Question

I want mix or dilute a different concentratins from absolut ethanol in or with cell culture media in 37 temprature degree, because of this I want to know what is the evaporation rate for above ? to avoid the evaporation also to keep the concentration that I prepared with cell culture is same .

please in details

Answer 1

We have to analize the heat transfer. The heat is going from air to the alcohol

When the evaporation occurs this means that the alcohol is gaining heat, that heat comes from the environment, in this case air.

We need 2 equations to model the heat transfer 1 for the Air and other for the alcohol

For the air we use the newton´s law of cooling

dQ / dT=- h*A Negative sign means that the air is loosing heat

if we integrate if on both sides we have:

Q =- h*A * (Talc - Tair)

For the evaporation we have to use a energy balance

Heat in - H out + Qgenerate - W = dQ/dt

or

Cp( Tout - T in) + m*+ Q generated - W = dQ/dt

we will only consider the evaporation of alcohol so T out = Tin, no Q is generated in the system (there´s not a electrical heater or something like that) and we are not takig out work from the system so the equation is as follows:

dQ/dt = m * if we integer we have

Q = m * * t wich is the mass of the alcohol multiplied by the heat of evaporation, we can express it in fuction of the volume

Q = where is the density of alcohol

so if we make equal this equations we have:

m**t = -h * A * (Talc - Tair)

t =( -h * A * (Talc - Tair) / m*

that´s the mathematical expression, to solve the problem you need to find the h = heat transfer coefficient of air, the which is the latent heat of alcohol and the heat transfer area which is the area of the recipe that contains the alcohol that is in contact with the environment.