Louver Array Research Articles

Orthogonal Pattern Louver Mixer for Two-Dimensional Air Mixing in HVAC Applications: Performance and Design Optimization

This article focuses on the investigation of the mixing and hydraulic performance of an orthogonal pattern louver mixer in a square duct. The investigation includes various configurations, including the following parameters: mixer spacing and louver pattern orientation for a pair of mixers, as well as louver angle and louver array size were for both a single and a pair of mixers. Additionally, operational parameters such as mixing length, total flow rate, and flow rate ratio between cold and warm air were considered. Experimental testing was conducted to assess the performance of the orthogonal pattern louver mixer across various parameter combinations. Additionally, a numerical model was developed to enhance understanding of the mixing pattern and flow behavior. Numerical results highlighted that the two-dimensional mixing flow, characterized by multiple vortices generated through the unique louver design, significantly contributed to rapid and robust mixing, effectively reducing maldistribution within a short mixing length. The performance of the orthogonal pattern louver mixer from the experimental results was compared to other mixer types, such as orifice type mixers and ASHRAE Standard 41.2-based “cheese grater” baseline louver mixers. The orthogonal pattern louver mixer was found to be outstanding, with a maximum mixing effectiveness of 88 % for a mixing length of 2.0 Dh. Although it caused a higher static pressure drop than the baseline louver mixers, it was still acceptable for industrial use. The findings indicate that the orthogonal pattern louver mixer is a promising option due to its simple design, easy fabrication, high mixing performance with low pressure drop, and two-dimensional mixing. The orthogonal pattern louver mixer was also less sensitive to flow rate and velocity maldistribution than orifice-type mixers. This article provides useful guidelines for designing and selecting the best mixer type for HVAC applications, considering factors such as cost-effectiveness, mixing performance, pressure drop, and sensitivity to flow rate and velocity maldistribution. In addition, the article offers valuable insights into the performance characteristics of single or dual-use orthogonal pattern louver mixers, as well as the importance of carefully selecting the louver angle and array size when configuring the mixer.

Assessment of fractional collection efficiency in louvered inertial particle classifiers

This study reexamines the literature data on performance of louvered inertial classifiers and offers a preliminary correlation of particle fractional collection efficiency, η. These classifiers incorporate a converging array of blades to intercept the inlet particle-laden gas and separate it into major and minor flows. A basic design concept in such classifiers is that particles, with larger Stokes number St, follow the minor flow for collection. The correlation is for rectilinear classifiers, with flat plate louvers, in turbulent flow where pressure loss is independent of Reynolds number. The fractional collection efficiency near 0.5, with 0.2<(St)1/2<1.0, increases with log(St1/2). The respective influences of orientation, chord and spacing of the louvers and the converging profile of the louver array are examined.

Modified Water Diversion Structures Can Behaviorally Deter Juvenile Chinook Salmon from Entrainment

AbstractJuvenile Chinook Salmon Oncorhynchus tshawytscha traveling in river systems can become entrained by unscreened water diversions when they encounter inflow velocities that exceed their avoidance (i.e., swimming) ability. We tested the efficiency of three devices for deterring fish entrainment; the devices reduced the diversion's maximum inflow velocity by dispersing the inflow across a greater area so as to reduce fish entrainment without causing a decrease in water diversion rates. Tests were performed in a river simulation flume at a 0.15‐m/s sweeping velocity in clear water conditions during the daytime and nighttime as well as in turbid water (daytime) conditions. Water was diverted at a rate of 0.57 m3/s through a 0.46‐m‐diameter pipe. The tested devices included (1) a widened box inlet (1.7 m long × 0.76 m wide × 0.76 m deep) with a trash rack mounted at its entrance (trash rack box), (2) a widened box inlet with a louver array mounted at the entrance (louver box), and (3) a 0.91‐m‐diameter cylinder perforated with 300 evenly spaced, 5‐cm‐diameter holes (perforated cylinder). During 2‐h experiments under daytime conditions, 51.5 of 80 fish (on average) were entrained into the pipe when no device was used (i.e., control), and a fish's mean risk of becoming entrained when passing the pipe once was 14%. The mean entrainment risk during a single pipe passage event was reduced to 7% in the trash rack box treatment (i.e., 50% of the control value), 0.17% in the louver box treatment, and 0.20% in the perforated cylinder treatment. In comparison with the control, the mean number of entrained fish was reduced by 50% in the trash rack box treatment, by 97% in the louver box treatment, and by 93% in the perforated cylinder treatment. These devices also reduced the number of fish that were entrained during darkness or turbid daytime conditions. Our findings suggest that behavioral deterrence devices offer effective, low‐cost alternatives to positive barrier fish screens by protecting juvenile Chinook Salmon from entrainment at water diversion pipes without reducing water pumping efficiency.

Use of telemetry and hydraulic modeling to evaluate and improve fish guidance efficiency at a louver and bypass system for downstream-migrating Atlantic salmon (Salmo salar) smolts and kelts

A fish protection system has been installed in a power canal at a hydroelectric facility on the Exploits River, Grand Falls-Windsor, Newfoundland, Canada. The river has an anadromous Atlantic salmon (Salmo salar)population in the order of 30000 returning adults. A louver and bypass were installed to protect downstream migrating smolt and kelt from entering the penstocks and turbines in the power canal at the generating facility. The efficiency and effectiveness of this protection system has been evaluated since 1997 through a combination of conventional telemetry, use of a digital spectrum processing (DSP) telemetry system with multiple antennae array, floy tagging, and velocity profiling along the louver array and throughout the canal. Initial monitoring in 1997 using conventional telemetry indicated low fish guidance efficiencies (FGEs) in the area of 25% for smolt. In 1998, a DSP telemetry system was installed along the louver array to attempt to identify problem areas where fish were passing through or under the louver. This work also recorded low smolt FGEs in 1998 (24.3%). However, the DSP system did identify sites along the louver array where fish were being lost, and hydraulic measurements suggested fish loss was related to hydraulic turbulence and irregularities in the guidance velocities. In 1999, a scale model of the power canal and bypass system was constructed at the University of Waterloo Engineering Department's Hydraulic Laboratory and a number of structural and operational changes to the system were evaluated. Based on the results of laboratory hydraulic modeling and DSP telemetry, a number of changes were made to the louver and bypass, prior to operation in 1999 and 2000. Monitoring of smolt out migration in 1999 and 2000 indicated a substantial improvement in smolt FGEs to 54.0 and 65.3%, respectively, and the DSP system identified areas where further improvements could be made. This paper demonstrates the utility of a sophisticated telemetry system in the evaluation of fish protection systems and how the technology can be applied towards the optimization of the effectiveness of fish by-passes.

Guidance of Yearling Shortnose and Pallid Sturgeon Using Vertical Bar Rack and Louver Arrays

Some populations of shortnose sturgeon Acipenser brevirostrum and pallid sturgeon Scaphirhynchus albus have been divided by hydroelectric dams, and migration downstream past the dams likely continues. No protection for downstream migrants is presently available, and the behavior of sturgeon to guidance structures has not been studied. We conducted experiments in a 5.4-m-long × 1.5-m-wide flume with a water depth of 37 cm to determine the guidance efficiency and behavior of yearling shortnose and pallid sturgeon to two guidance structures, a bar rack and a louver array. We tested one vertical bar rack configuration with slats spaced 3.9 cm apart (clear spacing). The bar rack slats were oriented directly into the approach flow, and the row of slats was oriented at a 45° angle to the flow. We tested two louver array configurations, one with slats spaced 3.9 cm apart and one with slats spaced 9.0 cm apart (clear spacing). Louver slats were oriented at a 90° angle to the flow, and the row of slats was oriented at a 20° angle to the approach flow. Mean approach velocity to both structures was 31–34 cm/s. Eighteen shortnose sturgeon tagged with passive integrated transponders were tested once in each configuration; 24–38 pallid sturgeon were tested in each configuration. Shortnose sturgeon showed some behavioral differences due to experience with the bar rack, but experience did not affect the percent guided. Both sturgeon species were guided efficiently by the louver array (96–100%) but less efficiently by the bar rack (58–80%). Shortnose sturgeon were more likely to contact the bar rack at night than during the day (P = 0.01) and at night were more likely to contact the bar rack than the louver array (P = 0.006). Bar racks guided fewer individuals at night than during the day. For pallid sturgeon, the percentages guided by day and night were 80 and 58, respectively; for shortnose sturgeon, the percentages were 80 and 67. Both species used vision to avoid structures because both increased contact with structures at night. Shortnose sturgeon were superior to pallid sturgeon at swimming off the bottom and avoiding structures.

Passage and Behavior of Adult American Shad in an Experimental Louver Bypass System

We tested 436 adult American shad Alosa sapidissima in an experimental louver bypass system, which was similar to a system operating at Holyoke Dam, Massachusetts, to determine guidance and passage efficiency and to study fish response to stimuli from physical structures, light intensity, and water velocity. Groups of 5–29 fish were exposed to combinations of two bypass exits (wide-shallow and vertical-slot sharp-crested weirs) and two louver arrays (7.6- and 15.2-cm slat spacing) oriented 20° to water flow direction. Underwater video observations showed fish responded to louvers as a physical barrier during the day, when they stayed 30–55 cm (1.3 cm/5 klx) away from and oriented parallel to louvers, and as a behavioral barrier at night, when they moved closer to louvers and oriented into the current. Both louver arrays guided fish effectively, (i.e., prevented fish from passing through the slats) 100% for narrow spacing and 97% for wide spacing. Adults avoided moving closer than 0.5 m to either exit type; instead, fish remained 0.8–1.4 bodylengths upstream, depending on light intensity (farther upstream during daytime, similar to behavior at louvers). At exits, water velocity increased from 0.4 m/s to 0.8 m/s or more in a distance of 0.9 m (rate of velocity increase, 0.44 m/s per meter). This rapid velocity increase elicited an avoidance response by fish that resulted in few fish (5%) passing. Our results provide behavioral explanations for the efficient guidance of adult American shad by louvers and for the fishes' avoidance of the exit at the Holyoke Dam. From this, we provide suggestions on how to prevent fish avoidance of exits.

Prediction of Heat Transfer and Friction for the Louver Fin Geometry

This paper is concerned with prediction of the air-side heat transfer coefficient of the louver fin geometry used in automotive radiators. An analytical model was developed to predict the heat transfer coefficient and friction factor of the louver fin geometry. The model is based on boundary layer and channel flow equations, and accounts for the “flow efficiency” in the array, as previously reported by Webb and Trauger. The model has no empirical constants. The model allows independent specifications of all of the geometric parameters of the louver fin. This includes the number of louvers over the flow depth, the louver width and length, and the louver angle. The model was validated by predicting the heat transfer coefficient and friction factor of 32 louver arrays tested by Davenport, which spanned hydraulic diameter based Reynolds numbers of 300–2800. At the highest Reynolds number, all of the heat transfer coefficients were predicted within a maximum error of −14 / + 25 percent, and a mean error of ± 8 percent. The high Reynolds number friction factors were predicted with a maximum error −22 /+ 26 percent, with a mean error of ± 8 percent. The error ratios were slightly higher at the lowest Reynolds numbers.

Visualization of thermal behavior of fluid by laser holographic interferometry

Visualization of four phenomena associated with thermal and fluid flow fields effectively using laser holographic interferometry are reviewed: airflow in a narrow passage between louver arrays, steam absorption into an aqueous solution of LiBr, Marangoni convection effect of steam absorption into a solution with the addition of high molecular weight alcohol, and pressure distribution on a plate induced by air-jet impingement. The observation result obtained in the first case is useful for designing louvered fins used in a heat exchanger. In the second case, the mass diffusivity of water into a solution of LiBr is shown to be measurable. In the third case, the effect of Marangoni convection on steam absorption is both qualitatively and quantitatively elucidated. The last case is a new visualization method of fluctuating pressure on a wall that can be used to resolve eddy-motion behavior near a wall.

An experimental study of the local heat transfer characteristics in automotive louvered fins

This paper describes experimental devices for measuring the distribution of heat transfer coefficients in multilouvered fins. The devices are composed of louverlike thin elements having a three fold structure—a base metal, an electrical insulator, and an evaporated nickel film as both heating film and resistance thermometer. The locally averaged heat transfer coefficient for the individual louvers in the louver array is obtained by measuring the electric power input for the film and the temperature difference between the element and air. The validity of the method was verified in comparison with an analytical solution for a flat plate, numerical solutions for two-dimensional louver arrays, and another method for measuring the mean heat transfer coefficient. The relation between the distribution of heat transfer coefficients in the louvered fins and the fin geometries was elucidated. The device developed for measuring the heat transfer coefficients for the individual louvers is useful for achieving optimum design of louvered fin geometries.

Research on fins for air conditioning heat exchangers. (3rd report. Heat transfer analysis for louver array).

Research on fins for air conditioning heat exchangers. (3rd report. Heat transfer analysis for louver array).

Heat transfer and pressure drop characteristics of flat tube and louvered plate fin surfaces

Performance data are presented for a range of flat tube and louvered plate fin surfaces. The Stanton number curves demonstrate characteristics that are consistent with the notion that at high Reynolds number the fluid flow is predominantly parallel to the louvers but that as Reynolds number is reduced the flow direction becomes increasingly determined by the plate fins. This effect causes a flattening of the Stanton number curves as the effective heat transfer configuration changes from “flat plate” to “duct flow.” This flattening of the Stanton number curves with reducing Reynolds number is clearly demonstrated to be a genuine effect and not to result from the problems of experimental accuracy that arise at very low Reynolds number. The results of other work by Achaichia and Cowell, which uses numerical methods to describe flow through louver arrays, have been used to develop a very simple nondimensional correlating equation for Stanton number. An equation for friction factor has also been developed, but a dimensional form was found to be necessary for it to retain useful accuracy.

Experimental study on heat transfer from parallel louvered fins by laser holographic interferometry

The objectives of this paper are to study experimentally the details of the heat transfer process in louver arrays and to propose the geometrical arrangement of louvers that would be most effective in improving the performance of heat exchangers. That goal is approached via the following steps. In the first step, the temperature field around louvers is visualized, employing the simple flat-louver model made of a thin bakelite plate and thin nichrome foil heaters, and at the same time the heat transfer coefficient on the louvers is measured. The isotherms are visualized by means of laser holographic interferometry. The isotherms for various louver arrangements were obtained; the thermal boundary layer and the wake generated by an upstream louver extending toward the downstream louvers were observed. It is found that the heat transfer coefficient on the downstream louver is sensitive to the behavior of those boundary layers and wakes. In the second step, the arrangement of louvers is examined with the purpose of enhancing heat transfer. A displacement of a downstream louver out of the influence of the heated air wake from the preceding upstream louver is proposed on the basis of both the observation of isotherms and the measurement of heat transfer coefficients in staggered louver arrays. The experimental results indicate that the performance of heat exchangers may be improved by rearranging the louvers with a small-magnitude displacement.

Louvered Offshore Intake for Diverting Fish

The developmental work on louvered offshore intakes is presented. The model studies included: (1) Preliminary studies in a test flume, capped with plexiglass, and equipped with 15 L-shaped louvers; (2) a 1:9 scale hydraulic model to study the flow distribution along various louver geometrics, louver array angles, and location of the base-wall; and (3) 1:1 (full) scale model testing with live fish. The biological test results were variable and ranged from about 91 to 23 percent. The concept is unique is unique and requires further development prior to being considered a practical solution for fish diversion. The study is presented to report on the developmental work done to date in order to guide researchers in the field.

Improved Fish Protection at Intake Systems

Experimental studies in the diversion and removal of fishes entrained in cooling water flow, and in entrainment reduction at offshore intake structures, were done with coastal marine species of Southern California. Testing was done in a cylindrical tank horizontal-flume facility at Southern California Edison Company's Redondo Generating Station. Diversion studies evaluated fish guidance to variously angled screen and louver arrays. A bypass system was designed by which diverted specimens can be returned safely to sea. Entrainment reduction studies with modeled intake structures led to development of a circular capped structure featuring uniform entrance velocity and a horizontal run prior to a vertical drop. Fish avoidance of various sounds was explored.

“Interference Pattern Method” of Measuring Sound Reflection from Uneven Surfaces

In previous works [Y. Ando, Electron. Commun. (Japan) 51, 10–18 (1968) and, partially, Y. Ando, J. Acoust. Soc. Amer. 45, 1563(L) (1969)] the complex reflection coefficients from even surfaces were accurately measured by this method, considering directivity and acoustic center of the transducers and excluding sphericity error and effect of diffraction by finite dimension of test materials. The reflection of sound from uneven walls has been a problem of interest in architectural acoustics for some time. It is shown that the method is also useful in the scattered near boundary field under certain conditions. Measurements were performed on a semicylindrical boss on rigid plane, a periodically uneven surface of rectangular profile, and a louver array obliquely covered on an absorbing material. Tests were made as a function of distance from reflecting point and angle of incidence. Measured values of the first two cases were compared with those calculated values. Agreements between them were satisfactory for the lower frequency range. In the last case, measured values were greatly dependent on the sign of incident angle, though no theoretical analysis has been attempted.

Efficiency of a Combined Electrode and Louver Array in Guiding Juvenile Steelhead Trout (Salmo gairdneri)

Transactions of the American Fisheries SocietyVolume 96, Issue 4 p. 422-423 Short Papers and Notes Efficiency of a Combined Electrode and Louver Array in Guiding Juvenile Steelhead Trout (Salmo gairdneri) Gerald E. Monan, Gerald E. Monan Bureau of Commercial Fisheries, Fish-Passage Research Program, Seattle, Washington, USASearch for more papers by this authorJohn R. Pugh, John R. Pugh Bureau of Commercial Fisheries, Fish-Passage Research Program, Seattle, Washington, USASearch for more papers by this authorJim R. Smith, Jim R. Smith Bureau of Commercial Fisheries, Fish-Passage Research Program, Seattle, Washington, USASearch for more papers by this author Gerald E. Monan, Gerald E. Monan Bureau of Commercial Fisheries, Fish-Passage Research Program, Seattle, Washington, USASearch for more papers by this authorJohn R. Pugh, John R. Pugh Bureau of Commercial Fisheries, Fish-Passage Research Program, Seattle, Washington, USASearch for more papers by this authorJim R. Smith, Jim R. Smith Bureau of Commercial Fisheries, Fish-Passage Research Program, Seattle, Washington, USASearch for more papers by this author First published: October 1967 https://doi.org/10.1577/1548-8659(1967)96[422:EOACEA]2.0.CO;2Citations: 4AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume96, Issue4October 1967Pages 422-423 RelatedInformation

Analysis of movable louvers for temperature control

Movable shutters or louvers are being employed on several spacecraft for active thermal control. The present analysis of an infinite louver array led to seven equations; six of them form a simultaneous set (three linear integral equations and three linear algebraic equations) which describes the heat-transfer characteristics of the array, and the seventh gives its relative thermal performance in terms of an effective emissivity. The equations are solved numerically, and effective emissivity is plotted as a function of louver blade position for various values of the dimensionless parameters that appear in the governing heat-transfer equations. The results are compared with experimental results obtained for the Mariner II spacecraft louver system; agreement is good when the test data are corrected for power dissipation from auxiliary hardware and the end losses of the finite array. The remaining 4.5% discrepancy at the full-open position is attributed to specular (rather than the assumed diffuse) reflection from the blades.