Reversible Fan Research Articles

Heat Recovery Using PCM in Decentralised Façade Ventilation

A study of heat recovery in a façade ventilation unit was carried out under laboratory conditions using a climate chamber that allowed stable outdoor and indoor conditions to be simulated. The unit, equipped with a reversible fan and a chamber for the heat exchanger, controlled by an automation control system, was designed to exchange air in the room by alternating supply and exhaust cycles of specific durations. Three types of heat exchangers were tested, which were filled with different phase change materials, in order to estimate the efficiency of the façade ventilation unit in terms of its heat recovery capability. The efficiency of the unit was determined based on the temperature efficiency of heat recovery for 144 setting combinations. The best efficiency results between 73.56% and 76.29% were obtained with a solution using a heat exchanger consisting of cylinders with an external diameter of 10 mm and a wall thickness of 1 mm filled with jojoba oil in a one minute cycle. The tests confirmed that the heat exchangers, which are part of the façade ventilation unit, fulfil their function and allow heat recovery from the exhaust air to pre-heat the supplied air. The study complements the existing scientific knowledge on the efficiency of heat exchangers filled with phase change material, operating in winter conditions with work cycles up to 5 min.

Design characteristics and validation of the turbine model — Case of development of turbine effect in sloped collector solar chimney plant

Blade design for a solar chimney power plant turbine is modeled geometrically. NACA 4412 blade is selected for its favorable lift to drag characteristics in the considered diameter range. The constructed model is integrated into a solar chimney plant and validated against existing examples in literature. A similar process is applied using a reverse fan model. Margins of discrepancies obtained from the turbine and reverse fan models are used as indicators for the total deviation expected from using the reverse fan model with a sloped collector plant. Here, the effect of turbine pressure change on the temperature rise and air flow are examined to set the upper limit of pressure drop and check the capacity of the system for power generation. The maximum air flow velocity at the center of the sloped collector reached 9.8 m/s. The highest achievable temperature difference was 37 °C. The favorable working zone for turbine operation inside the tower of a sloped collector solar chimney in terms of pressure drop and air flow rate is marked based on a constant efficiency.

Aerodynamic performance of the reversible axial fan for high air temperatures

The paper presents the aerodynamic performance of an axial reversible fan for high air temperatures, obtained by applying the similarity theory and numerical flow simulations. This analysis was performed for the possibility of installing the existing structure of an impeller of a reversible fan in a jet fan for the longitudinal ventilation of a tunnel. The direction of forced flow in tunnels changes, and it is always towards low atmospheric pressure, i.e. in the direction of natural air-flow. These fans often work with high air temperatures in the event of a fire. The paper shows the performance of fans for high operating air temperatures, up to 400?C. The results were obtained through numerical simulations of the flow in an original design fan, whose performance was experimentally determined for normal atmospheric operating conditions (? = 1.2 kg/m3). Performances are given for two fan speeds. Unnecessary corrections of the existing impeller design for use in jet fans for tunnel ventilation were also considered.

Investigation of aerodynamic schemes of reversible mine fans

The article considers the aerodynamic scheme of the main ventilation fan with high aerodynamic properties in reverse operation mode based on the use of a rotating input guide vanes. The dependences of the setup angles of the blades of the input guide vanes and the rotor, when the fan is switched to the reverse mode, on the required flow coefficients and fan pressure at certain parameters of the profile cascades at a mean radius are revealed. Using the example of the designed aerodynamic schemes, the influence of the swirl of the flow in the guide device, the solidity of the blade cascades of the rotors and the torsion of the blades on the aerodynamic characteristics of the reversible fan operation mode, calculated in the ANSYS CFX, is shown. Obtained fan aerodynamic scheme provides a performance in the reverse mode operation equal to 0.96 of the performance of the direct mode in the same ventilation network.

Investigating the opportunity for cooling the London underground through waste heat recovery

Recovering waste heat from urban infrastructures is becoming increasingly important as the UK strives to decarbonise heat, which remains one of the main challenges in the transition towards net zero. The Bunhill Waste Heat Recovery (WHR) System represents a first of its kind scheme that will recover waste energy from a ventilation shaft of the London Underground (LU) transport network. The system is based upon the installation of a heat recovery heat exchanger that consists of cooling coils and a reversible fan. The coils are connected to a heat pump that supplies low-carbon thermal energy to the Bunhill Heat Network in Central London. One particularly important aspect of the Bunhill WHR system is its ability to operate in a way that not only provides heating to the local heat network, but can also simultaneously supply cooled air to the LU tunnels depending on the operation of the reversible fan. The current paper estimates the potential cooling benefit that could be achieved with the WHR system based upon the development of a mathematical model. The model is able to predict the condition of the coil surface according to air inlet parameters, and this is used to calculate the latent and sensible cooling loads, which are applied to simulate how the system affects the local tunnel environment, with peak temperature reductions of up to 7.2 K being estimated for adjacent stations in 2030. The results from the investigation are presented together with recommendations for further development and future deployment of heat recovery from metro systems, as this technology could be applied across London and elsewhere to deliver significant carbon and cost savings while improving the thermal environment of railway tunnels. Practical Application This work investigates the cooling potential behind a practical project that involves recovering waste heat from the LU network. As electrification leads to an increased deployment of heat pump and district heating systems, waste heat could become a valuable resource for maximising energy efficiency, even more so when additional cooling benefits can be achieved. This paper aims to explore the impacts of cooling on railway tunnels, emphasising how secondary benefits, which are many times overlooked, could be critical to making waste heat recovery economically feasible, maximising its potential as a key technology for decarbonising heat.

The design and fulfillment of a Smart Home (SH) material powered by the IoT using the Blynk app

Home Automation System (HAS) has attracted great interest as communication technology advances. A Smart Home (SH) is an Internet of Things (IoT) app that utilizes the Internet to surveillance and control devices through the use of a smart home automation system (SHAS). Current home automation systems (HASs) are limited by a lack of IoT technology, an unfriendly user interface, a limited wireless transmission range, and high costs. This paper describes an affordable, safe and energy-efficient WiFi-based system smart home or intelligent home, which enables home appliances to be monitored by homeowners in local and remote locations via mobile phone/PC. Raspberry Pi 3 Model B+ and Arduino Mega 2560 were used to configuring the server automation framework. Moreover, various sensors that are connected to the Arduino Mega controller have been used to monitor current, voltage, power, energy, frequency, humidity, temperature, motion, flame, smoke, gas, doors, windows and other household conditions, and also to successfully control household appliances (lights, fans, reverse fan, water pump, etc.) either automatically or via relays. The proposed automation system can surveillance and control home conditions via the Blynk app for both Android or IOS.

New Design of the Reversible Jet Fan

This paper presents two designs of the axial reversible jet fan, with the special focus on the impeller. The intention was to develop a reversible axial jet fan which operates in the same way in both rotating directions while generating thrust as high as possible. The jet fan model with the outer diameter 499.2 ± 0.1 mm and ten adjustable blades is the same, while it is in-built in two different casings. The first construction is a cylindrical casing, while the second one is profiled as a nozzle. Thrust, volume flow rate, consumed power and ambient conditions were measured after the international standard ISO 13350. Results for both constructions are presented for three impeller blade angles: 28°, 31° and 35°, and rotation speed in the interval n = 400 to 2600 rpm. The smallest differences in thrust, depending on the fan rotation direction, as well as the highest thrust are achieved for the first design with the cylindrical casing and blade angle at the outer diameter of 35°. Therefore, it was shown that fan casing significantly influences jet fan characteristics. In addition, the maximum thrust value and its independence of the flow direction is experimentally obtained for the angle of 39° in the cylindrical casing.

Case Series on Four Treated Cases of Embryonal Rhabdomyosarcoma in Children.

We report four cases of embryonal rhabdomyosarcoma treated successfully with multimodality therapy which included surgery, chemotherapy and radiotherapy. Our first case was a 2year old who admitted with the chief complaint of swelling of the upper lip. Biopsy was taken, which showed embryonal rhabdomyosarcoma. It was followed by a CT scan (face + neck), MRI face, USG abdomen and bone scan of the patient. Pre operatively chemotherapy was given. After completion of chemotherapy regimen, wide local excision of the lesion along with a reverse fan flap and bilateral modified radical neck dissection type 3 was done. This was followed by post operative chemotherapy and radiotherapy. There was no recurrence at 6months post operatively. The second patient was 6years old with similar complaints, after undertaking all the investigations as in the previous case, patient was given neoadjuvant chemotherapy following which wide local excision of the lesion along with reconstruction with the help of bilateral nasolabial flap was done. This was followed by post operative chemotherapy. No recurrence was present 6months post operatively. The third patient was a 17year old male presenting with complaints of left sided nasal obstruction and left nasal swelling. Examination revealed left sided nasal mass which on biopsy turned out to be embryonal rhabdomyosarcoma. The patient underwent surgery followed by chemoradiation. At 6months the patient had no evidence of recurrence. The fourth patient was 16-year-old male who presented with complaints of right sided nasal swelling and nasal obstruction. Radiological investigation showed the tumor involving the right sinonasal cavity with extension to anterior cranial fossa and with neck nodes. Patient was given concurrent chemoradiation. Patient was followed up for 6months when the patient presented with recurrence of disease with distant metastasis. Patient is currently on palliative chemotherapy. To summarise, embryonal rhabdomyosarcoma in young children when treated aggressively with surgery and chemotherapy has better prognosis than with chemo-radiation alone.

Hydrodynamic and thermodynamic enhancement of a solar chimney power plant

The present paper investigates the effect of geometrical parameters by using energy and exergy analysis and hydrophobic surfaces as an innovative method were proposed to enhance the performance of Solar Chimney Power Plant (SCPP). Furthermore, the best radiation model for SCPP simulation was represented. Hereupon, firstly large- scale SCPP using reverse fan model was validated based on Manzanares constructed power plant. For reducing the computational cost, nine different small scale 3-D models defined respect to prior experimental study under Tehran-Iran meteorological condition. The first and second laws of thermodynamics were studied, and an optimization was done for representing the best functional diameter, height and turbine pressure jump by the means of improvability rate and clarified optimization factor. Results show that the optimal state of chimney can be defined in relation to a certain condition; hence, the geometrical parameters under investigation should simultaneously be evaluated in system designs. Furthermore, applying the slip condition on walls to simulate hydrophobic surfaces was attempted to reduce shear stress on walls which led to roughly 11% performance enhancement. Consequently, Discrete Ordinates (DO) radiation model could be trusted based on its more factual outcomes with referred to prior experimental results of Heat flux method.

Anatomical Basis for Lip Reconstruction: The Role of the Modiolus.

The aim of this study was to establish the anatomic basis for functional upper and lower lip reconstruction with locoregional flaps. This article is an anatomic fresh cadaver study. For lower lip reconstruction, the modified Bernard-Webster and Karapandzic flaps preserve the modiolus, buccinator, zygomaticus major muscle, and buccal branches of the facial nerve. The Bernard-Webster flap allowed for a larger oral aperture despite a larger defect, but required transection of the lower lip depressors and orbicularis oris. For upper lip reconstruction, the reverse fan flap preserves the modiolus and its muscle attachments. The reverse Karapandzic flap required transection of the lower lip depressors, buccinator, and the zygomaticus major. Locoregional flaps remain the workhorse for lip reconstruction. This study provides the anatomic basis for the modiolus and its muscular attachments that permit techniques such as the Bernard-Webster flap and the Karapanzic flap to achieve functional lip reconstruction with innervated and denervated tissue.

Performance Analysis of Elliptic-Profile Airfoil Cascade for Designing Reversible Axial Flow Fans

Because reversible fans must be able to provide similar performance in either rotation direction, they need to have completely symmetrical blades. In the present study, an elliptic profile with its maximum thickness of 8% chord length at the middle of the chord line is studied. For verification, the NACA 0012 airfoil was once analyzed two-dimensionally in the isolated formation and once in cascade formation with 0.55 and 0.83 solidities, and the obtained results were compared with numerical and experimental results. Three well-known Reynolds-averaged Navier–Stokes turbulence models including Spalart–Allmaras, realizable , and shear-stress transport were used to find the suitable turbulence method. After making sure of the accuracy of the modeling procedure, lift and drag coefficients were calculated for the elliptic profile for a wide range of velocities, solidities, and angles of attack. A number of issues not previously addressed in detail by previous works, such as the important stall phenomenon at low solidities, were solved, and the obtained aerodynamic coefficients were corrected by considering the occurrence of the stall. Finally, the method of using the colored cube for the design procedure of these blades was also proposed to reduce the gap between the design and the desired outcome.

Scale model test for the acoustical design of Arts Center Incheon concert hall and acoustic measurement after construction

The Arts Center Incheon (ACI) concert hall was designed to have 1,760 seats, the volume of 18,000 m3 and the reverberation time of 2.1s with seats fully occupied. To achieve the auditory and visual intimacy, the concert hall had a reverse fan shape with a combination of vineyard and balcony. Various scale models and computer simulation were used to determine the acoustical design including the volume of hall, locations of walls and shapes of finishing materials. Three types of sound diffusers were applied according to wall locations. Appropriate protrusion heights were determined based on sound diffusion targets by each part such as the stage and the sides and back of the auditorium. During the execution design stage, a 1:10 scale model of this concert hall was fabricated to measure acoustic characteristics. An auralization experiment was conducted to assess psycho-acoustic responses to the diffusion design. The acoustic measurements after construction matched the design objectives.

Design and performance of low-pressure reversible axial fan with doubly curved profiles of blades

Reversible axial fans are used to achieve air (gas) flow in both directions. An axial fan only has an impeller that can achieve the reverse flow by changing the direction of the impeller rotation. In order to obtain the same performance for both directions, the profiles of the impeller blades should be completely symmetrical, in the shape of the ellipse. This paper presents the design and performance for a reversible axial fan with blades that have a slightly doubly curved profile. The shape of the profile, whose design is shown here, was previously obtained on the basis of the numerical simulation in the profile cascade. For the experimental tests, an axial reversible fan model with double curved profiles of the blades was made. Fan performance was obtained by testing a fan for three blade positions on a standard test installation. The performance curves were compared with the performance of the reversible axial fan blades with straight profiles. The fan with doubly curved profile blades achieved a greater increase in pressure and flow than the fan with straight profiles, with approximately the same efficiency. Low pressure axial reversible fans are used in drying chambers for wood and such a design can achieve higher drying efficiency.

Analysis of fluid flow and heat transfer on a solar updraft tower power plant coupled with a wind turbine using computational fluid dynamics

The objective of this study was to develop a more realistic numerical model for solar updraft tower power plants. To accomplish this, a three-dimensional (3-D) simulation for the geometric parameters of the Manzanares prototype coupled with a real turbine was carried out using computational fluid dynamics (CFD). The RNG k-ε turbulence closure, discrete ordinates (DO) non-grey radiation model and solar ray-tracing algorithm were employed. In addition, a comparatively simpler simulation using a reverse fan model to implement pressure drop across the turbine was conducted. The pressure, velocity and temperature distributions through the system were considered, and the results of the simplified model were compared to those of a system coupled with a real turbine, to assess the proper pressure jump value to be assigned in the reverse fan model. Results showed that, compared to the real turbine model pressure drop, the reverse fan model with a 43.7% lower assigned pressure jump predicted the same performance. The numerical model developed in this study provides a highly accurate and reliable approach for predicting the performance of a solar updraft tower power plant, taking into account all the main phenomena of the system.

Ducted Fan Flying Object with Normal and Reverse Ducted Fan Units

Recently, UAV such as single / multi rotor helicopter is used in fields of aerial photography and aerial investigation. But rotor blades of UAV thrust device are not covered, and the thrust is generated by high rotational speed. Thus UAV has a high risk of damage. In previous study, we presented inverted pendulum type flying object (DFO1 and DFO2) using ducted fans instead of rotor blades. P I- D control was employed for roll, pitch and yaw attitude control. We succeeded to achieve stable hovering by 3-axes (roll, pitch and yaw axis) attitude control. However, small oscillation and small steady state error appears. These oscillation and steady state error can be attributed to Gyro moment of ducted fan tilting motion. In this study, we report a newly developed DFO3 equipped with normal and reverse rotation ducted fan to cancel Gyro moment effect. We succeeded to achieve stable take off / landing and hovering.

The Conceptual Design of High Pressure Reversible Axial Tunnel Ventilation Fans

Tunnel ventilation fans, classically, must have the ability to both supply and extract air from a tunnel system, with the operator's choice dependent on the tunnel ventilation system's operating mode most appropriate at any given point in time. Consequently, tunnel ventilation fans must incorporate a reversible aerodynamic design which limits the maximum fan pressure rise. This paper presents three high pressure reversible fan concepts. These comprise a two-stage counter rotating fan, a single-stage high speed fan, and a two-stage fan with a single motor and impeller on each end of the motor shaft. The authors consider the relative merits of each concept. The third concept offers the most compact fan, transform, silencer, and damper package size. The authors discuss the mechanical design challenges that occur with a two-stage fan with a single motor and impeller on each end of the motor shaft. They present and consider a selected motor bearing arrangement and casing design for maintainability. Finally, the authors present both prototype fan and full-scale package aerodynamic and acoustic performance, before discussing the challenges presented by high temperature certification in accordance with the requirements of EN 12101-3: 2012.

Efficiency enhancement mechanisms of a new type of full reversible axial-flow fan

A row of airfoil-shaped support struts has been proposed to be installed on both sides of the rotor, so as to remedy the configuration asymmetry of a conventional fully reversible fan in its forward and reverse flow modes. In the forward mode, the upstream support struts act as inlet guide vanes (GVs), and the downstream ones as outlet GVs; whereas in the reverse mode, the roles played by the two support-strut rows switch over. Among the five representative airfoils, symmetric airfoil NACA0012-64 is found to be the most suitable airfoil used as the section of the two rows of the airfoil-shaped support struts. Detailed numerical investigations on four such new fans, whose design points cover a wide range, reveal that the installation of the two rows of blades improves the performance of the new type fan, when compared with the one-rotor fully reversible axial-flow fan without such support-struts. The upstream blade row has little influence on the direction of incoming flow and causes little aerodynamic losses. By contrast, the downstream blade row plays an important role in efficiency improvements: (1) the downstream blade row, which acts as outlet GVs, significantly reduces the rotor-exit tangential velocity and recovers part of the swirl energy in the flow downstream of the rotor, although sometimes the aerodynamic losses caused by such support-strut-like outlet GVs may be high at a large incidence; (2) due to the obviously reduced tangential components of the flow velocities downstream of the outlet GV, the air travels a much shorter distance toward the exit of the annular diffuser, compared with that in the fan without outlet GVs. This leads to a markedly reduced friction loss. In addition, the larger the equivalent divergence angle of the annular diffuser is, the more effectively does the installation of the two rows of the support-strut-like blade improve the performance of the new type fans.

Numerical Investigation on a New Type of Fully Reversible Axial Fan with Two Blade Rows on Both Sides of the Rotor

The fully reversible axial flow fans,which can rotate reversibly to ventilate in the opposite direction with the same performance curves,are widely demanded in subways,tunnels,underground warehouses and many other fields. A new configuration method,which can obviously improve the efficiency of reversible axial flow fans,is proposed to meet this special requirement. The new approach is to install two rows of blade with reverse symmetrical airfoil section at stagger angle of 90° on both sides of the rotor of reversible axial fans. The same computational domain is used for reversible flow fans with and without the two-row guide vanes,and the detailed numerical studies reveal that the upstream blade row has little influence on the direction of the incoming flow while the downstream blade row working as a straightener reduces the circumferential velocity of the rotor-exit air remarkably and makes the outlet air flow in nearly axial direction in the diffuser. This leads to a greatly decreased friction loss,and the greater the rate of divergence in the diffuser is,the more obvious the effect will be. In addition,part of the swirl dynamic energy of the rotor-exit air is recovered and changed into static pressure rise. The above two mechanisms contribute to the evident increase in both total pressure rise and efficiency of the new type of reversible axial fans with additional blade rows than those without any stators. Furthermore,the installation of the blade rows on both sides of the fully reversible axial fan guarantees a symmetric configuration and consequently guarantees the fully reversible performance also.

A New Blade Profile for Bidirectional Flow Properly Applicable to a Two-stage Jet Fan

Abstract A reversible axial flow fan called jet fan has been widely used for longitudinal ventilation in road tunnels to secure a safe and comfortable environment cost-effectively. As shifting the flow direction is usually made by only switching the rotational direction of an electric motor due to heavy duty, rotor blades having identical aerodynamic performance for bidirectional flow should be necessary. However, such aerodynamically desirable blades haven’t been developed sufficiently, since most of the related studies have been done from the viewpoint of unidirectional flow. In the present paper, we demonstrate a method to profile the blade section suitable for bidirectional flow, which is validated by studying the aerodynamic performances of rotor blades of a two-stage jet fan experimentally and numerically. Keywords : Blade profile, Wall curvature, Bidirectional flow, Jet fan, Aerodynamic performance, Turbulent flow analysis 1. Introduction A reversible axial flow fan called jet fan has been widely used for longitudinal ventilation in road tunnels to secure a safe and comfortable environment cost-effectively. Various researches and developments of jet fan have been made, and it is said that the fan has the satisfactory performance for the present needs. However, if the future need is concerned, it is still necessary to develop a jet fan having higher aerodynamic performance, for efficient usage of energy in every engineering system is vital in the low carbon society. From the aerodynamic view, a cambered airfoil is regarded as favorable for the rotor (or impeller) blade like a unidirectional axial fan and the variable pitch mechanism is used to set the blade oppositely if the flow direction should be reversed in case of emergency. But, owing to very heavy duty as a safety measure, a reversible fan without this kind of mechanism has been adopted in actual cases. That is, such a method to drive the rotor in the reverse direction is used for switching the flow direction. As the fan should provide almost the same performance in both flow directions, those symmetrical blades without camber are used in the case of single stage fan rotor. The other structure is a 2-stage jet fan where two rotors are assembled to both sides of motor shaft. If higher speed jet from the fan is expected, the latter will be preferable. Though there are vast amounts of studies treating airfoil sections (e.g.: Abbot and von Doenhoff [1]), most of them have been done from the viewpoint of unidirectional flow. Thus, aerodynamically desirable airfoil sections for bidirectional flow are still regarded as unresolved. As one of the typical sections is a symmetrical circular-arc airfoil, this section has been actually used for the rotor blade of a jet fan (Nishioka, et al.[2]). Generally, airflow easily separates from the leading edge at a certain angle of attack for a blade having the sharp edge. However, it is known that aerodynamic performance of the blade doesn’t deteriorate, once the separating flow reattaches the blade surface downstream. This knowledge indicates that the key to secure the performance is attributed to the stable reattachment of the separating flow on the surface. From this view, the wall surface consisting of concave and convex curves shown in Fig. 1 is taken up for consideration. Though it will be nice if this profile is usable for the blade in bidirectional flow, stable reattachment of separating flow shown in Fig. 1 is really accomplished in actual flow cases. Thus, we have investigated the capability of the proposed blade profile for bidirectional flow by using a two-stage jet fan experimentally and

Experimental study of regenerative desiccant integrated solar dryer with and without reflective mirror

An indirect forced convection with desiccant integrated solar dryer has been built and tested. The main parts are: a flat plate solar air collector, a drying chamber, desiccant bed and a centrifugal blower. The system is operated in two modes, sunshine hours and off sunshine hours. During sun shine hours the hot air from the flat plate collector is forced to the drying chamber for drying the product and simultaneously the desiccant bed receives solar radiation directly and through the reflected mirror. In the off sunshine hours, the dryer is operated by circulating the air inside the drying chamber through the desiccant bed by a reversible fan. The dryer is used to dry 20 kg of green peas and pineapple slices. Drying experiments were conducted with and without the integration of desiccant unit. The effect of reflective mirror on the drying potential of desiccant unit was also investigated. With the inclusion of reflective mirror, the drying potential of the desiccant material is increased by 20% and the drying time is reduced. The drying efficiency of the system varies between 43% and 55% and the pick-up efficiency varies between 20% and 60%, respectively. Approximately in all the drying experiments 60% of moisture is removed by air heated using solar energy and the remainder by the desiccant. The inclusion of reflective mirror on the desiccant bed makes faster regeneration of the desiccant material.