1-s2.0-S1359431198000647-main

Performance evaluation of a radiator in a diesel engineÐacase study

D. Ganga Charyulu a, *, Gajendra Singhb, J.K. Sharmac

aEnergy Systems Division, Thapar Corporate Research and Development Centre, Bhadson Road, Post Box 68, Patiala,

Punjab 147 001, IndiabThapar Institute of Engineering and Technology, Patiala-147 001, IndiacBeant College of Engineering and Technology, Gurdaspur, Punjab, India

Accepted 28 April 1998

Abstract

Performance evaluation of a radiator mounted on a turbo-charged diesel engine has been made withand without fouling factor. Heat transfer estimation indicates that the radiator is over designed. Thecharacteristics of the radiator have been analyzed for di�erent tube rows with varying air mass velocitiesto enable the design engineer to select the size depending upon the requirement and application. Thestudy also examines the e�ect of di�erent materials of construction of ®ns and tubes. It has beenobserved that the copper ®ns with copper, brass and carbon steel tubes o�er the same heat transfer andpressure drop characteristics. However, the designer must look into the mechanical properties of thesematerials as they suit the requirements. # 1999 Elsevier Science Ltd. All rights reserved.

Keywords: Radiator; Heat transfer; Fouling factor; Turbo-charged diesel engine; Pressure drop

Nomenclature

A total heat transfer surface area, m2

A0 free ¯ow areas on one side of the exchanger, m2

Af surface area of ®n exposed to heat transfer, m2

A fr air side frontal area on one side of the exchanger, m2

A nf non ®n area, m2

Applied Thermal Engineering 19 (1999) 625±639

1359-4311/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved.PII: S1359-4311(98)00064-7

PERGAMON

* Corresponding author. Tel.: 91 175 393 607; fax: 91 175 212002/012; e-mail: [email protected].

b ®n spacing, mB ¯uid ¯ow (air) length, mCf circumference of ®n exposed to heat transfer, mCP speci®c heat of ¯uid at constant pressure, J/kg 8CDh hydraulic diameter of ¯ow passage, mf fanning friction factor, dimensionlessG mass velocity, kg/m2 sH total water ¯ow length, mh heat transfer coe�cient, W/m2 8Cj Colburn factor, dimensionlessk ¯uid thermal conductivity, W/m 8Ckf thermal conductivity of ®n material, W/m 8Cl ®n length for heat conduction from primary to the mid point between plates for symmetric

heating, mL non-¯uid ¯ow length, mm ®n parameter, mÿ1

P pressure, PaPr Prandtl number, dimensionlessRe Reynolds number based on hydraulic diameter, dimensionlessrh ¯ow passage hydraulic radius, mr fouling resistance, (W/m2 8C)ÿ1

rt tube wall resistance, (W/m2 8C)ÿ1

T ¯uid temperature, 8CU overall heat transfer coe�cient, W/m2 8CV volume, m3

W ¯uid mass ¯ow rate, kg/sa ratio of total heat transfer area of one side of the exchanger to its volume, m2/m3

r density, kg/m3

d thickness of ®n, mm ¯uid dynamic viscosity, Pa.ss ratio of free ¯ow area to frontal area, dimensionless

Subscripts

a airc cold ¯uid sideh hot ¯uid sidew water1 inlet condition2 outlet condition

D.Ganga Charyulu et al. / Applied Thermal Engineering 19 (1999) 625±639626

1. Introduction

The recent high power diesel engines with 6, 8 and 12 cylinders are being produced in thecategory of naturally aspirated; turbocharged and turbocharged and aftercooled versionshaving a power range from 188 to 368 kW (160 to 500 H.P.) depending on the application.These are water cooled; water cooled and turbocharged and water cooled, turbocharged andaftercooled versions. The rpm varies from 1500 to 2500 and the compression ratio varies from1:16.5 to 1:14.6. These diesel engines [1, 2] are associated with three compact heat exchangersi.e. radiator, oil-cooler and after-cooler to dissipate the generated heat in the system to theenvironment. Radiator, oil-cooler and after-cooler are used in turbo-charged diesel engines forcooling the engine body cooling water, lubricating oil and turbo-charged air, respectively. Airis the cooling ¯uid for the radiator and water is the cooling medium for oil-cooler and after-cooler. The layout of the diesel engine is shown in Fig. 1.The radiator mounted on the present turbo-charged diesel engine of type TBD 232 V-12 is

required to dissipate 147.06 kW (529.65 MJ/h) heat. It is a cross ¯ow compact heat exchanger

Fig. 1. Diesel engine layout.

D.Ganga Charyulu et al. / Applied Thermal Engineering 19 (1999) 625±639 627

with unmixed ¯uids and air is being used as coolant. The type of the radiator core is shown inFig. 2. It consists of 644 tubes with six tube rows. The tube cross section is rectangular withcircular ends. There are 346 ®ns and these are continuous ®ns. The materials of constructionfor tubes and ®ns are brass and copper, respectively.The objective of this study is to assess the performance of the existing radiator under the

following conditions of operation:

1. The characteristics of the radiator core [3, 4] for any number of tube rows, water ¯ow rateand air ¯ow rate. It will help the designer selecting the number of tube rows for a givenapplication.

2. The performance evaluation with varying fouling factors. Performance is evaluated on thebasis of fouling factors given in the literature [7, 8] (TEMA standards). Since, the quality of¯uids viz. air, water and oil in India are di�erent from TEMA standards and also variesfrom region to region, it is, therefore, thought desirable that the performance of heatexchanger should be evaluated with di�erent fouling factors.

3. The performance and economic feasibility for various materials in construction of ®n andtube. In this context, it is thought desirable to analyze the radiator for di�erent materials [9]for ®ns and tubes i.e. copper±copper, copper±brass, copper±carbon steel, aluminum±aluminum, cupro nickel±cupro nickel, carbon steel±carbon steel and stainless steel±stainlesssteel.

Fig. 2. Radiator core.


2. Useful relations for surface and core geometry

Certain geometrical relations [3] are necessary in the application of the basic heat transfer and¯ow friction data to the design problem. The following geometrical factors are required as a designresult for each of the two sides of the complete exchanger core:A total heat transfer area, m2;A0 free ¯ow area of one side of exchanger, m2;A fr frontal area of one side of the exchanger, m2;B air ¯ow length in the exchanger, m;V total volume of the exchanger, m3;aa ratio of total heat transfer area of one side of the exchanger to its volume, m2/m3.The equations below give the relations between surface and core factors for one side of the

exchanger.

rh � L�A0=A� �1�

A0 � �sAfr� � �Arh=L� � fAs=�La�g �2�

Afr � LH �3�

V � LBH �4�

a � A=V � fA=�LAfr�g � �s=rh� �5�

s � �A0=Afr� � fArh=�LAfr�g � �Arh�=V �6�

3. Equations used for the calculations [3]

3.1. Air side calculations

(1) Stream heat capacity rate, Ca

Ca �Wa � Cp;a: �7�(2) Heat transfer coe�cient [4], ha

ha � jaGaCP;a=�Pr;a�2=3; �8�

ja � 0:174=�Re;a�0:383 �9�where

Ga � core mass velocity �W=A0 �W=Afrsa; �10�


Re;a � Reynolds number � Ga �Dh;a=ma: �11�(3) Temperature e�ectiveness of ®ns (®n e�ciency)

Zf � Tanh�ml�=�ml� �12�where

m � �2� ha=�kf � d��1=2: �13�(4) Total surface temperature e�ectiveness

Z0 � 1:0ÿ �1:0ÿ Zf� � Af=A: �14�(5) Pressure drop (neglecting the expansion and contraction loss coe�cients)

DPa � PiG2a=�2Piri� � ��1ÿ s2a� � 2f�ri=r0� ÿ 1g � �fBri=rh��1=r�m ÿ �1ÿ s2a��ri=r0�� 15�

where

f � 0:3778=R0:3565e;a ; �16�

�1=r�m � f�1=ri� � �1=r0�g=2: �17�

3.2. Water side calculations

(1) Stream heat capacity rate, Cw

Cw �Ww � Cp;w: �18�(2) Heat transfer coe�cient [3]

hw � Nu;w � kw=Dh;w �19�where Nusselt number,

Nu;w � 0:023� �Re;w�0:8 � �Pr;w�0:3; �20�Reynolds number,

Re;w � Gw �Dh;w=mw: �21�(3) Pressure drop

DPw � G2w � fw �H=�2� r� �Dh;w=4�� 22�

where

fw � 0:079� �Re;w�ÿ0:25: �23�Heat capacity rate ratio, C*


C� � Cmin=Cmax � Ca=Cw � Cc=Ch: �24�Heat exchanger e�ectiveness, E

E � Ch � �Th1 ÿ Th2�=�Cmin � �Th1 ÿ Tc1�� 25�or

E � Cc � �Tc2 ÿ Tc1�=�Cmin � �Th1 ÿ Tc1�� 26�Overall heat transfer coe�cient, based on air side area (Ua).(1) Neglecting the very small wall resistance,

1=Ua � 1=�Z0ha� � 1=��aw=aa�hw�: �27�(2) Considering wall resistance and fouling factors

1=Ua � 1=�Z0ha� � 1=��aw=aa�hw� � rh � rc � rt: �28�Rate of heat transfer(1) Heat gained by air through ®ns

Qf � �hakfAfCf�1=2 � Tanh�ml� � DT� 2� no: of fins �29�(2) Heat gained by air through the non ®n area

Qnf � Ua � Anf � DT: �30�(3) Total heat gained by air

QT � �Qf �Qnf� � no: of tubes: �31�

4. Computer program

For implementing the analysis, a PC based computer program in FORTRAN is developed forthe compact heat exchanger of the turbo-charged diesel engine. This program is useful inestimating the ¯uid properties at operating temperatures [5, 6], surface core geometry of cross¯ow heat exchanger, heat transfer coe�cients, pressure drops, overall heat transfer coe�cientand heat transfer rate.The program utilizes a subroutine for evaluating the thermal properties of air based on the

operating temperatures, and a subroutine for calculating the thermal properties of water basedon the operating temperatures.The computer program requires the following inputs:

. ¯ow rates and temperatures of ¯uids;

. heat exchanger core dimensions;

. details of ®ns and tubes including thickness and thermal conductivities;

. number of tube rows;


. fouling factors.

5. Design speci®cations

Engine dataEngine type TBD 232 V-12Engine, kW 368Bore� stroke, m 0.12� 0.13Rated speed, RPM 2300Heat dissipation requirement, kW 147.06 (529.65 MJ/h)

6. Radiator design speci®cationsÐsee Appendix

7. Results and discussion

The existing radiator with copper ®ns and brass tubes is analyzed to compute heat transferrate from water to air with no fouling and no tube wall resistance and with fouling and tubewall resistance, and these computed values are 191.56 kW (689.95 MJ/h) and 184.23 kW(663.54 MJ/h), respectively, whereas the heat dissipation requirement is 147.06 kW (529.65 MJ/h).The characteristics of radiator core is analyzed for di�erent tube rows, i.e. for a total of 2

rows, 3 rows and the like up to 9 rows for heat transfer and pressure drop. The abovesituation is also analyzed for various air mass velocities ranging from 4.0 to 16.0 kg/m2 s andthe results are presented graphically in Fig. 3. This shows the heat transfer and pressure dropcharacteristics of the above said core with air ¯ow rates varying from 9000 to 30,000 m3/h andhaving an increment of 500 m3/h. The main aim of providing this type of graph is to enablethe design engineer to decide the number of tube rows required for a given heat dissipationrequirement for the same frontal area and select the appropriate fan to overcome the pressuredrop developed in the radiator core.The existing radiator is then considered for performance evaluation with varying fouling

factors. Initially, performance is evaluated on the basis of fouling factors given in theliterature [7, 8] (TEMA standards). The quality of ¯uids viz. air, water and oil in India aredi�erent from TEMA standards and also varies from region to region. Therefore, the


performance of the heat exchanger is evaluated for di�erent fouling factors, having values upto 50% extra than the TEMA standards. Based on these results a graph is plotted betweenpercent reduction in heat transfer rate against percent excess in fouling and is given in Fig. 4.With this study, even for the worst operating conditions of the radiator, the design engineercould be in a position to design the radiator to meet the heat dissipation requirement.

Fig. 3. Radiator core characteristics.


Radiator performance is also evaluated for di�erent materials of construction [9] of ®ns andtubes, say, copper, brass, aluminum, cupro-nickel, carbon steel and stainless steel 304 and 316types by assuming that the bonding e�ciency between tubes and ®ns is 100%. Theperformance evaluation is carried out for various combinations of di�erent materials for ®nsand tubes under normal operating conditions of the radiator and is given in Table 1.

Table 1

Heat transfer rates for various combinations of di�erent materials of ®ns and tubes under normal operating con-ditions*

S No Fin Tube Q1, kW (MJ/h) Q2, kW (MJ/h)

1 Copper Copper 191.56 (689.95) 184.23 (663.56)2 Copper Brass 191.56 (689.95) 184.23 (663.54)3 Copper Carbon steel 191.56 (689.95) 184.22 (663.51)4 Aluminum Aluminum 188.42 (678.63) 181.25 (652.79)

5 Carbon steel Carbon steel 167.11 (601.87) 160.96 (579.72)6 Cupro-Nickel Cupro-Nickel 160.48 (577.99) 154.64 (556.96)7 Stainless steel Stainless steel 130.86 (471.30) 126.34 (455.04)

304 and 316 304 and 316

*Here Q1 and Q2 are the rates of heat transfer from water to air with no fouling and no tube wall resistance andwith fouling and tube wall resistance, respectively.

Fig. 4. Reduced rate of heat transfer against excess fouling.


The performance evaluation is also done for four cases of di�erent sets of parameters asgiven in Table 2, and the results are shown in Figs. 5, 6, 7 and 8.From the graphs shown in Figs. 5±8, it is observed that for a given set of core geometry and

¯uid parameters, there is an excess of the heat transfer of the order of 30%, while using copper®ns with copper tubes, brass tubes and carbon steel tubes. Aluminum material for ®ns andtubes shows an excess of 28% in heat transfer. Also, with carbon steel for ®ns and tubes thisexcess is reduced to 13%, while cupro-nickel as material for ®ns and tubes provide an excess of

Fig. 5. Rate of heat transfer and pressure drop against air ¯ow rate.

Table 2

S No Parameter Case-1 Case-2 Case-3 Case-4(Fig. 5) (Fig. 6) (Fig. 7) (Fig. 8)

1 Air ¯ow rate, m3/h Variable 23,386 23,386 23,386

(5000±50,000)2 Air inlet temperature, 8C 50 Variable 50 50

(25±75)3 Water ¯ow rate, 1pm 290 290 Variable 290

(50±500)4 Water inlet temperature, 8C 94 94 94 Variable

(80±98)


Fig. 6. Rate of heat transfer and pressure drop against air inlet temperature.

Fig. 7. Rate of heat transfer and pressure drop against water ¯ow rate.


9% only. However, the stainless steel material for ®ns and tubes do not meet the requirementfor a given set of parameters. The system parameters should, therefore, be selected verycarefully when stainless steel is selected. Based on these observations, it is clear that theselection of ®n material is very important.It is also observed that the copper ®ns with copper, brass and carbon steel tubes o�er the

same heat transfer and pressure drop characteristics. The designer should, therefore, look intothe mechanical properties of these materials suiting the requirement of the radiator.

8. Concluding remarks

A mathematical model and computer software package is developed for the radiator of aturbo-charged diesel engine. This software is useful for predicting the heat transfer rate andpressure drop. A nomograph is presented for selecting the number of tube rows suiting therequirement of the radiator. All variables, i.e. ¯ow rates of ¯uids, inlet temperature of ¯uids,fouling factors and materials of construction, that may in¯uence the performance of a corehaving a particular ®n pitch, are considered during the study.

Fig. 8. Rate of heat transfer and pressure drop against water inlet temperature.


Acknowledgements

The authors express their gratitude to Dr M. P. Kapoor, Director, TCRDC, Patiala and M/sGreaves Limited, Pune for providing the necessary facilities during the conduct of this researchwork.

Appendix

Fluid parameters (normal operating conditions)

S No Description Air Water

1 Fluid ¯ow rate, m3/h 23,386 17.4(290 l per min)

2 Fluid inlet temperature, 8C 45±50 943 Fluid temperature rise/drop, 8C 28 6

Core dimensions of radiator. Core width, m, 0.937; core height, m, 0.940; core depth, m, 0.111

S No Description Tube Fin

1 Materials of construction Brass Copper2 Size 1/2 in� 1/8 in 937 mm3 Total number 644 3464 Number of tube rows 6 Ð5 Type of tube Rectangular with circular end Continuous sheet ®n6 Fin pitch Ð 9.5 (®ns/inch)

Surface and core geometry of ¯at tubes, continuous ®ns

S No Description F.P.S. units S.I. units

1 Fin pitch 9.5 ®ns/inch 374 ®ns/meter2 Fin spacing, b, 0.105 in 2.674� 10ÿ3, m3 Fin thickness 2.756� 10ÿ3, in 0.07� 10ÿ3, m4 (Free ¯ow area/ 0.621 0.621

Frontal area) sa5 (Total heat transfer area/ Ð 745.0

total volume) aa, m2/m3

6 Fin area/total area 0.748 0.7487 Hydraulic diameter, 4rh 0.1313 in 3.335� 10ÿ3, m


Fouling factors [7, 8]

S No Fluid Units TEMA standards

1 Air (W/m2 8C)ÿ1 3.52175� 10ÿ4

2 Water (W/m2 8C)ÿ1 8.80437� 10ÿ4

References

[1] L.R.C. Lilly, Diesel Engine Reference Book. Butterworths, London, 1984.

[2] N. Watson, M.S. Janota, Turbocharging the Internal Combustion Engine. MacMillan Press, London, 1982.[3] W.M. Kays, A.L. London, Compact Heat Exchangers. 3rd ed, McGraw-Hill, New York, 1984.[4] D.G. KroÈ ger, Radiator Characterization and Optimization. no. 840380, vol. 93, SAE Transactions, 1984, pp.

2.984±2.990.[5] R.H. Perry, D.W. Green, J.O. Maloney, Perry's Chemical Engineers' Handbook. 6th ed, Int. Student ed.,

McGraw-Hill, Tokyo, 1984.

[6] E. Krasnoshchekov, A. Sukomel, Problems in Heat Transfer. Mir Publishers, Moscow, 1977.[7] K. Ramesh, Shah, Fouling of heat exchangers. Advanced study institute on Heat Transfer equipment design.

Vol. 2, National Chemical Laboratories, Pune, India, 1986, pp. 9.89±9.129.[8] Heat exchangers design handbook, Thermal and Hydraulic Design of Heat Exchangers. Vol. 3, Hemisphere,

New York, 1984.[9] Handbook Metals, 9th ed. volumes 2 and 3. Properties and selection. American Society for Metals, Metals

Park, Ohio, 1979.


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