The main findings from the simulation are as follows:

The heat exchanger effectiveness increases with

• Smaller sand grain size

• Air inflow velocity

• Heat exchanger dimensions (height and width)

With the air and sand inflow temperatures of 800 °C and 200 °C, the obtainable average sand and air output temperatures are in the range TSand= 720-740 °C, TAir= 250-270 °C and heat exchanger effectiveness in the range sHX = 85-90 %.

Further results are

• For sand grain sizes < 3 mm and heat exchanger dimension of 50 cm height and 5 cm width (as given in the heat exchanger set-up described below) a smaller grain size has limited effect on the heat transfer

• Dynamic behaviour: short-term sand blockage with blocking period below 20 s are uncritical with respect of air outflow temperatures increase due to the sand bed heat capacity

• To minimize pressure drop and to increase specific heat flux per volume (dimension of 1 MW/m3) a sand grain size dSand =1-3 mm is favourable