March 09, 2009

Heat capacities of dissolved solids & Organic solutions - Quickest Method

In my previous article on the topic, I suggested a method called dimoplon rule for estimating the heat capacity for solution with dissolved solids.

The method was giving a detailed estimate with accurate prediction for such values of specific heat capacities.

However, I am also giving a very quick method for such evaluations with some approximation. The results from this method are accurate enough for preliminary estimates and are not too far from experimental values compared to previous method.

The Quick method is known as Vosseller method proposed by him in 1973.

Cpsolution = 1 - 0.7 x W1
Where W1 is Wt% of solids in solution.

So for our example of Sodium Carbonate solution of 20% in previous post will result in as below.

For 20% solids W1 = 0.2
So specific heat of solution shall be 1 - 0.7 x 0.2 = 0.86

Now compare this with literature data & previous detailed method.

Literature data = 0.85
Dimoplon method = 0.848
Vosseller method = 0.86

So error is still only 1.2% but the method is quite quick for initial understanding of the system & calculations.

Similarly Vosseller also proposed this kind of equation for organic solutions with water where the equation is

Cpsolution = 1 - 0.45 X W1
Here W1 is the Wt % of Organics in water. So for 20% Ethanol mixture the heat capacity can be assumed as = 1 - 0.45 x 0.2 = 0.91 which is quite close to experimental value.

Hope it will be useful for many of you in different industries.

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