Photochemistry of [Ru(pytz)(btz)2]2+and Characterization of a κ1-btz Ligand-Loss Intermediate

We report the synthesis, characterisation and photochemical reactivity of the triazole-containing complex [Ru(pytz)(btz)2]2+ (1, pytz = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole, btz = 1,1’-dibenzyl-4,4’-bi-1,2,3-triazolyl). The UV-visible absorption spectrum of 1 exhibits pytz- and btz-centred 1MLCT bands at 365 and 300 nm respectively. Upon photo-excitation, acetonitrile solutions of 1 undergo conversion to the ligand loss intermediate, trans-[Ru(pytz)(2-btz)(1-btz)(NCMe)]2+ (2, 363 = 0.013) and ultimately to the ligand loss product trans-[Ru(pytz)(btz)(NCMe)2]2+ (3), both of which are observed and characterised by 1H NMR spectroscopy. Time-dependent density functional theory calculations reveal that the S1 state of the complex has primarily HOMOLUMO pytz-based 1MLCT character. Data show that the 3MLCT and 3MC states are in close energetic proximity ( 0.11 eV to 2 d.p.) and that the T1 state from a single point triplet state calculation at the S0 geometry suggests 3MC character. Optimisation of the T1 state of the complex starting from the ground state geometry leads to elongation of the two Ru-N(btz) bonds cis to the pytz ligand to 2.539 and 2.544 Å leading to a psuedo 4-coordinate 3MC state rather than the 3MLCT state. The work therefore provides additional insights into the photophysical and photochemical properties of ruthenium triazole-containing complexes and their excited state dynamics

Fretting Wear Analysis of Different Tube Materials Used in Heat Exchanger Tube Bundle

Research on heat exchange is being carried out for more than five decades because of its importance in process industries and power generation plants. Heat exchanger experiencing cross flow are vulnerable to flow induced vibration. These vibration causes the interaction of tubes with the baffle resulting in a fretting wear of the tubes. Present study focuses on the fretting wear analysis of different tube materials. Fretting wear tests were performed on aluminum, copper and stainless steel instrumented central tubes against mild steel baffle. For each tube material the tests were performed for three different test durations i.e. 60 minutes, 120 minutes and 180 minutes at a cross flow velocity of 0.55 m/s. It was observed that vibrational amplitude of the flexible test tube is affected by its weight. A scanning electron microscope was used to analyze and measure the sizes of wear scar. The results indicated that wear loss in case of aluminum tube is the highest while that in case of stainless steel tube is the lowest

INCORPORATION OF WHEAT STRAW ASH AS PARTIAL SAND REPLACEMENT FOR PRODUCTION OF ECO-FRIENDLY CONCRETE

The depletion of natural sand resources occurs due to excessive consumption of aggregate for concrete production. Continuous extraction of sand from riverbeds permanently depletes fine aggregate resources. At the same time, a major ecological challenge is the disposal of agricultural waste ash from biomass burning. In this study, an environmental friendly solution is proposed to investigate the incorporation of wheat straw ash (WSA) by replacing 0, 5, 10, 15, and 20% of sand in concrete. Characterization results of WSA revealed that it was well‐graded, free from organic impurities, and characterized by perforated and highly porous tubules attributed to its porous morphology. A decrease in fresh concrete density and an increase in slump values were attained by an increase in WSA replacement percentage. An increasing trend in compressive strength, hardened concrete density, and ultrasonic pulse velocity was observed, while a decrease was noticed in the values of water absorption with the increase in WSA replacement percentages and the curing age. The WSA incorporation at all replacement percentages yielded concrete compressive strength values over 21 MPa, which complies with the minimum strength requirement of structural concrete as specified in ACI 318‐19. Acid resistance of WSA incorporated concrete improved due to the formation of pozzolanic hydrates as evident in Chappelle activity and thermogravimetric analysis (TGA) results of WSA modified composites. Thus, the incorporation of WSA provides an environmentally friendly solution for its disposal. It helps in conserving natural aggregate resources by providing a suitable alternative to fine aggregate for the construction industry

Investigation of the Effects of the Incident Flow Angle on Vibration Behavior in Heat Exchanger Tube Bundle

Experimental study of incident flow angle effects on vibration behavior has been carried out on aluminum tube in parallel triangular tube bundle with P/D ratio of 1.375. Fluid elastic instability is the most fatal mechanism from all of the vibration mechanisms and therefore must be dealt with a lot of attention. Experiments were performed on low speed water tunnel with the velocity of water ranges from 0.3 m/s to 0.7 m/s. The experiments were designed in a unique way to study the effects of incident flow angle on vibration behavior. The monitored tube was mounted flexibly in an array of rigid tubes. Experiments were conducted on a flexible tube for different velocities ranging from 0.3 m/s to 0.7 m/s with different array rotated angles (0 to 90 degrees). It was observed that the vibration level was significantly high at 75 degree configuration as compared to other rotated angle configurations. Also it was observed that the damping response is dispersed with all positive values, indicating that there is no instability in the tube

An experimental study of PCM based finned and un-finned heat sinks for passive cooling of electronics

This experimental study determines and compares the thermal performance of unfinned and finned PCM based heat sinks. For the analysis considering pin-fins as thermal conductivity enhancer (TCE), triangular configuration is considered. It is further classified into inline and staggered pin-fin arrangements. Three popular variants of paraffin namely paraffin wax, RT-44 and RT-35HC are incorporated as phase change materials (PCMs) inside the heat sink. The volume fraction of pin-fins and PCMs are kept constant at 9% and 90% respectively. The heat input at the base of heat sinks ranges from 5 W to 8 W. The results are presented in two different cases, charging and discharging, and the analysis of temperature variation and comparison of fin arrangements in three different heat sinks with and without PCM. Further the enhancement ratios are determined to quantify the thermal performance in operation time of heat sink for passive cooling with the influence of PCMs and TCEs. The results suggest triangular inline pin-fin as the dominant heat sink geometry and RT-44 as the most efficient PCM for passive thermal management of electronic devices

Analysis of Flow-Induced Vibrations in a Heat Exchanger Tube Bundle Subjected to Variable Tube Flow Velocity

Tube bundles of shell and tube-type heat exchangers often fail because of vibrations produced in tubes due to flow. The turbulence in the flow is the primary cause of vibrations in the tubes. In this study, a tube positioned in the third row of the tube bundle was considered to determine the vibrational response of the heat exchanger tubes. The tube bundle was parallelly arranged in a triangular (60°) configuration having a pitch to diameter (P/D) ratio of 1.44. The internal tube flow velocity ranges from 0 to 0.371 m/s and the shell side velocity ranges from 0.5 m/s to 2 m/s. The experimentation shows that the amplitude of vibration without flow inside the tube is less as compared to the amplitude with the flow. Furthermore, as the velocity of internal tube flow escalates; the amplitude of tube vibrations tends to escalate as well even when the shell side flow velocity is kept constant. The data points from experiments tend to reside in the unstable region of the stability map and particularly on the map’s left side, although the tube shows stable vibration behaviour as confirmed by the experimental results. Thus, further, development can be done by modifying the theoretical models to predict the realistic stability behaviour of tubes with internal tube flow

Photochemistry of [Ru(pytz)(btz)₂]²⁺ and Characterization of a κ¹‑btz Ligand-Loss Intermediate

We report the synthesis, characterization, and photochemical reactivity of the triazole-containing complex [Ru­(pytz)­(btz)₂]²⁺ (<b>1</b>, pytz = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole, btz = 1,1′-dibenzyl-4,4′-bi-1,2,3-triazolyl). The UV–vis absorption spectrum of <b>1</b> exhibits pytz- and btz-centered ¹MLCT bands at 365 and 300 nm, respectively. Upon photoexcitation, acetonitrile solutions of <b>1</b> undergo conversion to the ligand-loss intermediate, <i>trans</i>-[Ru­(pytz)­(κ²-btz)­(κ¹-btz)­(NCMe)]²⁺ (<b>2</b>, Φ₃₆₃ = 0.013) and ultimately to the ligand-loss product <i>trans</i>-[Ru­(pytz)­(btz)­(NCMe)₂]²⁺ (<b>3</b>), both of which are observed and characterized by ¹H NMR spectroscopy. Time-dependent density functional theory calculations reveal that the S₁ state of the complex has primarily HOMO → LUMO pytz-based ¹MLCT character. Data show that the ³MLCT and ³MC states are in close energetic proximity (≤0.11 eV to 2 d.p.) and that the T₁ state from a single-point triplet state calculation at the S₀ geometry suggests ³MC character. Optimization of the T₁ state of the complex starting from the ground state geometry leads to elongation of the two Ru–N­(btz) bonds <i>cis</i> to the pytz ligand to 2.539 and 2.544 Å leading to a pseudo-4-coordinate ³MC state rather than the ³MLCT state. The work therefore provides additional insights into the photophysical and photochemical properties of ruthenium triazole-containing complexes and their excited state dynamics