Calculation of Heat Transfer Coefficient for Intenral and External Flow

Determination of Heat Transfer Coefficient for Internal Flow

Laminar Flow

• The Dittus-Boelter equation is a widely used empirical equation that relates the average heat transfer coefficient for forced convection to the fluid properties, the flow conditions, and the geometric properties of the system.

• The equation for heat transfer coefficients  is given by:

h = Nu * k/d

where h is the average heat transfer coefficient, k is the thermal conductivity and D is the hydraulic diameter of the pipe or duct.

• The Reynolds number is defined as:

Re =ρ* V * D/ μ

         where, ρ is the fluid density, V is the fluid velocity, D is the hydraulic diameter, and μ is the dynamic viscosity of the fluid.

• The Prandtl number is defined as:

             Pr = μ*Cp / k

• where Cp is the specific heat at a constant pressure of the fluid.

The assumption for Equations Dittus -Boelter equation

• The Dittus – Boelter equation is valid for
  • Fully developed for thermal and fluid flows
  • Turbulent flow in a circular pipe, Reynolds numbers > 2300
  • Constant Wall Temperature.
• However, it has been found to give reasonably accurate results for a wide range of geometries and flow conditions.

Calculator For Internal Heat Transfer

Validation with CFD Results

• The heat transfer from the experimntal correlations need to be comparedCFD Results for validation of any internal heat transfer problems as presented in the post.
• Difference up to 20% is acceptable depending on complexicity of case

Heat Transfer Coefficient for Different Geometries

HTC Calculator tab — 6 geometries supported:

• Flat Plate (laminar/mixed correlations)
• Cylinder (Churchill–Bernstein)
• Sphere (Whitaker)
• Pipe – internal flow (Dittus–Boelter / laminar)
• Annulus (hydraulic diameter method)
• Finned Surface (efficiency-weighted)

Both Forced Convection and Natural Convection modes, with automatic regime detection (laminar/turbulent/mixed). Fluid presets for Air, Water, Engine Oil, Ethylene Glycol, and Steam are included.

Unit Converter tab — 15 quantity categories: HTC, heat flux, power, temperature (°C/°F/K/°R), ΔT, thermal conductivity, resistance, diffusivity, length, area, velocity, pressure, viscosity, density, and specific heat — with a live conversion table.

Reference tab — dimensionless numbers with definitions and typical HTC ranges

Heat Transfer Coefficient Table for internal flow

 

The heat transfer coefficient (h) for internal flow in ducts and pipes depends on factors such as fluid properties, flow type (laminar or turbulent), and pipe geometry. Below is a general table summarizing approximate values for different cases.

Heat Transfer Coefficient ($h$) for Internal Flow in Ducts and Pipes

Flow Type	Fluid Type	Heat Transfer Coefficient, $h$ (W/m²·K)	Remarks
Laminar Flow ($Re<2300$)	Air	5 – 25	Low heat transfer due to no turbulence
	Water	100 – 1000	Higher heat transfer due to high thermal conductivity
	Oil	50 – 300	Lower than water due to low thermal conductivity
Turbulent Flow ($Re>4000$)	Air	30 – 300	Strong mixing enhances heat transfer
	Water	500 – 10,000	High heat transfer due to turbulence
	Oil	100 – 1000	Moderate improvement over laminar flow
Boiling Flow (Two-Phase)	Water (boiling)	3000 – 100,000	Phase change greatly enhances heat transfer
Condensing Flow (Two-Phase)	Steam	5000 – 100,000	Condensation significantly increases $h$

Common Equations for Convective Heat Transfer Coefficient

1. Laminar Flow (Constant Wall Temperature)

   • Circular Pipe:
     • Nu=3.66​
   • Parallel Plates: Nu=4.86​

2. Turbulent Flow (Dittus-Boelter Equation,

   • Valid for 0.7<Pr<160

   • Re>10,000

   • Nu=0.023*Re^0.8*Pr^0.3

3. Sieder-Tate Correlation (Includes viscosity effects)