scholarly journals Computing the heat flux required for warming up of frozen wooden prisms for veneer production in the beginning of their autoclave steaming

2021 ◽  
Vol 1208 (1) ◽  
pp. 012021
Author(s):  
Nencho Deliiski ◽  
Dimitar Angelski
Keyword(s):  
Heat Flux ◽  
Moisture Content ◽  
Steam Generator ◽  
Heat Fluxes ◽  
Heat Power ◽  
Wood Moisture ◽  
Medium Temperature ◽  
Suggested Approach ◽  
Loading Level ◽  
In The Beginning

Abstract An approach for computing the heat flux required for warming up of frozen wooden prisms in the regimes for their autoclave steaming at limited heat power of the steam generator, depending on the dimensions of the prisms cross section, wood moisture content, and loading level of the autoclave has been suggested. The approach is based on the use of two personal mathematical models: 2D non-linear model of the temperature distribution in subjected to steaming frozen wooden prisms and model of the non-stationary heat balance of autoclaves for steaming wood materials. For numerical solving of the models and practical application of the suggested approach, a software program was prepared in the calculation environment of Visual FORTRAN Professional developed by Microsoft. Using this program computation and research of the non-stationary change of the processing medium temperature and heat fluxes in an autoclave with a diameter of 2.4 m, length of 9.0 m and loading level of 50% at a limited heat power of the steam generator, equal to 500 kW during the initial part of the steaming in it of frozen beech prisms with different moisture content have been carried out. The suggested approach can be used for computing and model based automatic realization of energy efficient optimized regimes for autoclave steaming of different wood materials.

scholarly journals Influence of Selected Factors on the Duration and Energy Efficiency of Autoclave Steaming Regimes of Non-Frozen Prisms for Veneer Production

Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 7433
Author(s):  
Nencho Deliiski ◽  
Ladislav Dzurenda ◽  
Dimitar Angelski ◽  
Natalia Tumbarkova
Keyword(s):  
Energy Efficiency ◽  
Moisture Content ◽  
Cross Section ◽  
Steam Generator ◽  
Atmospheric Pressure ◽  
Energy Efficient ◽  
Initial Temperature ◽  
Heat Power ◽  
Wood Moisture ◽  
Loading Level

This paper puts forward a methodology for calculating the duration and energy efficiency of regimes for autoclave steaming of wooden prisms for veneer production at limited heat power of the steam generator, depending on the dimensions of the prism’s cross section, wood moisture content, and loading level of the autoclave. The methodology is based on the use of two personal mathematical models: the 2D non-linear model of the temperature distribution in non-frozen wooden prisms subjected to steaming and subsequent conditioning in an air medium, and the model of the non-stationary heat balance of autoclaves for steaming wood materials. Using the suggested methodology, the calculation and research into the duration and energy efficiency of regimes for heating of beech prisms have been carried out. The variables used were an initial temperature of 0 °C, cross-section dimensions 0.3 × 0.3 m, 0.4 × 0.4 m, and 0.5 × 0.5 m, moisture content of 0.4, 0.6, and 0.8 kg·kg−1, during their steaming in an autoclave with a diameter of 2.4 m, length of 9.0 m and loading level of 40, 50, and 60% at a limited heat power of the steam generator, equal to 500 kW. It has been determined that the duration of the autoclave steaming regimes, at a loading level of 50% being most often used in the practice beech prisms with moisture of 0.6 kg·kg−1, does not exceed 9 h, 13 h, and 20 h for prisms with cross-section 0.3 × 0.3 m, 0.4 × 0.4 m, and 0.5 × 0.5 m, respectively. This duration is less than half of the corresponding duration of the steaming regimes at atmospheric pressure. The energy needed for warming up such prisms themselves does not exceed 60, 65, and 69 kWh·m−3, respectively, and the energy consumption of the whole autoclave then is equal to about 90, 99, and 105 kWh·m−3, respectively. The energy efficiency of the autoclave steaming regimes changes between 62.2% and 68.8% for the studied ranges of the influencing factors and it turns out to be more than 2–3 times larger in comparison with the efficiency of the steaming at atmospheric pressure. The methodology can be used for various calculations with ANSYS and to create the software for systems used for computing and model-based automatic realization of energy-efficient regimes for autoclave steaming of different wood materials from various species. This could be useful in developing similar methodologies in different areas of thermal treatment at increased pressure of various capillary-porous materials of plant or technical origin.

Engineering Approach for Computation of the Energy Consumption Needed for Defrosting and Subsequent Heating of Frozen Wood Chips

2016 ◽  
Vol 688 ◽  
pp. 50-56
Author(s):  
Nencho Deliiski ◽  
Anton Geffert ◽  
Jarmila Geffertova ◽  
Veselin Brezin ◽  
Izabela Radkova
Keyword(s):  
Energy Consumption ◽  
Moisture Content ◽  
Wood Chips ◽  
Specific Mass ◽  
Wood Moisture ◽  
Suggested Approach ◽  
Engineering Approach ◽  
Easy Calculation ◽  
Subsequent Heating

An engineering approach for the calculation of the specific mass energy consumption, which is needed for defrosting and the subsequent heating of the frozen wood chips above the hydroscopic range, (in kWh·t-1), has been suggested. Equations for easy calculation of have been derived, depending on the wood moisture content u, on the fiber saturation points of the wood species at 20 °C and at –2 °C (i.e. at 293.15 K and at 271.15 K), and respectively, on the initial chips’ temperature, T0 , and on the final temperature of the heated after their defrosting chips, T1.For the calculation of the according to the suggested approach and equations a software program has been prepared in MS Excel 2010. With the help of the program calculations have been carried out for the determination of the energy consumption , which is needed for defrosting and subsequent heating of oak, acacia, beech, and poplar frozen chips with moisture content in the range from u = 0.4 kg·kg-1 to u = 1.0 kg·kg-1, initial temperature t0 = –20 °C and t0 = –10 °C until reaching of the chips‘ mass temperature of t1 = 80 °C, t1 = 100 °C, and t1 = 120 °C at the end of the heating.

scholarly journals The Effect of Environmental Moisture Conditions on the Calculated Incident Radiant Heat Flux by Plate Thermometers

2020 ◽  
Vol 6 (4) ◽  
pp. 102
Author(s):  
Lahiru Jayathunga-Mudiyanselage ◽  
Haejun Park ◽  
Virginia Charter ◽  
Rob Agnew
Keyword(s):  
Heat Flux ◽  
Moisture Content ◽  
Radiant Heat ◽  
Fire Spread ◽  
Radiant Heat Flux ◽  
Absorbed Energy ◽  
Wood Moisture ◽  
Moisture Equivalent ◽  
Two Phases ◽  
Moisture Conditions

This study investigates the effect of environmental moisture conditions on the calculated incident radiant heat flux (irradiance) by plate thermometers (PT). Alterations were made to the moisture content of the PT insulation layers to achieve these conditions. Irradiance was calculated using a pre-determined equation based on fully insulated conditions and validated using a Schmidt-Boelter radiometer. The study consisted of two phases; (i) investigating the effect of preheating PT to the accurate irradiance, (ii) investigating the effect of moisture in the PT on the measurement of irradiance. Calculated irradiance agreed with measured for preheated PT, but not with unheated PT. Four representative moisture conditions were identified for phase two, whereby samples were equilibrated at 0, 45, 65, and 98 wood moisture equivalent (%WME). No noticeable difference identified between measured and calculated irradiance was detected within 0–65%WME. PT with 98%WME showed a difference between the irradiance as the moisture inside the PT insulation absorbed energy from the PT to vaporize. Therefore, using preheated PT with any %WME under 65 is recommended to obtain accurate enough irradiance measurements. The result can use to improve determining the fire spread mechanisms and accurate measurements of irradiance in outdoor fires such as informal settlements fires.

Examination of moisture content variation within an operational wet deck

TAPPI Journal ◽  
2013 ◽  
Vol 12 (1) ◽  
pp. 45-50 ◽  
Author(s):  
LAURENCE SCHIMLECK ◽  
KIM LOVE-MYERS ◽  
JOE SANDERS ◽  
HEATH RAYBON ◽  
RICHARD DANIELS ◽  
...  
Keyword(s):  
Moisture Content ◽  
Southeastern United States ◽  
Forest Products ◽  
Time Domain Reflectometry ◽  
Water Application ◽  
Wood Moisture ◽  
International Paper ◽  
Content Variation ◽  
Moisture Variation

Many forest products companies in the southeastern United States store large volumes of roundwood under wet storage. Log quality depends on maintaining a high and constant wood moisture content; however, limited knowledge exists regarding moisture variation within individual logs, and within wet decks as a whole, making it impossible to recommend appropriate water application strategies. To better understand moisture variation within a wet deck, time domain reflectometry (TDR) was used to monitor the moisture variation of 30 southern pine logs over an 11-week period for a wet deck at the International Paper McBean woodyard. Three 125 mm long TDR probes were inserted into each log (before the deck was built) at 3, 4.5, and 7.5 m from the butt. The position of each log within the stack was also recorded. Mixed-effects analysis of variance (ANOVA) was used to examine moisture variation over the study period. Moisture content varied within the log, while position within the stack was generally not significant. The performance of the TDR probes was consistent throughout the study, indicating that they would be suitable for long term (e.g., 12 months) monitoring.

scholarly journals Assessing IDDES-Based Wall-Modeled Large-Eddy Simulation (WMLES) for Separated Flows with Heat Transfer

Fluids ◽  
2021 ◽  
Vol 6 (7) ◽  
pp. 246
Author(s):  
Rozie Zangeneh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Large Eddy Simulation ◽  
Skin Friction ◽  
Heat Fluxes ◽  
Separated Flows ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Isothermal Wall

The Wall-modeled Large-eddy Simulation (WMLES) methods are commonly accompanied with an underprediction of the skin friction and a deviation of the velocity profile. The widely-used Improved Delayed Detached Eddy Simulation (IDDES) method is suggested to improve the prediction of the mean skin friction when it acts as WMLES, as claimed by the original authors. However, the model tested only on flow configurations with no heat transfer. This study takes a systematic approach to assess the performance of the IDDES model for separated flows with heat transfer. Separated flows on an isothermal wall and walls with mild and intense heat fluxes are considered. For the case of the wall with heat flux, the skin friction and Stanton number are underpredicted by the IDDES model however, the underprediction is less significant for the isothermal wall case. The simulations of the cases with intense wall heat transfer reveal an interesting dependence on the heat flux level supplied; as the heat flux increases, the IDDES model declines to predict the accurate skin friction.

scholarly journals Drift kinetic theory of alpha transport by tokamak perturbations

2021 ◽  
Vol 87 (2) ◽  
Author(s):  
Elizabeth A. Tolman ◽  
Peter J. Catto
Keyword(s):  
Heat Flux ◽  
Kinetic Theory ◽  
Alpha Particle ◽  
Heat Fluxes ◽  
Alpha Particles ◽  
Alpha Power ◽  
Mode Amplitude ◽  
Effective Collision Frequency ◽  
Perturbation Frequency ◽  
Particle Confinement

Upcoming tokamak experiments fuelled with deuterium and tritium are expected to have large alpha particle populations. Such experiments motivate new attention to the theory of alpha particle confinement and transport. A key topic is the interaction of alpha particles with perturbations to the tokamak fields, including those from ripple and magnetohydrodynamic modes like Alfvén eigenmodes. These perturbations can transport alphas, leading to changed localization of alpha heating, loss of alpha power and damage to device walls. Alpha interaction with these perturbations is often studied with single-particle theory. In contrast, we derive a drift kinetic theory to calculate the alpha heat flux resulting from arbitrary perturbation frequency and periodicity (provided these can be studied drift kinetically). Novel features of the theory include the retention of a large effective collision frequency resulting from the resonant alpha collisional boundary layer, correlated interactions over many poloidal transits and finite orbit effects. Heat fluxes are considered for the example cases of ripple and the toroidal Alfvén eigenmode (TAE). The ripple heat flux is small. The TAE heat flux is significant and scales with the square of the perturbation amplitude, allowing the derivation of constraints on mode amplitude for avoidance of significant alpha depletion. A simple saturation condition suggests that TAEs in one upcoming experiment will not cause significant alpha transport via the mechanisms in this theory. However, saturation above the level suggested by the simple condition, but within numerical and experimental experience, which could be accompanied by the onset of stochasticity, could cause significant transport.

scholarly journals Air–Sea Interaction in the Central Mediterranean Sea: Assessment of Reanalysis and Satellite Observations

2021 ◽  
Vol 13 (11) ◽  
pp. 2188
Author(s):  
Salvatore Marullo ◽  
Jaime Pitarch ◽  
Marco Bellacicco ◽  
Alcide Giorgio di Sarra ◽  
Daniela Meloni ◽  
...  
Keyword(s):  
Heat Flux ◽  
Mediterranean Sea ◽  
Seasonal Cycle ◽  
Heat Fluxes ◽  
Meteorological Variables ◽  
Central Mediterranean ◽  
High Quality ◽  
Central Mediterranean Sea ◽  
In Situ Observations

Air–sea heat fluxes are essential climate variables, required for understanding air–sea interactions, local, regional and global climate, the hydrological cycle and atmospheric and oceanic circulation. In situ measurements of fluxes over the ocean are sparse and model reanalysis and satellite data can provide estimates at different scales. The accuracy of such estimates is therefore essential to obtain a reliable description of the occurring phenomena and changes. In this work, air–sea radiative fluxes derived from the SEVIRI sensor onboard the MSG satellite and from ERA5 reanalysis have been compared to direct high quality measurements performed over a complete annual cycle at the ENEA oceanographic observatory, near the island of Lampedusa in the Central Mediterranean Sea. Our analysis reveals that satellite derived products overestimate in situ direct observations of the downwelling short-wave (bias of 6.1 W/m2) and longwave (bias of 6.6 W/m2) irradiances. ERA5 reanalysis data show a negligible positive bias (+1.0 W/m2) for the shortwave irradiance and a large negative bias (−17 W/m2) for the longwave irradiance with respect to in situ observations. ERA5 meteorological variables, which are needed to calculate the air–sea heat flux using bulk formulae, have been compared with in situ measurements made at the oceanographic observatory. The two meteorological datasets show a very good agreement, with some underestimate of the wind speed by ERA5 for high wind conditions. We investigated the impact of different determinations of heat fluxes on the near surface sea temperature (1 m depth), as determined by calculations with a one-dimensional numerical model, the General Ocean Turbulence Model (GOTM). The sensitivity of the model to the different forcing was measured in terms of differences with respect to in situ temperature measurements made during the period under investigation. All simulations reproduced the true seasonal cycle and all high frequency variabilities. The best results on the overall seasonal cycle were obtained when using meteorological variables in the bulk formulae formulations used by the model itself. The derived overall annual net heat flux values were between +1.6 and 40.4 W/m2, depending on the used dataset. The large variability obtained with different datasets suggests that current determinations of the heat flux components and, in particular, of the longwave irradiance, need to be improved. The ENEA oceanographic observatory provides a complete, long-term, high resolution time series of high quality in situ observations. In the future, more similar sites worldwide will be needed for model and satellite validations and to improve the determination of the air–sea exchange and the understanding of related processes.

Inverse Heat Conduction Applied to the Measurement of Heat Fluxes on a Rotating Cylinder: Comparison Between an Analytical and a Numerical Technique

2008 ◽  
Vol 130 (8) ◽  
Author(s):  
Fabien Volle ◽  
Michel Gradeck ◽  
Denis Maillet ◽  
Arsène Kouachi ◽  
Michel Lebouché
Keyword(s):  
Heat Flux ◽  
Numerical Technique ◽  
Rotating Cylinder ◽  
Local Heat ◽  
Heat Fluxes ◽  
Inverse Heat Conduction ◽  
Analytical Technique ◽  
Inner Radius ◽  
Direct Model ◽  
Stable Estimation

A method using either a one-dimensional analytical or a two-dimensional numerical inverse technique is developed for measurement of local heat fluxes at the surface of a hot rotating cylinder submitted to the impingement of a subcooled water jet. The direct model calculates the temperature field inside the cylinder that is submitted to a given nonuniform and time dependent heat flux on its outer surface and to a uniform surface heat source on an inner radius. In order to validate the algorithms, simulated temperature measurements inside the cylinder are processed and used by the two inverse techniques to estimate the wall heat flux. As the problem is improperly posed, regularization methods have been introduced into the analytical and numerical inverse algorithms. The numerical results obtained using the analytical technique compare well with the results obtained using the numerical algorithm, showing a good stable estimation of the available test solutions. Furthermore, real experimental data are used for the estimation, and local boiling curves are plotted and discussed.

Sign in / Sign up

Export Citation Format

Share Document