Gas Temperature History Research Articles

Fire tests on full-scale steel portal frames against progressive collapse

This paper presents experimental investigations on the collapse behavior of a full-scale 36 m × 12 m steel portal frame exposed to natural fires. Extensive thermal and structural responses of the frame are measured and presented. The frame collapses after 15-min fire exposure with a critical temperature of about 1100 °C in the heated column. The measured gas temperature history has a short growth period of 3 min, and reaches its peak temperature of 1100 °C within 8 min (400 °C higher than standard fire). It is found that a two-zone model can be assumed with uniform temperature distribution in the lower and upper half region, respectively. The temperature gap of these two zones reaches 200 °C. The gas temperature at top region decreases due to the deformation-induced opening of roof and fire walls. The surface facing the environment has higher gas temperatures than that inside the fire compartment (more than 200 °C). The temperature of rafters beyond the fire compartment reaches 700 °C due to the spread hot smoke. Outward bending of the external unexposed column and pulling out of corner column base are observed, which should be prevented in practical design to mitigate fire spread to adjacent buildings and ensure life safety of fire fighters. Numerical simulation is conducted and compared to experimental results which can be used for calibrating numerical models.

The role of initial tank temperature on refuelling of on-board hydrogen tanks

The influence of the initial tank temperature on the evolution of the internal gas temperature during the refuelling of on-board hydrogen tanks is investigated in this paper. Two different types of tanks, four different fuel delivery temperatures (from ambient temperature refuelling to a pre-cooled hydrogen at −40 °C), several filling rates and initial pressures are considered. It has been found that the final gas temperature increases linearly with the increase of the initial tank temperature while the temperature increase (ΔT) and the final state of charge (SOC) decrease linearly with increasing the initial temperature. This dependency has been found to be larger on type III than on type IV tank and larger the larger the initial pressure. Additionally CFD simulations are performed to better understand the role of the relevant phenomena on the gas temperature histories e.g. gas compression, gas mixing, and heat transfer. By comparing the results of calculations with adiabatic and diathermal tank walls, the effect of the initial gas temperature has been separated from the effect of the initial wall temperature on the process.

Transient Heat Transfer of a Hollow Cylinder Subjected to Periodic Boundary Conditions

The purpose of this paper is to study the transient temperature responses of a hollow cylinder subjected to periodic boundary conditions, which comprises with a short heating period (a few milliseconds) and a relative long cooling period (a few seconds). During the heating process, the inner surface is under complex convection heat transfer condition, which is not so easy to approximate. This paper first calculated the gas temperature history and the convective heat transfer coefficient history between the gas flow and the inner surface and then they were applied to the inner surface as boundary conditions. Finite element analysis was used to solve the transient heat transfer equations of the hollow cylinder. Results show that the inner surface is under strong thermal impact and large temperature gradient occurs in the region adjacent to the inner surface. Sometimes chromium plating and water cooling are used to relief the thermal shock of a tube under such thermal conditions. The effects of these methods are analyzed, and it indicates that the chromium plating can reduce the maximum temperature of the inner surface for the first cycle during periodic heating and the water cooling method can reduce the growth trend of the maximum temperature for sustained conditions. We also investigate the effects of different parameters on the maximum temperature of the inner surface, like chromium thickness, water velocity, channel diameter, and number of cooling channels.

Thermocouple thermal inertia effects on impingement heat transfer experiments using the transient liquid crystal technique

The transient liquid crystal technique is widely used for impingement heat transfer experiments. Additionally, due to the difficulty of producing pure temperature steps in the flow, many authors assumed the fluid temperature evolution as a series of step changes using Duhamel's superposition theorem. However, for small impingement configurations where the jets are fed from the same plenum chamber, and hence flow velocities are relatively small, thermal inertia of commercial thermocouples causes a delay, lagging from the real plenum temperature history. This paper investigates thermal inertia characteristics of thermocouples and their effect on the calculation of impingement heat transfer coefficient. Several thermocouples with exposed junction and different wire diameter were considered over a range of plenum flow conditions typically found in impingement heat transfer experiments. The effect of thermocouple time constant on the evaluation of the heat transfer rate was investigated in a narrow channel consisting of five inline impingement jets. The results indicated a significant effect of thermocouple response on the stagnation point region heat transfer, while lower local heat transfer rates are negligibly affected as liquid crystal signals appear later in time and the driving gas temperature history has a smaller influence on the evaluated data.

Investigation of multi-species (H2O2 and H2O) sensing and thermometry in an HCCI engine by wavelength-agile absorption spectroscopy

Absorption spectra spanning 1410–1490 nm, with a spectral resolution of ∼0.3 nm, were recorded in a piston engine operating in homogeneous charge compression ignition engine (HCCI) mode. Spectra were recorded every 126 µs using a wavelength-agile laser, corresponding to 0.45 crank angle degrees under the 600 rpm condition tested. The dominant absorber is H2O vapour, but a weaker interfering absorption attributed to H2O2 vapour was also observed. H2O2 mole fraction, H2O mole fraction and gas temperature histories were estimated from the measured spectra. Estimated H2O2 mole fractions are compared to mole fractions simulated using Chemkin; the agreement is within a factor of 2. This effort represents the first attempt to monitor H2O2 in a combustion environment; the simultaneous measurement of multiple species in an engine by a single laser is also novel.

Gas Temperature Rise in a High-Pressure Gas Tube by an Adiabatic Compression

Serious fire accidents have occurred in oxygen supplying systems in which an adiabatic compression of oxygen has been identified as an ignition source. For exploring the ignition mechanism of oxygen compression, a fluid flow in a tube having a closed end has been studied by experimental and CFD approaches. The simulation results on gas pressure history are in good agreement with the experimental results; whereas the simulated gas temperature history was not in agreement with the experimental results. Ignition tests for a small sample piece placed at the end of the tube were conducted under the same adiabatic compression conditions. Nylon 6,6 and PTFE are used as the polymeric samples. The ignitions for Nylon 6,6 samples have been observed more frequently with higher initial pressures. It should be also noted that the maximum temperature simulated by CFD at the initial pressure of 25 MPa is close to the autogenous ignition temperature of Nylon 6,6, suggesting that the gas temperature simulated by CFD would be more realistic than that in experimental results because of the difficulty in keeping the adiabatic condition in experiments.

How do galaxies get their gas?

We examine the temperature history of gas accreted by forming galaxies in smoothed particle hydrodynamics simulations. About half of the gas follows the track expected in the conventional picture of galaxy formation, shock heating to roughly the virial temperature of the galaxy potential well (T ∼ 106 K for a Milky Way type galaxy) before cooling, condensing and forming stars. However, the other half radiates its acquired gravitational energy at much lower temperatures, typically T < 105 K, and the histogram of maximum gas temperatures is clearly bimodal. The ‘cold mode’ of gas accretion dominates for low-mass galaxies (baryonic mass Mgal ≲ 1010.3 M⊙ or halo mass Mhalo ≲ 1011.4 M⊙), while the conventional ‘hot mode’ dominates the growth of high-mass systems. Cold accretion is often directed along filaments, allowing galaxies to efficiently draw gas from large distances, while hot accretion is quasi-spherical. The galaxy and halo mass dependence leads to redshift and environment dependence of cold and hot accretion rates, with the cold mode dominating at high redshift and in low-density regions today, and the hot mode dominating in group and cluster environments at low redshift. The simulations reproduce an important feature of the observed relation between the galaxy star formation rate (SFR) and the environment, namely a break in star formation rates at surface densities σ∼ 1 h275 Mpc−2, outside the virial radii of large groups and clusters. The cosmic SFR tracks the overall history of gas accretion, and its decline at low redshift follows the combined decline of cold and hot accretion rates. The drop in cold accretion is driven by the decreasing infall rate on to haloes, while for hot accretion this slower mass growth is further modified by the longer cooling times within haloes. If we allowed hot accretion to be suppressed by conduction or active galactic nuclei feedback, then the simulation predictions would change in interesting ways, perhaps resolving conflicts with the colours of ellipticals and the cut-off of the galaxy luminosity function. The transition at Mhalo∼ 1011.4 M⊙ between cold-mode domination and hot-mode domination is similar to that found by Birnboim & Dekel using one-dimensional simulations and analytic arguments. The corresponding baryonic mass is tantalizingly close to the scale at which Kauffmann et al. find a marked shift in galaxy properties, and we speculate on possible connections between these theoretical and observational transitions.

Transient Temperature Measurement of Unburned Gas Using Optical Heterodyne Interferometry.

This paper demonstrates an application of the optical heterodyne interferometry, a laser-based technique for measuring the temperature history of gas in combustion devices, such as internal combustion engines. The technique is based on refractive index measurements using laser interferometry along a line of sight. The temperature history of gas can be determined from the pressure history in the combustion chamber, the gas composition, and the laser interference intensity. A polarization-preserving fiber was used to deliver the test beam to and from the test section to improve the feasibility of the system as a sensor probe. The temperature of the unburned mixture in the end-gas region of a constant volume combustion chamber and in an engine cylinder were measured during flame propagation. The accuracy of the measurement and the feasibility of this system are discussed. The measurement accuracy of our system was sufficient to be applied to temperature history measurement of an unburned gas compressed by flame propagation in an engine cylinder. The uncertainty of this method is within ±10K. The resolution of the temperature measurement was approximately 0.5 K, and was dependent upon both the sampling clock speed of the A/D converter and the length of the test section. This optical heterodyne interferometry system may also be used for other applications that require a fast response time to measure the density and pressure of a gas, and thereby obtain a transient temperature record.

Flow Visualizations and Transient Temperature Measurements in an Axisymmetric Impinging Jet Rapid Thermal Chemical Vapor Deposition Reactor

Abstracts Carrier gas flow in a rapid thermal chemical vapor deposition (RTCVD) reactor was studied using flow visualization and laser induced Rayleigh light scattering (RLS). The flow field consists of a downward axisymmetric jet of carrier gas impinging on a wafer which undergoes transient heating. Flow visualization results showed three stable flow regimes as the surface rose from ambient to high temperature: momentum dominated, buoyancy dominated, and a second momentum dominated regime at high temperature; each separated by unstable, chaotic flows. RLS temperature measurements provided transient gas temperature histories, documenting flow visualization results. Regions of momentum dominated, buoyancy dominated, and unstable flows were defined as a function of Grashof number, Reynolds number, pressure, and wafer temperature.

C105 ヘテロダイン干渉法によるエンジンシリンダ内未燃混合気温度の計測(オーガナイズドセッション16 : 新世代エンジンのための燃焼改善と排気低減技術)

A fiber optical heterodyne interferometry system was developed to obtain high temporal resolution temperature histories of unburned gas in an SI engine cylinder non-intrusively. The effective optical path length of the test beam changes with the gas density and corresponding changes of the refractive index. Therefore, the temperature history of the gas can be determined from the pressure and phase shift of the interference signal. The fiber optical heterodyne interferometry has the advantage of resisting the mechanical vibration. In this study, this system was applied to a homogeneous charge compression(HCCI) engine. The measured temperature history of unburned gas in a HCCI engine just before generation of cold flame was almost equal to the calculated value using the equation of state of ideal gas.

An experimental and modeling study of fires in ventilated ducts. Part II: PMMA and stratification

A theoretical and experimental treatment of fire processes in horizontal, ventilated passages, containing an axial distribution of fuel, is presented. Experiments for radially well-mixed flows are performed where gas temperature histories and fire-shaped solid fuel mass axial distributions are acquired from polymethyl methacrylate (PMMA)-fueled fires. The theory developed in part I is able to quantitatively model all the experimental results for PMMA fires. In particular, the solid fuel profiles (axial distributions) are modeled from gas-phase information alone. To assess the concept of an ignition temperature as a controlling mechanism for growth a brief fire growth analysis is also performed. A simple approach to study fires in stratified flow conditions is also presented. In conjunction with small-scale experiments on liquid-fueled fires it is shown that a modified one-dimensional model, requiring minimal computational effort, may be used to describe fire-front histories and the temperature profile of the fire plume. Both nonstratified and severely stratified fires display a direct dependence of the steady fire propagation speed with ventilation rate and inverse dependence with initial fuel mass loading. A general model requires a knowledge of the degree of stratification and mixing, in advance of experimentation. A new correlation for stratification using fuel/duct properties and air velocity is proposed as a means of predicting flow regimes.

An experimental and modeling study of fires in ventilated ducts. Part I: Liquid fuels

A theoretical model for fire propagation through a fuel-lined duct with a radially well-mixed axial flow is presented. The gas-phase is modeled as a steady-state process whereas the condensed-phase (fuel source) is taken to be the cause of transient fire propagation along the duct. Experiments were performed in a small-scale duct where fire propagation and gas temperature histories were acquired. Experimental results confirm hypotheses of pseudo-steady-state gas-phase processes. Theory and experiment display transient fire propagation for typical duct fire scenarios where initial fuel mass loading is constant with respect to duct length. The phenomenon observed, as predicted by theory, is an initial “jump” of the fully developed combustion process followed by convergence to a steady-state constant fire propagation speed. The theory is in all important aspects able to quantitatively model the experimental results.

Unburned Gas Temperatures in an Internal Combustion Engine. II:Heat Release Computations

Abstract A heat release model has been developed and applied to predict unburned gas temperature histories in both a knocking and a non-knocking engine.The model advances the state of the art in its treatment of boundary layers and by its formulation which uses algebraic equations of state instead of differential equations. The model predictions and unburned gas temperature agree exceptionally well with measured temperatures during the compression stroke.During combustion the predictions are slightly'less than the measurements but agree-within the error bounds of each.Similar temperature profiles are realized in both the knocking and the non-knocking cases providing an opportunity to study the role of pressure in the chemistry leading to autoignition.

Heat Transfer to Oil Shale in a Closely Spaced Bundle as an Approximation to a Packed Bed

The heat transfer to a single cylindrical sample of oil shale in a staggered tube bundle was studied both numerically and experimentally in order to evaluate the thermal and chemical processes associated with the retorting of oil shale in packed beds particular to in-situ processing. The cylinders were subjected to constant gas temperatures and to gas temperature histories experienced in an actual combustion retort. The results of the numerical modeling were compared with the experimental data in order to evaluate the model’s performance. It was found that the model satisfactorily described the thermal processes experienced during the combustion retorting of oil shale within the limits of the accuracy of published data on oil shale thermal properties and chemical kinetics. Net heat transfer to cylindrical oil shale samples in a staggered bundle configuration was also calculated and was shown to nearly duplicate published data related to gas-solid heat transfer in a packed bed combustion retort.