Thermosyphons have high effective thermal conductivity and are applicable for different heat transfer purposes including cooling devices and heat exchangers. In the present study, thermal performance of a thermosyphon is experimentally investigated by using Ni/Glycerol-water nanofluid in three concentrations including 0.416, 0.625 and 1.25 g/lit. Experimental results revealed that using the nanofluid with 0.625 g/lit concentration leads to lowest thermal resistances. Afterwards, a thermosyphon-based heat exchanger is designed and numerically investigated to compare its performance with copper heat exchanger. Since the effective thermal conductivity of thermosyphon depends on temperature difference between condenser and evaporator, a novel approach is applied to achieve precise modeling. Effects of mass flow rates of cold and streams and inlet temperature of hot stream on heat transfer rate are evaluated. Results revealed that using thermosyphon instead of copper tubes with the same dimensions results in more than 100% improvement in heat transfer capacity. Moreover, it is concluded that increase in the mass flow rates of the streams and inlet temperature of hot stream lead to increase in heat transfer rate. A 3D graph is represented to evaluate the influences of hot stream temperature and mass flow rate on the heat transfer rate of thermosyphon-based heat exchanger.

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Geothermal energy is one of the most suitable sources of energy since it is possible to use it continuously for generating power and providing heat. Firstly, recent trends in geothermal energy are discussed and compared with other types of renewable energies. According to the results of this section, geothermal energy is an attractive choice for future power generation due to its low carbon dioxide emission and levelzied cost of electricity in comparison with other renewable energy sources. Afterwards, applications of nanofluid in geothermal-based energy systems are reviewed and their important results are represented. On the basis of literature review, using nanofluids can result in augment in geothermal systems. The enhancement is dependent on several factors including the type of nanofluid, concentration and system specification. According to the results of a study, the effect of using nanofluid on heat transfer rate became more significant at higher flow rates. In addition, using nanofluids can reduce the size of heat exchangers used in geothermal-based system. The main effects of employing nanofluids is increase in convective heat transfer and pressure loss.