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[en] Mass transfer time relaxation parameters for condensation affect the amount of the mass transfer in the phase change. In the present study, a numerical investigation has been implemented with four different parameters for the condensation process in a thermosyphon, with the parameter of 0.1 for the evaporation process. The numerical results were compared with the experimental results to validate the numerical methods. When the mass transfer time relaxation parameter for the condensation was set to the value considering the density ratio out of the four parameters, the numerical result was in good agreement with the experimental result. This numerical process is expected to be used to predict the temperature distribution in the thermosyphon more accurately.
[en] A new experimental facility is being developed for materials irradiation and testing at the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor (HFIR). Details of this facility have been presented before. A prototype of this facility, the Thermosyphon Test Loop (TSTL) has been built, and experimental data have been obtained and analyzed. Pretest calculations for this facility with the RELAP5-3D code have been presented previously as well as other calculations with the TRACE code. The results of both codes were very different. RELAP5-3D predicted much higher pressures and temperatures than TRACE. This paper compares calculated results with the TSTL experimental data. Comparison of calculations with the codes RELAP5-3D and TRACE with experimental data of the new TSTL facility has shown that TRACE results agree well with the data and that RELAP5-3D calculates very high pressures and temperatures. The TRACE code is well suited to model this facility and is being used for future calculations. (authors)
[en] Two-phase closed thermosyphon (TPCT) is vertically oriented wickless heat pipe that has working fluid in the interior. The TPCT transports a large amount of heat from evaporator to condenser by phase change of working fluid, and the working fluid passively returns to evaporator by gravity. Due to these advantages of the TPCT, the TPCT is considered as method of PRHR (Passive Residual Heat Removal) system in nuclear system. Parametric studies have done to investigate the heat transfer characteristics of the TPCT. Different working fluids such as water, ethanol, methanol and acetone were used at various filling ratios and at different operating temperatures to find maximum heat transport capabilities of TPCT. Effect of heat transfer rate, filling ratio and aspect ratio were investigated. Inclined angle effect was investigated at several filling ratios and working fluids. This study is interested in silicon oil effect on the TPCT. To carry out the experiment, experimental apparatus is designed and manufactured. In design process, the TPCT operation limit is considered This study is interested in silicon oil effect on the TPCT. Experiments were carried out at three oil weight percent with three input power. Effect of oil on the TPCT is evaluated by inner wall temperature distribution and thermal resistance. In this study, silicon oil effect on TPCT was investigated. The TPCT was operated with several oil weight percent and input power. From experiment, overall, the silicon oil reduced evaporator thermal performance, but enhanced condenser thermal performance. However, the TPCT total thermal performance was reduced by 100 c St silicon oil
[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] 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)
[en] The critical heat fluxes (CHFs) of two-phase closed thermosyphons with and without fins were studied. The thermosyphons were fabricated using 1.25-mm-thick iron tubes with inner diameters of 16, 21 and 26 mm. The lengths of the evaporator, adiabatic, and condensation sections were 20, 10 and 20 cm, respectively. Pure water, ethanol, and R134a refrigerant were used as the working fluids with 50 % filling rate of the evaporation length. CHF data when using fins of different thicknesses (1.0, 1.5 and 2.0 mm), radii (5, 10 and 15 mm), and spacing (10, 20 and 30 mm) were recorded. The CHF increased with the fin thickness and radius but decreased with the increase in fin spacing. In addition, the CHF increased with the diameter of the thermosyphon tube. Overall, the CHF of thermosyphons with fins was higher than that of thermosyphons without fins regardless of the working fluid
[en] Highlights: • A shaft cooling structure is designed based on loop thermosyphons. • A single loop thermosyphon is studied during heating and cooling of the same tube. • The optimal liquid filling ratio is obtained under the special condition. • Cooling effects of the cooling structure are simulated on the motorized spindle. - Abstract: In this paper, a shaft cooling structure of a grinding motorized spindle was designed based on loop thermosyphons. The evaporation and condensation sections of the loop thermosyphons were located on the same tube due to the thermal conductivity of the shaft. The experimental studies on both heat transfer performance and start-up characteristics of a single loop thermosyphon were performed under the special condition. Then, the cooling effect on the shaft was simulated depending on the obtained experimental data. Results demonstrated that the optimal liquid filling rate of a loop thermosyphon ranged between 50 and 60% under the special condition. Furthermore, a critical value of heating power between 20 W and 40 W was found. When the heating power exceeded this value, the temperature of the evaporation section increased rapidly without any fluctuation. The violent fluctuation of temperature at the upper evaporation section could be utilized as an indicator for the heat transfer limit. Finally, according to the simulation, the maximum temperature of the motorized spindle was reduced by approximately 28% under the effect of the designed cooling structure.
[en] Passive cooling mechanism for a nuclear reactor has been proven to be very important since the Fukushima Daiichi Reactor accident that was caused by active cooling system malfunction due to total loss of electrical power source. In the Center for Nuclear Reactor Technology and Safety of BATAN, the cooling mechanism was studied by using a natural circulation test loop named FASSIP-01 that applied thermosyphon mechanism of water inside pipes of 1'' diameter. This study aimed to analytically predict the thermal characteristics of the loop including its response time towards steady condition using the MATLAB calculation program. This prediction derived the influence of several parameters such as the heat transfer coefficient of the cooler side (h-cooler), the heater power, the elevation difference between the heater and cooler (ΔZ), and the effects of the insulation thickness of pipe (IT) on the flowrate, temperature, and the heat power distribution across all components in the loop. The result showed that by avoiding boiling condition, for transferring the heater power of 1000 W and 2000 W, the needed h-cooler exceeds 200 and 400 W m-2 °C-1, respectively. For a h-cooler of 200 W m-2 °C-1, the circulation flow rate increased from 0.04 to 0.06 kg/s-1 for heater power increase from 1000 W to 2000 W. Those flow rates were decreased to 0.037 and 0.052 kg s-1 by increasing h-cooler to 1000 W m-2 °C-1. The results were in agreement with other studies on rectangular loops in the literature. The time needed to reach 95 % towards steady state was predicted to be more than 13 hours. Reduction of this time to less than five hours was possible by reducing the heater tank volume from 100 L to 30 L or by modifying the starting heater input power. (author)
[en] Study of the heat transfer characteristics of a Thermosyphon heat transport device, which can be employed for passive heat transfer, is taken up in the present paper. In the present work, a thermosyphon heat transport device designed at BARC is being considered for its performance evaluation. A CFD model was prepared and parametric studies have been conducted to determine the heat transport capacity of the device. Different parameters considered for parametric studies are hot fluid temperature, heated length and sleeve length. The frictional pressure drop inside the device is calculated empirically also and validated against the CFD results. The paper presents the results of the studies carried out with Lead-Bismuth eutectic as the working fluid. (author)