Abstract
This article presents the results of an experimental research on the thermal efficiency (TE) of an evacuated tube solar collector (ETSC) working with a nano-suspension of carbon nanotubes dispersed in distillated water. The efficacy of filling ratio (FR) of the heat pipes; the tilt angle (TA) of the collector, and the dispersion mass fraction of the carbon nanotubes within the distillated water on the TE of the collector was investigated. A model was developed based on the response surface methodology (RSM) to optimize the operating conditions in order to maximize the TE of the collector. The accuracy of the RSM model was verified with some additional experiments. It was found that the RSM model is able to optimize the TE of a collector with the accuracy of 1.6%. Also, it was found that the presence of carbon nanotubes inside the evaporator of the heat pipes can promote the nucleate boiling mechanism which in turn increased the TE of the solar collector. Also, the optimum filling ratio value and the installation angle were identified which were 0.6 and 55°, respectively. This was ascribed to a trade-off trend identified between the exist region inside the thermosyphon heat pipe and the amount of the vapor transported between the condenser and evaporator units, and also a trade-off between the residence time of the carrying fluid and the gravity effect, respectively.
•Response surface methodology was used to optimize the performance of a collector.•Statistical Pareto chart was used to find the effective parameters.•Optimum filling ratio and installation angle were calculated.•Relationship and interactions between the parameters were identified.•Nanofluid’s stability was examined using time-settlement experiments.