Heat Transfer Coefficient Converter

About Heat Transfer Coefficient

The heat transfer coefficient (also known as the film coefficient or convective heat transfer coefficient) is a proportionality constant that quantifies the rate of heat transfer between a solid surface and a fluid (liquid or gas) moving over it. It represents how efficiently heat is transferred across the boundary layer between a solid and fluid, measuring the heat flux per unit temperature difference.

Understanding Heat Transfer Coefficient Units

Heat transfer coefficient is measured in various units depending on the system of measurement and specific application:

• Watt per square meter-kelvin (W/(m²·K)): The SI unit for heat transfer coefficient, measuring the heat energy transferred per unit area per degree temperature difference
• Watt per square meter-celsius (W/(m²·°C)): Functionally identical to W/(m²·K) since a one-degree change in Celsius equals a one-degree change in Kelvin
• BTU per hour-square foot-fahrenheit (BTU/(h·ft²·°F)): The imperial unit commonly used in HVAC, construction, and energy applications in the US
• BTU per second-square foot-fahrenheit (BTU/(s·ft²·°F)): Used for high-intensity heat transfer applications
• Calorie per second-square centimeter-celsius (cal/(s·cm²·°C)): Formerly used in scientific applications
• Kilocalorie per hour-square meter-celsius (kcal/(h·m²·°C)): Sometimes used in European heating and energy calculations

Common Heat Transfer Coefficient Conversions

• 1 W/(m²·K) = 1 W/(m²·°C)
• 1 W/(m²·K) = 0.1761 BTU/(h·ft²·°F)
• 1 W/(m²·K) = 0.00004892 BTU/(s·ft²·°F)
• 1 W/(m²·K) = 0.00002388 cal/(s·cm²·°C)
• 1 W/(m²·K) = 0.86 kcal/(h·m²·°C)

Typical Heat Transfer Coefficient Values

Heat transfer coefficient values vary widely depending on the fluid type, flow regime, geometry, and surface conditions:

Applications of Heat Transfer Coefficients

Heat transfer coefficients are crucial for designing and analyzing many systems:

• Heat exchangers: Designing efficient heat exchangers for industrial processes, power generation, and HVAC systems
• Building thermal design: Calculating heat losses through walls, windows, and roofs in buildings
• Electronics cooling: Designing cooling systems for electronic components and devices
• Food processing: Calculating heating and cooling times for various food products
• Chemical reactors: Designing temperature control systems for chemical processes
• Aerospace applications: Analyzing heat transfer for aircraft and spacecraft components
• Automotive design: Cooling systems for engines, brakes, and exhaust systems
• Energy systems: Solar collectors, boilers, and steam generators

Factors Affecting Heat Transfer Coefficient

Several factors influence the heat transfer coefficient value:

• Fluid properties: Viscosity, thermal conductivity, density, and specific heat capacity
• Flow characteristics: Velocity, flow regime (laminar or turbulent), and boundary layer thickness
• Surface geometry: Shape, orientation, and roughness of the surface
• Temperature difference: Between the surface and the fluid
• Phase changes: Such as boiling or condensation, which dramatically increase heat transfer rates
• Surface enhancements: Fins, ribs, or other features that increase surface area or turbulence

Calculating Heat Transfer Coefficient

Heat transfer coefficient (h) relates to several key equations:

• Newton's Law of Cooling: q = h·A·(Ts - T∞), where q is the heat transfer rate, A is the surface area, Ts is the surface temperature, and T∞ is the fluid temperature
• Dimensionless analysis: Heat transfer coefficients are often calculated using dimensionless numbers like the Nusselt number (Nu), which is related to h by Nu = (h·L)/k, where L is a characteristic length and k is the fluid's thermal conductivity
• Overall heat transfer coefficient (U): In heat exchangers, the overall heat transfer coefficient considers the combined effects of conduction through walls and convection on both sides: 1/U = 1/h₁ + Δx/k + 1/h₂

Relationship to Other Heat Transfer Concepts

The heat transfer coefficient is related to other heat transfer concepts:

• Thermal resistance: R = 1/(h·A), the convective thermal resistance is inversely proportional to the heat transfer coefficient
• Heat flux: q" = h·ΔT, heat flux (heat transfer rate per unit area) is proportional to the heat transfer coefficient and the temperature difference
• Conduction: At the solid-fluid interface, the conductive heat flux must equal the convective heat flux
• Radiation: In many applications, both convective and radiative heat transfer occur simultaneously. The radiative component is often approximated with a radiative heat transfer coefficient

Our heat transfer coefficient converter provides accurate conversions between all these units, making it easy to translate between different measurement systems for engineering calculations, thermal analysis, and energy applications.