Elsevier

Thermochimica Acta

Volume 617, 10 October 2015, Pages 1-7
Thermochimica Acta

Viscosity measurements of hydrocarbon fuel at temperatures from (303.2 to 513.2) K and pressures up to 5.1 MPa using a two-capillary viscometer

https://doi.org/10.1016/j.tca.2015.08.005Get rights and content

Highlights

  • A two-capillary viscometer was proposed for hydrocarbons at supercritical pressures.

  • The two-capillary viscometer was calibrated with pure substance and binary mixture.

  • The uncertainty of viscometer was within (2.22–5.28) % (coverage factor k = 2).

  • Viscosities of hydrocarbon fuel were measured and a fitting formula was proposed.

Abstract

A two-capillary method based on the Hagen–Poiseuille theory was proposed for on-line measurements of dynamic viscosity of hydrocarbons at high temperatures and high pressures. A two-capillary viscometer was designed and proved to be applicable to the viscosity measurements in a mini-tube. The standard uncertainty of dynamic viscosity measurements is identified as (2.22–5.28) % (coverage factor k = 2). N-heptane, n-octane and their binary mixture were tested respectively in the calibration experiments of the viscometer. Results showed that the measured maximum relative deviations of all substances were all within 2% and the average absolute deviations were within 0.72%. Finally viscosities of a kerosene kind hydrocarbon fuel were measured using the two-capillary viscometer at temperature from (303.2 to 513.2) K and supercritical pressures of (3.00 and 4.00) MPa.

Introduction

Viscosity as an important transport property is widely applied in many fields, such as chemicals, food industry, petrochemicals, biomedical, environmental science and so on. In the heat management technology for scramjet, hydrocarbons are always applied as fuel and coolant in a regenerative cooling system [1], [2], [3], [4]. Thermophysical properties of hydrocarbon fuel are deeply demanded in the cooling system design for future application. As a key property, viscosity is directly bound up with the resistance and kinetic energy of fluid in the cooling process. A fundamental understanding of the viscosity is an indispensable part in the theoretical analysis and numerical simulation for the hydrocarbons. The present paper aims at proposing a viscosity measurement method to obtain the dynamic viscosity of hydrocarbon fuel at high temperatures and high pressures.

Some viscosity measurement methods have been proposed, such as rolling ball viscometer [5], falling-body viscometer [6], [7], vibrating wire-viscometer [8], [9], capillary tube viscometer [10], [11], [12] and so on [13], [14], [15], [16]. Most researches were conducted on the pure compounds [5], [8], [10], [11], [12], [14] and binary mixtures [6], [7], [10], [16]. And data were concentrated at low temperature and different pressures. Viscosities of hydrocarbon mixtures and oils were studied in some researches. Boned et al. [6] measured the viscosities of two hydrocarbon mixtures representative of some heavy petroleum distillation at (293.15–343.15) K and up to 100 MPa by a falling-body viscometer and a capillary viscometer respectively. Tate et al. [12] modified the Saybolt viscometer and measured the kinematic viscosities of three biodiesel fuels at temperatures up to 573 K. Gascoin et al. [15] proposed a novel measurement method to determine the kinematic viscosity of pure and multi-species mixture, which was based on fluid permeation through characterized porous media. The viscometer was validated to apply to the hydrocarbons under pyrolysis. Xing et al. [16] used an Ubbelohde viscometer to measure the viscosity of binary mixtures tricycle [5.2.1.02.6] decane (JP-10), a high density fuel, and methylcyclohexane (MCH) at several temperatures. The viscosity of a typical endothermic hydrocarbon fuel (RP-3) at critical and supercritical conditions was measured with a capillary method by Deng et al. [11]. It covers a temperature range of (298–788) K under pressures (2.33–5) MPa.

The advantages of capillary method are low cost, high accuracy particularly with longer tubes, and the ability to achieve very high shear rates, even with high viscosity samples. A two-capillary method was first proposed based on the Hagen-Poiseuille theory by May et al. [17] on the ratio measurement of viscosities of sample gases. They measured the zero-density viscosities of H2, CH4 and Ar by a two-capillary viscometer at temperatures ranging from 200 K to 400 K, and Xe for the range from 200 K to 300 K [18]. Zhang et al. [19] presented an investigation on the effect of connecting tubing in a two-capillary viscometer. They found that the incompatibility of connecting tubing could cause a systematic error in the measurement of dilute gas viscosity and the error diminishes with Dean Number decreases. The two-capillary method is more accurate than an absolute viscosity method, which requires accurate knowledge of the flow field and geometric parameter. More important, it is an on-line technique for the viscosity measurements at high temperatures and high pressures.

In this paper, a two-capillary method was first applied to the on-line measurements of dynamic viscosity of hydrocarbons under liquid phase or supercritical state. A theoretical formula is deduced and a novel two-capillary viscometer was designed for hydrocarbons at high temperatures and pressures. Validations of the viscometer were validated by pure fluid and mixtures. Viscosities of a kerosene kind hydrocarbon fuel were measured at temperature from (303.2 to 513.2) K and supercritical pressures of 3.00 and 4.00 MPa by the two-capillary viscometer.

Section snippets

Experimental system

Experiments were performed in a home-designed multiphase flow test platform in our laboratory. The schematic diagram of the experimental system is shown in Fig. 1.

Test fluid was driven by a constant flow pump (P230II) with 9.999 mL/min supply capacity. A 7 μm filter is attached to the pump to protect the devices from entrained impurity. The prepared fluid flowed through two coils capillaries made of 316 steel stainless in series. The capillaries had an external diameter of 1/32 inch and a nominal

Results and discussion

For high-pressure viscosity ratio measurements, a stable flow should be satisfied in capillaries. Some measures and good signal-to-noise ratios were adopted in experiments. Small flow rate (0.3–1.2 mL/min) was used with obvious pressure drop (20–248 kPa) in a minitube (0.25 mm). The internal bore of T unions matching the capillaries reduced the entrance and the exit effects. A coiled capillary was located ahead of each ensemble to suppress flow-induced instabilities. Good signal-to-noise ratios

Conclusions

A two-capillary method is proposed for the viscosity measurements of hydrocarbon fuel at supercritical pressure. The measurement theory and experimental system were described in detail. The accuracy of the viscometer was calibrated by n-heptane, n-octane and their binary mixture. The viscosity of n-heptane was measured at the temperature range of (303.2–503.2) K at a pressure of 3.10 MPa. The measured average absolute deviation (AAD) was 0.72% and the maximum absolute deviation (MAD) was 1.91%,

Acknowledgements

This work is supported by the National Natural Science Foundation of China (Grant No. 21306147), the National Science Foundation for Post-doctoral Scientists of China (Grant No. 2013M532044) and the Fundamental Research Funds for the Central Universities. Their financial supports are grateful acknowledged.

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