Using the Newton's Law of Cooling calculator, you can quickly determine how long it takes for an object to cool from one temperature to another.
What Is Newton's Law of Cooling?
“The rate of heat loss of a body is directly proportional to the difference between its temperature and the surrounding (ambient) temperature.”
In simple terms, it describes how the temperature of an object changes when exposed to surroundings with a different temperature. Heat transfer occurs mainly through conduction and convection for this law to be applicable.
Newton's Law of Cooling Formula
The differential form of Newton's Law of Cooling is:
\(\dfrac{dT}{dt} = -k (T - T_s)\)
- T = temperature of the object at time t
- Tₛ = surrounding (ambient) temperature
- k = cooling constant
Solving this differential equation gives the temperature as a function of time:
\(\displaystyle T(t) = T_s + (T_0 - T_s)e^{-k t}\)
- T₀ = initial temperature of the object
- t = time elapsed
- k = cooling constant
This allows you to calculate the temperature of a body at any given time. For more details, see Wikipedia.
How to Calculate Newton’s Law of Cooling
Follow these steps:
- Determine the Ambient Temperature: Measure the temperature of the surrounding air or medium.
- Determine the Initial Temperature: Measure the object's initial temperature (°C or K).
- Determine the Cooling Coefficient (k): Estimate based on material properties and exposed surface area.
- Measure the Final Temperature: Use the formula \(T(t) = T_s + (T_0 - T_s)e^{-k t}\) to find the temperature at time t.
Example:
Find the final temperature of a body after 3 seconds using Newton’s Law of Cooling. Given:
- Ambient temperature (Tₛ) = 20 °C
- Initial temperature (T₀) = 3 °C
- Surface area (A) = 0.003 m²
- Heat capacity (C) = 4 J/K
- Heat transfer coefficient (h) = 1 W/(m²·K)
Solution:
- Calculate the cooling constant: \(k = \dfrac{hA}{C} = \dfrac{1 \times 0.003}{4} = 0.00075\)
- Use the cooling formula: \(\displaystyle T(t) = T_s + (T_0 - T_s)e^{-k t}\)
- Substitute values: \(\displaystyle T(3) = 20 + (3 - 20)e^{-0.00075 \times 3}\)
- Calculate: \(\displaystyle T(3) = 20 - 17 \times e^{-0.00225} \approx 20 - 16.96 = 3.04 °C\)
Instead of manual calculations, the Newton’s Law of Cooling calculator can provide accurate results instantly.
Limitations of Newton’s Law of Cooling
- The temperature difference between the object and surroundings should be small.
- Heat loss should primarily occur through convection and conduction.
- The surrounding temperature must remain constant during the process.
Frequently Asked Questions (FAQs)
Why Is Newton's Law of Cooling Important?
- Predicts how the temperature of an object changes over time
- Analyzes heat transfer between an object and surroundings
- Useful in practical engineering applications
What Factors Affect Newton's Law of Cooling?
- Surface area of the object
- Temperature difference between object and surroundings
- Heat transfer coefficient (k)
How Do You Find k in Newton's Law of Cooling?
The cooling constant k can be determined in two ways:
- Using temperature difference over time: \(\displaystyle k = \frac{T_1 - T_2}{t}\), where t = t₂ - t₁
- Using heat transfer coefficient and area: \(\displaystyle k = \frac{hA}{C}\), where h = heat transfer coefficient, A = area, C = heat capacity