https://orcid.org/0000-0002-9395-3534
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ABSTRACT
This study focused on investigating the drying behaviors of nectarine slices under varying drying temperatures (Tdrying) through the utilization of energy and exergy analysis methodologies, alongside an exploration of the drying kinetics employing diverse mathematical models. The drying process was carried out using a closed-type heat pump drying (HPD) system. The findings revealed a reduction in drying time with an increase in temperature. Notably, the condenser, compressor, and drying cabinet exhibited their highest exergy efficiencies at a Tdrying of 45 °C, while the evaporator demonstrated its highest exergy efficiency at 35 °C. The highest exergy efficiencies were achieved at a Tdrying of 45 °C and calculated as 65.94%, 77.95% and 80.53% for the condenser, dryer and compressor, respectively. Among the considered models, Aghbashlo et al. demonstrated the most optimal fit for moisture ratio. The Deff values ranged from 5.476 × 10−10 to 1.095 × 10−9 m2/s within the Tdrying range of 35 to 45 °C. As the Tdrying elevated, the Deff also raised. Using an Arrhenius-type equation, the expression for the temperature dependence of Deff was established. The determined activation energy value for moisture diffusion was 56.50 kJ/mol.
Nomenclatures
| COP | = | Coefficient of Performance |
| = | Power consumption of compressor, kW | |
| = | heat delivered rate in condenser, kW | |
| = | Power consumption of fan, kW | |
| = | mass flow rate (air, kg/s) | |
| = | mass flow rate (refrigerant, kg/s) | |
| A | = | surface area (m2) |
| ρ | = | density of air (kgm−3) |
| υ | = | air speed (m/s) |
| Cpam | = | specific heat of moist air (kJ/kg−1K−1) |
| Cpa | = | specific heat of dry air (kJ/kg−1K−1) |
| Cpv | = | specific heat of water vapor air (kJ/kg−1K−1) |
| = | specific humidity of air (kJkg−1) | |
| P0 | = | athmosperic pressure (kPa) |
| T0 | = | dead state temperature (K) |
| H0 | = | dead state relative humidity (%) |
| TA | = | condenser outlet air temperature/dryer inlet air temperature (K) |
| TB | = | dryer outlet air temperature (K) |
| TC | = | evaporator inlet air temperature (K) |
| TD | = | evaporator outlet air temperature (K) |
| TE | = | condenser inlet air temperature (K) |
| hA | = | specific enthalpy (condenser air outlet, kJkg−1) |
| hB | = | specific enthalpy (dryer air outlet, kJkg−1) |
| hC | = | Specific enthalpy (evaporator air inlet, kJkg−1) |
| hD | = | Specific enthalpy (evaporator air outlet, kJkg−1) |
| hE | = | Specific enthalpy (internal condenser air inlet, kJkg−1) |
| Ƞ | = | efficiency |
| Deff | = | effective moisture diffusivity (m2/s) |
| L | = | half-thickness of samples (s) |
| Mt | = | moisture content |
| M0 | = | initial moisture content |
| Me | = | moisture content at equilibrium (kg water/kg dry matter) |
| RMSE | = | root mean square error |
| χ | = | reduced chi-square |
| R2 | = | coefficient of determination |
| t | = | Time (s) |
| MRexp,i | = | Experimental dimensionless moisture ratio |
| MRpre,i | = | Predicted dimensionless moisture ratios |
| N | = | Number of observations |
| Subscripts | = | |
| a | = | Air |
| r | = | Refrigerant |
| h | = | Enthalpy |
| comp | = | Compressor |
| f | = | Fan |
| hp | = | Heat pump |
| sys | = | System |
| HPD | = | Heat pump drying |
| total | = | Total |
| loss | = | loss |
| dry | = | dryer |
| in | = | Inlet |
| out | = | outlet |
| cd | = | condenser |
| ev | = | evaporator |
Disclosure statement
No potential conflict of interest was reported by the author(s).
Additional information
Notes on contributors
Cüneyt Tunçkal
Cüneyt Tunçkal is an Associate Professor at Yalova University, Yalova Vocational School, Electric and Energy Department. He is mainly engaged in energy and exergy analysis, heat pump drying systems, air conditioning and refrigeration systems, ejector, drying Technologies.
Mehmet Direk
Mehmet Direk is an Associate Professor at Yalova University, Faculty of Engineering, Department of Energy Systems Engineering. His main areas of study are energy and exergy analysis, thermal systems, refrigeration systems, heat pump systems, ejectors and automotive air conditioning systems.
İ̇brahim Doymaz
Dr. İbrahim Doymaz is a Professor in the Department of Chemical Engineering, Yildiz Technical University, Istanbul, Turkey. He received his doctorate from Yildiz Technical University in 1998. His research area includes food preservation methods, drying technologies and coal technology. He has published 125 articles in Web of Science so far and his h-index is 41.