Based on preliminary investigations under controlled condition of drying experiments, a mixed-mode solar DRYER with FORCED CONVECTION using smooth and rough plate solar collector was constructed. This paper describes the development of DRYER considerations followed by the results of experiments to compare the performance of the smooth and the roughed plate collector. The thermal performance of solar collector was found to be poorer because of low convective heat transfer from the absorber plate to air. Artificial rib roughness on the underside of the absorber plate has been found to considerably enhance the heat transfer coefficient. The absorber plate of the DRYER attained a temperature of 69.2oC when it was studied under no-load conditions. The maximum air temperature in the DRYER, under this condition, was 64.1oC. The DRYER was loaded with 3 kg of grapes having an initial moisture content of 81.4%, and the final desired moisture content of 18.6% was achieved within 4 days while it was 8 days for open sun drying. This prototype DRYER was designed and constructed to have a maximum collector area of 1.03 m2. This solar DRYER been be used in experimental drying tests under various loading conditions.

Monitoring the effective parameters of drying crops is necessary to evaluate and determine system performance under real conditions. Hence, a monitoring system was constructed to determine the performance of a vegetation FORCED-CONVECTION solar DRYER. Digital temperature sensors were set up in the air inlet and outlet of the collector and the air outlet of the drying chamber. A program was written using visual Basic 6 software to register sensor data and make calculations. To evaluate the DRYER, experiments were carried out over eight hours between 10 am and 6 pm during the summer. Mint was used for drying in all experiments on 5Cm high trays of the DRYER chamber. The results showed that the radiation energy, the heat energy absorbed by the collector and the energy required for product evaporation had linear relationships with temperature. Radiation energy increased at first and decreased later during the drying time. The results showed that the average temperature in the collector air inlet, outlet and drying chamber air outlet were 38.1oC, 54.7oC and 45.5oC, respectively. The average maximum and minimum energy efficiency were 49% and 14.7%, respectively. The average radiation energy and required energy for product evaporation were 4572.4 and 2772.2 KJ, respectively. The drying curve was Mwb=1.827e-0.4857t with R2=0.945.

One of the most important applications of solar energy is its utilization in solar DRYERs to maintain agricultural products for long-term storage. These DRYERs work based on passing warm air through fresh materials by natural or FORCED CONVECTION. So, they have a direct dependence on the intensity of the sun’ s irradiance to their collector, which it disrupts the drying process in the absence of a thermal energy source in the hours when the sun is not available. In order to solve this problem, the phase change material (PCM) as thermal energy storage is used. The materials that have the capacity to absorb the thermal energy (charge phase) and, they release the absorbed energy (discharge phase) when the intensity of the solar radiation is low or during the night and cause the uniformity of the outlet temperature solar collector, and inside the drying chamber. As well as they provide the necessary thermal energy for hours when the sun is not available and increase the duration of use of the DRYER. In the present research, the experimental studies have been carried out through designing and construction of an indirect cabin type solar DRYER equipped with a heat pipe evacuated tube collector and using PCM material as energy storage in the expansion tank. In the present research, the experimental studies have been carried out through designing and construction of an indirect cabin type solar DRYER equipped with a heat pipe evacuated tube collector and use of PCM material as energy storage in the expansion tank. The effect of various parameters such as inlet and outlet temperatures of the collector, temperature, and humidity of the drying chamber and ambient, the intensity of the solar irradiance on the drying process is investigated, with and without PCM and at two different speed of FORCED CONVECTION through the drying chamber. The results show that the effectiveness of FORCED CONVECTION on the drying process is more than the effect of PCM.

To increase agricultural crops’ quality and to minimize losses in the final product and used energy during the drying process, major drying system parameters should be continuously controlled. Precise control of such parameters is attained by using automatic control systems. To optimize the overall DRYER efficiency in a FORCED convective solar DRYER, a controller was designed, constructed and evaluated. The DRYER fan speed was chosen to be the controlled variable. Based upon the mathematical relations and a monitoring of the air inlet temperature to the collector, the air outlet temperature from the collector and the air outlet temperature from the drying chamber, the DRYER efficiency was determined. Using the DRYER control program the current and the optimized DRYER efficiencies were calculated, compared and the fan speed changed accordingly to maintain the optimized efficiency. Experiments were carried out in three replications (in three days) with the results showing that the system was capable of controlling the fan speed to obtain the optimum efficiency. The DRYER equipped with the designed control system worked with its highest efficiency throughout the day. Statistical analysis showed that the control system highly improved the DRYER efficiency throughout its operation at a 1% probability level.

Introduction: Many vegetables such as mint are highly seasonal in nature. They are available in plenty at a particular period of time in specific regions that many times result in market glut. Due to perishable nature, huge quantity of vegetables is spoiled within a short period. The post-harvest loss in vegetables has been estimated to be about 30-40 % due to inadequate post-harvest handling, lack of infrastructure, processing, marketing and storage facilities. …

This paper presents a numerical investigation for laminar FORCED CONVECTION flow of a radiating gas in a rectangular duct with a solid element that makes a backward facing step. The fluid is treated as a gray, absorbing, emitting and scattering medium. The governing differential equations consisting the continuity, momentum and energy are solved numerically by the computational fluid dynamics techniques. Since the present problem is a conjugate one and both gas and solid elements are considered in the computational domain, simultaneously, the numerical solution of Laplace equation is obtained in the solid element for temperature calculation in this area. Discretized forms of these equations are obtained using the finite volume method and solved by the SIMPLE algorithm. The radiative transfer equation (RTE) is also solved numerically by the discrete ordinate method (DOM) for computation of the radiative term in the gas energy equation. The streamline and isotherm plots in the gas flow and the distributions of convective, radiative and total Nusselt numbers along the solid-gas interface are presented. Besides, the effects of radiation conduction parameter and also solid to gas conduction ratio as two important parameters on thermo hydrodynamic characteristics of such thermal system are explored. It is revealed that the radiative Nusselt number on the interface surface is much affected by RC parameter but the radiation conduction parameter has not considerable effect on the convective Nusselt number. Comparison between the present numerical results with those obtained by other investigators for the case of non-conjugate problems shows good consistency.

This research focuses on the need for preserving fruits in rural areas to prevent waste. The solar drier is made of vital chambers i. e. the concentrator chamber (that harvests the solar irradiance), the transport pipe (that transports the heat generated by CONVECTION) and hanger chamber (where the fruits are placed). The temperature within the concentrator chamber and hanger chamber was monitored. The design allowed heat transfer by CONVECTION from the collector to the chamber at an efficiency of 92 %. The design allowed the temperature build up in the solar collector to be transported faster through hanger chamber with the help of incorporated detachable low power dc fan. This arrangement makes the DRYER to either operate in the natural CONVECTION DRYER mode (without the fan) or as a FORCED CONVECTION DRYER (with the fan attached). It is observed that the FORCED CONVECTION provided higher air in-flow and hence greater drying capability. However, regions with moderate precipitation may have challenges of delayed fruit drying and growth of microorganism over the surfaces of the dried fruit.

This paper presents mathematical models of thin layer FORCED CONVECTION solar drying of Cuminum cyminum using two drying methods (mixed and indirect) at different operating conditions. The average initial moisture content of the seeds for all tests was about 43% d.b. and the drying was performed continuously, in each test, for a uniform period of 90 minutes drying time in a solar cabinet DRYER to obtain an average final moisture content of 8% d.b. Three airflow rates (0.084, 0.127 and 0.155 m3 s-1) were adopted and the experiments were run each sunny day from 11:30 to 13:00 with an average solar intensity of 750 W m-2 (±50 W m-2), ambient air temperature of 27°C (±1°C) and relative humidity of 30% (±1%). In order to find the most suitable form of thin layer solar drying model, eleven different mathematical models were selected using the experimental data to determine the pertinent coefficients for each model by applying the non-linear regression analysis technique. The goodness of fit was evaluated by calculating and comparing the statistical values of the coefficient of determination (R2), reduced chi-square (c2) and root of mean square error (RMSE) for any model and for the two drying methods. The best results were found for the approximation of diffusion model with R2= 0.995, c2=0.0023 and RSME= 0.0199 in mixed mode type, and the Midilli model with R2= 0.994, c2=0.0045 and RSME= 0.0225 in indirect mode type thin layer solar drying.

An evacuated tube solar collector drier is designed and developed to study analytically and experimentally drying kinetics of Thompson seedless grapes in Pune, India. Drying experiments are carried out in the month of April- June for continuous three years from 2013-2015. During the experimentation, temperatures of hot and cold air at various places, ambient relative humidity and humidity variation in drying chamber, wind velocity and mass of the grape are measured on hourly basis.10 kg of Thompson seedless grapes are dried in FORCED CONVECTION heat transfer mode from initial moisture content of 76% (wb) to final moisture content of 15% (wb) in 37 hours. The drying is carried out under the uncontrolled conditions. The average evacuated tube solar collector efficiency is found to be 24.5% whereas the stacked type DRYER which is insulated from outside has given drying efficiency up to 37.1%. To study drying behavior analytically nine different drying models have been tested. It is observed that, Page model describes the drying behavior accurately with highest coefficient of determination (R2=0.993), lowest reduced chi-square (X2=5.19x10-5) and lowest root mean square error (RMSE=0.02071).

In this paper the energy and exergy analyses in chamber drying process of thin layer drying of tomato in a FORCED solar drying was investigated. The experiments were carried out with two thicknesses of 5 and 7 and two airflows 0.5 m.s-1 and 1 m.s-1. During the experimental process, ambient temperature was between 22 and 36, air relative humidity between was 14 and 50, and solar radiation ranged from 150 to 850 W.m-2. The effects of drying variables on energy utilization, energy utilization ratio, exergy loss and exergy efficiency were studied by applying the first law of thermodynamics. In chamber drying at airflow of 1 m.s-1 and thickness of 5mm,the values of energy utilization, energy utilization ratio, exergy loss and exergy efficiency varied from 6.62 to 152.72W, 0.02 to 0.45, 2.42 to 32W and 32 to 80, Respectively. In addition, the results showed that both energy utilization rate and exergy loss efficiency of the drying chamber decreased with increasing drying mass flow rate and drying thickness while the exergetic efficiency and energy utilization of the drying chamber increased.