{"id":393985,"date":"2024-11-15T07:28:48","date_gmt":"2024-11-15T07:28:48","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/energy-balance-total-heat-transfer-rate-manual-vs-simulated-calculations\/"},"modified":"2024-11-15T07:28:48","modified_gmt":"2024-11-15T07:28:48","slug":"energy-balance-total-heat-transfer-rate-manual-vs-simulated-calculations","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/energy-balance-total-heat-transfer-rate-manual-vs-simulated-calculations\/","title":{"rendered":"Energy balance \/ Total heat transfer rate – manual vs simulated calculations"},"content":{"rendered":"

<p>Hello,<br><br>I’m currently simulating what, at least in theory, should be a fairly simple heat transfer problem, and while everything seems to be running smoothly without errors, I can’t get the energy equation that Fluent is giving me to add up. There’s probably just a term I’m missing in my own calculations, but I’d appreciate any help from you to identify what this is.<br><br>I have two 2D heat generating solid bodies encapsulated by a flow volume with a 1 mm slot inlet\/outlet (see attached DM screenshot & mesh). The cooling fluid is oil based, and the properties are set to vary with temperature. Otherwise, the simulation is static and, according to my Re calculations, laminar.<\/p><p>\"\" \"\"<\/p><p>I then run the simulation and it converges nicely after some 260+ iterations, with no console errors or warnings, and the energy and mass balance within reasonable tolerances. Attached is a readout from the console after I ran my simulation.<\/p><p>\"\"<\/p><div id=”post_message_876708″>However, this is where the problem arises: The first time I received the results, I found it curious that the temperature difference between inlet and outlet was so low, so I wanted to do a simple control volume calculation to see if the energy balance was respected.<br><br>Since the temperature difference is so low, I have assumed that the fluid properties are constant for this CV calculation.<\/em><br><br>The heat generated from both the bodies amount to <u>1081 W<\/u>.<br><br>The mass flow rate is an input parameter for my setup, so with this, the inlet temperature, the simulated outlet temperature and the cp, we have:<br>Q = m cp dT ~= 858 W<br><br>Using the average enthalpy and mass flow rate given from the simulation, we have:<br>Q = m dh ~=844 W (which is slightly lower, but within reason)<br><br>Neither of these, however, account for the remaining approx. 230 W generated by the solids.<br><br>The most frustrating thing is that when Fluent calculates the <u>Total heat transfer rate<\/u> (as shown in the console readout), the energy balance seems to be respected without issue, but I can’t for the life of me figure out how the program arrives at the 130+ kW at the inlet\/outlet, since this doesn’t correspond to enthalpy x mass flow rate as I would expect. I’ve tried looking at the documentation, but it doesn’t seem to give me much more of a clue.<br><br>Could anyone here help me find out what I’m missing or doing wrong?<\/div><\/p>\n","protected":false},"template":"","class_list":["post-393985","topic","type-topic","status-publish","hentry","topic-tag-energy-balance-1","topic-tag-energy-conservation","topic-tag-fluid-solid-heat-transfer","topic-tag-totalheattransferrate-1"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t