Ocean Thermal Energy Conversion (OTEC) is a renewable energy technology that has to overcome several key challenges before achieving its ultimate goal of producing baseload power on a commercial scale. The economic challenge of deploying an OTEC plant remains the biggest barrier to implementation. Although small OTEC demonstration plants and recent advances in subsystem technologies have proven OTEC’s technical merits, the process still lacks the crucial operational data required to justify investments in large commercial OTEC plants on the order of 50-100 megawatts of net electrical power (MWe-net). A pre-commercial pilot plant on the order of 5-10 MWe-net is required for an OTEC market to evolve. In addition to the economic challenge,OTEC plants have potential for adverse environmental impacts from redistribution of nutrients and residual chemicals in the discharge plume. Although long-term operational records are not available for commercial sizeOTEC plants, synergistic operational data can be leveraged from the desalination industry to improve the potential for OTEC commercialization. Large capacity desalination plants primarily use membranes or thermal evaporator tubes to transform enormous amounts of seawater into freshwater. Thermal desalination plants in particular possess many of the same technical, economic, and environmental traits as a commercial scale OTEC plant. Substantial long-term economic data and environmental impact results are now widely available since commercial desalination began in the 1950s. Analysis of this data indicates that the evolution of the desalination industry could be akin to the potential future advancement of OTEC. Furthermore, certain scenarios exist where a combined OTEC-desalination plant provides a new opportunity for commercial plants. This paper seeks to utilize operational data from the desalination industry as a progressive approach towards OTEC commercialization.

Throughout recent years, computer based programs have been applied to solve and analyse industrial problems encountered global fields such as automobile design for reduction of CO2-gas, designing wind parks aimed at increasing power output etc. One of these developed programs is Computational Fluid Dynamics (CFD) which numerically solves complex flow behaviour based on computer power. As there is an ongoing expansion of CFD usage in industry, certain issues need to be addressed as they are becoming more frequently encountered. The general demand for the simulation of larger control volumes and more advanced flow processes result in an extensive requirement of computer resources. Moreover, the implementation of commercial CFD codes in small-scaled industrial companies seems to generally be utilised as a black box based on the knowledge of fluid mechanic theory. Increased partnerships between industry and the academic world involving various CFD based design processes generally yield to a verbal communication interface, which is a crucial step in the process given the level of dependency between both sides. Based on these notions, a method for establishing time efficient CFD-models with implementation of volume forces as sink terms in the momentum equation is presented. The internal structure, or parts of the structure, in the simulation domain is removed which reduces the geometrical complexity and along with it, computational demand.  These models are the basis of assessing the benefits of utilizing a numerical based design process in industry in which the CFD code is used as a communication tool for knowledge sharing with counterparts in different fields. / As there is an ongoing expansion of CFD usage in industry, certain issues need to be addressed as they are becoming more frequently encountered. The general demand for the simulation of larger control volumes and more advanced flow processes result in an extensive requirement of computer resources. Moreover, the implementation of commercial CFD codes in small-scaled industrial companies seems to generally be utilised as a black box based on the knowledge of fluid mechanic theory. Increased partnerships between industry and the academic world involving various CFD based design processes generally yield to a verbal communication interface, which is a crucial step in the process given the level of dependency between both sides. Based on these notions, a method for establishing time efficient CFD-models with implementation of volume forces as sink terms in the momentum equation is presented. The internal structure, or parts of the structure, in the simulation domain is removed which reduces the geometrical complexity and along with it, computational demand.  These models are the basis of assessing the benefits of utilizing a numerical based design process in industry in which the CFD code is used as a communication tool for knowledge sharing with counterparts in different fields.

O presente trabalho trata do estudo do modelo computacional, EVSIM, que permite a simulação e caracterização da transferência de calor e massa entre o ar úmido externo e o refrigerante em evaporadores utilizados em sistemas frigoríficos e condicionadores de ar domésticos. O modelo é capaz de levar em conta a distribuição do refrigerante ao longo da serpentina mesmo em circuitos complexos. O desempenho do evaporador é calculado através de uma análise tubo a tubo. Os cálculos em cada tubo são baseados no cômputo da distribuição do ar, da vazão mássica do refrigerante e dos estados termodinâmicos determinados para cada tubo, assim como dos processos de transferência de calor e massa em cada tubo, respectivamente. A principal vantagem do modelo está na análise termodinâmica local, e na consideração dos mecanismos de transferência de calor e equações de estado para diferentes substâncias. Este trabalho acrescenta em relação ao código inicialmente desenvolvido, diferentes correlações de transferência de calor para escoamento bifásico. Os resultados de simulação obtidos são coerentes com resultados experimentais e de razoável confiabilidade. / This work concerns about a study of the computational model, EVSIM, which allows simulating and characterizing the heat and mass transfer between the humid air and the refrigerant in evaporators used in frigorific and domestic air-conditioning systems. The model is able to consider the refrigerant distribution through the coil even in complex geometrical designs. The evaporator thermal performance is calculated through a tube-by-tube analysis. The computation in each tube is based on the air distribution calculation, refrigerant mass flow rate and the thermodynamic states determination for each tube, as well as on the computation of the heat and mass transfer processes, respectively. The main advantage in this model is the ability in performing local thermodynamic analysis, and in the consideration of heat transfer mechanisms and state equations for different substances. This work brings, in relation to the original code, an update on heat transfer correlations for simulating a two-phase flow heat transfer process. The results obtained are coherent with experimental data and show a reasonable accuracy.

O objetivo do trabalho é apresentar o desenvolvimento, simulação e resultados práticos de um Sistema de controle de temperatura, para Experimentos Biomédicos que utilizam soluções aquecidas com vazão variável. O Sistema utiliza um Trocador de Calor projetado para aquecer uma solução que entra no dispositivo a uma temperatura inferior ou igual à do ambiente e sai com o valor programado. A solução é aquecida a partir da água de um reservatório com temperatura controlada. O Controlador de temperatura é do tipo proporcional-integral-derivativo digital e utiliza um microcontrolador para implementação do algoritmo de controle, da aquisição do sinal dos sensores de temperatura, do comando de atuadores e da interface com o usuário / The objective of the work is to present the development, simulation and practical results of a temperature control System for Biomedical Experiments that utilize heated solutions with variable outflow. The System uses a Heat Exchanger designed to heat the solution that enters into device with a lower or the same temperature as the environment and leaves with the programmed value. The Biomedical solution is heated using the Heat Exchanger and water of the reservoir where the temperature is controlled. The digital proportional-integral-derivative temperature Controller takes use of a microcontroller for implementation of the control algorithm, data acquisition of the temperature sensors, command of actuators and user interface

É apresentado um estudo de distribuição do tempo de residência nas etapas de um processo de pasteurização contínuo por trocador de calor a placas (aquecimento, resfriamento, regeneração e retenção). Para o estudo experimental, foi adotada a técnica condutimétrica usando cloreto de sódio em solução aquosa como traçador. Foram verificadas as influências da vazão, da configuração do trocador de calor a placas (número de passes para o arranjo em série) e do tipo de tubo de retenção (tubo em \"S\" e tubo helicoidal). Modelos de distribuição foram usados para representar o comportamento experimental (dispersão axial, tanques em série, laminar modificado, combinado PFR+CSTR). Este estudo foi aplicado para as condições de pasteurização HTST de leite, visando a futura implementação de uma modelagem matemática rigorosa do processo, para otimização do projeto e operação do processo. / It is presented a study of residence time distribution in the steps of a process of continuous pasteurization by plate heat exchanger (heating, cooling, regeneration and holding). For the experimental study, it was adopted a conductimetric technique using sodium chloride in aqueous solution as a tracer. It was also studied the influence of the flow rate, the configuration of the plate heat exchanger (number of passes in series arrangement) and the type of holding tube (\"S\"- shaped tube and helicoidal tube). Distribution models were used for representing the experimental behavior (axial dispersion, tank in series, modified laminar, combined PFR+CSTR). This study was applied for the conditions of HTST pasteurization of milk, targeting the future implementation of a rigorous mathematical modeling of the process, which can be applied for the process operation and optimization of the project design.

O principal objetivo do trabalho foi desenvolver uma ferramenta de simulação, para servir de base para o projeto e dimensionamento de processos contínuos de pasteurização de alimentos líquidos em trocadores de calor a placas, possibilitando minimizar perdas de qualidade sensorial e nutricional, bem como gastos desnecessários com aquecimento e resfriamento, decorrentes do sobreprocessamento, tendo o controle sobre o histórico de temperatura. Foi desenvolvida uma modelagem matemática para o processo contínuo de pasteurização HTST (High Temperature Short Time) de leite em trocador de calor a placas com três seções, para determinação da distribuição de temperatura ao longo do processo e avaliação do impacto sobre o leite. Foram desenvolvidos três modelos e seus resultados confrontados com os dados experimentais, realizados com água e leite. Os três modelos forneceram resultados similares e próximos ao comportamento experimental. O cálculo de letalidade permitiu detectar sobreprocessamento no processo estudado. Ensaios com indicador enzimático (fosfatase alcalina em tampão fosfato) foram realizados para quantificar o impacto do processo sobre o produto e comparar com a letalidade calculada pelos modelos. / The aim of this work was to develop a simulation tool to be used in the design of continuous pasteurization of liquid foods using plate heat exchangers, enabling to minimize the nutritional and sensorial losses as well as unnecessary costs during heating and cooling, caused by the overprocessing. The control is made by the temperature profile. A mathematical model was developed for continuous milk HTST (High Temperature Short Time) pasteurization with a three section plate heat exchanger to determine the temperature profile and to evaluate the process impact on the product. Three models were tested and the simulation results compared with the experimental data using water and milk. The results of the three models were similar among them and close to the experimental behavior. Calculating the lethality of the process showed it was overprocessing the product. Tests using enzymatic indicator (alkaline phosphatase in phosphate buffer) were held to quantify the impact of the process on the product and compare to the lethality calculated using the models.

O processamento térmico contínuo usando trocadores de calor é uma forma muito comum de industrialização de alimentos líquidos. Atrelada à inativação de micro-organismos e enzimas pela alta temperatura, está a perda de qualidade do produto; portanto, o estudo e avaliação deste tipo de processo é fundamental para garantir a inocuidade e a melhora da qualidade do produto. Neste trabalho foi desenvolvida a modelagem matemática de um processo térmico contínuo em trocadores bitubulares para determinação da distribuição da temperatura média do produto e da letalidade sobre um atributo de segurança ou qualidade. No modelo, foram considerados os trocadores de aquecimento e de resfriamento, bem como o tubo de retenção. Admitiu-se regime permanente, escoamento pistonado e leva-se em conta a troca de energia com o ambiente. Para a aplicação do modelo, foi adotado um sistema em escala de laboratório com vazão de processamento entre 10 e 50 L/h, trocadores com quatro módulos de troca térmica e área total de 0,13 m² e sistema de indicação e aquisição de dados de temperatura. Como fluidos de trabalho foram usados: mistura de glicerina/água 80 % (Newtoniano) e solução 1 % de carboxi-metil-celulose (CMC, não-Newtoniano). Fluidos e utilidade foram água quente pressurizada e água gelada. Os parâmetros de troca térmica do modelo foram ajustados com sucesso através de ensaios experimentais. Foram ajustados: 1) coeficientes de convecção natural do ar sobre as seções de aquecimento e de resfriamento; 2) parâmetros da correlação de Nusselt x Reynolds para o coeficiente de convecção dos fluidos de trabalho; 3) coeficiente global de troca térmica com o ambiente no tubo de retenção. A validação do modelo ajustado foi realizada através da comparação das distribuições de temperatura experimental com a predição do modelo. A letalidade, levando em conta o tempo espacial no percurso do produto foi calculada e avaliada, indicando importante contribuição da seção de aquecimento e forte influência da elevação de temperatura na entrada do tubo de retenção para compensar as perdas para o ambiente. O modelo proposto mostra-se útil para a avaliação de processos térmicos em sistemas tubulares. / The continuous thermal processing using heat exchangers is a very usual form of industrialization of liquid foods. Linked to the inactivation of microorganisms and enzymes by high temperature is the loss of product quality; thus, the study and evaluation of this type of process is critical to ensure the safety and improve product quality. In this work, it was developed a mathematical model of a continuous process with tubular heat exchangers to determine the distribution of the average temperature of the product and the lethality considering a safety or quality attribute. In the model, are considered the exchangers for heating and cooling and the holding tube. It was assumed steady state plug-flow and it was taken into account the energy exchange with the ambient air. For the application of the model, it was adopted a laboratory system with processing flow rate between 10 and 50 L/h, exchangers with four heat transfer modules and total area of 0.13 m² and a temperature indication and acquisition system. The working fluids used were: a mixture of glycerol/water 80 % (Newtonian) and a 1 % solution of carboxymethylcellulose (CMC, non-Newtonian). Utility fluids were pressurized hot water and cold water. The heat transfer parameters of the model were adjusted successfully using the experimental data. Were adjusted: 1) the coefficients of natural convection of the air over the heating and cooling sections; 2) the parameters of the Nusselt x Reynolds correlation for the convective coefficient of the working fluid; 3) the overall heat exchange coefficient between the product and the ambient air in the holding tube. The validation of the fitted model was performed by comparing the experimental temperature distributions with the prediction from the model. Lethality, taking into account the space-time in the path of the product was calculated and evaluated, indicating a significant contribution of the heating section and a strong influence on the temperature rise in the entrance of the holding tube to compensate for losses to the surroundings. The model proves useful for the evaluation of thermal processes in tubular systems.

Electromagnetic (EM) heat exchangers are devices that absorb EM radiation and convert its energy to thermal energy for a specific purpose such as to power a turbine. They have recently been of growing interest, yet the field is predominantly studied with thermal resistance network models and is in need of more rigorous continuum modeling. Homogenization has been used in low and high frequency electromagnetics to describe macroscopic behavior of traveling waves. While dielectric material parameters vary with temperature, coupling the energy equation with Maxwell’s equations, little effort has been made toward homogenization techniques that capture the effects of this dependence, which is necessary to accurately model porous medium heat exchangers. Firstly, we have examined the effect the wave-geometry interactions of high-frequency illumination has on a triple-layer laminate, which approximates the unit cell of a homogenization problem. Secondly, we develop an extension to a high-frequency homogenization (HFH) method developed for photonics. The extension is made by developing a three-dimensional vector-valued HFH of Maxwell’s curl-curl equation that includes dielectric loss. It is validated for a one-dimensional geometry where the exact solution to the scattering problem is known by implementing the Transfer Matrix Method. The HFH model produces perturbation approximations to the dispersion curves showing the nonexistence of band gaps and generates low attenuation outside the band gap regions.

Cryogenic carbon capture process can be used to efficiently eliminate CO2 emissions from fossil-fueled power plants. The energy-storing embodiment of cryogenic carbon capture (ES-CCC) integrates energy storage with cryogenic carbon capture and uses natural gas as a refrigerant. ES-CCC captures CO2 from slowly varying or steady-state sources even as it absorbs and replaces large amounts of energy on the grid for energy storage. These large transients occur in the LNG generation as the process moves through energy storing to energy recovery operations. Additionally, raw natural gas often includes CO2 that forms an azeotrope with ethane. Breaking this azeotrope and separating CO2 from other hydrocarbons to meet natural gas pipeline and liquefied natural gas (LNG) standards is very energy intensive. The purpose of this work is to (a) describe a dynamic heat exchanger that reduces the heat exchanger performance and efficiency losses experienced under transient conditions and (b) introduce an alternative extractive distillation system for CO2 separation from ethane that requires less capital and has a lower operating cost than the conventional system for the same purification. This investigation demonstrates theoretically and experimentally that the dynamic heat exchangers can absorb sudden and large changes in flow rates and other properties without compromising either the heat exchanger efficiency or creating thermal or other stresses. These heat exchangers play an essential role in the ES-CCC process. Designs for retrofitting existing heat exchangers and for replacing existing heat exchangers with new designs are both theoretically and experimentally tested. The ES-CCC process requires natural gas processing to meet pipeline and LNG standards in many applications, depending primarily on the CO2 content of locally available NG. The energy, cost, and dynamic response of such processing hinges primarily on the most difficult step, breaking the CO2-ethane azeotrope. This project proposes and analyzes an alternative process for breaking this azeotrope and a control scheme that dramatically improves the dynamic response of natural gas processing plants, including steady and transient control scheme and processing simulations. These contributions to the ES-CCC capture process all have much broader applications in many chemical and energy processes. These contributions to ES-CCC and other industrial processes improve energy efficiency and dynamic performance of many processes and are ready for larger scale demonstration.

Transport Membrane Condenser (TMC) is an innovative technology based on the property of a nano-scale porous material which can extract both waste heat and water from exhaust gases. This technology tremendously improves the efficiency of boilers and gas/coal combustors by lowering waste heat and increasing water recovery. Contaminants in the flue gases, such as CO2, O2, NOx, and SO2 are inhibited from passing through the membrane by the membrane’s high selectivity. The condensed water through these tubes is highly pure and can be used as the makeup water for many industrial applications. The goal of this research is to investigate the heat transfer, condensation rate, pressure drop and overall performance of crossflow heat exchangers. In this research, a numerical model has been developed to predict condensation of water vapor over and inside of nano-porous layers. Both capillary condensation inside the nanoscale porous structure of the TMC and the surface condensation were considered in the proposed method using a semi-empirical model. The transport of the water vapor and the latent heat of condensation were applied in the numerical model using the pertinent mass, momentum, turbulence and energy equations. By using the proposed model and simulation procedure, the effect of various inlet parameters such as inlet mass flow rate, inlet temperature, and water vapor content of the inlet flow on the performance of the cross-flow TMC heat exchanger was studied to obtain the optimum performance of the heat exchangers at different working conditions. The performance of the TMC heat exchangers for inlet flue gas rate 40 to 120 kg/h, inlet water rate 60 to 140 kg/h, inlet flue gas relative humidity 20 to 90%, and tube pitch ratio 0.25 to 2.25 has been studied. The obtained results show that the water condensation flux continuously increases with the increase of the inlet flue-gas flow rate, water flow rate, and the flue-gas humidity. The total heat flux also follows the same trend due to the pronounced effect of the latent heat transfer from the condensation process. The water condensation flux and the overall heat transfer increase at the beginning for small values of the tube pitches and then decreases as the tube pitch increases furthermore. In addition to the cross-flow TMC heat exchangers, the performance of a shell and tube TMC heat exchanger for high pressure and temperature oxy-combustion applications has been investigated. The performance analysis for a 6-heat exchanger TMC unit shows that heat transfer of the 2-stage TMC unit is higher than the 2-stage with the same number of the heat exchanger in each unit.