Experimental study on flow and heat transfer enhancement by elastic instability in swirling flow

Abstract

Elastic turbulence has shown great potential to improve mixing and heat transfer performance. Most of the studies, however, are focused on the mixing behaviour, heat transfer characteristics induced by elastic turbulence are still not well established. This work investigates systematically the flow and heat transfer performance by elastic turbulence in a swirling flow region. The heat transfer enhancements in the bulk fluid and between the fluid and the wall are characterised by the effective thermal conductivity and the Nusselt number, respectively. The variations of statistical properties, such as probability distribution functions and spectra profiles are analysed for the characterization of elastic turbulence. The results indicate that viscoelastic fluid intensifies the heat transfer performance with gradually increasing swirling velocity, and a six-times enhancement comparing to the Newtonian fluid at the maximum given swirling velocity is obtained. Particularly, the statistical properties imply that the flow is still in the transition regime to elastic turbulence at Wi = 5.5.

Characterization of Effective Diffusion within Viscoelastic Fluids with Elastic Instabilities

“…Time-varying dye front data are also well represented using the approach of Ottino [16], as expressed using an equation given by 𝐴 = 𝐴 1 exp 𝑔𝑡 (11) where A = r/R1, 𝐴 is equal to 1.0, t is time, and g is the effective mixing/diffusion rate. Larger g values are thus associated with increased mass species transport, with greater local mixing for particular experimental conditions.…”

“…Larger g values are thus associated with increased mass species transport, with greater local mixing for particular experimental conditions. Figure 16 shows comparisons of Equation (11) with normalized dye front variations with time t, provided as r/R values, for different polymer concentrations. The predicted data using Equation (11) are generally in agreement with the experimental results.…”

“…Figure 16 shows comparisons of Equation (11) with normalized dye front variations with time t, provided as r/R values, for different polymer concentrations. The predicted data using Equation (11) are generally in agreement with the experimental results. Parameter g values are determined so that A values determined using Equation (11) for different times match the experimentally measured results.…”

“…Such results indicate that polymer relaxation times from all three approaches are in approximate agreement for a polymer concentration ρ of 50 ppm. Using complex viscosity measurement procedures described by Yao et al [11], the dependence of η"/(η'ω) on angular frequency ω is also determined using a rheometer oscillatory frequency-sweep test. Here, η' is the in-phase viscosity (also referred to as the elastic portion of complex viscosity) and η" is the out-of-phase viscosity (also referred to as the viscous portion of complex viscosity).…”

Turbulent Flow Heat Transfer through a Circular Tube with Novel Hybrid Grooved Tape Inserts: Thermohydraulic Analysis and Prediction by Applying Machine Learning Model

“…Active methods of heat transfer enhancement utilize the power from external sources to enhance the thermal transfer and the equipment required to do so is very costly [1][2][3][4]. Hence, researchers switched to passive technique of thermal enhancement in which swirl devices [5][6][7][8][9], roughness [10][11][12][13][14][15], nanoparticles [16][17][18][19][20][21], obstructions of various geometries, channel modification [22][23][24][25][26][27][28], surface enhancement [29][30][31], etc. are employed to promote the disturbance in the flow field which results in a higher heat transfer rate.…”