Dynamic Heat Balance Research Articles

Fast dynamic heat and mass balance model of walking beam reheat furnace with two-dimensional slab temperature profile

A fast dynamic heat and mass balance model of a walking beam reheat furnace was developed and validated with the data from a 275 t h−1 industrial furnace. The model divides the furnace into well stirred zones, and from air and gas flowrates into individual zones, preheated air temperature and slab locations, calculates in each zone the temperature of gas and temperature profile of refractory, two-dimensional temperature profile of slabs and scale thickness on horizontal surfaces of slabs. The model can be used for offline analyses and is fast enough for online use, where it can handle the steady operation and the special cases like delay, empty furnace and the gradual filling or emptying of the furnace. The details of the model and the validation results are presented here, together with the sensitivity analysis of the key parameters, and the study of options for fuel savings and the reduction in skidmark severity.

Impact of aeration and agitation on metabolic heat and protease secretion of Aspergillus tamarii in a real-time biological reaction calorimeter

The effects of aeration and agitation on metabolic heat, alkaline protease production and morphology for Aspergillus tamarii MTCC5152 are reported in this manuscript. Measurement of metabolic heat has been attempted by the continuous and dynamic heat balance method in a biological real-time reaction calorimeter. At lower agitation intensities, growth-related processes were dominating. As a result the protease activity and the product heat yields were lower than those for 350 and 450 rpm. Although biomass growth was necessary to obtain maximum protease yield, agitation seemed to play a vital role in the protease production process. Energy dissipation per circulation function of the process is also deduced from power input. At optimal conditions, 350 rpm and 1 vvm, the gassed power required was 0.133 W. Pellet morphology and protease production were studied under different aeration and agitation intensities of A. tamarii. Pellet structure was considerably influenced by DO, a higher DO level resulted in denser pellets (1,018.4 kg/m(3)) leading to higher protease activity. Coupling of hydrodynamics and bio-reaction highlighted the complex relationship between energy dissipation, substrate uptake rate and fungal physiology. This study emphasised the potential of biocalorimetry as a reliable monitoring and robust control tool for aerobic fermentation of A. tamarii, using agricultural by-products.

Transient Thermal Network Modeling Applied to Multiscale Systems. Part II: Application to an Electronic Control Unit of an Automobile

This paper applies the methodology of transient thermal network modelling (TTNM) introduced in Part I to the heat transfer analysis of an electronic control unit (ECU) located in the engine enclosure of a motorcar. The complexity of the geometry, the diverse heat transfer mechanisms involved and the duration of the operating cycle prevent the use of both simple, lumped models and detailed numerical simulations. The TTNM methodology relies instead in steady, approximate heat transfer correlations and a division of the system into the largest possible isothermal elements, based on the analysis of characteristic time and length scales. The dynamic heat balance of each element is then written down, conforming the TTNM of the system, which is numerically integrated with an adequate time step. The practical aspects of the TTNM methodology (design stage) are finally demonstrated; in this particular case-study, the model reveals a very high risk of damage of electronic components due to the radiative heat load received from the exhaust pipe of the engine. A design modification consisting of a radiative shield is proposed and model-tested, achieving an appropriate reduction of heat flux and temperatures, and thus an adequate protection of critical components.

Control of Heat Transfer in Continuous Casting Process Using Neural Networks

摘要: In continuous casting, the cooling-solidification process must be based on the adaptation of heat transfer, which is directly connected to casting conditions such as casting speed, casting temperature, and cooling parameters. Most control schemes are based on the static relation between casting speed and water flow rate in each cooling zone; this constitutes an open loop that does not consider the dynamic surface temperature, which is an important parameter for the final slab quality. In steelmaking, the casting-speed changes affect the global heat transfer. An optimal operation requires an adjustment of the process control variables, i.e., global heat transfer. A learning neural network (NN) allows the identification and the control of a nonlinear heat transfer model in the continuous casting process. A heat transfer model was developed using the dynamic heat balance. A comparison between the experimental open loop results and those of the model simulation is considered. Following adaptation, the model is used for controlling the slab surface temperature in closed loop, using NN technology and PID controllers. The NN identification and control strategy gives a stable temperature closed loop control comparatively to the conventional PID. 关键词: Neural networks / identification / control / heat transfer / continuous casting

Thermal comfort of closed spaces. Fundamentals of static and dynamic heat balance of human body

The growing mechanization and industrialization of society has resulted in most people spending greater part of their lives - 85-90% - in artificial climate. In this climate, thermal comfort can be basically predicted by the environment parameters such as temperature, humidity, air velocity and by the personal parameters as activity and clothing resistance. This paper intends to present the basic equations of the classical comfort theory, the equations of the human body´s static heat balance, and the so called comfort equation as well as its sensitivity depending on the thermic parameters of the microclimate. The PMV expression describs the thermal comfort of the human body and its sensitivity. The concept of dynamic thermal sensation and the possibilities of its research will be introduced.

Core temperature differences between males and females during intermittent exercise: physical considerations

We examined differences in dynamic heat balance between males and females during intermittent exercise. Six males (M) and six females (F) performed three 30-min bouts of exercise (Ex1, Ex2, Ex3) at a constant rate of metabolic heat production (M - W) of approximately 500 W separated by three 15-min periods of inactive recovery. Rate of total heat loss (M - W) was measured by direct calorimetry, while M - W was determined by indirect calorimetry. Esophageal (T (es)) was measured continuously. Exercise at a constant M - W of approximately 500 W, was paralleled by a similar HL between sexes at the end of Ex1 (M: 462 +/- 30 W, F: 442 +/- 9 W, p = 0.117), Ex2 (M: 468 +/- 28 W, F: 508 +/- 18 W, p = 0.343), and Ex3 (M: 469 +/- 17 W, F: 465 +/- 13 W, p = 0.657). Consequently, changes in body heat content were comparable after Ex1 (M: 218 +/- 21 kJ, F: 287 +/- 35 kJ, p = 0.134), Ex2 (M: 109 +/- 18 kJ, F: 158 +/- 29 kJ, p = 0.179), and Ex3 (M: 92 +/- 19 kJ, F: 156 +/- 35 kJ, p = 0.136). However, females had greater overall increases in T (es) at the end of Ex3 (M: 0.55 +/- 0.25 degrees C, F: 0.97 +/- 0.26 degrees C, p <OR= 0.05). Differences in core temperature between sexes appear to be solely related to differences in physical characteristics, and not due to concurrent differences in whole-body thermoregulatory responses.

Batch top-spray fluid bed coating: Scale-up insight using dynamic heat- and mass-transfer modelling

A mathematical model was developed for batch top-spray fluid bed coating processes based on Ronsse et al. [2007a, b. Combined population balance and thermodynamic modelling of the batch top-spray fluidised bed coating process. Part I—model development and validation. Journal of Food Engineering 78, 296–307; Combined population balance and thermodynamic modelling of the batch top-spray fluidised bed coating process. Part II—model and process analysis. Journal of Food Engineering 78, 308–322]. The model is based on one-dimensional discretisation of the fluid bed into a number of well-mixed control volumes. In each control volume, dynamic heat and mass balances were set up allowing the simulation of the contents of water vapour, water on core particles and deposited coating mass as well as fluidisation gas, particle and chamber wall temperature. The model was used to test different scale-up principles by comparing simulation results with experimental temperature and humidity data obtained from inorganic salt coating of placebo cores in three pilot fluid bed scales being a 0.5 kg small-scale (GEA Aeromatic-Fielder Strea-1), 4 kg medium-scale (GEA Niro MP-1) and 24 kg large-scale (GEA MP-2/3). Results show good agreement between simulated and experimental outlet fluidisation air temperature and humidity as well as bed temperature. Simulations reveal that vertical temperature and humidity gradients increase significantly with increasing scale and that in fluid beds as the simulated 900 kg (RICA-TEC Anhydro) production-scale, the gradients become too large to use the simple combined drying force/relative droplet size scale-up approach without also increasing the inlet fluidisation air temperature significantly. Instead, scale-up in terms of combinations of the viscous Stokes theory with simulated particle liquid layer profiles (obtained with the model) is suggested. In this way, the given fluid bed scale may be optimised in terms of low agglomeration tendency for a given process intensity across scale.

Control of Heat Transfer in Continuous Casting Process Using Neural Networks

In continuous casting, the cooling-solidification process must be based on the adaptation of heat transfer, which is directly connected to casting conditions such as casting speed, casting temperature, and cooling parameters. Most control schemes are based on the static relation between casting speed and water flow rate in each cooling zone; this constitutes an open loop that does not consider the dynamic surface temperature, which is an important parameter for the final slab quality. In steelmaking, the casting-speed changes affect the global heat transfer. An optimal operation requires an adjustment of the process control variables, i.e., global heat transfer. A learning neural network (NN) allows the identification and the control of a nonlinear heat transfer model in the continuous casting process. A heat transfer model was developed using the dynamic heat balance. A comparison between the experimental open loop results and those of the model simulation is considered. Following adaptation, the model is used for controlling the slab surface temperature in closed loop, using NN technology and PID controllers. The NN identification and control strategy gives a stable temperature closed loop control comparatively to the conventional PID.

Heat Balance Is Attained During Postexercise Recovery Despite Residual Body Heat Storage

A rapid decay in local heat loss responses has been demonstrated during recovery from exercise despite sustained elevations in core temperature. However, it is unclear how dynamic heat balance changes during recovery relative to exercise. PURPOSE: To measure dynamic human heat balance during exercise followed by recovery. METHODS: Concurrent rates of metabolic heat production (M-W) and whole-body heat loss (HL) were measured by whole-body direct calorimetry to give rate of body heat storage (S) and change in body heat content from rest (ΔHb) in six male participants throughout 60-min of cycle ergometry at 40% of VO2peak and 60-min recovery at 30°C and 30% relative humidity. Core temperature was measured in the esophagus (Tes) and rectum (Tre), and regional muscle temperature in the vastus lateralis (Tvl) and triceps brachii (Ttb). RESULTS: After 60-min exercise, S approached zero and ΔHb was 289±38 kJ, paralleled by core temperature elevations of 0.82±0.17°C for Tes and 0.53±0.13°C for Tre, and muscle temperature elevations of 2.45±0.63°C for Tvl and 2.27±0.57°C for Ttb. After 10-min recovery, M-W returned to pre-exercise levels, and only 22.5±6.9% of the exercise-induced increase in HL remained despite core temperature elevations of 0.40±0.23°C for Tes and 0.43±0.14°C for Tre. After 60-min recovery S approached zero, due to a pre-exercise level of M-W and only 5.1±2.9% of the exercise-induced increase in HL remaining. However Tes was elevated by 0.22±0.14°C and Tre by 0.20±0.10°C, and muscle temperature was elevated by 1.00±0.47°C for Tvl and 0.93±0.51°C for Ttb. At the end of recovery, ΔHb from pre-exercise rest was 148±40 kJ. CONCLUSION: A balance between the rates of whole-body heat production and heat dissipation (i.e. S≈0) was attained after 60-min of exercise and again after 60-min postexercise recovery. However the accumulation of body heat content was greater during exercise than the dissipation of body heat content during recovery, primarily due to a greater rate of decay of total heat loss. This resulted in ~51% of exercise-induced heat content remaining in the body, giving elevated postexercise core and muscle tissue temperatures. Supported by U.S. Army Medical Research and Material Command and NSERC

Sex-Related Differences in Dynamic Heat Balance: Metabolic Heat Production Considerations

Sex-related differences in thermoregulatory responses during exercise in the heat have typically been attributed to anthropometric characteristics. After accounting for such characteristics, and when working at the same relative oxygen consumption (VO2), females have been shown to sweat less than males, while maintaining similar core temperatures. However, workloads based upon relative maximal VO2 do not take into consideration differences in rates of metabolic heat production (M-W). Therefore, we evaluated the hypothesis that sex-related differences in rates of evaporative heat loss (EHL) during exercise at the same relative VO2 are due to differences in M-W. PURPOSE: To determine if different rates of M-W elicited by workloads of the same percentage of maximal VO2 would result in proportional differences in EHL between sexes. METHODS: 8 males and 7 females cycled for 60-min at 40% VO2 in a hot dry environment (40°C, 30% RH) within the modified Snellen whole-body air calorimeter. Subjects were matched for body surface area to mass ratio and for maximal VO2 relative to lean body mass. EHL and dry heat gain (DHG), as well as changes in body heat content (ΔHb) were determined by direct calorimetry. M-W was concurrently measured using indirect calorimetry. Rectal temperature (Tre) was measured continuously. RESULTS: Throughout exercise, M-W was higher in males compared to females (209±26 vs 249±35 W·m−2, p=0.05). Consequently, rates of EHL (225±28 vs 253±37 W·m−2, p=0.05) were proportionally higher. This resulted in a greater ΔHb (306±71 vs 455±127 KJ, p=0.05). This body heat storage resulted in a larger rise from baseline in Tre (0.82±0.20 vs 1.21±0.29°C, p=0.05) for males despite their greater total body mass and mean specific heat of body tissues. When accounting for differences in total heat load (M-W+ DHG) however, there were no differences in EHL between sexes (p>0.05). CONCLUSION: Despite working at the same percentage of VO2, the higher metabolic heat load in males throughout exercise resulted in a higher absolute EHL but also a greater ΔHb. Therefore, it is important to consider metabolic heat production when comparing possible thermoregulatory sex-related differences during exercise. Supported by Natural Sciences and Engineering Research Council and US Army Medical Research Acquisition Activity Grants.

Numerical Spray Model of the Fluidized Bed Coating Process

In this study, a new model for the batch top-spray fluidized bed coating process is presented. The model is based on the one-dimensional (axial) discretization of the bed volume into different control volumes, in which the dynamic heat and mass balances for air, water vapor, droplets, core particles, and coating material were established. The coupling of the droplet phase's mass and heat transfer terms with the gas and solid phases was established by means of a droplet submodel in which droplet trajectories were individually simulated. The model calculation method combines a Monte Carlo technique for the simulation of the particle exchange with the first-order Euler's method for solving the heat and mass balances, enabling the prediction of both the dynamic coating mass distribution and the one-dimensional (axial) thermodynamic behavior of the fluidized bed during batch operation. The simulation results were validated using experimental two-dimensional spatial air temperature and air humidity distributions, which were measured in a fluidized bed pilot reactor using a scanning probe. Sensitivity analysis was carried out to study the effect of controllable process variables, such as fluidization air and atomization air properties, as well as the properties of the spraying liquid upon the simulated dynamic temperature and humidity distributions. Also, the effects of relevant process variables on growth rate uniformity and process yield were studied. Based on these sensitivity studies it was concluded that nozzle parameters, such as air pressure and positioning with respect to the bed, are as important as the fluidization air properties (humidity, temperature, and flow rate) for the coating growth rate uniformity and process yield.

Combined population balance and thermodynamic modelling of the batch top-spray fluidised bed coating process. Part I—Model development and validation

A combined population balance and thermodynamic model was developed for the batch top-spray fluidised bed coating process. The model is based on the one-dimensional discretisation of the fluidised bed into different control volumes, in which the dynamic heat and mass balances for air, water vapour, core particles and coating material were established. The calculation method involves a Monte Carlo technique for the simulation of the particle exchange in combination with the first-order Euler’s method for solving the heat and mass balances. The model enables the prediction of both the dynamic coating mass distribution and the one-dimensional thermodynamic behaviour of the fluidised bed during batch operation. The simulation results were validated using the results from tests on a Glatt GPCG-1 fluidised bed unit.

Modelling and Simulation of Heat Transfer in Stored Rough Rice with Aeration

A mathematical model based on dynamic heat and mass balances was developed to simulate grain and air temperature in a bin storage during rough rice forced aeration periods. The mathematical model includes several experimentally obtained expressions to determine thermo-physical grain properties. Model validation was carried out by comparing predicted with experimentally measured grain temperatures in different points of a pilot silo, ventilated with cool air at constant air temperature and humidity. Predicted and measured data were in close agreement. The model can be used to predict the development of grain temperature and the time needed to cool stored grain under different ventilation conditions.

Measurement of metabolic heat in a production-scale bioreactor by continuous and dynamic calorimetry

Measurement of metabolic heat has been attempted in an industrial-scale bioreactor using continuous and dynamic heat balance calorimetry. The contributions of individual heat sources influencing the temperature of the broth were evaluated and the magnitude of metabolic heat was calculated from general energy balance. Good correlations were obtained between oxygen uptake rate (OUR) and metabolic heat with heat yield under continuous and dynamic conditions with the values of Y Q/O =444 kJ/mole O 2 and Y Q/O =431 kJ/mole O 2 , respectively. There was also correlation between biomass production and heat generation. The value of heat yield, Y Q/X , was calculated to be 14546 kJ/kg; however, this was not constant and slightly decreased towards the end of fermentation. A similar value for heat yield was obtained under dynamic conditions and found to be 14667 kJ/kg. The consistency of experimental data was checked using carbon, electron, and heat balances. It was shown that reasonable accuracy could be achieved in an industrial environment. The difficult-to-measure variable biomass concentration was estimated using continuous metabolic heat flux, and good correlation was obtained between measured and estimated biomass concentrations. The results of this study suggest that heat balance around an industrial bioreactor can be simplified by accurately identifying individual heat sources as opposed to laboratory bioreactors where the contribution of each source can have significant impact. This reduces the number of measurements for accurate heat balance and makes use of heat balance feasible in a large scale.

The crystallization kinetics of polyamide-12

The crystallization kinetics of polyamide-12 has been investigated using a combination of differential scanning calorimetry (DSC) and hot-stage optical microscopy. The DSC data for isothermal crystallization were consistent with a simple two-parameter Avrami model for isothermal crystallization and optical measurements of the spherulite growth rates and nucleation density. On the basis of semiempirical expressions for these quantities, it is shown that with small adjustments the model can also account for DSC data for nonisothermal crystallization, provided that corrections are made for the dynamic heat balance between the sample and the DSC oven.

Dynamic simulation of a PVC suspension reactor

The scope of this contribution is to present a comprehensive methodology for the dynamic modelling of an industrial PVC suspension reactor. The paper analyses the main features, but brings also some new insights on the polymerisation kinetics, the dynamic heat balance and the action of the control system. The model is implemented in SPEEDUP™ and can be used for the optimisation of process operation and recipe development, as well as a core component of a training simulator.

Dynamic Heat Balance Model for Industrial Batch Reactors and its Applications

A dynamic heat balance model which can be generically applicable to various industrial batch reactors has been proposed. The proposed model is composed by considering the detailed heat balance around the cooling jacket, which has been overlooked in the existing modeling approaches, as well as the heat balance for the reactor contents. In the proposed model, the local heat transfer coefficient in the reactor side is selected as a tuning parameter. The proposed model has been utilized to investigate reactor behaviors as well as to improve control methods for PBL and EPS polymerization reactors.

SIMULATION OF A ROTARY DRYER FOR SUGAR CRYSTALLINE

Dynamic heat and material balances were developed, and residence time, heat and mass transfer rates were calculated using literature correlations. The model equations were solved numerically using the Speedup simulation package and tested against industrial data. Comparison of model predictions with industrial data show that the model is accurate for steady state operation and predicts dynamic trends that are consistent with engineering judgment. Predicted outlet moisture and temperatures differ by about ±10 % from the industrial data.