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Analysis on the Influence of Nano Particles of Alumina, Copper Oxide and Zirconium Oxide on the Performance of a Flat Plate Solar Water Heater Yuvarajan Devarajan, and Dinesh Babu Munuswamy Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b02264 • Publication Date (Web): 07 Oct 2016 Downloaded from http://pubs.acs.org on October 13, 2016

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Analysis on the Influence of Nano Particles of Alumina, Copper Oxide and Zirconium Oxide on the Performance of a Flat Plate Solar Water Heater Yuvarajan Devarajan1 and Dinesh Babu Munuswamy 2,* 1

Department of Mechanical Engineering, Vel Tech Dr.RR & Dr.SR Technical University, Chennai, India. Department of Mechanical Engineering, Panimalar Engineering college, Chennai, India.

2*,

1

[email protected]

2

[email protected]

Abstract

In this work, solar flat plate collector integrated with four riser tubes having 0.5m2 area is designed and fabricated. Experiments were conducted using three working nanofluids namely, Alumina, Copper Oxide and Zirconium Oxides along with the base working fluid water of different weight fractions. Efficiency of collector and storage tank is calculated using ASHRAE method the obtained results were compared. Experimental result shows that Alumina nanofluid influences the collector efficiency nearly about 17% for collector and 13.5% for the storage tank as compared to the base working fluid water. The efficiency of solar collector by appending 0.4% of Al2O3, CuO, ZrO2 and water is found to be 55, 51.3,47 and 38% respectively. Experimental results raveled that addition of nanoparticles to water as heat transfer fluid enhances the heat transfer thereby the increasing the efficiency of the collector.

Keywords: Flat plate collector, solar water heater, nanoparticles and efficiency.

ACS Paragon Plus Environment

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1. INTRODUCTION

Inclination towards utilizing solar energy for all applications is it thermal or electrical, is on the rising trend owing to exponentially increasing fossil fuel cost and better environmental awareness. The major stumbling block towards using solar energy, for all the applications and at all levels, is the requirement of higher capital investment. Researchers across the globe are finding alternate and cheaper materials towards constructing solar systems so as to reduce the investment. Employing solar energy for water heating is a very simple and well proven technology. Among the types of solar water heating systems, flat plate is preferred owing to its ruggedness and generation of hot water in the moderate temperature range without requirement of any tracking mechanisms. Several research works were conducted to improve the efficiency of solar water heaters viz., reducing the surface heat losses using selective coatings, employing vacuum in collectors, adopting special transparent collector covers, employing multiple collector covers and better insulation. Yet another productive and most effective method identified to increase the efficiency of solar collectors is replacement of water (conventionally used as working fluid) with high thermal conductivity fluids. With the advent of nano particles, experiments were conducted towards using nano fluids in lieu of water towards improving the performance of solar water heaters. In an effort towards reducing the cost of conventional solar water heating system it was proposed to replace conventionally used water with the nano particles of alumina, copper oxide and zirconium oxide. The reason being an increase in efficiency by 10% would help in reducing the collector area by 10% and hence ultimately reducing the investment on solar water heaters. Sokhansefat et al. 1 investigated a parabolic trough collector tube using Al2O3 nanofluid and found improvement in heat transfer at different operational temperatures. Lenert and Wang2 employed carbon-coated cobalt (C-Co) nanoparticle and Therminol VP-1 in solar power application and found 35% increase in the efficiency. Suresh et al.3 performed a comparative study on AI2O3 and CuO with water in straight circular duct fitted with helical screw tape inserts and found that the


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CuO nanofluid gives a better Performance than the Al2O3. Gupta et al4 theoretically compared the conventional flat-plate collector with a direct absorption solar collector (DAC) and observed the former to be 10% more efficient. Kundan and Sharma

5

evaluated the CuO + water nanofluid-

based low-flux solar collector and concluded that CuO nanofluids increases the efficiency increases in the order of 4% to 6%, which is comparable with water and CuO nanofluid with 0.005%volume fraction, with a gain of 2%-2.5% in efficiency than the 0.05%volume fraction. They have also concluded that a higher efficiency is obtained due to the tiny size element increases the amalgamation ability of the nanofluid. Natarajan and sathish 6 reported that nanofluids as transport medium in solar water heaters enhances the thermal conductivity of nanoparticles thus increasing the collector efficiency. Otanicar et al.7 showed that mixing nanoparticles in a liquid has a dramatic effect on the liquid’s thermo physical properties. Their study accounts for efficiency improvement of up to 5%. For 20-nm silver particles, a maximum improvement of 5% has been reported. Yousef et al.

8, 9

studied that by increasing the weight fractions of nanoparticles,

there is a 28.3% increase in efficiency for the collectors in comparison with water as the absorbing medium. Michael et al

10

showed an improvement in the efficiency of the solar water

heater by 10.88% using nanofluids at 0.025% volume fraction. Sabiha et al.

11

conducted a

performance evaluation of evacuated tube solar collector using single walled carbon nanotubes and found that the thermal conductivity of water is lower when compared to metals. Further it was also concluded that the efficiency of the collector using water alone is 58% but increases to 73% with single walled carbon nanotubes. Liu et al.12 showed the thermal performance of an open thermosyphon using nanofluids for high-temperature evacuated tubular collectors with the waterbased CuO nanofluids showing a greater influence on heat transfer. Maryam et al. 13 investigated the thermal performance of cylindrical heat pipes using Al2O3, CuO and TiO2 nanofluids and found that CuO nanofluids showed improve efficiency than Al2O3 and TiO2 nanofluids. Kim et al.14 deliberated the pool boiling characteristics of dilute dispersions of alumina, zirconia and silica


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nanoparticles in water and found significant enhancement in critical heat flux. Shareef et al

15

Abbas Sahi

studied the effect of 0. 5% of Al2O3 in water and showed that the maximum

difference between outlet and inlet temperatures of the solar collector using Al2O3 was 14.4 ̊ C with the solar irradiance of about 788 W/m2 while in case of water the maximum temperature difference was 10.7 ̊C with a solar irradiance of about 781 W/m2 . Umang et al

16

analysed an heat transfer

enhancement by tilting the angle from 20° to 31.5° of wickless heat pipe flat plate solar collector by using CuO-BN /water hybrid nanofluid followed by conventional working fluid pure water and it was inferred that higher enhancement for both nanofluid and water but a decrease in heat transfer was observed when tilting the collector angle beyond 31.5° to 50°. Boyaghchi 17 studied the effect of CuO nanofluid in flat plate solar collectors and found 12% increase in collector efficiency. Dasaien

18

studied the effect of copper oxide nanofluid in the thermosyphon flat plate solar water heater and concluded that the inclusion of copper oxide nanofluid to water improves the thermal performance and efficiency of the collector. In this present work, the study the consequence of nanofluids and water as a working fluids medium on the thermal performance of solar flat plate collector is investigated. Results showed that addition of nanoparticles enhances the heat transfer thereby the efficiency of the collector is increased when compared to that of base working fluid water.

2. SELECTION OF NANOPARTICLES

The major criteria adopted for selecting the nano particles towards employing them as working fluids were their cost, availability, inertness to the collector material & tank, corrosiveness, dispersion in water, scaling & fouling tendency, ease of synthesizing them at nanometer scale and thermal conductivity. With this background three different nano particles were selected Copper Oxide (CuO), Aluminum Oxide (Al2O3) and Zirconium Oxide (ZrO2). Among the selected nano particles thermal conductivity of CuO was the highest followed by Al2O3 and ZrO2. However on the ease of dispersion in water ZrO2 was observed to disperse better than Al2O3 followed by CuO.


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Settling of CuO was highly predominant and a surfactant CTAB (Cetyl Triammonium Bromide) was used towards retaining CuO nanoparticles in suspension mode. Table 1 shows the properties of nano particles employed in this work.

Table 1. Properties of additives

Additive

Chemical formula

Alumina oxide

Al2O3,

Copper Oxide

CuO

Zirconium Oxide

ZrO2

Thermal conductivity (W/mk) 30

Density (g/cm

Apperance

3.95

White solid

22

6.31

Black powder

2.7

5.68

White powder

3. Experimental Set up

To analyze the effectiveness of nanoparticles in solar water heating systems, a double loop 25 LPD solar water heating system was designed and fabricated. The motive behind fabricating double loop system was that the nanoparticles laden water will absorb solar energy in the collector (primary loop) and will transmit it to the water in the storage tank though the secondary loop. Both the loops were designed to be of ladder type construction. The collector area was fixed as 1m by ½ m. Four riser tubes made of copper, 13mm OD and 12 mm ID, with thickness being 0.5 mm were used. Longitudinal corrugated fins were brazed on either side of the tubes. A fin of copper material was used and the dimensions of pitch width were 100mm with thickness being 1mm. Spacing between the tubes were maintained uniformly at 100mm. A copper tube of 25mm diameter serves as the common header to supply cold water from the storage tank to the riser tubes and another copper tube of same 25mm diameter serves as the outlet header for collecting the hot water fromthe riser tubes. The riser tubes were covered on all sides by a chamber made of aluminum walls. In between the walls glass wool was used for insulation. Aluminum foil was laid above and along the collector walls so as to reflect the insolation incident on it. The entire collector assembly was covered with a


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transparent single glass cover so as to reduce the surface heat loss. The glass cover was firmly attached to the collector by suitable gasket and screwing arrangements. The water holding capacity of the so constructed primary loop was observed to be about 2.5 liters. The outlet header from the collector was connected to the storage tank through a 25mm diameter pipe. The storage tank was made of copper and the dimensions were diameter of 300mm and length of 360mm .The tank was insulated with Poly Urethane Foam (PUF) to prevent heat loss and was covered with carbon steel. Hot water from the collector was made to pass though a ladder type of heat exchanger. During the course of flow in the ladder sort of arrangement, the water lost its heat and the resultant water is circulated back to the collector using another 25mm diameter pipe. The water in the storage tank absorbs heat from the hot water and thus generates hot water for the intended application. Provisions were made before the collector in the pipe for draining and feeding the primary circuit fluid. Photograph of the fabricated experimental setup is shown in Figure1. Schematic of the instrumentation set up is shown in Figure.2.

Figure 1. Solar collector with primary riser tube and secondary storage tank


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Figure 2. Instrumentation flow diagram for solar Flat plate collector

4. Instrumentation Set up

Suitable instruments along with logging devices were used for recording the variations in temperature and insolation to observe the variations of temperature and pressure across the fabricated solar water heater system operating under varying degrees of solar insolation. Temperature was monitored across 15 locations in the system and pressure at upstream & downstream of the flat plate collector. T-type thermocouples copper constantan was used for temperature measurements as the temperature range in the entire system was anticipated to be less than 100⁰C. Six thermocouples were mounted in the thermo well created in the bottom portion of the four riser tubes. Bottom sides of the riser tube were selected for nullifying the influence of solar insolation on temperature measurement. The first thermocouple (T1) was mounted on the lower end of the first riser tube, T2 on the middle of the second riser tuber, T3 on the top end of the third riser tube while T4, T5 and T6 were mounted at the bottom, middle and top end of the final riser tube. Any difference of temperature indicated between T1 and T4, T2 and T5, T3 and T6 reveals improper flow distribution among the 4 riser tubes.

This methodology of placing 6 thermocouples in lieu of 9 was adopted for reducing the pressure drop across the riser tubes because of the presence of thermo well. T7 and T8 indicate the


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temperature of hot water from the collector and temperature of cold water to the collector respectively. Ambient temperature and collector wall temperature are indicated by T9 and T10. Temperature stratification in the storage tank was monitored with the help of thermocouples T11, T12 and T13. Thermocouples T14 and T15 were used for measuring the temperature of air gap inside the collector and surface temperature of glass cover respectively.

Two bourdon type pressure gauges with a range from 0 to 0.5 bar were installed to monitor the pressure drop across the collector. Insolation data was recorded using the watchdog apparatus. Table 2 shows the technical details of solar water heater and Table 3 shows Collector Specifications.

Table 2. Details of solar water heater PARAMETERS

UNIT

INSTRUMENT

TYPE

Temperature

°C

Thermocouple

T-Type

Logging

-

Data logger

Agilent

Solar Insolation(global radiation)

W /m

2

Pyranometer

-

Table 3. Collector Specifications S.NO

PARAMETER

DIMENSION

1

Collector length

1040 mm

2

Collector breadth

535 mm

3

Tube inner diameter, di

12 mm

4

Tube outer diameter

12.5 mm

5

Pitch of the tube

100 mm

6

Total number of tubes

4

7

Thermal Conductivity of plate material , km

-1 -1 386 W m k


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8

Plate Thickness

0.001 m

9

Back Insulation Thickness

10

Insulation Thermal Conductivity (k)

11

Centre to Centre Between two tube

5 cm -1 -1 0.04 W m k 100 mm

12

Total Number of riser tubes

4

13

Fin thickness

1mm

Fin width

100 mm

Insulation material

Glass Wool

14 15

5. Determination of Efficiency

Efficiency of solar flat plate collector is calculated by ASHRAE method. Due to introduction of nanoparticle, the overall efficiency also depends on the thermal stratification inside the storage tank, Heat effectiveness of heat exchanger and volume fraction of nano-fluid.

The overall efficiency is calculated by using

ηOverall = {m Cp (T2- T1)/( AC X I d t) }

(Eq.1)

The instantaneous efficiency, ηi is calculated by

{Qu / AcxI(t)}

(Eq.2)

Where I (t) is the intensity of incident radiation .The input for the collector for the whole day is calculated by multiply with area of absorber plate, the area (Ac) is 0.5 m2 for the collector.

5. Results and Discussions

In this study, a solar flat plate collector of collector area 1mx0.5m is subjected to three different nanofluids for weight fractions 0.2% and 0.4% of Al2O3, CuO and ZrO2. The solar flat plate


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collector is operated at a very lower nanofluid concentration with the base fluid (water). The collector area is 0.5m². It is observed that the higher thermal stratification and larger rise in temperature were observed by nanofluid when compared to that of base working fluid (Water). The efficiency of solar collector is calculated based on the heat gained by the storage tank (W/m2).

Average Temperature Attained By Storage Tank Vs Commutative Insolation for Different Nanofluids with Base Working Fluid Water

The solar collector was tested with different nanofluids for weight fractions (0.2% & 0.4%) with base working fluid water in secondary loop heat exchanger. The Figure 3 to 5 shows the average temperature of storage tank for different nanofluids for a weight fraction of 0.2% and 0.4% with water is plotted versus the Cumulative Insolation. Increasing the fluid temperature in conventional collectors causes an increase in heat loss. However, at 0.4% weight fraction of heat loss decreases when compared to 0.2% weight fraction. In addition, the average temperature attained in the storage tank is higher for 0.4% of nanofluids.

The experiment was conducted using different mass fraction and working nanofluids and compared with water. It is observed that Al2O3 nanofluid attains a higher average temperature for both 0.4% and 0.2% mass fractions respectively owing to its better heat transfer rate and good dispersion medium. The graph is plotted for the weight fractions of 0.2% and 0.4% for individual working nanofluids and compared with water. The experiments result shows that nanofluids emphasis the better heat transfers than that of water. In addition, the average temperature attained in the storage tank for the different working nanofluids with base working fluid water is compared for weight fractions of 0.2% and 0.4% for a lower concentration. Addition of nanoparticles reduces the heat flow at a higher temperature differences. The results also found that at 0.4% weight fractions, higher temperatures is attained for all different working nanofluids when


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compared with water. Al2O3 nanofluid achieves a higher temperature for both weight fractions. The maximum temperature in the storage tank is achieved within a short duration for Al2O3 nanofluid followed by CuO, ZrO2. Thermal conductivity of Al2O3 nanofluid is increased owing to increase in molecules speed of bulk liquid as a result of higher temperature.

water 0.2% Al2O3

60

0.4% Al2O3 55

Avg. Storage Tank (°C)

50

45

40

35

0

10000

20000

30000

40000

50000

60000

2

Cummulative Insolation(W/m )

Figure 3. Average storage tank temperature of 0.2%and 0.4% weight fractions of AI2O3 nanofluid water

water 0.2% CuO 0.4% CuO

60

55


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50

45

40

35

30 0

10000

20000

30000

40000

50000

60000

Cummulative Insolation

Figure 4. Average storage tank temperature of 0.2%and 0.4% weight fractions of CuO nanofluid water


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Water 0.2% ZrO2

60

0.4% ZrO2 55


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50

45

40

35

30 0

10000

20000

30000

40000

50000

60000

70000

2

Cummulative Insolation (W/m )

⁰

Figure 5. Average storage tank temperature of 0.2%and 0.4% weight fractions of ZrO2 nanofluid water

Instantaneous Efficiency Vs Cumulative Insolation

Figure 6 and 7 shows the performance efficiency curves of solar collectors with different nanofluids and water with cumulative insolation. It was observed that the instantaneous collector efficiency for Al2O3 nanofluid is higher than CuO, ZrO2 and water. This is due to higher thermal conductivity of working fluid by doping Al2O3 to base fluid which improves heat transfer of the collector. In addition it is also noted that the temperature difference between inlet and outlet is higher by inclusion of Al2O3 nanofluid. This result confirms the less significant heat loss. Efficiency by doping 0.2% weight fraction of Al203, CuO, ZrO2 to water is 32%, 29% and 26% respectively. Further by doping 0.4% weight fraction of Al203, CuO, ZrO2 to water is 36%, 32% and 24% respectively


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Water 0.2% ZrO2

40

0.2% CuO 0.2% Al2O3

Instantaneous Efficiency(%)

35 30 25 20 15 10 5 0 0

10000

20000

30000

40000

50000

60000

2

Cummulative Insolation (W/m )

Figure 6. Efficiency graph for 0.2% weight fractions of different nanofluids and water.

Water 0.4% ZrO2 0.4% CuO 0.4% Al2O3

35

Instantaneous Efficiency (%)

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30

25

20

15

10 0

10000

20000

30000

40000

50000

60000

2

Cummulative Insolation(W/m )

Figure 7: Efficiency graph for 0.4% weight fractions of different nanofluids and water.

Day Average Efficiency Comparison for Different Nanofluids for Primary and Secondary Side

Figure 8 to 11 shows the efficiency comparison on primary side (Collector) and secondary side (storage tank) operated by three nanofluids of different weight fractions in heat exchanger with base working fluid water. In both (primary and secondary section) the efficiency of Al2O3 nanofluid is higher than the other (CuO, ZrO2 and water) working fluids.


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The experimental results show an enhancement in heat transfer on collector side which emphasis the increase in efficiency for the different nanofluids.

Table 4. illustrates the comparison in

efficiency of working fluids.

Table 4. Comparison Table for the Efficiency Working Fluids

Particle Size (nm)

Weight Fractions

Collector Efficiency (%)

Storage tank Efficiency (%)

(%) Al2O3

40

0.4%

55

35.7

Al2O3

40

0.2%

51.5

32

CuO

40

0.4%

51.3

32.4

CuO

40

0.2%

49

29

ZrO2

40

0.4%

47.2

28.1

ZrO2

40

0.2%

45

25

Water

-

-

38

22

49%

50

51.5%

45% 40

Efficiency (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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38%

30

20

10

0 water

ZrO2

CuO

Al2O3

working fluid

Figure 8. Comparison of 0.2% weight fractions of different nanofluids and water.


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32 % 30

29%

25% 25

Efficiency (%)

22% 20

15

10

5

0 Water

ZrO2

CuO

Al2O3

working fluids


47.24%

50

51.34%

55%

38% Efficiency

40

30

20

10

0 water

ZrO2

CuO

Al2O3

Working fluid


37.75%

40 35

32.43% 28.12%

30 25

Efficiency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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22%

20 15 10 5 0 water

ZrO2

CuO

Al2O3

Working fluid


6. Conclusion


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Influence of Nano Particles on Alumina, Copper Oxide and Zirconium Oxide on the Performance of a Flat Plate Solar Water Heater Solar flat collector has been investigated. The efficiency of nanoparticles were calculated and compared with water as a base line in secondary loop heat exchanger. The following are the conclusions derived from this study

•

Al2O3 having a particle size of 40 nm with weight fractions of 0.4% & 0.2% shows an increase in the collector efficiency of 17and 13.5 % respectively when compared with water.

•

CuO having a particle size of 40 nm with weight fractions of 0.4% & 0.2% shows an increase in the collector efficiency of 13.3and 11 % respectively when compared with water.

•

ZrO2 having a particle size of 40 nm with weight fractions of 0.4% & 0.2% shows an increase in the collector efficiency of 9.2 and 7 % respectively when compared with water.

The experimental results confirm that Al2O3 nanofluid has higher thermal conductivity and collector efficiency when compared with CuO, ZrO2 nanoparticles with respect to water as a base line in secondary loop heat exchanger.

References (1) Sokhansefat, T.; Kasaeian, A. B.; Kowsary, F. Heat transfer enhancement in parabolic trough collector tube using Al2O3/synthetic oil nanofluid. Renew. Sustain. Energy Rev 2014, 33, 636-644. (2) Lenert, A.; Wang, E. N. Optimization of nanofluid volumetric receivers for solar thermal energy conversion. Sol. Energy 2012, 86, 253-265. (3) Suresh, S.; Venkitaraj, K. P.; Selvakumar, P.; Chandrasekhar, M. A comparison of thermal characteristics ofAl2O3/water and CuO/water nanofluids in transition flow through a straight circular duct fitted with helical screw tape inserts. Exp. Therm. Fluid Sci. 2012, 39, 37-44.


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(4) Gupta, H.K.; Agrawal, G.D.; Mathur, J. An experimental investigation of a low temperature Al2O3-H2O nanofluid based direct absorption solar collector. Sol. Energy 2015, 118, 390–6. (5) Tyagi, H.; Phelan, P.; Prasher, R. Predicted efficiency of a low-temperature nanofluid based direct absorption solar collector. J. Sol. Energy Eng 2009, 131, 041004. (6) Natarajan, E.; Sathish, R. Role of nanofluids in solar water heater, Int. J. Adv. Manuf. Technol 2009, 008, 1876-8. (7). Otanicar, T. P.; Phelan, P. E.; Prasher, R. S.; Rosengarten, G.; Taylor, R. A. Nanofluid-based direct absorption solar collector. J. Renew. Sust. Energy 2010, 3, 033102. (8) Yousefi, T.; Veysi, F.; Shojaeizadeh, E.; Zinadini, S. An experimental investigation on the effect of Al2O3-H2O nanofluid on the efficiency of flat-plate collectors. Renew. Energ 2012, 39, 293-298. (9) Yousefi, T.; Veysi, F.; Shojaeizadeh, E.; Zinadini, S. An experimental investigation on the effect of MWCNT-H2O nanofluid on the efficiency of flat-plate collectors. Exp. Therm Fluid Sci 2012, 39, 207-212. (10) Michael, J.J.; Iniyan, S. Performance of copper oxide/water nanofluid in a flat plate solar water heater under natural and forced circulations. Energy Conv. Manage 2015, 95,160–9. (11) Sabiha, M.A.; Saidur, R.; Hassani, S.; Said, Z.; Mekhilef, S. Energy performance of an evacuated tube solar collector using single walled carbon nanotubes nanofluids. Energy Convers.

Manage. 2015, 105, 1377–88. (12) Liu, Z.H.; Hu, R.L.; Zhao, F.; Xiao, H.-S. Thermal performance of an open thermosyphon using nanofluid for evacuated tubular high temperature air solar collector. Energy. Convers. Manage. 2007,

73, 323-334.


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