scholarly journals A new argument against cooling by convective air eddies formed above sunlit zebra stripes

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ádám Pereszlényi ◽  
Dénes Száz ◽  
Imre M. Jánosi ◽  
Gábor Horváth
Keyword(s):  
The Body ◽  
Schlieren Imaging ◽  
Air Stream ◽  
Stream Drift ◽  
Calm Weather ◽  
Air Streams ◽  
Stream Formation

AbstractThere is a long-lasting debate about the possible functions of zebra stripes. According to one hypothesis, periodical convective air eddies form over sunlit zebra stripes which cool the body. However, the formation of such eddies has not been experimentally studied. Using schlieren imaging in the laboratory, we found: downwelling air streams do not form above the white stripes of light-heated smooth or hairy striped surfaces. The influence of stripes on the air stream formation (facilitating upwelling streams and hindering horizontal stream drift) is negligible higher than 1–2 cm above the surface. In calm weather, upwelling air streams might form above sunlit zebra stripes, however they are blown off by the weakest wind, or even by the slowest movement of the zebra. These results forcefully contradict the thermoregulation hypothesis involving air eddies.

Second Law Analysis of Solid Desiccant Rotary Dehumidifiers

1988 ◽  
Vol 110 (1) ◽  
pp. 2-9 ◽  
Author(s):  
E. Van den Bulck ◽  
S. A. Klein ◽  
J. W. Mitchell
Keyword(s):  
Local Maximum ◽  
Operating Conditions ◽  
Second Law ◽  
Transfer Coefficients ◽  
Adiabatic Flow ◽  
Transfer Processes ◽  
Air Stream ◽  
Second Law Analysis ◽  
Pass Through ◽  
Air Streams

This paper presents a second law analysis of solid desiccant rotary dehumidifiers. The equations for entropy generation for adiabatic flow of humid air over a solid desiccant are developed. The generation of entropy during operation of a rotary dehumidifier with infinite transfer coefficients is investigated and the various sources of irreversibility are identified and quantified. As they pass through the dehumidifier, both the process and regeneration air streams acquire nonuniform outlet states, and mixing both of these air streams to deliver homogeneous outlet streams is irreversible. Transfer of mass and energy between the regeneration air stream and the desiccant matrix occurs across finite differences in vapor pressure and temperature and these transfer processes generate entropy. The second law efficiency of the dehumidifier is given as a function of operating conditions and the effect of finite transfer coefficients for an actual dehumidifier is discussed. It is shown that operating the rotary dehumidifier at conditions that minimize regeneration energy also yields a local maximum for the second law efficiency.

Diffusion Driven Desalination for Simultaneous Fresh Water Production and Desulfurization

2010 ◽  
Vol 2 (3) ◽  
Author(s):  
Jameel R. Khan ◽  
James F. Klausner ◽  
Donald P. Ziegler ◽  
Srinivas S. Garimella
Keyword(s):  
Fresh Water ◽  
Fluid Transport ◽  
Transport Model ◽  
Waste Heat ◽  
Feed Water ◽  
Low Grade ◽  
Water Production ◽  
Air Stream ◽  
Mass Transport Model ◽  
Air Streams

The diffusion driven desalination (DDD) process has been previously introduced as a process for distilling water using low-grade waste heat. Here, a configuration of the DDD process is introduced for simultaneously distilling water and scrubbing sulfur dioxide (SO2) out of heated air streams, which is also known as flue gas desulfurization (FGD). This novel DDD/FGD process utilizes the low-grade waste heat carried in industrial discharge air streams. There are many applications, where the industrial air discharge also contains SO2, and in order to utilize the waste heat for the DDD process, the SO2 must be scrubbed out of the air stream. The two major components of the DDD process are the diffusion tower and the direct contact condenser. In the present work, a thermal fluid transport model for the DDD/FGD process, that includes SO2 scrubbing, is developed. It is an extension of the heat and mass transport model previously reported for the DDD process. An existing laboratory scale DDD facility was modified and tested with SO2 in the air stream and with seawater as the feed water to the diffusion tower. The experimental investigation has been completed to evaluate the fresh water production and SO2 scrubbing potential for the DDD/FGD process. The experimental results compare favorably with the model predictions. Chemical analysis on the condenser water demonstrates the capability of the DDD/FGD process to produce high quality fresh water using seawater as the input feed water to the process.

Biological odour control by diffusion into activated sludge basins

2000 ◽  
Vol 41 (6) ◽  
pp. 127-132 ◽  
Author(s):  
R. P. Bowker
Keyword(s):  
Wastewater Treatment ◽  
Activated Sludge ◽  
Wastewater Treatment Plants ◽  
High Strength ◽  
Air Stream ◽  
Fine Bubble ◽  
Treatment Facilities ◽  
Odour Control ◽  
Odour Emissions ◽  
Air Streams

Diffusion of odourous air into activated sludge basins is an effective and economical approach for odour control at wastewater treatment plants. Over 30 facilities in North America practice this technique. Most of these applications are for dilute or moderate strength air streams with relatively low hydrogen sulfide (H2S) levels. Unfortunately, the lack of data documenting the effectiveness of the process and concerns for blower corrosion have limited its acceptance as a method for controlling odour emissions. This paper presents a compilation and review of wastewater treatment facilities that are currently using activated sludge diffusion. Performance data are tabulated, and information on operation and maintenance of the blower/diffuser systems are summarized. New data are presented that compare the effectiveness of coarse vs. fine bubble diffusers for treatment of a high strength, high-H2S air stream from sludge holding tanks at Concord, NH. Designand performance information is presented on a dedicated odour control system installed at Phoenixville, Pennsylvania in 1996 that collects high-H2S air streams from an influent chamber and primary clarifiers and diffuses it into a mechanically-aerated activated sludge basin. A cost-effectiveness analysis is presented for a blower/diffuser system installed exclusively for odour control. Methods used to overcome initial operational problems are discussed.

Differential effects of ambient temperature on warm cell responses to infrared radiation in the bloodsucking bug Rhodnius prolixus

2014 ◽  
Vol 111 (6) ◽  
pp. 1341-1349 ◽  
Author(s):  
Lydia M. Zopf ◽  
Claudio R. Lazzari ◽  
Harald Tichy
Keyword(s):  
Infrared Radiation ◽  
Thermal Environment ◽  
Radiant Heat ◽  
Rhodnius Prolixus ◽  
Background Information ◽  
Cell Responses ◽  
Air Stream ◽  
Different Types ◽  
Flow Information ◽  
Air Streams

Thermoreceptors provide animals with background information about the thermal environment, which is at least indirectly a prerequisite for thermoregulation and assists bloodsucking insects in the search for their host. Recordings from peg-in-pit sensilla and tapered hairs on the antennae of the bug Rhodnius prolixus revealed two physiologically different types of warm cells. Both types responded more strongly to temperature pulses produced by switching between two air streams at different constant temperatures than to infrared radiation pulses employed in still air. In addition, both warm cells were better able to discriminate small changes in air temperature than in infrared radiation. As convective and radiant heat determines the discharge, it is impossible for a single warm cell to signal the nature of the stimulus unequivocally. Individual responses are ambiguous, not with regard to temperature change, but with regard to its source. We argue that the bugs use mechanical flow information to differentiate between pulses of convective and radiant heat. However, if pulses of radiant heat occur together with a constant temperature air stream, the mechanical cues would not allow avoiding ambiguity that convective heat introduces into radiant heat stimulation. In this situation, the warm cell in the tapered hairs produced stronger responses than those in the peg-in-pit sensilla. The reversal in the excitability of the two types of warm cells provides a criterion by which to distinguish the combination of convective and radiant heat from the stimuli presented alone.

Experimental Investigation of Composite Desiccant Wheel Dehumidifier

2015 ◽  
Vol 813-814 ◽  
pp. 1080-1084
Author(s):  
P.D. Dipinlal ◽  
S. Shankara Narayanan ◽  
Seranthian Ramanathan ◽  
S. Prabhu
Keyword(s):  
Honeycomb Structure ◽  
Coefficient Of Performance ◽  
Work Study ◽  
Performance Indices ◽  
Desiccant Wheel ◽  
Air Stream ◽  
Inlet Conditions ◽  
Pass Through ◽  
Air Streams ◽  
Study Performance

Desiccant wheel dehumidifier is filled with solid desiccants, looks like a honeycomb structure which is open on both ends. Air is allowed to pass through the honeycomb passages, giving moisture to the solid desiccant contained in the wheel. The wheel constantly rotates through two separate air streams. The first air stream, called the process air is dried by the desiccant. The second air stream, called reactivation or regeneration air is heated and dries the desiccant. The combination of desiccant materials such as chloride desiccant and organic desiccant is used here and dehumidification in the composite desiccant wheel has been studied experimentally. In this work, study performance of composite desiccant wheel with different air velocities, regeneration temperatures and at different inlet conditions was conducted and calculated the different performance indices of the desiccant wheel dehumidifier such as Dehumidification Effectiveness and Dehumidification Coefficient of Performance (DCOP).

Investigation of Methanol Based Air-Air Thermosyphon Heat Exchangers

2013 ◽  
Author(s):  
Bharath Viswanath Ravi ◽  
Mukilan Sebastiraj Michael ◽  
S. Audithya Krishna ◽  
Lakshmanan Arunachalam ◽  
Suresh Mariappan
Keyword(s):  
Heat Exchanger ◽  
Heat Recovery ◽  
Systematic Approach ◽  
Hvac Systems ◽  
Transport Systems ◽  
Working Fluid ◽  
Cold Air ◽  
Air Stream ◽  
Fin Spacing ◽  
Air Streams

Thermosyphons are self-actuated heat transport systems in which the circulation of the working fluid is brought about by a combination of gravity and buoyant forces. In the recent years, thermosyphons have been considered for widely diverse heat recovery applications, especially in HVAC systems. In this work, a systematic approach for design and analysis of finned air-air thermosyphon heat exchanger system based on effectiveness-NTU method is presented. Furthermore, the effect of mass flow ratio of the hot and cold air stream, temperature difference between the hot and cold air streams, transverse tube spacing, fin spacing and length of the thermosyphon on the effectiveness of the system is predicted by numerical simulation. In addition, the thermal performance of unfinned thermosyphon heat exchanger system has also been investigated experimentally.

Characteristics of Heat Dissipation from a Block Heat Source Module in a Three-Dimensional Cabinet to Ambient Natural Convective Air Stream

2012 ◽  
Vol 229-231 ◽  
pp. 2589-2592
Author(s):  
Y.L. Tsay ◽  
J.C. Cheng
Keyword(s):  
Natural Convection ◽  
Rayleigh Number ◽  
Heat Source ◽  
Heat Dissipation ◽  
Three Dimensional ◽  
Thermal Interaction ◽  
Air Stream ◽  
Conjugate Conduction ◽  
Air Streams ◽  
Thermal Conductivities

This study combined the numerical analysis and experimental measurement to investigate the conjugate conduction and natural convection for a block heat source module in a three-dimensional cabinet filled and surrounded by air. The effects of Rayleigh number Ra, module position C1, ratio of block to air thermal conductivities Kbf, and ratio of board to air thermal conductivities Kpf are examined. Moreover, efforts are carried out to explore the influence of thermal interaction between the air streams inside and outside the cabinet.

An Experimental Examination of the Spontaneous Ignition of Fibrous Materials in Heated Air Streams

1988 ◽  
Vol 110 (1) ◽  
pp. 48-54 ◽  
Author(s):  
S. A. Mehta ◽  
G. A. Karim
Keyword(s):  
Ignition Delay Time ◽  
Effective Activation Energy ◽  
Spontaneous Ignition ◽  
Stream Velocity ◽  
Physical Parameters ◽  
Fibrous Materials ◽  
Heated Air ◽  
Air Stream ◽  
Ignition And Combustion ◽  
Air Streams

The behavior of a bed of fibrous combustile material, exemplified by pure cotton (ASTM, 1982), when subjected to a controlled stream of heated air, was examined experimentally. The effects of some controlling basic physical parameters, such as sample compactness and ventilation, air stream temperature, and air stream velocity on the spontaneous ignition and combustion characteristics were established. Moreover, the observed spontaneous ignition delay time was correlated in terms of these variables. The effective activation energy during the ignition reactions was derived and shown to be dependent on the compactness of the sample.

Neuro-Muscular Control of Dipteran Flight

1967 ◽  
Vol 47 (1) ◽  
pp. 77-97 ◽  
Author(s):  
WERNER NACHTIGALL ◽  
DONALD M. WILSON
Keyword(s):  
The Body ◽  
Total Power ◽  
Impulse Frequency ◽  
Wingbeat Frequency ◽  
Air Stream ◽  
Separate Control ◽  
Turning Behaviour ◽  
Frequency Changes ◽  
Distribution Of Power ◽  
Two Sides

1. Electrical activity from the indirect, myogenic muscles of calliphorid flies was recorded during flight. The animals were suspended from an aerodynamic balance in the laminar air-stream from a wind-tunnel. Muscle action potentials, recorded with 25µ wire, were 5-7 msec. in duration, up to 10mV. in amplitude and positive in sign. Frequencies were mostly under 20/sec. 2. Frequencies in all the indirect muscles were similar, but these varied together with changes in aerodynamic power. 3. Frequencies in the indirect muscles of the two sides varied by no more than ± 10% during extreme turns to right or left (only left or only right wing beating). 4. Electrical records from the non-myogenic direct muscles were made during tethered flight. The potentials were 2-4 msec. in duration, up to 2 mV. positive and had frequencies up to 180/sec. 5. A nearly linear positive correlation exists between impulse frequency in the musculus latus (pleurosternal muscle), the inward movement of the pleural wall, and the wingbeat frequency, suggesting that this muscle is the basic frequency determiner. 6. Strong turning behaviour is associated with opposed frequency changes in the pairs of antagonistic adductor and abductor muscles of the wings on the two sides of the body. 7. The musculus dorsoventralis IV (tergo-trochanteral) is activated by a short impulse burst at the beginning of flight. It apparently acts as an oscillation starter. 8. Flight initiation normally requires 30-60 msec. Usually activity begins in the musculus latus, which stiffens the thorax. Then simultaneously the myogenic muscles are activated and the ‘starter’ muscle causes a jump and the beginning of oscillation of the thorax. Then the wings are drawn gradually forward and full wingbeat amplitude develops within the first six wingbeats. Flight begins with maximal lift and wingbeat frequency and a nearly synchronous burst discharge in all the indirect muscles. 9. Power production and the transmission and distribution of power are under separate control. The myogenic indirect motor varies only in total power output, this being influenced by its own state of excitation and by a muscle-controlling wingbeat frequency. Steering is accomplished by non-myogenic direct muscles which are capable of differentially engaging the two wings with the motor.

Application of Computional Fluid Dynamics for Study of the Occurrence of Aerodynamic Effect for its Application in the Construction of Electric Race Car

2015 ◽  
Vol 809-810 ◽  
pp. 956-961
Author(s):  
Łukasz Grabowski ◽  
Andrzej Baier ◽  
Andrzej Buchacz ◽  
Michał Majzner ◽  
Michał Sobek
Keyword(s):  
Fluid Dynamics ◽  
Aerodynamic Drag ◽  
The Body ◽  
Air Velocity ◽  
Race Car ◽  
Drag Forces ◽  
Graphic Analysis ◽  
Aerodynamic Effect ◽  
Air Streams ◽  
The Ideal

In this article the issues related to Computional Fluid Dynamics of the occurrence of innovative aerodynamic effect were presented. Analysis were performed to determine the occurrence of Kammback aerodynamic effect and its application in a shape of a body of the real racing car in order to minimize drag forces of the vehicle. For the analysis, ideal aerodynamic shapes were modeled, subsequently they were subjected to modifications which were used to determine the occurrence of effect. The basic modeled shape was the raindrop shape solid, which is generally regarded as the ideal shape in terms of aerodynamics. The result of analysis was compared with the drag values known from the literature. Afterwards changes in the shape of the base solid were made to verify and determine the optimum Kammback shape, selected from a set of possible solutions, in which the geometrical changes has the lowest difference of values of drag force and drag coefficientCx(Cd)in comparison to the basic raindrop shape. Results of the study were subjected to graphic analysis, especially the distribution of air pressure on the surface of a solid and in a virtual wind tunnel, distribution of the air velocity and the course of air streams around the shape. The results were used to design the body of electric race car. The main objective was to minimize the aerodynamic drag of the vehicle.

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