of life and is therefore commonly marked as the end point of battery aging studies. To exploit the potential applications of a given cell, an understanding of degradation trends beyond 80% capacity is needed and requires the collection of data at various standard use conditions.This work details a multi-year cycling study of commercial LiFePO4 (LFP), LiNixCoyAl1−x−yO2 (NCA), and LiNixMnyCo1−x−yO2 (NMC) 18650 cells, varying the discharge rate (C-rate), state of charge (SOC) ranges, and environment temperature. This work builds on a previously published analysis performed up to 80% capacity, now focusing on post 80% analysis[1]. The capacity degradation of each chemistry, under varying conditions, were compared. Cycling at varying discharge C-rates (0.5C, 1C, 2C, 3C), SOC ranges (0-100%, 20-80%, and 40-60%) and temperatures (15, 25, and 35 °C) affected each chemistry to different extents. Therefore, the relative importance of each parameter in cyclic aging is different for different chemistries.Overall, we find that each cell chemistry can conduct significant cycling post 80%, in some cases to a capacity retention of 40%, with minimal loss of round-trip efficiency (RTE). We find that SOC range is the most consistent factor in cell capacity fade rate for all chemistries considered. Temperature had varied impacts on capacity fade depending on cell chemistry, for example NCA cells show no clear trend before 80% capacity, but post 80%, increased temperatures caused an increase in the rate of capacity fade. C-rate of discharge has a more prominent impact on capacity as cells age. LFP cells are the only ones that showed a clear trend of the highest and lowest C-rates causing the most rapid fade before 80%. Post 80%, the NMC and NCA cells start to show a similar trend and the LFP trend becomes more pronounced.Most batteries do not display a distinct knee point, instead exhibiting a more linear degradation with gradual increase in slope. When they do experience knee points, there is no consistent trend across chemistries and conditions that appear to cause knees. Other metrics such as RTE, total discharged energy, and internal resistance (IR) are also being considered to identify trends. This study represents the broadest public report of post 80% capacity cycling across multiple chemistries and will be valuable in lifetime prediction modelling for efficient battery usage.

CFD-based unsteady simulation and performance analysis of scroll compressor

The scroll compressor is an essential part of the heat pump air conditioning system in electric vehicles, with its performance and efficiency having a significant impact on the vehicle's range. This paper employs a combination of experimental and numerical simulations (using the dynamic mesh method) to study the scroll compressor in electric vehicles, exploring the effects of rotational speed and pressure ratio on compressor performance. The results reveal a significantly uneven temperature distribution across the chambers, primarily due to tangential leakage, which results in elevated temperatures in the central areas of the chambers and reduced temperatures near the meshing points. As the rotational speed increases, both the mass flow rate and the isentropic efficiency of the scroll compressor rise, whereas the discharge temperature declines; notably, discharge temperature drops by an average of 1.6 % for 600 r·min-1 increase in rotational speed. For each unit increase in the pressure ratio, the discharge temperature increases by an average of 12.22 K, while the mass flow rate decreases by 7.95 %. The study also shows that the isentropic efficiency initially rises with increasing pressure ratio, reaching a maximum of 67.06 % before starting to decline. These findings provide valuable insights into the performance characteristics of scroll compressors and offer theoretical support for optimizing compressor efficiency in practical applications.

Theoretical analysis and experimental validation of optimal vapor injection conditions for a low-pressure ratio scroll compressor

This study investigates the impact of vapor injection parameters and positions on the performance of a low-pressure ratio scroll compressor in electric vehicle thermal management systems under extremely low temperatures. The research combines experimental and simulation methods to analyze five injection ports designed at different positions. Key performance metrics, including mass flow rate, discharge temperature (Tdis), coefficient of performance (COP), compression work, and heating capacity (Qh) were evaluated under various conditions. A low-pressure ratio (scroll number N = 2) vapor injection scroll compressor was designed with an optimized injection port configuration. This design was rigorously validated through experimental results, confirming its efficacy. Notably, the findings reveal that the enhancement in Qh and COP is more pronounced in extremely low-temperature working conditions compared to non-injection conditions, with improvements of 10.7 % and 4.6 %, respectively. Compressor performance increases with increasing vapor injection pressure, and compressor speed and performance increment are more significant under low-temperature working conditions. Finally, an injection coefficient, denoted as k, is proposed to determine the optimal injection pressure for diverse discharge and suction pressures in cold climates. According to the experimental results, the value of k associated with the best heating COP ranges between 0.65 and 0.85.

Seasonal performance comparison of R-410A and R-454B in a variable-speed air-cooled scroll chiller

In recent years, there has been increasing concern about the impact of air conditioning and refrigeration on global warming. This is particularly related to the emissions of refrigerants with high global warming potentials (GWP), such as R-410A, which is used in air conditioning and chiller systems. There has been a concerted effort within the HVAC industry to find lower GWP refrigerants to replace R-410A in HVAC systems. In this paper, a 10.5 kW (3 TR) air-cooled variable-speed scroll chiller has been utilized to conduct an experimental comparison of R-410A (GWP of 2088) and its low GWP A2L alternative R-454B (GWP of 466) according to AHRI 551/591 testing condition at rating and part load condition with optimized charge. The compressor speed and suction superheat were matched for both refrigerants at all the test conditions. R-454B shows 98 % capacity and 102 % efficiency compared to R-410A at rating conditions of 35 °C outdoors and water return temperature of 12 °C. The IPLV of the R-454B chiller was just 1 % higher than R-410A. The discharge temperature of R-454B and compressor isentropic efficiency is 8 % higher and almost like R-410A, respectively. The optimized charge of R-454B was 5 % lower refrigerant charge compared to R-410A. The LCCP analysis for major Indian cities over a 15-year operational span demonstrates a notable reduction, ranging from 6.6 % to 7.3 %, in overall R-454B emissions compared to R-410A. The study demonstrates that R-454B is a drop-in replacement to R-410A designs and reduces the direct GHG emission from the chiller by 76 %.

Single-screw extrusion performance for LLDPE resin as a function of compression ratio

High-quality polyethylene film and sheet must be free of solid polymer fragments and degraded resin. Moreover, the products must be produced at high rates to minimize conversion costs. Thus, the extruder must produce a homogenous extrudate at the proper discharge temperature and pressure. The screw design and process operating parameters are key. A key screw design parameter is the compression ratio. This paper experimentally studies how the compression ratio affects a linear low-density polyethylene (LLDPE) resin extrusion process. A 2.8 compression ratio screw was optimal for LLDPE resin. Significant solid polymer fragments were observed in the extrudate for 2.8 to 3.6 compression ratio screws at 110 rpm and higher. For 2.0 and 2.4 compression ratio screws at less than 50 rpm, the internal pressures in the extruder were relatively low. At screw speeds 50 rpm and higher, the specific rates for all screws were higher than the calculated specific rotational rate, creating negative axial pressure gradients in the metering sections.

An experimental and comparative study on passive and active PCM cooling of a battery with/out copper mesh and investigation of PCM mixtures

The carbon emission contribution to global warming accelerated both research on and transition to electric vehicles (EVs). Drivers demand high power, fast acceleration and less charging times. All these demands require high C rate charging/discharging demands from batteries. The rate of heat generation is exponentially proportional to C rates which decreases battery lifetime and may lead to thermal runaway. However, a battery thermal management system decreases thermal runaway risk and decelerates battery degradation via controlling battery temperature. In this paper, we first document the thermal conductivity enhancement via copper foam into phase change material (PCM) domain to uncover their possible use in EV thermal management applications. Maximum 15.93 times increment is achieved with a specific copper foam. Then, physical properties and behaviors of distinct PCM mixtures are documented. Homogeneity of mixtures is associated with the chemistry of PCMs and the mixture melting point is proportional to the volume weighted average of melting temperatures. The results document that the PCM with relatively lower melting point is beneficial when end of discharge temperatures considered, except for high discharge rate of 2C. Temperature uniformity across the battery increases with relatively higher melting point PCM. Experiments also document that the amount of PCM volume lost via insertion of copper foam yields higher end of discharge temperatures. Overall, both PCM and copper foam enhances temperature homogeneity and their benefit becomes more sensible during drive cycles relative to continuous charge/discharge use cases.

Experimental and numerical study on transcritical CO2 air source heat pump water heater

As environmental problems become more and more serious, CO2 is widely used as a natural work material in heat pump water heaters. In order to better improve the performance of CO2 air-source heat pump water heater, a trans-critical CO2 quasi-two-stage compression heat pump system with ejector (TCIEJ) is proposed. And a transcritical CO2 air-source heat pump water heater experimental bench was built. The effects of parameters such as cooling water flow rate, high pressure and compressor frequency on the performance of the heat pump were tested. A simulation model of TCIEJ was also developed to simulate the system performance. The results show that when the cooling water flow rate is increased from 70 kg/h to 122.5 kg/h the COP is improved by 30 %, while the cooling water discharge temperature is reduced by 15.4 %. System performance can be enhanced by increasing the cooling water flow rate within the temperature range required to meet hot water demand. When the high-pressure pressure of the TCIEJ system was increased from 8.0 MPa to 10.4 MPa, the cooling water discharge temperature increased by 17.66 °C on average. Even in the ambient temperature of 0 °C high-pressure pressure of 10.4 MPa, the compressor discharge temperature is only 85.77 °C. It shows that the combination of make-up air technology and ejectors effectively reduces the compressor discharge temperature, which is conducive to improving the compressor’s service life.

THE EFFECT OF THERMAL CYCLING ON DEPOSITION IN AN IMPINGEMENT/EFFUSION COOLING GEOMETRY

Abstract Experiments were conducted in a high-pressure deposition facility to study the effect of engine cycling on the successive buildup of deposits as aircraft shut down and power up. The test facility simulates the pressure and temperature environment of a combustor liner cooling circuit. The coolant flow temperature reaches 894K (1150 °F) and discharges into a 17atm (250 psi) cavity pressure at a nominal pressure ratio of 1.027. AFRL05 test dust with a 0-10micron size distribution is added to the coolant . The cooling circuit consists of a double-walled impingement/effusion cooling plate with nominal hole sizes on the order of 0.5mm. To simulate cycling, the facility is brought up to the desired operating conditions where the first batch of dust is delivered (2-8g). The facility is then ramped down to ambient conditions. Following a “dwell” period of approximately 24 hours, another batch of dust is delivered once the facility is brought back up to the desired operating condition. Test data were acquired for one, two, and four cycles with different dust mass delivered. Values such as discharge coefficient, pressure ratio, Reynolds Number, and temperature are used to evaluate the effects of dust deposition on the impingement/effusion plate setup. Dust capture efficiency is shown to be insensitive to cycling whereas flow blockage is negatively impacted by increased number of cycles for the same total mass delivered. The sloughing of deposit structures during cooling circuit cool down is postulated to be responsible for the observed behavior.

A new simulation approach of air source heat pump adopting the holistic process distributed parameter method and hybrid PID-bisection control algorithm

Air source heat pump (ASHP) faces problems of performance deterioration when operating at low ambient temperature due to the low compression ratio, high discharge temperature, frost accumulation, etc., and may even become nonfunctional at sub-zero-centigrade ambient temperature, requiring attention and tools for studying. This paper proposed a kind of holistic process distributed parameter simulation approach of ASHP system adopting the hybrid PID-bisection (PID: proportional-integral-derivative) control algorithm. Main components of the ASHP are modeled with the distributed parameter method. An adiabatic compression model of two-phase fluid based on thermodynamics is proposed. The PID-bisection control algorithm and variable speed integral PID & bisection control algorithm are proposed and applied to iterative computation of the model. A single/two-stage compression ASHP with an intercooler is simulated by this approach. The average deviation of simulation results of the model from experimental data is not more than 7 %, and the maximum deviation is not more than 18 %. For simulation of single-stage compression mode, the maximum error is not more than 4%. For simulation of two-stage compression mode under low-evaporating-temperature operating conditions, the maximum error is not more than 4 %. Computational speed of the ASHP model is significantly improved by using the PID-bisection control algorithm, and could be further accelerated by using the variable speed integral PID & bisection control algorithm. The proposed simulation approach is not only effective in sophisticated simulation of performance of single-stage and two-stage compression ASHP, but also potential for research on the optimization of the ASHP in cold regions.

Battery temperature estimation at wide C-rates using the LSTM model based on polarization characteristics

Data-driven based approaches have achieved significant results in estimating battery temperature. Nevertheless, the present challenge emanates from the dearth of theoretical guidance governing the training strategy of the model, leading to an inefficient training process and constrained accuracy, especially under specific conditions. In this paper, a Long Short-Term Memory (LSTM) neural network based on polarization characteristics is proposed to estimate the battery discharge temperature. Firstly, the LSTM temperature estimation model is established and the hyperparameters are optimized by Genetic Algorithm (GA). The results show that the accuracy of the traditional model is less satisfactory, with the Maximum Error (ME) of 3.79 °C. Subsequently, the voltage and polarization heat production characteristics of the battery are analyzed under various discharge conditions. It is found that the heat production of the battery is smaller at 0–1.5C, and the heat production characteristics are similar at medium-rate, but the change of heat production is significant when C-rate exceeds 3C. Finally, a LSTM temperature estimation model based on polarization characteristics is proposed, which divides the datasets according to heat production characteristics. Further, a strategy for predicting temperatures in later stages based on limited data from the current condition is also proposed, this mothed combines with the transfer learning method to rapidly develop models for different high-rate conditions. The ME of the model on the test set is 1.1 °C, and the training time is reduced by 32.93 s. The results show that the LSTM temperature estimation model based on polarization characteristics has higher accuracy and training efficiency than the traditional LSTM temperature estimation model.

Thermodynamic analysis of a modified two-stage transcritical CO2 refrigeration cycle with an ejector and a subcooler

In the application scope of large-scale supermarkets, the practicality of transcritical CO2 refrigeration device has been confirmed to be quite satisfying. A modified two-stage transcritical CO2 refrigeration cycle with an ejector and a subcooler (MTC) is proposed in this paper. In the modified cycle, the ejector recovers expansion works and reduces irreversible losses in the throttling process. The subcooler provides subcooling degree for the CO2 entering the low-temperature (LT) evaporator, thus increasing the refrigeration capacity and improving the COP of the modified cycle. Thermodynamic analysis has shown that the exergy efficiency (ηex) and COP of MTC under given operating condition has been enhanced by 13.7 % and 14.2 % compared to BTC. The discharge temperature at the outlet of high-pressure compressor in MTC is decreased by 8.3℃. Under typical operating condition, the optimal discharge pressure of MTC is 9.07 MPa, which is lower than that of BTC. The correlation to calculate optimal discharge pressure for single-stage CO2 refrigeration cycle is also suitable for MTC under given operating conditions. The MTC has also shown better performance under variable operating conditions. For MTC, when the temperature at the outlet of gas cooler increases from 35 – 45℃, the COP and ηex are enhanced by 14.1 % - 16.1 % and 12.8 % - 14.2 % compared to BTC, respectively. When gas cooler outlet pressure decreases from 11.0 to 7.5 MPa, the COP and ηex are enhanced by 14.0 % - 22.8 % and 13.4 % - 18.7 %. As the evaporating temperature at the cold side of subcooler increases from -25 to -15℃, the COP and ηex increase from 1.82 to 1.98 and 27.4 % to 29.7 %. With the ratio of refrigeration capacity (Rec) between medium-temperature evaporator and low-temperature evaporator varies from 0.7 to 1.2, the COP and ηex are improved by 10.7 % - 16.3 % and 10.7 % - 15.4 % compared to BTC. There is the maximum exergy loss at gas cooler in the MTC, whereas that of BTC is located in the expansion valve before LT evaporator. The economic analysis shows the cost per unit of exergy of MTC is decreased by 11.5 % under typical operation condition. According to simulation results, the modified cycle has better performance in severe working conditions such as high gas cooler outlet temperature and low gas cooler outlet pressure in the given range of working conditions compared to BTC.