Computational fluid dynamics analysis of a high throughput viscous heater to process feces and a fecal simulant using temperature and shear rate-dependent viscosity model

C L German; J T Podichetty; A Muzhingi; B Makununika; J Smay; G L Foutch

doi:10.2166/washdev.2017.103

Computational fluid dynamics analysis of a high throughput viscous heater to process feces and a fecal simulant using temperature and shear rate-dependent viscosity model

J Water Sanit Hyg Dev. 2017 Dec 6;8(1):27-32. doi: 10.2166/washdev.2017.103.

Authors

C L German¹, J T Podichetty², A Muzhingi³, B Makununika³, J Smay⁴, G L Foutch^{3

5}

Affiliations

¹ Chemical Engineering, Oklahoma State University, Stillwater, OK 74078, USA.
² Integrative and Molecular Physiology, University of Michigan, Ann Arbor, MI 43018, USA.
³ Pollution Research Group, University of KwaZulu Natal, Howard College Campus, Durban 4001, South Africa.
⁴ Materials Science and Engineering, Oklahoma State University, Tulsa, OK 74106, USA.
⁵ Computing and Engineering, University of Missouri Kansas City, Kansas City, MO 64110, USA.

Abstract

Open defecation and poor fecal management facilitates the spread of disease. Viscous heating can pasteurize fecal sludge by creating a high shear field in the annular gap between a stationary, cylindrical outer shell and a rotating inner core. As sludge flows axially through the annular gap, thorough mixing and frictional heating eliminate cool spots where microbes may survive. A viscous heater (VH) compares favorably to a conventional heat exchanger, where cool slugs may occur. Computational fluid dynamics (CFD) was used to determine the effects of geometry and fluid rheology on VH performance over a range of conditions. A shear-rate and temperature-dependent rheological model was developed from experimental data, using a sludge simulant. CFD of an existing VH used the model to improve the original naïve design by including temperature and shear rate-dependent viscosity. CFD results were compared to experimental data at 132 and 200 L/hr to predict design and operating conditions for 1,000 L/hr. Subsequent experimentation with fecal sludge indicated that the CFD approach was valid for design and operation.

Keywords: CFD; fecal pasteurization; viscous heating.