CHEMICAL ENGINEERING TRANSACTIONS

VOL. 81, 2020

A publication of

The Italian Association
of Chemical Engineering
Online at www.cetjournal.it

Guest Editors: Petar S. Varbanov, Qiuwang Wang, Min Zeng, Panos Seferlis, Ting Ma, Jiří J. Klemeš

ISBN 978-88-95608-79-2; ISSN 2283-9216

Extending the Use of Welded Plate Heat Exchangers to Multi-

Stream Applications

Guillermo Martínez-Rodríguez, Jamel E. Rumbo-Arias, Martín Picón-Núñez*

University of Guanajuato, Department of Chemical Engineering, Noria Alta S/N, Guanajuato, Guanajuato, Mexico

picon@ugto.mx

Compabloc is a trademark of Alpha Laval and is one of the most efficient types of welded plate compact

exchangers (WPHE). Their construction features and thermal performance make this technology suitable for

application in a wide range of temperatures and pressures. This work focuses on the compabloc type of welded

plate and presents a conceptual extension of the design to the case of multi-stream applications. WPHE units

are finding wider application in heat recovery systems due to their construction features that enable them to

operate at high temperatures and pressures. Besides, the corrugated surfaces employed by this type of units

create high heat transfer performance at the expense of increased pressure drop which makes them transmit

the required heat duty within a smaller exchanger size compared with conventional geometries. Their

geometrical characteristics make it suitable for applications where more than two streams can meet their thermal

duties within the same structure. This paper presents the design considerations for the use of compabloc

exchangers that handle multiple streams. The multi-stream capabilities can be potentially used in the reduction

of the number of heat exchanger units in heat recovery networks. The paper looks first at a thermohydraulic

approach for the design of compabloc exchangers based on the full absorption of the pressure drop, then the

methodology is extended to the case of multi-stream applications. The approach is demonstrated on a case

study.

1. Introduction

Heat exchanger technologies such as the welded plate (WPHE) type represented by the commercially known

Compabloc exchanger of Alpha Laval, are suitable for applications where not only high temperature and

pressures prevail but also where high fouling is a serious problem as in the case of crude oil preheating trains

(Andersson et al., 2009). The heat transfer surface of the WPHE heat exchanger consists of corrugated plates

which create high turbulence and wall shear stress that, apart from increasing the heat transfer rate, tend to

increase pressure drop. Additional benefits of using compabloc units are less complicated handling compared

to conventional exchangers due to the smaller size required for the same duty, and smaller downtime for

maintenance (Anipko et al., 2006). Further investigations on the use of compabloc heat exchangers in refinery

applications show that better thermo-hydraulic performance is achieved when multi-passes are used (Tamakloe

et al., 2013).

There are some critical features that must be kept in mind in the development of new exchanger technologies,

for instance, from the mechanical point of view, the exchanger must have the mechanical strength to operate

under a wide range of operating conditions, and from the thermal side, the unit should exhibit a large heat

transfer coefficient and low pressure drop for a given fluid velocity. For instance, the fact that in WPHE the plates

are welded instead of being sealed with polymer gaskets gives them the capacity to operate under a wide range

of pressures and temperatures.

Cabezas-Gómez et al. (2012) developed a new cross flow arrangement for a single-phase unit and proposed

an expression for the thermal effectiveness of the new unit. The new layout arrangement resulted in an

improvement of the performance, particularly at large number of heat transfer units (Ntu). Such development

finds its best application in large exchangers. Sammeta et al. (2011) analysed the performance of 9 different

plate corrugations and derived a numerical model to determine thermal effectiveness-Ntu charts which are

DOI: 10.3303/CET2081081

Paper Received: 02/04/2020; Revised: 04/05/2020; Accepted: 15/05/2020
Please cite this article as: Martínez-Rodríguez G., Rumbo-Arias J.E., Picón-Núñez M., 2020, Extending the Use of Welded Plate Heat
Exchangers to Multi-Stream Applications, Chemical Engineering Transactions, 81, 481-486 DOI:10.3303/CET2081081

481

useful to determine the performance of such units under different operating conditions. These charts are valid

for Ntu ranging from 0 to 6 and Reynolds’s number 80 – 28,000 for constant heat capacity ratios, R.

The design and optimisation of compabloc heat exchangers was studied by Arsenyeva et al. (2016). The main

targets in their approach were the selection of the corrugation pattern of the surfaces and at the adjustment of

the number of passes. They proposed an optimisation model seeking to minimise fouling in crude preheat trains.

The construction of compabloc plate heat exchangers is such that the fluids flow in a crossflow arrangement in

each pass. Cross flow arrangements exhibit poorer thermal behaviour than counter-current units; however, the

linking of a cross flow unit with other cross flow units in series, making up an overall counter-current

arrangement, is a practical way of improving the overall thermal performance of the unit. Such a structure is

referred to as a complex assembly (Sammeta et al., 2011). The sizing of such units requires the determination

of the correction factor of the logarithmic mean temperature difference (Picón-Núñez et al., 2014).

A multi-stream heat exchanger is a heat transfer device that takes advantage of the construction features of

certain technologies that have the flexibility to accommodate more than three different streams within the same

structure (Picón-Núñez et al., 2006). In principle, the use of multi-stream heat exchangers could reduce the

complexity of existing heat recovery networks (Polley and Haslego, 2002). In this work, a methodology for the

design of compabloc heat exchangers is presented; the approach is extended to consider the case of multi-

stream applications.

2. Multi-stream arrangement

A compabloc heat exchanger consists of stacks of corrugated plates which constitute the heat transfer core of

the unit. The separation between the plates, which are welded to one another, form the channels for fluid flow.

Inside the unit, streams flow in crossflow fashion either in single or multiple passes. There are many possible

flow array combinations in a compabloc exchanger. In the case of multi-pass arrangements, the system is

arranged overall in counter-flow fashion for maximum thermal performance. Figure 1 shows different flow pass

arrangements that are possible in a compabloc unit. The construction characteristics of the compabloc

exchanger make it suitable for the processing of more than two units within the same frame. This feature could,

in principle, represent the capability for multi-stream applications. Figure 2 shows a basic diagram where a

single hot stream H1, exchanges heat with two cold streams C1 and C2. Subject to layout restrictions, the heat

recovery network of Figure 3a shows two possible multi-stream applications out of the various options in the

network. Figure 3b shows that the number of units has been reduced from 7 to 4.

Figure 1: Basic construction features of a compabloc heat exchanger. Different flow arrangements: a) four

passes on both streams, b) one pass on hot stream and four passes on cold stream.

Figure 2: Schematic of a compabloc exchanger handling three process streams.

Cold stream

inlet

482

3. Design considerations

The strategy for the design of compabloc multi-stream heat exchangers is composed of two main steps. In the

first, the dimensions of the plate are selected from the viable commercial dimensions. The selection is based

on the pressure drops allocated to the streams. The stream that has been assigned the lower pressure drop

determines the required plate dimensions. All other streams must conform to the given dimensions but the

number of passages is a function of the heat duty. The final design will give a block with the same type of plate

and the total height being the summation of the different units that are to be brought together into the same

frame. The sizing definition of a compabloc heat exchanger involves the definition of the following geometrical

features: the plate size (length), the height or number of plates, the number of passes per stream and the number

of plates per pass. The sizing of a heat exchanger proceeds after the calculation of each of the terms of the

design equation:

lm
TFU

Q
A


= (1)

W
khh

U


++=
21

11
1 (2)

Where Q is the heat duty, ΔTlm is the logarithmic mean temperature difference, U is the overall heat transfer

coefficient expressed for clean conditions in Eq(2), and F is the correction factor of the log mean temperature

difference. The terms h1 and h2 refer to the heat transfer coefficient of stream 1 and 2, τ is the thickness of the

separating wall and kw is the thermal conductivity of the material of construction.

Figure 3: Potential strategy for the simplification of a heat recovery network: a) simplified heat recovery network,

b) use of compabloc multi-stream exchangers.

In this work, the correction factor of the logarithmic mean temperature difference is obtained from (Kays and

London, 1984):

ta rra n g emeno th er

cu rren tco u n ter

Ntu

Ntu
F −= (3)

The term Ntuother arrangement refers to the number of heat transfer units of an arrangement different from counter-

current and Ntucountercurrent refers to the number of heat transfer units if the arrangement is counter-current. For

a given design problem, the overall thermal effectiveness (ε) can be determined from the inlet and outlet

temperatures. For example, for a case where the hot stream experiences the largest change in temperature

compared to the cold stream, the thermal effectiveness can be expressed as:

( )
( )

inCinh

outhinh

−

−
= (4)

The thermal effectiveness as a function of Ntu and C for a counter-current arrangement is calculated from:

)1(

1
CNtu

CNtu

e
−−

−−

−

−
= (5)

The overall thermal effectiveness (εoverall) of a heat exchanger exhibiting the same number of passes on each

stream (Figure 1a), is:

2C H1

C2 E1

E2 E3

a) b)

2C H1

483












−








−

−












−








−

−
= C

CC
n

overall 






1

1
1

(6)

Where C is the ratio of the mass flow rate-heat capacity of the for a given number of passes (n) and εp is the

thermal effectiveness per pass. From the equation of the thermal effectiveness of the single cross flow

exchanger, Eq(7), the Ntupass is obtained.

( )
























 −














−

−=

1
78.0

22.0
1

pas sN tuC

pas s
eNtuC

p
e

(7)

Then the total number of heat transfer units for the four-pass cross flow arrangement is:

passtarrangemenother
NtunNtu = (8)

The number of thermal plates in a compabloc unit is calculated from the overall heat transfer area and the

surface area per plate. The number of channels equals the number of thermal plates plus 1. The pressure drop

(ΔP) across the unit can be determined from:

h
dnfWGP 

2
2= (9)

Where n is the number of passes, G is the mass flow rate per unit area, W is the length of the plate, f is the

friction factor and ρ is the density. The value of G is determined from:

C
AmG = (10)

And dh is the hydraulic diameter given by:

2=
h

d (11)

Where , is the spacing between plates and φ is the factor of elongation. The cross-sectional area (Ac) to fully

absorb the specified pressure drop can be determined from Eq(12):

( )

( )y

P
y

h
d

nW
yy

c
A

−


+

−
















21

2
2




(12)

The number of plates is:

( )

( )y

plateshydraulic
Pd

nWxm

W
N

−











=

2
21






(13)

Where W is the plate length. Typical plate dimensions are in the range between 0.2 and 2.2 m. On the thermal

side, once the heat transfer surface area (A) is determined from Eq(1), the number of thermal plates (Nthermal

plates) is computed from the surface area of the plate (Aplate) as:

plateplatesthermal
AAN = (14)


2

WA
plate

= (15)

4. Heat transfer performance

The thermal design of single-phase heat exchangers in complex assembly requires that a close attention be

given to the determination of the heat transfer coefficients on both stream sides as well as the determination of

the correction factor of the logarithmic temperature difference. According to Hesselgreaves (2001), the type of

plate used in compabloc units exhibit a like performance to the type of plates used in plate and frame units.

Typical heat transfer and friction correlations for plate and frame surfaces are expressed in the form:

484

( ) 14.04.0PrRe
W

b
aNu = (16)

y
xf

−
= Re (17)

Where Re is the Reynolds number and Pr the Prandtl number. The values of coefficients and exponents of

Eq(16) and Eq(17) have been reported for various surface types by Arsenyeva et al. (2011). These values are

used in this work.

5. Case study

To demonstrate the proposed approach for multi-stream compabloc unit, the operating conditions and physical

properties of a three-stream problem, composed of one hot and two cols streams, is presented in Table 1. The

match between stream H1 and stream C1 (exchanger 1) transfers 1,491 kW, and the match between stream

H1 and stream C2 (exchangers 2) transfers 1,278 kW. The schematic of the heat recovery problem is depicted

in Figure 4. The plate dimension chosen for the design of exchanger 1 is also chosen as the basis for the design

of exchanger 2 that becomes the section of the multi-stream unit. The rationale being that for the two exchangers

to fit in the same structure, they must have the same plate dimension. At this stage, the design considers only

the possibility of both streams having the same number of passes. The plate dimensions are plate width: 0.9 m;

plate thickness: 2 mm; plate spacing: 5 mm; plate elongation: 1.15 and number of passes: 4. The values of a, b

x and y of Eq(16) and Eq(17) are: 0.265, 07, 10.7 and 0.07. The results of the design exercise are presented in

Table 2.

Figure 4: Schematic of the heat recovery problem for the design of a multi-stream compabloc exchanger.

Table 1: Physical properties and operating conditions of three-stream problem

H1 C1 C2

Mass flow rate (kg/s) 15.0 10.95 25.35

Inlet temperature (°C) 95 30 18

Outlet temperature (°C) 30 85 30

Pressure drop (Pa) 35,000 35,000 50,000

Density (kg/m3) 750 961.8 995

Heat capacity (J/kg °C) 2,840 3,180 4,200

Viscosity (Pa· s) 0.0008 0.00166 0.00089

Thermal conductivity (W/m °C) 0.19 0.66 0.59

Table 2: Design results of the three stream compabloc exchanger

Exchanger 1 Exchanger 2

Correction factor (F) 0.946 0.946

Thermal conductivity of material (W/m °C) 80

Exchanger surface area (m2) 108.35 72.62

Overall heat transfer coefficient (W/m2°C) 798.74 946.61

Heat load (kW) 1,491 1,278

Total number of channels 118 78

Exchanger height (m) 0.821 0.704

Pressure drop hot stream (Pa) 24,454.7 19,491.7

Pressure drop cold stream (Pa) 10,968.5 41,563.2

Multi-stream exchanger dimensions

Width (m) 0.9

Height (m) 1.52

485

6. Conclusions

This paper shows the development of a design methodology for the sizing of compabloc heat exchangers. The

methodology stems from the design principle of maximisation of the pressure drop. This objective can be

achieved provided the plates were available at any width. However, plates are available only in standard

dimensions so, full pressure drop absorption cannot effectively be achieved. Despite of this, the approach is still

valid and leads the designer to find the plate dimension that absorbs the highest pressure drop without

surpassing the established limit. The design approach presented in this work applies to conventional two-stream

applications but, it is extended to look at the possibility of incorporating, in the same unit, a second or even a

third exchanger. This gives rise to extending the compabloc geometry to fit multi-stream applications. There is

a limit to the number of exchanger blocks that can be fit together in a single frame. The limitation is the total

height of the resulting unit.

A basic assumption for the development of this work is that the expressions to determine the thermohydraulic

performance of the heat transfer surfaces are readily available. This may not be case for a special surface

corrugation. Since the main flow arrangement in a compabloc heat exchanger is crossflow, the number of

passes is an effective means of increasing the overall thermal effectiveness of the exchanger. Consideration of

the number of passes gives rise to more complex flow arrangements since in some cases, it is only one of the

streams that need to increase its velocity. The work considers these other situations has not been included due

to space limitations in this work.

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