## 1 Introduction  
Heat transfer fluids (HTF) play a crucial rule to remove the excess of heat from a system with various applications ranging from building heating, ventilation and air-conditioning (HVAC) systems, electronics, automotive, or biomedicine [1]. In cold regions, such as Canada, Alaska, the Arctic, or subarctic regions, a huge amount of energy is expended for heating industrial and residential buildings since during winter, the ambient temperature may reach regularly \(-40\)\({}^{\circ}\)C. Therefore, it is a common practice to use ethylene-glycol or propylene-glycol mixed with water in different proportions as an HTF to lower the freezing point of liquid water. For high temperature applications like in car radiators or industrial heat exchangers, mixtures of ethylene-glycol and water (EG-W), or propylene-glycol and water (PG-W), are used to elevate the aqueous boiling points. Tables 1 and 2 summarize the given freezing and boiling points of both EG-W and PG-W mixtures. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline Ethylene Glycol Solution (\% by Volume) & 0 & 10 & 20 & 30 & 40 & 50 & 60 \\ Temperature (\({}^{\circ}\)C) & 0 & \(-3.4\) & \(-7.9\) & \(-13.7\) & \(-23.5\) & \(-36.8\) & \(-52.8\) \\ \hline Propylene-glycol solution (\% by volume) & 0 & 10 & 20 & 30 & 40 & 50 & 60 \\ Temperature (\({}^{\circ}\)C) & 0 & \(-3\) & \(-8\) & \(-14\) & \(-22\) & \(-34\) & \(-48\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Freezing points of ethylene-glycol- and propylene-glycol-based water solutions at various temperatures [2]. As shown in Tables 1 and 2, EG-W solutions exhibit lower freezing points and higher boiling points compared to PG-W solutions. However, it is strongly recommended to use PG-W mixtures especially in human interaction applications such as heating residential buildings because propylene-glycol is non-toxic and easily decomposes in the environment, contrary to ethylene-glycol, which is toxic and takes a longer time to degrade [3; 4; 5; 6; 7]. Ethylene- and propylene-glycol mixtures are also characterized by a thermal conductivity about three-times lower than that of water at 20 \({}^{\circ}\)C (Table 3). This constitutes the primary limitation in the development of thermally-efficient systems. The other limitations are due to their lower heat capacities and higher dynamic viscosities, which are severe limiting factors regarding their capacity of thermal energy storage and the pumping power required to transport them, respectively. During the last few decades, engineers and researchers made substantial efforts to improve the heat transfer efficiency of these HTFs by means of passive or active methods: chaotic advection, enhanced turbulence (turbulators), HTFs with higher thermal properties, or any combination [8]. Among these methods, nanofluids have proven to be an effective way to achieve that objective without increasing the size, cost, and complexity of thermal equipments too much. Ethylene- and propylene-glycol-based nanofluids have been then widely considered for their applications, mainly to remove heat in car radiators [9; 10; 11; 12], diesel electric generators [22], industrial heat exchangers [23], and electronic devices [24; 25]. General reviews on nanofluids have been published so far in the literature focusing on the preparation and stability of nanofluids [26; 27], on the synthesis, thermo-physical properties, and heat transfer mechanisms of nanofluids [28], or on their applications in heat exchangers [29]. [PERSON] and [PERSON] [30] and then [PERSON] and [PERSON] [25] proposed also detailed reviews on the theoretical and/or numerical methods dedicated to the simulation of nanofluids and nano-lubricants, respectively. [PERSON] et al. [31] summarized the thermophysical properties and performance of nano-refrigerants in a refrigeration system. All these aspects are also discussed in detail in the monograph of [PERSON] et al. [32]. To the best of our knowledge, there is then no updated review up to 2018 specific to ethylene- and propylene-glycol-based nanofluids.