Measuring Heat Transfer with a wattnode

In summary: With this information, you can then determine the amount of steam needed to increase the relative humidity to 50%. In summary, you will use your temperature and wattage data to calculate the heat transfer rate, which will then be used to determine the effective R-value of your oven and the mass flow rate of air out of the oven. This will help you determine the amount of steam needed to increase the relative humidity to 50%.
  • #1
Paul Lucas
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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
 

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  • #2
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.
 

FAQ: Measuring Heat Transfer with a wattnode

1. What is a wattnode and how does it measure heat transfer?

A wattnode is a type of sensor that is used to measure the flow of electrical energy in a circuit. It works by converting the electrical current passing through it into a proportional voltage signal, which can then be measured and used to calculate the amount of heat transferred.

2. What are the different types of wattnodes available for measuring heat transfer?

There are two main types of wattnodes used for measuring heat transfer: current transformer (CT) wattnodes and Rogowski coil wattnodes. CT wattnodes use a magnetic core to measure the current passing through a wire, while Rogowski coil wattnodes use a coiled conductor to measure the current.

3. What factors can affect the accuracy of a wattnode when measuring heat transfer?

The accuracy of a wattnode can be affected by a number of factors, including the quality of the electrical connections, the condition of the wattnode itself, and the level of electrical noise present in the circuit. It is important to regularly calibrate and maintain the wattnode to ensure accurate measurements.

4. How can wattnodes be used to measure heat transfer in different types of systems?

Wattnodes can be used in a variety of systems to measure heat transfer, including HVAC systems, industrial processes, and renewable energy systems. They can also be used in combination with other sensors to monitor and optimize heat transfer in complex systems.

5. Are there any safety precautions that should be taken when using wattnodes to measure heat transfer?

Yes, it is important to follow all safety guidelines when using wattnodes to measure heat transfer. This includes wearing appropriate personal protective equipment, working with a qualified electrician, and ensuring that all equipment is properly installed and maintained to prevent electrical hazards.

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