Dave Dickey Forum Moderator 290 Posts
Re: How do we ensure two liquids at different temperatures are mixed properly?5 June 2012 at 1:29pm
The answer to this question is simple and not the desired one. If a small quantity of warm biodiesel fuel is added to a tanker truck 80% full of 25 degree diesel, the added quantity of biodiesel will rapidly approach the tanker temperature of 25 degrees. Even with rapid mixing, some portion of the biodiesel can always drop below 32 degrees somewhere in a large quantity of 25 degree diesel. No computer model or comprehensive calculation is needed. The only way to assure that the biodiesel temperature never goes below 32 degrees it to assure that the tanker trucker of diesel is always above 32 degrees when the biodiesel is added.
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We need to splash blend two liquids at different temperatures but need to ensure that unmixed pockets of the warmer liquid never are cooled to below a certain temperature as once cooled below that specific temperature they undergo irreversible changes. How can we determine what the temperature limits for the two liquids, and flow rates for the injected liquid are? We assume that this would require some testing in the laboratory and then the use of theory to scale up. We are mixing warm biodiesel into diesel fuel into a tanker truck. The tanker truck is 80% full, and the remainder will be filled with biodiesel. Diesel temperatures would be expected to be ambient, i.e., varying depending on weather conditions but a reasonable worst case would be 25 degrees F, and we can modify input pipe diameter, flow rate and to some extent biodiesel temperature (although at considerable expense). We want to ensure that none of the biodiesel, including small pockets of biodiesel that at first are not well mixed into the diesel, do not cool to below about 32 degrees F. We are looking to understand how to solve this problem so to set appropriate guidelines about what conditions are necessary before mixing. (1) If bench scale tests are recommended, how would those results be scaled up? (2) Is it appropriate to use a computer model, and in that case which one? Can these computer programs be run by the average chemical engineer or is a consultant required?
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