# Exergy Analyses of Onion Drying by Convection: Influence of Dryer Parameters on Performance

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## Abstract

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## 1. Introduction

^{−1}, and temperature of 313 K. The results demonstrated that higher temperature, air flow rate, and eggplant samples’ lesser diameter increased energy consumption.

## 2. Methodology

^{−1}, respectively. Table 1 shows the variation of air flow rate at different conditions.

#### 2.1. Energy Balance

#### 2.2. Entropy Balance

#### 2.3. Exergy Balance

_{d}is the destroyed exergy and ε

_{q}is the exergy associated with heat losses in kJ/h. The destroyed exergy due to irreversibilities is calculated as

_{0}is the environment temperature, and S

_{gen}is the generated entropy in the process expressed in kJ/K.

_{0}and P

_{0}are the reference temperature and pressure considered as 298 K and 1 atm, respectively, T and P are the flow temperature and pressure.

_{da}is the specific heat of the drying air (kJ/kg K), ω is the specific humidity (kg water/kg dry air), ${\omega}_{0}$ is the reference humidity (0.009 kg water/kg dry air). The specific heat of the drying air is calculated as [12]

_{0}and P

_{0}are the temperature and pressure of environmental state taken as a reference, respectively. The temperature and pressure are equal to 298 K and 1 atm, respectively.

## 3. Results and Discussion

^{−1}, respectively. The exergy loss rate related to the onion drying increases with temperature and the velocity (Figure 1). The highest values of these rates are reached at velocity equal to 2 ms

^{−1}and temperature equal to 80 °C. The losses rate value is 218.89 kJh

^{−1}, representing 28.6% of the whole inlet exergy at the drying chamber. It is important to take into account that one of the thermodynamic inefficiencies of these systems is the exergy loss from the drying chamber to the environment. With the temperature and velocity increase, the input exergy to the drying chamber grows, and then, a large amount of the input exergy comes out without evaporating moisture contained in the onion. Additionally, exergy loss rate is diminished at lower drying air temperatures and velocities because the overall heat transfer coefficient decreases [5]. Corzo et al. [12], Azadbakht et al. [9] and Nazghelichi [18] obtained analogous observations.

^{−1}, respectively; demonstrating that the convective drying is a process moderately poor, considering the exergy efficiency.

^{−1}, respectively, the calculated exergy efficiency was 80.7%. Aghbashlo et al. [19] obtained values close to 87% and the values obtained for Khanali et al., 2013 varied between 65% and 74%, approximately. For a drying temperature equal to 70 °C, the exergy efficiency was about 73%, and these researchers found values about 67%.

^{−1}. The IP rate, under studied operative conditions, vary from 21–29.9% of the total input exergy. These values show that the exergy efficiency of onion drying process can be ameliorated. Aghbashlo et al. [14] founded IP rate values between 37.21% and 73.2% to fish oil microencapsulation process by spray drying. Beigi et al. [22] reported values between 27.3% and 59.21% of this parameter for the deep-bed drying of rough rice. Instead, its value increases when the temperature. However, the influence of the air velocity is not clear. Similar results were found by Kuzgunkaya and Hepbasli [23] by Icier, et al. [24]. Considering that the exergy is conserved only for reversible processes, the growth in exergy destruction moves away the process of reversibility, causing IP rate increase. The onion drying process, consequently, presents a potential for exergy efficiency growth. It is important to note that different efforts should be oriented to improve the exergy efficiency of the studied process. In this case, considering the studied ranges of the operation variables, onion drying could be carried out at a temperature equal to 50 °C and an air velocity equal to 2 m/s.

## 4. Conclusions

## Acknowledgments

## Author Contributions

## Conflicts of Interest

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Air Velocity (m/s) | Inlet Air Temperature (°C) | Air density (kg/m^{3}) | Mass Air Flow Rate (kg/h) | Volumetric Air Flow Rate (m^{3}/h) |
---|---|---|---|---|

0.5 | 50 | 1094 | 122.38 | 0.11 |

60 | 1061 | 73.99 | 0.07 | |

70 | 1030 | 52.99 | 0.05 | |

80 | 1001 | 41.25 | 0.04 | |

1 | 50 | 1094 | 245.06 | 0.22 |

60 | 1061 | 147.48 | 0.14 | |

70 | 1030 | 106.09 | 0.10 | |

80 | 1001 | 82.08 | 0.08 | |

2 | 50 | 1094 | 490.11 | 0.45 |

60 | 1061 | 294.96 | 0.28 | |

70 | 1030 | 212.18 | 0.21 | |

80 | 1001 | 164.16 | 0.16 |

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**MDPI and ACS Style**

Castro, M.; Román, C.; Echegaray, M.; Mazza, G.; Rodriguez, R. Exergy Analyses of Onion Drying by Convection: Influence of Dryer Parameters on Performance. *Entropy* **2018**, *20*, 310.
https://doi.org/10.3390/e20050310

**AMA Style**

Castro M, Román C, Echegaray M, Mazza G, Rodriguez R. Exergy Analyses of Onion Drying by Convection: Influence of Dryer Parameters on Performance. *Entropy*. 2018; 20(5):310.
https://doi.org/10.3390/e20050310

**Chicago/Turabian Style**

Castro, María, Celia Román, Marcelo Echegaray, Germán Mazza, and Rosa Rodriguez. 2018. "Exergy Analyses of Onion Drying by Convection: Influence of Dryer Parameters on Performance" *Entropy* 20, no. 5: 310.
https://doi.org/10.3390/e20050310