Abstract
Effects of natural convection on coaxial tube ground heat exchanger was investigated by experiment and numerical simulation. Heating a fluid in upward flow through the annular channel (or cooling in down ward flow) resulted in an increased velocity gradient near the ground side wall, thereby increasing the heat transfer rate and heat transfer coefficient. Heating a fluid in downward flow (or cooling in upward flow) has the reverse flow near the ground side wall, and flow temperature is closer to ground temperature. Hence the heat transfer rate and heat transfer coefficient decreased in these case.
