No description available.

No description available.

The convective fluid-to-particle heat transfer coefficient (hfp ) is one of the critical factors influencing the process design for multi phase food products, in continuous tubeflow systems. Determination of hfp associated with moving particles poses a unique challenge to investigators because of the difficulty in monitoring the temperature of moving particles without interfering with the particle motion. Two different techniques involving particle motion were developed to evaluate hfp and to study the effects of factors influencing hfp, associated with spherical particles under tube-flow conditions. / Spherical Nylon particles with centrally located fine-wire flexible thermocouples, were suspended from the upper mid-section of a curved glass tube in order to provide lateral movement of the particle as the tube was subjected to oscillatory motion. / A full factorial experimental design was studied involving spherical particles made of Aluminum epoxy and Nylon of different diameters (12.7 to 17.5 mm), particle linear velocities (0.06 to 0.21 m/s), heating medium viscosities (0 to 1% Carboxymethyl cellulose, CMC) and fluid temperatures (60 to 80°C). The above factors had a significant (p < 0.001) effect on hfp. Depending on experimental conditions the values of h fp varied from 350 to 2000 W/m2K. Overall, hfp values associated with the aluminum epoxy particle were about 30% higher than that for the Nylon particle. / A calorimetric method was developed to evaluate hfp associated with a freely moving particle. / The calorimetric method was used to evaluate the effect of fluid flow rate, viscosity and temperature, as well as particle size on the associated hfp under tube-flow conditions. Experiments were carried out using different flow rates (9 to 19 L/min), fluid viscosity (0 to 1% CMC solution) and fluid temperature (50 to 70°C) as well as Aluminum spherical particles of different sizes (19 to 25.4 mm). Values of hfp varied from 650 to 2660 W/m2K, and increased significantly (p < 0.001) with an increase in fluid flow rate and particle size, whereas a decrease was observed with CMC concentration and temperature. / Several correlations were developed in the form of Nusselt number as a function of other influencing dimensionless numbers. Nusselt numbers estimated from the developed equations showed good agreement with the experimental data (0.88 < R2 < 0.99). (Abstract shortened by UMI.)

No description available.

No description available.

Bibliography: leaves 290-303 / xxi, 303 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemical Engineering, 1993?

Doctor of Philosophy / The main contribution of this work is to answer several important questions relating to natural draft wet cooling tower (NDWCT) modelling, design and optimisation. Specifically, the work aims to conduct a detailed analysis of the heat and mass transfer processes in a NDWCT, to determine how significant the radial non-uniformity of heat and mass transfer across a NDWCT is, what the underlying causes of the non-uniformity are and how these influence tower performance. Secondly, the work aims to determine what are the consequences of this non-uniformity for the traditional one dimensional design methods, which neglect any two-dimensional air flow or heat transfer effects. Finally, in the context of radial non-uniformity of heat and mass transfer, this work aims to determine the optimal arrangement of fill depth and water distribution across a NDWCT and to quantify the improvement in tower performance using this non-uniform distribution. To this end, an axisymmetric numerical model of a NDWCT has been developed. A study was conducted testing the influence of key design and operating parameters. The results show that in most cases the air flow is quite uniform across the tower due to the significant flow restriction through the fill and spray zone regions. There can be considerable radial non-uniformity of heat transfer and water outlet temperature in spite of this. This is largely due to the cooling load in the rain zone and the radial air flow there. High radial non-uniformity of heat transfer can be expected when the cooling load in the rain zone is high. Such a situation can arise with small droplet sizes, low fill depths, high water flow rates. The results show that the effect of tower inlet height on radial non-uniformity is surprisingly very small. Of the parameters considered the water mass flow rate and droplet size and droplet distribution in the rain zone have the most influence on radial noniv uniformity of heat transfer. The predictions of the axisymmetric numerical model have been compared with a one dimensional NDWCT model. The difference between the predictions of tower cooling range is very low, generally around 1-2%. This extraordinarily close comparison supports the assumptions of one dimensional flow and bulk averaged heat transfer implicit in these models. Under the range of parameters tested here the difference between the CFD models predictions and those of the one dimensional models remained fairly constant suggesting that there is no particular area where the flow/heat transfer becomes so skewed or non-uniform that the one dimensional model predictions begin to fail. An extended one dimensional model, with semi-two dimensional capability, has been developed for use with an evolutionary optimisation algorithm. The two dimensional characteristics are represented through a radial profile of the air enthalpy at the fill inlet which has been derived from the CFD results. The resulting optimal shape redistributes the fill volume from the tower centre to the outer regions near the tower inlet. The water flow rate is also increased here as expected, to balance the cooling load across the tower, making use of the cooler air near the inlet. The improvement has been shown to be very small however. The work demonstrates that, contrary to common belief, the potential improvement from multi-dimensional optimisation is actually quite small.

Doctor of Philosophy / The main contribution of this work is to answer several important questions relating to natural draft wet cooling tower (NDWCT) modelling, design and optimisation. Specifically, the work aims to conduct a detailed analysis of the heat and mass transfer processes in a NDWCT, to determine how significant the radial non-uniformity of heat and mass transfer across a NDWCT is, what the underlying causes of the non-uniformity are and how these influence tower performance. Secondly, the work aims to determine what are the consequences of this non-uniformity for the traditional one dimensional design methods, which neglect any two-dimensional air flow or heat transfer effects. Finally, in the context of radial non-uniformity of heat and mass transfer, this work aims to determine the optimal arrangement of fill depth and water distribution across a NDWCT and to quantify the improvement in tower performance using this non-uniform distribution. To this end, an axisymmetric numerical model of a NDWCT has been developed. A study was conducted testing the influence of key design and operating parameters. The results show that in most cases the air flow is quite uniform across the tower due to the significant flow restriction through the fill and spray zone regions. There can be considerable radial non-uniformity of heat transfer and water outlet temperature in spite of this. This is largely due to the cooling load in the rain zone and the radial air flow there. High radial non-uniformity of heat transfer can be expected when the cooling load in the rain zone is high. Such a situation can arise with small droplet sizes, low fill depths, high water flow rates. The results show that the effect of tower inlet height on radial non-uniformity is surprisingly very small. Of the parameters considered the water mass flow rate and droplet size and droplet distribution in the rain zone have the most influence on radial noniv uniformity of heat transfer. The predictions of the axisymmetric numerical model have been compared with a one dimensional NDWCT model. The difference between the predictions of tower cooling range is very low, generally around 1-2%. This extraordinarily close comparison supports the assumptions of one dimensional flow and bulk averaged heat transfer implicit in these models. Under the range of parameters tested here the difference between the CFD models predictions and those of the one dimensional models remained fairly constant suggesting that there is no particular area where the flow/heat transfer becomes so skewed or non-uniform that the one dimensional model predictions begin to fail. An extended one dimensional model, with semi-two dimensional capability, has been developed for use with an evolutionary optimisation algorithm. The two dimensional characteristics are represented through a radial profile of the air enthalpy at the fill inlet which has been derived from the CFD results. The resulting optimal shape redistributes the fill volume from the tower centre to the outer regions near the tower inlet. The water flow rate is also increased here as expected, to balance the cooling load across the tower, making use of the cooler air near the inlet. The improvement has been shown to be very small however. The work demonstrates that, contrary to common belief, the potential improvement from multi-dimensional optimisation is actually quite small.

Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Co-Chair: Ahrens, Fred; Committee Co-Chair: Patterson, Tim; Committee Member: Aidun, Cyrus; Committee Member: Empie, Jeff; Committee Member: Frederick, Jim.

Thesis (M. S.)--Nuclear Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Abdel-Khalik, Said; Committee Co-Chair: Yoda, Minami; Committee Member: Ghiaasiaan, S. Mostafa. Part of the SMARTech Electronic Thesis and Dissertation Collection.