Design Concept

In the research stage, we have found a lot of information about toaster and the principles behind. We know that a toaster uses infrared radiation to heat a piece of bread. Yet, we try to think of other mode of heat transfer in a bid to speed up the heating time---convection. Convection is the movement of molecules within fluids. Suppose we consider heating up a local region of air. As the air heats, the molecules spread out, causing this region to become less dense than the surrounding unheated air. Hot air will subsequently rise due to buoyant forces - this movement of hot air into a cooler region is then said to transfer heat by convection. In order to speed up the heating process, we adopt forced convection current. In forced convection, fluid movement results from other forces, such as a fan or pump.
Convection is described by Newton's law of cooling, which states that the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings. The law is given as the differential equation:


 \frac{d Q}{d t} = \dot{Q} = h \cdot A( T_{\text{env}}- T(t)) = - h \cdot A \Delta T(t)\quad

Where
Q is the thermal energy in joules
h is the Heat transfer coefficient
A is the surface area of the heat being transferred
T is the temperature of the object's surface and interior (since these are the same in this approximation)
Tenv is the temperature of the environment; i.e. the temperature suitably far from the surface
ΔT(t) = T(t) − Tenv is the time-dependent thermal gradient between environment and object.

Based on the equation, as the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings, we aim at decreasing the difference in temperatures between the body and its surroundings as well as keeping the internal temperature steady. Hence, we thought of making use of a fan.

Referring to the existing products in the market, we found a convection oven. It often cooks food faster at a lower temperature than the standard one as it creates a uniform temperature with internal fans that circulate hot air. Fans blow the hot air throughout the oven, ensuring that the same temperature reaches the top and bottom of food. Thus, fans actually blow pre-heated air, rather than distributing the already-heated air. Because the heated air transfers heat more efficiently to cooking containers and exposed food surfaces, food will take less time to cook and baked goods will be more evenly browned.

Incorporating the concepts of convection current and fan, we made use of a heat gun. A heat gun is a device used to emit a stream of hot air. They are superficially similar in shape and construction to a hair dryer, though they run at much higher temperatures, ranging from 100-550°C.


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