Temperature Distribution In Cross Section Research Articles

Optimization of exhaust ejector with lobed nozzle for marine gas turbine

To attain high-performance ejector configurations, an ejection characteristic testing system was established initially to validate the reliability of the Realizable k-ε turbulent model. Subsequently, optimization investigations were conducted on lobed nozzle ejectors with various structural parameters. The effects of four key structural parameters, including lobed nozzle expansion angle α, lobed nozzle width d, number of lobes in the nozzle n, and height of the square-to-circle section h, were systematically studied. Furthermore, the CRITIC method was employed for multi-objective evaluation to identify the optimal design configuration for the casing ejector. The research findings revealed that among the structural parameters, the lobed nozzle expansion angle α exerted the greatest influence on the ejection coefficient and pressure loss coefficient. The weights of the evaluation criteria were determined by the CRITIC method as follows: ejection coefficient (49.38%) < pressure loss coefficient (50.62%). The optimal design configuration determined by the CRITIC method included α = 45°, d = 150 mm, n = 14, and h = 600 mm. The resulting enclosure design ensures smooth airflow within the system, preventing the backflow of high-temperature mainstream fluid and heating the enclosure. It also maintains a temperature distribution in the typical cross-section that meets specified requirements. Additionally, it facilitates improved mixing of mainstream and secondary fluid and reduces exhaust gas temperature.

Study on the decompression behavior during large-scale pipeline puncture releases of CO2 with various N2 compositions: Experiments and mechanism analysis

Impurities in the captured CO2 stream from various industrial sources may introduce uncertainty into the transient releases of transportation pipelines. Due to limitations in the experimental scale, there is currently limited analysis of the vertical cross-sectional temperature distribution and the pressure response along the pipeline during the releases of impure CO2. The mechanism by which impurities affect the decompression wave and the alterations in phase-change pathways remains unclear. In this study, building upon the existing large-scale pipeline, we established an impurity injection system. Using the common impurity, N2, as a variable, the decompression behavior of the CO2+N2 mixture in the puncture releases and the influence mechanism of N2 were investigated. The results show that the effect of N2 on sound velocity causes a significant decrease in the decompression wave speed. N2 raises the minimum temperature, and it is more pronounced in large-diameter releases; for instance, the minimum temperature during the 100 mm release is always higher than that in the 50 mm release. The gas-liquid mixture closely follows the dew point line, conforming to the Gibbs equilibrium criterion. The experimental scale mirrors real-world operating conditions, endowing the research findings with practical applicability. Concurrently, it furnishes dependable data for numerical researches.

Fire and post-fire performance of unbonded semi-precast prestressed reinforced concrete beams

The integration of semi-precast concrete beam preparation methods with prestressing structural measures aims to achieve superior mechanical properties while complying with green construction principles. However, the damage mechanism of semi-precast prestressed concrete beams (SP-PCBs) under fire conditions is not clear. In this study, the cross-section temperature distribution, prestressing loss pattern, and residual load-carrying capacity of the SP-PCBs were investigated by conducting standard fire tests. The results show that increasing the thickness of the protective layer of prestressing bars can delay the time of damage by high temperature and thus increase the fire resistance limit of the SP-PCBs. Higher prestressing levels and rebar ratios contribute to the cracking resistance of the SP-PCBs, although the stress loss is obvious. After the fire, the distinct SP-PCBs showed different degrees of reduction in load-carrying capacity and stiffness, but still exhibited excellent fire resistance and avoided brittle damage. Increasing the reinforcing ratio increases the residual load-carrying capacity of the SP-PCBs, while increasing the prestressing level has a relatively small effect. Increasing the height of the post-cast layer slightly reduces the stiffness and ductility of the SP-PCBs, but does not significantly affect the load-bearing capacity. In addition, this paper establishes a theoretical calculation model for the residual load-bearing capacity of the SP-PCBs after the fire, and verifies the accuracy of the model by experimental results, which provides a practical theoretical basis and reference for the design and evaluation of the fire resistance performance of the SP-PCBs.

Effect of flow maldistribution on heat transfer performance and temperature field of plate-fin heat exchangers

Plate-fin heat exchangers (PFHEs) are widely utilized in aviation precoolers, emphasizing not only heat transfer performance but also the outlet temperature distribution, with flow maldistribution impacting both parameters. This study developed a numerical model of crossflow PFHE and a two-dimensional flow distribution model under the condition of flow maldistribution. Experimental validation shows a standard deviation of 6.9%. This investigation delves into the effects of flow distribution offset (ξ) and non-uniformity (ε) on heat transfer performance and outlet temperature distribution. With large temperature differences, variations in fluid properties due to temperature lead to changes in the surface heat transfer coefficient (SHTC). The combined effects of SHTC and temperature difference determine the heat transfer performance. The results indicate optimal heat transfer performance and outlet cross-sectional temperature distribution at ξ= − 0.67 and 1, respectively. For a given ξ, increased non-uniformity deteriorates heat transfer efficiency and outlet cross-sectional temperature distribution. At ε=0.66, relative to the uniform flow, the heat transfer performance and standard deviation of outlet temperature distribution decrease by 10.3% and 45.1%, respectively.

Deep-learning model for predicting hardness and phase distributions from two cross-sectional temperature distribution images in laser heat treatment of AH36 steel

Laser heat treatment of carbon steel is generally performed to increase the hardness of the specimen. However, when the heating temperature is high, softening of the specimen can occur along with melting. It is important to predict both hardening and softening processes, but such research has been limited so far. In this study, a deep learning model was developed that predicts both hardening and softening during laser heat treatment of AH36 steel using two cross-sectional temperature distributions obtained at 0.5-s intervals as inputs. Two temperature distributions were used as inputs to provide accurate information about cooling rate to the model. The input temperature distribution of the cross-section was calculated by solving the heat conduction equation using finite element method, and the hardness and phase distributions used as ground truth were obtained through a 2 kW multi-mode fiber laser experiment. The model was constructed based on a generative adversarial network with a residual network. It was found that when two temperature distributions were used, both softened and hardened areas were predicted accurately. However, when only one temperature distribution was used, only hardening could be predicted. On the other hand, both models could predict phase distributions, but much more accurate results were obtained when two temperature distributions were used as inputs.

Experimental and numerical study on the validity of the energy-based time equivalent method for evaluating the fire resistance of timber components exposed to travelling fires

An energy-based time equivalent method that is capable of converting the fire resistance design of timber components exposed to the realistic fire to that of the standard fire was proposed. To verify the effectiveness of the method applied to the improved Travelling Fires Methodology (iTFM) fires, a series of iTFM fires and their corresponding equivalent standard fire tests were implemented on six glued laminated timber columns. The effectiveness of the method was fully confirmed by comparing the fire effects, the temperature distribution of the pyrolysis layer, and the remaining load-bearing capacity after fire for the timber columns under the iTFM fires and their equivalent standard fires. Meanwhile, it was well illustrated that the adhesive layer was almost no effect on the fire resistance of the timber columns by comparing the cross-sectional temperature distribution, charring depth and charring rate in two directions of the timber columns. To simplify the application of the energy equivalence method, the thermal properties relationships applied to the finite element heat transfer analysis of timber were modified. The accuracy of the modified thermal property relationships was demonstrated by comparing the surface temperature, charring depth, and charring rate obtained from finite element simulations with those measured by the experiment. The simplified energy equivalence method based on the finite element was not only easy for designers to apply, but also helped to promote the development of performance-based fire protection design for timber structures.

Development of a Temperature Distribution Measurement System for Transmission Oil for Transportation Equipment

In this study, an optical sensor using thermo-sensitive phosphor and its measurement system for visualizing and measuring the temperature distribution in an arbitrary cross-section of transmission oil using one type of phosphor, whose peak wavelength changes with temperature, is proposed. Because the intensity of the excitation light is gradually attenuated by the scattering of the laser light owing to microscopic impurities in the oil, we attempted to reduce the scattering effect by increasing the excitation light wavelength. Therefore, Pyrromethene 597 was selected as the optical sensor using thermo-sensitive phosphor, and a DPSS (Diode Pumped Solid State) laser with a wavelength of 532 nm was used as the excitation light. Using this measurement system, we measured the temperature distribution of a vertical buoyant jet of transmission oil and validated the measurement method. In addition, it was shown that this measurement system could be applied to the measurement of the temperature distribution in transmission oil with cavitation foaming.

Lateral Torsional Buckling Resistance and Design of High Strength Steel Beams Subjected to Nonuniform Temperature

The mechanical characteristics of high-strength steel (HSS) at high temperatures vary significantly from those of mild steel, so fire design regulations derived from mild steel cannot be transferred to HSS structures. Therefore, this paper investigates the fire resistance of beams made of HSSs, which will facilitate the design and application of HSS structures. Due to the heat dissipation of the concrete floor, steel beams are generally heated from three sides, and the temperature distribution in the steel beam cross-section is nonuniform. For such cases, the fire resistance of HSS beams is assessed using finite element models (FEMs) with nonuniform temperature distribution. A Ramberg–Osgood model was used to predict stress–strain relationships of Q460, Q690, and Q960 HSSs at elevated temperatures, and the model was verified by material tests. In the FEM, the proposed stress–strain relationships of HSSs at elevated temperatures, initial geometric imperfections and residual stress are considered for better accuracy. After verifying the established model against experimental results, the influence of nonuniform temperature distribution, load pattern, steel grade, and slenderness ratio on the resistance of HSS beams is investigated by conducting parametric analyses using the verified FEM. It is found that the critical bending moment of steel beams at elevated temperatures associated with lateral-torsional buckling highly depends on the reduction of elastic modulus of steel. By comparing FEM results with EN 1993-1-2, it is evident that EN 1993-1-2 is unsuitable for assessing the fire resistance of HSS beams. Therefore, the expression specified in EN 1993-1-2 is modified by fitting the finite analysis results to more accurately evaluate the fire resistance of HSS beams considering the nonuniform temperature distribution.

Swirl influence on thermo-hydraulic performances within a heat exchanger/reactor with macro deformed walls in laminar flow regime

In this article, numerical simulations are used to analyze thermal intensification in a high efficiency heat exchanger/reactor operating in laminar flow regime. Studied configurations which combined wall macro deformations are characterized by external sinusoidal wall deformations and an internal swirled core. Special attention is paid to the swirl pitch influence on the thermo-hydraulic performances for a Reynolds number ranging from 200 to 1000. A detailed analysis of the different complex intensification mechanisms is carried out for several values of the swirling core by considering the flow topology and temperature distribution in cross-sections for a given Reynolds number (equal to 600). Results show the influence of the cross-averaged vorticity flux evolution along the flow path on the heat transfer and pressure drop throughout the whole heat exchanger/reactor. Finally, overall performances are assessed considering the Performance Evaluation Criteria (PEC) for the studied Reynolds number range. It is found that a PEC as high as 3.10 can be reached for the geometry characterized by the smallest pitch at Re = 1000, which is of great interest for process intensification involving heat exchanger/reactors.

Numerical investigation on the thermal performance of parabolic trough solar collector with synthetic oil/Cu nanofluids

Nanofluids as the advanced heat transfer fluids, could be used in the parabolic trough solar collector system because of the enhanced thermal transport properties. In this paper, the effects of the same nanoparticles with two different base fluids on the thermal performance of the collector are numerically investigated by finite element method. Moreover, the effect of nanofluids on the cross-sectional temperature distribution of the absorber tube, which is well-known to affect the collector performance is here investigated. The numerical study is divided into two groups according to the value range of inlet velocity and inlet temperature, which represents different application scenarios of the collector. The results show that the synthetic oil/Cu nanofluids could increase the convective heat transfer coefficient under wide working conditions, but more pumping work is required because of the increase in pressure drop. The cross-sectional temperature difference of the absorber tube is greatly decreased with synthetic oil/Cu nanofluids. Furthermore, it’s found that Cu nanoparticles could trigger thermal and exergetic efficiency increment, especially at a low flow rate and high working temperature. The thermal performance improvement of these two thermal oils by Cu nanoparticles is different, and Syltherm 800 is more suitable for being the base fluid of nanofluid.

Assessment of fire exposure on the load bearing capacity of basement storey walls

This paper presents the numerical modelling of the fire exposure on structural element and its static analysis taking account of the material properties reduction due to elevated temperature.
 The reinforced concrete wall of basement storey was subjected to one side fire exposure.
 Advanced calculation methods were used to assess the fire exposure on the structural element as most reliable and approximate to fire test results. Thermal analysis was performed with LIRA-CAD software by the simulating of three main heat-transfer ways: thermal conductivity, convection and radiation. As a result of the thermal analysis, temperature distribution in the concrete and reinforcement parts of the structural element cross-section was obtained. The thermal analysis of the wall structural element was performed for 120 minutes in standard fire exposure. Reduction factors for the strength of concrete and reinforcement steel were determined based on the temperature distribution in the wall structural element cross-section. The cross-section is divided into a number of parallel zones of equal thickness where the mean temperature and the corresponding mean compressive strength is assessed according to the Zone method procedure. The fire damaged zone of thickness az at the fire exposed sides and reduced cross-section were obtained.
 Static analysis of the wall load-bearing capa-city was performed using the procedure applicable for normal temperature design. The Deformation method for normal temperature design taking to account concrete deformation was used. The Deformation method for normal design taken to account concrete deformation at every step of iteration was used. The reduced load-bearing capacity of the fire damaged wall taking into account residual concrete strength was calculated and relevant load-bearing capacity diagrams were determined.

Structural Fire Analysis of Beams and Slabs Using ANSYS and FEAST Software Program

In recent years, building fire has become more frequent event and fire accidents have increased all over the world. Major problem with fire is it provides very less time to handle the situation and due to elevated temperature, reduction in strength of structural member with increase in fire exposure time has been observed. To evaluate this reduced strength of structural members and design for fire load, it is necessary to have the parameters such as fire load, fire exposure time and temperature variation across the structural members. In this paper, evaluation of fire load, equivalent time of exposure and temperature distribution of beams and slabs using finite element analysis software FEAST and ANSYS has been done. For temperature variation, transient heat thermal analysis, in which temperature is increasing continuously over the time, is used. For this analysis, beams and slabs are exposed to surface fire on different surfaces and the temperature distribution of cross section has been evaluated. The results are compared and found to be matching with the European Standard procedure.

Optimization of Ti-6Al-4V ring rolling process by FE simulation using RSM

Ring rolling is a process to manufacture seamless rings. The process is characterised by high non-linearity, asymmetry, unsteady state and non-uniformities in plastic strain and temperature distribution in the ring cross-section. Inhomogeneities in distribution of plastic strain and temperature have significant effects on deformation behavior, microstructure and mechanical properties. Fishtail defect, one of the form defects, is also a major concern. In this study, a reliable coupled 3D thermo-mechanical finite element model of the ring rolling process was developed using dynamic explicit code in ABAQUS/Explicit environment. Nine simulations with different combinations of feed rate and rotational speed were ascertained using Central Composite Design (CCD). CCD model is an integral part of Response Surface Methodology (RSM). Strain and temperature heterogeneities and fishtail defect were predicted using the simulated models. Coefficient of Variation (CoV) was introduced as a heterogeneity index for strain and temperature analysis. The fishtail coefficient was used to quantify fishtail defect. ANOVA was carried to find out the significant factors and interactions affecting the ring rolling process. Feed rate was found to be the only significant factor in the range of parameters studied. Multi-response optimization was performed to find out the feed rate at which the process is most optimized with an aim to minimize both strain and temperature heterogeneity and fishtail defect. Feed rate of 1.61 mm/s was found to be the most optimized process parameter.

Effect of active cooling on the thermal effect of electromagnetic rail under single launch mode

In order to investigate the influence of active cooling on the rail thermal effect of electromagnetic gun under single launch mode, characteristics of the peak temperature, cross-section current density and temperature distribution, axial temperature distribution of rail with and without active cooling are simulated. In addition, the time-varying characteristics of the rail axial temperature distribution, the temperature time-varying characteristic in different temperature parts on the rail and the influence of the cooling water flow velocity on the temperature in different temperature parts are experimentally studied. The results show that during the launch, there is almost no difference between the rail peak temperature and its location with and without active cooling, and the peak temperature is basically located at the initial position of the armature. Without active cooling, the rail axial temperature distribution shows a trend of higher at the gun tail and lower at the gun muzzle. The current density and temperature distribution of rail cross-section show a trend of higher on the rail inner side and lower on the rail outer side, and the diffusion of heat lags behind the diffusion of current. Under the action of active cooling, the rail peak temperature will move to the muzzle along the armature moving direction, and there is a “thermal inversion” phenomenon. The rail cross-section temperature drops faster, and the lowest temperature region appears near the middle cooling channel. Active cooling has different effects on rail temperature in different temperature parts. In the high-temperature part, the rail temperature decreases monotonically with the increase of cooling water flow velocity, increasing the water velocity can accelerate the decline of rail temperature. In the middle-temperature parts, the variation trend of rail temperature is different with different water flow velocities. At low water velocity, the rail temperature increases gradually. When the water flow velocity is greater than 0.75 m/s, the phenomenon of “thermal inversion” will occur. i.e., the rail temperature increases first and then decreases. In the low-temperature part, “thermal inversion” will occur at different flow velocities, that is, the rail temperature increases first and then decreases. When the water flow velocity is greater than 1.0 m/s, the improvement of rail cooling effect will no longer be obvious. It is suggested that the appropriate water flow velocity is 0.75–1.0 m/s under the present experimental conditions.

Numerical modeling and design approach on restrained Q690 steel beams in fire

This paper presents a comprehensive numerical analysis of high-strength Q690 steel beams in fire. A FE model is developed and validated against the full-scale experiments on restrained high-strength Q690 steel beams in fire presented in a previous study by the authors. The FE model adequately replicates the deflection, axial force, and actual failure modes identified experimentally. An extensive parametric investigation was performed to determine the variables affecting the behavior of restrained Q690 steel beams in fire. The analysis indicates that several factors, including load ratio, cross-section temperature distribution, rotational restraint stiffness, and span-to-depth ratio are critical for the fire resistance of restrained high-strength Q690 steel beams. Furthermore, additional numerical analysis for the ultimate bearing capacity of high-strength Q690 steel beams under bending was carried out to estimate the flexural-torsional buckling behavior of Q690 steel beams at elevated temperatures. Additionally, based on the results of the FE models, design curves for determining the flexural-torsional buckling strength of high-strength Q690 steel beams at high temperatures were proposed. The findings were compared to the design curves specified by several design standards.

Temperature distribution simulation and thermal properties investigation of hollow slab beam based on meteorological data

Natural environment has a great impact on the performance of bridge structures, such as the ambient temperature, solar radiation, climate extremes and so on. Due to the lack of regional pertinence in the provisions of the existing specifications on the temperature load standard, and the lack of verification of its adaptability of hollow slab beam bridge in the reconstruction and expansion project, it is necessary to study the temperature load of the beam based on the temperature data of the area where the bridge site is located. Based on the measured meteorological data, the cross-section temperature distribution characteristics of the hollow slab beam and the temperature load effect were investigated. The vertical temperature load model of the short and medium-span hollow slab beam was proposed according to the simplified temperature curve. Firstly, based on the annual measured meteorological data, the plane model was established to analyze the temperature distribution characteristics of the hollow slab beam. Secondly, according to the temperature field distribution of the beam cross-section, the solid model of 16 m hollow slab beam was established to analyze the distribution of the temperature load effect. Finally, based on the preliminarily proposed temperature curve, vertical temperature load models were proposed by introducing the theory of extreme value extrapolation. The studies have shown that the temperature of the hollow slab beam is approximately horizontal distributed, and temperature extreme value appear at the location of the beam web. The roof and floor of the hollow slab beam are compressed and the webs are tensioned in the positive temperature difference state, the stress condition is opposite under the negative temperature difference state. The positive and negative temperature load models can meet the extrapolation requirements of the bridge design reference period. This study innovatively proposed a temperature load model based on the temperature curve corresponding to the most unfavorable effect of the beam. The extrapolation idea in the derivation of vehicle load model is introduced as well. And a temperature load model suitable for the extension of hollow slab bridges in Guangdong is established in this study.

Modelling Thermal Performance of Unloaded Spiral Strand and Locked Coil Cables Subject to Pool Fires

Structural cables are used to design critical bridge structures. These are not typically redundant; a loss or compromise of a few cables can lead to the progressive collapse. Previous experimental research has shown that the degradation of material properties and thermal expansion of structural cables is more onerous than the standard carbon prestressing steel. Despite its importance for design no well-validated methodology exists to aid in the thermal performance of structural cables in the event of a fire, particularly for spiral and locked-coil cables which inherently are complex due to their cross-sectional geometry. A state-of-the-art methodology for modelling structural cables' thermal response is presented. The methodology will enable the development of an understanding of the temperature distribution and thermal deformation in a cable cross-section and allow estimation of post-fire resilience. Validation is performed against experiments of locked-coil and spiral cables, subjected to realistic pool fires. The cables range from 22 to 100 mm in diameter and are constructed of galvanized or stainless steel. The cables are modelled undergoing non-linear thermal analysis in LS-DYNA. 2D models are found to provide conservative estimates for critical values such as peak temperature with 90% accuracy, while 3D models provide slightly more conservative estimates.

Improvement on uniformity of diamond coatings on PCB milling cutters with specific cutting edge structures

Recently, specially-designed printed circuit board (PCB) milling cutters with specific cutting edge structures have been extensively applied. Hot filament chemical vapor deposition (HFCVD) diamond coatings uniformly deposited on cemented carbide (WC-Co) cutters can effectively improve their performance. To improve the coating uniformity, the complex cutters were precisely modeled and the temperature field generated by the HFCVD setup was simulated, using the finite volume method (FVM), taking spiral milling cutters as a reference for comparison. Temperature measurements revealed deviations between simulated and measured temperatures smaller than 4%, verifying the accuracy of the constructed model. Effects of some critical HFCVD setup parameters, including the filament height (Hf), the material and height of the sample holder (Ms and Hs), the material and dimensions of the heat insulating block (Mh, Hh and Ah), and the surface convection coefficient (h), were studied by the control variable method. Under the optimized conditions, the axial temperature deviation on cutting edges dropped from 193.3 °C to 64.3 °C for a PCB milling cutter, and from 53.3 °C to 29.6 °C for a spiral cutter, ensuring appropriate temperature ranges for fabricating high-quality diamond films. Besides, the two-dimensional plane temperature field and received radiation field of a cutter were both calculated by MATLAB. The results showed that heat conduction hindrance and heat convection reduction could effectively reduce energy consumption and improve the uniformity of substrate temperature. With the aim to study the specific cutting-edge structures, cross-sectional temperature distributions were further examined by presenting both simulations and numerical calculations. It was seen that the temperature distribution for PCB milling cutters was complicated, which was attributed to the densely-distributed cutting edges and long flute. Lastly, under the optimized HFCVD setup parameters, it was found that the grain size and thickness uniformity of diamond coatings, at different positions along the axial direction, were significantly improved, revealing the effectiveness of simulation as an optimization method.

Fire resistance assessment of RC columns with advanced calculation methods

This paper contains the results of fire resistance calculation of reinforced concrete columns with advanced calculation methods.
 For columns that are tested unloaded, determine the cross-sectional temperature distribution and values of temperature in reinforcement. The fire resistance of columns that have been tested without load is determined according to temperature measurements, with calculation methods according to the requirements of DBN B.1.1-7 andDBN B.1.2-7.
 According to the tabulated method, the fire resistance of reinforced concrete columns is determined by geometric parameters such as cross-section width, axis distance of the reinforcement, amount of reinforcement, length or height of the element, load level during the fire exposure, heating conditions during the fire exposure (number of fire exposed sides).
 Accidental combination of actions during the fire situation consists of characteristic values of permanent and variable long-term actions taking into account the safety factor for the consequence class of the object (CC2) and the type of design situation (accidental).
 Thermal analysis of the column was performed under conditions of the standard fire exposure. In such conditions it was assumed that the column is exposed to fire with four sides for 120 minutes that corresponds to the required fire resistance class R120.
 The thermal state of the column was determined using transient thermal models that take into account radiation-convective heat transfer in the ambient from the heat source to the structural surface, convective heat transfer in the structure, radiation-convective heat exchange from the structure to the ambient environment.
 The residual load-bearing capacity of the reinforced concrete column after the fire exposure was calculated with the reduced cross-section determined using zone method in accordance with the requirements of DSTU-N B B.2.6-197 and DSTU-N B EN 1992-1-2.
 The fire resistance period of columns for the load-bearing criterion was determined on the basis of the results of of thermal and static analysis.

Investigation of concrete box girder positive temperature gradient patterns considering different climatic regions

Due to the inevitable exposure of bridges to complex ambient environment, the effects of temperature variation on the structure itself should be considered. Accurate evaluation of the cross-sectional temperature distribution is a significant concern in the bridge design phase. Temperature gradient patterns have been provided by current bridges codes with the consideration of the thermal effects on the structures. However, the current codes are insufficient to describe the temperature gradients of different climatic regions in China. This paper aims to develop a more efficient positive temperature gradient pattern considering different climatic regions within a 100-year return period. Long-term numerical simulations of two-year continuous thermal actions regarding seven different regions have been conducted to investigate the thermal effects on concrete box girders. Then, the comparison of the simulated results and current bridge design specifications illustrates the deficiencies of the current specifications. Furthermore, a 2-step method with curve fitting and extreme values analysis (EVA) has been utilized to determine the temperature gradient patterns. The curve fitting shows that the temperature gradient patterns of different regions can be described by a piecewise function with parabola. And, EVA shows that all the temperature gradients fit well with the Weilbull distribution. The representative values of different regions have also been obtained through the EVA. Finally, a positive temperature gradient pattern with the consideration of both the locations and design period has been proposed in this paper. The proposed temperature gradient pattern shows a better applicability in different regions comparing with the current Chinese codes. It hopes that the present study could contribute to further application of bridge temperature gradients and the investigation of other infrastructural areas in respect of the temperature gradients.