Heat Transfer Of Methane Research Articles

Correction for Nusselt Number Correlations of Transcritical Methane Based on Radial Velocity Distribution

This article conducts three-dimensional simulations for transcritical flow and heat transfer of methane in a rectangular channel under asymmetric heating conditions and compares the accuracy of three different Nusselt number correlations. A correction method for the Nusselt number correlation based on the secondary correction of the radial velocity distribution is proposed. The results show that by correcting the three correlations using the proposed method, the error of the average Nusselt number under the condition of heat transfer deterioration between the calculated values and the ones obtained from numerical simulations are reduced from 88.26%, 11.41%, 19.29% to 13.71%, 0.47%, and 6.02%, respectively. Compared with the correlation obtained by directly modifying based on the heat transfer deterioration condition data, the Nusselt number correlations modified by the proposed method achieve higher accuracy, and the calculation error are limited to within 15%. Overall, the modified Bishop correlation has the highest calculation accuracy among the three correlations, and the errors between the calculated values and those obtained from numerical simulations are limited within 6% under different mass flow rates.

Effect of rolling motion with large radius on flow and heat transfer characteristics of supercritical methane in a mini channel

• Rolling results in the violent fluctuation of flow and heat transfer in supercritical methane. • Additional force along the flow direction is the key to affect the flow and heat transfer. • Hysteresis exists in the coupling of rolling, flow fluctuation and temperature fluctuation. • Rolling produces greater fluctuation in the near-wall area than that in the inner center area. The offshore floating storage and regasification unit (FSRU) is developing rapidly as a new type of storage and gasification system for liquefied natural gas (LNG), and the heat transfer and system stability of offshore LNG vaporizers are greatly affected by ocean rolling. To reveal the regular pattern and mechanism of supercritical methane heat transfer performance under ocean motion, this research numerically studied the flow and heat transfer characteristics of supercritical methane in a 1 × 1 × 100 mm mini channel under the additional inertial force by large radius rolling. Based on the non-inertial coordinate system, the normal inertial acceleration, radial inertial acceleration and Coriolis inertial acceleration were considered. Moreover, Nusselt number, degree of fluctuation and friction factor were investigated. The ranges of Reynolds number and Nusselt numbers are 15,000 to 45,000 and 35 to 130 respectively. The results show that the Nusselt number and friction factor violently fluctuate under rolling motion, and the fluctuation period is similar to the rolling period. Besides, the fluctuation degree of Nusselt number is greater than that of friction factor, and the largest fluctuation degree of Nusselt number is 27.9%. The effect of the fluctuation increases with the decrease of the rolling period and the increase of the rolling amplitude. Hysteresis exists in the coupling of rolling, flow fluctuation and temperature fluctuation. In addition, the degree of fluctuation is reduced with the increase of fluid temperature and mass flux. For the effect of rolling, the additional force in the mainstream direction plays a leading role. Besides, the influence of radial force is greater than that of normal force for horizontal flow condition.

Improved Heat-Transfer Correlation for Transcritical Methane Based on a Velocity Profile Correction Term

Abstract In this paper, three-dimensional numerical simulations of the transcritical flow and heat transfer of methane are performed in a rectangular channel under asymmetric heating. The accuracy of four different Nusselt number correlations in the calculation of transcritical methane flow and heat transfer is compared, and two improved heat transfer correlations are proposed based on the Bishop correlation with and without adding a velocity profile correction term. The obtained results show that the proposed heat transfer correlations can accurately predict the heat transfer of transcritical methane. It is also shown that by adding a velocity profile correction term, the error between calculated values and those obtained from numerical simulations is reduced from 6.33% to 2.82%. Moreover, it is revealed that under severe heat transfer deterioration conditions, the proposed heat transfer correlations overestimate the convective heat transfer coefficient near the inlet. When the heat transfer is significantly improved, the variation of convective heat transfer coefficient becomes very different from the base case. A large error is noticed between the calculated results of correlation Modified 1 and the results obtained from the numerical simulations, while the correlation Modified 2 with velocity profile correction term still proves satisfactory calculation accuracy.

Mechanism and influence factor analysis of heat transfer deterioration of transcritical methane

A three-dimensional simulation, of transcritical flow, and heat transfer of methane, under asymmetric heating conditions, were performed. The simulation results demonstrated that the drastic changes in density at the pseudo critical temperature lead to an M-type velocity distribution, which plays a dominant role in the deterioration of heat transfer. The specific heat affects the location of the deterioration, while the thermal conductivity and viscosity affect only the wall temperature magnitude, whereas they do not affect the occurrence and location of heat transfer deterioration. The M-type velocity gradually disappears with the inlet mass flow rate increasing, indicating that heat transfer deterioration was eliminated. In addition, there is a critical inlet pressure of 10 MPa. When the inlet pressure is less than critical inlet pressure, heat transfer is improved with the inlet pressure's increase. However, when the inlet pressure is higher than critical inlet pressure, with inlet pressure increasing further, the decrease in the peak specific heat value will weaken the heat absorption capacity of methane, making the deterioration more severe. The deterioration of heat transfer will be improved by increasing the wall roughness, while the pressure drop will also be increased. The optimal wall roughness of 7 μm can be selected by using the thermal performance factor.

Turbulent convective heat transfer of methane at supercritical pressure in a helical coiled tube

The heat transfer of methane at supercritical pressure in a helically coiled tube was numerically investigated using the Reynolds Stress Model under constant wall temperature. The effects of mass flux (G), inlet pressure (Pin) and buoyancy force on the heat transfer behaviors were discussed in detail. Results show that the light fluid with higher temperature appears near the inner wall of the helically coiled tube. When the bulk temperature is less than or approach to the pseudocritical temperature (T pc ), the combined effects of buoyancy force and centrifugal force make heavy fluid with lower temperature appear near the outer-right of the helically coiled tube. Beyond the T pc , the heavy fluid with lower temperature moves from the outer-right region to the outer region owing to the centrifugal force. The buoyancy force caused by density variation, which can be characterized by Gr/Re2 and Gr/Re2.7, enhances the heat transfer coefficient (h) when the bulk temperature is less than or near the T pc , and the h experiences oscillation due to the buoyancy force. The oscillation is reduced progressively with the increase of G. Moreover, h reaches its peak value near the T pc . Higher G could improve the heat transfer performance in the whole temperature range. The peak value of h depends on Pin. A new correlation was proposed for methane at supercritical pressure convective heat transfer in the helical tube, which shows a good agreement with the present simulated results.

A CFD-derived correlation for methane heat transfer deterioration

ABSTRACTMethane heat-transfer deterioration can occur in the regenerative cooling channels of future liquid-oxygen/liquid-methane rocket engines with chamber pressures higher than about 50 bar. Aiming to improve the prediction capabilities for the design of such systems, in the present study, a Nusselt number correlation able to describe the convective heat-transfer characteristics of supercritical flow exhibiting deterioration and with negligible buoyancy effects is obtained using data from numerical simulations. The adopted numerical solver of the Navier–Stokes equations is first validated against the experimental data of near-critical hydrogen in heated tubes and then used to collect heat-transfer data of supercritical methane in a heated tube for different levels of pressure, temperature, and mass flux.

Numerical study of supercritical-pressure fluid flows and heat transfer of methane in ribbed cooling tubes

Regenerative engine cooling, which generally occurs at supercritical pressures, plays a very important role in maintaining engine lifetime and performance in many propulsion and power-generation systems. In this paper, a numerical study of turbulent fluid flows and heat transfer of cryogenic methane in ribbed cooling tubes at a supercritical pressure of 8MPa is conducted. The conservation equations of mass, momentum, and energy are properly solved, with accurate calculations of thermophysical properties, which undergo drastic variations and thus produce strong effects on fluid flows and heat transfer at supercritical pressures. The present study examines the effects of several key influential parameters on both heat transfer enhancement and pressure loss, including the rib geometry, rib height, wall thermal conductivity, and surface heat flux. Numerical results reveal that a ribbed tube surface leads to significant heat transfer enhancement, and in particular, the physical phenomenon of heat transfer deterioration at a supercritical pressure, which occurs in a smooth cooling tube, is drastically weakened in a ribbed cooling tube. A thermal performance factor is applied for combined evaluation of both heat transfer enhancement and pressure loss. Under the tested conditions, results indicate that an optimum rib height exists for achieving the best overall thermal performance.

Parametric Analysis of Heat Transfer to Supercritical-Pressure Methane

Parametric Analysis of Heat Transfer to Supercritical-Pressure Methane

Thermal Stability and Heat Transfer Characteristics of Methane and Natural Gas Fuels

The thermal decomposition and heat transfer characteristics of gaseous, high-purity methane, several methane–hydrocarbon mixtures, and a typical natural gas fuel were evaluated using an electrically heated, stainless-steel tube test apparatus. Of several candidate heat transfer correlations, the Dittus–Boelter heat transfer correlation provided the best fit of the methane heat transfer data over the range of Reynolds numbers 10,000 to 215,000. The thermal stability (i.e., deposit formation) characteristics of the methane–hydrocarbon mixtures and the natural gas fuel were established and compared with the deposition characteristics of high-purity methane. Testing was conducted at wall temperatures up to 900 K (fuel temperatures to 835 K) for durations of up to 60 hours. Measurements of deposit mass indicated that there was essentially no deposit buildup for wall temperatures below 650 K. Deposit began to form at wall temperatures between 650 K and 775 K. Above 775 K, there was a rapid monotonic increase in deposition. The data suggest that the use of high-purity methane instead of natural gas at temperatures above 775 K could reduce the deposit thickness under similar operating conditions by as much as a factor of three, or permit operation at correspondingly higher temperatures.