This invention relates generally to transport refrigeration and, more particularly, to the evaporator air management system of a trailer refrigeration system.
Trailer refrigeration systems are broadly composed a power system, refrigeration circuiting, air management systems and a control system which are all packaged in a unit mounted to the trailer. These systems are configured with a thermal barrier (or pod) that separates the refrigerated trailer side of the unit from the exterior side containing the engine, compressor and condenser. The power system traditionally consists of a diesel engine and mechanical power transfer devices such as shafts, clutches and belt drives. More recently electric generators have been coupled to the diesel engine and power is then transferred to other system components electrically. The basic refrigeration circuit includes the compressor, evaporator heat exchanger, condenser heat exchanger, expansion device, piping and valves. The compressor is driven by the power system either mechanically or electrically as described above, and represents the primary load on the power system. Evaporator and condenser air management systems consist of mechanically or electrically powered (motorized) fans which drive flow through the heat exchangers and other flow-path systems associated with the equipment. The fans generally consume much less power than the compressor, but otherwise represent the remaining significant power load. Design of the air management systems encompasses the coordination of fans, heat exchangers and flow-path arrangement, and the choice of design has a significant affect on the fan power requirement. Finally, the control system includes the hardware (electrical circuiting and sensors) and software necessary to manage all aspects of system operation.
The present invention relates specifically to the evaporator air management system for trailer refrigeration, the function of which is to circulate air through the trailer cargo load and back through the evaporator coil, which subsequently removes heat from the air stream and thereby cools the cargo.
Centrifugal fans are customarily used for trailer evaporator air management, representing the majority of prior art. In the case of the mechanical drive system, a single large centrifugal fan is typically used (however, systems are produced which use a single cross-flow fan). The newer systems which use electrically powered fans also utilize centrifugal fans. Two smaller fans are typically used in these electric systems. In either case, the centrifugal fans are generally encased in scroll housings which improves the fan performance and in some cases provides a natural 90 degree flow turn which can be advantageous. The fans are typically oriented in a draw-through arrangement with the evaporator coil discharging directly into the trailer. Traditional belt drive evaporator fans are generally oriented with the shaft horizontal to reduce mechanical complexity. Electrically powered fans may have a vertical shaft orientation.
The aforementioned centrifugal fan systems tend to occupy a disproportionate amount of space in the trailer refrigeration system, particularly due to their large scroll housings. In many cases this leads to non-optimized coordination with the evaporator heat exchanger and excessive flow losses. Those losses must then be overcome by the fan, leading to excessive fan power consumption. Furthermore, this space problem can be invasive with respect to design of the condenser air management system. That is, less useable space and options are available when designing the condenser air system.
Therefore, a real need exists for a compact, high efficiency evaporator air management system arrangement for trailer refrigeration systems. The applicant has developed configurations utilizing single or dual, high speed, electrically powered axial fan arrangements that satisfy that need. The designs are therefore suitable for systems using an engine driven electric generator which can power the fans and/or compressor. The designs incorporate circular to rectangular outlet nozzles with approximately 90 degree flow turning. The designs have been developed using fan and flow-path analysis techniques including three-dimensional computational fluid dynamics. The performance and packaging benefits have also been verified experimentally.
Briefly, in accordance with one aspect of the invention, an electrically powered, vertical axis, axial flow fan is arranged so as to draw air through a horizontally mounted evaporator coil and drive it upward through a nozzle which turns the flow 90° and discharges into the trailer.
By another aspect of the invention, the nozzle shape graduates from a circular to a wide aspect ratio rectangular cross-section (width to height ratio greater than 3) while turning through 90°.
By another aspect of the invention, a pair of side-by-side axial fans may be used or a single fan/nozzle can be used and can be placed in the center or off-set transversely in the system.
By another aspect of the invention, the fan is specifically of the vane-axial type, incorporating outlet guide vanes.
In the drawings as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternate constructions can be made thereto without departing from the spirit and scope of the invention.
A truck trailer refrigeration system in accordance with the prior art is shown at 11 in
In the interior section 14, which is located on the interior of the trailer, an evaporator coil is provided, together with the fan or fans for drawing air through the coil. The return air from the trailer is therefore drawn into the opening 16 passed through the evaporator coil to be cooled and is then blown out of a top opening 17 to be circulated rearwardly in the truck trailer 12 to cool the cargo therein.
While both the condenser fans and the evaporator fans have generally been belt driven by the system engine located in the lower portion of the exterior section 13, a more recently implemented approach has been to directly drive a generator by the system engine, and then provide electrical power to drive the centrifugal evaporator fans.
Shown in
An evaporator fan arrangement in accordance with the present invention is shown in
The evaporator coil 32 is disposed in a lower portion of the evaporator section 31 and is preferably placed at an angle as shown to increase the effective surface area and assist in condensate drainage. Inlet opening 33 is provided for the inward flow of return air from the interior of the trailer unit.
Mounted on a support deck 34 is the fan and nozzle unit 36. Mounted in the bottom of the fan and nozzle 36 is an axial fan 37 and its electric drive motor 38, with their axes being vertically oriented, and with the drive motor 38 disposed above the axial fan 37. The axial fan is of the vane-axial type, incorporating outlet guide vanes.
The nozzle 39 is, of course, round near its lower end so as to surround the axial fan 37. As it rises upwardly from the circular lower end, it decreases in cross sectional area and gradually transitions from the circular shape to a wide aspect ratio rectangular cross section while turning 90° to an opening 41 facing rearwardly. The opening 41 has a width to height ratio which is greater than 3 in order to maintain the consistent airflow pattern that will carry through into the trailer.
Although the fan and nozzle unit 36 has been shown as being centrally located within the evaporator section 31, it should be understood that it may be placed in a laterally offset position to either side of the centerline for a particular desired application. For example, such an offset position may accommodate the installation of other components in one side or the other thereof.
Referring now to
While the present invention has been particularly shown and described with reference to the particular exemplarily embodiment as illustrated in the drawings, it will be understood by one skilled in the art that various modifications or changes, some of which had been discussed herein, may be affected therein without departing from the spirit and scope of the invention.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US07/16631 | 7/24/2007 | WO | 00 | 12/30/2009 |