Renewable energy technologies have been developed in recent years due to the limited sources of fossil fuels, the possibility of depletion of fossil fuels and the related environmental issues. In these types of systems, it is crucial to reach optimum sizing in order to have an affordable system based on solar and wind energy and energy storage. In this study, a powerful optimization scheme based on tabu search, called discrete tabu search, has been proposed for sizing three stand-alone solar/wind/energy storage (battery) hybrid systems. For validating the applied algorithm effectiveness, the results are compared with the results found by the discrete harmony search. The obtained outcomes are compared on the basis of total annual cost. The components of the scheme are analyzed in different operating conditions by applying meteorological data in addition to real time information from three typical regions of Iran. According to the obtained data, applying ‘discrete tabu search’ leads to better outputs on the basis of mean, standard deviation and worst indexes.
Summary
Heat pipes are useful devices in heat transfer and particularly, in cooling systems. Given the high demand for cooling systems in various applications, an improvement in the performance of heat pipes has gained much attraction in recent years. In this study, the effects of utilizing working fluids with different thermal properties on the performance of pulsating heat pipes (PHP) are experimentally studied. Hence, nano‐encapsulated phase change material (NPCM), reduced graphene oxide nanosheets, and their mixture, as a novel hybrid nanofluid, are prepared and dispersed in water as a working fluid. NPCM at 3 concentrations of 5, 10, and 20 g/L, as well as nanosheets at three concentrations of 0.3, 0.6, and 1.2 g/L, are synthesized and investigated. Moreover, both additives are mixed at five various concentrations to form a hybrid nanofluid. All experiments are conducted in the vertical orientation and filling ratio of 50%. It is found that due to the increase in viscosity with the increment of concentration, the highest concentration is not always the optimum concentration and the PHP's performance for each additive is optimized in a specific concentration. NPCMs could prevent the working fluid's temperature to rise by changing the phase, as a result, the effective specific heat of the working fluid is slightly augmented. Also, the thermal conductivity of the working fluid increased up to 13% using nanosheets. It is illustrated that using the mixture of nanosheets and NPCM leads to a 38% decline in thermal resistance. Meanwhile, it is found that the enhancement in the thermal performance of the PHP using nanofluids is not only purely due to the increase in thermal properties of nanofluids but also due to the increase in turbulence intensity and boiling nucleation sites created by the nanoparticles.
Highlights
Nano‐encapsulated phase change material (PCM), reduced graphene oxide (RGO) nanosheets, and their mixture are used as working fluid in a pulsating heat pipe (PHP).
The thermal performance of PHP is improved using PCM nanocapsules, RGO nanosheets, and their mixture.
Nanosheets have a higher impact on the performance of PHP compared with nano‐encapsulated PCM.
The better performance of PHP using RGO nanosheets is due to the higher thermal conductivity and mixing of fluid containing them compared with pure water.
The better performance of PHP using nanocapsules is attributed to the better mixing of the fluid.
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