Experimental and numerical study of a water-to-water heat pump working with CO2

[SPA] En esta tesis, se analiza numérica y experimentalmente una bomba de calor agua-agua en un ciclo de transcrítico de CO2 de una etapa en la producción de agua caliente para calefacción y ACS. Se estudian y comparan diferentes configuraciones comúnmente utilizadas en el mercado para las mismas temperaturas del agua evaporador y condensador. A partir de ahora, dado que en los ciclos transcríticos del CO2 no existe cambio de fase, el condensador se denomina Gas Cooler. Inicialmente, se presentan cuatro configuraciones (C#), tres de ellas son con evaporador seco, C1 y C2, incluyen receptor de líquido, control de alta presión y control de sobrecalentamiento, y la restante, C4, no usa receptor de líquido, ni tiene control de alta presión, solo control de sobrecalentamiento. La diferencia entre C1 y C2 es un bypass que se usa en C1, pero cuando el bypass está cerrado, el ciclo está funcionando en C2. La otra configuración, C3, es un sistema de evaporador inundado, con control de alta presión, pero sin sobrecalentamiento ya que es un ciclo de evaporador inundado. Uno de los estudios más importantes de esta tesis fue la presión óptima del Gas Cooler. Se ha desarrollado y validado experimentalmente un modelo numérico para describir el comportamiento de una bomba de calor transcrítica de CO2 para la producción de agua caliente. Este modelo ha permitido obtener expresiones relativamente simples que se pueden programar en un PLC para regular la presión en el Gas Cooler midiendo la temperatura del refrigerante en tres puntos del ciclo. El modelo propuesto es capaz de limitar la temperatura de descarga del compresor a 140 °C manteniendo el COP con desviaciones teóricas inferiores al 2% respecto a las condiciones óptimas de presión. La presión del depósito de líquido, la temperatura de evaporación, la eficiencia del Intercambiador de calor interno (IHX) y el grado de recalentamiento tienen una influencia relativamente baja en el comportamiento del sistema. Además, dado que la influencia de la eficiencia del compresor también es relativamente baja, el modelo es aplicable para una amplia gama de modelos de compresores semi-herméticos alternativos, que son los más comunes en el campo de las bombas de calor estacionarias. Considerando la comparación de las diferentes configuraciones, una de las primeras decisiones luego de realizar las pruebas experimentales, fue eliminar el C4 ya que esta configuración no podía competir con las otras tres por falta de control de alta presión. La segunda decisión tras analizar que la influencia del depósito de líquido era insignificante mostrando rendimientos ligeramente mejores cuando el bypass estaba totalmente cerrado y seguido de totalmente abierto, las dos primeras configuraciones se trataron como una única configuración, denominada “C1&C2”. Así, las comparaciones solo se realizaron entre “C1&C2” y C3, con todas las configuraciones utilizando Intercambiador de Calor Interno (IHX) totalmente abierto ya que se ha concluido previamente en la literatura y probado experimentalmente durante esta tesis, para ciclo transcrítico, el rendimiento del sistema aumenta cuando aumenta la eficiencia de IHX. La superficie de los intercambiadores de calor (HX) también se estudió en calefacción. Para aplicaciones de calefacción y ACS, las diferencias entre “C1&C2” y C3 son despreciables. Sin embargo, en los ciclos de evaporador seco, si el depósito de líquido suele estar regulado por un bypass de gas con el objetivo de reducir la presión de las líneas que distribuyen el líquido a los evaporadores, para permitir un rango de regulación de presión adecuado, el depósito de líquido debe dimensionarse según resto de componentes y a las condiciones habituales de funcionamiento. El aumento de la superficie de los diferentes intercambiadores de calor (HX), mostró una mejora en la mayoría de los casos estudiados numéricamente para la aplicación de calefacción, pero existe una superficie óptima para los diferentes rangos de temperatura y esto debe tenerse en cuenta al diseñar los intercambiadores de calor, al menos para temperaturas baja/media y altas/muy altas. In this thesis, a one-stage transcritical CO2 water-to-water heat pump is numerically and experimentally analyzed in the production of hot water for the applications of space heating and domestic hot water generation. Different configurations commonly used in the market are studied and compared for the same wáter temperatures at the heat sink (evaporator) and heat source (condenser). From now on, since in CO2 transcritical cycles does not exist phase change, the condenser is called Gas Cooler. Initially, four configurations (C#) are presented, three of them belong to the dry evaporator group, C1 and C2 include liquid receiver, high pressure control and superheating control, and the remaining one, C4, doesn’t use liquid receiver, neither has high pressure control, only superheating control. The difference between C1 and C2 is a bypass that is used in C1, but, when the bypass is closed, the cycle is working in C2. The other configuration, C3, is a flooded evaporator system, with high pressure control, but without superheating since it is a flooded evaporator cycle. One of the most important studies in this thesis was the Gas Cooler optimal pressure. A numerical model to describe the behavior of a CO2 transcritical heat pump for hot water production has been developed and experimentally validated. This model has allowed obtaining relatively simple expressions that can be programmed in a PLC to regulate the pressure in the gas cooler by measuring the temperature of the refrigerant in three points of the cycle. The proposed model is capable of limiting the compressor discharge temperature to 140 °C while maintaining the COP with theoretical deviations of less than 2 % respect to optimal pressure conditions. The liquid receiver pressure, the evaporation temperature, the Internal Heat Exchanger (IHX) efficiency and the Superheating degree, have relatively low influences on the system behavior. Furthermore, since the influence of the compressor efficiency is relatively low as well, the model is applicable for a wide range of reciprocating semihermetic compressor models, which are the most common in the field of stationary heat pumps. Considering the comparison of the different configurations, one of the first decisions after performing the experimental tests, was eliminating the C4 since this configuration was not able to compete with the other three due to the lack of high pressure control. The second decision after analyzing that the influence of the liquid receiver was negligible showing slightly better performances when the bypass was totally closed and followed by totally opened, the first two configurations were treated as a single configuration, called “C1&C2”. Thus, the comparisons were only performed between “C1&C2” and C3, with all configurations using Internal Heat Exchanger (IHX) totally opened since it has been previously concluded in the literature and experimentally tested during this thesis, for transcritical cycle, the system performance increases when IHX efficiency increases. The Heat Exchangers (HX) surface was also studied for space heating applications. For the space heating and domestic hot water applications, the differences between “C1&C2” and C3, are negligible. However, in the dry evaporator cycles, if the liquid receiver is usually regulated by a gas bypass with the aim of reducing the pressure of the lines that distribute liquid to the evaporators, to allow an adequate pressure regulation range, the liquid receiver should be sized according to the rest of the components and to the usual operating conditions. Increasing the Heat Exchangers (HX) surfaces, showed improvement in most cases numerically studied for space heating application, but there exists an optimal surface for the different temperatura range and this should be considering when designing the heat exchangers, at least for low/medium and high/very high temperatures.Escuela Internacional de Doctorado de la Universidad Politécnica de CartagenaUniversidad Politécnica de CartagenaPrograma de Doctorado en Tecnologías Industriale

SET2022 : 19th International Conference on Sustainable Energy Technologies 16th to 18th August 2022, Turkey : Sustainable Energy Technologies 2022 Conference Proceedings. Volume 4

Papers submitted and presented at SET2022 - the 19th International Conference on Sustainable Energy Technologies in Istanbul, Turkey in August 202

Engineering Thermodynamics - A Graphical Approach

This open educational resource is intended to be a totally self-contained learning resource in Engineering Thermodynamics. It is designed to be suitable for a two course sequence for Mechanical Engineering majors. It may, however, be used in any format and for any purpose, including self-study. The various unique pedagogical features of this web resource are discussed in Paper AC 2010-47 (see additional files below), presented at the 2010 ASEE Annual Conference (refer also to the OU Video). It is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International license and as such is freely available. Comments and constructive criticism are welcomed by the author. There is normally a printed Thermodynamics Properties Tables booklet which accompanies the web resource. If this is unavailable then this booklet can be downloaded and printed (see additional files below). In Part 1 we introduce the First and Second Laws of Thermodynamics. Rather than applying these laws in terms of components and processes we have chosen a more interesting approach of applying them to complete cycles or systems. The ideal Stirling cycle machine is developed as a prime example of both Laws (refer to a paper: A Meeting between Robert Stirling and Sadi Carnot in 1824 (see additional files below) presented at the 2014 ISEC), and complete ideal heat engines, steam power plants and refrigeration systems are evaluated in Chapters 3 and 4. Where appropriate, we introduce graphical two-dimensional plots to evaluate the performance of these systems rather than relying on equations and tables. This enables intuitive visualization of the solutions to a high degree of accuracy. The section on Carbon Dioxide as a refrigerant does not appear in any textbook that I am aware of. Because of the Global Warming crisis, the currently used refrigerant, R134a, will be banned from usage in automobile air conditioning systems in Europe within a few years. Among the alternatives being developed we prefer to return to Carbon Dioxide as the refrigerant of choice.https://ohioopen.library.ohio.edu/opentextbooks/1009/thumbnail.jp

SET2023 : 20th International Conference on Sustainable Energy Technologies 15th to 17th August 2023, Nottingham, UK: Sustainable Energy Technologies 2023 Conference Proceedings. Volume 2

Papers #101 to #200 presented at SET 202

Mathematical Modelling of Energy Systems and Fluid Machinery

The ongoing digitalization of the energy sector, which will make a large amount of data available, should not be viewed as a passive ICT application for energy technology or a threat to thermodynamics and fluid dynamics, in the light of the competition triggered by data mining and machine learning techniques. These new technologies must be posed on solid bases for the representation of energy systems and fluid machinery. Therefore, mathematical modelling is still relevant and its importance cannot be underestimated. The aim of this Special Issue was to collect contributions about mathematical modelling of energy systems and fluid machinery in order to build and consolidate the base of this knowledge

Best Environmental Management Practice for the Food and Beverage Manufacturing Sector

This report describes best environmental management practices for food and beverage manufacturers. Best environmental management practices are those techniques, measures and actions that can be implemented by food and beverage manufacturers to minimise their impact on the environment all along the value chain of their products. They were identified together with sectoral experts on the basis of practices actually implemented by environmental frontrunners. The report outlines best environmental management practices that are broadly applicable to all food and beverage manufacturers, such as the carrying out of an environmental assessment, sustainable supply chain management, cleaning operations, improvement of energy efficiency, use of renewable energy, optimisation of transport and distribution, refrigeration and freezing operations and food waste prevention. Additionally, specific best practices for nine individual subsectors are presented, namely the processing of coffee, manufacture of olive oil, manufacture of soft drinks, manufacture of beer, production of meat and poultry meat products, manufacture of fruit juice, cheese making operations, manufacture of bread, biscuits and cakes and manufacture of wine. Alongside best environmental management practices, the report also identifies suitable sector specific environmental performance indicators related to the topic of each best practices, and, when possible, benchmarks of excellence, corresponding to the level of performance achieved by frontrunners. This report can be used by food and beverage manufacturers as a source of information to identify relevant actions they can implement to improve their environmental performance. On its basis, the EMAS (EU Eco-Management and Audit Scheme) Sectoral Reference Document on Best Environmental Management Practice for the food and beverage manufacturing sector was developed (according to Article 46 of Regulation (EC) No 1221/2009).JRC.B.5-Circular Economy and Industrial Leadershi