Hot Gas Temperature Research Articles

Experimental investigation on the temperature and heat-transfer characteristics of rotating-detonation-combustor outer wall

The thermal management on rotating detonation engine is attracting much attention in recent years. In this study, the experiments were performed on a rotating detonation combustor to study the temperature and heat-transfer characteristics of the outer wall. Hydrogen, which was used as fuel, was injected into chamber through 120 orifices uniformly distributed in front of combustor, and air, which was functioned as an oxidiser, was injected into combustion chamber through an annular slot. An infrared thermal imaging was used to measure the temperature of outer wall. All the experimental test cases could obtain a stable rotating detonation wave, and the hot-gas temperature decreased with the increase of axial-direction length. The temperature initially increased and then decreased from the head of the wall towards the back. The heat which transferred from the hot gas to the outer wall was further large than the value of losing during the combustor operation, resulting in an approximately linear relationship for the temperature rise. There was a similar distribution trend for the outer-wall heat flux under the conditions of different equivalence ratios, and the location of 20% distance, relative to combustor length, had a biggest heat flux.

Experimental study on fallout behaviour of tempered glass façades with different frame insulation conditions in an enclosure fire

Tempered glass is a safety glass required by fire codes for use in building façade systems. However, as previous studies were primarily focused on the ordinary float glass, little is known about the fire performance of tempered glass panels and the interaction between its fallout and enclosure fire dynamics. In this study, eight small-scale experiments investigated the influence of frame insulation conduction on the fallout behaviour of tempered glass. Tempered single-glazing panels, 815 × 815 mm2 and 6 mm thick, were installed in the front wall of a compartment with a dimension of 1000 × 1000 × 1000 mm3. The glass panels were heated by a square pool fire of 200 × 200 mm2, positioned at the compartment center. Glass frames were made of either stainless steel or insulated materials, and important parameters, including the fallout time, glass surface temperature, hot gas temperature, incident heat flux and heat release rate of pool fire, were recorded. The experiments showed that the critical temperature difference and heat flux of tempered glass are respectively around 340 °C and 46 kW/m2, which are significantly larger than those for float glass panels. The frame with higher thermal conductivity can increase the fire resistance of the glazing systems. The occurrence of glass fallout may cause unexpected ejected flame with a height of more than 2 m and has a significant influence on the fire growth, temperature distribution and neutral plane height in the compartment (i.e., the zero pressure plane). The results can deepen the understanding of glass fallout in fire and propose to provide the reference to glass façades fire safety design in practical engineering.

An Experimental Technology of Drying and Clean Combustion of Biomass Residues

In the present study, the drying and combustion of solid biomass residues are developed. The combustion of the residues inside a boiler and a stove have been done. We used three types of solid biomass residues (i.e., cork, pine pellet and olive pomace). These residues have been dried by using screw dryers. Experimental installation has been used for a series of thermal drying tests of the residues by measuring the temperature inside the dryer and their moisture contents. A laboratory screw dryer was used to dry the olive pomace by using hot gases from a chimney of a biomass stove. Elemental and proximate analyses, as well as the higher heating value (HHV) of the raw materials, have been determined. In the experiments, moisture content variation of the residues and drying temperatures are obtained. These residues are dried several times under the same drying conditions to achieve the final moisture content rate. On the other hand, the temperature of combustion chamber of the boiler has been measured under different conditions. It has been found that by increasing hot gas temperature, the drying rate is increased. Finally, it has been found that the drying of these residues increases their calorific values and reduces the emissions.

On the X-ray temperature of hot gas in diffuse nebulae

X-ray emitting diffuse nebulae around hot stars are observed to have soft-band temperatures in the narrow range [1-3]$\times10^{6}$ K, independent of the stellar wind parameters and the evolutionary stage of the central star. We discuss the origin of this X-ray temperature for planetary nebulae (PNe), Wolf-Rayet nebulae (WR) and interstellar wind bubbles around hot young stars in our Galaxy and the Magellanic Clouds. We calculate the differential emission measure (DEM) distributions as a function of temperature from previously published simulations and combine these with the X-ray emission coefficient for the 0.3-2.0 keV band to estimate the X-ray temperatures. We find that all simulated nebulae have DEM distributions with steep negative slopes, which is due to turbulent mixing at the interface between the hot shocked stellar wind and the warm photoionised gas. Sharply peaked emission coefficients act as temperature filters and emphasize the contribution of gas with temperatures close to the peak position, which coincides with the observed X-ray temperatures for the chemical abundance sets we consider. Higher metallicity nebulae have lower temperature and higher luminosity X-ray emission. We show that the second temperature component found from spectral fitting to X-ray observations of WR nebulae is due to a significant contribution from the hot shocked stellar wind, while the lower temperature principal component is dominated by nebular gas. We suggest that turbulent mixing layers are the origin of the soft X-ray emission in the majority of diffuse nebulae.

Validation of the Remote Method of Determining the Temperature and Concentration of High-temperature Water Vapor from the Reference Transmission Spectra

The remote method of simultaneous determination of the temperature and concentration of hot gases from experimental spectral characteristics is validated on the example of the transmission spectra of water vapor measured with an average error of 5% at temperatures in the range 500–1770 K and concentrations 0.17–1 atm with resolution of 1 cm–1. When solving the direct optical problem, the parameters of water vapor spectral lines comprised in the HITEMP2010 database are analyzed with allowance for the last measurements of the absorption spectra with high resolution at Т ≈ 1300 K. It is demonstrated that overestimated values of the intensities of some hot water vapor spectral lines can be a reason for the deviation of the theoretical absorption predicted on the basis of the HITEMP2010 database from the experimental one. To increase the accuracy of solving the inverse optical problem, the data from several (up to eight) fragments of the spectral ranges 1000–2500 and 2600–4400 cm–1 are used. As a result, it is demonstrated that this allows the average error of determining reference values of the water vapor temperature and concentration to be decreased approximately to 0.3%, which corresponds to the average approximation error of theoretical values of its transmission function.

Numerical investigation on fluid-solid coupled heat transfer with variable properties in cross-wavy channels using half-wall thickness multi-periodic boundary conditions

In the present work, based on half-wall thickness multi-periodic boundary conditions, a 3D fluid-solid coupled heat transfer model considering variable properties and mutual influence between high temperature hot gas and compressed cold air is established to predict the flow and heat transfer in the cross-wavy (CW) channels. The present model is verified by comparing the Nusselt numbers of the numerical results with those of experimental results. On the base of model validation, the flow and heat transfer characteristics of the different CW channels are further investigated in a wide Reynolds number range (gas side: 100–2200; air side: 100–2800). The secondary flow which is responsible for the enhancement of heat transfer and the increase of the pressure loss is successfully captured, and its influence on the thermal and flow boundary layers is analyzed. By comparing the heat transfer and pressure loss of five configurations, the effecting law of geometrical parameters is revealed. Based on a large number of simulation results, the correlations of heat transfer and Fanning friction factor involving Reynolds number, Prandtl number and geometrical parameters are proposed using the least-squares method, which are helpful to the design of CW primary surface recuperator in the microturbine.

Numerical Modeling of Transpiration-Cooled Turbulent Channel Flow with Comparisons to Experimental Data

Transpiration cooling is a promising active cooling technique that provides coolant through a porous wall at a rate sufficient to maintain temperatures below a desired limit. The present study uses ANSYS® CFX to numerically investigate the influence of cooling gas injection on the temperature, velocity, and wall skin friction in the boundary layer of a subsonic turbulent hot-gas channel flow for various blowing ratios (), hot-gas temperatures (), and Mach numbers (, ). Here, a cooled permeable porous ceramic matrix composite sample with a hot-gas channel flow is simulated using a monolithic and two-domain approach. For the two-domain approach, separate solvers are used for the hot-gas and porous domains, respectively. These are applied alternatively and coupled to each other by boundary conditions imposed at the respective interface. The simulations are validated against experimental data and provide complementary insight into the effects of the cooling, which cannot be assessed from experimental measurements alone. The results show that, although a monolithic approach would be more convenient from a numerical point of view, a two-domain approach has proven to be superior in matching experimental data for this study. Furthermore, improved thermal boundary-layer profiles downstream of the porous sample are obtained by including the aft wall in the coupling process. This study adds to the limited theoretical and numerical investigations found in the literature on transpiration cooling.

A Refined Model for Calculation of the Vortex Tube Thermal Characteristics

The article deals with the main types of vortex tubes, provides a brief description of the fundamental principles of the vortex interaction hypothesis. A physical process is represented reflecting the physical essence of the gas flow energetic separation process in the vortex tube due to the intensive turbulent heat exchange from the forced vortex to the free one. A method for refinement of the design characteristics for the cold and hot gas temperatures in a vortex tube through the employment of the gas-dynamic and thermodynamic corrections is proposed. A refined calculation method allows reaching close agreement between the cold gas temperature and the experimental values.

Investigations on the use of Lanthanum Strontium Zirconate coating in maintaining temperature distributions of gas turbine blades

Increase in the efficiency of a gas turbine system is possible by operating it at increased temperature of hot working gases. However, it puts a direct thermal load on the material of the blade, which in turn demands for increased cooling capacities for the blade. Present paper deals with simulation based investigations on the effects of a ceramic coating of lanthanum strontium zirconate layer onto the surface temperature profile of a TMW4 gas turbine blade through an in-between bond coat layer of NiCoCrAlY. The blade model was simulated in ANSYS Workbench v14.5 for an ultra-high temperature of 1700 °C as operating temperature and calculated convection conditions from the gases and coolant air side. Steady state thermal results show a significant effect of coating in lowering substrate temperatures of blade. The results were evaluated for models with variable thickness of coating, maintaining overall dimensions of the blade constant. A blade model of 150/200 (150 microns thick bond coat and 200 microns thick top coat) experienced 8.4% reduction in maximum temperature of the substrate, while this value increased to 26.5% for a 350/1000 model.

Preheating Technology Can Save Energy in the Tanzania Iron and Steel Industries

This paper is focused on means of reducing consumption of electricity in the Tanzania iron and steel industries so as to save energy through preheating Technology. The iron and steel industry is one of the largest energy consuming manufacturing sectors in Tanzania due to the fact that the technology used is old and inefficient. Furnaces used to melt iron scrap consume high electricity which is around 0.85 MWh/Ton. Electricity demand does not fulfill the country need since there is frequent unexpected power cut offs all over the country. The paper analyses maximum temperature of furnace and maximum temperature of hot gases so as to determine the energy lost through these flue gases and recovering them. However, the future outlook necessitates looking into ways of developing the backup systems for the country to utilization all other alternative sources to save energy. From the results the energy saved during preheating technology is 21.63% of the total energy used. This is the target recovered in this paper.

The Circum-Galactic Medium of Massive Spirals. II. Probing the Nature of Hot Gaseous Halo around the Most Massive Isolated Spiral Galaxies

We present the analysis of the XMM-Newton data of the Circum-Galactic Medium of MASsive Spirals (CGM-MASS) sample of six extremely massive spiral galaxies in the local Universe. All the CGM-MASS galaxies have diffuse X-ray emission from hot gas detected above the background extending $\sim(30-100)\rm~kpc$ from the galactic center. This doubles the existing detection of such extended hot CGM around massive spiral galaxies. The radial soft X-ray intensity profile of hot gas can be fitted with a $\beta$-function with the slope typically in the range of $\beta=0.35-0.55$. This range, as well as those $\beta$ values measured for other massive spiral galaxies, including the Milky Way (MW), are in general consistent with X-ray luminous elliptical galaxies of similar hot gas luminosity and temperature, and with those predicted from a hydrostatic isothermal gaseous halo. Hot gas in such massive spiral galaxy tends to have temperature comparable to its virial value, indicating the importance of gravitational heating. This is in contrast to lower mass galaxies where hot gas temperature tends to be systematically higher than the virial one. The ratio of the radiative cooling to free fall timescales of hot gas is much larger than the critical value of $\sim10$ throughout the entire halos of all the CGM-MASS galaxies, indicating the inefficiency of gas cooling and precipitation in the CGM. The hot CGM in these massive spiral galaxies is thus most likely in a hydrostatic state, with the feedback material mixed with the CGM, instead of escaping out of the halo or falling back to the disk. We also homogenize and compare the halo X-ray luminosity measured for the CGM-MASS galaxies and other galaxy samples and discuss the "missing" galactic feedback detected in these massive spiral galaxies.

Flow visualization of microscale effusion cooling within mainstream boundary layer on a flat plate

Effusion cooling can be one of the attractive methods of cooling in a current high-efficiency gas turbine which has a very hot gas temperature above 1600 °C. For higher effectiveness of the air cooling for a gas turbine vane and blade, the air-cooled flow through effusionholes should not overshoot into the mainstream flow but still remain within the mainstream boundary layer. The present study is intended to examine flow structure of a microscale effusion cooling for gas turbine applications through flow visualization which is highly effective to obtain better understanding of the flow physics. The air flow through effusion-holes can be visualized with an oil atomized droplets, a laser-sheet and a high-speed CCD imaging system. The qualitatively visualized results show their flow patterns and characteristics with different effusion hole size and blowing ratio for effusion cooling. A series of vortical structure can be observed within the boundary layer along the microscale effusion flat plate which provided that the effusion cooling can be a plausible candidate up to the effusion-hole size of 0.7 mm.

Mapping the hot gas temperature in galaxy clusters using X-ray and Sunyaev-Zel’dovich imaging

We propose a method to map the temperature distribution of the hot gas in galaxy clusters that uses resolved images of the thermal Sunyaev-Zel’dovich (tSZ) effect in combination with X-ray data. Application to images from the New IRAM KIDs Array (NIKA) and XMM-Newton allows us to measure and determine the spatial distribution of the gas temperature in the merging cluster MACS J0717.5+3745, at z = 0.55. Despite the complexity of the target object, we find a good morphological agreement between the temperature maps derived from X-ray spectroscopy only – using XMM-Newton (TXMM) and Chandra (TCXO) – and the new gas-mass-weighted tSZ+X-ray imaging method (TSZX). We correlate the temperatures from tSZ+X-ray imaging and those from X-ray spectroscopy alone and find that TSZX is higher than TXMM and lower than TCXO by ~ 10% in both cases. Our results are limited by uncertainties in the geometry of the cluster gas, contamination from kinetic SZ (~10%), and the absolute calibration of the tSZ map (7%). Investigation using a larger sample of clusters would help minimise these effects.

Lack of thermal energy in superbubbles: hint of cosmic rays?

Using analytic methods and $1$-D two-fluid simulations, we study the effect of cosmic rays (CRs) on the dynamics of interstellar superbubbles (ISBs) driven by multiple supernovae (SNe)/stellar winds in OB associations. In addition to CR advection and diffusion, our models include thermal conduction and radiative cooling. We find that CR injection at the reverse shock or within a central wind-driving region can affect the thermal profiles of ISBs and hence their X-ray properties. Even if a small fraction ($10-20\%$) of the total mechanical power is injected into CRs, a significant fraction of the ram pressure at the reverse shock can be transferred to CRs. The energy transfer becomes efficient if (1) the reverse shock gas Mach number exceeds a critical value ($M_{\rm th}\gtrsim 12$) and (2) the CR acceleration time scale $\tau_{\rm acc}\sim \kappa_{\rm cr}/v^2$ is shorter than the dynamical time, where $\kappa_{\rm cr}$ is CR diffusion constant and $v$ is the upstream velocity. We show that CR affected bubbles can exhibit a volume averaged hot gas temperature $1-5\times10^{6}$ K, lower by a factor of $2-10$ than without CRs. Thus CRs can potentially solve the long-standing problem of the observed low ISB temperatures.

Development of Gas Dynamic Probe for High Total Temperature Measurement in High Speed Flow

Total temperature measurement in high speed and high temperature exhaust of air breathing engines like scramjet, ramjet and turbojets with afterburner is a challenging problem. The temperature of such hot gases is approximately 2000-2200 K. Conventional technique of temperature measurement by thermocouple suffers oxidation, doesn’t withstand aerodynamic load, and lacks robustness. Unconventional technique like optical method is expensive. These limitations have withheld the temperature measurement in high speed high temperature exhaust streams. Present work describes the design and development of a water cooled gas dynamic probe for total temperature measurement of high speed and high temperature gases. The probe consists of two choked nozzles in series. The hot flow is cooled after passing through the first nozzle, in a small settling chamber, using a heat exchanger. The flow from settling chamber is accelerated to Mach 1 in second nozzle. Using gas dynamic relations and measured parameters, the incoming flow total temperature is obtained. The probe has been calibrated for probe constant at total temperature range of 1200 to 1700 K at inlet Mach number 2. Probe constant varies proportional to the square of incoming flow total temperature. First restriction with C-D nozzle gave higher probe constant value than convergent nozzle.

Numerical Simulation of Evaporating Two-Phase Flow in a High-Aspect-Ratio Microchannel with Bends

Effusion cooling is one of the attractive methods for next generation high-efficient gas turbine which has a very hot gas temperature above 1,600oC. For higher effectiveness of the air cooling, the air-cooled flow through effusion-holes does not penetrate into the mainstream flow but still remains within freestream boundary layer. So the air-cooled surface temperature maintains at relatively lower than film cooling. Effusion cooling is generally known as operating in small effusion-hole size which is less than 0.2 mm. This study is intended to examine optimum effusion-hole size of the microscale effusion cooling through flow visualization. The air flow through effusion-holes is visualized using an oil atomizer, a DSPP laser-sheet illumination, and a high-speed CCD imaging. The visualized results show flow patterns and characteristics with different blowing ratio, BR = ρcUc / ρ∞U∞, (BR = 0.17 and 0.53) and effusion-hole size (D = 0.2 mm, 0.5 mm and 1.0 mm). The flow visualization condition is fixed at the mainstream Reynolds number of 10,000 and hole-to-hole spacing of 4 (S/D = 4). For larger effusion-hole of 1.0 mm [(a) and (b)], the effusion flow can penetrate into boundary layer which exhibits a film cooling. However the effusion flow is observed to be remained within boundary layer which shows an effusion cooling for smaller effusion-hole of 0.2 mm [(e) and (f)]. In case of (c) and (d), a series of vortical structure is also observed to be within the boundary layer along the effusion flat plate. Note that the effusion-hole size of 0.5 mm can be a candidate for making effusion cooling possible. [This work was supported by National Research Council of Science and Technology (NST) grant funded by the Ministry of Science, ICT and Future Planning, Korea (Grant No. KIMM-NK203B).]

Evaporative Cooling of Gas Turbine Exhaust Gas: CFD Simulation, Experimental Verification and Sensitivity Analysis

When large amount of gas turbine hot exhaust gas is required to be cooled for reuse in a closed cycle system, the conventional cooling methods will no longer be successful. The great temperature difference, the little space available for cooling, the large speed by which the exhaust gas is expelled, and finally the low exhaust gas pressure represent a great challenge for such a practice. Evaporative cooling is increasingly used as an efficient method to enhance thermal comfort in exhaust gas recirculation. In a water spray system, a cloud of very fine water droplets is produced using pressure nozzles. Analysis of spray penetration and evaporation requires a careful integration of the process conditions such as exhaust gas velocity, nozzle spray pattern, and water flow rate. The droplet size distribution is a critical input to calculations of droplet trajectory, evaporation time, and quenching rate. Computational Fluid Dynamics (CFD) is considered a valuable tool when assessing the potential and performance of evaporative cooling. In this paper, a systematic evaluation of the Lagrangian-Eulerian (LE) approach for evaporative cooling provided by the use of a water spray system with a hollow-cone configuration of two nozzles differs in rate and particle size distribution is presented. The evaluation is based on grid-sensitivity analysis and verified using experimental measurements. The effect of the hot exhaust gas temperature, the cooling water flow rate and nozzle Sauter Mean Diameter (SMD) is also presented. The results show that CFD simulation of evaporation by the LE approach, in spite of its limitations, can accurately predict the evaporation process. Finally, a good matching with the experimental measurements of the cooled exhaust gas temperature is achieved.

Development of Advanced Thermal Barrier Coatings With Improved Temperature Capability

Continuously increasing hot gas temperatures in heavy duty gas turbines lead to increased thermal loadings of the hot gas path materials. Thermal barrier coatings (TBCs) are used to reduce the superalloys temperature and cooling air needs. Until now 6–8 wt. % yttria stabilized zirconia (YSZ) is the first choice material for such coatings, but it is slowly reaching its maximum temperature capability due to the phase transformation at high temperature and sintering. New thermal barrier coating material with increased temperature capability enables the next generation of gas turbine with >60% combined cycle efficiency. Such material solutions have been developed through a multistage selection process. In a first step, critical material performance requirements for thermal barrier coating performance have been defined based on the understanding of standard TBC degradation mechanisms. Based on these requirements, more than 30 materials were a preselected and evaluated as potential coating materials. After carefully reviewing their properties both from literature data and laboratory test results on raw materials, five materials were selected for coating manufacturing and laboratory testing. Based on the coating manufacturing trials and laboratory test results, two materials have been selected for engine testing, in a first step in GT26 Birr Test Power Plant and afterward in customer engines. For such tests, the original coating thickness has been increased such to achieve coating surface temperature ∼100 K higher than with a standard thermal barrier coating. Both coatings performed as predicted in both GT26 Birr Test Power Plant and customer engines.

Analyses of the Effect of Cycle Inlet Temperature on the Precooler and Plant Efficiency of the Simple and Intercooled Helium Gas Turbine Cycles for Generation IV Nuclear Power Plants

Nuclear Power Plant (NPP) precooler coolant temperature is critical to performance because it impacts the work required to increase the coolant pressure. Variation of the coolant temperature results in varied precooler hot gas temperatures, which are cooled before re-entry. For recirculation, the heat sink (usually sea water), could exit the precooler at unfavourable temperatures and impact the re-entering coolant, if not recirculated properly at the source. The study objective is to analyse the effects of coolant inlet temperature on the heat sink and cycle efficiency. The cycles are Simple Cycle Recuperated (SCR), Intercooler Cycle Recuperated (ICR), and Intercooled Cycle without Recuperation (IC). Results show that the co-current precooler provides favourable outlet heat sink temperatures but compromises compactness. For a similar technology level, the counter-current precooler yields excessive heat sink outlet temperatures due to a compact, robust, and efficient heat transfer design, but could be detrimental to precooler integrity due to corrosion, including the cycle performance, if not recirculated back into the sea effectively. For the counter-current, the ICR has the best heat sink average temperature ratio of 1.4; the SCR has 2.7 and IC has 3.3. The analyses aid the development of Gas Cooled Fast Reactors (GFRs) and Very High Temperature Reactors (VHTRs), where helium is used as the coolant.

A Study Regarding Smoke Exhaust from an Atrium Type Building in a Fire Situation

This paper presents the analysis of the effect of smoke exhaust and hot gases from an atrium type building using techniques for numerical simulation of a fire situation. Several scenarios regarding smoke exhaust are considered for that purpose and the variation of the following parameters is monitored: minimum and maximum temperature of hot gases as well as the smoke layer height inside the atrium. Using engineering techniques, the development of fire, in compliance with the European legislation has been modelled, by means of a specialized computer program in order to simulate the phenomena of both the fluid flow and the heat transfer manifested in a fire situation.