Patent Application
20090185592
This invention relates generally to systems for thermal management and more specifically to supplying a fluid to a heat exchanger for thermal management.
High-power semiconductor laser diodes are finding ever increasing industrial applications such as pumping of solid-state lasers (SSL) and direct material processing, namely cutting, welding, and heat treating. Frequently, such laser diodes are part of a system installed on a mobile mount such as a translation stage or a robotic arm. Other applications for high-power semiconductor laser diodes include a variety of electro-optical systems for a field use such as LIDAR, target illuminators, target designators, or high-energy lasers that may be operated on a land or air vehicle. In all such instances, it is essential to reduce the weight and volume of the high-power laser diode system.
As a byproduct of generating optical output, laser diodes produce large amount of waste heat. To avoid overheating, laser diodes may be mounted on a suitable heat sink. Such a heat sink may be constructed as an actively cooled heat exchanger (HEX). Suitable HEX may use microchannels or impingement cooling. To achieve their target heat transfer performance, such HEX operate at high coolant velocities around 2 to 3 m/s. This results in very high coolant consumption. At the same time, the coolant temperature rise in the HEX is only about 2-3° C., which translates to a rather low coolant utilization.
For high-power applications, multiple semiconductor laser diodes may be mounted on a common semiconductor substrate known as a bar, which is then mounted on a HEX to form a diode bar assembly.
To achieve even higher optical output, multiple diode bar assemblies may be arranged to form a diode bar stack.
The wavelength of laser diode output light is known to be sensitive to coolant temperature. This creates a design challenge in applications requiring wavelength stability, such as when pumping SSL where the diode wavelength must be precisely matched into an absorption band of a laser crystal. In this situation, coolant feeds to individual high-power laser diode bar assembly in an array cannot be connected in series, but rather must be connected in parallel. As a result, coolant must be supplied to such arrays at very high flow-rates to maintain the diodes at their design temperature.
Traditional high-power laser diodes employs a cooling system with a forced convection loop that transports waste heat from the diodes to a chiller or a thermal energy storage. When operating with a powerful laser diode array, large quantities of coolant may be circulated between the array and the chiller. In applications where the laser diodes and the chiller are separated by a large distance, this results in long, large size piping and large coolant inventory. In addition, when laser diodes are mounted on a translations stage or a robotic arm, heavy coolant lines present undesirable inertia and impede motion. The traditional cooling system also stresses the volume and weight carrying capacity of mobile platforms such as land and air vehicles. All such applications would greatly benefit from a cooling system operating with low coolant consumption that is lightweight and compact.
Furthermore, a traditional laser diode systems may require a large amount of coolant inventory. In the event of an accidental coolant release from the system, such a large coolant inventory may pose significant safety, health, and environmental hazards. In addition, a large coolant inventory has a large inertia, which must be overcome during flow start and stop conditions. The above size, weight, energy consumption, coolant inventory, and inertia characteristics of traditional thermal management system may make it less desirable in applications requiring compactness, lightweight, reduced energy consumption, improved safety, and fast startup.
The subject invention provides a simple, compact, lightweight laser diode system offering reduced coolant inventory and energy consumption. In particular, the subject invention provides coolant at a very high flow rate to a laser diode HEX. A portion of the coolant flow downstream of the HEX outlet is separated and pumped by a fluid-dynamic pump back into the HEX inlet. The fluid dynamic pump is operated by a fresh coolant supplied at high-pressure that may be provided by a pump, a high-pressure tank, or other suitable source. Because a substantial portion of the flow leaving the HEX is recirculated back to the HEX inlet, the amount of fresh coolant consumed is substantially reduced compared to a traditional laser diode system. A portion of the coolant downstream of the HEX that is not recirculated back to the HEX may be fed to the suction port of a pump, or stored in a tank or an accumulator, or it may be released to environment. See, for example, a publication entitled “Improved Cooling for High-Power Laser Diodes,” authored by John Vetrovec in proceedings from Photonics West, San Jose, Calif., Jan. 20-24, 2008, SPIE vol. 6876, and “Lightweight and Compact Thermal Management System for Solid-State High-Energy Laser,” in proceedings from the 21st Annual Solid-State and Diode Technology Review, held in Albuquerque, N.Mex., Jun. 3-5, 2008, both of which are hereby expressly incorporated by reference in their entirety.
If the coolant provided to the driving nozzle of the fluid dynamic pump is substantially in a gas or vapor form, the fluid dynamic pump may be an ejector. If the coolant provided to the driving nozzle of the fluid dynamic pump is substantially in a liquid form, the fluid dynamic pump may be a jet pump.
In one preferred embodiment of the subject invention, one or more laser diodes are mounted on a HEX, and an external fluid-dynamic pump recirculates portion of the coolant through external passages.
In another preferred embodiment of the subject invention, diode bar stack is connected to a recirculator containing internal fluid-dynamic pump and recirculation passages. The recirculator, which is connected to a supply of fresh coolant, then feeds coolant to the diode bar stack and drains coolant therefrom, while recirculating a portion thereof.
In yet another preferred embodiment of the subject invention, fluid dynamic pump and recirculation passages are made integral to a diode bar assembly HEX.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.
Accordingly, it is an object of the present invention to provide a lightweight and compact laser diode system.
It is another object of the invention to provide a laser diode system for reduced coolant inventory.
Selected embodiments of the present invention will now be explained with reference to drawings. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments of the present invention are merely exemplary in nature and are in no way intended to limit the invention, its application, or uses.
Referring to
If the heat transfer fluid is gas, the fluid dynamic pump may be an ejector. Suitable ejectors with a single driving nozzle are Series 20A ejectors made by Penberthy, Prophetstown, Pa. Alternative ejectors may have multiple driving nozzles and/or lobed driving nozzles. If the heat transfer fluid is liquid, the fluid dynamic pump may be a hydraulic ejector also known as a jet pump. Suitable hydraulic ejectors with a single driving nozzle are Series 60A ejectors made by Penberthy, Prophetstown, Pa. Alternative hydraulic ejectors may have multiple driving nozzles and/or lobed driving nozzles.
In operation, the fluid dynamic pump 220, HEX 282, return passage 236, and interconnecting passages 232, 238 and 239 are substantially filled with suitable coolant. The laser diode 290 is connected to a source of electric power and generates optical output 214. As a by-product of generating optical output, the laser diode 290 generates heat that is conducted to HEX 282. High-pressure coolant is supplied by a stream 275 via the supply line 248 to the driving nozzle 240 where it forms a jet 242 that is directed into the throat portion of the pump body 234. The jet 242 entrains coolant in the suction chamber 228 and pumps it. Stream 276 containing both the jet flow and the pumped coolant exits the fluid dynamic pump 220 through the discharge port 264 and flows through the passage 232 into the inlet port 254 of HEX 282. The coolant removes heat from the HEX 282 and exits the HEX 282 through the outlet port 256 as a stream 276′ flowing in the passage 238. A portion of the coolant stream 276′ is separated and directed as a recirculating stream 272 into the return passage 236. The un-separated portion of the stream 276′ forms an exit stream 274 that is released from the laser diode system 20 through he back pressure valve 252. The back pressure valve 252 may be adjusted so that a large portion of the stream 276′ is directed in the form of the recirculating stream 272 into the return passage 236. As a result, a large flow may be maintained through the HEX 282 while the overall consumption of fresh coolant as, for example, measured by the flow in the stream 275 fed to the driving nozzle 240 is substantially smaller. Coolant supplied to the nozzle 240 may be provided at a temperature such that the stream 276 (which is a mixture of nozzle flow and the stream 272) fed to the HEX 282 is provided at a predetermined temperature value. In particular, if the coolant is a gas, this gas provided in the line 248 may be chilled in a heat exchanger, a vortex tube, or a turboexpander prior to being fed to nozzle 240. Temperature of laser diode 290 may be controlled by appropriately adjusting the backpressure valve 252. An alternative method for controlling the temperature of laser diode 290 may be achieved by appropriately adjusting the pressure of coolant supplied to the nozzle 240.
An alternative embodiment of the invention is particularly suitable for use with diode bar stacks. Referring now to
The recirculator 320 includes a fluid dynamic pump 320, return passage 336, a backpressure valve 352, and interconnecting passages 332, 338, and 339. The recirculator may be machined from a block of suitable material (such as metal, plastic, or ceramic) and the fluid dynamic pump, return passage, backpressure valve, and interconnecting passages may be formed therein. The passage 332 of recirculator 330 is arranged to fluidly couple to the end cap inlet port 392. The passage 338 of the recirculator 330 is arranged to fluidly couple to the end cap outlet port 396.
In operation, the fluid dynamic pump 320, return passage 236, and interconnecting passages 332, 338, and 339 as well as the internal passages and HEX of the diode bar stack 330 are substantially filled with suitable coolant. The diode bar assemblies 386 are connected to a source of electric power and generates optical output. As a by-product of generating optical output, the diode bar assemblies 386 generate heat that is conducted to HEX 382. High-pressure coolant is supplied by a stream 375 to the driving nozzle 340 where it forms a jet 342 that is directed into the throat portion of the pump body 334. The jet 342 entrains coolant in the suction chamber 328 and pumps it. Stream 376 containing both the jet flow and the pumped coolant exists the fluid dynamic pump 320 and flows through the passage 332 into the end cap inlet port 392, and therefrom to the inlet ports 354 of HEX 382. The coolant removes heat from the HEX 382 and laser diode bars 346 attached thereto, exits the HEX 382 through the outlet port 356, and flows out of the diode bar stack 330 through the end cap outlet port 396 as a stream 376′ flowing in the passage 338. A portion of the coolant stream 376′ is separated and directed as a recirculating stream 372 into the return passage 336. The un-separated portion of the stream 376′ forms an exit stream 374 that is released from the laser diode system 30 through the back pressure valve 352.
Another alternative embodiment of the invention is particularly suitable for use with diode bar assemblies. Referring now to
In particular,
Referring now to
In operation, all of the internal volumes of HEX 482′ are substantially filled with coolant. The laser diode bar 446 is connected to a source of electric power and generates optical output 414. As a by-product of generating optical output, the laser diode bar 446 generates heat that is conducted to at least one wall of the zone 450 of the HEX 482′. High-pressure coolant streams 475a and 475b are supplied by the inlet port 454 to the respective driving nozzles 440a and 44b where they forms jet directed into the throat portion of the pump bodies 434a and 434b (
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” and “includes” and/or “including” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
HTF suitable for use with the subject invention include 1) liquids such as water, aqueous solution of alcohol, antifreeze, and oil, 2) gases including air, helium, natural gas, and nitrogen, and 3) vapors such water steam, Freon, and ammonia.
The terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. For example, these terms can be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies.
Moreover, terms that are expressed as “means-plus function” in the claims should include any structure that can be utilized to carry out the function of that part of the present invention. In addition, the term “configured” as used herein to describe a component, section or part of a device includes hardware and/or software that is constructed and/or programmed to carry out the desired function.
While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the present invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the present invention as defined by the appended claims and their equivalents. Thus, the scope of the present invention is not limited to the disclosed embodiments.
This application claims priority from U.S. provisional patent application U.S. provisional patent application U.S. Ser. No. 61/011,691, filed Jan. 18, 2008; U.S. provisional patent application U.S. Ser. No. 61/066,249, filed Feb. 19, 2008; and U.S. provisional patent application U.S. Ser. No. 61/130,419, filed May 31, 2008.
| Number | Date | Country | |
|---|---|---|---|
| 61011691 | Jan 2008 | US | |
| 61066249 | Feb 2008 | US | |
| 61130419 | May 2008 | US |
