# How to extract values @ 2 different positions [hot & cold sides] - liquid evaporation

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September 25, 2019, 21:28
How to extract values @ 2 different positions [hot & cold sides] - liquid evaporation
#1
Senior Member

Kumaresh
Join Date: Oct 2016
Posts: 162
Rep Power: 5
Hello Foamers,
This evaporation problem is a part of work in my main problem. The problem is simple, a rectangular 1D channel is considered where right end is symmetry, left end (wall) is with the temperature of 1323K, other faces are empty (1D problem). With supply of heat (temperature) from the left wall end, the liquid inside the channel will be evaporated, and the heat is slowly propagated from left to right end. The liquid is evaporated based on the condition (also shown in the ATTACHMENT) as follows:
Quote:
 CONDITION: @ T= 100deg ==> (alpha) -->xb(-) =0 Based on it, mass and heat balances are calculated at the boiling plane (surface) as, Mass balance (r) = (rho*alpha) -->xb(+) * fvm::ddt(xb) [kg/m2.s] Heat balance (-K dT/dx) -->xb(-) = (r) * 2.257*e6 [W/m2] where, alpha = moisture content, rho = density, xb =distance of plane from high temp side, (+) (-) cold and hot temp sides
How to extract values at two different positions - (+) hot (high) and (-) cold (low) temperature sides during evaporation of liquid ??

Quote:
 (alpha) -->xb(-) =0 @ hot temperature side - constant value based on condition (alpha) -->xb(+) @ cold temperature side - calculated based on cell centre I guess
During evaporation, the changes in hot and cold side should be calculated based on cell based solution ?? like T[labelOfClosestCell] (or) T[nearestCellIndex]
I have gone through links, which is helpful somehow, but I'm not sure with my approach.
How to identify cell neighbours
transient source term

Kindly someone guide me by sharing ideas.
Thank you
Attached Images
 Boiling.jpg (77.1 KB, 10 views)

 September 28, 2019, 01:48 #2 Member   Atul Kumar Join Date: Dec 2015 Location: National Centre for Combustion Research and Development Posts: 46 Rep Power: 5 what is boundary type ??? if its region model and coupled boundary use nbrRegion to extract neighbour region values Kummi likes this.

September 30, 2019, 02:16
Movement of evaporating plane
#3
Senior Member

Kumaresh
Join Date: Oct 2016
Posts: 162
Rep Power: 5
Dear Atul Kumar,
Thank you for your response. There is no problems in boundary type and I'm not using any coupled boundary. Let me explain you the gist of my main confusion again.

The evaporation is based on the condition followed by the calculation of mass and heat fluxes. And most importantly, the progression (movement) of evaporating plane is taken into account based on sign changes [(+) low temp side, (-) high temp side)].

As we discussed about the the sample code below, where I am not sure with the code, because I didn't defined the progression (movement) of evaporating plane based on sign changes [(+) low temp side, (-) high temp side)]. Attachment in previous post gives clear overview. Please share the ideas. I need help in constructing the OpenFOAM code.

Quote:
 forAll(mesh.cells(),celli) { if (T[celli] = scalar(100.0)) // CONDITION { moisture[celli] = scalar(0.0); } /* else if (Tb[cellI] < Tsat) { moisture[cellI] = moisture[cellI]; } */ evapRate +=rho[cellI] * moisture [cellI] * fvm::ddt(xb_); // kg/m2.s heatFlux +=evapRate * Enthalp.value(); //W/m2 }