Heat pipes are one of the most preferred equipment because they have a variety of superior specifications. In this paper, the improvement of heat transfer properties of a thermosyphon heat pipe that was filled with bauxite nanofluid was experimentally investigated for different nanoparticle concentrations (1%, 2%, and 4%) and surfactant types (Triton X-100 and Sodium Dodecyl Benzene Sulfonate). Bauxite nanoparticles at different concentrations were utilized for the preparation of nanofluid suspensions. Different kinds of surfactants were also doped into the prepared nanofluid suspensions to show off how a surfactant affects the thermophysical properties of the nanofluid. The experiments were done under several heating powers and various mass flow rates of the cooling water circulating on the evaporator section. Temperature distributions both upon the evaporator and the condenser sections were recorded via 8 different K type thermocouples. Cooling water inlet and exit temperatures were also recorded and utilized for theoretical calculations. For doing an experimental comparison, thermal efficiency and resistance of the thermosyphon heat pipe were determined both for distilled water and prepared nanofluid suspensions. Moreover, contact angle-wettability analysis was carried out to determine how nanoparticles affect the surface tension. The encountered problems during the tests were addressed and discussed. The obtained experimental data illustrated that the thermosyphon heat pipe efficiency was increased by up to 20.9% with the usage of a 2% (mass) concentration of bauxite nanofluid and an anionic surfactant. The maximum enhancement in heat pipe’s thermal resistance was found as 24.3%, through bauxite nanofluid usage.

When exposed to an ascending flow, pendant drops oscillate at magnitudes determined by windspeed, drop diameter, and needle diameter. In this study, we investigate the retention stability and oscillations of pendant drops in a vertical wind tunnel. Oscillation is captured by a high-speed camera for a drop Reynolds number Re = 200–3000. Drops at Re ≲ 1000 oscillate up to 12 times the frequency of drops with high Re. Increasing windspeed enables larger volume drops to remain attached to the needles above Re = 500. We categorize drop dynamics into seven behavioral modes according to the plane of rotation and deformation of shape. Video frame aggregation permits the determination of a static, characteristic shape of our highly dynamic drops. Such a shape provides a hydraulic diameter and the evaluation of the volume swept by the oscillating drops with time. The maximum swept volume per unit drop volume occurs at Re = 600, corresponding to the peak in angular velocity.

In this paper, the effect of using CaMg(CO₃)₂/Ethylene Glycol-water (50:50%) as a working fluid on the thermal performance of thermosyphon heat pipe was experimentally studied. Nanofluid was prepared by two-step method using 2% concentration of CaMg(CO₃)₂ nanoparticle and 0.05% surfactant (Sodium dodecylbenzene sulfonate). For the experimental set-up, a straight copper pipe of one-meter length was used. The inner diameter of the pipe is 13 mm, and the outer diameter is 15 mm. Experiments were conducted at three different cooling water mass flow rates (5, 7.5, and 10 g/s) and different heating powers (200, 300, 400 W) to test heat pipe performance. It was observed that the CaMg(CO₃)₂ nanofluid reduced the average wall temperature of the heat pipe according to the base fluid. Furthermore, the efficiency and thermal resistance of the heat pipe were investigated separately for EG/water and CaMg(CO₃)₂ nanofluid. The maximum heat transfer enhancement was obtained as 9.55% under 400 W heating power and 10 g/s cooling water mass flow rate conditions and the maximum improvement in thermal resistance was observed as 21% at 200 W and 10 g/s cooling mass flow rate. Viscosity and specific heat of base fluid and CaMg(CO₃)₂ nanofluid were also determined and compared to each other.

In this study, bauxite/deionized water nanofluid was prepared by two-step method and its thermopyhsical properties were experimentally investigated. Bauxite was milled by high-energy spex-type ball milling attritor. Bauxite nanoparticles with a size of 38 nm (2% by weight) and Sodium Dodecyl Benzene Sulfonate (0.5% by weight) were doped into the deionized water while preparing the bauxite nanofluid. Ultrasonication was applied for three hours to obtain stable colloidal dispersions of nanoparticles. It has been seen that the thermal characteristics of bauxite nanofluid was better than that of deionized water. The bauxite nanofluid has the lower surface tension and smaller contact angle than that of base fluid. However, the thermal conductivity and the specific heat of bauxite nanofluid increased by 8.47% and 4.4% compared to deionized water, respectively.