Louver Angle Research Articles

Heat Transfer From an Isothermal Vertical Surface With Adjacent Heated Horizontal Louvers: Validation

The present study examines the influence of heated, horizontal, and rotateable louvers on the convective heat transfer from a heated or cooled vertical isothermal surface. The system represents an irradiated Venetian blind adjacent to the indoor surface of a window. Detailed temperature field and local surface flux data were obtained using a Mach-Zehnder Interferometer for two window temperatures (warm and cool compared to ambient) and irradiation levels, two louver to plate spacings, and three louver angles. The results have been compared to a steady, laminar, two-dimensional, conjugate conduction/convection/radiation finite element model of this problem. The effect of the heated louvers on the heat transfer rate from the plate surface has been demonstrated and the results of the numerical study have been validated.

Effect of inlet humidity condition on the air-side performance of an inclined brazed aluminum evaporator

The effect of air inlet humidity condition on the air-side heat transfer and pressure drop characteristics for an inclined brazed aluminum heat exchanger has been investigated experimentally. For a heat exchanger with a louver angle of 27°, fin pitch of 2.1 mm and flow depth of 27.9 mm, a series of tests are conducted for the air-side Reynolds numbers of 80–400, with variation of inlet humidity condition. The heat transfer data are obtained for wet condition only and the pressure drop data are measured for both dry and wet conditions. The inlet air temperature and relative humidity range are 12 °C and 60–90%, respectively. The inclination angles ( θ) from the vertical position are 0, 14, 45, and 67° clockwise (leeward direction). The inclination angles affect moderately the sensible heat transfer coefficient for wet condition, and the pressure drops for both dry and wet conditions increase systematically with the inclination angle. The heat transfer and pressure drop characteristics under wet condition are not influenced substantially by the air inlet humidity for θ ⩽45°. The effect of the louver directions at the inlet and outlet of the inclined heat exchanger on the performance is also addressed.

Scaling of heat transfer coefficients along louvered fins

Louvered fins provide a method for improving the heat transfer performance of compact heat exchangers without a prohibitive increase in the pressure drop. Spatially resolved heat transfer coefficients along the louvers protruding from the fins are needed to understand the details of compact heat exchanger performance. Experiments were conducted in a number of large-scale louver models with varied fin pitch and louver angle over a range of Reynolds numbers. This paper presents a method for evaluating the spatially resolved louver heat transfer coefficients using various reference temperatures, such as the bulk flow temperature and adiabatic wall temperature, to define the convective heat transfer coefficients. The results from this study indicate that the thermal field surrounding a particular louver is the overriding influence on the heat transfer from that louver.

Air-side thermal hydraulic performance of multi-louvered fin aluminum heat exchangers

An experimental study on the air-side heat transfer and pressure drop characteristics for multi-louvered fin and flat tube heat exchangers has been performed. For 45 heat exchangers with different louver angles (15–29°), fin pitches (1.0, 1.2, 1.4 mm) and flow depths (16, 20, 24 mm), a series of tests were conducted for the air-side Reynolds numbers of 100–600, at a constant tube-side water flow rate of 0.32 m3/h. The inlet temperatures of the air and water for heat exchangers were 21 and 45°C, respectively. The air-side thermal performance data were analyzed using effectiveness-NTU method for cross-flow heat exchanger with both fluid unmixed conditions. The heat transfer coefficient and pressure drop data for heat exchangers with different geometrical configurations were reported in terms of Colburn j-factor and Fanning friction factor f, as functions of Reynolds number based on louver pitch. The general correlations for j and f factors are developed and compared to other correlations. The f correlation indicates that the flow depth is one of the important parameters for the pressure drop.

Effect of inclination on the air-side performance of a brazed aluminum heat exchanger under dry and wet conditions

This study presents the effect of an inclination angle from the vertical position on the air-side thermal hydraulic performance for a multi-louvered fin and flat tube heat exchanger. For a heat exchanger with a louver angle of 27°, fin pitch of 1.4 mm and flow depth of 20 mm, a series of tests for dry and wet surface conditions were conducted for the air-side Reynolds numbers of 100–300. The inclination angles from the vertical position were 0°, ±30°, ±45°, and ±60° clockwise. The heat transfer performance for both dry and wet conditions was neither influenced significantly by the inclination angle (−60°< θ<60°), nor by the presence or absence of an upstream duct, while the pressure drops increased consistently with the inclination angle. The heat transfer coefficients and the pressure drops for the wet conditions revealed the importance of the role of condensate drainage.

A numerical investigation of louvered fin-and-tube heat exchangers having circular and oval tube configurations

A numerical investigation of the airside performance for fin-and-tube heat exchanger having circular and oval configuration is presented in this study. The geometrical parameters of louver angle, louver pitch, and louver length are examined. For a fixed louver length (6.25 mm) and louver angle (14°), a 10% decrease of heat transfer performance is observed and a 41% decrease of pressure drop is seen for oval tube configuration. The calculated results indicate that the pressure drops always with increase in louver angle. However, an optimal value of heat transfer performance is observed due to the difference in the development of thermal boundary layer on the upper and lower louver surface. Both the heat transfer and friction performance increase with louver length. However, the rate of the increase of heat transfer performance is about the same as the increase of pressure drops.

Geometry effects on flow transition in multilouvered fins – onset, propagation, and characteristic frequencies

The effect of fin pitch, louver angle and thickness, and flow depth on the onset, propagation, and characteristic frequencies of instabilities in multilouvered fins is investigated. The initial instability appears in the wake of the exit louver. Subsequently, instabilities are established in the interior of the louver bank which spread upstream as the Reynolds number increases. It is shown that the interior instabilities are completely independent of the exit wake instability. On the other hand, the exit wake instability is not only dependent on the exit louver geometry but also on the internal geometry of the louver bank. Increasing louver thickness and angle increases the propensity of the flow to become unstable. Increasing fin pitch, louver angle, and thickness enhances the propagation of instabilities into the louver bank. It is shown that the characteristic frequencies in the interior of the louver bank, scale with the fin pitch rather than the louver thickness or louver pitch. The exit wake frequencies, on the other hand scale with the projected length of the exit louver in the flow direction. A simplified model for estimating the onset of instabilities in the interior of the louver bank is proposed.

ルーバーフィンまわりの渦の振動特性

Research results pertinent to heat exchangers are available in existing literature and heat transfer text books. However, it was short of sufficient flow visualizations in louver fins because of the difficulty in its flow visualization. Flow visualization by means of the dye injection method and the laser Doppler velocimetry (LDV) was performed to disclose flow characteristics in louver fins. Fin pitches Pf and louver angles θ in louver fins were varied. Flow patterns in each louver fins are visualized using the fluorescein dye illuminated a laser light sheet. The LDV data were used to calculate Reynolds stress distributions and power spectrum distributions. It is disclosed that vortices in cases of θ=15° and 20° for Pf =100mm exhibit a distinctive periodic characteristics, and the Strouhal number is uniquely related to the Reynolds number.

Velocities in moving granular bed filters

This paper concerns the velocity fields of three symmetric louver-walled moving-bed systems. The louver angles were 10°, 20° and 50° in the three experimental tests. The particle-tracking method and image-processing technology were employed to measure the granule velocity fields in the louver sections. The horizontal and vertical velocity distributions extracted from the velocity fields at five levels of the louver section were plotted and discussed. The velocity profiles of filter granules are influenced by the louver geometry. In the steeper louver–angle system, the velocity profile of filter granules is similar to plug flow. The stagnant zones exist along the louver walls in the filter system with shallow louver sections.

00/02700 A study of the U-factor of the window with a high-reflectivity venetian blind

Venetian blinds are a common type of shading. They can reflect and transmit light efficiently into buildings by adjusting the louver angle and at the same time allow some view to the outdoors. This paper presents a systematic method for calculating projected view (or shaded) fractions for venetian blinds of any shape (flat and curved) as a function of rotation angle, taking into account edge effects and slat thickness. General analytical direct transmittance equations and charts – derived from pure geometrical characteristics – were also developed for flat slats (including thickness and edge effects) and curved slats (circle arcs) as a function of blind tilt angle and profile angle. The last part of the paper investigates the impact of slat shape and reflectance on window-blind system effective reflectance and the associated contribution to the inter-reflected component for different window areas.

A208ルーバーフィンまわりの流れの可視化

Research results pertinent to heat exchangers are available in existing literature and heat transfer text books. However, it was short of sufficient flow visualizations in louver fins because of the difficulty in its flow visualization. Flow visualization by means of the dye injection method and the laser Doppler velocimetry (LDV) was performed to disclose flow characteristics in louver fins. Three kinds of louver angles of θ=10°, 15° and 20° were tested. Flow patterns in each louver fins are visualized using the fluorescein dye illuminated a laser light sheet. The LDV data were used to calculate Reynolds stress distributions and power spectrum distributions. It is disclosed that flows in cases of θ =15° and 20° exhibit a distinctive periodic characteristics, and the Strouhal number is uniquely related to the Reynolds number.

Entry region of louvered fin heat exchangers

Abstract The dominant thermal resistance for most compact heat exchangers occurs on the gas side and as such an understanding of the gas side flowfield is needed before improving current designs. Louvered fins are commonly used in many compact heat exchangers to increase the surface area and initiate new boundary layer growth. For this study, detailed flowfield measurements were made in the entry region of several louvered fin geometries whereby the louver angle, ratio of fin pitch to louver pitch, and Reynolds number were all varied. In addition to mean velocity measurements, time-resolved velocity measurements were made to quantify unsteady effects. The results indicated larger fin pitches resulted in lower average flow angles in the louver passages and longer development lengths. Larger louver angles with a constant ratio of fin pitch to louver pitch resulted in higher average flow angles and shorter development lengths. As the Reynolds number increased, longer development lengths were required and higher average flow angles occurred as compared with a lower Reynolds number case. Time-resolved velocity measurements indicated some flow periodicity behind the fully developed louver for a range of Reynolds numbers. The Strouhal number of these fluctuations was constant for a given louver geometry, but the value increased with increasing fin pitch.

Velocity profiles of granules in moving bed filters

The velocity fields in three symmetric and two asymmetric louver-walled moving bed systems were studied experimentally. The horizontal and vertical velocity distributions at five levels of the louver section were plotted. The results indicate that the velocity profiles of filter granules are influenced by the louver geometry. When the louver angle is steep, the velocity profile of filter granules is close to plug flow. When the louver section is shallow, the quasi-stagnant zones exist along the louver walls. The kinematic model for predicting the granule velocity distribution is used for analyzing the three symmetric louver configurations at different height levels.

Experimental design for flowfield studies of louvered fins

The dominant thermal resistance for most compact heat exchangers occurs on the gas side and as such an understanding of the gas side flowfield is needed before improving current designs. Louvered fins are commonly used in many compact heat exchangers to increase the surface area and initiate new boundary layer growth. Detailed measurements can be accomplished with large-scale models of these louvered fins to gain a better understanding of the flowfield. This paper describes a methodology used for designing an experimental model of a two-dimensional louvered fin geometry, scaled up by a factor of 20, that allows for flowfield measurements. The particular louver geometry studied for these experiments had a louver angle of 27° and a ratio of fin pitch to louver pitch of 0.76. Simulations using computational fluid dynamics (CFD) both aided in designing the large-scale louver model, resulting in a total number of 19 louver rows, and identified the region where the flowfield could be considered as periodic. This paper also presents two component velocity measurements taken in the scaled up model at Reynolds numbers of Re=230, 450, and 1016. For all three Reynolds numbers the flow was louver directed rather than duct directed. The results indicated that significant differences between the three Reynolds numbers occurred. While the flow entering the louver passage at Re=1016 still had remnants of the louver wake convected from two louvers upstream, the Re=230 case did not. Time-resolved velocity measurements were also made in the wake region of a fully developed louver for a range of Reynolds numbers. For 1000 < Re < 1900, there was an identifiable peak frequency for the velocity fluctuations giving a constant Strouhal number of St=0.17.

Stagnant zones in granular moving bed filters for flue gas cleanup

The flow patterns in three symmetric and two asymmetric louver-walled granular moving bed systems are studied experimentally. The flow pattern histories of granular solids in moving beds were recorded by videocamera throughout the whole test period. The image processing system including a frame grabber was used. Selected discrete images showing the flow pattern development were digitized and stored in files. Individual granular flow frames show a development of quasi-stagnant zones close to the louvered walls, the shear zones and a central flow region with width depending on the louver angle. The vertical shift of one or the other louvered wall in asymmetric configuration considerably influences the history of quasi-stagnant zones.

A generalized heat transfer correlation for Iouver fin geometry

A generalized heat transfer correlation for louver fin geometry is developed with the aid of a large data bank. This data bank consists of 91 samples of louvered fin heat exchangers with different geometrical parameters, including louver angle, tube width, louver length, louver pitch, fin length and fin pitch. For the corrugated louver fin geometry, it is shown that 89.3% of the corrugated louver fin data are correlated within ± 15% with mean deviation of 7.55%. The inclusion of the plate-and-tube louver fin data in the heat transfer correlation (equation (Al)) results in a mean deviation of 8.21%.

96/00821 Energy efficiency in new houses. Heat demand reduction versus cogeneration?

Venetian blinds are a common type of shading. They can reflect and transmit light efficiently into buildings by adjusting the louver angle and at the same time allow some view to the outdoors. This paper presents a systematic method for calculating projected view (or shaded) fractions for venetian blinds of any shape (flat and curved) as a function of rotation angle, taking into account edge effects and slat thickness. General analytical direct transmittance equations and charts – derived from pure geometrical characteristics – were also developed for flat slats (including thickness and edge effects) and curved slats (circle arcs) as a function of blind tilt angle and profile angle. The last part of the paper investigates the impact of slat shape and reflectance on window-blind system effective reflectance and the associated contribution to the inter-reflected component for different window areas.

96/00825 Extending Prague's district heating system — The strategy

Venetian blinds are a common type of shading. They can reflect and transmit light efficiently into buildings by adjusting the louver angle and at the same time allow some view to the outdoors. This paper presents a systematic method for calculating projected view (or shaded) fractions for venetian blinds of any shape (flat and curved) as a function of rotation angle, taking into account edge effects and slat thickness. General analytical direct transmittance equations and charts – derived from pure geometrical characteristics – were also developed for flat slats (including thickness and edge effects) and curved slats (circle arcs) as a function of blind tilt angle and profile angle. The last part of the paper investigates the impact of slat shape and reflectance on window-blind system effective reflectance and the associated contribution to the inter-reflected component for different window areas.

Flow visualization of convex louver fin arrays to determine maximum heat transfer conditions

A flow visualization study was performed for the convex louver fin geometry. The visualization was achieved using dye in a 20:1 scale model with water as the fluid. The louver angle and fin pitch were varied to determine the conditions that produced maximum mixing and therefore are expected to produce maximum heat transfer. The mixing efficiency was described using a dye mixing angle. The Reynolds number based on louver length was varied from 400 to 3000. For most configurations, the mixing angle increased with Reynolds number. Louver angles of 19 and 24° were tested. For each value of fin pitch ( F p) to chevron height ( H), the larger louver angle resulted in a large mixing angle. F p/4 H = 1, 1.5, 2 and 3 were tested the F p/4 H = 1.5, producing the largest mixing angle. The separation structure produced by the convex louver geometry was also studied using flow visualization.

Experimental study of thermal performance of automated venetian blind window systems

This article presents an operational and thermal performance study on automated venetian blind window systems. They are systems with pivoted louvers installed horizontally, sealed hermetically between two glass panes and controlled automatically following the thermal needs. The experimental studies were carried out in two identical test cells (2.43 m high, 1.48 m wide, and 1.92 m deep) used as variable temperature calorimeters. One was equipped with an automated window system and the other double glass window without louvers. Various parameters were measured and recorded: louver angle, inside and outside air temperatures, cloud cover. The operational and thermal performances of the automated louver system have been demonstrated and compared with that of the ordinary system.