Solar hybrid tunnel dryer has a huge potential in drying large-scale agricultural products with solar energy and forced hot air inside the tunnel. This project involves design, CFD analysis and experimentation of portable solar hybrid tunnel dryer for a new pipe line configuration. The problem of uneven distribution of temperature inside the solar tunnel dryer was observed in few research articles. To overcome the above problem, a detailed research is required to study the temperature distribution of the solar hybrid tunnel dryer.    

  A Computational Fluid Dynamics (CFD) analysis had been performed to study the even distribution of temperature at the outlets of the pipeline using the ANSYS-Fluent v16.2. A comparative CFD analysis for the conventional and the proposed new pipeline configuration by the application of both convection and radiation heat transfer modeling had been done. Hot air flowing at 12m/s and 323.15 K had been provided at the inlet of the pipeline while the outlet was set to atmospheric pressure condition. For the new pipeline configuration, the temperature drop of less than 1 K had been predicted at the outlets of the pipeline when compared to the temperature drop of 24 K for the conventional pipeline configuration. An even distribution of temperature had been achieved for the proposed new pipeline configuration. Hence, we have to conduct an experimental study for the new pipe line configuration to prove the idea and the analysis.

 

Key Words

        Tunnel dryer, temperature distribution, pipeline configuration.

 

 

 

 

1.      Project Description:

Introduction:

 Drying is one of the essential operations performed for preservation and also for improvising the lifespan and quality of the agricultural products. Traditional method includes open drying process where the products are exposed to direct sunlight for a particular duration of time. However, in this method, the rate of drying is not con-trolled which may lead to the deterioration of food products by favouring the growth of microorganisms in relatively high humid weather conditions. In spite of its simplicity and economic nature, this method has a significant threat posed by birds, rodents, pests, dust, storm, and rain, all of which affects the quality of the dried products.

           

 This problem is overcome with the help of solar dryers where the drying process is carried out in an enclosed chamber using the solar energy and natural convection of the air. Saravanapriya G. et al. 1 stated that the solar and biomass integrated drying  system reduced the drying time from 5 to 7 days in conventional open sun drying method to 2 days with improved quality of dried copra. Further, this technique is improvised by using the electrical forced convection systems where the preheated air is forced into the drying chamber with the help of pipelines. Prashant Singh Chauhan et al. 2 stated that thermal modelling plays a significant role in ideal design and development of the greenhouse dryer. The study concluded that the performance of the greenhouse dryer under the forced convection mode was found better for high moisture content crops, on the other hand, natural convection mode was found better for low moisture content crops. Even though this development seems promising, a few disadvantages were observed. There is a significant drop in temperature within the pipeline system making it consume a lot of energy for the drying process.

      Moreover, the huge size of the solar dryers, especially the tunnel dryers, makes it unfit for the home applications. Sanket Khamitkar and O. D. Hebbal 3 carried out a computational fluid dynamics (CFD) analysis of a solar air collector called the un-glazed transpired collector (UTC) to determine its thermal characteristics. The study predicted that the rise in temperature decreases with the increasing mass flow rate whereas the efficiency increases with the increasing mass flow rate. M. Augustus Leon et al. 4 briefed a review of the existing evaluation methods and parameters used for the evaluation of solar dryers along with their limitations. Based on the re-view, he developed a comprehensive procedure by including additional parameters. The study revealed that the results of the observations reported using evaluation sheets along with the graphs representing the drying curves and cumulative drying energy consumption could provide a complete picture of the absolute and comparative performance of the dryers. Lalit M. Bal et al. 5 stated that the use of finned tubes as well as a metal matrix or sand, for example, resulted in an increase of one-to-five fold of the effective thermal conductivity of heat storage medium and increases the rate of heat transfers. A.I.Ambesange and Kusekar. S. K 6 carried out a computational fluid dynamics (CFD) analysis using ANSYS-Fluent v.14.5 to simulate the fluid flow and heat transfer characteristics of a solar air heater providing artificial roughness to its ducts. The study predicted that the combined effect of the turbulence and reattachment of the fluid was responsible for the increase in the rate of heat transfer.

 

The main challenge here is to design an efficient solar hybrid tunnel dryer in which the temperature distribution is uniform across the pipeline. Taking advantage of the pipeline configuration against the variation of temperature, a new design is proposed. The design is further modeled and analyzed using the Computational Fluid Dynamics (CFD) software ANSYS- Fluent v16.2. A simple model of the solar hybrid tunnel dryer which can be incorporated into homes to dry the agricultural products is de-signed.

     

Objective

·         Even distribution of heat at all the pipeline outlets by optimizing the pipe configuration in the solar hybrid tunnel dryer.

·         Maintaining uniform optimum temperature throughout the solar hybrid tunnel dryer.

·         Increasing the drying rate of the crops so that the overall drying time is reduced.

 

Relevant works reported in literatures

·         Saravanapriya .G et al. 1 conducted studies and proved that the solar and biomass integrated drying system reduced the drying time from 5 to 7 days in conventional open sun drying method to 2 days with improved quality of dried copra.

·         AtulSharma et al. 2 proposed a comprehensive review of the various designs, details of construction and operational principles of the wide variety of practically realized designs of solar-energy drying system.

·         Prashant Singh Chauhan et al. 3 explained the effects of thermal modeling playing a significant role in ideal design and development of the greenhouse dryer. The performance of the greenhouse dryer under forced convection mode was found better for high moisture content crops, on the other hand, natural convection mode was found better for low moisture content crops.

·         Lalit M. Bal et al. 4 suggest that using Heat storage ‘phase change materials’ is a wise alternative. The use of finned tubes as well as metal fiber and metal matrix or sand resulted in an increase of one-to fivefold of the effective thermal conductivity of the PCM and increases the rate of heat transfer. Also using bamboo in the solar dryer may reduce cost as it has good thermal insulation and mechanical strength compared to metal.

·         Shobhana Singh and Subodh Kumar 5 proposed methodology facilitates to generate single generalized characteristic curve representing 16 drying kinetics and a dimensionless parameter called Dryer Performance Index. (DPI) characterizing the effectiveness of dryer system is identified.

·         Gauhar A. Mastekbayeva et al. 6 described the design and experimentation of a solar-biomass hybrid dryer. While overcoming the limitations of solar drying during cloudy days, the solar-biomass hybrid dryer also enables drying during night time. The facilitating of continuous year-round operation of the dryer and the 60-80% reduction in drying time in comparison with open sun drying and solar drying, increase the utilization of the dryer and improves the financial viability of the tunnel dryer considerably.

·         S. Boughali et al. 7 reviewed that different thin layer mathematical drying models were compared according to their coefficient of determination (R2) and reduced chi-square (v2) to estimate experimental drying curves. The Middli model in this condition proved to be the best for predicting drying behavior of tomato slice with (R2 = 0.9995, v2 = 0.0001). Finally, an economic evaluation was calculated using the criterion of payback period which is found very small 1.27 years compared to the life of the dryer 15 years.

·         M.V. Ramana Murthy 8 has proved that various types of driers are available to suit the needs of farmers. The performance evaluation procedure of driers can be simplified by using ”Evaporative Capacity” concept.

·         M. Augustus Leon et al. 9 attributes about the sources of existing evaluation methods and parameters used for the evaluation of solar dryers has been carried out and their limitations discussed. Based on the review, a comprehensive procedure has been developed. Additional parameters have been included in the proposed procedure. The results of the observations could be reported using evaluation sheets, which together with the graphs representing the drying curves and cumulative drying energy consumption could provide a complete picture of the absolute and comparative performance of the dryers.Overall Summary             From the above literature, it is found that the flow inside the tunnel is not uniform over the entire drying process. There are very few journals and papers found regarding Computational Fluid Dynamic analysis for temperature distribution of the solar tunnel dryers. And also the conventional pipeline design used earlier has drawbacks like decrease in temperature range along its length. Hence this project is based on designing a new pipeline configuration and further analyzing to ensure optimized flow distribution over the entire process of drying.  Conclusion and discussion:

The following conclusions are drawn from the simulations performed for the solar hybrid tunnel dryer:

·         The current solar hybrid tunnel dryer has employed conventional pipeline configuration, which leads to the non-uniform temperature in the pipeline.

·         The proposed new pipeline configuration reduces the drop in temperature across the pipeline so that the hot air exiting at every outlet has a fairly uniform temperature whose magnitude is close to that of the inlet temperature.

The present simulation does not incorporate the type of crop with moisture content and geographical conditions. However, it is to be noted that experimental validation cannot be performed due to unavailability of research articles in solar hybrid tunnel dryer testing. Further, it is planned to establish an experimental setup in solar hybrid tunnel dryer and perform the temperature distribution for the new pipeline configuration.

Scope of the project

Ø  To utilize the available solar energy efficiently so that the large-scale drying process can be done at a low cost.

Ø  Improvisation in the design of pipelines leads to the even distribution of heat energy throughout the solar hybrid tunnel dryer, thereby minimizing the energy losses.

Ø  Improving the distribution of heat improves the drying rate of the crops which in turn reduces the time taken for the drying process.

 

 

 

 

 

References

1         Saravanapriya G, Mahendiran R, Kamaraj S and Karthik C, “Copra drying in the solar and biomass integrated dryer”, International Journal of Agriculture Sciences, pp. 3218-3221, 2016.

2         Atul Sharma, C.R. Chen, Nguyen Vu Lan, “Solar-energy drying systems: A review”, Renewable and Sustainable Energy Reviews 13, pp.1185–1210, 2009.

3         Prashant Singh Chauhan, Anil Kumar, and Bhupendra Gupta, “A review of thermal models for greenhouse dryer”, Renewable and Sustainable Energy Reviews, pp.1-11, 2016.

4         Lalit M. Bal, Santhosh Satya and S. N. Naik, “Solar dryer with thermal energy storage system for drying agricultural food products: A review”, Renewable and Sustainable Energy Reviews 14, pp. 2298-2314, 2010.

5         Shobhana Singh, SubodhKumar, “New approach for thermal testing of the solar dryer: Development of generalized drying characteristic curve”, Solar Energy Journal 86, pp.1981–1991, 2012.

6         Gauhar A. Mastekbayeva, Chandika P. Bhatta, M. Augustus Leon and S.Kumar, “Experimental studies on a hybrid dryer”, International Solar Energy Society 99 Solar World Congress, pp. 1-7, 1999.

7         S. Boughali, H. Benmoussa, B. Bouchekima, D. Mennouche,H. Bouguettaia, D. Becki, “Crop drying by indirect active hybrid solar – Electrical dryer in the eastern Algerian Septentrional Sahara”, Solar Energy 83, pp.2223–2232, 2009.

8         M.V. Ramana Murthy, “A review of new technologies, models and experimental investigations of solar dryers”, Renewable and Sustainable Energy Reviews 13, pp.835–844, 2009.

9         M. Augustus Leon, S. Kumar, and S. C. Bhattacharya, “A comprehensive procedure for performance evaluation of solar food dryers”, Renewable and Sustainable Energy Reviews 6, pp. 367-393, 2002.

10      Prof. A. I. Ambesange and Prof. Kusekar S. K, “Analysis of flow through solar dryer duct using CFD”, International Journal of Engineering Development and Research, pp. 534-552, 2017.