Heat Flow Research Articles

Numerical simulation of film boiling heat transfer in immersion quenching process using Eulerian two-fluid approach

This paper presents a Computational Fluid Dynamics (CFD) simulation of the quenching process based on ISO 9950, focusing on the heat flux and heat transfer coefficient integrated over a metal specimen. The numerical method, which employs the two-fluid VOF method and frozen turbulence approach (Cukrov et al., Appl. Sci. 2023, 13, 9144), is used for the transient simulation. Since quenching processes involve complex boiling phenomena shifting from film boiling to nucleate boiling, a standard method based on VOF cannot be applied. The comparison of the simulation results with the ones obtained using correlation, and the data obtained using the Inverse Heat Transfer Analysis (IHTA) method have revealed that the proposed method can accurately predict the heat flux and heat transfer coefficient in the film boiling regime of the immersion quenching process. Note that the previous paper (Cukrov et al., Energies. 2023, 16, 7926.) presented the immersion process modeling and the temperature distribution, while the current paper examines the heat transfer characteristics of the immersion quenching process.

Flow boiling of HFE-7100 for cooling Multi-Chip modules using manifold microchannels

Two-phase manifold microchannel heat sinks have gained significant interest for their efficient use of the coolant’s latent heat. Despite this, manifold microchannel flow boiling heat transfer has not yet been applied to wide-bandgap semiconductor power modules with multiple chips, primarily due to the complexity of the process and challenges related to electrical insulation. This study introduces a novel embedded manifold microchannel design that ensures uniform mass flow distribution, tailored for the thermal management of multi-chip power modules. The microchannels were laser-etched onto direct bonded copper (DBC) to reduce thermal resistance while maintaining electrical insulation. Thermal test vehicles (TTVs) for multi-chip power modules, featuring two different microchannel widths, were assembled using silver sintering. Experimental tests were then conducted using HFE-7100 as the coolant to evaluate two-phase heat dissipation performance. Results indicate that during flow boiling heat transfer, the temperature difference between chips in a power module strongly correlates with the exit quality. A higher coolant mass flow rate significantly reduces temperature variation between chips, particularly under high chip heat flux. At a coolant mass flow rate of 9 g/s, with a chip heat flux of 357 W/cm2 and total heat dissipation of 536 W, the minimum thermal resistance reached 0.15 cm2∙K/W, yielding a COP of 1391. With a slight sacrifice in thermal resistance, 0.17 cm2∙K/W and 0.20 cm2∙K/W were achieved at mass flow rates of 6 g/s and 3 g/s, respectively. Correspondingly, the COPs reached 2179 and 6749. This research offers valuable insights for applying flow boiling heat transfer with dielectric coolants to cool multi-chip power modules.

Vapor separation in minichannel heat sink flow boiling application using gradient porous copper ribs

The accumulation of a significant amount of vapor in minichannels severely limits their flow boiling heat transfer performance, posing a challenge for efficient thermal management in high-power electronic devices. To address this issue, we propose an innovative gradient porous copper rib minichannel with a vapor separation function. This design incorporates micro-pore porous copper and open-cell porous copper, where the unique structure of the micro-pore porous copper is crucial for achieving effective vapor separation. This innovative design not only expands the vapor discharge pathways within the minichannel but also significantly enhances the overall efficiency of vapor removal. Using water as the working fluid, flow boiling experiments were conducted across a range of mass fluxes (G = 26.1 kg/(m2s) ∼ 156.9 kg/(m2s)) and heat fluxes (qeff = 38.2 kW/m2 ∼ 267.5 kW/m2). The experimental results demonstrate that vapor separation significantly alleviates backflow and enhances heat transfer performance. Specifically, our findings indicate that the average temperature of the heat transfer surface decreases by 0 to 10 °C, while the maximum heat transfer coefficient increases by 2.3 times compared to conventional designs. This work presents a practical and innovative approach to mitigating vapor accumulation in minichannels, providing valuable insights for the design of high-performance minichannel heat sinks.

The Importance of Pocket Parks on Air Quality: A Comparative Approach

Population growth, increasing construction, and impervious surfaces are among the factors leading to the deterioration of the natural balance. Increasing population density has led to a gradual decrease in green areas for living spaces, transport routes and car parks. In addition, the rate of urbanisation and related environmental problems are one of the biggest threats to the sustainability of open green spaces. Accurate identification of problems, such as air, water, and soil pollution is critical to addressing current environmental problems and preventing future problems. Air pollution poses a significant threat to the global community and has sequential impacts on health systems, ecosystems and economies in both developed and developing countries. Cities are home to 50 per cent of the world's population and are expected to reach 70 per cent by 2050. The rapid urbanisation process leads to the transformation of natural and semi-natural landscapes into impervious surfaces and increased heat absorption rates. This study focuses on Jumeirah Island in Dubai. This artificial island is home to many businesses that support social life. Each café in these areas is located with public green areas in front of it and its own open spaces. In the study, 40 measurement points were established in two contrasting environmental conditions and air quality measurements were made manually. The stations are divided into blue and red stations and have contrasting characteristics. While the red measurement points have more green areas, water elements, qualified landscape texture, the blue measurement points have these characters to a lesser extent. Thanks to this comparison, the effect of vegetation texture and pocket parks on air quality in the study area was analysed. As a result of the analyses, the air quality in both areas was found to be good and acceptable, while the results at the red measurement points were found to be of better quality than the blue measurement stations. As a result of the study, the effect of water elements, qualified landscape design and vegetative texture on air quality has been proved with numerical data.

HEAT TRANSFER ANALYSIS AND TURBULENCE MODELS INVESTIGATION OF NUCLEATE BOILING FLOW IN NUCLEAR REACTOR APPLICATION

Boiling water exhibits an exceptionally high heat transfer coefficient, making it a valuable tool across numerous applications. However, once the heat flux surpasses a certain elevated threshold, the heated surface can no longer sustain continuous liquid contact. This is associated with a significant decline in heat transfer efficiency. The result may be a sudden spike in surface temperature within a heat flux-controlled system, or a dramatic decrease in power transferred in a temperature-controlled system. In the present study, the heat flux has been investigated in a circular channel heated by two roads. Parameters with emphasis on water flow velocity correlated with different heat transfer values from the roads. The methodology contains both laboratory experiments and a simulation model. The obtained results indicate that different heating surfaces play an important role in boiling heat transfer. Also, there is a clear relationship between the water flow and surface temperature. The amount of absorbed temperature increases by about 13% in a flow of 0.45 m/s. while in the water flow velocity 0.89 m/s and 1.34 m/s vary to 16.3% and17% respectively. The other impressive result is the phenomenon of alternate water temperature values due to certain regional temperatures. It's observed that there is a difference in heat absorption based on the amount of heat flux from the surface. The general rate of heat flux in the system was 6736.557 W/1°C for each square meter of heat generation. The obtained information is useful in controlling the boiling water reactor from sudden shutdown and also in controlling the boundaries in the design phase.<p> </p><p><strong> Article visualizations:</strong></p><p><img src="/-counters-/soc/0789/a.php" alt="Hit counter" /></p>

Thermal and hydrodynamic characteristics of microencapsulated phase change materials slurry flow in wavy microchannels

Microencapsulated phase change material slurry (MPCS) is a novel cooling fluid with promising performance. This study numerically investigates heat transfer and flow characteristics of MPCS within wavy microchannels. MPCS is modeled as a homogeneous, Newtonian fluid. Five wavy geometries were examined across a Reynolds number range of 50 to 250 (laminar flow regime), varying in amplitude and wavelength. The model results show that with increase in Reynolds number and decrease in the amplitude and radius of curvature of wavy microchannels, the pressure drop and Nusselt number also increase. Furthermore, the results reveal that Dean vortices intensify with increasing wave amplitude and Reynolds number. Conversely, these vortices weaken as channel wavelength and radius of curvature increase. The formation of Dean vortices enhances fluid mixing and consequently improves the thermal performance of the slurry. The study concludes that in wavy microchannels employing MPCS, increasing the Reynolds number, increasing the channel amplitude with respect to wavelength, and decreasing the radius of curvature improves the overall performance. Also, the results reveal that in higher Reynolds numbers, the radius of curvature is the most effective parameter on the overall performance of wavy microchannels.

Harmonic and Heat Flow Representations of the Gaussian White Noise

Harmonic and Heat Flow Representations of the Gaussian White Noise

Temperature‐dependent heat transfer deterioration in ordered graphene/ceramic composites

AbstractBoosting heat transfer of ultrahigh temperature ceramics (UHTCs) with dimensional‐crossover graphene has become an increasing challenge for improving the thermal protective performance of new‐generation spacecraft. Yet its characteristics of anisotropic and high interfacial thermal resistance inevitably cause heat transfer deterioration at high temperatures. Here we develop a few ZrB2/graphene/ZrB2 interface‐dominated diffuse models that are driven by bonding configurations and thermal converger. It has been found that forming stronger bonding configurations by Zr‐C interfacial bonding and designing a preferred thermal converger by ordered graphene are both unarguable ways of suppressing high‐temperature heat transfer deterioration. Each Zr‐C interfacial bonding serves as an independent sluice gate to accelerate heat flow. More high‐frequency phonons are excited at high temperature, which augments the interfacial thermal conductance from 38.5 to 335.4 MW·m−2·K−1 at 700 K. Impressively, a concept of thermal converger inspires us to adopt ordered graphene for changing the diverging behavior in isotropic ZrB2 composites. Its convergent process combines with anisotropic characteristics to transform the isotropic heat flow into the highly ordered graphene. Their thermal conductance can be regulated from minimum (2.5) to maximum (80.8 W·m−1·K−1) by rotating the ordered graphene from 90° to 7.5°. This work paves an optimal way for manipulating the heat transfer of UHTCs.

Study on the Effect of Heat Transfer Characteristics of Energy Piles

The thermal performance of energy piles equipped with new metal fins to improve heat transmission is examined in this research. The solid heat transfer module of COMSOL Multiphysics was used to create a 2D numerical model of the energy pile, utilizing the energy pile at a field test site in Nanjing as an example. By contrasting the experimental data, the COMSOL Multiphysics model’s correctness was confirmed. After that, a new kind of energy pile fin was created to improve the heat transfer of the pile. The impact of the new fin type on the energy pile’s heat transfer efficiency was assessed, and the temperature change within the soil surrounding the pile before and after the fin was set was examined by contrasting the parameters of pipe configuration, buried pipe depth, and concrete thermal conductivity. The results indicate that after setting the fins to run for 336 h, the temperature of the concrete area increases by 10.8% to 12.3%, and the temperature of the region surrounding the pile increases by 5.3% to 8.7% when the tube diameter is chosen to be between 20 and 40 mm; The fins maximize the heat transfer temperature between the surrounding soil and the concrete, and as the tube diameter increases, the temperature drops. For 336 h of pile operation, the temperature of the concrete may be raised by 10.8% to 12.3% after the fins are set, and the temperature around the pile can be raised by 5.3% to 8.7%. The heat transmission efficiency of the energy pile can be improved by raising the temperature of the soil surrounding the pile through an increase in the concrete’s thermal conductivity; however, the degree of improvement diminishes as the conductivity rises. It is intended that this study will offer insightful information on the best way to design energy pile heat transfer efficiency.

Dicke superradiant heat current enhancement in circuit quantum electrodynamics

Controlling the flow of energy and heat at the microscale is crucial to achieve energy-efficient quantum technologies, for on-chip thermal management, and to realize quantum heat engines and refrigerators. Yet, the efficiency of current quantum technologies is affected by thermal noise, and efficient cooling of quantum devices remains challenging in various solid-state implementations such as superconducting circuits. Collective effects, such as the Dicke superradiant emission, have been exploited to enhance the performance of quantum devices. However, the inherently transient nature of Dicke superradiant emission raises questions about its impact on steady-state properties. Here, we study how to enhance the steady-state heat current flowing between a hot bath and a cold bath through an ensemble of N qubits, that are collectively coupled to the thermal baths. Remarkably, we find a regime where the heat current scales quadratically with N in a finite-size scenario. Conversely, when approaching the thermodynamic limit, we prove that the collective scenario exhibits a parametric enhancement over the noncollective case. We then consider the presence of a third uncontrolled bath, interacting locally with each qubit, that models unavoidable couplings to the external environment. Despite having a nonperturbative effect on the steady-state currents, we show that the collective enhancement is robust to such an addition. Finally, we discuss the feasibility of realizing such a Dicke heat valve with superconducting circuits. Our findings indicate that in a minimal realistic experimental setting with two superconducting qubits, the collective advantage offers an enhancement of approximately 10% compared to the noncollective scenario. Published by the American Physical Society 2024

Tectonostratigraphic models of an extensional back-arc basin: inferences for the evolution of the Pannonian Basin System

The subsidence history and sedimentary architecture of extensional basins are controlled by the interplay between tectonics, mantle dynamics and climatic variations. Observations from outcrop to regional seismic scales coupled with numerical modelling techniques, including basin-scale stratigraphic, crustal-scale tectonic and mantle-scale subduction models, contribute to the quantification of basin evolution. Here, we review and discuss both tectonic and stratigraphic applications of such models and compare them with observations from the Pannonian Basin system of Central Europe. We show that diachronous localization of back-arc extension, crustal thinning, asthenospheric upwelling and subsequent thermal relaxation are superimposed on an overall slow plate convergence. These processes result in contrasting subsidence and uplift patterns and a variable heat flow evolution in different parts of the basin system. The crustal stress-field of the sub-basins does not always reflect their contrasting vertical motions. Extensional deformation generally migrates from the basin margins towards the basin centre. Structural inversion is localized along hot and weak inherited zones from the Middle Miocene to Present. Tectonic subsidence focuses sedimentation along deep depocentres, sourced by exhumed footwalls and from the neighbouring orogens. The overall post-rift sediment progradation is influenced by inherited bathymetries from the preceding syn-rift stage and by enhanced differential vertical motions.

Thermal characterization methodologies for experimental minichannel heat sink designs in printed circuit board assemblies

There has been a growing demand for novel, highly efficient, power-saving cooling solutions in recent years. In many cases, standard cooling techniques offer only limited opportunities to prevent the overheating of circuits. Such issues concern high-speed Printed Circuit Board Assemblies (PCBA) in data centers and telecommunication racks, where the flow of the cooling medium is obstructed due to the lack of space. Size limitations can also be a serious problem when cooling high-power devices because the devices consume a large space. Since the heat sink-based cooling solutions and the sophisticated IC packages only deal with one possible heat flow path, we were given the idea of enhancing the secondary heat flow path towards the Printed Circuit Board (PCB). Led by this intention, the idea of creating an embedded minichannel system inside the circuit board and circulating the cooling agent was realized. Through this method, we could decrease the board-to-ambient thermal resistance significantly. This paper presents the demonstration and feasibility study of this method. One of the main aims of this study is to demonstrate the applicability of the proposed concept in PCBAs, where the primary concerns are the low-cost manufacturability and available space. The other goal is to create an adaptation of the standard thermal characterization methodologies to deal with the specific dissipating components in the PCBA demonstrators. In the first part, the manufacturing technology is elaborated on, and its efficiency is characterized by thermal transient testing and Computational Fluid Dynamics (CFD) simulations. For these use cases, it was noted that the cumulative thermal resistance decreased by approximately 60 % when a volumetric flow rate of 100 ccm was applied in the minichannels. In the second part, a more sophisticated technology demonstration is realized and characterized by adding the proposed embedded minichannel heat sink to an existing high-speed PCBA. A specific thermal transient testing was implemented specifically for this use case, and it was carried out on programmable logic devices by utilizing general-purpose programmable logic to construct the necessary measurement methods. In the future, this feature can be used in different logic circuit designs where it is not possible to determine the junction temperature directly.

Effect of agitation during the early-age hydration on thixotropy and morphology of cement paste

The effect of agitation during the early-age hydration on thixotropy and morphology of cement paste prepared with and without superplasticizers (SP) is investigated by applying penetration test, small amplitude oscillatory shear sweep test (SAOS), isothermal calorimetric test, scanning electron microscopy (SEM) and energy dispersive X-ray analyses (EDX). The results show that the agitation of cement paste during the induction period increases the heat flow rate and destroys existing structures of samples without changing the mineral composition of samples. Yet, if the agitation is applied during the acceleration period, the heat flow rate is significantly lowered and the morphology and mineral composition of samples undergo irreversible change, freshly formed syngenite is destroyed and no longer restored. The penetration force and the static yield stress grow linearly during the induction period and exponentially during the acceleration period. Agitation during the induction period destroys the structure, which causes the static yield stress and the penetration force values becoming nearly equal to zero. However, during the acceleration period, even after agitation the static yield stress and the penetration force exhibit high residual values, which indicates the impact of hydration to the structural build-up.

Experimental investigation of pool boiling on Ti-Cu composite coated surfaces prepared using Electric Discharge Coating

Boiling heat transfer has become a very potent two-phase heat transfer mechanism for cooling high heat-producing devices such as microelectronic devices, fusion reactors or turbine blades. Increasing research has shown that micro/nano-structures on surfaces increase the number of nucleation sites for bubble formation, which ultimately results in a major improvement in boiling performance. This led to studies on developing various coated surfaces in order to generate micro/nano-structures on surfaces. In the current study, microstructured boiling surfaces were prepared using the Electric Discharge Coating (EDC) process. Titanium-copper (Ti-Cu) composite microparticles were coated on copper surface under reverse polarity in the Electric Discharge Machine. Four surfaces were prepared by using current settings of 3 A, 4 A, 5 A and 6 A. It was followed by characterisation of the surfaces which included, wettability analysis, porosity, pore size estimation, mean roughness measurement and elemental analysis, in order to better understand the boiling results on the surfaces. The surfaces formed were hydrophilic in nature, with contact angles varying from 47° to 65°. Pool boiling were performed with the developed surfaces and critical heat flux (CHF) and nucleate boiling heat transfer coefficient (NBHTC) improvement of 37.17 % and 172 % respectively were observed with the best performing surface compared to the bare surface. The best performing surface was also compared with relevant published literature to determine its standing against the present state of the art.

Optimization Investigation of Bionic Fin Structure by Experimental and Numerical Modelling

Drawing inspiration from the fast-swimming shark’s structure and skin, we developed the bionic shark fin, featuring two distinct types: bionic curved fins and bionic curved slotted fins. The present study assessed the impact of mainstream Reynolds number, fin curvature, and fin slot thickness on thermal fluid performance. The findings demonstrated that the curved fin structure can enhance the fluid mixing, benefiting local thermal-hydraulic performance. Simultaneously, the slotted curved fins expanded the heat transfer surface area, and the local injection in slots significantly reduced hydraulic resistance, offering a novel solution for heat sink optimization. Optimal flow and heat transfer performance for bionic curved fins were achieved with the fin thickness of 2.4 mm, while for bionic curved slotted fins, the overall optimal thermal performance was attained with a fin thickness of 2.6 mm with the slot thickness of 1 mm. Overall, the bionic fins exhibited thermal performance improvements of 8.7% and 29% over straight fins, respectively. More importantly, the heat transfer and flow friction correlations with criterion of fin parameters were developed, and the robust predictive accuracy was verified.

Temperature Distribution in a Two-Scale Porous Structure of a Catalyst Made of Spherical Particles

The research deals with the determination of the temperature distribution in a two-stage porous catalytic medium when the heat flow passes through. The peculiarity of the proposed model of heat and mass transfer in a porous catalyst is to consider the change in the volume of the spherical particle that makes up the catalyst.A program for calculating the temperature distribution in a two-scale porous structure of a catalyst made of spherical particles that change in volume with time has been developed. It should be noted that the temperature gradient is rather high, and the temperature in the central region of the particle becomes high enough for the process of catalytic reaction initiation only after 3.25 s. The developed program together with analytical and empirical studies allow to find the range of temperature and time of heat treatment at which the given thermophysical characteristics of porous material will be observed.The work will be useful for engineers and scientists studying the problems of thermochemical reactors and heat transfer in catalytic fills.

An experimental investigation examining the usage of a hybrid nanofluid in an automobile radiator

Several modifications have been made to the radiator’s dimensions and materials as part of the evolution of the automotive cooling cycle. Coolant is an important factor that greatly affects the efficiency of the cooling cycle. In applications involving heat transmission, nanofluids have become a viable possibility coolant. Two distinct types of nanoparticles floating in the base fluid make up the hybrid nanofluid, a newly invented class of nanofluids. Tests of hybrid nanofluids as a working fluid substitute for conventional fluids have been assisted by the current study. In the radiator of a 2005 Honda, the MWCNT–Al2O3/water nanofluid was tested at various volumetric concentrations (Φ) using a 50:50 mixing ratio. The outcomes of the experiments were compared with those obtained by using pure water. The radiator’s performance was evaluated by adjusting the fluid flow rate and operating the fluid at two distinct temperatures (60, 80 °C). The outcomes demonstrated that the convection heat transfer coefficient increased with a ratio reached 28.5% over the distilled water at the same temperature and flow rate. Both effectiveness and the Nusselt number had improved, coming in at 22.54% and 23.74%, respectively. Depending on the fluid concentration there is an increase in the pressure drop up to 24% than ordinary fluid. It discovered considerable agreement between the research outcomes by comparing them with earlier publications. An experimental correlation was inferred from the results to estimate the Nusselt number as a function of the Reynolds number and (Φ).

Effects of Fly Ash Particle Size and Chemical Activators on the Hydration of High-Volume Fly Ash Mortars.

This study investigated the effects of the fly ash (FA) particle size and chemical activators on the hydration reactions of high-volume fly ash (HVFA) cement pastes and the mechanical properties of HVFA mortars, with five types of FA with varying proportions of particles smaller than 10 μm prepared to assess the influence of particle size. In addition, the effect of chemical admixtures on the early-age hydration of the HVFA cement paste was evaluated. Quartz powder with the same fineness as that of normal FA was prepared to specifically examine the pozzolanic reaction of FA. The hydration reactions of the HVFA cement pastes were analyzed using isothermal calorimetry to measure the heat of hydration for 72 h. The results showed that an increase in the contents of FA particles with a diameter lower than 10 μm increases specific heat flow. Chemical activators, including Na2SO4, triethanolamine (TEA), and triisopropanolamine (TIPA), promote early-age hydration of HVFA cement pastes. The mechanical properties of the HVFA mortar were evaluated by measuring its compressive strength at 3 d, 7 d, and 28 d, with the findings revealing that the compressive strength of HVFA mortar improved with an increased proportion of FA particles smaller than 10 μm. Na2SO4, TEA, and TIPA consistently increased the compressive strength of the HVFA mortars.

Impact of Thermal Energy on Water and Ethylene Glycol (50:50)-Based Rotating Hybrid Nanofluid Past A Riga Surface with Radiation, Homogeneous and Heterogeneous Reactions

Hybrid nanofluid is crucial in improving the efficiency of heat transmission in thermal engineering applications, particularly the cooling of electrical equipment, heat exchangers, fuel cells, printing machines, etc. This study sought to investigate the augmentation of heat and mass transmission by the use of a rotating hybrid nanofluid consisting of a mixture of gold and silver nanoparticles suspended in water and ethylene glycol (50:50) past a heated Riga surface with velocity slip and suction. The energy equation is constructed using nonlinear radiation and heat consumption. The impact of both homogeneous and heterogeneous processes on the hybrid nanofluid is also explored. The governing mathematical model begins with partial differential equations that are converted into ordinary differential equations using a suitable conversion technique. The results of numerical computations are recorded as graphs and tables using the bvp4c scheme in MATLAB. It is noticed that both directional velocities undergo significant negative changes as a result of enhanced values of the rotational parameter. The higher levels of the radiation parameter resulted in significant enhancements in the thermal profile. The falling behavior of the nanoparticle concentration profile is recorded against a greater quantity of both chemical reaction parameters. Based on our analysis, when the Biot number changes from 0.4 to 0.8, the most significant heat transmission gradient occurs.

The influence of lymphatic vessels on nanoparticle distribution and heat transfer within tissue

AbstractThis study analytically investigates the dynamics of nanoparticle transport within a three‐dimensional porous cylinder simulating a lymphatic vessel, without external heat sources. The governing equations and boundary conditions are transformed to yield a system of ordinary differential equations, which are solved numerically using MATLAB built‐in function, bvp4c. Key parameters are visually examined and physically interpreted in relation to temperature, velocity, concentration, and Nusselt number profiles. The study reveals that the distribution of temperature and Nusselt number are maximized by increasing the heat transfer coefficient, whereas NP concentration is increased by decreasing it. Furthermore, the Brownian motion parameter enhances both heat transmission and NP concentration. It is also observed that simpler extravasation into lymphatics decreases tissue nanoparticle levels and heat conduction. Ultimately, optimal intra‐lymphatic nanoparticle distribution pathways are achieved by specifically varying heat transfer and interstitial mass flux patterns. By simulating biological barriers and lymphatic drainage, this model enhances our understanding of the underlying transport mechanisms controlling nanoparticle mobilization.