A STUDY ON THE EFFECTS OF THE USE OF THERMAL INSULATION IN
PLATE HEAT EXCHANGERS
Maria Fernanda Côrtes Bastos Maia1, Sérgio Ricardo Lourenço2, Deovaldo de Moraes Júnior3
Abstract  The present study analyzed the importance
of thermal insulation in plate heat exchangers, in order to
increase the efficiency
of these
equipments.
The
experimental work was carried out in laboratory
at Universidade Santa Cecília. The study analyzed
experimentally the performance of different types of
insulations by comparison of the results of heat transfer in
equipment insulated and uninsulated, within the same
operating conditions. A 5% level of significance variance
analysis (Anova) was carried out to compare the averages.
The analysis was performed by quantifying the heat received
by the cold fluid (water), heat lost to the environment,
methods of thermal performance of the heat exchangers. The
responses showed that ceramic wool was the best
performance for thermal efficiency of the equipment with the
outlet temperatures averages of 43.7°C (316.85 K), 24,17 W
of heat lost to the environment and thermal effectiveness (ε)
of 1.24%, under the conditions proposed.
Index
Terms
 Energy conservation,
efficiency, insulated plate heat exchangers.
energy
INTRODUCTION
The concern with the issue of the energy efficiency in the
industry has gained relevance both in the national and the
international scenarios, and this is one of the guides of the
economy. In addition to the economic aspect, the manner in
which the process interacts with the environment, occupies
each time more room as a propulsion agent in projects of
energy efficiency.
Nowadays the industrial plants must consider in their
projects the efficient utilization of the energy associated with
clean technology as a way to increase the competitiveness of
the company [1]. The heat transfer is largely utilized in the
industry, in various segments of the economy. Its efficient
usage is of utmost importance in the decrease of the use of
energy resources and in the determination of the cost of
energy.
This research has been targeted at establishing the
relevance, in terms of efficiency, of the use of thermal
insulation in the plate heat exchangers although it is not a
customary practice.
Utilizing the thermal insulation in these equipments
means modifying the condition in which the heat transfer
occurs, once the insulation reduces potentially the heat flow
1
2
3
to the environment. This happens due to the decrease of the
thermal conductivity and the increase of the thickness of the
wall. The choice of the insulator and the thickness
determines the reduction of the heat flow to the
environment. Therefore, improving the thermal transfer of
the equipment, with the utilization of thermal insulators,
depends on the reduction of the heat flow to the environment
and the absorption of this heat to the cold fluid.
Minimizing the heat lost to the environment, through
the thermal insulation, is an opportunity for an improvement
of efficiency in the final use of the vapor and consequently,
a reduction of the consumption of energy for its production.
In this respect, the purpose of this work is to evaluate
the thermal performance of the plate heat exchangers in
pilot-scale to different conditions of insulation, having as a
paradigm the heat exchanger without the insulation.
FUNDAMENTAL EQUATIONS
Kandilli and Koclu [2] presented several studies related to
Laws of Thermodynamics as a way to evaluate the
performance of the exchangers. Among the studies there is
the study done by Yilmaz et al. [3], which analyzed the
performance of the heat exchangers in general under the
optics of the Second Law of Thermodynamics, utilizing the
entropy and the exergy as parameters of evaluation. Ogulata
et al. [4], under the same optics, presented studies with plate
heat exchangers, working in counter-current.
Focusing on the recovery of the heat lost, also applying
the Second Law of Thermodynamics, Naphon [5] presented
in his study the analysis of a shell and tube heat exchanger
which utilizes hot and cold water as fluids. Departing from
the experimental and theoretical results the study was able to
determine the effects of the conditions of input of the fluids
on the characteristics of heat transfer, the generation of
entropy and the loss of exergy. Gut [6] utilized techniques of
optmization to determine the optimal configurations of the
plate heat exchangers and Fernandes [7] studied the thermal
hydraulic performance, in a specific type of plates, also for
the plate heat exchangers.
Evaluating the performance of the heat exchangers, in
accordance with the Laws of the Thermodynamics is a way
to determine the heat transfer rates in these equipments and
the effects of the mass flow and of the temperature. Another
consequence of the evaluation of the thermal performance of
Maria Fernanda Côrtes Bastos Maia - Universidade Federal do ABC , Av. dos estados, 5001, Santo André, São Paulo, Brazil, [email protected].
Sérgio Ricardo Lourenço- Universidade Federal do ABC , Av. dos estados, 5001, Santo André, São Paulo, Brazil, [email protected].
Deovaldo de Moraes Junior, Universidade Santa Cecília –Rua Oswaldo Cruz, 277, Santos, São Paulo, Brazil, [email protected].
DOI 10.14684/SHEWC.13.2013.10-14
© 2013 COPEC
July 07 - 10, 2013, Porto, PORTUGAL
XIII Safety, Health and Environment World Congress
10
these equipments is to determine the optimal operation
condition [2].
A heat exchanger which utilizes as hot fluid the vapor
and as cold fluid the water and which changes to the liquid
state, at a temperature below its vapor point, will have a
small parcel of its heat supplied in the way of sensitive heat.
Its application can be represented in the way of the “(1)” and
“(2)”, which express the heat rate supplied by the hot fluid
and the heat rate received by the cold fluid, respectively.
qs  whf ,out . hlv  whf ,out .c p T
(1)
qr  wcf ,out .c p T
(2)
The difference between the heat supplied by the system
and the heat received by the cold fluid is determined by
“(3)”.
qls  q s  qr
(3)
The evaluation of the thermal performance of the heat
exchangers is an important tool in the choice of the final
configuration of this equipment. Bejan et al. [1] state that
the mere calculation of the heat transfer is not the
determining factor of the project of the equipment. Factors
as the currents, the energy required for their circulation and
the easiness of maintenance are examples of conditions
which affect the project of the heat exchanger.
In this context, the application of methods of analysis of
thermal performance of the exchangers may help in the
construction and in the subsequent evaluation of the
equipment. Wang et al. [8] emphasize as one of the methods
broadly utilized in the industrial practice for the project of
the plate heat exchangers, the thermal effectiveness methods
(ε - NTU).
This method of evaluation of the thermal performance
of the heat exhangers is based in the relations of thermal
effectiveness and the number of units of transfer of the heat
exchanger.
According to Kandilli and Koclu [2] the thermal
effectiveness (ε) is an important parameter for the studies of
projects of the plate heat exchangers. It relates the rate of the
heat effectively transferred with the maximum transfer rate
which can be reached, as “(4)”.

q
qmax
NTU 
UA
C min
(5)
For equipments in which there is a phase change, as
the evaporator, heaters that use the vapor and condensers,
the parameter R is 0 (zero), due to the fact that one of the
fluids remains at a constant temperature throughout the
exchanger. Therefore, its thermal capacity or effective
specific heat is, by definition, equal to infinite [9].
In this case the expression which determines the thermal
effectiveness at parallel flow, cross flow and counterflow is
defined by “(6)”.
  1  e  NTU
(6)
EXPERIMENTAL WORK
The experimental unity utilized was composed basically by
an electric steam generator with a steam production capacity
of 20 kg/h, a pressure reducing valve in the vapour line, four
temperature indicators, a rotameter and a plate heat
exchanger with an area of 0,032 m2 per plate. The
experimental system is schematically shown in Fig. l.
(1) water tank for boiler charging; (2) pump; (3) check valve; (4) gate
valve; (5) boiler; (6) discharge; (7) electric heater; (8) level visor; (9)
control panel (10) pressure gauge; (11) pressure switch ; (12) lifting ring;
(13) discharge valve; (14) relief valve; (15) steam discharge duct; (16)
vapor flow rate control valve; (17) insulated steam pipe; (18) gate valve;
(19) gate valve; (20) pressure reducing valve; (21) pressure gauge; (22) )
insulated steam pipe; (23) insulated PHE; (24) inlet vapor temperature
indicator; (25) outlet vapor temperature indicator; (26) gate valve; (27)
outlet collector; (28) outlet collector; 29) gate valve; (30) inlet water valve;
(31) rotameter; (32) heater; (33) inlet water temperature indicator; (34)
outlet water temperature indicator; (35) gate valve.
(4)
In addition to the thermal effectiveness, another
important factor to evaluate the performance of the
exchanger is the number of transfer units (NTU), which is
defined by the relation between the global coefficient of
thermal transfer (U), the transfer area and the lowest thermal
capacity between the fluids, as shown in “(5)”.
FIGURE I – The experimental system
In order to represent the behavior of different insulators,
the following materials were tested: ceramic wool, rock
wool, ceramic cloth, microporous plate, for the external
coating of the heat exchanger. Subsequently, utilizing the
same pilot installation, the performance was evaluated using
the insulators inside the heat exchanger. For that only the
© 2013 COPEC
July 07 - 10, 2013, Porto, PORTUGAL
XIII Safety, Health and Environment World Congress
11
ceramic cloth and the natural rubber were chosen, as both
have appropriate shape and compactness to cover the flat
extension of the plates and sustain the pressure from the
shutting of the exchanger, respectively.
The insulators were applied to the fixed and mobile
plates of the exchanger as they were considered the regions
of the exchanger with great area of heat transfer.
We tested the performance of the heat exchanger
without thermal insulation and subsequently with all the
insulation conditions mentioned, with the purpose of
evaluating the performance of each insulator in the external
and internal coatings.
The procedures utilized in the experiment were divided
in 3 phases: preparation, pre-operation and operation. In the
preparation phase it was necessary to correct the pH of the
water stored in the the boiler and in the pre-operation phase
it took approximately 45 minutes for the pressure for the
operation to reach 7,5 kgf/cm². Once this pressure was
reached, the vapour output valve was open and the vapour
flow was restricted by the reduction valve, before getting
inside the heat exchanger.
This condition represented an absolute pressure of 1,6
kgf/cm², which corresponds to a vapour temperature of
113,3 °C.
In the operation phase the input and output temperature
and flows of the fluids were verified through reading and
analogical thermometers, located in wells in the inlet and
outlet of the heat exchanger. The output of the cold fluids
(water) and hot fluids (condensated vapour) were collected
with recipients and then weighed for the calculation of flows
respectively.
Some additional devices were installed in order to
guarantee the maintenance of the operating conditions such
as a reduction valve and a temperature control system for the
inlet
of the water composed by a thermal heater and
thermal control shower. This procedure prevented the inlet
water temperature to vary with the environmental
temperature. Fig. II shows the heat exchanger with the
insulators studied.
(a)
ceramic wool; (b) rock wool; (c) ceramic cloth; (d)
microporous plate; (e) inside ceramic cloth; (f) inside natural rubber.
FIGURE II – Plate heat exchanger with differentes
insulators.
Considering the conditions of repetition in which the
experiments were conducted, (6) replicates for each
condition of isolation, the results for the successive
variations were estimated random errors, calculated to
determine the uncertainty of values. The uncertainty
analysis for temperature was ± 0,38ºC and the propagated
uncertainties of the lost heat was ± 31,77 W.
RESULTS AND DISCUSSION
The experiments were evaluated for three different analyses.
The first analysis was the heat lost considering the
operational conditions presented.
In the comparison between the averages, the results
indicate a small reduction in heat loss, as seen in Figure III.
Under the analysis of the ANOVA, at the level of 5% of
significance, there was significant difference in the behavior
of the heat loss with the variation of the insulation condition.
FIGURE III – Heat loss with the variation of the
insulation condition
With regard to the cold fluid outlet, the results indentify
that the averages of the highest temperatures of water output
indicate the insulation with ceramic wool, with a maximum
temperature increase of 17 °C with relation to the paradigm
without insulation. Fig IV shows the outlets temperatures.
FIGURE IV – Outlet temperatures
© 2013 COPEC
July 07 - 10, 2013, Porto, PORTUGAL
XIII Safety, Health and Environment World Congress
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The analysis of the thermal performance of the heat
exchanger under different insulation situations was carried
out with the method of thermal effectiveness (ε- NUT).
For the purpose of application of this method of thermal
performance of the heat exchangers, it was considered that
the vapor only changes phase when running through the last
plate for the determination of the thermal effectiveness (ε).
Observing the results obtained for the analysis of the
thermal performance it was possible to identify the insulator
ceramic wool as having the best thermal performance, for
the conditions studied, as shown by the curves of Figures V,
VI and VII.
With a view to the statistical validation of this
conclusion the results of the e- NUT were analyzed under
the views of the ANOVA at the level of 5% of significance,
with the purpose of verifying the existence of significant
difference among the results. The analysis of the ANOVA
proved the graphic behavior, identifying the ceramic wool
insulation as having the best thermal performance under the
conditions tested.
Table 1 summarizes the results of the experiments in
terms of the average as a way to illustrate the best
performance under the conditions of insulation tested.
TABLE 1 - Summary of results
Evaluated
parameter
Lost heat
Best
performance
Ceramic wool
Statistics
significance.
(α = 0,05%)
Significant
Cold fluid outled
temperature
Ceramic wool
Significant
Thermal
effectiveness
Ceramic wool
Significant
CONCLUSIONS
FIGURE V – Overall heat transfer coefficient (U).
FIGURE VI – Number of the heat transfer units (NTU).
FIGURE VII – Effectiveness (ε)
The use of thermal insulation in plate heat exchangers was
assessed by the following analyses:
1. Heat lost;
2. Cold fluid outlet temperature;
3. Analysis of the thermal performance, according to
the method e- NUT.
The methods utilized for the comparison of the results,
under the situations with and without insulation have served
as reference for the evaluation of the performance of the heat
exchanger. The data obtained in the tests are limited to the
technical conditions of the equipment.
The main conclusions, which may be drawn from the
results of this study, are listed as follows:
a. The analysis of variance (ANOVA) was utilized to
evaluate the relationship among fluid outlet
temperatures, lost heat and thermal performance
and the results found significant differences among
the values obtained;
b. The best performance for cold fluid outlet
temperatures, lost heat and thermal effectiveness
was ceramic wool;
c. The lowest heat lost to the environment was 24,17
W for plate heat exchanger insulated with ceramic
wool;
d. The effectiveness, NTU and U has the best values
for plate heat exchanger insulated with ceramic
wool;
e. The results of the outlet temperatures averages for
the ceramic wool, rock wool and the condition
without insulation (43,7°C, 42,5°C and 43,3°C
© 2013 COPEC
July 07 - 10, 2013, Porto, PORTUGAL
XIII Safety, Health and Environment World Congress
13
f.
respectively) did not show significant difference,
suggesting that the use of the thermal insulation to
the plate heat exchangers can be negligible;
The results showed that the difference between the
ceramic wool insulation and the paradigm without
insulation (0.4 °C) might be the uncertainty of the
measured temperatures (0.38 °C) once they are very
close. Therefore the use of insulation in plate heat
exchangers may imply in additional costs to the
process without the effective increase of its energy
efficiency under the conditions tested.
ACKNOWLEDGMENT
This study was carried out at the Laboratory of
Thermodynamics located at Universidade Santa Cecília
in the city of Santos-SP.
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[3]
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[7]
Fernandes, C.S.V. “Optimising the design and performance of
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<http://www.scielo.br/scielo.php?script=sci_arttext&pid=S010466322007000400005&lng=en&nrm=iso>. ISSN 0104-6632.Â
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>.
Acesso em: 19 abr. 2012
“Plate
heat
performance”.
© 2013 COPEC
July 07 - 10, 2013, Porto, PORTUGAL
XIII Safety, Health and Environment World Congress
14