# Analysis of Nanofluids Behavior in a PV-Thermal-Driven Organic Rankine Cycle with Cooling Capability

^{1}

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## Abstract

**:**

_{2}O

_{3}, CuO, Fe

_{3}O

_{4}and SiO

_{2}on the performance the hybrid system composed of PV Thermal, ORC and cooling coil. The quaternary refrigerant mixture used in the ORC cycle to enhance the ORC efficiency is an environmentally sound refrigerant mixture composed of R152a, R245fa, R125, and R1234fy. It was shown that the enhancement of the efficiency of the hybrid system in question is significantly dependent upon not only the solar radiation but also the nanofluids concentration and the type of nanofluid as well as the fluid temperature driving the ORC. A higher hybrid system efficiency has been overserved with nanofluid CuO. Moreover, it has been also shown that on the average, the hybrid system efficiency was higher 17% with nanofluid CuO compared to water as the heat transfer fluid. In addition, it was also observed that the higher cooling effect produced is significantly increased with the use of the nanofluid CuO compared to the other nanofluids under investigation and water as heat transfer fluid. The results observed in this paper on ORC efficiency and PV solar panel efficiency are comparable to what has been published in the literature.

## 1. Introduction

_{2}O

_{3}, CuO and water was used. The results of the study showed that the cooling fluid, which contains smaller particulate nanoparticles (CuO), show a thermal conductivity greater than the larger particles. Reference [28] developed two experimental equations to evaluate the effective thermal conductivity o nanomaterials and dynamic viscosity. In this study, the improvement in heat transfer by the dispersion of solid nanoparticles in the base fluid was calculated with different weights and temperatures ranging from 21 °C to 51 °C. The researchers used nanoparticles Cu, Al

_{2}O

_{3}and TiO

_{2}with cooling fluid (water and ethylene glycol). Al-Waeli et al. [27] initiated a numerical simulation of heat transfer in a wavy channel and the improvement obtained using nanofluids made of nano-copper and water. The results showed that the use of nano cooling fluid with wavy walls enhanced the heat exchange between the wall and the flow significantly. The results of the study showed that the addition of nanoparticles by 10% to water resulted in improved heat exchange by 25%. Furthermore, A.H.A. Al-Waeli et al. [27] concluded that among these seven mechanisms, thermophoresis and Brownian diffusion can be considered the most important. The study also showed clearly that nanoparticles move homogeneously with fluid in the presence of turbulent eddies, so their negative impact on the density of disturbance is doubtful.

## 2. Mathematical Model

#### 2.1. PV Thermal Model

_{abs}: overall absorption coefficient, G: total Solar radiation incident on the PV module and S

_{p}: total area of the PV module.

- T
_{C}: PV cell temperature - mC
_{p}_{_module}: thermal capacity of the PV module - t: time
- Q
_{in}: energy received due to solar irradiation - Q
_{conv}: energy loss due to convection - Q
_{elect}: electrical power generated

#### 2.2. PV Model

- I
_{p}: output current of the PV module - I
_{L}: light generated current per module - Io: reverse saturation current per module
- V: terminal voltage per module
- R
_{s}: diode series resistance per module - R
_{sh}: diode shunt resistance per module - q: electric charge
- k: Boltzmann constant
- A: diode ideality factor for the module.

#### 2.3. ORC Model

- h
_{1}: enthalpy at the outlet of the waste heat boiler (kj/Kg) - h
_{2}: enthalpy at the exit of the vapor turbine (kj/Kg) - h
_{3}: enthalpy at the condenser outlet (kj/kg) - h
_{4}: enthalpy at ORC pump outlet (kj/kg) - h
_{5}: enthalpy at inlet of cooling/freezing coil (kj/kg) - h
_{6}: enthalpy at outlet of cooling/freezing coil (kj/kg) - h
_{7}: enthalpy at the outlet of regenerator (kj/Kg) - m
_{ref}: refrigerant mass flow rate (kg/s)

- ${W}_{ORC}$: power produced by ORC (KW)
- $p\left(t\right)$: PV solar output (kW) defined by Equation (4)
- $Qcc$: cooling coil thermal capacity (kw) and defined by Equation (9)
- ${W}_{{P}_{ORC}}$: pump power consumption defined by Equation (8)
- ${Q}_{in}$: solar radiation (kw) and defined by Equation (1)

## 3. Nanofluid Heat Transfer Fluid

_{total}= α

_{particles}+ α

_{base fluid}

_{total}, can be calculated as follows [19,20]:

_{total}= α

_{base fluid}+ α

_{particles}(Φ)

- ρ
_{pf}: density of the nanoparticle.

## 4. Numerical Procedure

_{2}O

_{3}, CuO, Fe

_{3}O

_{4}and SiO

_{2}and water as the heat transfer fluid. The system equations were integrated into the finite-difference formulations to determine the behavior of the process shown in Figure 1. Iterations were performed using MATLAB iteration techniques until a converged solution was reached with less than 0.05. With the known values of the solar radiation, the mass flow rate of the nanofluid circulating in the thin tubes welded to the PV solar collector was determined. Then, the thermophysical properties and the heat transfer characteristics of the base fluid, water, and nanofluids at different concentrations were determined. Then, the parameters describing the behavior of PV-Thermal solar panels, ORC and the cooling coil were determined at different conditions. Finally, the hybrid system efficiencies were calculated.

## 5. Discussion and Analysis

_{2}O

_{3}, CuO, Fe

_{3}O

_{4}and SiO

_{2}at different concentrations and water as base heat transfer fluid. Table S1 presents the thermophysical properties of nanofluids used in this study. In the following sections, the predicted results are presented under different inlet conditions, such as solar insolation, heat transfer fluid flow rates from the PV-Thermal, heat transfer fluid temperatures and various nanofluids at different volumetric concentrations. In the numerical simulation, 100 PV solar panels were assumed with 300 watts per each PV solar panel. Solar radiations were taken as 500, 750, 1000 and finally, 1200 w/m

^{2}and heat transfer fluid temperature varied from 176 °F to 212 °F. As reported in Sami and Marin [7], calculations using Equations (1)–(4) yielded the efficiency of the PV solar panels used in this study varies between 19% and 23% depending on the solar radiation that varies between 500 w/m

^{2}to 1200 w/m

^{2}. These values will be taken and considered as base values for comparison between the hybrid system efficiency of the PV-Thermal and ORC system and that of the PV solar panels. The heat transfer fluid flow rate circulating in the loop, driving the waste heat boiler of the ORC between 8.89 GPM (4208 lb/hr) to 22.6 GPM (10550 lb/hr) at temperatures varied between 176 °F to 212 °F. For comparison purposes, the pressure in the refrigerant mixture cycle of the ORC was kept constant between the waste heat boiler and the condenser at 133 psi and 55 psi, respectively. The boiling temperature of the refrigerant mixture was at –28 °F. The refrigerant mixture exits the waste heat boiler to the vapor turbine at vapor saturation conditions. Appropriate heat exchanger and vapor turbine efficiency values were used for the ORC cycle calculations as well as the cooling capacity. The Carnot cycle efficiency of the ORC conditions was 27.38% and on average, the ORC efficiency was 8.3% using the environmentally sound quaternary refrigerant mixture composed of R152a, R245fa, R125, and R1234fy. In the following sections, the impact of the solar radiations on the Hybrid system performance, and cooling/freezing effect produced as defined by Equation (9) and the efficiency of the hybrid system composed of the PV solar panel, PV-Thermal and the ORC, as calculated by Equation (11) are analyzed and discussed. The aim of this study was to illustrate the role of nanofluids in the enhancement of the Hybrid system efficiency and the cooling effect produced over that of the PV solar panels and ORC, respectively.

## 6. Conclusions

_{2}O

_{3}, CuO, Fe

_{3}O

_{4}and SiO

_{2}under different conditions: solar radiations, heat transfer fluid temperatures, nanofluid volumetric concentrations. In particular, the hybrid system efficiency and the cooling effect produced were the the main focuses of this study. It has been shown that the enhancement of the efficiency and the cooling effect produced by the hybrid system in question are significantly dependent on not only the solar radiation but also the nanofluids concentration and the type of nanofluid as well as the heat transfer fluid temperature driving the ORC. It was found that the higher the nanofluid concentrations, solar radiation, and heat transfer fluid temperature, the higher the cooling effect. It also has been demonstrated that the higher the heat transfer fluid and the higher the nanofluid concentrations, the higher the hybrid system efficiency and the higher the cooling effect produced.

## Supplementary Materials

## Funding

## Acknowledgments

## Conflicts of Interest

## Nomenclature

h_{1} | enthalpy at the outlet of the waste heat boiler (kj/Kg) |

h_{2} | enthalpy at the exit of the vapor turbine (kj/Kg) |

h_{3} | enthalpy at the condenser outlet (kj/kg) |

h_{4} | enthalpy at ORC pump outlet (kj/kg) |

h_{5} | enthalpy at inlet of cooling/freezing coil (kj/kg) |

h_{6} | enthalpy at outlet of cooling/freezing coil (kj/kg) |

h_{7} | enthalpy at the outlet of regenerator (kj/Kg) |

m_{ref} | refrigerant mass flow rate (kg/s) |

α_{abs} | Overall absorption coefficient |

G | Total Solar radiation incident on the PV module |

S_{p} | Total area of the PV module |

${W}_{ORC}$ | power produced by ORC (KW) |

$p\left(t\right)$ | PV solar output (kW) defined by Equation (4) |

$Qcc$ | cooling coil thermal capacity (kw) and defined by Equation (9) |

${W}_{{P}_{ORC}}$ | pump power consumption (9) |

${Q}_{in}$ | solar radiation (kw) and defined by Equation (1) |

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**Figure 3.**Hybrid system efficiency for Nanofluid SiO

_{2}at different temperatures and 20% volumetric concentration.

**Figure 4.**Hybrid system efficiency for Nanofluid Fe

_{3}O

_{4}at different temperatures and 20% volumetric concentration.

**Figure 5.**Hybrid system efficiency for Nanofluid CuO at different temperatures and 20% volumetric concentration.

**Figure 6.**Hybrid system efficiency for Nanofluid Al

_{2}O

_{3}at different temperatures and 20% volumetric concentration.

**Figure 7.**Hybrid system efficiency for Nanofluid SiO

_{2}at different temperatures and 10% volumetric concentration.

**Figure 8.**Hybrid system efficiency for Nanofluid Fe

_{3}O

_{4}different temperatures and 10% volumetric concentration.

**Figure 9.**Hybrid system efficiency for Nanofluid CuO different temperatures and 10% volumetric concentration.

**Figure 10.**Hybrid system efficiency for Nanofluid Al

_{2}O

_{3}different temperatures and 10% volumetric concentration.

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**MDPI and ACS Style**

Sami, S.
Analysis of Nanofluids Behavior in a PV-Thermal-Driven Organic Rankine Cycle with Cooling Capability. *Appl. Syst. Innov.* **2020**, *3*, 12.
https://doi.org/10.3390/asi3010012

**AMA Style**

Sami S.
Analysis of Nanofluids Behavior in a PV-Thermal-Driven Organic Rankine Cycle with Cooling Capability. *Applied System Innovation*. 2020; 3(1):12.
https://doi.org/10.3390/asi3010012

**Chicago/Turabian Style**

Sami, Samuel.
2020. "Analysis of Nanofluids Behavior in a PV-Thermal-Driven Organic Rankine Cycle with Cooling Capability" *Applied System Innovation* 3, no. 1: 12.
https://doi.org/10.3390/asi3010012