Search Results (227)

To address the limitations of individual battery thermal management technologies, this study proposes a hybrid battery thermal management system coupling static immersion cooling with refrigerant-based direct cooling. The system employs parallel upper and lower direct cooling plates, with the refrigerant flow split regulated to enhance buoyancy-driven convection within the sealed immersion chamber. Numerical simulations are conducted to compare an R134a direct cooling system with a 50% ethylene glycol solution indirect cooling system over total flow rates of 6–18 L⋅min⁻¹ and upper plate flow ratios of 10–90%. The effects of the total flow rate and flow distribution on the pressure drop, battery temperature, temperature uniformity, flow characteristics, and pumping power are systematically evaluated. The R134a direct cooling system reduces the average battery temperature by approximately 0.5–1.0 °C compared with the indirect cooling system. Increasing the upper plate flow ratio strengthens the natural convection within the immersion chamber and alleviates vertical temperature non-uniformity, whereas excessive flow redistribution weakens the cooling capacity of the lower plate. A Kriging surrogate model coupled with a multi-objective genetic algorithm identifies the optimal condition at a total flow rate of 8.82 L⋅min⁻¹ and an upper plate flow ratio of 56.45%. Relative to the baseline condition of 9 L⋅min⁻¹ and an upper plate flow ratio of 10%, the optimized condition reduces the average battery temperature, maximum temperature difference, and pumping power by 10.1%, 7.2%, and 52.1%, respectively, while maintaining a low cell temperature standard deviation of 0.032 °C. Full article

This paper proposes a novel solar-assisted inter-cooling air source heat pump (SCAS–HP) system that integrates a solar collector/evaporator into the intermediate injection branch to utilize solar energy for increasing the refrigerant flow rate at intermediate pressure. A numerical model of the system was developed and validated against the literature data, and then employed to investigate performance under varying operating conditions. Three configurations were examined—two-stage throttling (T–SCAS–HP), single-stage throttling (S–SCAS–HP), and parallel evaporators (P–SCAS–HP)—and their performance was compared with a conventional vapor injection air source heat pump (VI–ASHP) across solar radiation intensities of 10–1000 W/m², outdoor air temperatures of −20 °C to 10 °C, and outlet water temperatures of 35 °C and 55 °C. Hourly performance, economics, and CO₂ reduction were further assessed for Lhasa, Beijing, and Harbin. The results show that the COP_h improvement of SCAS–HP over VI–ASHP rises with increasing solar radiation intensity. Furthermore, the solar radiation threshold at which the COP_h of SCAS–HP begins to exceed that of VI–ASHP lies within the range of 100–200 W/m². Moreover, the COP_h increase rate of SCAS–HP rises with larger solar collector area and higher outdoor air temperature, but declines as the outlet water temperature rises. Among the three configurations, T–SCAS–HP outperformed S–SCAS–HP and P–SCAS–HP by 0.37 and 0.42 in COP_h at outlet water temperatures of 35 °C and 55 °C, respectively. In typical-day simulations, the COP_h showed a relative increase of 50.9% compared to that of the VI-ASHP system, corresponding to an absolute rise from 3.73 to 5.62 with a 130 m² collector at 35 °C outlet water temperature. The energy saving rate ranked highest in Lhasa, followed by Beijing and Harbin. The shortest payback period (5.6 years) was achieved in Harbin with a 130 m² collector area at the outlet water temperature of 55 °C. The proposed system is particularly suitable for large heating demand and long heating seasons in cold climates with abundant solar resources. Full article

This paper introduces a non-invasive ultrasonic sensing system for two-phase refrigerant flow characterization in heat pump circuits used in building energy systems, validated through machine learning (ML)-based regression of the acquired signals. Heat pumps play a crucial role in energy-efficient buildings. However, the absence of a low-cost, non-invasive instrument capable of measuring mass flow rate, mixture density, and vapor quality without disrupting the thermodynamics of a refrigerant circuit remains a gap for smart HVAC systems. A carbon dioxide (CO₂) refrigerant circuit was designed to calibrate such a sensing system under representative operating heat pump conditions. Ultrasonic measurements were conducted using piezoelectric transducers clamped onto the refrigerant pipeline. A calibration framework was structured with ground-truth flowmeter labels, establishing a thermodynamic envelope across 10–20 bar and down to −25 °C, and achieving R² = 0.901 for flow rate, 0.997 for density, and 0.971 for quality, with an overall R² = 0.956. The proposed measurement system is a plug-and-play kit enabling more efficient next-generation heat pumps, supporting building energy management and performance monitoring. The labeled dataset and calibration methodology provide a basis for training and validating ML regression models for real-time flow property inference in operational HVAC systems. Full article

This study investigated a high-temperature heat pump for industrial steam production at 200 °C. Considering refrigerant thermal degradation at elevated temperatures, R1336mzz(Z) was selected because of its thermal stability. Two systems were analyzed: a flash tank (FT) cycle producing steam using a water valve and flash tank, and a steam generator (SG) cycle directly generating steam in the gas cooler. Unlike previous studies focusing primarily on cycle-level thermodynamic performance, this study systematically compares two steam production configurations for a 3 MW-class HTHP by considering heat pump–steam loop interactions and further evaluates their economic and environmental feasibility through LCC and LCCP analyses. Applying an internal heat exchanger reduced the operating pressure and increased the heat pump coefficient of performance (COP) by up to 13%, depending on the pressurized water temperature. In the FT cycle, lowering the valve outlet temperature from 180 °C to 150 °C increased the heat pump COP to a maximum of 3.06. However, the additional mechanical vapor recompression (MVR) power limited the overall system COP to 2.29–2.44. In the SG cycle, the system COP ranged from 1.94 to 2.54 according to the saturated water temperature at the gas cooler inlet, although operation at lower water temperatures approached the critical region, resulting in a narrower operating margin. LCC and LCCP analyses showed that replacing conventional boilers with heat pumps reduced operating costs by 26–59%, depending on regional energy prices, with payback periods of 2.27–8.76 years. Heat pump adoption also reduced life cycle climate impacts by 13–72%. These results demonstrate that high-temperature heat pumps can provide an economically and environmentally viable alternative for industrial steam production at 200 °C. Full article

Naval surface ships are generally propelled by diesel engines and/or gas turbines. The waste gas from the gas turbines is released into the atmosphere at high temperatures and with high energy. Using this energy to cool and heat the naval surface ship will provide energy efficiency and reduce emissions. In this study, the cooling and heating needs of a naval surface ship will be met using exhaust gas from the gas turbine outlet, with an LM2500 gas turbine drive and a steam ejector cooling and heating system. In a study of two ship types (corvette and frigate), the required steam flow rates, heating loads, heating–cooling COPs, saved fuel rate, saved fuel cost, and reduced CO₂ emissions for the required cooling capacities have been calculated. For a corvette with a cooling capacity of 540 kW, it saved 830.68 USD/h in cost and reduced CO₂ emissions up to 2123.61 kg/h, given a steam inlet pressure of 9.5 bar, evaporation pressure of 0.8 kPa, and a 1/ω (inverse of the entrainment ratio) of 5. For the frigate with a cooling capacity of 720 kW, it saved up to 1107.58 USD/h in cost and reduced CO₂ emissions by up to 2831.48 kg/h, given a steam inlet pressure of 9.5 bar, evaporation pressure of 0.8 kPa, and a 1/ω of 5. Full article

The use of non-certified commercial electronics for cryogenic applications may be attractive due to their reduced cost and high availability, but they also carry risks related to reliability, performance, and thermal compatibility. The decision to use commercial components that are not certified for cryogenics instead of components specifically designed for such applications must be carefully weighed based on specific project needs and risk tolerances. This work presents the characterisation of a Low-Noise Amplifier (LNA) at cryogenic temperatures for use in astronomical instrumentation applications with a microwave kinetic inductance detector (MKID) readout system. The cooling system comprises a cryostat, a cold head operating in a closed-cycle helium refrigeration system based on the Gifford–McMahon principle, a compressor, connectors, cables, a vacuum pump, pressure and temperature sensors, and a temperature control system. The circuit was characterised over the temperature range of 295.4 K to 78.3 K. Full article

The increase in neutron flux at the Oak Ridge National Laboratory (ORNL) Spallation Neutron Source (SNS), currently operating at 2.0 MW proton beam power, has created new opportunities for higher-throughput neutron scattering experiments while also increasing the importance of minimizing background scattering and optimizing sample-environment operations. To address these challenges faced by the Backscattering Silicon Spectrometer (BASIS), several upgrades were developed and evaluated, including boron carbide (B₄C) masking for flat-plate sample containers, multi-cell sample holders used with a vertically translating sample stick, and an automated helium pump-and-purge (HPP) system for closed-cycle refrigerators. Neutron diffraction measurements demonstrate that B₄C masks reduce background scattering by 49–67%, outperforming both borated aluminum and boron nitride masks while introducing no additional Bragg reflections within the instrument’s accessible Q-range. Commissioning tests of a double-cell flat-plate sample container showed no measurable crosstalk between adjacent sample compartments and confirmed a stable thermal performance, enabling multiple samples to be measured without repeated temperature cycling. In addition, the automated HPP system provided reproducible sample-space gas handling with approximately ±1 mbar precision while reducing the need for operator intervention and supporting remote operation. Together, these developments improve signal-to-noise performance, increase experimental throughput, and enhance operational efficiency at BASIS, supporting the instrument’s continued operation under higher neutron flux conditions. Full article

Heat pumps are core equipment for efficient low-grade thermal energy utilization and low-carbon transformation of the energy structure, offering significant energy-saving potential in building heating and industrial waste heat recovery. This paper reviews the research progress and technical challenges of compression, absorption, and adsorption heat pumps as well as nanofluid-enhanced heat transfer technology and elastocaloric heat pump systems. Air source heat pumps can delay frosting through variable frequency, heat storage, and waste heat recovery. However, accurate prediction models for performance degradation under extreme cold conditions are lacking. Although ground source and water source heat pumps exhibit significant energy efficiency advantages, ground source systems may suffer from performance degradation due to underground thermal imbalance. The application of water source systems is strictly constrained by water resource conditions. Driven by low-grade waste heat, absorption heat pumps employing traditional working pairs suffer from crystallization, corrosion, or high rectification energy consumption. The COP of a single-effect cycle under 80~100 °C waste heat is only 1.2~1.9, while hybrid cycles can reach approximately 3.2 at 120~150 °C. Although adsorption heat pumps achieve significantly improved performance under continuous heat recovery cycles, the full-scale power density of novel adsorbents such as metal–organic frameworks is inferior to the power density of traditional silica gel. Moreover, under off-design conditions, the performance drops by 23~48% compared to theoretical values. Nanofluids can enhance heat transfer, but the long-term effects of particle agglomeration at high temperatures on pump power consumption and system compatibility remain to be systematically evaluated. Elastocaloric heat pump systems can achieve refrigerant-free cooling, but current prototypes still cannot compete with traditional vapor compression systems in long-cycle fatigue reliability and power density. Current heat pump technologies generally face challenges such as insufficient adaptability to extreme conditions, bottlenecks in working fluids and materials, and a lack of long-term validation. Future research must construct a multi-source coupling optimization system, address common problems in working fluids and materials, promote long-term validation and kilowatt-level prototype demonstrations, and drive the large-scale deployment and engineering application of heat pump technology toward high efficiency, intelligence, and high reliability. Full article

The phasing out of high-GWP refrigerants and the growing diversity of working fluids used across heat pumps, refrigeration systems, and closed-cycle power applications have made drop-in fluid replacement a question of significant practical interest. Centrifugal compressors are designed around the thermophysical properties of a specific fluid, and the performance penalty is incurred when working fluid is replaced without redesigning the impeller. This study presents a CFD comparison of direct drop-in fluid replacement in a fixed geometry centrifugal compression system. Eight working fluids that span the property range relevant to current drop-in substitutions are evaluated: air, nitrogen, argon, carbon dioxide, R22, R134a, R1234yf, and R1234ze(E). A reference centrifugal impeller was reconstructed in ANSYS BladeGen, meshed in ANSYS TurboGrid using the Automatic Topology and Meshing method, and simulated in ANSYS CFX (2024 R2) as a single periodic passage with Frozen Rotor interfaces and Spalart–Allmaras turbulence closure. Performance maps were generated for each fluid across a range of rotational speeds and mass flow rates, with a common inlet reference condition applied across all cases to isolate the influence of fluid properties from an inlet state. The resulting dataset enables a like-for-like comparison of pressure ratio, efficiency, and shaft power requirement, providing a basis for assessing the aerodynamic implications of drop-in fluid substitution in centrifugal compression systems. Air, nitrogen, argon and carbon dioxide achieved similar peak efficiencies (~88%) and comparable pressure ratios (PR), indicating they can be used as drop-in substitutes without performance loss. Refrigerants R1234yf and R1234ze(E) matched R134a in efficiency (peak ~90%) while offering higher pressure ratios and significantly lower power requirements at peak efficiency. At 20,000 RPM and a mass flow rate of 2 kg/s, compared to a PR of 1.45 for air, nitrogen, carbon dioxide and argon achieved PRs of 1.4, 1.9 and 2.4, respectively. At the same settings, R134a and R1234 refrigerants reached PRs of 5 and 6, respectively. The power requirement was ~8 × 10⁴ W for air and similar fluids, and ~11 × 10⁴ W for refrigerants. Full article

Carbon dioxide (CO₂/R744) is a natural refrigerant that has been widely studied as a replacement for conventional hydrofluorocarbon-based refrigerants in HVAC&R systems. However, the performance of CO₂ heat pumps depends strongly on the system architecture, component parameters, operating conditions, and pressure control. This study examines a CO₂-based heat pump integrated into an AHU with two-stage heat recovery. Heat recovery from the exhaust air is initially performed using a regenerative sorption wheel and then in an R744 heat pump with fin-and-tube heat exchangers located directly in the airflows. The operating performance of the heat pump was evaluated through system-level simulation based on commercially available component data and iterative balancing of the refrigeration cycle and air-side processes. For the investigated configuration and selected components, the proposed R744 system is compared with a conventional R410A-based reference system under the same air-side boundary conditions. Therefore, this comparison is interpreted as a system-level benchmark rather than an isolated effect of the refrigerant itself, since performance depends on the refrigerant’s properties, compressor performance, heat exchanger configuration, system architecture, and the operating limitations of the components. Simulations are performed for both heating and cooling modes, while preliminary experimental measurements from a physical prototype are presented for qualitative comparison with the simulated heating-mode trend. Full article

Since the Kigali Amendment entered into force globally, propane (R290) has been regarded as one of the most promising next-generation alternative refrigerants for refrigeration and air conditioning. However, its flammability limits its maximum charge amount and leads to higher flow resistance loss. In this paper, a novel refrigeration cycle with an additional independent compression process was simulated and experimentally tested. The simulation error of capacity was less than 7.1%. The intermediate evaporation temperature was optimized. The results show that the new cycle delivers stable performance advantages over the conventional R290 heat pump in both cooling and heating modes, with average capacity and COP improvements of 4.8% and 7.8% for cooling, and 8.3% and 7.5% for heating. System flow resistance loss decreases by 33.0%, which raises the refrigerant mass flow rate by 12.5% and reduces the required compressor displacement by 6.6% at equivalent cooling capacity on average. Full article

Rankine cycle CO₂ pumped thermal energy storage (R-CPTES) offers high-density, emission-free grid storage, but existing designs are limited by modest turbine inlet temperatures and produce electricity only, leaving their thermal potential unused. This paper introduces a Rankine CO₂ storage cycle driven by a high-concentration parabolic dish collector (PDC) and configured solely for combined heat and power, representing a combination of point focus solar energy with CO₂ pumped thermal storage that has received limited attention in the literature. During discharge, the dish superheats the working fluid and raises the high temperature turbine inlet from 456 °C to 500 °C, boosting net power. A heating recovery exchanger placed ahead of the second regenerator then extracts useful heat from the turbine exhaust for district or process supply, without the absorption refrigeration subsystem used in comparable cooling inclusive designs. The aim is to characterise this system through energy, exergy, and parametric analysis. A closed, pinch-consistent model is developed under steady-state assumptions using the Span–Wagner equation of state, with the discharge low pressure, discharge mass flow rate, and PDC outlet temperature varied independently and jointly at a fixed 10 MPa high-pressure boundary. The analysis reveals a power-versus-heat trade-off governed by the discharge pressure and bounded by physical limits rather than interior optima, shows that the solar superheat is a prerequisite for cogeneration, and identifies the system as heat-transfer destruction dominated, with the latent cold storage the largest single source of irreversibility. At the design point the system delivers 16.1 MW of power and 2.5 MW of heat, attaining a storage round-trip efficiency of 73.2% (electricity-only), a solar-inclusive electrical efficiency of 58%, an energy utilization factor of 67%, and an overall exergy efficiency of 61.3%. A preliminary economic assessment gives a levelised cost of storage of 0.10–0.18 $/kWh, competitive with comparable CO₂ storage systems. The proposed system thus provides a simple, fossil-free cogeneration solution for high-DNI regions based on a modular, point focus solar configuration. Full article

Plate heat exchangers (PHEs) play a critical role in the energy efficiency of heat pump systems. However, non-uniform two-phase flow distribution across parallel channels remains a key limitation, as it may cause local dryout and degrade heat transfer performance. To address the limitations of existing prediction approaches, a hybrid modeling framework coupling computational fluid dynamics (CFD) simulations with a distributed parameter model is developed. The model is validated against experimental data under 12 representative operating conditions. The results show that the average prediction errors for the total mass flow rate, pressure drop, and heat transfer rate are within 3%, ±10%, and ±5%, respectively. The influences of refrigerant outlet conditions and inlet distributor geometry on flow distribution uniformity are systematically investigated, identifying the dominant factors governing pressure drop and the mechanism by which distributor orientation improves uniformity. Quantitative optimization shows that an orifice orientation of 225° reduces flow non-uniformity by 67.8% and enhances the heat transfer rate by 4.33% compared with the distributor-free design. The proposed method is robust across various operating scenarios and provides a reliable, quantitative tool for optimizing PHE inlet distributor designs. Full article

To clarify the heating characteristics of the refrigerant direct condensing capillary pipe floor (CPF) used in an air source heat pump (ASHP), simulation studies were conducted. Based on a practical CPF structure with a pipe diameter of 3 mm, the heating characteristics of the condensing and superheated sections were simulated in a steady state. For the refrigerant condensing section, the heating parameters of floor surface temperature (FST) and heat flux (HF) are analyzed by considering different floor surface material, pipe spacing, room temperature, and condensing temperature. For the superheated section, possible solutions to reduce the high FST are the main concern. It is found that mean FST and HF generally increase with higher thermal conductivity of the surface material, smaller pipe spacing, higher condensation temperatures, and lower indoor temperatures. The results are arranged in linear diagrams, which can be referred to easily in the design and operation of the CPF system. Increasing the covering thickness is found to be more effective than increasing the pipe spacing to decrease the FST of the superheated section. Considering practical feasibility, increasing covering thickness with enlarged pipe spacing is recommended. The study provides comprehensive data of HF and FST under different CPF structures, which can be referred to to guide the application of this heating technique in ASHP systems. Full article

Solid-state heat pumps based on caloric effects are emerging as a promising alternative to conventional vapor. compression systems owing to their use of solid refrigerants with zero global warming potential. However, single-effect caloric technologies are intrinsically limited by the temperature-dependent nature of the caloric response, which typically exhibits a peak adiabatic temperature change within a narrow temperature range. In this context, multicaloric approaches offer a promising pathway to enhance thermal performance by combining multiple external fields. This work focuses on the comparison between simultaneous and sequential (cascade) multicaloric operation, with particular attention to the interaction between field application and the temperature-dependent caloric behavior of the material. A finite element model is developed to investigate a multicaloric solid-state heat pump operating in the air conditioning temperature range. A representative material is considered: Mn_0.6Ni_0.6Fe_0.4Co_0.4Si_0.95Ga_0.05, characterized by distinct magnetocaloric and barocaloric responses occurring at different temperature ranges. The analysis explores different field application strategies, including both simultaneous and sequential configurations. The preliminary results suggest that simultaneous multicaloric operation enables a more effective exploitation of the caloric response by aligning the field activation with temperature regions closer to the corresponding peaks. In this framework, cascade strategies appear to offer additional flexibility in tuning system performance under realistic operating conditions. The proposed approach provides a new perspective for the design of multicaloric heat pumps, highlighting the potential role of thermodynamic matching between field activation and material response. Ongoing work is focused on further quantifying these effects and identifying optimal operating conditions. Full article