The performance of a solar assisted heat pump dryer integrated with biomass furnace has been designed and evaluated for drying red chillies, and drying kinetics of red chillies were evaluated. The red chillies were dried from 22 kg with moisture content of 4.26 db to moisture content of 0.08 db which needed 11 hours, with the average drying chamber temperature, drying chamber relative humidity, and an air mass flow rate of 70.5°C, 10.1%, and 0.124 kg/s, respectively, while the open sun drying needed 62 hours. Compared to open sun drying, this dryer yielded 82% saving in drying time. The drying rate, the specific moisture extraction rate, and thermal efficiency of the dryer were estimated in average to be about 1.57 kg/h, 0.14 kg/kWh, and 9.03%, respectively. Three mathematical models, the Newton, Henderson-Pabis, and Page models, were fitted to the experimental data on red chillies dried by solar assisted heat pump dryer integrated with biomass furnace and open sun drying. The performance of these models was evaluated by comparing the coefficient of determination (
Indonesia is an agricultural country and produced 1,075,000 tons chilli in the year 2014, including red chilli [
Commonly, fresh red chillies are dried using open sun drying. It is very simple and has low investment and operating costs. However, the open sun drying has disadvantages such as depending on the weather conditions, low quality products, and slow drying rate or long drying times. Solar dryer is one of the alternatives to solve this problem.
Some researchers have developed and tested several types of solar dryer to reduce drying time and to maintain the quality of red chillies obtained by open sun drying. Fudholi et al. [
Solar assisted heat pump dryer integrated with biomass furnace can be used for drying red chillies to resolve the disadvantages of the current drying techniques. It has many advantages such as low relative humidity, and the drying processes can be conducted at cloudy, rainy days and the night time.
Indonesia is a tropical country and is located in the equator line. The country receives a daily average solar radiation about 4 kWh/m2 [
A solar assisted heat pump dryer integrated with biomass furnace was designed and installed at the Institute of Technology, Padang, West Sumatra, Indonesia. The drying system consists of solar collector array, heat pump, biomass furnace, drying chamber, and blower shown in Figures
Photograph of the solar assisted heat pump drying integrated with biomass furnace.
Schematic diagram of the solar assisted heat pump drying integrated with biomass furnace.
Dimensions of a double-pass solar collector with fin.
Dimensions of evaporator and condenser of heat pump.
Dimensions of biomass furnace.
Dimensions of drying chamber.
The experiments were carried out at Padang Institute of Technology, West Sumatra, Indonesia. Fresh red chilli was purchased at the local market in Padang. As much as 22 kg was placed into the drying chamber for the drying process shown in Figure
Photograph of red chilli in drying chamber.
Incoming and outgoing air temperature of solar collector, heat pump, biomass furnace, and drying chamber during the operation of the drying system were measured by using T type copper-constantan thermocouples with an accuracy of ±0.1°C and operating temperature range (−200°C to 400°C). The solar radiation was measured by an LI-200 pyranometer in ±0.1 Wm−2 accuracy and with maximum solar radiation of 2000 Wm−2, operating temperature range (−40°C to 400°C) and operating relative humidity range (0% to 100%). The air velocity was measured with 0–30 ms−1 range, an HT-383 anemometer, an accuracy of ±0.2 ms−1, and operation temperature range (−10°C to 45°C). The air temperature and the solar radiation were recorded by an AH4000 data logger with reading accuracy of ±0.1°C. The weight change of the red chilli was measured by 0–15 kg range, an TKB-0.15 weighing scale, an accuracy ±0.05 kg. Red chillies were weighed every 60 minutes and temperature was measured every 30 minutes.
The performance of solar assisted heat pump dryer integrated with biomass furnace is characterized by drying rate, specific moisture extraction rate, and dryer thermal efficiency. It is highly depending on the performance of each of the drying system components such as solar collector, heat pump, and biomass furnace.
The thermal efficiency of a solar collector is the ratio of useful heat gain by solar collector to the energy incident in the plane of the collector. It is calculated as [
The coefficient of performance of a heat pump is the ratio of useful heat or heat energy released by the refrigerant in the condenser to the electrical energy consumed by compressor. It is calculated as [
The electrical energy consumed by compressor was calculated using the following equation [
The thermal efficiency of a biomass furnace is the ratio of useful heat by biomass furnace to the heat energy generated by the combustion of the biomass fuel. It is calculated as [
The moisture content of the red chillies can be estimated by two methods such as wet and dry basis using the following equation [
The moisture content wet basis was calculated as
The moisture content dry basis was calculated as
The drying rate is the mass of water evaporated from the wet red chillies per unit time. It is calculated using the following equation [
The mass of the water evaporated (
The specific moisture extraction rate (SMER) is the ratio of the moisture evaporated from wet red chillies to the energy input to drying system. It is calculated as [
The thermal efficiency of dryer is the ratio of the energy used for moisture evaporation to the energy input to drying system. It is calculated as [
The heat energy used by the drying system for drying red chillies is a contribution from the drying system components such as solar collector, condenser, and biomass furnace. The percentage of heat energy contribution by the solar collector, condenser, and biomass furnace is calculated using (
The percentage of heat energy contribution by solar collector can be calculated as follows:
The experimental drying data obtained were fitted to the three best drying models given in Table
Mathematical models used for drying curves.
Model name | Model | References |
---|---|---|
Newton | MR = exp (−kt) | [ |
Henderson and Pabis | MR = |
[ |
Page | MR = exp (−k |
[ |
The regression analysis was performed using Statistica computer program. The correlation coefficient (
In the drying experiments of the red chillies the data was obtained by appropriate instrument; however, errors and uncertainties can arise because of the situations such as instrument selection, condition, environment, observation, reading, and test planning. Uncertainty was calculated using the following equation [
The variations of solar radiation and inlet and outlet air temperatures of the solar collector with time of the day are shown in Figure
Uncertainties of the parameters during drying experiment of red chilli.
Parameters | Unit | Uncertainty comment |
---|---|---|
|
||
Ambient air temperature | °C | ±0.17 |
Inlet air temperature of heat pump | °C | ±0.17 |
Outlet air temperature of heat pump | °C | ±0.17 |
Inlet air temperature of condenser | °C | ±0.17 |
Outlet air temperature of condenser | °C | ±0.17 |
Inlet air temperature of solar collector | °C | ±0.17 |
Outlet air temperature of solar collector | °C | ±0.17 |
Inlet air temperature of biomass furnace | °C | ±0.17 |
Outlet air temperature of biomass furnace | °C | ±0.17 |
Inlet air temperature of drying chamber | °C | ±0.17 |
Outlet air temperature of drying chamber | °C | ±0.17 |
Ambient air relative humidity | % | ±0.22 |
Inlet air relative humidity of heat pump | % | ±0.22 |
Outlet air relative humidity of heat pump | % | ±0.22 |
Inlet air relative humidity of drying chamber | % | ±0.22 |
Outlet air relative humidity of drying chamber | % | ±0.22 |
Solar radiation | W/m2 | ±0.14 |
Air velocity | m/s | ±0.24 |
Mass loss of samples | g | ±0.014 |
Mass loss of products | kg | ±0.11 |
Reading values of table ( |
— | ±0.1–0.2 |
Time measurement | min | ±0.1 |
|
||
|
||
Air mass flow rate | kg/s | ±0.26 |
Power consumption of compressor | kW | ±0.056 |
Power consumption of blower | kW | ±0.037 |
Thermal efficiency of solar collector | % | ±0.39 |
Coefficient of performance of heat pump | — | ±0.37 |
Thermal efficiency of biomass furnace | % | ±0.458 |
Moisture content | g water/g wet material | ±0.024 |
Drying rate | kg/h | ±0.18 |
Specific moisture extraction rate | kg/kWh | ±0.336 |
Thermal efficiency of dryer | % | ±0.350 |
Contribution heat energy by condenser | % | ±0.736 |
Contribution heat energy by solar collector | % | ±0.736 |
Contribution heat energy by biomass furnace | % | ±0.736 |
The variation of solar radiation and temperature with time of the day.
The variations of solar radiation and efficiency of solar collector with time of the day are shown in Figure
The variations of solar radiation and efficiency of solar collector with time of the day.
The variations of air temperatures and relative humidities inlet and outlet of the heat pump are shown in Figure
The variation of temperature and relative humidity with time of the day.
The variations of inlet and outlet air temperatures and COP of the heat pump are shown in Figure
The variation of temperature and COP of the heat pump with time of the day.
The variations of inlet and outlet air temperatures and efficiency of the biomass furnace are shown in Figure
The variation of temperature and efficiency of the biomass furnace with time of the day.
The variations of air temperature and ambient, inlet, and outlet relative humidity of the drying chamber with drying time are shown in Figure
The variation of temperature and relative humidity with drying time.
The variation of weight change of red chillies with drying time is shown in Figure
The variation of weight change of red chillies with drying time.
The variations of moisture content of dried red chilli in the solar assisted heat pump integrated with biomass furnace and open sun drying with drying time are shown in Figure
The variation of moisture content of dried red chilli in the solar assisted heat pump integrated with biomass furnace and open sun drying with drying time.
The variation of drying rate with drying time is shown in Figure
The variation of drying rate with drying time.
The variations of SMER and dryer thermal efficiency with drying time are shown in Figures
The variation of SMER with drying time.
The variation of dryer thermal efficiency with drying time.
The variation of the contribution of heat energy with drying time.
The variations of the contribution of heat energy with drying time are shown in Figure
The experimental results of drying of red chilli using a solar assisted heat pump integrated with biomass furnace were compared with open sun drying and several types of solar dryers in references are shown in Table
Performances of solar assisted heat pump integrated with biomass furnace compared with open sun drying and several types of solar dryers in references.
Number | Type of dryer | Drying capacity (kg) | Moisture content (% wb) | Drying time | Saving in time (%) | Thermal efficiency (%) | SMER (kg/kWh) | Refs. | |
---|---|---|---|---|---|---|---|---|---|
|
| ||||||||
1 | Open sun drying | — | 80 | 10 | 65 h | — | — | — |
[ |
Solar drying | 40 | 80 | 10 | 33 h | 49 | 28 | 0.19 | ||
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2 | Open sun drying | — | 74 | 9 | 5 days | — | — | — |
[ |
Solar greenhouse dryer | 500 | 74 | 9 | 3 days | 40 | — | — | ||
|
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3 | Open sun drying | — | 76 | 9 | 105 h | — | — | — |
[ |
Solar tunnel dryer | 350 | 76 | 9 | 50 h | 52.38 | — | — | ||
|
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4 | Open sun drying | — | 90 | 10 | 93 h | — | — | — |
[ |
Double-pass solar dryer | 40 | 90 | 10 | 32 h | 65.59 | — | — | ||
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5 | Open sun drying | — | 75 | 15 | 5 days | — | — | — |
[ |
Solar greenhouse dryer | 300 | 75 | 15 | 3 days | 40 | — | — | ||
|
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6 | Open sun drying | — | 76.7 | 8.4 | 4 days | — | — | — |
[ |
Solar assisted biomass drying | 22 | 76.7 | 8.4 | 32.5 h | 66 | — | — | ||
|
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7 | Open sun drying | — | 4 db | 0.08 db | 64 h | — | — | — |
[ |
Solar assisted heat pump dryer | 15 | 4 db | 0.05 db | 32 h | 50 | — | — | ||
|
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8 | Open sun drying | 7.5 | 4.26 db | 0.08 db | 62 h | — | — | — | Present study |
Solar assisted heat pump dryer integrated with biomass furnace | 22 | 4.26 db | 0.08 db | 11 h | 82 | 9.03 | 0.14 |
The variations of dimensionless moisture content data of dried red chilli in a solar assisted heat pump integrated with biomass furnace and open sun drying with drying time are shown in Figure
The variation of dimensionless moisture content data of dried red chilli in a solar assisted heat pump integrated with biomass furnace and open sun drying with drying time.
The dimensionless moisture content data of dried red chilli in a solar assisted heat pump integrated with biomass furnace and open sun drying were fitted in three drying models such as the Newton model, Henderson-Pabis model, and the Page model. The regression constant, the values of the coefficient of determination (
Statistical results mathematical modelling of drying curves.
Model | Method of drying | Model coefficients and constants |
|
MBE | RMSE |
---|---|---|---|---|---|
Newton | Open sun drying |
|
0.7235 | 0.0376 | 0.1939 |
Dryer |
|
0.8687 | 0.0137 | 0.1172 | |
|
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Henderson and Pabis | Open sun drying |
|
0.7946 | 0.0662 | 0.2574 |
Dryer |
|
0.9093 | 0.0037 | 0.0609 | |
|
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Page | Open sun drying |
|
0.9410 | 0.0051 | 0.0713 |
Dryer |
|
|
|
|
The variations of dimensionless moisture content data of dried red chilli in a solar assisted heat pump integrated with biomass furnace and open sun drying with drying time fitted with the Page model are shown in Figure
The variation of dimensionless moisture content data of dried red chilli in a solar assisted heat pump integrated with biomass furnace and open sun drying and Page model with drying time.
The variation of drying rate with dimensionless moisture content of dried red chilli in a solar assisted heat pump integrated with biomass furnace is shown in Figure
The variation of drying rate with dimensionless moisture content of dried red chilli in a solar assisted heat pump integrated with biomass furnace.
The performance of a solar assisted heat pump dryer integrated with biomass furnace has been designed and evaluated for drying red chillies, and drying kinetics of red chillies were evaluated. The averages of the solar collector efficiency, COP of the heat pump, and the efficiency of biomass furnace were estimated to be about 35.1%, 3.84, and 30.7%, respectively. The red chillies were dried from 22 kg with moisture content of 4.26 db to moisture content of 0.08 db which needed 11 hours, with the average drying chamber temperature, drying chamber relative humidity, and an air mass flow rate of 70.5°C, 10.1%, and 0.124 kgs−1, respectively, while the open sun drying needed 62 hours. Compared to open sun drying, this dryer yielded a 82% saving in drying time. The drying rate was estimated in average to be about 1.57 kg/h, while the specific moisture extraction rate and thermal efficiency of the dryer were estimated in average to be about 0.14 kg/kWh and 9.03%, respectively. The contributions of heat energy by the collector, condenser, and biomass furnace were estimated in average to be about 14.74%, 47.39%, and 37.87%, respectively. The biomass fuel (coconut shell charcoal) was needed during drying of about 11 kg. Drying of red chilli occurred in falling rate period; constant drying rate period was not observed. The Page model fitted best with the experimental data compared with the Newton and Henderson-Pabis drying models. It resulted in the highest
Area of collector (m2)
Power factor
Drying constant
Mean bias error
Specific heat of air (Jkg−1C−1)
Line current (ampere)
Solar radiation (Wm−2)
Air mass flow rate (kg/s)
Biomass fuel consumption rate (kg/h)
Mass of water evaporation rate (kg/h)
Mass of wet red chillies (kg)
Energy incident in the plane of the solar collector (kW)
Line voltage (Volt)
Caloric value of biomass fuel (kcal/kg)
Electrical energy consumed by blower (kW)
Heat energy generated by the combustion of biomass fuel (kW)
Electrical energy consumed by compressor (kW)
Percentage of heat energy contribution (%)
Latent heat of vaporization of water (J/kg)
Mass of bone dry of the red chillies
Equilibrium moisture content on dry basis
Final moisture content on wet basis (%)
Initial moisture content on wet basis (%)
Initial moisture content on dry basis
Moisture content at any time on dry basis
Mass of water of the red chillies (kg)
Number of observations
Drying constant
Useful energy (kW)
Coefficient of determination
Root mean-square error
Temperature (°C).
Biomass furnace
Solar collector
Compressor
Condenser
Heat pump
Inlet
Outlet.
The author declared that this current paper has no competing interests.
The author would like to thank to Higher Education Directorate of Education and Cultural Ministry of Indonesia (DIKTI) for research funding through the Hibah Bersaing Research Grant scheme.