Question

A concrete wall of thickness 15 cm has inside temperature 25°C and outside temperamre 5°C. The rate of heat loss through per square meter of wall(thermal conductivity 0.81J/(smK)) is?
1) 108 J/s
2) 120 J/s
3) 163 J/s
4) 54 J/s​

Answer 1

Step by step ans:

what is heat transfer ?

Heat transfer is the process of transfer of heat from high temperature reservoir to low temperature reservoir. In terms of the thermodynamic system, heat transfer is the movement of heat across the boundary of the system due to temperature difference between the system and the surroundings.

conduction conviction are types of heat transfer

now coming over to the given numerical we are given-

given data = 1. Temp 1 = 25° C

                         Temp 2= 5° C

                        Thermal conductivity = 0.81J/(smK))

                        width = 15cm or 0.15mtr

      Formula for calculating heat transfer =

                       dQ/dt=h A (T₁−T₂) / dL

              dq = change in heat

               dt = per unit time

               h = thermal conductivity

               A= area across wall

              T₁and T₂ are temperature across wall

               dL = width of wall

         dq/dt = 0.81 * 1mtr² * (25-5) / 0.15 mtr

              heat transfer rate = 108 J/sec ANS