scholarly journals Specific Features of Calculating the Radiant Component of the Heat Flow of Horizontal Bunch from Finned Tubes with Exhaust Shaft

2020 ◽  
Vol 63 (4) ◽  
pp. 380-388
Author(s):  
A. B. Sukhotski ◽  
G. S. Marshalova ◽  
Е. S. Danil’chik
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Heat Flow ◽  
Engineering Practice ◽  
Angular Coefficient ◽  
Radiant Heat Transfer ◽  
Zonal Method ◽  
Single Row ◽  
Finned Tubes ◽  
Wide Range

The article discusses the heat exchange of radiation of bunches of round finned tubes with the environment and the exhaust shaft. The system of equations describing the entire set of primary processes that make up the radiation heat exchange of finned bundles is very complex mathematically; therefore, the calculations of radiant heat transfer are usually based on a number of simplifying assumptions with a involuntarily distortion of the real physical picture. The main methods for calculating radiation used in engineering practice, viz. calculation by the average angular coefficient and the zonal method are briefly considered. A refined zonal method for calculating the radiant component of the heat flow of a horizontal bunch of finned tubes with an exhaust shaft is proposed. An experimental study of single-row bunches of finned tubes with different annular steps S1 (64 and 70 mm) was carried out for small Reynolds numbers Re = 130–720 in a wide range of the determining temperature at the beam inlet (16–83 °C). The aluminum finning of the bunch tube had the following parameters: screw finning diameter d = 0.0568 m; diameter of the tube at the base d0 = 0.0264 m; height, step and average fin thickness, respectively, h = 0.0152 m, s = 0.00243 m and Δ = 0.00055 m. Air movement in the bunch was carried out by gravitational traction created by a rectangular exhaust shaft. The experimental bunch was installed above the shaft, and the air was preheated before entering the shaft, which allowed expanding the temperature range of the air at the entrance to the bunch. It was found that incorrect accounting for a bunch reemission with an exhaust shaft when calculating single-row finned bunches causes a decrease in convective heat transfer by 7–25 %.

Tube Banks Heat Transfer Enhancement Using Conical Fins

2010 ◽  
Author(s):  
Ignacio Carvajal-Mariscal ◽  
Florencio Sanchez-Silva ◽  
Georgiy Polupan
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Pressure Drop ◽  
Finned Tube ◽  
Hot Water ◽  
Experimental Results ◽  
Tube Bank ◽  
Finned Tubes ◽  
Tube Banks ◽  
Annular Fins

In this work the heat transfer and pressure drop experimental results obtained in a two step finned tube bank with conical fins are presented. The tube bank had an equilateral triangle array composed of nine finned tubes with conical fins inclined 45 degrees in respect with the tube axis. The heat exchange external area of a single tube is approximately 0.07 m2. All necessary thermal parameters, inlet/outlet temperatures, mass flows, for the heat balance in the tube bank were determined for different air velocities, Re = 3400–18400, and one constant thermal charge provided by a hot water flow with a temperature of 80 °C. As a result, the correlations for the heat transfer and pressure drop calculation were obtained. The experimental results were compared against the analytical results for a tube bank with annular fins with the same heat exchange area. It was found that the proposed tube bank using finned tubes with conical fins shows an increment of heat transfer up to 58%.

scholarly journals Heat Exchange Modeling in Cooling Fins

2020 ◽  
pp. 669-676
Author(s):  
Evgeniy N. Vasil'ev
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchange ◽  
Transfer Coefficient ◽  
Heat Conduction Problem ◽  
Rectangular Cross Section ◽  
One Dimensional ◽  
Wide Range ◽  
Simulation Results ◽  
The Heat Transfer Coefficient

The article discusses the process of heat exchange of a finned wall with a coolant. The temperature field in the wall volume was determined on the basis of a numerical solution of the two-dimensional heat conduction problem, and the analysis of the characteristics of temperature distributions was carried out according to the simulation results. The values of the heat transfer coefficient of cooling fins with rectangular cross section were calculated for two variants of heat transfer conditions at the end of the fins in a wide range of dimensionless parameters. The error in calculating the heat transfer coefficient in the approximation of a thin fin was determined by means of a one-dimensional computational model

scholarly journals The Namib Turbulence Experiment: Investigating surface-atmosphere heat transfer in three dimensions

2021 ◽  
Keyword(s):  
Heat Transfer ◽  
Surface Layer ◽  
Temperature Field ◽  
Heat Exchange ◽  
High Resolution ◽  
Three Dimensional ◽  
Temperature Fluctuations ◽  
Near Surface ◽  
Turbulent Heat Exchange ◽  
Wide Range

Abstract The Namib Turbulence EXperiment (NamTEX) was a multi-national micrometeorological campaign conducted in the Central Namib Desert to investigate three-dimensional surface layer turbulence and the spatio-temporal patterns of heat transfer between the sub-surface, surface, and atmosphere. The Namib provides an ideal location for fundamental research that revisits some key assumptions in micrometeorology that are implicitly included in the parameterizations describing energy exchange in weather forecasting and climate models: Homogenous flat surfaces, no vegetation, little moisture, and cloud-free skies create a strong and consistent diurnal forcing, resulting in a wide range of atmospheric stabilities. A novel combination of instruments was used to simultaneously measure variables and processes relevant to heat transfer: A three km fibre-optic distributed temperature sensor (DTS) was suspended in a pseudo-three-dimensional array within a 300 m x 300 m domain to provide vertical cross-sections of air temperature fluctuations. Aerial and ground-based thermal imagers recorded high resolution surface temperature fluctuations within the domain and revealed the spatial thermal imprint of atmospheric structures responsible for heat exchange. High-resolution soil temperature and moisture profiles together with heat flux plates provided information on near-surface soil dynamics. Turbulent heat exchange was measured with a vertical array of five eddy-covariance point measurements on a 21-m mast, as well as by co-located small- and large-aperture scintillometers. This contribution first details the scientific goals and experimental set-up of the NamTEX campaign. Then using a typical day, we demonstrate i) the coupling of surface layer, surface, and soil temperatures using high-frequency temperature measurements, ii) differences in spatial and temporal standard deviations of the horizontal temperature field using spatially distributed measurements, and iii) horizontal anisotropy of the turbulent temperature field.

scholarly journals DETERMINING OF PARAMETERS OF HEAT EXCHANGE FOR VAPORIZATION OF THE MIXED REFRIGERANT ON THE HIGH THERMAL CONDUCTIVITY SINTERED POWDER CAPILLARY-POROUS COATINGS

2018 ◽  
Vol 61 (1) ◽  
pp. 70-79 ◽  
Author(s):  
A. V. Ovsyannik ◽  
E. N. Makeeva
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Exchange ◽  
Experimental Studies ◽  
Nucleate Boiling ◽  
High Thermal Conductivity ◽  
Porous Coating ◽  
Transfer Coefficients ◽  
Porous Coatings ◽  
Wide Range

The results of experimental research of heat exchange under the nucleate boiling of refrigerants R404a, R407c and R410a on the tubes with capillary-porous coating are presented. Experimental studies were carried out with the aid of an experimental installation in conditions of a large volume at pressures of saturation pн = 0.9–1.4 MPa and densities of the heat flux q = 5–35 kW/m2. For the first time the criterion equation for the calculation of the intensity of heat transfer during evaporation of ozone safe refrigerants on surfaces with high thermal conductivity sintered capillary-porous coating was obtained. Experimental data are summarized satisfactorily in a wide range of parameters of the porous layer, i.e. the pressure (pн = 0.9–1.4 MPa) and heat loads (q = 5–35 kW/m2). The ratio makes us possible to calculate the heat transfer coefficients within ±20 %. The dependence can be used in engineering calculations of the characteristics of the heat exchangers of the evaporative type. The coefficient of heat transfer during boiling of refrigerants on the investigated surfaces with the sintered capillary-porous coating, 4 times higher than on a smooth one and 1.5 times higher than on the finned surface, that allows us to come to a conclusion about the advantage of porous coatings. Boiling in capillary-porous coating leads to a decrease in weight and size of the installations due to the heat exchange intensification and the size of the tubes smaller as compared to the size of the finned ones.

Based on the Matrix of Silicon Nanocrystals a Modeling Study of Thermo-hydraulic Properties of Micro-channel Heat Transfer Elements

2021 ◽  
Vol 19 (3) ◽  
pp. 38-45
Author(s):  
Forat H. Alsultany ◽  
Qasim S. Kadhim
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Thermal Stabilization ◽  
Specific Power ◽  
Heat Sources ◽  
Ambient Temperatures ◽  
Pressure Losses ◽  
Geometric Configurations ◽  
Wide Range ◽  
The Matrix

The construction of a heat exchange element based on a matrix of silicon whiskers for thermal stabilization systems of miniature heat sources with specific power up to 100 W/cm2 operating over a wide range of ambient temperatures is proposed. Based on the developed mathematical model of convective heat transfer in a microchannel compact heat exchanger with a developed heat exchange surface, numerical simulation of the hydrodynamics and heat transfer processes for various configurations of microchannel insertions was carried out. Fields of pressures, flow velocities, coolant temperatures and matrix from silicon single crystals have been obtained in a wide range of coolant flow rates, criteria dependencies for the Nusselt number and pressure losses of various geometric configurations of heat exchangers have been determined. Critical operation modes are investigated; optimization directions are proposed. According to the developed technology, prototypes for testing have been manufactured.

Heat transfer

2019 ◽  
Author(s):  
Владимир Чередниченко ◽  
Vladimir Cherednichenko ◽  
Валерий Синицын ◽  
Valeriy Sinicyn ◽  
Александр Алиферов ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Physical Interpretation ◽  
Electrical Engineering ◽  
Thermal Power ◽  
Radiant Heat ◽  
Radiant Heat Transfer ◽  
Main Attention ◽  
Methods Of Calculation ◽  
Wide Range

The basic provisions of the theory of heat transfer, including thermal conductivity, convective and radiant heat transfer. The information about the methods of calculation of heat transfer in power engineering, electrical engineering, electromechanics and electrical engineering is given. The first edition was published in 2004, the Material of the second edition in part updated and supplemented, the main attention is paid to the physical interpretation of the issues involved. The manual can be useful for students of thermal power, Electromechanical, electrotechnological and engineering specialties, as well as a wide range of engineering and technical workers.

scholarly journals Convective Heat Exchange of Single-Row Bundles from Tubes with Rolled Aluminum Fins of Various Height at a Low Values of the Reynolds Number

2021 ◽  
Vol 64 (4) ◽  
pp. 336-348
Author(s):  
A. B. Sukhotski ◽  
Е. S. Danil’chik
Keyword(s):  
Heat Transfer ◽  
Tube Bundle ◽  
Thermal Studies ◽  
Reynolds Numbers ◽  
Bearing Steel ◽  
Steel Tube ◽  
Outer Diameter ◽  
Cross Sectional ◽  
Single Row ◽  
Finned Tubes

The experimental study of the heat flow intensity of a single-row horizontal air-cooled tubular bundle of heat exchanger with spiral aluminum rolling fins at low Reynolds numbers (Re < 2000) is performed. The geometrical dimensions of the bimetallic finned tubes of the bundle, the following: the outer diameter of the fins d = 56.0 mm; the diameter of the tube at the base d0 = 26.8 mm; fin height h = 14.6 mm; pitch of fins s = 2.5 mm; the average fin thickness Δ = 0.5 mm; the coefficient of finned tubes φ = 19.3; heat transfer length l = 300 mm. The outer diameter of the load-bearing steel tube dн  = 25 mm; wall thickness d = 2 mm. The research was carried out by the method of full thermal modeling at a specially designed experimental stand with electric heating of tubes and an exhaust shaft installed above the bundle. The air flow rate through the bundle was regulated by changing the height and cross-sectional area of the exhaust shaft. Calibration experiments were carried out and confirmed the reliability of the data obtained. Then the fins were sanded so to form new types of tubes, which were arranged in a single-row six-tube bundle with a constant relative cross-step σ1 = S1/d = 1.14 = const, and the thermal studies were repeated. As a result, a generalized criterion equation for heat transfer of a finned horizontal single-row bundle at small Reynolds numbers for various heights of the tube finning h = 0-14.6 mm was obtained. The effective height of the tube finning (h = 8 mm) for a single-row horizontal bundle was determined by dimensional and metal-intensive criteria.

Reflective insulation assemblies for above-ceiling applications

2020 ◽  
Vol 44 (3) ◽  
pp. 272-283
Author(s):  
Kah Wei Yam ◽  
Khar San Teh ◽  
Patrick Loi ◽  
David W Yarbrough
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Flow ◽  
Transfer Coefficient ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Overall Heat Transfer Coefficient ◽  
Wide Range ◽  
Air Space ◽  
Flow Directions

Previously published hot-box data have been used to construct equations for the thermal resistance of enclosed reflective air spaces (reflective insulation assemblies) for a wide range of temperatures, air gap dimensions, thermal emittances, and heat flow directions. The thermal resistances or R-values (RSI) calculated with the equations compare favorably with previously published thermal resistances. Significant differences from RSI values (m2 K/W) calculated using ISO 6946 were observed. Equations for calculating heat transfer coefficients for conduction–convection with constants for the heat flow directions up, 45° up, horizontal, 45° down, and down are contained in this article. The conduction–convection coefficient for planar air spaces oriented at any angle and heated above can be obtained by interpolation between heat flow down and heat flow at a downward angle of 45° or heat flow down at an angle of 45° and horizontal heat flow. The overall heat transfer coefficient is obtained by adding the thermal radiation contribution to the conduction–convection contribution. The RSI of enclosed reflective air spaces is the reciprocal of the overall heat transfer coefficient for the air space. This air space RSI is especially useful as input for the calculation of U-values for ceiling–roof assemblies located in hot climates.

A New Method for Direct Exchange Area Calculation in Zonal Method of Radiant Heat Transfer Modeling in Combustion Furnaces

2014 ◽  
Author(s):  
G. Malikov ◽  
V. Lisienko ◽  
A. Titaev ◽  
R. Viskanta
Keyword(s):  
Heat Transfer ◽  
Radiation Heat Transfer ◽  
Radiant Heat ◽  
New Method ◽  
Computational Time ◽  
Test Case ◽  
Radiant Heat Transfer ◽  
Zonal Method ◽  
Direct Exchange ◽  
Exchange Area

A new method based on the discrete transfer modeling technique for calculating the direct exchange areas (DEA) in zonal methods of radiation heat transfer is presented. The key feature of this method is a fast DEA matrix evaluation. The computational time was found to be short in comparison to other methods for direct exchange areas calculation based on numerical quadrature integration. The accuracy of the procedure is assessed by comparing the predictions with those based on the numerical integration for a test case (IFRF furnace).

Thermal Hydraulic Study of a Single Row Heat Exchanger With Helically Finned Tubes

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
H. Huisseune ◽  
C. T’Joen ◽  
P. Brodeoux ◽  
S. Debaets ◽  
M. De Paepe
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Data Reduction ◽  
Mean Deviation ◽  
Heat Transfer Correlation ◽  
Test Rig ◽  
Reduction Procedure ◽  
Single Row ◽  
Finned Tubes ◽  
Tube Pitch

In this study, the heat transfer and friction correlation of a single row heat exchanger with helically finned tubes are experimentally determined. The transversal tube pitch was parametrically varied. A detailed description of the test rig and the data reduction procedure is given. A thorough uncertainty analysis was performed to validate the results. The proposed heat transfer correlation can describe 95% of the data within ±11% and shows a 4.49% mean deviation. The friction correlation predicts 95% of the data within ±19% with a mean deviation of 6.84%. The new correlations show the same trend as most correlations from open literature, but none of the literature correlations are able to accurately predict the results of this study.

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