Enhancements of thermal conductivities with Cu, CuO, and carbon nanotube nanofluids and application of MWNT/water nanofluid on a water chiller system

Abstract

In this study, enhancements of thermal conductivities of ethylene glycol, water, and synthetic engine oil in the presence of copper (Cu), copper oxide (CuO), and multi-walled carbon nanotube (MWNT) are investigated using both physical mixing method (two-step method) and chemical reduction method (one-step method). The chemical reduction method is, however, used only for nanofluid containing Cu nanoparticle in water. The thermal conductivities of the nanofluids are measured by a modified transient hot wire method. Experimental results show that nanofluids with low concentration of Cu, CuO, or carbon nanotube (CNT) have considerably higher thermal conductivity than identical base liquids. For CuO-ethylene glycol suspensions at 5 vol.%, MWNT-ethylene glycol at 1 vol.%, MWNT-water at 1.5 vol.%, and MWNT-synthetic engine oil at 2 vol.%, thermal conductivity is enhanced by 22.4, 12.4, 17, and 30%, respectively. For Cu-water at 0.1 vol.%, thermal conductivity is increased by 23.8%. The thermal conductivity improvement for CuO and CNT nanofluids is approximately linear with the volume fraction. On the other hand, a strong dependence of thermal conductivity on the measured time is observed for Cu-water nanofluid. The system performance of a 10-RT water chiller (air conditioner) subject to MWNT/water nanofluid is experimentally investigated. The system is tested at the standard water chiller rating condition in the range of the flow rate from 60 to 140 L/min. In spite of the static measurement of thermal conductivity of nanofluid shows only 1.3% increase at room temperature relative to the base fluid at volume fraction of 0.001 (0.1 vol.%), it is observed that a 4.2% increase of cooling capacity and a small decrease of power consumption about 0.8% occur for the nanofluid system at a flow rate of 100 L/min. This result clearly indicates that the enhancement of cooling capacity is not just related to thermal conductivity alone. Dynamic effect, such as nanoparticle dispersion may effectively augment the system performance. It is also found that the dynamic dispersion is comparatively effective at lower flow rate regime, e.g., transition or laminar flow and becomes less effective at higher flow rate regime. Test results show that the coefficient of performance of the water chiller is increased by 5.15% relative to that without nanofluid.

Thermal Conductivity and Specific Heat Capacity of Dodecylbenzenesulfonic Acid-Doped Polyaniline Particles—Water Based Nanofluid

“…It was reported that the Brownian motion effect of nanoparticles on thermal conductivity was more pronounced at low mass fraction of nanoparticles [31]. However, in this case, the increase in thermal conductivity was rather small compared to the one containing inorganic or oxide nanoparticles [21,32,33]. It is anticipated that polyaniline as well as DBSA molecules (doped DBSA) could interact with water molecules to form hydrogen bonding [34].…”

Experimental study on critical heat flux of highly efficient soft hydrophilic CuO–chitosan nanofluid templates

“…Sodium lauryl sulfate (SLS), a surfactant, contains a hydrophilic head and a hydrophobic tail; these amphiphilic molecules can self-assemble into a variety of organized structures in solution, such as normal and reverse micelles, micro emulsions, vesicles, and lyotropic liquid crystals. Such organized systems have been used successfully for templating hollow porous capsules; we were able to obtain regular porous CuO-CS NCs using the solution chemistry method [16,21]. With this method, larger crystals grow from smaller-sized ones, which have a higher solubility than the former.…”

“…The purpose of this study was to maximize the pool boiling CHF of NFs by introducing a novel NC material due to use of high wt% of CuO NPs and their practical applications are limited [14][15][16][17]. Specifically, we developed a new NC made from CuO anchored with CS (CuO-CS).…”

A survey on experimental and numerical studies of convection heat transfer of nanofluids inside closed conduits

“…Examples are double pipe or plate heat exchangers (PHEs) used in power production and recovery, food processing, chemical industry, and mechanical appliances such as air conditions, refrigerators, and ventilators. 39,40 In recent years, efforts have been made to enhance heat transfer performance of heat exchangers. The applied methods mostly include creation of turbulent flow, 41,42 use of fins, twisters, and baffles.…”