သေဘ္ာေတြမွာ Cooler ဆိုတဲ႕ Heat Exchanger ေတြကို၊ ၁။ shell & tube type heat exchanger (STHE), ၂။ open-flow type heat exchanger, ၃။ contact heat type exchanger နဲ႕ ၄။ plate type heat exchanger (PHE) ရယ္လို႕ ခြဲၿခားအသံုးၿပဳႀကပါတယ္။
shell and tube type heat exchanger ေတြကို၊ U tube heat exchanger နဲ႕ straight tube heat exchanger ေတြ ရယ္လို႕ထပ္မံခြဲၿခားနိဳင္ၿပီး၊ တခါ straight tube heat exchanger ေတြကို၊ one pass နဲ႕ two pass ဆိုၿပီးထပ္မံ ခြဲၿခားနိဳင္ပါတယ္။
Fig. U tube heat exchanger
Fig. one pass straight tube heat exchanger
Fig. two pass straight tube heat exchanger
straight tube heat exchanger ေတြကို steam condensate system, fresh water cooling system, LO cooling system, refrigerant cooling system နဲ႕ hydraulic fluid cooling system ေတြအတြက္၊ သံုးႀကပါတယ္။ U tube heat exchanger ေတြကို engine အေသးေလးေတြ၊ gear box အေသးေလးေတြရဲ႕ LO cooling system အပါ အဝင္၊ capacity နည္းတဲ႕ deck machinery ေတြရဲ႕ hydraulic fluid cooling system အတြက္၊ အသံုးၿပဳေလ႔ရိွ ပါတယ္။
open-flow type heat exchanger ေတြကို charging air cooler အၿဖစ္အသံုးၿပဳသလို၊ contact heat type exchanger ေတြကိုေတာ႕ air conditioning & refrigeration plant, windlass ေတြ၊ mooring winches ေတြနဲ႕ crane ေတြရဲ႕ cooler ေတြအၿဖစ္အသံုးၿပဳႀကပါတယ္။
Fig. plate type heat exchanger
shell & tube type heat exchanger ေတြနဲ႕ plate type heat exchanger ေတြကိုနိွဳင္းယွဥ္ႀကည္႔ရင္၊ U overall heat transfer coefficient တန္ဘိုးပမာဏကို အမၽားဆံုးရရိွနိဳင္တာေတြ႔ရပါတယ္။ U ဆိုတဲ႕ overall heat transfer coefficient ဟာ၊ h ဆိုတဲ႕ heat transfer coefficient နဲ႕မတူပါဘူး။
h ကိုတိုင္းတာတဲ႕ယူနစ္ဟာ W/(m2K) ၿဖစ္ပါတယ္။
ΔQ = Heat input or heat lost (W),
A = Heat transfer surface area m2 နဲ႕
ΔT = Difference in temperature between the solid surface and surrounding fluid area (K or Deg. C) ရယ္လို႕သတ္မွတ္ပါတယ္။
h ကို အရည္ fluid နဲ႕ အစိုင္အခဲ solid ေတြရဲ႕ အပူကူးေၿပာင္းမွဳ heat transfer ကိုတြက္ခၽက္တဲ႕ေနရာမွာ အသံုးၿပဳႀကပါတယ္။
U ဆိုတဲ႕ overall heat transfer coefficient ကိုေတာ႕ အရည္အၿဖစ္စီးဆင္းေနရင္း အရည္တခုမွ၊ အၿခား အရည္ တခုသို႕ အပူကူးေၿပာင္းမွဳ heat transfer ကိုတြက္ခၽက္တဲ႕ေနရာ တနည္းအားၿဖင္႔ plate type heat exchanger ေတြနဲ႕ shell & tube type heat exchanger ေတြမွာသာ အသံုးၿပဳပါတယ္။
Q = UAΔTLM ဆိုၿပီး U ရဲ႕တန္ဘိုးကိုတြက္ယူရာမွာ W/(m2K) ဆိုတဲ႕ unit နဲ႕သတ္မွတ္ပါတယ္။
Q = Heat transfer rate (W),
A = Heat transfer surface area (m2),
ΔTLM = log mean temperature difference (K or Deg. C) ၿဖစ္ပါတယ္။
ΔTLM တန္ဘိုးဟာ၊ primary fluid ေပါါမူတည္ၿပီး၊ ကြာၿခားေလ့ရိွပါတယ္။ plate type heat exchanger ေတြ နဲ႕ shell & tube type heat exchanger ေတြရဲ႕ overall heat transfer coefficient ဟာ (၃) ဆမွ (၄) ဆေလာက္ အထိ ကြာတတ္ပါတယ္။
ဒါ႔အၿပင္ design အရ compact ၿဖစ္ၿခင္း၊ maintenance နဲ႕ cleaning လုပ္တဲ႕အခါပိုမိုလြယ္ကူၿခင္းနဲ႕ temperature Control လုပ္တဲ႕အခါ ပိုမိုလြယ္ကူၿခင္း၊ စတဲ႕အခၽက္ေတြကိုလည္းေတြ႕ရပါတယ္။ PHE ဆိုတဲ႕ plate type heat exchanger ေတြရဲ႕ အားနည္းခၽက္ေတြကေတာ႕
၁။ plate တခုနဲ႕ တခုႀကားမွာ rubber gasket ေတြသံုးကာ ဆက္ထားတာမို႕ potential for leakage ဆိုတဲ႕ အလြယ္တကူယိုစိမ္႕နိဳင္ၿခင္း၊ ၂။ overall heat transfer coefficient ကိုအမၽားဆံုးရရိွနိဳင္ေပမယ္႔၊ ၿဖတ္သန္း စီးဆင္းတဲ႕ အရည္စီးဆင္းမွဳ fluid flow မွာ higher pressure drop ၿဖစ္တာမို႕၊ pumping rate ႀကီးမားတဲ႕ pump ေတြကို တတ္ဆင္အသံုးၿပဳရၿခင္း၊ ၃။ heat transfer လုပ္ရာမွာ အပူခၽိန္ကြဲလဲမွဳပမာဏ အမၽားႀကီး large temperature difference ကိုမရရိွနိဳင္ၿခင္း နဲ႕ ၄။ gasket ေတြအသံုးၿပဳထားရတဲ႕အတြက္ high temperature fluids အပူခၽိန္ၿမင္႔တဲ႔၊ အရည္ေတြကိုအေအးခံဖို႕ မၿဖစ္နိဳင္ၿခင္း စတဲ႕အခၽက္ေတြကို ေတြ႔ ရပါတယ္။
Plate Type Heat Exchanger (PHE) ေတြအသံုးၿပဳထားတဲ႔ Cooling System ကို၊ ၁။ Direct Sea Water Cooling System၂။ Central Cooling System နဲ႕ ၃။ Central Cooling with Separate Cylinder/ Piston Cooling System ရယ္လို႕အေၿခခံအားၿဖင္႕ (၃) မၽိဳး ခြဲၿခားနိဳင္ပါတယ္။
| Sea Water | 1. Main Engine | 7. Lubricating Oil Cooler, Main Engine | 13. Charging Air Cooler, Auxiliary Engine | |
| 2. Auxiliary Engine | 8. Lubricating Oil Cooler, Auxiliary Engine | 14. Fresh-water Pump | ||
| Fresh Water- Low Temp. | 3. Sea-water Filter | 9. Gear Oil Cooler | 15. Destination Unit | |
| 4. Sea-water Pump | 10. Compressor | 16. Heat Exchanger For Central Heating | ||
| Fresh Water- High Temp | 5. Fresh-water Cooler (Central Cooler) | 11. Condenser | 17. Heat Exchanger For Utility Water | |
| 6. Fresh-water Cooler (Cylinder Cooler) | 12. Charging Air Cooler, Main Engine | 18. Expansion Tank |
Fig. direct sea water cooling system
cooler တိုင္းဟာသီးသန္႕စီရိွေနႀကၿပီး၊ sea water ကိုအသံုးၿပဳကာအေအးခံပါတယ္။ main sea water pump ကတဆင္႕၊ sea water filter ကိုၿဖတ္သန္းလာတဲ႕၊ sea water ဟာ၊ main engine နဲ႕ generator engine ေတြရဲ႕ charging air cooler ဆီကိုအရင္ဆံုးသြားပါတယ္။ air coolers ေတြဟာ အေအးဆံုး sea water ကိုရရိွၿပီး၊ sea water ဟာ LO coolers ေတြထံသို႕ ထပ္မံစီးဆင္းပါတယ္။
ေနာက္ဆံုးမွ fresh water cooler သို႕မဟုတ္ jacket cooling water cooler ထံသို႕စီးဆင္းပါတယ္။ 2 stroke low speed main engine ေတြမွာ၊ oil cooled piston ေတြလဲပါဝင္လာတာမို႕၊ LO ရဲ႕ temperature ဟာအနည္းငယ္ မၽားေနေလ့ရိွပါတယ္။ charging air cooler နဲ႕ LO cooler ေတြမွာ sea water piping ကို parallel တတ္ဆင္ထား သလို၊ တခါတရံမွာေတာ႕ cooling capacity မၽားမၽား ထုတ္ေပးနိဳင္မယ္႕၊ cooling surface area ႀကီးတဲ႔၊ LO cooler အႀကီးစားေတြ တတ္ဆင္အသံုးၿပဳ ပါတယ္။
shell & tube type coolers (heat exchangers) ေတြကို၊ direct sea water cooling system မွာသံုးတဲ႕ အခါ၊ ေဈးနံွဳးအရသက္သာေပမယ္႕ control လုပ္ရာမွာ၊အနည္းငယ္ရွဳပ္ေထြးၿပီး၊ tube ေတြနဲ႕ end covers ေတြဟာလည္း sea water နဲ႕ အၿမဲထိေတြ႕ေနရတာမို႕၊ corrosion ၿဖစ္လြယ္ပါတယ္။
| Sea Water | 1. Main Engine | 7. Lubricating Oil Cooler, Main Engine | 13. Charging Air Cooler, Auxiliary Engine | |
| 2. Auxiliary Engine | 8. Lubricating Oil Cooler, Auxiliary Engine | 14. Fresh-water Pump | ||
| Fresh Water- Low Temp. | 3. Sea-water Filter | 9. Gear Oil Cooler | 15. Destination Unit | |
| 4. Sea-water Pump | 10. Compressor | 16. Heat Exchanger For Central Heating | ||
| Fresh Water- High Temp | 5. Fresh-water Cooler (Central Cooler) | 11. Condenser | 17. Heat Exchanger For Utility Water | |
| 6. Fresh-water Cooler (Cylinder Cooler) | 12. Charging Air Cooler, Main Engine | 18. Expansion Tank |
Fig. central cooling system
direct cooling sea water system နဲ႕ central cooling system တို႕ကိုနိွဳင္းယွဥ္ႀကည္႕တဲ႕အခါ၊ direct cooling sea water system မွာ fresh water cooler တနည္းအားၿဖင္႕ jack cooling water သို႕မဟုတ္ cylinder cooling water cooler တတ္ဆင္ထားတာကိုေတြ႕ရမွာၿဖစ္ပါတယ္။ central cooling system မွာေတာ႕ fresh water cooler အစား၊ central cooler ကိုတတ္ဆင္ထားပါတယ္။
| Sea Water | 1. Main Engine | 7. Lubricating Oil Cooler, Main Engine | 13. Charging Air Cooler, Auxiliary Engine | |
| 2. Auxiliary Engine | 8. Lubricating Oil Cooler, Auxiliary Engine | 14. Fresh-water Pump | ||
| Fresh Water- Low Temp. | 3. Sea-water Filter | 9. Gear Oil Cooler | 15. Destination Unit | |
| 4. Sea-water Pump | 10. Compressor | 16. Heat Exchanger For Central Heating | ||
| Fresh Water- High Temp | 5. Fresh-water Cooler (Central Cooler) | 11. Condenser | 17. Heat Exchanger For Utility Water | |
| 6. Fresh-water Cooler (Cylinder Cooler) | 12. Charging Air Cooler, Main Engine | 18. Expansion Tank |
Fig. central cooling with separate cylinder/ piston cooling system
central cooling with separate cylinder/ piston cooling system မွာေတာ႔ central cooler ရဲ႕အထြက္ မွာ fresh-water cooler (cylinder piston cooling water cooler) ကိုတတ္ဆင္ထားပါတယ္။
Credit to : ကိုထြန္း
Image credit to : http://www.norco-oslo.no
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