D. Ian Wilson

Surface morphology and surface energy of anode materials influence power outputs in a multi-channel mediatorless bio-photovoltaic (BPV) system

Bio-photovoltaic cells (BPVs) are a new photo-bio-electrochemical technology for harnessing solar energy using the photosynthetic activity of autotrophic organisms. Currently power outputs from BPVs are generally low and suffer from low efficiencies. However, a better understanding of the electrochemical interactions between the microbes and conductive materials will be likely to lead to increased power yields. In the current study, the fresh-water, filamentous cyanobacterium Pseudanabaena limnetica (also known as Oscillatoria limnetica) was investigated for exoelectrogenic activity. Biofilms of P. limnetica showed a significant photo response during light-dark cycling in BPVs under mediatorless conditions. A multi-channel BPV device was developed to compare quantitatively the performance of photosynthetic biofilms of this species using a variety of different anodic conductive materials: indium tin oxide-coated polyethylene terephthalate (ITO), stainless steel (SS), glass coated with a conductive polymer (PANI), and carbon paper (CP). Although biofilm growth rates were generally comparable on all materials tested, the amplitude of the photo response and achievable maximum power outputs were significantly different. ITO and SS demonstrated the largest photo responses, whereas CP showed the lowest power outputs under both light and dark conditions. Furthermore, differences in the ratios of light : dark power outputs indicated that the electrochemical interactions between photosynthetic microbes and the anode may differ under light and dark conditions depending on the anodic material used. Comparisons between BPV performances and material characteristics revealed that surface roughness and surface energy, particularly the ratio of non-polar to polar interactions (the CQ ratio), may be more important than available surface area in determining biocompatibility and maximum power outputs in microbial electrochemical systems. Notably, CP was readily outperformed by all other conductive materials tested, indicating that carbon may not be an optimal substrate for microbial fuel cell operation.

Pulsed Flow Cleaning of Whey Protein Fouling Layers

This article reports on the use of intermittent pulsing superimposed on a slow steady flow to enhance the rate of cleaning of a model food soil—namely, a whey protein deposit—in a well-characterized flow geometry. Whey protein deposits were generated by recirculating 3.5 wt% WPC solutions through an electrically heated annular test section and then cleaned using recirculating solutions of 0.5 wt% NaOH, simulating industrial cleaning-in-place operations. Protein removal was monitored by local measurements of fouling resistance (at low heating power) and a total protein assay. Bulk flow velocities of 0.1–0.3 m/s and waviness ratios (amplitude of velocity pulse/baseline flow velocity) of 0.33–5.0 were studied at room temperature. Cleaning at these temperatures is a relatively slow process and allows the effect of flow regime to be followed readily. The resulting cleaning profiles showed that protein was removed in two stages: an initial rinsing stage, followed by protein swelling and gradual dissolution. Only the rinsing stage was observed in the absence of NaOH at a noticeably lower rate. Slow flow pulsing enhanced the overall cleaning rate, which exhibited a noticeable increase when the waviness of the flow exceeded unity and backflow of the fluid occurred. The results are discussed in terms of cleaning enhancement as a function of extra flow rate and extra energy input to the process.

The Disintegration Process in Microcrystalline Cellulose Based Tablets, Part 1: Influence of Temperature, Porosity and Superdisintegrants

Disintegration performance was measured by analysing both water ingress and tablet swelling of pure microcrystalline cellulose (MCC) and in mixture with croscarmellose sodium using terahertz pulsed imaging (TPI). Tablets made from pure MCC with porosities of 10% and 15% showed similar swelling and transport kinetics: within the first 15s, tablets had swollen by up to 33% of their original thickness and water had fully penetrated the tablet following Darcy flow kinetics. In contrast, MCC tablets with a porosity of 5% exhibited much slower transport kinetics, with swelling to only 17% of their original thickness and full water penetration reached after 100s, dominated by case II transport kinetics. The effect of adding superdisintegrant to the formulation and varying the temperature of the dissolution medium between 20°C and 37°C on the swelling and transport process was quantified. We have demonstrated that TPI can be used to non-invasively analyse the complex disintegration kinetics of formulations that take place on timescales of seconds and is a promising tool to better understand the effect of dosage form microstructure on its performance. By relating immediate-release formulations to mathematical models used to describe controlled release formulations, it becomes possible to use this data for formulation design.

Scheduling the cleaning actions for a fouled heat exchanger subject to ageing: MINLP formulation

Abstract This paper addresses the problem of scheduling the cleaning actions of a heat exchanger undergoing fouling and ageing. The existence of two discrete layers leads to the use of two cleaning methods which differ in their ability to remove the aged layer. A mixed integer nonlinear programming (MINLP) model is presented and solved for three case studies with different ageing rates. The optimal schedule consists of: (i) the timing of the cleanings and (ii) the cleaning mode in each instant.

A scanning fluid dynamic gauging technique for probing surface layers

Fluid dynamic gauging (FDG) is a technique for measuring the thickness of soft solid deposit layers immersed in a liquid environment, in situ and in real time. This paper details the performance of a novel automated, scanning FDG probe (sFDG) which allows the thickness of a sample layer to be monitored at several points during an experiment, with a resolution of ±5 µm. Its application is demonstrated using layers of gelatine, polyvinyl alcohol (PVA) and baked tomato puree deposits. Swelling kinetics, as well as deformation behaviour—based on knowledge of the stresses imposed on the surface by the gauging flow—can be determined at several points, affording improved experimental data. The use of FDG as a surface scanning technique, operating as a fluid mechanical analogue of atomic force microscopy on a millimetre length scale, is also demonstrated. The measurement relies only on the flow behaviour, and is thus suitable for use in opaque fluids, does not contact the surface itself and does not rely on any specific physical properties of the surface, provided it is locally stiff.

The Effect of Fouling on Heat Transfer, Pressure Drop, and Throughput in Refinery Preheat Trains: Optimization of Cleaning Schedules

Optimizing cleaning schedules for refinery preheat trains requires a robust and reliable simulator, reliable fouling models, and the ability to handle the thermal and hydraulic impacts of fouling. The interaction between thermal and hydraulic effects is explored using engineering analyses and fouling rate laws based on the “threshold fouling” concept; the potential occurrence of a new phenomenon, “thermo-hydraulic channeling” in parallel heat exchangers, is identified. The importance of the foulant thermal conductivity is highlighted. We also report the development of a highly flexible preheat train simulator constructed in MATLAB/Excel. It is able to accommodate variable throughput, control valve operation, and different cost scenarios. The simulator is demonstrated on a network of 14 heat exchangers, where the importance of optimizing the flow split between parallel streams is illustrated.

Extraction of Crude Oil Fouling Model Parameters from Plant Exchanger Monitoring

Most of the semi-empirical “threshold fouling” models for crude oil fouling in shell-and-tube exchangers have been developed and validated using data collected at what may be considered to be “point” or localized conditions. In practice, both velocity and wall temperature can vary significantly within a heat exchanger, leading to difficulty in applying the models in exchanger design and extracting fouling information from exchanger performance monitoring. A partial simulation model is presented here, incorporating a linear temperature distribution. This short-cut model is compared with a more detailed simulation in order to establish its reliability. Pressure drop using a smooth layer model is also considered. The short-cut approach is employed in a data reconciliation study of an operating crude preheat train, which indicates that the original threshold fouling model of Ebert and Panchal gives a better description of the observed fouling behavior.

Chapter 3 Extrusion—spheronisation

Publisher Summary Extrusion–spheronisation (E–S) is used to manufacture spherical or cylindrical pellets by extruding a semi-solid wet powder mass through a single die, a series of dies, or a screen featuring many holes, and then breaking up and rounding the extrudate on a rotating friction plate. E–S is also known as extrusion–marumerisation, where a “Marumeriser” is the name for the spheroniser originating from the Japanese word for “pellet,” which appeared on the original Fuji–Paudal patent for their device. When optimized, the process yields a dense and quite spherical product with good integrity. These properties can be tailored via coating, which is amenable to the spherical shape of the granules. E–S is used widely in the manufacture of controlled release pharmaceuticals, polymers, detergents, fertilizers, and herbicides (particularly in water-dispersible granule form). The spheronisation step is often omitted when cylindrical pellets are the desired product form, as in fertilizer and herbicide manufacture where the extrudates can be broken up in a fluidized bed drier to manufacture products with the required size. This chapter focuses on the use of E–S in pharmaceutical granulation and related applications, where the material extruded is a wet powder mass and extrudate diameters are in the range of 500–1500 μm. In practice, the largest particle sizes achievable are ∼5 mm. The free-flowing granules obtained by E–S are used in tabletting or in filling capsules for oral dosage forms. This particular process is favored by the pharmaceutical industry because pellets formed with a small amount of active ingredient show a slower release profile compared to those made by other techniques.

Management of Crude Preheat Trains Subject to Fouling

Crude oil refinery preheat trains are designed to reduce energy consumption, but their operation can be hampered by fouling. Fouling behaviors vary from one refinery to the next. Effective management of preheat train operation requires inspection of historical plant performance data to determine fouling behaviors, and the exploitation of that knowledge in turn to predict future performance. Scenarios of interest can include performance based on current operating conditions, modifications such as heat exchanger retrofits, flow split control, and scheduling of cleaning actions. Historical plant monitoring data are frequently inconsistent and usually need to be subject to data reconciliation. Inadequate data reconciliation results in misleading information on fouling behavior. This article describes an approach to crude preheat train management from data reconciliation to analysis and scenario planning based around a preheat train simulator, smartPM, developed at Cambridge and IHS. The proposed methodology is illustrated through a case study that could be used as a management guideline for preheat train operations.

Experimental investigation of interactions between the temperature field and biofouling in a synthetic treated sewage stream

Biofouling causes significant losses in efficiency in heat exchangers recovering waste heat from treated sewage. The influence of the temperature field on biofouling was investigated using a flat plate heat exchanger which simulated the channels in a plate and frame unit. The test surface was a 316 stainless steel plate, and a solution of Bacillus sp. and Aeromonas sp. was used as a model process liquid. The test cell was operated under co-current, counter-current, and constant wall temperature configurations, which gave different temperature distributions. Biofouling was monitored via changes in heat transfer and biofilm thickness. The effect of uniform temperature on biofouling formation was similar to the effect of uniform temperature on planktonic growth of the organisms. Further results showed that the temperature field, and particularly the wall temperature, influenced the rate of biofouling strongly. The importance of wall temperature suggests that fouling could be mitigated by using different configurations in summer and winter.