Colorado Sool of Mine CHEN43 Stirred ank Heater Develoing ranfer untion from Heat & Material Balane Examle ranfer untion Stirred ank Heater,,, A,,,,, We will develo te tranfer funtion for a tirred tank eater by etting u te eat & material balane equation for te ae were te volume migt ange (ine flow out of te tank i ontrolled by a valve) e overall ma balane on ti ytem will be: d V were te volume in te tank, V, migt be anging wit time (ine te liquid level migt be anging) If we imlify te yial roertie by auming a ontant liquid denity,, and if te valve a linear flow arateriti, Cv, ten: d A d A Cv Remember tat te teady tate verion of ti equation i: Cv e energy balane will be: d VHˆ Hˆ Hˆ Jon Jeura (jjeura@mineedu) - - Coyrigt 27 Aril 23, 27
Colorado Sool of Mine CHEN43 Stirred ank Heater We an lit aart te time derivative term: ˆ d H ˆ d V V H Hˆ Hˆ and ten inert te ma balane ODE for te eond time derivative: d Hˆ V Hˆ Hˆ Hˆ Doing a little bit of mat give: d Hˆ V Hˆ Hˆ Hˆ Hˆ d Hˆ V Hˆ Hˆ d Hˆ V Hˆ Hˆ dhˆ V H H ˆ ˆ We would till like to onvert te entaly term into term tat diretly relate to temerature Even wit a temerature deendent eat aaity te time derivative an be lit into: ˆ d VC ˆ ˆ H H If we aume tat te eat aaitie are ontant and tat tere i no reation, ten: and: ˆ Hˆ C H ˆ and Hˆ H ˆ ref ref ref, ref, ˆ d VC ˆ C Jon Jeura (jjeura@mineedu) - 2 - Coyrigt 27 Aril 23, 27
Colorado Sool of Mine CHEN43 Stirred ank Heater or final imliity let aume te denity i eentially ontant, o and: ˆ d VC ˆ C e teady tate verion of ti equation i: Cˆ Canging temerature, ontant inlet flow rate Let develo te tranfer funtion uing tee ODE a our tarting oint Let aume tat te only indeendent variable tat an ange are and We will old ontant, o V (and ene ) will be ontant, too So we only need to deal wit te energy balane equation Wen we linearize ti we need to ut it in term of te deviation variable and (for te indeendent variable) and (for te deendent variable): ˆ d VC ˆ C C ˆ C ˆ ˆ d VC ˆ ˆ C C ˆ d VC ˆ ˆ C C Note tat ti equation ow ow te tirred tank fluid temerature i affeted by ange in te oter temerature i ODE get onverted to tranfer funtion by taking te Lalae tranform : VCˆ ˆ ˆ C C ˆ ˆ ˆ VC C C Jon Jeura (jjeura@mineedu) - 3 - Coyrigt 27 Aril 23, 27
Colorado Sool of Mine CHEN43 Stirred ank Heater Cˆ VCˆ ˆ ˆ ˆ C VC C i ow tat we ave two tranfer funtion: were: Cˆ ˆ ˆ VC C and ˆ VC ˆ C Notie tat bot of tee tranfer funtion ome from te ame firt order ODE, o bot are referred to a firt order tranfer funtion We ll ee in a later etion tat we would like to ut te equation into a tandard form tat arie wen te multilier on te term i unity (ie, one) i an be done by dividing everyting by te exiting fator on te term, C ˆ Starting wit te deviation variable form of te ODE: VCˆ ˆ d C Cˆ ˆ ˆ C C We an imlify te form of te equation by defining new ymbol for te grouing: o: VCˆ Cˆ, Cˆ K Cˆ, and K C d K K K K K K and te tranfer funtion are now: ˆ Jon Jeura (jjeura@mineedu) - 4 - Coyrigt 27 Aril 23, 27
Colorado Sool of Mine CHEN43 Stirred ank Heater K and K A blok diagram for te tirred tank eater an be drawn a follow + + + Allow Inlet low Rate to Cange e reviou et of tranfer funtion were derived from te energy balane ODE linearized only for ange in temerature If te inlet flow rate alo ange ten we mut alo take ti into aount in bot ODE Wen we linearize tee ODE we need to ut tem in term of te deviation variable,, and (for te indeendent variable) and & (for te deendent variable) e overall material balane beome: d A Cv Cv Cv Cv Cv d A Cv d A Cv Jon Jeura (jjeura@mineedu) - 5 - Coyrigt 27 Aril 23, 27
Colorado Sool of Mine CHEN43 d A C v and: Stirred ank Heater e energy balane beome (remember to firt divide by to ut all variable on te leftand ide of te ODE): ˆ ˆ d C A C Cˆ Cˆ Cˆ Cˆ ˆ ˆ ˆ d C C AC Cˆ 2 2 Cˆ ˆ ˆ ˆ d C C AC Cˆ 2 2 Cˆ Jon Jeura (jjeura@mineedu) - 6 - Coyrigt 27 Aril 23, 27
Colorado Sool of Mine CHEN43 Stirred ank Heater ˆ ˆ ˆ ˆ d C C C AC Cˆ 2 2 We an multily troug by te teady tate level, ˆ d A ˆ ˆ ˆ C C C C ˆ C Notie tat te term multilying i te teady tate energy balane and i zero, o: A ˆ ˆ ˆ ˆ C d C C C Now we an get te tranfer funtion by onverting to Lalae variable & algebraially maniulating irt from te ma balane: A C v A C v : A C v Next from te energy balane: ˆ ˆ ˆ ˆ A C C C C Cˆ A ˆ ˆ C C Cˆ ˆ ˆ ˆ ˆ A C C A C C Jon Jeura (jjeura@mineedu) - 7 - Coyrigt 27 Aril 23, 27
Colorado Sool of Mine CHEN43 Stirred ank Heater Now tere are tree tranfer funtion from te energy balane: were: Cˆ A ˆ ˆ C C Cˆ A ˆ ˆ C C A ˆ ˆ C C ere i only one tranfer funtion from te ma balane: were A C v e full blok diagram relating te indeendent & deendent variable are own in te following figure + + + Jon Jeura (jjeura@mineedu) - 8 - Coyrigt 27 Aril 23, 27