I have quite a bit of experience with hydroponics, but not with the heat issues you have.

You mention the venturi effect for cooling the nutrient solution, but I'm not sure if that is what it does. A venturi will draw air into the solution, which will aerate it and increase the dissolved oxygen level, which should help improve the root health and overall plant health.

There are a lot of variables that you haven't described about your setup. You really need to go to a hydroponic forum and study more there. Do searches that are specific to the type of system you are using, the crops you are growing, and the issues you are dealing with before you start asking a lot of questions. Many of your questions will be answered already and you will get the answers that are specific to your situation quicker, because you will be better informed about the basics and will be able to ask more specific questions.

Although I don't know your specifics, I'd think the best way to combat heat would be to use NFT (nutrient film technique) or aeroponics (root misting), actually I'd do "low tech aeroponics" which is a low pressure spray that's simpler & less expensive.

These designs have a lot of air & water mixing which cools the water, by evaporation and also increases the dissolved oxygen level. So, your root will be cooler and oxygenated.

Anything you can do to cool your nutrient solution will help. There are other ways to cool your nutrients that might work better, depending on your situation. You'll have to consider things like the type of crop, the scale of your setup, etc. to decide what will be the most feasible solution.