Patent Publication Number: US-7717069-B2

Title: Engine cooling system having two cooling circuits

Description:
TECHNICAL FIELD 
   This disclosure relates, generally, to engine cooling systems and methods, and more particularly, to an engine cooling system having two cooling circuits and the related methods. 
   BACKGROUND 
   Internal combustion engines used to operate motor vehicles or heavy mechanical equipment generate considerable heat that must be dissipated. If not properly dissipated, heat reduces operating efficiency of the engine and can ultimately lead to damage of the engine. 
   Engine cooling systems typically flow a cooling fluid through the block of the engine to cool the engine. The cooling fluid captures heat from the engine and releases the heat through a heat exchanger in which the cooling fluid passes in heat exchange relationship with air or liquid. An air-to-liquid heat exchanger may include a series of tubes through which the cooling fluid is pumped, and airflow induced by a fan cools the tubes, and hence the cooling fluid flowing through the tubes. The cooling fluid can be pumped through various engine components, such as the engine head and block, an engine oil cooler or the like, to remove heat from the various engine components. 
   In the operation of an internal combustion engine, the amount of combustion air that can be delivered to the intake manifold of the engine, for combustion in the engine cylinders, is a limiting factor in the performance of the engine. Atmospheric pressure is often inadequate to supply the required amount of air for proper and efficient operation of an engine. 
   Thus, an engine may include one or more turbochargers for compressing air to be supplied to one or more combustion chambers within corresponding combustion cylinders. The turbocharger supplies combustion air at a higher pressure and higher density than existing atmospheric pressure and ambient density. The use of a turbocharger can compensate for lack of power due to altitude, or to increase the power that can be obtained from an engine of a given displacement, thereby reducing the cost, weight and size of an engine required for a given power output. The turbocharger typically includes a turbine driven by exhaust gases from the engine, and one or more compressors driven by the turbine through a turbocharger shaft common to both the turbine and the compressor or compressors. A stream of exhaust gases from the engine is conducted from the exhaust manifold to the turbine, and the exhaust gas stream passing through the turbine causes a turbine wheel to rotate. Rotation of the turbine wheel rotates the common shaft interconnecting the turbine wheel and one or more compressor wheels in the compressor section, thereby rotating the compressor wheels. Air to be compressed is received in the compressor section, wherein the air is compressed and supplied to the air intake system of the engine. 
   The boost air flowing from the compressor or compressors may be conditioned to affect the overall turbocharger performance and/or the engine efficiency. In turbochargers having multiple stage compressors, compressing the air in the first compressor significantly raises the temperature of the air, increasing the power required by the second compressor to achieve a desired pressure boost. To overcome the detrimental effects of the increase in temperature, so called “intercoolers” have been provided in the flow path between the first compressor outlet and the second compressor inlet. Similarly, so called “aftercoolers” have been used after the turbocharger in turbochargers having both single stage and multi-stage compressors. The aftercooler cools the compressed air being supplied to the intake manifold, thereby increasing the oxygen content per unit volume, to better support combustion in the cylinders and decrease engine operating temperatures. 
   Certain cooling systems use cooling fluid from the engine cooling system to circulate through the aftercooler, providing a heat exchange medium for the compressed air also flowing through the aftercooler. Heat from the compressed air stream is removed by the cooling fluid and absorbed in the heat exchanger. Reducing the temperature of the charge air can reduce engine emissions and increase engine efficiency. 
   An aftercooler system may also provide a separate cooling fluid circuit from the heat exchanger to the aftercooler, including a separate circuit aftercooler (SCAC) pump for circulating the cooling fluid to the aftercooler. However, the cooling efficiency of such systems has not always met expectations under all operating conditions. 
   U.S. Pat. No. 6,609,484 describes a cooling system for an internal combustion engine, with a radiator assembly including a first group of radiator cores and a second group of radiator cores. Some cooling fluid cooled in the first group of radiator cores is passed from the radiator assembly to an engine cooling circuit. Another portion of cooling fluid cooled in the first group of radiator cores is passed to the second group of radiator cores, for additional cooling thereof. From the second group of radiator cores, cooling fluid is passed to the separate circuit aftercooler cooling circuit. A turbocharged engine cooling system using a two-pass heat exchanger and a separate circuit aftercooler pump in an aftercooler cooling circuit is also shown in U.S. Pat. No. 6,158,399. 
   In view of the engine efficiency and emissions reduction benefits obtained from adequate aftercooling of the combustion air, it is desirable to have an improved cooling system that provides adequate aftercooler cooling while maintaining sufficient cooling of various other engine components under various operating conditions. 
   The present disclosure is directed to addressing one or more needs as set forth above. 
   SUMMARY OF THE INVENTION 
   One aspect of the present disclosure provides a cooling system for an internal combustion engine having one or more turbochargers. The cooling system includes a first cooling circuit having a first heat exchanger configured to reduce the temperature of a first cooling fluid flowing through one or more cooling conduits of an engine head and block. The cooling system further includes a first cooling unit in fluid communication with the first heat exchanger. The first cooling unit is configured to receive the first cooling fluid from the one or more cooling conduits of the engine head and block to reduce the temperature of a charge air directed from the one or more turbochargers. The cooling system may also include a second cooling circuit that includes a second cooling unit configured to reduce the temperature of the charge air directed from the first cooling unit. The second cooling circuit may also include a second heat exchanger in fluid communication with the second cooling unit. The compressed or charge air, after the two-stage cooling, may then be directed to an air intake system of the internal combustion engine. 
   Another aspect of the present disclosure provides an internal combustion engine having one or more turbochargers and a cooling system that includes a first cooling circuit having a first heat exchanger configured to reduce the temperature of a first cooling fluid flowing through one or more cooling conduits of an engine head and block. The cooling system further includes a first cooling unit in fluid communication with the first heat exchanger. The first cooling unit is configured to receive the first cooling fluid from the one or more cooling conduits of the engine head and block to reduce the temperature of a charge air directed from the one or more turbochargers. The cooling system may also include a second cooling circuit that includes a second cooling unit configured to reduce the temperature of the charge air directed from the first cooling unit. 
   A further aspect of the present disclosure provides a method of cooling a compressed or charge air in an internal combustion engine having one or more turbochargers. The method may include directing the charge air from the one or more turbochargers to a first cooling unit, which is part of a first cooling circuit having a first heat exchanger configured to reduce the temperature of a first cooling fluid flowing through one or more cooling conduits of an engine head and block. The first cooling unit may be in fluid communication with the first heat exchanger and receive the first cooling fluid flowing through the one or more cooling conduits of the engine head and block. The method may further include directing the charge air from the first cooling unit to a second cooling unit, which is part of a second cooling circuit having a second heat exchanger in fluid communication with the second cooling unit. The second cooling circuit may be configured to reduce the temperature of a second cooling fluid flowing through at least one of a plurality of cooling components adapted to cool engine oil, transmission oil, hydraulic oil, and brake oil of the internal combustion engine. The method may also include directing the charge air from the second cooling unit to an air intake system of the internal combustion engine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates an engine cooling system according to one embodiment of the present disclosure that includes one water pump. 
       FIG. 2  illustrates an engine cooling system according to another embodiment of the present disclosure that includes two water pumps. 
       FIG. 3  illustrates an engine cooling system according to another embodiment of the present disclosure that includes two water pumps and a heat exchanger between the two cooling circuits. 
   

   DETAILED DESCRIPTION 
   Referring now more specifically to  FIG. 1 , an internal combustion engine cooling system  10  is shown, for and as part of an engine  12 . The cooling system  10  includes a first cooling circuit  14  and a second cooling circuit  16 . Common to the first cooling circuit  14  and the second cooling circuit  16  is a water pump  18 . 
   In the illustrated embodiment, the radiator assembly  20  is also common to the first cooling circuit  14  and the second cooling circuit  16 . The radiator assembly  20  may be a multi-pass jacket water heat exchanger, and as shown, includes a first group of radiator cores or the first heat exchanger  19  and a second group of radiator cores or the second heat exchanger  21 . Accordingly, in the illustrated embodiment, the first and second heat exchangers  19  and  21  are part of a multi-pass radiator assembly. In alternative embodiments, the first and second heat exchangers may include separate or independent radiator assemblies or radiator units. 
   The first cooling circuit  14  further includes the water pump  18 , the radiator assembly  20  and more specifically the first heat exchanger  19 , the engine head and block  22 , and a first cooling unit  24 . The water pump  18  can be a jacket water pump and help circulate a first cooling fluid  15  through the first cooling circuit  14 . Accordingly, the first cooling circuit  14  provides cooling for the engine head and block  22  by directing the first cooling fluid  15  to flow through one or more cooling conduits embedded therein. Further, the first cooling circuit  14  also provides a first-stage cooling of a compressed or charge air directed from one or more turbochargers (or the turbocharger system)  26  to and through the first cooling unit  24 . The first heat exchanger or the first heat exchanger  19  reduces the temperature of the first cooling fluid  15  after it has been circulated through the one or more cooling conduits of the engine head and block  22  and the first cooling unit  24 . 
   The second cooling circuit  16 , as shown, also includes the water pump  18 , the radiator assembly  20  and more specifically the second heat exchanger  21 , a second cooling unit  28 , and one or more other cooling components  30 . A second cooling fluid  17  is circulated through the second cooling circuit  16 , and the second heat exchanger  21  is configured to reduce the temperature of the second cooling fluid  17  after it has been circulated through the second cooling unit  28  and at least one of a plurality of cooling components  30 . The one or more other engine cooling components may include an engine oil cooler, a transmission oil cooler, a hydraulic oil cooler, a brake oil cooler, as well as various cooling fluid conduits and valves and sensors (not shown) known in the art. Accordingly, the second cooling circuit  16  provides cooling for one or more other engine components and a second-stage cooling of the compressed or charge air flowing directed from the first cooling unit  24  to and through the second cooling unit  28 . 
   As shown in  FIG. 1 , a single water pump  18  is common to both the first cooling circuit  14  and the second cooling circuit  16 . The use of a single water pump may allow for mixing of the first cooling fluid  15  and the second cooling fluid  17  and therefore heat exchange between the first cooling circuit  14  and the second cooling circuit  16 . 
   Further, the first cooling circuit  14 , as shown, may include a temperature sensor and control  32  operably linked to a bypass conduit  34 . The temperature sensor and control  32  measures the temperature of the cooling fluid flowing from the first cooling unit  24 , and, when the measured temperature is below a first pre-determined threshold temperature, directs the cooling fluid to flow through the bypass conduit  34  to the water pump  18 , thereby bypassing the first heat exchanger  19 . 
   The second cooling circuit  16 , as shown, may also include a temperature sensor and control  23  operably linked to a bypass conduit  25 . The temperature sensor and control  23  measures the temperature of the cooling fluid flowing from the water pump  18 , and, when the measured temperature is below a second pre-determined threshold temperature, directs the cooling fluid to flow through the bypass conduit  25  to the second cooling unit  28 , thereby bypassing the second heat exchanger  21 . 
   Referring now more specifically to  FIG. 2 , an internal combustion engine cooling system  100  is shown, for and as part of an engine  102 . The cooling system  100  includes a first cooling circuit  104  and a second cooling circuit  106 . Common to the first cooling circuit  104  and the second cooling circuit  106  is a radiator assembly  108  that includes a first heat exchanger  110  and a second heat exchanger  112 . As shown in  FIG. 2 , the first cooling circuit  104  utilizes the first heat exchanger  110 , whereas the second cooling circuit  106  utilizes the second heat exchanger  112 . 
   The first cooling circuit  104  further includes a first water pump  114 , such as for example, a jacket water pump, the radiator assembly  108  and more specifically the first heat exchanger  110 , the engine head and block  116 , and a first cooling unit  118 . Accordingly, the first heat exchanger  110  provides heat exchange for the first cooling circuit  104 , configured to reduce the temperature of a first cooling fluid  105  after it has been circulated through one or more cooling conduits embedded in the engine head and block  116  and the first cooling unit  118 . The first cooling circuit  104  therefore provides cooling for the engine head and block  116  and a first-stage cooling of compressed or charge air directed from one or turbochargers (or the turbocharger system)  120  to and through the first cooling unit  118 . 
   The second cooling circuit  106  further includes a second water pump  122 , the radiator assembly  108  and more specifically the second heat exchanger  112 , a second cooling unit  124 , and one or more other cooling components  126 . The one or more other engine cooling components may include an engine oil cooler, a transmission oil cooler, a hydraulic oil cooler, a brake oil cooler, as well as various cooling fluid conduits and valves and sensors (not shown) known in the art. Accordingly, the second heat exchanger  112  provides heat exchange for the second cooling circuit  106 , configured to reduce the temperature of a first cooling fluid  107  after it has been circulated through the second cooling unit  124  and one or more other cooling components  126 . The second cooling circuit  106  therefore provides cooling for one or more other engine components and a second-stage cooling of the compressed air flowing directed from the first cooling unit  118  to and through the second cooling unit  124 . 
   As illustrated in  FIG. 2 , the first cooling circuit  104  includes a first temperature sensor and control  128  operably linked to a first bypass conduit  130 . Similarly, the second cooling circuit  106  includes a second temperature sensor and control  132  operably linked to a second bypass conduit  134 . The first temperature sensor and control  128  measures the temperature of the cooling fluid flowing from the first cooling unit  118 , and, when the measured temperature is below a first pre-determined threshold temperature, directs the cooling fluid flow through the first bypass conduit  130  to the first water pump  114 , thereby bypassing the radiator assembly  108 . The second temperature sensor and control  132  measures the temperature of the cooling fluid flowing from the one or more other cooling components  126 , and, when the measured temperature is below a second pre-determined threshold temperature, directs the cooling fluid flow through the bypass conduit  134  to the second water pump  122 , thereby bypassing the radiator assembly  108 . 
     FIG. 3  shows an internal combustion engine cooling system  200  that is identical to the cooling system  100  as shown in  FIG. 2 , except that the cooling system  200  further includes a third heat exchanger  236  and its operably linked temperature sensor and controls ( 238 ,  240 ). Same as the cooling system  100 , the cooling system  200  includes a first cooling circuit  204  and the second cooling circuit  206 . Common to the first cooling circuit  204  and the second cooling circuit  206  are a radiator assembly  208  and the third heat exchanger  236 . The first cooling circuit  204  further includes a first water pump  214 , whereas the second cooling circuit further includes a separate, second water pump  222 . 
   As illustrated in  FIG. 3 , the temperature sensor and control  238  and the temperature sensor and control  240  measure the temperature of the first and second cooling fluids ( 205 ,  207 ) flowing from, respectively, the first heat exchanger  210  and the second heat exchanger  212 . When the temperature sensor and control  238  detects a temperature of the first cooling fluid  205  flowing out of the first heat exchanger  210  higher than a first heat exchange threshold temperature, or the temperature sensor and control  240  detects a temperature of the second cooling fluid  207  flowing out the second heat exchanger  212  lower than a second heat exchange threshold temperature, or both, they will direct all or a portion of the respective cooling fluids to flow through the third heat exchanger  236  and then to the respective water pumps ( 214 ,  222 ), thereby allowing for the transfer of heat from the first cooling fluid  205  of the first cooling circuit  204  to the second cooling fluid  207  of the second cooling circuit  206 . 
   In certain embodiments, the second cooling circuit  206  may operate at a higher temperature than the first cooling circuit  204 . For example, during a retarding cycle in off-highway truck applications, a brake oil cooler in the one or more other cooling components  226  can be overheating, resulting in the second cooling circuit  206  operating at a higher temperature than that for the first cooling circuit  204 . Under this circumstance, when the temperature sensor and control  238  detects a temperature of the first cooling fluid  205  flowing out of the first heat exchanger  210  lower than a third heat exchange threshold temperature, or the temperature sensor and control  240  detects a temperature of the second cooling fluid  207  flowing out the second heat exchanger  212  higher than a fourth heat exchange threshold temperature, or both, they will direct all or a portion of the respective cooling fluids to flow through the third heat exchanger  236  and then to the respective water pumps ( 214 ,  222 ), thereby allowing for the transfer of heat from the second cooling fluid  207  of the second cooling circuit  206  to the first cooling fluid  205  of the first cooling circuit  204 . 
   An engine described herein, such as for example, the engine  12  as shown in  FIG. 1 , typically includes an engine head and block having one or more cooling fluid channels or conduits embedded therein, with a cooling fluid inlet and one or more cooling fluid outlets. The engine head and block further defines one or more combustion cylinders in which fuel and air are combusted, and the engine typically further includes pistons, valves, manifolds and the like. 
   A cooling unit as used herein may also be termed an aftercooler, such as the aftercooler described in U.S. Pat. No. 6,609,484, the content of which is incorporated by reference herein in its entirety. The cooling unit may be a jacket water cooler configured to facilitate the transfer of heat to or from the air that flows through the cooler. The aftercooler may include a tube and shell type heat exchanger, a plate type heat exchanger, or any other type of heat exchanger known in the art that can facilitate the transfer of heat to or from the air flowing through the aftercooler. 
   INDUSTRIAL APPLICABILITY 
   During use of an engine cooling system as described herein, the engine is operated in a known manner, with the resultant and inevitable generation of heat. The engine may further operate one or more turbochargers, to compress charge air which is then passed through the aftercooling system, such as for example, the system including the two aftercoolers (or cooling units) as described herein, for cooling thereof. A radiator assembly with at least two groups of radiator cores provides cooling by circulating a cooling fluid through both the first cooling circuit and the second cooling circuit as described herein, to cool engine, as well as the compressed or charge air. 
   According to one embodiment as illustrated in  FIG. 1 , the first cooling fluid  15  flows through the first heat exchanger  19  to the water pump  18 . A portion of the first cooling fluid  15 , of the first cooling circuit  14 , is directed by the water pump  18  to the engine head and block  22  through the channels or conduits (not shown) therein, thereby cooling those engine components. The first cooling fluid  15  continues to flow into the first cooling unit  24 , thereby providing the first-stage cooling of charge air compressed by the turbocharger system  26  operated by the engine  12 . The first cooling fluid  15  may then return to the first heat exchanger  19 , thus allowing heat to dissipate from the first cooling fluid  15  and be absorbed by the first heat exchanger  19 . 
   The temperature sensor and control  32  measures the temperature of the cooling fluid flowing out of the first cooling unit  24 , and when the measured temperature is below a first pre-determined threshold temperature, will operate to direct the first cooling fluid  15  to the water pump  18  through the bypass conduit  34 , thereby bypassing the radiator assembly  20  (or more specifically the first heat exchanger or the first heat exchanger  19 ). When the measured temperature of the first cooling fluid  15  flowing out the first cooling unit  24  is above the first pre-determined threshold temperature, the temperature sensor and control  32  will operate to direct the cooling fluid into the radiator assembly  20 , and more specifically, the first heat exchanger  19 , thereby allowing heat to dissipate from the first cooling fluid  15 . 
   The water pump  18  may also direct flow of another portion of the cooling fluid, the second cooling fluid  17  for the second cooling circuit  16 , to the radiator assembly  20 , and more specifically, the second heat exchanger  21 , for further cooling thereof. The second cooling fluid  17  then flows from the second heat exchanger  21  into the second cooling unit  28 , providing the second-stage cooling of the compressed or charge air cooled by and flowing from the first cooling unit  24 . The compressed or charge air, after the two-stage cooling by the first and second cooling units  24  and  28 , then flows into the engine air intake system or intake manifold (not shown) as typically controlled by the intake valves (not shown). 
   The second cooling fluid  17  subsequently flows from the second cooling unit  28  into one or more other cooling components  30 , such as for example, a transmission oil cooler, a brake oil cooler, a hydraulic oil cooler, and a lube oil cooler. The second cooling fluid  17  then flows back into the water pump  18 . Accordingly, the first cooling fluid  15  and the second cooling fluid  17  intersect at the water pump  18 , which, depending on the water pump design, may allow heat exchange between the two cooling fluids (and therefore the two cooling circuits). 
   According to another embodiment as illustrated in  FIG. 2 , the first water pump  114  directs the first cooling fluid  105  from the first heat exchanger  110  to the engine head and block  116  through the channels or conduits (not shown) therein, thereby cooling those engine components. The first cooling fluid  105  continues to flow into the first cooling unit  118 , thereby providing the first-stage cooling of the charge air compressed by the turbocharger system  120  operated by the engine  102 . 
   The first temperature sensor and control  128  measures the temperature of the first cooling fluid  105  flowing out of the first cooling unit  118 , and when the measured temperature is below a first pre-determined threshold temperature, will operate to direct the cooling fluid flow to the first water pump  114  through the bypass conduit  130 , thereby bypassing the first heat exchanger  110 ). When the measured temperature of the first cooling fluid  105  flowing out the first cooling unit  118  is above the first pre-determined threshold temperature, the first temperature sensor and control  128  will operate to direct the cooling fluid flow into the first heat exchanger  110 , thereby allowing heat to dissipate from the first cooling fluid  105 . 
   The second water pump  122  directs the second cooling fluid  107  of the second cooling circuit  106  from the second heat exchanger  112  into the second cooling unit  124 , which provides the second-stage cooling of the compressed or charge air flowing from and cooled by the first cooling unit  118 . The second cooling fluid  107  subsequently flows from the second cooling unit  124  into other cooling components  126 , such as for example, a transmission oil cooler, an engine or lube oil cooler, a brake oil cooler, and a hydraulic oil cooler. After passing through these other cooling components  126 , the temperature of the second cooling fluid  107  is measured by the second temperature sensor and control  132 , and if the measured temperature is below a second pre-determined threshold temperature, the second temperature sensor and control  132  will operate to direct the cooling fluid flow through the bypass conduit  134  and into the second water pump  122 , thereby bypass the second radiator assembly  112 . When the measured temperature of the second cooling fluid  107  flowing out the other cooling components  126  is above the second pre-determined threshold temperature, the second temperature sensor and control  132  will operate to direct the cooling fluid flow into the second heat exchanger  112 , thereby allowing heat to dissipate from the cooling fluid. 
   Yet another embodiment of the present disclosure is illustrated in  FIG. 3 . The cooling system  200  has essentially the same components and operates in essentially the same manner as the cooling system  100  as shown in  FIG. 2 , except that the cooling system  200  includes a third heat exchanger  236 , allowing the transfer of heat from the first cooling circuit  204  to the second cooling circuit  206  as operated by the temperature sensors and controls  238  and  240  under certain conditions as described above. 
   An exemplary total heat load for an engine cooling system as described herein may be 325 or 323 kW, which excludes the heat generated by air conditioning systems. For the illustrated embodiments, the heat generated by various engine components to be dissipated and absorbed by a radiator assembly (including two heat exchangers) and the cooling of each component are shown in the following table. The simulation results as shown below are based on the assumption that ambient air temperature is at 25° C., and the cooling fluid and other fluids (e.g., engine lube oil, transmission oil, hydraulic oil) have the same ambient temperature of 43° C. 
   
     
       
         
             
             
             
           
             
                 
             
             
                 
                 
               Two-Water Pump 
             
             
                 
                 
               Embodiment (e.g., FIG. 2 
             
             
                 
               Single Water Pump 
               and FIG. 3) 
             
             
                 
               Embodiment (FIG. 1) Heat 
               Heat Dissipated and 
             
             
               Components of 
               Dissipated and Relevant 
               Cooling Fluid 
             
             
               Cooling Circuit 
               Temperatures 
               Temperatures 
             
             
                 
             
           
          
             
               Engine Head and 
               94 kW 
               94 kW 
             
             
               Block 
               Cooling fluid at the outlet: 
               Cooling fluid at the outlet: 
             
             
                 
               101° C. 
               105° C. 
             
             
               First Cooling Unit 
               102 kW  
               99 kW 
             
             
                 
               Charge air temperatures: 
               Charge air temperatures: 
             
             
                 
               Inlet: 270° C.; Outlet: 83° C. 
               Inlet: 270° C.; Outlet: 87° C. 
             
             
               Second Cooling Unit 
                8 kW 
               12 kW 
             
             
                 
               Charge air temperatures: 
               Charge air temperatures: 
             
             
                 
               Inlet: 83° C.; Outlet: 69° C. 
               Inlet: 87° C.; Outlet: 66° C. 
             
             
               Transmission Oil 
               40 kW 
               40 kW 
             
             
               Cooler 
               Oil temperatures: 
               Oil temperatures: 
             
             
                 
               Inlet: 104° C.; Outlet: 95° C. 
               Inlet: 100° C.; Outlet: 91° C. 
             
             
               Hydraulic Oil Cooler 
               40 kW 
               40 kW 
             
             
                 
               Oil temperatures: 
               Oil temperatures: 
             
             
                 
               Inlet: 114° C.; Outlet: 92° C. 
               Inlet: 110.5° C.; Outlet: 88° C. 
             
             
               Lube Oil Cooler 
               40 kW 
               40 kW 
             
             
                 
               Oil temperatures: 
               Oil temperatures: 
             
             
                 
               Inlet: 109° C.; Outlet: 100° C. 
               Inlet: 104° C.; Outlet: 95.5° C. 
             
             
               Total Heat 
               323 kW  
               325 kW  
             
             
               Generated 
             
             
                 
             
          
         
       
     
   
   
     
       
         
             
             
             
           
             
                 
             
             
                 
                 
               Two-Water Pump 
             
             
                 
               Single Water Pump 
               Embodiment (e.g., 
             
             
                 
               Embodiment (FIG. 1) 
               FIG. 2 and FIG. 3) 
             
             
                 
               Heat Absorbed and 
               Heat Absorbed and 
             
             
               Components of 
               Cooling Fluid 
               Cooling Fluid 
             
             
               Cooling Circuit 
               Temperatures 
               Temperatures 
             
             
                 
             
           
          
             
               First Heat Exchanger 
               178 kW 
               193 kW 
             
             
                 
               Inlet: 106° C.; Outlet: 97° C. 
               Inlet: 110° C.; Outlet: 101° C. 
             
             
               Second Heat 
               145 kW 
               132 kW 
             
             
               Exchanger 
               Inlet: 96° C.; Outlet: 88° C. 
               Inlet: 90° C.; Outlet: 85° C. 
             
             
               Total Heat to be 
               323 kW 
               325 kW 
             
             
               Absorbed 
             
             
                 
             
          
         
       
     
   
   Accordingly, the illustrative embodiments include a liquid-cooled system, which may provide certain advantages. First, it may incur lower costs, because the multi-pass radiator assembly as shown is usually less expensive than the conventional ATAACs. Second, it provides good serviceability. Third, the first cooling circuit typically operates at a higher temperature than the second cooling circuit, as indicated by the tables above and generally understood, and by allowing heat exchange between the two circuits, the illustrative systems may have overall improved thermal efficiency and be used to reduce fan parasitics. 
   Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims.