Installation of flat solar collectors (FSCs) has been increasing due to the zero cost of renewable energy. However, the performance of this equipment is limited by the area, the material and the thermophysical properties of the working fluid. To improve the properties of the fluid, metal and metal oxide nanoparticles have mainly been used. This paper presents the performance assessment of the FSCs using simple and hybrid carbon nanofluids of low thermal capacity. Energy and mass balance modeling was performed for this study. A parametric analysis was conducted to examine the impact of key variables on the performance of the solar collectors using simple graphite and fullerene nanofluids, as well as hybrid metal–oxide–carbon nanofluids. From the results of heat transfer in FSCs, using graphite and fullerene nanofluids, it can be concluded that adding these nanoparticles improves the convection coefficient by 40% and 30%, respectively, with 10% nanoparticles. The graphite and fullerene nanoparticles can enhance the efficiency of FSCs by 2% and 1.5% more than base fluid. As the decrease in efficiency using fullerene with magnesium oxide is less than 0.2%, fullerene hybrid nanofluids could still be used in FSCs.

In this paper, an evaluation of the performance and operating parameters of a hybrid compression/absorption chiller coupled with a low-capacity solar concentrator is presented. The study was carried out using energy and mass balances applied to each component of each system. The variables evaluated in the hybrid chiller were the cooling power, the supply power, the Coefficient of Performance (COP) of both cooling systems and the ratio between heat and power. The diameter and temperature of the hot spot as well as the performance of the dish collector were evaluated. The changed parameters were the heat removed by each refrigeration system, the condenser temperature, the evaporator temperature, the concentration ratio and the irradiance. Results have shown that the compression system can produce up to 53% more cooling power than the heat supplied to the hybrid system. Meanwhile, the absorption system produces approximately 20% less cooling power than the supplied heat. It has also been found that, for the cooling power produced by the hybrid cooler to be always greater than the heat supplied, the cooling power provided by the absorption system should preferably be between 20% and 60% of the total, with a Stirling engine efficiency between 0.2 and 0.3 and a condensation temperature from 28 to 37 °C. Likewise, it has been found that the compression system can produce cooling power up to 3 times higher than the heat of the Stirling engine hot source, with T_h = 200 °C and η_s = 0.3. Finally, it has been found that, in a low-capacity solar concentrator, on a typical day in Mexico City, temperatures in the hot spot between 200 and 400 °C can be reached with measured irradiance values from 200 to 1200 W/m².

En este artículo se presenta el modelado y simulación de un sistema de aire acondicionado continuo mediante refrigeración por absorción de simple efecto, alimentado por energía solar térmica a baja temperatura (85°C) mediante colectores solares de placa plana, para ser empleado en zonas tropicales. El modelado se realiza principalmente mediante balances de energía y de masa en cada componente del sistema. Para una potencia de enfriamiento de 3.517 kW, el calor requerido por el generador del sistema de refrigeración por absorción, fue de 4.8 kW. En tanto que el área del colector requerido mayor fue de 16 m2 aproximadamente.

One of the applications of ammonia has been the use of this element as a refrigerant in air conditioning systems for buildings, process industries and residential homes. The high electrical consumption of conventional chillers is one of the main reasons why alternative cooling systems have been sought. This chapter presents the analysis and modeling using energy and mass balances, as well as the simulation of absorption chillers. In addition, the analysis and discussion of the results of performance parameters of adiabatic and non-adiabatic absorption chillers using the lithium-ammonia-nitrate solution are presented. From the results presented in this section, it can be seen that although the heat flow and circulation ratio are higher and the cop is lower for absorption chillers, when the condensation temperature is lower and the evaporation and generation temperatures are higher, these design parameters are closer to those of non-adiabatic absorption chillers.