Wet Compression Process Research Articles

Study on the jet breakup-propagation evolution characteristics of wet compression process in a single screw steam compressor

In the wet compression process of a single screw steam compressor (SSSC), the evolution characteristics of the liquid water jet (LWJ) in the chamber directly affect the heat and mass exchange during compressor pressurization, thereby influencing the thermodynamic performance and operational efficiency of the compressor. To elucidate the breakup-propagation evolution process of the LWJ during compressor’s wet compression process, a constructed model for the breakup-propagation evolution process of the LWJ was introduced in this paper. Using this model, the penetration distance, mass differentiation characteristics, surface area, and other evolution characteristics of LWJ under different water injection parameters were investigated. On this basis, the heat transfer between different forms of liquid water such as water film and water droplets and steam within a single working period is analyzed by constructing the water-steam heat transfer equation in the elementary volume. The results demonstrate that the penetration distance of the LWJ is significantly improved in the wet compression process of a SSSC with the increase of the injection velocity (IV). After entering the chamber, the LWJ gradually differentiates into three forms: Eulerian continuous-phase water (ECPW), Lagrangian-phase water droplets (LPWDs), and wall-attached water film (WAWF). The heat exchange effect between LPWDs and steam in the working chamber is 2.83 times that of ECPW and WAWF. With the increase of the IV, the mass proportion of the WAWF in the total injected liquid water decreases from 34.30% to 24.30%, while the mass proportion of the LPWD formed by breakup increases from 0.55% to 2.13%. The total heat exchange area of each form of water increases by 569.54%, and the total heat exchange amount increases by 560.16%.

Optimization of ticagrelor tablet for gastro-retentive drug delivery using full factorial design

Purpose: To identify the optimized region of formulation using quality by design for developing ticagrelor gastro-retentive (GR) tablets. 
 Methods: A 23 + 3 full factorial design of experiments study was used to identify three factors (polyethylene oxide (PEO), compression, and volume of granulating fluid) involved in the wet granulation and compression process of ticagrelor GR tablets. Hardness, friability, content, dosage unit uniformity, and pH 1.2 dissolution rate (at 4, 8, and 12 h) were evaluated as critical quality attributes via analysis of variance using Design Expert software. 
 Results: All seven models were significantly influenced based on analysis of variance results (p < 0.05). Hardness and friability were significantly affected by compression (p < 0.0001). Content uniformity was significantly affected by the interaction between compression and granulating water volume for wet granulation (p < 0.05), and dosage unit uniformity was significantly affected by the volume of granulating fluid for wet granulation (p < 0.05). However, all results were within acceptable ranges. Polyethylene oxide (PEO) (4 h, p < 0.05; 8 h, p < 0.05; 12 h, p < 0.05) and compression (4 h, p < 0.05; 8 h, p < 0.05; 12 h, p < 0.05) had negative effect on pH 1.2 dissolution rate. 
 Conclusion: Design of experiment (DoE) approach has been used to optimize region of PEO, compression, and volume of granulating fluid for formulation development. This outcome is expected to be a basis for further research to develop TCG GR tablets on a large production scale.

Study on pressurization characteristics of single-screw steam compressor with water spray cooling under fluctuating heat source operating conditions

For a water-injected single-screw steam compressor (SSSC), the performance of the compressor is significantly affected by the water spray rate. However, the precise relationship between the water injection parameters and the operating parameters of the heat source under fluctuating heat source operating conditions (FHSOC) has not been elucidated. This paper introduces a constructed thermodynamic analysis model for the wet compression process under FHSOC aiming to explore the impact of fluctuating heat source parameters such as inlet steam temperature (IST) and inlet steam dryness (ISD) on the thermodynamic performance parameters of the compressor. The operational performance of the SSSC is then analyzed and compared under two distinct conditions: optimal water spray rate (OWSR) and fixed water spray rate (FWSR). The results demonstrate that when the IST of the SSSC increases within the range of 375 K–400 K, there is an initial decline followed by an increase in both the leakage rate and volumetric efficiency. Simultaneously, displacement and power consumption decrease, while adiabatic indicated efficiency and OWSR increase. Within this range, an optimal synergy is observed between IST and water spray parameters enabling the compressor to exhibit superior lubrication, sealing, and pressurization performance. On the other hand, when the ISD increases within the range of 0.92–1, the total heat transfer in the compression chamber decreases, and the leakage, OWSR, displacement, power consumption, adiabatic indicated efficiency, and volumetric efficiency all show varying degrees of increase. Regarding the volumetric efficiency corresponding to the OWSR, the impact of ISD on volumetric efficiency surpasses that of IST to a significant degree.

Effect of recycled fibers and shredded intermediates variation on the mechanical properties and energy absorption of fiber‐reinforced composite panels

AbstractThe global composite industry generates large quantities of waste which mostly ends up in landfills due to a lack of established end‐use applications for multiple waste streams. The scrap from end‐of‐life (EoL) includes manufacturing waste such as dry chopped fiber tows, loose fibers, shredded fibers from fabric textile operations, cured/semi‐cured prepregs, and fully cured composite structure waste from aircraft, automobiles, wind blades, boats, and pressure vessels. In this work, different composite waste streams were reduced to shredded intermediates, followed by simple blending, and subjected to wet compression molding to produce composite panels. The panels/plaques were tested for mechanical properties (flexure and impact), fiber‐matrix wet‐out, and property bounds. It was found that wet‐compression molding was a viable and scale‐able approach to produce recycled panels from EoL composites shredded scrap. Furthermore, full‐scale size panels for use in truck bodies and intermodal shipping container flooring were manufactured and their impact resistance was tested using a drop weight impact test. They were tested both for high‐ and low‐velocity load. In the case of high‐velocity load, the average impact load was 14,673 N; the average absorbed energy was 101.6 J; the average elastic energy was 11.7 J and the impact resistance was 1065 J/m. In the case of the low‐velocity drop weight impact test, it was found that the average impact load was 7877.358 N; the average absorbed energy was 9.718 J; the average elastic energy was 9.14 J, and the impact resistance was 184.1 J/m. The shredded composite was shown to be a candidate material for the manufacture of truck bodies and intermodal containers’ flooring panels.Highlights By using shredded intermediates from different composite waste streams, it is possible to manufacture composite panels. Wet–compression process is an appropriate technique for manufacturing recycled fiber composite panels. Regardless of the source of scrap, the mechanical properties of the produced composite panels were improved. The recycling process technology can be transformed to commercial scale to produce full‐size transportation flooring panels. A product pathway is established in consideration of lower cost and improved recyclability.

Microstructural Tuning of Twisted Carbon Nanotube Yarns through the Wet-Compression Process: Implications for Multifunctional Textiles

Microstructural Tuning of Twisted Carbon Nanotube Yarns through the Wet-Compression Process: Implications for Multifunctional Textiles

Thermo-Fluid Analysis on the Efficiency of Wet Compression Process

Wet compression has been well known as a promising technology to effectively increase the power output of the gas turbine engine by introducing fine droplets of water into the compressor stages. This lessens the temperature rise throughout the compression process of gas, thus leading to the reduction in the compressor work. A considerable amount of research on the wet compression process has been performed to date, but the detailed compression process of the two-phase gas media and fine droplets is not well understood yet. In the present study, the thermo-fluid analysis has been done on a simple flow model that has a spherical droplet of water inside a cylinder-piston system. The model is validated by using a quasi-steady D2 – Law of evaporation model. The compression rate is varied by employing the piston movement under various flow conditions such as percentage of overspray, water droplet diameter, relative humidity, and temperature. The results obtained show that for a higher percentage of overspray, smaller droplet diameters and a slower compression rate the efficiency obtained is high. Which results in lesser compressor work. The effects of compression rate, droplet diameter, overspray, and the efficiency of the wet compression have been explained and analyzed in detail.

Mean-line model development for off-design performance prediction of transonic axial compressor of an industrial gas turbine based on computational fluid dynamics database

In this work, a mean-line model with the row-by-row stacking scheme is developed to simulate the off-design operation of a multi-stage transonic axial compressor of an industrial gas turbine. A database of computational fluid dynamics (CFD) simulation results validated with the field data is generated at different rotating speeds and pressure ratios by using CFD simulation tools and available detail geometry of the studied compressor. The compressor characteristic parameters including inlet/exit blockage factor, deviation angle parameter, rotor temperature and pressure coefficients, and the pressure loss of the stator for all stages, plus variable inlet guide vane, are extracted from CFD simulation results. Based on analytical/empirical relations in the literature, a generic formulation for the characteristic parameters is defined as a function of airflow parameters such as inlet Mach number, inlet flow angle, and velocity ratio. Since the accuracy of this type of model depends on the formulated characteristic parameters, and due to the error propagation potential of the sequential stacking solutions, a multi-objective optimization program is developed to specify the coefficients and exponent values of the generic formulations. The functionality of characteristic curves versus airflow parameters for different compressor rows is comprehensively investigated. The comparison between the results of the mean-line model and CFD simulations shows the high accuracy of the model. The developed model can be used in applications such as condition monitoring of in-service gas turbines, studying the effects of rescheduling the variable stator vanes, and investigating the wet compression process.

Formulation development and evaluation of duloxetine extended-release tablets

Duloxetine is an anti-depressant drug which is used in depression. The aim of present investigation was to prepare an ER tablet of duloxetine with similar dissolution profile matching to Effexor ER. An immediate release core tablet of 100mg was prepared and it was compression coated using HPMC matrix system. HPMC of three viscosity grades i.e., K4M, K15M, K100M and different concentrations of 15% polymer, 25% polymer, 35% polymer & 45% polymer were taken. With the above polymers by using wet granulation and direct compression process 11 formulations were prepared. The data obtained from in vitro drug release was used to determine the similarity factor between marketed and optimized product. Out of all F11 formulation (K15M 35% polymer) is optimized and is matching with the marketed product.

Analysis and prediction of gas turbine performance with evaporative cooling processes by developing a stage stacking algorithm

Water injection in stationary gas turbines is effective strategy for power augmentation and gas turbine efficiency improvement, in particular, at high ambient temperatures. In this study, a developed method for simulation of wet compression processes is introduced. This method is followed by the droplet evaporation analysis, aero-thermodynamic stage-stacking model, and a map zooming technique for evaluation the unknown parameters in the generalized performance curves by using grey wolf optimization (GWO) algorithm. The validity of the proposed algorithm is assessed through the comparison of the results with two experimental studies. The operating results are calculated for five different cities and 18 gas turbines organized in three classes. Moreover, a sensitivity analysis on the main input parameters is investigated with the use of variable importance (VI) analysis by constructing and training an artificial neural network. The results show that the variation of the output parameters is highly sensitive to the ambient temperature, relative humidity, and turbine inlet temperature (TIT). Results demonstrate that saturated fogging plus 1% overspray leads to a relative increase of 24.84% and 6.70% in net power output and thermal efficiency, respectively, at the corresponding ambient condition. It is observed that 23.94% of the increase in the inlet mass flow rate in this cooling approach is due to the injected water directly, where the compressor operating point is matched at a point with a higher inlet mass flow rate comparing to dry condition.

Energy efficiency analysis of wet compression systems through thermo-fluid dynamic considerations

Wet compression systems are deployed in gas turbine power plants for energy savings in the compressor. The system works by injecting fine water droplets in the form of mist into the air stream ahead of the compressor. The water droplets evaporate both before entering the compressor and within the compressor and reduce the air temperature by absorbing latent heat of evaporation. In this study, an analysis is done on two-phase compression of air-water droplet mixture. The work is focused on understanding the fundamental concepts associated with two-phase compression. Hence, a simple piston-cylinder system is used as the domain to simulate the compression of air-water droplet mixture. During the processes, the pressure, temperature and relative humidity inside the cylinder have been monitored. Parametric studies are then performed for various values of starting relative humidity of the air, overspray percentage of water droplets, droplet diameter, and compression speed of the piston. In these studies, the deviation of PV and TV curves from the dry air compression curves, resulting from latent heat of vaporizing droplets are investigated. The studies show that smaller droplets, higher overspray and slower compression speeds significantly reduces the compressor work requirement, thereby increasing cost savings and environmental benefits of power generation. Interestingly, it is seen that the effect of initial relative humidity of the working fluid on energy savings is minimal. The corresponding efficiencies achieved through wet compression process are determined and tabulated.

A High-Gain Observer for a Wet Gas Centrifugal Compressor

Subsea wet gas compression is an enabling boosting technology for cost-efficient production of small and remote gas condensate fields. These wet gas compressors are capable of compressing gases containing up to 5% liquid, removing the need for pre-separation and thereby reducing the investment and maintenance costs. However, the presence of liquid in the gas significantly changes the compression performance from that of dry gas, resulting in a reduced process gain and an increased normal operating region for increasing liquid content. A novel backstepping process controller was previously proposed to track and stabilize a desired pressure reference inside the normal operating region, requiring feedback from several variables, including the mass flow. Mass flow is an inaccurate and expensive measurement. Therefore, a full-order high-gain observer is derived for the wet gas compression process with proven local exponential convergence. The performance of the derived observer is studied in simulations.

Flow Assessment on the Effects of Water Droplets on Rotor Region of Wet Compression

Wet compression process has been widely accepted as a measure of increasing the performance of industrial gas turbine, in the present work, in-depth analysis on the principle aspects of wet compression, more specifically, the influence of injected water droplets diameter, surface temperature, and their effects on the behavior of axial flow transonic compressor and gas turbine performance were analyzed using computational fluid dynamic. Injected water droplets and gas flow phase change was most intense in the area adjacent to shockwaves and were the slip velocity of the droplet is highest. Water injection in to the compressor rotor is a little perturbation to the flow field due to the formation of flow separation, evaporation rate, increasing weber number, reduction in the inlet temperature, and velocity vortex pattern relatively different from that of the dry case. The effects of water droplets on the rotor region at injection rate of 1%, shows decrease in the inlet temperature of 11%, outlet temperature 5% and uplift the efficiency to 1.5%.

Thermo-fluid dynamic analysis of wet compression process

Wet compression systems increase the useful power output of a gas turbine by reducing the compressor work through the reduction of air temperature inside the compressor. The actual wet compression process differs from the conventional single phase compression process due to the presence of latent heat component being absorbed by the evaporating water droplets. Thus the wet compression process cannot be assumed isentropic. In the current investigation, the gas-liquid two phase has been modeled as air containing dispersed water droplets inside a simple cylinder-piston system. The piston moves in the axial direction inside the cylinder to achieve wet compression. Effects on the thermodynamic properties such as temperature, pressure and relative humidity are investigated in detail for different parameters such as compression speeds and overspray. An analytical model is derived and the requisite thermodynamic curves are generated. The deviations of generated thermodynamic curves from the dry isentropic curves (PVγ = constant) are analyzed.

Analytical modeling and assessment of overspray fogging process in gas turbine systems

In this study, analysis of the overspray fogging process, which consists of inlet fogging and wet compression processes in gas turbine cycle, is carried out with a non-equilibrium analytical modeling based on liquid droplet evaporation. The transient behaviors of droplet diameter and air temperature are examined. Special attention is paid to the effects of system parameters such as pressure ratio, water injection ratio, and initial droplet diameter on the process performances, including evaporation time of droplets, compressor outlet temperature, and compression work. Process performances are also estimated under the condition of critical water injection ratio above which complete evaporation of injected water droplets within a compressor is not possible. The analytical results indicate that the overspray fogging process has a potential of lowering compressor outlet temperature and saving significant compression work when compared to dry compression, and this technique is more effective for a higher pressure ratio and smaller size of injected water droplet.

Performance Analysis of Wet Compression Process under Critical Conditions of Water Injection

In wet compression process water is injected at an inlet of compressor and continuous cooling occurs due to evaporation of water droplets during the compression process of air, which can save the compression work and enhance the performance of gas turbine system. In this work, performance analysis of the wet compression process is carried out under the critical conditions of water injection which are defined as the maximum water injection which can be evaporated completely inside the compressor. For various ambient conditions the important variables of wet compression process such as water injection ratio, temperature-averaged polytropic coefficient, compressor outlet temperature, and compression work are estimated under the critical injection conditions. Parametric studies show that compression work decreases with ambient temperature, however, the reduction ratio of compression work relative to dry increases with ambient temperature.

An Assessment of Wet Compression Process in Gas Turbine Systems with an Analytical Modeling

Recently humidified gas turbine systems in which water or steam is injected have attracted much attention, since they can offer a high efficiency and a high specific power with a relatively low cost compared to combined-cycle gas turbine systems, and therefore they have a potential for future power generation. In this study, performance analysis of the wet compression process is carried out with an analytical modeling which was developed from heat and mass transfer, and thermodynamic analyses based on droplet evaporation. Wet compression variables such as temperature-averaged polytropic coefficient, compressor outlet temperature, and compression work are estimated. Parametric studies show the effect of system parameters such as droplet size, water injection ratio or compression ratio on transient behavior.

Fuel and diluent property effects during wet compression of a fuel aerosol under RCM conditions

Wet compression of fuel aerosols has been proposed as a means of creating gas-phase mixtures of involatile diesel-representative fuels and oxidizer+diluent gases for rapid compression machine (RCM) experiments. The intent of this study is to investigate the effects of fuel and diluent gas properties on the wet compression process, specifically to: (a) explore a range of fuels which could have applicability in aerosol RCM experiments, and illustrate important limitations due to fuel properties, and (b) fundamentally understand how fuel and diluent gas properties affect the wet compression process and assess which ones are most important. Insight gained from this work can be utilized to aid the design and successful operation of aerosol RCMs. A spherically-symmetric, single-droplet wet compression model is used where n-heptane, n-dodecane, 2,2,4,4,6,8,8-heptamethylnonane (isocetane), n-hexadecane (cetane) and n-eicosane are investigated as the diesel-representative fuels, while comparisons are made to water droplets. Nitrogen, neon and argon are selected as the gas-phase diluents while the oxidizer is considered to be oxygen at atmospheric concentrations. Initial droplet diameters of d0=3 and 8μm are used based on results of previous studies where the overall compression time is set to 15.3ms with the maximum volumetric compression ratio 13.4. An overall equivalence ratio of φ=1.0 is used.It is shown that under these conditions, involatile fuels up to ∼n-hexadecane appear to be candidates for aerosol RCM experiments. However, the use of small droplets (d0<5μm) will be necessary in order to ensure complete vaporization and adequate gas-phase mixing in advance of low temperature chemical reactivity. Fuels with higher boiling points might not be useable unless extremely small droplets (d0<1μm) and low pressures (e.g., P0<0.5bar) are employed along with longer compression times. In addition, the boiling curve (i.e., saturation pressure) and Lf are found to be the dominant fuel properties while the density-weighted mass diffusivity, ρgDg, which controls the rate of gas phase mass diffusion, and thus compositional stratification, generally plays a secondary role. The heat capacity and molar mass are the dominant diluent properties that affect the near-droplet and ‘far-field’ conditions. The gas-phase mixture Lewis number (Leg) contributes to either greater compositional (Leg>1) or thermal (Leg<1) stratification. For large hydrocarbons and oxygenated hydrocarbons that are representative of diesel fuels Leg∼3–5, and therefore compositional stratification could be significant; this characteristic has the potential to complicate interpretation of ignition/oxidation data acquired from these machines.

Wet Compression Analysis Including Velocity Slip Effects

Injection of water droplets into industrial gas turbines in order to boost power output is now common practice. The intention is usually to saturate and cool the intake air, especially in hot and dry climates, but in many cases, droplets carry over into the compressor and continue to evaporate. Evaporation within the compressor itself (often referred to as overspray) is also central to several advanced wet cycles, including the moist air turbine and the so-called TOP Humidified Air Turbine (TOPHAT) cycle. The resulting wet compression process affords a number of thermodynamic advantages, such as reduced compression work and increased mass flow rate and specific heat capacity of the turbine flow. Against these benefits, many of the compressor stages will operate at significantly off-design flow angles, thereby compromising aerodynamic performance. The calculations presented here entail coupling a mean-line compressor calculation method with droplet evaporation routines and a numerical method for estimating radial and circumferential slip velocities. The impingement of droplets onto blades and the various associated processes (including film evaporation) are also taken into account. The calculations allow for a polydispersion of droplet sizes and droplet temperature relaxation effects (i.e., the full droplet energy equation is solved rather than assuming that droplets adopt the wet-bulb temperature). The method is applied to a generic single-shaft 12-stage compressor. Results are presented for computed droplet trajectories, the overall effect on compressor characteristics (and how this depends on droplet size), and the effects of deposition and subsequent film evaporation. As with previously published wet compression calculations (with no velocity slip), it is found that pressure rise characteristics shift to higher mass flow and pressure ratio with increasing water injection rate and that aerodynamic efficiency falls due to the stages moving away from their design point. For droplet sizes typical of fog boosting, the overall effect of slip is to slightly increase the evaporative cooling effect through the enhanced heat and mass transfer rates.

Analytical modeling of wet compression of gas turbine systems

Evaporative gas turbine cycles (EvGT) are of importance to the power generation industry because of the potential of enhanced cycle efficiencies with moderate incremental cost. Humidification of the working fluid to result in evaporative cooling during compression is a key operation in these cycles. Previous simulations of this operation were carried out via numerical integration. The present work is aimed at modeling the wet-compression process with approximate analytical solutions instead. A thermodynamic analysis of the simultaneous heat and mass transfer processes that occur during evaporation is presented. The transient behavior of important variables in wet compression such as droplet diameter, droplet mass, gas and droplet temperature, and evaporation rate is investigated. The effects of system parameters on variables such as droplet evaporation time, compressor outlet temperature and input work are also considered. Results from this work exhibit good agreement with those of previous numerical work.

Droplet evaporation characteristics due to wet compression under RCM conditions

The vaporization characteristics of a single fuel droplet subjected to rapid gas-phase compression (i.e., wet compression) are computationally investigated using two spherically-symmetric models: quasi-steady (QS) and fully transient (TS). Features of the wet compression process under rapid compression machine (RCM) conditions are discussed with these compared to simulations where the far-field conditions are essentially invariant. It is observed that wet compression can significantly increase the rate of evaporation primarily due to the increase in droplet temperature and corresponding saturation pressure (fugacity); an increase in the density-weighted mass diffusivity is also beneficial in reducing the droplet consumption times. The QS model predicts substantially longer rates of evaporation relative to the TS model due to transient behavior associated with the initial evaporative cooling process, and the gas-phase compression heating process. Increases in the rate of volumetric compression can lead to more rapid droplet consumption, however there is a corresponding increase in spatial stratification in the gas- and liquid-phases which may not be advantageous for RCM applications. An ‘operating map’ has been developed based on parametric simulations of an n -dodecane droplet evaporating into nitrogen.