research paper computational fluid dynamics on … · 2015. 4. 9. · when a dimpled wall is used...

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Int. J. Mech. Eng. & Rob. Res. 2014 Mukund Y Pande and Atul Patil, 2014

COMPUTATIONAL FLUID DYNAMICS

ON DIFFERENT PASSAGES OVER A PLATE

COIL EVAPORATOR FOR 40 LITER

STORAGE TYPE WATER COOLER

Mukund Y Pande1* and Atul Patil1

*Corresponding Author: Mukund Y Pande � [email protected]

By using ANSYS Fluent 14.5 In computational Fluid Dynamics (CFD) analysis, Dimpled Platecoil evaporator with different passage likes six passages and eight passages are simulatedusing the appropriate boundary conditions and fluid properties specified to the system withsuitable assumptions. The process in solving simulation consists of modeling and meshing thebasic geometry of the Dimpled plate coil evaporator using CFD package ANSYS 14.5. Theobjective of the project is to study the temperature field of the coil using ANSYS software tools.The temperature contours was plotted using ANSYS 14.5 for different passages of Dimpledplate coil evaporator. Different Dimpled plate coil evaporator passages configurations is analyzedusing CFD software for validation of experimental values determined the output temperature ofPlate coil evaporator to improving the coefficient of performance of the System.

Keywords: Bonded coil Evaporator, Plate coil evaporator (PHE), Dimpled plate andComputational Fluid Dynamics (CFD)

INTRODUCTION

Dimpled surface is shown in Figure 1. Thissurface is machine punched and swaged, priorto welding, to increase the flow area in thepassage. As compared with other two surfacesconcept dimpled surfaces are successfullyemployed in many industries. Most commonexample is bulk milk cooler used in dairyindustry.

Int. J. Mech. Eng. & Rob. Res. 2014

1 Deprtment of Mechanical Engineering, Godavari College of Engineering, Maharashtra India.

Over the last decade, numerical andexperimental work in channel flow has shownthat flow over dimpled surfaces develop vortexlike structures inside and in the wake area ofthe dimples, increasing the overall drag dueto inertial and viscous effects in the fluid.However, dimples also increase the surfaceheat transfer coefficient without a substantialrise in drag penalties observed in other heat

Research Paper

ISSN 2278 – 0149 www.ijmerr.com

Vol. 3, No. 4, October 2014

© 2014 IJMERR. All Rights Reserved

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transfer enhancement devices such as ribtabulators and pin fins. Fluid motion insidedimples is self-organized: it is induced by thepresence of the dimple with no physicallyprotruding part projecting into the flow ordeflecting it to create the vortices; therefore,dimples lack the pressure loss associated withform drag. Heat transfer is enhanced becausevortex structures promote mixing, drawing coldfluid from outside the thermal boundary layerinto contact with the wall and ejecting hot fluidfrom the near wall area into the stream, thusenhancing the overall convective heat transfer.When a dimpled wall is used in channel flow,dimple geometry play a key role in the heattransfer and drag coefficients. The optimumconfiguration should provide the higher heattransfer improvement with less drag for aspecific application. As of today, there existsno road map to determine the optimum dimpleconfiguration. During the last few years, studieson turbulent flow over dimpled walls haveprovided some insight into the application ofthis technology for turbine blade and jetimpingement cooling. However, application ofdimples in laminar flow was scarcely explored.Microelectronic cooling and micro fluids, where

the flow regime is mostly laminar, are twopotential fields of application for dimpletechnology. Surface dimples producesubstantial surface heat transferaugmentations with relatively small pressuredrop penalties in internal passages. As such,arrays of surface dimples are useful for avariety of practical applications, such aselectronics cooling, heat exchangers, turbineblade internal cooling passages, micro-scalepassages, bio-medical devices, andcombustion chamber liners. Of several earlystudies (mostly conducted in Russia), Murzinet al. (1986) describe the flow over and withinshallow spherical depressions and concludethat this flow is mostly symmetric, with stablere-circulatory flows inside of the depressions.Kesarev and Kozlov (2003) presentdistributions of local heat transfer coefficientsinside of a single hemispherical cavity andindicate that the convective heat transfer fromthe cavity is higher, especially on thedownstream portion, than that from the surfaceof a plane circle of the same diameter as thecavity diameter. Afanasyev et al. (1993)experimentally studied the heat transferenhancement mechanism for flows in adimpled channel with several different shapes.Enhancements of 30–40%, with pressurelosses that are not increased appreciablyrelative to a smooth surface, are reported.Terekhov et al. (1995) present experimentalmeasurements of flow structure, pressurefields, and heat transfer in a channel with asingle dimple on one surface. According to theauthors, pressure losses increase (comparedto a smooth wall) with an increase of cavitydepth and decrease as the Reynolds numberincreases. Cavity heat transfer enhancements

Figure 1: Dimpled Surface

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are also noted, especially for shallow holes,mainly as a result of an increase in heat transferarea and the changes to flow structureproduced by the dimple.

LITERATURE REVIEW

Xiao et al. The present study provides thesystematic set of data which illustrate theeffects of an array of dimples on local andspatially averaged surface Nusselt numberdistributions, as well as on friction factors inchannels with laminar flow. Trends of spatially-averaged Nusselt numbers and friction factorsare provided as they vary with dimple depth,channel height, Reynolds number and the useof protrusions on the opposite channel wall.When compared with turbulent flow results, thepresent laminar data illustrate changes due tothe absence of turbulence transport. Forexample, in contrast to turbulent flows, thepresent laminar flow data show that there isno overall benefit from the use of a top wallwith protrusions. In addition, spatially-averaged Nusselt number ratios and frictionfactor ratios measured on a deep dimpledsurface with a smooth top wall show trendswhich are opposite from ones observed inturbulent flows, since lower laminar heattransfer augmentations are present for smallerchannel heights when compared at the sameReynolds number.

Derya Burcu Ozkan et al. examineparameter affecting the frost formation on theevaporator of a refrigerator and the structureof frost. Air velocity both at the air inlet andoutlet channels of the evaporator wereperformed, and the effect of the air velocity onfrost formation was examine. In this experimentparameter affecting on frost formation on the

evaporator and structure of the frost wereexamined and frost thickness on the chosen finwas measured. In this experiment thecompressor of the refrigerator operated at100% load and cooling was carried out for 5 h.

N. Xiao et al. The present study providesthe systematic set of data which illustrate theeffects of an array of dimples on local andspatially averaged surface Nusselt numberdistributions, as well as on friction factors inchannels with laminar flow. Trends of spatially-averaged Nusselt numbers and friction factorsare provided as they vary with dimple depth,channel height, Reynolds number and the useof protrusions on the opposite channel wall.When compared with turbulent flow results, thepresent laminar data illustrate changes due tothe absence of turbulence transport. Forexample, in contrast to turbulent flows, thepresent laminar flow data show that there isno overall benefit from the use of a top wallwith protrusions. In addition, spatially-averaged Nusselt number ratios and frictionfactor ratios measured on a deep dimpledsurface with a smooth top wall show trendswhich are opposite from ones observed inturbulent flows, since lower laminar heattransfer augmentations are present for smallerchannel heights when compared at the sameReynolds number.

The present investigation leads to thefollowing conclusions

a. As the dimple depth increases, highermagnitude of stream wise vorticity, vortexcirculation and Reynolds normal stress areobtained, which implies strong vortices andincreasing turbulence transport associatedwith increase of the depth of the dimples.

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b. The maximum heat transfer rates areobtained downstream of the dimples. Theminimum heat transfer rates occur along therow containing the dimples.

Silva et al. In present study, numerical andexperimental work was performed todetermine the effect of dimpled surfaces onthe convective heat transfer in the channel flowunder a laminar regime with the Reynoldsnumber (based on the channel height) between500 and 1000. This study identified the best-performance dimple geometry and conductedexperiments to validate the numerical results.The following findings/conclusions can bedrawn from the work done

CFD MODELING

CFD is a sophisticated computationally-baseddesign and analysis technique. CFD softwaregives you the power to simulate flows of gasesand liquids, heat and mass transfer, movingbodies, multiphase physics, chemicalreaction, fluid-structure interaction andacoustics through computer modeling. Thissoftware can also build a virtual prototype ofthe system or device before can be apply toreal-world physics and chemistry to the model,and the software will provide with images anddata, which predict the performance of thatdesign. Computational fluid dynamics (CFD)is useful in a wide variety of applications anduse in industry. CFD is one of the branches offluid mechanics that uses numerical methodsand algorithm can be used to solve andanalyses problems that involve fluid flows andalso simulate the flow over a piping, vehicle ormachinery. Computers are used to perform themillions of calculations required to simulate theinteraction of fluids and gases with the complex

surfaces used in engineering. More accuratecodes that can accurately and quickly simulateeven complex scenarios such as supersonicand turbulent flows are ongoing research.Onwards the aerospace industry hasintegrated CFD techniques into the design,R&D and manufacture of aircraft and jetengines. More recently the methods have beenapplied to the design of internal combustionengine, combustion chambers of gas turbineand furnaces. Furthermore, motor vehiclemanufactures now routinely predict dragforces, under bonnet air flows and surroundingcar environment with CFD. Increasingly CFDis becoming a vital component in the designof industrial products and processes.

Figure 2: Overview of Modeling Process

CFD PROCEDURE

For numerical analysis in CFD, it requires fivestages such as:

a. Geometry creation

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b. Grid generation

c. Flow specification

d. Calculation and numerical solution

e. Results

Based on control volume method, 3-Danalysis of fluid flow and dimpled plate hasbeen done on ANSYS FLUENT 14.5 software.All the above mentioned processes are doneusing the three CFD tools which are pre-processor, solver and post-processor.

Geometry Creation

A 3-d model of Dimpled Plate Evaporator hasbeen created using design modeler of ANSYSas shown in Figures 3 and 4.

Mesh Generation

The mesh of the model is shown in Figures 5and 6. It depicts that the domain was meshedwith rectangular cells. Grid independence wasstudied by doing different simulation withtaking different no cells.

Figure 3: 6 – Passage of DimplePlate Evaporator

Figure 4: 8 – Passage of DimplePlate Evaporator

Figure 5: Meshing of 6 Passageof Dimple Plate Evaporator

Figure 6: Meshing of 8 Passageof Dimple Plate Evaporator

The assumptions used in this model were

1. The flow was steady and incompressible.The fluid density was constant throughoutthe computational domain.

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2. R-134 a was the working fluid. The fluidproperties constant throughout thecomputational domain.

3. The effect of heat conduction through thetube material is small.

Relaxation Factors

Mass flow rate was given at the inlet whereasstatic temperature was given at inlet for velocityinlet and pressure outlet boundary conditionand static pressure was given at the inlet as

Pressure Momentum Energy Density Body

Force

0.3 0.7 1 1 1

Table 1 : Relaxation Tablein ANSYS FLUENT 14.5

No. of Passages Experimental Values CFD Analysis Value

INLET OUTLET INLET OUTLET

6- Passage Dimpled plate Evaporator 275 282 275 285.079

8- Passage Dimpled plate Evaporator 284 298 284 296.744

Table 2: Comparison of Exit Static Temperature with Experimental Value

well as at the output for pressure inlet andpressure outlet boundary condition. The inputparameters were indirectly taken from theReynolds number value.

Figure 7: Contour of Temperature Distribution for 6-passage

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CONCLUSION

The Static temperature at out let of a dimpledplate can be visualized from the contourdiagrams of temperature distribution whichhave been plotted using ANSYS FLUENT14.5. from above table static outlettemperature of 6 and 8 passages of dimpledplate evaporator is validated and by using thisdifferent passage improve the coefficient ofperformance (COP) of the system as generallyused in storage type water cooler.

REFERENCES

1. Afanasyev et al. (1993) “Experimentallystudied the heat transfer enhancementmechanism for flows in a dimpled channelwith several different shapes” ThermFluid Sci Vol. 7, pp. 1–8.

2. Apu Roy and D H Das, “CFD analysis ofshell and finned tube heat exchngerfor waste

heat recovery application”, InternationalJournal of Mechanical & IndustrialEngineering, Vol. 1, No.1, pp. 77-83.

3. Flavio C C G, Raquel Y M, Jorge A W Gand Carmen C T (2006), “Experimentaland numerical heat transfer in a plate heatexchanger”, Vol. 61, No. 21, pp. 7133-7138.

4. Jader R Barbosa Jr., Chirstan J L Hermesand Claudio Melo (2010), “CFD Analysisof tube fin ‘No Frost’ Evaporator”,International Journal of Emerging Trendsin Engineering and Development, Vol. 1,No. 3.

5. Kesarev and Kozlov (2003) “Presentdistributions of local heat transfercoefficients inside of a singlehemispherical cavity” Turbo Expo 2003,Vol. 5.

Figure 8: Contour of Temperature Distribution for 8-passage

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6. Murzin V N, Stoklitskii S A andPchebotarev A (1986), “Creation ofsolitary vortices in a flowaround shallowspherical depressions,” Soviet TechnicalPhysical Letters, Vol. 12, No. 11, pp.547–549.

7. N Xiao, Q Zhang, P M Ligrani and RMongia (2009), “Thermal performance ofdimpled surfaces in laminar flows”International Journal of Heat and MassTransfer, Vol. 52, pp. 2009–2017.

8. Piotr A Domanski, David Yashar andMinsung Kim (2005), “Performance offinned tube evaporator optimized fordifferent refrigerants and effect on systemefficiency”, International Journal ofRefrigeration, Vol. 28, pp. 820-827.

9. Terekhov et al (1995).” Flow Structure andHeat Transfer on a Surface With a UnitHole Depression” Russ, J. Eng.Thermophys, Vol. 5, pp. 11-33.

research paper computational fluid dynamics on … · 2015. 4. 9. · when a dimpled wall is used...

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