In the present work, the experimental studies performed through the thermo-economical analysis of Jerusalem artichoke slices dried by an indirect cabinet solar dryer with evacuated tube collectors and phase change materials. It shows that in the drying process of 5 mm thickness of Jerusalem artichoke slices the effect of using phase change materials in the solar dryer on the movement of the water content from the crops was significant (P < 0.05). The drying time decreased with increasing the airflow rate, but it was not significant (P > 0.05). Using phase change materials increased activation energy (33.4 kJ/mol) and improved the overall drying efficiency 1.51–7.81%. Specific energy consumption with PCM usage decreases from 14.51 to 13.38 MJ/kg. In addition the exergy efficiency for the drying process about 35.3–59.7%. The optimized condition for the system was obtained, and it showed that payback time for the solar dryer with optimized condition could be decreased to 22 months which was lower than basic condition (15%). Moreover, artificial neural network, computational fluid dynamic and evolutionary polynomial regression were considered to predict the variations of thermal behavior of the system. The values of RMSE and COV for artificial neural network method are lower and R2 is higher than the computational fluid dynamic method. The result of evolutionary polynomial regression implied that it predicted outlet temperature, and the collector thermal efficiency with the acceptable accuracy (R2 > 0.98). According to the exergetic, economic and quality consideration the proper condition was obtained with 0.9 kg/s for air flow rate assisted with PCM. 

Thermo-economic analysis of solar drying of Jerusalem artichoke (Helianthus tuberosus L.) integrated with evacuated tube solar collector and phase change material

There are numerous applications of solar energy technology, among which an air heating system is commonly used for space heating, wood seasoning, industrial drying, etc. Previous research focuses on the bulk usage of different latent heat storages, which is a costly method for performance improvement, especially for solar heating systems. Another major problem with bulk energy storage is that it takes a long time to be charged completely, which results in low-rate air heating at the start. The present research focuses on an economical solution for solar air heating, especially under India's mild cold climatic conditions. About 36 tiny cylindrical containers have been used to carry the two low-cost phase change materials (PCMs), i.e., coconut oil and paraffin wax. These materials have been filled inside the small containers and placed over the solar absorbers of modified models of air heaters, namely, SAHS-2 (with coconut oil) and SAHS-3 (with paraffin). A total of 02 configurations have been developed to conduct the air heating trials on natural and forced convection. To the best of the author's knowledge, likely methodology has not been applied to any air heating system to improve performance for extended hours, especially in a cold climate. Results have been compared with the same size conventional solar heater (SAHS-1) and some other relevant designs of SAHS to observe the significance of PCMs and their appropriateness for air heating. Finally, the model SAHS-3 is found to be the best-configured air heater, capable of performing efficiently under mild cold climates. Experimental studies showed that the best model provides enhanced heat transfer of about 372.81 W/m2 K, thermal efficiency of about 75.9%, a heat loss coefficient of about 4.93 W/m2 K, and outlet air temperature of about 44.07 °C under forced convective operations. The estimated cost of the modified heater is approximately $61, while its payback period is about 4.38 years. 

Experimental studies of latent heat storage based solar air heater for space heating: A comparative analysis

Energy, exergy, economic and environmental (4E) analysis of passive and active-modes indirect type solar dryers while drying guava slices

Performance analysis of a novel thermal energy storage integrated solar dryer for drying of coconuts

This paper presents a numerical simulation approach to investigate the water effect as an auxiliary fluid in direct contact with various phase change materials (PCMs). The technique is defined as a hybrid method due to the using of an external intermediary for melting process improvement. Oleic acid (OA), coconut oil (CO), hexadecane, and heptadecane are selected as PCMs due to immiscibility in water and differences in density, melting point, and enthalpy of fusion. An auxiliary fluid is embedded above PCM in an enclosure subjected to sinusoidal wall temperature for melting rate increase through density differences improving heat transfer rate due to materials displacement during process. Based on water accessibility and price, this approach would be preferable to costly enhancement methods such as nanoparticles addition or utilizing extending heat transfer surfaces. Each PCM melting process in the hybrid system with a volume ratio of 50% PCM - 50% water is simulated and compared with a pure (100% PCM) reference melting process. A 23%, 30%, 62%, and 98% increase in energy storage capacity can be attributed to hybrid systems with OA, CO, hexadecane, and heptadecane, respectively. Also, stored heat rate computation shows that using water increases 177% stored heat rate per PCM kg in the system. Meanwhile, it accelerates PCM melting process. Higher density differences cause a dynamic flow field and faster melting process, increasing stored heat rate about twice, which is a significant result for system design and optimization. 

Melting process of various phase change materials in presence of auxiliary fluid with sinusoidal wall temperature

Organic paraffin wax, a phase change material (PCM), was used as the heat-storing material in this study. The novelty of this work is the application of a PCM-packed floor in a conventional solar dryer to reduce the absolute drying time of crops. A PCM-packed solar dryer prototype model was constructed with an extendable drying chamber for easy loading, unloading, tilting, and shuffling the food products. The innovative drying setup was constructed to reduce human efforts and improve the drying in the preservation of food products. Four crops (guava, banana, coconut, ladies’ finger) were chosen for the experimental testing of the fabricated model. The samples were tested using the solar dryer with and without the PCM. The outcomes revealed that PCM usage helped retain the heat longer than the test without PCM. The drying time of all four crops was decreased by about 3-4 hours by installing the PCM, thereby reducing the crop drying time per day. The peak temperature attained by the crops in the presence of PCM had considerably improved, i.e., 7.81 % for guava, 4.55 % for banana, 3.125 % for coconut, and 8.33 % for ladies’ finger. The outcomes revealed that the colour, fragrance, and quality of the solar-dried products were better than the sun-dried products.

G.R. Gopinath

Papers

Experimental investigation of the performance of paraffin wax-packed floor on a solar dryer