12 Replies Latest reply on May 25, 2017 1:30 PM by Ryan Dark

    Determining Cooling Time of Part

    Allan Wong

      Hi Guys,


      Is a way to determine the cooling time of a part using the Transient Thermal Analysis on SolidWorks? I have applied an initial temperature load to a part as well as my desired temperature for it to reach as a temperature loading. Would this be the appropriate approach in determining the cooling time of a part given initial temperature and my desired temperature? I do not want to use any convection or radiation just temperature loads.

       

      Message was edited by: Allan Wong

        • Re: Determining Cooling Time of Part
          Ryan Dark

          Hi Allan,

          This is likely not the loading condition you want to apply to your model.  The initial temperature is fine but the application of a temperature load at the environmental temperature is not something that would generally be true to real life.  Temperature loads provide an infinite reservoir of heat (or in your case heat dissipation) with perfect conduction from your model into the outside environment.  You have ruled out convection and radiation, however, these are (for 99.9% of cases) the main modes of heat transfer in cooling.  What is the real life object you are attempting to cool and what environment is it being placed in to cool it?

            • Re: Determining Cooling Time of Part
              Allan Wong

              Hi Ryan,

               

               

              I basically am trying to model a freezer like situation for a problem. The component is put in at a specific temperature into an environment where it will reach the equilibrium temperature i.e. cool down. I just need to determine the amount of time it takes from initial temperature to environment temperature for my problem, however this is more involved than I had thought. I assume that my surrounding is a fluid and not convecting or radiating as this is negligible.

                • Re: Determining Cooling Time of Part
                  Joseph Dunfee

                  There are other issues you may be unaware of.  There is a boundary layer of air, that inhibits convection.  In most situations, it is about equal an R-value of 1 (in U.S. units)   But, that boundary layer is larger on the ceiling, since there is less air flow from convection there. (sorry don't know that value).

                   

                  Another important consideration, for a real-world freezer, is that it will occasionally have its door opened.  If this is many times a day, this large scale infiltration of air will be a major part of the load.

                   

                  -Joe

              • Re: Determining Cooling Time of Part
                Ryan Dark

                Hi Allan,

                At low temperatures you can ignore radiation.  The same assumption is not true of convection.  What is your fluid?  Is this an actual object placed into a freezer?

                  • Re: Determining Cooling Time of Part
                    Allan Wong

                    Hi Ryan,

                     

                     

                    It is submersed in an arbitrary cooler liquid than the part. You can imagine kind of like heat treating a part i.e. taking it out of the furnace and dumping it into a buck of liquid. The idea is to determine how long it takes to cool it down given the initial hot temp and liquid temp when it is fully submersed.

                      • Re: Determining Cooling Time of Part
                        Ryan Dark

                        Hi Allan,

                        Your situation is definitely undergoing the effects of convection.  You would want to, for a simple model, apply convection to all surfaces touching the fluid (that sounds like all surfaces in this case).  Various online sources put submersion of an object in still liquid (free convection) somewhere between 75-400 W/m^2*K.  A reasonable convection value to apply to your own situation would likely also be found in that range.  Here is one source showing values for oil and water in free convection (Convective Heat Transfer Coefficients Table Chart | Engineers Edge).

                          • Re: Determining Cooling Time of Part
                            Allan Wong

                            Hi Ryan,

                             

                            I was hoping that this was not the case to include free flow convection into the heat dissipation of the model, but is there no other way of potentially doing this i.e. start the model at a low temp and let it rise to my desired temp of quenching? Do you also have resources for free flows with nitrogen?

                              • Re: Determining Cooling Time of Part
                                Ryan Dark

                                Hi Allan,

                                There are tables for common liquids (air, water, oil) but for other liquids (nitrogen) you may need to calculate the heat transfer coefficient specific to that liquid through common heat transfer equations here (Heat transfer coefficient).  This gives equations to find heat transfer coefficient values to place on both vertical and horizontal walls of your body which tend to be pretty different.

                                  • Re: Determining Cooling Time of Part
                                    Allan Wong

                                    Ryan,

                                     

                                    Just to bounce an idea off of you. Is it possible to just model this item with an initial temperature of my cooled part and then apply a temperature load for which the part will jump up to? Essentially this is the reverse of what I said earlier in the model. I would determine the time for it to warm up the part to it's initial temperature from being cool to determine the time it would take if I were to cool it down in the submersion.

                                      • Re: Determining Cooling Time of Part
                                        Ryan Dark

                                        Hi Allan,

                                        The very same rules apply to adding heat into the system as there are for taking heat out of the system.  The direction of heat flow does not matter.  You will still need to calculate and use heat transfer coefficients for convection to obtain accurate results.

                                          • Re: Determining Cooling Time of Part
                                            Allan Wong

                                            Hi Ryan,

                                             

                                            I attempted to solve the free convections as you suggested. However, I had some difficulties finding resources for vapors and liquids like nitrogen. Do you know of any good resources for such thermal property tables?

                                              • Re: Determining Cooling Time of Part
                                                Ryan Dark

                                                Hi Allan,

                                                It does seem difficult to find data on free convection values for gas/liquid nitrogen.  I did not find a definitive source myself but I did find some on slow flow-rate forced convection which could give you a ballpark to put your own natural convection into.  You may wish to speak with a professor of Low Temperature Physics at a university to see if they can provide insight on these values for you.