Non-uniform Heating Conditions Research Articles

Probabilistic design and optimization of thermal protection system with variable thickness based on non-uniform aerodynamic heating

Thermal Protection System (TPS) is a critical component of space vehicles to protect them from damage by extreme aerothermal heating conditions. The uncertainty of the aerothermal heating conditions, including approaching velocities, atmospheric density, pressure, etc., significantly affects the aerothermal heating imposed on the TPS, vastly changing the initial design conditions. In this study, we developed a new uncertainty quantitative (UQ) analysis method to comprehensively consider all the uncertainty of TPS materials, structures, and aerothermal heating conditions. To address the challenges of a massive amount of input and determined optimization parameters, we first induced the response surface method and Monte Carlo algorithm to produce a large number of analysis samples for Probabilistic Design. Then, the key affecting factors, not all the input design parameters, were chosen for optimization with sequential optimization and reliability assessment (SORA) strategy by a sensitivity analysis. With such improvements, the optimization for UQ analysis becomes practical. We used this new UQ method to analyze the effects of uncertainty of the aerothermal heating conditions on the thermal protection layer. A variable thickness design is proposed to adapt the non-uniform aerothermal heating conditions for the TPS. The results show that significant light-weighting can be achieved without the reliability penalty. The optimized structure also reduces internal temperature gradients and facilitates a more uniform temperature field distribution for the TPS. This study provides a new UQ engineering design approach for the system with many designed parameters.

Thermal Characterization of Subcooled Flow Boiling in a Pin-Fin Coldplate With Non-Uniform Heating

Abstract Coldplates are a crucial component in various cooling applications, such as cooling data center servers and power electronics. The unprecedented growth in electronics power density, along with the resulting ultrahigh heat fluxes, demands a transition from single-phase forced convection to two-phase flow boiling heat transfer. The majority of studies in the literature have focused on flow boiling in fin-enhanced silicon microgaps and microchannels, with only a few addressing flow boiling in millimeter-scale heat sinks. In the present study, flow boiling of HFE-7200 dielectric fluid in a millimeter-scale pin-fin coldplate is experimentally investigated under nonuniform heating conditions. Four background heaters represent the low-dissipating-power devices. On the other hand, five hotspot heaters mimic the high-heat-flux devices and generate heat fluxes ranging from 50 W/cm2 to 1000 W/cm2, corresponding to hotspot heat inputs ranging from 62.5 W to 1.25 kW, respectively. The coldplate's thermohydraulic performance is investigated for various flow rates and inlet temperature ranging from 0.5 L/min to 1.5 L/min and from 25 °C to 60 °C, respectively. A high-speed camera is utilized for a narrow field of view (FOV) flow visualization at a frame rate of 2229 fps while a digital camera is used for a wider FOV at 60 fps. Flow visualization demonstrated the transition between bubbly, slug/churn, and stratified two-phase flow regimes.

Research on the flow and heat transfer characteristics of RP-3 and structural optimization in parallel bending cooling channels

The regenerative cooling channel is curved due to the unique structural form of the combined nozzle of the turbine-based combined cycle engine for hypersonic flight. Research on the flow and heat transfer characteristics of fuel in the parallel bending cooling channels is insufficient, which causes difficulties in properly designing the thermal protection structure of the combined nozzle. This paper numerically investigated of the flow and heat transfer characteristics of hydrocarbon fuel RP-3 under non-uniform heating conditions in parallel bending cooling channels. The basic heat flux is 0.50 MW/m2, and the heat flux ratio of the upper and lower channels is 1.2, 1.5, and 2.4 respectively. The heat transfer and flow distribution mechanisms of RP-3 in parallel bending channels are revealed. The bending structure is beneficial to reduce thermal stratification and prevent heat transfer deterioration caused by buoyancy. In the pseudo-critical region of the channel, a “thermal insulation zone” is formed due to the low thermal conductivity of RP-3, which hinders the transfer of heat to the mainstream and causes heat transfer deterioration. When the fluid temperature is below 455 K, viscosity is the primary factor affecting the flow resistance difference between parallel channels. As the temperature further increases, the density difference and velocity difference between the parallel channels dominate in the flow resistance differences. Additionally, a connected hole structure in the middle of the bending section has been applied to optimize the flow deviation of parallel bending channels, which promotes the secondary distribution of flow. Finally, the influence mechanism of the connected hole on flow distribution has been studied under different heat flux ratios and connected hole widths.

Thermal buckling behavior of 3D printed foams: Plain, graded, and sandwich variants

The present work focuses on the experimental investigation of the thermal buckling response of 3D printed functionally graded glass micro balloon (GMB) reinforced high density polyethylene (HDPE) composites and their respective sandwiches under non-uniform heating conditions. The influences of GMB loading and its graded composition on temperature distribution are analyzed. The reinforcement of hollow GMB rendered lower thermal conductivity due to enhanced thermal resistance with an increase in filler percentage. An increased thermal buckling strength is also observed. Due to their non-uniform thermal expansion, functionally graded sandwich beams exhibited less deflection than plain beams. Among the cases of three heating conditions (One end heating: case-1, Center heating: case-2, both end heating: case-3), maximum deflection is observed in case 2 while the minimum deflection is noted in case 1. These printed foams can be utilized for lightweight thermal insulating pipes.

Thermal and aging performance characteristics of pouch-type lithium-ion battery using heat pipes under nonuniform heating conditions

Lithium-ion (Li-ion) batteries are excellent energy storage technologies for electric vehicles. However, the performance and life cycle of a battery can be degraded by extremely high temperatures under nonuniform heating conditions. This study aims to investigate the performance improvement of a battery thermal management system (BTMS) using heat pipes (HP) under various heat generation conditions. The cooling performances of the BTMS using aluminum plates (AP) and HP were compared by analyzing battery temperature and life cycle while varying the discharge rate (C-rate) from 1C to 5C and the ambient and liquid temperatures from 25 °C to 40 °C. Furthermore, the nonuniform heat ratio, defined as the heat ratio between the tab and bottom of the battery, was introduced to emulate the uneven temperature distribution, ranging from 1 to 3. The average temperature (Tavg) increases of AP and HP decreased by 22.7 % and 32 %, respectively, compared with that using natural convection (NC). HP showed a much lower maximum temperature (Tmax) and temperature difference (ΔT) of the battery than AP, owing to the effective heat transfer using the heat pipe. During cyclic operation, HP maintained stable Tmax and ΔT within 34.3 °C and 4 °C, respectively. As the nonuniform heat ratio increased, Tmax increased significantly, which was more severe in AP than in HP. HP exhibited up to a 41 % higher normalized performance index of Tmax than AP. Additionally, with the nonuniform heat ratio increasing from 1 to 3 at a C-rate of 5C, the ΔT of AP and HP increased by 7.6 °C and 4.4 °C, respectively. Finally, the normalized equivalent full cycles of AP and HP at a nonuniform heat ratio of 3 and a C-rate of 5C decreased by 4.3 % and 1.6 %, respectively, compared to their performance under uniform heat.

Experimental study of a two-phase thermosyphon loop with a horizontal parallel tube evaporator under non-uniform heating conditions

Experimental study of a two-phase thermosyphon loop with a horizontal parallel tube evaporator under non-uniform heating conditions

Comparison of uniform and non-uniform surface heating effects on in-canyon airflow and ventilation by CFD simulations and scaled outdoor experiments

Many studies have simplified the thermal buoyancy in urban areas as a uniform surface heating effect. However, a realistic scenario under solar shading conditions corresponds to non-uniform surface heating. Furthermore, effective validations of Computational Fluid Dynamics (CFD) simulations under realistic meteorological conditions are still limited. As a novelty, this study adopted scaled outdoor experimental data to validate CFD simulations. The validated CFD model was then utilized to investigate the flow characteristics with non-uniform surface heating in a full-scale street canyon (building height/street width, H/W = 2; H = 12 m). Moreover, we numerically quantified the differences between the impacts of uniform and non-uniform surface heating on in-canyon airflow and ventilation under various thermal conditions.In the absence of surface heating, there was a single vortex in the street canyon. However, for uniform and non-uniform surface heating, thermal buoyancy resulted in the appearance of three in-canyon vortices. The ventilation differences between these two surface heating conditions increased with thermal buoyancy. When the dynamic force dominated the urban airflow (Richardson number, Ri = 0.1), the flow structures for both surface heating conditions were similar, with a ventilation difference of only 3.77%. When both the dynamic and thermal buoyancy forces were significant (Ri = 3.54), the flow patterns of the two surface heating conditions differed near the windward wall. The corresponding ventilation difference reached 27.36%. This study emphasizes the importance of examining urban flows and ventilation under non-uniform surface heating conditions, particularly when the thermal effects are significant.

Numerical analysis of transient heat and mass transfer for a water heat pipe under non-uniform heating conditions

Non-uniform loads are widely present in heat pipe applications and have significant effects on their performance. In this work, a transient 3D CFD model is developed to investigate the liquid–vapor flow and heat transfer for a water heat pipe under various non-uniform loads. The source terms are added to the governing equations using the User-Defined Function (UDF) to simulate the evaporation and condensation process. The model is verified using the experimental and simulated data under uniform and non-uniform loads in the literature. The effects of key parameters including adiabatic length, heating power, and heat distribution on the thermal performance of heat pipes are analyzed. The results show that the non-uniform conditions would shift the maximum axial velocity of vapor to the unheated side and induce a significant circumferential flow in the wick region, especially in the evaporator section. The short adiabatic length and high heating power could reduce the elapsed time of reaching the steady state. The heat distribution in the evaporator section exhibits little effect on the elapsed time reaching the steady-state and the average steady-state vapor temperature

Defect Detection and Depth Estimation in Composite Materials for Pulsed Thermography Images by Nonuniform Heating Correction and Oriented Gradient Information.

Pulsed thermography is a nondestructive method commonly used to explore anomalies in composite materials. This paper presents a procedure for the automated detection of defects in thermal images of composite materials obtained with pulsed thermography experiments. The proposed methodology is simple and novel as it is reliable in low-contrast and nonuniform heating conditions and does not require data preprocessing. Nonuniform heating correction and the gradient direction information combined with a local and global segmentation phase are used to analyze carbon fiber-reinforced plastic (CFRP) thermal images with Teflon inserts with different length/depth ratios. Additionally, a comparison between the actual depths and estimated depths of detected defects is performed. The performance of the nonuniform heating correction proposed method is superior to that obtained on the same CFRP sample analyzed with a deep learning algorithm and the background thermal compensation by filtering strategy.

An efficient parametrized optical infrared thermography 3D finite element framework for computer vision applications

Matching infrared thermography (IRT) with deep learning-based computer vision has recently gained a lot of interest for automated defect assessment in materials. One of the remaining bottlenecks concerns the necessity of a large and diverse experimental and/or virtual training dataset in order to achieve a sufficiently generalizable computer vision algorithm. This paper presents a parametrized 3D finite element (FE) framework, implemented in Fortran90, for efficiently simulating optical infrared thermographic inspection of multi-layer anisotropic media and establishing large-scale virtual dataset with sufficient diversity. The interface element is introduced for the modelling of an imperfect thermal contact, allowing to simulate a variety of defect types. The flexibility of the interface element makes it possible to simulate delaminations with different thickness using the same discretized model. Validation is done for two benchmark cases which are representative for a fiber reinforced polymer laminate with delamination-like defects. In order to achieve true-to-nature thermographic simulation data, non-uniform heating conditions are adopted from experiment, and a stochastic morphology generator is introduced for modelling realistic irregular defect geometries. To demonstrate the added value of a large, diverse and true-to-nature virtual database for computer vision applications, a Faster-RCNN model was trained on a generated virtual dataset for the detection of delamination-like defects in fiber reinforced polymer laminates. Application of the trained Faster-RCNN on experimental thermographic data yields excellent inference results, illustrating the high generalization ability of the virtually trained object detector.

Numerical Investigation on Two-Phase Water Density Wave Oscillations in a Pipe under Various Heating Conditions

This study utilizes the finite volume method with a two-fluid model to analyze water characteristics in a boiling channel when density wave oscillation occurs. A 2-D numerical model is utilized to characterize both axial and radial mass and energy exchange, as well as the mechanisms involving flow and heat transfer during density wave oscillation under uniform and non-uniform heating conditions. The numerical model was used to predict the heating power threshold values of two-phase water flowing upward in a vertical pipe under type II density wave oscillation at the working pressure and an inlet–outlet pressure difference of 125 kPa, when the average heating power increased from 44.06 kW/m2 at a speed of 0.5 kW/(m2·s). The flow and heat transfer characteristics before and after the type II density wave oscillation were determined and compared to the flow and temperature fields at various moments. Along the pipe axis, the wall heat flux was loaded under uniform, standard-sine, and inverted-sine types, which represent three typical types of wall heat flux arrangements. Flow oscillation appeared the earliest under the inverted-sine-type heat flux with low vapor quality (approximately 0.13) with a void fraction of 0.6 at the outlet.

Experimental and theoretical study on the onset of nucleate boiling in non-uniform heating tube bundle channel

The transverse non-uniform heating tube bundle exists in steam generator and will affect the heat transfer and flow conditions in the shell side. It is important for the operational performance of the steam generator. In this study, a non-uniform heating tube bundle channel experimental device was set up. The channel consisted of two groups of heating tube bundles which were non-uniform heating in the transverse direction and uniform heating in the axial direction. Experiments and theoretical analysis were conducted to evaluate the influence of transverse non-uniform heating on the Onset of Nucleate Boiling (ONB). The locations of ONB during the experiments were determined from the heat transfer coefficient variations and the tube wall temperature variations. Experimental results at ONB were compared with existing well-known correlations under uniform heating conditions. And then under non-uniform heating conditions, the experimental wall superheat at ONB were furthermore compared with results predicted by the verified existing correlation. It was found that the correlation can’t predict the experimental wall superheats well under transverse non-uniform heating conditions. Therefore, the influence of transverse non-uniform heating on ONB was theoretically analyzed. Correction factors were theoretically introduced and a new correlation was proposed. This new correlation was examined with experimental data and the result showed the correction factors need to be further studied.

Experimental Study on the Effect of Inclination Angle on the Heat Transfer Characteristics of Pulsating Heat Pipe under Variable Heat Flux

This paper aims to deeply explore the influence of different inclination conditions on the heat transfer characteristics and broaden the application scene of a pulsating heat pipe. A test device for the heat transfer performance of a pulsating heat pipe under different inclination angles is designed and built. Under the condition of 70% liquid filling rate, ethanol and HFE-7100 are selected to carry out the experimental test with heating power of 40–140 W and dimensionless thermal difference of 0–0.56. The heat transfer performance, the temperature in the evaporation section and the internal pressure fluctuation of the pulsating heat pipe were experimentally studied. The results show that under the condition of uniform heat flux, for ethanol working medium, when the pulsating heat pipe is heated at 40 W, the operating thermal resistance varies significantly with different installation angles. At this time, the operating thermal resistance of a pulsating heat pipe with installation angles of 45°, 70°, 90° and D90° is 1.38 °C/W, 1.60 °C/W, 1.73 °C/W and 2.07 °C/W, respectively. With the increase in installation angle, the operating thermal resistance also increases gradually, reaching the maximum at 90°. At low heating power, the effect of the installation angle on the ethanol working medium is significantly greater than that of HFE-7100 working medium. The HFE-7100 working medium showed lower operating thermal resistance at low heating power, but with the increase in heating power, the operating thermal resistance of the two working medium gradually approached a 70% filling rate. Under non-uniform heating conditions, when HFE-7100 is used as a working fluid, the operating thermal resistance of a pulsating heat pipe under different heating power was lower than that of the ethanol working medium. The operating thermal resistance is less affected by the installation angle, and the overall heat transfer performance is better. The phenomenon in which the ethanol working medium is obviously affected by the installation angle can be improved by non-uniform heating conditions. For ethanol working medium, when the dimensionless heat difference reaches 0.33 under the condition of a 45° installation angle, the average temperature fluctuation in the evaporation section appears gentle. At this installation angle, the internal working medium of the four elbow pulsating heat pipe devices used in this research more easily forms a cycle in the pipe than the 90° installation angle.

Experimental study on sub-cooled flow boiling heat transfer in inclined non-uniform heating tube bundle channel

• Sub-cooled flow boiling experiments are conducted to study heat transfer. • The radial heat transfer under non-uniform heating conditions is deduced. • Present non-uniform heating and inclined data are evaluated by correlation. • A new correlation under inclined and non-uniform heating conditions is developed. Since the specific structure of the U-tube, non-uniform heating (NUH) occurs on the shell side of the U-tube steam generator or exchanger. When the above equipment are applied in ocean environments, they may be in an inclined condition. The coupled conditions of NUH and incline can enhance the complexity of the heat transfer on the shell side, especially in terms of the sub-cooled flow boiling, during which the heat transfer mechanism changes. In this paper, sub-cooled flow boiling in a tube bundle channel under the coupled conditions of NUH and incline are performed experimentally. The result shows that the Gungor-Winterson correlation is in good agreement with the experimental data under uniform heating (UH) conditions and the mean relative error is only about 10.05%, while the predicted ability is poor under the coupled conditions of NUH and incline. The heat transfer characteristics are affected by radial heat and mass transfer, convective flow, bubbles behavior, and bubbles migration, which are introduced by the coupled action of NUH and incline. At last, an improved Gungor-Winterson correlation is proposed for UH, NUH, and inclined NUH conditions. Its average relative error is only 5.56% in total, and less than 0.91% of data has a larger deviation than 15%.

Effect of the aspect ratio of the shallow enclosure and built‐in rectangular blockage on MHD double‐diffusive free convection subjugated to non‐uniform boundary conditions

AbstractIn this study, the lattice Boltzmann method is used to explore the double‐diffusive natural convection within a shallow enclosure with a built‐in rectangular blockage at its geometric center. The enclosure is exposed to an external magnetic field. One of the enclosure walls is subjected to linearly/sinusoidal heating and concentration conditions. The rectangular blockage is at higher temperature and concentration conditions. Numerical experimentation is executed for a range of parameters such as Rayleigh number , Lewis number , buoyancy ratio , aspect ratio of the enclosure , aspect ratio of the built‐in blockage , and Hartmann number . The working fluid is assumed to be liquid metal (sodium–potassium alloy, ). The complex interaction of flow parameters with the nonuniform heating and concentration conditions has been explored. Higher heat and mass transfer (HMT) rates are noticed for the sinusoidal temperature and concentration profile compared to linear for a given . and showed enhancement by , and for sinusoidal temperature and concentration profile of the enclosure as compared to linear for . The increase in the blockage and the enclosure aspect ratio shows augmentation in the HMT rate. The consequences of the study are also summarized in terms of empirical correlations of the and numbers showing functional dependence on the considered range of parameters.

Numerical study on buckling capacity of steel H-beams under non-uniform temperature distribution

PurposeThe strength and stiffness of steel deteriorate rapidly at elevated temperatures. Thus, the characteristics of steel structures exposed to fire have been concerned in recent years. Most studies on the fire response of steel structures were conducted at uniformly distributed temperatures. This study aims to evaluate the buckling capacity of steel H-beams subjected to different loading conditions under non-uniform heating.Design/methodology/approachA numerical investigation was conducted employing finite element analysis software, ABAQUS. A comparison between the numerical analysis results and the experimental data from previous studies was conducted to verify the beam model. Simply supported beams were loaded with several loading conditions including one end moment, end equal moments, uniformly distributed load and concentrated load at midspan. The effects of initial imperfections were considered. The buckling capacities of steel beams under fire using the existing fire design code and the previous study were also generated and compared.FindingsThe results showed that the length-to-height ratio and loading conditions have a great effect on the buckling resistance of steel beams under fire. The capacity of steel beams under non-uniform temperature distribution using the existing fire design code and the previous study can give unconservative values or too conservative values depending on loading conditions. The maximum differences of unconservative and conservative values are −44.5 and 129.2% for beams subjected to end equal moments and one end moment, respectively.Originality/valueThis study provides the buckling characteristics of steel beams under non-uniform temperature considering the influences of initial imperfections, length-to-height ratios, and loading conditions. This study will be beneficial for structural engineers in properly evaluating structures under non-uniform heating conditions.

Numerical study of convective heat transfer to supercritical CO2 in vertical heated tubes

Supercritical heat transfer is important to design and operate advanced power generation system. Non-uniform heating is frequently encountered such as for sCO2 boiler and solar receiver applications. Here, 3D numerical simulations are performed in turbulent regime, coupling solid wall and sCO2 in tubes. Non-uniform heating is simulated by applying heat via a thin metal layer at the outer tube wall, covering half circumference of tube wall. Calculation results matched experimental data well. Heat transfer is compared between uniform heating and non-uniform heating. Numerical results are re-processed by the pseudo-phase transition theory, including a liquid-like region in tube core and a gas-like layer near the tube wall. The two layers of structure are interfaced by a terminating temperature T+ which is determined by thermodynamics. Hence, supercritical heat transfer is evaluated based on the relative importance of thermal resistances induced by the liquid-like region and the gas-like film region. It is found that wall temperatures for uniform heating are higher than those for non-uniform heating, which is explained by larger thermal resistance of the gas-like film for uniform heating than that for non-uniform heating. This difference ensures better heat transfer for non-uniform heating than uniform heating. We conclude that in turbulent regime, the gas-like film dominates the magnitudes of wall temperature and the occurrence of heat transfer deterioration for both uniform and non-uniform heating. Our work is important for heat transfer facilities in supercritical domain, especially under non-uniform heating condition.

Mathematical modeling of unsteady flow with uniform/non-uniform temperature and magnetic intensity in a half-moon shaped domain

The mathematical modeling of two-dimensional unsteady free convective flow and thermal transport inside a half-moon shaped domain charged in the presence of uniform/non-uniform temperature and magnetic effects with Brownian motion of the nanoparticles has been conducted. Thirty-two types of nanofluids in a combination of various nanoparticles and base fluids having different sizes, shapes, and solid concentrations of nanoparticles are chosen to examine the better performance of heat transfer. The circular boundary is cooled while the diameter boundary is heated with uniform/non-uniform temperature. An external uniform/non-uniform/periodic magnetic field is imposed along diameter. The powerful partial differential equations solver, finite element method of Galerkin type, has been engaged in numerical simulation. The numerical solution's heat transfer mechanism reaches a steady state from the unsteady situation within a very short dimensionless time of about 0.65. The thermal transport rate enhances for increasing buoyancy force whereas decreases with higher magnetic intensity. The uniform thermal condition along the diameter of half-moon gives a higher thermal transport rate compared to non-uniform heating conditions. The non-uniform magnetic field provides greater values of the mean Nusselt number than the uniform field. In addition, the outcomes also predict that a better rate of temperature transport for kerosene-based nanofluid than water-based, ethylene glycol-based, and engine oil-based nanofluid. The heat transfer rate is observed at about 67.86 and 23.78% using Co-Kerosene and Co-water nanofluids, respectively, with an additional 1% nanoparticles volume fraction. The blade shape nanoparticles provide a better heat transfer rate than spherical, cylindrical, brick, and platelet shapes. Small size nanoparticles confirm a higher value of average Nusselt number than big size. Mean Nusselt number increases 22.1 and 5.4% using 1% concentrated Cu-water and Cu-engine oil nanofluid, respectively than base fluid.

Experimental investigation on thermal characteristics of a novel mesh flat-plate heat receiver in a solar power tower system

In solar power tower systems, the heating surface of a heat receiver is prone to local overheating, thermal fatigue, and thermal ratcheting under nonstationary, nonuniform, and high-heat-flow-density loads, resulting in failure of the heat receiver. Therefore, this paper proposes a novel high-temperature, mesh, flat-plate heat receiver (FPHR) comprising multiple micro heat pipe loops. A series of tests were conducted to investigate the heat transfer characteristics and cooling start-up performance of the mesh FPHR. The results indicate that the larger cooling rates can reduce successful start-up times by more than 12%, and the FPHR has excellent isothermal performance (<35.05 °C) and heat transfer performance, which can withstand high-heat-flow-density loads and effectively prevent the harm caused by thermal stress. In addition, the nonuniform heating condition has a greater impact on the isothermal performance of FPHR, and the maximum temperature difference of the heat absorption surface with the change of the tilt angle is only reduced by 2.03 °C. The efficiency of the FPHR can exceed 83.98% and the air outlet temperature can exceed 714.5 °C. The results will contribute to the further development of heat receivers used in solar power tower systems.

Design equations for buckling strength of steel I-beam under non-uniform heating condition

This paper presents a numerical study on lateral-torsional buckling strength of the simply supported beam under fire subjected to general loading conditions. The influence of length to height ratio and the non-uniform temperature distribution in the steel beam was considered to evaluate the buckling strength of the beam. The numerical simulations were carried out by utilizing a commercial finite element program, ABAQUS. The buckling strengths of steel beams using buckling design curves at elevated temperature of Eurocode 3 Part 1–2 were also generated and compared. The results showed that the buckling resistance of the steel beam under fire using Eurocode 3 can give unconservative values for beams subjected to positive moment and give very conservative values for beams subjected to negative moment. The new correction factor was proposed to take into account the effect of length to height ratio and non-uniform heating condition on buckling strength. The proposal equation was suggested to determine the lateral-torsional buckling capacity of the steel beam under fire and general loading conditions.