Abstract
Hybrid air heater is a device taking advantage of two or more energy sources directly or indirectly for heating air. This study aims to analyze energy and exergy for a hybrid air heater. It is assumed that no thermal gradient exists along glass thickness and one-directional variation of temperature is in flow direction and thermal capacity of glass, absorber plate, and thermal insulations are negligible. To avoid food oxidation in dryers, effects of heating fluid such as air, carbon dioxide, and nitrogen on temperature, heat transfer, and thermodynamic first and second law efficiencies are also investigated along with the effects of hybrid heating on the aforementioned parameters. The problem is solved using MATLAB software and invoking iterative method with convergence criterion of 0.0001 for temperature. Results indicate the positive effects of using carbon dioxide. Applying hybrid system is also shown to increase the efficiency of air heater.
Highlights
Solar energy is among the most important renewable energy sources on Earth which is compatible with environment, and it is always available in the large part of Earth's surface and human beings have always tried to harness this energy and utilize it optimally
Solar energy has the wide range of applications such as supply of hot water for urban and rural consumption, air-conditioning in constructions, and dehydration of agricultural products, electricity generation in power plant with solar collectors, etc
Air leakage, conductivity of absorber plate, and freezing of fluid do not pose problems in air collectors and they are considered as the advantages of this kind of collectors over solar collectors in which water is used as the working fluid
Summary
Solar energy is among the most important renewable energy sources on Earth which is compatible with environment, and it is always available in the large part of Earth's surface and human beings have always tried to harness this energy and utilize it optimally. Gawande et al [7] in 2016 conducted numerical and experimental studies on roughened solar air heater and reviewed the effect of angle and direction of ribs on heat transfer from air heaters. For the purpose of drying systems, Hakim et al [17] recently investigated experimentally the application of heat pipe on low enthalpy geothermal energy utilization for agricultural products dryers They showed that the smallest and the biggest effectiveness related to this system is 23.7% and 61.4% respectively. As a summary of experimental, numerical and analytical works performed in the field of air heaters, the effect of various variables has been investigated on the performance of air heaters such as number of collectors, mass flow inlet, angle of positioning, gap, length to thickness ratio, roughness, flow path, etc. The novelty of this research can be explained in two ways: 1) Exergy analysis for a thermal air heater with auxiliary heat source. 2) Evaluation of thermal performance of the heater using inactive gases instead of air in the drying process
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