This chapter studies the fluid flow within pipes subjected to thermal asymmetrical boundary conditions. The phenomenon at hand takes place in many real-world industrial situations, such as solar thermal devices, aerial pipelines. A steady-state analysis of laminar forced-convection heat transfer for an incompressible Newtonian fluid is studied. The fluid is considered to flow through a straight round pipe provided with straight fins. For the case studied, axial heat conduction in the fluid has been considered and the effects of the forced convection have been considered to be dominant. A known uniform temperature field is applied at the upper external surface of the assembly. The 3D assembly has been created combining cylindrical and Cartesian coordinates. The governing differential equation system is solved numerically through suitable discretization in a set of different finite volume elements. The results are shown through the thermal profiles in respect of longitudinal and radial-azimuthal coordinates and the problem characteristic length. To facilitate the resolution of this phenomenon, an open computing platform called HEATT©, based on this model, has been developed, and it is also shown here. The platform is now being built and is expected to be freely available at the end of year 2022.

Distillation is one of the most common processes in companies of the chemical sector. Its overall performance cannot be based only on physical-chemical processes carried out, but as a whole, including maintenance and operation costs and trying to achieve the best possible energy efficiency. By means of predictive maintenance techniques, such as vibration analysis, ultrasound, thermography, etc., it is possible to anticipate equipment failures, avoiding unnecessary stops and significant losses, and identify dangerous or inappropriate functional conditions to achieve proper operating dynamics. This article describes a methodology to analyze the functional conditions of the agitators of large distillers and reactors. Based mainly on vibration analysis techniques, this methodology tries to find the best operating conditions for the equipment, both electromechanically and energetically, and identifying, if that were the case, those that are dangerous for the equipment. This methodology is currently being applied in a large process plant, and has been extended to gradually integrate all the agitators of the industrial plant, obtaining a substantial improvement in its energy efficiency, as well as a significant reduction of failures, particularly in the mechanical seals, a very expensive and essential element to maintain the correct pressure and temperature required for the process. Uno de los procesos más comunes en las empresas del sector químico es sin duda el proceso de destilación. Su rendimiento global no solo puede basarse en los procesos físico-químicos llevados a cabo sino que debe contemplarse en su conjunto, esto es, incluyendo el coste de operación y mantenimiento y procurando la mejor eficiencia energética posible. La utilización de técnicas de mantenimiento predictivo, tales como el análisis de vibraciones, ultrasonidos, termografía, etc., permite adelantarse al fallo de los equipos, evitando paradas innecesarias y pérdidas considerables, y hace posible identificar condiciones funcionales peligrosas o inadecuadas para lograr una correcta dinámica de operación. En este artículo se expone una metodología para el análisis funcional de agitadores de grandes destiladores y reactores. Basada principalmente en técnicas de análisis de vibraciones, persigue encontrar las mejores condiciones operativas del equipo, tanto desde el punto de vista electromecánico como energético, e identificar -si las hubiere- aquellas otras que pueden exponer peligrosamente al fallo del equipo. Esta metodología se está aplicando actualmente en una gran planta de proceso y se ha ido ampliando gradualmente para integrar a todos los agitadores de la planta, consiguiendo una mejora sustancial en su rendimiento energético así como una drástica reducción de los fallos, particularmente en los cierres mecánicos, un costoso elemento mecánico esencial para mantener las correctas condiciones de presión y temperatura del proceso.

Solar electric and solar thermal energies are often considered as part of the solution to the current energy emergency. The pipes of flat plate solar devices are normally heated by their upper surfaces giving rise to an asymmetric temperature field in the bulk of the fluid, which influences the heat transfer process. In the present work, a study of the characteristic length of tubes, or most efficient distance at which heat transfer occurs, in flat photovoltaic-thermal (PVT) hybrid solar devices has been carried out using three heat transfer fluids: water, [Emim]Ac ionic liquid and ionanofluid of graphene nanoparticles suspended in the former ionic liquid. The mean objective of the study was to know whether the heat transfer occurs in optimal conditions. Experimental measurements have been made on a commercial PVT device, and numerical simulations have been performed using the HEATT^® platform to determine the characteristic length of the process. The tests conducted showed a clear improvement in the temperature jump of the fluid inside the collector when INF is used compared to water and ionic liquid and even a higher overall energy efficiency. Electricity generation is not greatly affected by the fluid used, although it is slightly higher when water is used. Slower fluid velocities are recommended if high fluid outlet temperatures are the goal of the application, but this penalizes the overall thermal energy production. The characteristic process length is not typically achieved in parallel tube PVT collectors with ordinary flow rates, which would require a speed, and consequently, a flow rate, about 10 times lower, which penalizes the performance (up to four times), although it increases the fluid outlet temperature by 234%, which can be very interesting in certain applications. Ionanofluids may in the medium term become an alternative to water in flat plates or vacuum solar collectors for applications with temperatures close to or above 100 °C, when their costs will hopefully fall. The results and methodology developed in this work are applicable to solar thermal collectors other than PVT collectors.

Los flujos térmicos en condiciones de contorno asimétrico son frecuentes en todo tipo de conducciones en condiciones reales, dando lugar a distribuciones de temperaturas también asimétricas en el seno del fluido. Ejemplos de esto en instalaciones frigoríficas serían conducciones de frigorífero defectuosamente aisladas a temperaturas negativas, con producción de hielo en una de sus caras, etc. En el presente trabajo se estudia la distribución de temperaturas en el seno de tuberías de líquidos de uso en instalaciones frigoríficas (frigorígenos, frigoríferos u otros productos) sometidas a condiciones térmicas asimétricas en condiciones de flujo laminar. Para ello se hace uso de la herramienta informática de libre uso HEATT®, basada en el Método de Simulación por Redes, que proporciona el mapa térmico en diferentes secciones de la tubería, lo que permite determinar la porción de tubería cuyas condiciones se alejan de las de operación.