Heat sink and method of making same

Abstract

A heat sink includes a fluid channel and a cooling wall in contact with coolant flowing in the fluid channel. The channel is configured to vary the velocity of coolant along the length of the fluid channel to vary the coolant's heat transfer coefficient and thereby compensate for the coolant's temperature rise along the length of the fluid channel. The result is a heat sink that is isothermal along its length.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:

FIG. 1 is a schematic representation of fluid temperature increase in a typical heat sink or manifold;

FIG. 2 is a schematic cross-sectional side view of one embodiment of a heat sink in accordance with the subject invention;

FIG. 3 is a schematic cross-sectional side view of another embodiment of a heat sink in accordance with the present invention including a tapered body;

FIG. 4 is a schematic cross-sectional side view of a further embodiment of a heat sink in accordance with the present invention;

FIG. 5 is a schematic cross-sectional side view of another embodiment of a heat sink in accordance with the present invention showing a tapered body therein;

FIG. 6 is a schematic three-dimensional exploded view of an embodiment of a heat sink in accordance with the subject invention including a tapered body and showing a transmit/receive integrated multichannel module (T/RIMM) attached thereto;

FIG. 7 is a schematic cross-sectional side view of another embodiment of a heat sink in accordance with the present invention including an increased heat transfer area;

FIG. 8 is a schematic end view of the heat sink of FIG. 7;

FIG. 9 is a schematic cross-sectional side view of another embodiment of a heat sink in accordance with the present invention including an increased heat transfer area and a tapered body;

FIG. 10 is a schematic three-dimensional top exploded view of an embodiment of a phased array radar system including an array of T/RIMMs disposed between heat sinks in accordance with the subject invention;

FIG. 11 is a schematic three-dimensional view of an embodiment of a T/RIMM based phase array radar system including heat sinks in accordance with the subject invention;

FIG. 12 is a flow chart depicting the primary steps associated with one example of a heat transfer method in accordance with the subject invention; and

FIGS. 13-14 are flow charts depicting the primary steps associated with examples of heat transfer methods in accordance with the subject invention.

DETAILED DESCRIPTION OF THE INVENTION

Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.

As discussed in the Background section above, thermal gradients occur in fluid cooled heat sinks because, as the fluid travels through the heat sink, it picks up heat from the heat sources. Consequently, the coolant further downstream is at a higher temperature. This condition is shown schematically in FIG. 1. In this example, for an isothermal heat sink, it is desirable that the temperature at all points of surface 10 of heat sink wall 14 should be the same. In one example, the temperature at location 11 of surface 10, namely T_surface-1, and the temperature at surface location 12 of surface 10, namely T_surface-2, should each be 32° C. In such a case thermal gradients on cooling surface 10 would be eliminated.

With typical heat sinks, however, as coolant flows in the direction of arrow X in channel 15, it picks up heat from the heat sources 16 on cooling surface 10. The temperature of the coolant or fluid T_cool-in nearer the entry point or upstream 18 of manifold or heat sink 20 is thus lower than the temperature of the coolant T_cool-out farther downstream or closer to the exit 22 of the manifold 20. In the case of a typical coolant where the specific heat remains constant, if T_{cool-in is} 20° C. for example, T_cool-out will be 28° C., or 8° C. warmer than T_cool-in. This results in less effective cooling downstream and a consequent thermal gradient because T_surface-2 ends up much greater than the desired 32° C.

This less than desirable result is a consequence of the heat introduced into the fluid as well as the fluid qualities. It is known that T_cool-out is a function of the fluid mass flow rate, the fluid properties, Q_in, and T_cool-in, according to equation (1):

Q _in =mc _p(T_cool-out−T_cool-in)   (1)

where Q_in is the heat dissipated into the coolant, m is the mass flow of the fluid, and c_p is the specific heat of the fluid. Also, the thermal resistance R_hin=1/h_inA, where h_in is the heat transfer coefficient of the coolant at point 11a and A is the heat transfer area in contact with the coolant. The thermal resistance R_hout=1/h_outA, where h_out is the heat transfer coefficient of the coolant at point 12a. Additionally, the temperature T_surface-1 at point 11 is a function of the temperature of the coolant or fluid T_cool-in and the thermal resistance R_hin upstream, the thermal resistance R_conduction of wall 14, and the heat Q_in. Consequently, the temperature T_surface-2 at point 12 is a function of the temperature of the coolant or fluid T_cool-in, the thermal resistance R_hout downstream near exit 22, R_conduction and the heat Q_in.

However, it is also known that heat transfer is a function of the heat transfer coefficient according to:

Q=hA(ΔT)   (2)

where Q is the heat transferred into the fluid, h is the is the heat transfer coefficient of the fluid, ΔT is change in temperature of the fluid, and A is the heat transfer area.

The inventors have observed that the heat coefficient h is a function of and proportional to the velocity of the coolant or fluid, and that by increasing the fluid velocity, the heat coefficient h can also be increased. The inventors further observed that according to equation (2), if Q were constant, the change in temperature ΔT would decrease. Thus, in the example of FIG. 1, the surface temperature, T_surface-2, associated with point 12 on surface 10 could be decreased by a desired amount depending on the amount of increase in velocity of the fluid at that point.

The inventors further observed that the velocity of the fluid or coolant could be varied—increased in the example of FIG. 1—by configuring the fluid channel of the manifold or heat sink to vary the velocity and thus the coolant's heat transfer coefficient, thereby compensating for the coolant's temperature rise along the length of the fluid channel of the heat sink.

In one example, heat sink or manifold 30, FIG. 2 in accordance with the present invention includes fluid channel 32, and cooling wall 34 in contact with coolant 36 flowing in fluid channel 32. Cooling wall 34 is configured to vary the velocity of the coolant along the length of the fluid channel to vary the heat transfer coefficient of coolant 36, and thereby compensate for the coolant's temperature rise along the length of fluid channel 32. Coolant 36 may be a gas, such as air, or a liquid, such as water.

In this example, fluid channel 32 is configured to form a tapered channel along its length as shown. The area 33 that coolant 36 passes through on the upstream end of the coolant flow in heat sink 30 is larger than area 33a at the downstream end. Thus, because a constant amount of fluid 36 must pass through both areas 33 and 33a, the velocity of coolant 36 increases as it flows downstream and eventually passes through area 33a and beyond. Also in the example of FIG. 2, heat transfer area 35 in contact with coolant 36 decreases as coolant 38 flows downstream, partially reducing the positive effect gained by increasing the coolant velocity. However, these two conflicting effects can be used individually or together to achieve a lower thermal gradient and can be tailored for a specific purpose, and when used in conjunction with a tapered body can be tailored to particular advantage as discussed more fully below.

In another embodiment, cooling wall 34, FIG. 3 has a constant area 37 along the length of channel 32 and fluid channel 32 includes tapered body 38 therein, that forms a tapered annulus. In one example, fluid channel is round. Preferably, tapered body 38 tapers upward in the direction of coolant flow, as shown by arrows B, in fluid channel 32. In this example, the circumference 40 of tapered body 38 is at a greater distance d, from cooling wall 34 upstream in the fluid flow, and at a lesser distance d₂ from cooling wall 34 further downstream. Tapered body 38 and cooling wall 34 may be made of any material as desired for a particular application, but in one preferred example cooling wall 34 is made of aluminum and tapered body 38 is made of plastic or aluminum.

Typically, cooling wall 34 defines cooling surface 42 and the area of cooling wall 34 and tapered body 38 are selected to maintain a constant temperature cooling surface 42. As discussed in the example above, to compensate for the temperature change of coolant 36 as it flows through fluid channel 32—and thus avoid thermal gradients—the heat transfer coefficient h of coolant 36 is varied as it passes through channel 32 by varying the velocity of coolant 36. In one example, the velocity can be varied by selecting the area of tapered body 38 such that it has a greater area at the downstream end 40a, which would result in increased coolant velocity downstream. Alternatively or in addition, the area of cooling wall 34 may be selected to be smaller at the downstream end (not shown), also resulting in increased fluid velocity downstream.

Thus, it can be seen that the amount of change in velocity, and thus the amount of change to the heat transfer coefficient h at desired points along the length of heat sink 30′, can be varied as desired for a particular application in order to maintain a constant temperature cooling surface 42 by selecting the areas of cooling wall 34 and tapered body 38. The same “tuning” can be accomplished absent the tapered body, by selecting the area of cooling wall 34 as appropriate for a particular application to prevent thermal gradients. As shown in the example of FIG. 2, the area 33 of cooling wall 34 of heat sink 30 is varied such that it is less upstream and area 33a is greater downstream. This is also the case in FIG. 4, which shows heat sink 30″ with fluid channel 32 configured to form stepped portions 44 of increasing diameter along the length of channel 32.

In each of the FIGS. 2-4, the velocity of the coolant continues to increase as it flows downstream, but this is not a necessary limitation of the invention. In addition, the velocity of the coolant may be varied as it flows downstream, as shown in FIG. 5 for example.

In FIG. 5, tapered body 38′ has a variable taper, such that it tapers upward for the first approximately one-third of its length L, and does not taper for the remaining approximately two-thirds of its length L. This variable tapered body 38′ may be used, for example, where there are a number of heat sources 50 on cooling wall 42 only near the second one-third of tapered body 38′ and greater cooling is required in this region in order to minimize thermal gradients.

FIG. 6 shows a three-dimensional exploded view of an example of heat sink 30^IV in accordance with the subject invention including tapered body 38 and showing a heat sources 50 (only one of which is shown) mounted thereon or attached thereto. In this embodiment, heat sources 50 are transmit/receive integrated multi-channel modules or T/RIMMs.

As noted above however, the subject invention is not limited to increasing or varying the coolant velocity in the heat sink. In other embodiments, the heat sink may be configured to vary the heat transfer surface—with or without varying coolant velocity—in order to compensate for coolant temperature changes along the length of the fluid channel in the heat sink.

In FIG. 7 heat transfer area 35 in contact with coolant 36 increases as coolant 36 flows downstream in the direction shown by arrow B, which provides greater cooling at the downstream end. In this example, as shown in FIG. 8, the heat transfer area is larger on the downstream end than on the upstream end, but because of the configuration of channel 32′ (a square at the upstream end and a thin rectangle at the downstream end) the velocity of coolant 36 decreases very little or not at all. Thus, the cooling effect is achieved nearly exclusively by the increase in heat transfer area as the coolant flows downstream. Other channel shapes may be used, and the subject invention is not limited to the square and rectangular shapes shown in FIG. 8.

In a further example, the addition of tapered body 38, FIG. 9, to channel 32 increases the velocity of coolant 38 at the downstream end, while also increasing heat transfer area 35 at the downstream end of annulus or channel 32. In one example channel 32 may be configured to form a tapered annulus along its length. Thus, in this embodiment the heat sink of the present invention allows both the velocity of the coolant and the heat transfer area to be tailored such that a constant thermal gradient is achieved at various locations on cooling wall 42.

In each embodiment, the heat sink in accordance with the present invention provides the advantage of reducing or eliminating thermal gradients. Additionally, the fluid channels—whether or not a tapered body is included therein—do not need to be tailored or customized to effect a particular “calibration”. Thus, the heat sink of the present invention is less complex to manufacture, provides more flexibility in actual usage, and its effectiveness is not reduced by changing conditions in the system with which it is used. Moreover, the fluid channel of the heat sink of the present invention may be drilled, such as by gun drilling, or it may be extruded to form the fluid channel.

Thus, the heat sink of the present invention does not suffer from the shortcomings of brazed aluminum heat sinks, for example, which have size limitations and are difficult to rework.

Also, as discussed in the Background section above, phased array radar systems specifically require control of thermal gradients at many levels. One phased array radar system 60, FIG. 10 in accordance with the present invention includes at least one heat sink 30^V including fluid channel 32′ and a cooling wall 34′ in contact with coolant 36′ flowing in fluid channel 32′, where cooling wall 34′ is configured to vary the velocity of coolant 36′ along the length of fluid channel 32′ to vary the heat transfer coefficient of coolant 36′ and thereby compensate for the coolant's temperature rise along the length of fluid channel 32′. Phased array radar system 60 further includes a plurality or array 55 of transmit/receive integrated multi-channel modules 50′ mounted on or attached to cooling wall 34′. Phased array radar system 60 may include any of the embodiments of the heat sinks in accordance with the present invention as described herein also including but not limited, for example, to a constant area cooling wall 34′ with a tapered body (not shown) in fluid channel 32′. Thus, although the temperature of cooling surface 42′ may increase, it remains uniform even if the power or duty cycle of the phased array radar system is increased. Accordingly phased array radar system 60, FIGS. 10 and 11, in its various embodiments in accordance with this invention, helps to meet the important and challenging requirements of controlling thermal gradients to effect better overall performance of the system.

Moreover, in accordance with the present invention, heat transfer methods and methods for controlling thermal gradients along a fluid channel may include the heat sink or manifolds described herein, or may be included in the heat sink or manifolds herein.

One heat transfer method 70, FIG. 12 includes placing heat sources on a cooling wall surrounding a fluid channel, step 72, driving a coolant through the fluid channel, step 74, and varying the velocity of the coolant along the length of the fluid channel to vary the coolant's heat transfer coefficient and thereby compensate for the coolant's temperature rise along the length of the fluid channel, step 76. In one example, the method includes the fluid channel forming a tapered annulus along its length. In another example, the method includes disposing a tapered body in the fluid channel. The method may further include tapering the body upward in the direction of the coolant flow in the fluid channel. In one preferred embodiment, the method includes configuring the cooling wall to define a cooling surface and selecting the area of the cooling wall and the tapered body to maintain a constant temperature cooling surface. The method may include varying the taper of the tapered body, configuring the fluid channel to be round, or configuring the fluid channel to form stepped portions of increasing diameter along its length. The method may include drilling the fluid channel, or extruding the fluid channel.

Another heat transfer method 90, FIG. 13 includes placing heat sources on a cooling wall surrounding a fluid channel, step 92, driving a coolant through the fluid channel, step 94, and varying the heat transfer area in contact with the coolant along the length of the fluid channel to compensate for the coolant's temperature rise along the length of the fluid channel, step 96.

A further heat transfer method 110, FIG. 14 includes placing heat sources on a cooling wall surrounding a fluid channel, step 112, driving a coolant through the fluid channel, step 114, varying the heat transfer area in contact with the coolant along the length of the fluid channel, step 116, and varying the velocity of the coolant along the length of the fluid channel to vary the coolant's heat transfer coefficient, to thereby compensate for the coolant's temperature rise along the length of the fluid channel, step 118.

Also in accordance with the present invention, one method for controlling thermal gradients along a fluid channel includes configuring the fluid channel to vary the velocity of a coolant therein along the length of the fluid channel to vary the coolant's heat transfer coefficient, thereby compensating for the coolant's temperature rise along the length of the fluid channel. In one example, the method includes forming the fluid channel as a tapered annulus along its length, and in another example the method includes disposing a tapered body in the fluid channel. The method may further include tapering the tapered body upward in the direction of fluid flowing in the fluid channel. In one preferred embodiment the method further includes configuring the cooling wall to define a cooling surface and selecting the area of the cooling wall and the tapered body to maintain a constant temperature cooling surface.

Another method for controlling thermal gradients along a fluid channel includes configuring the fluid channel to vary heat transfer area in contact with a coolant therein along the length of the fluid channel to compensate for the coolant's temperature rise along the length of the fluid channel.

A further method for controlling thermal gradients along a fluid channel includes configuring the fluid channel to: (i) vary the velocity of a coolant therein along the length of the fluid channel to vary the coolant's heat transfer coefficient; and (ii) vary the heat transfer area in contact with the coolant along the length of the fluid channel, thereby compensating for the coolant's temperature rise along the length of the fluid channel.

Accordingly, the heat sinks, phased array radar systems, and the methods of the present invention thus provide improved and effective control and reduction of thermal gradients.

Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. Other embodiments will occur to those skilled in the art and are within the following claims.

In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended.

Claims

1. A heat sink comprising: a fluid channel; anda cooling wall in contact with a coolant flowing in the fluid channel;the fluid channel configured to vary the velocity of the coolant along the length of the fluid channel to vary the coolant's heat transfer coefficient and thereby compensate for the coolant's temperature rise along the length of the fluid channel.

2. The heat sink of claim 1 in which the fluid channel is configured to form a tapered annulus along its length.

3. The heat sink of claim 2 in which the cooling wall has a constant area along the length of the channel and the fluid channel includes a tapered body therein.

4. The heat sink of claim 3 in which the tapered body tapers upward in the direction of the coolant flow in the fluid channel.

5. The heat sink of claim 4 in which the cooling wall defines a cooling surface and the area of the cooling wall and the tapered body are selected to maintain a constant temperature cooling surface.

6. The heat sink of claim 3 in which the tapered body has a variable taper.

7. The heat sink of claim 3 in which the fluid channel is round.

8. The heat sink of claim 4 in which the tapered body is made of plastic.

9. The heat sink of claim 4 in which the tapered body is made of aluminum.

10. The heat sink of claim 8 in which the cooling wall is made of aluminum.

11. The heat sink of claim 1 in which the fluid channel is configured to form stepped portions of increasing diameter along its length.

12. The heat sink of claim 1 in which said coolant is a gas.

13. The heat sink of claim 1 in which said coolant is a liquid.

14. The heat sink of claim 1 in which the fluid channel is drilled.

15. The heat sink of claim 1 in which the heat sink is extruded to form the fluid channel.

16. The heat sink of claim 5 wherein the cooling surface includes heat sources attached thereto.

17. The heat sink of claim 16 wherein the heat sources are transmit/receive integrated multi-channel modules.

18. A heat sink comprising: a fluid channel;a cooling wall in contact with a coolant flowing in the fluid channel; anda tapered body in the fluid channel which tapers upward in the direction of the coolant flow in the fluid channel to vary the velocity of the coolant along the length of the fluid channel to vary the coolant's heat transfer coefficient and thereby compensate for the coolant's temperature rise along the length of the fluid channel.

19. A phased array radar system comprising: at least one heat sink including: a fluid channel, anda cooling wall in contact with a coolant flowing in the fluid channel,the fluid channel configured to vary the velocity of the coolant along the length of the fluid channel to vary the coolant's heat transfer coefficient and thereby compensate for the coolant's temperature rise along the length of the fluid channel; anda plurality of transmit/receive integrated multichannel modules mounted on the cooling wall.

20. The phased array radar system of claim 19 in which the fluid channel is configured to form a tapered annulus along its length.

21. The phased array radar system of claim 20 in which the cooling wall has a constant area along the length of the channel and the fluid channel includes a tapered body therein.

22. The phased array radar system of claim 21 in which the tapered body tapers upward in the direction of the coolant flow in the fluid channel.

23. The phased array radar system of claim 22 in which the cooling wall defines a cooling surface and the area of the cooling wall and the tapered body are selected to maintain a constant temperature cooling surface.

24. The phased array radar system of claim 21 in which the tapered body has a variable taper.

25. The phased array radar system of claim 21 in which the fluid channel is round.

26. The phased array radar system of claim 22 in which the tapered body is made of plastic.

27. The phased array radar system of claim 22 in which the tapered body is made of aluminum.

28. The phased array radar system of claim 26 in which the cooling wall is made of aluminum.

29. The phased array radar system of claim 19 in which the fluid channel is configured to form stepped portions of increasing diameter along its length.

30. The phased array radar system of claim 19 in which said coolant is a gas.

31. The phased array radar system of claim 19 in which said coolant is a liquid.

32. The phased array radar system of claim 19 in which the fluid channel is drilled.

33. The phased array radar system of claim 19 in which the heat sink is extruded to form the fluid channel.

34. A heat transfer method comprising: placing heat sources on a cooling wall surrounding a fluid channel;driving a coolant through the fluid channel; andvarying the velocity of the coolant along the length of the fluid channel to vary the coolant's heat transfer coefficient and thereby compensate for the coolant's temperature rise along the length of the fluid channel.

35. The heat transfer method of claim 34 in which the fluid channel forms a tapered annulus along its length.

36. The heat transfer method of claim 35 including disposing a tapered body in the fluid channel.

37. The heat transfer method of claim 36 in which the tapered body tapers upward in the direction of the coolant flow in the fluid channel.

38. The heat transfer method of claim 37 including configuring the cooling wall to define a cooling surface and selecting the area of the cooling wall and the tapered body to maintain a constant temperature cooling surface.

39. The heat transfer method of claim 36 including varying the taper of the tapered body.

40. The heat transfer method of claim 36 including configuring the fluid channel to be round.

41. The heat transfer method of claim 34 including configuring the fluid channel to form stepped portions of increasing diameter along its length.

42. The heat transfer method of claim 34 in which the fluid channel is drilled.

43. The heat transfer method of claim 34 in which the fluid channel is extruded.

44. A method for controlling thermal gradients along a fluid channel, the method comprising: configuring the fluid channel to vary the velocity of a coolant therein along the length of the fluid channel to vary the coolant's heat transfer coefficient, thereby compensating for the coolant's temperature rise along the length of the fluid channel.

45. The method of claim 44 in which the fluid channel forms a tapered annulus along its length.

46. The method of claim 45 including disposing a tapered body in the fluid channel.

47. The method of claim 46 in which the tapered body tapers upward in the direction of the coolant flow in the fluid channel.

48. The method of claim 47 including configuring the cooling wall to define a cooling surface and selecting the area of the cooling wall and the tapered body to maintain a constant temperature cooling surface.

49. A heat sink comprising: a fluid channel; anda cooling wall in contact with a coolant flowing in the fluid channel;the fluid channel configured to vary the heat transfer area in contact with the coolant along the length of the fluid channel to compensate for the coolant's temperature rise along the length of the fluid channel.

50. The heat sink of claim 49 in which the fluid channel is configured to form a tapered annulus along its length.

51. The heat sink of claim 49 in which the fluid channel is round.

52. The heat sink of claim 49 in which the fluid channel is square.

53. The heat sink of claim 49 in which the fluid channel is rectangular.

54. The heat sink of claim 49 in which the cooling wall is made of aluminum.

55. A heat sink comprising: a fluid channel; anda cooling wall in contact with a coolant flowing in the fluid channel, the fluid channel configured to vary the heat transfer area in contact with the coolant along the length of the fluid channel;the fluid channel configured to vary the velocity of the coolant along the length of the fluid channel to vary the coolant's heat transfer coefficient, thereby compensating for the coolant's temperature rise along the length of the fluid channel.

56. A phased array radar system comprising: at least one heat sink including: a fluid channel; anda cooling wall in contact with a coolant flowing in the fluid channel, the fluid channel configured to vary the heat transfer area in contact with the coolant along the length of the fluid channel, and the fluid channel further configured to vary the velocity of the coolant along the length of the fluid channel to vary the coolant's heat transfer coefficient, to thereby compensate for the coolant's temperature rise along the length of the fluid channel.

57. The phased array radar system of claim 56 in which the fluid channel is configured to form a tapered annulus along its length.

58. The phased array radar system of claim 56 in which the fluid channel includes a tapered body therein.

59. The phased array radar system of claim 58 in which the tapered body tapers upward in the direction of the coolant flow in the fluid channel.

60. The phased array radar system of claim 58 in which the cooling wall defines a cooling surface and the area of the cooling wall and the tapered body are selected to maintain a constant temperature cooling surface.

61. The phased array radar system of claim 58 in which the tapered body has a variable taper.

62. The phased array radar system of claim 56 in which the fluid channel is round.

63. The phased array radar system of claim 56 in which the tapered body is made of plastic.

64. The phased array radar system of claim 56 in which the tapered body is made of aluminum.

65. The phased array radar system of claim 56 in which the cooling wall is made of aluminum.

66. The phased array radar system of claim 56 in which the fluid channel is configured to form stepped portions of increasing diameter along its length.

67. The phased array radar system of claim 56 in which said coolant is a gas.

68. The phased array radar system of claim 56 in which said coolant is a liquid.

69. The phased array radar system of claim 56 in which the fluid channel is drilled.

70. The phased array radar system of claim 56 in which the heat sink is extruded to form the fluid channel.

71. The phased array radar system of claim 56 wherein the cooling surface includes heat sources attached thereto.

72. The phased array radar system of claim 56 wherein the heat sources are transmit/receive integrated multi-channel modules.

73. A heat transfer method comprising: placing heat sources on a cooling wall surrounding a fluid channel;driving a coolant through the fluid channel; andvarying the heat transfer area in contact with the coolant along the length of the fluid channel to compensate for the coolant's temperature rise along the length of the fluid channel.

74. A method for controlling thermal gradients along a fluid channel, the method comprising: configuring the fluid channel to vary the heat transfer area in contact with a coolant therein along the length of the fluid channel to compensate for the coolant's temperature rise along the length of the fluid channel.

75. A heat transfer method comprising: placing heat sources on a cooling wall surrounding a fluid channel;driving a coolant through the fluid channel;varying the heat transfer area in contact with the coolant along the length of the fluid channel; andvarying the velocity of the coolant along the length of the fluid channel to vary the coolant's heat transfer coefficient, to thereby compensate for the coolant's temperature rise along the length of the fluid channel.

76. A method for controlling thermal gradients along a fluid channel, the method comprising: configuring the fluid channel to: vary the velocity of a coolant therein along the length of the fluid channel to vary the coolant's heat transfer coefficient, andvary the heat transfer area in contact with the coolant along the length of the fluid channel,thereby compensating for the coolant's temperature rise along the length of the fluid channel.