Thermal Flow Model Research Articles

Convection Cooling of Power Electronics Operating in Deep-Space

Abstract Since most traditional spacecraft are designed to operate in a vacuum environment, forced convection cooling has seen limited use in space-applications. This paper considers an ideal candidate–the Dragonfly Lander, a rotorcraft being sent into Deep-space to conduct experiments on Saturn's largest moon, Titan. A forced convection based thermal management solution is presented for the Rotor Drive Electronics (RDE) unit, a high-power electronics box responsible for controlling the rotors that allow the Lander to fly on Titan. A thermal flow model was built in Solidworks Flow Simulation to evaluate the effectiveness of a fan system integrated into the packaging design and used as the primary method for cooling the RDE. The model was validated with temperature data collected from custom designed ground support equipment. It was found that utilizing forced convection allows temperatures of the electronics within the tightly packaged RDE to remain within operational limits when conductive and radiative heat transfer alone are insufficient. Titan's dense atmosphere results in greater mass flow rates through fans compared to on Earth, making forced convection a particularly efficient method of heat transfer. This research may guide the use of forced convection in future space missions, or non-traditional environments.

Numerical and experimental investigation on the heat transfer and mass transport in LPBF in-situ alloying of Al/Cu alloy

PurposeLaser powder bed fusion (LPBF) in-situ alloying is a recently developed technology that provides a facile approach to optimizing the microstructural and compositional characteristics of the components for high performance goals. However, the complex mass and heat transfer behavior of the molten pool results in an inhomogeneous composition distribution within the samples fabricated by LPBF in-situ alloying. The study aims to investigate the heat and mass transfer behavior of an in-situ alloyed molten pool by developing a three-dimensional transient thermal-flow model that couples the metallurgical behavior of the alloy, thereby revealing the formation mechanism of composition inhomogeneity.Design/methodology/approachA multispecies multiphase computational fluid dynamic model was developed with thermodynamic factors derived from the phase diagram of the selected alloy system. The characteristics of the Al/Cu powder bed in-situ alloying process were investigated as a benchmark. The metallurgical behaviors including powder melting, thermal-flow, element transfer and solidification were investigated.FindingsThe Peclet number indicates that the mass transfer in the molten pool is dominated by convection. The large variation in material properties and temperature results in the presence of partially melted Cu-powder and pre-solidified particles in the molten pool, which further hinder the convection mixing. The study of simulation and experiment indicates that optimizing the laser energy input is beneficial for element homogenization. The effective time and driving force of the convection stirring can be improved by increasing the volume energy density.Originality/valueThis study provides an in-depth understanding of the formation mechanism of composition inhomogeneity in alloy fabricated by LPBF in-situ alloying.

Partially transient one-dimensional thermal-flow model of a heat exchanger, upwind numerical solution method and experimental verification

Partially transient one-dimensional thermal-flow model of a heat exchanger, upwind numerical solution method and experimental verification

Risk-Averse scheduling of integrated electricity-heat systems considering multi-energy network operations for resilience enhancement against contingencies

The increasing penetration of renewable energy and the growing frequency and severity of extreme weather events pose a significant challenge to the secure and economic operation of local energy systems. This paper presents a risk-averse scheduling model of the integrated electricity and heat system (IEHS) for resilience enhancement against contingencies. A tri-level formulation is proposed to formulate the worst line outage events and identify the optimal resilience enhancement strategies. The main idea is to find the least-cost scheduling solution that meets the predefined resilience requirements. The model incorporates multi-energy network operations that integrate network reconfiguration in the PDN and mass flow rate control in the DHN. This approach provides more flexibility for load restoration in the face of uncertainties. A nonlinear thermal flow model is adopted to realistically capture thermal dynamics, and a tractable linear approximation is then proposed to balance accuracy and tractability. To solve this tri-level mixed integer program, an efficient solution method based on the nested column-and-constraint-generation algorithm is developed for the proposed IEHS scheduling model. Numerical studies indicate that the proposed model provides optimal solutions that are cost-effective to enhance the resilience of IEHS at minimum expense.

Peer-to-Peer Transactive Energy Trading of a Reconfigurable Multi-Energy Network

This paper proposes a bi-level peer-to-peer (P2P) multi-energy trading framework for a coupled distribution network (DN) and district heating network (DHN). At the lower level, each nodal agent represents its intra-nodal prosumers to optimize the local energy scheduling and P2P trading strategies based on the modified Nash bargaining theory, and a distributed algorithm is then adopted to enable individual agents to make their strategies autonomously only with the sharing of trading information. Once the lower-level P2P bargaining is settled, each agent is required to submit its nodal net loads and trading adjustment tolerances to the network operators. At the upper level, the network operators minimize the line power losses while satisfying network operation constraints by reconfiguring the DN and DHN as well as enforcing necessary trading adjustments from the lower-level agents when the network violations incurred by the P2P trading cannot be fully solved by network reconfiguration. Mathematically, the DN operation is modelled based on the linearized DistFlow with a set of new radiality constraints to sufficiently ensure the radial structure of the DN. The DHN operation is formulated as a quasi-linear thermal flow model independent of mass flow rate and water temperature, by which the computation complexity and limitations associated with traditional DHN formulations are addressed. Finally, a multi-energy network consisting of an IEEE 33-bus DN and a 23-node DHN is used to demonstrate the effectiveness of the proposed P2P trading framework and the efficiency of the solution algorithms.

VARIATION OF THERMAL CONDUCTIVITY AND HEAT ON MAGNETIC MAXWELL HYBRID NANOFLUID VISCOUS FLOW IN A POROUS SYSTEM WITH HIGHER-ORDER CHEMICAL REACT

More demanding applications of nanofluids are of tremendous interest in research and engineering. The implementation of nanotechnology in modern science has prompted researchers to examine nanofluid models from a variety of directions. The current study's major goal is to characterize the impacts of an incompressible, time-independent, viscous, two-dimensional, and laminar Maxwell hybrid nanofluid flow in a porous system under the effect of magnetic field, thermal conductivity, and heat sink/source over a stretching sheet. The hybrid nanofluid is created by immersing various silver and titanium dioxide nanoparticles in a water simple fluid. Additionally, the actions of Joule heating, Maxwell parameter, and higher-order chemical reaction are considered in this model. Within the shooting mechanism, the resulting nonlinear ordinary differential equations are numerically computed utilizing the RKF45 solver given in the computational MATLAB program. It is found that heat and mass transfer are diminished by increasing the magnetic field, Maxwell parameter, and permeability of porous media. Furthermore, an increase in the order of chemical reactions increases mass transfer. Increasing thermal conductivity and heat source/sink increases mass transfer but decreases heat transfer. The created thermal flow model's results have applications in cooling systems, thermal engineering, nuclear heating, heating/cooling of diverse appliances, safety in astronomical equipment, solar problems, magnetic retention, and so on.

On the Simulations of Thermal Liquid Foams Using Lattice Boltzmann Method

Liquid foams exist in a wide variety of chemical and industrial processes, and they can contaminate the end-product and cause time and economical losses. Understanding and simulating foam is not a straightforward task, due to the highly dispersed time and length scales where the physical phenomena occur. Surfactants’ or proteins’ length scales are far beyond the capability of macroscopic and even mesoscopic numerical fluid solvers, yet the macroscales are still required to be resolved. Meanwhile, the lattice Boltzmann method (LBM) has gained much attention and success as a mesoscopic approach which can deal with complex multiphase multicomponent systems. The aim of this study is to implement LBM to simulate liquid foams while considering the accompanying thermal effects. A coupled multiphase multicomponent thermal flow model and its selected add-ons from the literature are tuned and explained, limitations and future suggestions are fairly discussed. Validations and a final study case are shown as an example for the proposed model and its applicability in thermal liquid foams. Finally, a delicate treatment to back couple the effect of temperature on the surface tension is proposed, hence considering one aspect of the Marangoni effect. Initial results show promising behavior, which can be material for future investigations.

Research on Fault Diagnosis of Switchgear Based on Temperature Cloud Image Technology

In the process of power system operation, contact aging, partial discharge and overcurrent faults are the main causes of switch cabinet faults. At the same time, it is difficult to install sensors inside the switch cabinet due to its closed operation. In this paper, in order to solve the over current problem of switchgear, according to the principle of high current heating, the thermal flow model of power switchgear is established, and the characteristics of heat flow inside the switchgear are studied. The infrared temperature detector is designed to collect the surface temperature cloud map of the switchgear. Combined with the internal heat flow law of the switchgear, the over current phenomenon in the switchgear is judged, so as to judge the operation state of the switchgear. In order to verify the correctness of the theory proposed in this paper, the operation state of the fault switch cabinet is designed for detection and comparative analysis. The test results show that the heat change caused by the over-current fault can be accurately fed back to the surface of the switch cabinet, which can be used as an effective means to diagnose the fault of the switch cabinet.

Numerical Simulation of the Effects of Scanning Strategies on the Aluminum Evaporation of Titanium Alloy in the Electron Beam Cold Hearth Melting Process.

In the production of titanium alloy, the electron beam cold hearth melting (EBCHM) process is commonly used due to its effectiveness and the high quality of the end product. However, its main drawback is the significant loss of elements such as aluminum (Al) due to evaporation under the vacuum environment. Numerical coupled thermal-flow models were here developed to investigate the effects of scanning strategies on Al loss in a titanium alloy during EBCHM. The validation model was successful in comparison with previously published experimental data. The Al mass fraction results at the outlet of the water-cooled hearth were strongly influenced by changes in the applied scanning strategies. The results indicated that the Al mass fraction loss could be reduced by using the full-hearth scanning strategies.

Origin of photoelastic phenomena in Ge-Se network glasses

The elastic properties of a series of Ge-Se glasses are measured during irradiation with sub-band-gap light using a laser-induced transient grating method. The elastic modulus is found to decrease prominently with increasing irradiation intensity. The process is found to be less prominent in glasses of high average coordination $\ensuremath{\langle}r\ensuremath{\rangle}$. Measured kinetics in the millisecond range are found to be too slow for a photoinduced electronic process and instead suggest a thermal origin. Infrared thermography is performed during irradiation to monitor temperature changes during photodarkening, photoexpansion, and photoelastic measurements. It is found that in the conditions of irradiation where photoelasticity is observed, all photostructural changes are directly associated with a change in temperature. comsol modeling of thermal flow through the sample closely reproduces the kinetics of photodarkening. Transient grating measurements as a function of temperature confirm that the change in elasticity during irradiation is essentially a thermally induced process. Currently available experimental evidence indicates that the photoelastic phenomena are not an optoelectronic process but rather the result of laser heating.

Impact of Hall current and homogenous–heterogenous reactions on MHD flow of GO-MoS2/water (H2O)-ethylene glycol (C2H6O2) hybrid nanofluid past a vertical stretching surface

The need for efficient heating and cooling systems in the automotive, aerospace, and chemical industries is driving the growth of heat transfer technologies. The hybrid nanomaterials are preferred over traditional nanofluids due to their exceptional thermal effectiveness. Keeping in mind the need for efficient cooling and heating systems, the thermal flow model based on the hybrid nanoparticles (GO-MoS2) immersed in hybrid base liquid C 2 H 6 O 2 − H 2 O is presented in this novel attempt by considering the influence of homogeneous–heterogeneous (H–H) reactions and Hall current with a magnetohydrodynamic effect induced by a vertical stretching sheet. A simplified examination is examined in the existence of solar radiation, mixed convection, and viscous dissipation. Suitable transformations provide the system of ordinary differential equations. Later, the solution is tackled numerically for the flow problems using the Runge–Kutta–Fehlberg process with a shooting technique. The role of influential parameters on involved distributions is discussed graphically and is explained logically in view of physical significance. Results reveal that, the thermal profile declines near convectively heated surface and upsurges away from the surface for incline in mixed convection parameter. An upsurge in the Biot number inclines the rate of heat transfer, but a contrary trend can be seen for escalating values of volume fraction.

A higher order slip flow of generalized Micropolar nanofluid with applications of motile microorganisms, nonlinear thermal radiation and activation energy

This communication aims to develop the thermal flow model for generalized micropolar nanofluid with insensitive applications of bioconvection, activation energy and nonlinear thermal radiation. The generalized micropolar fluid model is the extension of traditional micropolar fluid model with viscoelastic relations. The viscous nature of non-Newtonian micropolar material can be successfully predicted with help of this model. The motivating idea for considering the motile microorganisms is to control the nanoparticles suspension effectively. The higher order slip relations are incorporated to examine the bio-convective phenomenon. The simplified coupled equations in terms of non-dimensional variables are numerically treated with shooting scheme. The reliable graphical outcomes are presented for flow parameters governed to the transported problem. The flow pattern of each parameter is highlighted in view of viscous nature of micropolar fluid.

Numerical investigation on the stability of tunnel smoke stratification under the effect of water spray and longitudinal ventilation

Tunnel smoke stratification has been reported to exist in the vicinity of a fire source, even under moderate ventilation conditions, which is of importance for occupant evacuation. To understand the effects of a water spray on its stability, a two-layer thermal flow model was built, and a series of scenarios considering different ventilation rates, water spray rates and smoke temperatures were numerically investigated. The ability of the Fire Dynamic Simulation (FDS) tool to predict such a two-phase problem was determined by validating against experimental and zone model data found in the literature. Then the tracer method was adopted to closely observe the smoke and droplet interactions in the two-layer model used in this paper. General effects of the ventilation flows and water spray on the maximum smoke logging distance and its corresponding horizontal displacement were observed. It was found that increasing the ventilation rate promotes the horizontal displacement but weakens the maximum downward distance, while increasing the water spray rate boosts the movements in both directions. Models based on nondimensional analysis for predicting the smoke displacements and the heat loss due to water spray were obtained. The observation of droplets indicates that a water spray globally blocks the horizontal smoke movement, and the upstream part of the water spray contributes 56.7% of the total downward drag forces. This work is helpful in revealing some of the underlying mechanisms behind the interactions of water spray and smoke stratification in the presence of longitudinal ventilation.

AN ALGORITHM OF AUTOMATIC HISTORY MATCHING OF A THERMAL FLOW MODEL OF HYDROCARBON SYSTEMS TO THE LABORATORY DATA OF THE OIL COMPOSITION OF WESTERN SIBERIAN FIELDS

Background. Increasing the calculations accuracy of oil PVT-properties (Pressure, Volume, Temperature) is actual at present, since the higher the accuracy and the wider the scope of the model, the fewer experiments should be carried out. Aims and Objectives. Carry out the study of the problem of oil separation into pseudocomponents and develop an algorithm of automatic history matching of a thermal flow model of bed hydrocarbon system to the experimental data specific for a number of Western Siberia oil fields that can be used in prospective simulators of oil PVT-properties. Results. The algorithm was tested on oil fields operated by PJSC «NK Rosneft» in the territory of Western Siberia, and it showed results acceptable for applied calculations. The developed algorithm, implemented as an Excel macro, makes it possible to significantly reduce the time for setting up a thermodynamic model for experimental data, and simplifies the work with them. To compare the results of the constructed thermodynamic model of reservoir oil, calculations were made on the Schlumberger simulator, which also showed a sufficient match for applied computations.

Effects of non-local electron transport in one-dimensional and two-dimensional simulations of shock-ignited inertial confinement fusion targets

In some regions of a laser driven inertial fusion target, the electron mean-free path can become comparable to or even longer than the electron temperature gradient scale-length. This can be particularly important in shock-ignited (SI) targets, where the laser-spike heated corona reaches temperatures of several keV. In this case, thermal conduction cannot be described by a simple local conductivity model and a Fick's law. Fluid codes usually employ flux-limited conduction models, which preserve causality, but lose important features of the thermal flow. A more accurate thermal flow modeling requires convolution-like non-local operators. In order to improve the simulation of SI targets, the non-local electron transport operator proposed by Schurtz-Nicolaï-Busquet [G. P. Schurtz et al., Phys. Plasmas 7, 4238 (2000)] has been implemented in the DUED fluid code. Both one-dimensional (1D) and two-dimensional (2D) simulations of SI targets have been performed. 1D simulations of the ablation phase highlight that while the shock profile and timing might be mocked up with a flux-limiter; the electron temperature profiles exhibit a relatively different behavior with no major effects on the final gain. The spike, instead, can only roughly be reproduced with a fixed flux-limiter value. 1D target gain is however unaffected, provided some minor tuning of laser pulses. 2D simulations show that the use of a non-local thermal conduction model does not affect the robustness to mispositioning of targets driven by quasi-uniform laser irradiation. 2D simulations performed with only two final polar intense spikes yield encouraging results and support further studies.

Measurement and modeling of thermal flow in an enclosed tube containing superfluid helium film

We describe measurements of the thermal conductivity of a vertical tube partially filled with superfluid liquid helium at saturated vapor pressure. The tube was heated from the top while the bottom was maintained at 0.3K. Thermal conduction through superfluid film creep and vapor reflux has been modeled in the literature and previously measured at T⩾0.9K. From our measurements we assess the validity of the model at the lower temperatures, where significant temperature gradients develop, and consider the effect of ancillary thermal conductances. The work is motivated by the cryogenic requirements for a proposed cryogenic measurement of the electric dipole moment of the neutron.

Geomechanical modeling for CO2 storage in Nisku aquifer in Wabamun Lake area in Canada

During CO2 injection, increasing pore pressure and temperature reduction create geomechanical deformation of both the reservoir and surrounding rocks. One of the most important concerns with respect to the long term CO2 storage is that stress changes caused by injection could lead to formation fracturing or reactivation of fracture networks and fault movements which could potentially provide pathways for CO2 leakage through previously impermeable rocks.Nisku geological formation located in Wabamun lake area was chosen as storage target based on storage capacity, expected ease of injectivity, low leakage risks and lack of interference with current petroleum production in the area. In order to determine whether the injection-induced stress changes affect the viability of this target formation to act as an effective storage unit, the geomechanical assessment model of the injection process has been developed, which couples the thermal flow model and geomechanical model covering all layers from the basement to the surface, and incorporates the modeling of dynamic injection-induced fracture. This work established the methodology for investigating the increase of well injectivity by allowing fracturing, and assessing the effect of the injection temperature.The pressure and stress variations were modeled during and after CO2 injection utilizing a coupled flow and geomechanical software. Since injected CO2's temperature may be considerably lower than the formation temperature, thermal effects were incorporated into the models. In order to increase the well injectivity, the case of allowing fracture initiation and propagation in Nisku was considered. The modeling shows that total minimum in situ stress is not constant and can be dramatically reduced by injection of cold CO2, thus leading to spontaneous fracturing. The cases of isothermal and thermal injection (without containment) show that operating above the fracture pressure in Nisku will increase the well injectivity (from 1Mt/year to at least 2Mt/year) but creates potentially long fractures and also the possibility of fracturing the caprock.Decreasing temperature due to CO2 injection will result in stress reduction and smaller surface deformations compared to the isothermal model. Thermal effects of cold CO2 injection will also reduce the fracture (injection) pressure and enhance the horizontal fracture propagation through Nisku. However, to make recommendations on a design that does not jeopardize isolation capacity of the containment requires site specific geomechanical and in situ stress data for all overlaying strata, in order to assess the risk of vertical propagation more accurately.This study predicts that CO2 injection in the Nisku zone is not likely to cause any significant surface heave and is not likely to have any environmental impact associated with surface deformations.In summary, the geomechanical factors put significant constraints on CO2 storage in Nisku in terms of injection pressures that may be limited by fracture propagation, injection rates that can be achieved without compromising the seal and excessive fracture propagation, and the CO2 placement affected by a fracture. The demonstration of the importance of thermal effects on CO2 storage is the most important contribution of this work.

Constructing dynamic model for thermal flow forecasting based on experimental data

We consider an identification algorithm for a dynamic object. The algorithm allows for choosing any rows from the block of the transformed empirical input-output data. Moreover, the algorithm enables passing to a parameter space and involving a priori information on the domain of parameter existence to improve accuracy. These features serve to construct a model of the dynamic object with a smaller forecasting error. The algorithm is applied for mathematical modeling of a fuel assembly in a nuclear reactor based on experimental heat transfer data.

Mathematical Modeling of Thermal Flow in CI Engine: A Review of the Recent Literature

Mathematical Modeling of Thermal Flow in CI Engine: A Review of the Recent Literature

Thermal Structural Effects in a Gas-Lubricated Foil Journal Bearing

A theoretical model for gas-lubricated foil journal bearings that incorporates thermal structural effects is presented. Bending and membrane effects in the top foil resulting from temperature are included along with thermal expansion of the journal, subfoil, and bearing housing. The model includes thermal transport through the journal, foils, and bearing housing. Pressure in the gas film is predicted using the Reynolds equation, and a thermal bulk flow model is used to predict temperature. The results demonstrate that models will overpredict film thickness along the side edge of a bearing if thermal strain in the top foil is not included. In addition, the results show the need for a three-dimensional thermal flow model at the trailing edge of a bearing when backflow occurs.