DZ32793798

S. Bhagavathi Shankar, Dr. A. Manivannan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.793-798

Performance Evaluation of Solar Water Heater Using Nanofluid S. Bhagavathi Shankar*, Dr. A. Manivannan** *(Department of Energy Engineering, Regional Centre, Anna University Tirunelveli Region,Tirunelveli-07) ** (Assistant Professor, Department of Energy Engineering, Regional Centre, Anna University Tirunelveli Region, Tirunelveli-07)

ABSTRACT Solar water heater is the most popular means of solar energy utilization because of technological feasibility and economic attraction compared with other kinds of solar energy utilization. The system can supply hot water at 50 o C and 80 oC which can be used for both domestic and industrial purposes.

Heat transfer enhancement in solar devices is one of the key issues of energy saving and compact designs.

Nanofluids are the new kind of heat transfer fluid containing a very small quantity of nano particles that are uniformly and stably suspended in fluids.

Nanofluids are high thermal conductivity than conventional fluids. Numerical model of the solar water heating system has been developed by using water and nanofluid as a base fluid. The objective of this paper is to improve the efficiency of solar water heating system by using nanofluids as a working fluid and improving the efficiency of solar water heater than the water as a working fluid by theoretically. The theoretical calculations were made and the result shows that the 10.88% of an improved efficiency is observed at .025% volume fraction of the nanofluids.

Keywords: copper oxide, nanofluid, solar water heater systems, thermosyphon, volume fraction

I. INTRODUCTION Solar Water Heater (SWH) is a typical device that converts the solar energy into thermal energy to heat up a heat transfer fluid such as water, non-freezing liquid or air for domestic usage. Solar water heating is widely used in most of the countries in all over the world. Now a days, the world’s demand of energy has increased, and it the natural, safe and costless process to collect hot water by solar radiations. There are many applications of the hot water heated by the solar radiations. Where the solar hot water is used in the domestic purposes, it also is used in industrial applications, e.g. used for electricity generation.

mixture water with ethylene glycol and engine oil as cooling agent, but it is depend on the type of application use. However, it is found that the solubility of others base fluid such as ethylene glycol is lower than water at certain temperature although the thermal conductivity is low for ethylene glycol.

By the background of the solar water heater systems discussed and the thermosyphon solar water is used in the process to transfer fluid between the solar energy collector and hot water store is driven by buoyancy forces.

And the flat plate collector is used because of its simple construction for the fabrication of this system. And the Copper oxide nanofluid is mainly used for its cost effectiveness in the solar water heating system.

II. NUMERICAL ANALYSIS OF SOLAR WATER HEATING SYSTEM The procedure of solar water heating system is given and its components are discussed.

Performance of the system is done theorectically.

And the comparative analysis between both the working fluids are discussed and presented. The arrangement of solar collectors made for its better performance is given. Finally the design calculations of the system are performed for setup which is shown as following

Fig 1: Thermosyphon Solar Water Heater

The term ―Nanofluid’’ is envisioned to describe a solid liquid mixture which consists of nanoparticles and a base liquid, and which is one of the new challenges for thermo-science provided by the nanotechnology. The nanoparticles AL2O3, CuO, TiO2, ZnO and SiO2 are commonly use in the major research. The base fluid normally using water,

793 | P a g e

S. Bhagavathi Shankar, Dr. A. Manivannan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.793-798 V. NUMERICAL MODEL OF SOLAR WATER HEATER

Fig 2: Solar Water Heater Setup

III. SPECIFICATION OF FLAT PLATE COLLECTOR      

Length of the collector Lc = 2m Width of the collector = 1m Length of the absorber plate La= 1.95m width of the absorber plate = 0.95m Material of the absorber plate = Copper Thermal conductivity of the plate material K= 386 W/mK  Density of the plate material = 8954 kg/m3  Plate thickness δ = 2mm  Number of tubes used = 9  Glass cover=low iron class  Glass cover emissivity/absorptivity = 0.8  Diameter of header pipes = .025m  Diameter of the riser tube=.0125m  Insulating material used = Glass-wool  Insulating thickness=5c.m  Material of collector tray = Mild steel TABLE 1: Comparative Properties of Water and Cuo Nanofluid

IV. ASSUMPTIONS FOR SOLAR WATER HEATING SYSTEM     

The system was as a transient heat transfer mode because of its variations made by the heat transfer due to varying time.

The temperature of inlet water to be assumed as a 30oC with reference of ambient.

The wind velocity of the ambient was being assumed as 5m/s.

The volume of water require for primary side of solar water heater were assumed as 6.5litres.

The collector is placed in Chennai, so the latitude of 13oN was assumed as for the calculation has been made for winter season.

1. HEAT TRANSFER COEFFICIENTS 1.1 Convective heat transfer coefficient from plate to cover (h1c=1/r3) The convective heat transfer coefficient between plate and cover, parallel to each other and inclined at an angle β to the horizontal can be expressed as [18] h1c=Nu K / L where, h1c – convective heat transfer coefficient from plate to cover (W/m2K) K – Conductivity ( W/mK) β – angle of inclination (oC) where Nu is the nusselt number, ie. The ratio of the convective heat transfer to the conductive heat transfer in the fluid, K is the thermal conductivity of air and L is the spacing between the plate and the cover. The value of Nu can be obtained, using the expression given by Holland et al. for air as the medium between the plate and the cover.

1708

Nu=1+1.44 1 − Ra cos β + 1 − sin1.8β1.61708Ra cosβ+Ra cosβ583013−1 Ra is the Rayleigh number and is given by g β ∆T L 3

Ra=Gr . Pr =

ϑα Where, Gr – Grashof number Pr – Prandtl number g – gravity ϑ – kinematic viscosity of fluid (m2/s) α – diffusivity (m2/s) 1.2 From cover to ambient (h 2c=1/r1) The convective heat loss coefficient from the top glazing to the ambient is given by[18] h2c=2.8 + 3.0 V where, h2c – convective heat loss coefficient from Sl Properties Water CuO nano 1

Density

997 kg/m3

1025.2 kg/m3

2

Viscosity V,

0.831* 10−6 m2 /s 5.68

0.8834* 10−6 m2 /s 10.48

3

Prantl number Pr 4 Nusselt 4.63 number Nu 5 Thermal 0.6129W/mK conductivity K, cover to ambient(W/m2K) V – Wind speed (m/s)

15.64 0.3142 W/mK

1.3 Radiative heat transfer coefficient from plate to cover (h1r=1/r4)

794 | P a g e

S. Bhagavathi Shankar, Dr. A. Manivannan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.793-798 The amount of heat transferred from plate to cover, through radiation, can be given by expression qrad=h1r(Tp-Tg) Where Tp and Tg are the plate and glazing temperature in oC, respectively, and h1r is the coefficient of radiative heat loss from collector plate to the cover and is expressed as Tp +273 4 − Tg +273 4

h1r=єeff σ

Tp −Tg where σ=5.67 x 10-8 W/m2k4 is the stefan’s constant and єeff is the effective emissivity of plate glazing system, given by −1 1 1

єeff=

∈p

+

∈g

−1

The factor FR reduces the useful energy gain from the expected value is given by[18]

FR = [mCf/(AcUL)][1-exp(-AcULF’/(mCf))] 5. Heat Exchanger Factor A new collector performance equation that directly incorporates the effect of the heat exchanger will be derived. And the basic collector performance equation for 1m2 collector area

q = FR (ατ) I – FRUL( Tfi – Ta) If q is the net heat flux collected per unit collector area, then the heat transferred through the heat exchanger to the water of insulated tank is h=∆ Ux q

Ux = 52.7 1.4 From glazing cover to ambient (h2r = 1/r2) The coefficient of radiative heat loss from cover to the ambient depends upon the radiation exchange with sky at sky temperature Tsky given by Tsky = Ta – 6 The radiative heat transfer co efficient, h 2r, can thus be expressed as Tg +273 4 − Ts+273 4

h2r=єeff σ

Tg −Ta

1.5 Top loss coefficient The total heat transfer coefficient from collector plate to cover can be expressed as the sum of h 1c and h1r, ie.,

h1= h1c+h1r h2=h2c+h2r The effective top heat transfer coefficient from plate to ambient is given by

Ut=

1 h1

+

1

−1

h2

1.6 Overall Heat Loss Coefficient The overall heat loss coefficient UL is the sum of the top, and bottom UL=Ut+Ub 2. Fin Efficiency Factor The rate of heat transfer from the base of the fin (Tb) to the tube is given by, tan h m w −D /2 2 Ul F= and m = m w−D /2 Kϐ 3. Collector Efficiency Factor F’ The collector efficiency factor, F’ is defined as the ratio of actual useful heat collection rate to the useful heat collection rate when the collector absorbing plate (Tp) is at the local fluid temperature (Tf), 1/Ul

F’=

W

1 1 + Ul [ w −b F +b ] π dhs

4. Heat Removal Factor

Ac Ax

1 5

Lo

Since the heat loss in the connecting pipe between the storage tank and heat exchanger is negligible and the equation is given by −1 FRUL 1

Fx = 1 +

−1

mfcf ∈ 6. Heat Collection with Well Mixed Storage Tank In this case one turnover period, tT [18]of stratified storage tank is very small and this can be easily achieved in a horizontal storage tank with high circulating fluid flow rate as shown, well mixed storage might seem to be inherently less efficient due to high temperature of the fluid leaving storage tank. This loss is compensated by the high heat transfer factor attainable with large flow of fluid through the collector.

F’’x [(ατ )IT – UL (Ts−Ta)tT]

qT =

FxUltT

1+ 2mscs 7. Output Temperature qT

Tso = Tsi +

mscs

8. Density of Cuo Nanofluid The density of CuO Nanofluids, Kg/m3 CuO nanoparticle volume concentration[11],

Ρnf = Øρp + (1-Ø)ρbf

ρp =Density of CuO nanoparticles, Kg/m3 ρbf = Density of the base fluid, Kg/m3 The density data for water- propylene glycol (70:30 by volume percent) lend as a function of temperature is taken from ASHRAE (2009) Hand Book 9. Specific Heat of Cuo Nanofluid For a given volume concentration of nanoparticles in the base liquid, the specific heat can be calculated using the mixture formula. This formula[11] is valid for homogeneous mixtures and is given by 1−∅ ρ cp + ∅ ρ cp p

CPnf=

1−∅ ρbf + ∅ρp

795 | P a g e

S. Bhagavathi Shankar, Dr. A. Manivannan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.793-798 The specific heat of CuO Nanofluids at different temperatures are estimated for all the volume concentrations considered in the present work, using the Eq. ( of Pak and Cho (1998).

solar intensity were gradually decreased because of the solar movement.

10. Thermal Conductivity of Cuo Nanofluids The nanoparticles after large total surface area as a result of which higher thermal conductivities are expected in nanofluids. Many research finding reveal that traditional thermo fluids in the presence of nanoparticles exhibit better thermo physical properties.

solar intensity

CPnf = ∅Cp + 1 − ∅ Cbf

1400 1200 1000 800 600 400 200 0 10

12

13

14

15

16

Time (Hr)

Knf = Kbf [đ??žđ?‘?đ?‘˘đ?‘œ +2đ??žđ?‘?đ?‘“ −2∅( đ?‘˜đ?‘?đ?‘“ −đ??žđ?‘?đ?‘˘đ?‘œ )] [đ??žđ?‘?đ?‘˘đ?‘œ +2đ??žđ?‘?đ?‘“ +2đ??žđ?‘?đ?‘˘đ?‘œ đ??žđ?‘?đ?‘“ −đ??žđ?‘›đ?‘?đ?‘˘đ?‘œ ]

}

Knf = conductivity of nanofluid (Wm/k) Kbf = conductivity of base fluid (Wm/k) Kcuo = conductivity of copper oxide particle (Wm/k) 11. Viscosity Models Einstein has developed a viscosity correlation (Drew and passman- 1999) given by an equation in terms of nanoparticle volume concentration in the base fluid, when the nanoparticle volume concentration is lower than 5%, and is given by

Îźnf = Îźbf (1+ 2.5 Ă˜)

Îźnf = viscosity of nanofluid(Wm/k) Îźbf = viscosity of base fluid(Wm/k) 12. Nusselt Number of Nanofluid

Nunf = 0.4328 ( 1.0 + 11.285Ă˜0.754 Ped0.218) Renf0.333Prnf0.4 [18] Nunf = Nusselt number Ped =peclet number Renf =Reynold’s number of nanofluid Prnf =prandtl number of nanofluid The following procedure [16] of a solar water heating system has been used to done a theorectical calculation of a system for water and CuO nanofluid as a working fluid. And the calculations were done at a optimum working environment with traditional solar heating system.

Fig 3 comparison of solar intensity and time Heat energy of storage tank changes were made with corresponding time changes were briefly drawn in fig 4, the comparison of heat energy storage of water and nanofluid has greatly achieved by the percentage improvement of 11.6% for nanofluid usage in the system. And the graph explains the heat energy was gradually increased with time but at the certain period it decreased.

4.5 4 3.5 3 2.5 2 1.5 1 0.5 0

Heat energy

{

11

qt(nano) 10 11 12 13 14 15 16 (MJ/m^2) Time(Hr) qt(water) (MJ/m^2) Fig 4 comparison between heat energy of storage tank with time The comparisons of the output temperature with time were discussed in the fig 5 and the figure explains the increase of output temperature with increases of time from 10 to 16 hrs.

VI. RESULTS AND DISCUSSION The comparative analysis of the solar water heating system by use of water and nanofluid as working fluids were described in this chapter. The comparisons made for solar intensity and time were briefly explained in fig 3, and were the time increases gradually corresponding to the solar intensity were increased till the peak hour of 12:00 – 13:00 pm. And by increasing the time further the

796 | P a g e

100 90 80 70 60 50 40 30 20 10 0

Temp (°C)

Temp (oC )

S. Bhagavathi Shankar, Dr. A. Manivannan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.793-798

10 11 12 13 14 15 16

90 80 70 60 50 40 30 20 10 0

Tfi (oC) Tfo (oC)

Time(Hr)

9

solar intensity

The experimentally made comparison of solar intensity of the system with corresponding changes in time were explained in fig 6, it shows that the solar intensity were increased with time were at 12 to 13hrs and it gradually decreased with time till 16hrs.

1000 900 800 700 600 500 400 300 200 100 0 9

10

11

12 13 14 Time(Hr)

15

16

Solar radiation (w/m2) Fig 6 comparison of solar intensity with time Experimentally conducted results for the comparison of collector temperature were explained in fig 7. Due to the increase in time the collector temperature was increased because of it’s over circulation of hot fluid to the system each time of its cycle.

Time(Hr) Fig 7 comparison of collector temperature with time The comparison of tank temperature at three portions, like top, bottom and middle of tank were experimentally obtained by the using of temperature sensor at each portion of the tank. And the results were compared with the corresponding time. So it gradually increases with increase in time.

80 70

Tank temp (oC )

Fig 5 comparison between output temperature and time

10 11 12 13 14 15 16

60 50 40

(bottom)

30

(mid)

20

(top)

10 0 9

10 11 12 13 14 15 16 Time (Hr) Fig 8 comparison of tank temperature and time The experimentally conducted results of the solar water heating system by the usage of water and nanofluid as a working fluid were obtained. And the %improve of the nanofluid over the water in convective heat transfer coefficient were 45.63%, and the collector efficiency were 16.66% and the net useful energy were improved by 15.62% these data’s were explained in table 2.

797 | P a g e

S. Bhagavathi Shankar, Dr. A. Manivannan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.793-798 TABLE 2 Comparison of water and nanofluids are using working fluid in solar water heater Working Fluid Water Nanofluids(Cuo) Convective heat transfer coefficient Collector efficiency Heat removal factor Net rate of useful heat energy per m2(qu) Heat exchanger factor

213.77 W/m2k

393.22W/m2k

0.60

0.72

0.54

0.64

392.6W/m°C

465.31 W/m°C

0.72

0.83

[6]

[7]

[8]

[9]

VII. CONCLUSION Theoretically by using water as a working fluid in the flat collector type thermosyphon water heater maximum temperature reached was 76.83°C and by using copper oxide as a working fluid maximum temperature reached was 86.21°C at 0.025% volume fraction of the nanofluids. Theoretical results show that the 10.88% of an improved efficiency is observed at 0 .025% volume fractions of the nanofluids. And experimental results by using water as a working fluid in the flat plate collector type thermosyphon solar water heater system was found to be maximum temperature of 68.2°C. The experimental results show that the 44% of solar water heater efficiency is observed by using water as working fluids.

By thus we concluded, that the flat plate collector thermosyphon solar water heating system were obtained a improved efficiency by using CuO nanofluid as a working medium than the water as a working fluid.

[10]

[11] [12] [13]

[14]

[15]

REFERENCES [1]

[2]

[3]

[4] [5]

A Thesis Presented to the Faculty of the Graduate School University of Missouri In Partial(2009) ,Forced Convection in Nanofluids Over a Flat Plate.

Abdunnabi .M.J.R , and D.L. Loveday (2011), Optimization of Thermosyphon Solar Water Heaters Using TRNSYS. Part1: Improved Model development and Validation, International Conference on Future Environment and Energy.

Afif hasan(1997), Thermosyphon solar water heaters: effect of storage tank volume and configuration on efficiency, energy coneers. mgmr vol. 38. no. 9. pp. 847-854, 1997.

Ahmad Houri(2006), Solar water heating in Lebanon: Current status and future prospects, Renewable Energy 31 (2006) 663–675 Alireza Hobbi, and Kamran Siddiqui,(2009) Optimal design of a forced circulation solar water

[16] [17]

[18]

heating system for a residential unit in cold climate using TRNSYS, Solar Energy 83 (2009) 700–714.

Amirhossein Zamzamian, Shahin Nasseri Oskouie, Ahmad Doosthoseini , Aliakbar Joneidi, and Mohammad Pazouki, (2008) a Materials and Energy Research Center (MERC), Karaj, Iran. Experimental investigation of forced convective heat transfer coefficient in nanofluids of Al2O3/EG and CuO/EG in a double pipe and plate heat exchangers under turbulent flow.

Benghanem(2011), Optimization of tilt angle for solar panel: Case study for Madinah, Saudi Arabia, Applied Energy 88 (2011) 1427.

Chang.H, Y. C. Wu , X. Q. Chen, and M. J. Kao, (2008)National Taipei University of Technology, Department of Mechanical Engineering, 10608 Taipei, Taiwan . Fabrication of Cu Based Nanofluid with Superior Dispersion.

Eiyad Abu-Nada, and Hakan F. Oztop,(2009) Effects of inclination angle on natural convection in enclosures filled with Cu–water nanofluid, International Journal of Heat and Fluid Flow 30 (2009) 669–678.

Eiyad Abu-Nada, and Hakan F. Oztop(2009), Effects of inclination angle on natural convection in enclosures filled, International Journal of Heat and Fluid Flow with Cu–water nanofluid, International Journal of Heat and Fluid Flow 30 (2009) 669–678.

Preparation And Estimation Of Nanofluid Properties (2005) – chapter 3, pg 12- 103.

Rai G.D (2009), ‘solar energy utilization’, khanna publishers.

Rsdul-jabbar n. khalifa,(1998) Forced versus natural circulation solar water heaters: a comparative performance study, renewable energy, vol. 14, nos.

1-4, pp. 77-82, 1998.

SARIT KUMAR DAS (2006) Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, India Heat Transfer in Nanofluids—A Review-Heat Transfer Engineering, 27(10):3–19, 2006 Copyright C Taylor and Francis Group, LLC, -STEPHEN U. S. CHOI , Energy Technology Division, Argonne National Laboratory, Argonne, Illinois, USA. Soo Too Y.C, G.L. Morrison, and M. Behnia, (2009) Performance of solar water heaters with narrow mantle heat exchangers, Solar Energy 83 (2009) 350–362.

Suresh.S, K.P. Venkitaraj, P. Selvakumar, and M. Chandrasekar,(2009) Effect of Al2O3–Cu/water hybrid nanofluid in heat transfer.

Suresh.S, K.P. Venkitaraj, P. Selvakumar, M. Chandrasekar .A comparison of thermal characteristics of Al2O3/water and CuO/water nanofluids in transition flow through a straight circular duct fitted with helical screw tape inserts.

Tiwari G.N (2011), Solar energy, Fundamentals, design modeling and applications.

798 | P a g e