Sorry, 'Drop it in' was not a good term. I should have said.. "lower it into the vapour". If you took a cold board and just dropped it into the vapour cloud quickly, the temp rise rate would likely be very high, but if you did it slowly in a controlled way, it would be quite differnet no doubt.
What i know about my 'bucket' heater.. ( its about 400mm deep ). The amount of energy you stick in, will determine the height of the 'thick vapour'. once its at 'temp', if i run it at ~300W it will create a cloud that is about 20mm thick. If its 600W, it will create a cloud 60mm thick. Above the thick vapour is a 'soft' vapour zone, where the temp is around 150-190C .. Above that is an area of warm air. ( 80-120C or So ).. I think that in some of the commerical machines they use these varying temp zones to create a profile, by progressively dropping the board into the hotter areas.. ( counter intuivate, that the hotter area is at the bottom ).. They can keep the vapour cloud going, and control temp on the board by height.
In a bucket heater, you can acehive profile, by varying the amount of energy that you put into the system at any given time. This is easy, you just need a thermocouple probe at board height, and a way to control the amount of energy you are putting into the system. ( if you are using an AC heater, you can just use some Zero crossing Triacs, I'm controlling power in over 2seconds. ( 50Hz ) so i have 1% resolution.. Theres a lot of thermal mass in the system, so 2 seconds its not that long.
Sorry been just really busy today making stuff, so will try to get some photos/info together, this weekend. My new tanks are made from Stainless Steel. It was made from sheet, water jet cut, and then folded, and welded..