Fan Configuration Research Articles

Energy performance of PV integrated office buildings with fan-assisted double skin façades under tropical climates

ABSTRACTBuilding upon the knowledge accumulated from a comprehensive research program on double skin façades (DSFs), this study explores two design enhancements for buildings in tropical climates. Thermal and energetic benefits of the inclusion of mechanical ventilation within the DSF cavity and electricity generation from the PV systems have been determined across a wide spectrum of Brazilian climates. Using computational simulations, DSF models with two fan configurations, placed solely at the top of the DSF and distributed along the height of the cavity, are evaluated. Annual distribution of thermal comfort acceptance and impact on energy demands from HVAC systems and contribution from the PV systems is analyzed. Results demonstrated wide variations of energy performance in relation to the climatic conditions. The ‘Cool’ climate zone presented most significant benefits from the proposed design enhancements resulting in electricity surplus. On the other hand, electricity generated from PV in the moderate climate zone can only cover about 30% of the HVAC energy consumption, whereas energy savings in the ‘hot’ zone are the lowest with only 15% of electricity contributed from the PV systems. The results of this paper contribute to the early stage of design when considering the adoption of DSF in tropical climates.

Shepherd Chemical invests in the Vosges

Research related to personal comfort systems is growing due to their potential to increase an individual’s satisfaction with indoor environmental conditions and energy efficiency. At moderately high indoor temperatures, the use of ceiling fans can be a low-energy cooling strategy to enhance comfort in a working environment. This paper studies the performance of a personal ceiling fan and its influence on occupants’ satisfaction with the indoor environment, focusing on the effects of personal control, previous experience with fans, variations on participants’ activity level and air coming from different directions. In a laboratory study, 41 participants from two age groups were exposed to six different ceiling fan configurations either in sitting or standing positions, with and without control over the ceiling fan speed, and under two thermal conditions (balanced order of in total 24 conditions). Results showed that participants’ thermal comfort at indoor temperatures of 28 °C and 31 °C was fulfilled when they used the personal ceiling fan, independent of the direction of the supplied air coming from above. The possibility to control the fan speed showed a significant influence on the thermal perception of participants at a slightly higher activity level compared to fully sedentary. The influence of previous experiences with fans had a positive effect on the rating of the analyzed ceiling fan and thermal comfort. The positive acceptance of personal ceiling fans encourages its use in retrofitted office buildings to increase thermal comfort and motivate energy savings.

Gulf Coast plants open, and new ones are planned

Research related to personal comfort systems is growing due to their potential to increase an individual’s satisfaction with indoor environmental conditions and energy efficiency. At moderately high indoor temperatures, the use of ceiling fans can be a low-energy cooling strategy to enhance comfort in a working environment. This paper studies the performance of a personal ceiling fan and its influence on occupants’ satisfaction with the indoor environment, focusing on the effects of personal control, previous experience with fans, variations on participants’ activity level and air coming from different directions. In a laboratory study, 41 participants from two age groups were exposed to six different ceiling fan configurations either in sitting or standing positions, with and without control over the ceiling fan speed, and under two thermal conditions (balanced order of in total 24 conditions). Results showed that participants’ thermal comfort at indoor temperatures of 28 °C and 31 °C was fulfilled when they used the personal ceiling fan, independent of the direction of the supplied air coming from above. The possibility to control the fan speed showed a significant influence on the thermal perception of participants at a slightly higher activity level compared to fully sedentary. The influence of previous experiences with fans had a positive effect on the rating of the analyzed ceiling fan and thermal comfort. The positive acceptance of personal ceiling fans encourages its use in retrofitted office buildings to increase thermal comfort and motivate energy savings.

Process for reducing the total acid number in refinery feedstocks

Research related to personal comfort systems is growing due to their potential to increase an individual’s satisfaction with indoor environmental conditions and energy efficiency. At moderately high indoor temperatures, the use of ceiling fans can be a low-energy cooling strategy to enhance comfort in a working environment. This paper studies the performance of a personal ceiling fan and its influence on occupants’ satisfaction with the indoor environment, focusing on the effects of personal control, previous experience with fans, variations on participants’ activity level and air coming from different directions. In a laboratory study, 41 participants from two age groups were exposed to six different ceiling fan configurations either in sitting or standing positions, with and without control over the ceiling fan speed, and under two thermal conditions (balanced order of in total 24 conditions). Results showed that participants’ thermal comfort at indoor temperatures of 28 °C and 31 °C was fulfilled when they used the personal ceiling fan, independent of the direction of the supplied air coming from above. The possibility to control the fan speed showed a significant influence on the thermal perception of participants at a slightly higher activity level compared to fully sedentary. The influence of previous experiences with fans had a positive effect on the rating of the analyzed ceiling fan and thermal comfort. The positive acceptance of personal ceiling fans encourages its use in retrofitted office buildings to increase thermal comfort and motivate energy savings.

Effects of blade angle on combustion characteristics in a micro combustor with a swirler of micro fan type

In a micro combustor, various vortices can enhance the wall heat transfer rate and get the best combustion. For an efficient combustion, the swirler of micro fan type is introduced for a micro combustor. In general, the swirling flows can change significantly the wall heat fluxes and this feature is sensitively varied by the fan configuration. So, to examine the geometric effect of fan swirler on the combustion characteristics, reacting flows depending on six blade angles are numerically investigated. The highest efficiency and heat loss related to vortical flows are observed for the specific blade angles.

Internal insulation retrofit with ventilated wall and circulation of dry air – focus on airflow distribution and mitigation of noise

External façade retrofit changes the look, feel and aesthetics of the building and internal façade retrofit changes the heat and moisture conditions of the existing façade. The ventilated internal insulation wall is an existing solution for internal retrofit applications that promises to be an efficient and moisture resilient retrofit solution. It has a ventilated cavity and the moisture content in the cavity is actively controlled by a small dehumidifier unit mounted in the wall. The dehumidifier circulates air inside the air cavity and any excessive moisture is ejected into the room air. The focus of the paper is on mitigating noise from the dehumidifer by analyzing the required airflow rate, the air distribution inside the air cavity as well as optimizing the dehumidifier. CFD simulations were carried out to analyze airflow velocities and distribution and the final results show a possible 30% reduction in the airflow rate without compromising the drying performance. In addition, experimental studies in noise mitigation were performed. Different dehumidifier designs with different fan configurations were tested. A significant noise reduction was obtained from 39 dB(A) to a noise level of approx. 26 dB(A).

Acoustic Signal Separation and Noise Reduction of a Contra-Rotating Fan

How to reduce fan noise has always been a significant research topic in equipment ranging from small-scale devices, such as computer cooling fans and building ventilation fans, to large high bypass ratio turbo engines. In recent years, in order to produce higher pressure rise or larger flow rate with lower noise level in the fan stage, interest in the contra-rotating fan (CRF) configuration has been rekindled. The Vold-Kalman order tracking filter technique was employed to separate tonal and broadband noise components from CRF acoustic data to study the characteristics of the noise spectrum. Based on the spectrum peaks, noise reduction solution with casing treatment is proposed according to acoustic performance prediction by finite element simulation. In the simulation, the CRF is modelled at one end of a duct, which is surrounded by a semi-spherical space with perfect match layer to simulate the free field condition. The other end of the duct is modelled with non-reflecting boundary condition to simulate the anechoic termination. The simulated and experimental results show that casing treatment by micro-perforated panels can significantly reduce the CRF noise.

Effect of fan and shroud configurations on underhood flow characteristics of an agricultural tractor

ABSTRACTIn the current study, effects of two different underhood geometry modifications namely; fan position relative to shroud and fan tip clearance, on airflow through an agricultural tractor engine cooling system are investigated by utilizing CFD modeling. For the characterization of each modification, the underhood components are reduced to a domain of cooling systems including only fan, shroud, and radiator that allows saving in computational time and cost. The models are validated using a custom designed underhood flow setup, where hotwire velocity measurements at proximity to the radiator are conducted. The mass flow rate and the uniformity of the airflow through the radiator are quantified as performance parameters. For the former modification, position of fan relative to shroud, the computations are performed for the percentages of fan projection into shroud (FPiS) varying from 78% to 0% at fan rotational speeds of 2060 and 2800 rpm. The optimum fan location is found to be around 56–60% for both rotational speeds that leads 8% increase in mass flow rate compared with the pre-design location of 74%. In addition, a noticeable reduction in the relative magnitude of the RMS velocity through the radiator is obtained for the moderate FPiS values. For the latter modification, fan tip clearance, the computations are performed for the tip clearance values varying from 5.25to 12 mm at a fan rotational speed of 2060 rpm. As the tip clearance decreases up to 6 mm, air mass flow rate can be improved by 7%. However, further reduction in tip clearance does not improve the air mass flow rate instead it decreases, suggesting an optimum tip clearance value. The results suggest that the proper geometrical modifications in engine cooling systems might induce significant improvement in the aforementioned performance indicators.

Performance Testing of an Axial Flow Fan Designed for Air-Cooled Heat Exchanger Applications

An axial flow fan developed in the previous study is tested in order to characterize its performance. The M-fan, a 7.3152 m diameter rotor only axial flow fan was designed to perform well under the challenging operating conditions encountered in air-cooled heat exchangers. Preliminary computational fluid dynamics (CFD) results obtained using an actuator disk model (ADM) as well as a periodic three dimensional model indicate that the fan meets the specified performance targets, with an expected total-to-static efficiency of 59.4% and a total-to-static pressure rise of 114.7 Pa at the operating point. Experimental tests are performed on the M-fan in order to determine its performance across a full range of flow rates. A range of fan configurations are tested in order to ascertain the effect of tip clearance, blade angle, and hub configuration on fan performance. Due to the lack of a suitable facility for testing a large diameter fan, a scaled 1.542 m diameter model is tested on the ISO 5801 type A fan test facility at Stellenbosch University. A Reynolds-averaged Navier–Stokes CFD model representing the M-fan in the test facility is also developed in order to provide additional insight into the flow field in the vicinity of the fan blades. The results of the CFD model will be validated using the experimental data obtained. Both the CFD results and the experimental data obtained are compared to the initial CFD results for the full scale fan, as obtained in the previous study, by means of fan scaling laws. Experimental data indicate that the M-fan does not meet the pressure requirement set out in the initial study at the design blade setting angle of 34 deg. Under these conditions, the M-fan attains a total-to-static pressure rise of 102.5 Pa and a total-to-static efficiency of 56.4%, running with a tip gap of 2 mm. Increasing the blade angle is shown to be a potential remedy, improving the total-to-static pressure rise and efficiency obtained at the operating point. The M-fan is also shown to be highly sensitive to increasing tip gap, with larger tip gaps substantially reducing fan performance. The losses due to tip gap are also shown to be overestimated by the CFD simulations. Both experimental and numerically obtained results indicate lower fan total-to-static efficiencies than obtained in the initial CFD study. Results indicate that the M-fan is suited to its intended application, however, it should be operated with a smaller tip gap than initially recommended and a larger blade setting angle. Hub configuration is also shown to have an influence on fan performance, potentially improving performance at low flow rates.

Evaluation of nitrous oxide as a substitute for sulfur hexafluoride to reduce global warming impacts of ANSI/HPS N13.1 gaseous uniformity testing

The ANSI/HPS N13.1–2011 standard requires gaseous tracer uniformity testing for sampling associated with stacks used in radioactive air emissions. Sulfur hexafluoride (SF6), a greenhouse gas with a high global warming potential, has long been the gas tracer used in such testing. To reduce the impact of gas tracer tests on the environment, nitrous oxide (N2O) was evaluated as a potential replacement to SF6. The physical evaluation included the development of a test plan to record percent coefficient of variance and the percent maximum deviation between the two gases while considering variables such as fan configuration, injection position, and flow rate. Statistical power was calculated to determine how many sample sets were needed, and computational fluid dynamic modeling was utilized to estimate overall mixing in stacks. Results show there are no significant differences between the behaviors of the two gases, and SF6 modeling corroborated N2O test results. Although, in principle, all tracer gases should behave in an identical manner for measuring mixing within a stack, the series of physical tests guided by statistics was performed to demonstrate the equivalence of N2O testing to SF6 testing in the context of stack qualification tests. The results demonstrate that N2O is a viable choice leading to a four times reduction in global warming impacts for future similar compliance driven testing.

Effectiveness of Rack-Level Fans—Part I: Energy Savings Through Consolidation

In general, smaller fans operate at lower efficiencies than larger fans of proportional linear dimensions. In this work, the applicability of replacing smaller, 60 mm baseline fans from within the chassis of web servers with an array of larger, geometrically proportional 80 mm and 120 mm fans consolidated to the back of a rack is experimentally tested. Initial characterization of the selected fans showed that the larger fans operate at double peak total efficiency of the smaller fans. A stack of four servers were used in a laboratory setting to represent a rack of servers. When all four servers were stressed at uniform computational loadings, the 80 mm fans resulted in 50.1–52.6% reduction in total rack fan power compared to the baseline fans. The 120 mm fans showed similar reduction in rack fan power of 47.6–54.0% over the baseline. Since actual data centers rarely operate at uniform computational loading across servers in a rack, a worst case scenario test was conceived in which the array of larger fans were controlled by a single server operating at peak computational workload while the other three in the rack remained idle. Despite significant overcooling in the three idle servers, the 80 mm and 120 mm fan configurations still showed 35% and 34% reduction in total rack fan power compared to the baseline fans. The findings strongly suggest that a rack-level fan scheme in which servers share airflow from an array of consolidated larger fans is superior to traditional chassis fans.

Field-measured Performance of Lightweight Roof Chimney Integrated with DC fans

This paper present the results of an experimental comparative research investigation of the thermal performance and heat gain reduction between two houses built with light roof. The first one is installed with a lightweight roof chimney (LRC) integrated with a DC fan while the one is a house installed with a simple lightweight roof (SLR). The south facing roofs of the two houses were made of clear polycarbonate sheets with the same dimensions. The LRC with DC fan configuration consists of double-layer space with a small air gap and two openings located at the bottom (interior side) and at the top where an exhaust fan is installed (exterior side). This design is aimed to induce natural ventilation and indoor air circulation. The 12V-0.40A DC fans are employed to increase ventilation to remove polluted indoor air to the outside environment. The outer roofs and the inner roofs (ceiling) are made of polycarbonate sheets and gypsum boards respectively. The experiment revealed that indoor air temperature of the house with LRC and DC fans appears to be significantly lower than that of the house with SLR. As a result, this LRC integrated with DC fans can become a tool not only for reducing the attic and indoor temperatures but also inducing natural ventilation, saving energy and promoting solar energy integration in buildings and houses such that protecting the environment.

Numerical Investigations of Fan-in-Wing Aerodynamic Performance with Active Flow Control

Aerodynamic performance of a fan-in-wing configuration in hover is numerically investigated using a high-fidelity three-dimensional unsteady Reynolds-averaged Navier–Stokes flow solver based on unstructured grid technology. Fan-in-wing or ducted fan configurations offer the advantage of hover capability with enhanced thrust comparing to open fans, but they suffer from reduced efficiency and thrust levels at offdesign conditions. In this study, the aerodynamic performance and flowfield of a fan-in-wing configuration in hover are numerically investigated over a range of blade pitch angles at two operating speeds. The maximum thrust, peak efficiency, and stall margin of the system are among the main interests of this investigation. An innovative concept using an active flow control is introduced in this study to enhance the operating efficiency and thrust level of the system by increasing the circulation and duct mass flow rate in the fan-in-wing system. Numerical investigations indicate a 25–55% increase in the maximum system thrust, achieved without suffering the peak efficiency loss, when using the proposed active flow control concept. This potentially provides a viable technology to significantly enhance the aerodynamic performance of lift fan devices such as the ducted fans or fan-in-wing configurations to support the research of vertical takeoff and landing aircraft.

CFD Study of a New Annular Lift Fan Configuration with High Lift Efficiency

A new annular lift fan configuration that has very high lift efficiency is explored by using a numerical scheme. The inlet lip radius and diffuser angle are maximized by semicircle duct walls and the location of the lift fan is moved from the throat to the diffuser area to maximize the diffusion effect of the ducted fan. The improved lift fan achieves the figure of merit of 0.772 and the power loading of 9.03 lbs/hp without ground effect, very close to the theoretical limit. Under the ground effect, the figure of merit reaches 0.822 with the power loading of 9.62 lbs/hp. The improved lift efficiency deteriorates the transition characteristics with higher momentum drag and pitching moment. However, with the aid of jet thrusts directly providing part of the lift during transition, the peak of momentum drag and pitching moment can be lowered. A total thrust to weight ratio of 0.7 is enough for all of the requirements in transition and in hover and for the maximum speed of 0.75 Mach in cruise flight.

Fan–Intake Interaction Under High Incidence

In this paper, we present an extensive numerical study on the interaction between the downstream fan and the flow separating over an intake under high incidence. The objectives of this investigation are twofold: (a) to gain qualitative insight into the mechanism of fan–intake interaction and (b) to quantitatively examine the effect of the proximity of the fan on the inlet distortion. The fan proximity is altered using the key design parameter, L/D, where D is the diameter of the intake, and L is the distance of the fan from the intake lip. Both steady and unsteady Reynolds-averaged numerical simulations (RANS) were carried out. For the steady calculations, a low-order fan model has been used, while a full 3D geometry has been used for the unsteady RANS. The numerical methodology is also thoroughly validated against the measurements for the intake-only and fan-only configurations on a high bypass ratio turbofan intake and fan, respectively. To systematically study the effect of fan on the intake separation and explore the design criteria, a simplified intake–fan configuration has been considered. In this fan–intake model, the proximity of the fan to the intake separation (L/D) can be conveniently altered without affecting other parameters. The key results indicate that, depending on L/D, the fan has either suppressed the level of the postseparation distortion or increased the separation-free operating range. At the lowest L/D (∼0.17), around a 5 deg increase in the separation-free angle of incidence was achieved. This delay in the separation-free angle of incidence decreased with increasing L/D. At the largest L/D (∼0.44), the fan was effective in suppressing the postseparation distortion rather than entirely eliminating the separation. Isentropic Mach number distribution over the intake lip for different L/D's revealed that the fan accelerates the flow near the casing upstream of the fan face, thereby decreasing the distortion level in the immediate vicinity. However, this acceleration effect decayed rapidly with increasing upstream distance from the fan-face.

Study on Different Cable Configurations of Cable-Stayed Bridges Using Developed Seismic Risk Assessment

Changing the cable configuration in a cable-stayed bridge affects the period and damping of the structure and consequently changes the forces in bridge components, which results in change of their required dimensions. Based on this, it can be concluded that altering the cable configuration will result in a change in seismic risk and construction costs. It is therefore necessary to thoroughly investigate the common configurations in order to select an optimal option. In this paper, as a case study, a cable-stayed bridge is designed with three different configurations to compare dimensions and construction costs relatively. The loss due to probable earthquakes can then be investigated simultaneously with the construction costs using the developed seismic risk assessment (DSRA) process, for each configuration employment. The proposed process is performed based on a financial-comparative (FC) approach and consists of three steps: fragility assessment, loss assessment and cost-loss-benefit (CLB) assessment. Final decision-making is done by proposing benefit ratio (BR) as a profitability measure. Results show that the fan and harp cable configurations are the optimal options for cable-stayed bridges with 260 m and 100 m mid-span, respectively.

Numerical study of shock wave interaction in steady flows of a viscous heat-conducting gas with a low ratio of specific heats

Specific features of shock wave interaction in a viscous heat-conducting gas with a low ratio of specific heats are numerically studied. The case of the Mach reflection of shock waves with a negative angle of the reflected wave with respect to the free-stream velocity vector is considered, and the influence of viscosity on the flow structure is analyzed. Various issues of nonuniqueness of the shock wave configuration for different Reynolds numbers are discussed. Depending on the initial conditions and Reynolds numbers, two different shock wave configurations may exist: regular configuration interacting with an expansion fan and Mach configuration. In the dual solution domain, a possibility of the transition from regular to the Mach reflection of shock waves is considered.

Optimizing performance of ceiling-mounted personalized ventilation system assisted by chair fans: Assessment of thermal comfort and indoor air quality

This study investigates and optimizes the performance of ceiling-mounted personalized ventilation system when assisted with chair-mounted fans. Detailed computational fluid dynamics simulations were performed to study the velocity, temperature, and CO2 fields around the microclimate of the occupant. The computational fluid dynamics model was integrated with a bio-heat model to determine the corresponding segmental skin temperature and local and overall comfort and sensation. The computational fluid dynamics model was validated experimentally using a thermal manikin in a climatic chamber. The segmental skin temperature, velocity field, and CO2 field were validated experimentally. The predicted values and the measured values showed good agreement. The validated computational fluid dynamics model was used to optimize the height of the chair fan and the fan flow rate for the best combination of indoor air quality and thermal comfort. The chair fan's configuration to achieve the best thermal comfort and the best indoor air quality occurred at different fan heights. The optimal fan height and flow rate for best thermal comfort were 40 cm (15.75 in.) above floor level and 10 L/s (0.35 ft3/s), respectively. However, the optimal fan height and flow rate for best air quality were found to be 50 cm (19.69 in.) above the floor level and 10 L/s (0.35 ft3/s), respectively. At this configuration, the chair-mounted fans were able to reduce the thermal plumes and improve the performance of the personalized ventilation system by nearly doubling thermal comfort and ventilation effectiveness. The use of chair-mounted fans allowed for the achievement of energy savings up to 17% when compared with conventional mixing ventilation system.

Flow visualization and thermal resistance measurement of the LED heat sinks with a built-in piezoelectric fan and various flow-runner opens

This work experimentally investigated the fluid flow and heat transfer characteristics of specified finned heat sinks with the built-in piezoelectric fan and different configurations of flow-runner opens. Total three kinds of flow-runner opens were employed: the symmetrically lateral rectangular opens (Model A), the symmetrical lateral slot opens (Model B), as well as the bottom rectangular open (Model C) with/without bottom curved panel. The smoke flow visualization results indicate that various configurations of flow-runner opens resulted in different smoke flow fields. The Model C reduced the total thermal resistance by 10.4–21.3%; it was the optimal one to enhance cooling performance herein. The relevant results can be the base in designing such LED finned heat sink with a built-in piezoelectric fan.

Robust Flight Control Using Nonsmooth Optimization for a Tandem Ducted Fan Vehicle

AbstractThis work addresses the aerodynamic modeling and near‐hover‐flight control design for an unconventional aerial robot of the tandem ducted fan configuration, which is intended to be prototypical of a flight service vehicle. The main model elements of this novel unmanned vehicle, which exhibit highly nonlinear and unstable open‐loop modes, are presented. A frequency‐domain controllability analysis concerning the plant's behavior around the hovering flight condition is then adopted to determine the expected control performance, which is of important practical significance to controllability improvement through vehicle design changes. A robust controller that stabilizes the unmanned vehicle under wind disturbances is designed using a newly developed nonsmooth optimization algorithm, which rigorously and efficiently tunes the arbitrarily predefined structured controller against multiple control requirements. A successive two‐loop architecture is employed in the designed controller. In this architecture, the inner loop provides stability augmentation and decoupling, and the outer loop guarantees the desired velocity tracking performance. Simulation results under stochastic wind gusts are presented to verify the performance of the proposed controllers. Preliminary flight tests are also carried out to demonstrate the performance of the system.