Reduction In Mass Flow Rate Research Articles

CO2 thermal network prototype: Identifying control parameters for optimal operation in transcritical mode

An innovative concept has been developed and patented recently called CO2 Thermal Network (CO2TN) to improve the performance of heating and cooling systems in buildings. It is a decentralized system circulating two-phase CO2 at 20 ± 5 °C inside a building, instead of water, as a heat carrier fluid (HCF) in a single pipe. Heat pumps connected to this pipe provide heating and cooling inside a building using CO2 at their source side. Thus, the heat pumps operate with enhanced and consistent performance. The pipe also facilitates heat recovery between the connected units. Additionally, leveraging the latent heat of two-phase CO2, the CO2TN operates with a reduced mass flow rate in the loop, requiring a lower circulation energy consumption than conventional hydronic systems.This study introduces the concept and the first prototype of a CO2TN system. Then, the paper experimentally investigates the influential parameters that control the system’s operation and optimize its performance in transcritical mode. The results showcase that a CO2TN’s performance depends on its gas cooler (GC) temperature and pressure, the number of working heat pumps, and their mode of operation. An optimal GC outlet temperature exists for each GC pressure, which can improve system performance by up to 30%. Moreover, the GC pressure depends on the temperature range of the thermal energy sources used to balance the CO2TN. Additionally, the system shows significant performance improvement—up to 63%—when multiple heat pumps operate simultaneously in different modes.

Energy-economic-environmental analysis of bifacial photovoltaic thermal (BPVT) solar air collector with jet impingement

Jet impingement cooling enhances photovoltaic (PV) system efficiency by using high-speed fluid jets to reduce panel temperatures, improving performance and longevity. The effectiveness depends on factors like fluid flow rate, nozzle placement, and distance from the panel. While it boosts energy output, it may increase energy use for fluid circulation and add complexity to the system. This research explores a groundbreaking approach to enhancing the efficiency of bifacial photovoltaic thermal (BPVT) systems by integrating jet impingement technology. A novel design featuring a jet plate reflector is introduced, offering the dual benefit of cooling the PV panels while simultaneously reflecting light to optimize energy capture. The study comprehensively analyses the system’s performance, including energy output and a detailed techno-economic and environmental-economic evaluation. The modelling in this study was validated and reasonably consistent with experimental results. The system's output air temperature and thermal efficiency are 302.07–318.75 K and 33.83–62.28 %, respectively. The temperature and electrical efficiency range for PV systems are 304.39–339.54 K and 9.39–11.22 %. Reduced mass flow rate and increased solar irradiation are the most economically advantageous operating parameters for the proposed system, resulting in lower annual pumping costs and more significant annual energy gains for the system. CBR variations range from 0.1363 to 9.3445, with an average of 2. Additionally, by using BPVT with jet impingement to generate electricity rather than fossil fuels, it is possible to reduce annual carbon dioxide emissions by approximately 1.61 tons and save RM93.51 annually. In general, the proposed method should be used to minimize environmental pollution.

Thermal analysis of an integrated solar combined cycle power plant and its application in southern Iraq

Recently, simple cycle play a significant role in electric power production in Iraq. However, those units suffer from low thermal efficiency and low power output. In the present work, theoretical study is carried out aiming to improve the performance of (AL-Amara station 125MW). The present work includes three parts: the first part focus on the effect of ambient temperature on the performance of simple cycle including mass flow rate, power output, thermal efficiency and other parameters. In the second parts, a modification to simple cycle is implanted to be a combined cycle. The third part is studied the benefit of using solar unit for producing more steam to be supplied to the heat recovery steam generator wishing to produce more power and low emissing. Regarding, to simple gas turbine unit, the obtained results show that the mass flow rate is decreased nearly (10.8%) when the ambient temperature increased from (15-50) ºC. However, this reduction in mass flow rate of air is led to significant reduction in power output and thermal efficiency nearly (22.6%,13.2%) respectively. In the second parts, applying combine mode show a significant increase in power output and thermal efficiency nearly (32.5% and 32.3%) respectively. while the specific fuel consumption is decrease nearly (32.19%). Finally, the third parts when solar units are used, the gathered results show an acceptable increase for the amount of steam produced via solar units (21.02kg/s). The overall performance of the integrated cycle shows that the power output and the thermal efficiency increased nearly (11.28%and10%).

Design of a 130 MW Axial Turbine Operating with a Supercritical Carbon Dioxide Mixture for the SCARABEUS Project

Supercritical carbon dioxide (sCO2) can be mixed with dopants such as titanium tetrachloride (TiCl4), hexafluoro-benzene (C6F6), and sulphur dioxide (SO2) to raise the critical temperature of the working fluid, allowing it to condense at ambient temperatures in dry solar field locations. The resulting transcritical power cycles have lower compression work and higher thermal efficiency. This paper presents the aerodynamic flow path design of a utility-scale axial turbine operating with an 80–20% molar mix of CO2 and SO2. The preliminary design is obtained using a mean line turbine design method based on the Aungier loss model, which considers both mechanical and rotor dynamic criteria. Furthermore, steady-state 3D computational fluid dynamic (CFD) simulations are set up using the k-ω SST turbulence model, and blade shape optimisation is carried out to improve the preliminary design while maintaining acceptable stress levels. It was found that increasing the number of stages from 4 to 14 increased the total-to-total efficiency by 6.3% due to the higher blade aspect ratio, which reduced the influence of secondary flow losses, as well as the smaller tip diameter, which minimised the tip clearance losses. The final turbine design had a total-to-total efficiency of 92.9%, as predicted by the CFD results, with a maximum stress of less than 260 MPa and a mass flow rate within 1% of the intended cycle’s mass flow rate. Optimum aerodynamic performance was achieved with a 14-stage design where the hub radius and the flow path length are 310 mm and 1800 mm, respectively. Off-design analysis showed that the turbine could operate down to 88% of the design reduced mass flow rate with a total-to-total efficiency of 80%.

Design, fabrication, and performance assessment of a novel solar air heater based on recycled materials

In this paper, a solar air heater (SAH) is designed using recyclable materials, and its performance is analyzed. The device is composed of an absorbing plate made up of 36 cans of soda and an equal number of tins with bodies covered with black color and has resistivity against high temperatures. The laboratory research revealed that the collector's efficiency is enhanced considerably by increased airflow speed and the heat transfer coefficient between the absorbing plane and air. In addition, the effects of the radiation intensity and mass flow rate on parameters such as the absorbed heat, temperature difference, and thermal efficiency are investigated. The derived results for mass flow rates of 0.0104 (kgs-1) and 0.0078 (kgs-1) indicate that all mentioned parameters increase the radiation intensity. Furthermore, the thermal efficiency and the absorbed heat are increased by increasing the mass flow rate, while a reduced mass flow rate increases the temperature difference parameter. Moreover, studying the charts demonstrates that the tins absorb a larger portion of the sun's radiation and, consequently, enhance thermal transfer compared with the soda cans. Irreversibility increased with increasing radiation intensity. At 300 radiation intensity, the highest thermal and exergetic efficiencies occurred.

Dynamic mode characteristics of flow instabilities in a centrifugal compressor impeller

Centrifugal compressors are key parts of medium and small aircraft engines, the flow instabilities of centrifugal compressors have become the bottleneck of the developments of engines. It is vital to investigate the dynamic mode characteristics of flow instabilities in centrifugal compressors for solving the issues. In this study, unsteady full annular simulations of the centrifugal compressor flow are firstly implemented. It is found that the flow instability of the compressor primarily arises in the impeller. To capture the dominant transient modes in process of flow instabilities and accurately describe their temporal evolutions, a modified dynamic mode decomposition method (DMD-TC) is adopted to analyze the dynamic mode characteristics, which was proposed in our previous study. The results show that perturbations in the impeller can be mainly classified into three categories: impeller-diffuser interactions, self-excited perturbations, and vortex-induced perturbations. In detail, the modes induced by the impeller-diffuser interactions and self-excited perturbations are intrinsic modes, and they reflect the inherent flow unsteadiness in the impeller. On the one hand, the vortex-induced perturbations couple with the self-excited ones, which affect the spatial structures of modes induced by self-excited perturbations. The coupling effects enhance with the reduced mass flow rate, and the “resonance” effect might be excited. As a result, the mode of 4 RF (rotor frequency) grows during rotating stall process (RSP), which is a typical characteristic of rotating stall in the impeller. On the other hand, the vortex-induced perturbations emerge as different characteristic modes, due to the variant vortex structures with the mass flow rate. During the RSP, the growth of low-frequency characteristic modes is another typical feature of rotating stall in the impeller.

Influence of swirl and ingress on windage losses in a low-pressure turbine stator-well cavity

As part of the drive towards achieving net-zero flight by 2050, the development of ultra-high bypass ratio engines will place greater importance on the efficiency of the low-pressure turbine. Stator-well cavities can be a significant source of loss within this system, primarily due to the ingestion of annulus air, which can rotate at a speed less than that of the disc. This paper presents the results of a joint experimental/numerical campaign to relate windage torque to the flow physics in a scaled, engine-realistic stator-well geometry with superposed flows. The primary variables were the pressure ratio across the stator row and the swirl ratio at inlet to the cavity. This is the first paper to relate simultaneous torque and swirl measurements in a stator-well cavity. The numerical simulations have also provided insight into the fluid dynamic behaviour. A reduction in cavity windage torque with superposed flow rate was shown, consistent with the increase in swirl measured by experiments and predicted by computations. The pre-swirled superposed flows reduce the ingestion of negatively swirling fluid from the annulus, effectively increasing the swirl ratio of the flow in the cavity towards that of the rotor. This reduces windage losses; at the design condition with superposed flow, the cavity windage torque reduced by 60% of that of the reference case. Sealing effectiveness increased with superposed flow rate. This was demonstrated through gas concentration measurement/simulations, a reduced radial flow velocity into the cavity and a reduced mass flow rate across the interstage seal. The application of a turbulent transport model showed that ingestion could be explained by shear-driven diffusion. Ingestion increased as inlet swirl ratio reduced, while the pressure ratio was found to have a negligible influence on windage moment coefficient, swirl ratio and sealing effectiveness. In addition to providing fluid dynamic insight, the gas concentration results can be used for validating thermomechanical models. The results in this paper will be of practical interest to the engine designer who wishes to scale information to engine-operating conditions.

Physical Insight Into Whoosh Noise in Turbocharger Compressors Using Computational Fluid Dynamics

Abstract Whoosh is typically the primary noise concern for turbocharger centrifugal compressors without ported shroud recirculating casing treatments, utilized for spark-ignition automotive applications. Whoosh is characterized by broadband elevation of noise in approximately the 4–13 kHz range, where the lower frequency boundary is dictated by the cut-on frequency of the first multidimensional acoustic mode. At mid-to-low compressor flow rates, swirling, reversed flow emanates from the leading-edge tip region of the main impeller blades, comprising an annular zone at the inducer plane. High velocity gradients are observed near the shear layer between the bidirectional forward and reverse flow which results in the formation of rotating instability cells. Whoosh noise is generated due to the interaction of these rotating instabilities with the leading edge of main impeller blades. Along a line of constant rotational speed, whoosh noise exhibits a dome-like character, where its maximum value occurs in the mid-to-low flow region and the levels decrease at elevated and reduced mass flow rates. To provide insight into the variation of broadband whoosh noise with flowrate, this work includes experimentally validated computational fluid dynamics predictions for five mass flow rates at a fixed rotational speed. These predictions span the constant speed flow range from just below the peak efficiency to near the surge boundary. Computational predictions capture the physical mechanism responsible for the dome-like character of whoosh noise as a function of flowrate at a given rotational speed.

Experimental study on energy-exergy performance of single-phase natural circulation loop using mono/hybrid nano-oils

Thermal/vegetable oil-based mono/hybrid nanofluids (Nano-oils) may be potential working fluids in single-phase natural circulation loops for medium temperature applications due to their favorable thermophysical properties (high thermal expansion coefficient and low viscosity) and high Prandtl number; however, not studied yet. Hence, the present study investigates the different nano-oils in a natural circulation loop. Therminol-VP1 and soybean-based mono/hybrid nano-oils with different nanoparticles (Al2O3, CuO, SiC, and MWCNT) are used at a volume fraction of 0.1%. The influence of power input and loop inclination on the energy-exergy performance parameters (Effectiveness, Entropy generation rate and Induced mass flow rate) are presented. The use of nano-oil shows enhanced heat exchanger effectiveness and lower entropy generation rate, whereas the induced mass flow rate may increase or decrease depending on nanoparticle shape and power input. Al2O3+MWCNT nano-oil exhibits superior performance, with a maximum mass flow rate reduction of 8%, effectiveness enhancement of 36%, and entropy generation reduction of 20% as compared to base oil. Therminol-VP1 shows quick flow establishment than soyabean oil. The usage of nano-oil is more beneficial at the higher power input. Loop inclination reduces the mass flow rate while increasing the effectiveness and entropy generation; however, mass flow reduction is much lower for counter-clockwise inclination.

Experimental Study on the Half Flat Tip Serrated Trailing Edge for Stand Fan

The effectiveness of half flat tip serrations on reducing fan blade trailing edge noise was investigated using experimental methods. The experiments were conducted at an anechoic chamber under different rotating fan speeds. Numerical simulations were performed to investigate the mass flow rate generated by the serrated fan and compared with that by the baseline fan. The experimental results showed that the overall amount of noise reduction decreased with the increasing of the distance away from the fan. It was found that the effectiveness of the serrations was not proportional with the rotating speed of the fan where it was most effective at 263 rpm and 2041 rpm with noise reductions about 3.1 dBA and 3.5 dBA, respectively. This phenomenon might be depended on how trailing edge vortex would interact with the serrations at different speeds of the fan. The reduction of mass flow rate reduced with the increasing of the rotating speed and the highest reduction was found at 263 rpm which was about 18% and this reduction was accompanied by overall noise reduction of 3.1 dBA.

Research on optimizing turbo-matching of a large-displacement PFI hydrogen engine to achieve high-power performance

The output power of hydrogen engines is restricted due to the low volume energy density of hydrogen and lean burn, thus a turbocharger is necessary to boost the power intensity, especially for large-displacement hydrogen engines. However, turbine selection for hydrogen engines is complex comparing gasoline engines because of the different exhaust components and low exhaust temperature. In this research, the turbocharger-matching of a 5.13 L hydrogen engine is studied, and the results show the original turbine, whose maximum reduced mass flow is 0.00966 (kg/s)·Kˆ0.5/kPa, cannot achieve the desired power performance at high speeds. The reduced mass flow rate can be calculated, taking into account the effect that exhausts composition and temperature. The accuracy of the method is validated using data from a 2.3 L turbocharged H2ICE at various engine speeds and throttle openings, and the error between the measured and calculated expansion ratio is less than 5% mostly. At last, a well-matching turbine for high engine speeds of the 5.13 L hydrogen engine to meet the desired power of 120 kW, whose maximum reduced mass flow is extended to 0.0156 (kg/s)·Kˆ0.5/kPa, is selected according to the method, and the maximum power reaches 128.9 kW with a maximum torque of 662.6 N m, improving by 38.7% and 7.7% respectively comparing with the original turbine. However, the output torque reduces by 15.6% at 1200 rpm. The reduced mass flow rate varies significantly in comparison to the turbines that are well suited for low and high engine speeds respectively, thus the Variable Geometry Turbine may be the solution for both low and high speeds simultaneously for hydrogen engines.

Enhancing efficiency and reducing CO2 emission of a geothermal-driven polygeneration system: Environmental analysis and optimization

The limitations of the single-flash cycle (SFC) include low efficiency, limited power output, and the inability to produce multiple products simultaneously. Additionally, the SFC requires a large amount of water and can have negative environmental impacts. In this study, to improve performance and produce multiple products, subsystems such as a branched GAX cycle assisted by a thermoelectric generator, a domestic water heater, and a reverse osmosis unit are coupled with the SFC. Then, thermodynamic, environmental, sustainability, and net present value approaches are devoted to analyzing system performance. This study utilizes MATLAB software to achieve a two-objective optimization that uses both CO2 emission rate and exergetic efficiency as objectives. The CO2 emissions rate represents a downward inclination with an increase in temperature in the generator inlet. Net electricity, cooling load, and pure water rate have a downward inclination with an augmentation of the temperature in the generator inlet due to reducing mass flow rate in the branched GAX/TEG cycle. At the optimum point, the payback period of the designed system with increasing selling prices of the products is decreased. The polygeneration gain output ratio in the optimized conditions reduces compared to the base case, whereas the sustainability index increases. Compared to similar works, the designed system produces a higher output.

A Novel Similarity Solution Approach Based Thermal Performance Prediction and Environmental Analysis of Evacuated U-Tube Solar Collector Employing Different Mono/Hybrid Nanofluids

In this article, a novel similarity function-based two-dimensional steady-state model is developed to analyze the thermal performance of an individual evacuated U-tube solar collector (EUTC). Using the developed model, the energy and environment assessments of a EUTC have been carried out employing different water-based mono/hybrid nanofluids as energy exchange fluids (EEF). The influence of nanoparticle volume concentration on energy gain, mass flow rate reduction, and efficacy has been analyzed. The influence of Reynolds number on energy gain is also investigated. The results show that Al2O3+MWCNT (multiwalled carbon nanotube) has high energy gain, whereas MgO has high mass flow reduction compared to water as a base fluid at 2% volume concentration. The efficacy of EUTC has been enhanced using nanoparticles as an additive. Employing Al2O3+MWCNT as EEF, the impact of EEF flow rate, EEF inlet temperature, ambient temperature, and solar intensity on the energy gain and efficacy of EUTC have been analyzed. It is observed that solar intensity and ambient temperature have major and minimum influence on EUTC performance.

Numerical study on the straight, helical and spiral capillary tube for the CO2 refrigerant

A numerical study has been carried out for straight, spiral and helical capillary tubes and their performance has been compared with CO2 refrigerant. The numerical models are developed based on the fundamental conservation principles of mass, momentum, and energy. Within this, outer loop, the ordinary differential equations are solved from the inlet to the exit of the capillary tube. The study has been carried out to calculate the mass flow rate by bisection method where the mass is iteratively calculated at the specified capillary length or vice versa. In-house coding programming employs the finite difference approach for numerical solutions. The characterization of the capillary tube has been done by calculating the length for the given mass or by calculating mass for the given length. The comparison of the straight capillary with helical capillary tube (50 mm coil diameter) and spiral capillary tube (50 mm pitch) has been reported. For a change in tube diameter, surface roughness, and length, the percentage reduction in mass flow rate in capillary tubes (straight, helical, and spiral) is calculated. The percentage reduction in mass in a helical capillary tube compared to the straight capillary tube is about 7–9 %. The percentage reduction in mass in a spiral tube compared to the straight capillary tube is nearly 23–26 %. Additionally, the percentage reduction in mass in a spiral tube compared to the helical capillary tube is almost 17–19 %. Additionally, the percentage reduction in length in a spiral tube compared to straight capillary tube ranges from 37 % to 43 %. Similarly, the percentage reduction in length in a spiral tube compared to helical capillary tube is ranging from 25 % to 32 %

Gas–surface interactions of a Couette–Poiseuille flow in a rectangular channel

Reduced mass flow rates of a rarefied Couette and Poiseuille flow in a long rectangular channel are calculated in the whole range of the gas rarefaction and a wide range of the width to height ratio. Furthermore, walls may be made of different materials so that different tangential momentum accommodation coefficients (TMACs) may be applied. Analytical solutions are given for the slip regime, where all four surrounding walls may have a different TMAC. Due to a simplified modeling assumption, these solutions can be used to correct the well-known flow rates of a fully diffuse channel for different TMACs in the whole range of the gas rarefaction. If the slip solution and the diffuse solution are known, the procedure can principally be adapted for any channel shape. The results of the analytical model expressions are validated with simulation data of the plane Couette and Poiseuille flow and the Poiseuille flow through a pipe, which are found in the literature. In addition, the analytical solution is compared to results of the Direct Simulation Monte Carlo (DSMC) method of a Couette and a Poiseuille flow in a rectangular channel, which are provided as tabulated data for a variation of the gas rarefaction parameter at different aspect ratios and different combinations of TMACs. The procedure to calculate the mass flow rate of the certain flow as well as the application limits are discussed.

Numerical investigation of plasma actuator induced forcing direction on the performance of a low-speed isolated axial compressor rotor

This paper investigates the effects of changing the dielectric barrier discharge (DBD) plasma actuator forcing direction on stall margin improvement and aerodynamic performance of a low-speed axial compressor rotor. The effects of plasma actuator induced force at yaw angles of 0, +30, −30° relative to the rotational axis of the compressor were evaluated through the incorporation of body force spatial distribution into Navier-Stokes equation. The evaluations focused on compressor performance comprising rotor efficiency, total pressure rise coefficient, span-wise loss coefficient, and diffusion factor on one hand and the tip leakage flow structure on the other hand in each configuration. The results indicated that reduction of mass flow rate could be associated with rotor tip spillage and trailing edge backflow, leading to the occurrence of the stall phenomena and flow blockage in the rotor tip region. However, using plasma actuators led to the energized tip region flow structure and improved aerodynamic performance by reducing the size of the tip leakage vortex and flow blockage. Specifically, among proposed configurations, the forcing direction at a yaw angle of −30° improved the compressor stall margin by about 8%. This is mainly due to the higher plasma jet velocity in the relative frame of reference versus to other configurations resulting in higher injected momentum to the tip leakage flow. The results propose counter-flow induced forcing direction as a favorable configuration for stall margin improvement.

Flow Characteristics of a Mixed Compression Hypersonic Intake

The flow field in a two-dimensional hypersonic mixed-compression inlet in a freestream Mach numbers of M∞ =2.0, 3.0, and 5.0 are numerically solved to understand the effect of throat area variation. The exit area ratio variation is simulated by placing a plug insert at different axial locations at the exit of the model. The flow field is achieved computationally by solving the Reynolds Averaged Navier-Stokes equations in a finite volume framework. For each flow condition, the variation in shock structure is analyzed and the variation of the oblique shock wave angle with the mass flow rate is calculated theoretically and compared with the present CFD analysis. The variation in oblique shock angle is calculated in terms of the mass flow rate by considering the capture area and spillage flow through the inlet. The theoretical results suggest that the method can predict the inlet operating conditions at different freestream Mach numbers and area ratios. This method can quantify the reduction in mass flow rate due to the throttling effect by analyzing the flow field shock pattern. The effects of various important performance parameters such as free stream Mach number, total pressure recovery, and mass flow ratio were then numerically investigated. As the Mach number is increased, the total pressure recovery is reduced, but the maximum value of the mass flow rate is increased. The analysis is also focused on the effect of throat area variation on performance parameters at each Mach number. The characteristic curve of the inlet is then obtained for each free stream Mach number.

CFD Topology and Shape Optimization of Twin Ports in Integrated Exhaust Manifolds

<div class="section abstract"><div class="htmlview paragraph">The optimization of the exhaust port shape for best mass flow is an excellent opportunity to improve fuel economy, emissions, and knock sensitivity of internal combustion engines (ICE). This is valid for many different types of combustion systems including gasoline, alcohols, alternative fuels such as compressed natural gas (CNG) or hydrogen, and e-fuels. Nowadays, so-called cylinder-head integrated exhaust manifolds (IEM) guide the exhaust gas from the combustion chamber to the turbocharger. This specific design requires lots of strong bends and turnings of the exhaust ports in very narrow space, since they need to be guided through a labyrinth of bolts, water cores, and oil passages. In fact, this challenges the avoidance of increased pressure drops, reduced mass flow rates, and deterioration of port flow efficiencies. The optimization of the individual port by computational fluid dynamics (CFD) is a proper means to minimize or even eliminate these drawbacks. Meanwhile, there are several powerful optimization methods for three-dimensional flows on the market. In this paper, a combined strategy of CFD topology and shape optimization is presented. This method has been applied to several Ford four-valve engine designs with either twin (Siamese) exhaust ports as well as single ports within two separate IEMs. CFD optimizations have been done for various valve lifts resulting in improved mass flow rates by up to 14 % and an improved mass flow balance between the twin exhaust ports. New flow cross-sections such as L-, F-, and T-shapes have been identified. At the end, an initial design of flow-optimized ports has been generated including body-fitted water jacket surfaces. This allows the designer to already start with an optimized exhaust port design. The new workflow is highly efficient, reduces development time, improves result quality, and may reduce the number of expensive prototypes as well as time-consuming test-rig measurements.</div></div>

High-temperature ex-vessel corium spreading. Part 2: scaling principles for gravity-viscous spreading with slip at the melt–substrate interface

ABSTRACT Promoting the spreading of molten corium represents a key strategy in the dissipation of decay heat and in the maintainence of containment integrity in the aftermath of a severe nuclear accident. Precise repeatability is difficult to achieve during high-temperature melt spreading experiments, and so scaling factors are necessary to correct for differences in flow rate, viscosity, and density between comparative experiments. A gravity-viscous momentum balance derived for spreading in the two-dimensional spreading geometry employed during recent kg-scale VE-U9 experiments on ceramic and sacrificial concrete substrates establishes that no-slip spreading length scales with the square root of the mass flow rate. Scaling for the reduced mass flow rate and enhanced viscosity implied that the melt spread 37% further on the sacrificial concrete than on the inert ceramic substrate. The possibility of a lubricating film of molten concrete and ablation gases reducing friction at the lower boundary is investigated through the imposition of a slip velocity proportional to the shear at the melt–substrate interface. Simulations over a range of Navier slip lengths implied that spreading length scales with the ratio of slip length to the melt thickness and that spreading length can be augmented by as much as 68% in the case of a virtually frictionless interface.

Numerical investigation of partial admission losses in radial inflow turbines

Radial inflow turbines are taken as potential power conversion units for many power cycles where full admission is employed. The partial admission turbine is usually selected for small-scale power output due to the reduced mass flow rate and machining constraints, resulting in substantial low efficiency. The flow characteristics in different partial admission ratios are still unknown. The suitability of existing correlations for partial admission losses is also questionable since the partial admission loss model is usually established upon experimental results of axial turbines. In this paper, the three-dimensional computational fluid dynamics method is utilized to investigate flow characteristics within partial admission radial inflow turbines. The partial admission ratio varies from 0.05 to 0.9. The numerical loss break-down is then performed and compared against existing empirical correlations in literature, where the partial admission ratio from 0.158 to 0.526 is of interest. The suitable partial admission loss model (Stuter & Traupel windage loss model and Stenning expansion loss model) is finally selected and successfully employed to design partial admission radial inflow turbines preliminarily. The relative error of 3% is attained by comparing mean-line and numerical results. This paper provides insight into the partial admission loss mechanism within radial inflow turbines.