Rate Of Heat Addition Research Articles

Turbulent diffusion of scalar and heat in an off-source heated steady round jet

We study, using direct numerical simulation, the characteristics of an off-source heated jet (OSHJ), the rate of heat addition being proportional to the local concentration of a scalar. The heating disturbs the self-similar state of the unheated jet (UJ) entering the heat injection zone (HIZ). Based on the characteristics of the velocity and scalar statistics, the evolution of the OSHJ is demarcated into three axial zones. Zone I, which is dynamically the most active region, exhibits rapid variations in quantities like the mean radial velocity, the scalar-to-velocity width ratio and the second-order correlations. Zone II represents the relaxation of these quantities towards a new self-similar state which is realized in Zone III above the HIZ. We find that the temperature–velocity correlation is negative in the core of the OSHJ in Zone I, which becomes positive for all radial locations in Zones II and III. We interpret this behavior by decomposing the effect of heat addition into “heating” and “buoyancy” factors; the former describes the effect of axial velocity on heating while the latter describes the effect of added buoyancy on flow acceleration. The heating factor dominates in Zone I leading to the negative temperature–velocity correlation, which we conjecture to be the reason for the “disruption” of coherent structures in the OSHJ reported in the literature. Based on wavelet analysis of the scalar field we identify the length scale of the ring-like coherent structure that gets disrupted upon heat addition, which enhances the scalar homogeneity in the core of the OSHJ near the base of the HIZ. Where possible, we compare our results with the literature on heated jets within the context of the three demarcated zones. We find that external heating decreases the scalar-to-velocity flow widths relative to the UJ to a value in Zone III that is largely insensitive to the precise details of heat addition , such as the amount of heat added and the extent of the HIZ. We also present the effect of heat addition on turbulent Schmidt and Prandtl numbers. Our findings are relevant to the dynamics of cumulus clouds which are governed by a similar interplay of scalar, velocity and temperature fields as reported here.

Research Needs for the Solid Oxide Electrolyzer (SOEC) with a Proton-Conducting SOEC (H-SOEC) Electrochemical Hydrogen Compressor (EHC) Energy Conversion Network (ECN)

A high temperature solid oxide electrolysis cell (SOEC) for electrolysis of water is paired with a H-SOEC for hydrogen compression. SOEC and EHC have been integrated into an ECN in a series configuration and then simulated and analyzed. Adding heat and minimizing area specific resistance (ASR) would be highly desirable for further developing highly-efficient SOEC H-SOEC EHC ECN’s. It is important to note there is a maximum possible heat generation rate with a given ASR when operated below the thermoneutral point. There is a maximal heat addition rate for optimal efficiency of the SOEC, and it is not at thermoneutral. Many developers have expressed interest in the thermal management of electrolyzer cells and in the possible existence such an optimum. It is important to understand in general that heat removal can allow increase hydrogen production rate over the thermoneutral path at constant temperature. For this reason, the SOEC H-SOEC EHC ECN was simulated over a range of currents and ASR’s to determine the heat addition or removal required. If the internal resistance of an SOEC could be lowered sufficiently via the development of new, high-performing materials, the efficiency of hydrogen production could be very high, especially when supplementary heat is provided from solar or other waste heat sources such as nuclear or coal power plants. It is remarkable that a quarter to a third of the energy for the combined high-temperature electrolysis and hydrogen compression system could be provided by solar, nuclear or geothermal energy. The goal of HT electrolysis research and development should be to lower ASR and improve heat conduction or heat transfer into and out of the SOEC. The promise of the H-SOEC electrochemical hydrogen compressors depends on its stability, durability and improved transference numbers. The goal of future research should be to improve the potential of this new SOEC H-SOEC EHC ECN.

Research Needs for the Solid Oxide Electrolyzer (SOEC) with a Proton-Conducting SOEC (H-SOEC) Electrochemical Hydrogen Compressor (EHC) Energy Conversion Network (ECN)

A high temperature solid oxide electrolysis cell (SOEC) for electrolysis of water is paired with a H-SOEC for hydrogen compression (EHC). SOEC and EHC have been integrated into an electrochemical network (ECN) in a flow-series configuration and then simulated and analyzed. Adding heat and minimizing area specific resistance (ASR) would be highly desirable for further developing highly-efficient SOEC+EHC ECN’s. It is important to note there is a maximum possible heat generation rate with a given ASR when operated below the thermoneutral point. There is a maximal heat addition rate for optimal efficiency of the SOEC, and it is not at thermoneutral. Many developers have expressed interest in the thermal management of electrolyzer cells and in the possible existence of such an optimum. It is important to understand in general that heat removal can allow an increased hydrogen production rate over the thermoneutral path at constant temperature. For this reason, the SOEC+EHC ECN was simulated over a range of currents and ASR’s to determine the heat addition or removal required. If the internal resistance of an SOEC could be lowered sufficiently via the development of new, high-performing materials, the efficiency of hydrogen production could be very high, especially when supplementary heat is provided from solar or other waste heat sources such as nuclear or coal power plants. It is remarkable that a quarter to a third of the energy for the combined high-temperature electrolysis and hydrogen compression system could be provided by solar, nuclear, or coal.

Six Sigma based modeling of the hydraulic oil heating under low load operation

The hydraulic system is the backbone of industrial, construction, and agricultural machines. Its high-power density and efficiency execution make it the preferred choice for high-energy applications. This manuscript presents the evidence against the statement, Whenever the system runs to its full capacity, hydraulic oil heats up more as compared to partial loads.“ Our experimental study on Injection Molding Machine (IMM) hydraulic system tries to reshape the above statement by presenting the fact where we came across that lower system loading case is causing higher hydraulic oil temperatures than full loading.” The concern started when the machine at lower speeds results in frequent shutdowns due to increasing operating temperature high alarm!“ This article presents the study to resolve the stated issue completely. For the design evolution, a systematic diagnostic approach is displayed based on the six-sigma and the associated mathematical model. Our study concludes with an approach to find the self-balancing system for the case where the temperature increase is must be due to the higher rate of heat addition than the rate of heat rejection. Presented learning can be equally extended for the other fields of interest, as care should be taken to understand the passive system losses, which can result in elevated temperatures due to lower cooling capabilities.

Influence of potential liquid desiccants on solution cooling, heating, and pumping loads of membrane-based liquid desiccant air conditioning system: An analytical study

This paper is intended to study the methodology for choosing the suitable desiccant solution among LiCl, CaCl2, LiBr, and KCOOH solutions (commonly used potential solutions) at optimum heat capacity for an energy-efficient membrane-based liquid desiccant air conditioning system. An analytical model which is validated with existing experimental and numerical results was adopted in this study to find the output parameters. Performance indices considered in this study are solution pumping power, solution heat addition rate (Qadd), and chiller load (Qchiller). Considering the specified solutions at their maximum safe concentrations (0.40, 0.35, 0.55, and 0.75, which are just below their saturation concentrations), performance indices analyzed at fixed ambient condition and dehumidification rate at different heat capacity ratios (Cr* = 4.0, 3.0, 2.5, 2.0, and 1.5). At their corresponding optimum Cr*, Qadd is observed low for CaCl2, whereas it was high for LiBr. Solution pumping power and Qchiller are observed as lesser for the LiBr solution. At their corresponding design parameters, LiBr solution’s investment cost is found to be 30% higher than LiCl solution’s, but its operating cost (pumping power) is nearly 26% to 40% less than the LiCl solution, which suggests that the LiBr solution is the most efficient solution among the four.

Thermal energy analysis on liquid desiccant air conditioning system at different desiccant solution parameters

Selection of suitable liquid desiccant operating parameters plays a significant role in the design of energy efficient liquid desiccant air conditioning system. To achieve same dehumidification rate from ambient air, different combinations of solution parameters (heat capacity ratio, concentration, and vapor pressure) could be employed in the system. Considering dehumidifier air inlet condition and dehumidification rates are fixed, an analytical study is carried out on the thermal energy analysis of the system at different solution operating parameters. Operating parameters considered in this study are solution concentrations ( Cs = 0.25, 0.3, 0.35 and 0.40) and heat capacity ratios ([Formula: see text] = 2.5, 3, 4 and 5). Control volume which includes a pair of air and solution channels (half width channels) of full scale liquid-to-air membrane energy exchangers (LAMEE) has been chosen to analyze the energy transfer between air and solution. The results indicate system requires lesser chiller load ( Qchiller) at high concentration and low heat capacity ratio ( Cs = 0.40 and [Formula: see text] = 2.5) which is 0.29 kW to achieve 0.61 kW cooling load. This is 99% lesser than the Qchiller at high concentration and high heat capacity ratio ( Cs = 0.40 and [Formula: see text] = 5) and 30% lesser than the Qchiller at low concentration and low heat capacity ratio ( Cs = 0.25 and [Formula: see text] = 2.5). Solution heat addition rate ( Qadd) per kW cooling capacity ( Qcc) at this solution condition is found as 0.85 kW.

Study on desiccant solution control strategies for efficient liquid desiccant air conditioning system control performance

Frequent change in ambient conditions requires precise control of the desiccant solution operating parameters to suit the required conditioned space load. Either of the two control strategies shall be adopted for this, which are the dehumidifier solution inlet temperature (DSIT) control strategy and the dehumidifier solution inlet mass flow rate (DSIM) control strategy. This article aims to study the efficient control strategy selection approach for a specific air conditioning application since it leads to energy savings as well as thermal comfort. Initially, the optimum desiccant mass flow rate will be found for the liquid desiccant air conditioning system at peak ambient conditions. And the effect of the control strategies on system performance has been analytically investigated at different ambient conditions. A significant reduction in the solution heat addition rate has been observed with both control strategies with the addition of an air-solution heat exchanger. It has also been seen that the required chiller load is nearly same with both control strategies but a little drop (3%–14.5% variation) was observed with the DSIT strategy at low ambient conditions. However, a considerable drop in solution pumping power due to the significant reduction in solution mass flow rate and its pressure drop with the DSIM strategy suggests that it is an energy-efficient control strategy.

Earth Systems Thinking: Global Consumerism, Climate Change, and the Spiritual Value of the Earth

In this paper we consider the root cause of climate change to be the industrial waste heat by product of increasing global consumption. The embodied energy associated with the conversion of Earth’s resources into consumer goods has largely been driven by fossil fuel based energy. Using available data, we show how a) the rate of annual CO2 emissions to the atmosphere is increasing, b) the land+sea temperature anomaly index is increasing, particularly the last 3 years, c) the rate of heat addition to the world’s oceans is also accelerating as this is in direct response to a globally increasing consumption per capita. In short, all of our human induced rates related to consumption are accelerating with increasingly severe consequences to the Earth system that maintains us. This is occurring amidst the reality that humans are in a necessary physical partnership with nature. Despite this, many human cultures have pursued dominance over the Earth’s resources. This dominance is asserted by the mechanical philosophy of Descartes. Under this world view, the Earth is just a (soul-less) machine and man is distinct from nature and therefore entitled to dominate it; the Earth has no spiritual value. So this gives us license to dig up the planet to create the escalating distribution of products to global consumers and this is exactly what can be verified from the data. We refer to this as the business as usual trajectory. To correct this course trajectory, we propose two avenues: a) extend the concept and legality of the Public Trust Doctrine to all of Nature’s resources so that current generations have an obligation to ensure the future generations can same similar access to these resources, b) adopt a systems thinking approach that prioritizes human equity, dignity, environmental justice and environmental health over escalating global GDP. In short, global justice should be our priority, not global profit. From the systems thinking viewpoint, the Earth is not a market commodity subject to resource exhaustion, it is rather a sacred equilibrium system for the welfare of all.

Thermodynamic analysis of hybrid Rankine cycles using multiple heat sources of different temperatures

Past studies of hybrid power cycles using multiple heat sources of different temperatures focused mainly on case studies and almost no general theory about this type of systems was developed. This paper is a first comprehensive study of their general thermodynamic performance, with their comparison to their corresponding single temperature heat source reference system, focusing on three types of power cycles: simple Rankine cycle, Rankine cycle with reheat and Rankine cycle with heat regeneration. The generalized expressions for the energy and exergy efficiency differences between the hybrid and the corresponding single heat source system were developed. A number of simulation case studies were performed to help the understanding and confirm the thermodynamic generalization of the results. The results show that the energy and exergy efficiencies of the hybrid systems are higher than those of their corresponding single heat source reference systems if and only if the energy andexergy conversion efficiency (defined in the paper) of the additional heat source (AHS) is larger than that of the original heat source. The conditions that defined the effects of the AHS temperature and heat addition rate on the energy and exergy efficiencies of the hybrid systems as convex or concave curves were described. Comparisons across the first two types of hybrid power cycles were made, showing that the energy and exergy efficiencies of the reheat Rankine cycle is generally higher than that of the simple Rankine cycle as AHS is changed. Recommendations were made for obtaining the maximal energy and exergy efficiency as a function of the AHS temperature, of the heat addition rate by the AHS, and of the AHS position in the power cycle flow sheet. For the hybrid power generation systems with heat regeneration it was found that when using an AHS to raise the net system power by a given amount, using it to replace the higher-pressure extracted steam will result in a higher system energy efficiency than when using it to replace lower-pressure extracted steam. Hybrid cycles can have significantly lower emissions, cost, and fuel depletion.

Estimating Two Heat-Conduction Parameters From Two Complementary Transient Experiments

A desirable feature of any parameter estimation method is to obtain as much information as possible with one experiment. However, achieving multiple objectives with one experiment is often not possible. In the field of thermal parameter estimation, a determination of thermal conductivity, volumetric heat capacity, heat addition rate, surface emissivity, and convection coefficient may be desired from a set of temperature measurements in an experiment where a radiant heat source is used. It would not be possible to determine all of these parameters from such an experiment; more information would be needed. The work presented in the present research shows how thermal parameters can be determined from temperature measurements using complementary experiments where the same material is tested more than once using a different geometry or heating configuration in each experiment. The method of ordinary least squares is used in order to fit a mathematical model to a temperature history in each case. Several examples are provided using one-dimensional conduction experiments, with some having a planar geometry and some having a cylindrical geometry. The parameters of interest in these examples are thermal conductivity and volumetric heat capacity. Sometimes, both of these parameters cannot be determined simultaneously from one experiment but utilizing two complementary experiments may allow each of the parameters to be determined. An examination of confidence regions is an important topic in parameter estimation and this aspect of the procedure is addressed in the present work. A method is presented as part of the current research by which confidence regions can be found for results from a single analysis of multiple experiments.

An assessment of thermodynamic merits for current and potential future engine operating strategies

This work compares the fundamental thermodynamic underpinnings (i.e. working fluid properties and heat release profile) of various combustion strategies with engine measurements. The approach employs a model that separately tracks the impacts on efficiency due to differences in rate of heat addition, volume change, mass addition, and molecular weight change for a given combination of working fluid, heat release profile, and engine geometry. Comparative analysis between the measured and modeled efficiencies illustrates fundamental sources of efficiency reductions or opportunities inherent to various combustion regimes. Engine operating regimes chosen for analysis include stoichiometric spark-ignited combustion and lean compression-ignited combustion including homogeneous charge compression ignition, spark-assisted homogeneous charge compression ignition, and conventional diesel combustion. Within each combustion regime, the effects of engine load, combustion duration, combustion phasing, compression ratio,...

Early onset of sound in Rijke tube with abrupt contraction

Rijke tube is a system convenient for studying thermoacoustic instabilities both experimentally and theoretically. Common Rijke setups involve tubes with constant cross-sections. With the goal to reduce supplied heat necessary to excite acoustic modes, a segmented Rijke tube is constructed comprising two pipes of different diameters. Experiments with regulated mean flow and supplied heat demonstrate that thermoacoustic instability in the segmented tube occurs at about half of the heat addition rate required for sound onset in a tube with uniform cross-section. This finding suggests that simpler experimental means can be used for studying thermoacoustic instabilities due to significant reduction of required heat and highest temperatures in the system. Also, some practical devices with complicated resonators may appear to be more prone to instabilities of this sort. Stronger coupling between acoustic modes due to their enhanced non-orthogonality in segmented resonators can result in richer nonlinear effects. A simplified energy-based model is developed that predicts the onset of instability in both straight and segmented Rijke tubes.

Transition to Instability in Segmented Rijke Tube

Thermoacoustic instabilities can arise in systems where unsteady heat release is favorably coupled with acous- tic pressure oscillations. A modified Rijke tube with segments having different sections is found to have lower threshold levels of heat addition rate needed for exciting the fundamental acoustic mode of the tube. Experiments indicate that about 115 W of heating power is required to produce sound in the 90-cm-long segmented tube, while over 230 W is needed in 60-cm-long and 90-cm-long tubes with constant-area cross sections. One of the causes for lowering the threshold of heat addition rate is due to a significant reduction of the resonator natural frequency. The presented results suggest an impor- tance of including the system geometry details into analysis of practical devices prone to thermoacoustic instabilities.

Comparison between dynamics and control performance of mesophilic and thermophilic anaerobic sludge digesters

Two anaerobic digestion schemes, namely mesophilic and thermophilic processes, have been analysed for process stability and controllability. As in any control problem, three types of variable are distinguished in this study, i.e. disturbance, manipulated and controlled variables. Substrate concentration S i and influent temperature T i are the disturbance variables. The manipulated variables are sewage sludge influent rate Q and specific heat addition rate G u. The controlled variables are effluent substrate concentration S and digestion temperature T. A control system including a proportional—integral (PI) controller and variable groups is proposed. Multivariable steady state methods such as relative gain array, Niederlinski stability criterion, singular value decomposition and Morari integral controllability are employed. Several dynamic analyses such as biggest log-modulus tuning, robustness analysis and Tyreus load rejection criterion are carried out. Steady state analysis results are used for variable pairing. The results of multivariable analysis show that thermophilic anaerobic digestion is more favourable in terms of speed of response and disinfection capability. It also maintains dynamic and steady state stability if controlled properly.

Diabatic supersonic flows of dense gases

By adopting the van der Waals gas model the behavior of n-octane with addition or removal of heat in inviscid, steady, one-dimensional, supersonic flow is investigated. First, the given heat distribution is added in a constant area flow. Second, the effects in variable cross-sectional flows (nozzles) are shown for the additional condition of constant values of the Mach number or the static pressure, and for a given heat addition. As known from the isentropic flow of real gases, several gas-dynamic effects are inverted depending on the fundamental derivative Γ. Heat addition in a constant area duct at conditions near the thermodynamical critical point may cause an increase of the Mach number in transonic/supersonic flow, or a decrease in subsonic flow, which is the opposite behavior of a perfect gas. For heat addition at M=const a singularity is possible for Γ<0 in transonic/supersonic flow and for Γ≲1 in subsonic flow. Considering constant Mach number flows, the static pressure goes up for high values of Γ. Isobaric heat addition increases the Mach number for densities below the thermodynamical critical point. Perfect gas flow exhibits the opposite reaction in both cases without any singularity. Compared with the flow of a perfect gas (γ=1.4), in the dense gas the influence of the same rate of heat addition becomes much stronger.

Thermal effects of artificial heat sources and shaded ground areas in the urban canopy layer

The analytical cluster thermal time constant (CTTC) model, developed earlier by the authors, is used to simulate the effects of urban artificial heat release and increased shaded ground-layer areas on the urban canopy layer (UCL) climate. Hourly mean artificial heat addition of 55 W m−2, caused by transportation and electric use, is considered here as the anthropogenic energetic input to the urban atmosphere in summer. In an urban cluster composed of repeated similar street canyons oriented east-west with an aspect ratio (H/W, buildings' height to street width ratio) of 0.5, this heat addition rate causes a diurnal air temperature increase of 1–2.5 K peaking at 20:00. In summer, increasing the partially shaded ground area by adequate urban and building planning strategies can result in an appreciable temperature decrease at midday, provided that the mean sky view factor of the locality remains as high as possible.

The annular flow, electrothermal plug ramjet

The annular flow, electrothermal plug ramjet is examined as a possible means of achieving rapid projectile acceleration for applications such as direct space payload launches. Electrothermal plug ramjet performance is examined for cases when hydrogen propellant is treated 1) as a perfect gas and 2) as a gas that can dissociate and ionize and then recombine at finite rates in the nozzle. Performance results for these cases are compared to the performance of a conventional ramjet operating with a perfect gas hydrogen propellant. Models describing electrothermal plug ramjet and conventional ramjet operation are presented and it is shown that, for a given flight velocity, there is an optimum rate of heat addition per unit mass of propellant. Propellant dissociation and ionization losses are found to be small and the nozzle flow is shown to be near chemical equilibrium rather than in a chemically frozen state. Diffuser shock losses are found not to degrade performance to unacceptably low levels. Fluid particle residence times are found to be small compared with those required for significant flowfield changes and it is argued that assuming quasisteady flow does not introduce significant errors. Thermal efficiencies over selected launch cycles are between 30 and 40% and pressure, temperature, and power requirements are demonstrated to be reasonable.

Effect of Processing Variables on Flame Pasteurization of Liquids in Aluminum Cans

ABSTRACTStudies were performed with 203 x 413 aluminum cans using 1% bentonite suspension and 0.4% carbonated water as models, simulating fruit juices and carbonated beverages, respectively. The cans were heated in a pilot flame sterilizer. Of the variables studied at pasteurization temperatures (max. 85°C), the can rotational speed had only a small effect on the heating rate in the range 10‐100 rpm. Gas flow rate, on the other hand, was a very important factor controlling the process. In the range tested, the heat addition rate increased linearly with increasing gas flow rate. The optimum separation distance between the can and the burner was approximately 4 cm for 1 % bentonite and 2 cm for carbonated water. Optimum distances depended on the gas flow rates used.

Thermally induced low-frequency oscillations

This paper discusses nonlinear thermally induced oscillations in quasi-one dimensional flows in ducts. In practice such oscillations are frequently observed in furnaces and combustion chambers. The problem considered involves entropy disturbances which are convected through a nozzle at the end of a tube, thereby producing an acoustic wave which propagates upstream and leads to a modulation of the mass flow at the inlet of the tube. Alternatively, if the rate of heat addition (i. e. the rate of fuel addition in the case of a combustion chamber) responds only weakly or not at all to the oscillating pressure at the inlet, the modulated air flow produces an entropy oscillation (due to the oscillating equivalence ratio in the case of a combustor) downstream of the zone of heat addition (reaction zone). To obtain general stability limits for this kind of self-induced oscillation, a second-order analysis is developed which leads to a nonlinear wave equation. The convection of entropy disturbances introduces nonlinear memory effects which are responsible for a non-local character of the wave equation. The wave equation is solved with the help of a numerical evolution scheme, making use of a suitable scaling transformation which does not change the form of the equation.

An experimental investigation of two dimensional flame-vortex interactions

Experiments have been performed to study the interaction between a flame and a single vortex impulsively generated by the flame. The objectives are to investigate the amplitude of the cylindrically diverging acoustic wave produced by the interaction and to develop a quantitative approach to determine the degree of violence of the flame-vortex interaction. With the Reynolds number, defined as the ratio of the strength of the vortex to the kinematic viscosity of the unburned gas, characterizing the unburned gas flow condition quantitatively, the acoustic pressure Δ p(t) generated by the interaction has been measured at distances 1.5, 1.75 and 2.0 meters away from the interaction zone using a microcomputer-based data acquisition system and a storage oscilloscope. The dimensionless time rate of change in the heat addition rate, Q( t ), of the flame-vortex interaction, is deduced from the acoustic pressure data via the line source equation in linear acoustic theory. The Fast Fourier Transform has been used to perform the analysis. For the thirty experiments performed, the amplitudes of Q( t ) and Δ p(t) have been found to be dependent on Re, burning speed and two dimensionless geometric parameters. The results show that Q max increases with Re when the geometric parameters are fixed. An empirical logarithmic equation has been obtained to describe the variation of Q max for Re between 10 5 and 4.5×10 5 . The maximum Δ p max recorded was 72 mbar at 1.5 m from the interaction zone. The increase in the “violence” of the interaction has been found to be associated with an increase in the heat addition rate during the period of flame-vortex interaction.