System and method for using a flexible composite surface for pressure-drop free heat transfer enhancement and flow drag reduction

Abstract

A flexible composite sheet is disclosed. The flexible composite sheet (FCS) comprising a membrane, a substrate coupled to the membrane, and a plurality of ridges coupled between the membrane and the substrate, wherein a vibratory motion is induced from the flow to at least one segment of a membrane spanning a distance s, wherein the vibratory motion is reflected from at least one segment of the membrane to the flow, and wherein a reduction in fluctuations is caused in the flow pressure gradient and freestream velocity U at all frequencies except around f, where f≈U/s. When coupled to a heat exchanger fin, the FCS can enhance heat transfer without enhancing flow pressure drop. The FCS has other flow control applications, such as drag reduction when coupled to an aircraft wing.

What is claimed is:  
     
         1 . A flexible composite sheet comprising: 
 a membrane;    a substrate coupled to the membrane; and    a plurality of ridges coupled between the membrane and the substrate, wherein    the membrane is exposed to a region in a flow of fluid where the streamwise flow pressure gradient changes from favorable to adverse; wherein a vibratory motion is induced from the flow to at least one segment of a membrane spanning a distance s, wherein the vibratory motion is reflected from at least one segment of the membrane to the flow, and; wherein a reduction in fluctuations is caused in the flow pressure gradient and freestream velocity U at all frequencies except around f, where f≈U/s.    
     
     
         2 . The flexible composite sheet of  claim 1  wherein the flexible composite sheet can be wrapped around a leading edge of a plate facing an incoming flow of fluid.  
     
     
         3 . The flexible composite sheet of  claim 1  wherein the flexible composite sheet can be wrapped around an aerodynamic surface where a flow pressure gradient changes from favorable to adverse, in order to reduce the intensity of flow-induced unsteady forces and reduce aerodynamic drag.  
     
     
         4 . The flexible composite sheet of  claim 3  wherein the aerodynamic surface is a portion of a wing, in order to reduce aerodynamic drag, increase wing lift to drag ratio, delay the onset of flow separation and stall and reduce the intensity of flow-induced unsteady forces on the wing.  
     
     
         5 . The flexible composite sheet of  claim 1  wherein the fluid can be a gas, vapor, mixtures of gases and vapors or a liquid.  
     
     
         6 . A heat sink comprising: 
 a fin having a leading edge; and    a flexible composite sheet coupled to the fin leading edge, wherein heat is transferred from the fin to a fluid without incurring an added pressure drop in the fluid.    
     
     
         7 . The heat sink of  claim 6  wherein the flexible composite sheet comprises: 
 a membrane;  
 a substrate coupled to the membrane; and  
 a plurality of ridges coupled between the membrane and the substrate, wherein  
 the membrane is exposed to a region in a flow of fluid where the streamwise flow pressure gradient changes from favorable to adverse; wherein a vibratory motion is induced from the flow to at least one segment of a membrane spanning a distances, wherein the vibratory motion is reflected from at least one segment of the membrane to the flow, and; wherein a reduction in fluctuations is caused in the flow pressure gradient and freestream velocity U at all frequencies except around f, where f≈U/s.  
 
     
     
         8 . A heat exchanger comprising: 
 a plurality of fins, wherein the fins are staggered; and    a flexible composite sheet coupled to some or all of the fins of the plurality of fins, wherein heat is transferred from the fin to a fluid without incurring added flow pressure drop.    
     
     
         9 . The heat exchanger of  claim 8  wherein the plurality of fins form a plurality of flow passages.  
     
     
         10 . The heat exchanger of  claim 9  wherein the plurality of flow passages are parallel.  
     
     
         11 . The heat exchanger of  claim 9  wherein a principal flow through the plurality of flow passages has a component parallel to the local gravitational field thereby creating a compact natural convection surface.  
     
     
         12 . The heat exchanger of  claim 9  wherein the fins have a curved profile.  
     
     
         13 . The heat exchanger of  claim 9  wherein the (FCS) is configured in a fish-scale pattern.  
     
     
         14 . A heat spreader comprising: 
 a heat pipe;    a plurality of fins coupled to the heat pipe; and    a flexible composite sheet coupled to at least one of the fins of the plurality of fins,    wherein heat is transferred from the fin to a fluid without incurring a pressure drop in the fluid.    
     
     
         15 . A fan comprising: 
 a plurality of fan blades; and    a flexible composite sheet coupled to at least one leading edge of a fan blade of the plurality of fan blades, wherein heat is transferred from the fin to a fluid without incurring a pressure drop in the fluid and wherein the fan can be made to be more quiet and efficient.    
     
     
         16 . A method for transferring heat, the method comprising the steps of: 
 (a) providing a membrane coupled to a substrate and a plurality of ridges coupled between the membrane and the substrate;    (b) inducing a vibratory motion from fluctuations in the flow velocity U through the flow pressure gradient to at least one segment of a membrane spanning a distance s; and    (c) reflecting the vibratory motion from at least one segment of the membrane to the flow pressure gradient to sustain pressure fluctuations in the flow pressure gradient at a frequency f, where f≈U/s, wherein heat transfer from a solid surface downstream of the membrane segment to the fluid is enhanced while attenuating the flow pressure drop.    
     
     
         17 . The method of  claim 16  wherein the at least one segment of a membrane vibrates at a vibrating frequency and the flow pressure gradient fluctuates at the substantially the same vibrating frequency.  
     
     
         18 . The method of  claim 16  wherein a resulting flow velocity in the flow pressure gradient fluctuates around a frequency f=U/s, wherein U is the freestream velocity above the membrane and s is the distance between adjacent ridges on a substrate over which the membrane resides.  
     
     
         19 . The method of  claim 18  wherein f does not coincide with a fundamental flexural natural frequency of the segment of the membrane.