Computerized Finite-Difference Method to Calculate Transient Heat Conduction with Thawing

Transient temperature profiles of frozen logs subjected to axisymmetric thawing and heating were calculated by a temperature method and an enthalpy method. The present paper discusses only the temperature method, which uses the conventional (temperature) formulation of the nonlinear heat conduction equation. This approach required the specification of a thawing temperature interval over which the latent heal was incorporated in the specific heat. Thermal properties were varied with position and temperature, and changed discontinuously with the phase. The log surface temperature was specified. The computerized finite-difference program HEAT was used in conjunction with this method. Computed temperature profiles were in overall agreement with experimental data obtained from heating logs in agitated water

INTELLIGENT DISCRIMINATION MODEL TO IDENTIFY INFLUENTIAL PARAMETERS DURING CRYSTALLISATION FOULING

The introduction of redundant independent variables into any function approximation model, or the neglect of important variables, may result in a correlation with poor prediction and reduced reliability. This paper demonstrates that a novel integrated model of neural networks and genetic algorithms can deal with this problem robustly with good accuracy, while be far less time-consuming compared to lengthy conventional models Furthermore, a redundant variable input was imposed to the model to discern if the approach could identify it among other important variables. Genetic algorithms were exploited as a powerful optimisation tool for the selection of best set of inputs with the help of process “prior knowledge” rules. A comprehensive databank of crystallisation fouling under subcooled flow boiling was used. The resulting model was capable of handling the data and successfully discriminated among several independent inputs if there is any redundant input. The technique may be regarded as a robust method to prevent data over-fitting as well as processes where a large number of inputs are involved such as crude oil fouling

Analysis of Fouling Data Based on Prior Knowledge

Conventional regression methods are generally unable to analyse extremely complicated processes involving a considerable number of independent variables with poorly understood interaction. These methods use a defined equation for which the parameters of this equation have to be determined. It is however questionable whether any arbitrarily chosen equation is the best. This study aims to implement the powerful neural network architecture for a comprehensive data bank. The HTRI data bank contains a large and unique set of experimental data for cooling water fouling. Only a selection of the data bank is being used at the present time, due to the large number of independent variables investigated in this experimental study

Enthalpy Method To Compute Radial Heating And Thawing Of Logs

This paper discusses an enthalpy method to compute transient temperatures of logs. The logs may be initially frozen. It is assumed that the logs are subjected to radial heating in agitated water. The method handles phase change at a distinct temperature, which is an advantage over a previous (temperature) method. Calculations for four test logs were performed by a computerized, explicit finite-difference scheme called LOGHEAT. Model and experiment closely agreed with each other. Simplified "by hand" calculations were also satisfactory

Crystallisation Fouling Of Mixed Salts During Convective Heat Transfer And Sub-Cooled Flow Boiling Conditions

The mechanisms of mixed salt crystallisation fouling on heat transfer surfaces have been investigated for convective and sub-cooled flow boiling heat transfer. Effects of various operating parameters such as solution composition and hydrodynamics of the system, on crystallisation fouling of mixtures of calcium sulphate and calcium carbonate have been studied experimentally. The results of the experiments were used to develop a mechanistic model for prediction of fouling resistances. Model predictions were compared with the measured experimental data when calcium sulphate and calcium carbonate form and deposit on the heat transfer surface, simultaneously. Deviations ranging from 6% to 25% were observed which confirm the suitability of the model. Finally, the crystalline samples were analysed using Scanning Electron Microscopy, X-Ray Diffraction and Ion Chromatography techniques. Fractal analysis performed on Scanning Electron Microscopy photographs of the deposits was used to quantify deposit characteristics by introducing the fractal dimension as a new characteristic quantit

Fouling During the Use of Seawater as Coolant - The Development of a ‘User Guide’

ESDU International of London, UK has recently published a ‘User Guide’ on fouling in heat exchange systems using seawater as the coolant. Developed over a period of eighteen months in close collaboration with a team of oil refiners, heat transfer equipment and services suppliers and universities, with valuable input from the power industry, the User Guide is a practical guide to the current state of knowledge relating to fouling in cooling systems using seawater. Its objective is to provide the designer and the operator of both onshore and offshore equipment with a practical source of guidance on the occurrence, the mechanisms and the mitigation of seawater fouling in these systems. ESDU’s collaborative Oil Industry Fouling Working Party was formed in recognition of the huge economic and environmental importance of heat exchanger fouling and the potential benefits that can accrue from better understanding of mitigation strategies. The seawater fouling User Guide is the second in a group, following the development of the Crude Oil Fouling User Guide issued in 2000. Work is now underway on cooling water fouling, The development of the User Guide is discussed in this paper and its technical content is summarize

Heat Exchanger Fouling in Phosphoric Acid Evaporators - Evaluation of Field Data -

Multistage evaporators are frequently used in phosphoric acid plants to increase the concentration of dilute phosphoric acid to 52-55 wt% P2O5. The concentrated phosphoric acid solution is supersaturated with respect to calcium sulfate. As a result, part of the calcium sulfate in the liquor deposits on the heat exchanger tube walls. Since the thermal conductivity of these scales is very low, thin deposits can create a significant resistance to heat transfer. Therefore, regular cleaning of heat exchangers is required, frequently at less than biweekly intervals. As the major costs in modern phosphoric acid plants are the cost of energy, a thorough understanding of the fouling kinetics and of the effects of various operational parameters on the behavior of calcium sulfate is required to improve operation and design of the shell and tube heat exchangers, which are extensively used. In this investigation, a large number of heat exchanger data were collected from shell and tube heat exchangers of the phosphoric acid plant of the Razi Petrochemical Complex (Iran) and the fouling deposits were analyzed with respect to appearance and composition. The overall heat transfer coefficients and fouling resistances were evaluated at different times and a kinetic model for the crystallization fouling was developed. It is shown that the crystallization rate constant obeys an Arrhenius relationship with activation energy of 57 kJ/mol. The predictions of the suggested model are in good agreement with the plant data

EXPERIMENTAL INVESTIGATION OF CRYSTALLIZATION FOULING ON GROOVED STAINLESS STEEL SURFACES DURING CONVECTIVE HEAT TRANSFER

The beneficial aspects of enhanced or extended heat transfer surfaces may be off-set if operated under fouling conditions. In the present paper, preliminary experimental results for crystallization fouling of CaSO4 solutions onto surfaces with different structures are reported. Flat stainless steel plates (50 mm x 59 mm) with \u27V\u27 shaped grooves on the side of fluid flow were used as heat transfer surfaces. Experiments were carried out both under clean and fouling conditions to discern how the same surface structures perform under such circumstances. In addition, the impact of both, the direction of grooves with respect to fluid flow (crossed, longitudinal and mixed flow grooves) and the groove dimensions has also been investigated. Fouling trends are discussed in terms of delay time and fouling rate. Significant differences have been found for the various flow conditions