Efficiencies for Partially Wetted Spine Fins: Uniform Cross Section, Conical, Concave Parabolic, and Convex Parabolic Spines

2013 ◽  
Vol 135 (8) ◽  
Author(s):  
Worachest Pirompugd ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Cross Section ◽  
Transfer Rate ◽  
Approximate Equation ◽  
Sectional Area ◽  
Cross Sectional ◽  
Fin Efficiency ◽  
Conduction Heat Transfer ◽  
Uniform Cross Section

In this study, efficiencies for partially wetted fins for the uniform cross section spine, conical spine, concave parabolic spine, and convex parabolic spine are presented using an analytical method. Depending on the set of boundary conditions, there are two methods for deriving the efficiencies of partially wet fins for each spine. The eight equations for fin efficiencies were investigated. Fin efficiency is a function of the length of the dry portion. Thus, the equations for calculating the length of the dry portion are also presented. The findings indicate that a larger cross-sectional fin results in a higher conduction heat transfer rate. Contrarily, the fin efficiency is lower. This is different from the longitudinal fin, for which the trend lines of heat transfer rate and fin efficiency are the same. This converse relationship is due to the effect of the ratio of the cross-sectional area to the surface area. Moreover, partially wet fin efficiencies decrease with increased relative humidity. For convenience, the approximate equation for efficiencies for partially wet fins, which is derived from the equations for fully wet and fully dry fin efficiencies, is also presented.

Geometric Size Optimization of Annular Step Fin Using Multi-Objective Genetic Algorithm

2017 ◽  
Vol 9 (2) ◽  
Author(s):  
Abhijit Deka ◽  
Dilip Datta
Keyword(s):  
Heat Transfer ◽  
Genetic Algorithm ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Pareto Optimal ◽  
Objective Functions ◽  
Cross Sectional ◽  
Multi Objective ◽  
Multi Objective Genetic Algorithm ◽  
Design Variables

Although an annular stepped fin can produce better cooling effect in comparison to an annular disk fin, it is yet to be studied in detail. In the present work, one-dimensional heat transfer in a two-stepped rectangular cross-sectional annular fin with constant base temperature and variable thermal conductivity is modeled as a multi-objective optimization problem. Taking cross-sectional half-thicknesses and outer radii of the two fin steps as design variables, an attempt is made to obtain the efficient fin geometry primarily by simultaneously maximizing the heat transfer rate and minimizing the fin volume. For further assessment of the fin performance, three more objective functions are studied, which are minimization of the fin surface area and maximization of the fin efficiency and effectiveness. Evaluating the heat transfer rate through the hybrid spline difference method, the well-known multi-objective genetic algorithm, namely, nondominated sorting genetic algorithm II (NSGA-II), is employed for approximating the Pareto-optimal front containing a set of tradeoff solutions in terms of different combinations of the considered five objective functions. The Pareto-optimal sensitivity is also analyzed for studying the influences of the design variables on the objective functions. As an outcome, it can be concluded that the proposed procedure would give an open choice to designers to lead to a practical stepped fin configuration.

Heat Transfer and Pressure Loss in a Two-Pass, Rectangular Channel Featuring a Reduced Cross-Sectional Area After the 180- Degree Tip Turn with Different Turning Vane Configurations

2021 ◽  
pp. 1-44
Author(s):  
Sulaiman Alsaleem ◽  
Lesley Wright ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Cross Section ◽  
Pressure Loss ◽  
Guide Vane ◽  
Circular Cross Section ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Cross Sectional ◽  
Number Range

Abstract Serpentine, multi-pass cooling passages, are used in cooling advanced gas turbine blades. In open literature, most internal cooling studies use a fixed cross-sectional area for multi-pass channels. Studies that use varying aspect ratio channels, along with a guide vane to direct the flow with turning, are scarce. Therefore, this study investigates the effect of using different guide vane designs on both detailed heat transfer distribution and pressure loss in a multi-pass channel with an aspect ratio of (4:1) in the entry passage and (2:1) in the second passage downstream of the vane (s). The first vane configuration is one solid-vane with a semi-circular cross-section connecting the two flow passages. The second configuration has three broken-vanes with a quarter-circular cross-section; two broken vanes are located downstream in the first passage, and one broken vane is upstream in the second passage. Detailed heat transfer distributions were obtained on all surfaces within the flow passages by using a transient liquid crystal method. Results show that including the semi-circular vane in the turning region enhanced the overall heat transfer by around 29% with a reduction in pressure loss by around 20%. Moreover, results show the quarter-circular vane design provides higher overall averaged heat transfer enhancement than the semi-circular vane design by around 9% with penalty of higher pressure drop by 6%, which yields higher thermal performance by 7%, over a Reynolds number range from 15,000 to 45,000.

Effect of nano-fluid types on the improvement of heat transfer in a micro-channel with regular hexagonal pattern

2020 ◽  
Vol 234 (6) ◽  
pp. 657-664
Author(s):  
S Emami ◽  
MH Dibaei Bonab ◽  
M Mohammadiun ◽  
H Mohammadiun ◽  
M Sadi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Cross Section ◽  
Transfer Rate ◽  
Nano Particles ◽  
Working Fluid ◽  
Micro Channel ◽  
Hexagonal Cross Section ◽  
Micro Channels ◽  
Nano Fluids

Micro channels are widely used in different industries. The investgations on heat transfer improvments of these instruments are of significant inportance. At hte present study, the influence of different nano-fluids and geometrical charectrestics on the thermal performance of a heat sink which is especially for for micro-channels are investigated. In the present study, the authors investigated the Nusselt number and pressure drop in differential geometries and Reynolds numbers (Re). Then the micro-channel was investigated with different heat flux (q).In the first step, the micro-channel was examined and the final numerical results showed that the hexagonal cross-section can improve heat transfer about 9%. At the second step and after selecting appropriate parameters, the effect of three nano-particles (Al2O3 - CuO- TiO2) were studied. The results presented that aluminum oxide (Al2O3) has the best heat transfer rate among the mentioned nano-fluids. With the presence of nano-particles (Al2O3, φ = 4%) an increment of 40% in heat transfer rate, for the hexagonal cross section was achieved compare to rectangular cross section with water as working fluid.

scholarly journals Experimental implementation of thermal enhancement performance of air heat exchanger’s pipes utilizing unconventional turbulator

2021 ◽  
pp. 35-44
Author(s):  
Ali Abdulwahab Ismaeel ◽  
Nassr Fadhil Hussein ◽  
Kadhim H. Suffer ◽  
Zuradzman M Razlan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Heated Surface ◽  
Constant Heat Flux ◽  
Working Fluid ◽  
Practical Implementation ◽  
Cross Sectional

Heat exchangers are widely used in industry, however, raising their performance are important for the variety of applications. Consequently, efficiency improvement associated with low production cost is considered in this experimental work. The current study aims to enhance the rate of heat transfer in pipe-type heat exchangers experimentally by using a novel nozzle as a turbulator. The cross-sectional shape of the nozzle is hexagonal, and the diameter ratio DR is equal to 0.5. Constant heat flux was maintained in the vicinity of the section of the test tube, while the working fluid was pumped into the open system at six discrete Reynolds number values ranging from 6000 to 19500. To investigate the effect of distance among the pieces, three turbulators with different numbers were assigned and named as (N=4, 5 and 6). The results indicated an increase of 172 %, 194 % and 216 % of the heat transfer rate for cases 4, 5 and 6 respectively comparing to the benchmark tube. On the other hand, the friction factor values increased remarkably due to the inserting of turbulators by about of 722.9 % for N=4, 823.9 % for N=5 and 886.7 % for N=6 compared to a plain tube case. Moreover, it has been established that with the insertion of 6 pieces two enhancements was observed; heat transfer rate and thermal performance, where, thermal performance of all cases exceeds unity (maximum thermal performance of 1.62 has been obtained by inserting 6 pieces of hexagonal nozzles turbulators). A comparison with another types of vortex generators shows the gap between the turbulator and heated surface offers a solution for problems occurred in the pipes of heat exchanger. The study therefore suggests a wider practical implementation of the turbulators

scholarly journals Flow Induced Vibration of Cantilever Tapered Pipes Transporting Fluid

2021 ◽  
Vol 16 ◽  
pp. 8-13
Author(s):  
Mohamed Gaith
Keyword(s):  
Cross Section ◽  
Mass Fraction ◽  
Natural Frequencies ◽  
Fluid Velocity ◽  
Inviscid Fluid ◽  
Sectional Area ◽  
Flow Induced Vibration ◽  
Cross Sectional ◽  
Uniform Cross Section ◽  
The Mathematical Model

A cantilevered tapered slender pipe conveying an incompressible, inviscid fluid of one material is not a conserved system. For certain large fluid velocity, the pipe with uniform cross section would go unstable via flutter Hopf bifurcation. In this paper, the flow induced vibration for cantilever tapering pipe transporting a fluid is presented. Euler Bernoulli and Hamilton’s theories are applied to develop the mathematical model which will be solved using well known Galerkan’s procedure. The effect of smooth tapering of the circular cross sectional area, flow velocity and pipe to fluid mass fraction on the complex natural frequencies and stability will be investigated.

scholarly journals Experimental and CFD analysis of swirl, nozzle arrangement, cross-section and jets diameter on heat transfer in multi-jet air impingement cooling

2019 ◽  
Vol 23 (3 Part B) ◽  
pp. 2025-2035
Author(s):  
Palaniappan Chandramohan ◽  
Suruli Nagarajan ◽  
Sundaraganesan Arivazhagan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Rate ◽  
Cross Section ◽  
Transfer Rate ◽  
Cfd Analysis ◽  
Impingement Cooling ◽  
Line Arrangement ◽  
Air Impingement

Experimental investigation and CFD analysis were performed to study the effects of swirl, nozzle arrangement, cross section of nozzle, number of jets and jet diameter on heat transfer coefficient in multi-jet air impingement cooling for a target surface of 100 ?150 mm size supplied with a constant heat flux of 7666 W/m2. The normalized heat transfer coefficient based on unit volume of air is evaluated through measurement of temperature for flow Reynolds numbersin the range of 8000-22000 with H/D ratiosof 1, 2, 4, and 6. Investigations with and without swirl reveal that among the tested conditions, for 8 mm jets, introducing swirl reduces the heat transfer where as for 10 mm and 12 mm jets, swirl improves the average heat transfer rate. For sets of 12 nozzles configurations, the staggered arrangement for 6 mm and 8 mm nozzles results in higher heat transfer rate than in-line arrangement unlike in 4 mm nozzles where in-line arrangement is better. Heat transfer coefficients for circular, square and triangular cross-sections of same flow area have been compared. Circular cross-section offers better heat transfer coefficient for all the tested conditions. For a given number of nozzles, there is an optimum diameter corresponding to maximum value of normalized heat transfer coefficient. The results are corroborated with CFD analysis for a few representative conditions tested.

An optimum profile of a special pin fin: full solutions

2020 ◽  
Vol 30 (11) ◽  
pp. 4945-4954 ◽  
Author(s):  
Mustafa Turkyilmazoglu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Elementary Functions ◽  
Content Type ◽  
Excessive Heat ◽  
Fin Efficiency ◽  
Pin Fin ◽  
Extended Surface ◽  
Hot Surface

Purpose This paper aims to present an elegant exact solution in terms of elementary functions for a special pin fin without the classical length-of-arc approximation. Design/methodology/approach The temperature distribution along the fin and the surface function, both being the functions of a shape parameter, is inversely proportional to each other. The specialty of the spine is such that its shape and temperature profile are linked for a given Biot number. Findings Exact formulas for the pin fin tip temperature, pin fin base heat transfer rate, surface area of the spine and thermal fin efficiency are also given. Originality/value Without the traditional arc length assumption, the pin fin is shown to be an effective extended surface to remove the excessive heat from the hot surface it is pinned to. Optimum pin fin dimensions leading to the maximum base heat transfer rate are also worked out for a specified fin volume.

Experimental Study on Heat Transfer Characteristic of Plate Pulsating Heat Pipe

2009 ◽  
Author(s):  
Li Quan ◽  
Li Jia
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Cross Section ◽  
Heat Pipes ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Pulsating Heat Pipe ◽  
Operating Characteristics ◽  
Cross Sectional ◽  
Start Up

An experimental system of flat plate pulsating heat pipe was established and experimental research was carried out in this system to understand the mechanism of heat transfer and operating characteristics. The effects of start-up time, operating characteristics, and structures of passage, incline angle, fill ratio and working fluid on plate pulsating heat pipe were discussed. The results indicate that temperature of heating section decreases and the temperature of cooling section increases, then the thermal resistant of PHP is decreased once the plate pulsating heat pipe starts to work. Different start-up powers are needed for different fill ratios and incline angles. The inter pressure of PHP has some impacts on the start-up and operation of PHP. The pulsating heat pipes with different structures have different heat transfer performance. Increasing cross-sectional area and the number of turnings of the heat pipe can improve the heat transfer characteristics of heat pipes. Cross-section shape was also an important influencing factor. With the same cross-sectional area, heat pipe with triangular cross-section of the inner tubes gives better performance than that with rectangular cross-section.

Heat Transfer and Pressure Loss in a Two-Pass, Rectangular Channel Featuring a Reduced Cross-Sectional Area After the 180-Degree Tip Turn With Different Turning Vane Configurations

2020 ◽  
Author(s):  
Sulaiman M. Alsaleem ◽  
Lesley M. Wright ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Cross Section ◽  
Pressure Loss ◽  
Circular Cross Section ◽  
Sectional Area ◽  
Cross Sectional ◽  
Number Range

Abstract Serpentine, varying aspect ratio cooling passages, are typically used in cooling advanced gas turbine blades. These passages are usually connected by sharp, 180-deg bends. In the open literature, most of the internal cooling studies use a fixed cross-sectional area for multi-pass channels. Studies that use varying aspect ratio channels, along with a guide (turn) vane to direct the flow with turning, are scarce. In general, studies show that the incorporation of turning vanes in the bend region of a multi-pass channel keeps the heat transfer rate high while reducing pressure loss. Therefore, the current study investigates the effect of using different guide (turn) vane designs on both the detailed heat transfer distribution and pressure loss in a multi-pass channel with an aspect ratio of (4:1) in the entry passage and (2:1) in the second passage downstream of the vane (s). The first vane configuration is one solid-vane with a semi-circular cross-section connecting the two flow passages. The second configuration has three broken-vanes with a quarter-circular cross-section; two broken vanes are located downstream in the first passage (entering the turn), and one broken vane is upstream in the second passage (exiting the turn). For a Reynolds number range 15,000 to 45,000, detailed heat transfer distributions were obtained on all surfaces within the flow passages by using a transient liquid crystal method. The results show that the turning vane configurations have large effects on the heat transfer, in the turning bend and second passage, and the overall pressure drop. Results show that including the semi-circular vane in the turning region of a multi-pass channel enhanced the overall heat transfer by around 29% with a reduction in pressure loss by around 20%. Moreover, results show that the quarter-circular vane design provides higher overall averaged heat transfer enhancement than the semi-circular vane design by around 9% with penalty of higher pressure drop by 6%, which yields higher thermal performance by 7%, over the Reynolds number range.

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