Water at a temperature of T∞=25 °C flows over one of the surfaces of a steel wall (AISI 1010) whose temperature is Ts,1=

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Water at a temperature of T∞=25 °C
flows over one of the surfaces of a steel wall (AISI 1010) whose
temperature is Ts,1=40 °C. The wall is
0.35 m thick, and its other surface temperature
is Ts,2=100 °C. The thermal conductivities
of steel AISI 1010 and water are 61.7 W/(m⸱K) and 0.62 W/(m⸱K),
respectively.
Problem: What is the temperature gradient in the water
that is in contact with the wall? The answer should
be given using the unit of °C/m. Note that the
direction from the wall at Ts,2 to
the wall at Ts,1 is
positive.