Effective Temperature Difference Research Articles

Numerical study of heat transfer characteristics of intermittent flow cold storage surface heat exchanger

The intermittent flow cold storage surface heat exchanger is a key component of the new pulse tube expansion cryogenic refrigerator, which is responsible for the periodic heat transfer of cold and hot helium, and its heat exchange efficiency directly affects the thermodynamic efficiency of the whole machine. In this study, a three-dimensional model of the heat exchanger unit is established, and numerical simulation is employed to investigate its heat exchange characteristics. The analysis focuses on understanding the internal temperature distribution patterns within the heat exchanger and explores the influence of wall materials on its heat transfer characteristics. Results show that the existence of the temperature lag loop minimizes the effective heat transfer temperature difference, consequently decreasing the heat exchanger’s efficiency. Moreover, the choice of wall material significantly affects the performance of the heat exchanger, with optimal thermal conductivity and volumetric specific heat enhancing its efficiency. This research provides valuable insights for future design and improvement of similar heat exchangers.

Thermoelectric energy extraction in motion scenarios: Self-powered temperature and pressure detector in an automobile tire

Worldwide, there's a push for carbon reduction through energy conservation. Yet, the potential of employing thermoelectric technology to recover waste heat from moving vehicles remains largely unexplored. This study employs precise simulations to analyze temperature distribution in car tires, unveiling possibilities for energy recovery. At 20 ℃ and 120 km/h, tire temperature peaks at 91.2 ℃ due to friction and rubber deformation. A micro thermoelectric generator (micro-TEG) on the wheel hub, serving as a heat sink, reveals a 3.9 ℃ effective temperature difference. A roadmap, considering factors like ambient temperature, speed, and TE leg size, guides exploration of micro-TEG's maximum power. This leads to a designed module with 8 micro-TEG units (weight: 5.3 g, area: 16 × 4 mm2, fill factor: 20 %, TE leg: 0.4 × 0.4 × 1.2 mm3) in series. Exposed to a 20 ℃ temperature difference, it shows open circuit voltage and maximum power of 1.47 V/1.41 V and 12.06 mW/11.58 mW in flat and curved states. Rigorous testing confirms stability. The 8.96 g module integrates with energy management and Bluetooth circuits. During simulated driving, mobile software records signals with over 94 % consistency. This advances dynamic waste heat recovery, enabling passive tire sensing and innovative links to the Internet of Things (IoT), contributing to field progress.

Magneto-Induced Janus Adhesive-Tough Hydrogels for Wearable Human Motion Sensing and Enhanced Low-Grade Heat Harvesting.

Janus hydrogels with different properties on the two surfaces have considerable potential in the field of material engineering applications. Various Janus hydrogels have been developed, but there are still some problems, such as stress mismatch caused by the double-layer structure and Janus failure caused by material diffusion in the gradient structure. Here, we report a Janus adhesive-tough hydrogel with polydopamine-decorated Fe3O4 nanoparticles (Fe3O4@PDA) at one side induced by magnetic field to avoid uncontrollable material diffusion in the cross-linking polymerization of acrylamide with alginate-calcium. The magneto-induced Janus (MIJ) hydrogel has an adhesive surface and a tough bulk without an obvious interface to avoid stress mismatch. Due to the intrinsic dissipative matrix and the abundant catechol groups on the adhesive surface, it shows strong adhesion onto various substrates. The MIJ hydrogel has high sensitivity (GF = 0.842) in detecting tiny human motion. Owing to the synergy of Fe3O4@PDA-enhanced interfacial adhesion and heat transfer, it is possible to quickly generate effective temperature differences when adhering to human skin. The MIJ hydrogel achieves a Seebeck coefficient of 13.01 mV·K-1 and an output power of 462.02 mW·m-2 at a 20 K temperature difference. This work proposes a novel strategy to construct Janus hydrogels for flexible wearable devices in human motion sensing and low-grade heat harvesting.

Effect of operating conditions on the output performance of a compact TEG for low-grade geothermal energy utilization

Thermoelectric generators (TEGs) offer a promising solution for harnessing low-grade heat sources including geothermal energy. However, the limited ZT values of current thermoelectric materials and the absence of advanced material-to-system integration technology result in suboptimal performance compared to conventional power generation methods, thereby constraining their large-scale applications in practice. This study has developed a compact TEG, featuring mini-channel liquid–liquid heat exchangers, to simulate low-medium temperature geothermal fluid utilization. The TEG performance was experimentally investigated and the cause of the degradation in module-to-system performance was revealed. The impacts of operational conditions and several beneficial strategies for optimizing thermoelectric performance were systematically analyzed. The results showed that the primary factor contributing to the reduction in module-to-system conversion is attributed to a decrease in internal effective temperature difference, resulting in a 12% decline in open-circuit voltage and a 26% drop in TEG power performance. The implementation of strategies, such as optimizing the flow rate of cooling water, adjusting assembly pressure, and utilizing appropriate thermally conductive pads, resulted in significant increases in net power output by 7.07%, 27.9% and 24.3%, respectively. The economic analysis also suggests that our TEG design can achieve a competitive cost and higher power performance compared to other designs, showcasing its potential for large-scale application in geothermal energy utilization.

Modeling study on the geometric optimization of thermoelectric modules

Abstract The performance of thermoelectric power generators (TEG) primarily depends on the properties of the thermoelectric materials employed. For conventional thermoelectric modules (TEM) utilizing the same material, the geometric parameters also play a significant role in determining TEM performance. As such, optimizing the geometry of TEM can lead to improved performance. In this study, TEM were modeled, designed, fabricated, and tested to investigate the effects of different geometric parameters on their performance. Numerical simulations were conducted under both constant temperature and constant flow boundary conditions, and the results were validated through experimental testing. The simulation results under constant flow boundary conditions exhibited good agreement with the experimental results. The effects of thickness, cross-sectional area, and filling ratio of thermoelectric legs on TEM performance were investigated through numerical simulations and compared with findings from previous studies. It was observed that increasing the cross-sectional area of the thermoelectric legs led to a decrease in the power output of TEM. Conversely, increasing the filling ratio effectively enhanced the TEM's performance. Furthermore, an optimal thermoelectric leg thickness was identified through the numerical simulations that could yield the maximum power output of TEM. The underlying mechanism behind this observation was explained, shedding light on why different reports have identified different optimal thicknesses. Optimizing the thermoelectric leg thickness can help maintain a high effective temperature difference and low internal resistance, which can vary based on the specific type of TEM and the thickness and thermal conductivity of the insulating substrates and copper sheets.

Structural effects on the performance of microfabricated in-plane π -type thermoelectric devices composed of p-type Mg2Sn0.8Ge0.2 and n-type Bi layers

Miniaturized in-plane π-type thermoelectric devices composed of p-type Mg2Sn0.8Ge0.2 and n-type Bi layers were prepared by microfabrication techniques. Structural effects on thermoelectric device performance need to be evaluated and optimized to improve device performance and operation. In this study, a rational analysis of the correction of the open-circuit output voltages, output powers, and output power densities by using effective temperature differences was performed, and the effects of device geometries (e.g., the number of π junctions and the cross-sectional area ratio between p- and n-type layers) were determined by comparing different types of in-plane π-type thermoelectric devices. The results revealed that it is crucial to consider the heat transfer loss caused by thermal contact effects in the device and to optimize the structural geometries of the device. Proper structural trends and the effects of the number of p–n pairs on the device performance were observed, which indicated the reasonable device operation of microfabricated in-plane π-type thermoelectric devices.

Optimal Design of Wearable Micro Thermoelectric Generator Working in a Height-Confined Space

With the increasing development of self-powered wearable electronic devices, there is a growing interest in thermoelectric generators (TEGs). To achieve more comprehensive and reliable functionality of wearable devices, improving the power generation performance of thermoelectric devices will be the key. It has been shown that integrating a heat sink at the cold end of the TEG increases the effective temperature difference and, thus, maximizes the power output of the thermoelectric device. However, the space left for the power supply is often limited. How to optimize the integrated system of micro-thermoelectric generators and heat sinks in a height-confined space has become the key. In this study, we have established a corresponding model using a numerical calculation method, systematically studied the influence of TEG geometric size on the number of fins and fin height, and determined the optimal number of fins for the highest equivalent convective heat transfer coefficient corresponding to different fin heights. We also conducted the co-design of TEG and fin topological structure to study the effects of the ratio of leg height to fin height (l/H), the width of legs (w), and the number of thermoelectric leg pairs (N) on the maximum output power density per unit area (Pm1) and the maximum output power density per unit mass (Pm2) of the device. When N = 16, w = 0.3 mm, l/H = 2.5 (that is, l = 3.57 mm, H = 1.43 mm), and Pm1 reaches the maximum value of 30.5 μW/cm2; When N = 2, l/H = 0.25 and w = 0.3 mm, and Pm2 reaches a maximum value of 5.12 mW/g. The measured values of the open-circuit voltages of fabricated micro-TEGs with different thermoelectric leg heights (l = 0.49 mm, l = 1.38 mm, and l = 1.88 mm) are basically consistent with the simulated values. When N = 2, l = 0.49 mm, H = 3.74 mm, and w = 0.85 mm, and Pm2 reaches 0.44 mW/g. The results provide insights into the optimal design of wearable micro thermoelectric generator working in a height-confined space and highlight the importance of co-designing TEGs and fin topological structures for optimizing their performance.

High-Performance Wearable Bi2Te3-Based Thermoelectric Generator

Wearable thermoelectric generators (w-TEGs) convert thermal energy into electrical energy to realize self-powering of intelligent electronic devices, thus reducing the burden of battery replacement and charging, and improving the usage time and efficiency of electronic devices. Through finite element simulation, this study successfully designed high-performance thermoelectric generator and made it into wearable thermoelectric module by adopting “rigid device—flexible connection” method. It was found that higher convective heat transfer coefficient (h) on cold-end leads to larger effective temperature difference (ΔTeff) and better power generation performance of device in typical wearable scenario. Meanwhile, at same h on the cold-end, longer TE leg length leads to larger ΔTeff established at both ends of device, larger device output power (Pout) and open-circuit voltage (Uoc). However, when the h increases to a certain level, optimization effect of increasing TE leg length on device power generation performance will gradually diminish. For devices with fixed temperature difference between two ends, longer TE leg length leads to higher resistance of TEGs, resulting in lower device Pout but slight increase in Uoc. Finally, sixteen 16 × 4 × 2 mm2 TEGs (L = 1.38 mm, W = 0.6 mm) and two modules were fabricated and tested. At hot end temperature Th = 33 °C and cold end temperature Tc = 30 °C, the actual maximum Pout of the TEG was about 0.2 mW, and the actual maximum Pout of the TEG module was about 1.602 mW, which is highly consistent with the simulated value. This work brings great convenience to research and development of wearable thermoelectric modules and provides new, environmentally friendly and efficient power solution for wearable devices.

Analyzing the Performance of Thermoelectric Generators with Inhomogeneous Legs: Coupled Material–Device Modelling for Mg2X-Based TEG Prototypes

Thermoelectric generators (TEGs) possess the ability to generate electrical power from heat. As TEGs are operated under a thermal gradient, inhomogeneous material properties—either by design or due to inhomogeneous material degradation under thermal load—are commonly found. However, this cannot be addressed using standard approaches for performance analysis of TEGs in which spatially homogeneous materials are assumed. Therefore, an innovative method of analysis, which can incorporate inhomogeneous material properties, is presented in this study. This is crucial to understand the measured performance parameters of TEGs and, from this, develop means to improve their longevity. The analysis combines experimental profiling of inhomogeneous material properties, modelling of the material properties using a single parabolic band model, and calculation of device properties using the established Constant Property Model. We compare modeling results assuming homogeneous and inhomogeneous properties to the measurement results of an Mg2(Si,Sn)-based TEG prototype. We find that relevant discrepancies lie in the effective temperature difference across the TE leg, which decreases by ~10%, and in the difference between measured and calculated heat flow, which increases from 2–15% to 9–16% when considering the inhomogeneous material. The approach confirms additional resistances in the TEG as the main performance loss mechanism and allows the accurate calculation of the impact of different improvements on the TEG’s performance.

Thermal optimization research of vertical tube climbing film desalination system

Abstract Based on the pinch theory and energy cascade utilization principle, the performance of a multi-effect shipboard vertical tube climbing film desalination system combined thermal vapor compression with different preheating configuration has been analyzed. The mathematical model is established for thermodynamic simulation, in which various thermodynamic losses caused by boiling point elevation and pressure drop are considered, and the effective heat transfer temperature difference and the hot side temperature difference are used to analyze the influences of heating steam temperature, final effect evaporation temperature, and concentration ratio on thermal performance including gained output ratio (GOR)—specific heat transfer area for different preheating configuration. The results show that the internal average effective heat transfer temperature difference determines characteristics of multi-effect distillation (MED) system. While for system with similar average effective heat transfer temperature, the temperature difference of hot side is the controlling parameter. And the energy cascade utilization principle shows the controlling attribute in MED thermodynamic system, as GOR is improved mainly due to utilization of the secondary energy and residual energy of the heating steam for preheating process.

Reinforced temperature control of a reactive double dividing-wall distillation column

The mass and thermal coupling makes the control of the reactive double dividing-wall distillation column (R-DDWDC) an especially challenging issue with a highly interactive nature. With reference to the separation of an ideal endothermic quaternary reversible reaction with the most unfavorable ranking of relative volatilities (A + B ↔ C + D with α A > α C > α D > α B ), the operation rationality of the R-DDWDC is studied in this contribution. The four-point single temperature control system leads to great steady-state discrepancies in the compositions of products C and D and the reason stems essentially from the failure in keeping strictly the stoichiometric ratio between reactants A and B. A temperature plus temperature cascade control scheme is then employed to reinforce the stoichiometric ratio control and helps to secure a substantial abatement in the steady-state discrepancies. A temperature difference plus temperature cascade control scheme is finally synthesized and leads even to better performance than the most effective double temperature difference control scheme. These outcomes reveal not only the operation feasibility of the R-DDWDC but also the general significance of the proposed temperature difference plus temperature cascade control scheme to the inferential control of any other complicated distillation columns.

Timing the formation of the galactic thin disc with asteroseismic stellar ages

ABSTRACT The formation of the extended thin disc is the most spectacular event of our Galaxy in the past ∼8 Gyr. To unveil this process, obtaining precise and accurate stellar ages for a large sample of stars is essential although challenging. In this work, we present the asteroseismic age determination of 5306 red giant branch stars using Kepler and LAMOST data, with a thorough examination of how the age determination is affected by the choice of different temperature scales and stellar models. Thanks to the high precision of the asteroseismic and spectroscopic parameters of our sample stars, we are able to achieve age determination with an average accuracy of 12 per cent. However, the age determination is sensitively dependent on the adopted temperature scale, as 50 K difference in effective temperature may cause larger than 10 per cent systematic uncertainty in the age estimates. Using the ages derived with the most plausible set of the temperature scale, we study the age distribution of the chemical thin disc stars, and present an estimate of the formation epoch of the first Galactic thin disc stars. We find that the first (oldest) thin disc stars have an age of $9.5^{+0.5(\rm rand.)+0.5(\rm sys.)}_{-0.4(\rm rand.)-0.3(\rm sys.)}$ Gyr, where the systematic uncertainties reflect ages estimated using different stellar evolutionary models. At this epoch, the Galactic thick disc was still forming stars, indicating there is a time window when both the thin and thick discs of our Galaxy were forming stars together. Moreover, we find that the first thin disc stars exhibit a broad distribution of Galactocentric radii, suggesting that the inner and outer thin discs began to form simultaneously.

Energy Harvesting from Thermal Variation with Phase-Change Materials

Phase-change materials with temperature-dependent thermal conductivity have drawn lots of attention recently. They have exhibited promising potentials in devices such as the thermal diode, thermal memristor, etc. Here we investigate the heat exchange between two reservoirs through a bare phase-change material. In the presence of temperature variation in one of the reservoirs, we find a unidirectional thermal flux between those two reservoirs though they share the same average temperature, i.e., no temperature bias. By mapping such a system to the heat exchange between two reservoirs through a regular material with a constant thermal conductivity, we obtain an effective temperature difference ${T}_{\mathrm{eff}}$, which should present to maintain the unidirectional thermal flux. We then provide a semianalytical formula for ${T}_{\mathrm{eff}}$, which works well over an extensive parameter range. The parameter dependence of ${T}_{\mathrm{eff}}$ and the temperature dependence of the thermal capacity are then studied in detail. Our work thus provides a useful tool for calibration of heat conduction within phase-change materials and leads to potential applications related to energy extraction from the thermal variation of the environment.

Precise prediction of optical behaviour of mechanically stressed edge emitting GaAs devices

The presence of a thermally annealed metallization layer on top of a GaAs slab waveguide proofed to be of strong impact on the optical device behavior. Induced by the stress on the chip the elasto-optical effect imprinted a strong variation on the refractive index that led to anti-guiding and guiding effects. In order to enable precise prediction of the optical behavior we present a 3D mechanical device simulation which provides detailed insights to the overall stress state. The results are then used in a 2D in-house developed optical simulation that allows precise analysis of the microscopic optical behavior. Therefore, the accumulated stress effects are represented by an effective temperature difference between semiconductor and metallization, which allows a strong simplification of the model setup. The results are validated by comparison to the experimental derived data. As the simulation proves to be highly accurate, the stress load on the device can be calculated vice versa from the optical behavior.

Soft-covered wearable thermoelectric device for body heat harvesting and on-skin cooling

The recent emergence of self-powered wearable electronics gives rise to a growing demand for flexible, sustainable, and portable power supply. Wearable thermoelectric devices (WTEDs) are promising power sources for wearable electronics through directly converting body heat into electricity. However, the output power of WTEDs is still low due to the extremely small effective temperature difference across thermoelectric pillars, which hinders their practical applications. Commonly used strategies to enlarge the effective temperature difference for WTEDs, such as introducing metallic heat sinks or increasing the length of thermoelectric pillars, usually lead to clunky devices that are not suitable for wearable electronics. Here, we report on a soft-covered WTED for body heat harvesting and on-skin cooling, which demonstrates the desirable performance and wearer comfort. Distinct from the previously reported flat soft heat spreaders, this work presents the design and fabrication of a pin–fin soft cover that can serve as a flexible heat sink for WTEDs. The pin–fin soft cover was fabricated by curing the liquid metal/elastomer composite in a meltable wax mold. Systematic theoretical and finite element analysis was conducted to optimize the output power and wearability of the soft-covered WTED. The optimized WTED achieves a power density of 6.63 μW cm−2 on a stationary human body under natural convection condition with an ambient temperature of 20 °C, which is higher than the previously reported WTEDs with flat soft covers made of high-thermal-conductivity elastomers. Furthermore, our WTED can realize a 1.5 °C temperature drop for the human skin through Peltier cooling. This work demonstrates a new route to develop soft-covered WTEDs for self-powered wearable electronics and personal thermoregulation.

Theoretical Study on Thermal Hydraulic Expansion Process of Stainless Steel Lined Clad Pipe

Abstract The stainless steel lined clad pipe (SSLCP) can be widely used in different fields. Industrial SSLCP are generally manufactured by the cold hydraulic expansion (CHE) method which requires high hydraulic pressure and good sealing property. The interlayer bonding force is difficult to obtain by the CHE when there is little difference between the yield strengths of inner and outer pipes. Furthermore, the hydraulic expansion process nearly cannot be achieved when the yield strength of inner pipe is higher than that of outer pipe. The thermal hydraulic expansion (THE) method can overcome these difficulties. In this paper, the graph method was adopted to analyze the THE principles for “inner strong and outer weak (ISOW)” and “outer strong and inner weak (OSIW)” pipes. The effective hydraulic expansion criterion conditions of SSLCPs were proposed and can be used as basis of clad pipe material matching and forming process selection. Through the stress and strain analysis of inner and outer pipes during THE process, the deformation coordination conditions of elastic deformation and thermal deformation of the inner and outer pipe were established. The correlation between the residual contact pressure p*c, the hydraulic expansion pressure pi, and the effective temperature difference ΔTe were derived. The calculation formula of the maximum expansion pressure pimax and the minimum expansion pressure pimin was obtained. The maximum heating temperature of outer pipe was also derived. Furthermore, the finite element analysis (FEA) method was adopted and simulated results verify the feasibility and applicability of the theory study.

Fabrication and performance prediction of Ni/Bi0.5Sb1.5Te3 artificially-tilted multilayer devices with transverse thermoelectric effect

Artificially-tilted multilayer transverse thermoelectric devices (ATMTTDs) have a large degree of design freedom, which is convenient for designing devices for different working conditions. However, evaluation and preparation of ATMTTDs has generally been based on trial and error, and coherent performance optimization strategies for different ATMTTDs applications is still lacking. Here, the relationship between performance evaluation indicators, transverse thermoelectric properties, and geometric structure parameters of ATMTTDs has been established via theoretical calculation and experimental verification. The results show that the tilt angle (θ) has a key effect on the transverse thermoelectric properties of ATMTTDs. The optimal transverse thermoelectric figure of merit, power factor, and Seebeck coefficient of Ni/Bi0.5Sb1.5Te3 (BST) ATMTTDs are theoretically predicted at tilt angles of 11°, 21°, and 45°, respectively. Ni/BST ATMTTDs have been fabricated and the experimental results demonstrated that a maximum power generation efficiency of 1.01% and maximum effective refrigeration temperature difference of 0.4 K are reached at θ = 11°, maximum output power density of 411 W/m2 is obtained at θ = 21°, and a maximum response sensitivity of 420 μV/K is achieved at θ = 45°, which is in good agreement with theoretical predictions. This work provides theoretical guidance for manufacturing ATMTTDs for different applications.

The coupling process of steam condensation and falling film evaporation with non-condensable gas

For the steam condensation process inside a horizontal tube under small temperature difference, the operating parameters such as steam flow rate and temperature difference are narrowed in limited variation ranges to guarantee the high heat transfer performance. When the steam is mixed with non-condensable gas, the effective temperature difference shows more complexity compared with pure steam condensation. In this paper, the condensation process of the mixed steam in the tube cooled by the falling film evaporative seawater outside the tube is calculated with the steam mass flow rate of 2–9 kg/(m2·s), the evaporation temperature of the seawater of 50–70 °C, the total temperature difference of 2–4 °C and the inlet non-condensable gas (NCG) mass fraction of 1–4%. The mixed steam condensation heat transfer model combined with distributed parameter model is established and validated to couple the heat transfer on both sides of the tube. The local saturation temperature depression of the mixed steam condensation is divided into two factors, one caused by the flow resistance and the other caused by the non-condensable gas mass fraction. Both types of saturation temperature depression increase with the increase of the inlet non-condensable gas mass fraction. The mass flow rate and the temperature difference are found to have more significant impact on the total temperature depression on the saturation temperature. Besides, the saturation temperature is found to have no significant impact on the condensation heat transfer of the mixed steam. The mass flow rate corresponding to the maximum heat transfer of the heat transfer tube is presented.

Phase-Change Process Inside a Small-Radii Cylinder Subjected to Cyclic Convective Boundary Conditions: A Numerical Study

Abstract We numerically investigate the melting and solidification behavior of phase-change materials (PCMs) encapsulated in a small-radii cylinder subjected to a cyclic convective boundary condition (square-wave). First, we explore the effects of the Stefan and Biot numbers on the nondimensionalized time required for a PCM initially held at Tcold to melt and reach the crossflow temperature Thot (i.e., reference Fourier number T̃ref). The increase in either Stefan or Biot number decreases T̃ref which can be predicted accurately using the correlation developed in this work. The variations of the PCM melt fraction, surface temperature, and heat transfer rate as a function of Fourier number are reported and analyzed. We further study the effect of the cyclic Fourier number T̃ on the periodic melting and freezing process. The melting or freezing front initiates at the outer periphery of the PCM and propagates toward the center. At higher frequencies, multiple two-phase interfaces are generated (propagating inward), and the surface temperature oscillates in the vicinity of the melting temperature. This increases the effective temperature difference with the crossflow and leads to a higher overall heat transfer.

Mapping temperature contours for a long-span steel truss arch bridge based on field monitoring data

The temperature-induced response of long-span steel bridges can be more significant than the structural responses associated with operational loads or structural damage. These responses depend on the spatio-temporal temperature variation in bridge members, including the effective temperature and temperature difference within members. Bridges are designed to withstand the extreme temperature variations predicted for a given site. Hence, numerous studies have employed statistical analysis techniques to provide critical information for the design and maintenance of bridges during life cycles. However, the correlation between the effective temperature and temperature difference is usually ignored, which can result in inaccurate assessment of the extreme temperatures in members. In this work, the joint probability distribution for the temperature variation in a long-span steel truss arch bridge is investigated based on field monitoring data. The extreme temperature variations are mapped on contours with relevant return periods; the results show that the probability distribution of the effective temperature can be described using the normal distribution; the weighted sum of two lognormal distributions can describe the distribution of temperature difference. Moreover, extreme values of the effective temperature and temperature difference do not occur concurrently. The effective temperature and temperature difference in the structural member directly exposed to solar radiation vary significantly, while the temperature of the shaded member can be assumed uniform, which is mainly affected by air temperature. The study leads to more accurate estimation of the temperature extremes in long-span steel truss arch bridges, which is of great importance for proper design and maintenance of bridges.