Sc-CO2 phase transition evolution migration and heat–mass transfer characteristics

Pulsating flow of a Maxwell fluid through a tube with a homogeneous porous medium

This paper summarizes the development and flow characterization of the Osney Plasma Generator thermal arcjet facility at the University of Oxford. The small-scale facility is the first of its kind in the United Kingdom, capable of testing material responses under high-enthalpy flows and serving as a model preheating device for impulse facilities. The new plasma generator produces steady argon, nitrogen, and air plasma jets, utilizing currents up to 500 A DC and gas mass flow rates of up to 0.2 g/s. Measurements from hemispherical slug calorimeters and total pressure probes indicate a maximum stagnation point heat flux of 5.24 MW/m 2 and freestream stagnation pressure of 7.85 kPa, which corresponds to a mass-specific stagnation enthalpy of 19.67 MJ/kg. A fiber-coupled spectrometer was used to examine the species composition of the plasma from the broadband radiation between 300 nm and 1200 nm. The data showcased that the present facility could generate comparable heat fluxes to large-scale facilities at higher equivalent altitudes. A ground-to-flight extrapolation was performed using full plasma flow scaling, showcasing a range of conditions with flight-equivalent velocities of up to 6.23 km/s at altitudes of 51–67 km. The scaling also provided an initial comparison of the effective nose radii between the sub-scale model and the full-scale vehicle. • Development and characterization of a small-scale thermal arcjet facility. • Generation of steady plasma flows using argon, nitrogen, and air composition. • Stagnation-point heat fluxes comparable to those in large-scale arcjet facilities. • Compact, cost-effective platform for high-temperature material testing. • Ground-to-flight extrapolation reveals scaling of probe geometry to nose radius.

Experimental analysis of the performance of a semi-hermetic reciprocating compressor working with R744/R290 mixtures

CANDU reactors have fuel channels consisting of 12-13 CANDU fuel bundles, and the rotational angle of each fuel bundle is not controlled when it is loaded into the channel. Coolant behaviour, which may be affected by bundle rotational misalignment, can influence fuel performance; however, the degree of this impact is not yet well understood. This work performed Computational Fluid Dynamics (CFD) simulations with heat transfer using STAR CCM+ on two CANDU 37M fuel bundles with four different rotational misalignment angles (0°, 20°, 40°, and 60°). By comparing the predicted coolant behaviour and fuel temperature profiles, it has been determined that misalignment can alter subchannel mass flow rates by over 40% and increase the maximum fuel temperature by approximately 20 °C. This study also investigates the physical mechanisms by which a misaligned endplate affects these outcomes, through a detailed examination of coolant flow behaviour in the endplate region. • CFD simulations with heat transfer of CANDU 37M fuel bundles with rotational misalignment. • Misalignment changes subchannel mass flow rates by over 40%. • Maximum fuel temperature changed by ∼ 20 °C with bundle misalignment. • Endplate misalignment mechanisms analysed through detailed flow study.

Egypt has high levels of solar radiation throughout the year, making solar air heaters (SAHs) a practical and economical way to support sustainable energy applications and reduce reliance on traditional energy sources. This study experimentally investigates the energy, exergy, environmental, and economic (4E) performance of three SAH configurations under different air mass flow rates. The experiment was conducted at the Faculty of Agriculture, Ain Shams University, Egypt (30°11' N, 31°24' E). The tested configurations include an airflow channel above the absorber plate (SAH1), an airflow channel below the absorber plate (SAH2), and a modified design with airflow below the absorber plate integrated with perforated V-shaped fins (SAH3). The experiments were conducted during July 2025, and real-time monitoring of temperatures, solar radiation, and airflow was carried out. At a mass flow rate of 0.009kg/s, SAH3 achieved the highest average thermal efficiency of 62%, compared with 53% for SAH2 and 44% for SAH1. Regarding exergy efficiency at 0.006kg/s, SAH3 achieved an average of 3.7%, exceeding those of SAH2 (2.6%) and SAH1 (1.8%). At 0.009kg/s, the SAH3 achieved the lowest energy cost of 0.0003 $/kWh and mitigated CO2 emissions by approximately 1.07 tons annually, resulting in an estimated carbon credit of 53.43 USD. These results confirm that the proposed design is a promising option for sustainable solar thermal applications.

Influence of the mass flow rate ratio of inlet flows in microchannels on their mixing efficiency: modeling and experiment

Natural coastal blowholes are rare geomorphological features in which incident waves induce oscillatory motion within coastal cavities, compressing and venting air through a surface outlet and forming a naturally integrated analogue of an oscillating water column. This study evaluates natural blowholes as a nature-based solution for low-impact wave-energy extraction using a combined experimental-numerical-probabilistic framework, with Chabahar Bay in the Oman Sea as a case study. A laboratory flume model was constructed to reproduce blowhole airflow dynamics, and outlet air velocity measurements were used to compute mass flow rate and validate a CFD model under consistent boundary conditions. The validated CFD framework was then extended to the field geometry to estimate pneumatic kinetic power, yielding a peak outlet velocity of approximately 21.6m s⁻¹, a mass flow rate of approximately 13.0kg s⁻¹, and an associated kinetic power of about 3kW per vent. To represent variability in ocean forcing, a Monte Carlo framework comprising 5,000 realizations was parameterized using regional wave-climate statistics and propagated through the deep-water wave-power formulation to quantify uncertainty in wave-power flux. The mean wave-power flux is 8.7kW m⁻¹ with a 95% confidence interval of 1.6-22.5kW m⁻¹, and pronounced seasonal variability is observed, with mean flux ranging from approximately 4.5kW m⁻¹ in winter to 13.2kW m⁻¹ in summer. These results demonstrate that natural blowholes can provide measurable, site-specific energy yield while minimizing additional coastal infrastructure, and that probabilistic assessment is essential for quantifying uncertainty and seasonality governing long-term reliability.

In this paper, an additively manufactured heat exchanger featuring semi-circular minichannels fabricated using selective laser melting technique has been investigated experimentally and numerically. Thermohydraulic performance was characterized under balanced mass flow rate conditions (1.11-4.44kg/h) using a Nitrogen-Nitrogen open-loop test facility. The experimentally measured fanning friction factor and Nusselt number were consistently higher than values predicted by smooth-channel theoretical correlations due to additively manufactured induced surface roughness. Surface profilometry revealed average roughness values of 8.11μm in the channel region and 4.70μm in header regions. Numerical models (laminar, realizable k-ε, and transition SST) underpredicted Fanning friction factor and Nusselt number relative to experiments, with the Transition SST model providing the closest agreement with respective average percentage difference of 66.6 and 51.7%. Empirical correction factors ([Formula: see text] and [Formula: see text]) were developed to reconcile simulations with measurements, improving predictive accuracy. The equivalent sand-grain roughness approach was evaluated using Filonenko, Blasius, Halland, Dittus-Boelter, and Gnielinski correlations. A single relative roughness value could not simultaneously match Fanning friction factor and Nusselt number; therefore, independent roughness parameters of 16[Formula: see text] (momentum-related) and 4.5[Formula: see text] (heat-transfer-related) are proposed. Numerical flow visualization demonstrated multiple jets and flow recirculation regimes in converging outlet headers, causing mild flow maldistribution and localized variations in heat transfer. The study establishes a validated framework to predict additively manufactured minichannel heat exchanger performance, accounting for surface roughness effects, and provides correlation tools for its design optimization.

The downhole heater is a crucial equipment for realizing the in-situ pyrolysis process of Tar-rich Coal. The different structural performances of heaters can also affect the heat transfer effect underground. The article investigates the comprehensive heat transfer performance of circular horizontal baffle and spiral baffle heaters through digital modeling and simulation. The distribution characteristics of flow velocity, heat transfer coefficient and wall temperature of the heating tube, as well as the pressure drop in the shell side, were investigated for two types of heaters within a mass flow rate of 0.00693-0.05542kg s-1. The variation patterns of the Nusselt number and thermal resistance coefficient of the two type heaters under different mass flow rates were analyzed. The results showed that compared to the spiral baffle heater, the Nusselt coefficient of the circular baffle heater decreased by 3.82%, 10.75%, 0.73%, and 8.45%, respectively, at mass flow rates of 0.00693kg s-1, 0.01386kg s-1, 0.02078kg s-1, and 0.03464kg s-1, while the thermal resistance coefficient increased by 2.33%, 10.62%, 0.98%, and 7.59%. This indicates that the helical baffle heater is more suitable for the process parameters of in-situ pyrolysis of Tar-rich Coal. Based on numerical simulation results, a prototype of a spiral baffle heater with a pitch of 110mm was fabricated. Gas heating experiments were conducted at corresponding mass flow rates of 0.00693kg s-1, 0.01039kg s-1, and 0.01386kg s-1. The results indicate that the temperature values obtained from numerical simulation analysis are essentially identical to the actual experimental temperature data, with an average error of < ± 7% for the heater outlet temperature. This proves the accuracy and reliability of the numerical simulation analysis.

International compendia specify setting the flow for testing dry powder inhalers (DPIs) with the pressure ratio across the flow control valve ≤0.5. This guidance derives from thermodynamic theory, but there is no requirement that the flow control equipment demonstrates adherence to this theory. There is therefore a need to define and test for acceptable flow control valve performance, enabling DPI manufacturers to determine whether their test equipment is achieving the expected flow control. Herein, we present flow control data for two valves common in the inhaler testing community and describe the need for qualification specifications for flow control equipment with such valves. We devised a simple laboratory apparatus and method for determining the mass flow rate through two common flow control valves in their commercial configuration. In the test method, the pressure ratio across the valve is lowered from ∼0.7 to 0.3. This range of pressure ratio covers the standard test requirement that the pressure ratio must be 0.5 or less and maps the transition of compressible flow through the valve to the point where the air flow theoretically remains constant. A common industrial valve, mentioned specifically in Pharm. Eur. 2.9.18 and in earlier editions of United States Pharmacopeia 601, exhibits nearly constant flow when the pressure ratio is <0.5. Another valve in widespread use exhibits a continued slight increase in mass flow rate even as the pressure ratio is decreased below 0.5. Inhaler testing laboratories should test whether their equipment exhibits the constant flow condition that is often assumed when the pressure ratio across the flow control valve is 0.5 or smaller. Quantitative specifications, yet to be developed, for qualifying commercial flow control equipment must account for both the transient start-up and the steady-state flow in DPI testing.

This study proposes a multi-objective optimization framework for a cooling plate-based indirect liquid cooling system applied to a 6S2P lithium-ion battery module during 3C fast charging. A three-dimensional computational fluid dynamics (CFD) model coupled with the multi-scale multi-domain (MSMD)–Newman–Tiedemann–Gu–Kim (NTGK) battery heat generation model was developed to investigate the system thermal–hydraulic behavior. The numerical model was experimentally validated through single-cell charging tests, with temperature deviations below 5%, confirming its reliability. A systematic parametric analysis was conducted to evaluate the effects of coolant channel number, channel width, channel spacing, and coolant mass flow rate on maximum temperature (Tmax), temperature difference (ΔT), and pressure drop (ΔP). The results indicated that increasing the coolant flow rate significantly enhanced thermal performance but caused a substantial increase in hydraulic losses, whereas geometric parameters had comparatively smaller effects. To improve optimization efficiency, 30 design samples were generated using Latin hypercube sampling and used to train ANN surrogate models, which demonstrated high predictive accuracy with test R2 values of 0.9931, 0.9960, and 0.9842 for Tmax, ΔT, and pumping power (Ppump), respectively. Subsequently, NSGA-II combined with TOPSIS identified the optimal design with a channel width of 6.22 mm, channel spacing of 4.84 mm, and coolant flow rate of 2.55 LPM. Under these conditions, the optimized system achieved a Tmax of 30.47 °C, a ΔT of 4.50 °C, and a Ppump of 0.05879 W. The relative deviations between ANN predictions and CFD results were all below 1%, demonstrating the robustness of the proposed optimization framework. These findings provide an effective design methodology for enhancing heat transfer while minimizing pumping power in advanced battery thermal management systems.

The urgent need to adopt clean heat in industrial processes cannot be overstated in light of the pressing issue of climate change and the mandatory compliance with environmental regulations. The combined absorption – compression heat pump based on the Osenbrück cycle is a noteworthy high-temperature heating technology that holds great promise for industrial high temperature applications. In this work, a model of a combined absorption compression heat pump is developed. The system utilizes an ammonia/water mixture as natural working fluid. The model is used to simulate different working conditions, and the performances of the system are studied according to the ratio between the weak and strong solution mass flow rates f . The maximum of the sink heat load and the temperature lift are found at f = 0.4. For this working condition, COP is minimum. A trade-off between heat and temperature requirements and efficiency of the system occurs. The performances of the heat pump are evaluated for variable sink and source inlet temperatures and mass flow rates, as well as variable overall heat transfer conductance UA of absorber and desorber. To obtain the maximum sink heat load, high values of UA and sink mass flow rates should be implemented. Reducing the sink mass flow rate while keeping the UA high maximizes the temperature lift, decreasing at the same time the sink heat load. When ṁ sink = 0.3 kg/s, UA = 7 kW/K and T sink,in = 60 °C, the sink outlet temperature reaches 110.7 °C, which is the maximum temperature achieved in the simulations. • Developed a MATLAB model of a combined absorption–compression heat pump. • Used NH₃/H₂O mixture as a natural working fluid for high-temperature applications. • Identified optimum circulation ratio f = 0.4 for maximum thermal load and temperature lift. • Found trade-off: high heat and temperature output at expense of COP efficiency. • Demonstrated the strong impact of overall heat transfer conductance and mass flow rates on system performance.

Thermal performance evaluation of low-GWP refrigerant pairs in cascade refrigeration systems: An experimental and simulation study

Experimental study of flow boiling heat transfer in smooth and circular pin-fin minichannels

DEMO reactor aims to demonstrate the feasibility of electrical energy production from nuclear fusion source in a tokamak configuration. Within the DEMO pre-conceptual design assessment, the water-cooled lithium lead (WCLL) and helium-cooled pebble bed (HCPB) concepts were selected as Breeding Blanket (BB) candidates. Along the research pathway toward blanket selection, safety analyses of these two options were performed using selected postulated initiating events (PIEs) as reference scenarios. For the WCLL BB, the out-vessel loss of liquid metal was identified as a major safety concern. This paper presents a numerical analysis of this postulated accidental scenario, carried out adopting MELCOR code. Large rupture (double-ended 200%) and leak (5%), occurring at two different positions (middle and bottom) of lithium-lead (LiPb) Cold Leg (CL) in both the inboard (IB) and outboard (OB) loop, were simulated implementing a detailed MELCOR nodalisation. The exothermic reactions of LiPb with air and steam present in the DEMO building were evaluated, adopting an in-house conservative numerical model, since only pure lithium-air/steam chemical reactions are available in the default MELCOR version. The LiPb mass flow rate discharged into the building was evaluated along with the LiPb volume transients in the hot and cold leg and segments of both the IB and OB loops. The time-dependent mass evolution of the reactants and products involved in the LiPb-air/steam chemical reactions was also calculated. Moreover, the increase in temperature and pressure within the considered building volume due to the energy released is shown. These numerical analyses do not implement safety or mitigation functions and the results presented should be considered highly conservative.

• Provide innovative experimental data of filling/emptying CO 2 tanks. • Comprehensive analysis of the dynamic behaviour of the CO 2 tanks. • Better understanding of CCES operating process with liquid storages. Energy storage systems are becoming a highly topical issue with the increasing integration of solar and wind energy into the electricity mix. Thermomechanical energy storage systems are attracting growing interest. They are based on thermodynamic cycles to store electricity under mechanical and/or heat energy. Compressed CO 2 energy storage systems are one emerging example. Despite numerous modelling studies, experimental investigations remain very limited. Existing experiments are restricted to gaseous CO 2 at low pressures. However, these systems are mostly investigated with storage tanks containing liquid or supercritical CO 2 . This study addresses this gap by presenting the first experimental results on the dynamic behaviour of reservoirs containing CO 2 in multiphase conditions (coexistence of liquid – gaseous CO 2 ) and reaching supercritical pressures. For that purpose, an experimental test rig based on conventional and commercial components was developed. It is composed of a 320 L low-pressure storage, a 240 L high-pressure storage and a 3 kW CO 2 pump. The mass flow rate ranges from 100 to 320 kg.h −1 , corresponding to charging times from 1 to 1.8 h (including a balancing step) with a maximal pressure of 22 MPa. The results indicate an inability to maintain a constant pressure during a tank emptying or filling due to temperature changes. During a discharge, the pressure in the high-pressure storage drops from 22 to around 3 MPa. As a consequence, this study highlights the possibility to balance the pressure after a discharge.

Analysis on coupling characteristics of ventilated cavitation and supersonic exhaust jet of a supercavitating vehicle

Thermodynamic analysis for interchangeability of natural refrigerants R290, R744 in heat pump systems for electric vehicles using R1234yf

• Dry/wet overcomes line contact heat transfer limitations in conventional FPCs. • Three types of FPC were tested: water, dry sand, and wet sand-based systems. • Water-based FPC reached 62%, efficiency, 853 W heat gain at 570 W/m 2 radiation. • The wet sand-based FPC attained an efficiency of 56% and a heat gain of 770 W. • Financial analysis provide economic viability, payback of each configuration. Flat plate collectors (FPCs) are well-established, efficient, cost-effective technologies for solar energy utilization in heating applications. However, conventional designs often fall short in addressing non-contact heat transfer limitations, primarily due to the line contact between absorber plates and round riser tubes. Enhancing the contact area between the riser tube and the absorber plate by incorporating dry and wet-type materials has significant potential to improve thermal performance. This study evaluates the thermal performance of FPCs with different contact materials such as air, Water, dry sand and wet sand. In this study, water served as the heat transfer fluid for all collector types, with a constant mass flow rate of 1.85 litter/min maintained throughout the experiment. To ensure a reliable comparison, the inlet temperature and geometrical parameters were kept identical for both collector configurations. The findings demonstrate that the Water-based FPC achieved 35.72% higher efficiency than conventional FPC. Dry sand showing better thermal performance than conventional FPC but perform way lower than water based FPC. Both water and wet sand based FPC exhibited superior thermal performance in terms of both heat absorption and efficiency with different solar radiation and elevated wind speed conditions. Under a global radiation of 500.81 W/m 2 , the Water-based FPC achieved a heat gain of 794.14 W, representing a 21.54% increase Wet Sand-based FPC. With a higher solar radiation level of 600.68 W/m 2 Wet Sand-based FPC demonstrated 2.45% higher efficiency than water based FPC. The comparative techno-economic analysis reveals that integrating low-cost contact materials such as water and wet sand in FPCs can reduce LCOE by up to 75% and improve ROI up to 40.5%, demonstrating superior energy and financial performance over conventional designs. The study provides valuable insights into optimizing solar thermal systems, emphasizing the impact of material properties and interface conditions and comprehensive economic analysis on overall system performance and cost-effectiveness.