The present study aims to analyze the heat transfer variations in different models of shell and tube heat exchangers considering geometric variations in the baffle angles and in the tube’s profiles. Each baffle configuration and geometric variation in the profiles were tested under different mass flow rates (0.25, 0.5, 0.75, and 1 kg·s⁻¹) in the shell to study the heat transfer improvement. The models were simulated using a CFD simulation software ANSYS Fluent including an experimental geometry which was used to validate the simulation process. The experiment results are in good agreement with the CFD results. The analysis of the results shows that an angle of 60° in the baffles generated the highest heat flow (more than 40 kW) with an inclination to the cold flow inlet and a mixed distribution considering a mass flow rate of 1 kg·s⁻¹ in the shell. In addition, the horizontal elliptic profile achieved a heat flow higher than 29 kW with a mass flow rate of 0.5 kg·s⁻¹ in the shell.

There is a growing demand from the industrial sector and the population to cover the need for water temperature increases that can be covered with systems such as heat pumps. The present research aims to increase the heat transfer to the working fluid in a collector/evaporator, part of a solar-assisted direct expansion heat pump. This research was developed using a numerical analysis and by applying computational fluid dynamics; different simulations were performed to compare the performances of collector/evaporators with models exhibiting variations in the cross-section profile under similar conditions. An average incident solar radiation of 464.1 W·m⁻² was considered during the analysis. For the comparison, profiles with hexagon-, four-leaf clover-, and circular-shaped sections with floral shapes, among others, were analysed, resulting in a temperature increase at the outlet of the working fluid of 1.3 °C. In comparison, the collector/evaporator surface temperature varied between 4 and 13.8 °C, while the internal temperature of the fluid reached 11.21 °C. Finally, it is indicated that the best results were presented by analysing the profile corresponding to the circular section with the flower shape.

La presente investigación estudia una bomba de calor de expansión directa asistida por energía solar con un sistema de recirculación de agua. Los intercambiadores de calor utilizados fueron un colector/evaporador de cobre de 0.75 m2 y un condensador en forma de serpentín construido en tubería de cobre de 2.49 m de longitud y 8 espiras, inmerso en un tanque con 5 litros de agua. Para la recirculación del agua, se utilizó una bomba centrífuga de 20 L/min a 110 V. El compresor instalado es de velocidad variable a 12-24 V DC que utiliza R600a como fluido de trabajo. El dispositivo de expansión utilizado fue una válvula electrónica. Las pruebas experimentales se desarrollaron para una configuración con recirculación y sin recirculación de agua, considerando condiciones climáticas similares. De esta manera, se puede establecer cuál es la configuración que brinda un mayor rendimiento en el sistema. Para la obtención de datos de radiación solar, velocidad del viento y temperatura ambiente se empleó una estación meteorológica WS-1201. Este sistema proporcionó agua caliente sanitaria, a 45 °C en un tiempo entre 40 a 50 minutos dependiendo de las condiciones climáticas. El COP máximo del sistema con recirculación fue 9.83 un 8.04 % mayor que el sistema sin recirculación. El tiempo de calentamiento tardó 10 minutos menos para el sistema con recirculación, 16.67 % menos que al utilizar el sistema sin recirculación.

This investigation compared the efficiency of a flat-plate solar collector with triangular and square geometry, by using the finite element method (FEM). The design of the geometries and the utilized parameters for the simulation were obtained from previous publications. SolidWorks was used to model the two collectors, meanwhile, the Fluent module of the ANSYS software was used for the simulation by the FEM. Collectors integrated a pipe of 7 mm internal diameter with a plate thickness of 11 mm; the defined material was aluminum. An ambient temperature of 20 °C was considered, with solar radiation of 1000 W·m-2 and heat transfer surfaces of 61 250 and 122 500 mm2 for the triangular and square collectors, respectively. The quality of the mesh was excellent, obtaining a skewness of 0.2486, with which efficiencies of 62 and 39 % and maximum temperatures of 27 and 25.5 °C were obtained for the triangular and square collectors, respectively. Due to the geometries performing as fins, the temperatures are higher in the corners and, therefore, achieving higher efficiency is impossible.

El objetivo de la presente investigación es evaluar las propiedades del aceite vegetal y aceite mineral utilizados como dieléctricos y refrigerantes en transformadores de potencia, equipos que son usados en la explotación de los campos petroleros, utilizando. En base a la norma ASTM D1524, se realizó una prueba visual con cinco muestras de cada uno de los aceites, obteniendo valores promedio de 1,15 y 0,6 para el aceite mineral y aceite vegetal, respectivamente. Los resultados obtenidos mostraron que el aceite vegetal mantiene sus propiedades durante un tiempo prolongado, lo que ayuda a la vida útil del equipo. Para la prueba de rigidez dieléctrica según la prueba ASTM D1816, para el aceite vegetal se realizan cinco mediciones obteniendo como valores promedio 32,9, 29,6, 31,1, 30,7, 32,6; mientras que para el aceite mineral los resultados promedio de las cinco mediciones fueron de 31,2, 28,5, 29,6, 28,9, 30. Así se demostró que el aceite vegetal es mejor al poseer mayor rigidez dieléctrica.

The investigation purpose is to elaborate a detailed review about previous published investigations with direct-expansion solar-assisted heat pumps (DX-SAHP) used for water heating, in the last years. The growing energy consumption, the using of refrigerants that weaken the ozone layer, the greenhouse gases emission to the atmosphere and the global warming effect are the main problems that the conventional water heating systems present. Using hydrocarbons as refrigerants represents a pollution reduction and it is also the best option to replace hydrochlorofluorocarbons and chlorofluorocarbons, due to their low values of global warming potential and ozone depletion potential, close to 0. A DX-SAHP system takes advantage of the thermal solar energy directly by using a bare flat-plate solar collector. These systems provide domestic hot water over 50 °C and heating water volumes until 200 liters reaching COP values higher than 4. Solar energy and the using of alternative refrigerants with a low environmental impact are proposed to reach this purpose.