Parametric Analysis of Thermal performance of Earth-To-Air-Tunnel-Heat Exchanger (EATHE)

Abstract

The Earth-to-Air-Tunnel-Heat Exchanger (EATHE) is one of several ambient air conditioning systems with minimum cost. Several factors and conditions will enhance the performance of the installed EATHE in room air conditioning system. In this numerical study, the influence of ground soil considering its properties, such as soil thermal conductivity, room air conditions such as air velocity, and construction of the system such as pipe thickness and length on the EATHE is investigated. Later, different arrays of fins are introduced to enhance the system's performance further. Finally, the model has been validated by comparing the outlet temperature of the system with the experimental results conducted by other researchers.

The current study analyzes the thermal performance based on three miscellaneous soil samples, each with thermal conductivity of 0.65 Wm-1K-1, 1.25 Wm-1K-1, and 3.5 Wm-1K-1, respectively. The effect of the thermal conductivity of soil due to geographic locations on the thermal performance of the EATHE system is significant. The thermal efficiency of the EATHE has been determined by the reduction in air temperature caused by transient heat transfer between the air and soil around the pipe. The effect of the soil layer is negligible after a critical thickness. The critical thickness is considered to be ten times the pipe diameter. The maximum temperature reduction is 18.9 K for 3.5 Wm-1K-1 thermal conductivity at a specific air velocity of 3 ms-1. A new model for a 10 m long pipe with various fin/fins arrangements has been created. The effects of fins were analyzed by placing a single fin of 10 mm at 0.5 m from the inlet and getting an outlet temperature of 306.7 K. The drop in temperature evolves with four fins at 0.5 m, 1 m, 1.5 m, and 2 m, and the found minimum temperature is 306.1 K, which is 19.4% more improved than a straight pipe. If fins are spaced 1m apart, the temperature drop increases by 5.6%. The arrangement with four fins at 2 m spacing gives an outlet temperature of 305.3 K, which is 7% better than a single fin. A new arrangement of fins has been used to observe their effect on the heat dissipation rate. In this arrangement, fins of 10 mm in thickness and different heights have been used in diverging-converging patterns to restrict the flow of air and thus supply cooled air at the outlet. The investigation with two blocks improves outlet temperature by 5.88% over the analysis with one block. The value progresses to 10.53% for three blocks and 14.52% for four blocks relative to the temperature drop of one block. Overall, this study will provide a comprehensive understanding of the design parameters and associated conditions, leading to enhanced performance of the EATHE.