An experimental and numerical smoothed particle hydrodynamics (SPH) analysis was performed for the convective flow arising from a horizontal, thin cylindrical heat source enclosed in a glycerin-filled, slender enclosure at low Rayleigh numbers ($1.18leq {rm Ra}leq 242$). Both the experiments and the SPH calculations were performed for positive ($0.1leqDelta Tleq 10$ K) and negative ($-10leqDelta Tleq -0.1$ K) temperature differences between the source and the surrounding fluid. In all cases a pair of steady, counter-rotating vortices is formed, accompanied by a plume of vertically ascending flow just above the source for $Delta T>0$ and a vertically descending flow just below the source for $Delta T<0$. The maximum flow velocities always occur within the ascending/descending plumes. The SPH predictions are found to match the experimental observations acceptably well with root-mean-square errors in the velocity profiles of the order of $sim 10^{-5}$ m s$^{-1}$. The fact that the SPH method is able to reveal the detailed features of the flow phenomenon demonstrates the correctness of the approach.
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