Adsorbed natural gas (ANG) has the potential to replace compressed natural gas in mobile storage applications, such as in vehicles. Although a substantial research effort has been devoted to ANG, very few studies evaluate the impact of heat of adsorption on system performance. This paper concentrates on the impact of heat of adsorption on ANG performance during discharge, while the gas outflow rate is dictated by the energy demand of the application. The temperature drop and performance loss was measured with commercially available ANG cylinders under realistic conditions. Data show as high as a 37 degrees C temperature drop at high discharge rate, with a performance loss approaching 25% of isothermal capacity. The performance loss is expected to be 15-20% at moderate discharge rates. Analysis of data and predictions of a simple model indicate that the ANG system is neither adiabatic nor isothermal during discharge; the thermal capacity of the vessel wall and external heat transfer conditions have a significant effect on system behavior. The poor thermal conductivity of packed adsorbent is a major obstacle for the utilization of these energy sources. Changing the flow direction during discharge from axial to radial by a perforated tube inserted at the center of the cylinder significantly reduces the performance loss by increasing the heat transfer from the wall to the central region. At intermediate discharge rates, where the inserted tube has the largest impact, the performance loss is reduced to 12% from 22% without the tube under identical conditions.
