Nanofluids, due to their superior thermal properties, have immense applications in heat transfer process. In view of this, nanofluids, as working fluids in solar thermal systems, have gained importance. This review emphasizes the properties of nanofluids for solar thermal applications as well as typical nanomaterials and analyses experimental and numerical investigations on solar thermal systems utilizing nanofluids along with typical experimental setups and calculation methods used for determination of the performance of nanofluids in the same. The effect of nanoparticles concentration, flowrate, ambient temperature, solar intensity and inlet temperature on the solar thermal system performance utilizing nanofluids is also discussed. Further, challenges occurring during application of nanofluids in solar thermal systems are specified along with recommendations for scaling up of nanofluid-based solar thermal systems.

Performance evaluation of nanofluids in solar thermal and solar photovoltaic systems: A comprehensive review

Ag-doped TiO2 hybrid nanoparticles have been synthesized by ultrasonic-assisted method for nanofluid application for heat transfer in minichannel heat exchanger at constant wall temperature condition. Prepared nanoparticles were dispersed in water by ultrasonication to form an extremely stable nanofluid. Thermal conductivity of the nanofluid was found to be 1.84 W/mK at 45 ℃ for nanofluid concentration of 0.25 vol%. The overall heat transfer coefficient increased from 1211.71 to 2727.38 W/m2K as the nanofluid concentration increased form 0.01 vol% to 0.1 vol% at Reynolds number of 3480 ± 3. A new correlation for Nusselt number has been proposed. The pressure drop and friction factor of the nanofluids were also advantageously lesser than that of water. The overall performance of the Ag-doped TiO2 hybrid nanoparticles based nanofluid was assessed by comparing the heat transfer with the pumping power and by determining the entropy generation and thus the Bejan number.

Investigation on thermophysical properties, convective heat transfer and performance evaluation of ultrasonically synthesized Ag-doped TiO2 hybrid nanoparticles based highly stable nanofluid in a minichannel

Proton Exchange Membrane Fuel Cells (PEMFCs) are known as a promising alternative for internal combustion engines (ICE) to reduce pollution. Recent progress of PEMFCs is heading towards achieving higher power densities, reducing the refueling time, and decreasing the degradations, to facilitate the commercialization of hydrogen mobility. Model-assisted stack component development, diagnosis, and management are essential to ensure improved stack design and operation for tackling the existing implementation challenges of PEMFCs. Past reviews usually touched on a specific aspect, which can hardly provide the readers a complete picture of the key challenges and advances in water management. This paper aims at delivering a comprehensive source to review, from both experimental, analytical, and numerical viewpoints, the key operational challenges, and solutions of the stack to improve water/thermal management and cold start. In addition to presenting the fundamental theory to develop an analytical model, the recent advances in the flow field design, nanofluid coolants, and cold-start methods. Furthermore, the impacts of microstructural properties and the design of the porous layers on the water/thermal management are described. 

A review on the proton exchange membrane fuel cells (PEMFCs) water/thermal management: From theory to the current challenges and real-time fault diagnosis methods

A minireview on nanofluids for automotive applications: current status and future perspectives

A four-input artificial neural network (ANN) model has been presented for the prediction of thermal conductivity of rGO–metal oxide nanocomposite-based nanofluids. For this, data of five types of water-based nanofluids containing rGO–metal oxide nanocomposites particles were used from the available literature. The four-input variables considered were molecular weight of nanocomposite, average particle size of nanocomposites, concentration, and temperature of nanofluid which exhibited thermal conductivity of the nanofluids as output. Using the same architecture, two ANN models were developed, one using a total of 185 data points and the other by dividing the data points in two sets (training and testing). The model agreed well with the experimental data and exhibited an R2 value of 0.956 for the testing data set. Also, the magnitude of deviation of the predicted thermal conductivity for all the data points was very less with an average residual of ± 0.048 W/mK.

Artificial neural network for prediction of thermal conductivity of rGO–metal oxide nanocomposite-based nanofluids

Nanofluids are the type of fluid suspensions that contains nano-sized particles. Their thermophysical properties have been studied to a great extent. Nanofluids have outstanding thermal as well as optical properties. Carbon-based materials are also being used nowadays as nanofluid additives for solar thermal collectors. The preparation of nanofluids is the most important step which may affect its thermal properties. Properties of both the individual components play role in determining the properties of the nanofluid. Thermal conductivity of a nanofluid is the most important property which certifies its heat transfer performance. Viscosity is one of the most crucial properties of nanofluids. The widespread use of solar energy for heating and cooling buildings is affected by the cost of the flat-plate collector. Flat-plate solar collectors are classified as a special class of heat exchangers. The efficiency of solar cells can be improved by using cooling solar cells. The solution to this problem is by using nanofluids.

Applications of Nanofluids in Solar Thermal Systems

A new type of fluid, called nanofluid, has found numerous applications in engineering sector due to its outstanding properties. These are known as suspensions of nano-sized particles in fluids called basefluids. The suspension of these nanoparticles in the basefluid shows significant influence on its physical properties. In view of this, in the present book chapter, the properties of the nanofluid like its thermal conductivity, electrical conductivity and so on have been discussed and the notable studies carried out in the past have been summarized. Several factors that are responsible for the alteration of the properties of nanofluids at varying degrees are identified and discussed in this chapter. Further, these properties contribute to the distinctive applications of nanofluids in various engineering fields, which are reviewed and discussed in this chapter.

Kalyani K. Chichghare

Papers

Applications of Nanofluids in Solar Thermal Systems

Synthesis and Characterization of Nanofluids: Thermal Conductivity, Electrical Conductivity and Particle Size Distribution