In this thesis, several possible liquid desiccants (aqueous solutions of LiCl, LiBr, MgCl2 and CaCl2) are investigated to find the most appropriate working fluid to be used in a run-around membrane energy exchanger (RAMEE). The liquid desiccant is one of the main components of the RAMEE and indirectly conditions the outdoor ventilation air by using the energy of the exhaust air, significantly reducing the building energy consumption.<p> Numerical simulations, in this thesis, show that the total effectiveness of the RAMEE changes less than 0.5% when different salt solutions are used. However, the capital and operational costs of the RAMEE are significantly different for different desiccants. MgCl2 is the most inexpensive among the selected salt solutions and is followed by CaCl2, LiBr and LiCl. The price of a LiCl solution in the RAMEE is almost 20 times more than the price of MgCl2 solution. Different thermo-physical properties of the salt solutions result in different pumping energy consumptions for each specific salt solution. For example, the pumping energy consumption for a MgCl2 solution is 3.5 times more than for a LiBr solution in the RAMEE. The change in the volume of the liquid desiccant throughout a year is another characteristic which depends on the thermo-physical properties of the salt solution. Solutions with larger volume expansion require larger storage tanks and will experience longer transient delays. The difference between the volume expansions of different salt solutions is less than 5% of the total solution volume. MgCl2 solution expands more than 17% throughout a yearly operation of the system in Saskatoon.<p> Crystallization of the salt solution is another important parameter in the selection of the liquid desiccant. Simulations show that, for a specific indoor and outdoor operating condition the risk of crystallization is greatest for MgCl2, followed by CaCl2, LiCl and LiBr. The risk increases as the supply or exhaust airstreams become dryer. For a cross flow RAMEE with a total effectiveness of 55% (NTU=10 and Cr*=3) operating in a building with indoor RH of 50%, the critical outdoor humidity below which crystallization will begin to occur is 28% RH for MgCl2, 20% for CaCl2 and 0%RH for LiCl and LiBr. According to the simulations, all four investigated salt solutions can be used in North America (except the states of Nevada, Arizona, New Mexico and parts of Texas) with no risk of crystallization when the indoor humidity is 50% RH. However, with indoor humidity of 30% MgCl2 and CaCl2 solutions will have risk of crystallization for a large number of hours in a year in most of the central western United States. A mixture of 50% LiCl and 50% MgCl2 solution is suggested to be used when the cost-effective MgCl2 solution cannot be used due to crystallization issues. The price of this newly suggested mixture is 30% less than that of a pure LiCl solution and can be used in all North American climates with very small risk of crystallization.

In this thesis, several possible liquid desiccants (aqueous solutions of LiCl, LiBr, MgCl2 and CaCl2) are investigated to find the most appropriate working fluid to be used in a run-around membrane energy exchanger (RAMEE). The liquid desiccant is one of the main components of the RAMEE and indirectly conditions the outdoor ventilation air by using the energy of the exhaust air, significantly reducing the building energy consumption.<p> Numerical simulations, in this thesis, show that the total effectiveness of the RAMEE changes less than 0.5% when different salt solutions are used. However, the capital and operational costs of the RAMEE are significantly different for different desiccants. MgCl2 is the most inexpensive among the selected salt solutions and is followed by CaCl2, LiBr and LiCl. The price of a LiCl solution in the RAMEE is almost 20 times more than the price of MgCl2 solution. Different thermo-physical properties of the salt solutions result in different pumping energy consumptions for each specific salt solution. For example, the pumping energy consumption for a MgCl2 solution is 3.5 times more than for a LiBr solution in the RAMEE. The change in the volume of the liquid desiccant throughout a year is another characteristic which depends on the thermo-physical properties of the salt solution. Solutions with larger volume expansion require larger storage tanks and will experience longer transient delays. The difference between the volume expansions of different salt solutions is less than 5% of the total solution volume. MgCl2 solution expands more than 17% throughout a yearly operation of the system in Saskatoon.<p> Crystallization of the salt solution is another important parameter in the selection of the liquid desiccant. Simulations show that, for a specific indoor and outdoor operating condition the risk of crystallization is greatest for MgCl2, followed by CaCl2, LiCl and LiBr. The risk increases as the supply or exhaust airstreams become dryer. For a cross flow RAMEE with a total effectiveness of 55% (NTU=10 and Cr*=3) operating in a building with indoor RH of 50%, the critical outdoor humidity below which crystallization will begin to occur is 28% RH for MgCl2, 20% for CaCl2 and 0%RH for LiCl and LiBr. According to the simulations, all four investigated salt solutions can be used in North America (except the states of Nevada, Arizona, New Mexico and parts of Texas) with no risk of crystallization when the indoor humidity is 50% RH. However, with indoor humidity of 30% MgCl2 and CaCl2 solutions will have risk of crystallization for a large number of hours in a year in most of the central western United States. A mixture of 50% LiCl and 50% MgCl2 solution is suggested to be used when the cost-effective MgCl2 solution cannot be used due to crystallization issues. The price of this newly suggested mixture is 30% less than that of a pure LiCl solution and can be used in all North American climates with very small risk of crystallization.

Proefschrift (doctoral)--Technische Universiteit Eindhoven, 1990. / Includes bibliographical references (p. 265-275).

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 205-216).

Thesis (M.S.)--California Polytechnic State University, 2009. / Title from PDF title page; viewed on December 17, 2009. Major professor: Jesse Maddren, Ph.D. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Mechanical Engineering." "2009." Includes bibliographical references. Also available on microfiche.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

No description available.

Determination of the heat transfer coefficients for natural and mixed convection in horizontal annuli is important for designing double pipe heat exchangers and for energy storage systems. In part one and two of this study, the 2D numerical solution of the laminar natural convection of water in six internally finned horizontal annuli has been obtained. The fins are attached to the external surface of the inner cylinder. Only the symmetrical half of the horizontal annulus with three equally spaced longitudinal divergent solid and porous fins are considered. The parameters of the problem are Rayleigh number, fin height, permeability and porosity of the porous fin, etc. The above parameters are suitably varied to ascertain their effects on fluid flow and heat transfer. The results show that traditional solid fins provide much higher heat transfer rates compared to the porous fins. Part three of this work deals with mixed convective heat transfer (laminar natural and forced convections) of water in a vented annulus. The forced flow conditions are imposed by providing an inlet at the top and an outlet at the bottom. For various parameters of the problem, the average and local Nusselt numbers along the inner cylinder are calculated for water for both aiding and opposing flows. The fourth part of this study deals with numerical modeling of natural convection of nanofluids in a horizontal cylindrical annulus. Simulations are carried out for Cu-water nanofluids. The results, in general, show that nanoparticles systematically decrease the natural convective heat transfer coefficient on the inner cylinder. Practical and useful correlations are provided for calculating average heat transfer rates from the inner cylinder in the form of average equivalent thermal conductivity and average Nusselt number for all of the four cases discussed above. These correlations are new and will be helpful in designing heat exchangers.

No description available.

Heat exchanger fouling is the deposition of material onto the heat transfer surface causing a reduction in thermal efficiency. A study using Computational Fluid Dynamics (CFD) was conducted to increase understanding of key aspects of fouling in desalination processes. Fouling is a complex phenomenon and therefore this numerical model was developed in stages. Each stage required a critical assessment of each fouling process in order to design physical models to describe the process???s intricate kinetic and thermodynamic behaviour. The completed physical models were incorporated into the simulations through employing extra transport equations, and coding additional subroutines depicting the behaviour of the aqueous phase involved in the fouling phenomena prominent in crystalline streams. The research objectives of creating a CFD model to predict fouling behaviour and assess the influence of key operating parameters were achieved. The completed model of the key crystallisation fouling processes monitors the temporal variation of the fouling resistance. The fouling rates predicted from these results revealed that the numerical model satisfactorily reproduced the phenomenon observed experimentally. Inspection of the CFD results at a local level indicated that the interface temperature was the most influential operating parameter. The research also examined the likelihood that the crystallisation and particulate fouling mechanisms coexist. It was found that the distribution of velocity increased the likelihood of the particulate phase forming within the boundary layer, thus emphasizing the importance of differentiating between behaviour within the bulk and the boundary layer. These numerical results also implied that the probability of this composite fouling was greater in turbulent flow. Finally, supersaturation was confirmed as the key parameter when precipitation occurred within the bulk/boundary layer. This investigation demonstrated the advantages of using CFD to assess heat exchanger fouling. It produced additional physical models which when incorporated into the CFD code adequately modeled key aspects of the crystallisation and particulate fouling mechanisms. These innovative modelling ideas should encourage extensive use of CFD in future fouling investigations. It is recommended that further work include detailed experimental data to assist in defining the key kinetic and thermodynamic parameters to extend the scope of the required physical models.