Contact Heat Transfer Coefficient Research Articles

Comparing global sensitivity analysis methods for the joint thermal design parameters of a space manipulator based on the Sobol’ and PAWN

The Global Sensitivity Analysis method works well for screening and ranking impacting factors. It can help with thermal design optimization and thermal model calibration. This study compares the use of Sobol's variance-based method with PAWN's density-based method for 12 thermal design parameters (such as the properties of thermal control coating and the contact heat transfer coefficient between components) of a space manipulator joint thermal model. The two techniques have high consistent parameter sensitivity. The analysis's findings indicate that the junction electric box and shell's temperature variations are significantly influenced by the cooling surface's coating properties. The cooling surface's absorption rate has a bigger impact than emissivity does. Only the characteristics of the multilayer mask and the state of parcel coverage have a significant impact on the temperature of the joint shell. The outcomes offer technical backing for cooperative optimization in thermal design. The identical no-effect parameters are discovered to be recognized by Sobol' and PAWN at the same time, but they are ordered in different ways. The limitation of Sobol's technique, which uses variance as a sensitivity index, may be the cause of this outcome. Finally, the sensitivity response results are re-substituted into the finite element thermal model. The changing rule of temperature curve is used to further confirm the accuracy of the sensitivity results.

Contact heat transfer analysis in flighted rotary drums

Flights are used to improve the mixing of the material and the heat and mass transfer within rotary drums. They lift particles out of the bulk bed and throw them as curtains into the passing gas phase of the drum. This also affects the contact area and contact heat transfer between the rotating drum and the particles. In this study, the contact heat transfer is experimentally investigated in an indirectly heated rotary drum with flights. To determine the heat transfer coefficient, the drum is heated to 350 °C in batch mode with both ends of the rotary drum insulated to avoid axial gas flow. During heating, the temperature profiles of the gas, the particles and the flight and drum walls are measured. Based on the energy balances of the particles, the contact heat transfer coefficient is determined. Glass beads with particle diameters of 0.7 to 4 mm, expanded clay and steel beads (4 mm each) are used as test materials. Operational (rotational speed, filling degree) and flight design parameters (number of flights, flight length ratio) are varied. Models for calculating the contact heat transfer coefficient in flighted rotary drums cannot be found in the literature. In order to show the effect of installations, the measured values are compared with an existing contact heat transfer model for unflighted rotary kilns. This shows good qualitative agreement for most of the parameters investigated. However, most measured values exceed the model values, which indicates a positive effect of flights on the contact heat transfer.

Investigation of thermal mode of hot-rolling mill working rolls in order to improve the accuracy of calculating the thermal profile of their barrels’ surface

Thermal mode of the working roll barrel in a hot-rolling mill is a significant technological factor that affects the steel strip quality, its cross section, and durability of working rolls. A reliable calculation of the temperature mode parameters makes it possible to determine the thermal profile shape and the best profiling of the roll barrel surface, as well as to reduce defects in steel strip flatness. The most common is the balance model of roll thermal mode. Its accuracy is largely determined by thermophysical constants, in particular, the heat transfer coefficients of the rolls: contact – with the strip and convective – with cooling water. There are various data on the values ​​and methods for calculating these coefficients, but most of them do not take into account the presence of pauses in rolling rhythm of the finishing group of stands, the duration of which is significant. Failure to take this factor into account entails significant errors in calculations of the thermal mode. A passive experiment was carried out, during which surface temperatures of the working rolls’ barrels were measured using a thermocouple at several points along their length immediately after they fell out. Also, the parameters of steel strip rolling before roll change were determined: rolling rhythm coefficients, strip reduction in stands, water consumption for cooling rolls and some others. As a result, an empirical equation was obtained for calculating the contact heat transfer coefficient, taking into account the main technological factors. The use of refined coefficients for calculating the temperatures of the roll barrel significantly increased the accuracy of predicting the thermal mode, in particular, the thermal profile of the working roll, based on values ​​of the rolling parameters.

Interface heat transfer for hydronic heating: heating tests of concrete blocks and numerical simulations

ABSTRACT A comprehensive understanding of the heat transfer mechanism of hydronically-heated structures is crucial to predicting their heating performance. However, few studies considered the heat transfer at the interface of heating pipe and host material. In this paper, heat transfer at two critical interfaces for hydronically-heated concrete structures, e.g. pipe-concrete interface and concrete-air interface, has been tested and analyzed. Two concrete blocks, one with an embedded cross-linked polyethylene (PEX) pipe and one with an attached PEX pipe, were fabricated to represent heated bridge decks for the heat transfer study. The two blocks were tested inside a freezer box in a series of heating response tests at varied room and fluid temperatures. Measured temperatures at different depths were used to find the convection heat transfer coefficient and the thermal contact conductance between the concrete and PEX pipe through equations developed via finite difference method (FDM). Finite element models (FEM) of the two blocks were developed to verify the thermal contact values derived from a 1-D thermal resistance model. A comprehensive analysis of the temperature response of the models was performed, especially at the two interfaces, and the FEM models were able to predict the lab measurements accurately. The obtained contact heat transfer coefficient and the FEM models can be used for all hydronically-heated structures.

Coil-shaped rotating spiral gas-solid reactor – design procedure for catalytic reaction

A novel coil-shaped rotating spiral gas-solid contacting device was proposed. The spiral can be made by welding “long-elbows”, which are available as parts of boiler tubes. In the bottom of the spiral, particles form bed, through which whole gas flows without gas bypassing. The bed is transported with the rotation of the spiral. The authors have made transparent cold models and heat-resistant metal models, carried out experimental works, and revealed the properties of this type of reactor for transportation rate of solids, residence time distribution of solids, pressure drop when gas was fed, the maximum limit of gas feed rate to maintain stable bed, gas-solid contact efficiency, heat transfer between wall and solids, and influence of reactor size on above-mentioned properties. This work reveals the influence of scale-up on the maximum limit of gas flow rate at which stable bed is maintained. Gas-solid contact efficiency and heat transfer coefficient were also evaluated using models larger than that used in previous studies. By summarizing the past findings and the present results, a procedure to design a gas-solid catalytic reactor, i.e., determination of tube diameter, rotating rate, number of spiral cycles, and heat transfer rate, is discussed.

Steady-state modeling of a new continuous API dryer: Reduced-order model and investigation of dryer performance

In the present study, a reduced-order model is proposed to analyze a novel continuous dryer with an application in the pharmaceutical industry. The model was validated using process data from ibuprofen drying test runs, and the results were in good agreement with the experimental data. The test substance was an ibuprofen paste with an initial LOD of up to 30 w%. The simulations showed that the contact heat transfer coefficient can be correlated with the degree of wetness. Furthermore, a set of simulations was performed to analyze the influence of input parameters on the dryer’s performance: i) the inlet air flow rate and ii) the inlet air temperature. The simulation results demonstrated that a variation in the inlet air temperature significantly affects the air temperature profile, while the inlet air flow rate has a minor effect. Besides, it was also established that the inlet solid LoD has the most considerable effect on the product quality (e.g., final solid moisture content). The results showed a deviation of less than 10% for the product LoD and the product temperature in most cases.

Effects of Contact Conditions at Wire–Die Interface on Temperature Distribution during Wire Drawing

The effects of contact conditions at the wire–die interface on the temperature distribution of the specimen and die are investigated to understand the wire drawing process. Finite element analysis and experiments are performed to analyze the temperature distribution of a drawn wire and die based on different contact conditions using a low-carbon steel wire. The maximum temperature (Tmax) of the die decreases as the contact heat transfer coefficient at the wire–die interface increases, whereas that of the wire increases with the contact heat transfer coefficient. The Tmax of the die and wire decreases with the thermal conductivity of the die. As the thermal conductivity of the die increases, the heat generated by friction is rapidly absorbed into the die, and the Tmax of the die decreases, thus resulting in a decrease in the surface temperature of the wire. The Tmax of both the die and wire linearly increases with the friction factor. In particular, the Tmax of the die more sensitively changes with the friction factor compared with that of the wire. The Tmax of the die linearly increases with the drawing velocity, whereas that of the wire parabolically increases with the drawing velocity. The influence of bearing length on the temperature increase in both the wire and die is insignificant.

Three-dimensional finite discrete element-based contact heat transfer model considering thermal cracking in continuous–discontinuous media

This paper proposes a three-dimensional heat transfer model that considers contact heat transfer and thermal cracking in continuous–discontinuous media. The 3D heat transfer model comprises the heat conduction model inside the continuum and the contact heat transfer model between discrete blocks. The model is combined with the 3D Finite Discrete Element (FDEM) for coupled thermo-mechanical calculation, which includes the following three parts: the temperature distribution of the system is obtained by the 3D heat transfer model considering contact heat transfer; then, the thermal stress caused by the temperature is applied to the system equation to perform the mechanical fracture calculation; finally, the heat exchange coefficient of the newly generated broken joint element is updated for heat transfer calculation at the next time. Some examples are given to verify the 3D contact heat transfer model with analytical solutions. Moreover, the influence of the heat exchange coefficient of the joint element and the contact heat transfer coefficient is discussed. Finally, examples of contact heat conduction in 3D granular assemblage, and thermal cracking caused by contact heat transfer are demonstrated. These examples demonstrated excellent capacity of the model in simulating contact heat transfer and thermal cracking in continuous–discontinuous media.

A novel approach to generate non-isotropic surfaces for numerical quantification of thermal contact conductance

The quantification of heat flow between machine tool components is of major importance for a precise thermal prediction of the entire system. A common coupling condition between individual components is the contact heat transfer coefficient connecting the temperature field with the corresponding heat transfer at the investigated interface. However, the majority of numerical and analytical approaches assume isotropic contact surface profiles and neglect distinct surface structures caused by the manufacturing process. This assumption causes inaccuracies in the modeling as isotropic surfaces lead to an overprediction in heat transfer. Hence, this paper presents a novel approach to generate surface structures for numerical calculations considering the used machining parameters. Predicted contact heat transfer coefficients of the old as well as the new generation approach are presented and compared to experimental results offering the basis for future comprehensive investigations considering multiple parameters and materials.

Machine learning-based predictive modeling of contact heat transfer

Heat transfer phenomena at the interface between two contacting solids are highly complex involving multiple influencing factors. Over the years, a large amount of experiments were carried out to determine the contact heat transfer coefficients between two dissimilar joint materials. However, there are still no existing theoretical or physics-based models that satisfactorily predict the contact heat transfer coefficients. By taking advantage of the existing data, in contrast, machine learning promises a powerful method, capable of predicting the contact heat transfer coefficients for different material pairs and contact conditions. This research introduces a robust machine learning-based model that succeeds in precisely estimating the heat transfer across the interfaces between glass and steel, a material pair widely used in hot forming of glass. The data used for training and validating the machine learning models were determined experimentally by means of infrared thermography. The datasets consisted of contact heat transfer coefficients with dependence on three factors – interfacial temperature, contact pressure, and surface finishes. Aim of this study is to analyze the prediction accuracy and interpretability of various supervised learning algorithms in order to realize the machine learning models that are able to capture the underlying physics governing the heat transfer phenomena at the glass-mold interface. Finally, the results were compared with those estimated by a theoretical model and a numerical simulation model. The comparison demonstrates enhancements in prediction accuracy enabled by the data-driven method. This study indicates accurate and efficient strategies for solving thermal problems in hot glass forming processes.

Distributed parameter simulation of annular-finned tube sorption bed

A distributed-parameter model of a sorption bed heat and mass exchanger is presented. The model includes energy and mass balances for the heat transfer fluid, tube, annular fins, and adsorbent. The conservation equations are discretized and solved to determine the temperature and uptake profiles for a silica gel-water sorption bed during the isosteric heating and desorption stages of an adsorption heat pump cycle driven by 90°C water. The results show that during the beginning of the heating stage, there are substantial temperature differences (16.5 K over 3 mm) along the radial and axial directions. This temperature gradient translates to a difference in uptake of ~10% across an individual adsorbent cell. The effect of the contact heat transfer coefficient between the adsorbent and tube is also quantified. Significant but achievable improvements in contact heat transfer yield appreciable reductions in sorption bed cycle time.

Heat Transfer Model in a Rotary Drum During the Fermentation Process

A new mathematical model describing heat transfer during the fermentation process in a rotary drum is proposed. The model includes representations of the kinetic reactions, the temperature of the solid bed, and physical structures within the rotary drum. The model is developed using five ordinary differential equations and was then solved using the Runge-Kutta method embedded in MATLAB software. A reasonable behaviour for the temperature profile to the fermentation process is achieved. The results show that the mass of the solid bed, contact heat transfer coefficient, and the wall temperature has a significant effect on the fermentation process in a rotary drum.

A study of the heat transfer mechanism in resistance spot welding of aluminum alloys AA5182 and AA6014

This work investigates heat transfer mechanism of aluminum resistance spot welding process. The main target is to determine thermal contact conductance and heat transfer coefficients for natural convection and thermal radiation at ambient air and forced convection inside the water-cooled electrodes. For this purpose, the heat transfer of hot sheets in a welding gun for aluminum alloys AA5182 and AA6014 is analyzed experimentally and numerically. The transient temperature field is measured by several thermocouples in a simplified experimental setup. Subsequent thermal-mechanical coupled finite element simulations of the experiments were used to calibrate the heat transfer coefficients. The heat transfer coefficient for natural convection and thermal radiation to ambient air is 13 $\mathrm {\frac {W}{m^{2} K}}$ and the heat transfer coefficient for forced convection of electrode water-cooling is 25,000 $\mathrm {\frac {W}{m^{2} K}}$ . The results indicate that the thermal contact conductance can be assumed ideal for welding process. Additionally, the finite element model is validated by the measured and calculated dissipated heat due to forced convection. Finally, a sensitivity analysis is performed to compare the influence of maximum and minimum heat transfer coefficients of forced convection (water-cooling) on transient temperature field and dissipated heat of sample AA5182.

Numerical Study of Heat Transfer in Gravity-Driven Particle Flow around Tubes with Different Shapes

In the present paper, the heat transfer of gravity-driven dense particle flow around five different shapes of tubes is numerically studied using discrete element method (DEM). The velocity vector, particle contact number, particle contact time and heat transfer coefficient of particle flow at different particle zones around the tube are carefully analyzed. The results show that the effect of tube shape on the particle flow at both upstream and downstream regions of different tubes are remarkable. A particle stagnation zone and particle cavity zone are formed at the upstream and downstream regions of all the tubes. Both the stagnation and cavity zones for the circular tube are the largest, and they are the smallest for the elliptical tube. As the particle outlet velocity (vout) changes from 0.5 mm/s to 8 mm/s at dp = 1.72 mm/s, when compared with the circular tube, the heat transfer coefficient of particle flow for the elliptical tube and flat elliptical tube can increase by 20.3% and 15.0% on average, respectively. The proper design of the downstream shape of the tube can improve the overall heat transfer performance more efficiently. The heat transfer coefficient will increase as particle diameter decreases.

Experimental and numerical study of heat and mass transfer during contact heating of sliced potatoes

Studies concerning the contact heating of food products remain relatively rare in the literature despite the importance of this mode of heat transfer in many operations (grilling, pan-frying).To deal with this, kinetics of product water loss and temperature rise were recorded during contact heating of potato slices in order to examine the influence of the heating power and of the presence or not of an oil layer below the heated product. From the experimental data acquired, a 2D mathematical model based on a moving boiling-front approach was developed and validated allowing the determination of contact heat transfer coefficient values of 512.2 ± 12.4 W m−2.K−1 and 197.5 ± 5.8 W m−2.K−1 for experiments with and without oil respectively. The analysis of the simulation results showed that the overall heating of the product is limited by: (i) the evaporation of liquid water at the location of a boiling front propagating within the heated product and (ii) by the development of a dried region (crust) in the lower part of the product acting as a thermal insulating layer. It should also be noted that the determination of the contact heat transfer coefficient can become an incidental problem (especially for experiments with oil) since the thermal contact resistance is often much lower than the thermal resistance associated with conduction in the dried region of the product.

Production of three-layer steel bimetallic strips in the unit of continuous casting and deformation. Report 1

High technical and economic efficiency of the use of bimetals in chemical, oil, transport and energy engineering and other industries is described. The urgency of creating high-performance continuous processes for the production of bimetallic strips is substantiated. The authors have established the main technological tasks for development of the processes of obtaining bimetal of wide class. The paper describes resource-saving production technology of three-layer bimetals alloyed steel – constructional steel – alloyed steel at the unit of combined process of continuous casting and deformation. Possibilities of the proposed technology are outlined from the standpoint of improving the quality of bimetallic strips. The initial data are given to determine the temperature change over time of the main steel strip as it passes through the molten metal of the alloyed steel. The equations are given for non-stationary heat conduction, initial and boundary conditions for determining the temperature fields of main strip and cladding layer when obtaining a three-layer bimetallic strip on the unit of a combined process of continuous casting and deformation. The values of density, thermal conductivity and heat capacity for steel St3 were determined in a given temperature range. A procedure is described for calculating temperatures in the ANSYS package by solving a non-stationary heat conduction problem in a flat formulation by the finite element method. The authors have described the geometric model for calculating the temperature of strip and molten metal of the cladding layer. Values of the coefficient of heat transfer between the main strip and molten metal of the cladding layers of bimetallic strip are given adopted for calculation. Characteristic points are indicated in the model for calculating the temperatures of main strip and molten metal of the cladding layer. The graphs show temporal changes in these temperatures at production of a three-layer bimetallic strip on the unit of combined process of continuous casting and deformation. Calculated data on the time variation of temperature of main strip and molten metal of the cladding layer at characteristic points are given for different values of the contact heat transfer coefficient.

Numerical and experimental determinations of contact heat transfer coefficients in nonisothermal glass molding

AbstractHeat transfer at the interfacial contact is a dominant factor in the thermal behavior of glass during nonisothermal glass molding process. Recent research is developing reliable numerical approaches to quantify contact heat transfer coefficients. In most previous studies, however, both theoretical and numerical models of thermal contact conductance in glass molding attempted to investigate this factor by either omitting surface topography or simplifying the nature of contact surfaces. In fact, the determination of the contact heat transfer coefficient demands a detailed characterization of the contact interface including the surface topography and the thermomechanical behavior of the contact pair. This paper introduces a numerical approach to quantify the contact heat transfer by means of a microscale simulation at the glass‐mold interface. The simulation successfully incorporates modeling of the thermomechanical behaviors and the three‐dimensional topographies from actual surface measurements of the contact pair. The presented numerical model enables the derivation of contact heat transfer coefficients from various contact pressures and surface finishes. Numerical predictions of these coefficients are validated by transient contact heat transfer experiments using infrared thermography to verify the model.

Investigation of the heat transfer properties of granular activated carbon with R723 for adsorption refrigeration and heat pump

This paper investigates the heat transfer coefficient of the wall to packed carbon contact (h) and the thermal conductivity of the packed bed (λ) by using parameters estimation method. A numerical heat conduction method was used in conjunction with an iterative process of minimizing the Mean Square Error (MSE) between both experimentally measured and model predicted temperatures in order to estimate h and λ parameters simultaneously. Experimental work was carried out by measuring the wall and centre temperatures of the sample reactor when suddenly submerged in a temperature controlled water bath at around 90 °C. Four samples with packed bed density ranging from 600 kg m−3 to 750 kg m−3 were tested. The results for the GAC-R723 refrigerant pair show a quasi-linear increase in both thermal conductivity (λ) and wall contact heat transfer coefficient (h) with packed bed density. The thermal conductivity of GAC-R723 refrigerant varies between 0.77 W m−1 K−1 and 1.36 W m−1 K−1 (about three times the values without R723 refrigerant) while the wall contact heat transfer coefficient varied between 390 W m−2 K−1 and 735 W m−2 K−1 (up to 30% better than values without R723).

Contact angle and heat transfer characteristics of a gravity-driven film flow of a particulate liquid metal on smooth and rough surfaces

In the present research, an experimental investigation was conducted to identify the behaviour of gallium as a promising heat transfer fluid for cooling a high heat flux surface. Bismuth nanoparticles were dispersed within the gallium to compensate its poor thermal conductivity and to enhance its wettability. A high-fidelity experimental setup was fabricated to provide conditions for measuring the contact angle between the gallium and the surface and also to measure the heat transfer coefficient of a free surface liquid film flowing on the heating surface. Influence of different operating parameters including tilt angle of the surface, heat flux of the surface, surface roughness and time on the contact angle and heat transfer coefficient of the liquid film was experimentally investigated. Results showed that with an increase in the tilt angle of the surface, higher heat transfer coefficient can be achieved, which was attributed to the enhancement of the terminal velocity of the liquid metal. Also, an increase in the roughness of the surface intensified the contact angle of the liquid metal and caused a decrease in the wettability. It was also found that the contact angle of gallium was a function of time such that it decreased with time spanning and reached a constant value.

Experimental investigation of contact heat transfer coefficients in nonisothermal glass molding by infrared thermography

AbstractNonisothermal glass molding has recently become a promising technology solution for the cost‐efficient production of complex precision glass optical components. During the molding process, the glass temperature and its temperature distribution have crucial effects on the accuracy of molded optics. In nonisothermal molding, the glass temperature is greatly influenced by thermal contact conductance because there is a large temperature difference between the glass and mold parts. Though widely agreed to be varied during the molding process, the contact conductance was usually assumed as constant coefficients in most early works without sufficient experimental justifications. This paper presents an experiment approach to determine the thermal contact coefficient derived from transient temperature measurements by using infrared thermographic camera. The transient method demonstrates a beneficially short processing time and the adequate measurement at desirable molding temperature without glass sticking. Particularly, this method promises the avoidance of the overestimated contact coefficients derived from steady‐state approach due to the viscoelastic deformation of glass during the inevitably long period of holding force. Based on this method, the dependency of thermal contact conductance on mold surface roughness, contact pressure, and interfacial temperature ranging from slightly below‐to‐above glass transition temperature was investigated. The results reveal the dominance of interfacial temperature on the contact conductance while the linear pressure‐dependent conductance with an identical slope observed for all roughness and mold temperatures. The accurate determination of the contact heat transfer coefficients will eventually improve the predictions of the form accuracy, the optical properties, and possible defects such as chill ripples or glass breakage of molded lenses by the nonisothermal glass molding process.