A review on recent development of nanofluid utilization in shell & tube heat exchanger for saving of energy

Abstract

The principal goal of this paper is to provide a generic review of the utilization of nanofluid in shell & tube heat exchangers for energy-saving. Shell & tube heat exchanger is used in many industries like the aviation industry, renewable energy, heating and cooling of electronic equipment, oil and gas industries, automotive industries, thermal power plant, etc because of its smaller area and high heat transfer rate. The utilization of nanofluid in such equipment increases heat transfer rate very rapidly due to better thermophysical properties as compared to other fluids. In this research article, first, a brief introduction of shell & tube heat exchanger is provided after that nanofluid, properties of nanofluid and preparation of nanofluid are presented and then utilization of different nanofluid in shell & tube heat exchanger has been examined. This paper also provides the comparative results of utilization of different nanofluids in shell & tube heat exchangers. Finally, it is found that nanofluids enhance the heat transfer rate, reduces the size of the heat exchanger, and ultimately saving energy.

Full text

A review on recent development of nanofluid utilization in shell & tube
heat exchanger for saving of energy
Sanjeev Kumar Gupta
⇑
, Harshita Verma, Neha Yadav
Mechanical Engineering Department, IET, GLA University Mathura, Uttar Pradesh 281406, India
article info
Article history:
Available online xxxx
Keywords:
Nanofluid
Pressure drop
Nusselt number
Heat Exchanger
Energy saving
abstract
The principal goal of this paper is to provide a generic review of the utilization of nanofluid in shell & tube
heat exchangers for energy-saving. Shell & tube heat exchanger is used in many industries like the avi-
ation industry, renewable energy, heating and cooling of electronic equipment, oil and gas industries,
automotive industries, thermal power plant, etc because of its smaller area and high heat transfer rate.
The utilization of nanofluid in such equipment increases heat transfer rate very rapidly due to better ther-
mophysical properties as compared to other fluids. In this research article, first, a brief introduction of
shell & tube heat exchanger is provided after that nanofluid, properties of nanofluid and preparation of
nanofluid are presented and then utilization of different nanofluid in shell & tube heat exchanger has
been examined. This paper also provides the comparative results of utilization of different nanofluids
in shell & tube heat exchangers. Finally, it is found that nanofluids enhance the heat transfer rate, reduces
the size of the heat exchanger, and ultimately saving energy.
Copyright Ó2021 Elsevier Ltd. All rights reserved.
Selection and peer-review under responsibility of the scientific committee of the International Confer-
ence on ldquo;Materials Science and Mathematics for Advanced Technologyrdquo;
1. Introduction
The crisis of energy in India as well as all over the world is the
most important problem for humankind. Security of fuel, a regular
increase of the price of fuel, emission of greenhouse gases and cli-
mate change is also the major challenge in front of the world. The
problem of energy crisis and environmental concerns motivate
people to shift towards the utilization of renewable sources of
energy such as solar energy, tidal energy, hydro energy, wind
energy, geothermal energy, and many more [1–4]. The main goal
of the researcher is to solve the problem of the energy crisis now
these days. Effective utilization of energy is the best option to over-
come the crisis of energy worldwide. This can be achieved by uti-
lizing any kind of energy-saving technique such as energy
conversion, energy storage, energy conservation, and many more.
The heat exchanger is one of the important devices which can be
used for energy saving without any environmental concern. The
efficiency and effectiveness of many heat exchanger applications
might be upgraded by improving the operation of the heat exchan-
ger. There are several applications in heat exchangers likewise
space industry, automobile industry, electronic industry, aviation
industry, and many more [5–10]. Applications of heat exchangers
are shown in Fig. 1.
The energy efficiency of a heat exchanger can be enhanced by
improving the heat transfer characteristics. The major challenge
for design engineers is to design an effective system with less
energy consumption and reduce the overall cost of the system with
less space requirement. A great deal of research has been per-
formed to ameliorate the design and heat transfer rate by using
baffles, microchannels, and fins [11–13]. Researchers are now
focused to find a new way to aggravate the heat transfer rate to
save energy and decrease the space and also heat exchangers
expenses. The heat transfer rate of such types of devices can be
improved by utilizing a recent variety of working fluid knows as
nanofluid with higher thermal conductivity.
Numerous investigators identified that the nanofluid possess
higher thermal conductivity in comparison to base fluid but it is
https://doi.org/10.1016/j.matpr.2021.09.455
2214-7853/Copyright Ó2021 Elsevier Ltd. All rights reserved.
Selection and peer-review under responsibility of the scientific committee of the International Conference on ldquo;Materials Science and Mathematics for Advanced
Technologyrdquo;
Abbreviations: FEM, Finite Element Method; LMTD, Logarithmic Mean Temper-
ature Difference; MWCNT, Multi-Walled Carbon Nano Tubes; PCM, Phase Change
Material; PHE, Plate Heat Exchanger; STHE, Shell & Tube Heat Exchanger; STRHE,
Shell and Tube Recovery Heat Exchanger; SEM, Scanning Electron Microscopy; TEM,
Transmission Electron Microscopy.
⇑
Corresponding author.
E-mail address: sanjeev.mnnita@gmail.com (S.K. Gupta).
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings
journal homepage: www.elsevier.com/locate/matpr
Please cite this article as: Sanjeev Kumar Gupta, H. Verma and N. Yadav, A review on recent development of nanofluid utilization in shell & tube heat
exchanger for saving of energy, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2021.09.455

observed that the performance of heat exchangers mainly effec-
tiveness depends on many parameters of nanofluid such as viscos-
ity, density, thermal conductivity, volume concentration, specific
heat, etc. Most of the researchers concluded that nanofluid-
operated heat exchangers possess a higher heat transfer rate rela-
tive to base fluid-operated heat exchangers [14-18]. There are
many types of industrial heat exchangers that are used now these
days. The detailed classification of heat exchangers is shown in
Fig. 2. The main advantage of STHEs is that they can be used in both
situations whether a large amount of heat transfer rate is required
or a small amount of heat transfer rate is required in power plants,
automobile industries, chemical industries, etc. It can also be used
where large pressure is required. It is evident from the literature,
the heat transfer rate of heat exchangers is increased by utilizing
nanofluid but the energy effectiveness not only depends on the
heat transfer coefficient but also depends on many parameters.
The development of nanofluid and hybrid nanofluid is another
challenge in front of engineers and scientists to utilize these fluids
Nomenclature
e
Effectiveness
D
p Pressure drop
Re Reynolds number
U Overall Heat Transfer Coefficient
Fig. 1. Heat exchanger applications [5].
Fig. 2. Heat exchanger classification [19].
Sanjeev Kumar Gupta, H. Verma and N. Yadav Materials Today: Proceedings xxx (xxxx) xxx
2

properly for enhancement of effectiveness without any environ-
mental concern. The main purpose of this review paper is to pro-
vide insights into various parameters to aggravate the
effectiveness of STHEs for energy saving which can ultimately
diminish the overall expenses of the system.
2. Nanofluids
The thermal conductivity of fluids like water, ethylene glycol,
oil that are utilized in many industrial applications for example
cooling of electronic components, nuclear power plants, chemical
industries, thermal power plant, air conditioning systems is very
poor as compared to solid materials. Enhancement of thermal con-
ductivity and heat transfer rate of these fluids are new areas of
research for researchers and scientists [20,21]. Solid particles exhi-
bit better thermal conductivity relative to base fluid but the sus-
pension of these solid particles in the base fluid is a challenge for
scientists. The thermophysical characteristics of the base fluid are
enhanced enormously by the suspension of these particles in the
base fluid. The sizes of these particles are in micro and nanometers.
The problem of stability and agglomeration is the main challenge
for researchers [22,23]. The development of nanomaterial attracts
the attention of researchers and scientists because they have high
thermal conductivity and heat transfer rate relative to the base
fluid. The nanomaterial exhibit much better thermal, optical,
mechanical, and chemical properties as compared to other materi-
als [24–26]. A new kind of fluid known as nanofluid is now avail-
able for researcher and scientists, which exhibit high thermal
conductivity and high heat transfer rate with the development of
nanomaterial. Choi [27] was the first person who introduced the
term nanofluid. Nanofluid can be prepared as the requirement by
mixing nanomaterial in the base fluid by using a single-step or
two-step process. The thermal conductivity of different nanomate-
rials is shown in Fig. 3 [28].
3. Nanofluids properties
A lot of research articles [29–35] were published on nanofluid
characterization, synthesis, and their applications in various sys-
tems such as solar collectors, heat exchangers, and many more.
There are so many contradictions about the properties of nanoflu-
ids that’s why it creates a lot of confusion in researchers when they
utilized nanofluids. A proper understanding of thermophysical
properties and heat transfer characteristics is required for its uti-
lization. The experimental technique is more reliable as compare
to any other technique to predict the behavior of properties nano-
fluid. The artificial neural network is also used by few researchers
to predict its behavior [36,37]. The heat transfer rate is affected by
the thermophysical properties of nanofluid which increments with
an increment in the volume part of nanoparticles in the base liquid.
The properties of nanofluid are changed as per the nanomaterial
mixed in the base fluid. The thermophysical properties of nanofluid
are affected by nanoparticles concentration, level of purity, nano-
material structure. The thermophysical properties of nanofluid
are shown in Fig. 4. All researchers concluded from their experi-
mental as well theoretical analysis that the thermal conductivity
of nanofluid is enhanced with the enhancement of nanoparticles
in the base fluid. It is possible only due to the Brownian motion
of nanoparticles in the base fluid [22,38–40]. The particle size of
nanomaterial affected the thermal conductivity of nanofluid. Teng
et al. [41] concluded from their experimental observation that the
thermal conductivity of nanofluid is enhanced with a decrement in
the size of nanomaterial. Temperature is another parameter that
affects the thermal conductivity of nanofluids. Yu et al. [42] used
ZnO nanofluid and performed experimentation to find out the
change in thermal conductivity due to temperature variation. They
presumed that with the expansion of temperature, the thermal
conductivity increases. Viscosity is another important parameter
that affects the heat transfer rate as well as pumping power.
Nguyen et al. [43] utilized Al
2
O
3
/water nanofluid for their experi-
mentation and find the effects of volume fraction and temperature
on viscosity. Their results revealed that the nanofluid’s viscosity
increments with an increment in volume fraction while diminishes
with an increment in temperature. The heat transfer rate of nano-
fluid is also affected by another property know as specific heat.
Saeedinia et al. [44] experimented on CuO/oil nanofluid to investi-
gate the specific heat and concluded from their experiment that
nanofluid offers less specific heat relative to the base fluid. Their
result also revealed that with increment in volume concentration,
specific heat decreases. Most of the important parameters of heat
transfer such as Nusselt number (Nu), Peclet number (Pe), and
Prandtl number (Pr) are affected by important properties of nano-
fluid called density. Most of the researchers concluded from their
experimental observation that density is enhanced with enhance-
ment in the volume concentration of nanofluid.
4. Nanofluids preparation
Dispersing nanoparticles in a base fluid produces nanofluids.
The stability of nanofluid is enhanced by the use of surfactants.
Fig. 3. Thermal conductivity of different Nanomaterials in W/mK [28].
Sanjeev Kumar Gupta, H. Verma and N. Yadav Materials Today: Proceedings xxx (xxxx) xxx
3

Furthermore, surface modification of dispersed particles and the
application of high force to clusters of scattered nanoparticles
may improve nanofluid stability. There are two approaches to
nanofluid preparation (i) single-step approach (ii) two-step
approach. Another new technology for nanofluid preparation is
the chemical procedure. The volume percentage of nanoparticles
in the base fluid is measured by equation (1).
Volume fraction ¼W
np
=
q
np
W
np
=
q
np
þV
b
100 ð1Þ
Where W
np
= weight of nanoparticles,
q
np
= density of nanofluid,
V
b
= volume of the base fluid. Both the methods of nanofluid prepa-
ration are discussed below.
4.1. Single-Step approach
Nanoparticles are manufactured and distributed in the base
fluid in a single step using a single approach, and this approach fol-
lows the bottom-up strategy [45]. This approach achieves a high
level of dispersion stability. This procedure does not necessitate
the shipping, storage, or drying of nanoparticles. These are some
of the key benefits of producing nanofluids in a single process.
The formation of residuals as a result of incomplete reactions is a
constant feature of the suspension. This is the single-step
approach’s biggest drawback. Mukherjee, Mishra, and Chaudhari
[46] provided a detailed demonstration of the single-step approach
for fabricating nanofluid.
4.2. Two-Step approach
The two-step approach is very famous for the preparation of
nanofluids. In this approach, firstly nanoparticles are converted
into dry powders using a chemical process. Secondly, dry powder
is dispersed in a fluid using a magnetic steering technique. Surfac-
tant is used to enhance the stability of nanofluid. The production of
nanofluid using a two-step approach is very economical at a large
scale and commercial level [47,48]. The demonstration of the two-
step approach is shown in Fig. 5 [49].
5. Utilization of nanofluids in shell & tube heat exchanger
Many industries such as the oil industry, gas industry, chemical
industry, nuclear power plant, thermal power plant, aviation
industry, and electronic industry utilize heat exchangers for heat
transfer. The optimization of the design of heat exchangers is the
major challenge for a design engineer to save energy with a high
heat transfer rate and also without any environmental concern.
STHE is the most widely used heat exchanger because of its com-
pact space and high heat transfer rate [50–52]. The schematic dia-
gram of the STHE is shown in Fig. 6. Enhancement of heat transfer
rate is achieved by an alternate method such as utilizing a high
heat transfer fluid known as nanofluid. Utilization of nanofluid in
STHE leads to saving of energy, environment, and economy also.
The selection of nanofluid according to the situation is a challenge
for researchers and scientists. Nanofluids exhibits much better
thermophysical properties as compared to the based fluid.
Fig. 4. Thermophysical properties of nanofluid [40].
Fig. 5. Preparation of nanofluid by two – step method [49].
Sanjeev Kumar Gupta, H. Verma and N. Yadav Materials Today: Proceedings xxx (xxxx) xxx
4

Researchers and scientists are now focusing on the utilization of
such kinds of fluid in STHE for energy saving and reducing the
overall cost of the system [53–57]. The comparative analysis of dif-
ferent nanofluid utilized in STHE is shown in Table 1. In this section
utilization of nanofluid in STHE is discussed in detail.
Shahrul et al. [58] performed experimentation on STHEs using
Al
2
O
3
, SiO
2
, and ZnO nanofluid and taking water as base fluid to
investigate the effectiveness and efficiency of heat exchangers for
energy saving. They prepared nanofluid without any surfactant.
For stabilization of nanofluid polyvinylpyrrolidone, surfactant
was used. Different concentration of nanofluid was used during
this study which varied from 0.3 to 0.5 vol%. They investigated that
ZnO/water nanofluid had the highest effectiveness near about 50%,
rest two nanofluids Al
2
O
3
/water; SiO
2
/water had effectiveness
approximately 15% and 9%. The emolument in the overall heat
transfer coefficient was noted around 12%, 26%, and 35% for SiO
2
/
water, Al
2
O
3
/water, and ZnO/water nanofluids. Finally, they con-
certed that ZnO/water nanofluid has the highest performance with
an improvement of approximately 35% with polyvinylpyrrolidone
(PVP) surfactant which is shown in Fig. 7 and Fig. 8.
Lotfi et al. [59] experimented on STHEs using MWCNT/water
nanofluid to analyze their thermal behaviour. They used the cat-
alytic chemical vapour deposition method for the synthesis of car-
bon Nanotubes. A three-stage method was used for the purification
of MWCNTs. They used SEM and TEM characterization techniques
for MWCNT nanomaterial to find out agglomeration and uniform
distribution of nanomaterial in the base fluid. The SEM and TEM
image of MWCNT is depicted in Fig. 9. They examined from their
experimental perception that the presence of MWCNT enhanced
the performance of STHEs.
Aghabozorg et al. [60] used Fe
2
O
3
-CNT/water nanofluid in three
different conditions such as laminar, turbulent, and transient also
in an STHE to examine the enhancement in heat transfer. They
used magnetic nanofluid of different fluxes which was varied from
80 V to 150 V. They had taken 30 nm diameters of nanoparticles.
They observed enrichment in convective heat transfer coefficient
with enrichment in temperature and weight concentration of
nanofluid. The nanoparticles volume fraction was wide-ranging
from 0.1 to 0.2 wt% for all three situations. They identified that
the heat transfer coefficient is high in the case of hybrid nanofluid
relative to the base fluid. Their results revealed that an enhance-
ment of 13.5% and 27.6% in heat transfer coefficient for both the
flow situations laminar as well as turbulent flow respectively for
a weight fraction of 0.1% and it is further increased around 34%
and 37% for 0.2% weight fraction. The effective heat transfer coeffi-
cient is enriched with enhancement in temperature and voltage for
laminar flow which is shown in Fig. 10.
Du et al. [61] utilized molten salt in an STHE to investigate its
thermal behaviour and characteristics of heat transfer both exper-
Fig. 6. Schematic of STHE.
Table 1
Comparative analysis of nanofluid utilization in STHE.
Ref.
No.
Nanofluid Conditions Remark
59 Al
2
O
3
, SiO
2
,
and ZnO
Concentration
varied from 0.3 to
0.5 vol%.
ZnO/water nanofluid has the
highest performance with an
improvement of approximately
35% with polyvinylpyrrolidone
(PVP) surfactant
61 Fe
2
O
3
-CNT/
water
Volume fraction
varied from 0.1 to
0.2 wt%
An enhancement of 13.5% and
27.6% in heat transfer
coefficient for both the flow
situations for a weight fraction
of 0.1% and it is further
increased around 34% and 37%
for 0.2% weight fraction
64 Al
2
O
3
-Cu/
water
Reynolds number
varied from 800
to 2400
By utilizing hybrid nanofluid,
the heat transfer rate is
enriched approximately 139%
while only 25% enrichment in
heat transfer rate is noted by
utilizing Cu/water nanofluid.
65 Fe
2
O
3
/water
and Fe
2
O
3
/
ethylene
glycol
Concentration
varied from 0.02
to 0.08 vol%
Maximum pressure drop is
observed in turbulent flow
situations as compared to
laminar flow situations.
66 Cu/ethylene
glycol
Concentrations
varied from 0.002
to 0.01 vol%
By adding 1% Cu nanoparticles
in the ethylene glycol base
fluid, the heat transfer rate is
augmented by approximately
7.8% at a coolant mass flow rate
of 116 kg/s.
67 ZnO, Fe
3
O
4
,
CuO, TiO
2,
and
Al
2
O
3
Volume
concentration
0.03 vol%.
ZnO/water nanofluid has the
highest improvement in energy
effectiveness approximately
43% while Al
2
O
3
/water
nanofluid has a minimum
improvement of approximately
31% at 50 kg/min mass flow rate
68 Ag/water Volume fraction
varied from 0.01%
to 0.04%
Maximum increment of 6.14%
in effectiveness and 12.4% in
heat transfer coefficient.
70 Al
2
O
3
/water
and ZnO
Volume fraction
varied from 1 to
2%.
The maximum thermal
performance factor is found
approximately 3 for circular
curvature of coil pitch 18 mm at
a Reynolds number of 1800
71 SiO
2
/water Concentrations
varying from 0.5
to 0.25 vol%
Significant increment in
pressure drop of about 62.61%
and friction factor of about
52.61% using SiO
2
/water
nanofluid.
72 Graphene Volume
concentration
0.2 vol%.
The heat transfer coefficient
was approximately augmented
by 29%, and also the thermal
efficiency of STHE was
augmented by 14%.
Sanjeev Kumar Gupta, H. Verma and N. Yadav Materials Today: Proceedings xxx (xxxx) xxx
5

imentally and numerically. The Reynolds number during experi-
mentation was varied from 3514 to 5482. The schematic arrange-
ment of the STHE is shown in Fig. 11. Their experimental results
revealed that the Nusselt number enhanced from 42.6 to 65.95
with enhancement in Reynolds number from 3514 to 5482.
Because of enrichment in Nusselt number, heat transfer rate
increases which ultimately results in energy saving and overall
cost reduction of the system. They developed an empirical correla-
tion between different dimensionless numbers with a maximum
possible error of 11%.
M. R. Salem [62] experimented on STHEs and utilized MWCNT/
water nanofluid to investigate the hydrothermal performance. The
spacing ratio, volume concentration, Reynolds number shell side,
Prandtl number shell side varied from 0.157 to 0.472, 0 to 0.5%,
3351 to 13461, and 4.85 to 7.54 respectively. It was observed from
their experimental observation that shell average Nusselt number
and fanning friction factor shoot up with an increment in spacing
ratio and also with gain in volume fraction. Heat transfer rate on
shell side increases due to enrichment in Nusselt number. Pressure
drop also increases due to enrichment in fanning friction factor.
Finally, he concluded that the hydrothermal performance of STHE
is enhanced by utilizing MWCNT/water nanofluids.
Anitha et al. [63] experimented on single pass STHE utilizing
hybrid nanofluid to investigate heat transfer behaviour. They used
Al
2
O
3
-Cu/water hybrid nanofluid during experimentation and
check the effect of volume fraction of nanoparticles on heat trans-
fer rate. The FEM is utilized to solve the governing equations for
Fig. 7. Overall heat transfer coefficient v/s tube side volume flow rate [58].
Fig. 8. Overall heat transfer coefficient v/s shell side volume flow rate [58].
Fig. 9. A) SEM image B) TEM image of synthesized MWCNTs [59].
Sanjeev Kumar Gupta, H. Verma and N. Yadav Materials Today: Proceedings xxx (xxxx) xxx
6

numerical analysis which is used to validate the experimental
results. Their results revealed that by utilizing Al
2
O
3
-Cu/water
hybrid nanofluid, the heat transfer rate is enriched approximately
139% while only 25% enrichment in heat transfer rate is noted by
utilizing Cu/water nanofluid. The Nusselt number is enhanced
approximately 90% as compared to Al
2
O
3
/water nanofluid. Their
results also revealed that an enhancement of 124% in effectiveness
(
e
) of a heat exchanger by utilizing hybrid nanofluid which ulti-
mately reduces the energy consumption and also diminishes the
overall cost of the heat exchanger. The variation of effectiveness
and pressure drop (
D
p) with Reynolds number (Re) is depicted in
Fig. 12 and Fig. 13 respectively. It is observed from the Fig. 12 that
effectiveness is also enhanced with increment in Reynolds number.
From Fig. 13, it is obvious that pressure drop enriches with enrich-
ment in Reynolds number and also increases by utilizing hybrid
nanofluid relative to other nanofluids.
Kumar et al. [64] experimented on STHE using two different
types of nanofluid namely Fe
2
O
3
/water and Fe
2
O
3
/ethylene glycol
nanofluid to investigate the heat transfer characteristics consider-
ing both the flow situation laminar as well as turbulent. Different
concentrations of nanofluid which were wide-ranging from 0.02
to 0.08 vol% was utilized during the investigation. The thermal con-
ductivity and heat transfer rate are enhanced significantly by the
enhancement of nanoparticles in the base fluid. It is also revealed
from their experimental perception that thermal conductivity
aggravates significantly with the rise in the temperature of the
base fluid. Maximum pressure drop is observed in turbulent flow
situations as compared to laminar flow situations. It is also
revealed from their experimental observation that the heat trans-
fer attributes of both the nanofluid enhanced with Reynolds
number.
Leong et al [65] modeled experimentally shell & tube recovery
heat exchanger (STRHE) in which nanofluid is utilized as a coolant
to recover the waste heat for energy saving. They used copper
nanoparticles of different concentrations varied from 0.002 to
0.01 vol% in the base fluid either water or ethylene glycol. Their
outcome revealed that the overall heat transfer coefficient was
augmented by the utilization of nanofluid as compared to the base
fluid. By adding 1% Cu nanoparticles in the ethylene glycol base
Fig. 10. Effective heat transfer coefficient v/s temperature at different fluxes for laminar flow [60].
Fig. 11. STHE [61].
Fig. 12. Effectiveness (
e
) v/s Reynolds number (Re) [63].
Fig. 13. Pressure drop (
D
p) v/s Reynolds number (Re) [63].
Sanjeev Kumar Gupta, H. Verma and N. Yadav Materials Today: Proceedings xxx (xxxx) xxx
7

fluid, the heat transfer rate is augmented by approximately 7.8% at
a coolant mass flow rate of 116 kg/s which is shown in Fig. 14.
Their results also revealed that the convective heat transfer coeffi-
cient was enhanced by utilizing nanofluid relative to both the base
fluid. It is also observed that the thermal performance of STRHE is
enhanced with nanofluid coolant mass flow rate which ultimately
increases the energy saving by utilizing waste heat and also dimin-
ishes the cost of the system.
Shahrul et al. [66] experimented on STHE using distinct kinds of
nanofluid particularly ZnO, Fe
3
O
4
, CuO, TiO
2,
and Al
2
O
3
at different
mass flow rates keeping volume concentration constant at 0.03 vol
%. It was observed that Al
2
O
3
/water nanofluid has the utmost heat
transfer coefficient while CuO/water has the lowest at a 50 kg/min
mass flow rate. However, it is also observed that ZnO/water nano-
fluid has the highest improvement in energy effectiveness approx-
imately 43% while Al
2
O
3
/water nanofluid has a minimum
improvement of approximately 31% at 50 kg/min mass flow rate
which is shown in Fig. 15. It was also revealed from their experi-
mental observation that energy effectiveness enhanced with an
increment of the mass flow rate of base fluid and decrement in
mass flow rate of nanofluid. However, it was also observed that
very little improvement in energy effectiveness by changing the
mass flow rate of the base fluid. It is mainly because of the viscosity
of the fluid. They finally concluded that the better performance of
STHE can be acquired by utilizing the nanofluids of metal oxide and
also by maintaining the shell side mass flow rate higher and the
tube side mass flow rate lower.
Godson et al. [67] utilized Ag/water nanofluid and experi-
mented on STHE to investigate the various heat transfer character-
istics for energy saving. They used turbulent flow conditions
throughout the experimentation with Reynolds numbers varying
from 5000 to 25000. The volume fraction of nanoparticles wide-
ranging from 0.01% to 0.04%. They have also varied the heat flux
from 800 W/m
2
to 1000 W/m
2
that is obtained from a flat plate
solar collector. They have investigated different heat transfer char-
acteristics for example heat transfer coefficient, LMTD, effective-
ness, and pressure drop also which are influenced by volume
fraction, mass flow rate, and inlet temperature. Their experimental
observation revealed that effectiveness; pressure drop and heat
transfer coefficient is enhanced with a volume concentration of
Ag/water nanofluid. The variation of effectiveness with Reynolds
number and volume concentration is shown in Fig. 16. It is obvious
from Fig. 16 that effectiveness is enhanced with Reynolds number
and also with volume concentration. They have noticed a maxi-
mum increment of 6.14% in effectiveness and 12.4% in heat transfer
coefficient which is ultimately required for energy saving and cost
reduction of the STHE. It is possible only because of the enhance-
ment in thermophysical properties of nanofluid.
Naik et al. [68] experimented on STHE using three different
types of nanofluid such as Fe
2
O
3
, CuO, and Al
2
O
3
to investigate heat
transfer characteristics in comparison to base fluid carboxymethyl
cellulose. The volume fraction of nanoparticles is wide-ranging
from 0.2 to 1.0 wt%. They used the X-Ray diffraction technique
for the characterization of nanomaterial. Nanofluid is used on the
shell side while water is used on the tube side. They investigate
shell side Nusselt number & heat transfer coefficient in distinct sit-
uations by differing the mass flow rate of cold water from 0.5 to 5
lpm, the nanofluid temperature of shell side varying from 40 to
Fig. 14. Overall heat transfer coefficient v/s coolant mass flow rate [65].
Fig. 15. Energy effectiveness of different nanofluids [66].
Sanjeev Kumar Gupta, H. Verma and N. Yadav Materials Today: Proceedings xxx (xxxx) xxx
8

60 °C, volume concentration, Dean number (which is the ratio of
the mass flow rate of the coil to side water), etc. Their results
declared that Nusselt number & overall heat transfer coefficient
enhanced with volume concentration, mass flow rate, and shell
side temperature. They concluded that the better performance of
STHE can be obtained by utilizing Cuo/carboxymethyl cellulose
nanofluid relative to the other two nanofluids. The overall heat
transfer coefficient is enhanced with Dean number which is shown
in Fig. 17.
Rasheed et al. [69] performed numerical and experimental anal-
ysis on a shell & helically microtube heat exchanger to enquire the
heat transfer characteristics by utilizing Al
2
O
3
/water and ZnO
nanofluid. The volume fraction of nanofluid is wide-ranging from
1 to 2%. Three different types of curvature such as elliptical, circu-
lar, and oval are used to find out the maximum heat transfer situ-
ation. From their data-based perception, it is investigated that heat
transfer and friction factor augmented with Reynolds number as
well as volume concentration. They also concluded that the highest
heat transfer is attained in circular curvature at 2% volume concen-
tration by utilizing Al
2
O
3
/water nanofluid. They finally concluded
that the best thermal performance (which is increases with an
increase in Nusselt Number) is achieved with Al
2
O
3
/water nano-
fluid relative to ZnO/water nanofluid at Reynolds number of 1800
considering circular curvature which is shown in Fig. 18. The ther-
mal performance factor is enhanced with an increment in coil
pitch. The maximum thermal performance factor is found approx-
imately 3 for circular curvature of coil pitch 18 mm at a Reynolds
number of 1800.
Niwalkar et al. [70] experimented on shell & helically coiled
tube heat exchanger for enhancement of heat transfer using SiO
2
/
water nanofluid. Nanoparticles of distinct concentrations varying
from 0.5 to 0.25 vol% are used. SEM technique has been used for
the characterization of nanofluids. They have found a remarkable
augment in heat transfer coefficient of about 28.71% using SiO
2
/
water nanofluid in contrast to the base fluid water. They have also
found a significant increment in pressure drop of about 62.61% and
friction factor of about 52.61% using SiO
2
/water nanofluid relative
to the base fluid water.
Fares et al. [55] used graphene nanofluid and experimented on
STHEs to investigate the convective heat transfer coefficient. Gra-
phite foam is used to prepare the graphene flakes. The characteri-
zation of graphene flakes was done by electron microscopy and
Raman spectroscopy. The heat transfer performance of the STHE
is aggravated by using graphene nanofluid on the tube side. The
heat performance of STHEs is increased by using graphene/water
nanofluid. They concluded that by using 0.2% graphene/water
nanofluid, the heat transfer coefficient was approximately aug-
mented by 29%, and also the thermal efficiency of STHE was aug-
mented by 14%.
Maghrabir et al. [57] experimented on the helically coiled STHE
by utilizing SiO
2
/water and Al
2
O
3
/water nanofluid to investigate
the effect of inclination angle. They used different concentrations
of nanofluids varied from 0.15 vol% to 0.35 vol%. They had taken
coil Reynolds numbers in the range of 6000 to 15000. The inclina-
tion angle varied from 0
0
,30
0
,60
0
, and 90
0
which are calculated
from the horizontal axis of the STHE. They performed SEM analysis
for characterization of both the nanofluids. They investigated that
the effectiveness of the heat exchanger increases while pressure
drop diminishes with the rise in coil Nusselt number which shoots
up with the rise in inclination angle. They have found improve-
ment in coil Nusselt number by 12%, 8.5%, and 8.5% by changing
the orientation of STHE from horizontal to vertical at coil Reynolds
number 15,000 for base fluid water, 0.1 vol% Al
2
O
3
and SiO
2
nanofluids respectively. They have also developed empirical corre-
lations for coil Nusselt number as a function of coil Reynolds num-
Fig. 16. Effectiveness v/s Reynolds number [67].
Fig. 17. Overall heat transfer coefficient v/s Dean number [68].Fig. 18. Thermal performance factor v/s Reynolds number [69].
Sanjeev Kumar Gupta, H. Verma and N. Yadav Materials Today: Proceedings xxx (xxxx) xxx
9

ber, inclination angle, and volume concentration of nanofluid with
an error of ± 3%.
6. Conclusions, Challenges, and future recommendation
Nanomaterials and nanofluids utilization for energy saving is a
challenge for researchers and scientists. Most of the researchers
have recommended using laminar flow in the case of nanofluid
because convective heat transfer coefficient increases by the addi-
tion of nanoparticles but in the case of turbulent flow it decreases
and sometimes it remains constant. The convective heat transfer
coefficient is enhanced with enhancement in temperature and
weight concentration of nanofluid. The thermal conductivity of
nanofluid enriches by the inclusion of nanoparticles in both the
flow situation. It is a challenge to utilize nanofluid in the heat
exchanger in turbulent flow situations. It is a big research gap that
needs a lot of experimental and simulation work in the future.
Very little information is available on heat capacity. Some
researchers reported that the heat capacity diminishes with the
increment of the volume fraction of nanoparticles. This property
needs further investigation through experiment because coolant
possesses high heat capacity. The viscosity of nanofluid increases
with increment in nanoparticles. The pumping power increases
due to an increase in viscosity which is the major problem in the
utilization of nanofluid.
The Nusselt number, friction factor, and overall heat transfer
coefficient were enhanced with augmentation in Reynolds number,
volume fraction, and mass flow rate, and shell side temperature.
Because of augmentation in Nusselt number, heat transfer rate
increases which ultimately results in energy saving and overall
cost reduction of the system. Better performance of STHE can be
acquired by utilizing the nanofluids of metal oxide Effectiveness
and pressure drop are also enhanced with increment in Reynolds
number. The energy effectiveness of the heat exchanger is
increased by the proper selection of nanofluid without any envi-
ronmental concern. The major concern in utilizing the nanofluid
is the stability of nanofluid and the production cost of nanofluid.
This area of nanofluid is needed to be explored that can help in
the commercialization of nanofluid.
Only a few research articles are available on hybrid nanofluid
utilization in STHE to enhance its thermal performance. So it is rec-
ommended to use such variety of fluid in future. Experimental
results can also be validated with computational results. Nanoflu-
ids can be mixed with PCM to boost the thermal performance of
STHE. The design of STHE is a very important parameter for
researchers and scientists. They can modify the design of STHE
and make it more compact for space and energy saving.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
Acknowledgement
The communicating author (Sanjeev Kumar Gupta) might want
to recognize his younger brother late Mr. Ajit Kumar Gupta for his
inspiration regarding research activity and his unequivocal help.
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