Experimental Study of the Optimum Air Gap of a Rectangular Solar Air Heater

Hussam S. Dheyab; Manar Salih Mahdi Al-Jethelah; Tadahmun Ahmed Yassen; Thamir Khalil Ibrahim

Authors

Hussam S. Dheyab Mechanical Engineering Department, College of Engineering, Tikrit University, Tikrit, Iraq
Manar Salih Mahdi Al-Jethelah Mechanical Engineering Department, College of Engineering, Tikrit University, Tikrit, Iraq
Tadahmun Ahmed Yassen Mechanical Engineering Department, College of Engineering, Tikrit University, Tikrit, Iraq
Thamir Khalil Ibrahim Mechanical Engineering Department, College of Engineering, Tikrit University, Tikrit, Iraq

Keywords:

solar air heater, air gap, natural convection, inclined collector

Abstract

Many studies had investigated the optimum air gap of a solar air heater. Yet, no agreement has been indicated to find the optimum air gap height especially with different studied designs. In the present work, an experimental study was conducted to find an optimum air gap height for a rectangular solar air heater. To conduct the experiments, four solar air heaters with different air gap heights were designed and built. Each heater was 200 cm in length and 50 cm in width. The studied air gap heights were 3, 5, 7, and 9cm. The results showed that the highest air temperature difference was found for air gap height of 3 cm, i.e. 57.5 °C. An air gap of 3 cm resulted in highest air outlet temperature for all studied period. The highest mass flowrate, which consequently highest heat gain, was 9.0 g/s at 9cm and 13:00. The high mass flowrate resulted in high efficiency, i.e. 57.3% at 9 cm and 10:00. Both air mass flowrate and solar air heater efficiency showed insignificant increments as the air gap height exceeded 5cm.