Ratio Of Heat Flux Research Articles

Joule heating and buoyancy effects in electro-osmotic peristaltic transport of aqueous nanofluids through a microchannel with complex wave propagation

Electro-osmotic peristaltic transport of aqueous nanofluids in a two-dimensional micro-channel is examined analytically. Such flows arise in bio-mimetic pumping systems at the very small scale of interest in physiological treatment e.g. occular drug delivery systems. Complex waveforms are imposed at the walls to mimic sophisticated peristaltic wave propagation scenarios. Nano-particles are assumed to be in local thermal equilibrium. Joule electro-thermal heating is included. The dimensional conservation equations are linearized and transformed from the wave to the fixed (laboratory) frame under lubrication theory approximations. The emerging dimensionless model features a number of important thermo-physical, electrical and nanoscale parameter, namely thermal and solutal (basic density) Grashof numbers, nanoscale Brownian motion parameter, thermophoresis parameter, Helmholtz-Smoluchowski velocity (maximum electro-osmotic velocity), Debye electrokinetic length and Joule heating to surface heat flux ratio. Closed-form solutions are derived for the nano-particle volume fraction, temperature, axial velocity, averaged volumetric flow rate, pressure difference across one wavelength, skin friction (wall shear stress function), Nusselt number (wall heat transfer rate) and stream function distribution in the wave frame. The influence of selected parameters on these flow variables is studied with the aid of graphs. Bolus formation is also visualized and streamline distributions are observed to be strongly influenced and asymmetric in nature.

Experimental and Numerical Investigation of Convective Heat Transfer of Supercritical Carbon Dioxide at Low Mass Fluxes

Significant differences in the heat transfer behaviors of supercritical carbon dioxide in a heated channel have been observed at different mass fluxes. At low mass fluxes, a unique heat transfer characteristic is accompanied by a monotonously smooth temperature variation without any temperature peak, even though the ratio of heat flux to mass flux (q/G) is high. In this study, experimental and numerical investigations explore the hidden mechanism of the peculiar heat transfer characteristics of supercritical carbon dioxide at low mass fluxes in vertically upward tubes with inside diameters (ID) of 5 mm. The range of operating conditions examined within the study include a mass flux (G) between 0–200 kg/m2s, and a heat flux (q) of up to 120 kW/m2. The parametric effects within these experimental conditions were analyzed on the basis of the obtained heat transfer data. Furthermore, a qualitative modeling force analysis and quantitative numerical simulation of vertical flow at low mass flux reveal the heat transfer mechanism for these temperature profiles. In addition, the distribution of flow parameters and thermo-physical properties (such as shear stress, density, and specific heat) in the near-wall region were also studied. It is found that the heat transfer behavior of supercritical CO2 at low mass flux is similar to “film boiling” at subcritical pressure, where “vapor-like” fluid occupies the sublayer region. Due to reduced buoyancy, the fluid does not cause enough mixing/instability to bring it to the bulk flow.

Thermal-hydraulic analysis of research reactor core with different LEU fuel types using RELAP5

Abstract In the current work, comparisons between the core performances when using different LEU fuels are done. The fuels tested are UA1X-A1, U3O8-Al, and U3Si2-Al fuels with 19.7 % enrichment. Calculations are done using RELAP5 code to evaluate the thermal-hydraulic performance of the IAEA benchmark 10 MW reactor. First, a reassessment of the slow reactivity insertion transient with UA1X-A1 LEU fuel to compare the results with those reported in the IAEA TECDOC [1]. Then, comparisons between the thermal-hydraulic core performances when using the three LEU fuels are done. The assessment is performed at initial power of 1.0 W. The reactor power is calculated using the RELAP5 point kinetic model. The reactivity feedback, from changes in water density and fuel temperature, is considered for all cases. From the results it is noticed that U3Si2-Al fuel gives the best fuel performance since it has the minimum value of peak fuel temperature and the minimum peak clad surface temperature, as operating parameters. Also, it gives the maximum value of the Critical Heat Flux Ratio and the lowest tendency to flow instability occurrence.

Experimental and numerical heat transfer investigation of an impingement jet array with V-ribs on the target plate and on the impingement plate

The secondary vortex structure of an impingement jet system is enhanced by V-ribs on both the impingement and target plates. Numerical and experimental investigations are conducted to study the flow field and heat transfer resulting from V-rib turbulators in an impingement cooling configuration. Three different cases are tested: V-ribs on both the impingement and target plates (V-rib), V-ribs only on the impingement plate (V-rib-impingement) and V-ribs only on the target plate (V-rib-target). The experiment is carried out on a 9 by 9 inline impingement array test facility. For the transient measurements, narrow band thermochromic liquid crystals (TLC) and thermocouples are applied to obtain the local heat transfer distribution. Pressure taps are used to measure the pressure loss. The numerical simulation is carried out with ANSYS CFX 14, using a steady state Reynolds-Averaged Navier-Stokes (RANS) approach and the Shear Stress Transport (SST) turbulence model. All studies are done for a Reynolds number range of 15,000 to 35,000. There is a good overall agreement between the experimental and numerical results for the cases studied. The detailed flow field from the numerical simulation is used to understand and complement the phenomena observed in the experiment. The evaluation of the flow field confirms that the V-ribs enhance the secondary flow structure in the impingement system and induce a positive heat flux ratio compared to the baseline case. Both experimental and numerical results show a Nusselt number increase for the V-rib-impingement and V-rib configuration, with a highest Nusselt number ratio of 1.16. Notice that the experiment cannot take the rib part into account due to the invalid 1D semi-infinite wall assumption there, while the CFD simulation allows for the consideration of heat transfer on the rib surface and thus complements the heat flux data on the target plate. Depending on the configuration, the CFD simulation shows a heat flux ratio of 1.06–1.34. The pressure loss of the system is comparable to the case with a smooth impingement plate and a smooth target plate.

Caroli formalism in near-field heat transfer between parallel graphene sheets

In this work we conduct a close-up investigation into the nature of near-field heat transfer (NFHT) of two graphene sheets in parallel-plate geometry. We develop a fully microscopic and quantum approach using nonequilibrium Green's function method. A Caroli formula for heat flux is proposed and numerically verified. We show our near-field-to-black-body heat flux ratios generally exhibit $1/d^{\alpha}$ dependence, with an effective exponent $\alpha \approx 2.2$, at long distances exceeding 100 nm and up to one micron; in the opposite $d\rightarrow 0$ limit, the values converge to a range within an order of magnitude. We justify this feature by noting it is owing to the breakdown of local conductivity theory, which predicts a $1/d$ dependence. Furthermore, from the numerical result, we find in addition to thermal wavelength, $\lambda_{th}$, a shorter distance scale $\sim$ 10 - 100 nm, comparable to the graphene thermal length ($\hbar v_{F}/k_{B} T$) or Fermi wavelength ($k_{F}^{-1}$), marks the transition point between the short- and long-distance transfer behaviors; within that point, relatively large variation of heat flux in response to doping level becomes a typical characteristic. The emergence of such large variation is tied to relative NFHT contributions from the intra- and inter-band transitions. Beyond that point, scaling of thermal flux $\propto 1/d^{\alpha}$ can be generally observed.

Limit regimes of ice formation in turbulent supercooled water.

A study of ice formation in stationary turbulent conditions is carried out in various limit regimes of crystal growth, supercooling, and ice entrainment at the water surface. Analytical expressions for the temperature, salinity, and ice concentration mean profiles are provided, and the role of fluctuations in ice production is numerically quantified. Lower bounds on the ratio of sensible heat flux to latent heat flux to the atmosphere are derived and their dependence on key parameters such as salt rejection in freezing and ice entrainment in the water column is elucidated.

Dissipative particle dynamics investigation of heat transfer mechanisms in Al2O3-water nanofluid

The current paper applied dissipative particle dynamics (DPD) approach to investigate the effect of nanoparticles on the heat transfer mechanisms in natural convection using Al2O3-water nanofluids. The study investigated in detail the effect of nanoparticle concentration on the random heat flux (i.e., Brownian motion) and the total heat flux. The DPD model considered the viscosity and the thermal conductivity of the Al2O3-water nanofluid to be dual function of temperature and volume fraction of nanoparticles. The study covered a wide range of nanoparticles (1% ≤ φ ≤ 7%) and three Rayleigh numbers were considered, which are Ra = 104, Ra = 5 × 104, and Ra = 105. The DPD results predicted an enhancement in heat transfer due to the addition of nanoparticles. However, the results revealed that the relative of enhancement of the total heat flux in the cavity is more effective at low Rayleigh numbers than at high Rayleigh numbers. The regions around the hot wall of the cavity are found to experience the maximum enhancement in heat transfer in the cavity whereas the region adjacent to the cold wall experienced a deterioration in heat transfer due to the addition of nanoparticles. Also, the DPD results revealed that the role of Brownian motion in the vicinity of hot and cold walls was negligible where the ratio of random heat flux to the total heat flux was below 5%. However, this ratio reached a very large value around the center of the cavity and the bottom wall of the cavity, where this value at low Rayleigh number and high volume fraction of nanoparticles exceeded 65%. Moreover, the study revealed that the random heat flux enhances with increase of volume fraction of nanoparticles.

The eastern Tibetan Plateau geothermal belt, western China: Geology, geophysics, genesis, and hydrothermal system

The eastern Tibetan Plateau geothermal belt (ETGB), which is located in 98–102°E, 28–32°N, belongs to the eastern part of the Mediterranean–Himalayan geothermal belt. Recently, about 248 natural hot springs have been found in the ETGB. >60% of these springs have temperatures of >40°C, and 11 springs have temperature above the local water boiling point. Using the helium isotopic data, gravity, magnetic and seismic data, we analyzed the thermal structure and the relationship between hydrothermal activity and geothermal dynamics of the ETGB. Results show that: (1) the 248 springs can be divided into three geothermal fields: Kangding–Luhuo geothermal field (KGF), Litang–Ganzi geothermal field (LGF) and Batang–Xiangcheng geothermal field (BGF). The BGF and LGF have hot crust and warm mantle, and are characterized by the higher heat flux (66.26mW/m2), and higher ratios of crust-derived heat flux to total flux (47.46–60.62%). The KGF has cool crust and hot mantle, and is characterized by the higher heat flux and lower Qc/Qm; (2) there is a relatively 4–6m higher gravimetric geoid anomaly dome which is corresponding with the ETGB. And in hydrothermal activity areas of the BGF and LGF, there is a northwest – southeast-trending tensile stress area and the upper–middle crust uplift area; (3) an abnormal layer exists in the middle–lower crust at a depth of 13–30km beneath the ETGB, and this layer is 8–10km thick and is characterized by lower velocity (Vp<5.8km/s, Vs<3.2km/s), high Poisson's ratio (>2.5), high conductivity (~10Ω·m) and high temperature (850–1000°C). Finally, based on the heat source and geological and geophysical background, we propose Kangding-type and Batang-type hydrothermal system models in the ETGB.

Numerical Heat Transfer and Entropy Analysis on Liquid Slip Flows Through Parallel-Plate Microchannels

In this study, two-dimensional (2D) numerical simulations of liquid slip flows in parallel-plate microchannels have been performed to obtain heat transfer characteristics and entropy generation rate under asymmetric heating conditions. Heat transfer analysis has been conducted along with second-law analysis through utilizing temperature-dependent thermophysical properties. The results indicate that temperature-dependent thermophysical properties have a positive effect on convective heat transfer and entropy generation. Nusselt numbers of the upper and lower plates and global entropy generation rates are significantly affected by slip parameter and heat flux ratio. It is shown that Nusselt number of the lower plate may have very large but finite values at a specific heat flux ratio. This finding resembles to analytical solutions, where singularities leading to an infinite Nusselt number exist.

Quantifying Spatiotemporal Variations of Soil Moisture Control on Surface Energy Balance and Near-Surface Air Temperature

Abstract Soil moisture plays a crucial role for the energy partitioning at Earth’s surface. Changing fractions of latent and sensible heat fluxes caused by soil moisture variations can affect both near-surface air temperature and precipitation. In this study, a simple framework for the dependence of evaporative fraction (the ratio of latent heat flux over net radiation) on soil moisture is used to analyze spatial and temporal variations of land–atmosphere coupling and its effect on near-surface air temperature. Using three different data sources (two reanalysis datasets and one combination of different datasets), three key parameters for the relation between soil moisture and evaporative fraction are estimated: 1) the frequency of occurrence of different soil moisture regimes, 2) the sensitivity of evaporative fraction to soil moisture in the transitional soil moisture regime, and 3) the critical soil moisture value that separates soil moisture- and energy-limited evapotranspiration regimes. The results show that about 30%–60% (depending on the dataset) of the global land area is in the transitional regime during at least half of the year. Based on the identification of transitional regimes, the effect of changes in soil moisture on near-surface air temperature is analyzed. Typical soil moisture variations (standard deviation) can impact air temperature by up to 1.1–1.3 K, while changing soil moisture over its full range in the transitional regime can alter air temperature by up to 6–7 K. The results emphasize the role of soil moisture for atmosphere and climate and constitute a useful benchmark for the evaluation of the respective relationships in Earth system models.

What Determines the Distribution of Shallow Convective Mass Flux through a Cloud Base?

Abstract The distribution of cloud-base mass flux is studied using large-eddy simulations (LESs) of two reference cases: one representing conditions over the tropical ocean and another one representing midlatitude conditions over land. To examine what sets the difference between the two distributions, nine additional LES cases are set up as variations of the two reference cases. It is found that the total surface heat flux and its changes over the diurnal cycle do not influence the distribution shape. The latter is also not determined by the level of organization in the cloud field. It is instead determined by the ratio of the surface sensible heat flux to the latent heat flux, that is, the Bowen ratio B. This ratio sets the thermodynamic efficiency of the moist convective heat cycle, which determines the portion of the total surface heat flux that can be transformed into mechanical work of convection against mechanical dissipation. The thermodynamic moist heat cycle sets the average mass flux per cloud 〈m〉, and through 〈m〉 it also controls the shape of the distribution. An expression for 〈m〉 is derived based on the moist convective heat cycle and is evaluated against LES. This expression can be used in shallow cumulus parameterizations as a physical constraint on the mass flux distribution. The similarity between the mass flux and the cloud area distributions indicates that B also has a role in shaping the cloud area distribution, which could explain its different shapes and slopes observed in previous studies.

Effects of forest evapotranspiration on soil water budget and energy flux partitioning in a subalpine valley of China

Jiuzhaigou Valley (JZG) has been rated as World Heritage, National Nature Reserves and world-class places of interests, due to its fantastic beauty of water. In recent years, however, JZG is losing its beauty with runoff decreasing and stream drying up. An increase of evapotranspiration (ET) over the rehabilitating forest is assumed to be the main reason for runoff decreasing, however, this assumption remained untested for lack of long-term observing data. To test this assumption, a long-term field experiment was carried out from August 2013 to December 2015 in JZG over a typical secondary forest. Meteorological parameters and energy fluxes were measured by eddy covariance system, soil moisture by time-domain reflectometry probes, and ET by eddy covariance method and soil water budget. Results showed that (1) despite the limitation of high elevation, high atmospheric humidity and low annual air temperature, annual ET was quite large. It was 700mm and 739mm, respectively for 2014 and 2015, while the corresponding precipitation (P) was 1003mm and 782mm. ET/P was close or over 1, which meant that P was mostly used for forest ET and only a very small proportion of P contributed to runoff. (2) The ratio of latent heat flux (LE) to net radiation (Rn) was 0.69 and 0.75 in the growing season of 2014 and 2015, respectively. These high LE/Rn ratio values were considerably higher in JZG than in other areas of the Tibetan Plateau, which could be attributed to better forest rehabilitation in JZG. Our results also showed that ET at the forest site was limited by available energy. We conclude that ET in JZG was energy-limited, whereas forest ET consumed most precipitation. (3) The above assumption is verified to be true. The high ET rate after forest rehabilitation in JZG comes at a cost of decreasing runoff and leads to streams drying up. These results will be useful for sustainable managements of water and forest in JZG.

Energy balance and partitioning in partial plastic mulched and non-mulched maize fields on the Loess Plateau of China

Energy and water exchange processes between the land surface and atmosphere drive photosynthesis, evapotranspiration, sensible heat flux, energy storage in vegetation, and heating of the soil. Thus, understanding of energy exchange and partitioning is of importance for crop model development and water use efficiency improvement in raifed agro-ecosystems. The present study investigated the energy exchange and partitioning over rainfed maize croplands under two cultivation methods—conventional flat planting without mulching (CK) and a furrow-ridge system with plastic film partially mulching (MFR) for two growing seasons through synchronous measurements of eddy covariance system with multi micro-lysimeters on the eastern Loess Plateau of China, the effects of rainfall on the energy partitioning were also discussed. The results indicated that average energy balance closure were 0.89 and 0.84 for CK and MFR at half-hourly, 0.91 and 0.93 at daily interval, respectively. Each energy flux component presented typical diurnal variations during the entire growing stage, which was a single-peak curve. Latent heat flux (LE) showed typical seasonal variation that it increased during May to June, and reach a high value in July, then decreased gradually. However, compared to LE, sensible heat flux (H) and Bowen ratio showed a similar opposite trends, LE became the main consumer of available energy after maize plants grown quickly. LE of spring maize was the main component of net radiation (Rn), followed by H and soil heat flux (G), which accounted for 64.3%, 28.6%, and −0.2% for CK and 68.5%, 29.7%, and 0.1% for MFR in 2011, 56.8%, 20.1%, and 2.8% for CK and 58.0%, 25.5%, and 8.6% for MFR in 2012, respectively. Transpiration was the main component of LE, which accounted for 54.3%–76.6% of LE for the both treatments. Compared to the energy fluxes before rainfall, LE increased significantly while H and G decreased after rainfall in development stage, however in late stage, the changes in soil water content resulted by rainfall didn’t increase LE significantly for the both treatments due to the high canopy cover and senescent maize plants.

Neutronics and Safety Studies on a Research Reactor Concept for an Advanced Neutron Source

This paper presents preliminary neutronics and thermal hydraulics safety analysis results for a low-enriched uranium (LEU) fueled research reactor concept being studied at the National Institute of Standards and Technology (NIST). The main goal of this research reactor is to provide advanced sources for neutron scattering experiments with a particular emphasis given to high intensity cold neutron sources (CNSs). A tank-in-pool type reactor with an innovative horizontally split compact core was developed in order to maximize the yield of the thermal flux trap in the reflector area. The reactor concept considered a 20 MW thermal power and a 30-day operating cycle. For non-proliferation purposes, a LEU fuel (U3Si2-Al) with 19.75 wt% enrichment was used. The core performance characteristics of an equilibrium cycle with several representative burnup states—including startup and end of cycle—were obtained using the Monte Carlo–based code MCNP6. The estimated maximum perturbed thermal flux of the core is ~5.0 × 1014 n/cm2-s. The calculated brightness of the CNS demonstrates an average gain factor of ~4 compared to the current source operated at the existing NIST reactor. Sufficient reactivity control worth and shutdown margins were provided by hafnium control elements. Reactivity coefficients were evaluated to ensure negative feedback. Thermal hydraulics safety studies of the reactor were performed using the multi-channel safety analysis code PARET. Steady-state analysis shows that the peak cladding temperature and minimum critical heat flux ratio are less than design limits with sufficient safety margins. Detailed transient analyses for a couple of hypothetical design-basis accidents show that no fuel damage or cladding failure would occur with the protection of reactor scrams. All these study results suggest this new research reactor concept offers a demonstrable potential to greatly expand the cold neutron capability with a 20 MW power and certified LEU fuels.

Convective heat transfer in a porous-medium micro-annulus with effects of the boundary slip and the heat-flux asymmetry: An exact solution

Flow and heat transfer in a micro-annulus with the porous material is analytically investigated using local thermal equilibrium (LTE) and local thermal non-equilibrium (LTNE) models with effects of flow/thermal slips and asymmetric heat fluxes. Analytical solutions for velocity and temperatures are obtained. Effects of key factors on convective heat transfer are examined. An increase in the Knudsen number and the inverse of a modified Darcy number can homogenize the velocity. When heat flux (HF) ratio is –R2, the temperatures of solid and fluid show linear profiles. LTNE model must be considered for small duct scale, lower effective thermal conductivity ratio or poor local convective heat transfer between solid and fluid phases. A limit exists for heat transfer enhancement by homogenizing the flow field. Critical HF ratios corresponding to the asymptotic line are verified. The opposite effects of flow slip and thermal slip on heat transfer lead to the maximum heat transfer. This analytical solution predicts the thermal performance of porous medium micro-annulus in wide ranges of radius ratio, Knudsen number, and HF ratio.

Uncertainty assessment for loss of flow accident of a 5 MW pool-type research reactor

Best estimate plus uncertainty (BEPU) is a promising approach to the safety analysis of nuclear reactors, and the uncertainty calculation is a very important concern about it. BEPU ensures realistic safety margins and secures higher reactor effectiveness by adopting best-estimate codes and realistic input data with uncertainties, whereas the previous conservative analysis generates excessive conservatism by considering each input parameter separately. A loss of flow accident (LOFA) of a 5MW open-pool type research reactor was selected as a sample problem for a BEPU uncertainty assessment. We selected the failures of all primary cooling system (PCS) pumps, which would cause the abrupt reduction of flow and the reversal of core flow. The significant contributors to the reactor safety were identified and then input sets were sampled. For the uncertainty evaluation, 124 calculations were performed. This is the number of code runs required for a 95%/95% level with the 3rd order Wilk’s formula. The MOSAIQUE software developed by Korean Atomic Energy Research Institute (KAERI) was used for automated sampling of the uncertainty parameters, a global uncertainty calculation, and post processing of the results. The critical heat flux ratio (CHFR) and the fuel centerline temperature (FCT) were calculated at the 95%/95% level and were compared with those from conservative analyses. In addition, the impact of each design variables on the safety parameters was estimated by sensitivity analysis.

Multi-artery heat-pipe spreader: monolayer-wick receding meniscus transitions and optimal performance

For high heat flux and low thermal resistance, the multiple-artery heat-pipe spreader uses distributed high-permeability arteries (posts) for liquid supply and high-capillary pressure monolayer wick for liquid spreading and evaporation. Experiments indicate the receding meniscus transitions in monolayer play a role in sudden drop in thermal resistance prior to dryout. Using monolayer SEM images and the minimum surface energy principles, the meniscus dynamics up to dryout is analyzed, and the meniscus location, capillary pressure, effective thermal conductivity, and permeability are also predicted for heterogeneous, periodic sintered copper-particle (including bimodal particle size) unit cells. The liquid thickness is nonuniform within the heterogeneous unit cell, and with increase in the wick superheat local dryout occurs (meniscus snaps) in the loose-packed region influencing the wet-wick properties and the occurrence of the minimum thermal resistance. The monolayer wick continues to function under local dryout (away from post) until a receding dry front is formed followed by complete dryout. These predictions are in good agreement with experiments. The optimal wick thermal-hydraulic performance, i.e., dimensionless ratio of heat flux to thermal resistance (wick figure of merit Zm) is sought through analysis. The uniform, sintered, close-packed 30–50μm particles give the highest Zm over a range of superheat in the wet regime, and 30μm particles give a record low resistance near 2.5μK/(W/m2)

Numerical investigation of heat transfer in a micro-porous-channel under variable wall heat flux and variable wall temperature boundary conditions using local thermal non-equilibrium model with internal heat generation

The phenomenon of forced convective heat transfer with internal heat generation in a micro-channel filled with a porous material saturated with a rarefied gas is studied using finite element method by varying wall heat flux and wall temperature ratio under local thermal non-equilibrium (LTNE) conditions. The Darcy–Brinkman model is used to describe the flow inside the porous material. Numerical solutions are obtained for both the fluid and solid temperature distributions by considering the case A for variable wall heat fluxes, case B for variable wall temperature ratio and case C for temperature jump coefficient. The Nusselt number for the fluid at the channel walls is calculated. The effect of significant parameters such as Biot number, wall temperature ratio, fluid and solid internal heat generation, fluid to solid effective thermal conductivity ratio are discussed. Comparative study on Nusselt number is carried out in case A with constant wall heat flux as well as variable wall heat flux. The Nusselt numbers obtained for case B indicate a strong dependency on the variation of internal heat generation for Bi=0.5. The velocity slip coefficient is found to have negligible effect on the Nusselt numbers for all the three cases.

Simulation Research on the Thermal Performance of the Cooling Ceiling Embedded with Phase Change Material for Energy Storage

A radiant cooling ceiling which is embedded with capillary pipes and phase change material to store and supply cool was put forward. The mathematical model of such cooling ceiling which runs intermittently was set up to analyze its thermal performance. The influence of phase change material thermal storage performances on the average heat flux and energy storage ratio of the cooling ceiling was analyzed. The main factors affecting the thermal performance of the ceiling was obtained by sensitivity analysis. The cooling storage performance differences between the ceiling embedded with phase change material and the concrete ceiling were comparatively analyzed. The research results show that the energy storage ratio of the phase change energy storage ceiling is higher than that of the concrete ceiling.

Best estimate approach for the evaluation of critical heat flux phenomenon in the boiling water reactors

Abstract Because of the uncertainties associated with the definition of Critical Heat Flux (CHF), the best estimate approach should be used. In this paper the application of best-estimate approach for the analysis of CHF phenomenon in the boiling water reactors is presented. At first, the nodalization of RBMK-1500, BWR-5 and ABWR fuel assemblies were developed using RELAP5 code. Using developed models the CHF and Critical Heat Flux Ratio (CHFR) for different types of reactors were evaluated. The calculation results of CHF were compared with the well-known experimental data for light water reactors. The uncertainty and sensitivity analysis of ABWR 8 × 8 fuel assembly CHFR calculation result was performed using the GRS (Germany) methodology with the SUSA tool. Finally, the values of Minimum Critical Power Ratio (MCPR) were calculated for RBMK-1500, BWR-5 and ABWR fuel assemblies. The paper demonstrate how, using the results of sensitivity analysis, to receive the MCPR values, which covers all uncertainties ...