The Pax Group - PaxFan

PaxFan licenses the air movement technologies of PAX Scientific, Inc. to companies that utilize, manufacture, or sell fans for use in the appliance, refrigeration, process and HVAC industries.

Fans made using PAX Scientific technology are quieter and use less energy per flow unit than competitive products. PAX fans produce these benefits by reducing the amount of turbulence in the air before and after contact with the fan. The curved blades generate a laminar vortical flow on their downstream side, moving air centripetally and with markedly reduced turbulence.

A PaxFan license enables the licensee to use PAX design geometries for rotors and blades, and provides know-how for developing and manufacturing such products, either as stand alone products or incorporated into moving air systems.

Air movement is a big enterprise. In the United States alone, companies directly involved with airflow and air conditioning are nine times larger than the movie business and sixteen times bigger than the recording industry, yet they are rarely discussed and little known. For buildings and industry, air movement is as critical as breathing. Without air that is heated, cooled, or cleaned, commerce grinds to a halt. Fans propel airflows used by heat transfer equipment such as air conditioners, heat pumps, heat exchangers, dehumidifiers, compressors, chillers, filters, extractors, and kilns. Fans are central to refrigeration equipment such as soda machines, walk-in freezers, residential refrigerators and freezers, and refrigerated display cases. A broad range of appliances also contain fans, including microwaves, oven exhaust hoods, clothes dryers, dehumidifiers, vacuum cleaners, hair dryers, and hand dryers.

Fans have broad industrial and commercial uses. They are used to introduce air or other gases into process reactors for the chemical and pharmaceutical industries; to assist combustion in furnaces; to dry agricultural and manufactured products; to ventilate and filter the air for workers in factories; for pneumatic conveyances; for inflating domes in stadia (the Carrier Dome fans pump 1,000,000 cubic feet per minute); in air handling units for cleanrooms used in the pharmaceutical, biotechnology, hospital and micro-electronics industries; in all emergency air extraction systems; for roof and wall-mounted power ventilators; in commercial cooking exhaust fans; heat recovery ventilators; for materials handling; in gravity ventilators; in spot-cooling processes; for dust collection and many more. Fans power the lungs of industry. They account for 14 percent of industrial motor system energy use.

PAX fans have three principle benefits. In many applications, they increase the amount of airflow by 15-30 percent or more with no increase in power while reducing ambient sound. The main challenges facing the air movement industry are efficiency and noise. PAX technology addresses both while simultaneously reducing manufacturing and operating costs. The savings per fan unit in first costs and one-year operating expenses can range from one to one hundred dollars.

History of Air Movement
Fans

The human endeavor to control air currents has a long history. While the first fans were most likely pieces of rigid material that people picked up to cool themselves on hot days, subsequent air cooling came to take on various cultural roles. Slaves fanned Egyptian pharaohs with huge lotus leaves, while peacock feathers adorned the fans used by the Greeks and Romans. Some of the most ancient hand fans were those of the Chinese, known to date back to 3000 B.C. More than human comfort however impelled invention; ventilation in mines became particularly necessary. Fires were long used to create drafts in shafts, with the layout of mines in early Greece cognizant of the need for the circulation of air. Pliny (AD 23-79), describes how slaves used palm fronds to waft air along tunnels.

Ceremonial and ornamental functions developed alongside practical purposes. Folding fans are thought to have been invented by the Japanese in the 700’s and may have been modeled after the way a bat folds its wings. Fans became especially popular in the Ming Dynasty (1368-1644) where they were decorated by some of the most talented Asian painters and were carried by all social classes, including warriors. Medieval Europe saw decorated fans shoo flies in church services, crafted of parchment with gold and silver and ivory handles. Hand fans became widespread in Europe after the 1500’s, when Portuguese traders brought large quantities of hand fans over from Asia.

The earliest reference to the engineering of a mechanical fan appears in China circa 180 AD. Ting Huan, a famous inventor in the courts of the later Han dynasty, created a huge rotary fan for cooling. “[He] made a fan consisting of seven wheels, each ten feet in diameter. They were all connected with one another, and set in motion by [the power of] one man. The whole hall became so cool that people would even begin to shiver...”
Whether rotary fans were first created for air cooling or winnowing grain is unclear. Rotary blowers appear to have been used in the Han period for separating grain from its chaff after harvest. Winnowing was traditionally done with baskets, throwing the grain in the air and letting the breezes blow the chaff away from the grain. This process was facilitated with the production of both large open crank-operated fans, as well as enclosed fans in cylindrical casings that directed air over a grain chute. The fan, vannus in Latin, originally meant a specially shaped container, usually a basket, used in the agitation in draft air to remove the chaff. Only later did the word come to mean a vane that created a draught.

The earliest rotary blowers in Europe were used for mine ventilation in the mid-16th century. A number of the prints that show ventilating methods include diverting surface winds into the mouths of shafts, wooden centrifugal fans powered by men and horses, and bellows for auxiliary ventilation. A striking feature of the Chinese rotary fans is that the air intake was central, so they must be considered the ancestors of centrifugal compressors.
The principles of fan-powered ventilation were not used widely in buildings until the 18th century. In 1734 the Frenchman Desagulier designed a paddle fan to ventilate mines, a design that corrected problems with one of his initial building ventilating systems that relied on the convective flow of fires. He claimed that, to some extent, the failure of his first system was a result of poor cooperation from the housekeeping staff that had control of the upper rooms in his home and refused to light the requisite fires.

Humans move air primarily to do three things: heat, cool, or clean. By the late 1800s, there was widespread demand for a means to cool the air in theaters, hospitals, halls, and offices. It required 436 pounds of ice an hour to cool the dying President Garfield’s White House room in 1881. Then in 1882, Schuyler Skaats Wheeler invented the first electric fan, produced by the Crocker and Curtis Electric Motor Company.

Mechanized air movement is essentially an attempt to accelerate the 2nd Law of Thermodynamics. Air and energy move naturally from higher to lower gradients, pressure gradients in the case of air. Yet, the science of heat is astonishingly recent. German professor Hermann Rietchel pioneered the science of heating, ventilation and air conditioning with the publication in 1894 of his book Guide to Calculating and Design of Ventilation and Heating Installations. For the first time, science and engineering were combined in a step-by-step design process to accomplish air flow in buildings. But it wasn’t until Willis Carrier that air conditioning became generally practical and affordable.

Carrier, later to found the eponymous company, studied U.S. weather data to gain knowledge of atmospheric psychrometrics (the physical and thermodynamic properties of air-water vapor mixtures). By understanding atmospheric cooling, humidity, and heating, Carrier was able to design a system that could produce consistent temperature and humidity applications in buildings. In 1911, Willis Carrier disclosed his Rational Psychrometric Formulae to the American Society of Mechanical Engineers. The formula stands today as the basis for all fundamental calculations for the air conditioning industry.

Carrier said he received his ‘flash of genius’ while waiting for a train. It was a cold foggy night and he was going over in his mind the problem of temperature and humidity control. By the time the train arrived, Carrier had grasped the underlying relationship between temperature, humidity and dew point. He realized that he could actually remove moisture from the air (and thus reduce air temperature) by spraying chilled moisture into the air. From his study of weather, he realized that as he sprayed directly into the air, the temperatures of air and water would reach an equilibrium that was related to the air’s psychrometric properties: at saturation, the air’s dew-point and dry- and wet- bulb temperatures would be the same.

With the ability to control temperature and humidity levels during and after production, many industries flourished as never before. The quality of film, tobacco, processed meats, medical capsules, and textiles improved significantly because of air conditioning. Willis created the Carrier Engineering Corporation in 1915 with a starting capital of $35,000. With 2002 sales of $8.8 billion, it is still the world’s largest company dedicated to air conditioning.

With the advent of controlled air supplies for heating, cooling and ventilation, fan designs were modified by varying the number of blades, their depth, and their length, in relation to the diameter of the fan. By the 1930s, scientists announced that all improvements to fan blade and rotor design had essentially been accomplished. Although there have been design improvements since then, that dictate has proven true in that no major developments in fan geometries have occurred since that time. The functions of fans and blowers have expanded steadily and now cover a wide range of applications. Fans propel airflows used by heat transfer equipment such as air conditioners, heat pumps, heat exchangers, dehumidifiers, chillers, filters, extractors, and kilns. Fans are central to refrigeration equipment such as soda machines, walk-in freezers, residential refrigerators and freezers, and refrigerated display cases. They are used inside a broad range of appliances including microwaves, oven exhaust hoods, clothes dryers, dehumidifiers, vacuum cleaners, hair dryers, and hand dryers.

PaxFan develops and licenses PAX fan rotors and blades. Today, there are two basic types of mechanical fans, classified according to the direction of the airflow through the impeller: axial and centrifugal. Airflow in axial fans travels parallel with the axis of the fan. Air in centrifugal fans enters along the axis of the fan but leaves in a perpendicular direction, having been centrifugally pushed to the end of the blades.

Axial-flow fans resemble most residential fans that are plugged into the wall for space cooling. Axial fans generate high airflow rates at low pressures. They are commonly used in “clean air,” low pressure, high-volume applications. Because they do not generate a large pressure differential, they are usually not combined with extensive ductwork. Outside of the home, axial fans are used primarily in commercial HVAC applications or for very large-flow clean air applications in the mining, utility, and transportation (tunnel ventilation) sectors.

Axial fans are often directly connected to their motors, avoiding losses associated with a drive belt. They have a central hub that allows the motor to fit neatly behind the fan with little penalty in efficiency. The weight distribution of their blades allows for low starting torque.

Axial fans can be subdivided into three categories. Propeller fans are used to move high air volume against low or no static pressure. Tube-axial fans (essentially a propeller fan placed inside a cylinder) are used in medium-pressure, high airflow rate applications and are well suited for ducted HVAC installations. They are also frequently used in exhaust applications. Vane-axial fans are fans that use straightening fins to convert circular, twisting input air to maximize the flow through the fan. Because vanes at the inlet increase pressure, vane-axial fans are often used in medium to high-pressure applications, such as induced draft service for a boiler exhaust. Vane-axial fans tend to be the most efficient fans available with efficiencies in the high 80s, largely because the direction of the airflow is little changed as it passes through the fan.

The pitch of axial fan blades can be fixed, adjustable, or variable (adjustable during use). Fixed pitch is the norm for low-efficiency propeller fans and for constant-volume fans. Adjustable-pitch fans allow the user to manually adjust blade pitch to tune the flow; a useful feature for building in a safety factor without penalizing efficiency. Variable-pitch blades can be adjusted “in flight” by pneumatic or electric actuators; they provide efficient volume control without changing the speed of the fan.

PaxFan designs can be applied to manufacture all axial fan types.

Centrifugal fans have an entirely different design. The air, instead of passing straight through, makes a 90-degree-angle turn as it travels from the inlet to the outlet and is “thrown” from the blade tips. Centrifugal fans have more mass farther from the axle, which requires more starting torque, but they are generally quieter than axial fans.

Traditionally, there are several arrangements of fan blades for centrifugal impellers. The highest efficiency centrifugal fans use airfoil or backward-curved impeller blades. Airfoil blades are curved backward but have an airfoil cross-section, while backward-curved blades are of a single thickness of metal. Straight radial fan blades are used mostly in industrial applications. The main advantage of radial blades is that they permit the passage of foreign objects in the air stream such as sawdust, metal filings, and other debris. Forward-curved fan blades have low efficiency and are typically used to move high volume against low pressure in applications such as window air conditioners and hotel unitary packages. Low purchase cost and compactness are the principal advantages of fans with forward-curved blades; they are still being built and installed in great quantities.

The blades in PAX centrifugal fan design have a unique curvature. Despite their difference in shape, their operational characteristics suffice to classify them in a similar way to traditional fans. They can be used in most of the same systems as existing fans, and in some cases as a direct retrofit.