# Heat Transfer between Two Immiscible Liquids in Laminar Flow

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This Demonstration shows the velocity and temperature profiles of two immiscible liquids flowing concurrently in laminar flow between two flat parallel plates. The properties of the two liquids are assumed to be constant and their velocity profiles are assumed to be independent of axial location. In the inlet region , the fluid temperature is uniform; in the region , the wall is maintained at a constant temperature . This problem occurs in various industrial applications, including desalination processes, water film lubrication of oil pipelines and microfluidics. You can vary the ratio of the properties of the denser lower fluid to the upper fluid (water at 300 K) to determine the velocity and temperature profiles and the average temperatures of the two fluids.

Contributed by: Clay Gruesbeck (November 2018)

Open content licensed under CC BY-NC-SA

## Details

The dimensionless horizontal distance is , where is the length of the plates.

The dimensionless vertical distance is .

The dimensionless temperature is .

The temperature profile of the two liquids can be obtained by solving a single partial differential equation with two different sets of parameters, one for each fluid:

,

where is the thermal diffusivity , is the fluid velocity, and , and are the fluid thermal conductivity, density and heat capacity, respectively.

Let be the distance between the plates, be the fraction filled with the lower fluid, with the interface at , then the lower plate is at , the upper plate is at , and the initial and boundary conditions are:

,

,

and

.

Here

,

,

and

,

where 1 and 2 represent properties of the lower and upper fluid, respectively.

An analytic solution for fully developed flow of two immiscible fluids between two flat plates when the fluids have arbitrary viscosity ratios and arbitrary flow rate ratios is derived in [1]:

,

.

The dimensionless velocity is

.

Here is the horizontal pressure gradient; the average (cup) temperatures of the two fluids are:

,

and

.

These equations are solved with the built-in Mathematica function NDSolve, and plots of the temperature and velocity contours, as well as the average temperatures, are shown.

Reference

[1] B. A. Finlayson, "Poiseuille Flow of Two Immiscible Fluids between Flat Plates with Applications to Microfluidics." (Nov 19, 2018) www.chemecomp.com/poiseuille_immiscible.pdf.

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