Onset of Nucleate Boiling for subcooled flow through a one-side heated narrow rectangular channel

Al-Yahia, Omar S.,Jo, Daeseong Pergamon Press 2017 Annals of nuclear energy Vol. No.

<P><B>Abstract</B></P> <P>Onset of Nucleate Boiling (ONB) is an important limit in the design of nuclear reactors and most flow boiling systems. Preventing the ONB occurrence protects systems from unfavorable thermal hydraulic events, such as Onset of Flow Instability (OFI) and Critical Heat Flux (CHF). In this study, a simultaneous measurement and visualization experiment on the ONB is carried out for a narrow rectangular channel heated from one side. The rectangular channel has a thickness of 2.35mm, width of 54mm, and length of 560mm. The experiment is conducted for upward flow direction under nearly atmospheric pressure. The inlet conditions are chosen to cover a wide range of operational conditions: inlet temperature (35–65°C) and mass flow rate (0.015–0.130kg/s). Based on the inlet flow conditions, a uniform heat flux (50–800kW/m<SUP>2</SUP>) is applied in a stepwise manner to the heated surface. The slope of the wall temperature versus the heat flux curve decreases at the ONB point. Ten thermocouples (TCs) are installed into the heated block to measure the wall temperature distribution. On the other hand, a high-speed camera is used to visualize the ONB point and compare it with the wall temperature deviation point. Based on the experimental data, the influence of mass flow rate and inlet temperature on the bubble behavior along the test section is observed. The results show a new trend for the influence of inlet temperature on the superheated temperature of the wall at the ONB point. A similar trend is observed using CFX analysis for the test section. The present results are compared with other experimental studies conducted by different research institutes, with different ONB heat flux correlations such as in the studies of Jens and Lottes (1951), Bergles and Rohsenow (1964), and Thom et al. (1965). The correlations underestimate the experimental results. Therefore, a new correlation is developed to predict the ONB heat flux, which has good agreement with the experimental data within an error of ±16.5%.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Experimental study on ONB incipient for a narrow rectangular channel heated from one side has been conducted. </LI> <LI> Visualization method using a high-speed camera is consistent with wall temperature measurement method. </LI> <LI> A new trend is observed between inlet temperature and wall superheat temperature at ONB point. </LI> <LI> The influence of mass flux on the ONB heat flux, nucleating site density, and bubble departure diameter is observed. </LI> <LI> A new correlation is developed to predict the ONB heat flux. </LI> </UL> </P>

Bubble dynamic parameters during subcooled flow boiling under uniform and non-uniform transverse heat distribution

Al-Yahia, Omar S.,Yoon, Ho Joon,Jo, Daeseong Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.143 No.-

<P><B>Abstract</B></P> <P>Bubble behaviors and their interactions with each other affect the two-phase flow characteristics. In this study, experiments are conducted to investigate the bubble characteristics during subcooled flow boiling under uniform and non-uniform transverse heat flux distribution. The non-uniform heat flux distribution creates non-uniform bubble characteristics on the heated surface as opposed to under uniform heating. The working fluid is demineralized water that flows through a narrow rectangular channel heated from one side. The experimental loop used in the study operates at low pressure. A wide range of experimental operating conditions, such as inlet temperature (35–65 °C), thermal power (500–6250 W), and mass flow rates (0.03–0.13 kg/s), are applied to the upward flow channel. The bubble behaviors are visualized using a high-speed camera (2200 fps) at a resolution of 512 × 512 pixels. The results indicate that the bubbles exhibit different departure diameters, nucleation site density distributions, and bubble departure frequencies. In the uniform case, bubbles are generated uniformly across the whole transverse direction of the heated surface. In the non-uniform case, more bubbles are generated where the heat flux is concentrated, which disturbs the flow velocity profile in the transverse direction. The differences in bubble generation in the transverse direction result in differences in the two-phase flow instability through the heated channel. As a result, new empirical correlations are proposed based on the experimental results to estimate the bubble departure diameter, nucleation site density, and bubble departure frequency. The correlations are applicable for both heated surface conditions, uniform and non-uniform, under low-pressure conditions. CFD analysis using ANSYS FLUENT incorporates the RPI wall boiling model is conducted to validate the empirical correlations. Comparison of the CFD calculations with the experimental data for void fraction, wall temperature, and bulk temperature show good agreement. The simulation results show an accurate prediction of the ONB (Onset of Nucleate Boiling) and OFI (Onset of Flow Instability).</P> <P><B>Highlights</B></P> <P> <UL> <LI> Bubble behaviors have a significant influence on two-phase flow. </LI> <LI> Numerous discrepancies in the bubble parameters appear at different heating conditions. </LI> <LI> Bubble parameters are highly dependent on the local thermal hydraulic parameters. </LI> <LI> Accurate prediction of bubble parameters is critical for two-phase modeling. </LI> <LI> New empirical correlations can accurately predict the bubble parameters under uniform and non-uniform heating cases. </LI> </UL> </P>

Flow Instability (FI) for subcooled flow boiling through a narrow rectangular channel under transversely uniform and non-uniform heat flux

Al-Yahia, Omar S.,Kim, Taewoo,Jo, Daeseong Elsevier 2018 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.125 No.-

<P><B>Abstract</B></P> <P>Transversely non-uniform heating enforces high local heat fluxes at a few areas on the heated surface and low local heat fluxes at others. Differences in the heat flux distribution may generate differences in the boiling behavior when compared with that under uniform heating. Thus, the present experiments investigate the influence of transverse heat flux distribution on the flow instability through a narrow rectangular channel (2.35 mm × 54.0 mm × 566 mm). A wide range of experimental operation conditions, such as inlet temperatures (35–65 °C), thermal power (500–6250 W), and mass flow rates (0.03–0.13 kg/s), are applied to the upward flow channel. The working fluid corresponds to demineralized water under atmospheric pressure. The channel is heated from a side, and the other side is a transparent polycarbonate window from which the bubble behavior is visualized by using a high-speed camera. The heating surface is composed of aluminum with a width of 50 mm and a length of 300 mm. The experiments are performed by using two different procedures to achieve the flow instability, namely (1) constant mass flow rate with power increases and (2) constant power with mass flow rate decreases. The results show that the flow instability occurs at similar thermal power and similar mass flow rates for both uniform and non-uniform heating conditions. However, the pressure drop and wall temperature curves exhibit differences in the trends between the two heating conditions, especially after the fluctuation in the inlet pressure. In the uniform case, bubbles are generated uniformly on the whole transverse direction of the heated surface. In the non-uniform case, more bubbles are generated at the higher local heat flux, which disturbs the velocity profile in the transverse direction. The differences in bubble generation in the transverse direction leads to differences in the flow instability in a narrow rectangular channel.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Heat flux distribution has no effect under single-phase flow. </LI> <LI> Heat flux distribution has a high influence on the first bubble generation. </LI> <LI> Pressure drop trend is different between uniformly and non-uniformly heating conditions. </LI> <LI> Inlet pressure fluctuates after significant bubble generation. </LI> <LI> Void fraction oscillation is affected by the heat flux distribution. </LI> </UL> </P>

ONB, OSV, and OFI for subcooled flow boiling through a narrow rectangular channel heated on one-side

Al-Yahia, Omar S.,Jo, Daeseong Pergamon Press 2018 International journal of heat and mass transfer Vol. No.

<P><B>Abstract</B></P> <P>This paper presents an experimental investigation of the thermal hydraulic thresholds of the subcooled boiling instability in forced convective flow, such as the onset of nucleate boiling (ONB), the onset of significant void (OSV), and the onset of flow instability (OFI). The experiment was constrained to water flows in the upward direction under atmospheric pressure through a narrow rectangular channel heated on one-side having a gap of 2.35mm, a width of 54mm, and length of 566mm. The heated length and width were 300mm and 50 mm, respectively. The experiment was performed over a wide range of inlet temperature (35–65°C), mass fluxes (118–1400kg/(m<SUP>2</SUP>s)), and heat fluxes (50–650kW/m<SUP>2</SUP>). Two experimental methods were adopted to achieve and identify the ONB, OSV, and OFI: (1) the constant mass flow rate approach and (2) the constant heat flux approach. The results showed consistency between the two methods. The ONB was identified through visualized monitoring using a high-speed camera and by using the slope of the wall temperature deviation method. The ONB was predicted by Jens and Lottes’ correlation. The OSV was detected using the high-speed camera and the wall temperature–heat flux curve. Based on the experimental method, the OFI was identified using pressure drop and inlet pressure fluctuation. The data showed that the OSV and OFI could occur at similar points based on the experimental conditions. Furthermore, the OSV models, such as the modified Bowring model and Saha and Zuber’s model, can be used to predict the OFI. Additionally, some OFI correlations showed good agreement with the present data. However, many other correlations underestimated the OFI results, which might have been a result of differences in the experimental parameters. Therefore, a new empirical correlation that predicted the present data and other experimental data within very good accuracy was suggested. The present study describes and discusses the influence of the experimental parameters; inlet subcooling, mass flow rate, and the imposed heat flux on the ONB, OSV, and OFI incipience.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Experimental study on ONB, OSV, and OFI incipient for a narrow rectangular channel heated from one side has been conducted. </LI> <LI> Constant mass flux approach is consistent with constant heat flux approach. </LI> <LI> ONB occurs earlier than OSV and OFI, however, OSV and OFI may occur at the same moment. </LI> <LI> The influence of mass flux, heat flux, and inlet subcooled temperature on the ONB, OFI phenomena is observed. </LI> <LI> A new correlation is developed to predict the OFI mass flux and OFI heat flux. </LI> </UL> </P>

Transient analyses of the Jordanian 5MW research reactor under LOEP accident

Al-Yahia, O.S.,Lee, H.,Jo, D. Pergamon Press ; Elsevier Science Ltd 2016 Annals of nuclear energy Vol.87 No.2

The Jordanian 5MW 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 3kPa, (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 1.5kPa, 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.

Experimental study of bubble flow behavior during flow instability under uniform and non-uniform transverse heat distribution

Al-Yahia, Omar S.,Yoon, Ho Joon,Jo, Daeseong Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.12

Experiments are conducted to study bubble flow behavior during the instability of subcooled boiling under uniform and non-uniform transverse heating. The non-uniform heat distribution introduces nonuniform bubble generation and condensation rates on the heated surface, which is different from the uniform heating. These bubble generation and condensation characteristics introduce a non-uniform local pressure distribution in the transverse direction, which creates an extra non-uniform pressure on the flowing bubbles. Therefore, different bubble flow behavior can be observed between uniform and non-uniform heating conditions. In the uniform heating, bubble velocity fluctuations are low, and the bubbles travel straight along the axial direction. In the non-uniform heating, more fluctuation in the bubble velocity occurs at low mass flow rate and high subcooled inlet temperatures, and reverse flow is observed. Additionally, the bubbles show a zigzag trajectory when they pass through the channel, which indicates the existence of cross flow in the transverse direction.

Neutron diffraction studies of the Na-ion battery electrode materials NaCoCr₂(PO₄)₃, NaNiCr₂(PO₄)₃, and Na₂Ni₂Cr(PO₄)₃

Yahia, H.B.,Essehli, R.,Avdeev, M.,Park, J.B.,Sun, Y.K.,Al-Maadeed, M.A.,Belharouak, I. Academic Press 2016 Journal of solid state chemistry Vol.238 No.-

<P>The new compounds NaCoCr2(PO4)(3), NaNiCr2(PO4)(3), and Na2Ni2Cr(PO4)(3) were synthesized by sol-gel method and their crystal structures were determined by using neutron powder diffraction data. These compounds were characterized by galvanometric cycling and cyclic voltammetry. NaCoCr2(PO4)(3), NaNiCr2(PO4)(3), and Na2Ni2Cr(PO4)(3) crystallize with a stuffed alpha-CrPO4-type structure. The structure consists of a 3D-framework made of octahedra and tetrahedra that are sharing corners and/or edges generating channels along [100] and [010], in which the sodium atoms are located. Of significance, in the structures of NaNiCr2(PO4)(3), and Na2Ni2Cr(PO4)(3) a statistical disorder Ni2+/Cr3+ was observed on both the 8g and 4a atomic positions, whereas in NaCoCr2(PO4)(3) the statistical disorder Co2+/Cr3+ was only observed on the 8g atomic position. When tested as negative electrode materials, NaCoCr2(PO4)(3), NaNiCr2(PO4)(3), and Na2Ni2Cr(PO4)(3) delivered specific capacities of 352, 385, and 368 mA h g(-1), respectively, which attests to the electrochemical activity of sodium in these compounds. (C) 2016 Elsevier Inc. All rights reserved.</P>

Preparation of activated carbon from fly ash and its application for CO2 capture

Yahia Abobakor Alhamed,Sami Ullah Rather,Ahmad Hasan El-Shazly,Sharif Fakhruz Zaman,Mohammad Abdulrhaman Daous,Abdulrahim Ahmad Al-Zahrani 한국화학공학회 2015 Korean Journal of Chemical Engineering Vol.32 No.4

Power and desalination plants are one of the main anthropogenic sources for CO2 generation, which is oneof the key elements to cause greenhouse gas effect and thus contribute to the global warming. Fly ash (FA) generated indesalination and power plants was converted into activated carbon (AC) treated with KOH at higher temperature andtested for CO2 capturing efficiency. Morphological characteristics of FA such as BET specific surface area (SSA), porevolume, pore diameter, and pore size distribution (PSD) were performed using N2 adsorption isotherm. CO2 adsorptioncapacity and adsorption isotherms of CO2 over AC were measured by performing thermogravimetric analysis atdifferent temperatures. BET SSA of 161m2g−1 and adsorption capacity of 26mg CO2/g AC can be obtained by activationat KOH/FA ratio of 5 at 700 oC and activation time of 2 h. Therefore, great potential exists for producing AC fromFA, which will have the positive effect of reducing the landfill problem and global warming.

EXPERIMENTAL INVESTIGATION OF CONVECTIVE HEAT TRANSFER IN A NARROW RECTANGULAR CHANNEL FOR UPWARD AND DOWNWARD FLOWS

Jo, Daeseong,Al-Yahia, Omar S.,Altamimi, Raga'i M.,Park, Jonghark,Chae, Heetaek Korean Nuclear Society 2014 Nuclear Engineering and Technology Vol.46 No.2

Heat transfer characteristics in a narrow rectangular channel are experimentally investigated for upward and downward flows. The experimental data obtained are compared with existing data and predictions by many correlations. Based on the observations, there are differences from others: (1) there are no different heat transfer characteristics between upward and downward flows, (2) most of the existing correlations under-estimate heat transfer characteristics, and (3) existing correlations do not predict the high heat transfer in the entrance region for a wide range of Re. In addition, there are a few heat transfer correlations applicable to narrow rectangular channels. Therefore, a new set of correlations is proposed with and without consideration of the entrance region. Without consideration of the entrance region, heat transfer characteristics are expressed as a function of Re and Pr for turbulent flows, and as a function of Gz for laminar flows. The correlation proposed for turbulent and laminar flows has errors of ${\pm}18.25$ and ${\pm}13.62%$, respectively. With consideration of the entrance region, the heat transfer characteristics are expressed as a function of Re, Pr, and $z^*$ for both laminar and turbulent flows. The correlation for turbulent and laminar flows has errors of ${\pm}19.5$ and ${\pm}22.0%$, respectively.

Experimental study on the Onset of Nucleate Boiling in a narrow rectangular channel under transversely non-uniform and uniform heating

Kim, Taewoo,Al-Yahia, Omar S.,Jo, Daeseong Elsevier 2018 Experimental thermal and fluid science Vol.99 No.-

<P><B>Abstract</B></P> <P>Onset of Nucleate Boiling (ONB) in a narrow rectangular channel was experimentally studied under transversely non-uniform and uniform heating conditions. The experiment was performed under various mass fluxes and inlet subcooling conditions. The behavior of the bubbles was recorded using a high-speed camera, and was analyzed using an image processing technique. In the case of uniform heat flux, the wall temperature was uniformly distributed in the transverse direction. In the case of non-uniform heat flux, the wall temperature had the lowest value in the middle of the heated surface, and increased along the transverse direction toward the edges. At the same mass flux and inlet subcooling temperature, the thermal power at the ONB under non-uniform heat flux was lower than that under uniform heat flux. However, the local heat flux and wall temperature at the ONB were similar at both heating conditions. In the subcooled boiling region, it was found that the boiling heat transfer under non-uniform heat flux was lower than that under uniform heat flux. Additionally, the slope of the wall temperature-thermal power curve after the ONB was higher in the non-uniform heat flux case. Using the results elicited from image processing, the evaporation and quenching heat transfers were evaluated to analyze the differences in boiling heat transfers. The boiling heat transfer was less affected by evaporation and quenching in the case of non-uniform heat flux.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Experimental study on ONB in a narrow rectangular channel under transverse non-uniform heating. </LI> <LI> For uniform heating, wall temperature is uniformly distributed in transverse direction. </LI> <LI> For non-uniform heating, wall temperature increases along transverse direction toward the edges. </LI> <LI> For both heating conditions, local heat flux and wall temperature at ONB are similar. </LI> <LI> Evaporation and quenching heat transfers in non-uniform heating are approximately twice lower than in under uniform heating. </LI> </UL> </P>