Method of Optimum Controlled Outlet, Impingement Cooling and Sealing of a Heat Shield and a Heat Shield Element

Abstract

There is described a method for cooling and sealing of a heat shield element, comprising a main wall with an inner side, which is restricted by side walls or rims, and an outer side, which can be exposed to a hot fluid, and wherein a coolant is introduced into an impingement region of that heat shield element and an impingement flow of said coolant is directed on a surface area of that inner side through a plurality of impingement holes, effecting an impingement pressure drop. In the method discharge flow is metered through a number of discharge holes through said side wall or rims from the inner side to the outer side of the main wall, generating a discharge pressure drop in series with the impingement pressure drop. The impingement pressure drop and the discharge pressure drop are matched to one another so that a required coolant flow is generated which yields a required predetermined heat-transfer coefficient of the main wall. Discharging coolant into the gaps between side opposing walls of neighbouring heat shield elements only allows for an effective sealing against hot gas pingestion. Furthermore, the invention relates to a heat shield element, preferably to a single chamber or double chamber metallic heat shield element, which can be exposed to hot gases. In particular the heat shield element is suitable for being used in a combustion chamber of a gas turbine installation.

1 .- 26 . (canceled)  
   
   
       27 . A method for cooling a heat shield element attached to a carrier with a plurality of impingement holes, the heat shield element having a main wall with an inner side restricted by a side wall having a number of discharge holes, and an outer side, comprising: 
 exposing the outer side to a hot fluid;    introducing a coolant into an impingement region of that heat shield element;    directing an impingement flow of the coolant on the inner side through the impingement holes, causing an impingement pressure drop;    flowing the coolant along the inner side after impingement to convectively cool the main wall;    discharging the coolant through the discharge holes from the inner side to the outer side of the side wall, causing gap sealing and a discharge pressure drop in series with the impingement pressure drop;    matching the impingement pressure drop and the discharge pressure drop to one another to generate a required minimum coolant flow which yields a predetermined heat-transfer coefficient of the main wall; and    matching the discharge pressure drop to get at least 70% of the overall pressure drop to achieve a first heat transfer coefficient on the inner side of the main wall.    
   
   
       28 . The method according to  claim 27 , further comprising matching the discharge pressure drop getting at least 90% of the overall pressure drop to achieve a second heat transfer coefficient on the inner side of the main wall, wherein the first heat transfer coefficient is greater than the second heat transfer coefficient.  
   
   
       29 . The method according to  claim 28 , further comprising matching the discharge pressure drop getting at least 97% of the overall pressure drop to achieve a third heat transfer coefficient on the inner side of the main wall, wherein the second heat transfer coefficient is greater than the third heat transfer coefficient.  
   
   
       30 . The method according to  claim 27 , further comprising matching the cross sections of the impingement holes and the discharge holes to match the impingement pressure drop and the discharge pressure drop.  
   
   
       31 . The method according to  claim 30 , further comprising matching the number of the impingement holes and the discharge holes to match the impingement pressure drop and the discharge pressure drop.  
   
   
       32 . The method according to  claim 31 , further comprising matching the location of the impingement holes and the discharge holes to match the impingement pressure drop and the discharge pressure drop.  
   
   
       33 . The method according to  claim 27 , further comprising: 
 directing a first impingement flow on a first surface area, and    directing a second impingement flow on a second surface area, wherein the second surface area is separated from the first surface area.    
   
   
       34 . A method according to  claim 27 , further comprising taking air as the coolant from an air compressor of a gas turbine having a combustion chamber having the carrier to which the shield element is attached.  
   
   
       35 . A cooling system, comprising: 
 a heat shield element having: 
 a main wall with an inner side and an outer side exposed to a hot fluid,  
 side walls having a plurality of discharge holes, and  
 an impingement region adjacent to the inner side; and  
   a carrier with a plurality of impingement holes opposite to the inner side, 
 wherein the heat shield element is attached to the carrier,  
 wherein the inner side is impinged by a coolant flow introduced through the impingement holes to effect an impingement pressure drop,  
 wherein the coolant drains through the discharge holes to effect a discharge pressure drop in series with the impingement pressure drop, and  
 wherein the impingement holes and the discharge holes are matched to one another to effect a discharge pressure drop of at least 70% of the overall pressure drop to achieve a first heat transfer coefficient on the inner side of the main wall.  
   
   
   
       36 . The cooling system according to  claim 35 , wherein the impingement holes and the discharge holes are matched to one another to effect a discharge pressure drop of at least 90% of the overall pressure drop to achieve a second heat transfer coefficient on the inner side of the main wall, wherein the first heat transfer coefficient is greater than the second heat transfer coefficient.  
   
   
       37 . The cooling system according to  claim 36 , wherein the impingement holes and the discharge holes are matched to one another to effect a discharge pressure drop of at least 97% of the overall pressure drop to achieve a third heat transfer coefficient on the inner side of the main wall, wherein the second heat transfer coefficient is greater than the third heat transfer coefficient.  
   
   
       38 . The cooling system according to  claim 35 , wherein the cross-section of the impingement holes and the discharge holes are adjusted to match the impingement pressure drop and the discharge pressure drop.  
   
   
       39 . The cooling system according to  claim 38 , wherein the number of the impingement holes and the discharge holes are adjusted to match the impingement pressure drop and the discharge pressure drop.  
   
   
       40 . The cooling system according to  claim 39 , wherein the location of the impingement holes and the discharge holes are adjusted to effect matching the impingement pressure drop and the discharge pressure drop.  
   
   
       41 . The cooling system according to  35 , further comprising a double-chamber heat shield element having a dividing wall, wherein the impingement region is split in two sub-regions by the dividing wall.  
   
   
       42 . The cooling system according to  claim 41 , wherein the dividing wall is attached to the carrier.  
   
   
       43 . The cooling system according to  claim 42 , wherein the sub-regions comprise different impingement hole patterns in order to provide different heat-transfer coefficients.  
   
   
       44 . The cooling system according to  claim 41 , wherein the impingement holes of the first sub-region comprise larger hole diameters than that of the impingement holes of the second sub-region to reduce the heat-transfer coefficient in the first sub-region relative to the second sub-region.  
   
   
       45 . The cooling system according to  claim 41 , further comprising surface-increasing elements to create a higher heat-transfer coefficient resulting in a higher heat extraction, whereby the inner surface of the main wall is enlarged wherein the surface-increasing element is selected from the group consisting of: cooling fins, stiffening ribs, riblets, dimples and combinations thereof.  
   
   
       46 . The cooling system according to  claim 35 , further comprising a plurality of heat shield elements; 
 wherein at least two heat shield elements are arranged adjacent to each other;    wherein the side walls of the heat shield elements form a gap effectively sealed against hot gas ingestion by discharging the coolant flow through discharge holes.    
   
   
       47 . Combustion chamber with a cooling system, comprising: 
 a heat shield element having: 
 a main wall with an inner side and an outer side exposed to a hot fluid,  
 side walls having a plurality of discharge holes, and  
 an impingement region adjacent to the inner side; and  
   a carrier with a plurality of impingement holes opposite to the inner side, 
 wherein the heat shield element is attached to the carrier,  
 wherein the inner side is impinged by a coolant flow introduced through the impingement holes to effect an impingement pressure drop,  
 wherein the coolant drains through the discharge holes to effect a discharge pressure drop in series with the impingement pressure drop, and  
 wherein the impingement holes and the discharge holes are matched to one another to effect a discharge pressure drop of at least 70% of the overall pressure drop to achieve a first heat transfer coefficient on the inner side of the main wall.