Analysis of airflow in a full-scale room with non-isothermal jet ventilation using PTV techniques.ABSTRACT
Draft and non-uniform fresh air distribution are common problems in winter ventilation, especially for large animal buildings. Thermal-based anemometers have difficulties in accurately measuring non-isothermal and low-speed indoor airflow. A new technology, particle tracking velocimetry For other uses, see .
Particle tracking velocimetry (PTV) is one of velocimetry methods, i.e a technique to measure velocity of particles. The name suggests that the particles are tracked, and not only recorded as an image as it is suggested in another form, particle image (PTV PTV
1. pay television
2. public television
PTV (US) n abbr (= pay television) → Pay-TV nt (= public television ), which uses particles and their images to study indoor airflow, can overcome the traditional limitations in indoor airflow measurement. A PTV system was used to characterize indoor airflow in a full-scale ventilated ven·ti·late
tr.v. ven·ti·lat·ed, ven·ti·lat·ing, ven·ti·lates
1. To admit fresh air into (a mine, for example) to replace stale or noxious air.
2. room under nonisothermal ventilation conditions. Non-isothermal mild weather and winter ventilation conditions were simulated to analyze their effects on indoor airflow and air velocities in animal occupied zones and human breathing zones. It is found that winter ventilation created a totally reversed rotating ro·tate
v. ro·tat·ed, ro·tat·ing, ro·tates
1. To turn around on an axis or center.
2. airflow pattern. Air velocities in the animal occupied zone increased substantially compared with the corresponding isothermal i·so·ther·mal
Of, relating to, or indicating equal or constant temperatures.
having the same temperature. ventilation conditions. Winter ventilation strategies for improvement of airflow distribution were studied: (1) increasing inlet inlet /in·let/ (-let) a means or route of entrance.
pelvic inlet the upper limit of the pelvic cavity.
thoracic inlet the elliptical opening at the summit of the thorax. air velocity, (2) increasing inlet air jet momentum by use of air recirculation Noun 1. recirculation - circulation again
circulation - the spread or transmission of something (as news or money) to a wider group or area devices, and (3) decreasing ventilation temperature difference.
Indoor air quality Indoor Air Quality (IAQ) deals with the content of interior air that could affect health and comfort of building occupants. The IAQ may be compromised by microbial contaminants (mold, bacteria), chemicals (such as carbon monoxide, radon), allergens, or any mass or energy stressor of large-scale animal production facilities is increasingly recognized as important to the health, well-being, and productivity of building occupants. Ventilation is one of the major means of controlling the indoor environment and indoor air quality. In summer, indoor air temperatures of animal buildings are generally within 3[degrees]C of inlet air temperatures. It is generally accepted that summer ventilation can be assumed "isothermal" for most practical engineering purposes. In mild and cold weather, room air temperatures tend to be much higher than the inlet air temperature due to heat production from animals and equipment. Supply air is not heated during winter for most production animal facilities and thus is much colder than the room air. Therefore, non-isothermal ventilation is typical in realistic buildings during heating seasons. Draft and non-uniform fresh air distribution are common problems with winter ventilation, especially for large-scale animal buildings. Understanding airflow patterns under non-isothermal ventilation conditions, especially those typical in winter, is important in evaluating ventilation system ventilation system Public health An air system designed to maintain negative pressure and exhaust air properly, to minimize the spread of TB and other respiratory pathogens in a health care facility effectiveness and in developing environmental control strategies.
Ventilation research has been extensively studied over the past two decades (Nielsen et al. 1978; Timmons 1984; Sandberg 1987; Zhang et al. 1992; Jin and Ogilvie 1992; Riskowski et al. 1993; Heber and Boon Boon
A general term that refers to a benefit or improvement for investors. This can include such things as increased dividends, a stock market rally and stock buybacks.
Notes: 1993; Wang and Ogilvie 1996). It should be noted that most ventilation study cases simulated isothermal ventilation because it is simpler to measure, model, and analyze. Few studies were conducted on non-isothermal ventilation.
Under non-isothermal ventilation conditions, separation of the inlet air jet from the ceiling is mainly affected by the inertial force inertial force
An apparent force that appears to affect bodies within a non-inertial frame, but is absent from the point of view of an inertial frame. Centrifugal forces and Coriolis forces, both observed in rotating systems, are inertial forces. of the air jet, which is the result of jet momentum and buoyancy buoyancy (boi`ənsē, b`yən–), upward force exerted by a fluid on any body immersed in it. Buoyant force can be explained in terms of Archimedes' principle. force caused by heating loads. The room inlet Archimedes number An Archimedes number (not to be confused with Archimedes' constant, π), named after the ancient Greek scientist Archimedes, to determine the motion of fluids due to density differences, is a dimensionless number in the form:
1. One that diffuses, as:
a. A light fixture, such as a frosted globe, that spreads light evenly.
b. A medium that scatters light, used in photography to soften shadows.
c. air jet drops immediately after entering the room. Zhang et al. (1992) indicated an equivalent critical Ar value of 0.005 for the test room.
[A.sub.r] = [g[beta][DELTA][T.sub.0][D.sub.0]]/[U.sub.0.sup.2] (1)
[beta] = thermal expansion thermal expansion
Increase in volume of a material as its temperature is increased, usually expressed as a fractional change in dimensions per unit temperature change. coefficient of air, 1/K;
g = acceleration of gravity acceleration of gravity
n. Abbr. g
The acceleration of freely falling bodies under the influence of terrestrial gravity, equal to approximately 9.81 meters (32 feet) per second per second. , 9.8 m/[s.sup.2];
[DELTA][T.sub.0] = air temperature difference of inlet air and room air, K;
[U.sub.0] = inlet air velocity, m/s; and
[D.sub.0] = inlet width, m.
Randal and Battams (1979) found that a corrected Archimedes number (Arc) of inlets can predict airflow patterns of buildings under non-isothermal ventilation conditions. Zhang et al. (1992) intensively studied non-isothermal ventilation with slot inlet and outlet and revealed that both the critical Archimedes number (Ar) and the critical Arc for full-scale building ventilation were affected by room height. Heber and Boon (1993) studied air velocity characteristics in a full-scale simulation livestock building with non-isothermal jet ventilation jet ventilation Thoracic surgery A technique used during tracheal reconstructive surgery, in which a catheter is passed through the endotracheal tube into the distal main stem bronchus; a small tidal volume is delivered through the catheter at a high–60-150 and a high ventilation rate by using three-dimensional ultrasonic ultrasonic /ul·tra·son·ic/ (-son´ik) beyond the upper limit of perception by the human ear; relating to sound waves having a frequency of more than 20,000 Hz.
1. anemometry an·e·mom·e·try
Measurement of wind force and velocity.
ane·mo·met . Wang and Ogilvie (1996) further studied non-isothermal ventilation and developed critical wall jet Archimedes numbers (Arm), which directly reflect the balance of initial force and thermal buoyancy force for full rotating airflow patterns. However, in previous research, non-isothermal ventilation was simulated merely by adding a heat load onto the floor while keeping a normal inlet temperature. The temperature differences were 7[degrees]C-15[degrees]C (45[degrees]F-59[degrees]F). Therefore, typical winter ventilation of animal facilities has not been fully studied. Zhang and Strom (1999) developed jet drop models for non-isothermal free jets without detailed airflow measurement.
Study of non-isothermal ventilation was limited because of the complexity of the problem and the lack of proper measurement technologies. Most research used a hot-wire anemometer hot-wire anemometer
See under anemometer. to measure airflow. Traditional airflow measurement technology, thermal based anemometers, had inherent difficulty in measuring low-speed and non-isothermal airflow. High temperature sensing heads of thermal anemometers cause significant amounts of free convection and need accurate temperature compensation. For the non-isothermal indoor airflow case studies, both low-speed airflow and temperature fluctuation Fluctuation
A price or interest rate change. in the flow field causes measurement difficulties. Zhang et al. (1992) concluded a 25% uncertainty for air velocity measurement using a hot-wire anemometer. Furthermore, thermal anemometers can only measure limited locations with no direct airflow direction measurement.
Particle tracking velocimetry (PTV) technologies use particle streak tracking to measure air velocities of an entire flow field simultaneously. This technology is not limited by low-speed airflow and is not significantly affected by the air temperature. Airflow characteristics of non-isothermal ventilation can be measured more accurately using PTV techniques.
Therefore, the objectives of this study were
* to quantify airflow patterns and air velocity distribution in animal buildings under non-isothermal ventilation conditions using PTV technologies for evaluation of numerical models,
* to characterize airflow of non-isothermal ventilation under typical mild weather and winter weather conditions, and
* to analyze strategies for improvement of airflow distribution under winter ventilation conditions.
EXPERIMENTAL DESIGN AND MEASUREMENT
A room ventilation simulator (1) Software that enables the execution of an application written for a different computer environment. Same as emulator.
(2) Software that models the interactions of hypothetical or real-world objects or business processes. (RVS RVS Reverse
RvS Raven Shield (game)
RVS Roestvrij Staal
RVS Relative Value Scale
RVS Remote Video Surveillance
RVS Raytheon Vision Systems
RVS Relative Value Schedule
RVS Real Video Stream
RVS Regular Valve, Steam ) (Wu et al. 1990) was used to simulate the ambient Surrounding. For example, ambient temperature and humidity are atmospheric conditions that exist at the moment. See ambient lighting. environmental conditions. The RVS consists of a 9.1 x 12.2 x 3.6 m (30 x 40 x 12 ft) outer room, which can simulate weather conditions from -25[degrees]C (-13[degrees]F) to 40[degrees]C (104[degrees]F) any time during the year. Humidity in the outer room can be controlled by a humidifier humidifier,
n a device for adding moisture to dry air inside the home to help counteract the reduction in saliva that often occurs as a result of hyposalivation, radiation therapy, or other treatments that cause xerostomia. and dehumidifier Dehumidifier
Equipment designed to reduce the amount of water vapor in the atmosphere. There are three methods by which water vapor may be removed: (1) the use of sorbent materials, (2) cooling to the required dew point, and (3) compression with aftercooling. within a range of 20% to 90%. A full-scale, adjustable testing room having dimensions of 5.5 x 3.7 x 2.4 m (18 x 12 x 8 ft) and equipped with two ventilation plenums with dimensions of 1.1 x 3.7 x 2.4 m (3.6 x 12 x 8 ft) and 0.7 x 3.7 x 2.4 m (2.3 x 12 x 8 ft), respectively, was constructed within the RVS. This served to simulate typical mild weather and winter non-isothermal ventilation under two typical ventilation schemes, crossflow Cross´flow`
v. i. 1. To flow across, or in a contrary direction. and return flow ventilation (Figure 1). Air inlet and outlet were simulated on two sidewalls. In this study, air inlet refers to room air diffusers where fresh air enters the room and air outlet refers to room exhaust where mixed air was exhausted from the room. One long side wall of the test room is made of glass to permit convenient optical access. The other two side walls contain two glass slits to transmit light. The other walls, floor, and ceiling surfaces are painted with black and nonreflective paint to form a good optical background. The configuration and top view of the testing room was presented in Zhao et al. (1999).
[FIGURE 1 OMITTED]
Non-Isothermal Ventilation Simulation
Ventilation system A (Figure 1a) was constructed to simulate cross-flow ventilation of a typical swine swine, name for any of the cloven-hoofed mammals of the family Suidae, native to the Old World. A swine has a rather long, mobile snout, a heavy, relatively short-legged body, a thick, bristly hide, and a small tail. building. The air inlet was 2 in. (50 mm) wide and the air outlet was 8 in. (200 mm) wide. Non-isothermal airflow in mild weather was simulated with System A. This simulation was identical to the non-isothermal ventilation simulation of Zhang et al. (1992) under which detailed airflow patterns, air velocity distribution, and turbulence turbulence, state of violent or agitated behavior in a fluid. Turbulent behavior is characteristic of systems of large numbers of particles, and its unpredictability and randomness has long thwarted attempts to fully understand it, even with such powerful tools as intensity distribution were measured using a hot-wire anemometer. The test case was to verify the capability of the PTV measurement technology to study nonisothermal ventilation. The study results can be closely compared with the results of Zhang et al. (1992).
Typical swine grower-finisher buildings have air inlets on top of the two side walls and air outlets through the manure manure, term used in the United States to refer to excreta of animals, with or without added bedding; also called barnyard manure. In other countries the term often refers to any material used to fertilize the soil. pits. Two air jets meet in the center of the room and turn down toward the floor. Based on the assumption that the typical room layouts are symmetric No difference in opposing modes. It typically refers to speed. For example, in symmetric operations, it takes the same time to compress and encrypt data as it does to decompress and decrypt it. Contrast with asymmetric.
(mathematics) symmetric - 1. , System B (Figure 1b) simulated one-half of a typical ventilation setting for swine grower-finisher buildings. It represents return-flow ventilation. A 5 in. (130 mm) wide adjustable slot air inlet adjusted by 8 in. (200 mm) wide baffles was configured con·fig·ure
tr.v. con·fig·ured, con·fig·ur·ing, con·fig·ures
To design, arrange, set up, or shape with a view to specific applications or uses: on the top of the wall. A linear air outlet with a width of 8 in. (200 mm) was configured at the bottom of the wall. Non-isothermal ventilation in winter weather was simulated with System B.
The test plan is summarized in Table 1. With System A, Test 1 and Test 2 simulated mild weather ventilation conditions with a small temperature difference of 8[degrees]C (46[degrees]F) between inlet air and indoor air and its relevant isothermal ventilation condition, respectively. For mild weather ventilation conditions, the inlet temperature was controlled at 24[degrees]C (75[degrees]F). The air within the room was heated by a floor panel heating system and was controlled at 32[degrees]C (90[degrees]F). Air exchange rates for both cases were 19.5 ach (air changes per hour).
With System B, Test 3 and Test 4 simulated cold winter ventilation conditions with a temperature difference of 26[degrees]C (47[degrees]F) and its relevant isothermal ventilation condition, respectively. For winter ventilation conditions, the inlet temperature and indoor air temperature were controlled to remain at -2[degrees]C (28[degrees]F) and 24[degrees]C (75[degrees]F). Air exchange rates simulate typical low winter ventilation rates (5-10 ach) and were controlled at 8.6 ach. Test 5 is a purely experimental case to study ventilation strategies that may help to achieve better mixing airflow patterns for the improvement of winter ventilation.
Indoor Air Measurement System
A two-dimensional PTV system was used to measure airflow patterns and air velocity distribution. The PTV measurement system consists of a test room, an illumination system, a particle seeding system, an image acquisition system, an image processing image processing
Set of computational techniques for analyzing, enhancing, compressing, and reconstructing images. Its main components are importing, in which an image is captured through scanning or digital photography; analysis and manipulation of the image, accomplished and interpolating system, and a data analysis system. Helium-filled soap bubbles soap bubble An adjective referring to a dilated, smooth-contoured cyst-like or ballooned, occasionally loculated space(s). See Physaliferous Bone radiology An expansile, often eccentric, vaguely trabeculated space with a thin, sclerotic, sharply defined margin, with neutral buoyancy Neutral buoyancy is a condition in which a physical body's mass equals the mass it displaces in a surrounding medium. This negates the effect of gravity that would otherwise cause the object to . An object that has neutral buoyancy will neither sink nor rise. in the air were seeded into the ventilation plenum In a building, the space between the real ceiling and the dropped ceiling, which is often used as an air duct for heating and air conditioning. It is also filled with electrical, telephone and network wires. See plenum cable. of the test room and then allowed to enter the test room with the inlet airflow. As inlet air jets traveled through the test room, bubbles filled the airspace of the test room. One center section of the room was illuminated il·lu·mi·nate
v. il·lu·mi·nat·ed, il·lu·mi·nat·ing, il·lu·mi·nates
1. To provide or brighten with light.
2. To decorate or hang with lights.
3. with a light sheet. After 5 to 10 minutes of flow seeding, the bubble distribution reached its steady state. Tracks of traveling bubbles were then recorded by the image acquisition system. Proper exposure time was used to capture bubble pictures as streaks. An image shifting technology was used to resolve any ambiguity in the direction of the bubbles' travel. Streak images of bubbles were then processed by the image processing system to extract coordination and magnitude of the streaks. Air velocity vector maps Vector Map (VMAP), AKA Vector Smart Map, is a vector-based collection of GIS data covering the earth at various detail levels. and velocity distribution contour contour or contour line, line on a topographic map connecting points of equal elevation above or below mean sea level. It is thus a kind of isopleth, or line of equal quantity. maps were developed to describe airflow patterns and air velocity distribution in the test room. Regional air velocity can be extracted to examine airflow characteristics of certain zones, such as human and animal occupied zones. The PTV methodology and detailed measurement procedures were discussed in Zhao et al. (1999, 2001).
Temperature Distribution Measurement System
Twenty-nine T-type thermocouples and a data acquisition system were used for temperature measurement. The data acquisition has 30 analog inputs Refers to hardware interfaces that accept non-digital signals. For decades, all the plugs and sockets on traditional audio and video equipment connected analog lines (see illustration below). , and the input voltage ranged from 0 to 10 V. The measurement channels can be programmed to be scanned in any order. Acquisition parameters include sampling rate, acquisition period, trigger time, and data destination.
Uniform measurement grids were used to measure temperature distribution in the airflow field of the entire room. Since the temperature gradients temperature gradient
The rate of change of temperature with displacement in a given direction from a given reference point.
temperature gradient are not as large as the velocity gradient gradient
In mathematics, a differential operator applied to a three-dimensional vector-valued function to yield a vector whose three components are the partial derivatives of the function with respect to its three variables. The symbol for gradient is ∇. , air temperatures at 29 points of the flow field (Figure 2), including inlet, outlet, and two floor surface points, were measured.
Airflow Rate Measurement and Control System
The air delivery and measurement system consists of a measurement chamber and centrifugal centrifugal /cen·trif·u·gal/ (sen-trif´ah-gal) efferent (1).
1. Moving or directed away from a center or axis.
2. exhaust fan. The air delivery capability ranges from 0.05 to 1.4 [m.sup.3]/s (106-2966 cfm), which can meet the designed ventilation requirement of 0.118 to 0.897 [m.sup.3]/s (250 to 1901 cfm), corresponding to 8.6 and 66 ach. The centrifugal fan A centrifugal fan (also squirrel-cage fan, as it looks like a hamster wheel) is a mechanical device for moving air or other gases. It has a fan wheel composed of a number of fan blades mounted around a hub. was controlled by a variable-frequency controller. The air exchange rates were determined by measuring the drop in static pressure across sharp orifices on a perforated per·fo·ra·ted
Pierced with one or more holes. plate. The perforated plates were calibrated cal·i·brate
tr.v. cal·i·brat·ed, cal·i·brat·ing, cal·i·brates
1. To check, adjust, or determine by comparison with a standard (the graduations of a quantitative measuring instrument): with a fan test chamber that is designed according to according to
1. As stated or indicated by; on the authority of: according to historians.
2. In keeping with: according to instructions.
3. ASHRAE ASHRAE American Society of Heating, Refrigerating & Air Conditioning Engineers Standard 51-1985 (ASHRAE 1985) and maintained to the current ASHRAE Standard 51-1999 (ASHRAE 1999). The entire air delivery system was also calibrated with the fan test chamber. The test chamber was described by Hughes et al. (1988).
Cooling System cooling system: see air conditioning; internal-combustion engine; refrigeration.
Apparatus used to keep the temperature of a structure or device from exceeding limits imposed by needs of safety and efficiency. and Floor Heating
In non-isothermal ventilation conditions, the internal heat was provided with 24 0.6 m x 1.2 m (2 ft x 4 ft) heating panels uniformly arranged on the floor of the test room. Each heating panel consisted of an electrical heating element Noun 1. heating element - the component of a heater or range that transforms fuel or electricity into heat
bar - a heating element in an electric fire; "an electric fire with three bars" sandwiched between two pieces of 0.25 in. (6 mm) thick plywood plywood, manufactured board composed of an odd number of thin sheets of wood glued together under pressure with grains of the successive layers at right angles. Laminated wood differs from plywood in that the grains of its sheets are parallel. and then covered with 24-gauge galvanized gal·va·nize
tr.v. gal·va·nized, gal·va·niz·ing, gal·va·niz·es
1. To stimulate or shock with an electric current.
2. steel to improve the temperature uniformity on the surface of the heating panel. Each heating panel can provide 150 W with 240 V AC power supply. The temperature on the surface of the heating panel is 106.4 [+ or -] 1.5[degrees]F (41.3 [+ or -] 1[degrees]C). The 24 panels were switched on and off using a thermostat thermostat, automatic device that regulates temperature in an enclosed area by controlling heating or refrigerating systems. It is commonly connected to one of these systems, turning it on or off in order to maintain a predetermined temperature. set to maintain essentially constant room air temperature. The heating panels have the capacity to raise the room air temperature to 32[degrees]C (90[degrees]F) when the air exchange rate is 19.5 ach and the inlet air temperature is 24[degrees]C (75[degrees]F).
The outer room heating, ventilating ventilating
Natural or mechanically induced movement of fresh air into or through an enclosed space. The hazards of poor ventilation were not clearly understood until the early 20th century. Expired air may be laden with odors, heat, gases, or dust. , and air-conditioning system, a climate simulator, provided cold air. The climate simulator consists of an air-cooled condenser condenser
Device for reducing a gas or vapour to a liquid. Condensers are used in power plants to condense exhaust steam from turbines and in refrigeration plants to condense refrigerant vapours, such as ammonia and Freons. , compressors, evaporator evaporator
Industrial apparatus for converting liquid into gas or vapour. The single-effect evaporator consists of a container or surface and a heating unit; the multiple-effect evaporator uses the vapour produced in one unit to heat a succeeding unit. , electric heaters, a supply fan, and a control system. The capacity of the climate simulator control system is:
* Temperature control from -25[degrees]C (-13[degrees]F) to 38[degrees]C (100[degrees]F) when ambient temperature Outside temperature at any given altitude, preferably expressed in degrees centigrade. is 35[degrees]C (95[degrees]F) and -19.5[degrees]C (-3[degrees]F), respectively.
* Humidity control Humidity control
Regulation of the degree of saturation (relative humidity) or quantity (absolute humidity) of water vapor in a mixture of air and water vapor. Humidity is commonly mistaken as a quality of air. from 20% to 90%.
[FIGURE 2 OMITTED]
The cold air was uniformly distributed in the inlet plenum of the test room by a 10 in. perforated polyethylene polyethylene (pŏl'ēĕth`əlēn), widely used plastic. It is a polymer of ethylene, CH2=CH2, having the formula (-CH2-CH2-)n tube. Cold air was led down to the floor from air discharge holes of the distribution tube, which was hung near the ceiling of the inlet plenum. Thus, the cold air was well mixed in the plenum before being introduced into the test room.
RESULTS AND DISCUSSIONS
Mild Weather Non-Isothermal Ventilation
Temperature Distribution. Figure 3 shows spatial temperature distribution of Test 1: non-isothermal ventilation conditions with a small temperature difference. Temperature distribution is determined by air jets and room air distribution. The air entered the room at a temperature of 24[degrees]C (75[degrees]F). As the air jet traveled, adjacent warmer room air heated the cold air jet by mixing and thermal diffusion
Airflow Patterns. Figures 4 and 5 show the airflow patterns of Test 1 and Test 2, respectively. A flow pattern common to both was that the air jet attached to the ceiling after entering the room, due to Coanda effect Coanda effect or wall-attachment effect, the tendency of a moving fluid, either liquid or gas, to attach itself to a surface and flow along it. , which is the phenomenon that when an air jet enters a room through inlets close to the ceiling, then the air jet will bend toward the ceiling and finally attach to the ceiling due to the pressure difference between the two sides of the air jet caused by air entrainment Air entrainment is the intentional creation of tiny air bubbles in concrete. The bubbles are introduced into the concrete by the addition to the mix of an air entraining agent, a surfactant (surface-active substance, a type of chemical that includes detergents). and limited space between the air jet and the ceiling. The air jet traveled along the ceiling and then either reached the opposite wall (Test 2, isothermal ventilation) or separated from the ceiling and dropped toward the floor (Test 1, non-isothermal ventilation). Because of air jet separation in Test 1, a clockwise clock·wise
adv. & adj. Abbr. cw.
In the same direction as the rotating hands of a clock.
in the direction in which the hands of a clock rotate rotating airflow pattern formed near the inlet side of the room. Another weaker and smaller eddy formed near the outlet side of the room. The airflow on the right top corner of the room was much more turbulent and not stable. Sometimes airflow moved toward the outlet, and sometimes it moved toward the inlet. This may be because of variation in jet momentum and internal heating. A primary recirculation zone occupied approximately two-thirds of the room area and the temperature distribution in that zone was relatively constant and similar to the room temperature, as desired. Comparing these results with the flow patterns of Test 2, the correlated isothermal case, it is clear that even this relatively small temperature difference caused the air jet to fall sooner (approximately at three-fifths width of the test room). Under non-isothermal ventilation conditions, the major forces exerted on the air jet are inertial forces, thermal buoyancy forces, and friction force generated by surfaces. Thermal buoyancy force caused the air jet to fall down early (Zhang et al. 1992).
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
The general structure of these airflow patterns agrees with those of Zhang et al. (1992), which had exactly the same experimental settings but used a hot-wire anemometer for air velocity and a smoke gun for airflow pattern. One exception is that the PTV airflow patterns have more detailed structure and definitive airflow direction data. Another exception is that Zhang et al. (1992) showed that a reverse airflow pattern formed below the air jet under the isothermal ventilation, whereas the PTV-measured airflow pattern (Figure 6) showed not reverse airflow but a stagnant stagnant /stag·nant/ (stag´nant)
1. motionless; not flowing or moving.
2. inactive; not developing or progressing. zone. This discrepancy may be caused by limitations of the smoke gun flow observation in low airspeed airspeed
the speed of an aircraft relative to the air in which it moves
Noun 1. airspeed - the speed of an aircraft relative to the air in which it is flying
speed, velocity - distance travelled per unit time zones and the high turbulence level of the low airspeed zone. In summary, these results confirmed that the room airflow PTV system overcomes difficulties of traditional airflow measurement and visualization Using the computer to convert data into picture form. The most basic visualization is that of turning transaction data and summary information into charts and graphs. Visualization is used in computer-aided design (CAD) to render screen images into 3D models that can be viewed from all , yielding clearer and more quantitative airflow pattern results. It can effectively be used to study airflow of non-isothermal ventilation.
[FIGURE 6 OMITTED]
Air Velocity Distribution. Figure 6 shows the air velocity distribution of Tests 1 and 2 over the center section of the test room. The non-isothermal ventilation case with a small temperature difference had the same range of air velocities in the air jet and in the animal occupied zone as its isothermal counterpart. However, because of the temperature difference, the air jet was heavier than the room air. The air jet did not travel the whole room width and dropped early. According to ASHRAE (2005), air velocity greater than 25-30 fpm (0.1-0.15 m/s) with 60% turbulence intensity will cause cold draft conditions for 15% of the population. Indoor airflow of large animal buildings is fully turbulent, with turbulence intensity of up to 97% (Zhang et al. 1992). Therefore, when air velocity in the human breathing zone increases to 0.3 m/s (59 fpm) due to the air jet drop, it is likely that a cold draft will form at the human breathing zone in the center of the room. This also can be verified from temperature distribution (Figure 3). However, the jet drop did not significantly affect air velocities near the floor, which is normally recognized as the animal occupied zone in animal buildings.
Typical Winter Ventilation Conditions
Figure 7 shows the temperature spatial distribution of Test 3, which represents typical winter ventilation conditions. The inlet air temperature was only -2[degrees]C (28[degrees]F) when it entered the room. The temperature distribution pattern with low air temperature near the inlet wall and floor showed that the cold air jet dropped and traveled in a counterclockwise direction. The air temperature at the center space of the room rose quickly due to turbulent mixing and thermal diffusion between cold jet air, the heated floor, and warm indoor air. There is a high-temperature zone in the room near the air inlet.
[FIGURE 7 OMITTED]
[FIGURE 8 OMITTED]
Airflow Patterns. Figure 8 shows the airflow patterns of Test 3, a typical winter non-isothermal ventilation test case. Figure 9 shows the airflow pattern of Test 4, which is the correlated isothermal ventilation case of Test 3. When a heated hallway is used in a swine building to preheat pre·heat
tr.v. pre·heat·ed, pre·heat·ing, pre·heats
To heat (an oven, for example) beforehand.
pre·heater n. the inlet air, the winter ventilation case will likely be as in Test 4, an isothermal ventilation case with a low air ventilation rate.
Under typical non-isothermal ventilation conditions, the air jet dropped immediately after it entered the test room, and this resulted in a strong counterclockwise rotating airflow pattern. This phenomenon was detected by several previous researchers using flag airflow indictor INDICTOR. He who causes another to be indicted. The latter is sometimes called the indictee. (Wang and Ogilvie 1996), smoke gun (Zhang et al. 1992), and temperature sensors (Zhang and Strom 1999). The PTV-measured airflow pattern not only clearly showed the dropping jet but also revealed the resulting airflow patterns in the animal occupied zone and human breathing zone and the overall airflow pattern of the whole room airspace. The cold air jet dropped immediately after it entered the room because a cold air jet is heavier than room air, and then negative buoyancy forces caused the air jet to fall. The Archimedes number was 0.292, which is much larger than the Critical Archimedes number of 0.023 for the full-scale test room by Zhang et al. (1992).
[FIGURE 9 OMITTED]
The air jet directly traveled down to floor level, with little entrainment entrainment /en·train·ment/ (en-tran´ment)
1. a technique for identifying the slowest pacing necessary to terminate an arrhythmia, particularly atrial flutter.
2. or mixing with warm indoor air. A big vortex was formed at the other side of the test room. This location is the center of typical rooms. Likely in this ventilation mode, the contaminants will not be effectively removed. The floor-level air velocity was much higher in the non-isothermal ventilation conditions than in the isothermal ventilation conditions and will likely cause cold drafts. The overall airflow was not stable and fluctuated over a larger range. This is likely due to the temperature difference between the floor surface and room air. Thermal buoyancy due to the heat production from the floor contributes to the increase in room air turbulence (Zhang et al. 1992).
Under the same ventilation settings but with isothermal conditions, the airflow formed a desired clockwise rotating airflow pattern (Figure 9). The air jet travels along the ceiling and drops after reaching the opposite wall. The air jet entrains the room air and achieves good mixing before dropping down to the animal zone. The overall airflow pattern is much smoother than that of the non-isothermal ventilation case.
Air Velocity Distribution. Figure 10 indicates the air velocity distribution of Tests 3 and 4 over the center section of the test room. In comparison with air velocity distributions under isothermal ventilation, the floor-level air velocities increased from 0.1 to 0.2 m/s (20 to 39 fpm) due to counter rotating airflow patterns and buoyancy under this typical nonisothermal winter ventilation. Air velocities at the human breathing level also increased from 0.05 to 0.15 m/s (10 to 30 fpm). These changes from isothermal ventilation caused cold drafts in the animal occupied zones. Depending on where the human walkway walkway Rehabilitation medicine An instrument used to measure the timing of foot contact and or position of the foot on the ground is located, it will likely cause cold drafts in the human zone as well, especially when the walkway is at the inlet side. In addition, with this ventilation system, counter rotary airflow patterns will likely cause short-circuiting of air because the outlet is right underneath the air inlet on the same side wall.
Air Velocities at the Human Breathing Zone and Animal Occupied Zone. Air velocity directly affects temperature distribution, thermal comfort Human thermal comfort is the state of mind that expresses satisfaction with the surrounding environment, according to ASHRAE Standard 55. Achieving thermal comfort for most occupants of buildings or other enclosures is a goal of HVAC design engineers. , and air quality. Ultimately, the goal in studying airflow patterns of typical animal buildings is to optimize the thermal and air quality environments around animals and human workers. Regional characteristics of airflow, especially in the animal occupied zone and at the human breathing level, are most critical.
The ASAE ASAE American Society of Association Executives
ASAE American Society of Agricultural Engineers (Society for Engineering in Agricultural, Food, and Biological Systems)
ASAE Alkali-Sulfite-Anthraquinone-Ethanol (2001) Standard D321.2DEC94 provides typical dimensions for various animal species. For pigs, 0.7 m is defined as the highest point of a standing pig. Many researchers used 0.0 to 0.6 m (0 to 2 ft) as the animal occupied zone in swine buildings. Based on the ASAE standard and other research literature, the animal occupied zone was defined as 0.0 to 0.6 m (0 to 2 ft) from the floor and the human breathing level 1.4 to 1.7 m (4.6 to 5.6 ft) above the floor in this study.
Figure 11a shows a comparison of air velocities at the human breathing level under winter non-isothermal and isothermal conditions. It is clear that under non-isothermal ventilation conditions, due to cold drafts and floor heat, the air velocities at the human breathing level were much higher than for the isothermal ventilation cases. In winter, this velocity increase is not desirable. Because of counter primary rotating airflow patterns in the non-isothermal ventilation cases, the human breathing level has a reverse airflow. The reverse airflow resulted in air entrainment and higher air velocities at the human breathing level as it traveled toward the inlet wall. The air velocity fluctuated due to turbulence activities. Air velocities dropped dramatically at one place near the opposite wall because of the large vortex. Under the correlated isothermal ventilation case, because of primary rotating airflow patterns, air jets attached to the ceiling and gradually entrained room air. Therefore, air velocities at the human breathing level increased as the air jet traveled from the air inlet along the width of the room.
[FIGURE 10 OMITTED]
Figure 11b shows a comparison of air velocities in the animal occupied zone under winter isothermal ventilation and the correlated isothermal ventilation. Large differences in air temperature resulted in higher air velocities and large velocity fluctuations in the animal occupied zone. Because of a counterclockwise rotary airflow pattern, air velocities at the animal occupied zone decreased as the airstream traveled from the inlet wall to the opposite wall. In the isothermal ventilation case, airflow in the animal occupied zone was dominated by reverse airflow of the primary rotating airflow patterns. Because of friction of the floor and viscosity of airflow, the air velocity decreased as the reverse airflow progressed.
Evaluation of Strategies to Improve Winter Ventilation
Room airflow patterns are mainly affected by the air jets present in the mixing ventilation. Under non-isothermal ventilation conditions, air jet separation behavior is determined by Archimedes number. Critical Archimedes number (Ar) is a limit Ar value at which the diffuser air jet drops immediately after entering the room. An Ar less than the critical Ar is needed to create full rotary airflow in a ventilation air space. By analysis of the Archimedes number definition (Equation 1), we can learn that there are three ways to decrease Archimedes number: (1) decreasing temperature difference, (2) decreasing inlet opening to increase air velocity, and (3) increasing inlet air velocity by increasing airflow rate. In winter, the minimum ventilation rate is determined by maximum conservation of heat energy and optimum control of moisture and air quality.
The temperature difference is caused by ambient weather Ambient Weather, founded in 1999 by Ed Edelman, is an Arizona based weather station distributor and software manufacturer that specializes in customized solutions and products for the home and office, industry, schools, resorts, government and the media. conditions and indoor thermal comfort requirements. Decreasing temperature difference is an effective strategy to solve winter ventilation difficulties. Warming up the inlet air by means of a heated hallway and passing the ambient air through an attic are practical ways to increase inlet air temperature, thus decreasing the difference in air temperature. Air-to-air heat exchangers heat exchanger
Any of several devices that transfer heat from a hot to a cold fluid. In many engineering applications, one fluid needs to be heated and another cooled, a requirement economically accomplished by a heat exchanger. or geothermal heat pumps A geothermal heat pump system is a heating and/or an air conditioning system that uses the Earth's ability to store heat in the ground and water thermal masses. This system will take advantage of a land mass as a heat exchanger to either heat or cool a building structure. may also be feasible options with today's high Today's High
The intra-day high trading price.
In other words, this is the highest price that a stock traded at during the course of the day. More often than not this is higher than the closing price.
See also: Today's Low energy cost environment.
To evaluate the strategy for improving airflow patterns under winter ventilation conditions by reducing the inlet opening and simultaneously increasing the inlet air velocity, Test 5 was designed. Test 5 ventilation settings are similar to those of Test 3, except that the inlet opening decreased to a minimum limit of 6 mm (0.24 in.) so that the inlet air velocity was increased to 3.3 m/s (650 fpm), similar to that of a typical winter inlet opening of a swine building.
Figure 12 shows the airflow patterns of Test 5. Contrasting with the airflow patterns of Test 3 (Figure 8), it was found that the air jet was lifted up to the ceiling and traveled about 1.5 m (5 ft) from the inlet wall before it began to drop. Due to insufficient jet momentum and temperature difference with the resulting buoyancy effects, however, the inlet air jet still separated shortly after it was discharged into the test room and the air jet fell into the animal occupied zone. The draft was strong in the room. Two major rotating zones formed: one a clockwise rotating flow and the other a counterclockwise rotating flow. In the clockwise rotating zone, there were a few weak vortexes showing that the airflow was more turbulent. The overall floor-level velocity was also larger than that which occurred under isothermal ventilation conditions. A clear vortex formed on the other side of the test room.
[FIGURE 11 OMITTED]
By analyzing the winter non-isothermal ventilation cases, one can appreciate that it is not easy to design and manage winter ventilation systems for animal facilities. From Test 5, which was designed to improve airflow patterns in winter ventilation conditions, it was found that there is a limit to increasing inlet air velocity by decreasing the inlet openings. Inlet openings of 6 mm (0.24 in.), the minimum in realistic buildings, resulted in a maximum inlet air velocity of 3.3 m/s (650 fpm) with a typical 8.6 ach air exchange rate. The 3.3 m/s (650 fpm) inlet air velocity is not large enough to form a stable airflow pattern. An inlet air velocity of 1.6 m/s (315 fpm) was reported in Zhang et al. (1992) as the limit in forming stable airflow patterns under non-isothermal ventilation conditions with an 8[degrees]C (15[degrees]F) temperature difference. Therefore, inlet air velocities forming stable airflow patterns depend on the temperature difference. Because of the minimum inlet opening limit, this strategy did not resolve the winter ventilation challenge.
Another way would be to increase inlet air velocity by introducing recirculation air into the inlet airflow. This would increase airflow rate through the inlet and still keep the fresh airflow rate low, conserving energy.
The distance from jet separation point to the air inlet is considered the jet separation distance. The jet separation is defined as where the jet centerline cen·ter·line
1. A line that bisects something into equal parts.
2. A painted line running along the center of a road or highway that divides it into two sections for traffic moving in opposite directions, or, in the case of starts to curve downward. Li et al. (1995) developed the following equation to predict the air jet separation distance:
[X.sub.s] = C[square root of ([A.sub.0]/[A.sub.r])] (2)
[FIGURE 12 OMITTED]
[X.sub.S] = jet separation distance,
C = a constant,
[A.sub.r] = Archimedes number, and
[A.sub.0] = effective area of inlet, [m.sup.2].
In Test 5, [X.sub.s] is approximately 1.5 m (5 ft). If we consider adding a recirculation air volume of Q = 8.6 ach, then [X.sub.snew] = 2.82 [X.sub.s], which is approximately 4.24 m (14 ft). If the recirculation air volume is increased to one and a half times the winter ventilation rate, which is about 12.9 ach, then [X.sub.snew] = 3.86 [X.sub.s], which is approximately 5.78 m (19 ft) and larger than the room length. This means that by adding 1.5 times the recirculation airflow to the winter inlet airflow, the jet momentum will be enlarged and a stable and fully rotary airflow pattern will form. Winter ventilation problems such as cold drafts at the occupied zones will likely be resolved.
Particle tracking velocimetry could be an effective tool to measure non-isothermal indoor airflow. It can clearly visualize airflow patterns and quantitatively determine air velocity distribution in a full-scale room and low-velocity regions, which are needed for evaluation or development of numerical simulation models.
Non-isothermal ventilation conditions, especially with large temperature differences between the supply air and room air, present difficulty in maintaining a primary rotary (thus mixing) airflow pattern. It was found that even with a relatively small temperature difference (8[degrees]C [15[degrees]F]), the air jet will separate from the ceiling earlier than an isothermal jet will. Early dropping of inlet jet resulted in reversed rotary airflow pattern or several subrotating zones. Airflow patterns with subrotating zones are not effective for contaminant contaminant /con·tam·i·nant/ (kon-tam´in-int) something that causes contamination.
something that causes contamination. removal. Early jet separation also could cause short-circulation of the fresh air, which violates the ventilation purposes. It also causes cold drafts that result in animal discomfort and may hurt their performance.
Non-isothermal ventilation conditions generally result in higher air velocities with larger fluctuations in the animal occupied zone than those of isothermal ventilation at the same rate. The air velocity increment To add a number to another number. Incrementing a counter means adding 1 to its current value. is well correlated to the temperature difference between inlet air and room air.
There are ways to mitigate the above problems of the nonisothermal ventilation conditions: (1) decreasing the temperature difference, (2) increasing inlet air velocity by maintaining proper inlet opening and pressure, and (3) adding an air recirculation device to increase inlet air jet momentum. If the temperature difference is small, increasing inlet air velocity is an effective and simple way to achieve better mixing ventilation. If the temperature difference is large in winter, increasing inlet air velocity only may not be sufficient and an additional air recirculation device may be needed to increase inlet air jet momentum and maintain the primary rotating airflow patterns. Preheating of the inlet airflow is also an effective strategy to achieve a better mixing ventilation mode.
This work is supported by the Illinois Council for Food and Agricultural Research via an Internal Competitive Grant IDA Ida (ē`dä), city (1990 pop. 91,859), Nagano prefecture, central Honshu, Japan, on the Tenryu River. It is an agricultural market and railway junction. CF 98I-40-5.
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Lingying Zhao, PhD
Yuanhui Zhang, PhD, PE
Xinlei Wang, PhD
Gerald L. Riskowski, PhD, PE
Lingying Zhao is an assistant professor in the Department of Food, Agricultural and Biological Engineering, Ohio State University Ohio State University, main campus at Columbus; land-grant and state supported; coeducational; chartered 1870, opened 1873 as Ohio Agricultural and Mechanical College, renamed 1878. There are also campuses at Lima, Mansfield, Marion, and Newark. , Columbus. Yuanhui Zhang is a professor and Xinlei Wang is an assistant professor in the Department of Agricultural and Biological Engineering, University of Illinois at Urbana-Champaign Early years: 1867-1880
The Morrill Act of 1862 granted each state in the United States a portion of land on which to establish a major public state university, one which could teach agriculture, mechanic arts, and military training, "without excluding other scientific . Gerald L. Riskowski is a professor in the Department of Biological and Agricultural Engineering, Texas A & M University, College Station, TX.
Table 1. Summary of the Test Cases Test Ventilation Inlet Width Inlet Temperature Case System mm in. [degrees]C [degrees]F Test 1 A 50 2 24 75 Test 2 A 50 2 24 75 Test 3 B 41 1.6 -2 28 Test 4 B 41 1.6 24 75 Test 5 B 6 0.24 -2 28 Test Ventilation Outlet Temperature [DELTA]T Case System [degrees]C [degrees]F [degrees]C [degrees]F Test 1 A 32 90 8 15 Test 2 A 24 75 0 0 Test 3 B 24 75 26 47 Test 4 B 24 75 0 0 Test 5 B 24 75 26 47 Test Ventilation Air Exchange Rate Inlet Velocity Case System ach* m/s fpm Test 1 A 19.5 1.78 350 Test 2 A 19.5 1.78 350 Test 3 B 8.6 0.74 146 Test 4 B 8.6 0.74 146 Test 5 B 8.6 3.30 650 * ach = air changes per hour