Exploring the differences between forward osmosis and reverse osmosis fouling

A comparison of alginate fouling in forward osmosis (FO) with that in reverse osmosis (RO) was made. A key experimental finding, corroborated by membrane autopsies, was that FO is essentially more prone to fouling than RO, which is opposite to a common claim in the literature where deductions on fouling are often based solely on the water flux profiles. Our theoretical analysis shows that, due to a decrease in the intensity of internal concentration polarization (ICP), and thus an increase in the effective osmotic driving force during FO fouling tests, the similarity of experimental water flux profiles for FO and RO is in accordance with there being greater fouling in FO than RO. The specific foulant resistance for FO was also found to be greater than that for RO. Possible explanations are discussed and these include the influence of reverse solute diffusion from draw solution. Whilst this explanation regarding specific foulant resistance is dependent on the draw solution properties, the finding of greater overall foulant accumulation in FO is considered to be a general finding. Additionally, the present study did not find evidence that hydraulic pressure in RO plays a critical role in foulant layer compaction. Overall this study demonstrated that although FO has higher fouling propensity, it offers superior water flux stability against fouling. For certain practical applications this resilience may be important

Reverse osmosis and forward osmosis fouling: a comparison

Our previously reported exploration (Journal of Membrane Science 565 (2018) 241–253) on the differences between fouling in reverse osmosis (RO) and forward osmosis (FO), used alginate as a foulant with initial conditions that ensured that the starting fluxes were the same. That study found that for a cellulose triacetate (CTA) membrane the extent of fouling, based on the analysis of foulant resistance, was greater when the membrane was part of a FO system. Herein, using the same methodology, results for a thin film composite membrane with alginate as the foulant are presented and these confirm the same general conclusion namely that the extent of foulant accumulation in FO mode is more severe than in RO mode. Furthermore the specific fouling resistance with alginate fouling in FO is more than for RO. However examining the overall operation including cleaning as well as fouling, this study suggests that FO operation is potentially less sensitive to fouling phenomena than RO for similar feed materials. This is due to the driving force compensation coming from a changing level of ICP. Some preliminary work including that with silica particles is also reported

Effect of phase angle on the efficiency of beta type Stirling engine

A Stirling Engine is a mechanical device, which operates on a closed regenerative cycle, based on cyclic compression and expansion through a piston and a displacer respectively. It can be widely used for many thermodynamic purposes such as stationary power generation, heat pumps or co-generation systems. Due to the external supply of heat and increasing scope of solar energy utility in Pakistan, this engine can be operated successfully with this useful source of energy. Phase angle is an important parameter of the Stirling engine and is one of the key factors on which performance of the engine depends. It is the angle by which expansion space volume leads the compression space with respect to the volume variations in the engine cycle. This paper describes the optimization and modelling of the phase angle of a single cylinder beta Stirling Engine with Helium as the working fluid. Schmidt analysis is considered to be the standard during this research for analysing the output efficiency of the engine. The volume and pressure variations are computed at different values of phase angle for a complete cycle and ultimately values chart and pressure-volume diagrams are prepared. The work done for each case is calculated for finding the optimum phase angle. It is calculated that the best suitable phase angle for the maximum efficiency of the engine is around 90°. Along with maximum and minimum pressure inside the engine, the overlap volume in beta type Stirling engine plays a vital role and efficiency increases with increase in overlap region.&nbsp

THE PENETRATION OF OBLIQUE DIESEL SPRAYS UNDER COLD BOMB CHAMBER CONDITIONS

It has been analytically proved that the performance of compression ignition engine is spray characteristics related. The diesel engine performance can be enhanced by achieving improved combustion in the combustion chamber. An efficient combustion depends on the spray formation and ultimate penetration before the onset of combustion. The numerical simulation of fuel spray under varying chamber and injection conditions has been carried out for non-evaporating diesel sprays. The numerical simulations are carried out by using Fluent software. The geometrical modeling is done using gambit and meshing and boundary conditions are also applied in gambit before transferring the model into Fluent. The spray formation and spray penetration rate has been studied under given conditions and the results have been compared with the existing experimental results and theoretical correlations. The simulation is carried out using cold bomb conditions under varying chamber conditions such as gas pressure, nozzle diameter and fuel injection pressure. For comparison purpose the chamber conditions were kept identical as that of the experimental data

Evaluation of LC Resonant Pressure Sensor for Smart Stent Application

This paper aims to project the design and evaluation of inductor capacitor (LC) pressure sensor for smart stent application. The sensor was fabricated through ultraviolet (UV) patterning process using SU-8 polymer material because of its biocompatibility and suitability to fabricate small patterns. In the second phase of the research illustrates the measurement of pressure difference of blood and wireless monitoring inside the coronary artery having a stent implant equipped with LC resonant pressure sensor. This rectangular shaped pressure sensor (with and area of 4 x 4 mm2), consists of an inductive coil and a capacitive plate, which exactly matches with the radio frequency-identification (RFID) design. The LC pressure sensor circuit is able to communicate with external antenna by matching the resonance frequency of both circuits. The fabricated sensor has 1.3 pF capacitance, 100 nH inductance with the resonance frequency about 440 MHz. The fabricated sensor is placed in a small vacuum chamber and the chamber pressure is controlled by using a syringe pump. The change of 100 MHz in the resonance frequency is observed in a pressure range of 0 to 16 kPa. Through a series of experimental analysis, it has been perceived that the discussed sensor can effectively measure pressure difference inside the vacuum and the change in resonance frequency can be further detected by using wireless equipment. The sensor can be widely used in the applications to effectively monitor the pressure difference of blood inside the human coronary artery

DESIGN CHARACTERIZATION OF SHAPE MEMORY ALLOY HELICAL STENT FOR ENDOHYPERTHERMIA TREATMENT OF RESTENOSIS

This paper proposes a helical type stent made by using Shape Memory Alloy (SMA) material known as Nitinol. The stent is produced by laser cutting technique, having helical shaped zigzag loops in order to behave like an inductor. A capacitor is integrated on inductive stent to build an L-C tank circuit. This L-C resonant stent act as a wireless heater operated under Radio-Frequency (RF) magnetic field applied externally. The stent is fabricated by using 6 mm diameter Nitinol tubes with wall thickness of 0.1 mm having austenite finish (Af) temperature equals to 60°C. The helical stent is heated by applying potential difference across its ends and the results obtained from experiment were compared with the simulation results. It is concluded that the stent require 2.5 V or 1.5 Watts of energy to reach the temperature of 50° C which is an ideal temperature for hyperthermia treatment. The fabricated stent is electromechanically coupled with different types of capacitors in order to characterize its electrical properties and resonance frequency. The inductance of stent is found to be between 350 µH – 400 µH. At the end, mechanical properties of stent are also characterized and compared with commercial stent to ensure its practical validity

Membrane filtration: fouling and cleaning in forward osmosis, reverse osmosis, and ultrafiltration membranes

A comparison of fouling in osmotically driven processes with that in pressure driven processes is the main focus of the thesis. Forward osmosis (FO) and reverse osmosis (RO) have received considerable attention for water treatment and seawater desalination. This research compared the nature of fouling in FO mode with that in RO starting with the same initial flux in connection with cleaning effects and then comparing to those in ultrafiltration membranes. In all cases, with cleaning as an integral part, the extent of fouling reversibility, and the question whether a critical flux could be determined were examined. The work during the first phase (undertaken at Oxford) quantified the removal of reversible fouling through rinsing by cold and hot water for a range of concentrations using the foulants dextran and carboxymethyl cellulose. The flux-TMP relationship was conventionally compared to that of the clean water flux. The later phase (at Singapore) compared the fouling in FO and RO by alginate in terms of multiple parameters using cellulose tri acetate (CTA) and thin film composite (TFC) membranes. Silica and alginate were selected as model foulants. Whilst experimental water flux profiles in the present study did not exhibit significant differences in trend between FO and RO fouling, foulant resistance for FO was found to be increasingly greater than for RO with the progression of the fouling tests. This was further corroborated by membrane autopsies post fouling tests; both foulant mass deposition density and specific foulant resistance for FO were greater than for RO. The analysis clearly revealed that FO is essentially more prone to fouling than RO which was presumably due to less flux decline in FO (or greater average flux) as compared to that in RO in result of ICP-self compensation effect which is opposite to the prevailing claim in the literature. Additionally, the present study did not find evidence that hydraulic pressure in RO has a role in foulant layer compaction. FO membrane fouling by real waters was the focus of the final phase of the research at SMTC. Pilot scale FO experiments were conducted on spiral wound CTA membrane with treated waste water obtained from a NEWater factory (Singapore) as the feed. In the second stage, experiments were repeated at bench scale with membrane coupons taken from the spiral wound membranes used earlier. The key finding was that the mass transfer coefficients in the Spiral-Wound module were around 50% lower than the corresponding values in the flat sheet unit and this severely limited the fluxes. The reason could be attributed to strong internal concentration polarisation in the former, where tightly wound spacers act to increase the structural parameter.</p

Effect of laser surface remelting on Microstructure, mechanical properties and tribological properties of metals and alloys: A review

Surface defects like porosity, cracks, coarse grains, surface roughness, etc. have a huge impact on the strength and performance of materials. Due to this, surface treatments have become an important part in the field of materials to attain certain desirable mechanical properties and surface properties. Surface of parts treated with laser surface remelting exhibits excellent surface and mechanical properties. It is a computer-based technique which provides the advantage of treating selective surfaces. Laser surface remelting tends to enhance corrosion resistance, microhardness, wear resistance, fatigue strength, and tensile strength of the materials. To achieve certain mechanical properties with laser surface remelting, an optimized set of laser processing parameters is essential. Laser surface remelting has become a compulsory treatment for parts manufactured by Additive Manufacturing (AM) processes as these processes provide poor surface, porosity, and hot cracking defects which ultimately affect the performance of parts. This paper critically evaluates the advancements which have been made in the field of laser surface remelting to get better surface quality, improved mechanical and tribological properties.</p