Calculating Heat Convection Output: Clarification Needed

In summary, the formula Qconv = Pn x Qs x b x ϕ is used to determine the convective heat output of a cooking appliance in kW. The coefficients 'b' and 'ϕ' can easily be determined. However, there is confusion on whether to use the actual capacity or power rating for 'Pn', as it can result in a significant difference. There is also uncertainty about the meaning of 'Qs' and its units, as it can be expressed as W or W/kW. Further clarification is needed on these issues.
  • #1
afa13
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I need some clarification regarding the following formula:

Qconv = Pn x Qs x b x ϕ

this equation is used to determine the cooking appliance's convective heat output in kw, 'b' and 'ϕ' are coefficients easily determined. I am confused whether to use the actual capacity of the appliance for 'Pn' or its power rating which is higher and will result in a big difference. And 'Qs' is the sensible heat emitted in W and sometimes is expressed is W/kW.

Can anyone help clear this issue?
 
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  • #2
What do you mean by actual capacity is it scones per minute? I take it is some kind of electric oven. Is it a electric element in a oven where you are trying to work out the ratio of radiant heat to convective heat? Maybe the sensible heat in W/kW is a ratio of sensible heating to total heating ie the heat to heat up the scones divided by the heat to heat up the scones plus the heat of the steam coming out of them. Maybe you should not listen to me I have never studied oven design.
 

1. How is heat convection output calculated?

Heat convection output is calculated by using the formula Q = hA(Ts - T∞), where Q is the heat transfer rate, h is the convection heat transfer coefficient, A is the surface area, Ts is the surface temperature, and T∞ is the surrounding fluid temperature.

2. What is the difference between heat convection output and heat conduction?

Heat convection output involves the transfer of heat through the movement of fluids, while heat conduction involves the transfer of heat through a solid material. Convection is typically a more efficient method of heat transfer, as fluids can carry heat over longer distances compared to solids.

3. How does the shape of an object affect its heat convection output?

The shape of an object can greatly affect its heat convection output. Objects with a larger surface area will generally have a higher heat convection output, as there is more area for heat to be transferred through. Additionally, the shape of an object can affect the flow of fluid around it, which can impact the convection heat transfer coefficient.

4. Can heat convection output be increased or decreased?

Yes, the heat convection output can be increased or decreased by adjusting the variables in the convection heat transfer equation. The convection heat transfer coefficient can be increased by increasing the fluid velocity or using a fluid with a higher thermal conductivity. The surface area can also be increased to increase the heat transfer rate.

5. How do different materials impact heat convection output?

Different materials can impact heat convection output in several ways. Materials with a higher thermal conductivity, such as metals, will generally have a higher heat convection output compared to materials with lower thermal conductivity, such as plastics. Additionally, the surface roughness of a material can also affect the convection heat transfer coefficient, as rougher surfaces can disrupt the fluid flow and decrease heat transfer.

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