Research Article Thermohydraulic Analysis of Shell-and-Tube ...F : Shell-and-tube type heat...
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Hindawi Publishing CorporationISRN Chemical EngineeringVolume 2013, Article ID 548676, 5 pageshttp://dx.doi.org/10.1155/2013/548676
Research ArticleThermohydraulic Analysis of Shell-and-Tube HeatExchanger with Segmental Baffles
Amarjit Singh1 and Satbir S. Sehgal2
1 Department of Mechanical Engineering, RPC, Railmajra 144533, India2Department of Mechanical Engineering, Chandigarh University, Gharuan 140413, India
Correspondence should be addressed to Amarjit Singh; [email protected]
Received 30 June 2013; Accepted 1 August 2013
Academic Editors: C. Chen, I. Poulios, and A. M. Seayad
Copyright ยฉ 2013 A. Singh and S. S. Sehgal. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.
In this study, the experimental analysis was performed on the shell-and-tube type heat exchanger containing segmental baffles atdifferent orientations. In the current work, three angular orientations (๐) 0โ, 30โ, and 60โ of the baffles were analyzed for laminarflow having the Reynolds number range 303โ1516. It was observed that, with increase of Reynolds number from 303 to 1516, therewas a 94.8% increase in Nusselt number and 282.9% increase in pressure drop. Due to increase of Reynolds number from 303to 1516, there is a decrease in nondimensional temperature factor for cold water (๐) by 57.7% and hot water (๐) by 57.1%, respec-tively.
1. Introduction
A heat exchanger is a device built for efficient heat transferfrom one medium to another in order to carry and processenergy [1]. It is widely used in petroleum refineries, chemicalplants, petrochemical plants, natural gas processing, airconditioning, refrigeration, and automotive applications.Themost commonly used type of heat exchanger is the shell-and-tube heat exchanger. To increase the heat transfer rate inshell and tube type heat exchanger, the segmental baffles areintroduced inside the cover pipe [2โ6].The flow arrangementused in analysis is laminar counter flow as it is more efficientthan parallel flow arrangement [7].The different orientationsof baffles in heat exchanger [8โ10] are given in Figure 1.
The common focus of publication is to predict thevariation of LMTD, heat transfer coefficient, Nusselt number,and pressure drop with change in values of Reynolds numberfor 0โ, 30โ, and 60โ baffles situated in heat exchanger as shownin Figure 1.The Reynolds number will be varying from 303 to1516.
The enhancement of Nusselt number with increase inReynolds number will be presented by Zohir [11], Tandiroglu[12], and Promvonge [13]. The heat transfer coefficient values
are calculated using the log-mean-temperature-difference(LMTD) method [14] from the temperature difference andthe heat transfer area. Gay et al. [15] and Mehrabian et al.[16] concluded that the heat transfer coefficient increases withinserting baffles.Thundil et al. [17] observed that the pressuredrop will decrease with increasing baffle inclination angleand the heat transfer rate increases with increasing baffleinclination angle.
2. Test Specimen
A variety of different strategies are available to improvethe performance of shell-and-tube type heat exchanger asdiscussed byWalde [18].Thepresent papermainly attempts tostudy the different effects in shell-and-tube heat exchanger byincreasing Reynolds number with segmental baffles at 0โ, 30โ,and 60โ situated in the cover pipe. The model is situated withfour segmental baffles. The various dimensions used in heatexchanger are shown in Figure 2. The working fluid used isdeionized water. The material used for the design of model isgalvanized iron. The geometric parameters of shell-and-tubeheat exchanger are given in Table 1.
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2 ISRN Chemical Engineering
Cold water inletCold water outlet
AdapterShell
Inner pipe
Hot water outlet
Hot water inlet
Segmental baffle plate
(a)
Cold water inletCold water outletAdapter
ShellInner pipe
Segmental baffle plate
Hot water outlet
Hot water inlet
(b)
Cold water inletCold water outletAdapter
Shell
Inner pipe
Hot water outlet
Hot water inlet
Segmental baffle plate
(c)
Figure 1: Shell-and-tube type heat exchanger having (a) 0โ, (b) 30โ, and (c) 60โ baffle angles.
Da
La
Dh
Dc
Lc
Lh
Xc
๐
Figure 2: Dimensions used in heat exchanger.
3. Results and Discussion
In the present study, different cases were studied to under-stand the LMTD values, Nusselt number, heat transfer coeffi-cient, and pressure drop of shell-and-tube type heat exchan-ger having hot water and cold water inlets. Performancecomparison and other details are given in Table 2.
The variation of LMTD values with different Reynoldsnumbers is shown in Figure 3. The variation of heat transfercoefficient with Reynolds number at different inlet temper-atures is shown in Figure 4, and the variation of Nusseltnumber with Reynolds number is shown in Figure 5. Figure 6shows the variation of ratio of temperature difference (๐)for cold water with increasing Reynolds number, and thevariation of ratio of temperature difference (๐) for hot waterwith increasing Reynolds number is shown in Figure 7.
Figure 3 shows the variation of LMTD with Reynoldsnumber. It was observed that, with the increase of Reynolds
Table 1: Main dimensions and features in heat exchanger.
๐ผ ๐ฟ๐
/๐ท๐
1.86๐ฝ ๐ฟ
๐
/๐ท๐
2.67๐พ ๐ฟ
โ
/๐ทโ
16.6๐ฟ ๐ฟ
๐
/๐๐
2.86๐: 0โ, 30โ, and 60โ.
Table 2: Data reduction.
S.no. Parameters Data reduction
1. Heat transfercoefficient
โ =๐ โ ๐ถ โ ฮ๐ก
๐ โ ๐ท โ ๐ฟ โ ฮ๐ก๐
2.
Logarithmicmeantemperaturedifference
ฮ๐๐
=(๐โ(in) โ ๐๐(in)) โ (๐โ(out) โ ๐๐(out))
ln ((๐โ(in) โ ๐๐(in)) / (๐โ(out) โ ๐๐(out)))
3.
Nondimensionaltemperaturefactor for coldwater
๐ =๐ก๐(out) โ ๐ก๐(in)
๐ก๐(out)
4.
Nondimensionaltemperaturefactor for hotwater
๐ =๐กโ(in) โ ๐กโ(out)
๐กโ(in)
5. Nusselt number Nu = โ๐ฟ๐พ
6. Reynoldsnumber
Re =๐๐๐ท
๐
number from 303 to 1516 there was 23.15 to 38.5% increasein LMTD values.The increase in LMTD value with Reynolds
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ISRN Chemical Engineering 3
0
10
20
30
40
50
0 500 1000 1500 2000
LMTD
Test run 1: inlet fluid temp. at 70โ
Test run 2: inlet fluid temp. at 80โ
Re
Figure 3: Variation of LMTD with Reynolds number.
0
500
1000
1500
2000
0 500 1000 1500 2000Re
h(W
/m2
K)
Test run 1: inlet fluid temp. at31โTest run 2: inlet fluid temp. at 28โ
Test run 3: inlet fluid temp. at 70โ
Test run 4: inlet fluid temp. at 80โ
Figure 4: Variation of heat transfer coefficient versus Reynoldsnumber for different inlet fluid temperatures.
number may be attributed to less retention time within theheat exchanger for the same length of flow.
Figure 4 shows the variation of the heat transfer coef-ficient with Reynolds number. With increase of Reynoldsnumber from 303 to 1516, the increase of heat transfer coef-ficient was 95.1%. The increase of heat transfer coefficient isattributed to the increase of mass flow rate due to which theheat transfer rate increases.
Figure 5 shows the variation of Nusselt number withReynolds number. It was observed, that with the increaseof Reynolds number from 303 to 1516, there was a 94.8%increase in Nusselt number. The increase in Nusselt numberis attributed to the enhancement in heat transfer rate withincrease in velocity of fluid.
0
10
20
30
40
50
60
0 500 1000 1500 2000Re
Nu
Test run 1: inlet fluid temp. at 31โTest run 2: inlet fluid temp. at 28โ
Test run 3: inlet fluid temp. at 70โ
Test run 4: inlet fluid temp. at 80โ
Figure 5: Variation of Nusselt number with Reynolds number fordifferent inlet fluid temperatures.
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Test run 2: inlet fluid temp. at 28โ
0 500 1000 1500 2000Re
๐
Test run 1: inlet fluid temp. at 31โ
Figure 6: Variation of ๐ with Reynolds number (for cold waterinlet).
Figure 8 shows the change of pressure dropwith variationin Reynolds number. It was observed that the pressure dropincreases with the increase in Reynolds number up to 282.9%.The measured pressure drop is in good agreement with theestimated value. A gradual change in the pressure drop withReynolds number is attributed to the temperature depen-dence of fluid viscosity and the increasing contraction andexpansion pressure losses at the inlet and outlet portion ofthe heat exchanger, respectively.
Figure 9 shows the variation of the heat transfer coeffi-cient with Reynolds number for three different baffle orien-tations. It was observed that, with the introduction of thebaffles, the heat transfer coefficient increases leading to moreheat transfer rate due to introduction of swirl and moreconvective surface area. It was also observed that, as the angle
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4 ISRN Chemical Engineering
0
0.05
0.1
0.15
0.2
0.25
0.3
0 500 1000 1500 2000Re
Test run 1: inlet fluid temp. at70โ
Test run 2: inlet fluid temp. at 80โ
๐
Figure 7: Variation of ๐with Reynolds number (for hot water inlet).
0
5000
10000
15000
20000
0 500 1000 1500 2000Re
Pressure drop
ฮP
(N/m
2)
Figure 8: Variation of total pressure drop versus Reynolds numberfor 0โ baffle orientations.
2500
3000
3500
4000
0 500 1000 1500
h(W
/m2
K)
h ( without baffles)h (baffles at 0โ)
h ( baffles at 30โ)h (baffles at 60โ)
Figure 9: Variation of heat transfer coefficient versus Reynoldsnumber for different baffle orientation.
of inclination increases from 0โ to 60โ, the heat transfer coef-ficient value increases due to increase in swirl.
4. Conclusion
In this paper, experimental study of shell-and-tube heatexchanger is conducted to calculate the heat transfer coeffi-cient, LMTD, Nusselt number, and pressure drop at differ-ent Reynolds numbers (303โ1516). It is concluded that theincrease in Reynolds number has a significant impact on dif-ferent parameters of shell-and-tube type heat exchanger. Themajor findings are summarized as follows.
(i) The heat transfer coefficient increases with increasein Reynolds number in shell-and-tube heat exchangerfor both hot fluid inlet and cold fluid inlet.
(ii) The Nusselt number increases with increase in Reyn-olds number in shell-and-tube heat exchanger forboth hot fluid inlet and cold fluid inlet.
(iii) The value of LMTD increases with increase in Reyn-olds number from 303 to 1516.
(iv) The value of temperature constants ๐ and ๐ decreasedwith increase in Reynolds number.
(v) The value of pressure drop gradually increases withincrease in Reynolds number.
Nomenclature
๐ถ : Specific heat of water (J/kgK)๐ท๐: Diameter of adapter (m)๐ท๐: Diameter of cover pipe (m)๐ทโ: Diameter of inner pipe (m)โ: Heat transfer coefficient (W/m2 K)๐พ: Thermal conductivity of water (W/mK)๐ฟ๐: Centre distance between two adapters๐ฟ๐: Length of cover pipe (m)๐ฟโ: Length of inner pipe (m)๐: Mass flow rate (kg/s)Re: Reynolds number๐: Velocity of water (m/s)๐๐: Centre distance between two baffles๐: Density of water (kg/m3)๐: Viscosity of water (N s/m2)ฮ๐: Pressure drop (N/m2)ฮ๐: Change in temperature (โC)ฮ๐๐: Logarithmic mean temperature difference
๐: Inclination angle๐ผ: Ratio of adapter pitch to cover pipe
internal diameter๐ฝ: Ratio of length to internal diameter of
cover pipe๐พ: Ratio of length to internal diameter of
inner pipe๐ฟ: Ratio of length of cover pipe to baffle pitch.
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ISRN Chemical Engineering 5
Subscripts
๐: Adapter๐: Cold waterโ: Hot waterin: Water inletout: Water outlet.
References
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