ABSTRACT
In this study, an air source heat pump drying system with an external condenser circuit connected in series was developed. The system was designed to enable the external condenser to be activated serially with the internal one via the solenoid valves controlled by the digital thermostat when the drying temperature of the cabinet reaches the desired level. Temperature control of the drying chamber was achieved by activating the external condenser along with the internal condenser. Exergy analysis was conducted for the process of drying banana slices via a closed-loop air source heat pump dryer (HPD) at various drying temperatures. Exergy efficiencies and losses for the HPD system were calculated. As a result, the exergy efficiency of the dryer was calculated to be between 75.93% and 80.95%, while the exergy efficiencies of the system and heat pump were found to range from 7 to 13.07%. Moreover, the expansion valve was found to have the highest exergy efficiency with 93.32%. The highest exergy losses were also found in the compressor and condenser with 0.557 kW and 0.366 kW, respectively.
KEYWORDS:
Disclosure statement
No potential conflict of interest was reported by the author(s).
Nomenclature
Cpspecific heat, J/kgK
exspecific exergy rate, J/kg
Exexergy rate, W
hspecific enthalpy, J/kg
Mmoisture
Meequilibrium moisture content, g.water/g.dry matter
M0initial moisture content, g.water/g.dry matter
MRmoisture ratio
Mtmoisture content at any time, g.water/g.dry matter
mass flow rate, kg/s
sspecific entropy, J/kgK
Ttemperature, K
Ppressure (bar)
heat transfer rate, W
Ẇpower consumption, W
wmoisture content, g.water/g.dry air
Llatent heat, J/kg
Xmass fraction
HPDHeat pump dryer
PIDProportional integral derivative controller
RGas constant
Greek symbols
ηefficiency
φrelative humidity, %
Subscripts
1compressor inlet of refrigerant
2compressor outlet of refrigerant (internal condenser inlet)
3internal condenser outlet of refrigerant
external condenser outlet of refrigerant
4evaporator inlet of refrigerant
aair
Adryer inlet of drying air (condenser outlet)
Bdryer outlet of drying air
Cevaporator inlet of drying air
cdcondenser
chcarbohydrate
compcompressor
Devaporator outlet of drying air
Destrate of exergy destruction, kW
Econdenser inlet of drying air
evevaporator
evapevaporation
exexergy
expexpansion valve
extexternal
ffat
fifiber
hlossheat loss
hpheat pump
ininlet
intinternal
mmean, mass (kg)
odead point
outoutlet
pproduct
prprotein
rrefrigerant
ssurface
syssystem
vvapor
wwater
oDead state
uUncertainty in the independent variables
UFUncertainty
zFunction
FIndependent variables