Personalized ventilation: evaluation of different air terminal devices

Personalized ventilation (PV) aims to provide clean air to the breathing zone of occupants. Its performance depends to a large extent on the supply air terminal device (ATD). Five different ATDs were developed, tested and compared. A typical office workplace consisting of a desk with mounted ATDs was simulated in a climate chamber. A breathing thermal manikin was used to simulate a human being. Experiments at room air temperatures of 26 and 20 °C and personalized air temperatures of 20 °C supplied from the ATDs were performed. The flow rate of personalized air was changed from less than 5 up to 23 l/s. Tracer gas was used to identify the amount of personalized air inhaled by the manikin as well as the amount of exhaled air re-inhaled. The heat loss from the body segments of the thermal manikin was measured and used to calculate the equivalent temperature for the whole body as well as segments of the body. An index, personal exposure effectiveness, was used to assess the performance of ATDs in regard to quality of the air inhaled by the manikin. The personal exposure effectiveness increased with the increase of the airflow rate from the ATD to a constant maximum value. A further increase of the airflow rate had no impact on the personal exposure effectiveness. Under both isothermal and non-isothermal conditions the highest personal exposure effectiveness of 0.6 was achieved by a vertical desk grill followed by an ATD designed as a movable panel. The ATDs tested performed differently in regard to the inhaled air temperature used as another air quality indicator, as well as in regard to the equivalent temperature. The results suggest that PV may decrease significantly the number of occupants dissatisfied with the air quality. However, an ATD that will ensure more efficient distribution and less mixing of the personalized air with the polluted room air needs to be developed.     

Nanostructured manganese oxide on fullerene soot for water oxidation under neutral conditions

The sluggish kinetics of oxygen-evolution reaction (OER) through water-oxidation reaction results in high overpotentials for water splitting. Among different compounds, carbon-based material/Mn oxide composites were reported as OER catalysts. Fullerene soot (FS), which contains a mixture of fullerenes and carbon blacks, is low-cost compared to fullerenes and is commercially available. Herein, the Mn oxide/fullerene soot (MnO_x/FS) composite was investigated as an OER catalyst under neutral conditions. The composite was prepared through the reaction of KMnO₄ and FS as a facile, easy, and low-cost procedure. In this method, amorphous Mn oxide is formed directly on FS. The material was characterized by a number of methods. Then, the OER catalytic activity of MnO_x/FS was studied in a LiClO₄ solution (pH ≈ 6.3). Compared to pristine FS, the OER activity of MnO_x/FS is 2.5 times higher at 2.25 V vs. RHE. The Tafel slopes for OER are 450 and 240 mV per decade for FS and the reported composite, respectively.     

Migration of liquid film and grain boundary in Mo-Ni induced by temperature change

Migration of liquid films and grain boundaries in liquid phase sintered 95Mo-5Ni (wt%) alloy occurs if the sintered specimens are heat-treated at temperatures above or below those of the initial sintering treatment. Behind the migrating boundaries, solid solutions in equilibrium at the heat-treatment temperature are deposited on the parent grains and the process is analogous to discontinuous precipitation and diffusion induced grain boundary migration (DIGM). The migration rate is varied by changing the sintering temperature while keeping the heat-treatment temperature constant; it increases parabolically with the expected composition difference between the initial and the final solid solutions. This result agrees with Hillert's proposal that the coherency strain energy in a diffusion layer in the retreating grain is the driving force. The observed migration rate and retardation effect due to the boundary curvature also agree in an order of magnitude with the coherency strain energy as the driving force. The results show that chemically induced migration of liquid films between the grains can be readily controlled experimentally and analyzed theoretically in terms of well known thermodynamic and kinetic laws.     

The study of ignition and emission characteristics of hydrogen-additive hydro-processed renewable diesel

This study was conducted to understand the effects of hydrogen (H₂) addition on the combustion and emission characteristics of hydro-processed renewable diesel. Experiments were performed in a constant volume combustion chamber (CVCC) at varying H₂ concentrations (0%, 5%, and 10% (by vol.)) relative to air (100%, 95%, and 90% (by vol.)), initial temperatures (T_ini) of 600, 650 and 700 K, equivalence ratios (φ) of 0.5, 1.0, and 1.5 and a fixed initial pressure (P_ini) of 10 bar. Overall, HRD has lower ignition delay (ID) and total ID. However, H₂ addition to HRD delayed the fuel's auto-ignition due to excess H₂ oxidation (H₂+OHH₂O + H) reaction taking place, which turns the chain reactions from branching to propagation, resulting from increasing in ID. Moreover, increasing of H₂ concentrations enhanced the maximum pressure rise (P_max) and heat release rate (HRR), whereas carbon dioxide (CO₂) and unburned hydrocarbon (HC) were decreased due to the higher magnitude of the lower heating value of H₂ than that of pure HRD. Since H₂ itself is a carbon-free molecule, the carbon content of the fuel is reduced. H₂ has the characteristics of fast combustion, resulting in a more flammable and complete mixture, which also makes HC emissions to become lower. However, the higher energy density of H₂ significantly raises the combustion temperature, and subsequent nitrogen oxides (NOx) were increased. The kinetic modeling predictions revealed that the IDs for HRD-H₂ were elongated due to the increased hydroperoxyl (HO₂) and hydrogen peroxide (H₂O₂) mole fractions which led to improved stability.     

Novel Janus 2D structures of XMoY (X,Y = O,S, Se,Te) composition for solar hydrogen production

The successful fabrication of H-phase Janus transition metal dichalcogenides (TMDs) has received considerable interest due to its great potential in photocatalytic applications. Here, new A′-XMoY (X/Y = O, S, Se, Te) Janus-type structures belonging to the family of TMDs were theoretically investigated for the first time in terms of photocatalytic water splitting via DFT calculations. For all compounds, the Raman spectra were calculated. The SMoO, SeMoO, SMoSe, SMoTe and SeMoTe compounds are dynamically stable and are semiconductors. Among all considered structures SMoTe is the most promising candidate for solar hydrogen production because valence and conduction bands perfectly engulf the redox potentials of water at both neutral and acidic media, opposite to SMoSe, SMoO, SeMoO suitable only in the acidic media, and SeMoTe – in the neutral media. Moreover, A′-SMoTe demonstrates the outstanding values of the solar-to-hydrogen (STH) conversion efficiencies of 54.0 and 67.1 for neutral and acidic media.     

Influence of high compression ratio and hydrogen addition on the performance and emissions of a lean burn spark ignition engine fueled by ethanol-gasoline

This paper investigates the effect of ethanol-gasoline-hydrogen in a lean-burn SI engine with different proportions such as E5, E10, E20, E30, and E40 at compression ratio 10.5:1. The results infer that the E10 blend is the optimized one. Further, E10 mixture investigates for 5% and 10% hydrogen addition on energy basis. Overall, this study establishes that the addition of ethanol enhances brake power by 9% and brake thermal efficiency by about 7%. Hydrogen enrichment to E10 mixture shows a significant enhancement in brake power and brake thermal efficiency at a lower equivalence ratio. Further, it observes that the lean limit had extended to a 0.47 equivalence ratio compared to a 0.5 equivalence ratio with the E10, and 0.54 with pure gasoline. The addition of hydrogen to E10, improves the combustion process and heat release rate while it reduces cycle-by-cycle variations and hydrocarbon emissions.     

Numerical study on carbon dioxide removal from the hydrogen-rich stream by supersonic Laval nozzle

A hydrogen purification system with a supersonic nozzle pretreatment process is proposed to improve the performance of traditional CO₂ removal processes from hydrogen-rich streams. A mathematical model of the H₂–CO₂ double-component condensation was established to investigate the feasibility of CO₂ capture in a hydrogen-rich stream using a supersonic nozzle. Compared to the single-phase model, this model is more similar to the objective flow facts and can effectively correct the deviation of the single-phase flow model by 21.4%. Furthermore, the parameters in the H₂–CO₂ double-components spontaneous condensation process in the nozzle were analyzed, and the microscopic mechanism of CO₂ spontaneous condensation was clarified. Finally, the effects of the inlet parameters on the carbon capture efficiency were analyzed. The results indicated that the nozzle is more suitable for purifying hydrogen-rich streams with low temperatures and high carbon content, confirming the possibility of using a supersonic nozzle as a carbon capture method.     

Effects of CH4 and CO on hydrogen embrittlement susceptibility of X80 pipeline steel in hydrogen blended natural gas

The slow strain rate tensile experiments are carried out to investigate the tensile properties of X80 pipeline steel in hydrogen blended natural gas environments with different H₂/CH₄/CO contents. Mechanical properties and fracture morphologies are further analyzed. The results show that the hydrogen embrittlement susceptibility of X80 steel can be inhibited by the presence of CH₄/CO, and the inhibition mechanisms are discussed. When the CH₄ contents increase above 20 vol%, the inhibition on hydrogen embrittlement of X80 steel is stabilized. By comparison, the inhibitory effect of CO is more significant.     

Influence of chromium and lanthanum incorporation on the optical properties,catalytic activity,and stability of IrOx nanostructured films for hydrogen generation

Hydrogen production (HP) by photocatalytic water splitting (PWS) is becoming more and more popular on a global scale. The world's largest and most accessible renewable energy source—the Sun—as well as widely accessible metal oxide-based photoelectrodes are both utilized in this process. The preparation of pure and doped iridium oxide (IrO_x) films is attempted in this work in an effort to better understand how Cr and La affect optical and HP efficiency as well as electrode stability. By using FE-SEM, the films' varying thicknesses and nanorod-like morphologies were detected. UV–Vis spectra reveal that the composition has an impact on the films' absorption and reflectance. IrO_x has an optical band gap (E_g) of 2.9 eV, and this value decreased/increased after Cr doping/La codoping. The micro-Raman spectra, which showed that the E_g mode of Ir–O stretching was red-shifted from 563 to 553 cm⁻¹, validate the films' amorphous nature. The resultant (IrO_x) films were utilized in the HP via the solar photoelectrochemical (PEC) process. The codoped film, which has a solar-to-hydrogen conversion efficiency of 2.32% and a hydrogen evolution rate of 23.5 mmol h⁻¹cm⁻², is the most efficient and stable photoelectrode among the electrodes under examination. The highest absorbed photon-to-current conversion efficiency (APCE%) values for pure and codoped IrO_x photoelectrodes were 3.62%@460 nm and 5.54%@490 nm, respectively. With enhancement factors of 2.77, 1.89, and 2.90 for pure IrO_x, IrO_x:5% Cr, and IrO_x:Cr,2.5% La, respectively, the J_ph increased to 1.58, 1.70, and 1.83  mA cm⁻² at 90 °C. After ten runs, the codoped photoelectrode still has 99.2% of its initial photocurrent, compared to 80.8% and 82.8% for pure and Cr-doped IrO_x. Calculated Tafel slopes, corrosion rates, and PEC thermodynamic parameters show how codoping and doping affect photoelectrode performance and stability.