HEAT TRANSFER DURING MULTI SWIRL JET IMPINGEMENT · performed to study the effect of jet impingement on both flat plate were performed for various cases. Constant wall heat flux of

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 9, September 2017, pp. 349–356, Article ID: IJMET_08_09_037

Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=9

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

HEAT TRANSFER DURING MULTI SWIRL JET

IMPINGEMENT

N. V. S. Shankar

Research Scholar, Department of Mechanical Engineering, GITAM University,

Visakhapatnam

Dr. H. Ravi Shankar

Professor, Department of Mechanical Engineering, GITAM University, Visakhapatnam

ABSTRACT

Jet impingement heat transfer was finding its application in many areas from

heating to cooling. The ways of augmentation of heat transfer during jet impingement

has always been point of interest for researchers. For this, various methods were

being followed of which use of swirl impinging jets has been of great interest as swirl

increases turbulence and thus the heat transfer. There are no specific relations for

computing heat transfer coefficient during multi-swirl jet impingement. This work

aims at providing an empirical relation to this problem.

Keywords: Multi-Conventional Jet Impingement, Multi-Swirl Jet Impingement, CFD,

Nusselt Number Correlations

Cite this Article: N. V. S. Shankar and Dr. H. Ravi Shankar, Heat Transfer During

Multi Swirl Jet Impingement, International Journal of Mechanical Engineering and

Technology 8(9), 2017, pp. 349–356.

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=9

1. INTRODUCTION

Jet impingement finds its application from heating during baking to cooling electronic cooling

A lot of work happened during relating to conventional jet impingement and considerable

amount of work relating to swirl jet impingement.

1.1 Conventional Jet Impingement on Flat Plate

A detailed literature survey pertaining to jet impingement was given in [1,2]. Hadhrami, et al

[3] presented the Schematics of a general gas turbine cooling systems. A. Sarkar, et al [4]

discussed the applications of air jet impingement in food processing. Experimental

investigations into Conventional jet impingement were summarized in [5–9]. Numerical

investigations were performed by [6,9–11] to study the effect of various parameters.

Numerical expressions were summarized in [12,13]. Li, et al [14] developed predictive

correlations for stagnation and area-averaged Nusselt number in confined and submerged jet

N. V. S. Shankar and Dr. H. Ravi Shankar


impingement for separate fluids, based on experimental results obtained over a wide range of

thermos-physical properties. Brignoni, et al [15] experimentally investigated the effect of

changing the nozzle geometry on the pressure drop and local heat transfer distribution in

confined air jet impingement on a small heat source. Confined jet impingement was

experimentally studied in [16,17].

1.2 Swirl Jet Impingement Cooling with Flat Plate

Swirling Motion of fluids provides a lot of advantages like increase in mass transfer [18],

augmenting heat transfer etc. Experimental investigation in swirl jet impingement was

summarized in [19–25]. Numerical simulations techniques to study the swirl jet impingement

were summarized in [26–30]. Erik [31] gave expressions for mathematically modeling

swirling flow and evaluating various parameters in the flow. Expressions for predicting heat

transfer in single swirl jet impingement were given in [27].

2. PROBLEM STATEMENT

As per authors purview, there are no mathematical expressions given for Multi-Swirl Jet

Impingement (MSJI). Thus, it is aimed at investigating MSJI on flat plate. Simulations are

performed to study the effect of jet impingement on both flat plate were performed for various

cases. Constant wall heat flux of 8333W/m2

is simulated in both the cases. During

simulations, air is treated as incompressible fluid. k-ε model is used for simulations. 3x3 jet

impingement is simulated in all the cases. During simulation, Continuity, Momentum and

Energy equations are solved. k-ε model is chosen during simulation. During simulation of

Multi-Conventional Jet Impingement (MCJI), are carried out for different Re values (11000,

16000, 22000, 26000 and 33000) on with z/d ratio of 4, same jet spacing and plate dimensions

as that for Multi-Swril Jet Impingement (MSJI). During MSJI Simulation along with five

different Re values used in MCJI, three z/d ratios (4.0, 4.25, 4.5) and three different swirl

values (Si) are investigated. 40 test cases, summarized in table 1 are considered and

simulations are performed to extract the heat transfer coefficient. The results of these

simulations are used to define the correlation for heat transfer coefficient using regression

analysis. The dimensions of the models of flat plate and fluid considered during simulations

are shown in figure 1. Meshed models are shown in figure 2. Boundary conditions are shown

in figure 3. It may be noted here that grid independence tests were executed before taking the

results into consideration.

(a) MCJI on Flat Plate (b) MSJI on Flat Plate.

Figure 1: CAD Geometry used for Simulation

Heat Transfer During Multi Swirl Jet Impingement


Table 1: Summary of combination of parameters used during simulation

Z/d Swirl Re Value

4.00

0.783 11000, 16000, 22000 and 26000

1.566 11000, 16000, 22000 and 33000

3.132 11000, 16000, 26000 and 33000

4.25

0.783 11000, 16000, 22000, 26000 and 33000

1.566 11000, 16000, 22000, 26000 and 33000

3.132 11000, 16000, 22000, 26000 and 33000

4.50

0.783 11000, 16000, 22000, 26000 and 33000

1.566 11000, 16000, 22000, 26000 and 33000

3.132 11000, 16000, 22000, 26000 and 33000

(a) MCJI on Flat Plate (b) MSJI on Flat Plate.

Figure 2: Meshed Models used for simulation

Figure 3 Boundary conditions applied for simulating impingement on flat plate

3. RESULTS OF SIMULATION OF MCJI

The Nusselt for various Re values during MCJI are numerically computed using expression

(1) as listed in [12]. Wall Heat Transfer coefficient is then calculated using expression (2). A

maximum of 10% error existed between calculated and simulated values. Figure 4 shows the

comparative plot of calculated and simulated results for MCJI.

( )-0.725

-0.1230.71 0.33 jetpzNu = 2.85Re Pr

D D (1)

.Nu kh

L=

(2)

Where

k – Thermal Conductivity

L – Characteristic length (=p

A P )



Figure 4 Comparison of computed and simulated values of heat transfer coefficient for MCJI on flat

plate

5. RESULTS OF SIMULATION OF MSJI

As for MSJI, based on the literature survey done, there is no specific expression that has been

defined for computing Nu, by any researcher till now. For single swirl jet impingement with

constant wall temperature boundary condition, Otegra – Casanova [27] expressed heat

transfer coefficient as a function of Re, Si, z/D ratio and turbulent intensity (I) at jet exit. Swirl

is calculated using equation (3) as given in [13].

3

2

12

31

hub

swirli

hub

dd p

Sdd

d

π

− =

− (5)

Based on the simulation results (Heat transfer coefficient) executed for various cases as

listed in Table 1, Nusselt Number is computed using equation number (2). The obtained

values are tabulated and regression analysis is performed on the data to predict the expression.

Figures 5 to 7 show the heat transfer coefficient obtained during simulations for various

configurations. Based on the analysis it was found that Nusselt number varies as per equation

(6). This relation has been tested for three more configurations. In each case Nu is evaluated

numerically and h is computed using equation (2). It was found that the variation is less than

5%. This is summarized in table 2.

( )0.4454

0.8764 0.33 0.0364 0.048463.347834 Re Pr zNu Si ID

= (6)

Figure 5 Heat Transfer

Coefficient Plot for z/D=4.5







Table 2 Verification Data

Z/D Si Re h (W/m

2)

(from simulation)

h (W/m2)

(predicted using equation (6)) Error %

4 3.132 33000 350.137 343.5464731 1.88%

4 1.566 26000 270.946 271.610934 -0.25%

4 0.783 22000 234.286 226.7780724 3.20%

6. COMPARISON OF MCJI & MSJI

The greater turbulence due to higher vorticity that exist in MSIJ for the same Re when

compared to MCJI. Figure 8 compares vorticity in both the cases. The plot is an isosurface for

vorticity of 2000/s in both cases. Based on the plots, it can be observed that the vorticity is

more in MSJI compared to MCJI. This is an indication to higher turbulence.

(a)MCJI on flat plate (b) MSJI on flat plate

Figure 7 Isosurface for vorticity of 2000/s

Figure 9 gives the velocity distribution plots. The plots indicate higher jet bending due to

jet to jet interactions in MSJI. The above two are the reasons for increase in heat transfer

coefficient. Wall Heat Transfer coefficient plots are given in figure 10.

(a) MCJI on flat plate (b) MSJI on flat plate

Figure 9 Velocity distribution plots



MCJI on Flat Plate (b) MSJI on Flat Plate

Figure 10 Wall Heat Transfer Coefficient Distribution

6. CONCLUSIONS

Numerical simulations were executed to study the heat transfer during Multi-Conventional Jet

Impingement (MCJI) and Multi-Swirl Jet Impingement (MSJI). Simulations for MCJI were

carried out for z/D=4, and five Re values. The heat transfer coefficient obtained from

simulations was in good agreement with that calculated using the expression in [12].

Simulations were then executed with MSJI. Since there is no specific relation specified in any

literature as per authors purview, 40 different configurations are simulated to obtain the

expression. Swirl is calculated using the expression given in [13]. By performing regression

analysis on the obtained results, expression (6) is derived to compute heat transfer coefficient.

This expression is verified for three more configurations and it was found that the computed

result and simulated result are in good agreement. Comparing the results of simulation for

MCJI and MSJI, it can be observed that greater heat transfer coefficient is more in MSJI than

MCJI for flat plate. This is primarily because of the greater turbulence in MSJI when

compared to MCJI. This can be observed from Vorticity plots given in figure 7.

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HEAT TRANSFER DURING MULTI SWIRL JET IMPINGEMENT · performed to study the effect of jet impingement on both flat plate were performed for various cases. Constant wall heat flux of