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Heat Transfer Research
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Heat Transfer Research

DOI: 10.1615/HeatTransRes.2018016948
pages 1813-1823

THERMAL ANALYSIS OF EARTH–AIR HEAT EXCHANGERS UNDER HEATING CONDITIONS AT A CONSTANT SURFACE TEMPERATURE

Refet Karadag
Harran University, Engineering Faculty, Mechanical Engineering Department, Osmanbey Campuses, 63190, Sanliurfa, Turkey
Husamettin Bulut
Harran University, Engineering Faculty, Mechanical Engineering Department, Osmanbey Campuses, 63190, Sanliurfa, Turkey
Yunus Demirtas
Harran University, Engineering Faculty, Mechanical Engineering Department, Osmanbey Campuses, 63190, Sanliurfa, Turkey
Ismail Hilali
Harran University, Engineering Faculty, Mechanical Engineering Department, Osmanbey Campuses, 63190, Sanliurfa, Turkey

ABSTRAKT

Earth–air heat exchangers (EAHEs) are used for ventilation and air conditioning, taking advantage of the earth energy. Many experimental, analytical, and numeritical researches of EAHEs have been made so far due to their promising applications. In this study, the thermal performance of an earth–air heat exchanger is investigated numerically and experimentally depending on heating conditions. The computational fluid dynamics simulation soft ware FLUENT is used in the analysis. Numerical solutions are obtained by using computational fluid dynamics (CFD) analysis under constant surface temperature boundary conditions. Computational analysis is conducted for different outside air temperatures, pipe surface temperatures, air velocities (ranging from 0.5 m/s to 5.5 m/s), and different pipe lengths of the EAHE. The numerical results obtained at different outlet and inlet air temperatures and heat loads are compared with those measured experimentally under Sanliurfa climatic conditions during winter season. The relation between the Nusselt and Reynolds numbers for the inner surfaces of the EAHE is analyzed by using numerical values, and the results are compared with the equations given in the literature. The maximum and mean deviations between the experimental and numerical results were equal to 30% and 15%, respectively. The results are acceptable, and there is agreement with the literature data, because the average deviation between the results of numerical solutions and equations given in the literature varies from 1.8% to 35% depending on the length of the heat exchanger and flow Reynolds numbers.