design f a hot oil heat exchanger system · pdf filereasonable pressure drop in the heat...

International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 20 (2016) pp. 10102-10124

© Research India Publications. http://www.ripublication.com

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Design of A Hot Oil Heat Exchanger System

Karthik Silaipillayarputhur Ph.D. & Tawfiq Al Mughanam Ph.D.

Department of Mechanical Engineering King Faisal University, Kingdom of Saudi Arabia, 31982

Abdulmajeed Abdullah H Al Abdul Qader,

Moath Mohammed E Al Saikhan & Abdulrahim Abdulrazaq Al Abdulwahed

Department of Mechanical Engineering King Faisal University, Kingdom of Saudi Arabia, 31982

Abstract

This work presents the design of a hot oil heat exchanger

system wherein the heat exchanger and its associated pumping

system is developed by employing engineering standards. An

iterative mathematical approach is employed in the design of a

hot oil concentric tube heat exchanger (HX). The actual

conditions of the hot oil system from a chemical plant in

Chattanooga, TN is considered in this analysis. A

mathematical model is developed such that the required heat

exchanger’s dimensions and flow requirements are deduced to

necessitate a specified heat transfer. Thereafter, the

development of a pumping system for the hot oil heat

exchanger is examined.

Keywords: Heat Exchanger Modeling, Hot Oil System,

Concentric Tube Heat Exchanger

INTRODUCTION

Heat exchanger is an equipment used to transfer heat from a

higher temperature fluid to a lower temperature fluid. Therein,

a solid wall separates the two fluids. Heat exchangers can be

classified based on flow and construction. Based on

construction, heat exchangers can be classified as concentric

tube heat exchangers, shell and tube heat exchangers and

finned/unfinned heat exchangers. Likewise, based on flow,

they can be classified as parallel flow, counter flow or cross

flow. The choice of construction and flow circuiting are

dictated by the application and by the existing piping

connections available in the process plant.

In this paper, a hot oil concentric tube heat exchanger is

developed for a hot oil system in a chemical plant in

Chattanooga, TN. The hot oil is used for a certain process

heating application in the chemical plant. The hot oil flows

through the inner pipe, i.e., on the tube-side, and steam flows

through the annular space. It is assumed that abundant steam

flow rate is available to provide the required heating of the oil

in the concentric tube heat exchanger.

There are numerous references available in the literature

pertaining to heat exchanger performance modeling, and only

the most pertinent are discussed. Silaipillayarputhur and Idem

[1, 2] developed matrix approach for design and performance

evaluation of crossflow heat exchangers. Therein, the thermal

performance of the heat exchanger was evaluated at every

pass of the heat exchanger. Matrix approach helps the heat

exchanger designers to develop the optimum and a cost

efficient heat exchanger. Domingos [3] presented a general

method of calculating the total effectiveness and intermediate

temperatures of assemblies of heat exchangers. The

assemblies may consist of associations of any types of heat

exchanger. The method utilizes a transformation that relates

the inlet and outlet temperatures of the fluid streams and this

permits the derivation of closed form expressions. Pignotti

and Shah [4] and Shah and Pignotti [5] discussed the tools

developed previously (such as Domingos’ method, the

Pignotti chain rule, etc.) to determine the relationship for

highly complex heat exchanger flow arrangements. Navarro

and Gomez [6] developed a mathematical model for cross

flow heat exchangers for determining the Effectiveness-NTU

(number of transfer units) relations. The model developed

represents a useful research tool for theoretical and

experimental studies on heat exchanger performance. Gomez

et.al [7] studied the thermal performance of multi pass parallel

and counter cross flow heat exchangers by applying a new

numerical procedure. The thermal effectiveness of the heat

exchanger at various passes with respect to capacity rate ratio

and NTU are presented in the form of tables.

Silaipillayarputhur et.al [8] developed a pumping system for a

heat transfer fluid. Therein, the details for choosing an

appropriate pump, head loss calculations, net positive suction

head (NPSH) calculations are detailed and such concepts are

applied in this work while designing pumping system for the

heat exchanger.

LIST OF SYMBOLS

cp = specific heat (J/kgºC)

D = tube diameter (m)

f = friction factor (dimensionless)

f1 = function (dimensionless)



h = convection heat transfer coefficient

(W/m2ºC)

k = thermal conductivity (W/mºC)

L = tube length (m)

m = mass flow rate (kg/s)

NTU = number of transfer units (dimensionless)

NPSH = Net positive suction head (pressure units)

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Nu = Nusselt number (dimensionless)

Pr = Prandtl number (dimensionless)

q = rate of heat transfer (W)

Re = Reynolds number (dimensionless)

T = temperature (ºC)

mT = log mean temperature difference (ºC)

V = velocity (m/s)

Greek Symbols :

1 = absolute roughness (m)

= pump efficiency (dimensionless)

µ = viscosity (Ns/m2)

= density (kg/m3)

Subscripts:

1 = inlet

2 = outlet

w = tube wall

DESIGN OF A CONCENTRIC TUBE HEAT

EXCHANGER SYSTEM

Consider Figure 1 describing the existing set up of the hot oil

system in the process plant.

Figure 1. Hot Oil System in the Process Plant

The hot oil employed in the system is a Conoco diamond class

heat transfer fluid, rated for open systems, having a viscosity

grade of ISO 46. The operating temperature of the hot oil is at

200°C and it is proposed to raise the operating temperature of

hot oil to 210°C in the hot oil reservoir tank by employing 300

lb/in2 saturated steam.

A heating system is proposed for the hot oil reservoir tank

consisting of a concentric tube heat exchanger along with its

associated pumping system. The thermal properties of the hot

oil at the operating temperature are described in Table 1.

Table 1. Hot Oil Thermal Properties [12]

Hot Oil Thermal Properties Tavg

(oC)

(kg/m3)

CP

(J/kg-oC)

k

(W/m-oC)

(N-s/m2)

761 2558 0.133 0.00117 205

Mathematical heat exchanger model

This project initially aims to develop a mathematical heat

exchanger model that can be employed to design a concentric

tube heat exchanger. It is assumed that the steam flows on the

annular-side of the concentric tube heat exchanger, hot oil is

present on the tube-side, and the two fluids are separated by a

thin solid tube wall. The mass flow rate of 300 lb/in2 saturated

steam in the annular-side is sufficient to maintain the tube

wall at the steam saturation temperature. The heat exchanger

operates under steady conditions, and the effects of fouling

are disregarded in the analysis.

In this study, the required oil temperature raise is known and

the mass flow rate of oil is chosen based on the level

requirement in the hot oil reservoir tank. In addition,

reasonable pressure drop in the heat exchanger piping is fixed

based on industry practices. These are described in Table 2.



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Table 2. Inputs for heat exchanger design

Input Values

(kg/s)

T1

(˚C)

T2

(˚C)

Tw

(˚C)

Δp

(Pa)

0.48 200 210 214 34,500

The sensible heat transfer from the concentric tube heat

exchanger’s tube wall to the hot oil may be given as [10]

m12p πDLhΔTTTcmQ (1)

The log-mean temperature difference is the effective mean

temperature difference between the tube wall and the oil. This

can be described as [8]

2w

1w

2w1wm

TT

TTn

TTTTT

(2)

Assuming an adequate pipe length such that the flow is fully

developed, the average heat transfer coefficient along the pipe

may be expressed through Dittus-Boelter correlation [10]

0.40.8Pr0.023Rek

hDNu

(3)

10D

L

000,10Re

160Pr7.0

The dimensionless pressure loss expressed by Darcy friction

factor can be given as [9]

DρV

LΔP2

21

f (4)

For fully developed turbulent flow in a pipe the relation

between the friction factor, pipe relative roughness, and the

Reynolds number may be given as [9]

Re

6.9

3.7

Dε1.8log

11.11

1

f (5)

4000Re

The quantity D1 represents the relative roughness, and

the Reynolds number based on pipe diameter is defined as [9]

VDRe

(6)

The mean oil velocity in the pipe may be described as [9]

2D

m4V

(7)

Upon rearranging Equation 1 and employing Equation 3,

Equation 1 can be expressed in dimensionless form as follows

0

TT

TTln

1

k

cVD023.0

kL

cmf

2w

1w

4.0

p

8.0

p

1

(8)

Likewise, substituting Equation 4 in Equation 5 and upon

rearranging yields the following dimensionless expression

0VD

9.67.3

Dlog8.1

pD2

LVf

11.1

12

2

(9)

Similarly, upon rearranging Equation 7, yields the subsequent

dimensionless expression

0

4

m

VDf

2

3

(10)

The quantities f1, f2, and f3 represent simultaneous nonlinear

algebraic equations. By employing numerical techniques such

as Newton Raphson method, Secant method, etc., the

unknown quantities such as pipe diameter D, length of the

concentric tube heat exchanger L, and flow velocity V can be

iteratively determined.

MATLAB software has an inbuilt solver for solving

simultaneous nonlinear algebraic equations. A MATLAB

code was developed to solve these nonlinear algebraic

equations. Likewise, an Excel model employing Newton

Raphson method was employed to solve the nonlinear

algebraic equations. The results from the MATLAB matched

well with the Excel mathematical model.

Therefore, by solving the simultaneous nonlinear algebraic

equations, the design of the inner pipe of the concentric tube

heat exchanger is obtained. The required length, diameter, the

required flow velocity for the prescribed inlet conditions are

presented in Table 3. The diameter of the outer pipe (annulus)

is not of much concern as it is assumed that abundant flow

rate of steam is available to maintain the inner pipe wall at the

saturation temperature.

Table 3. Heat exchanger baseline geometry

Input Values Concentric Tube HX Design

(kg/s)

T1

(˚C)

T2

(˚C)

Tw

(˚C)

Δp

(Pa)

D

(m)

L

(m)

V

(m/s)

0.48 200 210 214 34,500 0.021 20.09 1.81

Pumping system

A separate pumping system for the hot oil heat exchanger was

erected to serve the heating requirements. Since the hot oil is

operating at elevated temperatures, and since material failure

could cause a catastrophic incident, it is very important to

select the pump, piping and its associated fittings per the

engineering requirements.

Silaipillayarputhur et al. [8] has previously described the

development of a pumping system, and the corresponding

methodology is applied herein.

Hot Oil Pump Selection It can be noted from [8] that the centrifugal pump is most

suitable when the mass flow rate is not of an absolute concern,

and when the kinematic viscosity of the fluid at operating

temperature is similar to that of water at room temperature.

Herein, at the operating temperature, the kinematic viscosity



10105

of the hot oil is very similar to that of water at room

temperature. In-addition, the hot oil mass flow rate variations

of +/- 5% is acceptable for the heat exchanger application.

Therefore, a centrifugal pump is chosen for circulating the hot

oil through the concentric tube heat exchanger. Also, from [8],

it can be noted that canned motor pumps are more suitable for

applications involving high temperature fluids, as they contain

the pumped fluid in case of a disastrous mechanical failure.

Thus, a canned motor centrifugal pump is chosen for the given

application.

NPSH Calculation for the Hot Oil Pump Per [8], it can be noted that performing net positive suction

head (NPSH) calculations is very important for smooth and

safe operation of the pump. The available net positive suction

head, NPSH(A), must be more than the required net positive

suction head, NPSH(R). NPSH(R) is provided by the pump

manufacturers. If NPSH(A) is less than NPSH(R), cavitation

will occur and would hamper the smooth operation of the

pump. It is a common industry practice to maintain NPSH(A)

> 25 psig for safe and reliable operation of a centrifugal

pump.

NPSH(A) is given as follows [8]:

NPSH(A) = Inlet Pump Pressure – Vapor Pressure of the

Fluid Being Pumped (11)

The inlet pressure is the summation of the available tank

pressure and the head pressure available in hot oil tank. Thus:

Inlet Pump Pressure

= Tank Pressure + Available Head in Tank (12)

Per the calculations as described in Appendix I, for the

existing conditions, NPSH(A) was determined to be 73.5 psig.

Thus, it can be presumed that the centrifugal pump is safe for

the given operating conditions. However, during the

procurement of the canned motor pump, this information must

be communicated with the pump manufacturer to ensure that

the NPSH(A) is actually safe for the operation of the canned

motor pump.

Hot Oil Pump Flow Rate Calculation The hot oil reservoir tank has a capacity of 100 gallons. 40

gallons per minute (GPM) of hot oil is consumed by the

plant’s process. It was also essential to maintain the tank level

at around 50%. Therefore, to maintain the desired tank level,

the flow rate of hot oil from the reservoir tank for heating

purposes was set at 10 GPM. Since the hot oil pump facilitates

the flow of hot oil from the reservoir tank and through the

concentric tube heat exchanger, the pump’s flow rate is set at

10 GPM as well.

Head Loss Calculation in the Pumping System Consider Figure 2 describing the hot oil system consisting of

the proposed concentric tube heat exchanger along with its

necessary piping.

Figure 2. Hot Oil System with the Heating Arrangement

While selecting the pump it is very essential to know the flow

rate along with the head it needs to develop.

The total head loss is a summation of frictional head loss and

head loss due to vertical piping. [8] Thus:



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Total head loss = Frictional Head Loss + Head Loss due to

Vertical Piping (13)

The required discharge pressure from the pump based on head

loss calculations can be given as [8]:

Required Dis. Pressure of Pump =

Total Head Loss + Total Pressure to Overcome in Tank +

Excess Pressure at Tank Inlet (14)

Thus, the pressure that the pump needs to develop can be

given as [8]

(ΔP)pump = Required Dis. Pressure of the Pump – Inlet

Pressure to the Pump

(15)

The head loss calculation and the required pump head

calculations are all detailed in Appendix I.

Based on calculations, it can be seen that the canned motor

pump (1.0” x 3/4”) must develop 10 GPM at 120 ft. of head

for the proposed heating arrangement.

Material Selection

DuPont Process Safety Management (PSM) standards [9], a

starting point for the Occupational Safety and Health

Administration (OSHA) regulations, is employed in this

project. DuPont PSM standards have been widely accepted

and implemented across the globe and is considered as one of

the best safety standards in the world. The material selection

by using the DuPont PSM standards for pipe, fittings, valves,

gaskets, insulation, studs and nuts are detailed in Appendix II.

By referring to the Appendix II, it can be observed that there

are various alternatives for material/equipment selection.

Pump: Canned motor pump (with stainless steel casing) or

conventional centrifugal pump (stainless steel casing) with

double mechanical seal

Heat exchanger and piping for the heat exchanger: ERW to ASTM A587* (NPS ½ - 4); or ASTM A106, ASTM

A53.

Fittings: Socket-welding, forged steel, ASTM A105, ASME B16.11

(or) Butt-welding, carbon steel, ASTM A234 Grade WPB

seamless

Valves: G37B Flanged gate valve or G35V Flanged gate valve. Valve

codes are described in Appendix II.

Gaskets for flanges: G63G4 (or) G63F4 flexattalic gaskets. Gasket codes are

described in the Appendix II.

Insulation: Type B or Type T or Type F insulation cover. Insulation

codes are described in Appendix II.

CONCLUSION

In this research work, the design of a hot oil heat exchanger

system has been considered. The heat exchanger employed in

the analysis is a concentric tube heat exchanger. Concentric

tube heat exchangers are regularly employed in process

industries and can be constructed by the technicians at the

process plant. A unique mathematical methodology was

presented for the design of a concentric tube heat exchanger.

Fundamental and widely accepted empirical expressions were

applied in the development of the mathematical heat

exchanger model. By applying this approach, the heat

exchanger’s length, flow velocity and diameter can be

determined iteratively. The proposed mathematical technique

is straightforward and can be readily applied for the design of

any concentric tube heat exchanger.

Thereafter, the required pumping system for the heat

exchanger was developed by employing DuPont engineering

standards. DuPont engineering standards are widely employed

in process industries around the globe, and these standards

provided the basis for the development of OSHA regulations.

Pump selection, pump head & flow rate calculations, material

selection for piping, fittings and insulation are detailed in this

document.

REFERENCES

[1] Silaipillayarputhur, K. and Idem, S., 2013, “A general

Matrix Approach to model steady state performance of

cross flow heat exchangers”, Heat Transfer

Engineering, Volume 34, Issue 4, page 338-348.

[2] Silaipillayarputhur, K. and Idem. S., 2013 “Practical

Validation of a Matrix Approach Steady State Heat

Exchanger Performance Model”, Journal of Applied

Global Research, ISSN: 1940-1841, Volume 6, Issue

17, page 1-22.

[3] Domingos, J. D. 1969. Analysis of Complex

Assemblies of Heat Exchangers, Int. J. Heat Mass

Transfer, Vol. 12, pp. 537-548.

[4] Pignotti, A. and Shah, R. K. 1992. Effectiveness-

number of transfer units relationships for heat

exchanger complex flow arrangements, Int. J. Heat

Mass Transfer, Vol. 35, No. 5, pp. 1275-1291.

[5] Shah, R. K. and Pignotti, A. 1993. Thermal Analysis of

Complex Crossflow Exchangers in Terms of Standard

Configurations, J. Heat Transfer, Vol. 115, pp. 353-

359.

[6] Navarro, H.A. and Cabezas-Gomez, L.C. 2007.

Effectiveness-NTU Computation with a Mathematical

Model for Cross-Flow Heat Exchangers, Brazilian J.

Chem. Eng., Vol. 24, No. 4, pp. 509-521.

[7] Cabezas-Gomez, L., Navarro, H.A., and Saiz-Jabardo,

J.M. 2007. Thermal Performance of Multipass Parallel



10107

and Counter Cross-Flow Heat Exchangers, J. Heat

Transfer, Vol. 129, pp. 282-290.

[8] Silaipillayarputhur, K., Al-Muhaysh, K., and Al Yahya,

O., 2016, “Design of a Dowtherm A Pumping System”,

International Journal of Applied Engineering Research,

ISSN: 0973-4562, Volume 11, Issue 1, page 265-272,

Research India Publications, India.

[9] Fundamentals of Fluid Mechanics; 6th edition; Munson,

Okiishi and Huebsch; Wiley Inc., 2009; ISBN: 978-

0470-26284-9.

[10] Incropera F.P., Dewitt, D.P., Bergman, T.L., Lavine,

A.S., Fundamental of Heat and Mass Transfer. 4th

Edition. John Wiley & Sons, Inc., NY, 2006.

[11] DuPont Technology Consulting; E.I. Du Pont Nemours

Engineering Standards; 2002 revision.

[12] Material Safety Data Sheet (MSDS) Conoco Diamond

Class heat transfer fluids rated of open systems, Philips

66 lubrican



10108

Appendix I

Inputs NPSH CalculationTank Pressure 75 psig

Diameter of Pipe D 0.021 m 5.10204082 barg

Length of pipe L 20.09 m 515306.122 N/m2

Velocity of hot oil V 1.81 m/s 69.0258301 m

Hot oil density ρ 761 kg/m3 Head Pressure 12 ft

Thermal conductivity k 0.13321 W/mK 3.66 m

Specific heat cp 2558.1 J/kg.K 27323.4006 N/m2

Kinematic viscosity ʋ 0.00000154 m2/s Vapor pressure of hot oil 0.078 psig

Flow rate Q 0.0006309 m3/s 0.00530612 barg

Mass flow rate mdot 0.48 kg/s 535.918367 N/m2

NPSH (A) (Tank Pr + Head Pr - Vapor Pr) 542093.605 N/m2

Diameter (in) 0.826771654 in 5.36726341 barg

Pipe size corresponding to pipe chart 3/4" 78.8987722 psig

Total Piping 50 m Pump is safe for operation as NPSH (A) > 25.0 psig

Pump ΔP Calculation

Total Piping 50 m Head loss due to 4 Elbows (minor loss) 0.20037309 m

Vertical piping 7 ft Head loss due to 6 Gate Valves (minor loss) 0.15027982 m

2.1336 m Head loss due to sudden expansion (minor loss) 0.16697757 m

Reynolds number Re 24681.81818 Head loss due to sudden contraction (minor loss) 0.08348879 m

Steel roughness ε1 0.000046 m Total minor losses 0.60111927 m

ε1/D 0.002190476 Total frictional head loss (major+minor) 11.5341747 m

f (from Moody chart) 0.0275 Total Head loss (total loss + vertical piping) 13.6677747 m

Frictional Head loss due to piping (major loss) 10.93305543 m

Pressure to overcome at inlet (tank pr + head pr) 72.6858301 m

Friction loss cofft - Elbow 0.3 Excess pressure desired at inlet (industry norm) 25 psig

Friction loss cofft - Gate Valve 0.15 for ease of entry back into the tank 1.70068027 barg

Friction loss cofft - Sudden Contraction 0.5 171768.707 N/m2

Friction loss cofft - Sudden Expansion 1 23.00861 m

# of Elbows 4 109.362215 m

# of Gate Valves 6 816433.772 N/m2

# of Sudden Expansion 1 8.0835027 barg

# of Sudden Contraction 1 118.82749 psig

Pump Inlet Pressure (Tank Pressure + Head Pressure) 72.6858301 m

Hence pump must develop (Dis. Pr - Inlet Pr) 36.6763847 m

120.329346 ft

273804.249 N/m2

2.71093316 barg

39.8507175 psig

Reqd Pump Dis. Pressure (Losses+Pr. To overcome+

Excess Pr. Desired)

Piping Calculations



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Appendix II

Selection of Pipe, Fittings and Insulation:



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design f a hot oil heat exchanger system · pdf filereasonable pressure drop in the heat...

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