Howard Cawte

Aspects of an expert design system for the wastewater treatment industry

A new computer aided design program has been created, which uses computer modelling and simulation techniques in order to automatically generate a design solution for a High Recirculation Airlift Reactor (HRAR) wastewater treatment plant. This program replaces a set of programs which could only be used by process design experts, as many decisions had to be made whilst using the design system. A new expert system is being created to automatically integrate expert knowledge into the design process. This expert system will sit above the design program and control the design process. The objective of the new work presented here was to investigate methods for implementing this new expert system onto the new design program. This consisted of creating prototype software in order to demonstrate the advantages of applying expert systems methods to the design of the HRAR treatment process. This paper introduces the approach taken to acquiring and formulating the expert knowledge, and presents simple software to demonstrate the approach.

Effect of lubricating oil contamination on evaporation in refrigerants R12 and R22

An investigation has been made into the effect of oil concentration on evaporation heat transfer coefficients in refrigerant-oil mixtures flowing in a horizontal tube. A new correlation is presented for heat transfer coefficients in convective evaporation of refrigerant-oil mixtures that predicts the results of the present study within approximately ±20%. The paper reports measurements of evaporation heat transfer coefficients in refrigerants R12 and R22, both oil-free and with two concentrations of Shell Clavus 32 oil. A 1·8 m long ⅜ in O/D copper tube (8·05 mm I/D) was used, at evaporation temperatures of −5°C, 0°C and +5°C. Heat flux and mixture mass velocity were kept constant at 2500 W m−2 and 155 kg m−2 s−1, respectively, and measured coefficients were in the range of 1400 to 3900 W m−2 K−1. The results showed that, for a complete evaporator, 2% oil may be expected to increase the heat transfer coefficient by 12%, but 10% oil returns the coefficient to oil-free values.

Simulation of a high recirculation airlift reactor for steady-state operation

This paper describes a new mathematical model of the fluid dynamic processes in a high recirculation airlift reactor. The model was created to provide information to assist in the design of a reactor, in particular considering the selection of parameters to adjust in order to achieve a steady state solution. The modelling of two phase-flow of air and water in small scale airlift bio-reactors is considered. This modelling was applied to the high recirculation airlift reactor process. A new computer simulation was created and a test program performed to evaluate the models used. The results of this evaluation are presented. The evaluation showed that variation of the superficial gas velocity or the simultaneous variation of the downcomer and riser diameters could be used to produce a steady-state design solution.

Computer modelling of single sludge systems for the computer aided design and control of activated sludge processes

The initial work for the creation of a new automatic CAD system for advanced effluent treatment processes is presented. The creation of a computer model for a completely mixed aerator is described. The computer model consisted of two interacting non-linear differential equations, which were linearised to give an approximate computer model. Optimal control theory was applied to the design of a controller for this system and a series of experiments examined the system performance using both the new computer model and the new controller.

Computer assistance for a disabled user/operator to navigate a vehicle through a doorway

A real time method of computer assistance for a disabled user/operator to move a vehicle through a doorway is presented. An electric wheelchair is used as an example vehicle. Automatic programming, motion planning, obstacle avoidance, sensor integration, and control methods are presented which assist a user/operator in controlling the wheelchair. Electric wheelchairs are generally directed along a path using manual controls, usually a joystick connected to switches. In the work described in this paper, data from ultrasonic sensors and other sensors is processed and combined with the information from these switches. The output is used to assist the user/operator in steering the vehicle. A veto is always left with the operator.<<ETX>>