Interfacial Heat Transfer Coefficient Research Articles

Numerical Simulation of Lost-Foam Casting for Key Components of A356 Aluminum Alloy in New Energy Vehicles

The intricate geometry and thin walls of the motor housing in new energy vehicles render it susceptible to casting defects during conventional casting processes. However, the lost-foam casting process holds a unique advantage in eliminating casting defects and ensuring the strength and air-tightness of thin-walled castings. In this paper, the lost-foam casting process of thin-walled A356 alloy motor housing was simulated using ProCAST software (2016.0). The results indicate that the filling process is stable and exhibits characteristics of diffusive filling. Solidification occurs gradually from thin to thick. Defect positions are accurately predicted. Through analysis of the defect volume range, the optimal process parameter combination is determined to be a pouring temperature of 700 °C, an interfacial heat transfer coefficient of 50, and a sand thermal conductivity coefficient of 0.5. Microscopic analysis of the motor housing fabricated using the process optimized through numerical simulations reveals the absence of defects such as shrinkage at critical locations.

Estimation of Multiple Contact Conductances in a Silicon-Indium-Silicon Stack

Estimation of Multiple Contact Conductances in a Silicon-Indium-Silicon Stack

Testing and identification method for the interfacial heat transfer coefficient between CFRTP and tools under fast hot-stamping conditions

Carbon fiber reinforced thermoplastic composites (CFRTP) are increasingly applied in automobile structures. Hot-stamping is a fast forming process for complex components of CFRTP. During hot-stamping process, the variations of temperature field occur in entire forming process, which ultimately have an impact on the forming quality and dimensional precision of the part. The interfacial heat transfer behaviour between CFRTP and tools directly determines the temperature distribution in the part. However, the existing heat transfer testing and identification methods are designed for sheet metal, which may not be applicable for CFRTP due to the differences in material properties and forming processes. Therefore, in this work, a new test device was developed to reproduce the interfacial heat transfer behaviour of CFRTP under various hot-stamping conditions, and an inverse identification method of the interfacial heat transfer coefficient (IHTC) between CFRTP and tools was proposed. The influences of contact conditions on the IHTC were investigated, including the interfacial contact pressure, interfacial clearance, heating temperature of tools and sheets. The results showed that the IHTC demonstrated a positive correlation with the contact pressure. However, the IHTC would significantly decrease with the existence of a clearance at the interface. Within the entire heat transfer process, it was also found that an increase in tool temperature resulted in a decrease in the IHTC, while initial sheet temperature didn't exert a significant influence. Furthermore, the reliability of proposed testing and identification methods had been verified by the hot-stamping for U-shaped CFRTP parts. The temperature error between the simulation and experiment was less than 5 %.

Transport phenomena in pasta drying: a dough-air double domain advanced modeling

In the realm of pasta drying, where precise prediction of temperature and water-content distribution is crucial, the application of modeling and simulation emerges as highly significant. This study endeavors to evaluate operational conditions ensuring the production of a safe, high-quality pasta product. An advanced two-domain model was devised and solved to estimate transport phenomena in both the food and air domains. Unlike conventional models relying on specified interfacial heat and mass transfer coefficients, the proposed model serves as a versatile tool applicable across a broad spectrum of process and fluid-dynamic conditions in real pasta driers. The system of non-linear unsteady-state partial differential equations governing the behavior of a “Rigatone" pasta sample in a drier was solved using the finite elements method to estimate how air characteristics influence drying performance. A pilot-scale drying chamber was used for model validation for inlet air temperature Ta,in=80°C at relative humidity values (RHin) of 50 % and 60 %, with error consistently below 10 %.

Impact of Local Thermal Non-Equilibrium and Gravity Fluctuations on the Onset of a Darcy-Brinkman Porous Convection

The numerical investigation of the Darcy-Brinkman convective problem with gravity fluctuations in a Local Thermal Nonequilibrium (LTNE) model is conducted. Utilizing linear stability analysis, the convective problem is explored, and the numerical values of the Rayleigh and wave numbers for onset convection are computed through the one-term Galerkin approach. Three distinct types of gravity fluctuations (linear, parabolic, and exponential) are considered. The results show the Darcy number and gravity parameter delay the onset of convection. The porosity-scald conductivity ratio and interface heat transfer coefficient have a significant effect on the stability of the configuration. Graphical representations depict the effects of various parameters, highlighting the significant impacts of incorporating gravity fluctuations and non-equilibrium conditions in determining convection stability thresholds.

Metallurgical Method of Determining Heat Transfer Coefficient in Simulations of Twin-Roll Casting

We herein suggest a metallurgical method using pure aluminum with no freezing temperature range to derive appropriate roll/melt interfacial heat transfer coefficients in simulation of twin-roll casting process. This method is inspired by the concept that the position of the kiss points where two solidifying shells encounter and the roll nip coincides under the condition where the roll load becomes zero as the roll rotation speed decreases. The conditions where the roll load becomes zero under various melt supply temperature conditions in the actual TRC process are found experimentally. These conditions are then applied to simulation models to derive heat transfer coefficient values. When comparing these values with those derived previously from the empirical relation for roll rotation speed and heat transfer coefficient, the conclusion is drawn that the deviation was reasonably low, around 10%.

Determination of interfacial heat transfer coefficient at the frozen sand mold casting process of ZL101 alloy

Compared to the resin sand mold casting process, frozen casting is more environmentally friendly, providing a better working environment and enhanced supercooling degree. The interfacial heat transfer coefficient (IHTC) between frozen sand mold and metal is an important parameter that significantly influences the final mechanical properties and microstructure of the castings. This paper solved the inverse heat conduction problem using the finite difference method (FDM). In addition, the conjugate gradient method (CGM) was adopted to calculate the temperature distribution and heat flux in the molten metal. At the same time, the particle swarm optimization algorithm (PSO) was used in temperature distribution determination in frozen sand mold. The interfacial heat transfer coefficient (IHTC) was estimated during the solidification of ZL101. The results showed a good agreement between calculated and experimental data, obtaining accurate casting interface temperature Tm, frozen sand mold interface temperature Ts, heat flux q, and IHTC. The analysis of the IHTC variation revealed a water content value within the range of 4 wt.% to 5 wt.% resulted in IHTC in two types of interpretation, called ‘fluctuation type’ and ‘turning type’.

A transient method for the experimental evaluation of interface heat transfer coefficients at different contact pressures: The case of aluminum and copper interplay

In most of the thermal engineering applications, where heat is transferred by conduction between two different objects, the contact resistance or the contact heat transfer coefficient plays a major role. The conductivity of materials as well as the surface roughness strongly affect heat transfer in ways that makes challenging a proper estimation of the contact resistance. Despite the efforts, literature lacks in the definition of a simplified method for an immediate evaluation of the contact resistance. This work presents an experimental method to measure the interface heat transfer coefficient between two flat metallic surfaces. The method is based on a one-dimensional transient model relying on the time–temperature trends of two cylinders, initially at different temperatures, placed in contact. An uncertainty analysis is carried out to assess the reliability of the method proposed.Experimental tests have been conducted using aluminum-copper coupling, a common contact material solution in heat exchangers and battery packs. Results of the experimental campaign showed that the method is effective and that it allows to correlate the interface heat transfer coefficient to the contact pressure.

Interfacial heat transfer coefficient of aluminum alloy in contact solid solution treatment process

Interfacial heat transfer coefficient of aluminum alloy in contact solid solution treatment process

Investigation and Application of Inverse Determination of Interfacial Heat Transfer Coefficient in Vacuum Investment Casting

Investigation and Application of Inverse Determination of Interfacial Heat Transfer Coefficient in Vacuum Investment Casting

Analysis of interfacial heat transfer coefficients in squeeze casting of AA6061 aluminum alloy with H13 steel die: Impact of section thickness on thermal behavior

A step die made of H13 steel was utilized in this investigation cast aluminum alloy AA6061 at a pressure of 95 MPa in sections measuring 3 mm, 6 mm, 9 mm, 12 mm, and 15 mm in thickness. Surface temperatures during the squeeze casting process, as well as temperatures at distances of 3 mm, 6 mm, and 9 mm from the inner wall of the die, were recorded using K-type thermocouples. Utilizing the inverse method to solve 1-D heat conduction equations, we successfully determined the interfacial heat transferring coefficients (IHTC) and the interfacial heat flux (IHF) of the cast and die surface. The calculations revealed that with the commencement of squeeze casting, there was a significant rise in the IHTC for each of the five sectional steps. These IHTC reached their peak before they began to decline. The peak range of IHTC incrementally increased with the section thickness, from the 3 mm of Step 1 up to the 15 mm of Step 5. Moreover, the rate at which the IHTC reached its peak and then stabilized at a low level was slower for steps with greater thicknesses.

Numerical investigation on heat and mass transfer characteristics of inclined plate falling film absorption with nano-lithium bromide solution

Nanofluids play an essential role in enhancing heat and mass transfer in falling film absorption processes. To reveal the underlying mechanisms of enhanced absorption by nanoparticles at the gas–liquid interface, an innovative model considering the Marangoni effect is proposed for falling film absorption on an inclined plate. The effects of copper oxide nanoparticles on heat and mass transfer for the inclined plate falling film absorption, utilizing lithium bromide solution as the working fluid, are numerically studied using the software COMSOL Multiphysics. The accuracy of the numerical model is verified by experimental and simulation results, showing superior agreement when the Marangoni effect is incorporated. The vapor absorption performance of lithium bromide solution is significantly enhanced by the addition of nanoparticles. Surface tension amplifies temperature and concentration gradients, playing a pivotal role in augmenting heat and mass transfer through the Marangoni effect. The largest temperature and concentration gradients occur at the gas–liquid interface. The interfacial heat transfer coefficient and mass transfer coefficient decrease along the length of the inclined plate and gradually stabilize at 15.01 W·m−2·K−1 and 1.12 × 10−4 m·s−1, respectively.

The Well-Posed Identification of the Interface Heat Transfer Coefficient Using an Inverse Heat Conduction Model

The Well-Posed Identification of the Interface Heat Transfer Coefficient Using an Inverse Heat Conduction Model

The Influence of Interfacial Thermal Conductance on the Tensile Strength of a Sn-Mg Solder Alloy

Sn-Mg alloys are potential Pb-free solder options. However, their mechanical strength and interfacial characteristics with electronic substrates remain barely understood. This study focuses on the interfacial heat transfer aspects, microstructure, and tensile strength of a Sn-2.1wt.%Mg alloy. Samples with various thermal histories were produced using a directional solidification apparatus. In these experiments, a Sn-2.1wt.%Mg alloy was solidified on Cu and Ni substrates, which are of interest in the electronics industry. Mathematical modeling was then employed, allowing for the determination of the overall and interfacial heat transfer coefficients (hov, and hi, respectively). The results show that the Ni substrate exhibits higher interfacial thermal conductance with the Sn-2.1wt.%Mg alloy compared to the Cu substrate, as indicated by the higher hi profiles. This fact occurs mainly due to their metallurgical interaction, resulting in a stronger bond with the presence of Sn-Ni-rich intermetallics at the interface. Finally, experimental equations based on the Hall–Petch relationship are proposed to describe how the refinement of the fibrous spacing of the Mg2Sn interphase (λG) and an increase in hi enhance both yield and ultimate tensile strengths.

Experimental artefacts affecting characterization of the evolving interfacial heat transfer coefficient in hot stamping of Al-Si coated 22MnB5 steel

In automotive hot stamping, knowledge of the interfacial heat transfer coefficient (HTC) between the blank and die is crucial for predicting the mechanical properties of the formed part. The HTC is derived from the ratio of the instantaneous heat flux between the blank and the die, and the corresponding difference between the blank and die surface temperatures. In many cases the heat flux and die surface temperatures are inferred from time-resolved subsurface temperature measurements using an inverse heat conduction analysis, while the blank is often modelled as thermally-lumped. This study highlights how seemingly subtle aspects of this experiment, like the positioning and time-constant of the thermocouples, may impact the inferred HTC. Furthermore, nonuniformity of the interfacial pressure appears to lower the target pressure at which the HTC saturates, and diminish the time-averaged HTC with increasing target pressures.

Influence of calendering process on the structural mechanics and heat transfer characteristics of lithium-ion battery electrodes via DEM simulations

Elucidating the intricate correlation between calendering, structure, and performance is crucial to comprehending the relationship between performance parameters and process steps of lithium-ion batteries (LIBs). Discrete element method (DEM) simulations were adopted in this work to calculate the interparticle force and stress tensor under incremental calendering process conditions, which revealed the effect of the anisotropy of complex contact force network on the anisotropy of heat transfer within porous electrode. The thermal conductivity of electrode was predicted using porosity to characterize the process–structure–performance correlation. The comprehensive influence of contact number and contact area between particles and current collector determines the magnitude of interfacial thermal resistance and interfacial heat transfer coefficient. For the first time, this work quantitatively analyzed the structural mechanics and heat transfer mechanism during calendering process of porous electrodes, and the results indicate a promising way to optimize and design battery electrode structures.

Numerical study of flashing pipe flow using a TFM-PBM coupled method: Effect of interfacial heat transfer and bubble coalescence and breakup

In the present work, the two-fluid model (TFM) is coupled with the population balance model (PBM) to trace the spatial and temporal change of bubble size and interfacial area concentration (IAC) in flashing flows. The model is first validated for bubble growing in stagnant superheated liquid, and satisfactory predictions of the bubble size under low and moderate superheat are obtained. It is then applied to flashing pipe flows, which are characterized by low superheat and high turbulence intensities. The results show that in these cases, coalescence and breakup are important phenomena changing the bubble size distribution in addition to growth. The neglect of their contribution leads to a significant under-prediction of the bubble size and consequently over-prediction of IAC. In addition, choosing an appropriate closure for interfacial heat transfer coefficient (HTC) is another key point in flashing simulation. In high-Reynolds cases (e.g. Re > 106), the enhancement due to turbulence is non-negligible.

Cooling channel free surface optimisation for additively manufactured casting tools

In the present study, an algorithm has been developed using the adjoint method to optimise the position and cross-section of an internal cooling channel for a 3D printed tool steel insert for use in the aluminium die-casting process. The algorithm enables the development of an optimised complex industrial mould with relatively low computational cost. A transient model is validated against multiple experimental trials, providing an adapted interface heat transfer coefficient. A steady state thermal model, based on the casting cycle and thermal behaviour at the mould surface, is developed to evaluate the spatial distribution of temperature and to serve as the initial solution for the subsequent optimisation stage. The adjoint model is then applied to optimise the cooling channel emphasising the minimisation of the temperature standard deviation for the mould surface. The original transient model is applied to the optimised mould configuration via calibration using experimental data obtained from a dedicated aluminium furnace. The optimised cooling channel geometry, which uses a non-uniform cross-section across the entire pipe surface region, improves the pressure drop and cooling uniformity across the mould/cast interface by 24.2% and 31.6%, respectively. The model has been used to optimise cooling channels for a range of industrial high-pressure aluminium die-casting (HPADC) inserts. This has yielded a significant improvement in the mould operational lifetime, rising to almost 130,000 shots compared to 40,000 shots for prior designs.

Natural convection due to lateral uniform heat flux in a slender porous cavity saturated with nanofluid: Departure from LTE state

The present article deals with the influence of the local thermal nonequilibrium (LTNE) state on natural convection in an enclosure filled with nanofluid-saturated porous medium. The flow is induced due to the maintenance of constant heat flux on the vertical walls and insulation of horizontal walls. The Darcy model has been adopted to describe the flow governing equations. These equations are solved numerically by using the alternate direction implicit method and analytically by applying parallel flow assumptions valid for large aspect ratios. Boundary layer analysis is performed to report the boundary layer thickness as well as the heat transfer rate of nanofluid ( The combined effect of LTNE state parameters (interface heat transfer coefficient (H), porosity scaled thermal conductivity ratio (γ)) and volume fraction of nanoparticle () is addressed on the flow dynamics and heat transfer mechanism. Rigorous analysis, indicates that the average heat transfer rate of nanofluid and solid porous matrix are increasing function of H and γ, however, the role of γ is accelerated for a relatively high value of H. For increasing the value of γ from 1 to 10, the enhancement in the heat transfer rate of nanofluid is reported to be up to 27% at 10% volume fraction of nanoparticles. The average Nusselt number of nanofluid, as well as solid phase, are reduced when the value of is increased under the LTNE circumstances. Furthermore, the flow structure is controlled by unicellular structure with rotating anticlockwise direction in the entire study. For the very small value of H the temperature distribution in the solid porous matrix is mainly by conduction mode and distribution is linear, however, for a relatively high value of H the distribution in the same is controlled by both conduction as well as convection, and it will be more pronounced for the higher value of γ.

Thermal Conductivity Enhancement of Graphene/Epoxy Nanocomposites by Reducing Interfacial Thermal Resistance

The application of graphene/epoxy composites in microelectronic devices has been greatly limited by interfacial thermal resistance (ITR), which has been widely studied to improve the composites’ thermal conductivity. However, the effect of changing ITR on the thermal conductivity of nanocomposites at the nanoscale remains unclear. Here, several common methods are used to decrease graphene–epoxy ITR and graphene–graphene ITR, and the enhanced degree of nanocomposites’ thermal conductivity is investigated by molecular dynamics. First, the graphene concentration is proven to influence thermal conductivity slightly. Then, nanocomposites are simplified as three representative volume element models: the non-contacted model, the stacked model, and the intersected model. For the non-contacted model, the graphene–epoxy interfacial heat transfer coefficient is increased by 303% by functionalizing the graphene edge with amino groups, and the thermal conductivity is improved by 45.3%. For the stacked model, the graphene–graphene ITR is decreased by 220% when vacancy defects are constructed in the stacking region, and the thermal conductivity is improved by 130%. The intersected model’s heat transfer coefficient in the intersecting node is increased by 590% by connecting two graphene sheets by covalent interactions, and the thermal conductivity is improved by 590%. Finally, the stacked and intersected models are combined to construct the graphene/epoxy nanocomposites with a graphene network, and the thermal conductivity can be adjusted by changing the vacancy coverage rate.