Newtons Law of Cooling   
Newtons Law of Cooling

  • State Newton’s law of cooling.
  • Calculate rate of heat flow by convection using Newton’s law of cooling.
  • Understand the governing equation relevant to natural convection.

Convection is expressed by Newton’s law of cooling as:

\[\dot{Q} = h A_{s}(T_{s} - T_{\infty}) = \rho V C_P \dfrac{dT}{dt}\]

Where h is the convection heat transfer coefficient
\( A_{s}\) is the surface area through which convection heat transfer takes place
\( T_{s}\) is the surface temperature
\( T_{\infty}\) is the temperature of the fluid sufficiently far from the surface

When heat is transferred from one particle of hot body to another by actual motion of the heated particles, it is referred to as heat transfer by: (SSC JE ME paper 6- March 2017 Morning)

Correct Answer: B

When heat is transferred by molecular collision, it is referred to as heat transfer by:

Correct Answer: B

Heat transfer in liquid and gases takes place by: (UPPCL JE March 2021-Shift I)

Correct Answer: B

In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by:

Correct Answer: C

Consider a hot boiled potato kept on a plate and cooled by natural convection in air. During the first minute, the temperature drops by 10$^{\circ}\mathrm{C}$. During the second minute, will the temperature drop be more than, less than or same as that during the first minute?

Correct Answer: B

Air at 300$^\circ$C flows over a plate of dimensions 0.50 m, by 0.25 m. if the convection heat transfer coefficient is 250 $W/m^2.K$; determine the heat transfer rate from the air to one side of the plate when the plate is maintained at 400$^\circ$C.

\begin{align*} q &=h A\left( T_{\infty }-T_{s}\right)\\ &= 250\left( 0.25 \times 0.50\right) \left(300-40\right)\\ &=8125\ W \end{align*}

Correct Answer: A

Film coefficient is defined as Inside diameter of tube

Correct Answer: B