Time-averaged Temperature Research Articles

Impact of Temperature Variation on Acute Myocardial Infarction in Karachi, Pakistan.

IntroductionEnvironmental triggers of acute myocardial infarction (AMI) have gained mounting evidence from various geographies of the world. However, due to geographic variations in seasonal temperature and other metrological parameters, it is difficult to generalize the findings in one population to another population with different climatic conditions. Therefore, the aim of this study was to assess the relationship between meteorological parameters and the number of primary percutaneous coronary intervention (PCI) procedures for AMI at a tertiary care cardiac hospital in Karachi, Pakistan.MethodsFor this cross-sectional study, data was obtained on the number of primary PCI procedures conducted at the National Institute of Cardiovascular Diseases (NICVD) Karachi, Pakistan during 1st June 2016 to 31st May 2018. Daily meteorological data of the Karachi region for the same period was obtained from the Pakistan Meteorological Department. It consists of temperature, atmospheric pressure, and relative humidity. Based on the weather conditions of Karachi, the data was divided into two seasons; summer (April to October) and winter (November to March). Multiple linear regression analysis was performed taken the number of primary PCI performed as regressand and time trend, average temperature, temperature variation, and relative humidity as regressors.ResultsA total of 115,494 hospital admissions were recorded during the study period out of which rate of primary PCI was 10.5% (12,107). A negative relationship between average temperature and number of primary PCI was observed with standardized regression coefficients of -0.13 (p < 0.001) on the overall regression model. A similar significant negative relationship of average temperature was observed on the regression model for the cold season with standardized regression coefficients of -0.17 (p < 0.001). While no such relationship was observed for the warm season.ConclusionThe average daily temperature was found to be negatively related to the number of primary PCI. Subgroup analysis revealed that the average daily temperature had a significant negative relationship with the number of primary PCI in the cold season; however, no such impact was observed in the warm season.

Experimental studies of temperature pulsations during the process of mixing non-isothermal coolant flows in nuclear reactor equipment components

One of the most important scientific and technical tasks of the nuclear power industry is to assure the reactor equipment life and reliability under random temperature pulsations. High-intensity temperature pulsations appear during the process of mixing non-isothermal coolant flows. Coolant thermal pulsations cause corresponding, sometimes very significant, fluctuations in the temperature stresses of the heat-exchange surface metal, which, added to static loads, can lead to fatigue failure of equipment components. The purpose of this work was to conduct an experimental study of the temperature and stress-strain states of a pipe sample under the influence of local stochastic thermal pulsations caused by the mixed single-phase heat coolant flows. To solve the set problems, an experimental section was created, which made it possible to simulate the process of mixing non-isothermal coolant flows accompanied by significant temperature pulsations. The design of the experimental section allowed us to study the thermohydraulic and life characteristics of pipe samples made of austenite steel (60×5 mm). Some tools were developed for measuring the pipe sample stress-strain state and the coolant flow temperature field in the zone of mixed single-phase media with different temperatures. The measuring tools were equipped with microthermocouples and strain sensors. As a result, we obtained experimental data on temperature pulsations, time-averaged temperature profiles of the coolant flow in the mixing zone as well as statistical and spectral-correlation characteristics of thermal pulsations. Based on the results of measuring the relative strains, the values of fatigue stresses in the mixing zone were calculated. In addition, some devices and methods were elaborated to measure the temperature and stress-strain states of the pipe sample under the influence of local stochastic thermal pulsations. The developed experimental section provided thermal-stress loading of the metal surface at a high level of alternating stress amplitudes causing rapid damage accumulation rates. The results were included in the database to verify the method for assessing the fatigue life of structural materials for nuclear power plants as applied to austenite steel 12Cr18Ni10Ti under the influence of random thermal cyclic loads.

Nonlinear optimal control strategies for buoyancy-driven flows in the built environment

We consider the problem of optimally controlling turbulent buoyancy-driven flows in the built environment, focusing on a model test case of displacement ventilation with a time-varying heat source. The flow is modeled using the unsteady Reynolds-averaged equations (URANS). A direct-adjoint-looping implementation of the nonlinear optimal control problem yields time-varying values of temperature and velocity of the inlet flow that lead to ‘optimal’ time-averaged temperature relative to appropriate objective functionals in a region of interest. The resulting dynamics of both ‘filling’ and ‘intruding’ added layers due to a time-varying source and inlet flow are discussed. The robustness of the optimal solution is demonstrated. It is found that for large enough values of time horizon the optimal steady solution is recovered, while for intermediate values a non-trivial deviation from this optimal steady state design is achieved. The computational framework is flexible, and can be applied to several problems of interest in optimal design and control of indoor airflow.

Thin Filament Pyrometry Field Measurements in a Medium-Scale Pool Fire

This paper presents the development of a thin filament pyrometry method to characterize the time-varying temperature field in a medium-scale pool fire burning in a quiescent environment. A digital camera with optical filters and zoom lens was used to record the high temperature emission intensity of 14 μm diameter, Silicon-Carbide filaments oriented horizontally at various heights above the center of a steadily burning 0.30 m diameter methyl alcohol (methanol; CH3OH) pool fire. Experiments collected 30 Hz video of the planar filament array. In a separate experiment, a 50 μm diameter thermocouple was used to acquire independent temperature measurements in the high temperature zone of the fire. A correlation was developed between the probability density functions of the radiation-corrected thermocouple measurements and the camera grayscale pixel intensity of the filaments. This arrangement enables measurement of the time-varying temperature field over a temperature range from about 1150 K to 1900 K with a spatial resolution of 160 μm, a temporal resolution of 0.033 s, and an expanded uncertainty of about 150 K (at a mean temperature of 1300 K). Measurements of the grayscale pixel intensities of the filaments were obtained. False color maps of the temperature field were produced to characterize the high temperature field as a function of time. Using statistical analysis, the local time-averaged temperatures and their variance for each location on the filaments were determined. Time-averaged temperatures were compared favorably to previously reported measurements. The dominant frequency of the puffing fire was determined. The temperature field time series was transformed to consider its character during consecutive phases of the fire's puffing cycle. The analysis emphasizes the cyclic nature of a pool fire, providing insight on its complex dynamic structure.

Energy Optimization of HVAC Systems in Commercial Buildings Considering Indoor Air Quality Management

To intelligently schedule heating, ventilation, and air conditioning (HVAC) systems for reducing energy cost of commercial buildings, indoor temperature and indoor air quality (IAQ) should be jointly considered. Otherwise, the health and productivity of occupants may be affected. In this paper, we investigate the problem of minimizing the sum of energy cost associated with HVAC systems and thermal discomfort cost related to occupants in multi-zone commercial buildings considering IAQ management. Firstly, by taking uncertainties of electricity price, outdoor temperature, number of occupants, temperature preference of each occupant, and external thermal disturbance into consideration, we formulate a time-averaged expected total cost minimization problem without violating the constraints of indoor temperature and IAQ. Due to the existence of uncertain system parameters, temporally and spatially coupled constraints, the nonconvex objective function, and nonconvex constraints, it is particularly challenging to solve the formulated problem. To this end, we propose a real-time algorithm based on the framework of Lyapunov optimization techniques. The key idea of the proposed algorithm is to construct virtual queues related to indoor temperatures and stabilize such queues so that indoor temperatures fluctuate around the ideal time-average indoor temperature. By dynamically controlling the average fluctuation level of indoor temperatures, the total cost could be optimized. Extensive simulation results show the effectiveness of the proposed algorithm.

Large Eddy Simulation of soot evolution in turbulent reacting flows: Presumed subfilter PDF model for soot–turbulence–chemistry interactions

In turbulent reacting flows, soot evolution is strongly influenced by small-scale soot–turbulence–chemistry interactions. Specifically, soot is formed during combustion of fuel-rich mixtures and, in non-smoking flames, is rapidly oxidized at slightly fuel-rich mixtures before being transported by turbulence into fuel-lean mixtures. Furthermore, different soot evolution mechanisms are dominant over distinct regions of mixture fraction. For these reasons, a new subfilter PDF is proposed to account for this distribution of soot in mixture fraction space. In this model, the sooting mode of a soot subfilter PDF is locally activated only at fuel-rich mixture fractions where surface growth is locally faster than oxidation. This model is first validated a priori against a recent DNS database of a turbulent nonpremixed jet flame. Compared to a subfilter PDF model without any mixture fraction dependence, a significant decrease in the oxidation source term is observed, while the surface growth source term remains hardly affected. This new model is implemented within a Large Eddy Simulation (LES) framework, applied to two laboratory-scale turbulent nonpremixed sooting jet flames, and validated via comparisons with experimental measurements of time-averaged centerline temperature and soot volume fraction. Both the new model and the previous model predict the temperature fairly well. However, compared to the previous model, the soot volume fraction predicted by the new model is significantly increased and in much better agreement with the experimental measurements. In addition, the sensitivity to the subfilter PDF is significantly greater than the sensitivity to grid resolution and is greater or at least comparable to the sensitivity to chemical mechanism.

Detailed flow development and indicators of transition in a natural convection flow in a vertical channel

A spatially developing transitional flow in a vertical channel with one side heated uniformly and subjected to random velocity fluctuations at the inlet is investigated in this experimental and numerical study. Two Rayleigh numbers are studied. Experimentally, Particle Image Velocimetry is used to obtain a complete two-dimensional velocity field of the streamwise flow development. A three-dimensional Large-Eddy-Simulation investigation is also performed to obtain a complete streamwise evolution of the flow. The results allow the definition of three transition indicators on the basis of the time-averaged velocities and temperatures fields as well as on the turbulent statistics of the flow. The detailed experimental and numerical spatial development of the transitional natural convective flow is then presented and the ability of the indicators to capture the early and the advanced stages of the transition is assessed. The numerical simulations were performed on the assumptions of a thermally stratified environment, submitted to an environmental noise, and for which wall to wall radiations were considered. These conditions aim at representing realistic experimental conditions.

Turbulent nonpremixed cool flames: Experimental measurements, Direct Numerical Simulation, and manifold-based combustion modeling

Turbulence, low-temperature chemistry, and their interactions in the form of turbulent cool flames are critical to understanding and improving advanced engines. Design of such engines requires tractable simulations which in turn necessitate turbulent combustion models that can account for cool flames. While manifold-based turbulent combustion models are an attractive option for hot flames, their applicability to cool flames is not yet fully understood. This is partially due to the lack of turbulent cool flame experiments, which has made model validation difficult. This work addresses these points with a combined experimental and computational investigation of turbulent nonpremixed dimethyl ether cool flames. First, a Co-flow Axisymmetric Reactor-Assisted Turbulent (CARAT) burner is developed and tested. Turbulent cool flames are studied using the formaldehyde planar laser-induced fluorescence (PLIF), acetone PLIF, and planar Rayleigh scattering techniques. The acetone PLIF signals are converted into mixture fraction values, and measurements of time-averaged temperature are derived from the Rayleigh scattering signals by taking advantage of the similarities between cool flames and unburned mixtures. Second, a Direct Numerical Simulation (DNS) of the CARAT burner is conducted. The flame is shown to be sensitive to thermal boundary conditions such that the stabilization method is dependent on a 10 K change in inlet temperature. Comparisons of first- and second-order statistics of temperature, mixture fraction, and formaldehyde between the DNS and experiment show good agreement. The validity of manifold-based turbulent combustion models in turbulent cool flames is then explored by first studying the effective Lewis numbers in the flame using a local differential diffusion parameter analysis. Turbulent cool flames are shown to have effective unity Lewis number transport even at a much lower Reynolds number than typically required for hot flames. Good agreement is shown for temperature and formaldehyde between DNS conditional means and one-dimensional nonpremixed flame solutions. Additionally, the motion of the cool flame in mixture fraction space is shown to be well described by one-dimensional nonpremixed flame solutions. These points indicate that the fundamental physics of turbulent cool flames are analogous to turbulent hot flames, implying that the same reduced-order manifold-based modeling approaches utilized for turbulent hot flames can be utilized for turbulent cool flames.

Convective heat transfer along ratchet surfaces in vertical natural convection

We report on a combined experimental and numerical study of convective heat transfer along ratchet surfaces in vertical natural convection (VC). Due to the asymmetry of the convection system caused by the asymmetric ratchet-like wall roughness, two distinct states exist, with markedly different orientations of the large-scale circulation roll (LSCR) and different heat transport efficiencies. Statistical analysis shows that the heat transport efficiency depends on the strength of the LSCR. When a large-scale wind flows along the ratchets in the direction of their smaller slopes, the convection roll is stronger and the heat transport is larger than the case in which the large-scale wind is directed towards the steeper slope side of the ratchets. Further analysis of the time-averaged temperature profiles indicates that the stronger LSCR in the former case triggers the formation of a secondary vortex inside the roughness cavity, which promotes fluid mixing and results in a higher heat transport efficiency. Remarkably, this result differs from classical Rayleigh–Bénard convection (RBC) with asymmetric ratchets (Jiang et al., Phys. Rev. Lett., vol. 120, 2018, 044501), wherein the heat transfer is stronger when the large-scale wind faces the steeper side of the ratchets. We reveal that the reason for the reversed trend for VC as compared to RBC is that the flow is less turbulent in VC at the same $Ra$. Thus, in VC the heat transport is driven primarily by the coherent LSCR, while in RBC the ejected thermal plumes aided by gravity are the essential carrier of heat. The present work provides opportunities for control of heat transport in engineering and geophysical flows.

Lithium-ion battery charging management considering economic costs of electrical energy loss and battery degradation

Technical challenges facing the development of battery economic charging for energy management arise from various contradictory objectives, immeasurable internal states, and hard constraints. Available solutions often resort to optimizing economic charging from the perspective of power grid, while few focus on the benefits of electric vehicle (EV) owners. This paper proposes a constrained multi-objective optimization framework to achieve economy-conscious battery charging management. Specifically, a coupled electrothermal-aging model is first applied to capture the nonlinear electrical, thermal, and aging dynamics of a lithium-ion battery with different timescales. Then an economic indicator considering the total charging cost caused by both the battery aging and electrical energy loss is formulated, based on a battery resale cost model and the Beijing peak-valley time-of-use (TOU) price. In addition, two crucial but contradictory objectives including the charging time and battery average temperature are also taken into account, along with hard constraints on the battery State of Charge (SOC), charging current, terminal voltage, and temperature. The complicated multi-objective charging problem is solved by using NSGA-II to optimize the multistage constant-current (MCC) profile. Sensitivities of the cut-off voltage, convection resistance, and ambient temperature are comparatively analysed via Pareto frontier. Numerical results of two extreme cases and several balanced charging cases demonstrate that feasible, economy-conscious battery charging management for various user demands can be achieved through suitable equilibrations among charging speed and thermal variations during charging.

Measuring the Temperature and Stress-Strain States of a Tube Sample under the Local Stochastic Temperature Pulsations

Provding a high level of durability of heat exchange equipment of water-cooled reactors under local stochastic temperature pulsations is an important scientific and technical problem for the nuclear power industry. Temperature pulsations produced by mixing non-isothermal coolant flows with high temperature gradient are most dangerous. This work is an experimental study of temperature and stress-strain state of a tube sample under local stochastic temperature pulsations caused by mixing of coolant flows.To solve the problems posed, aY-junction with «counter injection» was built, which was included in the thermal-hydraulic research facility. The design of theY-junction allows study of the thermal-hydraulic characteristics and durability of tube samples made of austenitic steel of 60 × 5 мм. Some tube samples had developed for measuring the temperature, stress-strain state of tube material and temperature field of coolant flow in mixing zone of single-phase coolants with different temperatures. Measuring tube samples were equipped with micro thermocouples and strain gauges.The experimental data of temperature pulsations, time-averaged temperature field in the coolant flow and on the outer surface of the sample were obtained, and statistical and spectral correlation characteristics of temperature pulsations were analyzed. According to results of measuring the relative strain, values of stresses were calculated.Devices and research techniques are developed. The combination of coolant flows parameters that provide thermal load of the metal surface at the highest level of stress intensity amplitude was obtained. The study results are used to verify the method for evaluating fatigue of reactor installations materials under stochastic temperature pulsations.

Heat transport in rotating-lid Rayleigh–Bénard convection

We perform a direct numerical simulation of three-dimensional Navier–Stokes equations for a Rayleigh–Bénard convection system in a stationary cylinder with the top cold lid rotating. This convection system with an imposed swirl flow is a canonical problem for investigating axial vortices under unstable thermal gradients. The base flow is established by rotating the top lid and the fluid moves azimuthally along the side vertical wall into a meridional flow in the r − z plane. This forms an axial vortex core at the axis of the cylinder. This axial core, under a certain rotational Reynolds number (Re), breaks down to a vortex breakdown bubble whose dynamics are modified under thermal convection. We study the effect of rotation on varying Re for a Rayleigh number Ra = 2 × 105. The equations are formulated in such a way that the rotating-lid cylinder and Rayleigh–Bénard convection are extreme cases of the same numerical set up. From the present study, we find that as the rotational rate is increased, the system dynamics shift from a convection-dominated flow regime to a rotation-dominated regime. This shift in dynamics is quantified using the volume-averaged and time-averaged temperature, the heat flux, the thickness of the Bödewadt boundary layer and the relative Nusselt number. These quantities are shown to demarcate the convection- and rotation-dominated regimes, as compared to the qualitative description of flow patterns from velocity and temperature contours.

Investigation of velocity and temperature measurement sensitivities in cross-correlation filtered Rayleigh scattering (CCFRS)

The cross-correlation filtered Rayleigh scattering method is presented for planar measurements of time-averaged velocity, temperature, density, and pressure using laser scanning, Rayleigh scattering, and cross-correlation-based signal processing. Of particular note, the methods and analyses presented show that velocity and temperature measurements are obtainable at acceptable uncertainties for many aerodynamic applications with or without particles present. In the current work, velocity and temperature measurement uncertainties for this method are analysed by Monte Carlo simulations and evaluation of the Cramér–Rao lower bounds for the signals generated in this approach with aerodynamic applications in mind. A key aspect considered is the relative strength of Rayleigh (molecular) scattering and Mie (particle) scattering contributions to the simulated flow signal. Compared to particle-based velocity estimation, the effects due to convolution between the molecular filter and the broadband Rayleigh scattering spectrum are found to increase the estimator variance of the velocity. For given flow conditions, the velocity error associated with the signal processing routine with noise-free signals is found to be less than , and bias error associated with discrete sampling in the laser frequency domain is within . For these same conditions, temperature measurement simulations indicate bias error bounds of 0. 014% with random uncertainty bounds of less than ±1.4% for a signal with no Mie scattering contribution, and bias error bounds of less than ±0.14% with random uncertainty bounds of less than 3.2% for flows contaminated with Mie scattering sources at a signal-to-noise ratio of 25 dB or greater. This technique is also being further developed to measure density and pressure using the principles of laser Rayleigh scattering in flows containing particles of unknown sizes and concentrations.

Experimental characterization of a ns-pulsed micro-hollow cathode discharge (MHCD) array in a N2/Ar mixture

An array of seven micro-hollow cathode discharges (MHCDs) operating in a N2/Ar mixture and ignited by a nanosecond pulsed high voltage is experimentally characterized in this work. Compared to other non-equilibrium discharges, high electron densities can be obtained with this type of microdischarge, and, thus, a high dissociation degree of the molecules is expected to be achieved. This is particularly suited for nitride deposition, which is the targeted application of this work, given that the atomic nitrogen density is a key parameter for this deposition process. The electrical diagnostics reveal that the energy deposited in the plasma during one voltage pulse increases with the Ar fraction in the gas mixture and the voltage pulse repetition frequency. A small effect of the repetition frequency is observed on the voltage and current characteristics of the discharge, while a significant increase in the amplitude of these two electrical parameters is observed with increasing Ar admixture. Consequently, a higher electron density is expected with increasing Ar fraction in the gas mixture and repetition frequency. Time-integrated optical emission spectroscopy is carried out to identify the excited emissive species in the plasma and to determine the time-averaged vibrational and rotational temperatures. For a discharge operating in pure N2, at a repetition frequency of 40 kHz, the time-averaged rotational temperature is found to be 390 K ± 40 K and the time-averaged vibrational temperature is 3580 K ± 200 K, revealing the non-equilibrium nature of the discharge. Both temperatures increase with the Ar fraction in the N2/Ar mixture, while they are almost independent of the repetition frequency. Finally, the different phases of the spatio-temporal evolution of the discharge are mapped using space-time resolved ICCD images. The spatial evolution of the discharge between two consecutive voltage pulses can be decomposed in four phases, corresponding to the different stages of the temporal evolution of the discharge voltage.

K2-287 b: An Eccentric Warm Saturn Transiting a G-dwarf

Abstract We report the discovery of K2-287b, a Saturn mass planet orbiting a G-dwarf with a period of P ≈ 15 days. First uncovered as a candidate using K2 campaign 15 data, follow-up photometry and spectroscopy were used to determine a mass , radius , period days, and eccentricity . The host star is a metal-rich V = 11.410 ± 0.129 mag G-dwarf for which we estimate a mass , radius , metallicity [Fe/H] = 0.20 ±0.05, and K. This warm eccentric planet with a time-averaged equilibrium temperature of K adds to the small sample of giant planets orbiting nearby stars whose structure is not expected to be affected by stellar irradiation. Follow-up studies on the K2-287 system could help constrain theories of planet migration in close-in orbits.

Experimental investigation of unsteady laminar mixed convection from a horizontal heated cylinder in contra-flow: Buoyancy and confinement effects on the three-dimensional heat transfer response

Abstract Transient laminar opposing mixed convection heat transfer from a circular cylinder confined inside a vertical closed-loop downward rectangular water channel has been studied experimentally. The cylinder is subjected to a constant wall heat flux boundary condition while the other bounding walls are insulated and adiabatic. The cylinder is placed horizontally at the mid-plane with a 40% blockage ratio ( B R , ratio between the cylinder diameter and the thickness of the rectangular section) and a cylinder aspect ratio ( A R , ratio between the length and diameter of the cylinder) of 6. Experiments are performed for flow conditions with Reynolds number based on cylinder diameter in the range 170 ≤ R e ≤ 260 , Prandtl number of P r = 7, and for values of the modified Richardson number, R i ∗ = G r ∗ / R e 2 , from 3.6 to 142.5. From experimental measurements, the variation in time-averaged local temperature distributions with angular position are obtained at nondimensional distances of 0.25, 0.5 and 0.75 of the cylinder span. Also, space-averaged surface temperatures and overall Nusselt number are obtained for a wide range in the parametric space. It is observed that for all values of R e and R i ∗ up to 40.1, a steep increase in the overall Nusselt number is observed with increasing buoyancy. However, because of the channel blockage, for values of R i ∗ > 40.1 and up to R i ∗ = 142.5, the overall Nusselt number reaches a plateau and its value remains practically fixed. Results indicate that for relatively large values of R i ∗ , because of the buoyancy-induced secondary flow resulting from the proximity of the cylinder to the channel walls, the three-dimensional (3D) configuration of the flow is no longer symmetric with respect to the channel centerline and the heat transfer rates vary along the span. The analysis brings out the significance of the end conditions and the buoyancy-induced secondary flow on the local and overall heat transfer characteristics of the bounded flow.

Experimental Study of Fire Plume Above a Fire Source with Simple Harmonic Oscillation in Horizontal Direction

In recent years, significant progress has been made in the development of maritime facilities such as floating storage and regasification units. In such offshore environments, the change in fire source position owing to temporal oscillation associated with maritime facilities affects fire plume properties. Because the properties of fire plumes in maritime facilities are important when dealing with problems related to fire detection, smoke filling, etc., we have focused attention on fire plume properties above a reciprocating fire source in an unconfined space as a first step. In particular, we experimentally investigated the characteristics of temperature rise and upward velocity along the fire plume axis formed above a 0.1 m square diffusion burner, which harmonically oscillates so as to simulate ship rolling motion under the condition of a small rolling angle. To clarify the time-averaged properties of such fire plumes, the temperature rise and upward velocity up to 5.8 m from the burner surface have been measured by varying the amplitude in three steps (0.1 m, 0.2 m, and 0.3 m) and the period in four steps (6 s, 8 s, 12 s, and 18 s). The results show that the time-averaged temperature rise and upward velocity changes from a two-dimensional plume to an axisymmetric plume. Such transition heights were determined from a simple theoretical model for predicting plume properties above a harmonically oscillating fire source. In addition, empirical correlations for effective heat release rates were also developed. These correlations allowed the existing engineering relationships for temperature rise and upward velocity along the plume axis formed above a fixed-point fire source to be utilised in order to estimate the characteristic properties of a plume formed over a harmonically oscillating fire source. This engineering knowledge can be useful for developing elemental models for the development of a two-layer zone model for ship fires.

Influences of Domain Symmetry on Supersonic Combustion Modeling

High-fidelity Improved Delayed Detached Eddy Simulation modeling is applied to examine the influence of the symmetry plane on the supersonic flow and combustion characteristics in a round-to-elliptic–transition scramjet combustor. A quarterly split domain and the full domain are modeled by using up to 0.14 billion cells and a third-order scale-selective discretization scheme. The combustion chemistry is described by the finite-rate partially stirred reactor model based on multicomponent diffusion and a skeletal kerosene mechanism with 19 species/53 reactions. Time-averaged pressure, temperature, Mach number, and heat release rate are compared to examine the influence of the symmetry assumption on the mean flow fields. The exchanges of mass, momentum, and energy across the symmetry planes are analyzed. Considerable increases in the combustion efficiency and total pressure loss occur when applying the full domain, although with the similar mixing efficiency. Turbulence spectrum analysis confirms the power-law for supersonic flows, and the inertial subrange is found to be shorter in the quarter-domain modeling. A comparison of the Borghi’s diagrams shows that the data points shift from the flamelet mode to the thin reaction zone mode when using the full domain, and at least of them cannot be described by fast-chemistry combustion models.

Thermal performances of glazed energy storage systems with various storage materials: An experimental study

In the literature, two materials (such as water and phase change materials) have been studied frequently as potential heat energy storage medium in building applications. Many perspectives have been mentioned by researchers but there is too little information about significance of its application. In this experimental study, water and PCM glazing systems were tested simultaneously in natural environment using test chambers. Temperature histories were recorded in the corresponding chambers at interior glass surface for each sample. Time lag, temperature damping and average temperature for each glazing system were comparatively analyzed. It was observed that temperature variation at interior glass surface over a period of 48 h changes differently for each material. Compared to the traditional air filled glazing system, it was found that water glazing system has most promising temperature damping properties, but significantly unfavorable average temperature, while PCM glazing system has significantly promising average temperature and temperature dumping properties.

Simultaneous reconstruction of the perfusion coefficient and initial temperature from time-average integral temperature measurements

• Reconstruction of perfusion coefficient and initial temperature from time-average temperature measurements is accomplished. • The conjugate gradient method is developed for the multiple unknowns identification. • Numerical results show that accurate and stable solutions are obtained. Inverse coefficient identification formulations give rise to some of the most important mathematical problems because they tell us how to determine the unknown physical properties of a given medium under inspection from appropriate extra measurements. Such an example occurs in bioheat transfer where the knowledge of the blood perfusion is of critical importance for calculating the temperature of the blood flowing through the tissue. Furthermore, in many related applications the initial temperature of the diffusion process is also unknown. Therefore, in this framework the simultaneous reconstruction of the space-dependent perfusion coefficient and initial temperature from two linearly independent weighted time-integral observations of temperature is investigated. The quasi-solution of the inverse problem is obtained by minimizing the least-squares objective functional, and the Fréchet gradients with respect to both of the two unknown space-dependent quantities are derived. The stabilisation of the conjugate gradient method (CGM) is established by regularising the algorithm with the discrepancy principle . Three numerical tests for one- and two-dimensional examples are illustrated to reveal the accuracy and stability of the numerical results.