Experimental investigation and correlation of two-phase frictional pressure drop of R410A–oil mixture flow boiling in a 5 mm microfin tube

This study presents experimental two-phase frictional data for R410A-oil mixture flow boiling in an internal spiral grooved microfin tube with outside diameter of 5 mm. Experimental parameters include the evaporation temperature of 5 °C, the mass flux from 200 to 400 kg m^?2 s^?1, the heat flux from 7.46 to 14.92 kW m^?2, the inlet vapor quality from 0.1 to 0.8, and nominal oil concentration from 0 to 5%. The test results show that the frictional pressure drop of R410A initially increases with vapor quality and then decreases, presenting a local maximum in the vapor quality range between 0.7 and 0.8; the frictional pressure drop of R410A–oil mixture increases with the mass flux, the presence of oil enhances two-phase frictional pressure drop, and the effect of oil on frictional pressure drop is more evident at higher vapor qualities where the local oil concentrations are higher. The enhanced factor is always larger than unity and increases with nominal oil concentration at a given vapor quality. The range of the enhanced factor is about 1.0–2.2 at present test conditions. A new correlation to predict the local frictional pressure drop of R410A-oil mixture flow boiling inside the internal spiral grooved microfin tube is developed based on local properties of refrigerant–oil mixture, and the measured local frictional pressure drop is well correlated with the empirical equation proposed by the authors.     

Lubricity evaluation of oil–refrigerant mixtures with R134a and R290

The article presents an assessment method of lubricity properties of oils for refrigeration compressors in a mixture with a refrigerant. The assessment has been based on sample wear volume in the block-on-ring node under the conditions similar to the operation of the compressor following an extensive standstill.The authors assessed the lubricity properties of the following mixtures POE/R134a and MO/R290 (three different oils for each group).In all the analyzed cases it was found that the sample wear after the tests in the oil–refrigerant mixture is significantly (2–32 times) higher than for the oil itself. The test results also showed significant differences in the lubricity properties of oils, which are substitutes in operating conditions. Therefore, the only valid method of assessing lubricity properties of oils for refrigerating compressors are studies on the mixtures of these oils with a refrigerant in the conditions similar to the real operation.     

Experimental investigation on TiO2 nanoparticle migration from refrigerant–oil mixture to lubricating oil during refrigerant dryout

The application of nanorefrigerant–oil mixture in refrigeration system requires continuous circulation of nanoparticles; however, only a small part of nanoparticles circulate by migration from the mixture to vapor within refrigerant dryout process. This study points out a more important nanoparticle circulation way by migration from bulk refrigerant–oil mixture to oil excess layer, and quantitatively evaluate the mixture-to-oil migration ratio affected by oil mass fraction, nanoparticle mass fraction and heat flux. The nanorefrigerant–oil mixture is TiO₂/R141b/NM56; experimental conditions cover oil mass fraction of 5%–20%, nanoparticle mass fraction of 0.2%–1.0%, and heat flux of 10–100 kW m⁻²; the mixture-to-oil migration ratio is measured by absorbance method. The results show that mixture-to-oil migration ratio ranges within 0.388–0.969, and increases averagely by 51.8%, 28.3% and 8.0% with increasing oil mass fraction, reducing nanoparticle mass fraction and lowering heat flux over the whole range of present conditions, respectively.     

Detailed experimental investigations on frictional pressure drop of R134a during flow boiling in 5 mm diameter channel: The influence of acceleration pressure drop component

This article presents detailed two-phase diabatic pressure drop data for refrigerant R134a at a saturation pressure of 5.5 bar corresponding to the saturation temperature of 19.4 °C. Study cases have been set for a mass flux varying from 100 to 500 kg m⁻² s⁻¹.The obtained data are used as a validation of the void fraction literature models, a set of graphs shows comparisons, for a representative set of experimental conditions, of the two-phase frictional pressure gradients for the adiabatic and diabatic flow.Verification of the acceleration pressure drop predictions for two-phase adiabatic flow showed that all correlations predict that over 60% of experimental data fit in the range of ±30%. The model proposed in this article predicts 63% of presented data within 10% error, and 96% of the data are predicted within 30% error.     

Pressure drop of slush nitrogen flow in converging–diverging pipes and corrugated pipes

Cryogenic slush fluids such as slush hydrogen and slush nitrogen are solid–liquid, two-phase fluids. As a functional thermal fluid, there are high expectations for use of slush fluids in various applications such as fuels for spacecraft engines, clean-energy fuels to improve the efficiency of transportation and storage, and as refrigerants for high-temperature superconducting equipment. Experimental flow tests were performed using slush nitrogen to elucidate pressure-drop characteristics of converging–diverging (C–D) pipes and corrugated pipes. In experimental results regarding pressure drop in two different types of C–D Pipes, i.e., a long-throated pipe and a short-throated pipe, each having an inner diameter of 15 mm, pressure drop for slush nitrogen in the long-throated pipe at a flow velocity of over 1.3 m/s increased by a maximum of 50–60% as compared to that for liquid nitrogen, while the increase was about 4 times as compared to slush nitrogen in the short-throated pipe. At a flow velocity of over 1.5 m/s in the short-throated pipe, pressure drop reduction became apparent, and it was confirmed that the decrease in pressure drop compared to liquid nitrogen was a maximum of 40–50%. In the case of two different types of corrugated pipes with an inner diameter of either 12 mm or 15 mm, a pressure-drop reduction was confirmed at a flow velocity of over 2 m/s, and reached a maximum value of 37% at 30 wt.% compared to liquid nitrogen. The greater the solid fractions, the smaller the pipe friction factor became, and the pipe friction factor at the same solid fraction showed a constant value regardless of the Reynolds number. From the observation of the solid particles’ behavior using a high-speed video camera and the PIV method, the pressure-drop reduction mechanisms for both C–D and corrugated pipes were demonstrated.     

Construction of algorithm for calculation of the flow rate of a gas–liquid mixture in a horizontal pipeline for the microprocessor of an information measurement system

Features of an algorithm for calculation of the flow rate of the liquid phase of a gas–liquid mixture with the use of a variable pressure-drop flow meter with constricting devices are considered. Corresponding dependences for use in calculating the concentration of liquid in a mixture and a correction factor based on the readings of the flow meter for use in determining the flow rate of a single-phase flow are obtained.     

Structural characteristics of a gas–liquid flow in a microchannel with a T-shaped mixer

The results of experimental studies of the structural characteristics of a nitrogen–water mixture flow in a horizontal microchannel provided with a T-shaped mixer are presented. The experiments are performed in a channel with a rectangular cross section of 250 × 315 μm under the conditions of a dominating influence of capillary forces. Structural characteristics of the flow are determined using the two-beam laser scanning and high-speed video capture at a distance of 500 calibers from the inlet in a wide range of reduced gas- and liquid-flow rates. A new method for the identification of flow regimes is proposed based on the statistical treatment of the laser-scanning data, and a map of flow patterns is constructed.     

Microstructural influence on small fatigue cracks in a ferritic–martensitic steel

Microstructure effects on fatigue crack initiation and propagation in ferritic–martensitic dual phase steel were investigated. Slip bands were formed in ferrite grains after several thousand cycles with ensuing crack initiation due to dislocation pile-up. Subsurface observations using a focused ion beam (FIB) and crystallographic analyses using electron backscatter diffraction (EBSD) measurements showed that crack initiation occurred as a result of the activation of a slip system having a high Schmid factor. Surface crack nucleation occurred quite frequently at ferrite/martensite and ferrite/ferrite boundaries, with crack propagation in the ferrite grains. This initiation mode can be attributed to the mismatch stresses at ferrite/martensite phase boundaries and at high angle grain boundaries.     

Visual experimental research on the effect of nozzle orifice structure on R124–DMAC absorption process in a vertical bubble tube

A visual experimental platform for R124–DMAC bubble absorption in a vertical tube absorber was designed and built for this research. The bubble behaviors, flow pattern characteristics and distributions are observed and the bubble absorption heights (BAHs) were measured when the two kinds of different structure nozzles (single-orifice or multi-orifice nozzle) were applied in the absorber. The results showed that the BAH will heighten with increases of vapor flow rate and nozzle flow area. Based on visual experimental observations, the BAH or bubble absorption performance was significantly affected by the velocity of vapor from the nozzle rather than by the nozzle structure. The proportion of slug flow in BAH or the BAH can be decreased by using a multi-orifice nozzle in the absorber under the same flow area condition. However, the flow resistance of the vapor through the nozzle will increase, which has a negative action on the performance of absorption refrigeration systems. So, using multi-orifice nozzle does not improve the absorption performance of the bubble absorber under the same nozzle flow resistance condition.     

Value enhancement in a dynamic environment—a constraint management expert system for the oil refinery industry

This paper analyses a case study of a dynamic expert system which was developed according to the theory of constraints (TOC) approach, and implemented at the Ashdod refinery of Oil Refineries Ltd in Israel, as part of an overall improvement process based on the focused management philosophy. The unique feature of the system is its ability to cope with dynamic bottlenecks typical of the continuous process industry, as well as frequent shifts from an external market constraint to internal capacity constraints. The paper examines the development and implementation stages, describes the expert system along with the new process control, and evaluates its impact. The system creates a dynamic, effective and immediate link between the production planning and the operation control, which enables the oil refinery to maximize its profits. During the first two years of its use, the system generated over $3 million of estimated benefits. Finally, we suggest practical implications to assist organizations in developing and utilizing similar applications, emphasizing knowledge gathering and maintenances, which are the major challenges facing expert systems projects.     

Investigation of the correlation between thermal properties and hardenability of Jominy bars quenched with air–water mixture for AISI 1050 steel

In this study, the hardenability of AISI 1050 steel has been investigated in different cooling media using Jominy test. The temperature values were recorded using the thermocouples that were placed on sample. The relations between the cooling media and the cooling curves, heat flux, hardenability and heat convection coefficient were shown in graphics. The correlation between thermal properties and hardenability was established. When Jominy water pressure decreased, hardenability decreased in Jominy bar. But hardenability of steel quenched by air–water mixture cooling media was observed that increasing surprisingly. As a result of air–water mixture quenching, heat transfer accelerated and the hardenability increased in the Jominy bar.     

Implementation of design of experiments approach for the micronization of a drug with a high brittle–ductile transition particle diameter

Objective: To optimize air-jet milling conditions of ibuprofen (IBU) using design of experiment (DoE) method, and to test the generalizability of the optimized conditions for the processing of another non-steroidal anti-inflammatory drug (NSAID).

Methods: Bulk IBU was micronized using an Aljet mill according to a circumscribed central composite (CCC) design with grinding and pushing nozzle pressures (GrindP, PushP) varying from 20 to 110?psi. Output variables included yield and particle diameters at the 50th and 90th percentile (D₅₀, D₉₀). Following data analysis, the optimized conditions were identified and tested to produce IBU particles with a minimum size and an acceptable yield. Finally, indomethacin (IND) was milled using the optimized conditions as well as the control.

Results: CCC design included eight successful runs for milling IBU from the ten total runs due to powder “blowback” from the feed hopper. DoE analysis allowed the optimization of the GrindP and PushP at 75 and 65?psi. In subsequent validation experiments using the optimized conditions, the experimental D₅₀ and D₉₀ values (1.9 and 3.6?μm) corresponded closely with the DoE modeling predicted values. Additionally, the optimized conditions were superior over the control conditions for the micronization of IND where smaller D₅₀ and D₉₀ values (1.2 and 2.7?μm vs. 1.8 and 4.4?μm) were produced.

Conclusion: The optimization of a single-step air-jet milling of IBU using the DoE approach elucidated the optimal milling conditions, which were used to micronize IND using the optimized milling conditions.     

Simulation of material flow in friction stir processing of a cast Al–Si alloy

The objective of the current paper is using DEFORM-3D software to develop a 3-D Lagrangian incremental finite element method (FEM) simulation of friction stir processing (FSP). The developed simulation allows prediction of the defect types, temperature distribution, effective plastic strain, and especially material flow in the weld zone. Three-dimensional results of the material flow patterns in the center, advancing and retreating sides were extracted using the point tracking. The results reveal that the main part of the material flow occurs near the top surface and at the advancing side (AS). Material near the top surface was stretched to the advancing side resulting in a non-symmetrical shape of the stir zone (SZ). Furthermore, macrostructure and temperature rise were experimentally acquired to evaluate the accuracy of the developed simulation. The comparison shows that the stir zone shape, defect types, powder agglomeration, and temperature rise, which were predicted by simulation, are in good agreement with the corresponding experimental results.     

Experimental analysis on particle fluctuation velocity in a horizontal air–solid two-phase pipe flow having a dune model

To further elucidate the mechanism of energy-conserving conveying in horizontal pneumatic conveying with the dune model, the high-speed particle image velocimetry is applied to measure particle fluctuation velocity near the minimum conveying velocity of the conventional pneumatic conveying. This study focuses on the effect of mounting dune models on the horizontal pneumatic conveying in terms of power spectrum, autocorrelation coefficients, two-point correlation coefficients, fluctuation intensity of particle velocity, skewness factor, and probability density function. It is found that the power spectrum peaks with the dune model are larger than those of the nondune system, suggesting the acceleration and suspending efficiency of the dune model, especially dune models mounted at the bottom of the pipe. Meanwhile, the profiles of particle fluctuation velocity intensity indicate that the large particle fluctuating energy is generated due to mounting the dune model so that the particles are more easily accelerated and suspended. This is one of the important reasons why the mounted dune model results in a low pressure drop and low minimum conveying velocity. Based on the distribution of skewness factor and probability density function, it is found that the particle fluctuation velocities of all cases follow the Gaussian distribution in the lower and middle parts of the pipe. The particle fluctuation velocities in the case of the dune models mounted at the bottom of the pipe obey the Gaussian-type fluctuation more.     

Prediction of flow stress in a wide temperature range involving phase transformation for as-cast Ti–6Al–2Zr–1Mo–1V alloy by artificial neural network

The isothermal compressions of as-cast Ti–6Al–2Zr–1Mo–1V titanium alloy in a wide temperature range of 1073–1323 K and strain rate range of 0.01–10 s⁻¹ with a reduction of 60% were conducted on a Gleeble-1500 thermo-mechanical simulator. The flow stress shows a complex non-linear intrinsic relationship with strain, strain rate and temperature, meanwhile the strain-softening behavior articulates dynamic recrystallization mechanism in α phase, dynamic recovery mechanism in β phase and their comprehensive function during phase transformation (α + β). Based on the experimental data, an artificial neural network (ANN) was trained with standard back-propagation learning algorithm to generalize the complex deformation behavior characteristics. In the present ANN model, strain and temperature were taken as inputs, and flow stress as output. A comparative study has been made on ANN model and improved Arrhenius-type constitutive model, and their predictability has been evaluated in terms of correlation coefficient (R) and average absolute relative error (ARRE). During α, α + β and β phase regime, R-value and ARRE-value for the improved Arrhenius-type model are 0.9824% and 6.02%, 0.9644% and 21.02%, and 0.9627% and 12.38%, respectively, while the R-value and ARRE-value for the ANN model are 0.9992% and 0.91%, 0.9996% and 1.47%, and 0.9975% and 2.17%, respectively. The predicted strain–stress curves outside of experimental conditions articulate the similar intrinsic relationships with experimental strain–stress curves. The results show that the feed-forward back-propagation ANN model can accurately tracks the experimental data in a wide temperature range and strain rate range associated with interconnecting metallurgical phenomena, and in further it has a good capacity to model complex hot deformation behavior of titanium alloy outside of experimental conditions.