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[en] Solar energy is one of the promising resources of renewable energy. It is of particular interest due to the energy shortage and environment pollution problems. Water heating by solar energy for domestic use is one of the most successful and feasible applications of solar energy. The thermosyphon SDHWS and the loop type thermosyphon systems are widely used for domestic hot water system. The loop type thermosyphon is a circulation device for transferring the heat produced at the evaporator area to the condenser area in the loop by a working fluid. The system has the advantage of high heat transfer rate. A phase change of the working fluid occurs at the evaporator section and the vapor is transported to the condenser by the density gradient. The loop type thermosyphon collector can be made of smaller area and has higher efficiency than the present thermosyphon SDHWS. In this study, the operating characteristics of various working fluids being used have been identified. The working fluids employed in the study were ethanol, water and a binary mixture of ethanol and water. The volume of working fluid used in this study were 30%, 40%, 50%, 60% and 70% of evaporator volume. An increased heat was applied with the increased volume of working fluid. It is observed that, in the thermosyphon with low volume of working fluid, such as 30% or 40%, the fluid was dried out. The average efficiency of the loop type thermosyphon was 46% with high solar irradiation and 43% with low irradiation. The flow pattern and mechanism of the heat transfer were identified through this study. Flow patterns of the binary mixture working fluid were also investigated, and the patterns were recorded in the camera. The system parameters were calculated using the thermal performance data. Modelling of the system was carried out using PSTAR method and TRNSYS program
[en] This paper presents an experimental investigation on the heat transfer characteristics of a vertical flat thermosyphon (VFT). Several tests were performed to assess the effects of filling ratios, hydraulic radius, working fluid, and aspect ratio (Le/4HR) at a vertical orientation on the heat transfer characteristics of the VFT. It was found that the filling ratios and hydraulic radius affect heat flux: while the aspect ratios of VFT increased, the heat flux decreased. In addition, the working fluid changed from water and ethanol to R123 as the heat flux increases
[en] This paper presents the results of an experimental study to investigate hoe the effectiveness of a commercial type two-phase thermosyphon coil loop run around air-to-air system using R-11 as its working fluid, will vary when subjected to changes in the temperature difference between hot and cold air streams for various air flow rates and for various amounts of working fluids resident in the evaporator
[en] Carbon steel is a sturdy but inexpensive material and is preferred to copper or stainless steel wherever a lower cost is desirable. However, carbon steel-water combination is known to be incompatible for heat pipes due to generation of non-condensible gases during operation. The life time of the carbon steel-water heat pipe was tested based on the Arrhenius model using accelerated life-test scheme. Mass generation of the non-condensible gas was estimated by measuring axial temperature distribution of the heat pipes. The test was conducted with 8 heat pipes and 2 thermosyphons with 1.2-m length and 2.54-cm outer diameter in an elevated temperature range, 165∼250 .deg. C. From the test results, the heat pipe with a chemical retardant added in the working fluid exhibited about 5 years of life time, which was much longer than the one without the additive.
[en] This study considers the transient physical phenomena in an open loop thermosyphon, where the wall heat conduction is coupled to the fluid hydrodynamics and heat transfer. Some simplifying assumptions allow a semi-analytical solution in several cases of practical importance. A U-shaped natural circulation loop open to the atmosphere and heated from one side is examined. The present analysis is applied to assess the performance of a natural convection system used for passive cooling of an advanced nuclear reactor containment. The present semi-analytical solution is found to favorably compare with a finite-difference solution of the full governing equations invoking the RELAP5/MOD2 code
[en] This study aims to experimentally investigate the heat transfer characteristics of a thermosyphon using nanofluids. A thermosyphon with three individual pipes, which share the internal volume of the evaporator section, was designed, and its performance was tested for various charge amounts, input powers of the evaporator section's heater, and concentrations of working fluids. The optimized charge amount of the thermosyphon using distilled water was 30%, and the thermal resistance of the thermosyphon with TiO2 nanofluid was 18.1% lower than that with Ag nanofluid. In addition, the heat transfer performance of the thermosyphon with TiO2 1% was optimized at an input power of 300W at the evaporator section's heater and a charge amount of 30%
[en] Highlights: • Annular thermosyphon shows higher heat transfer compared to concentric thermosyphon. • Annular thermosyphon requires new prediction model for flooding limit. • Fill ratio of working fluid affects the flooding limit of the annular thermosyphon. - Abstract: A passive in-core cooling system (PINCs) based on hybrid heat pipe can be adopted to enhance the passive safety of advanced nuclear power plants. A hybrid heat pipe is a heat transfer device that takes the dual roles of neutron absorption and heat removal by combining the functions of a heat pipe and a control rod. To observe the effect of neutron absorber material inside the heat pipe and fill ratio of the working fluid on the thermal performances of heat pipe including operation limit, an annular thermosyphon heat pipe (ATHP) that contains a neutron absorber inside a concentric thermosyphon heat pipe (CTHP) was experimentally studied in the condition of various fill ratios. The ATHP showed lower thermal resistances in the evaporator region with a maximum reduction of 20% compared to those of a CTHP. In terms of the operational limits, the ATHP showed a lower entrainment limit than the CTHP due to a smaller cross-section for vapor path in the evaporator region, which resulted in high shear at the vapor–liquid interface. In addition, increasing the fill ratio enhanced the entrainment limit by 18%.
[en] The R3B-Glad superconducting Magnet provides the field required for a large acceptance spectrometer, dedicated to the analysis of Reactions with Relativistic Radioactive ions Beams. In the framework of the FAIR Project to GSI and within NUSTAR physics program, the technical study started in 2006, and the engineering design is undertaken. One main feature of this butterfly-like magnet with graded, tilted and trapezoidal racetrack coils is the active shielding. It makes it possible to decreasing the field by two orders of magnitude within a 1.2 m length, despite the large opening on the outlet side of the magnet (around 0.8 square meters). The fringe field is lower than 20 mT in the target area beside the entry, while the main field is larger than 2 teslas, out of 2 m length. The other principal characteristics are as follows: first, a high level of magnetic forces (300 to 400 tons per meter), with little place to block the coils, requiring a very specific mechanical structure; then, the magnet protection system that is based on an external dump resistor, coupled to a strong quench-back effect, to prevent any damage of the coils which could be caused by the 24 MJ of stored energy; lastly, the indirect cooling of the cold mass with a two-phase helium thermosyphon. The overall size of the conical cryostat will be around 3.5 m long, 3.8 m high and 7 m broad. (authors)
[en] In typical pressurized water reactor (PWR), in case that one steam generator (SG) cannot be credited for the primary cooldown, it is necessary to homogenize primary coolant temperature among loops using at least one reactor coolant pump (RCP) for the plant cooldown. If the natural circulation condition is established due to unavailability of all the RCPs, the continuous cooldown using intact SGs causes to disturb the smooth depressurization because it leads to void generation in the top of the non-cooldown SG tube where the high temperature coolant is remained. For this purpose, W.Sakuma, et al. suggested the outline of asymmetric cooldown procedure without any RCPs restart. Since the suggested procedure is based on only one secondary condition (SG dry-out) of non-cooldown SG, and hence the impact of difference of the secondary condition should be investigated. In this paper, the sensitivity analyses were performed to confirm the impact on the asymmetric cooldown procedure , and consequently , it was confirmed that the coolable range used in the procedure was expanded if the water inventory exists in non-cooldown SG. Therefore it was concluded that the coolable range which was defined with the SG dry-out condition in non-cooldown SG can be conservatively applied for the operating procedure. (author)