Semi-empirical pressure loss model for viscous flow through high aspect ratio rectangular orifices

Background Currently, gas control stations use the gas cleaning systems based on filter net, which is the most cost effective for cleaning purposes. Aims and Objectives Development of a mathematical model to substantiate the value of pressure drop in the mesh-type filter element, at which the filter must be cleaned from mechanical impurities Results In this paper it is proved that the value of the pressure drop at the gas net-type filter element inversely impact on the capital investment into the filter, on the one hand, and on the operating costs associated with the removal of solid particles, on the other hand. On this basis a mathematical model was developed to substantiate the maximum allowed pressure drop in the filter element, caused by gradual clogging of the filter net. The model includes a block diagram, the efficiency function of the integral costs, equations of the balance of expenditure, and limitations of the control parameter. Minimal integral cost of the filter is the taken as a criterion to determine optimum of the efficiency function of the mathematical model. The adopted efficiency function is featured by fractional powers, which makes necessary to solve a complex transcendental equation, and this is a rather time-consuming process of successive iterations. Therefore, to determine the optimal pressure drop across the filter element the numerical method of solving the problem was used, that is, a set of values of the pressure drop with known geometric filter parameters being given, we determine the integral costs. The optimal pressure drop on filter element corresponds to the option with minimal costs. The proposed mathematical model determines the optimal value of the maximum allowable pressure drop on the gas filter.

We report the results of a study on heat transfer in microchannels. The fluid used is a nanofluid whose properties are temperature dependent. The energy dissipation is evaluated for various solid fraction contents along with the cooling effectiveness of this modern type of heat exchangers. The shape of the channels is also investigated. The evaluation parameter used for thermal energy dissipation is the Nusselt number while that used for cooling effectiveness is the static pressure drop between the inlet and the outlet of the microchannel. Conjugate convection-conduction energy conservation equations have been solved along with mass and momentum conservation equations in order to determine these parameters. The results obtained showed important heat transfer augmentation with solid fraction at the expense of an increased pressure drop, i.e high pumping cost (therefore low cooling effectiveness). The microchannel inlet section geometry was also found to contribute to the values of the Nusselt number and pressure drop. Among the tested geometries (elliptical, rectangular, trapezoidal) the rectangular section provided the best compromise between heat transfer augmentation and pumping cost. At the end of the study, a comparison was made between the results obtained by assuming Newtonian rheology and those obtained with non-Newtonian rheological behavior of the same nanofluid sample. It was found that the assumption of non-Newtonian rheological behavior of nanofluids gives higher Nusselt number values and much lower pressure drops.

A numerical study on pressure losses in asymmetric viscoelastic flow through symmetric planar gradual expansions

This article presents a novel cross-rib micro-channel (MC-CR) heat sink to make fluid self-rotate. For a thermal test chip (TTC) with 100 w/cm2, the cross-ribs micro-channel were compared with the rectangular (MC-R) and horizontal rib micro-channel (MC-HR) heat sinks. The results show that, with the cross-rib micro-channel, the junction temperature of the thermal test chip was 336.49 K, and the pressure drop was 22 kPa. Compared with the rectangular and horizontal ribs heat sink, the cross-rib micro-channel had improvements of 28.6% and 14.3% in cooling capability, but the pressure drop increased by 10.7-fold and 5.5-fold, respectively. Then, the effects of the aspect ratio (λ) of micro-channel in different flow rates were studied. It was found that the aspect ratio and cooling performance were non-linear. To reduce the pressure drop, the inclination (α) and spacing (S) of the cross-ribs were optimized. When α = 30°, S = 0.1 mm, and λ = 4, the pressure drop was reduced from 22 kPa to 4.5 kPa. In addition, the heat dissipation performance of the rectangular, staggered fin (MC-SF), staggered rib (MC-SR) and cross-rib micro-channels were analyzed in the condition of the same pressure drop, MC-CR still has superior heat dissipation performance.

This study performed the numerical simulation of the vortex finder (VF) diameter and depth effects on the separation performance of the hydrocyclone-type devices for multiphase fluid separation, namely the static pressure, pressure drop, split ratio, short-circuit flow, velocity field, and classification accuracy. The static pressure, pressure drop, and split ratio were found to be negatively related to the VF diameter. As the VF diameter increased from 0.26D2 to 0.56D2, the maximum static pressure dropped from 94483.56 to 26067.86 Pa, and the pressure drop was reduced from 93336.50 to 26408.69 Pa. Meanwhile, the steepness index increased with the VF diameter in a particular range. The results strongly indicated that an increased VF diameter led to reduced energy consumption and improved separation accuracy of the hydrocyclone, decreasing the tangential velocity, increasing the short-circuit flow, and disrupting the symmetry of the locus of zero vertical velocity (LZVV). The effects of the VF depth on the separation performance were as follows: with increasing VF depth, short-circuit flow and split ratio decreased, the steepness index increased within a specific range, and the symmetry of the LZVV gradually improved. This implies that increased VF depths can help enhance the separation performance of the hydrocyclone but excessively large VF depths would deteriorate it.

Multi-objective optimization of axial-flow-type gas-particle cyclone separator using response surface methodology and computational fluid dynamics

One of the most important components of fluid transmission systems is a control valve located in the pipelines of oil, gas, etc. The primary purpose of this valve is to control the rate of fluid flow passing through it under pressure changes and the most important issue is to investigate the flow’s characteristics in order to achieve a proper geometry to control the flow rate and pressure as desired. The valves used in pipelines add to the overall head loss of the system. Therefore, valves with proper geometry can reduce these minor losses and finally decrease total energy losses. In this paper, a globe control valve is modeled and then numerically investigated to extract its functional relation, which relates pressure ratio to inlet Reynolds number, and estimate its loss coefficient at the valve’s different opening states which have not been addressed completely before and can be beneficial for the selection and usage of globe valves under certain conditions. According to the results, it is found that pressure ratio and loss coefficient are functions of inlet velocity and the valve’s opening state’s percentage, which are directly related to the valve’s geometry. When the valve opens, the rate of change in pressure ratio and loss coefficient are very sharp. Gradually, this rate decreases and the results tend to the final value at the valve’s fully opened state.

The scope of this project is to investigate how the geometry of baffles affect heat transfer and pressure loss of a fluid flow at Re = 1000 through a square duct. For this purpose, Large Eddy Simulations are performed to investigate the effect of baffle height and baffle width. Focus is on the fully-developed flow that repeats itself at streamwise stations. The flow field predicted by Computational Fluid Dynamics simulations was validated using Particle Image Velocimetry. The different designs are evaluated in terms of Nusselt number, Nu and a loss coefficient, f, which are normalised using a reference geometry consisting of a square duct without baffles. The two parameters are additionally combined into a performance parameter eta η = (Nu/Nu0)/(f / f0)(1/3). It was found that adding baffles can result in a quadrupling of η. Reducing the height of baffles decreases heat transfer, while significantly reducing pressure loss and ultimately leading to a higher η. Reducing baffle height was also found to increase the temperature gradient at the upper wall and reduce it at the lower wall. Reducing baffle width resulted in the largest temperature gradient, but lead to poor heat transfer within the fluid.

The authors made flow experiments on the three kinds of right-angled pipe fittings which had correctly geometrical shapes and were set in the horizontal plane. Their diameter ratios were 53.2/53.2, 53.2/42.1 and 53.2 mm/28.0 mm. Flyash and sand slurries were run through them in the "hold up flow" and in the various upstream velocities of the main flow and the flow conditions. Then the authors obtained the following conclusions : (1) The densities of slurries in the downstream of the main flow and the branch flow are equivalent. At the same concentration in weight the coefficients of the pressure loss in the main flow and the branch flow are equivalent in the case of flyash and sand slurries respectively. Both coefficients of the pressure loss in the main flow and the branch flow increase with the increasing concentration in weight, but the incremental rate of the former is less than that of the latter. (2) The pressure loss in the main flow is equivalent to that of a sudden enlargement and the pressure loss in the branch flow is the sum of a sudden contraction and a sudden enlargement as in the case of water flow. As the pressure loss in the branch flow, especially in slurry, is greatly influenced by the contraction, roundness at the branch corner may be very useful in order to reduce its pressure loss. (3) The experimental results were expressed as the empirical formulae including also the previous experimental results with the water flow.

This study numerically analyzes the thermal-fluid performance of supercritical hydrogen in regenerative cooling channels with aspect ratios (AR) ranging from 1 to 8 for rocket engine combustion chambers. The study investigates the effects of channel geometry and inlet Reynolds number on heat transmission efficiency, flow behavior, and pressure drop. The SST k-ω turbulence model was validated and utilized in ANSYS FLUENT (2024 R1, (Ansys Inc., Canonsburg, PA, USA) CFD simulations to examine temperature distributions, turbulent kinetic energy, and velocity profiles. The results show that convective heat transfer is improved with higher Reynolds numbers, while pressure drops are increased; the best range for balanced performance is found to be between 35,000 and 45,000. The aspect ratio significantly influences thermal performance; increasing it from 1 to 8 reduces peak wall temperatures by 12–15% but exacerbates thermal stratification and pressure losses. An intermediate aspect ratio (AR = 2–4) was found to optimize both heat transfer enhancement and hydraulic performance. The study provides critical insights for optimizing cooling channel designs in high-performance rocket engines, addressing the trade-offs between thermal efficiency and flow dynamics under extreme operating conditions.

As global warming is rapidly emerging as one of the inherently global issues, one of the renewable energies, i.e. thermo-electric generation, has received attention. In order to increase the efficiency of thermo-electric generation, a maximum temperature difference in plain fins in a heat exchanger is needed, and an appropriate pressure drop is required to ensure stable flow of high temperature fluid. In the present study, the characteristics of the temperature difference and pressure difference for the 2 kW-class thermo-electric generator installed in exhaust pipes of a cogeneration plant were investigated numerically via thermal fluid analysis using ANSYS CFX. Then, size optimization for plain fins of a heat exchanger was carried out using SAS JMP, in which the temperature difference was maximized while meeting the requirement of a given pressure drop condition. A meta-model was generated by using the response surface model, and individual desirability functions were defined to derive the optimal solution that provided the maximal overall desirability function. The result obtained by size optimization showed that the temperature difference of the optimized plain fins of a heat exchanger increased by approximately 27% in comparison with the original model under the given pressure drop condition.

Atomization characteristics of impinging jets of gel material containing nanoparticles

Enhancement of cyclone solid particle separation performance based on geometrical modification: Numerical analysis

The flow diffuser characteristics of the St. Jude heart valve were investigated and compared to theoretical calculations based on the two dimensional geometry of the valve. Pressure recovery (Cp) and loss (K) coefficients were calculated for varying sized prostheses in both mitral and aortic valve configurations over a range of steady flow rates. In vitro experiments demonstrated that the pressure recovery (Cp = 0.36±0.04) and loss (K = 0.64±0.04) coefficients for flow through the central orifice were independent of the valve sizes and configurations examined. Comparison of ideal and experimentally determined pressure recovery coefficients yielded diffuser effectiveness (η = 0.62). We applied these flow diffuser characteristics to investigate the discrepancies between Doppler and catheter gradients across prosthetic St. Jude bileaflet valves. Transvalvular Doppler gradients can be reconciled with catheter measurements by multiplying the Doppler gradient by the pressure loss coefficient (K = 0.64) (r = 0.99, y = 1.11x-0.19).

For the design of the liquid-metal blanket in a fusion reactor, numerical calculations have been carried out on liquid-metal magnetohydrodynamic flows in rectangular ducts with sudden contractions. Conservation equations of fluid mass and fluid momentum and the Poisson equation for electrical potential have been solved numerically. The numerical calculations have been conducted for a Hartmann number of ~10 000; a Reynolds number of ~10 000; and contraction ratios (CRs) of 2, 3, and 4. The pressure loss through the contraction has been estimated by the loss coefficient ζ divided by the interaction parameter N, i.e. ζ/N. The loss coefficient ζ/N through the contraction parallel to the magnetic field is much larger than that through the corresponding contraction perpendicular to the magnetic field. The loss coefficient ζ/N increases consistently with the CR and does not change very much with N. While ζ/N also does not change very much with the wall conductance ratio for the contraction parallel to the magnetic field, ζ/N increases gradually with the wall conductance ratio for the contraction perpendicular to the magnetic field.