Section 1: Product Overview

The Mixed Flow Inline Duct Fan occupies a unique and strategically important position in the landscape of industrial and Commercial Ventilation fan technology. In the conventional fan performance map, axial fans occupy the high-flow, low-pressure region and centrifugal fans occupy the lower-flow, high-pressure region, with a significant performance gap between the two types where neither achieves optimal efficiency. The mixed flow fan design was developed specifically to fill this gap, delivering a performance combination — high flow rate at medium-to-high static pressure — that neither axial nor centrifugal designs can achieve efficiently at the same equipment size.

This performance positioning translates directly into practical engineering advantages for the building systems designer and HVAC contractor. Many real building ventilation, pressurization, and smoke exhaust duct system designs require fans that can deliver meaningful static pressure against duct system resistance while also moving substantial air volumes — system parameters that fall precisely in the range where mixed flow technology outperforms both alternatives. Using a centrifugal fan for such applications would require a physically larger unit than necessary. Using an axial fan would result in unacceptably high pressure losses and potential stall conditions. The Mixed Flow Inline Duct Fan provides the correct performance at a smaller physical size than either alternative.

The compact inline installation format further advantages this product in building applications. The fan connects directly between sections of round ductwork at both inlet and outlet flanges, requiring no transition between circular duct and non-circular fan housing as is required with centrifugal fan installations. This inline installation simplicity reduces ductwork fitting requirements, lowers installation labor, and minimizes the additional pressure losses that occur at duct-to-fan transitions in centrifugal fan installations.

Dezhou Pengkai Air Conditioning Equipment Co., Ltd. is a comprehensive HVAC manufacturer based in Dezhou, Shandong Province, integrating research and development, production, sales, installation, and after-sales service. We supply mixed flow duct fan products to HVAC engineering contractors, building developers, mechanical and electrical consultants, and equipment distributors across Southeast Asia and global markets.

Section 2: Product Structure and Key Components

Fan Casing — Cylindrical or Drum Configuration The fan housing is a cylindrical or drum-shaped metal casing fabricated from cold-rolled steel with corrosion-resistant surface treatment as the standard configuration. The cylindrical form factor allows direct inline connection to round ductwork at both the inlet and outlet faces using standard flanged connections, eliminating the transition pieces required when connecting rectangular centrifugal fan housings to round duct systems. The casing exterior profile is smooth and compact, occupying minimum space in mechanical shaft, plant room, and ceiling void installation environments.

Conical Hub and Twisted Aerofoil Blade Impeller The impeller is the defining structural element of the Mixed Flow Inline Duct Fan, embodying the meridional acceleration design principle in its geometry. The impeller uses a conical hub form rather than the flat disc hub of an axial fan, with twisted aerofoil-section blades attached to the hub at angles and curvatures that simultaneously generate axial thrust and centrifugal acceleration on the airstream. As air moves from the impeller inlet at the hub centerline to the blade tips at the casing wall, it is accelerated both axially — as in an axial fan — and radially outward — as in a centrifugal fan — by the combined effect of blade lift and centrifugal force. This dual acceleration mechanism is what produces the characteristic mixed flow performance combination of high volume and medium-to-high pressure. Each impeller undergoes G2.5 grade dynamic balancing — a precision balance specification that ensures smooth vibration-free operation across the full operating speed range.

Fixed Guide Vanes Downstream of the impeller, fixed guide vanes are installed within the casing to recover and redirect the rotational component of the airstream imparted by the impeller blades. Without guide vane correction, the rotational velocity component would represent wasted kinetic energy that reduces overall fan efficiency. The guide vanes convert this rotational velocity energy into additional static pressure, improving fan efficiency and reducing the swirl-related noise that would otherwise be generated as the rotating airstream meets the downstream ductwork.

Direct-Drive Motor The motor is co-axially mounted within the airflow stream, with the impeller mounted directly on the motor shaft. This direct-drive configuration eliminates all transmission components, achieving maximum mechanical efficiency between electrical input and fan shaft power. The motor is continuously cooled by the airflow passing over its external surface, maintaining winding temperatures within the rated insulation class limits throughout normal operation. Motor options include standard single-speed Y-series motors, dual-speed motors for two-speed operation, variable frequency compatible motors for stepless speed control, and explosion-proof motors for hazardous area applications.

Inlet Bell Mouth An inlet bell-mouth or streamlined inlet cone is fitted at the impeller inlet to guide incoming airflow smoothly onto the impeller face, reducing inlet turbulence and the associated efficiency and noise penalties that occur with abrupt-entry fan configurations. This component is particularly important for the Mixed Flow Inline Duct Fan because the meridional acceleration design is sensitive to inlet flow quality — smooth, uniform inlet flow allows the impeller blade geometry to perform as designed across the full blade span.

External Terminal Box All electrical connections are brought out to an external terminal box mounted on the casing exterior, accessible without disassembling the fan or disconnecting ductwork. This design feature allows electrical maintenance, insulation testing, and wiring modifications to be carried out conveniently without disturbing the installed fan or connected duct system.

Section 3: Technical Specifications

Representative Performance Data:

Complete performance data for all machine numbers and speed options available upon request. Please contact our sales team with your system airflow and static pressure requirements for model selection guidance.

Section 4: The Meridional Acceleration Principle — Engineering Basis of Mixed Flow Performance

The meridional acceleration design principle that underpins the Mixed Flow Inline Duct Fan represents a specific application of three-dimensional flow theory to fan impeller engineering that was developed to overcome the fundamental limitations of two-dimensional blade design approaches used in conventional axial and centrifugal fans.

Limitations of Conventional Two-Dimensional Design In a conventional axial fan impeller, blade profiles are designed based on two-dimensional flow theory applied at discrete radial stations from hub to tip. While this approach works reasonably well for low-pressure axial designs, it becomes increasingly inaccurate as blade loading increases, because the actual three-dimensional flow field in the impeller departs significantly from the two-dimensional assumption. The result is flow separation on blade surfaces at higher blade loading conditions, limiting the pressure that can be generated before efficiency deteriorates sharply.

Meridional Acceleration — Three-Dimensional Flow Control The meridional acceleration approach designs the impeller flow path as a complete three-dimensional system, specifying the velocity distribution along the meridional surface — the conical surface traced by the flow path from hub inlet to blade tip outlet — as the primary design variable. By controlling the velocity gradient along this meridional surface, the designer can ensure that the flow remains attached to the blade surfaces throughout the impeller passage, even at the higher blade loading levels required to generate medium-to-high static pressure alongside high volume flow.

Practical Performance Result The practical result of applying this three-dimensional design approach is a fan impeller that achieves simultaneously higher pressure and higher airflow than a conventionally designed impeller of the same dimensions, while maintaining the smooth, attached flow field that produces high efficiency and low noise. The High Pressure Axial Ventilation Fan achieves full-pressure efficiency in the operating range that justifies its description as genuinely high-efficiency — not merely adequate efficiency — at the mixed flow performance point.

G2.5 Balance Grade Contribution The G2.5 dynamic balance grade applied to each impeller is significantly more precise than the balance grades typically applied to standard industrial fan impellers. At the higher rotational speeds used in smaller machine numbers of the Mixed Flow Inline Duct Fan, even small residual imbalance generates significant vibration forces. G2.5 balancing reduces residual imbalance to the level where bearing loads from imbalance are negligible relative to aerodynamic loads, resulting in smooth operation, long bearing life, and consistently low vibration noise.

Section 5: How It Works — Operating Principle

Inlet Flow Conditioning Airflow approaching the fan inlet is guided by the bell-mouth inlet cone onto the impeller face with progressively accelerating velocity and minimal turbulence. This smooth inlet conditioning is essential for the impeller blade geometry to perform as designed — turbulent or non-uniform inlet flow reduces both the efficiency and the noise performance of the impeller.

Meridional Acceleration Through the Impeller As air enters the rotating impeller at the hub, the conical hub geometry and twisted blade angles direct the airstream along the meridional surface from the hub inlet radius to the blade tip outlet radius. Throughout this passage, the airstream is simultaneously accelerated axially by blade lift forces and accelerated radially by the centrifugal effect of the conical hub rotation. The controlled velocity gradient along the meridional surface maintains attached flow on blade surfaces throughout this passage, producing high pressure rise across the impeller at high flow rates.

Guide Vane Pressure Recovery Air exiting the impeller carries significant rotational velocity from the impeller blade forces. The fixed guide vanes downstream of the impeller redirect this rotational velocity component into the axial direction, recovering the associated kinetic energy as additional static pressure. This pressure recovery step is what allows the Low Noise Mixed Flow Blower to achieve higher total-to-static pressure ratios than would be possible from the impeller alone.

Discharge into Ductwork The conditioned, high-static-pressure airstream exits the fan through the outlet flange directly into the connected downstream ductwork, with uniform velocity distribution across the duct cross-section. This velocity uniformity reduces losses in downstream duct fittings and contributes to the overall duct system efficiency.

Section 6: Manufacturing Process and Quality Control

Dezhou Pengkai Air Conditioning Equipment Co., Ltd. applies comprehensive quality management to Mixed Flow Inline Duct Fan production:

Material Incoming Inspection Steel sheet, aluminum alloy materials for impeller components, motor units, and guide vane components are inspected against specification on receipt. Variable frequency and explosion-proof motor units receive additional function testing before assembly. Material certification records are retained.

Impeller Blade Fabrication Impeller blades are formed using hydraulic pressing processes that produce the specified twisted aerofoil cross-section with consistent geometry across production runs. The three-dimensional blade geometry of the mixed flow impeller requires higher-precision forming tooling than conventional flat or simple-curved blade designs. Blade profile dimensional verification is performed after pressing.

Hub and Blade Assembly Blades are welded to the conical hub at the specified angular positions. Weld quality at blade-hub junctions is verified by visual inspection. After full assembly, each impeller undergoes both transverse and longitudinal dynamic balance measurement and correction to achieve G2.5 balance grade.

Casing Fabrication The cylindrical casing is formed, welded, and flange-fitted to dimensional tolerances that ensure correct fit with standard ductwork flange dimensions. Internal surfaces are finished to minimize roughness that would add unnecessary friction losses to the airflow.

Guide Vane Installation Guide vanes are installed within the downstream section of the casing at the specified angular positions relative to the impeller blade exit angle. Vane position accuracy is verified after installation.

Motor Installation and Electrical Testing Motors are installed, connected to the external terminal box, and tested for correct insulation resistance, rated current draw, and for dual-speed or variable frequency models, correct control function across all operating modes.

Final Running Test Every completed Low Noise Mixed Flow Blower undergoes a full-speed running test verifying smooth operation, correct current draw, acceptable vibration levels, and for dual-speed models, correct speed switching function.

Section 7: Product Features and Advantages

Performance Between Axial and Centrifugal — Neither Compromise Needed The meridional acceleration design delivers genuine high-flow, medium-to-high pressure performance that sits between the capability ranges of axial and centrifugal fans, covering the system performance requirements where both alternatives would require oversizing, undersizing, or efficiency compromise.

Compact Inline Installation The cylindrical inline housing connects directly to round ductwork at both ends, requiring no housing-to-duct transition pieces and occupying minimum space in mechanical shafts, plant rooms, and ceiling voids. Installation footprint is smaller than a centrifugal fan of equivalent airflow by approximately 30 percent.

G2.5 Precision Balancing for Low Vibration Industry-leading G2.5 dynamic balance grade on every impeller minimizes vibration transmission to the building structure and connected ductwork, reducing noise from structure-borne vibration and extending motor bearing service life.

Four Motor Options for Any Application Single-speed, dual-speed, variable frequency, and explosion-proof motor options within the same product platform allow the Mixed Flow Inline Duct Fan to be specified for standard ventilation, two-speed comfort ventilation control, energy-saving variable airflow systems, and classified hazardous area applications without requiring different product lines.

Multiple Material Options Standard carbon steel, glass fiber reinforced plastic, and stainless steel housing and impeller options accommodate corrosive exhaust applications, coastal building environments, food and pharmaceutical production facility ventilation, and other applications where standard steel construction would be susceptible to premature corrosion.

Rooftop Version Available The rooftop installation version adds rain cap and weatherproof sealing to allow the High Pressure Axial Ventilation Fan to be installed as a roof exhaust unit for building exhaust systems, expanding the installation options beyond inline duct applications.

External Terminal Box for Easy Maintenance All electrical connections are accessible at the external terminal box without requiring duct disconnection or fan disassembly, significantly simplifying routine electrical inspection and maintenance access.

Section 8: Application Scenarios

Building HVAC Fresh Air and Supply Air Systems Fresh air handling unit supply duct systems, air conditioning supply air distribution systems, and central mechanical ventilation supply systems in commercial office buildings, hotels, shopping centers, and residential towers require fans that can overcome the static pressure of ductwork, filters, and terminal units while delivering the required supply air volumes. The Mixed Flow Inline Duct Fan performance range matches these systems precisely at smaller physical size than centrifugal alternatives.

Underground Car Park Ventilation and Pressurization Underground car park jet fan systems and main supply and extract duct systems require fans capable of delivering meaningful static pressure against duct system resistance while moving large air volumes for carbon monoxide dilution. The High Pressure Axial Ventilation Fan serves both the supply pressurization and exhaust extract functions in underground car park ventilation systems.

Stairwell and Corridor Pressurization Systems Building pressurization systems for stairwells, lobby ante-rooms, and corridor smoke prevention require fans delivering moderate-to-high static pressure at controlled airflow rates. The mixed flow performance range matches pressurization system requirements with smaller equipment than centrifugal alternatives.

Industrial Process Exhaust and Supply Industrial production facility exhaust systems, process air supply systems, paint booth air supply and exhaust, and cleanroom pressurization systems require fans capable of handling medium-to-high system resistance while maintaining required airflow rates. The Mixed Flow Inline Duct Fan serves these industrial applications in standard carbon steel, corrosion-resistant FRP, and stainless steel configurations depending on the exhaust medium characteristics.

Kitchen and Catering Exhaust Systems Commercial kitchen exhaust systems with multiple hoods connected to a common exhaust duct system require fans capable of overcoming the combined resistance of grease filters, duct runs, and roof discharge points. The Low Noise Mixed Flow Blower in stainless steel configuration is the appropriate specification for kitchen exhaust applications where grease and heat resistance are required.

Hospital and Laboratory Ventilation Hospital ward ventilation systems, laboratory fume exhaust systems, and pharmaceutical production facility ventilation require precise airflow control and high reliability. Variable frequency motor configurations of the Mixed Flow Inline Duct Fan allow precise airflow adjustment to maintain the specified air change rates and pressure relationships between clean and dirty areas in these sensitive environments.

Agricultural and Greenhouse Ventilation Large greenhouse growing facilities, poultry house ventilation systems, and mushroom cultivation facility climate control systems require high-volume ventilation fans with sufficient pressure to overcome duct system resistance in larger facilities. The wide machine number range of the High Pressure Axial Ventilation Fan covers the ventilation requirements of medium to large agricultural facility buildings.

Section 9: Customer Application Feedback

Our mixed flow inline duct fan products have been supplied to commercial, industrial, and institutional projects across Southeast Asia and international markets:

"We specified Pengkai mixed flow fans for the supply air duct systems of a large commercial office tower. The compact inline installation format simplified our mechanical shaft layouts compared to the centrifugal fans we had been using previously. Commissioning airflow measurements were within specification, and the G2.5 balance quality was evident from the low vibration levels during running tests." — Mechanical and Electrical Consultant, Southeast Asia

"For an underground car park pressurization and extract ventilation project, the Pengkai High Pressure Axial Ventilation Fan delivered the required static pressure for our duct system resistance calculations. The variable frequency motor option allowed us to tune the airflow precisely during commissioning. Documentation and export packaging were both correctly prepared for sea freight." — HVAC Engineering Contractor, Regional Project

"We have used the Pengkai Low Noise Mixed Flow Blower in FRP configuration for kitchen exhaust applications in multiple hotel projects. The stainless steel and FRP options handle the grease and heat conditions without the corrosion issues we experienced with standard steel units. After-sales support for technical queries is consistently responsive." — Building Services Engineering Company

Section 10: Installation Guidelines

Pre-Installation Checks Verify that the machine number, speed configuration, motor type, housing material, and flange dimensions match the project design documents. Inspect the casing, impeller, guide vanes, motor, and terminal box for transport damage. Rotate the impeller manually to confirm it turns freely without contact with the casing or guide vanes.

Mounting and Orientation The Mixed Flow Inline Duct Fan can be installed horizontally or vertically. For horizontal installation, the unit can be floor-mounted on anti-vibration mounts or suspended from structural supports using anti-vibration hangers. For vertical installation, verify that the motor mounting configuration and bearing specification are appropriate for the vertical shaft orientation. Maintain minimum 300mm clearance around the unit for maintenance access to the terminal box and motor.

Ductwork Connection Connect inlet and outlet ductwork to the unit flanges using flexible connectors — fire-rated fabric connectors for smoke exhaust applications, standard fabric connectors for ventilation applications. Flexible connectors prevent vibration transmission into the duct system and allow for minor positional adjustment. Ductwork must be independently supported and must not transfer weight or bending stress to the unit flanges.

Electrical Connection Connection must be performed by a qualified electrician. Access the terminal box on the casing exterior for all wiring connections. Verify supply voltage, phase configuration, and motor nameplate before connection. For three-phase motors, verify correct rotation direction with a brief test start before completing ductwork connection. For variable frequency drives, configure drive parameters per the motor nameplate before initial start.

Rotation Direction Verification The fan must rotate in the direction indicated by the arrow on the casing. Reverse rotation produces significantly reduced airflow and pressure and potential motor overload — do not operate continuously in reverse rotation.

Commissioning After installation, perform a running test monitoring for abnormal noise, vibration, or current draw. For dual-speed models, test both speed settings. Measure delivered airflow at commissioning and verify against system design requirements.

Section 11: Maintenance Schedule

Monthly Inspection Listen for changes in operating noise or vibration that may indicate developing bearing wear, impeller imbalance from dust accumulation, or guide vane damage. Verify terminal box cover is secure and sealing correctly.

Quarterly Cleaning Clean impeller blades and casing interior of accumulated dust using soft brush or low-pressure compressed air with power isolated. For kitchen exhaust and process exhaust applications, grease and contamination removal from impeller blades and guide vanes is recommended quarterly or more frequently as conditions require.

Annual Motor Bearing Lubrication For motors with grease nipples, apply the specified grease type and quantity per the motor manufacturer's recommendation. Sealed bearing motors require no lubrication service. Check terminal box connections for tightness. Inspect impeller blades for surface corrosion, erosion, or mechanical damage.

Section 12: Packaging, Shipping, and Lead Time

Packaging Each Mixed Flow Inline Duct Fan unit is packaged in protective carton packaging for smaller machine numbers, and wooden crate packaging for larger machine numbers, with foam padding and structural blocking appropriate to unit size and weight. Export-grade packaging is standard for all units shipped to international destinations.

Minimum Order Quantity We accept both single-unit project orders and multi-unit supply contracts. Please contact our sales team to discuss specific machine numbers, configurations, and project requirements.

Lead Time Standard machine numbers in single-speed carbon steel configurations are available with short lead times from production scheduling. FRP housing, stainless steel, dual-speed, variable frequency, and explosion-proof configurations are produced to order with lead times confirmed at order placement.

Shipping We ship from Dezhou, Shandong Province. Sea freight, air freight, and international express courier options are available. FCL sea freight is recommended for multi-unit project orders. We work with established freight forwarding partners serving Southeast Asia, the Middle East, and global destinations.

Sample Policy Product samples for pre-order technical evaluation are available by arrangement. Sample costs and shipping fees are agreed prior to dispatch.

Payment Terms We support T/T bank transfer and other payment arrangements as mutually agreed. Please contact our sales team for terms appropriate to your order value and procurement process.

Section 13: Certifications and Quality Assurance

Dezhou Pengkai Air Conditioning Equipment Co., Ltd. manufactures mixed flow inline duct fan products in compliance with applicable national standards for industrial and commercial ventilation fans. Production quality management covers incoming material inspection, three-dimensional blade profile verification, G2.5 dynamic balance testing of all impeller assemblies, guide vane installation verification, and finished product running tests before release. Product quality documentation is maintained for each production batch. Third-party pre-shipment inspection by buyer-nominated agencies is welcomed for project-specific orders.