Carbon-Based Nanofluids and Their Advances towards Heat Transfer Applications—A Review

Abstract

Nanofluids have opened the doors towards the enhancement of many of today’s existing thermal applications performance. This is because these advanced working fluids exhibit exceptional thermophysical properties, and thus making them excellent candidates for replacing conventional working fluids. On the other hand, nanomaterials of carbon-base were proven throughout the literature to have the highest thermal conductivity among all other types of nanoscaled materials. Therefore, when these materials are homogeneously dispersed in a base fluid, the resulting suspension will theoretically attain orders of magnitude higher effective thermal conductivity than its counterpart. Despite this fact, there are still some challenges that are associated with these types of fluids. The main obstacle is the dispersion stability of the nanomaterials, which can lead the attractive properties of the nanofluid to degrade with time, up to the point where they lose their effectiveness. For such reason, this work has been devoted towards providing a systematic review on nanofluids of carbon-base, precisely; carbon nanotubes, graphene, and nanodiamonds, and their employment in thermal systems commonly used in the energy sectors. Firstly, this work reviews the synthesis approaches of the carbon-based feedstock. Then, it explains the different nanofluids fabrication methods. The dispersion stability is also discussed in terms of measuring techniques, enhancement methods, and its effect on the suspension thermophysical properties. The study summarizes the development in the correlations used to predict the thermophysical properties of the dispersion. Furthermore, it assesses the influence of these advanced working fluids on parabolic trough solar collectors, nuclear reactor systems, and air conditioning and refrigeration systems. Lastly, the current gap in scientific knowledge is provided to set up future research directions.

Effect of Multi-Walled Carbon Nanotubes-Based Nanofluids on Marine Gas Turbine Intercooler Performance

“…The previous results clearly show the superiority of MWCNTs-based nanofluids over that of the base fluid as well as the sensitivity of the property towards the nanomaterial loading and fabrication temperature. Nevertheless, it must be mentioned that the added surfactant has a negative effect on the thermal conductivity of the mixture (i.e., it reduces the thermal property) [ 17 ]. This is because when adding the SDS surfactant, a thin layer forms on the outer surface of the nanomaterial in order to modify the attraction/repulsion force between the dispersed particles and the surrounding environment, and hence minimum nanomaterial clustering occurs (i.e., better physical stability can be achieved).…”

“…On the other hand, the 0.05 vol % and 0.10 vol % samples remained stable even on day 45 ( Figure 5 d). This suggest that the concentration of SDS used in forming the 0.01 vol % was not sufficient to change the head group charge of the dispersed MWCNTs due to the low volume ratio of surfactant to base fluid used [ 17 ].…”

“…The concentrations of nanopowders used were 0.01, 0.05, and 0.10 vol %, for each experimental set up. These were calculated through the mixing theory (Equation (2)) that is widely adopted by researchers working in this field [ 17 ]. …”

“…In previous literature [ 13 , 14 , 15 , 16 ] the studied nanofluids comprised dispersed nanoparticles of very low thermal conductivity (i.e., 40 W/m∙K and 401 W/m∙K for Al 2 O 3 and Cu at room temperature, respectively) compared to todays advanced nanomaterials (e.g., ~4000 W/m∙K for carbon nanotubes (CNTs) at room temperature) [ 17 ]. Furthermore, the approach used in preparing nanofluids has a crucial effect on the suspension’s thermophysical properties.…”

Pool Boiling Amelioration by Aqueous Dispersion of Silica Nanoparticles

“…Furthermore, the mixture temperature was controlled throughout the dispersion process using a BUENO BIOTECH company cooling and heating water bath (Nanjing, China), of type BGDC, with a 0.1 °C accuracy while being monitored using the ultrasonic temperature probe accessory, which is made of stainless steel and has a 1 °C accuracy. The previous suspension fabrication technique is widely used in the field and is known as the two-step nanofluid production method [ 30 ]. It is important to note that surfactants were not used in preparing the dispersions.…”