Results for the case study

In this section, effects of the drying air temperature and the mass flow rate of drying air on the system performance were discussed. Specific heats, enthalpies, and entropies of the broccoli florets were calculated from Eqs. (15.2), (15.10), and (15.11-15.12), respectively. The properties of the inlet and outlet air were calculated from the computer aided thermodynamic tables. The reference (dead state) temperature for exergy analyses was taken to be 23oC. Exergy analyses of single-layer drying process of broccoli florets in a heat pump conveyor dryer were performed by using the data obtained from the experiments (Table 15.2).

The variations of exergy efficiency and improvement potentials with drying air temperatures at various drying air velocities were illustrated in Figs. 15.2 and 15.3, respectively. As can be seen in Fig. 15.2, exergy efficiency of the drying chamber decreased as the drying air temperature increased at all velocities. When the air temperature was 45oC and velocity was 1.5 m/s, exergy efficiency of the system was determined to be 76.58%. It was obvious from Fig. 15.3 that the improvement potential rate of the drying chamber at 55oC and 0.5 m/s was found to be 13.86 kW as minimum value. Also, improvement potential value for 1.5 m/s was lower than the other velocities at 45oC .

Figures 15.4 and 15.5 show the exergy loss and destructions changing with drying air temperatures at various drying air velocities.

Table 15.2 Data from the experiments and calculations made.

Tda1

(oC)

(m/s)

(g/g)

(g/g)

(kJ/kg)

H2 (kJ/kg)

(kW/ oC)

(kW/ oC)

/k1 era

(kJ/kg oC)

45

0.5 1.0 1.5

0.0068 0.0075 0.0068

0.0073 0.0082 0.0073

337.278 339.087 336.771

336.041 338.364 335.634

6.914 6.919

6.915

6.919 6.926 6.919

3.845 3.845 3.845

2.096 2.096 2.096

50

0.5 1.0 1.5

0.0076 0.0082 0.0084

0.0078 0.0086 0.0089

343.599 346.071 345.673

339.455 343.248 343.724

6.919 6.923 6.926

6.922 6.927 6.930

3.845 3.845 3.845

2.101 2.101 2.101

55

0.5 1.0 1.5

0.0090 0.0094 0.0101

0.0097 0.0097 0.0109

351.191 351.731 355.480

348.642 348.533 353.985

6,929 6.931 6.936

6.935 6.935 6.943

3.845 3.845 3.845

2.106 2.106 2.106

Fig. 15.2 The variations of exergy efficiencies with drying air temperatures at different drying air velocities.

1 14

Drying air temperatures (°C)

Fig. 15.3 The variations of improvement potentials with drying air temperatures at different drying air velocities.

Fig. 15.3 The variations of improvement potentials with drying air temperatures at different drying air velocities.

45 50

Drying air temperatures (°C)

Fig. 15.4 Variations of exergy losses with drying air temperatures at different air velocities.

45 50

Drying air temperatures (°C)

Fig. 15.5 Variations of exergy destructions with drying air temperatures at different air velocities.

Was this article helpful?

0 0
Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

Get My Free Ebook


Post a comment