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This study presents an optimization approach to heat exchanger network synthesis (HENS). HENs are widely used in industry and bring several fluid streams into their desired temperatures by using available heat in the process for efficient usage of energy. Our aim is to provide a network design coupled with a detailed equipment design for heat exchangers. The suggested approach involves discretization of temperatures based on heat load equalities and reformulation as a shortest-path problem, rather than dealing with a nonlinear model and a previously structured HEN, which are common methods in the literature. We generate a shortest path network whose every node corresponds to a heat exchanger alternative and each path represents a HEN design alternative. A mixed-integer nonlinear programming model is solved to design each exchanger alternative in detail, considering all thermo-physical and transport properties of streams at their temperatures and pressures. Our approach has modeling flexibility and successfully finds the required number of heat exchangers and their connections. In addition, one can control the solution quality by deciding on the heat load steps between stream inlet and outlets. Several HEN examples from the literature are solved to assess the performance of our approach and comparable results are obtained.

In this masters thesis are discusses the possibilities of increasing the electrical efficiency of cogeneration units with an internal combustion engine with the power output 800 kWe. Technical and economical aspect the connection with steam turbine, steam engine and ORC turbine is compared. It include the design of heat exchanger for ORC cycle.

The aim of the thesis is to design a heat exchanger for heating natural gas in the mining process and subsequent treatment. The first part describes natural gas itself, its origin, mining and ways of treatment. There are described technologies used for finding the deposits itself or processes by which water, sulfur and solid particles are removed from the extracted gas. The next section deals with the types of heat exchangers most commonly used in industry. There are also described basic relations for heat-hydraulic calculation of heat exchanger. In the practical part the heat exchanger itself was designed. World-wide HTRI software was used for the heat-hydraulic calculation and for strength calculation according to the standard ČSN EN 13445 was used sofware Sant´ Ambrogio.

<p>Rising interest in high-performance servers in data centers to support the increasing demands for cloud-computing and storage have challenged thermal management systems. To prevent these increased power density servers from overheating due to the high heat fluxes dissipated, new cooling methods have continued to be investigated in recent years. One such solution is pumped two-phase cooling which shows promise over traditional air cooling due to the reduced power consumption it requires to operate, while also being able to dissipate large amounts of heat from the small components in servers.</p> <p>    </p> <p>Although pumped two-phase systems as a cooling strategy have existed for multiple decades, sub-optimal component design have hindered the potential efficiencies achievable. This is especially prevalent in the condenser where, in order to meet required metrics, these heat exchangers are commonly oversized due to maldistribution at low vapor qualities and a lack of understanding about the condensation behavior within certain geometries.</p> <p><br></p> <p>Through the work presented in this thesis, the capabilities of an air-cooled microchannel condenser model are explored for future use in optimization studies for data center applications. To perform this research, an investigation into the boundary conditions of these systems and common condenser modeling strategies were carried out. Using this knowledge, a flexible discretized condenser model was developed to capture the behavior of pumped two-phase cooling in data centers under a wide range of operating conditions. In conjunction, an experimental test setup was sized, designed, and constructed to provide validation for the model. Then, using the model, some initial parametric studies were conducted to identify the sensitivity effects of various parameters on overall condenser performance. In this initial study, some favored boundary conditions and geometries were found that both minimize refrigerant pressure drops and maximize heat transfer. For an air-cooled condenser operating with R1234ze(E), these include: refrigerant entering the condenser around 40% quality, operating at moderate refrigerant mass fluxes through the channels (130 - 460 kg/m^2-s), and designing microchannel condenser tubes with many tightly packed square ports. Continued investigation into the contributing parameters of weight in the future using the tools developed in this thesis will lead to further optimized condenser designs and operating conditions.</p>

The master's thesis deals with district heat exchangers in a thermal steam cycle of combined heat and power plants and with types of condensate cascades in the multilevel heating systems. Calculation of the thermal efficiency of electricity generation is provided for the investigated thermal cycle, which was modified for three different types of cascades. Besides that, a comparison of useful electric power and electricity generation through one year period of working is made. A significant part of the work is devoted to the design of district heat exchangers, including the calculation of thermal power and heat transfer area. Main dimensions are proposed for each exchanger together with a basic drawing.

Tesis por compendio / [ES] La tecnología de bombas de calor se ha vuelto estratégica en Europa, está extendiéndose rápidamente y se planea que reemplace las calderas de gas en un futuro cercano. Sin embargo, aún enfrenta desafíos, como encontrar refrige-rantes nuevos viables y altamente eficientes, y mejorar aún más el rendimiento del sistema. Para abordar este último problema, han surgido las bombas de calor de velocidad variable que prometen reducir el consumo anual e incremen-tar el confort adaptando la potencia suministrada a las necesidades cambiantes. Esta tecnología se está implementando ya, pero carece de una metodología estandarizada para diseñar y seleccionar sus componentes. Esta tesis tiene como objetivo establecer pautas de diseño generales para la selección y diseño de componentes de bombas de calor de velocidad variable, y ofrecer información valiosa que se pueda traducir en herramientas para asistir en la simulación, diseño, selección y detección de fallas en estos dispositivos. El contenido del estudio se puede dividir en tres áreas temáticas: En una primera parte, se estudian los compresores de velocidad variable. El compresor es el primer componente que se selecciona en una bomba de calor, modula la capacidad y es el principal consumidor de energía. Sin embargo, no existen metodologías bien establecidas para modelar su comportamiento. En esta parte, se realizan ensayos de caracterización de compresores de velocidad variable y sus inversores para comprender su comportamiento y proporcionar correlaciones compactas para modelar su rendimiento. En la segunda parte, se propone una metodología para dimensionar los intercambiadores de calor en bombas de calor de velocidad variable. Nor-malmente, se diseñan para una potencia fija y temperaturas de trabajo constan-tes, sin embargo, en las bombas de velocidad variable, la capacidad y las tempe-raturas de trabajo fluctúan significativamente con el tiempo. En esta parte, se estudia la evolución del rendimiento de los intercambiadores de calor con la capacidad (velocidad del compresor) y se propone una metodología de selec-ción/dimensionamiento que considera la evolución de la capacidad requerida y de las condiciones climáticas externas a lo largo del año. Por último, se evalúa la circulación del aceite en las bombas de calor de velocidad variable. Gestionar la lubricación en los compresores de velocidad variable es un problema típico ya que, para tener suficiente lubricación a bajas velocidades, el compresor termina bombeando un exceso de aceite a altas velo-cidades. En esta parte se estudia la evolución de las tasas de circulación de acei-te con la velocidad y se analiza teóricamente su efecto en el rendimiento de la bomba de calor. / [CA] La tecnologia de les bombes de calor s'ha tornat estratègica a Europa, s'està estenent ràpidament i es preveu que substituïsca les calderes de gas en un futur pròxim. Tanmateix, encara s'enfronta a desafiaments com trobar refrigerants nous viables i altament eficients, i millorar encara més el rendiment del sistema. Per abordar aquest darrer problema, han sorgit les bombes de calor de velocitat variable que prometen reduir el consum anual i incrementar el confort adaptant la potència subministrada a les necessitats variables. Aquesta tecnologia ja s'es-tà implementant, però manca d'una metodologia estandarditzada per dissenyar i seleccionar els seus components. Aquesta tesi té com a objectiu establir pautes de disseny generals per a la se-lecció i disseny de components de bombes de calor de velocitat variable, i oferir informació valuosa que es pugui traduir en eines per ajudar en la simulació, disseny, selecció i detecció de fallades d'aquests dispositius. El contingut de l'estudi es pot dividir en tres àrees temàtiques: En una primera part, s'estudien els compressors de velocitat variable. El compressor és el primer component seleccionat d'una bomba de calor, modula la capacitat i és el principal consumidor d'energia. Tanmateix, no hi ha metodo-logies ben establides per modelar el seu comportament. En aquesta part, es realitzen assajos de caracterització de compressors de velocitat variable i els seus inversors per comprendre el seu comportament i proporcionar correlaci-ons compactes per modelar el seu rendiment. En la segona part, es proposa una metodologia per dimensionar els inter-canviadors de calor en bombes de calor de velocitat variable. Normalment, es dissenyen per a una potència fixa i temperatures de treball constants, no obs-tant això, en les bombes de velocitat variable, la capacitat i les temperatures de treball fluctuen significativament amb el temps. En aquesta part, s'estudia l'evo-lució del rendiment dels intercanviadors de calor amb la capacitat (velocitat del compressor) i es suggereix una metodologia de selecció/dimensionament que considera l'evolució de les càrregues i de les condicions climàtiques externes al llarg de l'any. Finalment, s'avalua la circulació de l'oli a les bombes de calor de velocitat variable. Gestionar la lubricació als compressors de velocitat variable és un pro-blema típic, ja que per tenir suficient lubricació a baixes velocitats, el compres-sor acaba bombejant un excés d'oli a altes velocitats. En aquesta part s'estudia l'evolució de les taxes de circulació d'oli amb la velocitat i s'analitza teòricament el seu efecte en el rendiment de la bomba de calor. / [EN] Heat pump technology has become strategic in Europe, it is rapidly spread-ing, and it is planned to replace gas boilers in the near future. However, they still have challenges to solve, such as finding new viable and highly efficient refriger-ants and further increasing their system performance. For this latter issue, vari-able-speed heat pumps arise, which claim to decrease annual consumption and increase comfort by adapting the delivered capacity to the changing loads. This technology is being implemented but lacks a standardized methodology to de-sign and select its components. This thesis aims to establish comprehensive design guidelines for selecting and designing variable-speed heat pump components and give insights that can translate into valuable information and tools for engineers to assist them in the pump simulation, design, selection and fault detection. The content of the study can be divided into three thematic areas: In the first part, variable-speed compressors are studied. The compressor is the first selected heat pump component; it modulates the capacity and is the primary energy consumer. However, there are no well-established methodolo-gies to model their behavior. In this part, extensive testing of variable-speed compressors and their inverters was carried out to understand their behavior and to provide compact correlations to model their performance. The second part proposes a methodology to size heat exchangers for variable-speed heat pumps. Typically, they are designed for a fixed capacity and constant working temperatures. However, the capacity and working tempera-tures fluctuate significantly overtime in variable-speed pumps. In this part, the performance evolution of heat exchangers with capacity is studied, and a meth-odological selection/sizing technique is proposed that considers the evolution of external climatic conditions and loads over the year. Lastly, the oil circulation in variable-speed heat pumps is assessed. Man-aging lubrication in variable-speed compressors is a typical issue, as a design valid for sufficient lubrication at low compressor speeds will end up pumping excess oil at high speeds. In this final part, the evolution of oil circulation rates with speed is studied, and its effect on heat pump performance is theoretically analyzed. / I am indebted to the Spanish and European governments for their financial support with the grant PRE2018-083535, which made this research possible. Their commitment to academic excellence and research advancement has been crucial in successfully completing this thesis. / Ossorio Santiago, RJ. (2024). Modelling of Heat Pumps Working with Variable-Speed Compressors [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/203104 / Compendio