Comparison of solar dryer and solar-assisted heat pump dryer for cassava

Published Date
Solar Energy
15 October 2016, Vol.136:606–613, doi:10.1016/j.solener.2016.07.049

• Author 

• M. Yahya ^a,,
• Ahmad Fudholi ^b,,
• Hadyan Hafizh ^c
• Kamaruzzaman Sopian ^b

• aFakultas Teknologi Industri, Institut Teknologi Padang, Indonesia
• bSolar Energy Research Institute, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia
• cDepartment of Mechanical Engineering, City University College of Science and Technology, 46100 Petaling Jaya, Selangor, Malaysia

Received 26 October 2015. Revised 18 July 2016. Accepted 25 July 2016. Available online 29 July 2016. 

Highlights

• •
  A solar dryer (SD) and solar-assisted heat pump dryer (SAHPD) for cassava were investigated.
• •
  The drying rate of cassava using SAHPD is higher than SD.
• •
  Thermal and pick-up efficiencies were lower in SD compared to SAHPD.
• •
  The solar fraction was higher in SD compared to SAHPD.
• •
  The average COP of the heat pump was 3.38 from 3.23 to 3.47.

Abstract

The performance of a solar dryer (SD) and a solar-assisted heat pump dryer (SAHPD) for drying of cassava chips have been investigated. The SD and SAHPD decreased the mass of cassava from 30.8 kg to 17.4 kg within 13 and 9 h at average temperatures of 40 °C and 45 °C, respectively. The moisture content of cassava decreased from 61% (wet basis) to 10.5%, with a mass flow rate of 0.124 kg/s. The average thermal efficiencies were 25.6% and 30.9% for SD and SAHPD respectively. The average drying rate (DR) and specific moisture extraction rate (SMER) were 1.33 kg/h and 0.38 kg/kW h, respectively, for SD as well as 1.93 kg/h and 0.47 kg/kW h, respectively, for SAHPD. The pick-up efficiencies varied from 3.9% to 65.8% and 15.9% to 70.4% for SD and SAHPD, with average values of 39.3% and 43.6%, respectively. The average solar fractions were 66.7% for SD and 44.6% for SAHPD. The coefficient of performance of the heat pump ranged from 3.23 to 3.47, with an average of 3.38.

Keywords

Drying kinetic

Solar fraction

Pick-up efficiency

Thermal efficiency

Coefficient of performance

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Nomenclature

area of the collector (m²)

specific heat of air (J kg⁻¹ °C⁻¹)

COP

coefficient of performance

electrical energy consumed by the blower (kW)

electrical energy consumed by the compressor (kW)

E_evap

energy used for moisture evaporation (kW)

E_input

energy input to the drying system (kW)

thermal energy released by the condenser (kW)

energy incident in the plane of the solar collector (kW)

useful heat gain by the solar collector (kW)

latent heat of vaporization of water (kJ/kg)

G

solar radiation incident on the collector (W/m²)

I

current (A)

M_C

moisture content

M_f

final moisture content on wet basis (%)

M_i

initial moisture content on wet basis (%)

mass of the bone dry (kg)

initial mass of the product (kg)

mass of water (kg)

mass of water evaporated (kg)

air mass flow rate (kg/s)

mass flow rate of dry air (kg_dry air/s)

drying rate (kg/s)

T_{i, coll}

air temperatures at the inlet (°C)

T_{o, coll}

outlet of the solar collector (°C)

air temperatures at the inlet of the condenser (°C)

temperatures at the outlet of the condenser (°C)

T1

dry bulk ambient temperature or evaporator dry bulk inlet air temperature of heat pump (°C)

T2

wet bulk ambient temperature or evaporator wet bulk inlet air temperature of heat pump (°C)

T3

evaporator dry bulk outlet air temperature of heat pump (°C)

T4

evaporator wet bulk outlet air temperature of heat pump (°C)

T5

condenser dry bulk inlet air temperature of heat pump (°C)

T6

condenser wet bulk inlet air temperature of heat pump (°C)

T7

condenser dry bulk outlet air temperature of heat pump (°C)

T8

condenser wet bulk outlet air temperature of heat pump (°C)

T9

solar collector inlet air temperature (dry bulk) (°C)

T10

solar collector outlet air temperature (dry bulk) (°C)

T11

drying chamber dry bulk inlet air temperature (°C)

T12

drying chamber wet bulk inlet air temperature (°C)

T13

drying chamber dry bulk outlet air temperature (°C)

T14

drying chamber wet bulk outlet air temperature (°C)

t

drying time (s)

SF

solar fractions

SMER

specific moisture extraction rate

voltage (V)

adiabatic saturation humidity of air that enters the drying chamber (kg_water/kg_dryair)

absolute humidity of air that enters the drying chamber (kg_water/kg_dryair)

cos φ

power factor

pick-up efficiency

thermal efficiency

 Table 1

Table 1.

Fig. 1.

Fig. 2.

Fig. 3a.

Fig. 3b.

Fig. 4.

Fig. 5.

 Table 2

Table 2.

Fig. 6.

Fig. 7.

Fig. 8.

Fig. 9.

Fig. 10.

Fig. 11.

Fig. 12.

Fig. 13.

 Table 3

Table 3.

• ⁎ 
  Corresponding authors.

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