scholarly journals Kinetics of heat and moisture exchange and method for calculating the duration of the convective drying process of natural leather

2020 ◽  
Vol 65 (4) ◽  
pp. 464-475
Author(s):  
A. I. Alshansky ◽  
A. L. Klimentyev
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Drying Kinetics ◽  
Drying Process ◽  
Drying Time ◽  
Moisture Exchange ◽  
Kinetics Of ◽  
The Heat Transfer Coefficient

Methods for processing experimental data based on generalized variables of the drying process, which characterize the most general patterns of drying in a period of decreasing speed, are considered. A method for processing experimental data based on the expanded level of drying kinetics is presented, which allows obtaining all dependencies for calculating the main parameters of the drying process. Equations are given for determining the densities of heat fluxes, the intensity of moisture evaporation, the temperature of the material, and the duration of drying for the period of falling speed. A dependence is given for calculating the Rebinder number, which establishes a relationship between moisture exchange and heat exchange for the second drying period. The values of all the coefficients in the equation for the Nusselt heat transfer criterion, which are necessary for determining the heat transfer coefficients, have been established. Calculations of the heat transfer coefficient for a number of modes of natural leather drying are presented. On the basis of the method for calculating the drying kinetics developed by B.S. Sazhin, an equation was established to determine the drying time of leather, which describes the entire drying process, including both drying periods. This method of calculating the kinetics of drying contains a minimum number of coefficients determined empirically, which reduces the amount of work at processing these experiments and the number of necessary experiments. The main constants in the criterial heat transfer equation for determining the heat transfer coefficient have been determined. Verification of the reliability of all obtained equations and comparison of the calculated and experimental values for all parameters of the drying kinetics are given. The obtained results of the study of drying natural leathers make it possible to control the technological process, preventing overdrying of the leather, disturbing the temperature regime, which leads to a reduction in energy costs for drying.

scholarly journals Modeling Film-Coolant Flow Characteristics at the Exit of Shower-Head Holes

2000 ◽  
Author(s):  
Vijay K. Garg
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Coolant Flow ◽  
The Heat Transfer Coefficient

Abstract The coolant flow characteristics at the hole exits of a film-cooled blade are derived from an earlier analysis where the hole pipes and coolant plenum were also discretized. The blade chosen is the VKI rotor with three staggered rows of shower-head holes. The present analysis applies these flow characteristics at the shower-head hole exits. A multi-block three-dimensional Navier-Stokes code with Wilcox’s k-ω model is used to compute the heat transfer coefficient on the film-cooled turbine blade. A reasonably good comparison with the experimental data as well as with the more complete earlier analysis where the hole pipes and coolant plenum were also gridded is obtained. If the 1/7th power law is assumed for the coolant flow characteristics at the hole exits, considerable differences in the heat transfer coefficient on the blade surface, specially in the leading-edge region, are observed even though the span-averaged values of h match well with the experimental data. This calls for span-resolved experimental data near film-cooling holes on a blade for better validation of the code.

The Effect of Density Variation on Heat Transfer in the Critical Region

1961 ◽  
Vol 83 (2) ◽  
pp. 176-181 ◽  
Author(s):  
Yih-Yun Hsu ◽  
J. M. Smith
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Turbulent Flow ◽  
Transfer Coefficient ◽  
Critical Point ◽  
Critical Region ◽  
Large Density ◽  
The Heat Transfer Coefficient

The heat-transfer coefficient between fluid and tube wall in turbulent flow depends upon the physical and thermal properties of the fluid. When density changes across the diameter of the tube are large (for example, when the fluid is near the critical point), the variable density can affect the transfer of momentum and heat. Equations are developed for predicting the magnitude of this effect on the heat-transfer coefficient. Deissler’s [5] expressions for the eddy diffusivity are employed in solving the equations for heat and momentum transfer. For flow in vertical tubes large density variations can also affect the heat transfer by inducing natural convection. By considering the influence of body forces on the shear stress, equations are derived to predict the effect of natural convection on the heat-transfer coefficient for turbulent flow. The results indicate that the effect is significant only for relatively high Grashof numbers and low Reynolds numbers. Such conditions may be encountered in flow of a fluid near its thermodynamic critical point. The derived equations are applied for carbon dioxide flow in the critical region under the conditions for which experimental data were measured by Bringer and Smith [2]. Because of the high Reynolds and low Grashof numbers, natural convection is not significant. However, the effect of the large density variations is found to be significant, and the predicted results agree well with the experimental data.

scholarly journals Evaluation of Heat Transfer Coefficient of Two-Phase Flow Boiling with R290 in Horizontal Mini Channel

2021 ◽  
Vol 88 (3) ◽  
pp. 88-95
Author(s):  
Ronald Akbar ◽  
Jong Taek Oh ◽  
Agus Sunjarianto Pamitran
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
The Heat Transfer Coefficient

Various experiments have been conducted on the heat transfer coefficient of two-phase flow boiling in mini channel tubes. In addition to obtaining data on the heat transfer coefficients through experiments, many researchers have also compared their experimental data using existing correlations. This research aims to determine the characteristics of the heat transfer coefficient of refrigerant R290 from the data used by processing and knowing the best heat transfer coefficient correlation in predicting the experimental data so that the results are expected to be a reference for designing a heat exchanger or for further research. The experimental data predicted is the two-phase flow boiling in a horizontal tube 3 mm diameter, with the mass flux of 50-180 kg/m2s, heat flux of 5-20 kW/m2, saturation temperature of 0-11 °C, and vapor quality of 0-1. The correlation used in this research is based on the asymptotic flow model, where the model is a combination of the nucleate and convective flow boiling mechanisms. The results show an effect of mass flux and heat flux on the experimental heat transfer coefficient and the predicted R290 heat transfer coefficient with asymptotic correlations had a good and similar result to the experimental data.

High Resolution Heat Transfer Measurement on Flat and Contoured Endwalls in a Linear Cascade

2012 ◽  
Author(s):  
Benoit Laveau ◽  
Reza S. Abhari ◽  
Michael E. Crawford ◽  
Ewald Lutum
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Transfer Coefficient ◽  
High Resolution ◽  
Transfer Coefficient ◽  
Gas Turbines ◽  
Transfer Data ◽  
Numerical Predictions ◽  
Endwall Contouring ◽  
The Heat Transfer Coefficient

In order to continue increasing the efficiency of gas turbines, a significant effort is being made to reduce losses induced by secondary flows in turbine stages. In addition to their impact on aerodynamic losses, these vortical structures are also the source of large heat transfer variations across the passage. A substantial reduction of the secondary flow losses can be achieved with a contoured endwall. However, a change in the vortical pattern can dramatically impact the thermal loads on the endwall and lead to higher cooling requirements in those areas. This paper focuses on heat transfer measurements made in a passage with either flat or contoured endwalls. The experimental data are supplemented with numerical predictions of the heat transfer data. The measurements are carried out on an isothermal endwall equipped with symmetric NACA airfoils. The paper presents measurements at M = 0.3 corresponding to a Reynolds number ReCax = 4.6×105. An infrared camera is used to provide high-resolution surface temperature data on the endwall. The surface is equipped with an insulating layer (Kapton) allowing the calculation of heat flux through the endwall. The heat transfer quantities, namely the heat transfer coefficient and the adiabatic wall temperature, are then derived from a set of measurements at different isothermal plate temperatures. The numerical predictions clarify the link between the change in the heat transfer quantities and the changes in the flow field due to endwall contouring. Finally numerically predicted heat transfer data are deducted from a set of adiabatic and diabatic simulations that are compared to the experimental data. The comparison focuses on the differences in the regions with endwall contouring, where a significant difference in the heat transfer coefficient between flat and contoured endwalls is measured, but under-predicted numerically.

High Resolution Heat Transfer Measurement on Flat and Contoured Endwalls in a Linear Cascade

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Benoit Laveau ◽  
Reza S. Abhari ◽  
Michael E. Crawford ◽  
Ewald Lutum
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Transfer Coefficient ◽  
High Resolution ◽  
Transfer Coefficient ◽  
Gas Turbines ◽  
Transfer Data ◽  
Numerical Predictions ◽  
Endwall Contouring ◽  
The Heat Transfer Coefficient

In order to continue increasing the efficiency of gas turbines, a significant effort is being made to reduce losses induced by secondary flows in turbine stages. In addition to their impact on aerodynamic losses, these vortical structures are also the source of large heat transfer variations across the passage. A substantial reduction of the secondary flow losses can be achieved with a contoured endwall. However, a change in the vortical pattern can dramatically impact the thermal loads on the endwalls and lead to higher cooling requirements in those areas. This paper focuses on heat transfer measurements made in a passage with either flat or contoured endwalls. The experimental data are supplemented with numerical predictions of the heat transfer data. The measurements are carried out on an isothermal endwall equipped with symmetric airfoils. The paper presents measurements at M = 0.3, corresponding to a Reynolds number ReCax=4.6×105. An infrared camera is used to provide high-resolution surface temperature data on the endwall. The surface is equipped with an insulating layer (Kapton), allowing the calculation of heat flux through the endwall. The heat transfer quantities, namely the heat transfer coefficient and the adiabatic wall temperature, are then derived from a set of measurements at different isothermal plate temperatures. The numerical predictions clarify the link between the change in the heat transfer quantities and the changes in the flow field due to endwall contouring. Finally, numerically predicted heat transfer data are deduced from a set of adiabatic and diabatic simulations that are compared to the experimental data. The comparison focuses on the differences in the regions with endwall contouring, where a significant difference in the heat transfer coefficient between flat and contoured endwalls is measured but underpredicted numerically.

scholarly journals Improvement air condensers evaluation model

2018 ◽  
Vol 194 ◽  
pp. 01017
Author(s):  
Svyatoslav Tsibulskiy ◽  
Nikolay Galashov ◽  
Denis Mel'nikov ◽  
Alexandr Kiselev ◽  
Al'bina Bannova
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Evaluation Model ◽  
Finned Tubes ◽  
Advantages And Disadvantages ◽  
Methods Of Calculation ◽  
Air Condenser ◽  
The Heat Transfer Coefficient

The results of analysis of the literature on the calculation of the heat transfer coefficient of an air condenser in the flow past a bundle of finned tubes by an air flow. The methods of calculation are disassembled, marked advantages and disadvantages of each. Calculations of the heat transfer coefficient for each method are given; the results compared with the experimental data.

scholarly journals Model of R134a Liquid–Vapor Two-Phase Heat Transfer Coefficient for Pulsating Flow Boiling in an Evaporator Using Response Surface Methodology

Energies ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3540
Author(s):  
Peng Yang ◽  
Ting Zhang ◽  
Yuheng Zhang ◽  
Sophie Wang ◽  
Yingwen Liu
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Pulsating Flow ◽  
Two Phase ◽  
Modification Factor ◽  
The Heat Transfer Coefficient ◽  
Liquid Vapor

The present study proposes a model to predict the heat transfer coefficient in R134a liquid–vapor two-phase pulsating flow boiling in an evaporator using the experimental data and response surface methodology (RSM). The model is based on the current existing empirical correlation for R134a liquid–vapor two-phase continuous flow with an imposed modification factor. The model for the imposed modification factor is the function of the pulsating period and inlet/outlet vapor quality, which is obtained using the limited experimental data. An analysis of variance (ANOVA) is carried out to test the significance of the model and normal probability of residuals is analyzed as well. Results show that the regression model produces a mean error of −4.3% and a standard deviation of 15.4%, compared to experimental results. Of the data 95.1% is contained inside a ±50% error window, which indicates that the proposed model could predict the heat transfer coefficient of R134a liquid–vapor two-phase pulsating flow boiling well.

Condensation of Freon-114 in the Presence of a Strong Nonuniform, Alternating Electric Field

1970 ◽  
Vol 92 (4) ◽  
pp. 616-620 ◽  
Author(s):  
R. E. Holmes ◽  
A. J. Chapman
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Transfer Coefficient ◽  
Electric Field ◽  
Transfer Coefficient ◽  
Flat Plate ◽  
Transfer Rate ◽  
Reasonable Agreement ◽  
Alternating Electric Field ◽  
The Heat Transfer Coefficient

The condensation of Freon-114 in the presence of a nonuniform, alternating, 60-cycle, electric field was examined experimentally. The condensing surface was a grounded, cooled flat plate, and the electric field was produced by applying a voltage to a second plate placed above the first. Voltages up to 60 kv were imposed, and nonuniformities in the field were created by varying the angle between the plates. Analytical predictions were made of the expected heat-transfer rate, and reasonable agreement with the experimental data was obtained for voltages less than 40 kv. Above 40 kv the results were unpredictable, but increases in the heat-transfer coefficient as high as ten times that for no field were obtained.

Numerical Analysis of the Sludge Drying Behaviors with Bottom Periodic Heating

2012 ◽  
Vol 518-523 ◽  
pp. 1761-1766
Author(s):  
Zhi Gen Wu ◽  
Peng Yi Cui ◽  
Wen Quan Tao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mixing Time ◽  
Hot Water ◽  
Drying Process ◽  
Periodic Heating ◽  
Sludge Drying ◽  
The Cost ◽  
The Heat Transfer Coefficient

The drying of sludge can reduce its mass and the volume and consequently the cost of storage, handling and transport. In this paper, a one-dimensional model is established for the sludge drying process and hot water from the solar energy is applied as a discontinuous heat source (periodic heating). Based on the simplified physical model, the thermal behavior of the sludge drying process is investigated by numerical method. The effects of the sludge depth, mixing time and heat transfer coefficient are analyzed. The simulation results show that the most important effecting factor is the mixing time. One hour mixing cycle can increase heat transfer rate to 430%, 130% than that of without mixing and two hours mixing cycle, respectively. On the other side, both the sludge thickness and the heat transfer coefficient have some effects. For the cases studied the 40cm thick sludge with 1 hour mixing time is an optimal option.

At Nucleate Boiling Heat Transfer Zeotropic Mixtures A Horizontal Tubes

2016 ◽  
Vol 11 (3) ◽  
pp. 46-52
Author(s):  
Nadezhda Mezentseva ◽  
Ivan Mezentsev ◽  
Valentin Mukhin
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Diffusion Processes ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Horizontal Tubes ◽  
Nucleate Boiling Heat Transfer ◽  
The Heat Transfer Coefficient

Despite numerous empirical relationships, currently there is no sufficiently reliable and physically reasonable methodology for calculating the heat transfer coefficient at boiling the zeotropic binary blends. The main reason is the complexity of the boiling process mechanism. Zeotropic blends have the non-isothermal phase transition or the temperature glide. To perform the analysis, the results of experimental work on boiling the zeotropic blends inside the horizontal smooth tubes were processed. The studies were carried out with the horizontal smooth steel and copper tubes; the mass velocities were varied within 50–583 kg/m2 s; the specific heat flux was varied from 1 to 45 kW/m2 . The experimental data, corresponding to the region of nucleate boiling, were compared with the calculated dependencies. The dependences corresponding to pool boiling were also analyzed. It was proposed to determine the heat transfer coefficient by Gogonin’s dependence (2006); this coincides well with the experimental data. This dependence takes into account the effect of wall thermal properties and its roughness on heat transfer. Moreover, it was found out that, in contrast to pool boiling, for the forced vapor-liquid flow in pipes at nucleate boiling, the diffusion processes are not important.

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