Mathematical modeling and parameter estimation for an optimal Solar food dryer

Abstract

Food shortage in most countries is not only associated with unfavorable weather conditions, but also significantly blamed on ineffective post-harvest handling of food. This calls for an urgent need to address food insecurity in Kenya, in line with Vision 2030 and Government Big 4 Agenda. Eminent threat caused by post-harvest losses due to inadequate drying and poor storage is responsible for up to 40-60% loses of agricultural produce each season. In order to address this issue, this project seeks to model and simulate the characteristics of a solar dryer for the purpose of designing an effective and sustainable, low-cost thermal solar dryer suitable for dehydrating a variety of agricultural produce to ensure prolonged shelf life hence reduce losses. The proposed model is to be formulated using mathematical equations describing integration of four divisions, namely; solar heat collector, circulation of fluid in insulated closed loop pipe network, heat exchangers to generate heated air supplied to the drying chamber and dryer, equipped with humidity control systems, temperature, mass flow rate and energy balance. The mathematical model was formulated and simulation done in order to realize the objectives of delivering a solar drier suitable for drying a wide variety of food products. The simulation results showed that, a solar panel of it was found that a solar collector with aperture area of 𝐴𝑐 = 14.4𝑚2 and volume of 𝑉𝑐 = 500𝑙, when exposed to solar irradiation of 𝐼𝑐 = 1.367𝐾𝑊/𝑚2 at 𝜂𝑐 = 80% efficiency is able to heat water from 𝑇𝑖𝑛 = 220𝐶 to 𝑇𝑐𝑜 = 700𝐶 in 12 hours at a flow rate of 𝑣𝑐 = 1.128𝑙/𝑠, and cumulatively to1300𝐶 in 6 days. This energy if transmitted by insulated pipes to a set of 5 heat exchangers each of 𝐴 = 1𝑚2, and radiative heat transfer coefficient ℎ𝑟 = 100𝑊/𝑚2𝐾 cumulatively dissipates hot air of 2300𝐶 at 𝑣= 250𝑐𝑚3/𝑠, 1300𝐶 at � �=1000𝑐𝑚3/𝑠 and 900𝐶 at 𝑣= 2000𝑐𝑚3/𝑠 air mass flow rate. This output temperatures of dry air are regulated as desired according to the specifications of the food products to be dried. During the night or on cloudy day with minimum or no solar insolation, alternative supplementary source of heat is obtained from petroleum cooking gas, which is regulated automatically depending on the level of solar insolation. It is found that the optimal cost of the gas is 𝐾𝑠ℎ 180/𝑑𝑎𝑦 as opposed to 𝐾𝑠ℎ 560/𝑑𝑎𝑦 when used alone. This is over 67.86% reduction in cost, which makes the use of solar an ideal green energy.