Heat and mass transfer model to predict the operational performance of a steam sterilisation autoclave including productsby Wei Liang Lau, John Reizes, Victoria Timchenko, Sami Kara, Bernard Kornfeld

International Journal of Heat and Mass Transfer


Mechanical Engineering / Condensed Matter Physics / Fluid Flow and Transfer Processes


th ng ami



Steam sterilisation


Numerical modelling utocl . Unf ause u his pa the t for steam sterilisation, to include products, in this case, intravenous solution packed in plastic pouches and a steam flow controller. The external parameters supplied to the numerically modelled controller are the maximum steam flow rate and the autoclave temperature as a function of time which it needs to maintain. The numerical model is then used to predict the actual transient temperature and pressure profiles and the details of the mass transfers in the autoclave during a sterilisation cycle, the transient temperature distribution within the products as well as details of the transient thermal energy consumption. The results from numerical modelling were validated with measurements obtained under actual operating conditions. The simulated total steam consumption was within 3% of the measured data. A reduction of 8% in steam consumption was obtained due to insulation on the outer walls.  2015 Elsevier Ltd. All rights reserved. 1. Introduction

While the globe has benefited from the industrialisation of nations through improved access to necessities such as medical supplies and food products, manufacturing has been identified as a major consumer of energy [1]. Researchers and companies around the world have delved into the field of energy and resource efficiency in striving for achieving cleaner and sustainable manufacturing practices in order to reduce operational cost and lower carbon emission [2]. One of the major hurdles faced by industry practitioners is that the majority of currently operational processes develop novel approaches in the design of green-field (new) processes that are more energy efficient without compromising quality. For example, in the pharmaceutical industry, product quality is of paramount concern and guidelines are strictly enforced. At the same time, companies recognise that critical processes such as steam sterilisation, is a major consumer of thermal energy [4].

An appropriate approach to the aforementioned challenges would require the development of a modular solution that could provide an insight into the thermal energy consumption in existing processes and at the same time, allowing for the ability of modifications to be made to process parameters and equipment design. n approach, which extensive data colajor consumer of use of unnecessary

International Journal of Heat and Mass Transfer 90 (2015) 800–811

Contents lists available

International Journal of H .e lare located in brown-field facilities, where a significant amount of up front financial capital has been spent but the processes may have been designed and built at a time when energy efficiency may not have been the most important priority. This means that

This negates the option for a statistical top-dow lacks the capability for alternations without an lection. Furthermore, apart from being a m energy, steam sterilisation is regarded as the caHeat and mass transfer model to predict of a steam sterilisation autoclave includi

Wei Liang Lau, John Reizes, Victoria Timchenko ⇑, S

School of Mechanical and Manufacturing Engineering, University of New South Wales, a r t i c l e i n f o

Article history:

Received 16 February 2015

Received in revised form 30 June 2015

Accepted 30 June 2015 a b s t r a c t

Steam sterilisation using a pharmaceutical industries energy and is known to c parallel. The objective of t oped to simulate in detail journal homepage: wwwa solution towards achieving sustainability requires a two-pronged approach. Firstly, to address the inefficiencies that currently exist in brown-field manufacturing sites. The benefits of optimising existing processes and equipment have been documented in literature such as [3]. Secondly, there is a need to p s t i c t t a http://dx.doi.org/10.1016/j.ijheatmasstransfer.2015.06.089 0017-9310/ 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +61 2 9385 4148; fax: +61 2 9663 1222.

E-mail address: v.timchenko@unsw.edu.au (V. Timchenko).e operational performance products

Kara, Bernard Kornfeld , NSW 2052, Australia aves or retorts is a widely used thermal process in the food processing and ortunately, sterilisation, using steam, consumes a significant amount of nwanted peak energy demand when a number of autoclaves operate in per is to extend the previously published numerical methodology develhermal energy consumption of an industrial sized empty autoclave used at ScienceDirect eat and Mass Transfer sevier .com/locate / i jhmteak boiler demand when operating in a batch configuration as imilarly noted in the food processing industry. As such, any soluion should provide not only total steam consumption for a sterilsation process, but also include insights to transient steam onsumption so that future simulations would be able to provide hermal energy consumption for the purpose of optimising producion schedule [5].

The rapid improvement in computer processing capabilities has llowed for numerical models of manufacturing processes to be


A area, m2 c constant

Cp constant pressure specific heat capacity, J kg1 K1

D diameter

F factor g acceleration of gravity, m s2

Gr Grashof number h heat transfer coefficient, W m1 K1 hfg modified latent heat of vapourisation, J kg 1 k thermal conductivity, W m1 K1

L length, m

M molar mass of air, g kmol1 m mass, kg _m mass flow rate, kg s1

Nu Nusselt number

P pressure, Pa

Pr Prandtl number _Q rate of heat transfer, W

Re Reynolds number

Ru universal gas constant, J kmol1 K1 r radius, m

T temperature, C

U internal energy, J

Greek symbols b coefficient of thermal expansion, K1 c heat capacity ratio

Subscripts a air amb ambient atm atmosphere au autoclave boiler boiler bw bottom walls (in contact with water pool) c characteristic cond condensation f fluid film condensate liquid film surface i inner (radius/diameter/area) in into ins insulation initial initial simulation timestep (t = 0 s) l liquid (water) lw lower side walls mix mixture o outer (radius/diameter/area) out out of ow outer wall p pipe pid proportional integral derivative controller prod products s steam sat saturation sensible sensible (heat transfer)