Comparison of stability and thermophysical properties of CNT–GNP hybrid nanofluids using different surface modification techniques

AbstractThis study examines how non-covalent and covalent surface modification methods affect the stability and thermo-physical characteristics of carbon nanotubes (CNTs) and graphene platelets (GNP) when distributed in solar thermal fluids. Surfactants are employed for examining non-covalent surface modification, while acid treatment is utilized for investigating covalent modification. Nanofluid samples are created with concentrations of 0.0625%, 0.125%, 0.25%, and 0.5% by weight in pure ethylene glycol (EG) and EG–water (80:20). Zeta potential analysis was utilized to study the stability of the nanofluids. The oxidized CNT–GNP nanofluids showed outstanding stability, with zeta potential values remaining almost constant for 60 d. Experiments were conducted on pure, surfactant-dispersed, and oxidized CNT–GNP nanofluids. The thermal conductivity of oxidized CNT–GNP nanofluids increased by 16% when 0.5 wt% was dispersed in the EG–water (80:20) sample. Nanofluids with CTAB and SDS showed a 14% and 13% enhancement in thermal conductivity, respectively. Formulas were created to forecast thermal conductivity and dynamic viscosity values

Climate-Adaptive Façades with an Air Chamber

The development of energy-efficient technologies at all stages of a building’s life cycle is essential to achieving sustainable development goals. The object of the study is climate-adaptive façade structures with air gaps in the form of a Trombe wall and a double-skin façade. Cases using phase-change materials (PCM) and photovoltaic modules (PV) in climate-adaptive structures are analyzed separately. The research method is aimed to review and analyze the energy-saving potential from integrating the Trombe wall or double-skin façade in buildings. The work systematizes full-scale, physical, and mathematical experiments. Articles from Scopus and Web of Science systems from 2001 to 2022 inclusive were subject to consideration. The article presents a statistical analysis given by the scientific community on the current topic’s dynamics. The study’s significance is characterized by a lack of knowledge on the behavior of the mentioned façade systems in various climate zones and for different buildings types. The results have shown that comprehensive studies on the investigated systems are significant and can serve for further designs and energy efficiency improvements. For the first time, a scientometric analysis of articles on the topic “Climate-adaptive façades” was compiled

Optimization of wire-cut electric discharge machining process parameters for hybrid MMC(AA7475/ZrO2/gr) using Taguchi method: an experimental study

AbstractMetal-matrix composites (MMCs) and hybrid metal-matrix composites (HMMCs) are novel materials that possess distinctive mechanical characteristics, making them well-suited for industrial applications. This research implements an experimental study of the mechanical properties of HMMCs, where weight percentages (2, 3, and 4 wt. %) of zirconium dioxide (ZrO2) and graphite powder (Gr) are used as reinforcements and the aluminum alloy 7475 (AA7475) is used as a matrix. In this investigation, the stir casting method was used to prepare the composite by using AA7475 alloy with pre-heated reinforced particles of ZrO2 and graphite with various reinforcement weight percentages. Among these combinations, AA with 4 wt. % ZrO2 and 2 wt.% Gr showed enhanced mechanical properties. The mechanical properties of the ultimate tensile strength, yield strength, and hardness were evaluated. A Scanning Electron Microscope analysis was conducted to study the reinforcement distribution in the matrix. The input parameters for wire-cut electrical discharge machining (WCEDM) are pulse-on time (TON), pulse peak current (IP), and flushing pressure (PF). The material removal rate and surface roughness are the output responses. Determining the ideal set of process parameters in WCEDM for HMMC also involved the use of the Taguchi design technique known as the L9 orthogonal array. The peak current for the MRR and flushing pressure for the SR are the most prominent parameters