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Dive into the research topics where Alasdair N. Campbell is active.

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Featured researches published by Alasdair N. Campbell.


Physical Chemistry Chemical Physics | 2008

Effects of natural convection on thermal explosion in a closed vessel

Ting-Yueh Liu; Alasdair N. Campbell; Silvana S. S. Cardoso; A.N. Hayhurst

A new way of ascertaining whether or not a reacting mixture will explode uses just three timescales: that for chemical reaction to heat up the fluid containing the reactants and products, the timescale for heat conduction out of the reactor, and the timescale for natural convection in the fluid. This approach is developed for an nth order chemical reaction, A --> B occurring exothermically in a spherical, batch reactor without significant consumption of A. The three timescales are expressed in terms of the physical and chemical parameters of the system. Numerical simulations are performed for laminar natural convection occurring; also, a theoretical relation is developed for turbulent flow. These theoretical and numerical results agree well with previous experimental measurements for the decomposition of azomethane in the gas phase. The new theory developed here is compared with Frank-Kamenetskiis classical criterion for explosion. This new treatment has the advantage of separating the two effects inhibiting explosion, viz. heat removal by thermal conduction and by natural convection. Also, the approach is easily generalised to more complex reactions and flow systems.


Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering Sciences | 2005

A scaling analysis of Sal'nikov's reaction, P/A/ B, in the presence of natural convection and the diffusion of heat and matter

Alasdair N. Campbell; Silvana S. S. Cardoso; A.N. Hayhurst

Salnikovs chemical reaction is very simple; it consists of two consecutive first-order steps, producing a product B from a precursor P via an active intermediate A, in P→A→B. The first step is assumed to be thermoneutral, with zero activation energy, while the second step is exothermic and has a positive activation energy. These properties make this mechanism one of the simplest to display thermokinetic oscillations, as seen in cool flames. We consider a pure gas, P, undergoing Salnikovs reaction in a closed spherical vessel, whose walls are held at a constant temperature. Natural convection becomes significant once the temperature is high enough for the Rayleigh number to reach approximately 103. The subsequent behaviour of the system depends on the interaction between convection, diffusion of heat and mass, and chemical kinetics. By examining the governing equations, we develop and evaluate scales for the characteristic velocity, concentration of the intermediate A and the temperature rise during the progress of the reaction. These scales depend on the characteristic time-scales for the interacting phenomena of chemical reaction, diffusion and natural convection. Our theoretical predictions are verified by full numerical simulation for the two limiting cases when transport is dominated, respectively, by diffusion and natural convection.


Journal of Fluid Mechanics | 2010

Turbulent plumes with internal generation of buoyancy by chemical reaction

Alasdair N. Campbell; Silvana S. S. Cardoso

Turbulent plumes, which are seen in a wide number of industrial and natural flows, have been extensively studied; however, very little attention has been paid to plumes which have an internal mechanism for changing buoyancy. Such plumes arise in e.g. industrial chimneys, where species can react and change the density of the plume material. These plumes with chemical reaction are the focus of this study. An integral model describing the behaviour of a plume undergoing a second-order chemical reaction between a component in the plume (A) and a component in the surrounding fluid (B), which alters the buoyancy flux, is considered. The behaviour of a reactive plume is shown to depend on four dimensionless groups: the volume and momentum fluxes at the source, the parameter e which indicates the additional buoyancy flux generated by the reaction and γ which is a dimensionless rate of depletion of species B. Additionally, approximate analytical solutions are sought for a reactive plume rising from a point source of buoyancy when species B is in great excess. These analytical results show excellent agreement with numerical simulations. It is also shown that the behaviour of a reactive plume in the far field is equivalent to an inert plume issuing from a virtual source downstream of the real source, and the dependence of the location of the virtual source on e and γ is discussed. The effects of varying the volume flux at the source and the Morton source parameter Γ 0 are further investigated by solving the full governing equations numerically. These solutions indicate that e is important in determining the buoyancy generated by the reaction, and the length scale over which this reaction occurs depends on γ when γ > 1. It is also shown that when the dimensionless buoyancy e < - 1, the reaction can cause the plume to collapse.


Physical Chemistry Chemical Physics | 2006

The behaviour of Sal’nikov’s reaction, P → A → B, in a spherical batch reactor with the diffusion of heat and matter

Alasdair N. Campbell; Silvana S. S. Cardoso; A.N. Hayhurst

The behaviour of a simple chemical reaction, occurring with the release of heat in a closed batch reactor, is considered for the situation when matter and heat are transported only by diffusive processes; thus, the reacting fluid has negligible velocity, so that heat transfer is by thermal conduction. The reaction is Salnikovs, which consists of two, consecutive first-order steps, producing a product B, from a precursor P, via an active intermediate A, in P --> A --> B. The first of these steps is assumed to be thermoneutral, with zero activation energy, whilst the second is exothermic, with an appreciable activation energy. These features make Salnikovs reaction the simplest to display thermokinetic oscillations that characterise many, more complex schemes, e.g. cool flames in hydrocarbon combustion. This study involves identifying the regions of parameter space, in which these oscillations in the temperature and the concentration of the intermediate A occur, by means of numerical simulation. These regions are compared with previous analytical stability analyses in one-dimensional systems. It was found that oscillations occur over a much larger range of conditions in the case considered here, i.e. a reactor with spherical symmetry, than in the simple 1-D case, previously studied by Gray and Scott (P. Gray and S. K. Scott, Chemical Oscillations and Instabilities, Clarendon Press, Oxford, 1990, pp. 264-291). In addition, approximate analytical solutions for the temperature and concentration of A are presented for two limiting cases of non-oscillatory behaviour. These analytical solutions have been verified by comparison with full numerical solutions of the governing equations.


Heat Transfer Engineering | 2018

Measuring the Overall Volumetric Heat Transfer Coefficient in a Vapor-Liquid–Liquid Three-Phase Direct Contact Heat Exchanger

Hameed B. Mahood; Alasdair N. Campbell; Rex B. Thorpe; Adel O. Sharif

ABSTRACT An experimental investigation of the volumetric heat transfer coefficient in a three-phase direct contact condenser was carried out. A 75-cm-long cylindrical Perspex column with a 4 cm diameter was used. Only 48 cm of the column was utilised as the active direct contact condensation height. Pentane vapor at three different initial temperatures (40°C, 43.5°C, and 47.5°C), with differing mass flow rates, and tap water at a constant initial temperature (19°C) with five different mass flow rates were employed as the dispersed phase and the continuous phases, respectively. The results showed that the volumetric heat transfer coefficient increased with increasing mass flow rate ratio (variable dispersed phase mass flow rate per constant continuous phase mass flow rate), the continuous phase mass flow rate and holdup ratio. An optimal value of the continuous phase mass flow rate is shown for an individual dispersed phase mass flow rates. This value increases with increasing vapor (dispersed) phase mass flow rate. Furthermore, it was observed that the initial driving temperature difference had no effect on the volumetric heat transfer coefficient. While, the temperature gained by the continuous phase has a considerable effect.


Archive | 2017

Modelling of the Thermal Performance of SGSP using COMSOL Multiphysics

Argyrios Anagnostopoulos; Alasdair N. Campbell; Harvey Arellano-Garcia

Novel renewable energy sources are necessary to counter the current environmental crisis. The largest source of renewable energy is the sun. One possible application of solar energy is the harvesting and storage of low temperature thermal heat (< 100°C). A very promising technology that can harvest and store thermal energy is a solar pond. To assess the thermal performance of a solar pond, more accurate and reliable theoretical models need to be developed. The preponderance of models use empirical relationships with little justification. This work examines an existing 1D theoretical model and develops and validates a novel theoretical model in COMSOL Multiphysics in both 2- and 3-D. nThe new models were compared with experimental data from two different test sites, concerning mainly the temperature at the lower convective zone (LCZ) and the upper convective zone (UCZ). The 3D model was proven to be the most accurate with the 1D model being the least. Furthermore, the general radiative heat transfer equation, with an isotropic scattering phase function, solved using the discrete ordinates method was proven to give a satisfactory accuracy in terms of radiation in semi-transparent media.


Chemical Engineering Science | 2007

A comparison of measured temperatures with those calculated numerically and analytically for an exothermic chemical reaction inside a spherical batch reactor with natural convection

Alasdair N. Campbell; Silvana S. S. Cardoso; A.N. Hayhurst


Solar Energy | 2016

New theoretical modelling of heat transfer in solar ponds

Assad H. Sayer; Hazim Al-Hussaini; Alasdair N. Campbell


Combustion and Flame | 2010

On the occurrence of thermal explosion in a reacting gas: The effects of natural convection and consumption of reactant

Ting-Yueh Liu; Alasdair N. Campbell; A.N. Hayhurst; Silvana S. S. Cardoso


Energy Conversion and Management | 2015

Heat transfer efficiency and capital cost evaluation of a three-phase direct contact heat exchanger for the utilisation of low-grade energy sources

Hameed B. Mahood; Alasdair N. Campbell; Rex B. Thorpe; Adel O. Sharif

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