Thin Film Heat Transfer Research Articles

Magnetohydrodynamics Boundary Layer Flow of Hybrid Nanofluid in a Thin-Film Over an Unsteady Stretching Permeable Sheet

This analysis explored the computational process of heat transfer analysis in a thin-film MHD flow embedded in the hybrid nanoparticles, which combine the spherical copper and alumina dispersed in ethylene glycol as the conventional heat transfer Newtonian fluid model over a stretching sheet. The nonlinear ordinary differential equations (ODEs) was attained by transforming partial differential equation (PDEs) as governing equations when implementing the similarity transformations technique. The resulting nonlinear ODEs have been utilized by using the Keller box method. The natures of the thin-film flow and heat transfer through the various values of the pertinent parameters: unsteadiness, nanoparticle volume fraction, thin-film thickness, magnetic interaction and intensity suction/injection are deliberated. The approximate results for velocity and temperature distributions and physical quantities in terms of local skin friction and Nusselt number have been obtained and analyzed via graphs and tables. As a consequence, the suction expresses a more prodigious effect on the hybrid nanofluid rather than injection fluid for all the investigation parameters. It is worth acknowledging that the existence of the nanoparticles and MHD in the viscous hybrid nanofluid tends to enhance the temperature profile but decay the particle movement in the thin-film flow. It is perceived that the velocity and temperature profiles decline for the growth of the unsteadiness, thin-film thickness and suction/injection parameters.

Thermal energy transport in thin film flow of nanofluid over a decelerating rotating disk

The thin film flow in nanotechnology is one of the most modern progresses in the study of thin films. This includes coating with nanocomposite materials, thus providing the materials improved mechanical properties due to a so-called size effect. The ultimate functional properties that can be gained are of high adherence, wear resistance, thermal conductivity, oxidation resistance, higher toughness and hardness. This article studies the transient motion of nanofluid thin film over a disk rotating with angular velocity inversely proportional to the time. The importance of Lorentz force arises due to the axial projection of magnetic flux is studied on thin film flow and heat transfer. Two active mechanisms of nanoparticles, namely thermophoresis and Brownian diffusion, are discussed using Buongiorno model. By adopting a similarity method, the velocity distribution thermal and concentration fields above the rotating disk are simulated numerically and assessed graphically. Numerical illustrations for nanofluid film thickness, skin friction and heat and mass transfer rates are depicted against the impacts of several influential parameters. Results highlight that film thickness reduces with unsteadiness and rotation parameters. The results also spectacle that the involvement of a magnetic beam reduces the velocity of nanofluid film. Further, it is observed that thermophoresis and Brownian motion effects make a better influence in enhancing the heat transfer rate.

Molecular dynamics simulations of thin-film evaporation: The influence of interfacial thermal resistance on a graphene-coated heated silicon substrate

Two-phase liquid cooling on nanoengineered surfaces has shown great promise for tackling overheating in high performance microelectronics. At the nanoscale, phase change heat transfer can be affected substantially by the thermal resistance at the solid–liquid interface (also known as the Kapitza resistance). For example, surface modification by nanocoatings has been shown to efficiently enhance boiling heat transfer. However, there have been few studies on the effect of the Kapitza resistance on thin-film evaporative heat transfer. Here, the transport behavior of a liquid argon nanofilm evaporating on silicon (100) surfaces coated with different layers of graphene is analyzed using non-equilibrium molecular dynamics (MD) simulations. The results show that increasing layers of graphene coatings lead to a 136% increase in the Kapitza resistance and a 62% reduction in the evaporation rate. The large increase in Kapitza resistance is attributed to the strong repellence between graphene and argon molecules, manifested by a higher contact angle. These findings demonstrate the dominant role of interfacial thermal transport in the evaporation behavior of thin liquid films, and provide guidelines for selecting new materials when designing nanoengineered surfaces to realize improved evaporative cooling performance. • MD simulations of evaporation of liquid Ar on Si coated with graphene. • Influence of surface wettability on Kapitza resistance and evaporation. • Strong correlation between evaporative heat transfer and intermolecular interaction at solid–liquid interface.

Molecular Dynamics Simulation of Heat Transfer and Stresses in Thin Films Caused by a Short Laser Pulse

Molecular Dynamics Simulation of Heat Transfer and Stresses in Thin Films Caused by a Short Laser Pulse

Thermal diffusivity measurement of microscale slabs by rear-surface detection thermoreflectance technique

A new approach to measure the cross-plane thermal diffusivity of a microscale slab sample, which can be fabricated by the focused ion beam and attached to a substrate, is proposed. An intensity-modulated pump laser is applied to heat the front surface of the sample uniformly, and the thermoreflectance signal is observed at the rear surface to evaluate thermal wave transport in the material. The thermal diffusivity can be obtained by fitting the phase lags of the experimental data with a theoretical model. The model was developed for the sample with thin-film coatings and heat transfer to the substrate. Although the absorbed heat can cause a significant DC temperature increase in the microscale sample, a thin-film coating with high thermal conductivity can effectively reduce the DC temperature increase within low thermal conductivity samples. To validate the method, we conducted measurements of a fused silica sample of 2.16 µm thickness, coated with 95 nm Ti film on the front surface and 120 nm Au film on the rear surface. The measured thermal diffusivity is in good agreement with the literature value. The uncertainty analysis shows that the measurement uncertainty is within 6%. This proposed approach, designed for microscale samples, offers a unique option for thermal property measurements of special materials, such as irradiated nuclear fuel or other irradiated materials, to enable microscale property determination while minimizing sample radioactivity.

Analysis of unsteady magnetohydrodynamic radiative thin liquid film flow, heat and mass transfer over a stretching sheet with variable viscosity and thermal conductivity

The present article is related to the study of magnetohydrodynamic (MHD) heat and mass transfer in a thin liquid film over a permeable unsteady stretching surface in the presence of chemical reaction, applied magnetic field, viscous dissipation, and thermal radiation with variable viscosity and thermal conductivity. Computed results for unsteadiness parameter, temperature ratio parameter, radiation parameter in the presence/absence of the viscous dissipation and Ohmic heating are analyzed and discussed. The computed results reveal that the viscous and Ohmic dissipations reduce the temperature gradient profiles in the thin liquid film. Further, the thermal radiation decreases the cooling rate of the thin liquid film but the reverse effect is seen by increasing the Prandtl number.

Suction effect on an unsteady Casson hybrid nanofluid film past a stretching sheet with heat transfer analysis

This paper studies the heat transfer in the blood fluid-based copper and alumina nanoparticles over an unsteady permeable stretching sheet. The model is governed by the governing equations consist of a series of ODEs that are reduced from PDEs by implementing the similarity transformations subjected to mixed boundary conditions. The results of the transformed equations has been obtained by using the Keller-box method in MATLAB software. This paper focuses on the characteristics of thin-film flow and heat transfer through the governing parameters; unsteadiness parameter, nanoparticles volume fraction, Casson parameter, and intensity of suction. From this study, it is observed that the behavior of both fields for nanofluid is lower than hybrid nanofluid under the suction effect. It is noticed that enhance the physical parameters increase the velocity field of the fluid. Further, increase the physical parameter also deteriorate the temperature field except for nanoparticles volume fraction.

Simultaneous Condensation-Evaporation Heat Transfer on A Vertical Tube, II-Theoretical Study.(Dept.M)

In the present work, simultaneous condensation-evaporation heat transfer in thin films on a vertical tube is, experimentally, investigated. Condensation takes place on the outer surface of the vertical tube and the evaporation occurs inside it. The condensed steam outside the tested tube imparts its later heat to evaporate the thin liquid film, which flows inside the tube. Throughout this work, the range of Reynolds number for water film flow is from 50 to 800, while that of condensate outside the tube, takes values less than 100. The studied operating parameters, which affect the condensation-evaporation processes are water flow rate, its degree of subcool, the flow rate of the dry saturated heating steam and its pressure. The flow rate of the falling heated water is 3-50 kg/hr at constant pressure of 1.1 bar, while the heating steam flow rate is up to 5 kg/hr at a pressure which varies from 1.2 to 2 bar. The results show that, decreasing the Reynolds number of the falling water film, up to dry out a the end of the venical tube, causes an increase of heat transfer coefficient for different operating parameters. In addition, the Nusselt number for different values of Reynolds number are calculated and in accordance, an empirical correlation for the condensation - evap oration Nusselt number as a function of the studied operating parameters is proposed.

Simultaneous Condensation-Evaporation Heat Transfer on A Vertical Tube, I- Experimental Study.(Dept.M)

In the present work, simultaneous condensation-evaporation heat transfer in thin films on a vertical tube is, experimentally, investigated. Condensation takes place on the outer surface of the vertical tube and the evaporation occurs inside it. The condensed steam outside the tested tube imparts its later heat to evaporate the thin liquid film, which flows inside the tube. Throughout this work, the range of Reynolds number for water film flow is from 50 to 800, while that of condensate outside the tube, takes values less than 100. The studied operating parameters, which affect the condensation-evaporation processes are water flow rate, its degree of subcool, the flow rate of the dry saturated heating steam and its pressure. The flow rate of the falling heated water is 3-50 kg/hr at constant pressure of 1.1 bar, while the heating steam flow rate is up to 5 kg/hr at a pressure which varies from 1.2 to 2 bar. The results show that, decreasing the Reynolds number of the falling water film, up to dry out a the end of the vertical tube, causes an increase of heat transfer coefficient for different operating parameters. In addition, the Nusselt number for different values of Reynolds number are calculated and in accordance, an empirical correlation for the condensation - evaporation Nusselt number as a function of the studied operating parameters is proposed.

NUMERICAL SOLUTIONS FOR THE THIN FILM HYBRID NANOFLUID FLOW AND HEAT TRANSFER OVER AN UNSTEADY STRETCHING SHEET

This paper explores the mathematical model of thin-film flow and heat transfer utilizing hybrid nanofluid along with the two-dimensional time dependent stretching sheet. The influence of several parameters towards the model are discussed and solved by the method of collocation, namely bvp4c solver that can find in MATLAB software. In this paper, we focused on the effect of parameters are unsteadiness parameter λ, thermocapillarity number M, constant mass transfer parameter S, and concentration of towards the model. The numerical results have been obtained and shown in table and graph form. The effect of thermocapillarity number M and concentration of are explored and graphically portrayed through the velocity, temperature and concentration profile.

Improved two-temperature modeling of ultrafast thermal and optical phenomena in continuous and nanostructured metal films

In this work, a pump-probe experiment is used to study the ultrafast dynamics of heat transfer in thin gold films and gold nanostructures on glass substrates, following local heating by ultrashort laser pulses. Full spectrotemporal differential reflectivity and transmission maps were obtained for different film thicknesses (30, 50, 80, 150, and 200 nm) and different laser fluences $(0.38 \mathrm{to} 9.5\phantom{\rule{0.16em}{0ex}}{\mathrm{Jm}}^{\ensuremath{-}2})$. For arrays of gold nanorods, the two orthogonal probe polarizations were also acquired. We propose an improved model for these phenomena based on a modified two-temperature model that integrates thermal conduction and the three-dimensional finite element method model to link the spatiotemporal temperature maps to the spectrotemporal optical response maps. The impact of an underlying titanium adhesion layer is reported. Excellent agreement between numerical and experimental data for both the gold films and the nanostructures is shown.

Non-uniqueness solutions for the thin Carreau film flow and heat transfer over an unsteady stretching sheet

The present paper probed the problem of thin liquid film flow and heat transfer in the Carreau fluid past a permeable stretching sheet. The similarity transformation reduced the partial differential equations into a system of ordinary differential equations, which was then solved numerically by a collocation method. The influence of the governing parameters towards the model was discussed and presented graphically. The non-uniqueness solutions are observable as the governing parameters vary.

Triple Solutions of Carreau Thin Film Flow with Thermocapillarity and Injection on an Unsteady Stretching Sheet

Thin films and coatings which have a high demand in a variety of industries—such as manufacturing, optics, and photonics—need regular improvement to sustain industrial productivity. Thus, the present work examined the problem of the Carreau thin film flow and heat transfer with the influence of thermocapillarity over an unsteady stretching sheet, numerically. The sheet is permeable, and there is an injection effect at the surface of the stretching sheet. The similarity transformation reduced the partial differential equations into a system of ordinary differential equations which is then solved numerically by the MATLAB boundary value problem solver bvp4c. The more substantial effect of injection was found to be the reduction of the film thickness at the free surface and development of a better rate of convective heat transfer. However, the increment in the thermocapillarity number thickens the film, reduces the drag force, and weakens the rate of heat transfer past the stretching sheet. The triple solutions are identified when the governing parameters vary, but two of the solutions gave negative film thickness. Detecting solutions with the most negative film thickness is essential because it implies the interruption in the laminar flow over the stretching sheet, which then affects the thin film growing process.

Thin-Film Evaporation Heat Transfer of Liquid Nitrogen and Its Application in Cell Vitrification

Abstract Cell vitrification has been an important method of cell cryopreservation. The faster the cooling rate is, the higher the cell survival rate is. However, in conventional cell vitrification methods, film boiling forms a vapor-blanket on the surface, which hinders further improvement of the cooling rate. To eliminate the problem, this article attempted to replace film boiling with thin-film evaporation (TFE) of liquid nitrogen. The experimental system was developed to investigate the TFE heat transfer characteristics of liquid nitrogen. Then, prostate cancer cells were cryopreserved by TFE vitrification method, open pulled straw vitrification method, and equilibrium freezing method. The results showed that the vitrification method of TFE obtained a higher cooling rate and better cell survival rate than the two other cell cryopreservation methods. Thus, the feasibility of this method was preliminarily proved viable when applied to the cell vitrification process. In addition, both the cooling rate and the cell survival rate are affected by the concentration of the cryoprotectant in the cell suspension. The cooling rate decreases as the concentration of the cryoprotectant increases, but the cell survival rate increases first and decrease afterward with an increase in the cryoprotectant concentration, in which an optimum value exists. This study demonstrates the practicality of the new ultrafast cell vitrification method.

Numerical simulation of fractional non-Fourier heat transfer in thin metal films under short-pulse laser

In this paper, heat transfer is investigated in thin metal films subjected to a short-pulse laser. Due to the short temporal scales and high intensity of laser pulses during the heating process, the non-Fourier phenomenon can be observed in the temperature response of thin metal films. Therefore, the fractional non-Fourier model has been applied to investigate the heat transport in thin metal films to capture the thermal behaviors of nano-scale metal films. The fractional non-Fourier model is presented to investigate the heat transfer in single-layer gold film and gold‑chromium double-layer films under short-pulse laser. The governing fractional heat conduction equation is solved numerically using the finite difference method based on implicit scheme, and the obtained results are compared to the experimental data. The numerical results obtained from the fractional model represent its accuracy and suitability to predict the thermal behavior of the thin metal films irradiated by short-pulse laser. In addition, upon comparing the results of the fractional model with the results of other models which have been employed in this field, it can be seen that the fractional model has a higher capability than others to examine the non-Fourier effects during laser heating of thin metal films.

Numerical treatment of a physical problem in fluid film flow using the differential transformation method

The problem of thin liquid film flow over a heated horizontal stretching surface permitted by uniform transverse magnetic field in the presence of variable heat flux is studied numerically. The ordinary differential equations describing the physical problem are solved approximately by the differential transformation method (DTM). A study of the convergence analysis of the proposed method is given. The effects of the various parameters governing the thin film flow and heat transfer in this study are discussed and presented graphically. Our paper contributes to the existing literature by introducing the numerical treatment using the DTM for the nonlinear system of ordinary differential equations, which describe a thin film fluid flow affected by the variable heat flux.

The numerical solution for BVP of the liquid film flow over an unsteady stretching sheet with thermal radiation and magnetic field using the finite element method

The method introduced in this paper is based on the finite element method. As an application for this efficient numerical method, we employ it in solving the system of ordinary differential equations which describes the thin-film flow and heat transfer with the effect of thermal radiation, magnetic field and slip velocity. The effect of the parameters which govern the proposed problem is discussed. From this theoretical and numerical study, it is observed that the slip velocity parameter tends to decrease the fluid velocity, whereas both the magnetic parameter and the radiation parameter can enhance the temperature distribution.

Gas-driven thin liquid films: Effect of interfacial shear on the film waviness and convective heat transfer

This study is aimed at experimental investigation of hydrodynamics and convective heat transfer in gravity and gas-driven thin liquid wall films. The liquid film has been annularly applied on a vertically aligned heated tube mounted in a flow channel. In the arranged two-phase flow domain, both the liquid film flow and co-current air flow were thermally and hydrodynamically developing. The Reynolds numbers of liquid and gas flows have been varied between 80−800 and 104−105, respectively. The wall heat flux was kept constant at 15W/cm2. In order to elucidate the effect of the film waviness on the convective heat transfer between the heated wall and the liquid film, the wave frequencies and standard deviations of film thickness have been evaluated by applying high-speed shadowgraphy technique. The wall temperature distribution in streamwise direction has been measured. The experimentally obtained average Nusselt numbers have been compared with the wave frequencies and standard deviations of film thickness. Up to a gas Reynolds number of 4⋅104 and for liquid Reynolds numbers between 80 and 800, the convective heat transfer preliminary depends on the liquid Reynolds number rather than the Reynolds number of the gas flow. For this range, the average Nusselt numbers from the gas-driven film experiments are close to those for falling film flows. At the gas Reynolds numbers starting from 7⋅104, significant heat transfer enhancement with the gas flow has been registered over the full range of liquid Reynolds number.

Influence of Inclined Magnetic Field on Carreau Nanoliquid Thin Film Flow and Heat Transfer with Graphene Nanoparticles

The thermodynamics of a Carreau nanoliquid thin film embedded with graphene nanoparticles past a stretching sheet is studied in the presence of inclined magnetic field and non-uniform heat source/sink. Graphene is a new two-dimensional amphiphilic macromolecule which has great applications due to its electrical and mechanical properties. The basic constitutive equations of Carreau nanoliquid for velocity and temperature have been used. Similarity transformations are adopted to achieve the nonlinear coupled differential equations accompanying boundary conditions embedded with different parameters. HAM (Homotopy Analysis Method) is used to solve the transformed equations for expressions of velocity and temperature. Graphs are shown which illustrate the effects of various parameters of interest. There exists a nice agreement between the present and published results. The results are useful for the thermal conductivity and in the analysis and design of coating processes.

Thin film profile and interfacial temperature distribution of binary fluid sessile droplet evaporating on heated substrate

The interfacial profile and temperature distribution in the thin film region near the triple line is important for comprehensive modelling the transport process. For fluids with multi-components, typically binary fluids, the volatilities of the components are different from pure fluids and hence the interfacial characteristics needs to be properly modeled. In this work, a numerical analysis on the thin film profile, the interfacial temperature and the conjugate heat transfer characteristics in the thin film region of binary fluid sessile droplets of 5 wt% aqueous methanol and ethanol solutions evaporating on heated glass or copper substrates is given. The concentration of the components of binary fluid in the thin film region is assumed to be uniform for the low mass fraction of alcohol solution. The results show that the fluid property, substrate wettability and wall superheat have substantial effects on these parameters. The wall superheat has the greatest effect on the thin film heat transfer followed by the substrate wettability and fluid property. It also shows that surface tension gradients play a more important role in the formation of the Marangoni convection in the thin film region than the thermal-induced density differences and inertial motion. The effects of fluid properties and substrate wettability can be efficiently utilized for superior heat removal capacity in phase-change devices involving thin film heat transfer using binary fluids.