What factors affect the heat transfer coefficient?

Key factors include: fluid velocity (higher velocity = higher h), fluid properties (thermal conductivity, viscosity, specific heat), flow type (laminar vs turbulent), surface geometry, and phase change (boiling/condensation dramatically increases h). Temperature and pressure also affect fluid properties.

What's the difference between convective and overall heat transfer coefficient?

The convective coefficient (h) describes heat transfer between a surface and adjacent fluid. The overall coefficient (U) includes all resistances: inside convection, wall conduction, and outside convection. For a heat exchanger: 1/U = 1/h₁ + wall resistance + 1/h₂.

Why is boiling heat transfer so efficient?

During boiling, vapor bubbles form and rapidly carry heat away from the surface. This creates strong local turbulence and utilizes latent heat of vaporization. Heat transfer coefficients for boiling can be 10-100 times higher than single-phase convection.

How do I calculate heat transfer coefficient?

For simple cases, use empirical correlations like Nusselt number relationships. h = Nu × k / L, where Nu is Nusselt number, k is fluid thermal conductivity, and L is characteristic length. Different correlations apply for free convection, forced convection, internal flow, and external flow.

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About Heat Transfer Coefficient Conversion

The heat transfer coefficient (also called film coefficient, surface conductance, or convective heat transfer coefficient) measures how effectively heat transfers between a solid surface and an adjacent moving fluid. It's crucial for HVAC system design, heat exchanger calculations, electronics cooling, boiler and condenser design, and virtually all thermal engineering applications where convection plays a role. The coefficient depends on fluid properties, flow conditions, and surface geometry.

The SI単位 is watts per square meter kelvin (W/m²·K), representing the heat power transferred per unit area per degree of temperature difference between surface and fluid. In US applications, BTU per hour square foot degree 華氏 (BTU/hr·ft²·°F) is common in HVAC and building design. Higher coefficients mean more efficient heat transfer—forced convection has higher coefficients than free convection, and phase change (boiling/condensation) produces the highest values.

Our converter handles all standard heat transfer coefficient units for thermal engineering, HVAC, and process design applications.

Common Heat Transfer Coefficient Conversions

変換元	変換先	乗数
W/m²·K	BTU/hr·ft²·°F	0.1761
BTU/hr·ft²·°F	W/m²·K	5.678
W/m²·K	kcal/hr·m²·°C	0.8598
kcal/hr·m²·°C	W/m²·K	1.163
W/m²·K	W/cm²·K	0.0001
W/cm²·K	W/m²·K	10,000
BTU/hr·ft²·°F	kcal/hr·m²·°C	4.882
W/m²·K	cal/s·cm²·°C	0.0000239

Heat Transfer Coefficient 単位リファレンス

Watt per square meter kelvin (W/m²·K) – The SI単位 for heat transfer coefficient. Represents heat power transferred per unit area per degree of temperature difference between surface and fluid. Standard in engineering calculations worldwide. Typical values range from 5-25 W/m²·K for natural convection in air to over 10,000 W/m²·K for forced convection with water or phase change processes.

BTU per hour square foot degree F (BTU/hr·ft²·°F) – US customary unit common in HVAC design, building energy analysis, and industrial heat exchanger specifications. 1 BTU/hr·ft²·°F ≈ 5.678 W/m²·K. Widely used in American engineering practice and building codes. Equipment catalogs often list performance in these units.

Kilocalorie per hour square meter degree C (kcal/hr·m²·°C) – Older metric unit still found in European industrial references and legacy documentation. 1 kcal/hr·m²·°C ≈ 1.163 W/m²·K. Sometimes used in food processing and older chemical engineering literature.

Watt per square centimeter kelvin (W/cm²·K) – Used for high-intensity heat transfer applications like electronics cooling, high-power lasers, and nuclear engineering. 1 W/cm²·K = 10,000 W/m²·K. Convenient when dealing with small, high-power-density surfaces.

Calorie per second square centimeter degree C (cal/s·cm²·°C) – CGS unit occasionally found in scientific literature. Very large unit: 1 cal/s·cm²·°C = 41,868 W/m²·K. Rarely used in modern practice but appears in historical references.