scholarly journals Heat-Up Performance of Catalyst Carriers—A Parameter Study and Thermodynamic Analysis

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 964
Author(s):  
Thomas Steiner ◽  
Daniel Neurauter ◽  
Peer Moewius ◽  
Christoph Pfeifer ◽  
Verena Schallhart ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Surface Area ◽  
Internal Surface ◽  
Installation Space ◽  
Parameter Study ◽  
Thin Wall ◽  
Primary Role ◽  
Internal Surface Area

This study investigates geometric parameters of commercially available or recently published models of catalyst substrates for passenger vehicles and provides a numerical evaluation of their influence on heat-up behavior. Parameters considered to have a significant impact on the thermal economy of a monolith are: internal surface area, heat transfer coefficient, and mass of the converter, as well as its heat capacity. During simulation experiments, it could be determined that the primary role is played by the mass of the monolith and its internal surface area, while the heat transfer coefficient only has a secondary role. Furthermore, an optimization loop was implemented, whereby the internal surface area of a commonly used substrate was chosen as a reference. The lengths of the thin wall and high cell density monoliths investigated were adapted consecutively to obtain the reference internal surface area. The results obtained by this optimization process contribute to improving the heat-up performance while simultaneously reducing the valuable installation space required.

A General Approach to Analysis of Flow and Heat Transfer in Packed Beds

2008 ◽  
Author(s):  
Aleksander Vadnjal ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Surface Area ◽  
Hydraulic Diameter ◽  
Experimental Results ◽  
Transfer Coefficients ◽  
Internal Surface Area ◽  
The Media

It is postulated that proper scaling will collapse the multiplicity of data for friction and heat transfer coefficient to a usable reasonably general formulation by choosing the hydraulic diameter as Dh=4·〈m〉Sw where <m> is the average porosity and Sw is the surface area per unit volume. The chosen hydraulic diameter allows the transformation and comparison of correlation equations and experimental results obtained for diverse media morphologies. Also, it allows experimentally-determined characteristics of the media to be related to the closure relationship derived from the VAT analysis. The numerical results of closure are presented and are compared to various experimental results. The Nusselt number is based on the media internal local surface average transfer coefficient and the friction factor is the local internal value. Results obtained by VAT closure using direct numerical simulation show reasonable agreement between calculated local friction factors and local heat transfer coefficients and data confirming that the friction factor and heat transfer coefficient when correctly scaled can be computed numerically with satisfactory results. This conclusion will enable one to optimize the effectiveness of a compact heat exchanger in terms of porosity and internal surface area.

scholarly journals Experimental Determination of the Heat Transfer Coefficient of Real Cooled Geometry Using Linear Regression Method

Energies ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 180
Author(s):  
Asif Ali ◽  
Lorenzo Cocchi ◽  
Alessio Picchi ◽  
Bruno Facchini
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Linear Regression ◽  
Surface Temperature ◽  
Transfer Coefficient ◽  
External Surface ◽  
Internal Surface ◽  
Regression Method ◽  
Thermal Transient

The scope of this work was to develop a technique based on the regression method and apply it on a real cooled geometry for measuring its internal heat transfer distribution. The proposed methodology is based upon an already available literature approach. For implementation of the methodology, the geometry is initially heated to a known steady temperature, followed by thermal transient, induced by injection of ambient air to its internal cooling system. During the thermal transient, external surface temperature of the geometry is recorded with the help of infrared camera. Then, a numerical procedure based upon a series of transient finite element analyses of the geometry is applied by using the obtained experimental data. The total test duration is divided into time steps, during which the heat flux on the internal surface is iteratively updated to target the measured external surface temperature. The final procured heat flux and internal surface temperature data of each time step is used to find the convective heat transfer coefficient via linear regression. This methodology is successfully implemented on three geometries: a circular duct, a blade with U-bend internal channel, and a cooled high pressure vane of real engine, with the help of a test rig developed at the University of Florence, Italy. The results are compared with the ones retrieved with similar approach available in the open literature, and the pros and cons of both methodologies are discussed in detail for each geometry.

Increasing Condenser Capacity Without Adding Tubes to Support a Station Uprate

2010 ◽  
Author(s):  
Warren C. Welch ◽  
Timothy J. Harpster ◽  
Joseph W. Harpster
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Surface Area ◽  
Low Cost ◽  
Cooling Water ◽  
Steam Generation ◽  
Before And After ◽  
Generation Capacity ◽  
Almost All

A station uprate provides an economical opportunity to improve the generation capacity of a power plant if all the major system components are able to handle the effects of increased generation. The magnitude of uprate from increased steam generation will be limited by the maximum capacity of the weakest link in the cycle, which for many plants is the condenser. The condensers on many units are already pushed to their limit. This is especially true if a cooling tower is employed, where the condenser inlet cooling water temperatures are high on high wet-bulb temperature days. This condition forces many units to throttle down load to prevent excursions above the backpressure limits on their turbines. For condensers limited by the present duty, however, the options have been historically limited to rebundling the whole condenser with a larger surface area design and perhaps changing the tube material to a material with a higher heat transfer coefficient. Recently, a very low cost option has been demonstrated that should be considered by any plant looking to increase condenser duty or prevent station power reductions. Advances in the proper management of steam, condensate and noncondensable flows have permitted an upgrade for almost all vintage condensers, unlocking inactive surface area without a bundle replacement or complete redesign. This paper reports the results of a condenser retrofit effort, with emphasis on an upgrade applied to a load limited condenser concurrent with a major reduction in its operating backpressure. The performance of the condenser is presented before and after the upgrade showing significant backpressure reduction and heat transfer improvement accompanied by exceptional condensate chemistry results. It will be shown that 30% of the effective condenser surface area (or similarly, an additional 30% average heat transfer coefficient) was unlocked by activating the previously idle surface area.

scholarly journals Determination of long-term permissible currents in wires of power supply systems of railways

2019 ◽  
Vol 78 (2) ◽  
pp. 90-95 ◽  
Author(s):  
E. P. FIGURNOV ◽  
Yu. I. ZHARKOV ◽  
V. I. KHARCHEVNIKOV
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Solar Radiation ◽  
Transfer Coefficient ◽  
Surface Area ◽  
Meteorological Conditions ◽  
The Body ◽  
Additional Heating ◽  
The Heat Transfer Coefficient

In the standard for contact wires made from copper and its alloys, the values of long-term permissible temperatures have significantly decreased. This requires recalculation of previously valid values of long-term permissible currents. Authors considered revised method for calculating the long-term permissible currents, based on a more rigorous consideration of the laws of heat transfer and experimental studies of the conditions of heating and cooling of shaped (contact) and stranded wires. Technique is based on heat balance conditions, using which the sources of greatest inaccuracies become such quantities as cooled surface area, influence of wind direction, meteorological conditions, laws of change in heat transfer coefficient, effect on additional heating of solar radiation. Deviations when these indicators are taken into account by existing methods can cause errors of 40 % or more. Formulas for calculating the actual outer surface of stranded and shaped wires are given. The inadmissibility of calculating the surface area of the wires by their reference diameter is noted. Updated law of the change in heat transfer coefficient for stranded and shaped wires, as well as the degree of its dependence on wind speed and cooled surface, is given based on a summary of extensive domestic and foreign research. It is shown that with the longitudinal direction of the wind, the reduction of this coefficient occurs to a lesser extent than has been assumed so far. Authors propose method for taking into account an increase in the heat transfer coefficient under meteorological conditions characteristic of ice formation. The heat transfer coefficient of shaped and stranded wires in no case can not be taken as for round pipes with smooth surface. Existing method of accounting for solar radiation, which influences the additional heating of wires, leads to an unjustified and repeated exaggeration of this effect, since previously only the radiation incident on the wire was taken into account in the calculations. According to the laws of heat transfer, the temperature of the irradiated body does not depend on the incident, but on the resulting radiation, defined as the difference between the radiations incident on the body and emitted by it in accordance with its temperature. A formula for accounting for such heat transfer is proposed. The above methodology and calculation formulas allow performing reasonable calculations to determine the long-term permissible currents of individual stranded and shaped wires, as well as the contact network as a whole.

Experimental Study on Local Heat Transfer in a Rotating, Two-Pass Cooling Channel With Dense Array of Turbulence Promoters With Naphthalene Sublimation Method

2014 ◽  
Author(s):  
Tomoko Hagari ◽  
Katsuhiko Ishida ◽  
Kenichiro Takeishi ◽  
Masaharu Komiyama ◽  
Yutaka Oda
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Surface Area ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Cooling Channel ◽  
Overall Heat Transfer Coefficient ◽  
Rib Turbulators

Detailed heat transfer coefficient distributions in a rotating, two-pass, square channel with densely arranged rib turbulators on the leading and trailing walls are investigated. Rib turbulators have been used in a cooling channel of turbine airfoils. The dense arrangement of the ribs is one of the potential candidates to improve heat transfer performance because of its surface area enlargement effect. The ribs are arranged with a rib height to channel hydraulic diameter ratio (e/Dh) of 0.13, angles of attack to the mainstream of 60 and 90deg, and rib pitch-to-height ratios (P/e) of 3, 6 and 10. Both rib and floor surfaces are coated with naphthalene to measure their local mass transfer rate, which is correlated with heat transfer coefficient through heat/mass transfer analogy. Combination of a laser displacement sensor and a precision auto-traverse system enables detailed measurement of local heat transfer distribution on the floor surface between the ribs. Overall heat transfer coefficient including the effect of the rib is obtained by measuring the decrease in weight of the naphthalene test piece. Reynolds number is set at 50,000 and rotation numbers are up to 0.05. The results show that the effect of rotation on local heat transfer behavior depends on the rib spacing and orientation. Compared the overall heat transfer coefficients with the local ones on the floor surface, they showed different trend in some cases. This suggests that variation of rib heat transfer characteristics due to rotation might determine the overall heat transfer coefficient. Such tendency would be stronger for smaller rib spacing because surface area of the rib has large portion of the total heat transfer area. Further investigation on this effect is expected by measuring heat transfer of rib itself under rotating condition.

Theory Study and Numerical Analysis of Ultra-Thin Wall Injection Molding

2012 ◽  
Vol 538-541 ◽  
pp. 1145-1153 ◽  
Author(s):  
Su Feng Yin ◽  
Feng Ruan ◽  
Jian Yu Wang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Injection Molding ◽  
Transfer Coefficient ◽  
Wall Slip ◽  
Viscosity Model ◽  
Thin Wall ◽  
Wall Injection ◽  
Relationship Of ◽  
The Heat Transfer Coefficient

The article focuses on the discussion of size relationship of melt viscosity of ultra-thin wall injection molding, revising the viscosity model of traditional stimulant Cross-WLF. It takes the theory of Uhland wall-slip, trying to analyze the influence which the wall-slip of the molding makes on injection molding. It also points out the limitation of constant heat transfer coefficient in the molding. The change rules of the heat transfer coefficient is among the study. Using the method of numerical simulation and experience, the article verifies the consistency of experience result and the change of the factors, such as using ultra-thin viscosity model, wall-slip and the change of heat transfer coefficient while doing the simulation.

scholarly journals Small Diameter Film Cooling Hole Heat Transfer: The Influence of the Hole Length

1991 ◽  
Author(s):  
G. E. Andrews ◽  
F. Bazdidi-Tehrani ◽  
C. I. Hussain ◽  
J. P. Pearson
Keyword(s):  
Heat Transfer ◽  
Surface Area ◽  
Film Cooling ◽  
Small Diameter ◽  
Internal Surface ◽  
Internal Surface Area ◽  
Metal Thickness ◽  
Data Scatter ◽  
Cooling Hole

The overall surface averaged heat transfer was determined for air passing through arrays of small diameter holes drilled at 90° through thin metal walls. The influence of the wall metal thickness, L, was investigated for a range of hole diameters, D, and pitch, X. L/D was varied from 0.43 to 8.3 using 13 different test geometries. It was found that although the influence of L/D was significant, there was only a ±20% data scatter on a correlation of the results that ignored the influence of L/D for 0.8<L/D<10. The results showed that the heat transfer was dominated by the hole approach flow and this surface area Ax was the appropriate heat transfer area for the determination of the heat transfer coefficient. The dominant parameters that affected the heat transfer were G and X/D. An improved correlation for a range of L/D was achieved if the heat transfer surface area was taken as the sum of Ax and Ah, the hole internal surface area.

Film Condensation of Saturated Vapor Over Horizontal Noncircular Tubes With Progressively Increasing Radius of Curvature Drawn in the Direction of Gravity

2004 ◽  
Vol 126 (6) ◽  
pp. 906-914 ◽  
Author(s):  
Arijit Dutta ◽  
S. K. Som ◽  
P. K. Das
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Surface Area ◽  
Circular Tube ◽  
Saturated Vapor ◽  
Film Condensation ◽  
Radius Of Curvature ◽  
Equivalent Diameter

A theoretical study has been made to determine the heat transfer coefficient in film condensation of slowly downward flowing saturated vapor over horizontal noncircular tubes with progressively increasing radius of curvature drawn in the direction of gravity. The noncircular tube profile considered for the present work, is an equiangular spiral described by a curve in polar coordinate as Rp=aemθ (a and m being parametric constants). Nusselt number in case of noncircular tube has been determined on the basis of an equivalent diameter of a circular tube that equals the surface area of the noncircular tube with that of the circular one. It has been recognized that both the local Nusselt number Nuθ and average Nusselt number Nu¯ become a function of m, Ra/Ja1/4 and Nσ=σ/ρ−ρgR2. An enhancement in heat transfer coefficient has been observed in case of a noncircular tube over that of a circular tube of same surface area because of the combined effect of gravity force component and surface tension driven favourable pressure gradient in the direction of flow of the liquid film. The relative weightage of both the components in the enhancement of heat transfer has been reported. An estimation of pressure drop of cooling liquid flowing through the circular and noncircular tubes of same surface area has been made to compare the values against the enhancement in heat transfer rate.

scholarly journals How Big Is an Error in the Analytical Calculation of Annular Fin Efficiency?

Energies ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1787 ◽  
Author(s):  
Mladen Bošnjaković ◽  
Simon Muhič ◽  
Ante Čikić ◽  
Marija Živić
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchange ◽  
Transfer Coefficient ◽  
Surface Area ◽  
Analytical Calculation ◽  
Base Surface ◽  
Fin Efficiency ◽  
Annular Fin ◽  
Original Definition

An important role in the dimensioning of heat exchange surfaces with an annular fin is the fin efficiency. The fin efficiency is usually calculated using analytical expressions developed in the last century. However, these expressions are derived with certain assumptions and simplifications that involve a certain error in the calculation. The purpose of this paper is to determine the size of the error due to the assumptions and simplifications made when performing the analytical expression and to present what has the greatest impact on the amount of error, and give a recommendation on how to reduce that error. In order to determine the error, but also to gain a more detailed insight into the physics of heat exchange processes on the fin surface, computational fluid dynamics was applied to the original definition of fin efficiency. This means that a numerical simulation was performed for the actual fin material and for the ideal fin material with infinite thermal conductivity for the selected fin geometry and Re numbers from 2000 to 18,000. The results show that fin efficiency determined by numerical simulations is greater by up to 12.3% than the efficiency calculated analytically. The greatest impact on the amount of error is the assumption of the same temperature of the fin base surface and the outer tube surface and the assumption of equal heat transfer coefficient on the entire fin surface area. Using a newly recommended expression for the equivalent length of the fin tip, it would be possible to calculate the fin efficiency more precisely and thus the average heat transfer coefficient on the fin surface area, which leads to a more accurate dimensioning of the heat exchanger.

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