Asymmetric Temperature Distribution Research Articles

Ion current rectification coupled with asymmetric temperature and surface charge in ultrashort conical nanopores

Ion current rectification (ICR) is one of the electrodynamic properties in asymmetric nanochannels, which has been utilized to develop biosensors, heavy metal ion detection, and ion diodes. Previous studies on ICR mainly focused on long nanopores (length >500 nm), and relatively few studies on ion rectification performance in short nanopores. Here, we use a finite element numerical solution to simulate the effect of coupling asymmetric temperature and surface charge distribution on the ion rectification performance of ultrashort conical nanopores (length = 100 nm). The results show that the ion rectification performance is significantly improved when the inner and outer surfaces of the nanopore are charged non-uniformly, which is more than three times that when the inner surface of the nanopore is charged non-uniformly or the outer surface is charged non-uniformly. In addition, the positive temperature difference enhances the ion enrichment and dissipation and improves the ion rectification performance of nanopores. On the contrary, negative temperature difference inhibits ion enrichment and dissipation in pores, which is not conducive to improving ion rectification performance. Abnormal behavior is observed for nanopores non-uniform charged only on the outer wall surface, where the negative temperature gradient enhances the accumulation and dissipation of ions within the pores, thereby increasing the rectification ratio. In addition, in order to more clearly understand the ion transport behavior in the ultrashort nanopore under asymmetric temperature conditions, we further investigated the influence of the tip radius of the nanopore, the solution volume concentration, and the charge type of each surface charge distribution on the ion current rectification performance. The results reveal the ion transport mechanism of ultrashort conical nanopores and provide practical guidance for designing and optimizing nanofluidic devices.

Optimal design of supercritical He–H2 PCHE in SABER system by multi-objective genetic algorithm

A double-circle straight-channel printed circuit heat exchanger (PCHE) was first employed in a synergistic air-breathing rocket engine (SABER) system for supercritical He and H2 heat transfer. The heat transfer mechanism of the supercritical flow in the PCHE channel was numerically analyzed. For considered the pressure drop, heat transfer efficiency, and ratio of heat flux to weight, simultaneously, the design of the PCHE is multi-objective genetic optimized. The results shown that the supercritical H2 flow is chaotic near the pseudo-critical point, which is a coupled effect of buoyancy and gravity. Chaotic flow leads to an asymmetrical temperature distribution, which deteriorates the heat transfer performance. For 27 numerical experimental cases designed using the center composite surface method, the determine factors of the regression models of the three objectives for both cold and hot sides were all above 92 %. The Pareto optimal solutions for the supercritical He - H2 PCHE design and performance were obtained based on the nondominated sorting genetic algorithm II. From a comprehensive view of the three targets, the optimal designs were the A-4 and B-4 solutions for the cold and hot sides, respectively.

Abell 746: A Highly Disturbed Cluster Undergoing Multiple Mergers

We present deep XMM-Newton, Karl G. Jansky Very Large Array, and upgraded Giant Metrewave Radio Telescope observations of Abell 746, a cluster that hosts a plethora of diffuse emission sources that provide evidence for the acceleration of relativistic particles. Our new XMM-Newton images reveal a complex morphology of the thermal gas with several substructures. We observe an asymmetric temperature distribution across the cluster: the southern regions exhibit higher temperatures, reaching ∼9 keV, while the northern regions have lower temperatures (≤4 keV), likely due to a complex merger. We find evidence of three surface brightness edges and one candidate edge, of which three are merger-driven shock fronts. Combining our new data with published LOw-Frequency ARray observations has unveiled the nature of diffuse sources in this system. The bright NW relic shows thin filaments and a high degree of polarization with aligned magnetic field vectors. We detect a density jump, aligned with the fainter relic to the north. To the south, we detect high-temperature regions, consistent with the shock-heated regions and a density jump coincident with the northern tip of the southern radio structure. Its integrated spectrum shows a high-frequency steepening. Lastly, we find that the cluster hosts large-scale radio halo emission. A comparison of the thermal and nonthermal emission reveals an anticorrelation between the bright radio and X-ray features at the center. Our findings suggest that Abell 746 is a complex system that involves multiple mergers.

3D numerical simulation on thermal hydraulic characteristics in integrated sodium pool of PHENIX reactor during dissymmetric test

Temperature distribution of internals under different transient events is important for the design and safety analysis of pool-type sodium-cooled fast reactor (SFR). It is influenced by overall flow and thermal stratification phenomena in the multi-scale sodium pool. Due to the difficulty to perform experiment, three-dimensional (3D) numerical method is usually adopted for obtaining the temperature distribution and analyzing complex phenomena in pool-type SFRs. It needs to be further validated using the published benchmark, such as PHENIX Dissymmetric Test. The simplified model in system code and 3D model of local area in current study cannot capture the complex coupling effect of cold and hot pool during dissymmetric test. In this paper, an integrated 3D model of PHENIX reactor primary system both including cold and hot pools is established. The steady and transient simulation with 1800 s of PHENIX Dissymmetric Test process are carried out. The key parameters of simulation are compared with the available experimental and predicted data, which achieves good agreement. Overall flow and asymmetric temperature distribution phenomena in cold pool, hot pool and local area of IHX inlet are simulated. There is a temperature difference between different sides of IHX inlet during a period after scram, with the maximum value of 80 ℃ approximately at 90 s. This validated numerical method can be further used for the analysis of thermal hydraulic characteristics in other pool-type SFR. The obtained temperature distribution of internals can provide the reference for the stress assess of structures in the engineering design.

Thermoelectric Limitations of Graphene Nanodevices at Ultrahigh Current Densities.

Graphene is atomically thin, possesses excellent thermal conductivity, and is able to withstand high current densities, making it attractive for many nanoscale applications such as field-effect transistors, interconnects, and thermal management layers. Enabling integration of graphene into such devices requires nanostructuring, which can have a drastic impact on the self-heating properties, in particular at high current densities. Here, we use a combination of scanning thermal microscopy, finite element thermal analysis, and operando scanning transmission electron microscopy techniques to observe prototype graphene devices in operation and gain a deeper understanding of the role of geometry and interfaces during high current density operation. We find that Peltier effects significantly influence the operational limit due to local electrical and thermal interfacial effects, causing asymmetric temperature distribution in the device. Thus, our results indicate that a proper understanding and design of graphene devices must include consideration of the surrounding materials, interfaces, and geometry. Leveraging these aspects provides opportunities for engineered extreme operation devices.

The role of near-wall downdraught and asymmetric temperature distribution in dispersion of respiratory aerosols in radiant floor heating systems

In radiant floor heating (RFH) systems, the downdraught due to the asymmetric temperature distribution causes descending airflows towards the floor surface, where the warm air adjacent to the RFH system tends to be driven upwards by the buoyancy force. Hence, this conflict creates a zone that prevents the warm air to ascend affecting the streamlines of the indoor air. The present study aims to investigate the integrated effects of this phenomenon at different levels of the RFH temperature and thermal transmittance on the behaviour of indoor airborne particles (PMs2.5). In this context, a Eulerian-Lagrangian computational fluid dynamic (CFD) code is established, validated against experimental data, to address the dispersion and deposition patterns of PMs2.5. To generate different levels of the downdraught and non-uniform temperature distribution, five scenarios are considered regarding different thermal transmittance (U-value) levels, assessed for four RFH temperatures. Firstly, by introducing the near-wall and zonal spaces, the dispersion of particles in each scenario is evaluated. Then, the role of RFH system temperature in conjunction with each scenario is investigated. Finally, simple correlations are proposed allowing for fast evaluation of the decay rate coefficient of PMs2.5. According to the obtained results, the asymmetric temperature distribution causes a striking disparity in the zonal concentration of suspended PMs2.5, i.e., up to 32 % difference in the number of particles between quarters. It is shown that a faster decay rate of PMs2.5 is associated with a larger value of the characteristic temperature difference and the Rayleigh number (Ra). For a given RFH temperature, thermal performance improvement of the envelope reduces the number of deposited particles on the ceiling surface, whereas it gives a boost to the number of particles adhering to the floor. A sensitivity analysis on the results revealed that a 1 °C increment in the RFH temperature leads to an 8.4 % reduction on average in the number of suspended PMs2.5 in the breathing zone, regardless of the level of thermal transmittance from surrounding walls.

Numerical investigation of supercritical flow and heat transfer mechanism in printed circuit heat exchanger (PCHE) channels

A numerical study is conducted to investigate supercritical hydrogen flow and heat transfer mechanisms and characteristics in printed circuit heat exchanger (PCHE) channels. The impact of large variations of the thermal-physical properties due to a wide range of operating temperatures have been studied and analyzed in detail. The heat transfer mechanisms of supercritical hydrgen under horizontal and vertical flow conditions are studied numerically. In addition, the influence of different cross-section shapes of the channel is also analyzed. The results show that asymmetrical fluid temperature distributions near the top wall and bottom wall due to the buoyancy effect result in heat transfer deterioration. Spiral flow occurs in the heat transfer deterioration region, which further confirms that the heat transfer deterioration is related to the spiral flow effect caused by the buoyancy effect. The heat transfer coefficient without gravity is lower than that with gravity, indicating that the buoyancy effect enhances the overall heat transfer in the horizontal circular channel. Furthermore, the fluid temperature in the vertical upflow channel decreases slowly from the near wall to the core area, while the fluid temperature in the vertical downflow channel changes sharply, which directly leads to the difference in the temperature gradient near the wall. Compared with the square cross-section channel and semicircular cross-section channel, the supercritical hydrogen can achieve greater heat transfer performance in the circular cross-section channel.

Study of twisting of β-Ga2O3 crystals based on optical absorption and thermal conductivity anisotropy in the crystals grown by the Czochralski method

The effects of internal radiation and thermal conductivity anisotropy in β-gallium oxide crystals on heat and mass transfer in the Czochralski method were numerically studied. Specifically, we calculated the temperature and velocity distributions in a crystal and/or melt and the interface shape between the crystals and melt for the Czochralski method. We used the Rosseland approximation to include the internal radiation in the crystals to calculate the heat transfer in the crystal. Moreover, the thermal conductivity anisotropy in the crystals was considered to study the asymmetric temperature distribution.The results indicated that the temperature gradient in the semitransparent crystal was smaller than that in the opaque crystal. This result is attributed to the absorption of the outgoing heat flux from the interface between the crystal and melt in the crystal. We studied the asymmetric temperature distributions in the crystals caused by thermal conductivity anisotropy as a function of the crystal absorption coefficient.The results also indicated that the interface shape between a semitransparent crystal and the melt was convex to the melt, whereas the shape between an opaque crystal and the melt was almost flat.

Analysis of Evaporation of Droplet Pairs by a Quasi-Steady-State Diffusion Model Coupled with the Evaporative Cooling Effect.

Multidroplet evaporation is a common phase-change phenomenon not only in nature but also in many industrial applications, including inkjet printing and spray cooling. The evaporation behavior of these droplets is strongly affected by the distance between neighboring droplets, and in particular, evaporation suppression occurs as the distance decreases. However, further quantitative information, such as the temperature and local evaporation flux, is limited because the analytical models of multidroplet evaporation only treat vapor diffusion, and the effect of the latent heat transfer through the liquid-vapor phase change is ignored. Here, we perform a numerical analysis of evaporating droplet pairs that linked vapor diffusion from the droplet surface and evaporative cooling. Heat transfer through the liquid and gas phases is also considered because the saturation pressure depends on the temperature. The results show an increase in the vapor concentration in the region between the two droplets. Consequently, the local evaporation flux in the proximate region significantly decreases with decreasing separation distance. This means that the latent heat transfer through the phase change is diminished, and an asymmetrical temperature distribution occurs in the liquid and gas phases. These numerical results provide quantitative information about the temperature and local evaporation flux of evaporating droplet pairs, and they will guide further investigation of multiple droplet evaporation.

Temperature variation and influence on local mechanical properties assessed by nanoindentation in AA6061-AA7075 dissimilar FSW

The present study aims to elucidate the temperature advancement along and transverse to the weld direction during dissimilar friction stir welding (FSW) between AA6061-T6 and AA7075-T651 with two different tools. Temperature measurements by thermocouples near surface and inside the plates exhibited faster rise in temperature for the threaded with intermittent flat faces pin. Experimental measurements and finite element simulation shows asymmetric temperature distribution in-and-near the stir zone (SZ) with high temperature towards retreating side (AA7075) whereas at distant, temperature is slightly higher on advancing side (AA6061) owing to its higher thermal diffusivity. Additionally, asymmetricity is also noted under shoulder influence region, as well along the weld line with higher temperature towards the trailing side. The electron back scatter diffraction analysis shows regions experienced high temperature yielded high angle grain boundaries. Higher modulus and hardness for AA6061 in the recrystallized region is noted from nanoindentation tests as grain refinement along with the intense strain and dislocation pileup at grain boundaries prevailed the other strengthening mechanism. Recrystallized AA7075 within SZ demonstrated reduction in hardness with respect to base metal due to the dissolution of strengthening precipitates.

Numerical study of the effects of excess air ratio on passive pre-chamber jet performance and ignition mechanism

Pre-chamber (PC) ignition is a promising lean-burn technology to improve the efficiency of spark ignition (SI) engines while achieving ultra-low NOx emissions. However, the significant effects of the excess air ratio (λ) on the PC jet performance and ignition mechanism were still not fully unraveled. The current study numerically investigated the jet characteristics and combustion behaviors of a narrow-throat PC with two rows of orifices on a passive PC engine fueled with methane. The numerical model was validated extensively by the pressure, heat release rate, and natural flame luminosity (NFL) imaging of the PC flame jet. A detailed comparison of the NFL images of the jets and the simulated flame iso-faces presented excellent matching in the flame jet penetration and propagation process. The results reveal that the λ = 0.9 case has the best jet performance, but it doesn’t lead in every jet characteristic. For instance, the jet temperature is highest under λ = 1.0, and OH concentration is most under λ = 1.1. The transition from cold jet to flame jet produces noticeable jet non-uniformity, which is reported for the first time. This observation can be remarked as a more accurate indication of the initiation of pre-chamber flame jet discharge. The asymmetrical mixture inflow from the main chamber produces asymmetrical turbulent kinetic energy (TKE) and temperature distributions; these result in different flame propagation in the PC, jet non-uniformity, and varied stages of jet discharge. The upper jets are quenched in every case because of the much higher TKE, while the lower jets don’t present quenching when the λ ranges from 0.9 to 1.3; especially, the λ = 1.1 case has the best ignition performance for its most OH radicals. The “jet ignition regime”, in which flame quenching takes place, results in highly non-uniform flame propagation and low flame propagation speed. The ultra-rich case shows more signs of jet ignition and thus exhibits worse jet performance than the lean cases. This study uncovers the mechanisms and the optimal λ value for the pre-chamber ignition of the main chamber charge, providing valuable guidance for PC design.

Numerical Study of Heat Transport in Static Liquid Metal Exposed to Plasma with Magnetic Field

Suitable management of excessive heat in liquid metal is one of key roles to accomplish the proper liquid metal usage as future alternative fusion plasma facing components. In this work, theoretical heat transfer in liquid metal in contact with magnetized plasma was carried out, and a numerical solver for investigating temperature and induced velocity by j×B force has been developed. The study suggests the trends: 1. lower bulk temperature in liquid metal at which magnetic field is presented, compared to no magnetic field, by additional convection from j × B, stronger than natural convection; and 2. asymmetric temperature distribution in liquid metal along j × B.

Impact of installation error and tracking error on the thermal-mechanical properties of parabolic trough receivers

As the solar energy utilization technology for renewable clean energy, actual parabolic trough receivers are subject to tracking errors and absorber tube installation errors, and the bellows and Kovar ring under these errors have a significant impact on the receiver's safety. Based on the MCRT-FVM-FEM principles in this paper, a receiver's optical-thermal-stress mathematical model is modeled and the thermal-stress performance and safety of the receiver's key components under two errors are evaluated. The correlation between the bellows and Kovar ring's performance and the two errors is analyzed. The results demonstrate that the lower tracking errors and larger installation errors markedly increment the absorber's deformation and have a negative impact on the receiver safety. Bellows and Kovar ring's asymmetrical temperature distribution causes variable swell and uneven stress under tracking and installation errors. Temperature gradient variation of bellows is more sensitive under errors than Kovar rings. Kovar ring's compressive stress rises substantially as the Y-directional installation error varied from −15 mm to 15 mm compared to other errors. With tracking errors exceeding 8 mrad, bellows' tensile stress and Kovar ring's compressive stress diminish under installation error. Thus, larger tracking errors significantly reduce the threat to the receiver when installation errors exist.

Influence of geometrical design on the cooling process of double annular turbine section

The article describes the issue of gas turbine cooling after operation. Due to natural convection, an asymmetric temperature distribution occurs in the double annulus, which has a significant effect on the thermal bow of the rotor. At the same time, the desire to minimize radial clearances as this brings the advantage of higher engine efficiency is nowadays essential. On the other hand, it also requires the ability to understand and predict the cooling transient to avoid critical failures during engine restart. Based on a real engine, an experimental facility was designed to represent a simplified double annulus flow path in a section of the turbine flow path. Experimental measurements were performed and a computational model of natural convective flow during gas turbine cooling was developed. The time dependence of the temperature fields was observed and compared with computational model. Furthermore, the dependence of the temperature differences between the upper and lower double annulus was presented. The computational study is carried out with different geometrical setups, which were also validated by experimental measurements. It is shown that the thermal gradient of the rotor due to natural convection can be significantly affected by the choice of geometry and other constraints in this region. The results of the study showed several options to mitigate the rotor bow of a gas turbine. The applicability of the results may have a significant influence on the design and development of gas turbines nowadays.

Numerical evaluation of thermal stability of a W-shaped crushed-rock embankment with shady and sunny slopes in warm permafrost regions

The crushed-rock interlayer structure, crushed-rock revetment, and insulation board have been successfully applied in low-grade highways in low-temperature permafrost regions. However, it is doubtful whether the composite structure of the W-shaped crushed-rock embankment (W-CRE) composed of the three measures can be applied to high-grade highways in warm permafrost regions. For this reason, a model coupled with water, heat, and deformation in unsaturated soil was established for the high-grade highway with the W-CRE in warm permafrost regions. The cooling effect of the composite structure on the embankment with shady and sunny slopes in 20 service years was evaluated by numerical calculation, and the unfrozen water distributions and deformation characteristics were analyzed. The results show that (1) the W-CRE can cool the embankment of the high-grade highway in warm permafrost regions and improve the asymmetric ground temperature distributions caused by the shady and sunny slopes. (2) the W-CRE can improve the asymmetry of unfrozen water distributions, reduce the uneven settlement, and thus improve the mechanical stability of the embankment. (3) Although the cooling mechanisms of the three measures are different, the complementary thermal regulation mechanism formed by them in the composite structure effectively improves the thermo-mechanical stability of the embankment.

Thermal Analysis of a Modular Permanent Magnet Machine under Open-Circuit Fault with Asymmetric Temperature Distribution

A modular permanent magnet machine is composed of several stator modules, and the three-phase winding of each module can be controlled independently. The novel modular permanent magnet machine has good abilities in terms of fault tolerance when the machine is exposed to fault conditions. The current of each phase is different and will result in uneven loss distribution in each phase. Heat transfer occurs in the circumferential direction and temperature distribution will be asymmetric in the circumferential direction. This paper proposes a 3D finite element thermal model to accurately calculate the rise in temperature under open-circuit conditions for modular permanent magnet machines. When two modules are in operation, the machine can output rated torque. When one module is in operation and the temperature is 150 °C, the output torque is 0.76 times the rated torque. The temperature of the machine under the one-phase open-circuit condition with a zero-temperature-difference control strategy will be 0.8 °C lower than that with a minimum copper loss control strategy. Finally, a prototype with three stator modules is manufactured and the calculation results are validated by experimental test. It holds great significance for the accurate calculation of a machine with asymmetric temperature distribution in the circumferential direction.

Numerical simulation of natural circulation characteristics under different DHX layout schemes in pool-type SFR during station blackout accident

Decay heat removal system (DHRS) is an essential system for pool-type sodium-cooled fast reactor (SFR) to ensure natural circulation and remove decay heat during station blackout (SBO) accident. Decay heat exchanger (DHX) is the key equipment in DHRS. In China Experimental Fast Reactor (CEFR), DHX layout scheme consisting of two DHXs in hot pool (DHX Layout 1) is adopted. Different DHX layout scheme is designed in the advanced pool-type SFR, for example DHXs are installed in both cold and hot pool (DHX Layout 2). It is necessary to analyze the influence of different DHX layout schemes. In this paper, two DHX layout schemes were proposed. Numerical simulation was carried out, of which method was preliminarily validated. The numerical results show that DHX Layout 2 can reach long-term cooling stage of natural convection earlier than DHX Layout 1 with strengthened flow rate, resulting in more uniform temperature distribution in the hot pool. There is a local asymmetrical temperature distribution in the cold pool for DHX Layout 2. These findings by numerical simulations provide important numerical reference for the subsequent DHRS design of the advanced pool-type SFR.

Analysis of LBLOCA of APR1400 with 3D RPV model using TRACE

It is very difficult to capture the multi-dimensional phenomena such as asymmetric flow and temperature distributions with the one-dimensional (1D) model, obviously, due to its inherent limitation. In order to overcome such a limitation of the 1D representation, many state-of-the-art system codes have equipped a three-dimensional (3D) component for multi-dimensional analysis capability. In this study, a standard multi-dimensional analysis model of APR1400 (Advanced Power Reactor 1400) has been developed using TRACE (TRAC/RELAP Advanced Computational Engine). The entire reactor pressure vessel (RPV) of APR1400 has been modeled using a single 3D component. The fuels in the reactor core have been described with detailed and coarse representations, respectively, to figure out the impact of the fuel description. Using both 3D RPV models, a comparative analysis has been performed postulating a double-ended guillotine break at a cold leg. Based on the results of comparative analysis, it is revealed that both models show no significant difference in general plant behavior and the model with coarse fuel model could be used for faster transient analysis without reactor kinetics coupling. The analysis indicates that the asymmetric temperature and flow distributions are captured during the transient, and such nonuniform distributions contribute to asymmetric quenching behaviors during blowdown and reflood phases. Such asymmetries are directly connected to the figure of merits in the LBLOCA analysis. Therefore, it is recommended to employ a multi-dimensional RPV model with a detailed fuel description for a realistic safety analysis with the consideration of the spatial configuration of the reactor core.

A Simplified LPTN Model for a Fault-Tolerant Permanent Magnet Motor under Inter-Turn Short-Circuit Faults

This paper proposes a simplified lumped parameter thermal network (LPTN) model for thermal analysis under the inter-turn short-circuit (SC) faults of a five-phase fault-tolerant permanent magnet (PM) motor for electric vehicles. The proposed model can consider circumferential heat transfer, variable copper loss, and uneven loss distribution. Firstly, an analytical calculation formula of inter-turn SC current is proposed to separate the copper loss of SC turns from electromagnetic simulation, and the accuracy of the formula is verified by finite element analysis (FEA). Secondly, a simplified LPTN model is proposed, the calculation formulas of the thermal resistance are given, and the simplified principle is explained. By comparing the results of different simplifications, it is found that the error between the simplified model and the original model is small. Finally, the proposed model is verified by experiments. The results show that the simplified model can achieve not only a high calculation speed but also a high accuracy. Moreover, the proposed model is applicable to all cases of asymmetrical temperature distribution.

Performance of ceiling jet induced by dual unequal strong plumes in a naturally ventilated tunnel

• Thermal property of two unequal flames in a naturally ventilated tunnel is studied. • Temperatures induced by the small plume decay faster than that of the large plume. • A new model for maximum ceiling temperature of two unequal plumes is proposed. • Correlations for ceiling temperature decay profiles of dual plumes are developed. The catastrophic tunnel fire accidents are usually accompanied with multi-source burning. Ceiling gas temperature in tunnel is an important parameter in monitoring the daily operation process and unexpected combustion process. Previous studies are mainly focused on single fire or multiple equal fires in tunnel, while multiple unequal fires burning is common in real tunnel fires. Till now, the law of asymmetrical temperature distribution of multi-source below a ceiling is unknown. This paper aims to experimentally study the thermal performance of two unequal fire sources of propane in a naturally ventilated tunnel. A total of 90 experimental tests were conducted. The side lengths of two burners are fixed at 10 cm and 15 cm. The heat release rate (HRR) of each burner are changed with the HRRs ratio of 1–6. And the spacing between two sources along the longitudinal centerline of tunnel varied from 0–45 cm. Analysis shows that there is only one peak temperature with small spacings, while two peak temperatures appear with large spacings. Then the impingement point position and the maximum ceiling gas temperature of each burner are illustrated. The force analysis is adopted to explain the variation of impingement point position. A parameter α is innovatively introduced to characterize the promoting effect of spacing on maximum temperature at small spacings. Then a new normalized HRR is proposed to establish a unified model for the unequal maximum temperature rises below the ceiling of both sources, which indicates that the maximum temperature rise increases with the normalized HRR and then it maintains at 754 K. By introducing the plume radius, models for asymmetrical temperature decay profiles on both sides of two plumes below the ceiling are proposed, which shows that the temperature in the upstream of the small burner decays faster than that in the downstream of the large burner. The proposed models for maximum temperature and temperature decay profiles can be used to predict the ceiling gas temperatures of two unequal fires in tunnel.