SINGLE-PHASE AND TWO-PHASE SECONDARY COOLANTS: SIMULATION AND EVALUATION OF THEIR THERMOPHYSICAL PROPERTIES

Pedro Samuel Gomes Medeiros,Cleiton Rubens Formiga Barbosa,Francisco De Assis Oliveira Fontes

doi:10.15628/holos.2011.540

Abstract

This paper makes a comparative analysis of the thermophysical properties of ice slurry with conventional single-phase secondary fluids used in thermal storage cooling systems. The ice slurry is a two-phase fluid consisting of water, antifreeze and ice crystals. It is a new technology that has shown great energy potential. In addition to transporting energy as a heat transfer fluid, it has thermal storage properties due to the presence of ice, storing coolness by latent heat of fusion. The single-phase fluids analyzed are water-NaCl and water-propylene glycol solutions, which also operate as carrier fluids in ice slurry. The presence of ice changes the thermophysical properties of aqueous solutions and a number of these properties were determined: density, thermal conductivity and dynamic viscosity. Data were obtained by software simulation. The results show that the presence of 10% by weight of ice provides a significant increase in thermal conductivity and dynamic viscosity, without causing changes in density. The rheological behavior of ice slurries, associated with its high viscosity, requires higher pumping power; however, this was not significant because higher thermal conductivity allows a lower mass flow rate without the use of larger pumps. Thus, the ice slurry ensures its high potential as a secondary fluid in thermal storage cooling systems, proving to be more efficient than single-phase secondary fluids.

Highlights

The refrigerant fluids used in refrigeration and air conditioning processes are an environmental and economic concern, mainly in large systems with high thermal loads
The aim of this study was to assess the thermophysical properties of ice slurry for commercial applications in refrigeration processes with thermal storage, compared to conventional single-phase fluids
After comparative analysis of the conventional single-phase secondary fluids and ice slurries, it was concluded that their thermophysical properties show different characteristics for a more efficient use in heat transfer processes

Summary

Introduction

The refrigerant fluids used in refrigeration and air conditioning processes are an environmental and economic concern, mainly in large systems with high thermal loads. In the latter case, in addition to the non-feasibility of the project, owing to the high costs of such a large system (PRUZAESKY, 2008), the use of vast amounts of refrigerant fluid and possible leakages could cause environmental damage (EGOLF, 2004). An effective alternative is to use an indirect expansion refrigeration system with thermal storage, which contributes to more efficient refrigeration in more compact systems. This results in economy, operational flexibility and a significant reduction in the amount of refrigerant fluid. The stored coolness is used during the day, mainly at times of high thermal load and peak energy demand (ASHRAE, 2008)

Objectives

Methods

Results

Conclusion