Bob Cook <[email protected]> wrote:
> All measurements should be accomplished with as much precision > as possible, since adiabatic calorimetry is not possible without adiabatic > conditions. > You mean it is not perfectly insulated. No system is. When the level of heat is very small, such as the heat from the pump, the system soon reaches a terminal temperature. This instrument works for sustained power levels of ~2 W to ~30 W. The heat from the pump is too low to measure with confidence using this instrument. No calorimeter works well at any power level. It is not possible to make adiabatic conditions for any temperature or power level. > As Dave has indicated the heat lost of the pump to the ambient is not > adiabatic and of significant amplitude relative to excess heat generation > over time. > Yes. It is not adiabatic. If it were adiabatic, the water would not come to a terminal temperature. It would not record 14 hours at 17.85°C average, and the next 14 after that at 17.81°C. That is remarkably stable. Fluctuations from ambient air temperature hardly affect it. With such a low power level it soon converts into an isoperibolic system. I tried to estimate the pump power based on the difference between the ambient and the terminal temperature. I find this is not possible because the ambient temperature is unstable and it varies from one place to another. The air is being moved around by fans and room heaters. I see from my lab notes that when I placed the two Omega handheld thermocouple probes in different locations they often measured air temperature differences of 0.3°C and sometimes more. The Omega typically measured air temperatures close to the reactor at about 0.3°C lower than the reading from Mizuno's ambient thermocouple. So there's really no telling how much cooler the air was than the cooling water. It is somewhere between 0.6 and 1.2°C, I believe. That is more of a guess than a measurement. If I were trying to do calorimetry based on the difference between the cooling water and the air, the answer would be inaccurate to the point of being useless. Fortunately, I need only compare the cooling water at the start of the test to the end of the test. - Jed
