Small Mass Flow Rate Research Articles

Experimental study of CO2 jet field and CO2-MQL-assisted turning of Ti-6Al-4V based on mass flow rate and pressure

The effectiveness of jet cooling is significantly influenced by both mass flow rate and pressure, which are interrelated and exhibit a coupled relationship. This study examined the effects of mass flow rate and pressure from the perspectives of thermodynamic theory, jet field temperature, micromorphology, and the performance of CO2-MQL-assisted turning of Ti-6Al-4V alloys. Comparative experiments demonstrated that a small mass flow rate of CO2 (1.00 g/s) can achieve cooling and lubrication effects comparable to those of a larger mass flow rate (1.83 g/s) when applied at pressures of 7.38 and 6.00 MPa, respectively. For varying pressures, the maximum differences in improving the CO2-MQL on turning force, turning zone temperature, and surface roughness were 2.36%, 26.31%, and 39.63%, respectively. Conversely, the maximum differences for varying mass flow rates were 1.32%, 17.53%, and 19.66%. The results indicate that pressure has a more significant impact and that optimizing the combination of pressure and mass flow rate is substantial for cooling and lubrication. This study offers a reference for reducing CO2 consumption in CO2-MQL applications, thereby enhancing the alignment of CO2-MQL with sustainable manufacturing practices.

Investigations on cooling heat transfer of CO2-based mixtures in a novel airfoil fin mini-channel at supercritical pressure

Thermal-hydraulic characteristics of three supercritical CO2-based mixtures (CO2/H2S, CO2/Xe and CO2/propane) in an airfoil fin (AFF) mini-channel adopted in the printed circuit heat exchanger (PCHE) under cooling conditions are comprehensively investigated through numerical simulations. The results show that the CO2/H2S mixture, which has higher critical temperature and larger critical pressure than the pure CO2, exhibits the greatest heat transfer performance among three mixtures. This advantage is particularly pronounced at relatively large Reynolds number, with small mass fraction of the H2S and under near-critical conditions. The overall friction loss of mixtures with the additive mass fraction smaller than 0.3 is comparable to that of the pure CO2. The heat transfer coefficient of the mixtures presents fluctuations during the cooling processes, and this goes against the stable and safe operation of the PCHEs. These fluctuations could be mitigated at relatively small mass flow rate and with small mass fraction of the additive. Three widely-recognized buoyancy criteria are employed to predict the onset of the buoyancy effects in the AFF channel, and the superior heat transfer of the CO2/H2S mixture could be attributed to the fiercer buoyancy effects. Considering the buoyancy effects, modified correlations for the flow and heat transfer of pure CO2 and the CO2-based mixtures in the novel mini-channel are proposed. The maximum deviations of the modified Nusselt number and fanning friction factor correlations are ± 25 % and ± 20 %, respectively.

Characterization of loss, temperature, and stress on partial admission axial impulse turbines with liquid jet impingement cooling

The turbines for underwater applications can use abundant water as the cooling medium. However, the use of liquid water is associated with the multi-phase and multi-physics problems and presents additional losses. This paper proposes a numerical coupling method and corresponding loss breakdown approach to analyze the performance of this particular turbine cooling problem at different water mass flow rates. The results show that the cooling water induces additional loss, while the influence of the resulted structural deformation on turbine efficiency is comparatively small. Through numerical loss breakdown, it is found that the exit kinetic energy loss is significantly decreased, but other losses are increased correspondingly due to the cooling water. By examining the turbine stress and temperature distribution, the small water mass flow rate of 0.02 kg/s is sufficient to avoid damage to the disc, however, additional cooling is necessary to minimize the plastic region at the turbine blades. The suitable loss model for the turbine with cooling water is established and a relative difference less than 3 % is attained by comparing mean-line and numerical results. This work provides new insight into the analysis method and characteristics of the partial admission axial turbine with cooling water.

Performance analysis of a gas turbine engine with intercooling and regeneration process - Part 1

Abstract Auxiliary systems, such as regeneration and intercooling, have been integrated with the primary gas generator to improve power production and fuel economy in modern gas turbine power plants. Implementing these techniques in turbine engines is challenging due to size, weight, and complex flow patterns. A solution is to use a turboprop engine with a smaller mass flow rate and simpler gas paths. The current study involves the numerical analysis of performance parameters namely, specific power (SP), thermal efficiency (η), and enthalpy based specific fuel consumption (EBSFC) of a turboprop engine using thermodynamic parameters namely, pressure ratio (PR), nozzle pressure ratio (NPR), turbine inlet temperature (TIT), regeneration efficiency (R), and intercooling efficiency (E). The results prove that the introduction of regeneration and intercooling showed significant improvement in the power developed, and reduced fuel consumption.

CFD and Taguchi based optimization of air driven single stage partial admission axial turbine blade profiles

Single-stage axial flow turbines are typically used in underground mining machines and underwater vehicles due to their safety and small size. However, the high-pressure ratio and small mass flow rates force the flow inside the turbine to be supersonic. The blade design of such turbines with high-flow velocity leads to high losses and low turbine efficiencies at conventional design values. In this paper, the 1D design of the turbine is carried out using the meanline design method. The results of the design algorithm are compared with both experimental, CFD (Computational Fluid Dynamics), and a well-known commercial software AxSTREAM. After validating the design, Taguchi method is used to analyze 6 different parameters (Blade Shape, Nozzle Shape, Cord Length, Solidity Ratio, Nozzle Angle and Blade Thickness) affecting the turbine performance and the optimum blade profile is compared with the conventional blade design. The optimum design isentropic efficiency (68.267%) outperformed the conventional design turbine isentropic efficiency (61.759%) by about 11%. This paper provides a different insight into the conventional turbine design method.

Numerical investigation of natural circulation loop with supercritical CO2 on the thermal control system of micro spacecrafts

Aiming at the heat dissipation problem under the strict constraints of mass, volume, and power consumption in micro spacecrafts, the feasibility of applying a natural circulation loop (NCL) to the thermal control system is performed for the CubeSats (Cube satellites) of orbiting operations or the micro-rovers of extraterrestrial explorations. A 3-dimensional NCL model under variable gravity conditions corresponding the environment of aerospace is established, and the supercritical CO2 as the coolant. The heat transfer and thermal performance of NCL under gravity range of 10−6 g to 10 g are analyzed numerically, including the Earth orbit, the surface of the Moon and the Mars etc. The calculation results present that the gravity has a great influence on the flow circulation characteristics and thermal performance of the NCL. The applicability of employing NCL on the thermal control system of micro spacecrafts is validated with the gravity no less than 0.05 g. It is worth noting that, by designing the range of temperature from inlet to outlet of the heated tube covering the large specific heat region, the superior thermal performance can be obtained on account of the strong heat-carrying capacity of supercritical fluid, even under the low gravity with a small mass flow rate. Finally, a flow correlation is proposed considering the effect of gravity, flow regime, buoyancy force, and geometric factors, which is suitable on the NCL in the thermal control system of micro spacecrafts, and the R2 is 99.77%.

Performance evaluation of a micro partial admission impulse axial turbine in a combined ammonia-water cooling and electricity absorption cycle

The integration of an expander in an absorption machine allows it to produce cooling and electricity simultaneously. This technology holds great promise for its ability to harness low-temperature heat sources more efficiently than production with separate cycles. The integration of a turbine is currently being studied in an experimental ammonia-water absorption chiller at CEA INES. Given the very small mass flow rate and enthalpy drop, a partial admission impulse axial turbine has been selected for the application. Due to lack of experimental data, a 3D model of the impulse turbine was generated and its functioning studied with CFD simulations using pure ammonia. A compressible real gas 1D model of the turbine was later developed in EES® for the ammonia-water mixture and compared to CFD simulation, adjusting loss term parameters to match CFD results, thus achieving an average discrepancy below 7% in the considered range of operating conditions (inlet pressure 14-10 bar, outlet pressure 5 bar, inlet temperature 120 °C and rotational speed of 10–100 thousand RPM). The tuned 1D expander model was then integrated in a previously developed 0D model of the absorption cycle to demonstrate its robustness and potential to be used in the study of complex combined cycles. An overall energy efficiency is introduced and used to map the performance of the cycle for changing operating conditions. Results show the potential of the combined cycle to produce both power and cooling even at small scale, highlighting at the same time, the constraints imposed by this type of expander on the combined cycle.

Numerical Study on Characteristics of Convection and Temperature Evolution in Microchannel of Thermal Flowmeter.

During practical usage, thermal flowmeters have a limited range of applications. The present work investigates the factors influencing thermal flowmeter measurements and observes the effects of buoyancy convection and forced convection on the flow rate measurement sensitivity. The results show that the gravity level, inclination angle, channel height, mass flow rate, and heating power affect the flow rate measurements by influencing the flow pattern and the temperature distribution. Gravity determines the generation of convective cells, while the inclination angle affects the location of the convective cells. Channel height affects the flow pattern and temperature distribution. Higher sensitivity can be achieved with smaller mass flow rates or higher heating power. According to the combined influence of the aforementioned parameters, the present work investigates the flow transition based on the Reynolds number and the Grashof number. When the Reynolds number is below the critical value corresponding to the Grashof number, convective cells emerge and affect the accuracy of flowmeter measurements. The research on influencing factors and flow transition presented in this paper has potential implications for the design and manufacture of thermal flowmeters under different working conditions.

Study on flow and heat transfer characteristics of supercritical CO2 inside horizontal tube under ocean rolling condition

The flow and heat transfer characteristics of supercritical CO2 in a horizontal tube are studied numerically under the condition of ocean rolling. It is found that the rolling motion is beneficial to alleviate the deterioration of heat transfer at the top of the tube. However, the heat transfer deterioration is performed periodically with the rolling motion, which can cause periodic fluctuations in temperature and thermal stress of tube wall. This will affect the service-life. At a relatively small mass flow rate or large heat flux, the effect of rolling motion on the heat transfer performance increases since the density difference and buoyancy is relatively large. With the increase of inlet temperature and the decrease of buoyancy effect, the influence of rocking motion on heat transfer gradually decreases. The influence of rolling motion on the heat transfer for the floating nuclear power plant should be taken into consideration in the design.

Toward the Utilization of 3D Blading in the Cantilevered Stator from Highly Loaded Compressors

Three-dimensional blading is an efficient technique in compressor aerodynamic design, and its function mechanism in the cantilevered stator needs to be addressed. This paper focuses on the sweep and dihedral in the cantilevered stator and seeks to expose their effects through detailed flow field analysis. Results show that the forward sweep could alleviate the corner flow separation by preventing the accumulation of the secondary flow toward the corner region, resulting in stronger flow separation at the blade trailing edge; in summary, forward sweep with appropriate parameters could increase static pressure rise by 14.3%. The positive dihedral will carry the endwall flow to the upper-span sections, thereby reducing blade corner separation; hence, as much as 23.5% improvement in static pressure rise could be obtained with the appropriate dihedral. Moreover, the combination of a relatively large sweep height and a moderate sweep angle with a low dihedral height and a moderate sweep angle provides optimum aerodynamic performance; the static pressure rise coefficient sees an increment of 25.5% at the near stall point. An experiment is then performed to further validate the theory, which shows a 2% improvement in efficiency of 3D blading at small mass flow rates. However, the secondary leakage should be given attention at high mass flow coefficients, while the corner separation needs further elimination at small mass flow rates.

Analysis of spray characteristics of a jet-film injection element based on Voronoi tessellation

The present paper presents a computational study based on a validated Volume-of-Fluid method on the effects of film thickness and film width on spray characteristics for the simplified jet-film injection element with varying mass flow rate conditions. First, the spray characteristics of a typical jet-film collision were analyzed in terms of the spatial distribution of Sauter Mean Diameter and Voronoi tessellation. Both the Voronoi diagram and the Sauter Mean Diameter contour are useful to evaluate the spray characteristics because they show two different aspects of the sprays. Second, the jet-film spray characteristics were analyzed by decreasing either film thickness or film width to change the mass flow rate. The results show that decreasing film width results in approximately insensitive spray angle and improved uniformity of droplet distribution for different throttleable levels. The present computational results verified our design concept that adopting traditional jet-film injection at a large mass flow rate and modified jet-jet injection at a small mass flow rate to maintain good spray performance during the entire throttleable levels.

Effects of Duct Height and Fire Location on Fire Phenomena of Enclosure with Two Horizontal Vents Installed on Ceiling

The effects of duct height (DH) and fire location (FL) in an enclosure on the mass flow rate and flow pattern of horizontal vent (HV) flow and temperature distribution in the enclosure were investigated through numerical simulations under the condition that two HVs were installed on the ceiling of the enclosure. To evaluate the effect of DH, DHs of HV1 were set to 0.19 m (HV1_DH0.19) and 0.05 m (HV1_DH0.05) under the condition that DH of HV2 was 0.05 m (HV2_DH0.05). The effect of FL was evaluated in three cases where the fire sources were located in the center of the floor (F LC), below HV1 (F L1), and below HV2 (F L2). With respect to the DH effect, the total mass flow rate of the vent flow was slightly higher and temperature was slightly lower in the case of HV1_DH0.19 than that in the case of HV1_DH0.05. However, considering the error bars, the effect of DH in this numerical simulation condition was considered to be insignificant. Furthermore, bidirectional flow patterns appeared in HV1 and HV2 in both DH conditions. Meanwhile, with respect to the FL effect, a bidirectional flow dominated by the mass flow rate of outflow occurred in the HV where the fire source was located, and a unidirectional inflow dominated by the mass flow rate of inflow occurred in the HV where the fire source was not located. The total mass flow rates of FL1 and FL2 conditions were similar, which were higher than those of FLC condition. The temperature was higher in FLC than those in FL1 and FL2. This was due to the small mass flow rate through the HV in the FLC. Meanwhile, an increasing trend of the temperature with the rising measurement height from the floor was observed at most of the temperature measurement points. However, when the fire source was located below HV1 and HV2, as the height from the floor increased, the temperature decreased and the overall temperature was low at the temperature measurement points below the vent where the fire source was not located. This trend was attributed to the occurrence of a strong unidirectional inflow wherein a large volume of low-temperature air flowed into the enclosure from the HV where the fire source was not located.

Numerical study on a low mass flow rate cold compressor for 2 K helium cryogenic system

A cold compressor is a key equipment in a superfluid helium refrigeration system. It helps to make the 2 K helium refrigerator more compact, increase the cycle efficiency, and reduce the risk of air leakage. However, cold compressors have been applied only in relatively large 2 K helium refrigerators with mass flow rates of more than 25 g/s. To verify the feasibility of using a low mass flow rate cold compressor in the testing system of the China Initiative Accelerator Driven System (CiADS), the thermodynamic model of the 2 K cryogenic cycle was built. Then, a cold compressor with a low mas flow rate was designed, and its performance was numerically studied based on the one-dimensional self-written code and a three-dimensional computational fluid dynamics model, respectively. The total pressure ratio and isentropic efficiency of the cold compressor were 2.44 and 64.4 % at the design point of 3.5 g/s@36000 rpm, respectively. The small mass flow rate cold compressor was remarkably beneficial for the 2 K cryogenic systemas the exergy efficiency increased from 0.16 to 0.23 and the specific power consumption decreased from 604 W/W to 327 W/W. The research has preliminarily verified the practicality of using a small flow rate cold compressor in superfluid helium systems.

Behaviors of the long penetration mode with a hot counterflowing jet

When an aircraft flies at hypersonic speeds, a large aerodynamic drag and a significant amount of aerodynamic heat are generated around it. As an active flow control technology, counterflowing jets can effectively reduce the drag and heat flux and have therefore attracted broad attentions. However, the oscillation problem that accompanies counterflowing jets remains to be studied further. The present study aims to investigate the oscillation properties of the flow around a hypersonic vehicle with a hot counterflowing jet using a numerical solver with a single-temperature multi-component chemical reaction model. A hypersonic hemispherical-nosed is selected and the solver is developed on the OpenFoam platform. The drag reduction efficiency, the flow field structure, and the flow instability characteristics for different jet temperatures are discussed in detail. It is found that a high-temperature jet can reduce the amplitude of the drag force significantly and even suppress the flow oscillation, and the drag reduction efficiency per unit mass increases with the jet temperature. For the same efficiency, a high-temperature jet has a smaller mass flow rate which may reduce the load of flight and lead to savings in space and cost. Therefore, within the allowable range of heat flux, increasing the jet temperature might be a more effective method for reducing drag and stabilizing the flow field than increasing the jet pressure ratio as usually thought. It is hoped that the present results serve to advance the application and the development of hypersonic counterflowing jet technology.

Effect of mass flow rate on bubble size distribution in boiling flow in temperature-controlled annular test section

Subcooled flow boiling experiments were performed in an annular horizontal channel with inner diameter of 12 mm and the gap of 2 mm. The annular channel is designed as a double-pipe heat exchanger, where the inner tube of the channel is heated by a water flow, providing a temperature-controlled boiling surface. The influence of mass flow rate of the working fluid R245fa on flow boiling patterns and heat transfer has been studied. Subcooled flow boiling patterns were recorded with a high-speed camera. The recorded images of the flow patterns were then further processed to determine the bubble size distributions, characterized as distributions of the void (vapour) volume given per bubble size. The observed bubble size distributions followed two distinct distribution functions: the Rayleigh distribution at larger and bimodal distribution at smaller mass flow rates. This indicates the existence of two distinct boiling flow regimes at different mass flow rates. The heat flux was estimated by local temperature measurements with thermocouples positioned along the boiling surface and in the heating water. The heat flux increased moderately with increasing mass flow rate, apparently without disruption at the observed change in the flow regime. On the contrary, the total void volume in the observed part of the test section is declining moderately with increased refrigerant mass flow rate, which, in this mode of operation of the test section, acts as a prevailing mechanism. The experimental setup, methods of experimental analysis and the results are presented and discussed.

Experimental study of H2/air rotating detonation wave propagation characteristics at low injection pressure

H2/air rotating detonation wave (RDW) propagation characteristics were studied under low injection pressure. A small air mass flow rate and wide air injection ring were used to obtain low injection pressure. The formation of RDWs and the influence of different injection pressures on the RDW propagation process were studied and analyzed. The experimental results show that the lower limit of injection pressure for H2/air to form an RDW with stable propagation is 2.21 bar for hydrogen and 2.32 bar for air. At these injection pressures, the longitudinal pulsed detonation (LPD) mode and the single rotating detonation wave (SRDW) mode occur successively in the rotating detonation combustor (RDC), and the RDW velocity is 1491.4 m/s. The reasons for the generation, persistence and transformation of the LPD are analyzed. When the air mass flow rate is 370 g/s, the minimum air injection pressure to produce RDC ignition in a wide equivalence ratio range is 3.0 bar. With an equivalence ratio of 0.57–1.54, the RDW velocity and pressure first increase and then decrease, the maximum RDW velocity and pressure occur with an equivalence ratio of 1.2–1.3. RDW velocity and pressure increase with the air injection pressure rises. Flame characteristics during steady RDW propagation were analyzed using high-speed photography.

Machine-learning flow control with few sensor feedback and measurement noise

A comparative assessment of machine-learning (ML) methods for active flow control is performed. The chosen benchmark problem is the drag reduction of a two-dimensional Kármán vortex street past a circular cylinder at a low Reynolds number (Re = 100). The flow is manipulated with two blowing/suction actuators on the upper and lower side of a cylinder. The feedback employs several velocity sensors. Two probe configurations are evaluated: 5 and 11 velocity probes located at different points around the cylinder and in the wake. The control laws are optimized with Deep Reinforcement Learning (DRL) and Linear Genetic Programming Control (LGPC). By interacting with the unsteady wake, both methods successfully stabilize the vortex alley and effectively reduce drag while using small mass flow rates for the actuation. DRL has shown higher robustness with respect to different initial conditions and to noise contamination of the sensor data; on the other hand, LGPC is able to identify compact and interpretable control laws, which only use a subset of sensors, thus allowing for the reduction of the system complexity with reasonably good results. Our study points at directions of future machine-learning control combining desirable features of different approaches.

Aerodynamic design and experimental validation of high pressure ratio partial admission axial impulse turbines for unmanned underwater vehicles

High pressure ratio partial admission axial impulse turbines are typically employed for underwater vehicles due to small mass flow rate and machining constraints. However, little work has been focused on the generic design methodology for high pressure ratio partial admission axial impulse turbines. The experimental results and empirical correlations are mostly established upon low pressure ratio axial turbines. In this paper, the meanline turbine design method is first documented together with the performance prediction method at off-design points. The numerical loss breakdown method is then described to thoroughly verify empirical correlations. Both the meanline and numerical methods are thoroughly validated against experimental results and the difference among meanline, numerical and experimental results is less than 10%. A case study is then performed and a 13 kW partial admission axial impulse turbine is designed. The suitability of empirical correlations is confirmed by comparing the losses between the meanline and numerical methods, and the difference less than 5% at design and off-design points is attained. This paper provides the insight into the design methodology for high pressure ratio partial admission axial impulse turbines.

Canopy-to-canopy liquid cooling for the thermal management of lithium-ion batteries, a constructal approach

With the growing interest on electric vehicles comes the question of the thermal management of their battery pack. In this work, we propose a thermally efficient solution consisting in inserting between the cells a liquid cooling system based on constructal canopy-to-canopy architectures. In such systems, the cooling fluid is driven from a trunk channel to perpendicular branches that make the tree canopy. An opposite tree collects the liquid in such a way that the two trees match canopy-to-canopy.The configuration of the cooling solution is predicted following the constructal methodology, leading to the choice of the hydraulic diameter ratios. We show that such configurations allow extracting most of the non-uniformly generated heat by the battery cell during the discharging phase, while using a small mass flow rate.

Preliminary Design of an Axial-Flow Turbine for Small-Scale Supercritical Organic Rankine Cycle

A small-scale organic Rankine cycle (ORC) with kW-class power output has a wide application prospect in industrial low-grade energy utilization. Increasing the expansion pressure ratio of small-scale ORC is an effective approach to improve the energy efficiency. However, there is a lack of suitable expander for small-scale ORC that can operate with a high efficiency under the condition of large expansion pressure ratio and small mass flow rate. Aiming at the design of high-efficiency axial-flow turbine in small ORC system, this paper investigates the performance of a kW-class axial-flow turbine and proposes a method for efficiency improvement. First, the preliminary design of an axial-flow turbine is conducted to optimize the geometric parameters and aerodynamic parameters. Then, the effects of tip clearance and trailing edge thickness on turbine performance are analyzed under design and off-design conditions. The results show that the efficiency of the two-stage or three-stage turbine is evidently better than that of the single-stage one. The output power and efficiency of the three-stage turbine are close to that of the two-stage turbine while the speed is lower. Meanwhile, the trailing edge loss and leakage loss can be significantly reduced via reducing the trailing edge thickness and tip clearance, and thus the turbine efficiency can be improved significantly. The estimated efficiency arrives at 0.82, which is 33% higher than that of the conventional turbine. Considering the limitation of turbine speed, three-stage axial-flow turbine is a feasible choice to improve turbine efficiency in a small-scale ORC.