Chapter - 1
Introduction
- Introduction
- Drying Process
- Convective drying
- Drying periods
- Open Sun Drying
- Solar Drying
- Passive solar dryers
- Active solar dryers
- Thermal Energy Storage and Auxiliary Heating System
- Sensible heat storage (SHS) and latent heat storage (LHS)
- Solar Air Heater (SAH) or Collector
- Background and Primary Objective of This Study
- Structure of the Thesis
Smallholder farmers in the rural areas of the developing world (which produce about 80% of food products) practice open sun drying to dry food and agricultural products (Murthy, 2009). The process of solar drying is an efficient way to use solar energy in the drying process.
Chapter - 2
Literature Review
Review on Hybrid - Type Solar Dryers (HSD)
- HSD with thermal energy storage (TES)
- HSD with sensible heat storage (SHS)
- HSD with sensible heat storage and auxiliary heater
- HSD with auxiliary energy source and LHS
- Solar dryer with auxiliary heat source
- Solar assisted heat pump dryer
- Overall observations
The drying rate and efficiency increased with the increase in grain mass. The dryer performance was examined in solar, biomass, greenhouse and biomass heating modes.
Review on Drying Kinetics Studies of the Thin Layer Solar and Open Sun Drying Processes of Food and Agricultural Products
- Drying of vegetables and spices
- Drying of fruits
- Drying of herbs and medicinal plants
- Drying of fish and other products
- Overall observations
The drying process of white mulberry was developed in the period of falling rate, and Logarithmik and Verma et al. Effective moisture diffusivity increased with increasing drying air temperature and air mass flow rate. The best model to describe the drying process of Gelidium sesquipedale was the two-term model and the product was dried in the falling rate period.
The effective diffusion coefficient increased with increasing drying air temperature and mass flow rate. The drying process of the remaining studied fruits took place only in the period of the falling rate.
Energy and Exergy Analyses of the Solar Drying Process
- Review on energy and exergy analyses of the solar drying process
- Overall observations
The exergy efficiency showed decay behavior with increased inlet temperature in the drying chamber. The authors investigated the energy and exergy performances of the solar heater and the drying chamber. The exergy efficiency of the drying chamber on the 2nd day was more compared to the 1st day.
Energy and exergy analyzes are becoming a very important tool in thermodynamic analyzes of the drying system. In addition, the solar air heater plays an important role in the overall efficiency of the drying system.
Research Gaps and Objective
The structure and moisture content of the products greatly affect the energy consumption in the drying process. The use of the other phase change materials in the solar dryer needs to be investigated. Complete exergy analysis of the solar drying system integrated with the auxiliary heat sources and the thermal energy storage has not been reported in the literature.
The exergy analysis of the heat pump-assisted solar dryer and the mixed-mode type solar dryer has also not been reported in the literature. The best drying models representing the drying process of the Ghost pepper in the solar dryer and the solar dryer will be identified by applying non-linear curve fitting.
Chapter - 3
Design of the Solar Dryer with Thermal Energy Storage
Developed Solar Dryer
The energy requirement for removing the moisture from the materials is provided by the hot air. Therefore, the basic design calculations include the estimation of the energy and air flow requirements of the drying system. The drying system components are then sized based on energy and airflow requirements.
Estimation of Energy and Air Flow Requirements
- Drying of chilli
3.2, the dry-bulb air temperature increases, while the relative air humidity decreases. If π€π is the specific humidity of the air at the beginning of the drying process and π€π is the specific humidity of the air corresponding to the equilibrium state. The drying time is also affected by the size, shape and internal structure of the product.
However, an average value of the drying air temperature equal to 50 ο―C is assumed. The size of the other components of the drying system depends on the mass flow rate of the air.
Solar Air Heater
- Thermal Analysis of the Solar Air Heater
- Parametric study of the solar air heater
The higher the mass flow rate, the larger the size of the component. ππ1π = liquid temperature at the outlet of the first liquid passage, ππ = average temperature of the absorber plate,. ππ2 = average temperature of liquid in the second liquid passage, ππ = average temperature of the bottom plate, and.
The steady heat flux balances on various components of the air heater are discussed below. The outlet temperature of the double pass air heater is given by (Karim et al., 2014).
Sizing of the Energy Storage
The paraffin wax is stored in the shell side, and the air flows inside the tubes. During the charging process of the energy storage, the heat from the hot air is transferred through the wall of the tubes to the paraffin wax. The thermal storage was designed based on the method proposed by Shymasundar et al. 1992) which is useful for the preliminary design of the shell and tube latent heat storage.
The thermal food should supply air with an average temperature of 50 ΒΊC for 2 non-sunny hours of the day. The amount of paraffin wax required to supply air at this temperature is 38 kg.
Sizing of the Solar Air Heater
The first part of the right-hand side of the equation indicates the amount of heat needed to produce the warm air in t sunshine hours of the day. The second part represents the amount of heat stored in the storage unit to supply the warm air during the off - sunny hours. The average dry air temperature is 50 ΒΊC, although it changes with the change in solar radiation intensity during the day.
However, the collector was sized to supply the energy to heat the ambient air from 25 ΒΊC to 50 ΒΊC for 7 hours and also to supply the energy required to completely melt 38 kg of paraffin wax during 7 hours of solar operation of the dryer. . The total input of energy into the drying system (taking into account the 31.5% thermal efficiency of the solar air heater) is 342.85 MJ.
Sizing of the Drying Chamber
The design calculations in dimensioning the drying chamber include estimating the number of drying trays and the total size of the drying chamber. The number of trays can be obtained by knowing the total area of ββthe drying bed and the size of the drying trays. The area of ββthe drying bed can be estimated if the bulk density and thickness of the product to be dried and the porosity are known.
Height of drying chamber = (total height of loading part of the tray + height above the upper tray + height of the lower tray from the walls of the dryer). The distance of the lower and upper trays from the inner surface of the dryer is the same and is equal to 75 mm, then the height of the drying chamber is 0.4 m.
Summary
Chapter - 4
Fabrication and Detailed Instrumentation of the Solar Dryer
Working Principle of the Solar Dryer
- Fabrication of the solar air heater
- Fabrication of the drying chamber
- Fabrication of the shell and tube energy storage
The walls of the drying chamber are insulated with polyurethane foam with a thickness of 25 mm and then covered with thin GI sheet. One side of the box is used as the door to place the drying trays in the drying chamber. The instruments needed for the measurement of the operating parameters were connected to the drying system.
It is used to measure the intensity of solar radiation incident on the surface of the air heater plate. An oral meter was designed and manufactured to measure air flow.
Chapter - 5
Thin Layer Drying Kinetics Analysis of Ghost Chilli
Thin Layer Drying Kinetics
The detailed review of the thin-layer drying equations was carried out by Erbay and Icier, 2009 and Kucuk et al., 2014. The experimental method allows developing a thin-layer model of the drying process of a given product. The mass of the product is measured at regular intervals until the equilibrium moisture content is reached.
However, when the relative humidity of the drying air fluctuates, the MR is obtained by Eq. Where Deff is the effective moisture diffusivity, Ls is the length of the product thickness and t is the drying time.
4 2 eff
- Ghost Chilli (Capsicum Chinense Jacq.)
- Experimental Procedure
- Drying Analysis
- Summary
The change in moisture content of the chili sample with drying time is shown in Figure 5.9(a). Comparison of experimental and predicted MR with the Modified Page model for open sun drying. 5.9(b) Comparison of experimental and Page model predicted MR for open sun drying.
5.10 (b) and (c) show photographs of the same Ghost burner after open sun drying and solar dryer drying. The original color of the fresh harvested Ghost pepper was preserved in the sun-dried sample.
Chapter - 6
Energy and Exergy analyses of the Drying Process of Ghost Chilli and Sliced Ginger
- Experimental Procedure
- Energy Analysis
- Exergy Analysis of the Drying Chamber
- Drying of Ghost chilli
- Drying of sliced ginger
- Summary
The total mass of moisture (ππ£) evaporated from the products during the drying period (π‘π) was calculated as follows (Ayensu and Asiedu-bondzie, 1986). The change in pressure between the inlet and outlet of the drying chamber is negligible, and Eq. Therefore, the exergy inflow and outflow of the drying chamber can be expressed by Eq.
As a result, the exergy input and output from the drying chamber become almost the same. The exergy input and output, exergy losses, and exergy efficiency of the drying chamber are shown in Figs.
Chapter - 7
Performance Tests on the Solar Dryer with the Latent Heat Storage
- Introduction
- Experimental Procedure
- Energy Analysis
- Energy analysis of the energy storage
- Exergy Analysis
- Exergy analysis of the SAH
- Exergy analysis of the energy storage
- Results and Discussions
- Drying of Green Chilli
- Economic Analysis
- Summary
The exergy efficiency of the solar air heater increased with increasing solar radiation intensity. It was observed that the temperature of the air at the entrance to the storage varied with the intensity of the solar radiation, i.e. 7.13 (a) Photograph of freshly harvested green chilli (b) Photograph of chilli after solar drying (c) Photograph of chilli after sun drying.
The amount of product dried in the dryer per year is calculated as follows. The annual operating costs of the solar dryer are the operating costs of the fan.
Chapter - 8
Conclusions and Scope for the Future Work
Conclusions
- Thin layer drying kinetics analysis of Ghost chilli
- Energy and exergy analyses of the drying processes of the Ghost chilli and ginger
- Performance tests on the solar dryer with the latent heat storage
The thermal efficiency of the first solar air heater (SAH - 1) was found to be higher than that of the second solar air heater (SAH - 2). The overall exergetic efficiency of the drying process of the Ghost chili was higher than that of sliced ββginger. The exergy efficiency of the solar air heater increases as the solar radiation intensity increases.
A high energy and high exergy efficiency of the drying chamber is always desirable. Therefore, exergy analysis plays an important role in the thermodynamic analysis of the drying system.
Scope for Improvement of the Drying System and Future Study
- Recirculation of the exhaust air
- Improvement in the efficiency of the solar air heater
- Improvement in the drying chamber
- Quality analysis of the dried products
- Conversion of the dryer into mixed - mode - type
Chowdhury MMI, Bala BK and Haque MA (2011), Energy and exergy analysis of solar drying of jackfruit leather, Biosystem Engineering, Vol. Diamante LM and Munro PA (1993), Mathematical modeling of thin-layer solar drying of sweet potato slices, Solar Energy, Vol. Koua KB, Fassinou WF, Gbaha P and Toure S (2009), Mathematical modeling of thin layer solar drying of banana, mango and cassava, Energy, Vol.
Saidur R, Boroumandjazi G, Mekhlif S and Jameel M (2012), Exergy analysis of solar energy applications, Renewable and Sustainable Energy Reviews, Vol.16, pp.350β356. Sekyere CKK, Forson FK and Adam FW (2016), Experimental investigation of the drying characteristics of a mixed natural convection solar crop dryer with backup heater, Renewable Energy, Vol.
Appendix - 1
Sizing of Energy Storage
- Sizing of Energy Storage
- Design Method
- Determination of the LHS Shell and Tube Parameters
- MATLAB Programme
Calculation of πΉπ which is the area of ββsolid PCM formed at the inlet of the pipe at the end of the discharge period. Calculation of the non-dimensional time variable (ππ) It can be obtained by the following equation. The number of pipes can be estimated for a given length of pipe by the following equation.
The value of the non-dimensional time variable, which is equal to 4.52, is determined by applying Eq. Calculation of the melting fraction (Fo) of paraffin wax (% Melting fraction of paraffin wax, calculated by bi-section method).
