Physical Properties Of Liquid Research Articles

Estimation of gas hold-up in bubble columns using wall pressure fluctuations and machine learning

We present a novel approach to estimate gas hold-up in bubble columns using wall pressure fluctuations – without requiring knowledge of operating flow regime, column configuration or physical properties. The approach uses machine learning and pressure fluctuations acquired from a wall mounted pressure sensor. The approach is validated by carrying out experiments with different physical properties of liquid (deionised water, deionised water – alcohol [ethanol, propanol and butanol] mixture up to 2 % alcohol, deionised water – glycerine (30 %), tap water). The majority of the data was obtained with 0.1 m diameter bubble column. Data with tap water in this column was obtained for four different spargers. Data with tap water was also obtained for 0.15 m and 0.33 m diameter bubble columns. Gas velocity was varied up to 0.1 m/s. The covered physical properties, sparger configurations, column diameter and gas velocities span different flow regimes. An artificial neural network (ANN) based model was developed to relate characteristics of wall pressure fluctuations and superficial gas velocity to the gas hold-up. The approach was validated by comparing predicted results with the experimental data unseen by the ANN model. The approach demonstrates the feasibility of using wall pressure fluctuations with machine learning to estimate key characteristics without prior knowledge of column configuration, flow regimes or physical properties.

Core differences: Examining branched versus linear substituents’ influence on Tri(octyl)phosphonium-based ionic liquid physical properties

During the investigation of room temperature ionic liquids (RTILs) produced from tri(2-ethylhexyl)phosphine, it was discovered that the common core tri(n-octyl)phosphine was also significantly underreported. This void in the literature prompted an investigation to explore the influence of branched versus linear substituents’ influence on physical properties. To facilitate a thorough structure-property relationship study, 28 ionic liquids were prepared from tri(n-octyl)phosphine to compare against their branched counterparts. Thermal behavior was investigated by utilizing visual melting point determination, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA), with emphasis placed on the examination of physical states, phase transitions (including solid-solid), and degradation. Remarkably, all materials produced here are ionic liquids (mp < 100 °C), with 16 of the 28 being liquids at room temperature. Standard analytical methods were utilized to assess the physical properties of the compounds, namely density, viscosity, surface tension, and solubility/miscibility. Structure-property relationships were assessed, particularly focusing on the differences in physical properties between the tri(n-octyl)phosphine and tri(2-ethylhexyl)phosphine cores.

Pragmatic Prediction Model of Droplet Trajectory in a Turbine Cascade

Abstract Droplet deposition on a turbine cascade is important for the turbine system performance but its experimental analysis is difficult. Thus, the simulation of a droplet liquid phase in a gas flow field was studied to optimize turbine cascade design. However, the computational fluid dynamics (CFD)-based approach for such droplet problems requires enormous costs. Thus, the application of CFD simulation in the turbine blade's early-stage design is challenging, requiring iterative optimization for adjusting design with performance prediction. Therefore, this study proposed an analytical prediction method, having a reasonable cost and moderate accuracy, as an alternative to the whole multi-phase numerical simulation approach. The proposed method predicts droplet motion using the outline of the turbine blade and gas–liquid physical properties. Furthermore, the approach was validated by performing a three-dimensional Eulerian–Lagrangian simulation with low-pressure turbine blade T106. It was found that the droplet trajectories in the turbine cascade are governed by Stokes number. Furthermore, the streamlines of the gas flow were characterized by the shape of the turbine blade. The proposed model reproduced droplet trajectories obtained using CFD within an error margin of 10%. Consequently, it was concluded that the proposed analytical model is a promising approach to predict the droplet trajectory in a turbine cascade, obtained by the three-dimensional numerical simulation at a low cost.

Microscopic mechanism of nanofluids electrospray: A molecular dynamics study

Cone-jet electrospray is widely used in various fields, such as electrospinning, nanostructured porous coating preparation, and inkjet printing, for which it can produce a large number of monodisperse and high charge-to-mass ratio droplets. A molecular dynamics method is employed to investigate the cone-jet electrospray emission behavior of nanofluids, where the microscopic mechanism of cone-jet electrospray including the formation of the cone, disintegration of the jet, stability of hydrogen bond, and interactions between molecules is revealed. In this paper, the influence of operating parameters and liquid physical properties were numerically conducted and extensively analyzed. The results show that the cone-jet electrospray only occurs in a certain range of applied voltage and flow rate, and the temperature and concentration of nanoparticles have a great effect on the jet length and the number of clusters produced by jet disintegration. When the electric field intensity increases, the length of the jet and the number of clusters increase. However, regardless of the electric field intensity, the maximum axial density is always located near the capillary outlet and the maximum radial density is located at the central axis of the capillary. As the temperature increases, the number of clusters increases significantly due to the synthetical effect of electric field-induced disintegration and evaporation, whereas the jet length is reduced. With an increase in concentration of nanoparticles at room temperature, the Taylor cone not only appears earlier but also has a larger angle. Meanwhile, the non-bonded interactions between ethanol molecules become stronger. This work provides microscopic mechanisms of nanofluids cone-jet electrospray and is potentially useful to optimize the design parameters of industrial applications.

Direct numerical simulations of internal flow inside deformed bubble by phase-field-based lattice Boltzmann method

Internal flow mechanism inside deformed bubble was investigated through direct numerical simulation by Allen-Cahn phase-field-based lattice Boltzmann method and theoretical model developed from Bernoulli equations. The effects of key parameters such as bubble size and gas or liquid physical properties on bubble dynamic behaviors were systematically analyzed. The internal flow that gas flowed through bubble neck from the smaller part to the larger part was well simulated. Lower redistribution was observed at high gas viscosity due to enhanced viscous flow resistance, at low surface tension and high gas density due to the weaken driving force for internal flow, respectively. And, at high liquid viscosity, the time for cutting-off of bubble neck was longer than the time for internal flow due to decreased bubble rising velocity, finally the mother bubble failed to breakup. The internal flow velocity predicted by numerical simulation were in consistent with calculated value by theoretical model, which greatly validated our theoretical model and emphasized the great significance of internal mechanism.

Component Effects in Binary Droplet Impact Behaviors on the Heated Plate: Comparison Study of Ethanol/Propanol and Ethanol/Water Droplets and Observation of Novel Bubble Shrinkage Phenomenon

This work aims to investigate the effect of liquid physical properties on the behavior of binary droplets impact on the heated smooth aluminum alloy plate with a high-speed imaging system. Two groups of mixed solutions with similar boiling point differences are selected as the working liquid, in which the low-boiling-point components are both ethanol and the high-boiling point components are propanol and water, respectively. Compared to the ethanol/propanol binary droplets, the experimental results show that the ethanol/water binary droplets have diverse impact phenomena and significantly broad transition boiling regimes, as well as the reduced droplet residence time and increased Leidenfrost temperature point. With the decreasing ethanol content in ethanol/water binary droplets, these effects become more prominent. For secondary atomization, the ethanol/water binary droplet undergoes parent droplet breakup into fragment droplets with larger diameters (Ds &gt; 0.3 mm). Both binary droplets produce satellite droplets with small diameters (Ds &lt; 0.3 mm) by puffing and ejection. In terms of the ethanol/propanol binary droplet impact, the probability of puffing is higher and the satellite droplet diameters are small. In the ethanol/water binary droplet impact, the probability of ejection is higher and the satellite droplet diameter distribution is wider. When an ethanol/water binary droplet of 25 vol.% ethanol content impacts the heated wall at Ts = 120 °C, a novel large bubble shrinkage phenomenon occurs at the late stage of droplet evaporation. This phenomenon is proposed to be relevant to the increasing surface tension and saturation temperature with decreasing ethanol content, as well as the decreasing ambient temperature above the top surface of the bubble.

Effects of Thickening Agents on the Mucociliary Transport Function: Comparison by the Type of Thickening Agents and the Viscosity of Thickened Water.

Thickening agents effectively prevent liquid aspiration, but their impact on the ease of discharging aspirated liquids from the trachea remains unclear due to alterations in the physical properties of liquids. This study clarifies the effects of thickening agents, comprising various raw materials, on mucociliary transport function, focusing on the viscosities of thickened waters. The subjects were 23 healthy adults. Five types of saccharin solution were prepared: a solution without a thickening agent, a starch-based nectar-like solution, a starch-based honey-like solution, a xanthan-gum-based nectar-like solution, and a xanthan-gum-based honey-like solution. Using these five types of saccharin solutions randomly, each subject underwent five trials of the saccharine dye test to evaluate the mucociliary transport function of the respiratory tract. The saccharin time was defined as the time from the placement of the saccharin solution on the nasal vestibule of the subject to when the subject reported that they became aware of the sweetness. The saccharin transit times for all samples of thickened water were longer compared to those of water without a thickening agent (p < 0.01). A comparison between thickened water samples with different viscosities showed that the saccharin transit time was longer when thickened water samples with high viscosity were prepared using the same thickening agent (p < 0.01). This suggests that while thickening reduces aspiration, the use of thickening agents may increase the difficulty in discharging aspirated fluids from the trachea.

Advances in 4-cyanobiphenyl tethered discotic oligomers and supermolecular liquid crystalline materials

ABSTRACT A novel family of rod-like liquid crystals designed by Prof. G.W. Gray having nematic phase has been extensively used to make stable informative liquid crystal displays. These 4’-alkyl- and 4’-alkoxy-4-cyanobiphenyl molecules were created using his extensive understanding of liquid crystal chemical structure and physical properties. Following the discovery of this family of nematogens for display applications, the development of liquid crystal molecule designing and synthesising has resulted in the emergence of a broad new family of functional liquid crystals. This feature article presents the review of reports on the liquid-crystalline behaviour of 4-cyanobiphenyl-based oligomeric systems, which are ‘in-between’ polymeric and low molar mass systems and exhibit distinct molecular structures.

Tailored carbon dioxide capacity in carboxylate-based ionic liquids.

We have used a library of thermally stable tetraalkylphosphonium carboxylate ionic liquids that were easily prepared from available carboxylic acids. Depending on the pKa in water of the precursor acids, the resulting ionic liquids either dissolve or reversibly chemically absorb CO2, with some exhibiting notable gas capacities, reaching a CO2 mole fraction of 0.2 at 1 bar and 343 K. While equilibrium constants and ionic liquid capacities generally correlate with the pKa of the acids, certain exceptions underscore the influence of liquid structure and physical properties of the ionic liquids, elucidated through molecular dynamics simulations and density functional theory calculations. Unlike the trends observed in other CO2-absorbing ILs, phosphonium carboxylates do not experience increased viscosity upon gas absorption; instead, enhanced diffusivities are observed, facilitating efficient gas-liquid transfer.

Electrochemical Deposition in Vertical Tubes : An Hydrodynamic and Mass Transfer Study

The present work is part of the research project NXCHROME led by IRT M2P. It concerns the chemical engineering of metallic hard chromium coatings on internal surface of large tubular parts. These parts are intended to be used in several sectors of activity (aeronautics, armament, energy...). Thus, taking into account severe specifications related to these applications, the parts will be very strongly solicited thermomechanically during their use, which requested high performances to increase substrate's life. In the current process, tubes are treated vertically, by electrodeposition from a hexavalent chromium salt based (chromic acid) electrolyte. These electrolytes have the advantage of being efficient, easy to use, with well known functions. However, they have a low faradic yield (<20%), leading to an important production of bubbles (cathodic and anodic).These bubbles create the fluid motion, and eventually govern hydrodynamic, liquid flow and mass transfer of the species in the tube.It is important to note that the use of CrVI salts has been prohibited since 2017 (except for authorizations for applications without alternatives) by the European regulation REACh (Registration, Evaluation, Authorization and restriction of Chemicals). Indeed, hexavalent chromium is classified in Appendix XIV among SVHC (substances of very high concern), due to its high toxicity (CMR compound : Carcinogenic, Mutagenic and Reprotoxic) and the high danger it represents for coworkers using this compound. The objective of NXCHROME is to find a alternative process with a "REACh compatible" electrolyte based on an innovative trivalent chromium. The modus operandi and the electrochemical mechanisms involved are completely different and less well known, compared to the former electrolyte. Nevertheless, it keeps this low faradic yield and the liquid agitation mode in tubular parts will remains identical.Nevertheless, this change is a good opportunity for a deep investigation in the "bubble induced hydrodynamic" which occurs during plating time, and to collect all reliable information on fluids behavior. Then, two main research axis have been considered. The first one is done via the numerical simulation of the secondary current distribution, i.e. taking into account the electrical phenomena in the electrolyte (ohmic drop), the geometry of the system and the kinetics of the electrochemical reactions. This part is in collaboration with HIVELIX company. The second one trhought the design and elaboration of a large size experimental set-up in stainless steel and PMMA (φ = 40mm, L = 3000mm) Figure 1. This ste-up includes electrochemically active cathode parts (production of bubbles by hydrolysis), and transparent parts (windows of observations of the bubbles, according to the height of the tube). As it is the bubble production which puts in movement the fluid with their vertical displacement towards the surface, informations on their size and behavior are of primary importance. Their speed is determined by their size (depending on the distance covered and the coalescence) and the liquid physical properties.To mimic the chromium electrolyte, a transparent saline solution has been chosen and prepared by adjusting its parameters to be identical to the industrial electrolyte (viscosity, conductivity...), while allowing bubble production on the central electrode surface.Data collection and order of magnitude are done by various means, namely flow rate measurements, gas retention within the liquid and high frequency camera shots (bubble size, bubble velocity, coalescence...). Figure 1

Investigation of Solid–Liquid Phase Equilibria of Mg2+, NH4+//Cl–, SO42–H2O at T = 303.15 K and P = 88.35 kPa

Nitrogen and magnesium compound fertilizer is an important and efficient fertilizer in the fertilizer industry. It can solve the problem of lack of sulfur, magnesium, and nitrogen in soil. MgCl2 can react with (NH4)2SO4 to produce Mg–N compound fertilizer. Therefore, the solid–liquid equilibrium data and physical properties (density and viscosity) of the quaternary system Mg2+, NH4+//Cl–, SO42––H2O and its ternary subsystems Mg2+, NH4+//Cl––H2O and Mg2+//Cl–, SO42––H2O at T = 303.15 K ± 0.05 K and P = 88.35 kPa were studied by an isothermal stripping equilibrium method. According to the experimental data, the phase diagram and physical property composition diagram of each system were drawn. The ternary subsystem Mg2+, NH4+//Cl––H2O contains two invariant points and three crystallization regions. The ternary system Mg2+//Cl–, SO42––H2O contains four invariant points and five crystallization regions. The quaternary system Mg2+, NH4+//Cl–, SO42––H2O contains seven invariant points and nine crystallization regions. MgCl2·NH4Cl·6H2O and MgSO4·(NH4)2SO4·6H2O exist in the quaternary system, and the quality of crops can be significantly improved by using the latter kind of complex salt. Therefore, this project is of great significance for the production of N–Mg compound fertilizers from magnesium resources in salt lake or other underground brines.

Nanoliflerin Ayçiçeği (Helianthus annuus) Yağına Eklenmesinin Yağın Viskozitesi Üzerine Etkisi

The significant effect of the addition of very small proportions of nanofibres and nano-particulates on the physical and mechanical properties of solid materials has been long observed and described. The effect of addition of electrospun fibres on the physical properties of liquid has not been so widely examined. In this paper, the effect of the addition of polyvinyl alcohol (PVOH), and zein nanofibers in sunflower (Helianthus annuus) oil on its viscosity was observed and quantified. For a given amount of material, a trend of increasing effectiveness was found as fibre diameter reduced. The addition of 0.01% (by mass) of fibre increased the kinematic viscosity of oil samples by 15%. The presence of fibre in oil was confirmed by light microscopy whilst the size of the fibres was measured by the analysis of scanning electron microscope images (SEM). This phenomenon of a low concentration of nanofibers significantly increasing viscosity may find practical applications as a foodstuff thickener.

Reactive mass transfer of single bubbles in a turbulent flow chamber: The effect of temperature

Mass transfer at elevated temperatures is common in industrial equipments. In this work, the mass transfer coefficient between a single bubble and the surrounding liquid in a flow chamber at elevated temperatures was measured experimentally and analyzed from the following two aspects: liquid physical properties and molecular diffusion, where the latter is considered as the main factor. Based on Bao et al.’s work, a modified correlation was proposed to describe the effect of gas phase partial pressure resulted from the change of liquid temperature, from 25 °C to 85 °C, on the mass transfer coefficient. The volumetric mass transfer coefficient of single bubbles in the chamber can be compared to that in a stirred tank, even at elevated temperatures, especially at low stirring speeds.

Cavitation-induced shock wave behaviour in different liquids

This paper follows our earlier work where a strong high frequency pressure peak has been observed as a consequence of the formation of shock waves due to the collapse of cavitation bubbles in water, excited by an ultrasonic source at 24 kHz. We study here the effects of liquid physical properties on the shock wave characteristics by replacing water as the medium successively with ethanol, glycerol and finally a 1:1 ethanol–water solution. The pressure frequency spectra obtained in our experiments (from more than 1.5 million cavitation collapsing events) show that the expected prominent shockwave pressure peak was barely detected for ethanol and glycerol, particularly at low input powers, but was consistently observed for the 1:1 ethanol–water solution as well as in water, with a slight shift in peak frequency for the solution. We also report two distinct features of shock waves in raising the frequency peak at MHz (inherent) and contributing to the raising of sub-harmonics (periodic). Empirically constructed acoustic pressure maps revealed significantly higher overall pressure amplitudes for the ethanol–water solution than for other liquids. Furthermore, a qualitative analysis revealed that mist-like patterns are developed in ethanol–water solution leading to higher pressures.

Nature and characteristics of gas–liquid flow regimes in a micro‐packed bed reactor

AbstractMicro‐packed bed reactors (μPBRs) have the advantages of high heat and mass transfer efficiency and excellent safety, and they have been successfully applied to hydrogenation and oxidation reactions. However, the study of gas–liquid flow regimes in the μPBR, which is essential for the mass transfer modeling and reactor scale‐up, is still insufficient due to the limitation of micro‐scale and complexity of capillary force. In this work, the flow regimes in the two‐dimensional μPBR were systematically studied by visual method utilizing a high‐performance camera. Four typical flow regimes and characteristics were captured, and flow regime transition was revealed. Effects of gas and liquid superficial velocities, liquid physical properties, and particle sizes on liquid spreading areal fraction and pressure drop were investigated. Flow regime transition correlation of churn flow and pseudo‐static flow in the μPBR was provided for the first time based on the summary of the current and previous published results.

A new drag model for CFD modeling of bubble columns with surfactant

It is well known that a small amount of surfactant may significantly affect the flow stability in bubble columns, which cannot be interpreted by the slight variation of the liquid physical properties, e.g., surface tension, viscosity or density. The underlying mechanism is relevant to the interfacial dynamics due to surfactant concentration gradient. However, direct resolution of the micro-scale dynamics is challenging, as this requires complicated coupling of direct numerical simulation of interfacial dynamics and surfactant migration. In this study, a simplified correlative model was developed to take into account the surfactant effect on the average drag coefficient in the two-fluid model of CFD simulation. This novel drag model can improve the prediction of gas holdup in the homogeneous regime. By considering both the surfactant effect and swarm effect, the model can also reasonably estimate the gas holdup in the heterogeneous regime. A notable feature of this model is the reproduction of the peak of gas holdup at certain surfactant concentration in the experiments. Furthermore, although the model is based on the experimental data of ethanol solution, it can also predict the gas holdup in the bubble columns of other types of surfactants, e.g., butanol solution.

Is there a one-to-one correspondence between interparticle interactions and physical properties of liquid?

In this study, we present the original method for reconstructing the potential of interparticle interaction from statistically averaged structural data, namely, the radial distribution function of particles in many-particle system. This method belongs to a family of machine learning methods and is implemented through the differential evolution algorithm. As demonstrated for the case of the Lennard-Jones liquid taken as an example, there is no one-to-one correspondence between structure and potential of interparticle interaction of a many-particle disordered system at a certain thermodynamic state. Namely, a whole family of the Mie potentials determined by two parameters p1 and p2 related to each other according to a certain rule can reproduce properly a unique structure of the Lennard-Jones liquid at a given thermodynamic state. It is noteworthy that this family of the potentials quite correctly reproduces for the Lennard-Jones liquid the transport properties (in particular, the self-diffusion coefficient) over a temperature range as well as the dynamic structure factor, which is one of the key characteristics of the collective dynamics of particles.

Właściwości reologiczne cieczy sprężysto-lepkoplastycznej

A model for the motion of a compressible elastic-viscous-plastic fluid in a round pipe is proposed. The main indicators of the flow, volume flow and speed are obtained. Numerous hydrodynamic processes are associated with the properties of liquids. It is known that the mechanical and physical properties of liquids can be described by various models. Various models have been proposed that partially describe the processes of hydromechanics. The proposed model makes it possible to qualitatively describe the deformation processes that occur in various systems. To describe a closed theory of motion of a continuous medium and, in particular, between stress and strain, it is necessary to have a mechanical model. From the literature analysis it is known that there are simple models, which include elastic, viscous and plastic. At the same time, it should be noted that the mechanical model partially shows the mechanical state of the elastic body in the form of Hooke's law. Practice shows that there are more complex liquids that do not obey this law. One of these fluids is an elastic-viscous-plastic fluid. In this work, a model is proposed that describes the elastic-viscous-plastic properties of liquids, which sequentially connects the elastic and viscous-plastic elements. For such a medium, the total resistance will be the sum of the stress corresponding to the elastic deformation and the stress caused by the viscous-plastic resistance. Based on the proposed model, an equation is obtained taking into account the coefficient of volumetric elastic expansion, and an equation is obtained for determining the velocity distribution over the pipe section and volume flow for a given liquid. Calculations have shown that with an increase in compressibility, the flow rate of the liquid partially increases, which in some practical cases produces a positive effect.

The effect of the liquid physical properties on the wave frequency and wave velocity of co-current gas-liquid stratified two-phase flow in a horizontal pipe

The aim of the present study was to investigate the effect of the liquid physical properties on the liquid film thickness, wave frequency, and wave velocity in co-current gas-liquid stratified two-phase flow in a horizontal pipe. The present experimental study was conducted using an acrylic pipe with an inner diameter of 26 mm and a length of 9500 mm. The superficial velocity of liquid (JL) and gas (JG) were 0.02 m/s to 0.1 m/s and 4 m/s to 16 m/s, respectively. A highspeed video camera was used to take the visual data which is then processed by the developed image processing techniques to obtain the time series data of the liquid film thickness. The probability distribution function (PDF) and discrete wavelet transform (DWT) were used to analyze the time series of the liquid film thickness. In addition, the data were also analyzed using the power spectral density (PSD) in order to obtain the wave frequency and the wave velocity. Next, the experimental correlations to predict the wave frequency and the wave velocity were developed using the dimensional analysis. From the time series of the liquid film thickness, the effect of the viscosity and surface tension on the shifting of scale and frequency of the wavelet decomposition level, as well as the frequency and velocity of the waves were clarified. In addition, a correlation to predict the frequency and velocity of waves has been successfully developed, in which the Martinelli parameter, the ratio of gas and liquid Reynold numbers, and the Weber number play the important roles in the correlation.

Effects of thermostats/barostats on physical properties of liquids by molecular dynamics simulations

Thermostats/barostats that maintain temperature/pressure as constant (on average) in molecular dynamics (MD) simulations are essential for simulatingisothermal-isochoric (NVT) or isothermal-isobaric (NPT) systems. In order to simulate accurate physical properties, thermostats/barostats need not only sample a correct NVT/NPT ensemble but also minimally disturb the particles’ (Newtonian) dynamics. In other words, the NVT/NPT simulations need to yield accurate physical properties (dynamics properties included, e.g. diffusivity and viscosity) and also their fluctuations. However, few studies have studied in-depth the effects of thermostats/barostats on a comprehensively wide range of simulated properties. In this work, commonly used thermostats, e.g. Andersen, stochastic dynamics (SD), Berendsen, V-rescale and Nosé-Hoover thermostats, and barostats, e.g. Berendsen and Parrinello-Rahman barostats, with different coupling strengths were studied to see whether they can yield accurate simulated properties and fluctuations. The theoretical values of physical properties’ fluctuations were calculated via statistical mechanics to provide a comparison benchmark for MD simulations. Particularly, the accuracy of thermostats was studied in the context of NPT or non-equilibrium molecular dynamics (NEMD) simulations, which has long been overlooked. Berendsen thermostat/barostat suppresses the fluctuations of energy/volume (due to the exponential decay of deviation of the simulated temperature/pressure from the target value) and yields inaccurate simulated properties. In addition, Andersen and SD thermostats perturb the particles’ dynamics so violently (due to the random component in the algorithm) that they fail to accurately simulate dynamics properties. Overall, Nosé-Hoover/V-rescale thermostat, and Parrinello-Rahman barostat with moderate coupling strength are recommended for common NVT/NPT production simulations. NPT or NEMD simulations would require more efficient (or stronger coupling) thermostats than NVT equilibrium molecular dynamics (EMD) to maintain the simulated temperature close to the target.