Evaluation of thermal and evaporative resistances in cricket helmets using a sweating manikin

The main objective of this study is to establish an approach for measuring the dry and evaporative heat dissipation cricket helmets. A range of cricket helmets has been tested using a sweating manikin within a controlled climatic chamber. The thermal manikin experiments were conducted in two stages, namely the (i) dry test and (ii) wet test. The ambient air temperature for the dry tests was controlled to ∼23 °C, and the mean skin temperatures averaged ∼35 °C. The thermal insulation value measured for the manikin with helmet ensemble ranged from 1.0 to 1.2 clo. The results showed that among the five cricket helmets, the Masuri helmet offered slightly more thermal insulation while the Elite helmet offered the least. However, under the dry laboratory conditions and with minimal air movement (air velocity = 0.08 ± 0.01 ms⁻¹), small differences exist between the thermal resistance values for the tested helmets. The wet tests were conducted in an isothermal condition, with an ambient and skin mean temperatures averaged ∼35 °C, the evaporative resistance, R_et, varied between 36 and 60 m² Pa W⁻¹. These large variations in evaporative heat dissipation values are due to the presence of a thick layer of comfort lining in certain helmet designs. This finding suggests that the type and design of padding may influence the rate of evaporative heat dissipation from the head and face; hence the type of material and thickness of the padding is critical for the effectiveness of evaporative heat loss and comfort of the wearer. Issues for further investigations in field trials are discussed.     

Preparation and characterization of zinc modified calcium silicate/polycaprolactone with graphene oxide composite coating for bone repair applications

The goal of biomaterial interest is the ease of the bone tissue regeneration process or the replacement of damaged bone and other tissues with recently generated bone tissue. Calcium silicate (CaSi) bioceramic is a vital material for bone tissue engineering, predominantly for bone repair. Though, the low toughness of calcium silicate imitates its load-bearing applications. The electrophoretic deposition technique was used to coat various concentrations of Zn²⁺ substituted CaSi on TNT. In this work, a novel as-obtained an appropriate orthopedic implant hybrid material by charged calcium ions of mineralized calcium silicate united with PCL-negatively charged graphene oxide [Zn-CaSi (S₁-S₃)/PCL (P₁-P₃)/GO]. Hence, the effectively as-obtained [Zn-CaSi (S₁-S₃)/PCL (P₁-P₃)/GO] bone-like apatite on the ternary composite coatings on the surface was proven via XRD, FT-IR, FESEM with EDAX spectra, HR-TEM and BET analyses etc., Moreover, the TNT/S₂/P₂@GO ternary composite coatings exhibit better mechanical properties and antibacterial activity. The metal ions released from the coatings were calculated via ICP-AES studies. Moreover, the cell viability and also the live/dead staining of MG63 human osteoblasts cells on the subsequent composite coating material for better cell growth in orthopedic applications.     

A feasibility study of a ventilated beam system in the hot and humid climate: a case-study approach

The applications of ventilated beam systems in the hot and humid climate are limited. The main reason is the high risk of condensation. A case-study measurement was conducted in a typical office building in Singapore to investigate the feasibility of a ventilated beam system in the Tropics. The results show that the condensation in the beam system is possible to prevent and to reach dry cooling if infiltration is minimized, supply airflow rate is sufficient to extract humidity of people and tuning of the automation system has conducted probably.     

New approaches to determine the interface height of fire smoke based on a three-layer zone model and its verification in large confined space

Large confined space has high incidence of fires, which seriously threatens the safety of people working there. Understanding the distribution of smoke in such large space is critical to fire development prediction and smoke control. Three improved methods for the stratification interface prediction of fire smoke are developed, including of improved intra-variance, integral ratio and N-percentage methods. In these methods, the interface height is determined by the vertical temperature distribution based on a three-layer smoke zone model, which is an improvement of a two-layer zone model. Thereafter, the three improved methods are applied to several typical fire cases simulated CFD to predict the smoke interface, and their applicability and reliability are verified by comparison of the smoke stratification results with the filed simulation results. Results show that the three improved methods can effectively determine the location of the three-layer zone model's interface, and they have the ability to predict smoke interface for fires with different fire source types and ventilation conditions.     

Experimental Studies of Electromagnetic Wave Attenuation by Flame and Smoke in Structure Fire

Attenuation of electromagnetic waves in the fire scene is an important issue when the stability of wireless communication is concerned, especially in fire rescue scenarios of high-rise buildings. Therefore, it is of importance to study the effects of flame and smoke on the attenuation of electromagnetic waves in structure fire. In this article, the influence of flame was studied through using alcohol as fuel. Different types of fuels were used to produce different concentrations of smoke. Different ranges of electromagnetic wave frequency from 350 MHz to 400 MHz were also used to investigate the frequency-dependent properties of the attenuation effect. The results show that flame itself does not have significant effects on the electromagnetic wave attenuation, but smoke plays an important role. Smoke from diesel fuel results in larger signal attenuation than other fuels, with attenuation of 1.16 dB at 300 MHz. The relationship between the concentration of smoke and signal attenuation follows the first-order exponential function. It also indicates that electromagnetic wave attenuation is frequency-dependent. The attenuation is 5.43 dB at 360 MHz when the smoke concentration is 20 dB/m, but only 0.26 dB at 400 MHz. It is suggested that a frequency-dependent assessment should be considered for investigating the reliability of the wireless communication system in structure fire in high-rise buildings.     

Experimental and numerical investigation of the wake flow of a human-shaped manikin: Experiments by PIV and simulations by CFD

High-quality measurements of the flow structures induced by human movements are important for analyzing indoor air quality. This study measures the longitudinal and cross-sectional velocity and vortex fields behind the moving body, and investigates the effect of movement and body-shape on a wake flow structure. Experiments were conducted in a small-scale chamber with a moving human-shaped manikin, measured by the particle image velocimetry technique. The dynamic changes of the movement-induced wake flow were compared both in different times and movement stages. A strong downward airflow and an upward vortex were observed following the moving body. The measurements also revealed symmetric downward and expansive vortices in the wake flow. During the movement, a longitudinal recirculation region can be predicted around the manikin. Compared with a moving cylinder, this study shows that the specific shape of the legs exerts an obvious impact on the flow behind the lower limbs. In particular, a horizontal flow was observed penetrating from between the legs, with a velocity of 0.5 m/s, which was equal to the moving speed of the manikin. Meanwhile, a computational fluid dynamic model was also employed to simulate the unsteady instantaneous flow affected by the human movement. The numerical results can reveal different stages of the wake generation, development, and decay in detail during the movement. By quantitatively comparing with the experimental data, the LES method has rendered a good alignment with the experimental result, not only in the velocity magnitude value but also in fluctuating quantity.     

Experimental studies on time-dependent size distributions of smoke particles of standard test fires

The time-dependent size distributions of smoke particles are measured by SMPS spectrometer as experiments go on, respectively, for four standard fires, i.e. TF2, TF3, TF4 and TF5. The results suggest that, for the TF4, the normalized number distributions of smoke aerosol be best fitted with lognormal functions and little time-dependency be shown throughout the experiments. It is also indicated that the best fitting curves of the normalized number distributions of smoke particles change from the so-called under-lognormal fittings to over-lognormal fittings for the TF2, TF3 and TF5, as time moves. In addition, a common changing trend of the size distribution curves can be drawn for the three standard fires. Namely, the curves mainly drift toward larger diameters of smoke particles and the peaks of the curves keep increasing as time goes by for each standard test fire.     

Reinforcement of structural,thermal and electrical properties and antibacterial activity of PVA/SA blend filled with hybrid nanoparticles (Ag and TiO2 NPs): Nanodielectric for energy storage and food packaging industries‏

In this work, silver nanoparticles (Ag NPs) were prepared using a plant extract which is a cost-effective and environmentally friendly method. The sol-gel method was used to synthesize titanium dioxide nanoparticles (TiO₂ NPs). A solid polymer nanocomposite samples have been prepared via the well-known solution cast way. The present samples were examined using various analytical measurements. The XRD patterns showed a decrease in the degree of crystallinity of the PVA/SA blend due to the addition of the hybrid nanoparticles (Ag and TiO₂ NPs). It was evident by the ATR-FTIR measurement that there is an interaction between the functional groups of the polymeric matrix and the hybrid nanoparticles. XPS confirmed that Ag NPs were loaded onto the surfaces of the PVA/SA/TiO₂ organic-inorganic nanocomposite samples. The TGA curves of the doped samples showed an improvement in their thermal stability compared to the pure sample. From the AC conductivity and electrical modulus, the dynamic ions activity and the kind of relaxation process of the nanocomposites samples were examined. The highest conductivity was log −6.066 S/cm for the polymeric sample doped with 1.60% Ag@TiO₂ NPs, as showed by the AC conductivity measurement. A wide dispersion is observed in the dielectric constant spectra at low frequency. It was also evident from the data that the antibacterial activity of the pristine PVA/SA matrix was growing due to the inclusion of the hybrid nanoparticles to the polymeric matrix. Therefore, the obtained results indicate the applicability of these samples and their potential for use in the semiconductor industry, portable electrochemical batteries and energy storage industry, due to the remarkable improvement in the structural, thermal and electrical properties. Also, the good antibacterial activity of these films provides new samples as effective biomaterials and has the potential to be used in the food packaging industry.     

Rheology of fire-fighting foams

This paper examines the rheological properties of compressed-air foams and contains velocity profiles of foams flowing through straight horizontal tubes. It is shown that a master equation can be derived from the experimental data to account for a range of expansion ratios and pressures normally encountered during pumping of polyhedral-in-structure fire-fighting foams. The experimental data come from a Poiseuille-flow rheometer consisting of three stainless steel tubes 6.95, 9.9, 15.8 mm in diameter, with foam generated by mixing a pressurised solution of Class A foam with compressed air. Results are corrected for wall slip following the method of Oldroyd-Jastrzebski, which implies the dependence of slip coefficients on the curvature of the tube wall. The experimental results demonstrate the applicability of the volume equalisation method to the more expanded, polyhedral (ε>5) and transition, bubbly-to-polyhedral (5⩾ε⩾4) foams. (The method of volume equalisation was introduced by Valkó and Economides to correlate the viscosity of low expansion foams (ε<4), characterised by spherical bubbles.) The present results indicate that all data points align themselves along two master curves, depending on whether the foam consists of bubbles or polyhedral cells.     

负载贵金属催化剂在挥发性有机物氧化反应中的应用

挥发性有机物(VOCs)是大气污染的主要来源,危害人体健康。催化氧化法是消除挥发性有机物的有效手段,其核心是高效催化剂,新型、高活性、高稳定性催化剂的研发具有重要意义。简要综述近年来负载Au、Pd和Pt贵金属催化剂对VOCs氧化消除的催化性能,分析VOCs氧化在典型催化剂表面形成的活性物种及其对催化活性的影响,并展望VOCs催化氧化的未来发展趋势。