# Performance Investigation of Solar ORC Using Different Nanofluids

^{1}

^{2}

^{3}

^{4}

^{*}

## Abstract

**:**

_{2}O

_{3}/oil, CuO/oil, and SiO

_{2}/oil. A numerical model is validated using experimental data. The ORC analysis is done for a constant evaporator pressure of 2.5 MPa, and condenser temperature of 38 °C. Methanol is employed as the ORC’s working fluid and a non-regenerative, ideal ORC system with different turbine inlet temperatures is considered. Furthermore, a fixed solar heat transfer fluid flow rate of 60 mL/s and dish diameter of 1.9 m is investigated. Results show that, compared to pure oil, the thermal efficiency of the cavity receivers increases slightly, and the pressure drop increases with the application of nanofluids. Furthermore, results show that the cubical cavity receiver, using oil/Al

_{2}O

_{3}nanofluid, is the most efficient choice for application as the investigated solar ORC’s heat source.

## 1. Introduction

_{2}O

_{3}/water, TiO

_{2}/water and SiO

_{2}/water). Their results showed that the Cu/water nanofluid had the lowest entropy generation rate and the highest outlet temperature. Mahian et al. [13] reviewed the application of nanofluids in various types of solar systems including solar collectors. Loni et al. [14] considered a dish concentrator using different nanofluids (Cu/oil, Al

_{2}O

_{3}/oil, TiO

_{2}/oil and SiO

_{2}/oil). They also concluded that the Cu/oil nanofluid had the best thermal performance. Furthermore, Loni et al. [15] experimentally investigated a solar dish concentrator with multi-walled carbon nanotubes (MWCNT/oil) as the solar working fluid. It was found that the application of the nanofluid improved the thermal performance of the investigated dish system. Aramesh et al. [16] numerically investigated the effect of different nanofluids in a solar pond. They concluded that single-walled carbon nanotubes (SWCNT/water) showed the best performance among the investigated nanofluids.

_{2}O

_{3}/oil, CuO/oil, and SiO

_{2}/oil. The ORC cycle analysis is performed at the evaporator pressure of 2.5 MPa and condenser temperature of 38 °C; also, methanol is employed as the working fluid.

## 2. Materials and Methods

_{2}/oil and Al

_{2}O

_{3}/oil). A schematic of the investigated solar ORC system is presented in Figure 1. It should be mentioned that methanol is used as the ORC working fluid. The ORC system is investigated at constant evaporator pressure of 2.5 MPa and constant condenser temperature of 38 °C. In the current research, a numerical study is performed to determine the influence of nanofluids, and different nanofluid concentrations, on the ORC’s performance. The solar and ORC systems are presented in detail in the subsequent sections.

#### 2.1. Solar System

- Conduction and external convection heat losses

- Radiation heat loss

- Convection heat loss

_{2}O

_{3}, CuO, and SiO

_{2}(30–50 nm), were examined in the solar system. Table 3 shows the thermal properties of the nanoparticles at ambient temperature of 25 °C. It should be mentioned that the nanofluids were investigated based on volume fraction of 3%. Note that these nanoparticles have a low specific heat, high thermal conductivity and high density.

#### 2.2. Organic Rankine Cycle (ORC) System

#### 2.3. Validation with Experimental Results

_{2}O

_{3}) as selective coating for increasing absorption, and insulating the cavity receiver with mineral wool for reducing heat losses. The specifics of the materials used in the construction of the cavity receiver are given in Table 8.

## 3. Results

_{sun}is set to 1000 W/m

^{2}). Note that the surface temperature data for all of the investigated cavity receivers in Figure 7 compares well with the cavity heat flux data in Figure 8. The presented results in Figure 7 can be compared with the reported results by Refs. [17,18] for rectangular and cylindrical cavity receiver as solar dish absorber, respectively. In this research, variation of cavity surface temperature was presented and compared for three shapes of cavity receivers including hemispherical, cubical, and cylindrical cavities as a new achievement.

_{sun}is set to 1000 W/m

^{2}). Finally, Figure 11 shows the working fluid outlet temperature per element along the lengths of the cavity receivers. It should be mentioned that pure thermal oil was investigated as heat transfer fluid in this section of analyses. It is concluded that the outlet temperature of the hemispherical cavity receiver is the highest. According to Figure 11, the elemental outlet temperatures always increase along the cavity tube, since the heated working fluid from a previous element enters the next element. The outlet temperature increases more rapidly at the top wall elements of the cubical and cylindrical cavity receivers. This is because of higher solar heat flux at the cavity top wall as stated previously. Similar achievements are reported by other papers including [17,18] for a solar dish concentrator with rectangular and cylindrical cavity receiver. A comparison study was presented in this research for different thermal performance parameters such as solar heat flux, absorbed heat, and outlet temperature for three investigated cavity receivers including the hemispherical, cubical, and cylindrical cavities as a new result.

^{2}, respectively. Figure 12 shows variation of the total irreversibility versus turbine inlet temperature (TIT) for different shapes of the cavity receivers as the ORC heat source. Note that the total irreversibility rate of the cubical cavity receiver is the highest. This is because of a higher ORC mass flow rate required, for a specific inlet temperature, when using the cubical cavity receiver (Figure 13). The ORC mass flow rate for the cubical cavity receiver is the highest because it gains the most heat, based on Table 10. It is also concluded from Table 10 that the thermal efficiency and the pressure drop of the cubical cavity receiver is the highest. Furthermore, Figure 12 shows that the total irreversibility rate of the three investigated cavity receivers increases with increasing TIT of the ORC system. For all three cavity receivers, the mass flow rate of the investigated solar ORC decreases with increasing TIT of the ORC system. Similar results were concluded by Ref. [36] for a cubical cavity receiver as heat source of an ORC system. In the current study a performance comparison of different shapes of cavity receiver including hemispherical, cylindrical, and cubical cavity receivers is presented as heat source of the ORC system for selecting the best system for power generation.

_{2}O

_{3}, oil/CuO, and oil/SiO

_{2}nanofluids were considered as the solar working fluid with nanofluid concentration of 3% volume fraction. The solar system was investigated at solar radiation of 632.97 W/m

^{2}, working fluid inlet temperature of 40 °C, and working fluid flow rate of 60 mL/s. The ORC system was considered at constant turbine inlet temperature of 229 °C, and turbine inlet pressure (TIP) of 2.5 MPa. Table 11 displays the variation of the thermal parameters of the hemispherical cavity receiver using different nanofluids (oil/Al

_{2}O

_{3}, oil/CuO, and oil/SiO

_{2}) (also see Table 12 and Table 13 for the cubical and cylindrical receiver, respectively). Note that the thermal performance, in terms of cavity heat gain, thermal efficiency, and outlet temperature of the solar working fluid, has been increased slightly by the application of nanofluids. Also, note that the pressure drop of the solar system is increased by the application of nanofluids, when compared to pure oil. As seen, the cubical cavity receiver has the highest thermal performance using oil/Al

_{2}O

_{3}nanofluid as the solar working fluid. Similar studies were conducted (see Refs. [40,41]) where the influence of nanofluid application, as solar working fluid of a dish concentrator with a spiral cavity receiver, was investigated using energy and exergy analyses. Similar results were reported by Refs. [40,41]. In the current study, application of different oil-based nanofluids as heat source of an ORC system with different shapes of cavity receivers as the ORC heat source is presented as a new subject for study.

_{2}/oil nanofluid had the smallest effect on improving the ORC performance, while for the cubical cavity receiver, using Al

_{2}O

_{3}/oil, had the largest effect on improving the ORC performance. The cubical cavity receiver, using Al

_{2}O

_{3}/oil is, therefore, recommended as the heat source for the investigated solar ORC with the specific solar heat transfer fluid mass flow rate which was investigated in this work. The calculated results related to enhancement of the solar system performance can be compared with reported results by Ref. [42]. Bellos and Tzivanidis [42] investigated performance of a solar concentrator system using different nanofluids including 3% Al

_{2}O

_{3}/Oil, 3% TiO

_{2}/Oil, and 1.5% Al

_{2}O

_{3}/Oil and 1.5% TiO

_{2}/Oil. They reported improvement lower than 1% for the investigated solar system using different nanofluids. The cavity receivers have very small thermal losses and so there is not such a high thermal enhancement margin. Therefore, the use of nanofluids as a thermal enhancement method can enhance the performance up to 2%–3% maximum. The calculated results can be compared with the results reported in Ref. [43], where the effect of alumina/oil nanofluid, with different size and volume fractions, was investigated as solar working fluid for a solar ORC. In the current research, performance of the solar ORC system using different nanofluids including oil/Al

_{2}O

_{3}, oil/CuO, and oil/SiO

_{2}nanofluid of the solar working fluid is a new subject for assessment.

_{2}O

_{3}, oil/CuO, and oil/SiO

_{2}were considered as the solar working fluid. The solar system was investigated at working fluid inlet temperature of 40 °C, and solar radiation of 632.97 W/m

^{2}. The ORC system was considered at constant turbine inlet temperature of 229 °C, and turbine inlet pressure of 2.5 MPa. Methanol was used as the ORC working fluid. As shown in Figure 14, the thermal efficiency resulted higher improvement using application of Al

_{2}O

_{3}/oil nanofluid with higher nanofluid concentration. Generally, thermal performance improvement was calculated to be between 1% and 2%, as was reported in results by Ref. [42].

## 4. Conclusions

_{2}O

_{3}/oil, CuO/oil, and SiO

_{2}/oil were considered as the solar heat transfer fluid. Experimental results of the hemispherical cavity receiver operating with thermal oil were used to validate a numerical model. The solar ORC analysis was under superheated conditions, with a constant evaporator pressure of 2.5 MPa, and a condenser temperature of 38 °C. Methanol was considered as the ORC working fluid. A fixed solar heat transfer fluid mass flow rate of 60 mL/s and dish diameter of 1.9 m was investigated. Results showed that the working fluid outlet temperature, and thermal efficiency is the highest for the cubical cavity receiver. Also, the total irreversibility rate of the ORC, the ORC mass flow rate, and the ORC overall efficiency are the highest for the cubical cavity receiver. Furthermore, it was shown that the total irreversibility rate of the three cavity receivers investigated is increased by increasing the TIT of the ORC system. Results showed that the pressure drop through the cavity receivers was increased by the application of nanofluids. For all three cavity receivers, different thermal parameters were insignificantly increased with the application of nanofluids. Further improvements are recommended based on the optimization of variables, such as the mass flow rate, fixed in this work. The application of the SiO

_{2}/oil nanofluid had the lowest effect on improving the ORC performance. The cubical cavity receiver, using oil/Al

_{2}O

_{3}, was found to be the most efficient choice for application as the investigated solar ORC’s heat source. Finally, the thermal efficiency improved with about 2%–3% using the application of Al

_{2}O

_{3}/oil or CuO/oil nanofluid with higher nanofluid concentration as the solar ORC system’s working fluid.

## Author Contributions

## Funding

## Conflicts of Interest

## Nomenclature

a | receiver aperture side length, m |

A | surface area, m^{2} |

c_{2} | constant used in linear equation |

${c}_{p}$ | constant pressure specific heat, J/kgK |

d | receiver tube diameter, m |

D | diameter, m |

F_{n-j} | view factor between surface n and surface j |

${f}_{r}$ | friction factor |

g | gravitational constant, m/s^{2} |

Gr | Grashof number |

h | convection heat transfer coefficient, W/m^{2}K |

h_{rec} | cavity depth, m |

h^{*} | enthalpy, kJ/kg |

${I}_{sun}$ | solar irradiance, W/m^{2} |

$\dot{I}$ | irreversibility rate, W |

k | thermal conductivity, W/mK |

m_{2} | slope of linear equation |

$\dot{m}$ | system mass flow rate, mL/s |

N | number of tube sections |

N_{RC} | radiation-conduction number |

Nu | Nusselt number |

ORC | organic Rankine cycle |

P | pressure, Pa |

Pr | Prandtl number |

$\dot{Q}$ | heat transfer rate, W |

${\dot{Q}}_{net}$ | net heat transfer rate, W |

${\dot{Q}}^{*}$ | rate of available solar heat at receiver cavity, W |

${\dot{Q}}_{loss}$ | heat loss rate from the cavity receiver, W |

${\dot{Q}}_{solar}$ | rate of available solar heat at dish concentrator, W |

R | thermal resistance, K/W |

Ra | Raleigh number |

Re | Reynolds number |

t | thickness, m |

T | temperature, K |

T_{R} | temperature ratio |

TIT | turbine inlet temperature, K |

V | volumetric flow rate (mL/s) |

${V}_{wind}$ | wind speed, m/s |

$\dot{W}$ | power, W |

$\Delta T$ | temperature difference |

Greek symbols | |

ϕ | volume fraction |

$\stackrel{\xb4}{\beta}$ | volume expansion coefficient, 1/K |

β | nanolayer-thickness to nanoparticle-diameter ratio |

δ | error |

ϑ | kinematic viscosity of the fluid, m^{2}/s |

σ | Stefan–Boltzmann constant, W/m^{2}K^{4} |

$\epsilon $ | emissivity |

$\eta $ | efficiency |

$\theta $ | cavity inclination angle, ^{o} |

$\mu $ | dynamic viscosity, Pa.s |

$\rho $ | density, kg/m^{3} |

Subscripts | |

0 | initial inlet to receiver |

a | air |

amb | ambient |

ap | cavity aperture |

ave | average |

bf | base fluid |

bp | boiling point |

c | condenser |

con | condenser |

conc | concentrator |

cond | due to conduction |

conv | due to convection |

cr | critical |

D | diameter |

evp | evaporator |

Ex | experimental |

exch | heat exchanger |

f | fluid |

forced | due to forced convection |

H | heat source of the organic Rankine cycle |

in | inner |

inlet | at the inlet |

inner | on the inside of the tube |

ins | insulation |

L | cold heat sink of the organic Rankine cycle |

mt | turbine mechanical |

n | tube section number |

N | total number of tube elements |

natural | due to natural convection |

net | net |

nf | nanofluid |

np | nanoparticle |

Num | numerical |

oil | thermal oil |

out | at the outlet |

outer | outside of the cavity |

ORC | organic Rankine cycle |

P | pump |

rad | due to radiation |

rec | receiver |

refl | reflection |

s | surface |

st | turbine isentropic |

T | turbine |

th | thermal |

∞ | environment |

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**Figure 2.**Heat flux distribution per hemispherical cavity receiver coil (shown for dish diameter of 1.9 m and rim angle of 50.82°) [23].

**Figure 4.**(

**a**) A schematic of the ORC system, and (

**b**) The T-s diagram of the ORC system for methanol.

**Figure 6.**Deviation between experimental and numerical thermal efficiency results for the hemispherical cavity receiver.

**Figure 7.**Variation of the cavity surface temperature along the cavity tube length with pure thermal oil for weather conditions of 20 October 2016, Tehran, Iran.

**Figure 8.**Variation of heat flux rate along the cavity tube in the cavity receivers with pure thermal oil, when the solar beam irradiance is 1000 W/m

^{2}(for η

_{refl}= 100%).

**Figure 9.**Variation of the net heat transfer rate along the cavity receivers with pure thermal oil using weather conditions of 20 October 2016, Tehran, Iran.

**Figure 10.**Variation of available solar power along the cavity tubes with pure thermal oil, when the solar beam irradiance is 1000 W/m

^{2}(for η

_{refl}= 100%).

**Figure 11.**Variation of the outlet temperature along the cavity receiver tube length, with pure thermal oil using weather conditions of 20 October 2016, Tehran, Iran.

**Figure 12.**Variation of the total irreversibility rate versus turbine inlet temperature (TIT) with pure thermal oil using the weather conditions of 20 October 2016, Tehran, Iran.

**Figure 13.**Variation of the ORC mass flow rate versus turbine inlet temperature (TIT) with pure thermal oil using the weather conditions of 20 October 2016, Tehran, Iran.

**Figure 14.**Variation of overall efficiency improvement of the solar ORC system with variation of nanofluid concentration at T

_{inlet,oil}= 40 °C, TIT = 229 °C, and turbine inlet pressure (TIP) = 2.5 MPa.

**Table 1.**Receiver specifications [23].

Cubical | Cylindrical | Hemispherical | |
---|---|---|---|

Concentrator diameter (m) | 1.9 | 1.9 | 1.9 |

Focal length (m) | 1.351 | 1.351 | 1.351 |

Rim angle of paraboloid | 36.84° | 36.84° | 36.84° |

Collector aperture area (m^{2}) | 2.545 | 2.545 | 2.545 |

Receiver tube outer diameter (mm) | 10 | 10 | 10 |

Receiver tube inner diameter (mm) | 9 | 9 | 9 |

Number of tube coils | 12 | 14 | 10 |

Cavity inner diameter, D_{in} (m) | - | 0.140 | 0.140 |

Cavity outer diameter, D_{outer} (m) | - | 0.160 | 0.160 |

Outer aperture length of cubical cavity, a_{outer} (m) | 0.145 | - | - |

Inner aperture length of cubical cavity, a_{in} (m) | 0.125 | - | - |

Cavity depth, h_{rec} (m) | 0.125 | 0.14 | 0.07 |

Wind speed (m/s) | 2.1 |

Solar beam irradiance (W/m^{2}) | 632.97 |

Ambient temperature (°C) | 20.2 |

**Table 3.**Properties of nanoparticles [12].

Property | Al_{2}O_{3} | SiO_{2} | CuO |
---|---|---|---|

Specific heat (J/kg K) | 765 | 745 | 532 |

Thermal conductivity (W/m K) | 40 | 1.4 | 77 |

Density (kg/m^{3}) | 3970 | 2220 | 6320 |

Evaporating pressure | P_{evp} | 2.5 MPa |

Condensing temperature | T_{con} | 38 °C |

Thermal oil mass flow rate | ${\dot{m}}_{oil}$ | 60 mL/s |

Thermal oil inlet temperature | T_{inlet} | 40 °C |

Turbine mechanical efficiency | ${\eta}_{mt}$ | 100% |

Turbine isentropic efficiency | ${\eta}_{st}$ | 100% |

Pump efficiency | ${\eta}_{P}$ | 100% |

Heat exchanger efficiency | ${\eta}_{exch}$ | 100% |

**Table 5.**Thermo-physical properties of the working fluid [35].

Working Fluid | Type | Molecular Mass (kg/kmol) | T_{bp} (°C) | T_{cr} (°C) | P_{cr} (MPa) |
---|---|---|---|---|---|

Methanol | wet | 32.04 | 64.48 | 239.45 | 8.104 |

**Table 6.**Dimensions and properties of the experimental dish and cavity receiver [36].

Parameter | Value |
---|---|

Concentrator diameter | 1.9 m |

Focal distance | 1 m |

Rim angle | 50.82° |

Collector aperture area | 2.835 m^{2} |

Cavity tube outer diameter | 10 mm |

Cavity tube inner diameter | 9 mm |

Number of cavity coils | 10 |

Cavity inner diameter | 0.141 m |

Cavity outer diameter | 0.161 m |

Absorber emittance | 0.1 |

Mirror reflectance | 0.84 |

Depth of the cavity receiver | 0.07 m |

**Table 7.**Accuracies and ranges of the measuring instruments [36].

Instrument | Accuracy | Range | % Uncertainty |
---|---|---|---|

K-type thermocouples | ±0.55 °C | 0–800 °C | 0.25 |

Solar power meter | ±0.1 W/m^{2} | 0–2000 W/m^{2} | 0.25 |

Anemometer | ±0.2 m/s | 0.9 to 35.0 m/s | 10 |

Volume flow meter | ±0.05 mA | 0–20 mA | 1 |

**Table 8.**The materials used in the construction of the cavity receiver [36].

Used Instrument | Properties | Reason |
---|---|---|

Stage 1 | ||

Copper tube | Thermal conductivity of 386 W/m.K | High conductivity |

High melting point of 1000 °C | ||

Stage 2 | ||

Black chrome coating | Emittance of 0.1 | High absorptivity |

Absorbance of 0.84 | ||

Stability up to 400 °C | ||

Stage 3 | ||

Mineral wool insulation | Mineral wool thickness of 0.02 m | High thermal resistance |

Average insulation conductivity of 0.062 W/m·K |

Time (hh:mm) | T_{inlet} (°C) | T_{out} (°C) | I_{sun} (W/m^{2}) | T_{s, top} (°C) | T_{s, side} (°C) | T_{amb} (°C) | V_{wind} (m/s) | V (mL/s) | Experimental | Numerical | Deviation |
---|---|---|---|---|---|---|---|---|---|---|---|

η_{th} | η_{th} | ||||||||||

9:30 | 41.10 | 118.10 | 752.82 | 150.00 | 101.00 | 26.90 | 1.20 | 10.00 | 0.6259 | 0.6793 | 7.87% |

10:00 | 40.00 | 120.40 | 774.27 | 151.00 | 124.00 | 27.80 | 0.50 | 10.00 | 0.6357 | 0.6802 | 6.54% |

10:30 | 51.23 | 135.89 | 790.79 | 160.00 | 127.00 | 28.00 | 1.30 | 10.00 | 0.6600 | 0.6764 | 2.43% |

11:00 | 46.38 | 133.82 | 805.02 | 160.00 | 106.00 | 29.00 | 0.80 | 10.00 | 0.6707 | 0.6779 | 1.05% |

11:15 | 47.35 | 137.06 | 824.22 | 170.00 | 112.00 | 29.00 | 1.20 | 10.00 | 0.6708 | 0.6768 | 0.89% |

11:45 | 43.77 | 137.26 | 849.04 | 199.00 | 131.00 | 31.30 | 1.00 | 10.00 | 0.6807 | 0.6774 | 0.48% |

12:30 | 42.27 | 137.75 | 859.22 | 226.00 | 123.00 | 31.60 | 1.60 | 10.00 | 0.6801 | 0.6770 | 0.47% |

13:00 | 43.20 | 135.43 | 841.63 | 273.00 | 160.00 | 31.50 | 1.40 | 10.00 | 0.6773 | 0.6773 | 0.01% |

13:30 | 46.10 | 136.73 | 833.46 | 283.00 | 177.00 | 31.00 | 0.50 | 10.00 | 0.6738 | 0.6779 | 0.61% |

13:45 | 47.86 | 135.65 | 810.56 | 276.00 | 202.00 | 31.00 | 2.10 | 10.00 | 0.6714 | 0.6764 | 0.74% |

14:00 | 56.00 | 134.30 | 774.60 | 292.00 | 220.90 | 30.00 | 0.60 | 10.00 | 0.6267 | 0.6766 | 7.38% |

14:30 | 46.80 | 118.00 | 728.86 | 278.00 | 199.00 | 30.00 | 2.20 | 10.00 | 0.5992 | 0.6778 | 11.60% |

**Table 10.**The thermal parameters and pressure drop for the cavity receivers with pure thermal oil using the weather conditions of 20 October 2016, Tehran, Iran.

Hemispherical | Cubical | Cylindrical | |
---|---|---|---|

${\dot{Q}}_{\text{}net}$ (W) | 1095 | 1118 | 1044 |

η_{th,rec} | 0.68 | 0.69 | 0.65 |

T_{out,rec} (°C) | 50.77 | 51.00 | 50.42 |

T_{inlet,rec} (°C) | 40 | 40 | 40 |

$\dot{m}$ (mL/s) | 60 | 60 | 60 |

ΔP (Pa) | 1562 | 10633 | 7547 |

T_{s,ave} (°C) | 286.70 | 106.41 | 116.08 |

**Table 11.**Variation of the thermal parameters and pressure drop for hemispherical receiver using nanofluids with volume fraction of 3% for weather conditions of 20 October 2016, Tehran, Iran.

Oil | Oil/Al_{2}O_{3} | Oil/CuO | Oil/SiO_{2} | |
---|---|---|---|---|

${\dot{Q}}_{\text{}net}$ (W) | 1094.80 | 1100.11 | 1100.21 | 1098.75 |

η_{th, rec} | 0.680 | 0.683 | 0.683 | 0.683 |

T_{out,rec} (°C) | 50.77 | 50.01 | 49.25 | 50.50 |

ΔP (Pa) | 1561.62 | 1717.93 | 1864.63 | 1637.66 |

**Table 12.**Variation of the thermal parameters and pressure drop for cubical receiver using nanofluids with volume fraction of 3% for weather conditions of 20 October 2016, Tehran, Iran.

Oil | Oil/Al_{2}O_{3} | Oil/CuO | Oil/SiO_{2} | |
---|---|---|---|---|

${\dot{Q}}_{\text{}net}$ (W) | 1117.69 | 1139.16 | 1135.96 | 1130.57 |

η_{th, rec} | 0.694 | 0.708 | 0.706 | 0.702 |

T_{out,rec} (°C) | 51.00 | 44.72 | 49.56 | 50.81 |

ΔP (Pa) | 10632.68 | 25277.24 | 12695.80 | 11150.45 |

**Table 13.**Variation of the thermal parameters and pressure drop for cylindrical receiver using nanofluids with volume fraction of 3% for weather conditions of 20 October 2016, Tehran, Iran.

Oil | Oil/Al_{2}O_{3} | Oil/CuO | Oil/SiO_{2} | |
---|---|---|---|---|

${\dot{Q}}_{\text{}net}$ (W) | 1044.25 | 1061.53 | 1066.08 | 1058.35 |

η_{th, rec} | 0.649 | 0.659 | 0.662 | 0.657 |

T_{out,rec} (°C) | 50.42 | 50.29 | 49.11 | 49.69 |

ΔP (Pa) | 7546.83 | 7914.33 | 9011.18 | 8382.50 |

**Table 14.**Percentage improvement of the ORC net power output for the different shapes of the cavity receivers with volume fraction of 3% for weather conditions of 20 October 2016, Tehran, Iran.

Oil/Al_{2}O_{3} | Oil/CuO | Oil/SiO_{2} | |
---|---|---|---|

Hemispherical | 0.49% | 0.49% | 0.36% |

Cubical | 1.92% | 1.63% | 1.15% |

Cylindrical | 1.66% | 2.09% | 1.35% |

**Table 15.**Percentage improvement of the overall efficiency of the different cavity receivers with volume fraction of 3% for weather conditions of 20 October 2016, Tehran, Iran.

Oil/Al_{2}O_{3} | Oil/CuO | Oil/SiO_{2} | |
---|---|---|---|

Hemispherical | 0.49% | 0.49% | 0.36% |

Cubical | 1.92% | 1.63% | 1.15% |

Cylindrical | 1.66% | 2.09% | 1.35% |

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Loni, R.; Najafi, G.; Asli-Ardeh, E.A.; Ghobadian, B.; G. Le Roux, W.; Yusaf, T.
Performance Investigation of Solar ORC Using Different Nanofluids. *Appl. Sci.* **2019**, *9*, 3048.
https://doi.org/10.3390/app9153048

**AMA Style**

Loni R, Najafi G, Asli-Ardeh EA, Ghobadian B, G. Le Roux W, Yusaf T.
Performance Investigation of Solar ORC Using Different Nanofluids. *Applied Sciences*. 2019; 9(15):3048.
https://doi.org/10.3390/app9153048

**Chicago/Turabian Style**

Loni, Reyhaneh, Gholamhassan Najafi, Ezzatollah Askari Asli-Ardeh, Barat Ghobadian, Willem G. Le Roux, and Talal Yusaf.
2019. "Performance Investigation of Solar ORC Using Different Nanofluids" *Applied Sciences* 9, no. 15: 3048.
https://doi.org/10.3390/app9153048