Urea Mass Research Articles

Two-Staged Dielectric Barrier Discharge-Urea Configuration for the Removal of NO of NOx in a Simulated Coal-Combustion Flue Gas

NO is a deadly pollutant that makes up more than 90% NOx in a flue gas. NO is insoluble in water; thus, its removal is extremely difficult using the SCR method. This study investigates the feasibility of NO removal and energy efficiency from a coal-combustion flue gas connected to a DBD reactor merged with urea. The results showed that the combined effect of urea and the DBD reactor gave a significant increase in the removal of NO. Comparing the removal efficiencies of NO at different urea mass percentages (9%, 17%, 23%, 29%, and 33%), it was found that the optimum concentration of urea for efficient NO removal was 23% because there is enough NH3 produced at this concentration and less H2O species generated to consume N• free radicals by OH to produce more NO in the system. The removal efficiencies of the optimum 23% urea concentration with oxygen [(NO/N2/O2/CO(NH2)2:23% w/w system] and without oxygen [(NO/N2/CO(NH2)2:23% w/w system] were also compared. It was also found that the addition of urea solution showed a considerably good energy efficiency which implies that the cost of this technology will be effective. The study complements past studies on the efficient removal of NO from the environment.

Prescription de la dose de dialyse

The concept of dose of dialysis is relatively recent. It evaluates the adequacy of extrarenal clearance, in order to provide the best chances of survival to chronic dialysis patients. Although it presents drawbacks, urea Kt/V is recognized as the most clinically relevant indicator. It can be easily calculated online thanks to the equipment of the dialysis monitors with ionic dialysance. The target of balanced Kt/V is greater than 1.2, provided the minimal Kt dialysis dose is received. To reach these targets, it is necessary to use dialysers of large surface, with high urea mass transfer coefficient. The blood pump flow must be high and dialysate flow rate sufficient. With the advent of online hemodiafiltration, a dose of convective dialysis was imposed. To achieve these convective targets, large surface dialysers with high hydraulic permeability must be used, with a high beta 2 microglobulin screening coefficient and low albumin loss. Prescribing the dose of dialysis is essential in an optimal quality-of-care based approach.

Balance and fall risk in peritoneal dialysis patients.

Vestibular, neurological and musculoskeletal functions are affected in patients with renal failure. These problems can in turn affect the balance system in peritoneal dialysis (PD) patients. Previously, postural balance changes were shown in hemodialysis patients. This is the first study that evaluates whether there are similar changes in patients with PD. This study aimed to compare balance and fall risk between patients undergoing PD treatment and healthy subjects, and aimed to determine the correlation between biochemical parameters and fall risk and balance assessments in PD patients. This controlled study included 58 patients receiving PD treatment (PD Group) and 75 healthy subjects (Control Group). The Berg Balance Scale (BBS) and Tetrax® Interactive Balance System were used for the comparison of balance between groups. For patients in the PD Group, duration of PD, blood pressure, Kt/Vurea (actual mass of urea removed via peritoneal dialysis), and serum biochemical parameters were recorded and correlation analysis was performed between these parameters and balance measurements. There were no statistically significant differences between groups in terms of demographics or BBS scores (p> 0.05). The fall risk of patients in the PD Group was significantly higher than those in the Control Group (p< 0.0001) according to Tetrax measurements. Female gender, older age, higher BMI, and higher blood glucose levels were negatively correlated with balance parameters of PD patients (r> 0.3). There was no statistically significant correlation between duration of PD, blood pressure, and Kt/Vurea with balance parameters or fall risk. Balance was impaired in patients undergoing PD in comparison to healthy subjects. Fall risk may be evaluated using the Tetrax® instead of BBS for this population. Serum glucose level, BMI and age appear to affect balance and fall risk. Therefore, optimization of body weight and normalization of serum glucose levels are important factors for improving balance. The duration of PD, blood pressure, and Kt/Vurea do not affect balance system.

A new technique for low-volume continuous sampling of spent dialysate: a validation study.

The measure of hemodialysis (HD) adequacy recommended nowadays by most guidelines, Kt/V-urea, presents significant drawbacks. Direct dialysis quantification (DDQ) through total dialysate collection (TDC), considered the gold standard measure of HD adequacy, is cumbersome, which precludes its widespread use in clinical practice. The present study aims to validate a low-volume continuous sampling of spent dialysate (CSSD). Cross-sectional study carried out at a university hospital. Throughout 4-h hemodialysis sessions, urea removal was measured by three DDQ methods: TDC, CSSD, and fractional sampling of dialysate (FSD). The primary outcome was the comparison between the total mass of urea removed measured by TDC and the dialysate sampling techniques. The comparison between urea distribution volume (UDV) estimated by anthropometric method and through DDQ was a secondary outcome. The analysis was done through linear regression and Bland-Altman concordance method. Twenty HD sessions were studied. The mean amount of urea collected in TDC and calculated from the 40-mL sample of CSSD were 33.70 ± 11.70g and 33.90 ± 11.70g, respectively [r 0.96, p < 0.0001; bias - 0.2 (95% CI - 1.8 to 1.4); limits of agreement - 6.8 to 6.4]. The anthropometric measure, when compared with DDQ method, underestimated UDV in patients with smaller body size. This new simple, inexpensive, and small volume CSSD technique can provide accurate information about the total amount of solutes removed by hemodialysis.

Calculating Standard Kt/V during Hemodialysis Based on Urea Mass Removed

Background/Aims: We derived a novel equation for calculating weekly urea standard Kt/V (stdKt/V) during hemodialysis (HD) based on urea mass removed, comparable to the approach during peritoneal dialysis. Methods: Theoretical consideration of urea mass balance during HD led to the following equation for stdKt/V, namely, stdKt/V = N × (URR + UFV/V), where N is the number of treatments per week, URR is urea reduction ratio per treatment, UFV is ultrafiltration volume per treatment, and V is postdialysis urea distribution volume. URR required corrections for postdialysis rebound and intradialytic urea generation. We compared the accuracy of this approach with previous equations for stdKt/V by numerical simulations using a 2-compartment model of urea kinetics for thrice-weekly and more frequent HD prescriptions. Results: The proposed equation based on urea mass removed predicted values of stdKt/V that are equivalent to those calculated by previous equations for stdKt/V. Conclusion: This work provides a novel approach for calculating stdKt/V during HD and strengthens the theoretical understanding of stdKt/V.

Characterisation of acid–base surface free energy components of urea–water solutions

The objective of this study is to determine the Lifshitz–van der Waals/Acid–Base (LW/AB) surface energy components of urea–water-solutions (UWS) for different urea mass fractions. The surface energy parameters are evaluated by ring tensiometry and contact angle measurements of sessile drops placed onto pre-determined solid substrates. Therefore, the energetic characteristics of UWS are evaluated in relation to probe liquids. The results indicate that aqueous solutions of urea become less polar with increasing urea mass fraction while their overall surface tension is also increased. This is attributed to a significant grow of the Lifshitz–van der Waals surface energy component that compensates the reduction of the polar part. In addition, aqueous solutions of urea are characterised by a significant electron donor (γl−) capacity compared to pure water while their electron acceptor parameter (γl+) is reduced. Subsequently, γl+/γl− is continuously reduced with increasing urea concentration. The enhancement of electron-donicity is also reflected to the pH of the solutions while the overall trends are independent from the selection of acid-to-base ratio for pure water. The above findings are related to physicochemical aspects based on molecular and intermolecular interactions.

Sodium acetate–urea composite phase change material used in building envelopes for thermal insulation

Integrating phase change material with building envelopes is an effective way to reduce cooling or heating loads, improve indoor thermal comfort and save building energy consumption. In this paper, the composite phase change material of sodium acetate and urea is prepared and its thermal–physical properties with different mixing mass ratios are investigated through experiment and T-history method. Moreover, the heat transfer model of building envelopes with phase change material is established and different phase change material locations in external walls for thermal insulation are compared based on integrated uncomfortable degree. The results show that (1) with rising urea mass fraction, both phase change temperature and latent fusion heat (enthalpy) decline; (2) strontium sulfate is an effective nucleating additive to decrease super-cooling degree for such phase change material solidification and (3) to improve indoor thermal comfort, it is preferable to put phase change material in the middle of external walls. Furthermore, the illustrative example of an office building in Chengdu indicates that phase change material insulation can lead to time lag and decrement for indoor air temperature variations. It also indicates that after inserting such phase change material into building external wall, the highest indoor temperature can be decreased by 7℃, leading to 60% cooling energy saving in one typical summer day. This work can provide guidance for building thermal design with phase change materials. Practical application:The studied sodium acetate–urea composite phase change material has been used as energy storage and thermal insulation materials inserted in envelopes for the demonstration project of low/zero energy consumption passive buildings in China.

Thermal Performance Test and Improvement for Phase Change Material Composite through Nucleating Additive

Solid-liquid phase change material (PCM) is of high phase change heat and application potentials of thermal energy storage. In this paper, the thermal performance of PCM composites of sodium acetate and urea are investigated through experiment. Moreover, the main thermal-physical properties of such PCM composites with different mixing mass ratios are obtained through T-history method. The results show that with the rising urea mass fraction, both the phase change temperature and latent heat of fusion (enthalpy) decline. It also indicates that strontium sulfate is an effective nucleating additive to decrease super-cooling degree during solidification process for such composite PCM. This work is of high significant in improving the thermal performance of PCM composite and extending its applications.

Urea-Water-Solution Properties: Density, Viscosity, and Surface Tension in an Under-Saturated Solution

A temperature-concentration dependent surface fit for the relative viscosity of a urea-water-solution (UWS) is calculated based on experimental and literature data. For the surface fit, a 2D Lorentzian function was used, where the x-axis was assigned to a urea mass fraction and the y-axis to the solution temperature and the rest of the Lorentzian function parameters were optimized based on the experimental and literature data. The surface model describes the relative viscosity of under-saturated urea-water-solution. The experimental data for the kinematic viscosity was measured with an Ubbelohde capillary viscometer whose temperature was controlled with a thermostat. The temperature and concentration range was from 293.15 to 353.15 K in 10-K increments and for urea mass fractions from 0.325 to 0.7. The kinematic viscosity values from the experiment were converted to relative viscosity by calculating the density of the UWS. An exponential fit was calculated to describe the specific gravity of the UWS based on literature data. Additionally, the surface tension of the UWS was measured at room temperature (293.15 K) in a mass fraction range from 0.302 to 0.596. As a result, simple models describing UWS properties were obtained and these models can be implemented into computational fluid dynamics (CFD) simulations.

Model-Based Fault Detection and Fault-Tolerant Control of SCR Urea Injection Systems

This paper aims at developing integrated onboard diagnosis and fault-tolerant control methods with experimental validation for a urea selective catalyst reduction (SCR) aftertreatment system to reduce vehicle tailpipe emissions. Diagnostics are performed for an SCR urea injection system by estimating and monitoring the injected urea mass flow with no need for a costly physical flow sensor. The estimation is derived from a first-principle-based urea injection system model, and the model parameters are identified by using system identification. During vehicle transient maneuvers, a Kalman filter (KF) is formulated to further reduce the estimation noise and improve diagnostic robustness. Once an injection fault is detected, an adaptation control algorithm is applied to compensate the urea injection command, thus correcting certain types of urea under/overdosing faults and maintaining the SCR $\mbox{NO}_{x}$ conversion performance. These methods have been validated through vehicle tests by utilizing an onboard rapid prototyping control system.

Formation of porous and Hollow polymer particles by urea treatment

In this article, core/shell microspheres are synthesized by multistep seeded polymerization, using methyl methacrylate (MMA), acrylic acid (AA), divinylbenzene (DVB) and styrene (St) as raw materials. Hollow microspheres containing novel surface and inner morphology are fabricated by the process of urea post-treatment of core/shell microspheres. The morphology of microspheres is investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). On the basis of the experimental results, it is reasonable to conclude that the formation of hollow spheres is due to the reaction of ammonia which is produced by decomposition of urea, meanwhile the emission of gas makes the mesoporous shell. The results also suggested that the urea treatment time, temperature and the amount of urea are the key factors to obtain the hollow structured particles. When the urea treatment temperature was below 90°C, the microsphere morphology was nearly unchanged. The addition of ethanol could promote the formation of hollow structure. Moreover, the ratio of hollow spheres increased with increasing urea content. The optimal process to obtain hollow structured microsphere during the urea treatment is treated at 95°C for 5 h with urea mass concentration of 0.054 g/mL.

Deposition of activated alumina powder on SiC diesel particulate filters with wall flow type through in-situ hydrothermal process

A modified mesoporous alumina powder by urea mass percent and glycerol addition was deposited on SiC diesel particulate filters (SiC-DPFs). The activated alumina layer was successively synthesized by a surfactant-templating route through in-situ hydrothermal technique with the aim of depositing homogeneous and well-adhered layers. The effect of the urea mass percent and glycerol addition on the deposition process was also examined.The mineral phase, surface area and structural morphology of the activated alumina layers were investigated by different physicochemical techniques such as X-ray diffraction, N2-physisorption and scanning electron microscopy. The resultant deposited alumina powder layers possessed surface areas and pore volumes of about 20–28m2g−1supp and 0.15–0.31cm3g−1, respectively.

Synthesis of porous g-C3N4/La and enhanced photocatalytic activity for the degradation of phenol under visible light irradiation

A series of porous g-C3N4/La (PGCN/La) materials used as photocatalyst for the degradation of phenol were prepared by two steps. The photocatalysts were characterized by X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), thermogravimetry (TG), Brunauer–Emmett–Teller (BET), Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). From the TEM morphology, the porous structure of g-C3N4 could be successfully controlled; from BET results, BET specific surface area of porous g-C3N4 (PGCN) sample increases with the increasing of urea mass ratio. Compared with PGCN material (PGCN-50), PGCN/La sample (PGCN-50/La-5) could exhibit an enhanced photocatalytic activity and has the best degradation efficiency of 98.6% within 50min under visible light irradiation. Photocatalytic reaction follows the first-order model kinetics; and PGCN-50/La-5 photocatalyst shows the largest reaction rate among all samples which is nearly 2.96 times higher than that of pure PGCN-50. The present work illustrates that the photocatalytic activity of porous g-C3N4 was improved by the addition of La and PGCN-50/La-5 has potential application in the removal of phenol or other organic molecular from wastewater.

Modeling analysis of urea direct injection on the NOx emission reduction of biodiesel fueled diesel engines

In this paper, a numerical simulation study was conducted to explore the possibility of an alternative approach: direct aqueous urea solution injection on the reduction of NOx emissions of a biodiesel fueled diesel engine. Simulation studies were performed using the 3D CFD simulation software KIVA4 coupled with CHEMKIN II code for pure biodiesel combustion under realistic engine operating conditions of 2400rpm and 100% load. The chemical behaviors of the NOx formation and urea/NOx interaction processes were modeled by a modified extended Zeldovich mechanism and urea/NO interaction sub-mechanism. To ensure an efficient NOx reduction process, various aqueous urea injection strategies in terms of post injection timing, injection angle, and injection rate and urea mass fraction were carefully examined. The simulation results revealed that among all the four post injection timings (10°ATDC, 15°ATDC, 20°ATDC and 25°ATDC) that were evaluated, 15°ATDC post injection timing consistently demonstrated a lower NO emission level. The orientation of the aqueous urea injection was also shown to play a critical role in determining the NOx removal efficiency, and 50 degrees injection angle was determined to be the optimal injection orientation which gave the most NOx reduction. In addition, both the urea/water ratio and aqueous urea injection rate demonstrated important roles which affected the thermal decomposition of urea into ammonia and the subsequent NOx removal process, and it was suggested that 50% urea mass fraction and 40% injection rate presented the lowest NO emission levels. At last, with the optimized injection strategy, the engine presented significantly reduced NO emission from 131ppm to 55ppm compared to the case of pure biodiesel combustion, achieving a reduction efficiency of 58%, suggesting that urea direct injection could be an effective method to reduce the NOx emissions of a biodiesel fueled diesel engine.

Measurements of liquid film thickness, concentration and temperature of aqueous NaCl solution by NIR absorption spectroscopy

A multi-wavelength near-infrared (NIR) diode laser absorption sensor has been developed and demonstrated for real-time monitoring of the thickness, solute concentration, and temperature of thin films of urea–water solutions. The sensor monitors the transmittance of three near-infrared diode lasers through the thin liquid film. Film thickness, urea mass fraction, and liquid temperature were determined from measured transmittance ratios of suitable combinations of lasers. Available laser wavelengths were selected depending on the variation of the NIR absorption spectrum of the solution with temperature and solute concentration. The spectral database was measured by a Fourier transform infrared spectrometer in the range 5500–8000 cm−1 for urea solutions between 5 and 40 wt% and temperatures between 298 and 338 K. A prototype sensor was constructed, and the sensor concept was first validated with measurements using a calibration cell providing liquid layers of variable thickness (200–1500 µm), urea mass fraction (5–40 wt%) and temperature (298–318 K). Temporal variations of film thickness and urea concentration were captured during the constant-temperature evaporation of a liquid film deposited on an optically polished heated quartz flat.

Experimental analysis of the influence of urea injection upon NOx emissions in internal combustion engines fueled with biodiesels

The effect of urea injection on NOx emissions in a six-cylinder, four-stroke internal combustion engine fueled with B80 biodiesel has been experimentally investigated. The results reveal that urea injection leads to a reduction of NOx emissions of B80 biodiesel fuel. Moreover, the influence of injection parameters on NOx reductions has been studied. The findings show that increasing the injection temperature results in lower NOx emissions. Also urea mass flow rate increment leads to more NOx reduction. The same result has been obtained by an increase in spray angle. In addition, increasing the number of nozzles indicates more depletion in NOx emissions while a “three-nozzles spray system” has the most considerable effect on NOx reductions.

The Hermeticity of Compression Seals in Microchannel Hemodialyzers

Most end stage renal disease patients receive kidney hemodialysis three to four times per week at central medical facilities. At-home kidney dialysis increases the convenience and frequency of hemodialysis treatments which has been shown to produce better patient outcomes. One limiting factor in realizing home hemodialysis treatments is the cost of the hemodialyzer. Microchannel hemodialyzers produced using compression sealing techniques show promise for reducing the size and cost of hemodialyzers. Challenges include the use of a 25 μm thick elastoviscoplastic (EVP) mass transfer membrane for gasketing. This paper provides a framework for understanding the hermeticity of these compression seals. The mechanical properties of a Gambro AN69ST membrane are determined and used to establish limits on the dimensional tolerances of the polycarbonate (PC) laminae containing sealing bosses used to seal the hemodialyzer. The resulting methods are applied to the fabrication of a hemodialysis device showing constraints on the scaling of this method to larger device sizes. The resulting hemodialysis device is used to perform urea mass transfer experiments without leakage.

Amplified Spontaneous Green Emission and Lasing Emission From Carbon Nanoparticles

In this work, the optical properties of carbon nanoparticles (CNPs) can be modulated by the dopant‐N atom and sp2 C‐contents. CNPs prepared with the low urea mass ratio of 0.2:1 (CNP1) exhibit blue emission (maximum PL quantum yield: 15%). Increasing sp2 C‐ and dopant‐N atom contents, as determined in CNPs prepared with high urea mass ratio of 2:1 (CNP2), lead to green emission (maximum PL quantum yield up to 36% in ethanol aqueous solution). Amplified spontaneous emission (ASE) can be observed only in CNP2 ethanol aqueous solution. Green lasing emission is achieved from CNP2 ethanol aqueous solution in a linear long Fabry‐Perot cavity, indicating the potential of CNP2 as a gain medium for lasing. CNP2 shows superior photostability compared with C545T dye. The green emission from CNP2 is speculated to arise from electron‐hole recombination (intrinsic state emission). The high PL quantum yield and small overlap between absorption and emissions of CNP2 ethanol aqueous solution are the key factors in realizing lasing emission.

Adaptive network based on fuzzy inference system for equilibrated urea concentration prediction

Post-dialysis urea rebound (PDUR) has been attributed mostly to redistribution of urea from different compartments, which is determined by variations in regional blood flows and transcellular urea mass transfer coefficients. PDUR occurs after 30–90min of short or standard hemodialysis (HD) sessions and after 60min in long 8-h HD sessions, which is inconvenient. This paper presents adaptive network based on fuzzy inference system (ANFIS) for predicting intradialytic (Cint) and post-dialysis urea concentrations (Cpost) in order to predict the equilibrated (Ceq) urea concentrations without any blood sampling from dialysis patients. The accuracy of the developed system was prospectively compared with other traditional methods for predicting equilibrated urea (Ceq), post dialysis urea rebound (PDUR) and equilibrated dialysis dose (eKt/V). This comparison is done based on root mean squares error (RMSE), normalized mean square error (NRMSE), and mean absolute percentage error (MAPE). The ANFIS predictor for Ceq achieved mean RMSE values of 0.3654 and 0.4920 for training and testing, respectively. The statistical analysis demonstrated that there is no statistically significant difference found between the predicted and the measured values. The percentage of MAE and RMSE for testing phase is 0.63% and 0.96%, respectively.

Correlation between Microalbuminuria and Glucose/ Leptin ratio in a sample of Iraqi patients with type 2 diabetes mellitus

o study the association of serum leptin and glucose/leptin ratio with microalbuminuria in patients with type 2 diabetes mellitus at different durations, and to predict their effect on their renal function. A case control study was conducted in the International Diabetic Center at Al-Mustansiryia University in Baghdad-Iraq from 1st September 2008 to the 30th of July 2010. One hundred and eight male patients with type 2 diabetes mellitus (DM) were introduced in this study. Fifty three healthy subjects were used as a control. Fasting serum glucose, insulin, leptin, urea, creatinine and body mass index were estimated in both patient and control groups. Fifty three 49.07% out of 108 were diabetic for ≤2 years, while 55 patient 50.93% were diabetic &gt;2 years. All patients were obese while healthy control subjects were not. Fasting serum glucose, insulin and leptin levels were found elevated in patients group while in control group their levels were found within normal range. Both urea and creatinine were also within the normal range for patients and control groups. Level of albumin in urine of patients with diabetes mellitus for ≤ 2years was found normal while in those with 3 to 6 or more than 6 years of DM, level of urinary albumin was found within the micro rang. A positive correlation with highly significant p value (&lt;0.01) was found between patients (≤ 2 years and &gt;2 years) serum leptin, glucose/leptin ratio and microalbuminuria. Conclusions: a strong association was found between serum leptin and glucose/leptin ratio with microalbuminuria in type 2 diabetic patients which can be used to predict the efficiency of their renal function at different durations and can be used as additional marker for the diagnosis of early stage of nephropathy.