The performance of the heat pipe depends largely on the thermofluid properties of the operating fluid used and its filling ratios,
which is the focus of current work. In this paper, an experimental study was conducted to evaluate the performance of the heat
pipe under different operating conditions. A smooth tube heat pipe with four operating fluids of different thermofluid properties,
which are water, ethanol, methanol, and acetone were studied. Investigation parameters were examined at ranging for filling ratios
and power inputs between 30-60% and 80-200W, respectively. The experimental main results showed that the best operating fluid
that provided the higher performance was water at a 60% filling ratio and a power input of 200W%, while the lowest performance
of the heat pipe was with acetone. The increase in heat input led to an increase in the condensation and evaporation heat transfer
coefficients of the heat pipe by approximately 87.5% and 45.2%, respectively.