Foundations — Ablative cooling — charring, blowing

3.3.30 · D1 · Physics › Rocket Propulsion › Ablative cooling — charring, blowing

Is page mein yeh assume kiya gaya hai ki aap kuch nahi jaante. Hum parent note ka ek bhi letter use nahi karenge jab tak woh plain words mein define na ho aur ek picture se pin na ho. Upar se neeche padho; har block agla earn karta hai.

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0. Setting: hot gas, ek wall, aur ek flux

Kisi bhi symbol se pehle, situation ko picture karo.

Left par bahut hot gas hai (hazaron kelvin). Right par woh cold structure hai jise hume protect karna hai. Beech mein hamaara sacrificial material baitha hai. Heat left se right flow karti hai, hot se cold ki taraf — yahi ek direction hai jisme heat kabhi apne aap chalti hai.

Upar wala chhota dot, $\dot{q}$, apni ek alag line ka haqdaar hai.

Hume ek rate kyun chahiye aur total nahi? Kyunki ek heat shield ek bahut bada total absorb kar sakta hai, phir bhi fail ho sakta hai agar heat bahut tezi se aaye. Rate hi fair tarika hai arrival ko removal se compare karne ka.

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1. Temperature $T$ aur do subscripts

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2. Convection law: ${\dot{q}}_{conv}=h(T_{gas}-T_{wall})$

Parent ka pehla equation padhne se pehle hume $h$ letter own karna hoga jo usme baitha hai — toh hum $h$ pehle define karte hain, phir law assemble karte hain.

Ab law mein har symbol defined hai, toh hum ise likh sakte hain.

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3. Mass, density, aur ek moving front

Wall cooling ki keemat mass mein chukati hai. Hume teen linked symbols chahiye.

Ab front. Jaise-jaise surface andar tak jalta hai, ek imaginary line — pyrolysis front — block ke andar aur gehri creep karti hai.

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4. Energy per kilogram: $Q_p$, $c_p$, $Q^{\ast }$

Ablation ek trade hai: kilograms out joules absorbed khareedte hain. Toh hume "joules per kilogram" symbols chahiye.

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5. Enthalpy $H$ — temperature ka grown-up cousin

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6. Blowing parameter $B^{\prime }$ aur logarithm

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7. Sensible heating — jahan solid ka $c_p$ rehta hai

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Prerequisite map

Har arrow kehta hai "right box ko samajhne ke liye left box chahiye." Koi bhi path follow karo aur aap parent topic tak pahunch jaate ho: Ablative cooling — charring, blowing (index 3.3.30).

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Aage kahan jaata hai yeh sab

• Convection law aur $h$ in mein aur gehre hote hain Convective Heat Transfer (Stanton number) aur Boundary Layer Theory.
• $Q_p$ aur pyrolysis chemistry is mein unpack ki gayi hai Heat of Reaction and Pyrolysis.
• Rival cooling schemes: Regenerative Cooling aur Radiative Cooling.
• Extreme heating environment: Re-entry Aerothermodynamics.

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Equipment checklist

Recall Self-test — kya aap har ek ko ek plain sentence mein bol sakte ho?

• Ek symbol ke upar dot ka matlab kya hai? ::: ek rate — woh quantity per second.
• Double-prime ${}^{\prime \prime }$ kisi symbol mein kya add karta hai? ::: "per unit area" (per square metre).
• $\dot{q}$ words aur units mein? ::: heat jo har second ek m² cross karti hai; W/m².
• Is problem mein heat flow kyun hoti hai? ::: kyunki $T_{gas}>T_{wall}$; temperature gap push hai.
• $h$ kya hai aur blowing ke dauran iska kya hota hai? ::: gas se wall ka conductance; blowing ise shrink karti hai.
• ${\dot{m}}^{\prime \prime }$ ko recession speed $\dot{s}$ mein kaise convert karte ho? ::: density se divide karo, $\dot{s}={\dot{m}}^{\prime \prime }/{\rho }_v$.
• ${\dot{q}}_{net}$ mein kya include hai? ::: convective heat in, minus radiation aur blowing losses — woh heat jo wall ko actually handle karni padti hai.
• ${\dot{m}}_{total}^{\prime \prime }$ mein kya aata hai? ::: per area per second lost sabhi mass — pyrolysis gas plus char jo reaction/erosion se remove hua.
• $Q_p$ aur $Q^{\ast }$ mein difference? ::: $Q_p$ sirf chemistry sink hai; $Q^{\ast }$ sabhi cooling channels sum karta hai per kg lost.
• $B^{\prime }$ mein kiska $c_p$ aata hai versus sensible term mein? ::: $B^{\prime }$ mein injected gas ka $c_p$; sensible term mein solid material ka $c_p$.
• High heat par temperature $T$ ki jagah enthalpy $H$ kyun use karte hain? ::: $H$ dissociation se bond energy count karta hai jo thermometer miss karta hai.
• $B^{\prime }$ kya compare karta hai? ::: injected gas rate versus gas ki heat-delivery ability; yeh dimensionless hai.
• $\ln (1+B^{\prime })/B^{\prime }$ ka matlab "diminishing returns" kyun hai? ::: logarithm flatten ho jaata hai, toh extra blowing kabhi kam cooling khareedata hai.