[en] Highlights: •Smooth bubble condensation was examined in subcooled water. •Visual and acoustic analysis methods were used to examine the condensation phenomena. •Phase Interface Binarization determined bubble occurrence frequency, condensation time, and rising distance. •Tridimensional Reconstructing Assumption determined departure bubble size and condensation rate. •Acoustic analysis indicated differences in acoustic signals among various condensation conditions. -- Abstract: In this study, smooth bubble condensation that occurs in subcooled pool water was examined to understand condensation phenomena at the beginning of boiling. The behaviors of condensable and non-condensable bubbles were investigated with respect to various temperatures and bubble sizes. The experimental data were analyzed using visual and acoustic methods including Phase Interface Binarization (PIB), Tridimensional Reconstructing Assumption (TRA), and acoustic data conversion. For visual analyses, (1) the PIB method determined bubble departure frequency, condensation time, and rising distance, and (2) the TRA method determined departure bubble size and volume reduction rate. The bubble detached with smaller volume and occurred more frequently with a smaller nozzle and a higher subcooling degree. Because the condensation always occurred during the growth, necking, and detachment of a bubble, the bubble was detached before it grew sufficiently. Lower condensation time and rising distance were associated with higher subcooling degrees and smaller injected bubbles. With respect to the acoustic analysis, sound signals were measured using a hydrophone, and the obtained analog data were converted to sound pressure units. The results revealed that higher volume reduction rate resulted in stronger sound pressure. As a result, the condensation phenomena in the smooth bubble regime were visually observed, and the possibilities of acoustic monitoring for earlier boiling were investigated.

[en] The air-lift pump has been used in various applications with its merit that it can pump up without any moving parts. E.g. coffee percolator, petroleum industry, suction dredge, OTEC i.e. ocean thermal energy conversion and so on. By the merit, it has high durability for high temperature water or vapor, and fluid-solid mixture like waste water, muddy water and crude, which cause problems when it's pumped up with general pumps. In this regard, the air-lift pump has been one of the most desirable technology. A typical air-lift pump configuration is illustrated in Figure 01. The principle of this pump is very simple. When air is injected from the injector at bottom of a submerged tube, i.e., air bubbles are suspended in the liquid, the average density of the mixture in the tube is less than that of the surrounding fluid in the reservoir. Then hydrostatic pressure over the length of the tube is decreased. This buoyancy force causes a pumping action. The comparison of the simulated results, experimental result, and theoretical result is been able by data shown as Figure 04. They have similar trends but they also have a little differences because there are some limits of simulating the flow regimes. At the different flow condition, different coefficients for friction factor or pressure drop should be used, but this simulation uses a laminar condition and the theoretical equations are valid only for slug regime where the air flow rate is lower than the other regimes. From these causes, the differences has arisen, and difference comes bigger as the air flow rate increases, i.e., becoming annular flow regime or churn flow regime

[en] In the present study, the partial loss and distortion of turbine blades were acoustically detected while the turbine was rotating. An ultrasonic signal of a specific frequency (300 kHz) was transmitted in the form of continuous sine waves to the rotating turbine model. The signal was reflected on the turbine blade and received by a receiver. The amplitude of the given frequency component in the received signal was analyzed by signal processing. Because ultrasounds are attenuated easily when propagated into air and have a straight characteristic like light, the characteristics of the signals were examined by a quantitative test. The signal attenuation with respect to distance and the signal reduction by eccentricity were observed and compared with the experimental results. Partial loss decreased the sound reflection area; thus, the signal amplitude was reduced. The signal amplitude was inversely proportional to the size of the defect. Distortion caused larger eccentricity between the transmitter and the receiver. Weaker signals were detected with the more distorted blade. When the blade was distorted by more than 20 dg, the amplitude of the signal decreased significantly. In short, defects of turbine blades cause a reduction in the acoustic signal. It was verified that acoustic diagnosis can be applied to detect the partial loss and distortion of turbine blades.

[en] They investigated that the approximate bubble diameter and overall size in the upward heater surfaces are slightly larger than those in the downward heater surfaces. Nishikawa et al. observed remarkable effect on the low heat flux as the heater orientation increased, while no marked effect at high heat fluxes. Rainey and You investigated the effects of heater size and orientation on pool boiling heat transfer. The critical heat flux (qCHF) decreased with increasing heater size and orientation angle. The aim of present study is to investigate the bubble phenomena and CHF from horizontal, vertical, and inclined surfaces in a saturated pool. Several conclusions derived from this study are as follows; The CHF decreased with the increasing heater orientation from 0.deg. to 180.deg. angles. The maximum heat flux observed at 0.deg. orientation angle is 1.6 MW/m2, and decreased to 1.4 MW/m2, 1.2 MW/m2, 1.1 MW/m2 with the minimum CHF of 0.2 MW/m2 at 45.deg., 90.deg., 135.deg., and 180.deg. orientation angles respectively. The CHF data in the present study showed a good agreement with the correlations proposed by previous studies, which confirm that CHF is a strong function of heater orientation angle. In the upward facing orientation (at 0.deg. and 45.deg. angles), the buoyancy forces eliminated the vapor from the heater surface vertically. The behaviors of the bubble at various angle affected the bubble departure diameter. The bubbles that generated on the heater facing downward could not escape freely from the heated surface, the presence of the solid heater leads the bubble to drift upward before it detaches. For this reason, the bubble departure diameter on the heater facing downward is smaller compared to heater facing upward.

[en] Highlights: • Transient analyses are performed on the Jordanian 5 MW research reactor during LOEP. • Reactor behaviors are studied under various flap valve open conditions. • General behavior of the reactor during LOEP is similar. • Peak temperatures and flow inversion time are varied with flap valve opening criteria. - Abstract: The Jordanian 5 MW research reactor is simulated to investigate its transient behavior under a Loss Of Electric Power (LOEP) accident. The reactor cooling system is under downward force convection during normal operation, and upward natural convection through flap valves during training and shutdown modes. A coupled neutron kinetics and thermal hydraulic model is used to analyze the behavior of the reactor under various conditions: (1) a wide range of open positions of flap valves, with valve opening pressures ranging from 0.5 to 3 kPa, (2) three pump coastdown flow rates of 100%, 50%, and 25% of the nominal value, and (3) number of flap valves: one and two. As a reference, the evaluation of the reactor parameters in the hot and average assembly is performed when the pressure difference across the flap valves is reduced to 1.5 kPa, as the design value. The flow inversion times in the hot and average assembly are analyzed for all of the cases. The second temperature peaks of coolant and fuel are presented in the analysis. This study discusses the differences among these cases. The general behavior of the reactor during LOEP is similar, but there are variations in important parameters such as flap valve open time, flow inversion time, and maximum fuel and coolant temperatures.

[en] Highlights: • Effect of transverse power distribution on ONB incipient. • Uniform and non-uniform heat distribution is simulated in a narrow rectangular channel. • Simulations are performed using CFX and TMAP codes. • For uniform heating, ONB incipient by CFX occurs between predictions by TMAP analyses. • For non-uniform heating, ONB incipient by CFX occurs at a higher power than that by TMAP analysis. - Abstract: This study investigates the effect of transverse power distribution on the ONB (Onset of Nucleate Boiling) incipient. For this purpose, a subcooled boiling model with uniform and non-uniform heat flux distribution is simulated in a narrow vertical rectangular channel heated from both sides by applying a wide range of thermal power (8–16 kW). The simulations are performed using the CFX and TMAP codes. The CFX code incorporates both a two-fluid model and RPI wall boiling model to investigate coolant and wall temperature distributions along the heated channel. The TMAP code implements two different sets of heat transfer correlations to evaluate the wall temperature. The results obtained from the TMAP analyses show that the wall temperatures predicted by the Jo et al. heat transfer correlation are higher than the ones predicted by the Dittus and Boelter heat transfer correlation. The wall temperatures predicted by the CFX analyses lie between the predicted wall temperatures obtained by the TMAP analyses. Based on the superheated temperature on the heated surface, the ONB incipient is determined. The axial locations of the ONB incipient are predicted differently by the CFX and TMAP analyses. For uniform heating, the ONB incipient predicted by the CFX analysis occurs between the predictions made by the TMAP analyses. For non-uniform heating, the ONB incipient by the CFX analysis occurs at a higher power than the power required by the TMAP analyses.

[en] Highlights: • Neutronic and thermal hydraulic analyses of irradiated fuel plates for Molybdenum-99. • Heat production during and after irradiation was evaluated using MCNP and ORIGEN-APR. • Cooling capacities under various cooling conditions were evaluated using TMAP. • Natural convective cooling was adequate for the decay power after 0.03 h from withdrawal. • Maximum temperature of the target decayed for 24 h does not exceed the blistering threshold. - Abstract: Neutronic and thermal hydraulic analyses of irradiated fuel plates for Molybdenum-99 production in a research reactor were performed to investigate (1) the heat production during irradiation, (2) decay heat after irradiation, and (3) cooling capacities under various cooling conditions. The heat production on the target plates irradiated in the core was evaluated using the MCNP code. The decay heat after irradiation was evaluated using the ORIGEN-APR code, and compared against ANSI/ANS-5.1-1979. The cooling capacities of forced convective cooling during irradiation and natural convective cooling after irradiation were estimated using the TMAP code. An equilibrium core with different core statuses i.e., BOC, MOC, and EOC was used to evaluate power released from the targets and the axial power distribution. Based on the neutronic calculations, thermal margins i.e., the maximum wall temperature, minimum ONB temperature margin, and minimum CHF ratio were estimated, and the cooling strategy of the fission Mo targets was discussed. The targets were cooled by forced convective cooling during irradiation, and cooled by natural convective cooling after irradiation. For a further production process, the targets transported to a hot cell were exposed to the air, and cooled by natural convection cooling in air. As a result, the maximum wall temperature remained below the ONB temperature while the targets were under water, and the maximum wall temperature remained under the blistering limit while the targets were exposed to air

[en] Many researchers have investigated the Onset of Nucleate Boiling (ONB) in a narrow rectangular channel. The power released from the edge of plate-type fuel is higher than the middle of plate-type fuel. Al-Yahia et al. investi-gated the effect of transverse power distribution on the subcoold boiling in a narrow channel. They found different thermal-hydraulic characteristic between non-uniform and uniform power distribution. Thus, non-uniform heating must be considered in research reactors which use the plate-type fuel. The objective of this experimental study is to find the effect of transversely non-uniform heating on the ONB. The effect of transversely non-uniform heating on the ONB in a narrow rectangular channel is studied. The experiments under non-uniform and uniform heating are performed, and the results are compared. The thermal power at ONB is decreased under non-uniform heating. Since the non-uniform heating causes the local high heat flux and wall temperature, ONB occurs at relatively low thermal power compared to uniform heating condition. The local heat flux and wall temperature at ONB under non-uniform heating are similar with the results of uniform heating condition. Since bubble generation is depends on the local condition, under the same system condition, the non-uniform heating has no effect on the local heat flux and wall temperature at ONB.

[en] The location where the vapor bubble can first exist at the heated surface is called 'onset of nucleate boiling (ONB). The subcooled boiling is highly efficient to remove the heat owing to the high heat transfer coefficient. The heat transfer is affected by the motion of the bulk liquid as well as the latent heat transport of the liquid microlayer between the bubble and the heated wall. However, with increasing in the wall temperature, the bubble growth will increase and may they aggregate at the heated surface forming a vapor film, which will prevent the heat transport from the wall and that leads to highly rise in wall temperature. This phenomenon called departure from nucleate boiling (DNB). Many experimental and numerical CFD methods were carried out to investigate the subcooled boiling because of its importance in the industrial applications. In the present study, vertical narrow rectangular channel heated from both side was simulated by using CFX-14 to investigate the subcooled wall boiling, and identical simulation is done by using TMAP to compare the ONB location between numerical simulation and empirical correlations that implemented in TMAP. The numerical results using CFX-14 are discussed and compared with the results obtained from TMAP. The coolant temperature increases gradually (linearly) in the downward direction owing to the uniform applied heat flux.

[en] A research reactor core surrounded by a heavy water (D₂O) vessel uses heavy water as a reflector. A Heavy Water System (HWS) is installed to remove the heat generated in heavy water and the vessel itself. The HWS is separated from the primary cooling system of the core. Postulated Initiating Events (PIEs) in the HWS are evaluated for safety purposes. In the present study, transient thermal hydraulic analyses of HWS such as loss of heavy water flow owing to a pump failure, dilution of heavy water owing to a pipe rupture inside a pool, heavy water leakage owing to a pipe rupture outside a pool, and loss of heat removal owing to a secondary cooling system failure are analyzed