Patent Application
20160025425
The subject matter disclosed herein generally relates to heat exchangers, and more specifically, to guard fins for heat exchangers.
A typical air-to-air counterflow heat exchanger consists of a stack of brazed, thermally interconductive air flow sections or layers. Hot air and cold air are forced through alternate layers in order to exchange heat. In a gas turbine air conditioning system, the hot air comes from the engine bleed and flows through bleed layers. The cold air is outside air and flows through ram layers. These alternately stacked ram and bleed layers are joined together along a thermally conductive medium called the parting sheet, and heat from the bleed layers is transmitted through the parting sheets to the ram air flow.
The ram and bleed layers are similar and each includes an array of cooling fins and frames or closure bars which are positioned on the parting sheets to define each layer. Frames or closure bars are placed along the edges of the layers to support the ends of the parting sheets. In addition to supporting the ends of the parting sheets, theses bars close off each layer, except where there is an air inlet or an air outlet. At the air inlets and outlets the fins provide support for the parting sheets.
To fabricate the heat exchanger, the ram and bleed layers are stacked alternately one on top of another and then placed in a vacuum furnace for brazing. During the brazing process the stack is squeezed so as to force the layers together. The brazing is complete when the fins are brazed to the parting sheets and the edges of the sheets are uniformly brazed along the closure bars. The bleed and ram air flows are supplied from corresponding manifolds that are subsequently welded to the closure bars.
Due to their size, such heat exchangers may be subjected to significant thermal stresses when they warm up and cool down. These stresses may occur when the bleed air flow is started and stopped. During these heating and cooling cycles of the exchanger, the core expands and contracts. Over time, the high thermal stresses may degrade the fins thereby causing fractures that may lead to the deterioration of sections of the core. This may compromise the structural integrity of the heat exchanger and its ability to provide the required cooling performance.
In one aspect, a plate fin heat exchanger is provided. The heat exchanger includes a plurality of finned cold layers configured to conduct a first fluid and a plurality of finned warm layers configured to conduct a second fluid. The finned warm layers include an inlet side, an outlet side, a first portion of fins at the inlet side, and a second portion of fins at the outlet side. The fins of the first portion of fins have a thickness greater than a thickness of the fins of the second portion of fins
In another aspect, a dual core heat exchanger is provided. The heat exchanger includes a first core and a second core. The first core includes a first plurality of finned cold layers configured to conduct a first fluid, a first plurality of finned warm layers configured to conduct a second fluid, the first plurality of finned warm layers having an inlet side and an outlet side, and a guard fin positioned at the inlet side of each of the finned warm layers of the first plurality of finned warm layers. The guard fin has a fin thickness greater than a thickness of the fins of the first finned warm layers. The second core is fluidly separate from the first core and includes a second plurality of finned cold layers configured to conduct the first fluid and a second plurality of finned warm layers configured to conduct a third fluid. The second plurality of finned warm layers includes an inlet side and an outlet side.
In yet another aspect, a method of fabricating a heat exchanger is provided. The method includes providing a plurality of finned cold layers, providing a plurality of finned warm layers having an inlet side and an outlet side, and providing a plurality of guard fins having a fin thickness greater than a fin thickness of the fins of the finned warm layers. The method further includes orienting guard fins of the plurality of guard fins at the inlet side of the finned warm layers of the plurality of finned warm layers and coupling the plurality of finned cold layers, the plurality of finned warm layers, and the plurality of guard fins.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
Described herein are systems and methods for improved performance and structural integrity for heat exchangers. The systems include a heat exchanger with a thicker guard fin positioned at the hot circuit inlet face to improve thermal fatigue life. The guard fin may include a slot formed therein to facilitate expansion and contraction of the guard fin.
Heat exchanger 10 generally includes a primary core 12 and a secondary core 14. Each core 12, 14 includes a bleed air inlet side 16, a bleed air outlet side 18, a ram air inlet side 20, and a ram air outlet side 22. With reference to
Heat exchanger 10 includes a plurality of layers defined by parting sheets 32 and cooling fins 34 that are located between parting sheets 32. Cold or ram air is forced through inlet 20 in the direction of arrow 36 and flows through a plurality of ram air layers 38. The ram air layers 38 are located between hot air or bleed layers 40, which receive hot air through headers 24, 28. The hot air flows through the inlets defined between bleed closure bars 42, which seal off bleed layer 40 with respect to the ram flow direction 36. Similarly, ram closure bars 44 seal off ram air layers with respect to the bleed flow.
With reference to
Similarly, in the exemplary embodiment, upstream fins 48 are fabricated with a thickness greater than downstream fins 50 due in part because the bleed air is reduced in temperature as it travels from inlet 16 to outlet 18. Thus, the thermal stress on fins 34 decreases as the fins extend from inlet 16 to outlet 18, so the thickness of fins 34 may be reduced further downstream. Alternatively, upstream and downstream fins 48, 50 may have the same thickness while guard fins 46 are thicker. Guard fins 46 may be used in primary core 12 and/or secondary core 14. Moreover, in the exemplary embodiment illustrated in
In one embodiment, guard fins 46 are between 40% and 60% thicker than upstream fins 48 and between two and four times thicker than downstream fins 50. In another embodiment, guard fins 46 are between approximately 40% and approximately 60% thicker than upstream fins and between approximately two and approximately four times thicker than downstream fins 50. In one embodiment, guard fins 46 are 55% thicker than upstream fins 48 and three times thicker than downstream fins 50. In another embodiment, guard fins 46 are approximately 55% thicker than upstream fins 48 and approximately three times thicker than downstream fins 50.
In one embodiment, the thickness of guard fins 46 is between 0.008 inches and 0.01 inches. In another embodiment, the thickness of guard fins 46 is between approximately 0.008 inches and approximately 0.01 inches. In yet another embodiment, the thickness of guard fins 46 is 0.009 inches or approximately 0.009 inches. In one embodiment, the thickness of upstream fins 48 is between 0.004 inches and 0.006 inches. In another embodiment, the thickness of upstream fins 48 is between approximately 0.004 inches and approximately 0.006 inches. In yet another embodiment, the thickness of upstream fins 48 is 0.005 inches or approximately 0.005 inches. In one embodiment, the thickness of downstream fins 50 is between 0.002 inches and 0.004 inches. In another embodiment, the thickness of downstream fins 50 is between approximately 0.002 inches and approximately 0.004 inches. In yet another embodiment, the thickness of downstream fins 50 is 0.003 inches or approximately 0.003 inches. However, guard fins 46, upstream fins 48, and downstream fins 50 may have any thickness that enables the fins to function as described herein.
As illustrated in
In one embodiment, a slot depth 58 is between 20% and 40% of a fin length 60. In another embodiment, slot depth 58 is between approximately 20% and approximately 40% of fin length 60. In yet another embodiment, slot depth 58 is 30% or approximately 30% of fin length 60. In one embodiment, slot depth 58 is between 0.15 inches and 0.35 inches. In another embodiment, slot depth 58 is between approximately 0.15 inches and approximately 0.35 inches. In yet another embodiment, slot depth 58 is 0.25 inches or approximately 0.25 inches. In one embodiment, fin length 60 is between 0.8 inches and 0.1 inch. In another embodiment, fin length 60 is between approximately 0.8 inches and approximately 1.0 inch. In yet another embodiment, fin length 60 is 0.9 inches or approximately 0.9 inches.
In one embodiment, a slot width 62 is between 20% and 40% of a fin width 64. In another embodiment, slot width 62 is between approximately 20% and approximately 40% of fin width 64. In yet another embodiment, slot width is 30% or approximately 30% of fin width 64. In one embodiment, slot width 62 is between 0.05 inches and 0.07 inches. In another embodiment, slot width 62 is between approximately 0.05 inches and approximately 0.07 inches. In yet another embodiment, slot width 62 is 0.06 inches or approximately 0.06 inches. In one embodiment, fin width 64 is between 0.15 inches and 0.35 inches. In another embodiment, fin width 64 is between approximately 0.15 inches and approximately 0.35 inches. In yet another embodiment, fin width 64 is 0.25 inches or approximately 0.25 inches.
Heat exchanger 10 may be fabricated by stacking parting sheets 32 with closure bars 42, 44 and cooling fins 34 (including guard fins 46) in place. Weight is then applied to the layers so as to squeeze them together, and the assembly is then placed in a vacuum furnace where it is heated to a temperature at which parting sheets 32 become brazed to closure bars 42, 44 and fins 34. Slots 52 may then be formed in guard fin leading edges 54, for example by electric discharge machining. Headers 24, 26, 28, 30 are then attached to heat exchanger 10.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
