6.4.5 · D1Heat dissipation and cooling solutions
Ek kaam karta hua chip continuously ek chhoti si jagah mein heat daalti rehti hai, aur woh heat room mein escape karni chahiye warna chip khud ko cook kar leti hai. Is topic mein sab kuch yahi measure karna hai ki heat chip se thandi hawa mein kitni aasaani se flow karti hai — aur us flow ko aur aasaan banana hai.
Parent note mein koi bhi formula padhne se pehle, tumhe jaanna zaroori hai ki heat kya hoti hai, uske liye "flow" ka matlab kya hai, aur page pe har letter ka kya matlab hai. Hum yahan unhe ek-ek karke build karte hain, bilkul scratch se, us order mein jis order mein ek doosre pe depend karte hain.
T Temperature ek single number hai jo batata hai koi cheez kitni garam hai. Is topic mein hum ise degrees Celsius (°C) mein measure karte hain, jahan paani 0 pe freeze hota hai aur 100 pe boil karta hai.
Symbol: T Picture: ek thermometer — ek tall scale jahan marker upar jaata hai jab cheezein garam hoti hain.Kyun zaroori hai: ek chip ki ek safe temperature limit hoti hai (aksar ~100 °C). Jo bhi hum karte hain woh T
CPU ke andar sabse garam spot hota hai, jise junction kehte hain (jahan transistors actually switch karte hain). Uski temperature ka apna symbol hai:
T j junction temperature (chip ka sabse garam inner point)T ambi e n t ambient temperature (machine ke around ka room air)
Poora cooling ka kaam ek safar hai: heat T j T ambi e n t
Figure s01 — Heat ka safar. Neeche di gayi picture heat ke ek hisse ko trace karti hai: woh junction pe sabse zyada garam paida hoti hai (T j T ambi e n t
Intuition Difference, absolute nahiHeat ko move karne wali cheez yeh nahi hai ki koi cheez kitni garam hai, balki yeh hai ki woh apne surroundings se kitनी zyada garam hai. 25 °C ke room mein 90 °C ki chip ko 65 degrees ka "push" feel hota hai. Us push ka apna symbol aata hai aage.
Humne abhi do temperatures naam diye: T j T ambi e n t T hot T cold jinhe bhi do points tum compare kar rahe ho — main CPU example mein woh hain T j T ambi e n t
Symbol Δ mein change " ya "mein difference ". Toh:
Δ T = T hot − T cold T hot T cold T hot = T j T cold = T ambi e n t Δ T = T j − T ambi e n t
Simple words mein: ek jagah doosri jagah se kitne degrees zyada garam hai.Picture: chip aur hawa ke beech thermometer scale pe drop ki height .Kyun zaroori hai: heat tabhi flow karti hai jab difference ho. Koi difference nahi (Δ T = 0
Intuition Sign convention —Δ T Δ T ≥ 0 Δ T jaati (ek heating case) — jo normal cooling mein kabhi nahi hota. Toh: hamesha Δ T = T hot − T cold
Yeh poore parent note mein sabse zyada reuse hone wali quantity hai, toh ise pakad ke rakho.
Reveal Δ T = T hot − T cold T j − T ambi e n t gap jo heat flow drive karta hai, hamesha ≥ 0
Heat energy ka ek form hai. Lekin hum rarely energy ke ek hisse ki parwah karte hain; hum rate ki parwah karte hain jis pe woh aati hai — per second kitni heat.
Definition Power aur heat-flow ratePower P watts (W) mein measure ki jaati hai. Ek watt = har second ek joule energy.
Symbol: P Q same quantity ke liye jab unka matlab hota hai "ek slab ke through flow hoti heat." P Q P Q P Picture: ek tap se paani girna — flow rate (litres per second), total pool nahi.Sign/domain: P ≥ 0 produce karti hai heat, toh flow hamesha baahri hoti hai. Rest pe rakhi chip P = 0 Kyun zaroori hai: ek CPU ki TDP batati hai ki woh kitne watts of heat dump karti hai. Yahi woh "flow" hai jise cooler ko continuously carry away karna hai.
Intuition Bucket ki pictureEk bucket imagine karo jismein chhed hai. Paani andar aata hai rate P bahar nikalta hai (cooling). Agar chhed bahut chhota ho, paani ka level (temperature) chadhta rehta hai jab tak overflow nahi hota — overheating. Cooling design bas yahi hai "incoming P
Figure s02 — Bucket analogy. Paani upar se andar girta hai rate P
Heat chip se hawa tak sirf teen routes se ja sakti hai. Teeno ko naam se pehchanna chahiye.
Definition Conduction, convection, radiation
Conduction — heat ek solid ke through neighbours ko jostle karke crawl karti hai. Picture: hot chai mein ek metal ka chamach; handle garam ho jaata hai chahe usne chai ko touch nahi kiya. Yeh heat ko chip se heatsink mein carry karta hai. Convection — ek moving fluid (hawa ya paani) heat scoop up karke usse bodily le jaata hai. Picture: garm soup pe phoonkna; breeze surface se heat haul kar le jaata hai. Yeh heat ko heatsink se room air mein carry karta hai. Radiation — heat invisible light (infrared) ke roop mein nikalty hai. Picture: aag se bina chhoye warmth feel karna. Yahan minor hai (<5%) chip temperatures pe.
Electronics ke liye: pehle conduction phir convection , isi order mein, main path hai.
Kaunsa mechanism solid metal ke through heat move karta hai? Conduction.
Kaunsa mechanism moving air ya liquid chahiye? Convection.
Kaunsa sirf space mein ya bahut high temperatures pe dominate karta hai? Radiation.
Yahi woh idea hai jis pe poora parent note bana hai, toh hum ise dheere dheere earn karte hain.
Hamare paas already do quantities hain:
P Δ T
R t h P kitne degrees zyada garam ho jaata hai?" Ek path jo thodi power ke liye bahut garam ho jaata hai woh bura cooler hai; ek path jo thanda rehta hai woh accha cooler hai. Hum ek number chahiye jo "flow ki difficulty" capture kare.
Definition Thermal resistanceThermal resistance R t h R t h = P Δ T [ W °C ] Δ T ≥ 0 P ≥ 0 ≥ 0
Picture: ek narrow pipe. Ek narrow pipe se zyada flow (P Δ T R t h Yahi tool kyun? Kyunki yeh temperature predict karna simple arithmetic se possible banata hai har baar physics solve karne ki jagah. Rearrange karo toh Δ T = P ⋅ R t h
Intuition "Resistance" kyun — electricity analogyYeh electricity ke Ohm's law, V = I ⋅ R
voltage V Δ T
current I P
electrical resistance R R t h same trick kaam karti hai: resistances in series add up hoti hain. Isliye parent note unhe simply sum karta hai.
Figure s03 — Resistances in series. Teen resistances (chip, paste, heatsink) end to end baithi hain. Single red arrow woh heat hai jo seedha teeno ke through flow karti hai — kyunki use ek-ek karke cross karna hai, unki resistances simply add hokar T j T ambi e n t
Common mistake Bada number ≠ betterBada R t h bura hai (heat escape karna mushkil, chip garam hoti hai). Ek great cooler ka chhota R t h
Parent note ke do formulas extra letters use karte hain. Har ek ek plain physical cheez hai.
Definition Geometry aur material ke letters
k thermal conductivity — koi material naturally kitni achhi tarah heat pass karta hai. Copper k = 400 k = 205 k ≈ 0.025 A area — woh surface ka size jise heat cross karti hai, square metres mein. Picture: ek doorway ki width; zyada wide zyada cheezein jaane deta hai.d thickness — heat ko ek slab ke through kitni door travel karni hai, metres mein. Picture: doorway tunnel kitna lamba hai; lamba hona mushkil hai.h heat transfer coefficient — moving fluid ek surface se heat kitni achhi tarah carry karta hai (W/m²·K). k tez move karti hai us pe depend karta hai.
Intuition Kyun area aur thickness opposite ways pull karte hainZyada area A d
Yeh formula kahin se bhi pull nahi kiya gaya — yeh Fourier's Law of conduction ka rearranged form hai, aur yeh sirf teen simple assumptions ke under hold karta hai.
R t h , co n d = k A d d k A
Intuition Invisible blanketKisi bhi surface ke bilkul paas, hawa ki ek paper-thin layer chipki rehti hai aur muskil se move karti hai. Yeh boundary layer ek insulating blanket ki tarah act karti hai — breeze se pahle heat ko iske through slowly conduct karna padta hai. Fan ka asli kaam hai is blanket ko얇a rip karna , heat ko tez escape karne dena. Isliye h
Fan cooling ko itna dramatically kyun improve karta hai? Yeh ruke hue hawa ki insulating boundary layer ko얇a karta hai, h
Mechanisms conduction convection radiation
Material k area A thickness d
Series sum of resistances
Predict junction temperature
Design the cooling solution
Har arrow ek "pehle yeh jaanna zaroori hai" link hai: tum R t h Δ T P k A d
Har answer cover karo aur khud ko test karo. Agar koi ek bhi atka de, uska section upar se dobara padho.
T j Junction temperature — chip ka sabse garam inner point; woh sabse pehle safety limit hit karta hai.
CPU path ke liye Δ T Δ T = T j − T ambi e n t ≥ 0
Power P Watts; 1 watt = har second 1 joule heat energy.
P Q Same quantity (heat ke watts); parent note Q P
Teen heat-transfer mechanisms naam batao aur kaunse do PC mein dominate karte hain. Conduction, convection, radiation; conduction aur convection dominate karte hain.
Thermal resistance R t h R t h = P Δ T
Bada R t h Bura — iska matlab hai har watt pe badi temperature rise, yaani poor cooling.
Thermal resistances series mein kyun add hoti hain? Kyunki yeh Ohm's law (V = I R
Fourier's Law se R t h , co n d = d / ( k A ) Fourier: P = k A Δ T / d R t h = Δ T / P Δ T d / ( k A ) k
R t h , co n v = 1/ ( h A ) Constant h
Related: Heat dissipation and cooling solutions · Thermal Design Power (TDP) · Thermal throttling · Heat pipes · Reliability and MTBF
