Steady-state Experiments Research Articles

Processive kinetics in the three-step lanosterol 14α-demethylation reaction catalyzed by human cytochrome P450 51A1

Cytochrome P450 (P450, CYP) family 51 enzymes catalyze the 14α-demethylation of sterols, leading to critical products used for membranes and the production of steroids, as well as signaling molecules. In mammals, P450 51 catalyzes the 3-step, 6-electron oxidation of lanosterol to form (4β,5α)-4,4-dimethyl-cholestra-8,14,24-trien-3-ol (FF-MAS). P450 51A1 can also use24,25-dihydrolanosterol (a natural substrate in the Kandutsch-Russell cholesterol pathway). 24,25-Dihydrolanosterol and the corresponding P450 51A1 reaction intermediates, the 14α-alcohol and -aldehyde derivatives of dihydrolanosterol, were synthesized to study the kinetic processivity of the overall 14α-demethylation reaction of human P450 51A1. A combination of steady-state kinetic parameters, steady-state binding constants, dissociation rates of P450-sterol complexes, and kinetic modeling of the time course of oxidation of a P450-dihydrolanosterol complex showed that the overall reaction is highly processive, withkoffrates of P450 51A1-dihydrolanosterol and the 14α-alcohol and 14α-aldehyde complexes being 1 to 2 orders of magnitude less than the forward rates of competing oxidations. epi-Dihydrolanosterol (the 3α-hydroxy analog) was as efficient as the common 3β-hydroxy isomer in the binding and formation of dihydro FF-MAS. The common lanosterol contaminant dihydroagnosterol was found to be a substrate of human P450 51A1, with roughly one-half the activity of dihydrolanosterol. Steady-state experiments with 14α-methyl deuterated dihydrolanosterol showed no kinetic isotope effect, indicating that C-14αC-H bond breaking is not rate-limiting in any of the individual steps. The high processivity of this reaction generates higher efficiency and also renders the reaction less sensitive to inhibitors.

Reaction Mechanism Development for Methane Steam Reforming on a Ni/Al2O3 Catalyst

In this work, a reliable kinetic reaction mechanism was revised to accurately reproduce the detailed reaction paths of steam reforming of methane over a Ni/Al2O3 catalyst. A steady-state fixed-bed reactor experiment and a 1D reactor catalyst model were utilized for this task. The distinctive feature of this experiment is the possibility to measure the axially resolved temperature profile of the catalyst bed, which makes the reaction kinetics inside the reactor visible. This allows for understanding the actual influence of the reaction kinetics on the system; while pure gas concentration measurements at the catalytic reactor outlet show near-equilibrium conditions, the inhere presented temperature profile shows that it is insufficient to base a reaction mechanism development on close equilibrium data. The new experimental data allow for achieving much higher quality in the modeling efforts. Additionally, by carefully controlling the available active surface via dilution in the experiment, it was possible to slow down the catalyst conversion rate, which helped during the adjustment of the reaction kinetics. To assess the accuracy of the revised mechanism, a monolith experiment from the literature was simulated. The results show that the fitted reaction mechanism was able to accurately predict the experimental outcomes for various inlet mass flows, temperatures, and steam-to-carbon ratios.

HADES - high heat load testing - facility at CEA-IRFM

A new facility based on an electron beam for the testing of plasma facing components (PFC) has been built at CEA-IRFM (France). The aim of this facility, named HADES (High heAt loaD tESt), is to assess heat removal capabilities of PFCs exposed to high heat flux. The facility can cover thermal fatigue tests, critical heat fluxes and thermal shocks. This facility has been designed in order to provide the maximum performance and flexibility for the qualification of PFCs.This facility has been built collecting a former high heat load platform, named FE200 [1], and located in Le Creusot-France resulting from collaboration between CEA and Framatome in the 90′s. All the systems have been refurbished except the e-beam gun, which has been replaced by a brand new one with 150 kW and 45 kV of maximum power and accelerating voltage, respectively.The HADES e-beam gun will permit to simulate steady state experiments with thermal flux up to a few tens MW/m² and transient events with thermal energy up to 1 GW/m² during a few milliseconds. A programmable sweep system allows several kinds of energy repartition (uniform and peaked), on a ± 25° shooting angle with the normal to the surface.This paper will present in details the technical specifications related to the e-beam gun as well as to the auxiliary systems. Finally, the main results of the commissioning tests and first campaign, achieved at the end of 2020 will be presented.

Three-dimensional simulation of a gas-centered swirl coaxial injector spray under pulsation conditions

Based on steady-state experiments, a three-dimensional (3D) simulation study under pulsation conditions was carried out. This was performed to study the effect of pulsation of the supply system on the atomization characteristics of a gas-centered swirl coaxial injector. The results indicated that the spray shape resembled a pagoda when the Klystron effect occurred. When the low-frequency pulsation (200 Hz) was applied to the liquid inlet, the peak of the exit pressure was close to the trough of the inlet mass flow rate. Meanwhile, the exit mass flow rate and pressure were approximately sinusoidal. There was no significant lag effect in the response of the exit mass flow rate to the inlet mass flow rate but with a small sawtooth-like oscillation. Increasing the amplitude of the liquid inlet disturbance amplified the exit mass flow rate fluctuation, which was greater than the set amplitude of the inlet pulsation. The dominant frequency of the injector exit mass flow rate and pressure variation was significantly less than the inlet pulsation frequency when the frequency of the liquid inlet pulsation was increased to 1000 Hz. This was due to the low-pass filtering effect of the annular slit. There was no significant change in the overall spray morphology for the gas inlet pulsation. By applying the same amplitude and frequency of pulsation to the gas and liquid inlets of the injector, the pulsation of the liquid inlet had a stronger effect on the injector exit spray than that of the gas inlet.

Boosting the Efficiency of Dye-Sensitized Solar Cells by a Multifunctional Composite Photoanode to 14.13.

We report a new strategy to fabricate a multifunctional composite photoanode containing TiO2 hollow spheres (TiO2-HSs), Au nanoparticles (AuNPs) and novel NaYF4:Yb,Er@NaLuF4:Eu@SiO2 upconversion nanoparticles (UCNPs). The AuNPs are grown on the photoanode film including TiO2-HSs and UCNPs by a simple in-situ plasmonic treatment. As a result, an impressive power conversion efficiency of 14.13% is obtained, which is a record for N719 dye-based dye-sensitized solar cells, demonstrating great potential for the solar cells toward commercialization. This obvious enhancement is ascribed to a collaborative mechanism of the TiO2-HSs exhibiting excellent light-scattering ability, of the UCNPs converting near-infrared photons into visible photons and of the AuNPs presenting outstanding surface plasmon resonance effect. Notably, a steady-state experiment further reveals that the champion cell exhibits 95.33% retainment in efficiency even after 180 h of measurements, showing good device stability.

Photoinduced Dynamics of 13,13'-Diphenylpropyl-β-carotene.

Carotenoids are ubiquitous pigment systems in nature which are relevant to a range of processes, such as photosynthesis, but the detailed influence of substitutions at the polyene backbone on their photophysics is still underexplored. Here, we present a detailed experimental and theoretical investigation of the carotenoid 13,13'-diphenylpropyl-β-carotene using ultrafast transient absorption spectroscopy and steady-state absorption experiments in n-hexane and n-hexadecane, complemented by DFT/TDDFT calculations. In spite of their bulkiness and their potential capability to "fold back" onto the polyene system, which could result in π-stacking effects, the phenylpropyl residues have only a minor impact on the photophysical properties compared with the parent compound β-carotene. Ultrafast spectroscopy finds lifetimes of 200-300 fs for the S2 state and 8.3-9.5 ps for the S1 state. Intramolecular vibrational redistribution with time constants in the range 0.6-1.4 ps is observed in terms of a spectral narrowing of the S1 spectrum over time. We also find clear indications of the presence of vibrationally hot molecules in the ground electronic state (S0*). The DFT/TDDFT calculations confirm that the propyl spacer electronically decouples the phenyl and polyene π-systems and that the substituents in the 13 and 13' positions point away from the polyene system.

Rate constants for the reactions of chloride monoxide radical (ClO•) and organic molecules of environmental interest.

ClO• plays a key role in the UV/chlorine process besides Cl•, Cl2• - , and •OH. In many experiments, ClO• proved to be the main reactant that destroyed the organic pollutants in advanced oxidation process. About 200 rate constants of ClO• reactions were collected from the literature, grouped together according to the chemical structure, and the molecular structure dependencies were evaluated. In most experiments, ClO• was produced by the photolytic reaction of HClO/ClO-. For a few compounds, the rate constants were determined by the absolute method, pulse radiolysis. Most values were obtained in steady-state experiments by competitive technique or by complex kinetic calculations after measuring the pollutant degradation in the UV/chlorine process. About 30% of the listed rate constant values were derived in quantum chemical or in structure-reactivity (QSAR) calculations. The values show at least six orders of magnitude variations with the molecular structure. Molecules having electron-rich parts, e.g., phenol/phenolate, amine, or sulfite group have high rate constants in the range of 108-109 mol-1 dm3 s-1. ClO• is inactive in reactions with saturated molecules, alcohols, or simple aromatic molecules.

Heat Transfer Characteristics of Particle and Air Flow Through Additively Manufactured Lattice Frame Material Based on Octet-Shape Topology

Abstract Particle-to-supercritical carbon dioxide (sCO2) heat exchanger is a critical component in next-generation concentrating solar power (CSP) plants. The inherently low heat transfer between falling particles and sCO2 imposes a challenge toward economic justification of levelized cost of electricity produced through solar energy. Introduction of integrated porous media with the walls bounding particle flow has the potential to enhance the overall particle-to-sCO2 heat exchanger performance. This paper presents an experimental study on heat transfer characterization of additively manufactured lattice frame material based on Octet-shaped unit cell with particles and air as working fluids. The lattice structures were additively manufactured in stainless steel (SS) 316L and SS420 (with 40% bronze infiltration) via Binder jetting process, where the lattice porosities were varied between 0.75 and 0.9. The mean particle diameters were varied from 266 μm to 966 μm. The effective thermal conductivity and averaged heat transfer coefficient were determined through steady-state experiments. It was found that the presence of lattice enhances the effective thermal conductivity by 2–4 times when compared to packed bed of particles alone. Furthermore, for gravity-assisted particle flow through lattice panel, significantly high convective heat transfer coefficients ranging from 200 W/m2K to 400 W/m2K were obtained for the range of particle diameters tested. The superior thermal transport properties of Octet-shape-based lattice frame for particle flow makes it a very promising candidate for particle-to-sCO2 heat exchanger for CSP application.

Application of Machine Learning to Interpret Steady-State Drainage Relative Permeability Experiments

Summary A meticulous interpretation of steady-state or unsteady-state relative permeability (Kr) experimental data is required to determine a complete set of Kr curves. In this work, different machine learning (ML) models were developed to assist in a faster estimation of these curves from steady-state drainage coreflooding experimental runs. These ML algorithms include gradient boosting (GB), random forest (RF), extreme gradient boosting (XGB), and deep neural network (DNN) with a main focus on and comparison of the two latter algorithms (XGB and DNN). Based on existing mathematical models, a leading-edge framework was developed where a large database of Kr and capillary pressure (Pc) curves were generated. This database was used to perform thousands of coreflood simulation runs representing oil-water drainage steady-state experiments. The results obtained from these simulation runs, mainly pressure drop along with other conventional core analysis data, were used to estimate analytical Kr curves based on Darcy’s law. These analytically estimated Kr curves along with the previously generated Pc curves were fed as features into the ML model. The entire data set was split into 80% for training and 20% for testing. The k-fold cross-validation technique was applied to increase the model’s accuracy by splitting 80% of the training data into 10 folds. In this manner, for each of the 10 experiments, nine folds were used for training and the remaining fold was used for model validation. Once the model was trained and validated, it was subjected to blind testing on the remaining 20% of the data set. The ML model learns to capture fluid flow behavior inside the core from the training data set. In terms of applicability of these ML models, two sets of experimental data were needed as input; the first was the analytically estimated Kr curves from the steady-state drainage coreflooding experiments, while the other was the Pc curves estimated from centrifuge or mercury injection capillary pressure (MICP) measurements. The trained/tested model was then able to estimate Kr curves based on the experimental results fed as input. Furthermore, to test the performance of the ML model when only one set of experimental data is available to an end user, a recurrent neural network (RNN) algorithm was trained/tested to predict Kr curves in the absence of Pc curves as an input. The performance of the three developed models (XGB, DNN, and RNN) was assessed using the values of the coefficient of determination (R2) along with the loss calculated during training/validation of the model. The respective crossplots along with comparisons of ground truth vs. artificial intelligence (AI)-predicted curves indicated that the model is capable of making accurate predictions with an error percentage between 0.2% and 0.6% on history-matching experimental data for all three tested ML techniques. This implies that the AI-based model exhibits better efficiency and reliability in determining Kr curves when compared to conventional methods. The developed ML models by no means replace the need to conduct drainage coreflooding or centrifuge experiments but act as an alternative to existing commercial platforms that are used to interpret experimental data to predict Kr curves. The two main advantages of the developed ML models are their capability of predicting Kr curves within a matter of a few minutes as well as with limited intervention from the end user. The results also include a comparison between classical ML approaches, shallow neural networks, and DNNs in terms of accuracy in predicting the final Kr curves. The research presented here is an extension of the state-of-the-art framework proposed by Mathew et al. (2021). However, the two main aspects of the current study are the application of deep learning for the prediction of Kr curves and the application of feature engineering. The latter not only reduces the training/testing time for the ML models but also enables the end user to obtain the final predictions with the least set of experimental data. The various models discussed in this research work currently focus on the prediction of Kr curves for drainage steady-state experiments; however, the work can be extended to capture the imbibition cycle as well.

Assessing the photodegradation potential of compounds derived from the photoinduced weathering of polystyrene in water

Benzoate (Bz−) and acetophenone (AcPh) are aromatic compounds known to be produced by sunlight irradiation of polystyrene aqueous suspensions. Here we show that these molecules could react with •OH (Bz−) and •OH + CO3•- (AcPh) in sunlit natural waters, while other photochemical processes (direct photolysis and reaction with singlet oxygen, or with the excited triplet states of chromophoric dissolved organic matter) are unlikely to be important. Steady-state irradiation experiments were carried out using lamps, and the time evolution of the two substrates was monitored by liquid chromatography. Photodegradation kinetics in environmental waters were assessed by a photochemical model (APEX: Aqueous Photochemistry of Environmentally-occurring Xenobiotics). In the case of AcPh, a competitive process to aqueous-phase photodegradation would be volatilisation followed by reaction with gas-phase •OH. As far as Bz− is concerned, elevated dissolved organic carbon (DOC) levels could be important in protecting this compound from aqueous-phase photodegradation. Limited reactivity of the studied compounds with the dibromide radical (Br2•-, studied by laser flash photolysis) suggests that •OH scavenging by bromide, which yields Br2•-, would be poorly offset by Br2•--induced degradation. Therefore, photodegradation kinetics of Bz− and AcPh should be slower in seawater (containing [Br−] ~ 1 mM) compared to freshwaters. The present findings suggest that photochemistry would play an important role in both formation and degradation of water-soluble organic compounds produced by weathering of plastic particles.

High temperature thermal contact conductance measurement and correlation for pressure tube and calandria tube interface under CO2 environment

This investigation aims to develop a reliable and accurate experimental database for thermal contact conductance (TCC) across the sample of pressure tube (PT) and calandria tube (CT) interface. During a postulated accidental scenario of pressurized heavy water reactors (PHWR), the PT might meet CT owing to the thermomechanical deformation due to sagging, ballooning, or a combination of both. This initiates a high heat flow from the fuel bundle to PT, followed by PT to CT and further from CT to the moderator. The involvement of large heat fluxes demands the correct estimation of the associated heat transfer rate to the moderator, which largely depends on the contact conductance between PT and CT at similar working ranges. In this work, a unique experimental setup has been developed to precisely characterize interfacial interactions of the flat surfaces of PT and CT specimen subjected to axial force in the CO2 atmosphere to avoid oxidation at high temperature, which closely simulates the actual scenario of PHWR. Steady state experiments were performed under the contact pressures ranging from 0.6 to 8 MPa, whereas interfacial temperatures between PT and CT vary from 300 to 500 °C. Two-factor, three-level face-centered central composite design (CCD) was used to select the intermediate pressure and temperature parameters prior to performing the experiments. Finally, experiments were performed at the selected range of parameters and correlation for estimating TCC has been developed using Response Surface Methodology (RSM). The correlation is inherently expressed as the function of intermediate temperature and contacting pressure at PT-CT interface, which has been utilized in safety analysis codes for safety evaluation of reactors.

Correct relative permeability data from steady-state experiments for capillary end effects

Water-oil relative permeability curves can be obtained from co-injection experiments at steady-state (SS) conditions. The two-phase Darcy's law can be used to calculate the relative permeability directly only when water saturation is constant along the core. However, the capillary end effect (CEE) causes water accumulation or depletion at the end of the core depending upon the wettability. This work modifies the Intercept Method initially proposed by Gupta and Maloney. Similar to their work, we again envisage carrying out a steady-state (SS) co-injection experiment. For each ratio of water to oil flowrate (F=qwqo), we require experiments at different total flowrates. From each run, we obtain pressure drop across the core and average water saturation inside the core.We demonstrate mathematically that a plot of average water saturation vs. reciprocal of oil flowrate gives a straight line whose intercept is the water saturation in the unaffected region. A plot of pressure difference vs. oil flowrate yields a straight line whose slope gives the oil relative permeability which can be used to calculate water relative permeability. It is necessary to perform the SS experiment at least three times for the same F=qwqo (at different oil/water rates). The same procedure is used for other values of F to obtain more data points to construct the relative permeability curves. An experimental step-by-step procedure for experimental engineers to follow is given in appendix C.

Modelling and experimental validation of heat transfer behavior during trans-critical transients

Though designed to be operated in supercritical conditions, supercritical power systems could experience trans-critical transients in which the pressure transfers between supercritical and subcritical condition during startup, shutdown, or accident condition. In the present work the thermal–hydraulic code ATHLET-SC was upgraded to predict the heat transfer behavior during trans-critical procedures. Prediction model of dispersed droplet flow film boiling (DFFB) heat transfer correlation, critical heat flux (CHF) correlation, and the correlation of minimum film boiling temperature TMFB has been upgraded. It is demonstrated by the validation work that the prediction error is large in the inverted annular film boiling (IAFB) regime. However, steady-state IAFB heat transfer experiment at high-pressure condition is unavailable. Hence, a calibration approach to IAFB heat transfer correlation is developed based on trans-critical transient experiment. As validated, the change of the wall temperature during the trans-critical transient gets well predicted by the corrected Bromley correlation.

E6AP AZUL interaction with UBQLN1/2 in cells, condensates, and an AlphaFold-NMR integrated structure

The E3 ligase E6AP/UBE3A has a dedicated binding site in the 26S proteasome provided by the RAZUL domain of substrate receptor hRpn10/S5a/PSMD4. Guided by RAZUL sequence similarity, we test and demonstrate here that the E6AP AZUL binds transiently to the UBA of proteasomal shuttle factor UBQLN1/2. Despite a weak binding affinity, E6AP AZUL is recruited to UBQLN2 biomolecular condensates invitro and E6AP interacts with UBQLN1/2 in cellulo. Steady-state and transfer nuclear Overhauser effect (NOE) experiments indicate direct interaction of AZUL with UBQLN1UBA. Intermolecular contacts identified by NOE spectroscopy (NOESY) data were combined with AlphaFold2-Multimer predictions to yield an AZUL:UBA model structure. We additionally identify an oligomerization domain directly adjacent to UBQLN1/2UBA (UBA adjacent [UBAA]) that is α-helical and allosterically reconfigured by AZUL binding to UBA. These data lead to a model of E6AP recruitment to UBQLN1/2 by AZUL:UBA interaction and provide fundamental information on binding requirements for interactions in condensates and cells.

Performance analysis and optimal design of a water-cooled thermoelectric component for air cooling based on simulation and experiments

In the present study, a water-cooled thermoelectric component model for air cooling is established. To validate the present model, the results of transient and steady-state experiments are compared with numerical calculations. The effects of different air flow rates and water flow rates on the TEC performance and thermal-hydraulic characteristics of the plate-fin heat sinks (PFHS) are studied. The heat transfer and flow characteristics (JF) and coefficient-of-performance (COP) are adopted as optimization goals. A standard design of experiment (DOE) method called a partial factorial design (PFD) is applied in this experimental plan. The significant influential factors are distinguished from six parameters in the PFHS (fins width, fins length, substrate thickness, fins number, fin thickness, and fins height). The number and height of fins have a great effect on the heat transfer and flow characteristics of the PFHS, while the width of the PFHS and fin height have a great effect on the COP of the TEC. The aim is to maximize the response variable JF of the PFHS under the criterion of COP of the TEC. A three-level Box-Behnken design (BBD) based on the response surface methodology (RSM) has been established for predicting and optimizing the response variables JF and COP with the design constraints. The predicted results also indicate that the model proposed in this study is reasonable and accurate and can be used for describing the heat transfer and flow characteristics and coefficient-of-performance with the limitations of the factors studied. This work is expected to provide help in the analysis and optimization of thermoelectric components.

Model-Free VRFT-Based Tuning Method for PID Controllers

The main objective of this work was to develop a tuning method for PID controllers suitable for use in an industrial environment. Therefore, a computationally simple tuning method is presented based on a simple experiment on the process without requiring any input from the user. Essentially, the method matches the closed-loop response to the response obtained in the steady-state change experiment. The proposed method requires no prior knowledge of the process and, in its basic form, only the measurement of the change in the steady state of the process in the manually or automatically performed experiment is needed, which is not limited to step-like process input signals. The user does not need to provide any prior information about the process or any information about the closed-loop behavior. Although the control loop dynamics is not defined by the user, it is still known in advance because it is implicitly defined by the process open-loop response. Therefore, no exaggerated control signal swings are expected when the reference signal changes, which is an advantage in many industrial plants. The presented method was designed to be computationally undemanding and can be easily implemented on less powerful hardware, such as lower-end PLC controllers. The work has shown that the proposed model-free method is relatively insensitive to process output noise. Another advantage of the proposed tuning method is that it automatically handles the tuning of highly delayed processes, since the method discards the initial process response. The simplicity and efficiency of the tuning method is demonstrated on several process models and on a laboratory thermal system. The method was also compared to a tuning method based on a similar closed-loop criterion. In addition, all necessary Matlab/Octave files for the calculation of the controller parameters are provided online.

Experimental investigation on photovoltaic cooling cycle with R141b/R245fa mixture under the electric field

A cooling cycle experimental apparatus with a modified metal foam porous-wall mini-channel heat sink for the linear Fresnel concentrating photovoltaic (LFPV) system was established to investigate its operation characteristics. The maximum heat flux used in the test rig of the LFPV system was about 37,000 W/m2. In this study, R141b was mixed with different volume fractions of R245fa. The cooling effect of non-azeotropic mixture of different mixing ratios under the action of electric field was experimentally studied. In steady-state experiments, the wall temperature and heat transfer coefficient of the heat sink are investigated. The experimental results showed that the heat transfer coefficient of the heat sink increased by 171% at an applied voltage of 200 V and a flow rate of 80 mL/min for the R141b/R245fa-c mixture. In the dynamic experiments, the critical heat flux of the heat sink is studied and the results showed that the critical heat flux of the R141b/R245fa-b mixture increased by 45% at an applied voltage of 200 V with a flow rate of 75 mL/min. The use of R141b/R245fa mixture with the action of the electric field can greatly enhance the performance of the cooling system and improve the operating environment of the photovoltaic system.

Transient transmission of droplets and aerosols in a ventilation system with ceiling fans

Different droplet and aerosol particles are generated in various respiratory activities, and their transmissions behave differently under various indoor airflow patterns. Since the judicious use of fans can reduce aerosol transmission by dispersing nearfield aerosol concentration in steady-state tracer gas experiments, this study further investigates the effect of ceiling fans on the transient droplet and aerosol transmission in the coughing process. Both large-eddy simulation (LES) and experiments, including particle image velocimetry (PIV) technique, concentration measurements, and video recordings with the high-speed camera were conducted. The results showed that the operation of ceiling fans changed the particle trajectory downwards up to 0.4 m above the floor surface. Since the airflow from ceiling fans could settle down the large particles within a short period and dilute the concentration of small-diameter particles, the aggregated concentrations in the breathing zone were reduced by 87%. Compared to the supply air from diffusers, the ceiling fan airflow had a more significant effect on the droplet and aerosol transmissions and achieved better protection for the manikin located underneath from the cough exposure. The ceiling fans strongly affected the indoor airflow pattern and also showed a potential to reduce the exposure risk to horizontally directed coughs in the transient process.

Interaction of HPC with CTAB and Tween 40 at Water/Air and Water/Soya Oil Interfaces.

The bulk and interfacial shear rheological behavior of aqueous solutions of biocompatible polymer HPC has been investigated in the presence of cationic CTAB and nonionic Tween 40 having the same chain length but different head groups. Steady-state bulk experiments depict two distinct regions in the rheogram (Newtonian followed by pseudoplastic). Dynamic experiments suggest that the stability of HPC hydrogels decreases with the increase in surfactant concentration. Interfacial steady shear tests of 2D monolayers of 1 wt % HPC and 1 wt % HPC with varying concentrations of Tween 40/CTAB show a non-Newtonian dilatant behavior at the solution-air interface. However, two distinct dilatant regions separated by a Newtonian region were observed for the same films at the solution-soya oil interface. The strength of films formed at the two interfaces decreases with the increase of surfactant concentration as observed from oscillatory interfacial tests. HPC interacts more strongly with CTAB than Tween 40 both in bulk as well as at the interfaces studied.

Steady state performance of molten salt natural circulation loop with different orientations of heater and cooler

Molten salts are proposed as a coolant and sensible heat storage medium for Solar Thermal Power Plant (STPP) as well as fuel and coolant for Molten Salt Reactor (MSR). The objective of the present study is to investigate the steady state behavior of molten salt in natural circulation flow condition along with effect of different orientations of heater and cooler on the steady state mass flow rate. For which a Molten Salt Natural Circulation Loop (MSNCL) has been setup with molten nitrate salt (mixture of Sodium Nitrate and Potassium Nitrate in 60:40 ratio by wt.) as working fluid. Steady state experiments in four different orientations of heater and cooler [Horizontal Heater Horizontal Cooler (HHHC), Horizontal Heater Vertical Cooler (HHVC), Vertical Heater Horizontal Cooler (VHHC) and Vertical Heater Vertical Cooler (VHVC)] have been performed and data generated are compared with the steady state correlations available in open literature which are derived considering either standard friction factor correlations or friction factor correlations deduced from their experiments and theoretical studies. Based on the deviations observed in the experimental values and correlation predictions, an improved formulation has been derived. The steady state formulation has been improved by incorporating Wall Thermal Inertia (WTI) effect and Heat Loss (HL) effect considering the importance of WTI & HL in dealing with high temperature molten salt loop. The improved formulation has been compared with the experimental results for different orientations of heater and cooler. Further, a new friction factor correlation has also been deduced from the experiments for vertical heater orientation. Description of MSNCL along with validation studies performed for different steady state correlation against experimental data generated in MSNCL, are reported in this paper.