scope:

INTRODUCTION

It is well known that home cooking produces high levels of contaminants into the air. These contaminants are composed of particulate matter, moisture, heat, and odors, which usually pose adverse effects on comfort and even health (See et al. 2006; Svendsen et al. 2002). Therefore, the ways to remove cooking fumes are always important issues to residents for the air quality in the kitchen. Contemporary range hoods exhaust cooking fumes based on two principles (Li et al. 1997). Consider the heat at the cook-top, thermal plumes are generated. As a result, cooking contaminants are brought upwards by the nature of the thermal plumes. This mechanism facilitating cooking contaminants to be captured by the range hood over the cook-top is called buoyancy-capture principle (Figure 1). The range hood continues to collect and remove cooking fumes moving towards to it with powerful mechanical airflow, which is called velocity-capture principle.

Although the range hood exhibits its capability on the elimination of cooking fumes, it is sometimes left off during the cooking. That might reflect the annoyance of the acoustic noise generated from the exhaust fan (Grimwood 1997). Hence, in our early study, a range hood was proposed to switch its exhaust velocity to a proper level according to the detection of cooking fumes completed by a sensitive piezoelectric transducer in order to reduce the running noise (Liu and Young 2002). The average noise level of the proposed range hood is 72 dB while the exhaust velocity is fixed at its maximum (12.55 m/s) measured at the exhaust outlet (10 × 23 cm²). In stir-frying vegetables, a very common cooking in Oriental kitchens, the average noise level becomes 65.66 dB when the proposed range hood works with the given function.

Although the early proposed range hood can work with lower noise, its reliability needs to be further confirmed. First, the detection area of the piezoelectric transducer is not sufficient to cover all of the plume-like cooking fumes. Second, with the equivalent capacitance inside (Dally et al. 1993), the available output of the piezoelectric transducer always lags behind the detection. Third, although the peak level of the transducer output can be an estimate for the amount of the cooking fumes composed of the same constituent, as illustrated in the detection of water particles (Liu, 2007), it is hard to conclude this connection for all cooking processes and materials used. One evidence is that the peak levels induced by the same amount of water and oil particles separately on the piezoelectric transducer are different. Consequently, the peak level of the transducer output cannot be a common scale.

In this paper, a reliable self-contained range hood is presented to solve the issues mentioned above. Its reliability comes from the novel use of the piezoelectric transducers proposed here. From the design of the self-contained range hood with the use of piezoelectric transducers to the analysis of the detection performance achieved by these transducers, a general road map to create a demanded self-contained range hood is constructed.