Heat Transfer Boundary Conditions Research Articles

Experimental study on the influence of Peltier effect on the output performance of thermoelectric generator and deviation of maximum power point

Thermoelectric generator technology can convert heat into electricity based on Seebeck effect, but the Peltier effect cannot be neglected in the thermoelectric conversion process. In order to explore the influence of Peltier effect on the output performance of thermoelectric generator under the fixed heat transfer boundary conditions, an experimental system is set up. In the experiment, the hot side of the thermoelectric generator is heated by a thermostatic heater which can keep the heating temperature constant, and the cold side is cooled through the convective heat transfer with water. The effect of cooling water flow rate on the open-circuit voltage is first analyzed and the optimum cooling water flow rate is confirmed. Furthermore, the influence of Peltier effect on the cold side temperature and output performance of thermoelectric generator is investigated. The result shows that Peltier effect results in the less actual output power than the theoretical value and makes the maximum power point deviate from the point where the load resistance equals the internal resistance. Besides, as hot side temperature advances from 67 °C to 185 °C, the ratio of load resistance to internal resistance increases from 1.2 to 1.307 in the case of maximum output power.

Uncertainty Propagation Through a Simulation of Industrial High Pressure Die Casting

Abstract While numerical models are often used in industry to evaluate the transport phenomena in solidification processes, the uncertainty in the results propagated from uncertain input parameters is rarely considered. In this work, in order to investigate the effects of input uncertainty on the outputs of high pressure die casting (HPDC) simulations, the Center for Prediction of Reliability, Integrity, and Survivability of Microsystems (PRISM) uncertainty quantification (PUQ) framework was applied. Three uncertainty propagation trials investigate the impact of uncertainty in metal material properties, thermal boundary conditions, and a modeling parameter on outputs of interest, such as fraction liquid at different times in the process cycle and shrinkage porosity volume, in an industrial A380 aluminum alloy HPDC process. This quantification of the output uncertainty establishes the reliability of the simulation results and can inform process design choices, such as the determination of the part ejection time. The results are most sensitive to the uncertainty in the interfacial heat transfer (for both outputs of interest) and the feeding effectivity (FE) (a model parameter controlling porosity formation determination), while the other heat transfer boundary conditions, model parameters, and all the properties play a secondary role in output uncertainty.

Influence of gas fraction on wall-to-liquid heat transfer in dense bubbly flows

Bubbly flows are used in industrial processes to facilitate efficient mass and heat transfer for gas-liquid contact operations accompanied by chemical transformations, which are often associated with substantial heat liberation due to exothermic reactions. In this paper we study the heat transfer enhancement from a hot wall to bulk liquid, in the presence of bubbles. We use computational fluid dynamics, and specifically apply the local front reconstruction method as interface-tracking method. When a single bubble rises near a wall, the thermal boundary layer is sharpened enhancing heat transfer. This enhancement is initially located near the equator of the bubble, and then shifts to the wake of the bubble. Using stream wise periodic boundary conditions for flow and heat transfer, the wall-to-liquid heat transfer for developed flow conditions is quantified as function of gas fraction. The enhancement is strongly correlated with the relative bubble distance from the wall.

Analytical Thermal Modeling of Metal Additive Manufacturing by Heat Sink Solution.

Metal additive manufacturing can produce geometrically complex parts with effective cost. The high thermal gradients due to the repeatedly rapid heat and solidification cause defects in the produced parts, such as cracks, porosity, undesired residual stress, and part distortion. Different techniques were employed for temperature investigation. Experimental measurement and finite element method-based numerical models are limited by the restricted accessibility and expensive computational cost, respectively. The available physics-based analytical model has promising short computational efficiency without resorting to finite element method or any iteration-based simulations. However, the heat transfer boundary condition cannot be considered without the involvement of finite element method or iteration-based simulations, which significantly reduces the computational efficiency, and thus the usefulness of the developed model. This work presents an explicit and closed-form solution, namely heat sink solution, to consider the heat transfer boundary condition. The heat sink solution was developed from the moving point heat source solution based on heat transfer of convection and radiation. The part boundary is mathematically discretized into many heats sinks due to the non-uniform temperature distribution, which causes non-uniform heat loss. The temperature profiles, thermal gradients, and temperature-affected material properties are calculated and presented. Good agreements were observed upon validation against experimental molten pool measurements.

Analytical modeling of transient temperature in powder feed metal additive manufacturing during heating and cooling stages

This work presents a physics-based predictive model for transient temperature during heating state and cooling state in powder feed metal additive manufacturing (PFMAM). The deposition dimension, heat transfer boundary conditions, laser absorption, and latent heat are considered in the presented model. The temperature solution is constructed from the superposition of moving point heat source solution and heat sink solution based on a stationary coordinate with respect to the part boundary. The heat source solution is activated during heating state and deactivated during cooling state. The temperature profiles and molten pool evolution were predicted with respect to the processing time in single-track deposition of PFMAM of Inconel 718. Close-agreements were observed upon validation to the experimental results in the literature. The presented model has high computational efficiency without resorting to the mesh and iterative calculation. The high prediction accuracy and high computational efficiency allow the temperature prediction for large-scale parts, and process-parameter planning through inverse analysis.

Analytical modeling of 3D temperature distribution in selective laser melting of Ti-6Al-4V considering part boundary conditions

Selective laser melting (SLM) is widely used in metallic additive manufacturing to create geometrically complex parts, in which temperature distribution directly affects thermal stress and residual stress states of the build. Finite element models were developed by researchers to predict temperature distribution of the build part with a finite volume, but they were computationally expensive. Analytical models were developed based on a semi-infinite medium assumption because a closed-form solution has not been provided to apply the boundary conditions. In this work, an original physics-based analytical model is presented to predict 3D temperature distribution in SLM with consideration of heat transfer boundary conditions so that the effects of build edges and geometries can be considered in the context of a closed-form solution. Heat input from a laser heat source is calculated using point moving heat source solution. Heat loss at part boundaries due to heat conduction, convection, and radiation is calculated by modifying the heat source solution with equivalent power loss and using zero moving velocity. The temperature distribution is obtained based upon linear heat source solution and linear heat loss solution using the superposition principle. Ti-6Al-4 V is chosen to demonstrate the capability of the presented model. Molten pool dimensions are determined by comparing predicted temperatures to material melting temperature, and then validated with documented values in references. Close agreements were observed upon validation. The presented analytical model predicts the 3D temperature distribution in SLM with boundary conditions solved by a closed-form solution for the first time.

Application of mathematical modeling to optimize the operation of a tubular oil heating furnace

An energy balancing scheme has been developed for building a mathematical model of a tubular furnace for heating oil in accordance with the principle of its operation. This will allow taking into account all the heat fluxes, and the result of the work will be a reduction in fuel consumption for the tube furnace. The use of a particular calculation scheme depends on the nature of the task and the features of the boundary conditions of heat transfer. The main factors when choosing a calculation scheme are the accuracy and duration of the calculation. The scientific novelty is that for a tubular heating furnace for the first time it is proposed to use the method of energy balances in the chambers of radiation and convection. The practical significance of the work is to reduce fuel consumption for a tube furnace, as well as the possibility of utilizing the heat of oil refining products when building a mathematical model of a distillation column. The calculation algorithm using the energy balances method for mathematical modeling of heat transfer processes allows balance equations for all furnace sections, including the radiation chamber and the convection chamber. After which several successive approximations are carried out using linear programming. In addition, there are technological solutions to optimize fuel use.

A nanofluid MHD flow with heat and mass transfers over a sheet by nonlinear boundary conditions: Heat and mass transfers enhancement

In this paper, we have numerically examined the steady boundary layer of a viscous incompressible nanofluid and its heat and mass transfers above a horizontal flat sheet. The boundary conditions considered were a nonlinear magnetic field, a nonlinear velocity and convection. Such nonlinearity in hydrodynamic and heat transfer boundary conditions and also in the magnetic field has not been addressed with the great details in the literature. In this investigation, both the Brownian motion and thermophoretic diffusion have been considered. A similarity solution is achieved and the resulting ordinary differential equations (nonlinear) are worked numerically out. Upon validation, the following hydrodynamic and heat and mass transfers parameters were found: the reduced Sherwood and Nusselt numbers, the reduced skin friction coefficient, and the temperature and nanoparticle volume fraction profiles. All these parameters are found affected by the Lewis, Biot and Prandtl numbers, the stretching, thermophoretic diffusion, Brownian motion and magnetic parameters. The detailed trends observed in this paper are carefully analyzed to provide useful design suggestions.

Direct numerical simulation capability for strongly-coupled fluid-solid heat transfer in film-cooling structures

This paper applied the state-of-the-art flow simulation method, i.e. Direct Numerical Simulation (DNS), and strongly coupled the DNS with the heat-transfer governing equations to solve the flow and thermal problems in 3-dimensional (3D) film-cooling structures in the aero-engine. The strongly-coupled fluid-solid simulation was conducted to study the heat exchange on the wall surfaces and was compared to the case with the adiabatic heat-transfer boundary condition on the wall surface. The inlet condition was given as the uniform flow. The width of the delivery channel was used as the characteristic length. The Prandtl number was set at Pr = 0.71. The DNS was performed at lower Reynolds number of Re = 500 with the far-field condition being applied in the y and z directions. The dimensionless velocity, turbulence intensity, pressure, and temperature were analysed. The results suggested that the coolant flow was driven by the pressure in the delivery channel with strong vortical interactions and high turbulence shears. In the simulation with the strongly-coupled fluid-solid model, the solutions presented the interactions in the heat transfer near interfaces, the temperature wall boundary layer was observed and presented approximate linear profiles near the wall surfaces. The effects of the delivery channel were concentrated beyond the linear layers. The study discovered two important fluid-solid coupling parameters and pointed out the necessity of applying the strongly-coupled fluid-solid heat-transfer model in the thermal simulation.

Application of the Darcy-Stefan model to investigate the thawing subsidence around the wellbore in the permafrost region

A key challenge in Exploring oil and gas resources in permafrost regions is to predict the thawing subsidence of frozen soil around the wellbore. At present, the traditional thermo-hydro-mechanic (THM) model calculates thawing subsidence without actually considering the spatial-temporal evolution of the thawed-frozen boundary. The Darcy-Stefan model is used to describe the internal mobile interface problems in the heat transfer of saturated porous media due to ice/water phase transitions. In this paper, we established the coupling model of the Darcy-Stefan model and the elastic theory of porous media, including boundary conditions of heat transfer and Darcy flow on the moving boundary. The new model was validated through a series of small-scale examples and a test well in the Arctic region, which demonstrated the predicted subsidence amount of ground surface around the wellhead was in good agreement with the field test data. Further research indicated that with the increase of the thawing zone, the accuracy of calculation for the thawing subsidence could be significantly improved by using the THM model and considering the internal moving boundary. The models and conclusions in this paper can help design more reliable wellbore in permafrost regions throughout the expected life.

Unsteady MHD chemically reactive double‐diffusive Casson fluid past a flat plate in porous medium with heat and mass transfer

AbstractIn this paper, an attempt has been made to analyze the effects of various parameters, such as Soret and Dufour effects, chemical reaction, magnetic field, porosity on the fluid flow, and heat and mass transfer of an unsteady Casson fluid flow past a flat plate. Convective boundary conditions in heat and mass transfer and slip constant on velocity have been taken into account for analysis. The governing equations of the model have been solved numerically using the MATLAB program bvp4c. The impact of various parameters of the model on the velocity, temperature, and concentration profiles has been analyzed through different graphs. To get an insight into the physical quantities of engineering interest, viz, skin friction, Sherwood number, and Nusselt number, their numerical values have been computed for various parameters. The range of the parameters used in numerical computations are , , , , , , and . It has been noticed from the tabulated values that the skin friction gets enhanced with the increase in the thermal and solutal Grashof number, whereas its reverse effects have been observed with an increase in the Biot number. In limiting case, the present study is also compared with the available results in the literature.

Mechanical and thermal buckling loads of rectangular FG plates by using higher-order unified formulation

In this paper, by using the Carrera unified formulation, a higher-order plate theory, in the framework of FEM, the mechanical and thermal buckling loads of functionally graded (FG) plates have been formulated by linearized buckling analysis. The effects of convective heat transfer with the neighboring environments have been taken into account in the thermal buckling formulations. The buckling instability of several FG plates under mechanical loads as well as uniform, linear, and nonlinear thermal loads have been investigated. The obtained results indicate that the order of the plate theory and convective heat transfer boundary conditions significantly affects critical buckling loads.

Heat and mass transfer in a hollow fiber membrane contactor for sweeping gas membrane distillation

In practical sweeping gas membrane distillation (SGMD) with hollow fiber membrane tube banks (HFMTB), the tubes are often populated in a randomly distributed configuration. The brine and the sweeping gas countercurrently flow inside and between the tubes, whereby heat and moisture exchange. Water vapor transferred through the membranes from the hot brine side to the cold gas side is taken out of the HFMTB by the sweeping gas. Conjugate heat and mass transfer in the tube bank is investigated. Three square modules consisting of 20 fibers, the brine stream inside the fibers, and the sweeping gas stream between the fibers with various randomly populated features are selected as the computational domains. The equations governing the momentum and heat mass transports in the tube side, membrane side, and shell side are established and solved based on the conjugate heat and mass transfer boundary conditions. The friction factors, local and mean Nusselt and Sherwood numbers in the modules are obtained and validated. Effects of the tube distributions, packing fractions, and moisture diffusivities in membranes on heat and mass transfer are studied. The HFMTB is recommended to be the regularly distributed one. The automatic processing of the regularly distributed HFMTB should be realized in future.

Stagnation-point flow and heat transfer of upper-convected Oldroyd-B MHD nanofluid with Cattaneo–Christov double-diffusion model

Purpose The purpose of this paper is to investigate the two-dimensional stagnation-point flow, heat and mass transfer of an incompressible upper-convected Oldroyd-B MHD nanofluid over a stretching surface with convective heat transfer boundary condition in the presence of thermal radiation, Brownian motion, thermophoresis and chemical reaction. The process of heat and mass transfer based on Cattaneo–Christov double-diffusion model is studied, which can characterize the features of thermal and concentration relaxations factors. Design/methodology/approach The governing equations are developed and similarly transformed into a set of ordinary differential equations, which are solved by a newly approximate analytical method combining the double-parameter transformation expansion method with the base function method (DPTEM-BF). Findings An interesting phenomenon can be found that all the velocity profiles first enhance up to a maximal value and then gradually drop to the value of the stagnation parameter, which indicates the viscoelastic memory characteristic of Oldroyd-B fluid. Moreover, it is revealed that the thickness of the thermal and mass boundary layer is increasing with larger values of thermal and concentration relaxation parameters, which indicates that Cattaneo–Christov double-diffusion model restricts the heat and mass transfer comparing with classical Fourier’s law and Fick’s law. Originality/value This paper focuses on stagnation-point flow, heat and mass transfer combining the constitutive relation of upper-convected Oldroyd-B fluid and Cattaneo–Christov double diffusion model.

Effects of thermal radiation and magnetohydrodynamics on Ree-Eyring fluid flows through porous medium with slip boundary conditions

PurposeThe purpose of this paper is to investigate the three fundamental flows (namely, both the plates moving in opposite directions, the lower plate is moving and other is at rest, and both the plates moving in the direction of flow) of the Ree-Eyring fluid between infinitely parallel plates with the effects of magnetic field, porous medium, heat transfer, radiation and slip boundary conditions. Moreover, the intention of the study is to examine the effect of different physical parameters on the fluid flow.Design/methodology/approachThe mathematical modeling is performed on the basis of law of conservation of mass, momentum and energy equation. The modeling of the present problem is considered in Cartesian coordinate system. The governing equations are non-dimensionalized using appropriate dimensionless quantities in all the mentioned cases. The closed-form solutions are presented for the velocity and temperature profiles.FindingsThe graphical results are presented for the velocity and temperature distributions with the pertinent parameters of interest. It is observed from the present results that the velocity is a decreasing function of Hartmann number. Temperature increases with the increase of Ree-Eyring fluid parameter, radiation parameter and temperature slip parameter.Originality/valueFirst time in the literature, the authors obtained closed-form solutions for the fundamental flows of Ree-Erying fluid between infinitely parallel plates with the effects of magnetic field, porous medium, heat transfer, radiation and slip boundary conditions. Moreover, the results of this paper are new and original.

A parametric study for optimization of minichannel based battery thermal management system

Minichannel technology has been shown to be a promising solution for the battery thermal management system (BTMS). Since the design space of the BTMS using minichannel technology consists a large number of parameters, performing parametric study and optimization of such a system is challenging. To overcome this challenge, a simplified numerical model is developed. In this model, effective convective heat transfer (heff) boundary condition is used at the cell-minichannel interface to circumvent simulating conjugate heat transfer and fluid flow in the minichannel. After validation with past work based on a three-dimensional conjugate heat transfer model, the simplified model is used to conduct a parametric study to determine the effect of various design and operation parameters on the performance of the BTMS. For the proposed BTMS, it is found that cooling half of the cell surface on single side of the cell is enough to keep the maximum temperature difference in the pack to be less than 3 °C at 2C discharge rate. At module level, it has been found that minichannel cooling on only one side of the cell or on every other cell can significantly increase the system level energy density. The results from the parametric study would be useful in designing a robust, effective, and economical minichannel-based BTMS for Electrical Vehicles.

A general approach of unit conversion system in lattice Boltzmann method and applications for convective heat transfer in tube banks

A general unit conversion system based on the analogy with the Planck unit system is put forward in this article for most physical quantities in lattice Boltzmann simulations. Comparing with the traditional unit conversion methods, the approach has more systematic, programmatic and standardized operating process and can be applied in programming easily. In addition, a two-dimension exemplary simulation of convective heat transfer in tube banks is implemented to illustrate the feasibility and advantage of the approach, with verification of coupled flow and heat transfer by the empirical formula in literature. Furthermore, a uniform scheme for three kinds of boundary conditions for heat and mass transfer is developed and applied herein.

Fundamental heat and mass transfer analysis in a quasi-counter flow parallel-plate three-fluid membrane contactor

A quasi-counter flow parallel-plate three-fluid membrane contactor with cooling tubes installed in the solution channels (QCPMCC) is used for air/solution/water exchange. The air and the solution streams are separated by the selectively permeable membranes. Absorption heat generated in the solution can be taken away by the water flow in the cooling tubes. A three-dimensional mathematical model describing the heat and mass transports in the membrane contactor is built based on an element including a piece of the plate membrane, half of the air channel, half of the neighboring solution channel, and half of the row of the tubes. The momentum, energy and mass conservation equations are simultaneously solved. The mean product of friction factor and Reynolds number (fRe)m, Nusselt number and Sherwood number under the conjugate heat and mass transfer boundary conditions are then obtained. Effects of the tube numbers, tube outer diameters, Reynolds numbers, and various tube shapes on the basic data are analyzed. It can be found that both the tube numbers and the tube outer diameters have small influences on the mean Nusselt numbers and Sherwood numbers for the air stream, while they have large effects on those for the solution stream.

Numerical study of MHD effective Prandtl number boundary layer flow of γ Al2O3 nanofluids past a melting surface

This research article numerically studies the influences of an effective Prandtl number along with magnetic field on the melting heat transport characteristics of Ethylene glycol/Water with gamma Al2O3 nanoparticles over a stretching sheet. To analyse the impacts of effective Prandtl number, the non-dimensional melting heat transfer boundary conditions are derived for the first time with and without effective Prandtl number. A non-linear form of thermal radiation is used. The experimental based thermo-physical properties of gamma Al2O3 nanofluids are considered. The electric conductivities of Al2O3, water and ethylene glycol are used to calculate of effective electric conductivity to study the magnetic field effects. Mathematical models are developed and solved by numerical technique based on the Iterative Power Series (IPS) method with shooting strategy. The numerical outcomes are discussed through plots and tables.

A Coupled Rigid-viscoplastic Numerical Modeling for Evaluating Effects of Shoulder Geometry on Friction Stir-welded Aluminum Alloys

Shoulder geometry of tool plays an important role in friction-stir welding because it controls thermal interactions and heat generation. This work is proposed and developed a coupled rigid-viscoplastic numerical modeling based on computational fluid dynamics and finite element calculations aiming to understand these interactions. Model solves mass conservation, momentum, and energy equations in three dimensions, using appropriate boundary conditions, considering mass flow as a non-Newtonian, incompressible, viscoplastic material. Boundary conditions of heat transfer and material flow were determined using a sticking/sliding contact condition at tool / workpiece interface. Thermal history, as well as shear stress and rotational speed fields, forces and torque values for three shoulder geometry conditions were calculated. Numerical results of thermal history, torque and forces during welding showed good correlation with experimentally measured data.