High-temperature Drop Research Articles

Study on Water Wash Pretreatment and Al-Si Additives to Relieve the Sintering Behavior of Fungus Bran Combustion Ash

This study focuses on the sintering phenomenon that easily occurs during the direct combustion of molded fuel made from fungus bran (FB). To investigate the key factors influencing sintering, experiments are designed and conducted using a muffle furnace and a high-temperature drop furnace. The experimental results show that the combustion temperature is the primary factor triggering the sintering phenomenon. To effectively mitigate this issue, this study proposes two improvement strategies: water washing pretreatment and the use of additives. The analysis shows that water washing pretreatment effectively removes K and Mg elements, with the removal rates increasing as the washing temperature and time increase. Specifically, the removal rate of K ranges from 37.68% to 55.91%, and that of Mg ranges from 33.16% to 58.52%. Water washing pretreatment also reduces the degree of sintering; at 1400 °C, the TSF (tendency to slag formation) of the fuel increases by 25–40% after pretreatment, with a greater increases observed at higher washing temperatures and longer durations. Kaolin, used as an additive, significantly raises the ash melting point of FB and alleviates sintering, while P2O5 exacerbates it. Increasing the proportion of kaolin does not significantly enhance the TSF of high-temperature ash, but raising the P2O5 content from 5% to 10% lowers the TSF by 10–20% at the corresponding temperature.

First-principle and experimental investigation into the interfacial characters of Ti-doped ZTA and high chromium cast iron

Ti doping can improve the interfacial wettability and bonding condition between ZTA ceramic and high chromium cast iron (HCCI), but the underlying mechanism is still unclear. Therefore, the effects of Ti doping on the interfacial characters between ZTA and HCCI were investigated by experiment and first-principles calculations. Results of XRD, SEM, and high-temperature drop test indicate the presence of Ti at the interface and its effect on the formation of interfacial diffusion layer to improve the interface wettability and bonding obviously. The heat of segregation and work of adhesion obtained by first-principle calculations shows that the improvement in interface wettability and bonding is due to the promotion of dopped Ti atoms on the diffusion of Fe, Al, and Zr elements, but not the diffusion of Ti itself. Further investigation from the electronic level reveals that the doped Ti changes the charge distribution and orbital hybridization, and thus makes the formation or enhancement of strong ionic bonds and covalent bonds at the interface, improving the bonding strength and wettability of interfaces in ZTA/HCCI. The findings of this research can offer new insights into the modification of ceramics and enlarge the application of advanced ceramic materials.

Investigations of a turbine pre-swirl system with high temperature drop efficiency through the design of a novel vane-shaped receiver hole

The pre-swirl system, a vital system responsible for supplying cooling gas to the turbine blades. However, the pre-swirl system involves rotor-stator matching and intricate power-heat conversion challenges, which has led to a bottleneck in the development of its temperature drop potential. This study investigates the traditional pre-swirl system structure to identify factors limiting its temperature drop performance. A novel design idea is proposed to enhance the temperature drop performance by reducing the power consumption in the pre-swirl system. Subsequently, the structure optimization and performance improvement for pre-swirl system are conducted through the design of four vane-shaped receiver hole models. To assess the effectiveness of these enhancements, the thermodynamic and aerodynamic characteristics of the pre-swirl system before and after optimizations are evaluated using numerical simulations. Finally, the system temperature drop characteristics equipped with optimal receiver holes are thoroughly evaluated by experimental test analysis. The findings reveal that the new type of pre-swirl system, featuring a leading-edge vane-shaped receiver hole design and the removal of the cover-plate cavity, surpasses traditional designs. It exhibits a remarkable 35.3 % improvement in the receiver hole discharge coefficient, a 39.7 % reduction in system entropy increase, and a 6.36 kW/(kg/s) decrease in specific power consumption. Significantly, experimental verification demonstrates a 10 % increase in the nozzle pressure ratio, the temperature drop of pre-swirl system increased by 53.6 % from 23.5K to 36.1K, and the temperature drop efficiency of pre-swirl system increased from 0.567 to 0.872. Therefore, this study offers valuable insights for the design of high-performance pre-swirl systems, contributing to the overall improvement of turbine efficiency.

Influence of Process Parameters on the Efficiency of Pervaporation Pilot ECO-001 Plant for Raw Ethanol Dehydration.

Pervaporation is a membrane-based process used for the separation of liquid mixtures. As this membrane process is governed by the differences in the sorption and diffusivities of separated components, close boiling mixtures and azeotropic mixtures can effectively be separated. The dehydration of ethanol is the most common application of hydrophilic pervaporation. The pilot scale properties of hydrophilic composite poly(vinyl alcohol) PVA membrane (PERVAPTM 2200) in contact with wet raw bioethanol are presented. The wet raw bioethanol was composed of ethanol (82.4-89.6 wt%), water (5.9-8.5 wt%), methanol (2.3-6.9 wt%), cyclohexane (0.2-2.4 wt%), higher alcohols (0.2-1.3 wt%), and acetaldehyde (0.004-0.030 wt%). All experiments were performed using a SULZER ECO-001 plant equipped with a 1.5 m2 membrane module. The efficiency of the dehydration process (i.e., membrane selectivity, permeate flux, degree of dehydration) was discussed as a function of the following parameters: the feed temperature, the feed composition, and the feed flow rate through the module. It was found that the low feed flow rate influenced the dehydration efficiency as the enthalpy of evaporation caused a high temperature drop in the module (around 25 °C at a feed flow rate equal to 5 kg h-1). The separation coefficient during pervaporation was in the range of 600-1200, depending on the feed composition. The increase in temperature augmented the permeation flux and shortened the time needed to reach the assumed level of dehydration. It was revealed that dehydration by pervaporation using ECO-001 pilot plant is an efficient process, allowing also to investigate the influence of various parameters on the process efficiency.

A new methodology for measuring the enthalpies of mixing and heat capacities of molten chloride salts using high temperature drop calorimetry.

Molten salt reactors (MSRs) are a promising alternative to conventional nuclear reactors as they may offer more efficient fuel utilization, lower waste generation, and improved safety. The state of knowledge of the properties of liquid salts is far from complete. In order to develop the MSR concept, it is essential to develop a fundamental understanding of the thermodynamic properties, including the heat capacities (Cp) and enthalpies of mixing (ΔHmix), of molten salts at MSR operating conditions. Historically, the Cp values of molten salts were determined by drop-calorimetry or differential scanning calorimetry, whereas their ΔHmix values were typically measured using specialized high temperature calorimeters. In this work, a new methodology for measuring both the Cp and the ΔHmix of molten chloride salts was developed. This novel method involves sealing a chloride salt sample in a nickel capsule and performing conventional transposed temperature drop calorimetry using a commercially available Setaram AlexSYS-800 Tian-Calvet twin microcalorimeter. This methodology may be applied to calorimetric measurements of more complex salt mixtures, especially mixtures containing actinides and fission products.

PENGARUH GEOMETRI DAN PENAMBAHAN JUMLAH SIRIP TERHADAP DISTRIBUSI TEMPERATUR HEAT SINK SEBAGAI ALTERNATIF PENDINGINAN PADA PIRANTI ELEKTRONIK

This study aims to determine the effect of the geometry shape of the copper material heat sink fins on the surface temperature distribution of the heat sink. The material used in this research is pure copper, the shape of the heat sink fins is made rippled with the addition of the number of fins 5, 6, and 7 and the input temperature is varied from 40 C to 80 C with airflow variations from 0.2 m/s to 1 m/s. The first step is to create a heat sink design with Autodesk Inventor. Then the plan is simulated with Autodesk CFD to solve the continuity, momentum, turbulence, and energy equations. Based on the method that has been carried out, it is found that the addition of variations in the number of fins affects the decrease in surface temperature. The highest temperature drop on fin 5 ripples is 24.1 C. The heat energy transfer rate increased by 0.4657 W. The convection heat transfer coefficient increased by 3.47 W/m²C. Nusselt number shows an increase of 271. Fin performance has increased efficiency by 63.4 %, and effectiveness by 1.61. The results of this study are expected to provide practical alternatives that can be widely adopted on a heatsink plate that is very promising for future thermal developments.

An Experimental Investigation and Numerical Simulation of Photovoltaic Cells with Enhanced Surfaces Using the Simcenter STAR-CCM+ Software

This article proposes a passive cooling system for photovoltaic (PV) panels to achieve a reduction in their temperature. It is known that the cooling of PV panels allows for an increase in the efficiency of photovoltaic conversion. Furthermore, reducing the high temperature of the surfaces of PV panels is also desirable to ensure their long-lasting operation and high efficiency. Photovoltaic panels were modified by adding copper sheets to the bottom side of the panels. Two types of modification of the outer surface of the sheet were investigated experimentally, which differed in surface roughness. One was characterised by the nominal roughness of the copper sheet according to its manufacturer, while the other was enhanced by a system of pins. Numerical simulations, performed using the Simcenter STAR-CCM+ software, version 2020.2.1 Build 15.04.010, helped to describe the geometry of the pins and their role in the resulting reduction in the temperature of the PV panel surface. As a result, modifying a typical PV panel by adding a copper sheet with pins helps to achieve a higher decrease in the temperature of the PV panel. The addition of a copper sheet with a smooth surface to the bare PV panel improved the operating conditions by lowering its surface temperature by approximately 6.5 K but using an enhanced surface with the highest number of pins distributed uniformly on the copper sheet surface resulted in the highest temperature drop up to 12 K. The highest number of pins distributed uniformly on the copper sheet surface resulted in the highest temperature drop in its bottom surface, that is, on average by more than 12 K compared to the surface temperature of the bare PV panel surface. The validation of the numerical calculations was performed on data from the experiments. An analysis of the quality of the numerical mesh was also performed using a method based on the grid convergence index.

Effect of ammonia and coal co-firing on the formation mechanism and composition characteristics of particulate matter

Ammonia-coal co-firing is considered to be an effective method to reduce carbon dioxide emissions and the existing researches mainly focus on the combustion characteristics and NOx emission characteristics. In this study, co-firing of coal and ammonia was carried out in the high temperature drop tube furnace system with a large co-firing ratio of 0–50%. Firstly, the unburned fuels and the main composition of flue gas were measured as a baseline result. The results showed that ammonia co-firing will lead to the increase of NO and NOx concentration. Further, the particulate matters generated under different conditions were collected and tested. It was found that ammonia co-firing will affect the formation characteristics of particulate matter, especially sub-micron particulate matter. With the increase of co-firing ratio, the concentration of PM1 showed an overall increasing trend, but decreased at 20%. And ammonia co-firing will have an effect on the content of Si, Al, S and trace elements (As, Pb) in submicron particles. The content of water vapor, NOx in flue gas and combustion temperature have changed and affected the formation of SO3 and the gasification of silica and trace elements.

Decay Characteristics of Mechanical Properties of Asphalt Mixtures under Sizeable Wet Temperature Cycle

Asphalt mixtures will inevitably be affected by rainwater and the effect of the wet temperature cycle during a pavement’s life span. Especially in coastal areas such as Guangdong and Hainan in China, asphalt pavement is particularly susceptible to the sizeable wet temperature cycle formed by the high temperature and sudden temperature drop of rainstorms in summer. For this study, we used a homemade sizeable wet temperature cycle environment simulation device to analyze the decay characteristics and the mechanical properties of asphalt pavements in this environment; modified bending and tensile strength and shear strength tests were used to study the decay patterns of shear strength, bending, and tensile strength, and the stiffness modulus of asphalt mixtures with different air voids and different pavement depths under the action of a sizeable wet temperature cycle. In addition, the Grey correlation method was used to analyze the significance of each influencing factor on the decay of mechanical properties, and mathematical fitting was used to establish the prediction equation of the mechanical properties of asphalt mixtures. The results show that with the increase in the number of sizeable wet temperature cycles, the asphalt mixture’s shear strength, flexural tensile strength, and flexural tensile modulus decrease, the degree of decay increases, and the rate of decay gradually slows down. In the case of the same number of sizeable wet temperature cycles, the degree of decay of the asphalt mixtures gradually decreases with increasing depth or decreasing void ratio. After 100 sizeable wet temperature cycles, the maximum values of the decay of shear strength, modulus of strength, and flexural tensile strength were 22.30%, 23.29%, and 32.01%. The importance of the influence of each factor on the decay of the mechanical properties is as follows: the number of sizeable wet temperature cycles > void rate > depth. The prediction equations of the established mechanical properties have a good prediction effect, and the correlation between predicted values and actual values can be up to 0.925. The prediction equations can effectively predict the mechanical properties of asphalt mixtures with different air voids and depths under the action of sizeable wet temperature cycles.

Comparative Analysis of Three Near-Surface Air Temperature Reanalysis Datasets in Inner Mongolia Region

Near-surface air temperature is important for climate change, agriculture, animal husbandry, and ecosystems undergoing climate warming in Inner Mongolia. Land surface reanalysis products feature finer spatial and temporal resolutions, that can provide important data support for the determination of crop growth limits, grassland biomass growth, and desertification research in Inner Mongolia. In this study, 119 in situ observed sites were collected to compare and evaluate the performance of near-surface air temperature in three reanalysis products from 2018 to 2020 in Inner Mongolia. The three reanalysis products included three widely used products derived from the European Centre for Medium-Range Weather Forecasts (ECMWF) Fifth Generation Land Surface Reanalysis (ERA5-Land), and U.S. Global Land Data Assimilation System (GLDAS), as well as the latest reanalysis product from the High-Resolution Land Data Assimilation System reanalysis product by the China Meteorological Administration (HRCLDAS). Results are as follows: (1) The three reanalysis temperature products all reasonably reflect the characteristics of spatial and temporal changes in surface temperature in Inner Mongolia. Compared with ERA5L and GLDAS, HRCLDAS is more consistent with the observed results. (2) For the evaluation period, HRCLDAS has a certain underestimation of temperature, while ERA5-Land and GLDAS have a significant overestimation of temperature. (3) During high-temperature processes, HRCLDAS is more accurate in simulating higher temperatures than ERA5-LNAD and can demonstrate the changes in high-temperature drop zones. The major conclusion of this study is that the HRCLDAS product demonstrates a relatively high reliability, which is of great significance for the study of climate, ecosystem, and sustainable development.

Thermodynamic investigation of the NaCl-KCl salt system from 25 to 950 °C

NaCl-KCl molten salt system has been proposed as a primary component of several promising heat transfer eutectics and fuel host for Generation IV molten salt reactors (MSR). In this work, several key thermodynamic parameters, including high temperature enthalpies, isobaric heat capacities (Cp) and molar enthalpies of mixing (ΔHmix), of the NaCl-KCl system (NaCl, 75 mol% NaCl – 25 mol% KCl, 51 mol% NaCl – 49 mol% KCl, 25 mol% NaCl – 75 mol% KCl, and KCl) were measured by high temperature drop calorimetry (HTDC) utilizing laser sealed nickel and aluminum crucibles. Salts were checked for phase purity by X-ray diffraction (XRD), and water content by Karl Fischer coulometric titrimetry and thermogravimetric analysis (TGA). Thermo-mechanical analysis (TMA) utilizing custom-built boron nitride (BN) crucibles was employed to determine temperatures of phase transitions (solid → liquid) for the salts and plotted against the pseudobinary phase diagram for the NaCl-KCl system. Small deviations (3–10 %) were found among Cp values obtained from HTDC, differential scanning calorimetry (DSC), and NIST, comparable to the average uncertainty based on two standard deviations of measured data that are ∼6% for DSC and ∼3% for HTDC. Additionally, the measured enthalpies and Cp values of mixed NaCl-KCl salts (e.g., 51 mol% NaCl – 49 mol% KCl eutectic) were shown to behave as a nearly statistical mixtures of its pure endmembers, consistent with ΔHmix = −1.324 kJ/mol at 800 °C, and a regular interaction parameter of Ω = 4.77 ± 0.79 kJ/mol. This study represents a step towards improved accuracy and precision in determinations of thermodynamic parameters of molten salts by using DSC, TMA, and HTDC, in completion of the Molten Salt Thermal Properties Database (MSTDB).

Experimental and parametric analysis of exhaust heat exchanger used in thermoelectric generator

A thermoelectric generator system consists of an exhaust heat exchanger, a thermoelectric module, and water heat exchanger. Perfect heat exchangers recover as much heat energy as possible from engine exhaust with an acceptable pressure drop. The capacity and efficiency of the heat exchanger depend on its shape, type, and material of the heat exchanger. The main objective of this research was to perform a parametric analysis of the test section of the exhaust heat exchanger by using simulation tools. The simulation results were validated with the experimental results to ensure the performance of the simulation model. The performance of the test section was measured in relation to geometry, pressure drop, temperature distribution, fluid velocity, and temperature uniformity coefficient. The test section of 60 mm × 60 mm × 180 mm (F-type) shows a higher surface temperature with an allowable pressure drop than the other types of test section without inserts. The inserts played a vital role in enhancing the surface temperature distribution and uniformity coefficient. The cone type (G-type), cone-cylinder type (H-type), and cone-cylinder-cone type (I-type) inserts were used to improve the performance of the F-type test section. The G-type and H-type test sections of the exhaust heat exchanger have a high surface temperature, high-temperature uniformity, and allowable pressure drop.

Calorimetric Studies on Chemically Delithiated LiNi0.4Mn0.4Co0.2O2: Investigation of Phase Transition, Gas Evolution and Enthalpy of Formation

Li1.11(Ni0.4Mn0.4Co0.2)O2 powders were chemically delithiated by (NH4)2S2O8 oxidizer to obtain Lix(Ni0.4Mn0.4Co0.2)O2 powders. The thermal behavior of two delithiated specimens, Li0.76Ni0.41Mn0.42Co0.17O2.10 and Li0.48Ni0.38Mn0.46Co0.16O2.07, was studied compared to the pristine specimen. Phase transitions at elevated temperatures were investigated by simultaneous thermal analysis (STA) and the gas evolution accompanying the phase transitions was analyzed by mass spectroscopy and an oxygen detector. The enthalpy of two delithiated samples and a pristine specimen were measured by a high temperature drop solution calorimeter. Based on these results, the enthalpies of formation were calculated.

Density, Thermal Expansion, Enthalpy, Heat Capacity, and Thermal Conductivity of Calcium in the Temperature Range 720–1290 K

Thermophysical properties of solid and liquid calcium (99.75 wt % pure) were experimentally studied with high accuracy in the temperature range 720–1290 K using dilatometer measurements, gamma-ray attenuation measurements (the gamma-ray method), high-temperature drop calorimetry, and the laser flash method. The behaviors of the density, enthalpy, and thermal conductivity of calcium in the fusion–crystallization region were studied. The enthalpy of fusion was measured as 8075 J/mol, the relative density change upon fusion as 3.3%, and the relative change in thermal conductivity upon fusion as 26%. The results were compared to the respective values in the related literature. The measurements at temperatures above 720 K either significantly amend the available literature data, or are currently unique. The constancy of the heat capacity of liquid calcium in the temperature range 1115–1290 K was verified. Fitting equations were derived, and recommended values of the investigated properties of calcium were tabulated for 720–1290 K, the temperature range where calcium is in the condensed state.

Influence of H2O Thermal Effect on the Formation of Ultrafine PM During Char Combustion

ABSTRACT To clarify the influence of H2O thermal effect on the formation of ultrafine particulate matter (PM), Huangling coal char was burned in a high-temperature drop tube furnace at 1800 K under various O2/N2/H2O and O2/N2/H2O/Ar atmospheres. The introduction of Ar in the simulating atmosphere was designed to counteract the thermal effect of H2O. Results indicated that after eliminating the thermal effect of H2O, the yield of ultrafine PM continuously increased in higher H2O content. Compared with no H2O, the mass and number yield of ultrafine PM in O2/N2/H2O/Ar atmosphere with 30% H2O content increased by 35.5% and 58.9%, respectively. H2O thermal effect, gasification reaction, and char oxidation reaction during coal char combustion played a significant role in the formation of ultrafine PM. Oxidation reaction was the primary factor affecting the formation of ultrafine PM, and its relative contribution was more than 62.9%, whereas the thermal effect of H2O showed an overall negative net effect on the formation of ultrafine PM. With the H2O content varied from 5% to 30%, the contribution of H2O thermal effect to mass yield was in the range of −19.1% to −18.0%, while that to number yield was −33.1% to −30.6%. Once the H2O content reached 10%, the enhancing effect of H2O gasification reaction on the yield of ultrafine PM surpassed the negative contribution of H2O thermal effect. For a given H2O content, elevated O2 concentration weakened the negative contribution of H2O thermal effect.

THE AUTOTRANSFORMER METHOD OF CONNECTING THE INDUCTOR TO THE THYRISTOR CONVERTER

The issue of the correct coordination of the inverter parameters with the load parameters in order to obtain the highest output power of the converter at the necessary margin of its stability is considered. In order to avoid impermiassibly high temperature drops in the radial direction of the workpieces, the specific power of inductors is limited, as a result of which it is expedient to perform them for a voltage of 500 ... 750 V and higher. In addition, high-frequency furnace capacitors for compensating the reactive power of the load are produced with a rated voltage from 375 to 1000 V, so the connection of the inductor to the inverter with a reduced output voltage has to be carried out according to the autotransformer circuit. In order to simplify the calculations, it is assumed that the power factor along the length of the inductor has a certain constant averaged value and does not depend on the distribution of the temperature field along the inductor. Based on this assumption, the dependence of the active resistance of the load on the number of turns of the inductor can be presented as a linear function for various transformation ratios. When matching the parameters of the inverter with the parameters of the load circuit, it is necessary not only to ensure full compensation, but also to select the value of the equivalent active resistance of the circuit in such a way that the inverter give the most power, and at the same time, the time provided for restoring the controllability of the thyristors must remain within acceptable limits. Therefore, the estimation of the value of the equivalent active resistance of the load circuit at various transformation ratios is necessary.

Experimental Study on Effect of Nano ZnO on the Cooling Performance of Motorcycle Radiator

An internal combustion engine requires a proper cooling system to release heat from the engine. The working fluid or coolant in a water-cooled engine impacts the overall radiator cooling performance. Several studies show that nanopowder can increase the thermal performance of the base fluids, although the pressure drops increase significantly. This paper describes the experimental study of motorcycle radiator cooling performance using nanopowder ZnO with distilled water and commercial coolant as the base fluids. The study began by measuring the boiling point and the specific heat of the base fluid (distilled water and commercial coolant) and nanofluids. Then, the flow rate of the cooling fluid was measured as the function of the engine’s rotation speed. The results show that the boiling point of all nanofluids increases with the highest boiling point achieved by 0.5% ZnO – coolant, i.e., 110.06°C. Thus, the nanopowder will keep the cooling fluid in the liquid phase and lower the fluid's specific heat. The fluid with the lowest specific heat is nanofluid 0.5% ZnO – coolant. Low specific heat relates to the higher temperature drops. Nanofluid 0.5% ZnO – coolant has the highest temperature drop. Unfortunately, nanopowder also increases pressure drop by approximately twice the base fluid. Nanofluid 0.5% ZnO – coolant gives the highest overall heat transfer coefficient than other nanofluids or the base fluid, i.e., 42.7 W/m2.°C when its flow rate is 44.2 ml/s.

Thermodynamic properties of selected glasses in the CaO–Al2O3–TiO2 system

The thermodynamic properties of a Ca12Al14O33 (C12A7) binary glass and the impact of titania additions (+5 and 7 wt%) were studied for the first time using three different calorimetric techniques: low-temperature adiabatic, high-temperature drop solution and transposed temperature drop calorimetry. The enthalpy of formation from oxides at 298.15 K of the Ca12Al14O33 and Ca12Al14O33+7 wt% TiO2 glass samples (16.0±1.8 and 14.5±2.4 kJ/mol, respectively) and the enthalpy of dissolution of TiO2 (rut) at 1073.15 K were obtained by drop solution calorimetry in a 2PbO–B2O3 solvent. A close value (11.9±2.3 kJ/mol) was obtained for the same C12A7 glass by transposed temperature drop calorimetry. The investigation of the impact of TiO2 additions on the thermodynamic properties of glasses shows that there is no influence on heat capacity of C12A7 up to 7 wt% of TiO2. In contrast, a negative deviation of the enthalpy of formation from oxides at 298.15 K from the ideal-mixing straight line was observed.

Numerical analysis of thermal performance of waste heat recovery shell and tube heat exchangers on counter-flow with different tube configurations

This study investigates the effect of tube layout configurations on the hydraulic-thermal performance of shell-and-tube heat exchangers (STHXs) as waste heat recovery systems. The STHXs are triangular (30°, STHX-T), rotated triangular (60°, STHX-RT), and combined (STHX-C). Water at a temperature of 10 °C was circulated through a bundle of tubes inlet to recover waste heat from hot water at the temperature of 65 °C. Water was circulated through the shell inlet within the mass flow rate range of 0.5 ≤ ṁ ≤ 3.5 kg/s. ANSYS-Fluent was used to perform a three-dimensional computational study under steady-state conditions. The turbulence model, realizable k-epsilon, was adopted because of the possible transition from laminar to turbulence. The results were validated with the Kern correlation for shell-side heat transfer coefficient and pressure drop. The temperatures, pressure drop, velocity, and overall heat transfer coefficient for all the cases were compared. Temperature contours, pressure contour, velocity vector, and velocity contour were presented for flow visualization. When the simulation results of the different STHXs were compared, the results revealed that the STHX-T layout has the highest overall heat transfer coefficient of 2307.09 W/m2K. The maximum pressure drop of 242.42 Pa, highest temperature drop in the shell zone of 4.48 K, and highest temperature rise in the tube side of 6.67 K, followed by STHX-C and STHX-RT layout were obtained.

Energetic Systematics of Metal-Organic Frameworks: A Case Study of Al(III)-Trimesate MOF Isomers.

Thermal stability and thermodynamic properties of aluminum(III)-1,3,5-benzenetricarboxylate (Al-BTC) metal-organic frameworks (MOFs), including MIL-96, MIL-100, and MIL-110, have been investigated through a suite of calorimetric and X-ray techniques. In situ high-temperature X-ray diffraction (HT-XRD) and thermogravimetric analysis coupled with differential scanning calorimetry (TGA-DSC) revealed that these MOFs undergo thermal amorphization prior to ligand combustion. Thermal stabilities of Al-BTC MOFs follow the increasing order MIL-110 < MIL-96 < MIL-100, based on estimated amorphization temperatures. Their thermodynamic stabilities were directly measured by high-temperature drop combustion calorimetry. Normalized (per mole of Al) enthalpies of formation (ΔH*f) of MIL-96, MIL-100, and MIL-110 from Al2O3, H3BTC, and H2O (only Al2O3 and H3BTC for MIL-100) were determined to be -56.9 ± 13.7, -36.2 ± 17.9, and 62.8 ± 11.6 kJ/mol·Al, respectively. Our results demonstrate that MIL-96 and MIL-100 are thermodynamically favorable, while MIL-110 is metastable, in agreement with thermal and hydrothermal stability trends. The enthalpic preferences of MIL-96 and MIL-100 may be attributed to their shared trinuclear μ3-oxo-bridged (Al3(μ3-O)) secondary building units (SBUs) promoting stabilization of Al polyhedra by the ligands within these frameworks, in comparison to the sterically strained Al8 octamer cluster cores formed in MIL-110. Furthermore, similar ΔH*f of MIL-96 and MIL-100 explain their concurrent formation as physical mixtures often encountered during synthesis, implying the importance of kinetic factors that may facilitate the formation of Al-BTC framework isomers. More importantly, the normalized formation enthalpies of Al-BTC MOF isomers follow a negative correlation with the ratio of charged coordinated substituents to linkers (normalized per mole of Al within the MOF formula unit), with enthalpic preference given to systems with smaller (O2- + OH-)/ligand ratios. This trend has been successfully extended to the previously measured ΔH*f of several Zn4O-based frameworks (e.g., MOF-5, MOF-5(DEF), MOF-177, UMCM-1), all of which have been found to be metastable with respect to their dense phases (ZnO, H2O, and ligands). The result suggests that carboxylate MOFs with higher metal coordination environments attain more enthalpic stabilization from the coordinated ligands. Thus, the formation of some lanthanide/actinide, transition metal, and main group carboxylate frameworks may be energetically more favored, which, however, requires further studies.