scholarly journals Improvement of methods for calculating thermal characteristics of loop air heaters

2021 ◽  
Vol 1 (8 (109)) ◽  
pp. 36-43
Author(s):  
Volodymyr Yurko ◽  
Anton Ganzha ◽  
Oleksandra Tarasenko ◽  
Larysa Tiutiunyk
Keyword(s):  
Heat Transfer ◽  
Particle Size ◽  
Dust Particle ◽  
Thermal Characteristics ◽  
Heating Surface ◽  
Environmental Safety ◽  
Operating Conditions ◽  
Thermal Calculation ◽  
Transfer Coefficients ◽  
Air Heater

Utilization of heat from gases leaving the waelz process is a promising way to increase its energy efficiency and environmental safety. Taking into account the gas dustiness, the most rational is the use of a loop air heater, which is a multi-pass and multi-section heat exchanger with a complex mixed scheme of coolant movement. In modern conditions, when the methods and means of calculation of such devices are simplified, the task of obtaining improved methods and means of calculation, determining the efficiency and reliability of their work is relevant. Two mathematical models of the process of heat transfer and hydroaerodynamics in a multi-pass tubular air heater with a cross-circuit of coolants are used. The developed models for the loop air heater are based on the main methods of thermal calculation: a simpler method of correction factor to the average logarithmic temperature pressure and a discrete P-NTU method, which allows obtaining local thermal characteristics of the surface. Diagrams of distribution of heat transfer coefficients, heat transfer, local temperatures of flue gases, air and pipe walls are constructed. The influence of dust and dust particle size on heat transfer is determined. When the flue gas dust is 50 g/Nm3 and with a dust particle size of 1 μm, the heat transfer coefficient increases by 12 %. The application of the air heater design with different schemes of coolant movement is substantiated. The developed universal methods allow determining the thermal productivity of heat exchangers and obtaining the distribution of local temperature characteristics on the heating surface. It is also possible to identify places of possible overheating of the heat exchange surface and the course of corrosion processes, taking into account the design of recuperators, operating conditions, operating modes and different schemes of coolant movement

scholarly journals Heat Transfer in Rotating Serpentine Passages With Trips Normal to the Flow

1992 ◽  
Vol 114 (4) ◽  
pp. 847-857 ◽  
Author(s):  
J. H. Wagner ◽  
B. V. Johnson ◽  
R. A. Graziani ◽  
F. C. Yeh
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Large Scale ◽  
Flow Direction ◽  
Operating Conditions ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Flow Equations ◽  
Turbine Blade Cooling ◽  
Heat Transfer Coefficients

Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large-scale, multipass, heat transfer model with both radially inward and outward flow. Trip strips on the leading and trailing surfaces of the radial coolant passages were used to produce the rough walls. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant-to-wall temperature ratio, Rossby number, Reynolds number, and radius-to-passage hydraulic diameter ratio. The first three of these four parameters were varied over ranges that are typical of advanced gas turbine engine operating conditions. Results were correlated and compared to previous results from stationary and rotating similar models with trip strips. The heat transfer coefficients on surfaces, where the heat transfer increased with rotation and buoyancy, varied by as much as a factor of four. Maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels obtained with the smooth wall model. The heat transfer coefficients on surfaces where the heat transfer decreased with rotation, varied by as much as a factor of three due to rotation and buoyancy. It was concluded that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips and that the effects of rotation were markedly different depending upon the flow direction.

scholarly journals Thermo-Hydraulic Performance of Solar Air Collectors with Artificially Roughened Absorbers: A Comparative Review of Semi-Empirical Models

Energies ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3536 ◽  
Author(s):  
António Araújo
Keyword(s):  
Heat Transfer ◽  
Thermal Characteristics ◽  
Operating Conditions ◽  
Roughness Parameters ◽  
Energy Characteristics ◽  
Effective Roughness ◽  
Air Stream ◽  
Comparative Review ◽  
Efficiency And Effectiveness ◽  
Semi Empirical

Due to the poor thermal characteristics of the air, the absorber roughness of solar air collectors is commonly artificially increased in order to enhance the heat transfer to the air stream. However, this is also accompanied by an undesirable increase in the pumping power due to increased friction losses. As a result, several authors have experimentally investigated several ways of maximizing the heat transfer while minimizing the friction losses of different absorbers, resulting in the development of semi-empirical functions relating the Nusselt number (a measure of heat transfer) and the friction factor (a measure of friction losses) to the Reynolds number and the roughness parameters considered for each absorber. The present paper reviews, considering the publications from the last ten years, these semi-empirical functions. Moreover, the optimum roughness parameters and operating conditions of the absorbers were estimated by finding the maximum values of two performance parameters (the thermo-hydraulic efficiency and effectiveness), calculated using the semi-empirical functions, in order to classify the absorbers in terms of their energy characteristics. This approach proves to be a rather effective way of optimizing the roughness characteristics of solar air collector absorbers. It is also concluded that, considering the range of absorbers analyzed here, generally, multiple V-shaped ribs with gaps provide the most effective roughness geometry.

Spatial and Temporal Wall Temperature Fluctuations in Two-Phase Flow in Microgap Coolers

2010 ◽  
Author(s):  
Jessica Sheehan ◽  
Avram Bar-Cohen
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Volumetric Cooling ◽  
Very High

Heat transfer to an evaporating refrigerant and/or dielectric liquid in a microgap channel can provide very high heat transfer coefficients and volumetric cooling rates. Recent studies at Maryland have established the dominance of the annular flow regime in such microgap channels and related the observed high-quality peak of an M-shaped heat transfer coefficient curve to the onset of local dryout. The present study utilizes infrared thermography to locate such nascent dryout regions and operating conditions. Data obtained with a 210 micron microgap channel, operated with a mass flux of 195.2 kg/m2-s and heat fluxes of 10.3 to 26 W/cm2 are presented and discussed.

Thermal Anisotropy in Injection Molded Polymer Composite Fins

2010 ◽  
Author(s):  
Avram Bar-Cohen ◽  
Patrick Luckow ◽  
Juan G. Cevallos ◽  
S. K. Gupta
Keyword(s):  
Heat Transfer ◽  
Polymer Composite ◽  
Thermal Characteristics ◽  
Axial Direction ◽  
Transfer Coefficients ◽  
Thermal Anisotropy ◽  
Modeling Methodology ◽  
Numerical Predictions ◽  
Injection Molded ◽  
Global And Local

An integrated molding-heat transfer modeling methodology is used to study the thermal characteristics of polymer composite fins subjected to convective heat transfer coefficients. Numerical predictions of the fiber orientation in a representative, injection-molded plate fin, based on the Folgar-Tucker model, are used, via the classic Nielsen model, to determine the anisotropic variation of thermal conductivity in the fin. Thermal simulations are then performed to determine the effect of both global and local thermal anisotropy on the temperature distribution and heat transfer rate of the anisotropic fin. It is also shown that the harmonic mean conductivity, in the axial direction, can be used to represent the heat loss of an anisotropic fin to better than 10% accuracy.

scholarly journals Heat Transfer in Rotating Serpentine Passages With Trips Normal to the Flow

1991 ◽  
Author(s):  
J. H. Wagner ◽  
B. V. Johnson ◽  
R. A. Graziani ◽  
F. C. Yeh
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Large Scale ◽  
Flow Direction ◽  
Operating Conditions ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Flow Equations ◽  
Turbine Blade Cooling ◽  
Heat Transfer Coefficients

Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large scale, multi–pass, heat transfer model with both radially inward and outward flow. Trip strips on the leading and trailing surfaces of the radial coolant passages were used to produce the rough walls. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant–to–wall temperature ratio, Rossby number, Reynolds number and radius–to–passage hydraulic diameter ratio. The first three of these four parameters were varied over ranges which are typical of advanced gas turbine engine operating conditions. Results were correlated and compared to previous results from stationary and rotating similar models with trip strips. The heat transfer coefficients on surfaces, where the heat transfer increased with rotation and buoyancy, varied by as much as a factor of four. Maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels obtained with the smooth wall model. The heat transfer coefficients on surfaces, where the heat transfer decreased with rotation, varied by as much as a factor of three due to rotation and buoyancy. It was concluded that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips and that the effects of rotation were markedly different depending upon the flow direction.

scholarly journals Heat Transfer in Rotating Serpentine Passages With Trips Skewed to the Flow

1994 ◽  
Vol 116 (1) ◽  
pp. 113-123 ◽  
Author(s):  
B. V. Johnson ◽  
J. H. Wagner ◽  
G. D. Steuber ◽  
F. C. Yeh
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Large Scale ◽  
Flow Direction ◽  
Operating Conditions ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Flow Equations ◽  
Turbine Blade Cooling ◽  
Heat Transfer Coefficients

Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large-scale, multipass, heat transfer model with both radially inward and outward flow. Trip strips, skewed at 45 deg to the flow direction, were machined on the leading and trailing surfaces of the radial coolant passages. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant-to-wall temperature ratio, rotation number, Reynolds number, and radius-to-passage hydraulic diameter ratio. The first three of these four parameters were varied over ranges that are typical of advanced gas turbine engine operating conditions. Results were correlated and compared to previous results from similar stationary and rotating models with smooth walls and with trip strips normal to the flow direction. The heat transfer coefficients on surfaces, where the heat transfer decreased with rotation and buoyancy, decreased to as low as 40 percent of the value without rotation. However, the maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels previously obtained with the smooth wall model. It was concluded that (1) both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips, (2) the effects of rotation are markedly different depending upon the flow direction, and (3) the heat transfer with skewed trip strips is less sensitive to buoyancy than the heat transfer in models with either smooth walls or normal trips. Therefore, skewed trip strips rather than normal trip strips are recommended and geometry-specific tests will be required for accurate design information.

The heat transfer coefficients of the heating surface of 300 MWe CFB boiler

2012 ◽  
Vol 21 (4) ◽  
pp. 368-376 ◽  
Author(s):  
Haibo Wu ◽  
Man Zhang ◽  
Qinggang Lu ◽  
Yunkai Sun
Keyword(s):  
Heat Transfer ◽  
Heating Surface ◽  
Transfer Coefficients ◽  
Cfb Boiler ◽  
Heat Transfer Coefficients

Transient Forced Convection Heat Transfer to Helium During a Step in Heat Flux

1983 ◽  
Vol 105 (2) ◽  
pp. 350-357 ◽  
Author(s):  
P. J. Giarratano ◽  
W. G. Steward
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Forced Convection ◽  
Carbon Film ◽  
Convection Heat Transfer ◽  
Fast Response ◽  
Operating Conditions ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Forced Convection Heat Transfer

Transient forced convection heat transfer coefficients for both subcritical and supercritical helium in a rectangular flow channel heated on one side were measured during the application of a step in heat flux. Zero flow data were also obtained. The heater surface which served simultaneously as a thermometer was a fast response carbon film. Operating conditions covered the following range: Pressure, 1.0 × 105 Pa (1 bar) to 1.0 × 106 Pa (10 bar); Temperature, 4 K–10 K; Heat Flux, 0.1 W/cm2−10 W/cm2; Reynolds number, 0–8 × 105. The experimental data and a predictive correlation are presented.

Local Heat Transfer Coefficients around Horizontal Tubes in Fluidized Beds

1980 ◽  
Vol 102 (1) ◽  
pp. 152-157 ◽  
Author(s):  
R. Chandran ◽  
J. C. Chen ◽  
F. W. Staub
Keyword(s):  
Heat Transfer ◽  
Particle Size ◽  
Fluidized Beds ◽  
Local Heat Transfer ◽  
Local Heat ◽  
General Tendency ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes ◽  
System Pressure

The local characteristics of heat transfer from horizontal tubes immersed in fluidized beds were investigated experimentally. Steady-state heat transfer measurements were obtained in air-fluidized beds of glass beads, both for a single tube and a ten-row bare tube bundle. The test results indicated that local heat transfer coefficients are strongly influenced by angular position and gas flow rate, as well as by particle size and system pressure. The heat transfer coefficients, averaged around the circumference of the tube, exhibited a general tendency to increase with decreasing particle size and increasing system pressure. The heat transfer coefficients for a tube in an inner-row position within the bundle were found to be slightly higher than those for a tube in the bottom-row. Comparison of the average heat transfer coefficient data obtained in this study with some of the existing correlations for heat transfer from horizontal tubes showed that the correlations are unsatisfactory.

Design Optimization of Convective Heat Transfer Surface of Pressurized Oxy-Fuel Coal-Fired Boiler

2012 ◽  
Vol 614-615 ◽  
pp. 20-24
Author(s):  
Kai Ma ◽  
Wei Ping Yan ◽  
Fei Jin ◽  
Hai Xin Li
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Flue Gas ◽  
Convective Heat Transfer Coefficient ◽  
Heating Surface ◽  
Fuel Combustion ◽  
Thermal Calculation ◽  
Heat Output ◽  
Atmospheric Air

Based on the thermal calculation, the paper makes a contrastive analysis on the parameters of flue gas, and convection heat properties of the coal-fired boiler under atmospheric air combustion, atmospheric oxy-fuel combustion and pressurized (6MPa) oxy-fuel combustion conditions. It takes a 300MW pressurized(6MPa) oxy-fuel combustion boiler as research object, the result indicates that: compared to the coal-fired boiler atmospheric air combustion, the flue gas volume flow in the pressurized oxy-fuel combustion has a decrease of 98.79%; convective heat output has a decrease of 24.69% with the same difference in temperature. In the pressurized oxy-fuel combustion, both the flue gas convective heat transfer coefficient and the pressure drop are greater than the atmospheric oxy-fuel combustion, flue cross-sectional area is smaller than conventional boiler, and heating surface area is less than atmospheric oxy-fuel combustion. With a method named dynamic minimization of costs the best flue gas velocity in this paper is 1.07m/s

Sign in / Sign up

Export Citation Format

Share Document