I am exploring buying a flat plate heat exchanger for purposes of blending fuels and am wondering which size and how many plates are recommended?
http://cgi.ebay.ca/10-Plate-Brazed-Heat-Exchanger-SVO-W...sidZp1742.m153.l1262
A quick google search found this, after paying the exchange rate and shipping I guess I'd be looking at $100. Is this particular one adequate?

These are the best for the money
http://www.burnveg.com/forum/viewtopic.php?t=78

I like Omarsales.

Next question, how necessary is a FPHE when blending? Where I live it seldom gets below freezing. If one is careful to check viscosity and perform freezer tests in the winter is a FPHE required, or is it more of an insurance, just in case.

What's your concept of "necessary"? Is clean and complete combustion of the fuel a goal, or is just running good enough? Is engine life a factor? From what I've read searching this forum these are all things to consider, and its all been discussed before. I did a bunch of reading before I registered and posted anything. Most of the useful information is in the archives from people who don't post messages on this forum anymore.

^I'll take that as a yes (it's necessary). Clean combustion and normal engine life are factors for me.
I've done searches but didn't find this particular question addressed specifically.

The information I read indicates that the closer the fuel temperature is to normal coolant temperature then the cleaner the combustion, fewer deposits, etc., and even more so if the fuel contains veg-oil.

One of the basic premises of blending it that you don't NEED to modify the vehicle. Some people like to stick to that, Others don't mind doing some mods but don't want to go to the trouble of a full 2 tank conversion.

I found when Blending the addition of a small HE aided the Performance during the transition time of starting and the engine getting up to full temp. As blends are going to contain a percentage of oil and we know heat thins oil, then the logical benefits of blend heating are obvious.

Other benefits I believe comes from heating blends when a HE is installed before the filters is the ability of the warm oil to melt any fats out of the filters to keep them from blocking, The warmer oil blend will pass through the filters easier and the faster warm up of the fuel system components like the IP which I think really dictate the temp the fuel is injected at.

I think a small 10 plate HE would be fine for this application but make sure you plumb it so ALL your coolant is running through it and put the T after not before the HE for Max heating.

One thing to look out for is if you are planning blending with RUG. Heating can cause the RUG to boil and turn to vapor which will lead to poor running or even stoppages.
My experience indicates that this should not be a problem with blends below 15% RUG and that heating such blends in my car, dosen't seem to make much difference to the vapor issue because if there is no HE the fuel will boil between the lift pump and the IP causing the same problems. Other vehicles may be different but if you are going to blend with RUG, this is something you should keep in mind.

Adding a valve so you can regulate or shut off the heat is something a few people do but I don't see the benefit myself.

Thanks for the schoolin'! There are pros and cons to brewing bio and the same can be said for blending. I want to be fully aware of the possible pitfalls before I start.

Best price on FPHE I have found is here:

http://www.dudadiesel.com/heat_exchangers.php

I have not ordered from them, but will whenever I find another Benz to play with.