Pressure-fed cycle — simplest, used in upper stages

3.3.25 · Physics › Rocket Propulsion

Pressure-fed cycle KIYA hai?

Key players:

Pressurant gas (He/N₂) ek chhoti, bahut-high-pressure bottle mein stored.
Regulator: stored gas pressure ko ek steady feed value tak girata hai.
Propellant tanks: mazboot hone chahiye (ye hi "pump" hain).
Combustion chamber pressure $p_{c}$ par.

YE KAAM KYUN KARTA HAI? (First-principles pressure budget)

Flow sirf high pressure se low pressure ki taraf hoti hai. Pressure ko tank se chamber tak trace karo:

$p_{tank} = p_{c} + Δ p_{inj} + Δ p_{feed} + Δ p_{cooling} - ρ g h$

Tank pressure KITNI badi hoti hai? Kyunki $Δ p_{inj} \sim 0.25 p_{c}$ aur baaki losses, typically:

$p_{tank} \approx (1.3 - 1.5) p_{c}$

Yahi poori kahani hai ki pressure-fed engines low chamber pressure par kyun chalte hain: $1.5 p_{c}$ hold karne ke liye itne mazboot tanks bahut bhaari ho jaate hain, isliye designers $p_{c}$ kam rakhte hain (~5–20 bar).

LOW CHAMBER PRESSURE KYUN? (Mass penalty derivation)

Figure — Pressure-fed cycle — simplest, used in upper stages

YE KAHAN ISTEMAL HOTA HAI, AUR KYUN WAHAN?

Worked Examples

Common Mistakes

Flashcards

Pressure-fed cycle ko define karne wali ek feature kya hai?

Koi turbopumps nahi — propellants ko tanks par act karne wali stored high-pressure inert gas se push kiya jaata hai.

Tank pressure ko chamber pressure se zyada kyun hona chahiye?

Injector drop aur feed/cooling losses ke liye pay karne ke liye, taaki liquid flow kare aur chamber mein atomize ho.

Tank pressure aur chamber pressure ka typical ratio?

Chamber pressure ka lagbhag 1.3–1.5 ×.

Pressurant ke roop mein typically kaun sa gas use hota hai aur kyun?

Helium (ya nitrogen) — inert, halka, propellants ke saath react ya condense nahi karta.

Pressure-fed low chamber pressure kyun force karta hai?

Tank wall mass ∝ pressure (

t = p r /2 σ

), isliye high

p_{c}

matlab impossibly bhaare tanks.

Tank wall mass ka formula (sphere)?

m_{t ank} = \frac{3 ρ _{m}}{σ} p V

Upper stages par pressure-fed engines kyun pasand kiye jaate hain?

Ye low

p_{c}

par chalte hain (chhoti penalty) aur lambi coasts ke baad maximum reliability/restartability offer karte hain, almost koi moving parts nahi.

Spherical tank ke liye hoop-stress relation?

σ = p r /2 t

Regulator ka kya kaam hai?

Stored high-pressure gas ko tanks par constant feed pressure tak step down karta hai.

Pressure-fed cycle ka main disadvantage?

Bhaare tanks, ise low chamber pressures / lower performance tak limit karte hain.

Recall Feynman: 12 saal ke bachche ko explain karo

Ek juice box imagine karo. Agar tum chahte ho ki juice straw se tezi se nikle, to tum box ko squeeze karte ho — jitna zyada squeeze karo, utni tezi se aati hai. Ek pressure-fed rocket exactly wohi karta hai: tumhare haath ki jagah, ye ek trapped gas ki bottle use karta hai fuel tanks ko squeeze karne ke liye taaki fuel fire chamber mein shoot kare. Koi spinning pumps nahi, kuch bhi fancy nahi — bas ek bada squeeze. Pakad: zyada squeeze karne ke liye, box (tank) ko bahut mazboot hona padta hai, aur mazboot matlab bhaari. Isliye ye trick tabhi samajhdaari hai jab tumhe bahut zyada squeeze nahi karna — jaise space mein use hone wale chhote engines.