1 Reply Latest reply on Apr 9, 2014 4:23 AM by Jared Conway

    Why is not conservation of energy during heating air?

    Qi Hongming

      I simulated one electric process heater with flow simulation, air will pumped into inlet of heater at constant temp and pressure, some wattage will be generated via heating elements, the outlet face will be  goal, after simulation is finished, I found the following calculation formula is not correct? The formula:  (specific heat X mass flow X (Outlet temp-inlet temp) is not match  generate heat by heating elements?  Could you tell me the reasons? 

       

      BTW, the inlet and outlet is same size.Outlet temperature is bulk AV temperature

       

      Wall condition:

           default outer wall thermal condition: adiabatic wall

            default wall radiative surface: No-radiating surface

           default outer wall radiative surface: No-raditing surface

        • Re: Why is not conservation of energy during heating air?
          Jared Conway

          build a really simple example of a pipe with a heat element in the middle (no radiation, no heat tranfer outwards to make your hand calcs easy)

          draw your energy balance on paper and test that flow simulation matches

          i've done this test before and it matches exactly

          you can actually plot enthalpy directly in surface parameters rather than using the method you describe

           

          my guess is:

          1. you're missing some surfaces from your selections

          2. you aren't considering everything in the system (hence the recommendation to start simpler)

          3. it may be mesh related as you haven't noted spending anytime on mesh