Numerical Characterization of Viscous Heat Dissipation Rate in Oscillatory Air Flow

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
S. M. Jalil
Keyword(s):  
Temperature Field ◽  
Heat Dissipation ◽  
Air Flow ◽  
Womersley Number ◽  
Dissipation Term ◽  
Bulk Heating ◽  
Numerical Characterization ◽  
Viscous Heat ◽  
Wide Range ◽  
New Criterion

Abstract The effect of viscous heat dissipation (VHD) in raising the temperature field of incompressible oscillatory air flow is studied numerically. A threshold is established for when the viscous heat dissipation term in the thermal energy equation changes or does not change the temperature field for the case of oscillatory air flow in a tube connecting two reservoirs. This new criterion has not been specified clearly in earlier oscillatory flow research. According to the defined threshold and when VHD is important, the effect of dissipative bulk heating can be described by a proposed correlation in terms of Womersley number (Wo) and axial tidal displacement (ΔZ) of the oscillatory fluid. These results are determined using two-dimensional (2D) numerical simulations of laminar oscillatory air flow (Pr = 0.7) for different adiabatic unconductive tube-reservoirs' systems configurations over a wide range of oscillatory frequencies and tidal displacements. It is found that the low amount of fluid kinetic energy, which is converted into internal energy, is not sufficient to significantly heat up the fluid at a low rate of the viscous work. Therefore, the effect of viscous heat dissipation in oscillatory air flow can be ignored only below a specific limit of unsteadiness depending on Womersley number and axial tidal displacement. Also, the results showed that the VHD becomes more significant with increasing (Wo) and (ΔZ).

TLBM MODEL FOR THE VISCOUS HEAT DISSIPATION IN INCOMPRESSIBLE LIMIT

2007 ◽  
Vol 21 (01) ◽  
pp. 117-126 ◽  
Author(s):  
LIN ZHENG ◽  
BAO CHANG SHI ◽  
ZHEN HUA CHAI
Keyword(s):  
Evolution Equation ◽  
Viscous Dissipation ◽  
Heat Dissipation ◽  
Present Model ◽  
Distribution Functions ◽  
Temperature Fields ◽  
Equilibrium Density ◽  
Special Method ◽  
Dissipation Term ◽  
Viscous Heat

The viscous dissipation term in energy equation is investigated with the lattice Boltzmann method, and the double distribution functions (DDF) are applied, respectively, to simulate the velocity and the temperature fields. Compared with other existing models, the complicated evolution equation is simplified and the energy equilibrium density function is completely independent of the density distribution function in present model [unlike the authors He et al. [J. Comput. Phys.146, 282 (1998)]], when dealing with viscous dissipation term problem. In this paper, the viscous dissipation term is directly treated as a source term and the complex space discretion in the evolution equation can also be avoided by special method in part 2. Efficiency and accuracy of present model is validated through numerical experiments on Couette and natural convection flows.

URBAN FACADE GEOMETRY ON OUTDOOR COMFORT CONDITIONS: A REVIEW

2020 ◽  
Vol 4 (1) ◽  
pp. 45
Author(s):  
Elahe Mirabi ◽  
Nasrollahi Nazanin
Keyword(s):  
Thermal Comfort ◽  
Urban Areas ◽  
Natural Ventilation ◽  
Flow Behavior ◽  
Air Flow ◽  
Urban Geometry ◽  
Wide Range ◽  
Low Energy Buildings ◽  
Outdoor Comfort ◽  
Solar Access

<p>Designing urban facades is considered as a major factor influencing issues<br />such as natural ventilation of buildings and urban areas, radiations in the<br />urban canyon for designing low-energy buildings, cooling demand for<br />buildings in urban area, and thermal comfort in urban streets. However, so<br />far, most studies on urban topics have been focused on flat facades<br />without details of urban layouts. Hence, the effect of urban facades with<br />details such as the balcony and corbelling on thermal comfort conditions<br />and air flow behavior are discussed in this literature review. <strong>Aim</strong>: This<br />study was carried out to investigate the effective factors of urban facades,<br />including the effects of building configuration, geometry and urban<br />canyon’s orientation. <strong>Methodology and Results</strong>: According to the results,<br />the air flow behavior is affected by a wide range of factors such as wind<br />conditions, urban geometry and wind direction. Urban façade geometry<br />can change outdoor air flow pattern, thermal comfort and solar access.<br /><strong>Conclusion, significance and impact study</strong>: In particular, the geometry of<br />the facade, such as indentation and protrusion, has a significant effect on<br />the air flow and thermal behavior in urban facades and can enhance<br />outdoor comfort conditions. Also, Alternation in façade geometry can<br />affect pedestrians' comfort and buildings energy demands.</p>

Nitrogen Removal from Anaerobically-Treated Leachate

1984 ◽  
Vol 19 (1) ◽  
pp. 87-100
Author(s):  
D. Prasad ◽  
J.G. Henry ◽  
P. Elefsiniotis
Keyword(s):  
Nitrogen Removal ◽  
Air Flow ◽  
Operating Conditions ◽  
Air Flow Rate ◽  
Flow Rates ◽  
Anaerobic Filter ◽  
Ph Values ◽  
Wide Range ◽  
Ammonia Desorption ◽  
Effects Of Ph

Abstract Laboratory studies were conducted to demonstrate the effectiveness of diffused aeration for the removal of ammonia from the effluent of an anaerobic filter treating leachate. The effects of pH, temperature and air flow on the process were studied. The coefficient of desorption of ammonia, KD for the anaerobic filter effluent (TKN 75 mg/L with NH3-N 88%) was determined at pH values of 9, 10 and 11, temperatures of 10, 15, 20, 30 and 35°C, and air flow rates of 50, 120, and 190 cm3/sec/L. Results indicated that nitrogen removal from the effluent of anaerobic filters by ammonia desorption was feasible. Removals exceeding 90% were obtained with 8 hours aeration at pH of 10, a temperature of 20°C, and an air flow rate of 190 cm3/sec/L. Ammonia desorption coefficients, KD, determined at other temperatures and air flow rates can be used to predict ammonia removals under a wide range of operating conditions.

scholarly journals Bilayer ventilated labyrinthine metasurfaces with high sound absorption and tunable bandwidth

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jiayuan Du ◽  
Yuezhou Luo ◽  
Xinyu Zhao ◽  
Xiaodong Sun ◽  
Yanan Song ◽  
...  
Keyword(s):  
Sound Absorption ◽  
Air Flow ◽  
Single Layer ◽  
Sound Waves ◽  
Acoustic Metamaterials ◽  
Sound Barrier ◽  
Free Air ◽  
Relative Bandwidth ◽  
Wide Range ◽  
High Sound

AbstractThe recent advent of acoustic metamaterials offers unprecedented opportunities for sound controlling in various occasions, whereas it remains a challenge to attain broadband high sound absorption and free air flow simultaneously. Here, we demonstrated, both theoretically and experimentally, that this problem can be overcome by using a bilayer ventilated labyrinthine metasurface. By altering the spacing between two constituent single-layer metasurfaces and adopting asymmetric losses in them, near-perfect (98.6%) absorption is achieved at resonant frequency for sound waves incident from the front. The relative bandwidth of absorption peak can be tuned in a wide range (from 12% to 80%) by adjusting the open area ratio of the structure. For sound waves from the back, the bilayer metasurface still serves as a sound barrier with low transmission. Our results present a strategy to realize high sound absorption and free air flow simultaneously, and could find applications in building acoustics and noise remediation.

Respiratory Mechanics of Sound Production in Chickens and Geese

1978 ◽  
Vol 72 (1) ◽  
pp. 229-250
Author(s):  
J. H. BRACKENBURY
Keyword(s):  
Respiratory System ◽  
Simultaneous Measurement ◽  
Sound Production ◽  
High Pressures ◽  
Respiratory Mechanics ◽  
Air Flow ◽  
Tracheal Pressure ◽  
Wide Range ◽  
Range Of Values ◽  
Respiratory Movements

1. Air flow, air sac pressure and tracheal pressure were measured in chickens and geese during a variety of different vocal and non-vocal activities. 2. Air flow and air sac pressure may rise to 500 ml s−1 and 60 cmH2O (6 103 N/m2) respectively during a crow in the chicken. During a sequence of honks in the goose the corresponding values are 650 ml s−1 and 25 cmH2O(2.5 × 10 3 N/m2) respectively. 3. The volume of air delivered through the respiratory system during a single crow is more than 400 ml, almost equivalent to the total volume of the lung air sac system. 4. The efficiency of the chicken syrinx as a sound producing instrument, estimated by comparing the sound energy radiated with the energy consumed in the expulsion of air during a crow, appears to be less than 2 %. 5. Cutting the paired sternotrachealis muscles had no effect on vocalization. 6. The measured rates of clucking, cheeping and honking in adult chickens, young chicks and adult geese respectively are comparable to the characteristic rates of panting in these animals. This points to a similarity in the nature of the respiratory movements involved in each case. 7. Simultaneous measurement of tracheal flow and pressure indicate that the glottis is capable of controlling air flow over a wide range of values in the presence of high pressures. During defaecation the valve is closed whilst during coughing it is wide open.

scholarly journals Automobile Radiator’s Engineering and Analysation

2020 ◽  
Vol 9 (5) ◽  
pp. 554-558
Keyword(s):  
Flow Rate ◽  
Heat Dissipation ◽  
Cooling System ◽  
Volume Flow Rate ◽  
Air Flow ◽  
Temperature Drop ◽  
Inlet Temperature ◽  
Air Flow Rate ◽  
Air Velocity ◽  
Cooling Fan

The shape of a radiator cover is crucial either in determining the pattern of air flow or in increasing the same through the radiator core thereby increasing the thermal efficiency, thus making it a necessity to understand it. Moreover the parts circumjacent to the core namely the upper tank, lower tank, cooling fan, fins, tubes, etc promote the air flow rate. Also it is to note that the air flow rate of discharge gases from radiator core is one of the prime factors in determining the automobile cooling system. Initially factors such as temperature, pressure, air flow rate that affect the performance are obtained in order to derive out the entities of operation. One of the observations that can be made through this paper is that as the volume of the coolant increases, the rate of heat dissipation increases, also parameters like inlet temperature and volume flow rate of coolant, air velocity, temperature drop and drop in pressure of coolant are factors that contribute in radiator performance evidently.

Examination of a “Map-Based” Approach to Modeling Steady State Heat Pump Performance With Variable Air Flow Rates

1994 ◽  
Author(s):  
P. Mawasha ◽  
S. P. Rooke ◽  
R. Gross
Keyword(s):  
Steady State ◽  
Heat Pump ◽  
Heat Exchangers ◽  
Air Flow ◽  
Cooling Mode ◽  
Air Source Heat Pump ◽  
Performance Predictions ◽  
Wide Range ◽  
Steady State Heat ◽  
Rigorous Model

Abstract Performance map-based modeling has been commonly employed for the rapid prediction of air conditioning and heat pump steady state performance. This approach requires that performance characteristics of the compressor and heat exchangers can be expressed in the form of simple algebraic functions. The growth of microprocessor based control, particularly in residential systems, has led to more frequent off-design operation. This study explores the ability of the map-based modeling approach to predict off-design operating performance of a single air-source heat pump operating in the cooling mode. Off-design conditions were simulated by varying the evaporator air flow rate over a wide range. Performance predictions are compared with the predictions of a more rigorous heat pump simulation program which utilizes heat transfer correlations for the heat exchangers rather than performance maps. A PC math package was used to generate results for the map-based model, while a Fortran compiler was used to generate results for the more rigorous model. The benefits of the map-based approach in predicting system performance are presented and discussed.

High-Temperature Spin-On Adhesives for Temporary Wafer Bonding

2007 ◽  
Vol 4 (3) ◽  
pp. 105-111 ◽  
Author(s):  
S. Pillalamarri ◽  
R. Puligadda ◽  
C. Brubaker ◽  
M. Wimplinger ◽  
S. Pargfrieder
Keyword(s):  
High Temperature ◽  
Wafer Bonding ◽  
Heat Dissipation ◽  
Temperature Stability ◽  
High Temperature Stability ◽  
Performance Requirements ◽  
Wide Range ◽  
Bonding Properties ◽  
Partial List ◽  
Wafer Thinning

Wafer thinning has been effectively used to improve heat dissipation in power devices and to fabricate flexible substrates, small chip packages, and multiple chips in a package. Wafer handling has become an important issue due to the tendency of thinned wafers to warp and fold. Thinned wafers need to be supported during the backgrinding process, lithography, deposition, etc. Temporary wafer bonding using removable adhesives provides a feasible route to wafer thinning. Existing adhesives meet only a partial list of performance requirements. They do not meet the requirements of high-temperature stability combined with ease of removal. This paper reports on the development of a wide range of temporary adhesives to be used in wafer thinning applications that use both novel and conventional bonding and debonding methods. We have developed a series of novel removable high-temperature spin-on adhesives with excellent bonding properties and a wide range of operating temperatures for bonding and/or debonding to achieve a better processing window.

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