Study Of Transient Heat Transfer Research Articles

Transient heat transfer study of small-caliber barrel in continuous fire

In this paper, the barrel of small-caliber automatic rifle is taken as the research object. An experiment was taken on the gun barrel and an infrared thermal imager was used to measure the change of barrel temperature field during the continuous shooting, and the finite difference model of barrel heat transfer was established. The formula of the correction coefficient of heat transfer of gunpowder gas on the inner surface of the body tube was obtained by fitting with the experimental results. The barrel transient heat transfer analysis calculation software with independent intellectual property rights was developed by C++, and the characteristics of temperature field were analyzed. The experimental results show that the temperature of the outer surface of the barrel rises and then falls along the axial direction from the bottom of the barrel to the muzzle, and the rising slope will decrease in the next 30 rounds of continuous firing. The calculation results of the small-caliber barrel with chromium layer show that the temperature of the outer surface of the chromium layer of each shot rises instantaneously and then drops rapidly, in the form of pulse, and the temperature of the steel matrix rises continuously, but it is significantly lower than the peak temperature of the chromium layer, and the presence of the chromium layer provides buffer protection for the barrel matrix material. There is still an influence region in the matrix behind the interface between the chromium layer and the barrel matrix, and the temperature of the steel matrix in this region fluctuates. The thickness of the influence region is determined by analysis. The temperature of the inner surface of the barrel reaches a maximum at the tail of the barrel along the axial axis and then slowly decreases in the direction of the muzzle, the radial temperature distribution of the barrel is steeper at the tail end and the muzzle area is relatively flat. The calculation results of the model in this paper are basically consistent with the experimental results, which provides a rapid calculation model and tool for the thermal design and analysis of the gun barrel.

Transient heat transfer studies of aluminium graphene nanocomposite heat spreaders using digital interferometry

The thermal runaway caused by poor thermal management of batteries is one of the main challenges being faced by electric vehicles (EVs). An energy-saving, passive method for efficient thermal management of two and three wheeler battery packs is the use of aluminum (Al) heat spreaders with superior thermal conductivity, in conjunction with natural air cooling. Thermal conductivity of the (Al) heat spreaders can be enhanced by incorporation of graphene flakes. The present work focuses on extensive heat transfer studies of Al graphene nanocomposite (AGNC) heat spreaders with enhanced heat transfer capability. Few layered graphene (FLG) was synthesized by the liquid phase exfoliation method and characterized by X-Ray diffraction (XRD) analysis, Transmission electron microscopy (TEM), and Confocal Raman spectroscopy. AGNC heat spreaders were made by powder metallurgy. Mach-Zehnder interferometric (MZI) technique was employed to analyse the heat dissipation characteristics of AGNC heat spreaders, which infact is the novelty here. The slope of the local heat flux curve obtained by MZI was found to be less in the case of AGNC heat spreaders as compared to Al heat spreader indicating more uniform heat dissipation for AGNC heat spreaders. Transient heat transfer studies showed 63 % enhancement in the heat dissipation for AGNC heat spreader as compared to pure Al heat spreader. The transient temperature distribution was also visualized using Infrared (IR) thermography and the results show more uniform temperature distribution in the case of AGNC heat spreaders. The better phonon transport across the grain boundaries loaded with FLGs could be the reason for faster heat transport in AGNC heat spreaders.

Thermal performance of nano-enriched form-stable PCM implanted in a pin finned wall-less heat sink for thermal management application

Integrated and efficient circuitry has become a crucial part of modern technology which urged the necessity in development of efficient and robust Thermal Management (TM) system for its steady operation under higher heat dissipation. Thus the research work aims to analyse the heat transfer performance of a novel wall-less heat sink packed with highly stable synthesised Hexamethylene Diisocyanate cross-linked Polyethylene Glycol-6000 based Form-Stable Phase Change Material (FS-PCM) for its suitability in passive TM systems with chemical and thermal stability till 1000 thermal cycles. An inclusion of 1 wt% (Multi-Wall Carbon Nano Tubes /Graphene nano Platelets) in FS-PCM improved its thermal conductivity by 61.73% (0.448 W/m-K) and 84.48% (0.511 W/m-K) respectively. The characterisation was carried out for its micro and nano structural morphology, elemental composition, chemical composition and thermal properties like thermal degradation, phase transition attributes, specific heat and thermal conductivity via Field Emission Scanning Electron Microscope, Energy Dispersive X-ray Spectroscopy, Carbon Hydrogen Nitrogen analyser, Fourier Transform Infrared Spectroscopy, Thermogravimetric Analysis, Differential Scanning Calorimetry and KD2 pro analyser respectively. The transient heat transfer study of square pin finned heat sink was performed under a set of ON/OFF duty cycles for various heat rates with different aspects of FS-PCMs. In addition, the effect of nanoparticle reduced the thermal difference of FS-PCM in heat sink. Furthermore, involvement of FS-PCM in energy storage characteristics was improved reducing the heat sink base temperature to a maximum of 9.77%. Finally, the experimental results were numerically validated using COMSOL software establishing its reliability for real-time avionics TM application.

A Study of Transient Heat Transfer through a Moving Fin with Temperature Dependent Thermal Properties

In this article, heat transfer through a moving fin with convective and radiative heat dissipation is studied. The analytical solutions are generated using the two-dimensional Differential Transform Method (2D DTM) which is an analytical solution technique that can be applied to various types of differential equations. The accuracy of the analytical solution is validated by benchmarking it against the numerical solution obtained by applying the inbuilt numerical solver in MATLAB ($pdepe$). A good agreement is observed between the analytical and numerical solutions. The effects of thermo-physical parameters, such as the Peclet number, surface emissivity coefficient, power index of heat transfer coefficient, convective-conductive parameter, radiative-conductive parameter and non-dimensional ambient temperature on non-dimensional temperature is studied and explained. Since numerous parameters are studied, the results could be useful in industrial and engineering applications.

Analytical Study of Transient Heat Transfer in a Triangular Moving Porous Fin with Temperature Dependant Thermal Properties

The present work investigates heat enhancement through a moving porous fin of trangular profile. The interaction between the fluid and the porous media in not locally thermodynamic equilibrium. The transport through the porous medium is derived using Darcy’s model. The calculations are carried out using the two-dimensional Differential Transformation Method (2D DTM), which is an analytical solution technique that can be applied to various types of differential equations. The approximate analytical solutions are validated using the numerical solution obtained via the inbuilt numerical solver in MATLAB (pdepe). The results reveal that the 2D DTM can achieve accurate results in predicting the solution of such problems. The impact of the thermal parameters on temperature distribution is performed using the closed-form solution generated by DTM.

A fluid-structure coupling method to obtain parameter distributions in a combustion chamber with moving boundaries

A fluid-structure coupling method was put forward to obtain parameter distributions in a fluid field induced by the combustion of energetic materials. A one-dimensional two-fluid model was utilized to govern the transient combustion. The nonlinear mechanical behaviors were predicted basing on the engineering software ABAQUS. Different from most of the existed studies, we coupled the fluids and the structures through moving boundaries by using a user subroutine interface VUAMP in ABAQUS and realized the application of an irregularly distributed pressure by using a user subroutine interface VDLOAD. The coupling approach was validated by comparing the predicted results with analytical solutions and experiments. Based on the validated approach, parameter distributions in the combustion chamber of a large caliber gun were obtained and the influences of the irregularly distributed pressure were further discussed. The results indicated that the coupling approach is capable of obtaining parameter distributions of the fluid field in an expanding combustion chamber. The approach can be applied to provide accurate parameter distributions in determining boundary conditions for the study of transient heat transfer in the chambers.

Investigations on pool boiling critical heat flux, transient characteristics and bonding strength of heater wire with aqua based reduced graphene oxide nanofluids

In the present work, the pool boiling critical heat flux, transient heat transfer characteristics, and bonding strength of thin Ni-Cr wire with aqua based reduced graphene oxide (rGO) nanofluids are experimentally studied. Results indicate: (i) the critical heat flux (CHF) of 0.01, 0.05, 0.1, 0.2, and 0.3 g·L− 1 concentrations of rGO-water nanofluids varies from 1.42 to 2.40 MW·m− 2; (ii) the CHF remains same for the tested samples during transient heat transfer studies and (iii) a constant value of CHF upto 10 tests when the nanocoated Ni-Cr wire is tested with DI water and deterioration occurs beyond this which implies a chance of peel off of rGO layer below the critical coating thickness.

Transient Heat Transfer Study of Direct Contact Condensation of Steam in Spray Cooling Water

We conducted a transient experimental investigation of steam–water direct contact condensation in the absence of non-condensible gas in a laboratory-scale column with the inner diameter of 325 mm and the height of 1045 mm. We applied a new analysis method for the steam state equation to analyze the molar quantity change in steam over the course of the experiment and determined the transient steam variation. We also investigated the influence of flow rates and temperatures of cooling water on the efficiency of steam condensation. Our experimental results show that appropriate increasing of the cooling water flow rate can significantly accelerate the steam condensation. We achieved a rapid increase in the total volumetric heat transfer coefficient by increasing the flow rate of cooling water, which indicated a higher thermal convection between the steam and the cooling water with higher flow rates. We found that the temperature of cooling water did not play an important role on steam condensation. This method was confirmed to be effective for rapid recovering of steam.

Experimental and Computational Fluid Dynamics Analysis of Energy Storage in Packed Bed Direct Contact Heat Exchanger

This work presents a Computational and experimental study of transient heat transfer in fluid flow through porous media. The process of heat transfer and fluid flow through porous media is of interest to a wide range of applications of such as reactors, separators and dryers etc. Porous media used here is packed bed of spheres. The experimental arrangement comprises spheres of high carbon steel which are randomly packed in a 450 mm hollow tube of 45 mm inner diameter. The diameters of carbon steel spheres are 10 mm. The arrangement resulted in a porosity is 0.47. Hot air from a source was allowed to flow into the packed bed at various inlet conditions of velocity varying from 2.5 to 4 m/s and temperature ranging from 104°C to 39° C. The spheres were heated from initial temperatures of 30°C to near steady state conditions. ‘K’ type thermocouples were used to sense the temperatures. Three dimensional geometrical model of the storage system were modeled, meshed and simulated by using some commercial CFD software package. The thermal performance of storage system and also energy storage capacity were increased. The result of computational analysis was compared to the experimental analysis of validations.

Study of transient heat transfer at different proton beam energy in ADS windowless spallation target

Accelerator driven system (ADS) is a promising technique for reducing the amount of long-lived fission products in a safe manner. It consists of a subcritical core coupled with an accelerator by means of a spallation target arrangement. Thermal hydraulics of a spallation target is of great complexity due to the multiphase flow, the cavitation, and the coupling with the spallation reaction. In this paper, we firstly obtain the steady-state flow pattern of lead-bismuth eutectic (LBE) in the target, and then based on the flow pattern, the heat deposition with different proton beam energy is calculated via nuclear physics simulation. After that, the heat deposition is imported into CFD calculation to study the process of heat transfer. The transient temperature distributions with different proton beam energy are calculated. It is observed that the shape of temperature distribution varies with proton beam energy although the beam intensity is kept the same. The results also show that the temperature of recirculation zone is very effectively limited by adopting the annulus shaped proton beam. Above all, the temperature distribution depends on the heat deposition, the velocity and the flow pattern. The results are of great value and can be applied to the future design and optimization of the ADS windowless spallation target in China.

Study of transient heat transfer and synchronized flow visualizations during sub-cooled flow boiling in a small aspect ratio microchannel

The challenges that microchannel flow boiling technology faces are the lack of understanding of underlying mechanisms of heat transfer during various flow boiling regimes and a dearth of analytical models that can predict heat transfer. This paper aims to understand flow boiling heat transfer mechanisms by analyzing results obtained by synchronously captured high-speed flow visualizations with local, transient temperature data. Using Inverse Heat Conduction Problem (IHCP) solution methodology, the transient wetted surface heat flux and temperature as well as heat transfer coefficient are calculated. These are then correlated with the visual data. Experiments are performed on a single microchannel embedded with fast response temperature sensors located (630 µm) below the wetted surface. The height, width and length of the microchannel are 0.42 mm, 2.54 mm and 25.4 mm respectively. De-ionized, de-gassed water is used as the working fluid. Two heat fluxes are tested at each of the mass fluxes of 182 kg/(m2s) and 380 kg/(m2s). Because of vapor confinement, slug flow is observed for the tested conditions. The present study provides detailed insights into the effect of various events such as passage of vapor slug, 3-phase contact line, partial-dry-out and liquid slug on transient heat transfer coefficient. Transient heat transfer coefficient peaks when thin film evaporation mechanism is prevalent. The peak value is influenced by the distance of bubble incipience as well as downstream events obstructing the flow. Heat transfer coefficient during the passage of liquid slug and 3-phase contact line were relatively lower for the tested experimental conditions.

Experimental and numerical study of transient heat transfer for forced convection flow of helium gas over a twisted plate

Experimental and numerical study of transient heat transfer for forced convection flow of helium gas over a twisted plate

Flow distribution and heat transfer coefficients inside gas holes discharging into an orthogonal cross flow

Fluid flow and heat transfer coefficient associated with flow inside short holes (L/D=1) discharging orthogonally into a cross flow was investigated experimentally and numerically for Re¯ ranging from 0.5×105 to 2×105, and blowing ratio ranging from 1.3 to 3.2. The basic configuration studied consists of a feed tube with five orthogonally located gas holes. Four different hole configurations were studied. The transient heat transfer study employs an IR-camera to determine the local heat transfer coefficient inside each hole. Velocity measurements and numerical flow simulation were used to better understand the measured heat transfer distribution inside the hole. The Nusselt number distribution along the hole surface exhibits significant circumferential non-uniformity associated with impingement and separation, with localized high heat transfer regions caused by flow impingement. The Nusselt number was observed to be a strong function of the Reynolds number, but a weak function of the blowing ratio.

Local sensitivity analysis for the heat flux-temperature integral relationship in the half-space

This paper presents insight into the heat flux-temperature ( q″ − T) integral relationship based on constant thermophysical properties. This relationship is often used in one-dimensional, transient heat transfer studies involving null-point calorimetry and heat flux investigations. This study focuses on a short transient studies where energy has not fully penetrated the body as the result of an imposed surface heating condition. A full nonlinear heat transfer model is developed involving a half-space planar region. Temperature results are then introduced into the constant property integral relationship and a newly derived Kirchoff integral relationship for retrieving the local heat flux. Good agreement is observed between the fully nonlinear results and locally linearized system. Additionally, a sensitivity study is presented which involves perturbing the average thermophysical properties of thermal conductivity and heat capacity.

A Parallel Numerical Study of Transient Heat Transfer and Fluid Flow of Weld Pool during Laser Keyhole Welding

Numerical simulation provides a way to improve our understandings of the heat transfer and fluid flow behaviors of the weld pool during laser keyhole welding. However, current numerical studies are only limited to serial simulations which running on a single CPU. In this study, a parallel numerical study of the heat transfer and fluid flow of the weld pool is presented. A mathematical model considering the effect of Marangoni force, buoyancy force, friction force of the mushy zone region and the effect of keyhole is presented. A combined keyhole volume and surface heat source model is also developed. The coupled transient heat transfer and Navier-stokes equations are solved with a high order accuracy parallel projection method. The simulation code is parallelized with the OpenMP language. It is shown that 200% speedup can be achieved on a shared memory quad-core CPU using the presented parallel simulation system. The simulation results agree well with the in-situ high speed CCD video imaging experiments and the literature results.

RAPID SOLIDIFICATION STUDY OF STABILIZED ZIRCONIA UNDER PLASMA SPRAYING

This paper presents a numerical study of transient heat transfer and phase change of a thermal spray coating problem. The early solidification of yttria stabilized zirconia splat deposited on a cooled substrate is considered. These phenomena are quantified in terms of some working parameters such that: the splat thickness, the splat/substrate contact quality, the latent heat of solidification and the initial temperatures. A two-dimensional heat transfer model, extended phase change, is developed with an enthalpy formulation in order to predict the splat/substrate thermal story and its effects on plasma surface interaction. The results are in good agreement with an experimental one for the case of a nickel splatting on an alumina substrate.

Homogenization‐Based FEM Study of Transient Heat Transfer in Some Composite Materials

Effectiveness of the homogenization method for various heat transfer problems of engineering composites is the main aim of the paper. This comparative study is done for layered, fiber and particle reinforced Representative Volume Elements (RVE) for composites made of widely used components. Mathematical model is based on the effective modules method introduced for periodic composites ‐ effective heat conductivity is calculated in the closed form for specific spatial distribution of the components, while effective volumetric heat capacity is obtained from a simple spatial averaging. Such a homogenization scheme makes possible to significantly simplify the numerical analysis of transient heat transfer phenomena in various types of composites. The comparison of temperature histories obtained for the real and homogenized composite models is carried out using the Finite Element Method system ANSYS. As is demonstrated for various boundary problems, a homogenization technique in terms of composites types collected in the paper give satisfactory agreement with the real structure modeling; further numerical studies on composite cells discretization should increase modeling efficiency and diminish the numerical errors.

An Experimental Study of Transient Heat Transfer From Discrete Heat Sources in Water Cooled Vertical Rectangular Channel

Experiments are performed to study the single-phase transient forced convection heat transfer on an array of 4×1 flush-mounted discrete heat sources in a vertical rectangular channel during the pump-on transient operation. Water is the coolant media and the flow covers the wide range of laminar flow regime with Reynolds number, based on heat source length, from 800 to 2625. The applied uniform heat flux ranges from 1 to 7W∕cm2. For flush-mounted heaters the heat transfer characteristics are studied and correlations are presented for four chips as well as for overall data in the transient regime. The experimental results indicate that the heat transfer coefficient is affected strongly by the number of chips and the Reynolds number. Finally the general impacts of heat source protrusions (B=1, 2 mm) on heat transfer behavior of four chips are investigated by comparing the results obtained from flush-mounted (B=0) heaters.

Numerical study of transient heat transfer in semitransparent porous medium

Transient solutions were obtained for heat transfer through a semitransparent porous medium placed in a flow passage and submitted to incident radiation. The one-dimensional physical model takes into account, conduction, convection and radiation simultaneously. The porous medium is assumed to be homogenous continuum, which absorbs, emits and scatters thermal radiation. A fully implicit time-marching algorithm was used to solve the nonlinear coupled energy equations for gas and porous medium numerically. The present study utilizes the differential–discrete–ordinate (DDO) method to account for the radiation contribution. The effects of the Reynolds number, optical depth, anisotropic scattering, conduction–radiation parameter and scattering albedo on temperatures and fluxes profiles are investigated.

Heat Transfer during Transient Cooling of High Temperature Surface with an Inpinging Jet. Measurement of Wetting Velocity and Distribution of Wall Heat Flux and Wall Temperature.

An experimental study of transient heat transfer during cooling of a hot cylindrical block with an impinging water jet has been done at atmospheric pressure. The internal block temperatures and the radius of wetted region were measured for the following conditions : a fixed initial block temperature of 250°C, a degree of subcooling of 20-80 K, a jet velocity of 5=15 m/s, a fixed nozzle diameter of 2 mm and three block materials of copper, brass and carbon steel. Heat transfer on the surface consisted of single-phase convective heat transfer, annular nucleate boiling and film boiling. The radius of the wetting front, which bounds the nucleate boiling region and the dry region, was well correlated with a power function of time. The maximum heat flux along the radial direction occurred on the moving nucleate boiling region. It also compeared with the critical heat flux at steady state. In the case of a good heat conductor such as copper which is capable to supply enough large heat to the surface, the maximum heat flux was comparable with the CHF. Reversely that for a poor amount of conductor was significantly limited below the CHF.