Centrifugal Pump Capability in Closed Loop

[DDCPower]

I have a diesel engine-generator which has its own engine-driven 390 gpm centrifugal coolant pump with about 10 psi external restriction capability.

The problem is that this application requires the radiator to be 15 feet below the engine's pump. There will be a surge/expansion tank mounted above the engine with fill and vent lines(highest point in the system). The expansion tank will have a 14 psi pressure relief cap. The 50/50 water/glycol mix exits the engine at 200 Deg F, goes through 6" pipes (2 psi loss)passes through the radiator (about 4 psi loss) - now at 175 Deg F -and, hopefully returns to the engine. This is a closed loop system. The restrctions do not exceed the capability of the pump. But, it is 15' and it is a hot liquid.

Will the mixture flash to steam when the engine's centrifugal pump pulls on the liquid? Will it work without an additional pump in series with the engine's pump? Any suggestions?

 

[TBP]

This is exactly like a hot water heating system, only you're using a diesel engine as a heat source instead of a boiler. It's unlikely that the low-head centrifugal circulator will be able to cavitate. It may cause dissolved air to pop out of solution though, and in heating loops, this will sound like the pipes are full of BBs. In heating loops, the best way to remove dissolved air is to have the system arranged: boiler outlet, expansion tank, air separator, pump suction. This provides the air separator with the hottest liquid (just after the heat souce), at the lowest pressure (just ahead of the pump). The hotter the liquid, and the lower the pressure, the less dissolved air it can hold. The first while your system operates will be the time when the dissolved air is removed. This means you'll likely have to top-up the system with glycol. Once this is done, there will be no more air in the system, unless it's drained and re-filled, or there's liquid being added continuously to make-up for leaks. Once the system has operated for a couple of weeks, and the air is removed, and there are no leaks, the air release port on the separator is often just closed, as glycol will find leak paths that most other fluids will not.

I'm not sure about this particular application, or your whereabouts, but in most jurisdictions that subscribe to ASME, you can have 30 PSIG relief valves on hot water heating systems without falling under various act and code requirements.

Also remember to have the glycol checked annually. It can degrade and turn acidic. There are cases of neglected glycol eating expensive things like hot water boilers, and heavy truck diesel engines.