Nesusieto termohidraulinio baigtinių elementų modelio panaudojimas šilumos tiekimo tinklų skaičiavimuose

Abstract

Straipsnyje nagrinėjamas baigtinių elementų metodo taikymas vamzdynų hidrauliniams ir šiluminiams uždaviniams spręsti. Šie uždaviniai yra pakankamai sudėtingi, neturintys tiesioginio sprendimo. Inžinerinėje praktikoje jie sprendžiami priartėjimo būdu. Šilumnešio tekėjimo analizei taikomas programos ANSYS vamzdinis baigtinis elemementas, kuris leidžia spręsti hidraulinį ir šiluminį uždavinį, taikant nesusieto uždavinio formuluotę. Straipsnyje minėtų uždavinių sprendimo rezultatai palyginti su rezultatais, gautais sprendžiant inžinerinėje praktikoje naudojamais metodais.

In this paper the analysis of the heat supply networks by uncoupled thermal-hydraulic finite element model is presented. Uncoupled thermal-hydraulic finite element model is based on engineering practice assumption, that fluid physical properties are independent on temperature. The finite element formulation for the model is defined by equation (1.8) and is described on figure 4. Pipe flow problems are non-linear because the flow conductivity matrix depends on the pressure differential. Thermal analysis is deals with the two basic methods of heat transfer: conduction and convection. The thermal analysis is linear. In uncoupled thermal-hydraulic model, flow rate and temperature gradient are solved through an iterative process in which the flow conductivity matrix is updated with each iteration to reflect the new pressure differential. In fluid flow rate and pressures are the only factors of interest, the temperature components of the formulation can be deleted. For the thermal-hydraulic analysis of flow in heat supply networks by finite element method the thermal-fluid element type of finite element program ANSYS is used. The presented method is applied to example solution of, which is known literature. The fluid flow rate and pressures values of heat supply network have been calculated. The loading distribution in pipe network is presented in figure 6. The temperature components and heat flow rates values of heat supply network have been calculated. The loading distribution in pipe network is presented in figure 7. In the table 1-2 the results of hydraulic analysis in heat supply network with the solutions by H. Cross method are comparing. In the table 3-4 the results of thermal analysis with the solutions by engineering method are comparing. Results are presented to illustrate the accuracy of the finite element method in heat supply network analysis.