Author(s): Silva, Ana Margarida Barradinhas da
Date: 2012
Persistent ID: http://hdl.handle.net/10362/8473
Origin: Repositório Institucional da UNL
Subject(s): Wastewater; Heat recovery; Numerical modelling; Lax- Wendroff method; Mass balance equations; Heat balance equations
Dissertação para obtenção do Grau de Mestre em Engenharia do Ambiente, perfil Engenharia Sanitária
This thesis was carried as a collaboration of Delft University of Technology (TU Delft) and the companies Waternet and KWR. The main project aims to study the possibility of thermal energy recovery from wastewater, reducing the carbon dioxide (CO2) emissions linked to the energy sector. The present work is based on a previous computational model that was developed to simulate heat recovery from wastewater for constant flow rate and temperature of water. The first goal is to simulate a wastewater discharge. In order to achieve this, a Gaussian function was added to the boundary conditions for water flow rate and water temperature. As a second goal, this work aims to assess the significance of the terms present in the water heat balance and air heat balance equations. Binary coefficients were added in each term of both equations and then all the combinations were computed. The unsteady situation successfully simulated a main discharge and numerical predictions for water temperature and flow rate are presented. The deviations associated with the modified cases for the two equations suggest that the heat flux pipe to water (!!") and heat flux pipe to air (!!") terms are crucial for water and air heat balance predictions,respectively. In order to smooth extra oscillations, the time step (dt) was reduced and a smaller relative size of oscillations was obtained. This work concludes with a section of future developments in order to improve the results obtained. Despite of the fact that the current state of these routines does not allow us to accurately assess heat exchanges in pipes, promising results were obtained, proving that numerical modelling of heat recovery will contribute greatly to the development of the main project.
