Development of a Modular Mobile Solar Heater for Applications in Low-Temperature Grain Drying
Abstract
Crop drying is an energy intensive process and a major cost incurred in production agriculture. For example, about 60% of energy use in corn production in the Midwest is for drying corn to a safe moisture content, typically to 15% or below. Though solar energy is the most abundant renewable resource and a great heat source that can be used for drying without adversely impacting the environment, its efficient use for drying crops in commercial dryers or grain bins has not been realized. This research explores an evacuated heat pipe solar collector liquid system for low-temperature corn drying. This was accomplished by placing the collector on a mobile platform which enables its use in various applications such as, space heating of buildings and hot water systems. This increases its utilization, and thus, its return on investment. The system was conceived, designed and assembled as part of this research. Mini bins (5-gallon drums) were used to verify the experimental drying performance with regards to the solar unit's delivered air temperature and flow rate. The moisture content variations observed were 19% to 15.6%, 20.8% to 15% and 25% to 9% (w.b.), respectively. Heat transfer fluid flow rate was varied which allowed for the investigation of its correlation with drying air temperature rise. Results showed the best collector efficiency flow range. Its average efficiency (44.6%) was greater than the collector's rated efficiency (42.2%). A control bin operating with ambient air was used in order to establish a baseline for comparison of the solar drying performance under varied weather conditions. The results were compared and served for an empirical validation of a combined simulation model (an equilibrium model incorporating thin-layer drying equations). The model was evaluated on the basis of RMSE and MBE. Both parameters were below 3.2% demonstrating good agreement with the values in the experiment. Finally, the model was used to estimate low-temperature drying methods (natural air, continuous heat and solar) energy efficiency performance for corn being dried in a bin of 15 feet (4.57 m) diameter and 6.5 feet (1.98 m) depth. The simulation was run for a 10 points moisture removal (25 to 15%). The simulation was accomplished using as weather database the typical meteorological year (TMY3) for West Lafayette, IN, USA. TRNSYS and the solar collector performance data provided by SRCC were used to predict the system's performance. The outdoor test results showed the system successfully provided good air temperature rise during drying test conditions (up to 28 °C). The scaled-up simulation results showed the system is suitable for drying systems up to 919 bushel (23 tonne). It could provide energy savings of 3.1% when compared with natural air systems, and 91.4% when compared to continuous heat systems using liquid propane, considering all systems operating under the same schedule management.
Degree
M.S.
Advisors
Ileleji, Purdue University.
Subject Area
Alternative Energy|Agricultural engineering
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