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Heat Transfer Calculator

Calculate heat transfer through conduction, convection, and radiation.

Parameters

ⓘ
Select the type of heat transfer mechanism
°Cⓘ
Hot temperature
°Cⓘ
Cold temperature
m²ⓘ
Surface area for heat transfer
mⓘ
Material thickness (for conduction)
W/m·Kⓘ
Material thermal conductivity (for conduction)
Show Trail

Controls

xⓘ

Calculated Values

Heat Transfer Rate
480.00;W480.00;W

Examples

Heat Loss Through a Wall

Calculate the heat loss through a 2m × 3m wall with thickness 0.2m. The inside temperature is 20°C, outside temperature is -5°C, and the wall material has thermal conductivity of 0.8 W/m·K.

  • Heat Transfer Rate: 600.00600.00

Convection Heat Transfer

A hot plate with surface area 0.5m² is at 150°C. The surrounding air is at 25°C. If the convection coefficient is 15 W/m²·K, calculate the heat transfer rate.

  • Heat Transfer Rate: 937.50937.50

Radiation Heat Transfer

A black body with surface area 1m² is at 500°C. The surrounding environment is at 27°C. Calculate the heat transfer rate by radiation (emissivity = 0.9).

  • Heat Transfer Rate: 17800.0017800.00

Visualization

Heat Transfer Fundamentals

Heat transfer is the movement of thermal energy from one object or system to another due to temperature differences. There are three main mechanisms of heat transfer: conduction, convection, and radiation. Understanding these processes is crucial in engineering, physics, and everyday applications.

Conduction is the transfer of heat through a material without any bulk motion of the material itself. It occurs when there is a temperature gradient within a solid or stationary fluid. The rate of heat transfer by conduction is given by Fourier's law: Q = kA(T₁ - T₂)/L, where k is the thermal conductivity, A is the cross-sectional area, T₁ and T₂ are the temperatures at the two ends, and L is the thickness.

Convection is the transfer of heat through the movement of fluids (liquids or gases). It involves both conduction and fluid motion. Natural convection occurs due to density differences caused by temperature variations, while forced convection is driven by external forces like pumps or fans. The heat transfer rate is given by: Q = hA(T₁ - T₂), where h is the convection heat transfer coefficient.

Radiation is the transfer of heat through electromagnetic waves, primarily in the infrared region. Unlike conduction and convection, radiation can occur through a vacuum. The heat transfer rate by radiation is given by the Stefan-Boltzmann law: Q = εσA(T₁⁴ - T₂⁴), where ε is the emissivity, σ is the Stefan-Boltzmann constant (5.67 × 10⁻⁸ W/m²·K⁴), and temperatures are in Kelvin.

In real-world applications, heat transfer often occurs through multiple mechanisms simultaneously. For example, a hot object in air loses heat through both convection to the surrounding air and radiation to the environment. The total heat transfer rate is the sum of all individual components: Q_total = Q_conduction + Q_convection + Q_radiation.

Thermal conductivity (k) is a material property that indicates how well a material conducts heat. Metals like copper and aluminum have high thermal conductivity, while insulating materials like wood and fiberglass have low thermal conductivity. The unit is W/m·K.

The convection heat transfer coefficient (h) depends on the fluid properties, flow conditions, and surface geometry. It varies widely from about 5-25 W/m²·K for natural convection in air to 100-10,000 W/m²·K for forced convection with liquids.

Emissivity (ε) is a measure of how well a surface emits thermal radiation compared to a perfect black body. It ranges from 0 to 1, where 1 represents a perfect emitter. Polished metals have low emissivity (0.02-0.1), while black surfaces have high emissivity (0.8-0.95).

Explore Further

More thermodynamics tools

Physics Equations

Conduction Heat Transfer
Q=kAT1−T2LQ = kA\frac{T_1 - T_2}{L}
Convection Heat Transfer
Q=hA(T1−T2)Q = hA(T_1 - T_2)
Radiation Heat Transfer
Q=ϵσA(T14−T24)Q = \epsilon\sigma A(T_1^4 - T_2^4)

Step-by-Step Solution

See how the main results are calculated.

1

Identify Variables

List all given parameters

Result:

T1=100°C,T2=20°C,A=1m2,L=0.1mk=0.6W/m⋅K,h=undefinedW/m2⋅K,ε=undefinedT₁ = 100°C, T₂ = 20°C, A = 1 m², L = 0.1 m k = 0.6 W/m·K, h = undefined W/m²·K, ε = undefined

Explanation:

We need to identify all the parameters involved in the heat transfer calculation.

2

Apply Fourier's Law

Use Fourier's law for heat conduction

Equation:

Q=kAT1−T2LQ = kA\frac{T_1 - T_2}{L}

Calculation:

Q=0.6×1×100−200.1Q = 0.6 \times 1 \times \frac{100 - 20}{0.1}
Q=0.6×1×800.1Q = 0.6 \times 1 \times \frac{80}{0.1}
Q=480WQ = 480 W

Result:

Q=480.0000WQ = 480.0000 W

Explanation:

Fourier's law states that heat transfer by conduction is proportional to the temperature gradient and thermal conductivity.

Frequently Asked Questions (FAQ)

What is the difference between conduction and convection?

Conduction is heat transfer through a material without bulk motion, while convection involves heat transfer through fluid motion. Conduction occurs in solids and stationary fluids, while convection requires fluid movement.

Why does radiation not require a medium?

Radiation transfers heat through electromagnetic waves, which can travel through a vacuum. Unlike conduction and convection, which require physical contact or fluid motion, radiation can occur across empty space.

How does thermal conductivity affect heat transfer?

Higher thermal conductivity means better heat conduction. Materials with high thermal conductivity (like metals) transfer heat quickly, while low thermal conductivity materials (like insulators) transfer heat slowly.

What factors affect the convection coefficient?

The convection coefficient depends on fluid properties (viscosity, thermal conductivity, density), flow conditions (laminar vs turbulent), surface geometry, and temperature difference.

Why is emissivity important in radiation heat transfer?

Emissivity determines how efficiently a surface emits thermal radiation. Surfaces with high emissivity (close to 1) emit radiation effectively, while low emissivity surfaces (like polished metals) are poor emitters.

How do you calculate combined heat transfer?

For combined heat transfer, calculate each mechanism separately and add them together: Q_total = Q_conduction + Q_convection + Q_radiation. Each component uses its respective equation and parameters.

What units are used for heat transfer calculations?

Heat transfer rate is typically measured in watts (W) or kilowatts (kW). Temperature can be in Celsius or Kelvin, area in square meters (m²), and thickness in meters (m).

How does temperature difference affect heat transfer?

Greater temperature differences result in higher heat transfer rates. This is evident in all three mechanisms: conduction (proportional to ΔT), convection (proportional to ΔT), and radiation (proportional to ΔT⁴).

Practice MCQs

  1. Which heat transfer mechanism can occur through a vacuum?
  2. What is the unit of thermal conductivity?
  3. In the conduction equation Q = kA(T₁ - T₂)/L, what does 'k' represent?
  4. Which material would have the highest thermal conductivity?
  5. What is the Stefan-Boltzmann constant used for?
  6. For natural convection in air, typical convection coefficients range from:
  7. What is the relationship between heat transfer rate and temperature difference in radiation?
  8. Which surface would have the highest emissivity?

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