Heat exchange – With solids separator for exchange fluid
Reexamination Certificate
1999-05-20
2001-03-27
Flanigan, Allen (Department: 3743)
Heat exchange
With solids separator for exchange fluid
C165S154000, C210S183000
Reexamination Certificate
active
06206090
ABSTRACT:
TECHNICAL FIELD
The invention is directed to a compact combined heat exchanger and dual fluid filters that can be used in a gas turbine engine to simultaneously filter lubricating oil and fuel while transferring thermal energy between the oil and fuel.
BACKGROUND OF THE ART
Although the present description uses a gas turbine engine as an example, it will be understood that the present invention and background of the art encompass any application where a heat exchanger is combined with fluid filters in a compact unit.
In many engines, such as internal combustion engines, and in this example, a gas turbine engine, hydrocarbon fuel is pumped with a fuel pump from a fuel tank into the engine via a fuel line. To remove foreign particles and other impurities, a fuel filter typically is positioned as at an accessible point in the fuel line and optionally a fuel air separator as well. The fuel filter is usually a corrugated fabric cylinder positioned at a location in the engine, which is easily accessed for replacement during routine maintenance.
In a like manner, the oil filter is generally a corrugated fabric cylinder positioned at a conveniently accessible location in the oil distribution system. Lubricating oil is cycled between bearings and an oil reservoir, through an oil pump also positioned at an accessible location for routine maintenance.
In the case of a gas turbine engine, the relatively cool incoming fuel from the fuel tank is often used to cool the relatively hot oil scavenged from the bearings through use of a fuel/oil heat exchanger. The fuel is heated by the oil thereby reducing the risk of icing in the fuel circuit. In a gas turbine engine, the heat exchanger is also positioned at a convenient location for access and inspection at a point along the fuel and oil lines.
It is apparent however, that this collection of separate heat exchanger, oil filter and fuel filter require numerous interconnecting oil and fuel lines all of which are subject to damage or leakage. The cost of installing and maintaining separate components and interconnecting conduits, has in the past being considered to be a necessary feature of complex aircraft engine designs especially. However, even conventional mass-produced automobile engines include separate oil and fuel filters, with accompanying conduits.
It is an object of the invention to reduce the number of engine components, particularly the components related to oil filters, fuel filters and heat exchangers in order to simplify engine design and reduce cost of manufacture, assembly and maintenance.
It is a further object of the invention to combine the heat exchanger and at least one fluid filter to produce a robust combined device, which reduces the risk of leakage and a number of interconnecting fluid pipes in an engine.
It is a further object of the invention to produce a combined heat exchanger and fluid filter, which can be easily adapted to a number of different engine specifications in a simple and straightforward modular manner.
It is further object of the invention to replace conventional stacked plate heat exchangers with an inexpensively produced extruded heat exchanger. Further objects of the invention will be apparent from review of the disclosure and description of the invention below.
DISCLOSURE OF THE INVENTION
The invention relates to a combined heat exchanger and fluid filter particularly in a gas turbine engine to simultaneously filter lubricating oil and fuel while transferring thermal energy between the oil and fuel. Conventionally, fuel and oil filters as well as a heat exchanger are separately mounted in an engine with a multitude of pipes conducting fluids among them. The invention packages these components together and achieves several benefits as a result, including: a reduction in the number of parts and the cost of manufacture and installation; containment of the risk of physical damage or leakage; improved access for assembly, inspection and maintenance; and modular standard components to accomodate a number of different engines by merely extending the length of the filters/exchanger on a standard manifold. The combined heat exchanger and filter device has an enclosed housing separated into a first chamber and a second chamber by an impervious heat exchange wall adapted to transfer thermal energy between a first fluid and a second fluid circulated through the first and second chambers. A manifold in the housing has inlets and outlets in flow communication with the first and second chambers respectively, and a fluid filtering medium disposed within one or both of the chambers. Preferably for improved heat transfer between fluids, the inlets and outlets are disposed in the manifold to direct a counter-flow of fluids and the filtering medium is disposed to direct fluid flow normal to the heat exchange wall.
In this way, the fluids are circulated and remain in contact with the heat exchange wall for a relatively long resident period. The preferred arrangement uses standard cylindrical fuels and oil filters nested respectively inside and outside a capped cylindrical heat exchanger wall. The heat exchanger can be an extruded aluminium tube with longitudinal heat transfer fins on inner and outer surfaces that can be produced inexpensively compared to the labour intensive stacked plate heat exchangers conventionally used. The routing of conduits is reduced, as is the overall use of pressurised conduits in the engine. As a result, risk of damage, fire, leakage, exposure to the elements and icing are reduced. Packaging in a combined housing results in a more robust assembly, and ease of access for maintenance and inspection. The concentric enclosure of the fuel filter within the heat exchanger and the heat exchanger within the oil filter, significantly reduces the design pressures which the fuel filter and heat exchanger housing must withstand. The fuel filter and heat exchanger enclosures have no external housing surface, which is not under pressure, unlike conventional separate components. Conventional housings for filters and heat exchangers are externally exposed to atmospheric pressure and must withstand internal pressures of six times the operating pressure to ensure safety. By combining the fuel filter, oil filter and heat exchanger in a single housing, the net pressure resisted by the internally nested components is significantly reduced. Use of a simple cylindrical heat exchanger with internal and external fins significantly reduces the cost of the heat exchanger since very little labour is required during manufacture. An extruded aluminium cylinder can be used for example. Conventional stacked plate heat exchangers require brazing of multiple plates during assembly, with accompanying labour costs.
Further details of the invention and its advantages will be apparent from the detailed description and drawings included below.
REFERENCES:
patent: 2713422 (1955-07-01), James
patent: 3762467 (1973-10-01), Poon et al.
patent: 4878536 (1989-11-01), Stenlund
patent: 4923003 (1990-05-01), Stenlund
patent: 5326461 (1994-07-01), Legrand et al.
patent: 5406910 (1995-04-01), Wallin
patent: 5476139 (1995-12-01), Gire
patent: 5823987 (1998-10-01), Elgas et al.
Astle Jeffrey W.
Flanigan Allen
Pratt & Whitney Canada Corp.
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