Parametric study of aluminium alloy fouling in marine environment using RSM technique

ABSTRACT

Fouling is known to be a prominent industrial problem which is greatly affected by parameters like temperature, time and flowrate. The aim of this work was to simulate the fouling process in AA 6061 by developing a model through Minitab 16 and evaluate the models. Box Behnken design of Response surface methodology was applied for modelling and optimization of fouling propensity in artificial sea water. A response surface model was obtained and Analysis of Variance was performed to test the significance of the model. Fouling propensity was found in terms of weight gain. An experimental rig consisting of a recirculating loop mimicking the industrial conditions of fouling was used in the study. SEM analysis shows uneven deposits on the metal surface. Sharp, irregular deposits pressed deep into the metal was observed. The finding of this work would enable us to evaluate the individual and interactive effects of the parameters.     

Application of pulse detonation technology for boiler slag removal

Pulse detonation technology for removing slag and fouling deposits in coal-fired utility power plant boilers offers great potential. This technology offers a potentially convenient, inexpensive, yet efficient way for on-line slag removal. This paper presents a feasibility study that includes both Computational Fluid Dynamics (CFD) simulations and laboratory experiments. CFD simulations provided visual and quantitative data to study the potential mechanisms for removal of slag. Mechanisms included direct impact, flow scrubbing, wave reflection and negative velocity impact on the back side of the tubes. Several experiments were carried out to verify the potential of the pulse detonation technology. Experiments were done using a pulse detonation engine and heat exchanger tubes with different types of slag placed in different orientations on the tubes. Tubes were placed at various distances from the detonation tube and in different configurations. The results present a strong case for the application of this technology for online slag removal. It is especially effective for removal of slag on the back sides of the tubes where other traditional methods are not very successful. A preliminary cost analysis indicated that the technology can be paid for within the first year itself and provide substantial savings in the subsequent years.     

Optimising operating conditions in ultrafiltration fouling of pomegranate juice by response surface methodology

The resistance‐in‐series model was used to analyse flux behaviour, which involved the resistances of membrane itself, the fouling and solute concentration polarisation. Response surface methodology was used to establish the relationships between operating parameters and ultrafiltration (UF) efficiency and thus to determine optimal conditions. Experiments were performed according to Box–Behnken design by changing the levels of three parameters, namely transmembrane pressure, feed flow rate and temperature. The fitted mathematical models allowed us to plot isoresponse curves. It was shown that the resistance due to solute concentration polarisation (R_cp) dominated the flux decline (40–74%). The fouling resistance (R_f) varied from 12 to 46%. To optimise simultaneously the three responses studied (R_f, R_cp and permeate limit flux), we applied the desirability function approach which allowed us to determine the best acceptable compromise. The selected UF conditions of the compromise were as follows: three bars, 0.95 L min^?1 and 30 °C. Optimal values of R_f, R_cp and permeate limit flux were equal to 18%, 72% and 19 L h^?1 m^?2, respectively.     

Fouling control of a membrane coupled photocatalytic process treating greywater

Fouling in membrane coupled photocatalytic reactors was investigated in the case of greywater treatment by establishing the link between product type, dose, irradiation time and fouling rates in a cross flow membrane cell fitted with a 0.4 μm pore sized polyethylene membrane. Rapid fouling occurred only with shower gels and conditioners and was linked to changes in the organo-TiO₂ aggregate size postulated to be caused by polymers within the products. Fouling was reduced to a negligible level when sufficient irradiation was applied demonstrating that the membrane component of the process is not the issue and that scale up and implementation of the process relates to effective design of the UV reactor.     

横纹管污垢性能的实验研究

在实验室进行了横纹管的传热性能实验，得出了横纹管管内强制对流换热关联式。以硬度800mg/L的人工硬水作为工质，在流速0．38m/s，管外水浴温度60℃和相同管内工质入口温度的条件下，进行了横纹管及其对应光管管内污垢的对比实验。结果表明，横纹管不仅有较好的传热性能，还有较好的阻垢性能。     

A permeability-controlled microfiltration membrane for reduced fouling in drinking water treatment

A novel surface-modified polypropylene microfiltration membrane is investigated for its potential use in drinking water treatment. The flux decline rate of the modified membrane is substantially lower than the original polypropylene membrane for filtration of a soft, high-natural organic matter (NOM) surface water because a progressive adjustment in membrane permeability counteracts the flux decline due to fouling. In general, the prospects for reduced flux decline by membrane modification depend upon the characteristics of raw water such as hardness, particulate and NOM properties and concentration, and pretreatment strategies.     

Recovery of ammonium sulfate from fermentation waste by electrodialysis

Electrodialysis experiments of the lysine fermentation waste were performed to generate demineralized feed and ammonium sulfate, which can be utilized as a fertilizer and an animal feed, respectively. The electrodialysis performances were compared for different ion exchange membranes in terms of ammonium sulfate removal rate, resistance and conductivity change. Analysis of fouling phenomena revealed that organics fouled ion exchange membranes reversibly in electrodialysis of the fermentation waste. In this study, mitigation of membrane fouling with the pulsed electric field was examined for the electrodialysis of the fermentation waste containing strong foulants. The half-wave power reduced membrane fouling significantly. For a quantitative measure of the membrane fouling tendency, a membrane fouling index for electrodialysis was used. This study showed the potential use of pulsed power as an effective fouling mitigation method for the electrodialysis of fermentation waste.     

空分设备空气预冷系统循环水改造

由于空分设备循环冷却水系统水质不好，造成冷水机组、冷却器等内部结垢严重，导致设备运行不稳定。根据实际情况，将空分设备空气预冷系统的水系统独立设置，并对水系统设备进行防腐、自动控制等改造，大大提高了空分设备运行的安全性和稳定性。     

Computational analysis of fouling by low energy surfaces

Fouling is a cost increasing problem for a variety of industries including aerospace, chemical, petroleum, and food. There have been studies on mitigation of fouling some of which recommend use of lower surface free energy materials, manufactured by different techniques, as an alternative to conventional materials. Although modeling of fouling for a given surface has been an area of interest; there is a lack in the models about correlating the surface free energy with deposit amount computationally. In this study, computational model, including the effect of surface energy and operational parameters, was proposed and validated to estimate amount of foulants deposits and rate of deposition. Towards this purpose, four coated surfaces (Microlube/PTFE, TM117P, AMC148, and CNT) were compared with stainless steel (SS316 as control) for flow rates of 3 and 10 g/s and inlet milk temperatures of 40 and 60 °C. The percent error for the decrease in outlet milk temperatures between the experimental data and computed results was between 2% and 18% except for CNT (29.2%). The calculations of deposit amount for each test case and the surfaces tested were in good agreement with the experiments, i.e., average percent difference values between measured and calculated values were from 11.1% to 38.1% (except CNT) with overall average of 21.5%.     

Practical Assessment of Electronic Water Treatment for the Prevention of Fouling

Fouling or scaling, i.e., the occurrence of deposits on tubes, heat exchangers, and other devices, is a common problem in industrial and domestic processes. Many anti‐fouling techniques exist, both chemically and non‐chemically. The efficiency of non‐chemical methods is still controversial, although the use of these devices is already widespread in industry. In this contribution, a case study is presented in which the operation of such a device is demonstrated. The electronic water treatment device under study was connected to a 2 m‐long copper tube immersed in a water bath with a temperature of 65 °C. A short‐term experiment revealed that the device did not alter the water chemistry and that locally, fouling was prevented by the device. However, the potential for fouling further downstream was not reduced. A long‐term experiment further confirmed the findings of the short‐term experiment showing that locally, the device has an anti‐fouling action as a significant increase in weight was observed when the device was switched off and a significant decrease in weight was observed when the device was switched on.