C.A. Infante Ferreira

Thermodynamic and physical property data equations for ammonia-lithium nitrate and ammonia-sodium thiocyanate solutions

Abstract Thermodynamic and physical property data equations are presented for the NH 3 −LiNO 3 and NH 3 −NaSCN absorption refrigeration systems. These equations are presented in a form readily adaptable to a computer program for use by other investigators when thermodynamic and economic cycle calculations for NH 3 −LiNO 3 and NH 3 −NaSCN absorption systems are to be performed.

Refrigerant charge, pressure drop, and condensation heat transfer in flattened tubes

Horizontal smooth and microfinned copper tubes with an approximate diameter of 9 mm were successively flattened in order to determine changes in flow field characteristics as a round tube is altered into a flattened tube profile. Refrigerants R134a and R410A were investigated over a mass flux range from 75 to 400 kg m−2 s−1 and a quality range from approximately 10–80%. For a given refrigerant mass flow rate, the results show that a significant reduction in refrigerant charge is possible. Pressure drop results show increases of pressure drop at a given mass flux and quality as a tube profile is flattened. Heat transfer results indicate enhancement of the condensation heat transfer coefficient as a tube is flattened. Flattened tubes with an 18° helix angle displayed the highest heat transfer coefficients. Smooth tubes and axial microfin tubes displayed similar levels of heat transfer enhancement. Heat transfer enhancement is dependent on the mass flux, quality and tube profile.

Heat and mass transfer in vertical tubular bubble absorbers for ammonia-water absorption refrigeration systems

Abstract A model is developed for calculation of simultaneous heat and mass transfer processes in vertical bubble absorbers as used for ammonia-water absorption refrigeration systems. Some preliminary experiments have been performed in an absorber without heat removal. The results from these experiments are compared with the literature and give a first indication about the methods for prediction of the absorption process. Experiments have also been performed with simultaneous heat removal. The internal diameters of the absorbers tested were 10.0, 15.3, and 20.5 mm. The mass transfer coefficients resulting from these experiments are correlated by a modified Sherwood relation. An interative procedure is presented which allows design of vertical tubular bubble absorbers for ammonia-water absorption refrigeration systems.

Validation of the use of heat transfer models in liquid/solid fluidized beds for ice slurry generation

Heat transfer coefficients in a liquid/solid fluidized bed heat exchanger are investigated for application in ice slurry generators. A range of temperature driving forces is determined in which ice slurry generation is stable. In this range ice crystal formation or growth does not affect heat transfer coefficients. A model is proposed that accurately predicts heat transfer coefficients in the fluidized bed ice slurry generator. Due to lower temperatures and higher viscosity in ice slurry generation, heat transfer coefficients measured are lower than predicted with heat transfer correlations specific for liquid/solid fluidized bed heat exchangers. Heat transfer coefficients measured are however significantly higher than for single phase fluid flow.

Combined momentum, heat and mass transfer in vertical slug flow absorbers

Abstract Numerical solutions have been obtained for the system of equations of momentum, heat and mass transfer describing the absorption of a refrigerant vapour from a Taylor bubble into the refrigerant-absorbent solution film around the bubble. The numerical results are compared with Nusselts solution of the energy equation and with the penetration theory solution of the mass diffusion variation. Experimental data have been collected in vertical tubular absorbers in the slug flow region with the systems ammonia-lithium nitrate and ammonia-sodium thiocyanate. Four different absorber tubes have been tested with internal diameters of 10, 15, 20, and 25 mm. These data are compared with the numerical and theoretical results. The effect of the bubble nose on mass transfer is studied. Typical temperature profiles during the absorption process in absorption cooling/heating systems are shown.

Latent heat storage for solar heating and cooling systems

Abstract This chapter discusses the aspects that should be considered when selecting the latent heat storage for a specific solar heating and cooling application. It positions latent heat storage in relation to solar heating and cooling systems helping determine the storage size and the temperature level. It quantifies temperature losses and indicates how the major sources of irreversibilities can be quantified. It shows how the savings related to energetic performance can be determined. It distinguishes between stationary phase change materials (PCMs) and pumpable slurries of PCMs, and it illustrates the advantages of pumpable PCM slurries. Finally, a method is proposed to estimate the performance of different storage/heat exchanger concepts and a procedure for the selection of a latent heat storage type is proposed.