An experimental study for free convective heat transfer in a thermal diode type enclosure is presented. The thermal diode is a device which allows heat to be transferred in one direction by convection due to density difference of the fluid, and consists of a rectangular-paralle-logrammic enclosure with a guide vane. It is used as heat collection system of solar energy due to its simple construction and low cost. Experimental parameters were guide vane thickness, the inclination angles of the parallelogrammic enclosure, and the lengths of the rectangular enclosure part. The parameter range of the flux Rayleigh numbers was $2.4 imes{10}^8$~$9.8 imes{10}^8$. The heat transfer rate of this system was shown 10~47% higher than that of other earlier research results without the guide vane. The correlation for fixed $phi=60^circ$ was obtained, Nu=0.0037(Ra^*)^{0.429}(d^*)^ {0.050}(Lr/H)^{0.0415}$.