Determination Of Transfer Coefficient Research Articles

Shell side cfd analysis of a model shell-and-tube heat exchanger

In the present paper, a model-size shell-and-tube heat exchanger with horizontal baffles is investigated numerically and compared to the measured values using the commercial software SC-Tetra V11. Determination of the heat transfer coefficients for the shell side depends on the type of the flow and the type of the baffles. Without baffles the shell side medium leaves in the shortest way, and dead zones are formed. With the usage of these baffles, the flow path is artificially formed and the flow velocity will be increased because of the decreased flow area. These two effects will cause a better heat transfer but the other hand this will increase the weight of the heat exchanger. There are very simple experimental correlations for the segment and disk-and-donut types baffles. However, must be known the real heat transfer coefficient in case of an optimal design. This study investigated the effect of the type of the baffles, the space between them and the baffle cut to the real heat transfer coefficient and the necessary material quantity and compared the simulated heat transfer coefficients with analytically calculated ones based on the literature.

Determination of Volumetric Mass Transfer Coefficient in Gas-Solid-Liquid Stirred Vessels Handling High Solids Concentrations: Experiment and Modeling

Rigorous analysis of the determinants of volumetric mass transfer coefficient (kLa) and its accurate forecasting are of vital importance for effectively designing and operating stirred reactors. Majority of the available literature is limited to systems with low solids concentration, while there has always been a need to investigate the gas-liquid hydrodynamics in tanks handling high solid loadings. Several models have been proposed for predicting kLa values, but the application of neuro-fuzzy logic for modeling kLa based on combined operational and geometrical conditions is still unexplored. In this paper, an ANFIS (adaptive neuro-fuzzy inference system) model was designed to map three operational parameters (agitation speed (RPS), solid concentration, superficial gas velocity (cm/s)) and one geometrical parameter (number of curved blades) as input data, to kLa as output data. Excellent performance of ANFIS's model in predicting kLa values was demonstrated by various performance indicators with a correlation coefficient of 0.9941.

Comparison in determination of mass-energy transfer coefficients

The values obtained through definitions, specific software and measurements of the mass energy transfer coefficients referring to X-ray beams in air using the range of 30 to 150 kV. They allowed the spectra and calculated evaluation the respective mass coefficients. The results shown a decreasing behavior with energy, ranging from 0.3733 to 0.0439 cm2/g, differing from the behavior of monoergetic beams above 100 keV.

Combined numerical and experimental determination of the convective heat transfer coefficient between an AlCrN-coated Vanadis 4E tool and Rhenus oil

Regardless of the field of application, the reliability of numerical simulations depends on correct description of boundary conditions. In thermal simulation, determination of heat transfer coefficients is important because it varies with material properties and process conditions. This paper shows a combined experimental and numerical analysis applied for determination of the heat transfer coefficient between an AlCrN-coated Vanadis 4E tool and Rhenus LA722086 oil in an unloaded condition, i.e. without the tool being in contact with a workpiece. It is found that the heat transfer coefficient in unloaded conditions at 80 °C oil temperature is 0.15 kW/(m2·K) between the selected stamping tool and mineral oil. A sensitivity analysis of the numerical model was performed to verify the effects of mesh discretization, temperature measurement location and tool geometry. Among these parameters, mesh size and the thermocouple insert depth were identified as the critical parameters that affect the measured and calculated temperatures.

High Performance Tubular Heat Exchanger with Minijet Heat Transfer Enhancement

ABSTRACTIn the paper, the original cylindrical heat exchanger with minijets (MJHE) was introduced. The systematic experimental analysis of the prototype heat exchanger was described with special attention paid to such parameters as the heat transfer effectiveness, heat transfer rates, overall heat transfer coefficients, and pressure drop. The heat transfer coefficients were determined based on Wilson plot method, the most suitable approach for heat transfer coefficient determination in exchangers of complex geometry. The thermal-hydraulic characteristics of the in-house manufactured prototype of MJHE in water–water and gas–water configuration are also presented. The experimental results were compared with the predictions from well-known correlations found in the published research papers dedicated to the free-surface and submerged types of jets.

CFD Modeling and Simulation of Aeorodynamic Cooling of Automotive Brake Rotor

Braking system is one of the important control systems of an automotive. For many years, the disc brakes have been used in automobiles for the safe retarding of the vehicles. During the braking enormous amount of heat will be generated and for effective braking sufficient heat dissipation is essential. The thermal performance of disc brake depends upon the characteristics of the airflow around the brake rotor and hence the aerodynamics is an important in the region of brake components. A CFD analysis is carried out on the braking system as a case study to make out the behavior of airflow distribution around the disc brake components using ANSYS CFX software. We are interested in the determination of the heat transfer coefficient (HTC) on each surface of a ventilated disc rotor varying with time in a transient state using CFD analysis, and then imported the surface film condition data into a corresponding FEM model for disc temperature analysis.

Numerical determination of the heat transfer coefficient for volumetric air receivers with wire meshes

Volumetric receivers made of metallic plain-weave wire meshes are a promising technology that could lead to many different designs and configurations. This work deals with the numerical determination of the convective heat transfer coefficient between an air flow and stagger stacked plain-weave wire mesh screens that constitute the volumetric receivers. For that purpose, six geometries are studied with different geometrical characteristics, but with the constraint of finding pairs with similar porosities. The commercial code STAR-CCM+ was used for the detailed geometries for solving the microscopic equations. The numerical methodology, boundary conditions and main assumptions are presented. Based on a parametrical study over the velocity and wall temperature for each analyzed mesh, a correlation of the local volumetric convective heat transfer was found and depends on the Reynolds and Prandtl numbers. The different correlations were compared among them and with literature data showing similar trends and order of magnitudes. One of the correlations obtained was validated by using it in a homogeneous equivalent model assuming a local thermal non-equilibrium between the solid and fluid phases. The results were compared to the temperature profiles computed by a detailed simulation and show a very good agreement.

MODEL KINETIKA EKSTRAKSI FLAVONOID DARI BAYAM MERAH (Alternanthera amoena voss)


 Red spinach (Alternanthera amoena voss) contains vitamins, protein, and flavonoids. Flavonoid is polyphenol compounds having properties as a free radical catcher.The purpose of this research is to obtain the kinetic rate of flavonoid mass transfer from red spinach.Extraction is one of the way to take flavonoids contained in solids with the assist of solvents. Mass transfer in liquid solid extraction occurs by diffusion. The determination of mass transfer coefficient (KC) is to conduct the rate of mass transfer of flavonoids from solids. In this study, the effect of temperature on the extraction of flavonoids from red spinach with water solvent is observed. The temperatures extraction in this research are of 50°C, 60°C, and 70°C respectively. Determinationof total flavonoid, mass transfer coefficient, and antioxidant activity carried out using FT-IR Spectrophotometry and UV-VIS Spectrophotometry. This study concluded that the increase in extraction time and temperature will increase the total content of flavonoids and extract rendement.Mass transfer coefficient equation in this study is K = 3078645 . Antioxidants in red spinach are included in the group of very strong antioxidants.

Determination of heat-mass transfer coefficients within the apparatuses with jet-film contact devices

One of the ways of intensifying the heat and mass transfer processes in gas-fluid systems is designing jet-film contact devices with a developed surface of phase contact at high flow velocities. A contact jet-film device has been developed. The results of numerical investigation of the operation of this device are presented. There were determined the coefficients of heat transfer to the air from the surface of liquid inside of the drain cup of contact device. The criterion equations of convective heat transfer for engineering calculations of jet-film contact devices is corrected.

A new method for determination of gas–liquid mass transfer coefficients by direct measurement of gas uptake by flow NMR

Anin situmethod for determination of the overall volumetric mass transfer coefficients by direct observation and quantitation of dissolved gases that contain NMR active nuclei is presented.

Experimental determination of the heat transfer coefficient during evaporation and boiling of thin liquid film

Thin films evaporation of distilled water, ethanol and HFE-7100 liquid was experimentally studied. The dependences of heat transfer coefficients in time were determined. It has been established that with a decrease in the layer thickness of distilled water and ethanol, the heat transfer coefficient increases. For the HFE liquid, the nature of the change is different: as the time increases, the heat transfer coefficient decreases.

Heat flow and heat transfer coefficient during crystallization under the pressure

Estimation of the heat flow at the metal-mold interface is necessary for accurate simulation of the solidification processes. For the numerical simulation, a precise prediction of boundary conditions is required to determine the temperature distribution during solidification, porosity nucleation, microstructure development, and residual stresses. Determination of the heat transfer coefficients at the metal-mold interface is a critical aspect for simulation of the solidification process and the microstructure modeling of the castings. For crystallization under the pressure and for thin-walled castings, HTC evaluation is important due to the very limited freezing time.

Evaluation of selected methods of the heat transfer coefficient determination in fin-and-tube cross-flow heat exchangers

The work is a part of a thermodynamic analysis of a finned cross-flow heat exchanger of the liquid-gas type. The heat transfer coefficients on the liquid and the gas side and the area of the heat transfer are the main parameters describing such a device. The basic problem in computations of such heat exchangers is determination of the coefficient of the heat transfer from the finned surfaces to the gas. The differences in the heat transfer coefficient local values resulting from the non-uniform flow of mediums through the exchanger complicates the analysis additionally. Six Nusselt number relationships are selected as suitable for the considered heat exchanger, and they are used to calculate the heat transfer coefficient for the air temperature ranging from 10°C to 30°C and for the velocity values ranging from 2 m/s to 20 m/s. In the next step, the gas-side heat transfer coefficient is determined by means of numerical simulations using a numerical model of a repetitive fragment of the heat exchanger under consideration. Finally, the Wilson plot method is also used. The work focuses on an analysis of the in-house HEWES code sensitivity to the method of the heat transfer coefficient determination. The authors believe that the analysis may also be useful for the evaluation of different methods of the heat transfer coefficient computation.

The application of Fourier transform to the identification of temperature distribution in HFE-7100 flow boiling in an annular minigap

In the paper the results of investigations into HFE-7100 flow boiling heat transfer in a cylindrical minigap a 1 mm wide created between the external glass pipe and the copper pipe were discussed. A cartridge heater located axially heated fluid flowing along the minigap. The cooling fluid temperature and pressure at the inlet and the outlet to/from the minigap and temperature of the heater in 18 points were measured. Two-dimensional mathematical model for heat transfer coefficient determination was proposed. It was assumed that in the test section the heat transfer process was in steady state and the fluid flow was laminar. The temperature of the metal pipe near the heater was assumed to satisfy Laplace’s equation. The problem formulated in this way was solved by two methods: the Fourier transform and the Trefftz method. The working fluid temperature was calculated depending on the flow type: for single phase flow with boiling incipience and for two-phase flow, respectively. The heat transfer coefficient at the fluid – copper pipe interface was calculated due to the Robin condition. Local heat transfer coefficient values obtained from the Fourier transform and from the Trefftz method were similar. Results were presented and discussed.

The flow boiling heat transfer coefficient determination in a minichannel used the FEM combined with Trefftz functions

The method of solving the inverse heat conduction problem, by means of the FEM with Trefftz-type basis functions, during flow boiling in a minichannel was shown. This basis functions were constructed with using the Hermite interpolation and Trefftz functions. The aim of the numerical calculations was to determine the local heat transfer coefficient on the basis of experimental data in a horizontally oriented minichannel. The refrigerant flowing along the minichannel (HFE-649 or HFE-7100) was heated by a thin enhanced plate by vibration-assisted laser texturing. The temperature on an outer smooth side of the plate was detected by means of infrared thermography. On the heated wall–fluid contact surface in the minichannel the heat transfer coefficient was obtained from the Robin boundary condition. It was assumed that the temperature distribution in the heated plate was described by the Poisson equation. The unknown values of temperature and temperature derivatives at nodes were computed by minimizing the functional which describes the mean square error of the approximate solution on the boundary and along common edges of neighbouring elements. The results were presented as the heated plate temperature and heat transfer coefficient versus the minichannel length.

The heat transfer coefficient determination with the use of the Beck-Trefftz method in flow boiling in a minichannel

In this paper, the solution of the two-dimensional inverse heat transfer problem with the use of the Beck method coupled with the Trefftz method is proposed. This method was applied for solving an inverse heat conduction problem. The aim of the calculation was to determine the boiling heat transfer coefficient on the basis of temperature measurements taken by infrared thermography. The experimental data of flow boiling heat transfer in a single vertical minichannel of 1.7 mm depth, heated asymmetrically, were used in calculations. The heating element for two refrigerants (FC-72 and HFE-7100, 3M) flowing in the minichannel was the plate enhanced on the side contacting with the fluid. The analysis of the results was performed on the basis of experimental series obtained for the same heat flux and two different mass flow velocities. The results were presented as infrared thermographs, heated wall temperature and heat transfer coefficient as a function of the distance from the minichannel inlet. The results was discussed for the subcooled and saturated boiling regions separately.

Heat transfer coefficient determination using the FEM with time-dependent Trefftz-type basis functions in subcooled flow boiling in a minichannel

Results concerning flow boiling heat transfer in a vertical minichannel of 1.7 mm depth were shown. The channel was asymmetrically heated by a thin foil. Its surface temperature was recorded continuously in points by thermocouples. Measurements were carried out in 0.01 s intervals. The objective of the numerical calculations was to determine the heat transfer coefficient on the heated foil–fluid contact surface in the minichannel from the Robin boundary condition. Both the foil and fluid temperatures were the result of solving the nonstationary two-dimensional problem in the foil and flowing fluid. The problem was solved by using the FEM combined with Trefftz-type basis functions. The values of the time-dependent local heat transfer coefficient were presented and discussed.

The heat transfer coefficient determination with the use of the Beck-Trefftz method in flow boiling in a minichannel

The heat transfer coefficient determination with the use of the Beck-Trefftz method in flow boiling in a minichannel

An experimental and numerical study of endwall heat transfer in a turbine blade cascade including tangential heat conduction analysis

This paper presents an experimental and numerical investigation of heat transfer in the endwall region of a large scale turbine cascade. The steady-state liquid crystal technique has been used to obtain the map of the heat transfer coefficient for a constant heat flux boundary condition. In the presence of two- and three-dimensional flows with significant spatial variations of the heat transfer coefficient, tangential heat conduction could lead to error in the heat transfer coefficient determination, since local heat fluxes at the wall-to-fluid interface tend to differ from point to point and surface temperatures to be smoothed out, thus making the uniform-heat-flux boundary condition difficult to be perfectly achieved. For this reason, numerical simulations of flow and heat transfer in the cascade including the effect of tangential heat conduction inside the endwall have been performed. The major objective of numerical simulations was to investigate the influence of wall heat conduction on the convective heat transfer coefficient determined during a nominal iso-flux heat transfer experiment and to interpret possible differences between numerical and experimental heat transfer results. Results were presented and discussed in terms of local Nusselt number and a convenient wall heat flux function for two values of the Reynolds number (270,000 and 960,000).

EXPERIMENTAL STUDIES OF BOILING HEAT TRANSFER OF FOOD SOLUTIONS

Vacuum evaporation is widely used in the food technologies. The equipment for this process is well known and methods of calculation and design of vacuum evaporators are described in literature as well. However, in some cases the accuracy of existing methods is not enough. The problem of designing the new, more efficient ap-paratuses those work in regimes, which are not usual, needs to clarify some dependencies. It concerns the problem of boiling heat transfer coefficient determination for such solutes as food products because of the high or sometimes extremely high viscosity of many food staffs is. To take into account properties of products many authors use the Prandtl number. However, determination of these properties exact values is not always possible especially it con-cerns the viscosity of Non-Newtonian fluids, which are the most of food staff. For experimental verification of heat transfer coefficient values, an apple juice was chosen. At first, the theoretical value was obtained with Tolubinskiy dependency using. The vapor bulbs grows rate and surface tension coefficient were solved as for water. The de-pendencies between the heat transfer coefficient and heat flux for apple juice with concentration from 15 to 50 Brix were obtained as result. There are several different equations to calculate the properties of apple juice depending on temperature and concentration and several resulting dependencies that differ from each other were obtained. The comparison with the experimental data that was obtained by authors made possible to choose the right equa-tions for apple juice viscosity determination when the heat transfer calculation error did not exceed 20% that is standard error for used dependency and for many others. To reduce this error on the base of obtained experimental data the correction coefficient was calculated. Therefore, the equation to calculate the heat transfer coefficient for boiling apple juice where maximum error did not exceed 5% was obtained. The experimental research was conduct-ed under atmospheric pressure. To obtain the value of heat transfer coefficient in vacuum condition the Tolubinskiy dependency can be used or addition experiments should be conducted. It depends of required accuracy level.