Arvind Pattamatta

In the present work, surface wettability modifications were utilized to enhance the phase change heat transfer in a water-charged two-phase flat thermosyphon. A flat thermosyphon's thermal performance with various surface wettability modifications on evaporator and condenser plates was investigated for various heat inputs and filling ratios in the horizontal orientation. The evaporator and condenser's surface wettabilities were varied to superhydrophilic (contact angle of 0-1°) and superhydrophobic (contact angle of 155.4 ± 3°). Changing the evaporator's surface wettability to superhydrophilic nature increased the thermal resistance of thermosyphon due to the high superheat requirement and delay during bubble nucleation. A 43.74% decrease in the thermal resistance was observed for a thermosyphon with a superhydrophobic condenser due to the dropwise condensation and faster condensate return to the evaporator compared to the bare one. A lumped parameter model was used to predict the thermal resistance of flat thermosyphon with a superhydrophobic condenser and hydrophilic evaporator, which is in good agreement with the experimental results. The experimental results encourage research on a two-phase flat thermosyphon with a superbiphilic evaporator and superhydrophobic condenser as it can further improve thermal performance.

Heat transfer in magnetic nano-particle dispersion can be influenced by the presence of external magnetic-field. This paper presents an experimental investigation on effect of external uniform magnetic-field on natural convection heat transfer in magnetite and iron nano-dispersion in a differentially heated cubical cavity. The experiments are conducted between the Rayleigh number range of 4.23×105 to 1.0×107. The study includes experiments and discussion on the corroborating and suppressing effects of thermo-magnetic convection induced by the external magnetic-field on the natural convection heat transfer. Additionally, this study also reports the experimental results and pertinent explanation on the directional effect of magnetic-field on the heat transfer in magnetite and iron nano-dispersion. The paper quantitatively presents the extent of heat transfer depreciation/enhancement in different orientations of the cavity in the presence of magnetic-field. The study also explores the effect of particle volume fraction in magnetic fluid on heat transfer in each case.