Modeling of the minimized two-phase flow frictional pressure drop in a small tube with different correlations

The major parameters of interest in heat transfer research are the refrigerant charge, pressure drop, and heat transfer capacity. Smaller channels reduce the refrigerant charge with higher heat transfer capability due to the increased in surface area to volume ratio but at the expense of a higher pressure drop. Differences between the predicted and experimental frictional pressure drop of two-phase flow in small tubes have frequently been discussed. Factors that could have contributed to that effect have been attributed to the correlations used to model the flow, some being modified from the originals developed for a macro system. Experimental test-rigs have varied in channel geometry, refrigerant type, and flow conditions. Thousands of data have been collected to find a common point among the differences. This paper reports an investigation of four different two-phase friction factor correlations used in the modeling of the frictional two-phase flow pressure drop of refrigerant R-22. One had been specifically developed for laminar flow in a smooth channel, another was modified from a laminar flow in a smooth pipe to be used for a rough channel, and two correlations are specific for turbulent flow that consider internal pipe surface roughness. Genetic algorithm, an optimization scheme, is used to search for the minimum friction factor and minimum frictional pressure drop under optimized conditions of the mass flux and vapor quality. The results show that a larger pressure drop does come with a smaller channel. A large discrepancy exists between the correlations investigated; between the ones that does not consider surface roughness and that which does, as well as between flow under laminar and turbulent flow conditions

GAMBUT field experiment of peatland wildfires in Sumatra: from ignition to spread and suppression

Peat wildfires can burn over large areas of peatland, releasing ancient carbon and toxic gases into the atmosphere over prolonged periods. These emissions cause haze episodes of pollution and accelerate climate change. Peat wildfires are characterised by smouldering - the flameless, most persistent type of combustion. Mitigation strategies are needed in arctic, boreal, and tropical areas but are hindered by incomplete scientific understanding of smouldering. Here, we present GAMBUT, the largest and longest to-date field experiment of peat wildfires, conducted in a degraded peatland of Sumatra. Temperature, emission and spread of peat fire were continuously measured over 4-10 days and nights, and three major rainfalls. Measurements of temperature in the soil provide field experimental evidence of lethal fire severity to the biological system of the peat up to 30 cm depth. We report that the temperature of the deep smouldering is 13% hotter than shallow layer during daytime. During night-time, both deep and shallow smouldering had the same level of temperature. The experiment was terminated by suppression with water. Comparison of rainfall with suppression confirms the existence of a critical water column height below which extinction is not possible. GAMBUT provides a unique understanding of peat wildfires at field conditions that can contribute to mitigation strategies

Effect of initial seawater concentration on forming ice slurry for thermal energy storage in fishing vessel

Ice slurry technology has great potential in maximizing the chilling process of fish. Seawater is widely used as base solution of ice slurry due to Natrium Chloride content as freezing point depressant. In this study, effect of initial seawater concentration was investigated experimentally. The initial concentration of seawater was varied at 1, 1.5, 2, 2.5 and 3 wt%, respectively. Performance of systems and microscopic of ice particles were also observed. Ice slurry generated from 1 wt% seawater solution gives good agreement toward formation time of ice slurry. The diameter of particle ice increases with decrease in concentration. For application in thermal energy storage of fishing vessel, it is recommended to use low concentration of seawater

Experimental investigations of ice slurry flow based on monoethylene glycol at high ice fractions

Ice slurry has so many advantages as phase-change slurries due to the high latent heat of its particles. Ice slurry is one of a competitive alternative to conventional secondary refrigeration systems that have been successfully employed in many applications. In this research, ice slurry flow with monoethylene glycol (MEG) at high ice fractions was investigated. The experiment was carried out by measuring shear stress and flow rate as variable to calculate power law index. The experiment was performed in 14 mm, 21 mm, and 24 mm circular tubes, respectively. The Initial concentration of 5 wt%, 7 wt%, and 10 wt% of MEG was investigated. Ice fraction was maintained above 30% in a storage tank. Experimental results of the Darcy friction factor were compared to Poiseuille and Blasius model. The ice slurry flows exhibited a shear-thickening flow (n>1) for all initial concentration in the range 1.07 - 1.58. The Greater initial concentration of MEG tends to give smaller friction compared with another ice slurry flow with smaller initial concentration