No abstract

Nowadays, there is an increasing need for improving the inefficient ways for obtaining thermal energy from renewable sources to fulfil the industrial and typical needs in heat transfer processes that may be covered using solar assisted heat pumps due to their appropriate performance in the thermal energy transfer process. To improve the efficiency of the collector/evaporator by increasing the heat flux to the refrigerant, in this research, a numerical and computational fluid dynamics (CFD) analysis is conducted with geometrical variations in the surface section of a collector/evaporator. The performance was compared to the results of a base case, replicating its limit and environmental conditions such as the initial temperature of 5.5 °C, incident solar radiation of 464.1 W•m -2 , the operating temperature of 17.6 °C and other parameters. The surface geometrical variations involved in this study show a surface area similar to the base case. However, different lengths of the fluid path were considered due to the new geometrical shapes represented with less thermal resistances and correct distribution of the fluid in the collector/evaporator, obtaining temperature variations of 3.78, 5.47, 5.56 °C and a maximum value of 5.63 °C, including the corresponding variation of the heat flux. Considering the geometric changes in the superficial section of a flat-plate solar collector, it is possible to implement these variations in different kinds of heat exchangers in order to analyze the efficiency in these devices and the impact in the global systems where the heat exchangers are used.

El objetivo de la presente investigación fue realizar un análisis numérico mediante CFD de un colector solar de placa plana; además, se realizó una comparación con resultados experimentales. El fluido de trabajo alcanzó una temperatura máxima de salida de 20.16 °C a las 12:00, el valor de la radiación solar se determinó para las coordenadas geográficas latitud –0.2252 y longitud –77.84; de forma similar, en este horario fue posible obtener una temperatura de la superficie del colector de 27.12 °C, como valor pico. Se determinó el menor rendimiento del dispositivo de transferencia de calor a las 10:00 con un valor de temperatura de salida del agua y temperatura máxima en la superficie del colector de 18.65 y 20.48 °C, respectivamente. Los resultados experimentales mostraron una temperatura máxima de 20.93 °C y una temperatura mínima de19.4 °C, derivando en un error de 4.01 % entre la simulación computacional y los datos experimentales.

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.

El objetivo de la presente investigación fue realizar un análisis numérico mediante CFD de un colector solar de placa plana; además, se realizó una comparación con resultados experimentales. El fluido de trabajo alcanzó una temperatura máxima de salida de 20.16 °C a las 12:00, el valor de la radiación solar se determinó para las coordenadas geográficas latitud –0.2252 y longitud –77.84; de forma similar, en este horario fue posible obtener una temperatura de la superficie del colector de 27.12 °C, como valor pico. Se determinó el menor rendimiento del dispositivo de transferencia de calor a las 10:00 con un valor de temperatura de salida del agua y temperatura máxima en la superficie del colector de 18.65 y 20.48 °C, respectivamente. Los resultados experimentales mostraron una temperatura máxima de 20.93 °C y una temperatura mínima de19.4 °C, derivando en un error de 4.01 % entre la simulación computacional y los datos experimentales.