Optimization Design by Coupling Computational Fluid Dynamics and Genetic Algorithm

Nowadays, optimal design of equipment is one of the most practical issues in modem industry. Due to the requirements of deploying time, reliability, and design cost, better approaches than the conventional ones like experimental procedures are required. Moreover, the rapid development of computing power in recent decades opens a chance for researchers to employ calculation tools in complex configurations. In this chapter, we demonstrate a kind of modern optimization method by coupling computational fluid dynamics (CFD) and genetic algorithms (GAs). The brief introduction of GAs and CFD package OpenFOAM will be performed. The advantage of this approach as well as the difficulty that we must tackle will be analyzed. In addition, this chapter performs a study case in which an automated procedure to optimize the flow distribution in a manifold is established. The design point is accomplished by balancing the liquid-phase flow rate at each outlet, and the controlled parameter is a dimension of baffle between each channel. Using this methodology, we finally find a set of results improving the distribution of flow

Two-Phase Flow Boiling Heat Transfer Of R-410A and R-134A in Horizontal Small Tubes

Experimental investigation on two-phase flow boiling heat transfer of R-410A and R-134A in horizontal small tubes is reported. The pressure drop and local heat transfer coefficients were obtained over heat flux range of 5 to 40 kW/m2 , mass flux range of 70 to 600kg/ m2 s, saturation temperature range of 2 to 12°C, and quality up to 1.0 in test section with inner tube diameters of 3.0 and 0.5mm, and lengths of 2000 and 330mm, respectively. The section was heated uniformly by applying a direct electric current to the tubes. The effects of mass flux, heat flux, and inner tube diameter on pressure drop and heat transfer coefficients are presented. The experimental results are compared against several existing correlations. A new boiling heat transfer coefficient correlation based on the superposition model for refrigerants in small tubes is also presented

Optimal frictional pressure drop and vapor quality relationship of ammonia and R22 in two-phase flow

Research in two-phase flow in heat exchanging devices plays an important part in today’s applications in miniaturization of engineering systems. The phase change process factors in the flow conditions and heat transfer in evaporators and condensers. Numerous studies in the past have looked at the predicted and measured frictional pressure drop of coolants as the vapor quality increases. This paper reports a preliminary attempt at modeling of the relationship between the frictional pressure drop and vapor quality in an ammonia-cooled and R22-cooled mini-channel of 1.5 mm diameter under optimized conditions using multi-objective genetic algorithm. R22 is a being phased-out due to its ozone-depleting characteristic and ammonia is being considered as its potential replacement. The properties of ammonia and R22 used have been obtained experimentally at the saturation temperature of 5?C and 10?C respectively. Modeling of the minimized pressure drop per unit tube length together with the Lockhart-Martinelli parameter was completed under optimized flow rate and vapor quality.The outcomes obtained are similar to those that have been reported experimentally with other coolants, increasing pressure drop with increasing vapor quality

Effects of two-phase flow friction factor correlations on the optimal pressure drop-martinelli parameter pair in a mini-channel

Substantial research has been completed with more on-going on the flow pattern and heat transfer associated with two-phase flows. Discrepancies reported may have been as much as agreements, due to the different models, approaches, flow regimes, correlations, and new working fluids being utilized. This paper reports the outcome of a study to look at the effects of applying two different friction factor correlations on the simultaneous minimization of the pressure drop and Martinelli parameter under optimized flow rate and vapor quality, using genetic algorithm. The homogeneous model is assumed with ammonia as the working fluid, the coolant being environmentally friendly and having recently discovered as a potential replacement for the current refrigerants in micro and mini-channels. Results show that significant differences in the frictional pressure drop and Martinelli parameter arise due to the different correlations used, and this is only the outcome from two different correlations currently being considered by researchers in pressure drop analysis for two-phase flows in mini-channels. Thus, absolute agreement is indeed not possible between theoretical, experimental, and numerical work in view of the many different available correlations being utilized today with differences between 10 to 100 percent that has already been established

Condensation heat transfer of R22, R410A and R32 inside a multiport mini-channel tube

In the present study, the heat transfer coefficients are investigated experimentally for condensation of R22, R410A, and R32 inside a horizontal multiport rectangular mini-channel tube. The multiport tube having nine channels in 0.969mm of hydraulic diameter, the experimental measurements were carried out at the fixed saturation temperature of 48oC, by the varying refrigerant mass flux from 50 to 500kg/m2s, and the heat flux range from 3 to 15kW/m2. The test section was a double tube of counter-flow type; the refrigerant was flowed condensation inside the test tube by heat exchange with cooling water flowing in the annular side. The temperature and pressure of refrigerant were measured at the inlet and outlet of the test section, and the surface temperature of tubes was measured. The effect of vapor quality, mass flux and heat flux on condensation characteristics is clarified. The experiment results were compared with the existing heat transfer coefficient correlations, and a new correlation was proposed using the present data with good prediction

Condensation Heat Transfer of R410A Inside Multiport Minichannels with Different Cross-sectional Geometry

Condensation heat transfer of R410a in a multiport mini-channels tubes with different cross-sectional geometry is experimentally investigated. Three tubes with aspect ratio of 0.395, 0.385 and 0.446, and hydraulic diameters of 1.147 mm, 1.135 mm and 0.846 mm with number of channels (7, 11 and 18) are tested in this study. The experimented range of heat flux is from 3 to 15 kW/m2, mass flux from 50 to 500 kg/m2s. The data show that the heat transfer coefficient increases with heat flux, mass flux and vapor quality. A performance comparison was conducted among the 3 tested tubes and it was found out that the number of channels increases heat transfer coefficient significantly at low heat flux and mass flux, while this effect is damped at higher heat/mass flux condition. In addition, it was found that heat transfer in small hydraulic diameter and high aspect ratio channels deteriorated. Possible mechanism to this deterioration is proposed. Finally, a new correlation is developed to predict the heat transfer coefficient of R410a in a multiport mini-channels tube

A General Correlation to Predict The Flow Boiling Heat Transfer of R410A in Macro/Mini Channels

This study demonstrated a general correlation to predict the saturated flow boiling heat transfer of R410A in horizontal macro and mini-channels. The experimental data were observed in various tube diameters of 1.5, 3.0, 6.61 and 7.49 mm, mass fluxes of 100 – 600 kW m-2s-1 heat fluxes of 10 – 40 kW m-2 , saturation temperature of 5 – 15 ºC and vapor quality from 0.2 to 1. The database was compared with numerous well-known correlations. The proposed correlation was based on the superposition model of nucleate boiling and force convective evaporation contribution. The new modified correlation showed a good prediction with using our database