You have done a pretty good job of beating this horse Jed. Unless the power being delivered by the pump changes depending upon some parameter that varies with time it should be true that the heat due to the pump is constant throughout the duration of the experiment and balances out. I assume that the water levels remain constant at the input and output of the pump and that the small temperature changes do not impact the pump performance.
You stated the other day that the water is constantly being circulated. Is this completely true, or is there a holding vessel that collects water on each side of the pump? My curiosity is still active in a search for the source of the power being delivered by the pump and I visualize a small portion of the water stream being accelerated by the pumping action and thereby gaining kinetic energy. If I had time I would estimate the energy content of that stream over the time period during which it is imparted to reach a power figure. That power calculation should show energy being deposited into the holding vessel provided the water slows down in motion once it enters the tank. One interesting thought comes to mind when I read about the 1 meter head into which the pump can operate. The charts show that the rate of flow goes to zero at that height. If you happen to choose a point on that chart where the flow rate is real but small due to the head, you should be finding an operating point where pipe friction is very small. At the chosen operating point you could calculate the energy required to lift the water the height of the head and at the same time figure how much energy is imparted into the water stream due to kinetic motion. A second point where the head is zero and the flow at a maximum would suggest that most of the energy would be kinetic. I have a strong suspicion that heating is also going to enter the fray to make the total power come out near the specification. The pump is imperfect and water must be bypassing and reversing through the vanes of the pump due to the pressure head. This action will likely cause the water to be heated directly. I realize that you are not a pump designer just as I am not, but both of us share a curiosity as to where the specification comes from that the supplier states. If you want to pursue this subject further I feel confident that there are vorts around that can help us to understand exactly what should be happening. I suspect that the pump manufacturer has a good reason for listing the specifications as they are. It is always satisfying to understand a problem in greater detail. Dave -----Original Message----- From: Jed Rothwell <[email protected]> To: vortex-l <[email protected]> Sent: Fri, Nov 21, 2014 8:33 pm Subject: Re: [Vo]:Pump adds ~1 W I think Let me finish beating this subject to death. In the data Mizuno provided yesterday, you see that after 1.5 hours the system reaches the terminal temperature of 0.5 deg C above ambient. It can never climb higher than that, because losses equal the 0.2 W input from the pump. In other words, at this low power level, the system is functioning as an isoperibolic calorimeter, not adiabatic. In fact, because the pump is left on all the time, the baseline is always high, so we never measure pump input power. The only thing we use is the increase in temperature above the baseline, where the baseline includes the 0.5 deg C from the pump. So this method would never detect pump heat, unless you let the whole system cool overnight with the pump off, and then you turned on the pump and began the test immediately. Mizuno never does that. He always lets it run for while until the reactor surface temperature and water are uniform. - Jed
