Modeling and simulation of a thermostatic mixer with an anti-scalding or anti-cold system

This paper presents the detailed modeling of a thermostatic mixer for domestic use with an anti-scalding or anti-cold device, which is operated by the temperatures and pressures of the hot and cold streams entering the mixer. The response time of the anti-scalding/cold device is shorter than the response time of the temperature adjustment system, which is based on a bulb that expands or contracts when temperature changes, thus leading to the immediate closing of the mixer inputs if any of the hot or cold streams is absent. This can be critical when the mixer is used by people with long reaction times. The modeling describes the location of all the mixer mobile parts, as well as the temperature evolution along the various identifiable chambers in the mixer. The model is numerically implemented on a well-known modeling tool and is simulated with an implicit Runge–Kutta based method, suitable to the numerical integration of stiff systems. Results for the transient and steady-sate operations are presented, which are relevant both in what concerns the output mixture temperature and the main operating characteristics of the mixer.