Brazed microchannel heat exchanger with thermal expansion compensation

Abstract

A brazed aluminum microchannel heat exchanger comprising a stack of alternating tubes and serpentine fins includes an expansion relief feature that accommodates uneven thermal expansion in the heat exchanger. The expansion relief feature provides the heat exchanger with sufficient structural support, at least during assembly, so that components of the heat exchanger can be firmly clamped in compression during a controlled-atmosphere brazing process. In some examples, the expansion relief feature is a gap or sliding engagement between adjacent headers of the heat exchanger. In addition or alternatively, the expansion relief feature comprises one or more slits cut into the serpentine fins after the brazing process, wherein each slit extends generally parallel to the tubes.

1 . A microchannel heat exchanger for conveying an internal fluid in heat transfer relationship with an external fluid, the microchannel heat exchanger comprising:
 a first header defining an inlet for the internal fluid to enter the microchannel heat exchanger;   a second header;   a plurality of tubes each of which extend in a longitudinal direction between the first header and the second header, the plurality of tubes connecting the first header in fluid communication with the second header to convey the internal fluid therebetween, the plurality of tubes includes a first tube, a second tube and a third tube, the plurality of tubes being spaced apart from each other to define a plurality of spaces including a first space and a second space, the first space being between the first tube and the second tube, the second space being between the second tube and the third tube, and the second tube and the third tube being spaced apart over a separation distance; and   a plurality of serpentine fins interconnecting the plurality of tubes, the plurality of serpentine fins including a first serpentine fin and a second serpentine fin, the first serpentine fin being contained in the first space between the first tube and the second tube, the second serpentine fin being contained in the second space between the second tube and the third tube, the second serpentine fin defining a slit extending in the longitudinal direction for a slit length that is greater than the separation distance between the second tube and the third tube.   
     
     
         2 . The microchannel heat exchanger of  claim 1 , wherein the slit length is more than ten times as great as the separation distance between the second tube and the third tube. 
     
     
         3 . The microchannel heat exchanger of  claim 1 , wherein the slit length is shorter than a spaced-apart distance between the first header and the second header. 
     
     
         4 . The microchannel heat exchanger of  claim 1 , wherein the plurality of serpentine fins define a plurality of slits similar to the slit defined by the second serpentine fin. 
     
     
         5 . The microchannel heat exchanger of  claim 1 , further comprising a braze material bonding the second serpentine fin to the first tube and the second tube. 
     
     
         6 . The microchannel heat exchanger of  claim 1 , wherein the plurality of tubes include a plurality of substantially flat surfaces attached to the plurality of serpentine fins. 
     
     
         7 . A microchannel heat exchanger for conveying an internal fluid in heat transfer relationship with an external fluid, the microchannel heat exchanger comprising:
 a first header defining an inlet for the internal fluid to enter the microchannel heat exchanger;   a second header;   a third header adjacent to the first header;   a first plurality of tubes each of which extend in a longitudinal direction, the first plurality of tubes connecting the first header in fluid communication with the second header to convey the internal fluid from the first header to the second header;   a second plurality of tubes each of which extend in the longitudinal direction, the second plurality of tubes connecting the second header in fluid communication with the third header to convey the internal fluid from the second header to the third header;   a first plurality of serpentine fins interconnecting in a lateral direction the first plurality of tubes, wherein the lateral direction is generally perpendicular to the longitudinal direction;   a second plurality of serpentine fins interconnecting in the lateral direction the second plurality of tubes;   a braze material bonding the first header to the first plurality of tubes, bonding the second header to the first plurality of tubes, bonding the second plurality of tubes to the second header, bonding the second plurality of tubes to the third header, bonding the first plurality of serpentine fins to the first plurality of tubes, and bonding the second plurality of serpentine fins to the second plurality of tubes; and   an expansion relief feature existing between the first header and the second header, the expansion relief feature accommodating relative movement in the longitudinal direction between the first header and the third header in response to a difference in longitudinal thermal expansion of the first plurality of tubes relative to the second plurality of tubes.   
     
     
         8 . The microchannel heat exchanger of  claim 7 , wherein the expansion relief feature is the first header being in sliding abutment with the second header. 
     
     
         9 . The microchannel heat exchanger of  claim 7 , wherein the expansion relief feature is the first header being spaced apart from the second header to define a gap therebetween. 
     
     
         10 . The microchannel heat exchanger of  claim 7 , further comprising a serpentine fin interposed between the first plurality of tubes and the second plurality of tubes, the serpentine fin defining a slit extending in the longitudinal direction for a slit length greater than a separation distance between the first plurality of tubes and the second plurality of tubes. 
     
     
         11 . The microchannel heat exchanger of  claim 7 , further comprising:
 an elongate member interposed between the first plurality of tubes and the second plurality of tubes, the elongate member being elongated in the longitudinal direction, the elongate member being distinguishable from each of the first plurality of tubes by virtue of at least one of length and cross-sectional area;   a first serpentine fin and the braze material joining the first plurality of tubes to the elongate member; and   a second serpentine fin and the braze material joining the second plurality of tubes to the elongate member.   
     
     
         12 . The microchannel heat exchanger of  claim 11 , wherein the elongate member is tubular but conveys substantially none of the internal fluid. 
     
     
         13 . The microchannel heat exchanger of  claim 11 , wherein the elongate member is a solid bar. 
     
     
         14 . The microchannel heat exchanger of  claim 11 , wherein the elongate member is shorter than each of the first plurality of tubes. 
     
     
         15 . The microchannel heat exchanger of  claim 7 , wherein the plurality of tubes include a plurality of substantially flat surfaces attached to the plurality of serpentine fins. 
     
     
         16 . A microchannel heat exchanger for conveying an internal fluid in heat transfer relationship with an external fluid, the microchannel heat exchanger comprising:
 a first header defining an inlet for the internal fluid to enter the microchannel heat exchanger;   a second header;   a third header adjacent to the first header;   a first plurality of tubes each of which extend in a longitudinal direction, the first plurality of tubes connecting the first header in fluid communication with the second header to convey the internal fluid from the first header to the second header;   a second plurality of tubes each of which extend in the longitudinal direction, the second plurality of tubes connecting the second header in fluid communication with the third header to convey the internal fluid from the second header to the third header;   a first plurality of serpentine fins interconnecting in a lateral direction the first plurality of tubes, wherein the lateral direction is generally perpendicular to the longitudinal direction;   a second plurality of serpentine fins interconnecting in the lateral direction the second plurality of tubes;   a braze material bonding the first header to the first plurality of tubes, bonding the second header to the first plurality of tubes, bonding the second plurality of tubes to the second header, bonding the second plurality of tubes to the third header, bonding the first plurality of serpentine fins to the first plurality of tubes, and bonding the second plurality of serpentine fins to the second plurality of tubes;   an expansion relief feature existing between the first header and the second header, the expansion relief feature accommodating relative movement in the longitudinal direction between the first header and the third header in response to a difference in longitudinal thermal expansion of the first plurality of tubes relative to the second plurality of tubes;   an elongate member interposed between the first plurality of tubes and the second plurality of tubes, the elongate member being elongated in the longitudinal direction, the elongate member being shorter than each of the first plurality of tubes, the elongate member conveying substantially none of the internal fluid;   a first serpentine fin and the braze material joining the first plurality of tubes to the elongate member; and   a second serpentine fin and the braze material joining the second plurality of tubes to the elongate member.   
     
     
         17 . The microchannel heat exchanger of  claim 16 , wherein the expansion relief feature is the first header being in sliding abutment with the second header. 
     
     
         18 . The microchannel heat exchanger of  claim 16 , wherein the expansion relief feature is the first header being spaced apart from the second header to define a gap therebetween. 
     
     
         19 . The microchannel heat exchanger of  claim 16 , wherein the elongate member is tubular. 
     
     
         20 . The microchannel heat exchanger of  claim 16 , wherein the elongate member is a solid bar.