Simulation and Modelling of Solar Dryer in COMSOL: Analysis of Airflow

Abstract

"Solar Food: Reducing post-harvest losses through improved solar drying" is a project that is a collaboration between Lund University and the Royal University of Bhutan, financed by the Swedish Research Council. The goal of the project is to improve the quality and decrease post-harvest losses of food in rural Bhutan and Nepal through low-cost, efficient solar-powered food dryers.

In this diploma project, the airflow of the two existing designs was evaluated by running simulations in the software COMSOL. The results of the simulations were then analyzed to come up with design changes to improve the airflow of the two solar dryers and suggest a new solar dryer design.

There are some flaws in the two existing designs, as both have the same issues when it comes to airflow. Each design has issues with a significant amount of air flowing along the wall in the first drying chamber, and with an air vortex forming in the second drying chamber that can lead to uneven drying. The issue with the air vortex in the second drying chamber may lie in the design of the centre panel and how it restricts the airflow between the two drying chambers, leading to an increase in air velocity which creates the air vortex. The adjustments, such as a larger entry gap to the drying chamber and changing the placement of the internal fan, made to the two designs that are simulated in this project did not solve these two mentioned problems and only provided small indications of improved airflow. However, the size of these improvements cannot be determined and more calculations needs to be done to confirm these improvements and the size of them.

The results from the simulations using a new design with one drying chamber have raised more questions than answers, and therefore there is no reason to continue working on this design or to conduct any experiments on it. Regarding the first and second designs, the first design seems to have fewer problems to solve when it comes to airflow. To determined which of the two designs are better, more experiments needs to be conducted on the two designs.

Popular Abstract

Most types of food can only be harvested during certain seasons and this makes preservation important. Countries such as Bhutan and Nepal are struggling with unnecessary food losses due to the logistical challenges due to the mountainous landscapes. This makes the preservation of the food even more important since the transport of the food takes a longer time. The Swedish Research Council is attempting to solve this issue and has funded a project called, “Solar Food: Reducing post-harvest losses through improved solar drying”, coordinated by Lund University and with the help of the Royal University of Bhutan. The goal with the project is to improve the quality and decrease post-harvest losses of food in rural Bhutan and Nepal by developing a solar food dryer using only locally available material found in Bhutan and Nepal.

At this stage of the project, two different designs of a solar dryer have been developed and built. Tests have been carried out on the two designs, both on site in Bhutan but also in a laboratory in Lund. This report has examined if there are any design flaws on the two existing designs that have been produced and this was done by using a simulation program called COMSOL. The conclusions from these simulations were that the two designs had some issues with the air circulation which could affect how the crop or fruit would dry in the solar dryer. And to try to solve these issues, small design changes were made on the two designs and then new simulations were made to see if there was an improvement on the air circulation. For example two of the design changes were changing the placement of the fan inside the solar dryer and making the entry gap to the drying chambers larger. These changes gave a mixed result on the different issues, some were almost solved from these design changes and others were unchanged despite the design changes.

The report also looked at a potential new design of a solar dryer in hope that the new design would not have the same issues as the other two designs. The result from the simulation on the new design unfortunately did not show an improvement on the air circulation and still had some of the same issues as the two existing designs. The new design even had new issues such as the air moving more horizontally inside the drying chamber, it is uncertain if it is more efficient to have air moving vertically or horizontally over the product that is drying. One other issue with the new design is that the air moves back and forth in the bottom of the drying chamber rather than predominantly upward in the chamber. Due to lack of time, no further work was done on the new design and these issues were not solved in this report.

• author: Sörensson, Christoffer
• supervisor: Martin Andersson
• organization: Department of Architecture and Built Environment; Division of Energy and Building Design
• course: AEBM05 20232
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Solar dryer, Drying, Heat exchanger, Solar absorber, Drying rate, Air flow, COMSOL
• language: English
• id: 9151577
• date added to LUP: 2024-05-20 11:16:07
• date last changed: 2024-05-20 11:16:07