Measuring Heat Transfer with a wattnode

[Paul Lucas]

I am trying to measure the heat transfer from a sealant curing oven. My methods were to measure the surface temperatures of the inside and outside of the oven with 4 T-type thermocouples as well as the wattage supplied to the oven via a wattnode. The curing process is typically a 2 hour interval from cold start to finished. I have plotted the graph of watts vs time and calculated the areas under the curve to find the total energy during a two hour heating process (started from cold). The response of the wattage vs time is square as the controls on the oven are binary. I also have plotted the temperature vs time graphs. For some reason I cannot seem to wrap my head around my next step. By the principle of conservation of energy the watts in should equal the watts out of the oven (neglecting losses from the cables, etc). My problem is this. A watt is a J/s so if I multiply the watts by time (to find area under curve) I end up with a Joule and not the required watts for the units of heat flux. My goal is to find an effective R-value for the oven and eventually determine the mass flow rate out of the oven in order to determine how much steam I will need to increase the relative humidity too 50%. If anyone can point me in the right direction it would be truly appreciated. I have attached the graphs.

The response curves are for the inside/outside walls of the oven and door. The door is a single acrylic panel and the walls insulated and covered with steel panels on either side.

Cheers,
Paul

 

[Navin A S]

The first step in calculating the effective R-value of your oven is to calculate the total heat transfer rate. This can be done by using the temperature data you have collected and using the formula Q = mCpΔT, where Q is the heat rate, m is the mass of the oven, Cp is the specific heat capacity of the oven, and ΔT is the difference between the inside and outside temperatures. You can then use this rate to calculate the effective R-value of your oven. The formula for this is R = (1/Q)*(1/A), where R is the resistance, Q is the heat rate, and A is the area of the oven walls. Once you have the R-value, you can use it to determine the mass flow rate of air out of the oven. This can be done by using the equation m = Q/(Cp*T), where m is the mass flow rate, Q is the heat rate, Cp is the specific heat capacity of the air, and T is the temperature of the air.