LMTD (logarifmik o'rtacha harorat farqi) — issiqlik almashturgichda issiqlik uzatishni harakatlantiruvchi samarali o'rtacha harorat farqidir. U almashtirgich uzunligi bo'ylab issiq va sovuq suyuqliklar o'rtasidagi o'zgaruvchan harorat farqini logarifmik o'rtacha orqali hisobga oladi.

LMTD qanday hisoblanadi?

LMTD = (ΔT₁ − ΔT₂) / ln(ΔT₁/ΔT₂). For counter flow: ΔT₁ = T_h,in − T_c,out and ΔT₂ = T_h,out − T_c,in. For parallel flow: ΔT₁ = T_h,in − T_c,in and ΔT₂ = T_h,out − T_c,out.

Nima uchun qarama-qarshi oqim parallel oqimdan samaraliroq?

Qarama-qarshi oqim bir xil kirish/chiqish haroratlari uchun yuqoriroq LMTD hosil qiladi, ya'ni kamroq issiqlik uzatish yuzasi talab etiladi. Sovuq suyuqlik ham issiq suyuqlik kirish haroratiga yaqinroq qizdirilishi mumkin, bu esa parallel oqimda imkonsizdir.

LMTD qachon aniqlanmagan bo'ladi?

When ΔT₁ = ΔT₂ (equal temperature differences at both ends), the formula gives 0/0. In this special case, LMTD simply equals ΔT₁ = ΔT₂ (arithmetic mean equals log mean when both are equal).

What is Q = U × A × LMTD?

This is the basic heat exchanger design equation. Q is heat duty (W), U is overall heat transfer coefficient (W/m²K), A is heat transfer area (m²), and LMTD is the log mean temperature difference (K). Given any three, you can find the fourth.

Muhandislik uchun bepul vosita

Issiqlik almashturgich LMTD kalkulyatori

Calculate Log Mean Temperature Difference for parallel and counter flow heat exchangers. Optional Q=U·A·LMTD sizing.

LMTDQarshi & Parallel#181

Results

Qarshi Oqim LMTD

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Parallel Oqim LMTD

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Qarshi Oqim Yuzasi (agar U & Q berilgan bo'lsa)

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Parallel Oqim Yuzasi (agar U & Q berilgan bo'lsa)

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Hot Side ΔT

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Cold Side ΔT

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Harorat Profili (Qarshi Oqim)

LMTD Formula

Counter Flow

ΔT₁ = T_h,in − T_c,out | ΔT₂ = T_h,out − T_c,in

Parallel Flow

ΔT₁ = T_h,in − T_c,in | ΔT₂ = T_h,out − T_c,out

Hisoblash Tenglamasi

Qarshi oqim bir xil haroratlarda parallel oqimga nisbatan doimo yuqori LMTD hosil qiladi, ya'ni kamroq yuza talab etiladi.

LMTD Kalkulyatori — Qarshi va Parallel Oqimli Issiqlik Almashinuvchi

Published by Nikolai Shelkovenko on Fevral 15, 2026 Aprel 5, 2026

Results

LMTD Formula

Counter Flow

Parallel Flow

Hisoblash Tenglamasi

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