Top Cold Research Articles

Convection driven by a nonuniform radiative internal heat source in a cavity: Example of medical isotope production in liquid targets

In the present study we use two-dimensional direct numerical simulations (DNS) to understand the coupled heat transfer to fluid flow in a liquid target for the production of nuclear medicines. Fluid motion is driven by buoyancy created by heat generated by a proton beam. The internal heat source has a gaussian distribution in the vertical direction and a rapidly growing intensity in the horizontal direction until it reaches a range at the Bragg peak where the heating drops to zero. The structure of the heating imposes two convective cells, separated at the location of the range. We solve the governing fluid flow and energy equations in a square cavity subject to highly nonuniform internal heating generated by the energy deposition of a proton beam. While most studies of convection driven by an internal heat source in a fluid layer have been focused on a uniform heating of the fluid, our study shows that the nonuniformity in the heat source has important implications for the temperature and flow fields, the boundary heat fluxes, and the growth of convective instabilities in the flow. Interestingly, the scalings of the maximum and averaged temperatures with the Rayleigh number compare similarly to previously found power laws for uniformly heated fluid layers. At higher power levels, the layer of fluid near the top cold boundary becomes convectively unstable via Rayleigh–Taylor instabilities. By comparing the rate of growth of these instabilities to their rate of advection to the boundaries of the cavity, a model is developed that predicts the instability of the convective cells for different values of the range of the beam and the Rayleigh number. Crucially, we demonstrate that the disturbances in the production of isotopes due to convective instabilities and the design of the cooling system is dependent on the location of the Bragg peak and must be considered in design of future generation of this class of target.

The contradiction between lithospheric thermal and seismic structures reveals a nonsteady thermal state – A case study from Northeast China

The nature of the lithosphere, as the outermost layer of the solid Earth, has long been a focus of the Earth sciences. Many methods have been used to study the properties and structure of the lithosphere, including gravity, magnetism, electricity, seismic, and geothermics. Since the 1970 s, a coupled heat-flow heat-production steady-state model has been employed to study the thermal structure of the continental lithosphere and has helped researchers explain many geothermal observations. However, the steady-state model does not work well in some areas. Taking Northeast China as a case study, we systematically calculated the lithospheric thermal structure, compared the result with seismic research, and concluded that the lithospheric thermal state is nonsteady in the southern Songliao Basin, the southern Greater Xing’an Range and the Changbai Volcano. The lithosphere in southern Songliao Basin features a hot top and a cold bottom. The lithosphere in southern Greater Xing’an Range and the Changbai Volcano feature a cold top and a hot bottom. Our numerical simulation has demonstrated that the response of surface heat flow to thermal disturbance at the bottom of the lithosphere often lags by more than 20 Myr, resulting in a significant disparity between the thermal structure calculated based on surface heat flow and the velocity structure of seismic waves. In addition, this study of the thermal structure in Northeast China shows that the temperature of the Moho in Songliao Basin is very high (>600 °C), which may be an important cause of the lack of Cenozoic volcanism in the Songliao Basin.

Mixed convection characteristics in a long horizontal lid‐driven channel with periodically distributed local flow modulators

AbstractThis study explores the effectiveness of periodically placed rotating blades in enhancing heat transfer in a channel. The channel consists of a cold top plate moving at a constant speed and a fixed hot plate at the bottom. Thin rotating blades are placed periodically along the channel's centerline, with the spacing between their axes equal to the channel's height. This paper analyzes a transient, two‐dimensional, laminar flow problem using energy, momentum, and continuity equations. To address the challenges posed by moving blades, the Galerkin finite element method is implemented within an arbitrary Lagrangian–Eulerian framework, employing a triangular mesh discretization scheme. This study comprehensively explores thermal and hydrodynamic characteristics, including overall heat transfer, thermal frequency, and power consumption of the rotating blade for heat transfer in mixed convection scenarios with Richardson numbers (Ri) ranging from 0.1 to 10 at varying rotational frequency of the blade. Outcomes demonstrate that the inclusion of a rotating blade increases heat transfer up to 50% at lower Ri, after which the impact of the rotating blade diminishes and heat transfer reduces up to 20% at higher Ri. In addition, heat transfer enhances with increasing blade frequency up to Ri = 6.5, beyond which the effect of the frequency overturns. Examining thermal and hydrodynamic characteristics reveals that the blade achieves optimal performance when operating at f = 1 and Ri = 3. The study's insights into mixed convection heat transfer offer versatile applications, benefiting industries and equipment such as electronic cooling, chemical reactors, food processing, material fabrication, solar collectors, and nuclear reactor systems. Moreover, the findings are instrumental in the thermal ventilation of buildings and the development of micro‐electromechanical systems.

Stability analysis of sheared thermal boundary layers and its implication for modelling turbulent Rayleigh–Bénard convection

Predicting the heat flux through a horizontal layer of fluid confined between a hot bottom plate and a cold top one has always spurred theoretical, numerical and experimental work on Rayleigh–Bénard convection. Customarily, the Nusselt number (the heat flux in non-dimensional form) has been modelled in the form of one or several power-laws of three parameters, the Rayleigh, Prandtl and Reynolds numbers. Quantifying the large-scale flow that spontaneously develops in a turbulent Rayleigh–Bénard cell, the Reynolds number, unlike the Rayleigh and Prandtl numbers, is not a control parameter strictly speaking and, depending on the model, is sought as another power-law or introduced as an external input. Whereas balancing the different transport mechanisms can predict the exponents in these power laws, experimental and numerical results are required to adjust the various prefactors. The early and simple model of Malkus (1954) and Howard (1966) assumed that the value of the Nusselt number could be directly deduced from the marginal stability of the two sheared thermal boundary layers along the upper and lower plates, interacting via the large-scale flow. Maintaining this simplicity, this work shows that in the classical regime of turbulent convection, considering the linear critical conditions of absolute (as opposed to convective) thermo-convective instabilities alleviates the flaws of the original model. Revisiting available Direct Numerical Simulations from which a Reynolds number can be unambiguously extracted, the present approach then yields the Nusselt number as a function of the Rayleigh and Prandtl numbers agreeing well with the numerical results.

Magneto-thermo-gravitational Rayleigh–Bénard convection of an electro-conductive micropolar fluid in a square enclosure: Finite volume computation

This article presents both a theoretical and a numerical analysis of thermo-gravitational magnetic convection in electro-conductive Eringen micropolar fluids in a two-dimensional enclosure. The computational regime is bound with cold top, hot bottoms, and adiabatic side walls. The governing equations were transformed via scaled variables into dimensionless partial differential equations. A Finite volume method (FVM) is used to get a solution of the computational regime. Validation of the FVM solutions is included for non-magnetic special case from the literature. Streamline contours, isotherm contours, iso-microrotation contours (lines of constant angular velocity) and local Nusselt number at the left hot wall is depicted graphically for the impact of Hartmann (magnetic) number (Ha), Prandtl number (Pr), micropolar parameter (K) and Rayleigh number (Ra). A significant modification in internal circulation and micro-rotation in addition to temperature distribution is observed with increasing vortex viscosity parameter. Significant warping of isotherms is induced with stronger magnetic field and the mushroom-shaped core structure encountered at weak magnetic field transitions to a sigmoidal topology.

Lattice Boltzmann simulation of natural convection heat transfer phenomenon for thermal management of multiple electronic components

Thermal management of electronic components is becoming a vital necessity in view of the rapid development of electronics technology. It is a concern imposed by the miniaturization of electronic chipsets. The present work addresses this issue numerically, using the lattice Boltzmann method (LBM). It consists of an air-filled heat sink containing multiple protruding electronic components. The problem is modelled using 2D continuity, momentum, and energy conservation equations. The thermal and dynamic fluid flow are analysed for various enclosure inclinations (0°, 45°, and 90°) and Rayleigh numbers (Ra=103-106). A twin protruding heat sources are considered at the bottom wall. The top cold wall can be at a uniform temperature (case 1) or consisting of two protruding sinks maintained at a constant temperature (case 2). The results showed that the maximum heat transfer rate corresponding to Nusselt number (Nu¯=5.51) is achieved for Ra=106 on the hot wall for the horizontal cavity in case 1, illustrating the cavity with top cold uniform wall. Indeed, the heat transfer is improved by 80% by varying the Rayleigh number (Ra) from 103 to 106. Furthermore, for case 2 with a twin cold protruding, a quite complicated heat transfer behaviour is observed on the hot wall. For Ra>106, the horizontal cavity outperforms the other cavities in terms of heat transfer rate, however the horizontal position is the less performant for Ra<104. With a horizontal disposition and Ra=106, the heat exchange ratio is improved by 32.32% in case 2 compared to case 1. The outcomes of this study provide insights into design and implementation of natural convection cooling solutions for electronic devices, which can have significant practical implications in various industries.

Heat transfer and flow patterns in a minichannel with various acoustic standing wave configurations and thermal boundary conditions

In this work, we investigate the effects of acoustic standing wave configurations and thermal boundary conditions on heat transfer and flow patterns in the minichannel cavity subjected to acoustic standing wave fields. Upon differential heating, the fluid properties such as density, speed of sound, and acoustic impedance become inhomogeneous. When this heated inhomogeneous fluid is subjected to acoustic fields, the resulting acoustic body force which is proportional to impedance gradient induces fluid convection and determines the heat transfer. We observed that the heat transfer and fluid motion vary significantly with respect to thermal boundary conditions, wavenumber (quarter, half, and full-wave), and direction of the standing wave; this can be attributed to the fact that the acoustic body force is strongly dependent on the position of inhomogeneity. We have studied 18 different combinations of wave configurations and thermal boundary conditions to understand their effects on heat transfer and flow patterns. It is observed that certain combinations favor heat transfer, whereas few others don't. The results of all the cases are explained clearly and compared with natural convection to understand the effectiveness of the heat transfer process due to the acoustic field. For both ethanol and water, maximum heat transfer is achieved when the acoustic standing full wave is applied perpendicular to the hot bottom plate and cold top plate, we obtained the maximum heat transfer increase of 3.18 times in ethanol and 2.49 times in water when compared to the natural convection. For ethanol, heat transfer is reduced to 0.21 times of natural convection, when the quarter-wave is applied parallel to the hot bottom plate and top cold plate such that node is at top plate and antinode is at the bottom plate. For water, heat transfer is reduced to 0.51 times of natural convection, when half-wave is applied parallel to the hot bottom plate and cold top plate.

Micropolar nanofluid thermal free convection and entropy generation through an inclined I-shaped enclosure with two hot cylinders

A numerical study is conducted to evaluate the flow, heat exchange and irreversibilities of micro-polar Al2O3-water nanofluid during the thermal buoyancy convection engendered by two heated cylinders inside an inclined I-shaped enclosure having cold top and bottom walls and adiabatic sidewalls. A numerical approach based on the finite element method was used to solve the equations that govern the phenomenon. For various scenarios for the position of the active cylinders and inclination angle of the system, the macro-flow and micro-rotations structures, temperature fields, the origin of entropy production, and heat exchange rates were determined for varied values of the control parameters, namely: Rayleigh (Ra), vortex viscosity parameter (K), geometric aspect ratio (AR), enclosure inclination angle (χ), and nanoparticles' concentration (φ). All of these variables were discovered to have significant influences on the strength of macro-and micro-nanofluid flows, as well as the entropy production and the rate of heat transfer. The rate of heat exchange escalates as the Ra and AR parameters rise but decreases when the K parameter rises.

Impact of Cooling on Water and Salt Migration of High-Chlorine Saline Soils

Secondary salinization is a common problem in saline soil projects. In order to grasp the mechanism of water and salt migration of high-chlorine saline soil during the cooling process, the saline soils along the Qarhan-Golmud Highway in the Qinghai-Tibet Plateau were selected as test samples. Firstly, the basic physical parameter test and the soluble salt chemical experiment were carried out and obtained liquid and plastic limits, dry density, etc. Secondly, freezing temperature experiments and water-salt migration experiments under one-way cooling conditions were conducted according to the actual environmental conditions, and after the temperature gradient line of the soil sample was stable, water content and labile salt chemistry experiments were conducted to obtain the distribution of water and salt contents of soil samples. Finally, the effect of crystallization-water phase transition on water and salt migration and the effect of chloride salt on the temperature of crystallization-water phase transition were considered, and a mathematical model applicable to the water and salt migration of highly chlorinated saline soils under the effect of unidirectional cooling was established and solved with COMSOL Multiphysics software, and the correctness of the model was verified by comparing the simulation results with the experimental results. The study found that (1) during the one-way cooling process, both water and salt showed a tendency to migrate to the cold end. The MC (saline soil with medium chlorine content) with an initial water content of 16.9% and Cl− content of 3.373% was measured to reach a 17.6% water content and 3.76% Cl− content at the cold (top) end after the experiment. The HC (saline soil with high chlorine content) with an initial water content of 6.6% and Cl− content of 17.928% was measured to reach a 6.83% water content and 18.8% Cl− content after the experiment and (2) after the one-way cooling experiment of the MC, the water content at a distance of 1–2 cm from the cold end has abrupt changes, which may be caused by a small amount of crystallization—water phase transition at this location. At the same time, according to the temperature change graph during the cooling process, the phase change temperature was set to −9°C in the numerical simulation process to match the experimental results.

A Taguchi approach for optimization of design parameters on Rayleigh-Bénard convection in water-based Al2O3 nanofluids

PurposeThis study aims to deal with the optimization of experimental parameters to obtain maximum heat transfer rate in a Rayleigh–Bénard enclosure filled with the water-based Al2O3 nanofluids using the Taguchi method.Design/methodology/approachThe particle size and particle concentration of the Al2O3 nanoparticles are 40 nm and 0.01 Vol. %, respectively. A two-step approach has been used to prepare the nanofluids of the required concentration by mixing the nanoparticles in the distilled water (DW). A Rayleigh–Bénard enclosure, having a hot bottom and a cold top copper plate with insulated side walls, is used for the experiments. Experiments have been conducted first with the DW, for the validation of experimental facility, and second with nanofluid (Al2O3 + DW), for the heat transfer improvement, at three different values of enclosure aspect ratios (ratio of height to width of an enclosure), i.e. 0.5, 1.0 and 1.5.FindingsSignal-to-noise ratio (SNR) analysis has been used to determine the optimal levels of design parameters and their contribution toward heat transfer augmentation. The heat transfer, i.e. Nusselt number, is determined for L9 (33) orthogonal array designed by Taguchi method along with corresponding SNR values. The SNR values are plotted for DW and nanofluid to study the effect of different parameters and to identify their optimal levels. It was found that the aspect ratio has the maximum contribution ratio of 78% for the nanofluid and 76.12% for the DW, followed by the heat flux and the height.Originality/valueThe present results demonstrated the great reliability of the Taguchi method in the optimization of the thermal system to save the time and cost of experiments.

TrackLace: Data Management for Interlaced Magnetic Recording

Interlaced Magnetic Recording (IMR) is a promising technology which achieves higher data density and lower write amplification (WA) than Shingled Magnetic Recording (SMR). In IMR, top tracks and bottom tracks are interlaced so each bottom track is partially overlapped with two adjacent top tracks. Top tracks can be updated without any WA, but bottom track updates require reading and rewriting of affected valid data on the two neighboring top tracks. There are few published studies discussing WA in IMR drives. We propose TrackLace to reduce WA for IMR. TrackLace consists of three techniques: Z-Alloc allocates user data to the tracks in alternating directions and spreads unallocated tracks among allocated tracks; Top-Buffer opportunistically utilizes unallocated top tracks to buffer bottom track updates; and Block-Swap progressively swaps bottom track hot data with top track cold data during high space utilization. To further optimize TrackLace performance, we propose a virtual frame design that can keep the relocated block (due to Top-Buffer or Block-Swap) close to its original location and an adaptive buffering mechanism that can avoid unnecessary redirections depending on the write locality. Evaluations show that TrackLace can reduce WA by 45 percent and lower average latency by 31percent compared with baseline schemes.

Develop lattice Boltzmann method and its related boundary conditions models for the benchmark oscillating walls by modifying hydrodynamic and thermal distribution functions

Preset works aim to develop the lattice Boltzmann method ability to simulate the periodic supposed problems. Hence, a two-dimensional rectangular enclosure is considered so that its top cold lid oscillates horizontally with time. The stationary sidewalls are kept insulated. It would be necessary to present an appropriate boundary condition model of LBM for the oscillating lid, based on the hydrodynamic and thermal distribution functions. The influences of various lid oscillation frequencies (Strouhal number) are investigated at different values of Richardson numbers at free, mixed and force convections states by using D2Q9 lattice. It is seen that the lid oscillation frequency effect is more significant at less amounts of Richardson number.

Effect of the aspect ratio of an elliptical cylinder on mixed convective heat transfer within a lid-driven enclosure

This study examines the mixed convection inside a lid-driven enclosure containing an elliptical cylinder for Reynolds numbers of 100 ≤ Re ≤ 1000. A simulation conducted to study the effects of the aspect ratio, and the temperature boundary conditions (θcyi = θC or θC/2) of the elliptical cylinder. The heat transfer performances rely on the relative magnitude of the viscous force caused by the top lid movement. Another factor is the buoyancy force that occurred due to the temperature difference between the heated bottom and the cold top walls, which also strongly depends on the aspect ratio. At Re = 500, the value of increased by about 7.6 % at θCyl = 0 and AR = 4.00 compared to the results of a circular cylinder (AR = 1.00). Moreover, a correlation has been proposed to estimate the Nusselt nuber for the geiven Reynolds number, aspect ratio, and the temperature of cylinder based on the power law model with a high goodness of curve fitting.

Flow visualization of Rayleigh–Bénard convection for cubical cavity

AbstractNatural convective flow of air inside the cubical cavity is investigated numerically. The temperature of the bottom wall is kept higher than that of top cold wall, and other four walls are assumed to be adiabatic. Attention has been paid to the convective discretization schemes, like upwind, QUICK, total variation diminishing, normalized variable diagram (NVD) schemes that are compared with respect to accuracy. The output is validated with respect to the results available in the literature. A parallel computing message passing interface code is adapted to run the simulations. From the results, it is observed that the NVD scheme gives better results among all the employed convective discretization schemes irrespective of the mesh structure. Thus, in this article, self filtered central differencing which is a family of NVD, is used. From the enormous output data, along with the streamlines, contours of isotherms, the new technique of energy pathlines, and field synergy are used to visualize the fluid flow and heat transfer mechanism arising in the system in the range of Ra from 103 to 106. Free energy streamlines are observed with small Ra, whereas trapped energy streamlines are observed with high Ra. When Ra increases, synergy angle increases and implies that the synergy between the velocity vector and temperature gradient gets reduced and leads to increasing values of average Nusselt number (Nu).

Mixed convection of power-law fluids in cylindrical enclosures with a cold rotating top cover and a stationary heated bottom wall

Steady-state laminar mixed convection in cylinders with a rotating top cold cover and a heated bottom has been numerically analysed for inelastic shear-thinning/shear-thickening fluids by applying power-law model of viscosity. In this analysis, axisymmetric incompressible flow simulations have been conducted for a range of different values of Reynolds, Richardson, Prandtl numbers (i.e. 500≤Re≤2000;0≤Ri≤1.0; 10≤Pr≤1000) and power-law index (i.e. 0.6≤n≤1.8) for an aspect ratio (height/radius) of unity (i.e. AR=1.0). The thermal convective transport has been found to strengthen with increasing Re and Pr, which in turn gives rise to an increase in the mean Nusselt number Nu‾. By contrast, an increase in Ri leads to a mild increase in Nu‾ for small Richardson number values but Nu‾ becomes insensitive to the changes in Ri for large Richardson numbers within the range of 0≤Ri≤1.0 for all values of n considered here. The mean Nusselt number Nu‾ exhibits a non-monotonic trend (i.e. increases before reaching a maximum followed by a decreasing trend) with the variation of n. The influences of Ra,Pr and Ri on the mean Nusselt number Nu‾ have been explained in terms of scaling arguments. The scaling relations along with the numerical findings have been utilised to propose a correlation for the mean Nusselt number for the configuration and the parameter range considered here.

Statistical properties of thermally expandable particles in soft-turbulence Rayleigh-B\xe9nard convection

.The dynamics of inertial particles in Rayleigh-Bénard convection, where both particles and fluid exhibit thermal expansion, is studied using direct numerical simulations (DNS) in the soft-turbulence regime. We consider the effect of particles with a thermal expansion coefficient larger than that of the fluid, causing particles to become lighter than the fluid near the hot bottom plate and heavier than the fluid near the cold top plate. Because of the opposite directions of the net Archimedes’ force on particles and fluid, particles deposited at the plate now experience a relative force towards the bulk. The characteristic time for this motion towards the bulk to happen, quantified as the time particles spend inside the thermal boundary layers (BLs) at the plates, is shown to depend on the thermal response time, tau_{T}, and the thermal expansion coefficient of particles relative to that of the fluid, K = alpha_{p}/alpha_{f}. In particular, the residence time is constant for small thermal response times, tau_{T} lesssim 1, and increasing with tau_{T} for larger thermal response times, tau_{T} gtrsim 1. Also, the thermal BL residence time is increasing with decreasing K. A one-dimensional (1D) model is developed, where particles experience thermal inertia and their motion is purely dependent on the buoyancy force. Although the values do not match one-to-one, this highly simplified 1D model does predict a regime of a constant thermal BL residence time for smaller thermal response times and a regime of increasing residence time with tau_{T} for larger response times, thus explaining the trends in the DNS data well.Graphical abstract

Role of fluid-structure interaction in mixed convection from a circular cylinder in a square enclosure with double flexible oscillating fins

The problem of unsteady mixed convection in a square enclosure containing a heated circular cylinder is studied in this paper. Two solid elastic thin fins are attached on the top cold wall. The governing equations for fluid flow and energy in the fluid and structures domains are written in Arbitrary Lagrangian-Eulerian (ALE) formulation. Finite element method was used to obtain the approximate solutions of the governing equation. The governing parameters considered are the oscillating fin direction, fin amplitude and length with various elasticity values and cylinder sizes. The results show that the instantaneous heat transfer characteristics of the contrary oscillation differs greatly from the identical oscillation. The influence of the elasticity value on the heat transfer rate is significant at a sufficiently small amplitude oscillation.

Fabrication and characterization of phase change nanofluid with high thermophysical properties for thermal energy storage

The thermophysical properties of water were modified by adding MWCNT and the organic PAAS. The effects of MWCNT and PAAS on supercooling degree and phase change characteristics of water were experimentally studied. The results showed that the length of the water phase change platform increases by 41% and decreases by 19.6% when concentration of PAAS is from 0 wt% to 2 wt% and 2 wt% to 5 wt%, respectively; The maximum supercooling degree declines up to 95% by adding MWCNT with the variations of particle size and concentration. The interfacial free energy at MWCNT outer diameter of 8–15 nm is approximately 1.75 and 2.14 larger than particle size of 20–40 nm and >50 nm. The temperature homogeneity of composite material is better than that of DW in application test, and the increased percentage of cold discharge time is less than that of the small dose experiments. The cold discharge time of the optimum PCM at top cold plate and other three positions are 81.8% and 35.3% higher than those of DW.

Heat transport in rotating-lid Rayleigh–Bénard convection

We perform a direct numerical simulation of three-dimensional Navier–Stokes equations for a Rayleigh–Bénard convection system in a stationary cylinder with the top cold lid rotating. This convection system with an imposed swirl flow is a canonical problem for investigating axial vortices under unstable thermal gradients. The base flow is established by rotating the top lid and the fluid moves azimuthally along the side vertical wall into a meridional flow in the r − z plane. This forms an axial vortex core at the axis of the cylinder. This axial core, under a certain rotational Reynolds number (Re), breaks down to a vortex breakdown bubble whose dynamics are modified under thermal convection. We study the effect of rotation on varying Re for a Rayleigh number Ra = 2 × 105. The equations are formulated in such a way that the rotating-lid cylinder and Rayleigh–Bénard convection are extreme cases of the same numerical set up. From the present study, we find that as the rotational rate is increased, the system dynamics shift from a convection-dominated flow regime to a rotation-dominated regime. This shift in dynamics is quantified using the volume-averaged and time-averaged temperature, the heat flux, the thickness of the Bödewadt boundary layer and the relative Nusselt number. These quantities are shown to demarcate the convection- and rotation-dominated regimes, as compared to the qualitative description of flow patterns from velocity and temperature contours.

Modeling lightning density using cloud top parameters

The Price-Rind 92 parameterization (Price and Rind, 1992) that utilizes cloud top height as predictor for the estimation of lightning density is widely used by modelers in an attempt to forecast electrical activity in thunderstorms. In the present paper new parameterizations for the estimation of lightning density of convective clouds are formulated. LINET lightning data, NWC SAF (Satellite Application Facility on support to Nowcasting and Very Short-Range Forecasting) products and ERA-Interim (ECMWF-Re Analysis) data, covering the summer of 2016 over continental Europe, are used. The proposed models estimate the lightning density of convective clouds, using cloud top height, cloud top pressure and cold cloud depth as predictors. Model efficiency statistics calculated over an independent dataset, suggest that the proposed models can be considered successful over the specific area (continental Europe) and period (summer). The new cloud top height model differs from the PR92 and other parameterizations, which is not an unexpected result, since every model has its own characteristics, strengths and weaknesses. The new parameterizations could be utilized in numerical model simulations to produce quantitative estimations of the amount of strokes over convective areas.