Received: 13 March 2019
| Revised: 29 April 2019
| Accepted: 24 May 2019
DOI: 10.1002/htj.21502
ORIGINAL ARTICLE
Performance analysis of spiral and serpentine
tube solar collector with carbon nanotube
nanofluids under natural flow method
Abd Elnaby Kabeel1 | El‐Sayed El‐Agouz1 | Nakka Prakash2 |
Chandran Prasad2 | Ravishankar Sathyamurthy1,2 |
Athikesavan Muthu Manokar3
1
Mechanical Power Engineering
Department, Faculty of Engineering, Abstract
Tanta University, Tanta, Egypt This study communicates the performance analysis of spiral
2
Department of Automobile Engineering, and serpentine tube solar collector with carbon nanotube
Hindustan Institute of Technology and
nanofluids under natural flow method. Experiments were
Science, Chennai, Tamil Nadu, India
3
Department of Mechanical Engineering,
carried out at three different mass flow rates namely 3, 5,
BS Abdur Rahman Crescent Institute of and 7 kg/hour while the concentration of nanoparticles was
Science and Technology, Chennai, Tamil varied from 0.05% and 0.1%, respectively. Experiments were
Nadu, India
carried out under the same condition of ambient parameters
Correspondence for validation. Results show that the maximum exit water
Dr. Ravishankar Sathyamurthy,
temperature was found to be about 75°C with a maximum
Department of Automobile Engineering,
Hindustan Institute of Technology and concentration of 0.1% under a minimum flow rate of 3 kg/
Science, Chennai, Tamil Nadu, India. hour during the peak intensity. Similarly, the improvement
Email: raviannauniv23@gmail.com
in temperature of the water is found to be 6% under peak
intensity and decreased to about 4.3% and 4.2% for the flow
rates of 5 and 7 kg/hour, respectively
KEYWORDS
concentration, enhancement, nanofluids, natural convection, solar
collector
1 | INTRODUCTION
Heating of water to a higher temperature is usually carried out by burning fossil fuels. During
the 19th century, solar energy is collected by utilizing flat plate collectors and parabolic trough
collectors to heat up the water. For domestic purposes, the solar water heater is used only for
bathing purposes, whereas, in industries, parabolic and concentrating collectors were used to
Heat Transfer—Asian Res. 2019;1-12. wileyonlinelibrary.com/journal/htj © 2019 Wiley Periodicals, Inc. | 1
2 | KABEEL ET AL.
produce electricity. Flat plate collectors use serpentine or straight tubes and usually made of
copper or aluminum materials.1-8
Krishnavel et al9 experimentally investigated concrete absorber solar water heater with
and without insulation at different inclination angles. Also, experiments were carried out
with polyvinyl chloride (PVC) pipes and aluminum pipes with wire mesh and iron scraps.
The study revealed that the water heater with aluminum pipes and iron scraps was more
efficient than PVC pipes, whereas the slab 2 configuration with PVC and thermal
conductivity materials were more suitable for moderate temperatures. Maheswaran et al10
experimentally investigated a passive type spiral tube solar water heater. The mass flow rate
in the tube is constantly maintained at 0.0083 kg/second as the temperature of outlet water
temperature was found as 98.2°C. Michael and Iniyan11 investigated the performance of a
flat plate collector under forced and natural circulation model with CuO/water nanofluid.
The results concluded that the thermal efficiency of the collector improved by 6.3% with a
low volume concentration (0.05%). The efficiency of the flat plate collector was higher for the
mass flow of 0.1 kg/second. Sathyamurthy et al12 investigated a semicircular trough absorber
solar still and identified the utilization of its use as a solar water heater. Results showed that
the outlet water temperature was higher in the case of minimum mass flow in the absorber
with 10 baffles placed in a PVC absorber. Similarly, Sathyamurthy et al13 investigated
experimentally on semicircular trough absorber solar water heater. The results showed that
the temperature of the outlet water was increased by 46% than the other solar water heater
on the use of its domestic applications. Various comprehensive solar water heater review
articles have been studied.14-21 From the published manuscripts, it is clear that concrete
absorber is having greater flexibility toward the water heating system. This paper
communicates the experimental analysis of a simple solar water heater with the spiral and
serpentine tube arrangement. Also, the temperature of the outlet water completely depends
on the number of windings, the special distance between the consecutive tubes and the
contact area of the tube with the incidence of radiation.
2 | SYSTEM DESCRIPTION
Figure 1 shows the schematic diagram and experimental setup of a solar water heater with
spiral tube arrangement. It consists of a rectangular tray with a copper tube fixed in it with
spiral tube arrangement. The length of the copper tube is fixed at 2.5 m with an equivalent
area of the solar water heater as 0.65 m2. The specification of the copper tube used is given in
Table 1. The spacing between the copper tubes is maintained at a distance of 45 mm to facilitate
the flow of water and nanofluid inside the inner tube surface by gravity fed method under
different flow rate. To increase the temperature of surface and water, a glass cover is provided to
reduce the convective losses from the tube surface to the ambient. The fluid is sent through the
center to the exit of a collector in a spiral tube arrangement, whereas, in a serpentine tube
collector fluid is sent through the adjacent pipes kept parallel.
Experiments were carried out using two different concentrations of carbon nanotube (CNT)
nanofluids in the outdoor facility available in the Department of Mechanical Engineering, S.A.
Engineering College, Chennai. The solar intensity and wind velocity were measured using
TES1333R solar power meter and AM4836 Cup type anemometer respectively. The temperature
of absorber, glass, inlet and exit water were measured using PT100 (RTD sensors). Experiments
were conducted between 7 AM till 5 PM and parameters were set to be constant, while the
KABEEL ET AL. | 3
F I G U R E 1 Schematic diagram of spiral and serpentine tube solar water heater [Color figure can be viewed
at wileyonlinelibrary.com]
uncontrollable parameter is the environmental condition. Experiments were conducted and set
to be for similar solar intensity and ambient temperature. To get a better mixture of
nanoparticles in water, the nanofluid is initially held in a magnetic stirrer for almost 30 minutes
and stirred at a constant speed of 800 rpm. After stirring, the fluid is kept in an ultrasonicator
for 3 hours to attain better stability and dispersion of nanoparticle in the fluid. A bath type
T A B L E 1 Specification of tube
S. No Parameter Value
1 Diameter 12.5 mm
2 Length 2.5 m
3 Material Copper
4 Specific heat capacity 390 J/kgK
5 Thermal conductivity 401 W/mK
4 | KABEEL ET AL.
T A B L E 2 Specification of carbon nanotube (CNT)
S. No. Property CNT
1 Color Black
2 Purity >97%
3 Particle size 20‐30 nm
4 True density (kg/m3) 2100
5 Thermal conductivity (W/mK) 3007.4
6 Specific heat capacity (J/kgK) 9124
7 Morphology Cylindrical
2
8 SSA (m /g) 200
sonicator is used and the frequency of vibration and temperature of the bath is kept constant.
The physical properties of CNT's are given in Table 2.
2.1 | Uncertainty analysis
The uncertainty of the instrument used for the present experimental study on fluid temperature
and the flow rate is measured using the correlations of Jong et al.22 The radiative heat losses and
conduction losses through the bottom of absorber were minimized by perfect insulation and
these losses are negligible. Uncertainty of instruments such as a thermocouple, solar power
meter, anemometer, and fluid collector was calculated as 1%, 2.5%, 2.75%, and 3% respectively.
The uncertainty is mathematically expressed as,
U
Uncertainty = × 100, (1)
x
where
σ12 + σ22 + σ32 + σ42 + σ52 + ⋯ + σn2
U= (2)
N
N‐ Number of observations
σ‐ Standard deviation
∑ (X − X¯ )
σ= . (3)
N
3 | R E S U L T S AN D D I S C U S S I O N
The hourly variation of solar intensity, ambient temperature, and wind velocity measured
during the experiment are plotted in Figure 2. It is observed that the solar intensity during the
sunshine hours increases gradually and reaching the peak intensity around 1 PM and observed
as 987 W/m2 during the month of May 2017. Also, the ambient temperatures during the
KABEEL ET AL. | 5
FIGURE 2 Diurnal variations in solar intensity, ambient temperature, and wind velocity during the
experimentation
experiments were in the range of 34 to 36.8°C. The hourly variation in wind velocity is
abnormal during the consecutive days of experiments carried out. Since the convective heat
transfer between glass and ambient is negligible, the effect of wind velocity is not considered as
an important factor. The average wind velocity measured during the entire experiments carried
out is found as 1.3 m/second.
3.1 | Spiral tube solar water heating system with and without
nanofluids
The hourly variation of exit water temperature from the solar collector with a spiral tube
arrangement under different concentration of CNT nanoparticle and flow rate is shown in
Figure 3. It is observed that the effect of doping CNT in the fluid increases the water
temperature by a margin of 7.5°C while the maximum temperature of the fluid is found as 75°C
during the peak solar intensity under a constant flow rate of 3 kg/hour and a maximum
concentration of 0.1% nanoparticle. This increase in temperature is due to the effect of high
thermal conductivity of nanoparticle in the fluid. With an increase in the flow rate of fluid
inside the spiral tube arrangement, the convective heat transfer between fluid and wall surface
decreases and this decreases the exit temperature of the fluid. Also, it is observed that there is
only a marginal increase of about 2% in exit water temperature than water during the low‐
intensity period during all flow rates. Similarly, the hourly variation of improvement in exit
water temperature using a different concentration of nanoparticle in the fluid is depicted in
Figure 4. It is observed that the maximum improvement in temperature is found in the case of
maximum concentration of nanoparticle in the fluid. The reduced effect of convective heat from
the tube surface and reduced retention time of the fluid surface with the wall surface decreased
the improvement in temperature of the fluid at higher concentration. The further increase from
5 to 7 kg/hour of nanofluid in the tube there is no further improvement in the exit water
temperature. The maximum increase of 6% and 4.5% is observed in the case of flow rates with 3
and 5 kg/hour respectively and 0.1% concentration, while the maximum improvement in low
concentration is observed as 3.7% and 2.8% respectively.
6 | KABEEL ET AL.
FIGURE 3 Hourly variation of exit water temperature of solar collector under different flow rate (ϕ = 0%,
0.05%, and 0.1%)
The variation of average exit temperature of the fluid at different concentration against
different flow rates is shown in Figure 5. It can be observed that the increase in the
concentration of nanoparticle increase the average exit water temperature and increases
linearly. Also, it is observed that the increase in flow rate decrease the average exit fluid
temperature. The overall increase in the temperature is mainly due to the effect of thermal
conductivity of nanoparticle in the fluid and circumferential heat extraction by reducing the
retention time of fluid with the wall surface. It is also found that the increase in mass flow rate
from 5 to 7 kg/hour, the average temperature reduced by 2.5°C as the time for extraction of heat
from the tube surface to water is minimized.
KABEEL ET AL. | 7
F I G U R E 4 Hourly variation of improvement in water temperature for different flow rates (ϕ = 0.05% and
0.1%) [Color figure can be viewed at wileyonlinelibrary.com]
3.2 | Serpentine tube solar water heating system with and without
nanofluids
The hourly variations in exit temperature of the water and CNT doped nanofluid for
variation in mass flow rates on a serpentine tube solar collector are depicted in Figure 6 It is
observed that the increase in the concentration of nanoparticle in the base fluid increases
the exit temperature by 4.8% during the peak solar intensity. For variation in flow rates the
temperature increases by 3.5% and 2.5% for 5 and 7 kg/hour, respectively. While comparing
it with the spiral tube solar collector, the temperature at the exit is decreased by 10°C for the
flow rate of 3 kg/hour. This increase in temperature at the exit is due to the concentric
arrangements of the tube and reduction in the equivalent length of the copper tube, the
maximum temperature at the exit for 3, 5, and 7 kg/hour are found to be 65, 62.5, and 53°C
respectively. The variation in improvement in temperature at the exit of the serpentine tube
collector for various flow rates is shown in Figure 6. From Figure 6 it is also observed that
there is only a nominal increase in the temperature during off‐shine hours. It is observed
that the increase in the concentration of the fluid by 0.05% and 0.1% increases the rate of
8 | KABEEL ET AL.
FIGURE 5 Variation of average exit temperature at different concentration of CNT nanoparticles. CNT,
carbon nanotube
FIGURE 6 Hourly variation of exit water temperature of solar collector under different flow rate (ϕ = 0%,
0.05% and 0.1%)
KABEEL ET AL. | 9
F I G U R E 7 Hourly variation of improvement in water temperature for different flow rates (ϕ = 0.05% and
0.1%) [Color figure can be viewed at wileyonlinelibrary.com]
heat transfer under natural flow method. Improvement in temperature increases by using
0.1% concentration improved by two times as compared with 0.05% concentration of CNT
nanoparticles in the fluid.
Figure 7 shows the diurnal variations in the improvement in the temperature of the
fluid at different flow rates of fluid for a varied concentration of nanoparticle with the
fluid. It is observed that the increase in flow rate decreases the improvement in the
temperature of the fluid. The fluid temperature with increasing concentration decreases
the improvement in temperature as compared to the spiral tube collector. Similarly, a
maximum rise in improvement for fluid temperature is observed as 4.8% as compared to
fluid without nanoparticle at maximum solar intensity.
The variation of average exit temperature of the fluid at different concentration against
different flow rates is shown in Figure 8. It can be observed that the increase in the
concentration of nanoparticle increase the average exit water temperature and increases
linearly. Also, it is observed that the increase in flow rate decrease the average exit fluid
10 | KABEEL ET AL.
FIGURE 8 Variation of average exit temperature at different concentration of CNT nanoparticles. CNT,
carbon nanotube
temperature. There is a temperature increase of about 3.5°C with maximum concentration
with a minimum flow rate.
4 | C ON C LU S I O N S
The main contribution of this study work is enhancing the water temperature in concrete
absorber solar water heater by using high thermal conductivity nanofluids. From the
experimental investigation, the following conclusions have arrived:
• Experiments were carried out at three different mass flow rates namely 3, 5, and 7 kg/hour
while the concentration of nanoparticles was varied from 0.05% and 0.1%.
• Results show that the exit water temperature is maximum and found to about 75°C with a
maximum concentration of 0.1% under a reduced flow rate of 3 kg/hour during the peak solar
intensity.
• The improvement in temperature of the water is found to be 6% under peak intensity and
reduced to about 4.3% and 4.2% for 5 and 7 kg/hour respectively.
• The average temperature of water at a maximum concentration of nanoparticle in the
fluid on serpentine tube collector is observed as 48, 43.3, and 41°C for 3, 5, and 7 kg/hour
respectively.
• The spiral tube solar water heater with CNT nanoparticles reached the maximum water
temperature of 75°C whereas without nanoparticles reached only 68°C.
KABEEL ET AL. | 11
• The serpentine tube solar water heater with CNT nanoparticles reached the maximum water
temperature of 65°C whereas without nanoparticles reached only 58°C.
• As comparing the performance of the two solar water heating system it is concluded that the
performance of the spiral tube is best.
ORCID
Abd Elnaby Kabeel http://orcid.org/0000-0003-4273-8487
Ravishankar Sathyamurthy http://orcid.org/0000-0002-2881-3455
Athikesavan Muthu Manokar http://orcid.org/0000-0001-7523-6796
REFERENCES
1. Rosas‐Flores JA, Rosas‐Flores D, Fernández zayas JL. Potential energy saving in urban and rural households
of Mexico by use of solar water heaters, using geographical information system. Renewable Sustainable
Energy Rev. 2016;53:243‐252.
2. Li R, Dai Y, Wang R. Experimental investigation and simulation analysis of the thermal performance of a
balcony wall integrated solar water heating unit. Renewable Energy. 2015;75:115‐122.
3. Halawa E, Chang KC, Yoshinaga M. Thermal performance evaluation of solar water heating systems in
Australia, Taiwan and Japan–A comparative review. Renewable Energy. 2015;83:1279‐1286.
4. Kabeel AE, El‐Said EM, Abdulaziz M. Thermal solar water heater with H2O‐Al2O3 nanofluid in forced
convection: experimental investigation. Int J Ambient Energy. 2017;38(1):85‐93.
5. Bashir MJ, Jing OL, Sethupathi S, Aun NC. Evaluation of Energy Cost Saving and Pollutants Emission Reduction
for Solar Water Heater Development in Malaysia. In ICGSCE. 2014. Singapore: Springer; 2015:211‐218.
6. Chaabane M, Mhiri H, Bournot P. Effect of the water storage tank coverage with an outer glass tube on the thermal
performance of an integrated collector storage solar water heater. J Sol Energy Eng. 2015;137(1):011009.
7. Qiu S, Ruth M, Ghosh S. Evacuated tube collectors: a notable driver behind the solar water heater industry
in China. Renewable Sustainable Energy Rev. 2015;47:580‐588.
8. Wang Z, Rosas R, Qian C. Nonlinear observer design for a solar thermal water heater system. In Control and
Decision Conference (CCDC), 2015 27th Chinese, pp. 4817‐4822. IEEE, 2015.
9. Krishnavel V, Karthick A, Murugavel KK. Experimental analysis of concrete absorber solar water heating
systems. Energy Build. 2014;84:501‐505.
10. Maheshwaran S, Kalidasa Murugavel K. Experimental study on spiral flow passive solar water heater.
Applied Solar Energy. 2013;49(2):89‐92.
11. Michael JJ, Iniyan S. Performance of copper oxide/water nanofluid in a flat plate solar water heater under
natural and forced circulations. Energy Convers Manage. 2015;95:160‐169.
12. Sathyamurthy R, Nagarajan Pk, El‐Agouz SA, Jaiganesh V. Experimental investigation on a semi‐circular
trough‐absorber solar still with baffles for fresh water production. Energy Conversion Management.
2015;97:235‐242.
13. Taamneh Y, Muthumanokar A, Kabeel AE, et al. Experimental analysis of inclined solar water heater with
baffles. Chem Eng Transact. 2018;71:1339‐1344.
14. Casanovas‐Rubio MdM, Armengou J. Decision‐making tool for the optimal selection of a domestic water‐
heating system considering economic, environmental and social criteria: application to Barcelona (Spain).
Renewable Sustainable Energy Rev. 2018;91:741‐753.
15. Gautam A, Chamoli S, Kumar A, Singh S. A review on technical improvements, economic feasibility and
world scenario of solar water heating system. Renewable Sustainable Energy Rev. 2017;68:541‐562.
16. Sellami R, Kasbadji Merzouk N, Amirat M, Chekrouni R. Market potential and development prospects of the
solar water heater field in Algeria. Renewable Sustainable Energy Rev. 2016;65:617‐625.
17. Benli H. Potential application of solar water heaters for hot water production in Turkey. Renewable
Sustainable Energy Rev. 2016;54:99‐109.
12 | KABEEL ET AL.
18. Abd‐ur‐Rehman HM, Al‐Sulaiman FA. Optimum selection of solar water heating (SWH) systems based on
their comparative techno‐economic feasibility study for the domestic sector of Saudi Arabia. Renewable
Sustainable Energy Rev. 2016;62:336‐349.
19. Singh R, Ian L, Souliotis M. Recent developments in integrated collector storage (ICS) solar water heaters: a
review. Renewable Sustainable Energy Rev. 2016;54:270‐298.
20. Yurtsev A, Jenkins GP. Cost‐effectiveness analysis of alternative water heater systems operating with
unreliable water supplies. Renewable Sustainable Energy Rev. 2016;54:174‐183.
21. Nogueira C, Luiz Vidotto M, Toniazzo F, Debastiani G. Software for designing solar water heating systems.
Renewable Sustainable Energy Rev. 2016;58:361‐375.
22. Jong HK, Simon TW, Viskanta R. Journal of heat transfer policy on reporting uncertainties in experimental
measurements and results. ASME J Heat Transfer. 115, 1993:5‐6.
How to cite this article: Kabeel AE, El‐Agouz E‐S, Prakash N, Prasad C, Sathyamurthy
R, Manokar AM. Performance analysis of spiral and serpentine tube solar collector with
carbon nanotube nanofluids under natural flow method. Heat Transfer—Asian Res.
2019;1‐12. https://doi.org/10.1002/htj.21502
