Ehsan Bitaraf Haghighi

Fabrication, Characterization and Thermophysical Property Evaluation of SiC Nanofluids for Heat Transfer Applications

Nanofluids (NFs) are nanotechnology-based colloidal suspensions fabricated by suspending nanoparticles (NPs) in a base liquid. These fluids have shown potential to improve the heat transfer properties of conventional heat transfer fluids. In this study we report in detail on fabrication, characterization and thermo-physical property evaluation of SiC NFs, prepared using SiC NPs with different crystal structures, for heat transfer applications. For this purpose, a series of SiC NFs containing SiC NPs with different crystal structure (α-SiC and β-SiC) were fabricated in a water (W)/ethylene glycol (EG) mixture (50/50 wt% ratio). Physicochemical properties of NPs/NFs were characterized by using various techniques, such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fouriertransform infrared spectroscopy (FTIR), dynamic light scattering (DLS) and Zeta potential analysis. Thermo-physical properties including thermal conductivity (TC) and viscosity for NFs containing SiC particles (α- and β- phase) weremeasured. The results show among all suspensions NFs fabricated with α-SiC particles have more favorable thermo-physical properties compared to the NFs fabricated with β-SiC.The observed difference is attributed to combination of several factors, including crystal structure (β- vs. α-), sample purity, and residual chemicals exhibited on SiCNFs. A TC enhancement of ∼20% while 14% increased viscosity were obtained for NFs containing 9 wt% of particular type of α-SiC NPs indicating promising capability of this kind of NFs for further heat transfer characteristics investigation.

Shelf stability of nanofluids and its effect on thermal conductivity and viscosity

This study proposes a method and apparatus to estimate shelf stability of nanofluids. Nanofluids are fabricated by dispersion of solid nanoparticles in base fluids, and shelf stability is a key iss ...

Screening Single Phase Laminar Convective Heat Transfer of Nanofluids in a Micro-tube

Nano scale solid particles dispersed in base fluids are a new class of engineered colloidal solutions called nanofluids. Several studies reported enhancement of heat transfer by using nanofluids. This article reports convective single-phase heat transfer coefficients in an open 30 cm long, 0.50 mm internal diameter stainless steel test section. The setup is used for screening single phase laminar convective heat transfer with water and three different nanofluids: water based Al2O3, ZrO2, and TiO2 (all with 9 wt% of particles). A syringe pump with adjustable pumping speed is used to inject fluids into the test section. Thirteen T-type thermocouples are attached on the outer surface of the test section to record the local wall temperatures. Furthermore, two T-type thermocouples are used to measure inlet and outlet fluid temperatures. A DC power supply is used to heat up the test section and a differential pressure transducer is used to measure the pressure drop across the tube. Furthermore, the effective thermal conductivities of these nanofluids are measured using the Transient Plane Source (TPS) method at a temperature range of 20 – 50°C. The experimental average values of heat transfer coefficients for nanofluids are compared with water. Enhancement in heat transfer of nanofluids is observed only when compared at constant Reynolds number (Due to higher viscosity for nanofluids, higher velocity or mass flow rate is required for nanofluids to reach the same Reynolds number). The other methods of comparison: equal mass flow rate, volume flow rate, pressure drop and pumping power did not show any augmentation of the heat transfer coefficient for the tested nanofluids compared to water.

A hybrid cooling system for telecommunicatioin base stations

Huge amount of energy is consumed by a typical telecommunication base station in order to keep the indoor climate temperature low enough to avoid any damage to IT/electronic equipment. By increasing the number telecommunication base stations applying more energy efficient cooling strategies are urgently needed. Free cooling either in direct approach (e.g. extracting fresh air), or indirect approach (e.g. thermosiphon or air to air heat exchanger) is a well-proven strategy to reduce the total power consumption for cooling telecommunication base stations. This article proposes a hybrid cooling system, which is an integrated vapour compression unit with a thermosiphon unit in a single frame. In such a hybrid system the indoor air circulates through a closed loop with minimal interaction with the outdoor air. This article suggests a model to control and estimate the potential of energy savings by a hybrid cooling system. Based on the results for an indoor temperature set point of 25 °C the cooling load provides by the hybrid system can be divided among three different operating modes: 0-59% (thermosiphon), 12-41% (dual mode), and 12-88% (air conditioning) depending on the location of the base stations.

Free cooling: A complete solution on reducing total energy consumption for telecommunication base stations

Globalisation and modern economy are significantly depended on telecommunication industry. Accordingly the number of telecommunication base stations is increasing all over the world. Consequently network operators are looking for smart energy management architecture for their base stations. Cooling traditionally counted for 25-50% of the total energy consumption in a typical base station. This article addresses more energy efficient cooling strategies in order to reduce this figure. Combining air conditioning and free cooling systems (e.g. extracting fresh air into the envelope for the latter) is one of the promising and well-proven methods to reduce energy consumption in base stations. Furthermore, the potential of employing free cooling in either single zone (IT/electronic equipment and batteries in one envelope), or dual zones (IT/electronic equipment and batteries in two separate envelopes) strategies are investigated. Based on the results for an indoor temperature set point of 25 °C free cooling can cover approximately 21-94% of the total cooling demand depending on the location and the selected strategy.