Utilization of Zinc-Ferrite/ Water Hybrid Nanofluids for enhancing thermal performance of a Flat Plate Solar Collector -An Analytical Study


 Thermodynamic performance analysis is carried out on a flat plate solar thermal collector utilizing single and hybrid nanofluids. As heat transfer fluids, Fe2O4/water, Zn-Fe2O4/water hybrid nanofluids, and water are used, and its performance are compared based on the energy and exergy transfer rate. The thermo-physical properties are evaluated by regression polynomial model for all the working fluids. Developed codes in MATLAB solve the collector's thermal model iteratively, energy and exergetic performance are evaluated. The system was then subjected to parametric investigation and optimization for variations in fluid flow rate, temperatures, and concentrations of nanoparticles. The findings show that utilizing Zn-Fe2O4/water hybrid nanofluids with a particle concentration of 0.5 percent enhanced the solar collector's thermal performance by 6.6% while using Fe2O4/water nanofluids raised the collector's thermal performance by 7.83% when compared to water as the working fluid. While hybrid nanofluids give a better thermal alternative than water and single nanofluids, they have also produced a 5.36% increase in exergetic efficiency and an enhancement of 8.24 percent when used with Fe2O4/water nanofluids.


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Solar energy is a free, widely available, and non-polluting fastest developing renewable 27 energy source that may be utilized for power generation as well as heating applications like space

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The FPSC is a solar collector consist an absorber plate and it was covered by transparent 109 glass cover at top and thermal insulation at bottom for minimizing the heat losses. The riser tubes 110 integrated with the absorber plate to collect and transfer the heat to the working fluid. The solar 111 radiation penetrates over the transparent cover made up of glass and strike over the surface of the 112 absorber plate, which has an extremely higher rate of absorptivity. The absorber plate is designed 113 to collect the maximum amount of solar energy possible. By minimizing the stationary air 114 formulation between the glass cover and the heated absorber plate, decreases absorber plate heat 115 loss caused by the wind. It also aids in decreasing the collector's radiative heat losses by making 116 wave length of in the range of 3-100 μ released by the heated plate. The nano fluid running within 117 the risers absorbs a large amount of heat energy received by the hot absorber plate. Figure 1   118 represents astructure of the FPSC. The size and characteristics of the FPSC are listed in Table 2.
This section includes the equations that were utilized to describe the flat plate collector 120 (FPC). The system, nanofluids and fluid flow area are all detailed and modelled in the following 121 sections. The analytical work is carried out with an assumption that the system properties are not Where,Vw and L are the wind speed and collector length, respectively. The heat loss happens at 162 the bottom of the collector is directly proportional to the thermal conductivity (kb) of the insulation, 163 bottom heat loss coefficient (hb) and indirectly proportional to the thickness of insulation (tb).

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It is evaluated using the relation as follows (Mahian et al.2014): The energy loss from the edges of FPSC is given by Eq. (10).
Where FR stands for heat removal coefficient and may be computed using the following In the Eq.(13) (Kalogirou 2009), F' represents the collector efficiency factor. The following 178 formula can be used to compute the factor: In the above equation W indicates the tube spacing, D represents riser tube diameter at outer side, 181 hf indicates coefficient of heat transfer and Di denote, riser tube diameter at inner side respectively.

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The fin efficiency of the collector is evaluated using the relation as follows (Kalogirou 2009): Where, m=

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Exergy refers to the transformation of available energy into productive work or energy and so 199 specifies the compactness of the thermal system. Exergy efficiency is the maximum amount of 200 useful work that a system may generate, and it is defined as follows: . . ln .
(21) 208 Where, P is the pressure decrease in the system The exergy loss to the environment is calculated as follows (Mahian et al.2014).
The exergy lost due to friction that happens between flowing fluid and collector wall surfaces, 219 enhances the drop in pressure and pumping power. It is calculated as follows: The loss of exergy occurs due to temperature difference between the Sun (Ts) and the heated 222 absorber plate (Tp) is which is given by (Padilla et al.2014).
The exergy lost due to movement of the hot fluid inside the collecting tubes 1 .
, f dT E  can be 225 evaluated using the following formula: The entropy generation is evaluated by using the Eqs.(21)-(25) and Eq.(28).
The Bejan number indicates the fraction of entropy generation that happens in the system only due The dynamic viscosity of the nanofluid was estimated using the Brinkman model correlation, as 259 stated in Eq. (34) (Brinkman 1952), The correlations that were utilized to describe the thermal characteristics of hybrid nanofluids were 262 often taken from the earlier work, by (Mwesigye and Huan 2015) investigation pointed out. The following equations are applied for evaluating the properties of heating fluid is described below ( With respect to the findings, prior fundamental correlations described in this part is used to    The performance assessment of Zn-Fe2O4/water nanofluids was theoretically studied and

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The improvement in heat transfer coefficient of the system with the increment in rate of 320 flow rate is depicted in Fig.3. The heat transfer coefficient was weak for the water based FPSC 321 system. The FPSC system with Fe2O4/water nanofluid shows that the better heat transfer ΔT/I. Among the exergy input values only around 3-5.5% is converted to usable energy, since the 393 rest is lost due to exergy losses and exergy destruction factors. As the sun's energy is collected by 394 the collector, the system's total exergy is depleted. It's because of the large thermal gradient among 395 the solar collector and the source; as the temperature variation decreases, the destruction inexergy 396 is minimized to a lesser extent. It's also been found that utilizing hybrid Zn-Fe2O4/water nanofluids reduces the force of losses in exergy of the FPSC by maximum of 2.84 percent. Fe2O4/water 398 nanofluids have also been shown to effectively reduce the rate of irreversibilities with in process.

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The increased thermal conductivity properties of nanofluids are the reason for this. However, when 400 it comes to exergy losses in the system, Zn-Fe2O4/water hybrid nanofluids are a superior Temperature parameter. It is also fascinating to note that the accumulation of entropy gradually 406 decreases in water for 0.5% Fe2O4 nanofluid as well as for 0.5% Zn-Fe2O4/water hybrid nanofluid 407 as the working fluids have increased the reduction temperature parameter (Ti -Ta )/It .The inability 408 of a system to convert available energy into useful tasks is shown by entropy generation. It is not 409 typically advised to generate entropy at a faster rate. The entropy generation rate for the 0.5 percent 410 Zn-Fe2O4/water hybrid nanofluid is 5.39 W/K, whereas it is 5.41 W/K for 0.5 percent Fe2O4/water 411 nanofluids and 5.43W/K for water, respectively, among the selected working fluids. The physical 412 significance of the Bejan number is shown in Eq (29). It is a non-dimensional number that 413 represents the proportion of entropy generated by thermal energy transfer to the overall entropy generated by thermal energy transfer plus irreversibility induced internally by pressure drop and 415 frictional losses happens at adiabatic conditions. A shift toward a greater Bejan number indicates 416 that the system's dynamic responsiveness has improved. The Bejan number falls when the 417 reduction temperature parameter is increased for a constant particle volume concentration.

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Because entropy generation due to ΔP is less than that provided by irreversibility, the decrease in 419 Bejan number is progressive rather than rapid.  The following points highlight the key conclusions in the results.
 At a nanoparticle concentration of 0.5%, Zn-Fe2O4/water hybrid nanofluid provides a 431 thermal enhancement of 6.6 % in the collector when compared to Fe2O4/water nanofluid.

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When compared to water, single nanofluids improve the collector's thermal performance 433 by 7.83 %.

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 While hybrid nanofluids give a superior thermal alternative than water and single 435 nanofluids, they also showed a8.24% increase in exergetic efficiency over Fe2O4/water 436 nanofluids.