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I have been calculating a series of hypothesis for some aquariums/tanks situations, using heat transfer equations (conduction, convection, radiation, evaporation)

Typically we have aquariums that run at higher temperatures than the surroundings in winter and lower temperature than the surroundings at summer ... I stumble into a silly question in trying to establish the scenario

Question 1 is about Conductive heat transfer

Question 1 is about Conductive heat transfer

When the conduction is in a horizontal plane between two different fluids ( in this case air and water) instead of using Fourier's law

Q= K.A (ΔT/L)

should I do it

Q =

*= U A dT where U , overall heat transfer coefficient (W/(m2K), captures the individual fluid (air and water) convection heat transfer coefficient*

1 / U = 1 / hci + Σ (sn / kn) + 1 / hco

Is this a correct way of thinking ? Because the following 2 scenarios then will be more accurate ?

1 / U = 1 / hci + Σ (sn / kn) + 1 / hco

Is this a correct way of thinking ? Because the following 2 scenarios then will be more accurate ?

A. When in winter - water is higher in temperature than surrounding air, the heat transfer goes from the inside of the tank towards the surroundings - so I consider a loss of heat.

B. When in summer - water is lower in temperature than surrounding air, the heat transfer goes from the surroundings to the water inside - so I consider a gain in heat.

**Question 2 is about Convection heat transfer**

Does the same principle above applies to the rationale ? So using Newton's Law of Cooling

Q = = Hc A dT, where dT is temperature difference between the surface and the bulk fluid

I won't go into the details of calculating Hc_water (which is a all new thread...!) but my silly questions remains the same:

A. When in winter - water is higher in temperature than surrounding air:

so I consider the hot plane to be the superficial water film layer and the heat transfer is done from this layer to the surrounding air. I use here Hc_water ( convective heat coefficient of water). I consider a loss of heat ( regarding the aquarium)

B. When in summer - water is lower in temperature than surrounding air:

so I consider the hot plane to be the superficial air film layer and the heat transfer is done from this layer to water. I use here Hc_air ( convective heat coefficient of air). I consider a heat gain ( regarding the aquarium)

This is not looking as correct to me ... but I couldn't get my head around to be more accurate would greatly appreciate inputs and ideas

For now I am only considering the convective heat transfer in the open top of the aquarium.