The Reynolds number is the major parameter that relates fluid flow momentum to friction forces. How is the Reynolds number defin
1 answer:
Answer:
Reynolds number determines whether a flow is laminar or turbulent flow.
Explanation:
Reynolds number is defined as ratio of inertia force to the viscous force. it is a dimension less number. Reynolds number is used to describe the type of flow in a fluid whether it is laminar flow or turbulent flow. Reynolds number is denoted by Re.
When Reynolds number is in the range of 0 to 2000, the flow is considered to be laminar.
When Reynolds number is in the range of 2000 to 4000, the flow is considered to be transition.
And when Reynolds number is more than 4000, the flow is turbulent flow.
The boundary layer thickness for a fluid is given by
δ =
where δ is boundary layer thickness
x is distance from the leading edge
Re is Reynolds number
Thus from the above boundary layer thickness equation, we can see that the boundary layer thickness varies inversely to square root of reynolds number.
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Answer:
15.24°C
Explanation:
The quality of any heat pump pumping heat from cold to hot place is determined by its coefficient of performance (COP) defined as
Where Q_{in} is heat delivered into the hot place, in this case, the house, and W is the work used to pump heat
You can think of this quantity as similar to heat engine's efficiency
In our case, the COP of our heater is
Where T_{house} = 24°C and T_{out} is temperature outside
To achieve maximum heating, we will have to use the most efficient heat pump, and, according to the second law of thermodynamics, nothing is more efficient that Carnot Heat Pump
Which has COP of:
So we equate the COP of our heater with COP of Carnot heater
Rearrange the equation
Solve this simple quadratic equation, and you should get that the lowest outdoor temperature that could still allow heat to be pumped into your house would be
15.24°C