A three dimensional transient numerical model is done for a Thermosyphon heat pipe to visualize the steam and condensate flow patterns and interaction. The Computational Fluid Dynamics (CFD) model was arranged using Volume of Fluid solution model (VOF)in Fluent. A copper vertical pipe with 14.2mm inside diameter, 400 mm length, and 0.9mm thickness is selected. The heat input varies from (20-120) Watt. The cooling is made with water jacket heat exchanger around the condenser with outer diameter of 55 mm. Filling ratios of (40,50,60,70 and 100) % are tested. All cases show that the classical known flow pattern where the steam flow upward in the core and the condensate flow downward attached to the inner surface of the pipe do not occurs. The simulation results clear out a behavior that both the rising hot steam and the downward condensate flows near the inner pipe wall. So that, both phases face each other near the wall. The high momentum phase continue it flow in its way and shift the other phase from the wall. This flow behavior leads the steam and condensate to flow in a spatial unstable flow upward and downward respectively. The flow continues even when steady state was achieved and create a secondary mass and heat transfer between the phases.

The aim of this study was to investigate the effect of inserting a new internal tube packing (TP) on the thermal performance of a thermosyphon heat pipe (THP). The THP pipe was made from copper with an inner diameter of 17.4 mm and length of 600 mm. The new internal tube packing (TP) had a central copper disc with two copper tubes soldered onto both sides to transport vapor and condensate. The upper tube or riser had an inner diameter of 8.3 mm and was 300 mm long; it was connected to a hole in the disc from the upper side to transport the steam to the condenser section. The lower tube or downcomer had an inner diameter of 5 mm, was 225 mm long and was connected to the lower side of the disc to collect the condensate and transport it to the evaporator. The TP was inserted inside the THP to complete the design of the improved heat pipe (TPTHP). Experimental results showed that the TPTHP reduces the transit time from 16 to 11 min and the thermal resistance by 17–62% based on the input power and depending on the conditions of the THP. The results also showed that the inclination angle and filling ratio have no effect on the thermal resistance of the TPTHP.

In this paper, systematic experimental investigations were carried out for a wickless heat pipe with flat evaporator having dimensions (100x100x30) mm. Flat-square electrical element was used to simulate the heat source of electronic part with dimensions of (100x100) mm. The aim of this paper presents the effect of fill ratio and cooling water mass flow rate on thermal performance of a wickless heat pipe. Experiments were performed to evaluate performance of wickless heat pipe for range of input power from 10 W to 100 W. The fill ratios used in the present work were 15%, 25%50% and 85%. The cooling water mass flow rate was also changed from 0.0083 kg/s to 0.033 kg/s. Experimental results showed that the maximum value of wall evaporator temperature was 115°C at input power of 100 W and a fill ratio of 15%. Results also showed that the maximum value of the total resistance was 0.8°C/W.

Heat Pipe (THP) has a continues evaporation/ condensation cycles of the working fluid. The flow patterns of the two phases is founds by previous published articles, as a non-steady complex spatial flow pattern. This type of the flow blocks the easy moving of the two-phases and limits the thermal performance of the THP. In this study, a copper tubes packing (TP) is simulated numerically to control/manage the flow streams of the two phases inside the THP. The simulated THP is 600mm length made of copper partially filled with water. The TP is consist of a two copper tubes attached contrary to each other with a neighboring openings. The upper tube (Riser tube) facilitate the moving of steam streams from evaporator section to the top of the condenser section. The lower tube (Down-comer tube) facilitate the moving of the condensate streams from the condenser section to the bottom of the evaporator section. The tested filling ratios are (40,50,55,60 and 70) % of evaporator section volume. The supplied heats are (50,75,100,150 and 200) W. The Computational Fluid Dynamics solution are done for a three dimensional model (3DCFD) using ANSYS/ Fluent R19.0 software. The simulation result of the steam volume fractions contours shows that the insertion of TP control the flow streams of both phases. Also prevent the formation of complex flow patterns then enhance the axial velocity vectors and reduce cross velocity vectors. The inserted TP provide a regular circulation paths for the working fluid phases and enhance evaporation /condensation processes. Hence it’s reduce the thermal resistance of the THP about 55% and enhance the thermal performance with the same percentage. In addition, the thermal performance of the enhanced TPTHP is not/a little influence due to the variation of the filling ratio.