Thermal Hydrodynamic Model Research Articles

A heat transfer model for liquid film boiling on micro-structured surfaces.

High heat transfer coefficient (HTC) and critical heat flux (CHF) are achieved in liquid film boiling by coupling vibrant vapor bubbles with a capillary liquid film, which has thus received increased interest for thermal management of high-power electronics. Although some experimental progress has been made, a high-fidelity heat transfer model for liquid film boiling is lacking. This work develops a thermal-hydrodynamic model by considering both evaporation atop the wick and nucleate boiling inside the wick to simultaneously predict the HTC and CHF. Nucleate boiling is modeled with microlayer evaporation theory, where a unified scaling factor is defined to characterize the change of microlayer area with heat flux. The scaling factor η is found to be independent of wicking structure and can be determined from a few measurements. This makes our model universal to predict the liquid film boiling heat transfer for various micro-structured surfaces including micropillar, micropowder, and micromesh. This work not only sheds light on understanding fundamental mechanisms of phase-change heat transfer, but also provides a tool for designing micro-structured surfaces in thermal management.

A Thermal Hydrodynamic Model for Emulsified Oil-Lubricated Tilting-Pad Thrust Bearings

On maritime vessels, external factors such as explosions, collisions, and grounding can cause the emulsification of lubricating oil by seawater pollution, which can affect the lubrication of a ship’s thrust bearing. To explore the influence of the mixed emulsification of lubricating oil and seawater on the lubrication performance of thrust bearings, this study conducted an emulsification experiment, from which the viscosity equation of the oil–water mixture was obtained. A thermal hydrodynamic model (THD) of bearings considering oil–water mixed emulsification was established, and the Finite Difference Method (FDM) was used for analysis. The results show that according to the characteristics of the manifold, the mixture is divided into water-in-oil (W/O) and oil-in-water (O/W). In the W/O flow with higher viscosity, the film thickness becomes higher, but the power loss increases. In the O/W manifold with low viscosity, the thin film easily causes mixed friction. In the demulsification stage of the mixed liquid, the thickness loss of the film is huge, and the collision between the thrust-bearing pad and the inference plate may cause the pad to be ablated. The influence of specific heat capacity on temperature is greater than the temperature rise caused by viscosity.

Modeling of the thermal-hydrodynamic and chemical regime of Geyser reservoir (Valley of Geyser, Kamchatka)

The thermal-hydrodynamic and chemical eight-decade history of the Geysers production reservoir in the Valley of Geysers (Kamchatka) shows either linear multiyear trends, seasonal cycles, or stepwise changes synchronized with geological catastrophes. Recent changes, apparently caused by surface meteoric water inflow into the productive Geysers reservoir as a result of caprock erosion from the 2007 catastrophic landslide and 2014 mud-flow, include: (1) seasonality of deep component discharge, (2) a drop in CO2 fraction of the gas content of geysers followed by a decrease in geyser eruption capacity, (3) increases in standard geothermometers (Na/K and SiO2) and (4) increases in the sulfate component. 2D numerical thermal-hydrodynamic (TH) model was developed and applied to explain the seasonal decrease in deep component discharge as an effect of gas phase condensation and upflows capture caused by cold water infiltration from the surface during flood periods. Thermo-hydrodynamic-chemical (THC) models and total chemical discharge/recharge balances were used to explain CO2 sequestration, increased sulfate component, and increased standard geothermometers due to gypsum/calcite transformation in surface water infiltration pathways rather than reservoir heating.

Thermal dynamics of leader decay and reactivation in long air gap discharges

In this study, we present a comprehensive investigation of positive leader discharges, with the aim of enhancing our understanding of leader decay and reactivation. Our approach involved a detailed experimental and computational analysis of the phenomena. Specifically, we employed a time-resolved quantitative Schlieren platform, which provided us with high spatial resolution (60.0 μm pixel−1) and short exposure times (0.37 μs frame−1), allowing us to capture the 2D spatial–temporal evolution of gas temperature in positive leaders with a gap length of up to three meters. In addition, we employed a detailed thermal-hydrodynamic model coupled with a comprehensive kinetic scheme, consisting of 28 chemical species and 125 chemical reactions. Our simulations showed good agreement with the measured mean gas temperature and expansion rate of thermal radius. We conducted experiments under the same applied conditions to obtain both stable and decaying leaders. Our results show that once a positive leader starts to decay, the temperature drops below 3000 K. At the same time, both the electric field and conductivity decrease significantly compared to a stable leader. In addition, before the temperature drops below 2000 K and transforms into an aborted leader, a decaying leader might be reactivated.

Transition to Chaos in Five-Dimensional Porous-Medium Thermal-Hydrodynamic Model with Low Prandtl Number

In this paper, we investigate the transition to a chaotic regime of thermal convection in a five-dimensional model with low Prandtl number in a porous medium. The mathematical formulation of the model includes the heat equation coupled with the equations of motion under the Boussinesq–Darcy approximation. A system of five ordinary differential equations is derived using a spectral method. This system is solved numerically by using the fourth-order Runge–Kutta method. The results show that from a subcritical value of the Rayleigh number, a transition from steady convection to chaos via a Hopf bifurcation produces a limit cycle which can be associated with a homoclinic explosion. Furthermore, we find that for certain values of Rayleigh number and shape parameter which measures the ratio between the dimensions of the computational domain, the transition from periodic oscillatory convection to chaotic convection can occur via a period-doubling.

A thermal-hydrodynamic model to evaluate the potential of different tray designs for production of renewable aviation fuel through reactive distillation

Reactive distillation is an intensified technology that has demonstrated interesting economical and operational advantages in the production of renewable aviation fuel. In tray distillation columns with heterogeneous catalyst, the arrangement of the latter determines flow characteristics that can influence the trays performance. This paper presents a CFD-based model for the simulation of a sieve tray with catalyst containers, which works under the operating conditions of a reactive distillation column used for production of renewable aviation fuel. Modeling of a non-isothermal liquid-vapor flow through the system was considered. The model was used to analyze the effect of geometric design of sieve trays and catalyst containers on important hydraulic parameters, mixing and heat transfer between phases. Profiles of clear liquid height and flow patterns estimated for different designs follow a similar behavior to that reported in available experimental studies. Additionally, the applied modeling approach makes possible the prediction of undesired phenomena, like downcomer flooding and excessive displacement of liquid phase. From these points, it is concluded that the model can serve as a basis for the development of a CFD modeling strategy to evaluate the performance of different tray designs with a similar catalyst configuration for production of renewable aviation fuel.

The thermal response of small and shallow lakes to climate change: new insights from 3D hindcast modelling

Abstract. Small, shallow lakes represent the majority of inland freshwater bodies. However, the effects of climate change on such ecosystems have rarely been quantitatively addressed. We propose a methodology to evaluate the thermal response of small, shallow lakes to long-term changes in the meteorological conditions through model simulations. To do so, a 3D thermal-hydrodynamic model is forced with meteorological data and used to hindcast the evolution of an urban lake in the Paris region between 1960 and 2017. Its thermal response is assessed through a series of indices describing its thermal regime in terms of water temperature, thermal stratification, and potential cyanobacteria production. These indices and the meteorological forcing are first analysed over time to test the presence of long-term monotonic trends. 3D simulations are then exploited to highlight the presence of spatial heterogeneity. The analyses show that climate change has strongly impacted the thermal regime of the study site. Its response is highly correlated with three meteorological variables: air temperature, solar radiation, and wind speed. Mean annual water temperature shows a considerable warming trend of 0.6 ∘C per decade, accompanied by longer stratification and by an increase in thermal energy favourable to cyanobacteria proliferation. The strengthening of thermal conditions favourable for cyanobacteria is particularly strong during spring and summer, while stratification increases especially during spring and autumn. The 3D analysis allows us to detect a sharp separation between deeper and shallower portions of the basin in terms of stratification dynamics and potential cyanobacteria production. This induces highly dynamic patterns in space and time within the study site that are particularly favourable to cyanobacteria growth and bloom initiation.

Thermal effect on stability and minimum oil film thickness of a deep/shallow pockets conical bearing

PurposeThis paper aims to study the influence of thermal effect on the performance for a high-speed conical hybrid bearing including stability and minimum oil film thickness.Design/methodology/approachA thermal hydrodynamic (THD) model and dynamic model of single mass rigid rotor system were established by taking conical hybrid bearing with shallow and deep pockets as the research object, dynamic coefficient and stability parameters of bearing-rotor system were obtained by using finite element method (FEM) and finite difference method (FDM) to solve computational models of Reynolds equation, energy equation and viscosity-temperature equation. Minimum oil film thickness was obtained based on bearing force balance. Dynamic coefficient was compared with previous findings.FindingsAfter considering thermal effect, the dimensionless critical mass decreases, a significant decrease in the instability speed, and the stability of the system decreases greatly; the minimum oil film thickness decreases because of thermal effect.Originality/valueThe thermal effect is combined with dynamic characteristics to analyze stability of the rotor system for a conical hybrid bearing. Influence of thermal effect on minimum oil film thickness is studied.Peer reviewThe peer review history for this article is available at:https://publons.com/publon/10.1108/ILT-12-2019-0542/

Thermo-hydrodynamic modeling and analysis for circular bilayer self-lubricating bearing

The bilayer self-lubricating bearing can be used in complex condition, but it exhibits higher temperature—due to the lack of the external oil supply—which results in a poorer lubricating performance. Here, the thermal hydrodynamic model of the ring-face bilayer self-lubricating bearing was established. The heat generating/transfer mechanism and the pressure distribution of the oil film were discussed. Results show that the maximum temperature of the bearing system is located at the minimum film thickness of the external ring face. The heat generated by the oil film shearing is gradually transferred from the oil film to the porous medium through the heat conduction and convection. With the decrease in speed or increase in the central film thickness, the temperature decreases, thus enhancing the bearing capacities of the oil film.

Preliminary Numerical Modeling of CO2 Geological Storage in the Huangcaoxia Gas Reservoir in the Eastern Sichuan Basin, China

Depleted gas reservoirs are important potential sites for CO2 geological sequestration due to their proven integrity and safety, well-known geological characteristics, and existing infrastructures and wells built for natural gas production. The Sichuan Basin has a large number of gas fields in which approximately 5.89×109 tons of CO2 can be stored. The Huangcaoxia gas field has the best opportunity in the eastern Sichuan Basin for a pilot project of CO2 sequestration due to its relatively large storage capacity and the nearly depleted state. A coupled thermal-hydrodynamic model including faults is built based on the geological and hydrogeological conditions in the Huangcaoxia gas field. The results of the numerical simulations show that the downhole temperature is above 80°C at a downhole pressure of 14 MPa under the constraint of temperature drop in the reservoir due to the strong Joule-Thomson effect. The corresponding injection pressure and temperature at the wellhead are 10.5 MPa and 60°C, respectively. The sizes of the pressure and CO2 plumes after an injection of 10 years are 18 km and 5 km, respectively. The zone affected by temperature change is very small, being about 1-2 km away from the injection well. The injection rate in the injection well Cao 31 averages 6.89 kg/s (21.73×104 tons/a). For a commercial-scale injection, another four wells (Cao 9, Cao 30, Cao 6, and Cao 22) can be combined with the Cao 31 well for injection, approaching an injection rate of 35 kg/s (1.10×106 tons/a). Both the pressure and temperature of CO2 injection decrease with the increasing depleted pressure in the gas reservoir when the latter is below 6 MPa. With the technique of CO2-enhanced gas recovery (CO2-EGR), the CO2 injection rate is improved and approximately 1.58×107 kg of gas can be produced during a studied time period of 10 years.

Conjugate thermal-hydrodynamic model for the study of heavy oil transport

In the present work, the thermal impact induced by the environment on the hydrodynamics of heavy oil transport in pipelines is analyzed. Here, the thermal dependence of the dynamic viscosity of heavy oils, in addition to the mechanical heating caused by viscous dissipation are taken into account; therefore, the mathematical models that represent the flow and temperature fields of the heavy oil have to be solved in a coupled manner. Moreover, given that the pipeline is protected by a thermal insulation (soil), the domain of study defines a conjugate system between the heavy oil, the pipeline and the soil, which indicates that before knowing the temperature in the fluid region, temperatures in the other two zones must be calculated. To define properly how thermal energy is transferred and generated during the crude oil transport, the analysis is carried out in dimensionless form, solving the conjugate mathematical model by using numerical approaches and simplified asymptotic approximations. The main results reveal that the transport of heavy oils is seriously affected by a small reduction in temperature, increasing substantially the dynamic viscosity and the flow rate is reduced significantly in comparison with the case of a full thermal insulation condition. Then, we can infer that when the losses of thermal energy and its effects on the hydrodynamics are controlled, an efficient transport process is obtained. Employing the asymptotic analysis, results show that such a condition can be achieved by two ways: the first one by improving the thermal insulation, and the second one by optimizing the ratio of the internal radius to the length of the pipeline or increasing the volumetric flow rate, which indicates that the conjugate phenomenon is a modified version of the Graetz-Nusselt problem.

Thermal-permeability structure and recharge conditions of the Mutnovsky high-temperature geothermal field (Kamchatka, Russia)

The Mutnovsky geothermal area is part of the Eastern Kamchatka active volcano belt. Mutnovsky, 80kY old and an aging strato-volcano (a complex of 4 composite volcanic cones), acts as a magma- and water-injector into the 25-km-long North Mutnovsky extension zone. Magmatic injection events (dykes) are associated with plane-oriented MEQ (Micro Earth Quakes) clusters, most of them occurring in the NE sector of the volcano (2×10km2) at elevations from −4 to −2km, while some magmatic injections occur at elevations from −6.0 to −4.0km below the Mutnovsky production field. Water recharge of production reservoirs is from the Mutnovsky volcano crater glacier (+1500 to +1800masl), which was confirmed by water isotopic data (δD, δ18O) of production wells at an earlier stage of development. The Mutnovsky (Dachny) 260–310°C high-temperature production geothermal reservoir with a volume of 16km3 is at the junction of NNE- and NE-striking normal faults, which coincides with the current dominant dyke injection orientation. TOUGH2-modeling estimates of the reservoir properties are as follows: the reservoir permeability is 90–600 e-15m2, the deep upflow recharge is 80kg/s and the enthalpy is 1420kJ/kg. Modeling was used to reproduce the history of the Mutnovsky (Dachny) reservoir exploitation since 1983 with an effective power of 48MWe by 2016. Modeling also showed that the reservoir is capable of yielding 65–83MWe of sustainable production until 2055, if additional production drilling in the SE part of the field is performed. Moreover, this power value may increase to 87–105MWe if binary technologies are applied. Modeling also shows that the predicted power is sensitive to local meteoric water influx during development. Conceptual iTOUGH2-EOS1sc thermal hydrodynamic modeling of the Mutnovsky magma-hydrothermal system as a whole reasonably explains its evolution over the last 1500–5000years in terms of heat recharge (dyke injection from the Mutnovsky-4 funnel) and mass recharge (water injection through the Mutnovsky-2 and Mutnovsky-3 funnels) conditions as previously mentioned.

Thermal hydrodynamic modeling and simulation of hot-gas duct for next-generation nuclear reactor

A very high-temperature gas-cooled reactor (VHTR) is a fourth-generation nuclear power reactor that requires an intermediate loop that consists of a hot-gas duct (HGD), an intermediate heat exchanger (IHX), and a process heat exchanger for massive hydrogen production. In this study, a mathematical model and simulation were developed for the HGD in a small-scale nitrogen gas loop that was designed and manufactured by the Korea Atomic Energy Research Institute. These were used to investigate the effect of various important factors on the surface of the HGD. In the modeling, a porous model was considered for a Kaowool insulator inside the HGD. The natural convection and radiation are included in the model. For validation, the modeled external surface temperatures are compared with experimental results obtained while changing the inlet temperatures of the nitrogen working fluid. The simulation results show very good agreement with the experiments. The external surface temperatures of the HGD are obtained with respect to the porosity of insulator, emissivity of radiation, and pressure of the working fluid. The local Nusselt number is also obtained for the optimum design of a possible next-generation HGD.

Modeling and Analysis of High-Speed Journal Bearing Based on Thermal Hydrodynamic Lubrication Theory

Journal bearing in high-speed working conditions will generate a lot of heat, which affects its working performance. Based on hydrodynamic lubrication theory, a model of the thermal hydrodynamic lubrication was built, and the distributions of temperatures and pressures of the oil film were obtained from the simultaneous solution of generalized Reynolds, energy and viscosity-temperature equations. The results show that the temperature will increase and the pressure decrease of the lubrication oil film with the rising of the rotating speed, which will make the the bearing capacity decrease. Compared with the traditional isothermal model, the thermal hydrodynamic lubrication model is more consistent with the engineering practice.

Formation of the hydrothermal system in Geysers Valley (Kronotsky Nature Reserve, Kamchatka) and triggers of the Giant Landslide

Abstract The Geysers Valley hydrothermal system is hosted within a system of two permeable faults (revealed by mapping thermal features), located above a suggested partially melted magmatic body and recharged by meteoric water along the outcrops of rhyolite–dacite extrusions. Fast erosion is stimulating the significant discharge rate, the geyser’s cycling mode and landslide events. Natural state thermal hydrodynamic modeling shows that 20–30 ka of high temperature upflow of 250 kg/s and an enthalpy of 900 kJ/kg could build up the hydrothermal system in the Geysers Valley basin with output discharge parameters comparable to those at the current level. Modeling also shows that steam accumulation below an inclined caprock may have hydrothermal eruption potential. The Giant Landslide took place on June 3, 2007, when 20 × 10 6 m 3 of rocks were shifted 2 km downstream, more than 23 geysers were buried or submerged, and Podprudnoe Lake was dammed, injecting cold water into submerged geysers. Possible triggers of the Giant Landslide include the inclination of the sliding plane towards the Geysernaya river basin, a pressure increase in the fluid-magma system, hanging block saturation by water during spring flooding, hydrothermal alteration weakening of the sliding plane, and steam explosions. Recent geysers cycling activity monitoring data (2007–2010), hydrogeochemical sampling, and thermal area infra red (IR) survey data are also discussed.

Using numerical modeling for assessing the recoverable reserves of a geothermal steam field: The Pauzhetka geothermal field

A conceptual hydrogeological model has been created and a corresponding 3D numerical, thermal hydrodynamic model developed for the Pauzhetka geothermal field; the model covers an area of 13.6 km2 and includes three layers: a basement with conduits that supply the heat carrier, a hydrothermal reservoir, and an upper aquifer with percolation “windows.” Inversion is handled by the iTOUGH2 program; the model was calibrated using the 1960-2006 data on the natural state and extraction at 13675 calibration points. The inversion simulation has made it possible to identify and evaluate the key parameters of the model and to identify the sources that generate the recoverable reserves. Forecasting modeling for the period from 2007 to 2032 shows a sustainable extraction of 29 kg/s steam, provided five additional wells have been put into operation, which will provide 6.8 MWs of production by the geothermal power plant. The results of forecasting modeling, in combination with observations on long-term operation, allow an evaluation of the recoverable reserves in the industrial categories.

HELOKA facility: Thermo-hydrodynamic model and control

This paper presents the thermal-hydrodynamic model used to simulate the behavior of the Helium Loop Karlsruhe (HELOKA) facility and describes the mechanism used to control various loop parameters. An accurate control of the temperature during the warm-up and flat top phases is achieved solely by controlling the heater power. During testing campaign, when the helium flow has to be cooled, the power of the heater is set to zero and the temperature is controlled using a control valve installed in the by-pass of the heater. The adopted solution reduces the harmonic distortions when operating at reduced power while keeping the investment cost low.

Asymptotic Stability of a Stationary Solution to a Thermal Hydrodynamic Model for Semiconductors

The present paper concerns the existence and the asymptotic stability of a stationary solution to the initial boundary value problem for a one-dimensional heat-conductive hydrodynamic model for semiconductors. It is important to analyze thermal influence on the motion of electrons in semiconductor device to improve the reliability of devices by handling a hot carrier problem. We show the unique existence of the stationary solution satisfying a subsonic condition by using the Leray–Schauder and the Schauder fixed-point theorems. Then the asymptotic stability of the stationary solution is proved by deriving the a priori estimate uniformly in time. Here an energy form plays an essential role. We also prove that the solution converges to the stationary solution exponentially fast as time tends to infinity.

Thermal-hydrodynamic modeling of laboratory tests on the interaction of NaNO3-NaOH fluids with sandstone rock at a deep radionuclide repository site

Thermal-hydrodynamic modeling was used to reproduce laboratory tests involving sandstone samples collected from a deep radionuclide repository site at the Siberia Chemical Plant, Seversk (Russia). Laboratory tests included injection of alkaline fluids into sandstone samples at 70°C. Some minerals were forced in the model to precipitate or dissolve, according to laboratory test results. Modeling results were compared with observed test data (mineral phase changes, transient concentration data at the outlet of a sample column). Reasonable agreement was obtained between calculated and measured mineral phases (Na-smectite and kaolinite precipitation; quartz, microcline, chlorite, and muscovite dissolution). After the cation exchange option used in the model, the most abundant secondary mineral generated was dawsonite, which corresponds to sodium carbonates observed in the sample after the injection test. Time-dependent chemical concentrations (transient chemical concentration data) at the outlet of the sample column were qualitatively matched to the data observed.

안정성층류에서 선택취수의 수치해석

3차원 열동수역학 모형을 개발하여 지형학적으로 복잡한 자연 저수지에서 안정한 성층류의 선택 취수를 부정류 모의하였다. 지배방정식은 2차 정확도의 유한체적법을 이용하여 해석하였다. 개발된 수치모형을 3차원 난류, 성층화된 전단층흐름에 적용하여 검정을 하였다. 수치해석결과는 실험실에서 관측된 선택취수시의 속도 및 온도분포의 일반적인 형상을 양호하게 예측하는 것으로 나타났으나, 자연 저수지에서의 흐름에 대한 적용시에는 속도의 크기를 과대모의 하는 것으로 나타났다. 수치모의에서 구해진 선택취수의 물리적 특성을 논하였다. A three-dimensional thermal hydrodynamic model is developed for carrying out unsteady simulation of the selective withdrawal of the stably stratified flow in a geometrically complex, natural reservoir The governing equations are discretized on a non-staggered grid using a second-order accurate, finite-volume scheme. The numerical model is validated by applying it to simulate three-dimensional, turbulent, stratified, shear-layer flow case. The numerical predictions appear to capture reasonably well the general shape of velocity and temperature profiles observed in the laboratory experiments, while significant overestimation of the magnitude of velocity profiles is observed in the application to the flow in a natural reservoir. The physics of selective withdrawal as emerge from the numerical simulations are also discussed.