Range Of Mass Flow Rates Research Articles

Aerodynamic Similarity Principles and Scaling Laws for Windmilling Fans

Windmilling requirements for aircraft engines often define propulsion and airframe design parameters. The present study is focused on two key quantities of interest during windmill operation: fan rotational speed and stage losses. A model for the rotor exit flow is developed that serves to bring out a similarity parameter for the fan rotational speed. Furthermore, the model shows that the spanwise flow profiles are independent of the throughflow, being determined solely by the configuration geometry. Interrogation of previous numerical simulations verifies the self-similar nature of the flow. The analysis also demonstrates that the vane inlet dynamic pressure is the appropriate scale for the stagnation pressure loss across the rotor and splitter. Examination of the simulation results for the stator reveals that the flow blockage resulting from the severely negative incidence that occurs at windmill remains constant across a wide range of mass flow rates. For a given throughflow rate, the velocity scale is then shown to be that associated with the unblocked vane exit area, leading naturally to the definition of a dynamic pressure scale for the stator stagnation pressure loss. The proposed scaling procedures for the component losses are applied to the flow configuration of Prasad and Lord (2010). Comparison of simulation results for the rotor-splitter and stator losses determined using these procedures indicates very good agreement. Analogous to the loss scaling, a procedure based on the fan speed similarity parameter is developed to determine the windmill rotational speed and is also found to be in good agreement with engine data. Thus, despite their simplicity, the methods developed here possess sufficient fidelity to be employed in design prediction models for aircraft propulsion systems.

Investigation of the structure of detonation waves in a non-premixed hydrogen–air rotating detonation engine using mid-infrared imaging

The structure of detonation waves propagating through the annular channel of an optically accessible non-premixed rotating detonation engine (RDE) are investigated using mid-infrared imaging. The RDE is operated on hydrogen–air mixtures for a range of air mass flow rates and equivalence ratios. Instantaneous images of the radiation intensity from water vapor are acquired using a mid-infrared camera and a band-pass filter (2.890 ± 0.033 µm). The instantaneous mid-infrared images reveal the stochastic nature of the detonation wave structure, position and angle of oblique and reflected shock waves, presence of shear layer separating products from the previous and current cycles, and extent of mixing between the reactants and products in the reactant fill zone in front of the detonation wave. The images show negligible signal directly in front of the detonation waves suggesting that there is minimal mixing between the reactants and products from the previous cycle ahead of the detonation wave for most operating conditions. The mid-infrared images provide insights useful for improving fundamental understanding of the detonation structure in RDEs and benchmark data for evaluating modeling and simulation results of RDEs.

Experimental Study of a Bubble Mode Absorption with an Inner Vapor Distributor in a Plate Heat Exchanger-Type Absorber with NH3-LiNO3

Absorption systems are a sustainable solution as solar driven air conditioning devices in places with warm climatic conditions, however, the reliability of these systems must be improved. The absorbing component has a significant effect on the cycle performance, as this process is complex and needs efficient heat exchangers. This paper presents an experimental study of a bubble mode absorption in a plate heat exchanger (PHE)-type absorber with NH3-LiNO3 using a vapor distributor in order to increase the mass transfer at solar cooling operating conditions. The vapor distributor had a diameter of 0.005 m with five perforations distributed uniformly along the tube. Experiments were carried out using a corrugated plate heat exchanger model NB51, with three channels, where the ammonia vapor was injected in a bubble mode into the solution in the central channel. The range of solution concentrations and mass flow rates of the dilute solution were from 35 to 50% weight and 11.69 to 35.46 × 10−3 kg·s−1, respectively. The mass flow rate of ammonia vapor was from 0.79 to 4.92 × 10−3 kg·s−1 and the mass flow rate of cooling water was fixed at 0.31 kg·s−1. The results achieved for the absorbed flux was 0.015 to 0.024 kg m−2·s−1 and the values obtained for the mass transfer coefficient were in the order of 0.036 to 0.059 m·s−1. The solution heat transfer coefficient values were obtained from 0.9 to 1.8 kW·m−2·K−1 under transition conditions and from 0.96 to 3.16 kW·m−2·K−1 at turbulent conditions. Nusselt number correlations were obtained based on experimental data during the absorption process with the NH3-LiNO3 working pair.

Semitheoretical Prediction of the Wetting Characteristics of Aqueous Ionic Liquid Solution on an Aluminum Finned-Tube Desiccant Contactor

This study involves exploring a new design of an internally cooled/heated desiccant contactor by using a new ionic liquid (IL) solution as the sorptive solution. In order to optimize its operative performance, a semitheoretical model based on the principle of minimum energy is developed to predict the film rupture and wetting ability of the IL solution over a comprehensive range of IL mass fraction and flow rates. A first experimental validation of the fundamental equations of the theoretical model is presented and used as a reference to minimize deviations between predicted results and measured data by calibrating dedicated characteristic coefficients. The noteworthy quantitative and qualitative agreement in the whole range of IL mass fractions and flow rates is promising for contributing to the design of optimized system configurations and control strategies.

Performance evaluation of a new counter flow double pass solar air heater with turbulators

Performances of the new Double Pass Solar Air Heater (DPSAH) with and without turbulators has been studied experimentally in the present investigation. Aluminum cans are attached to the upper and lower surface of the absorber plate and used as turbulators to enhance the heater efficiency. Effects of aluminum cans on Nusselt number and pressure drop of SAHs have been investigated. In addition, guide blades are attached to DPSAH entrance for ensuring adequate air distribution over the surface of the absorber which in turns enhancing the performance. Each case is compared with another Single Pass Solar Air Heater (SPSAH) at the same time. The air mass flow rate range is from 0.02 kg/s to 0.05 kg/s. Three variously designed absorber plates for DPSAH are tested: (a) flat plate absorber without cans, (b) absorber with cans in aligned configuration, (c) and the third one contains cans arranged in a staggered configuration. The purpose of the aluminum cans is to create turbulence intensity in the flow field and enlarge the heat transfer area of DPSAHs; hence, and consequently enhance heat transfer rate. Results showed that the maximum daily efficiency was 68% at 0.05 kg/s for the staggered DPSAH.

Cost analysis of a humidification dehumidification desalination system with a packed bed dehumidifier

In this paper, a water-heated humidification dehumidification (HDH) desalination system, which is powered by the waste exhaust gas from a furnace, is applied to produce water. In order to overcome the corrosion from the seawater on the dehumidifier with a general heat exchanger, the packed bed is used to achieve the dehumidification process. Based on the mathematical models for the HDH desalination system, the relevant thermodynamic and economic performance are acquired. Furthermore, the influences from the effectiveness, top and ambient temperatures on the aforementioned performance are also investigated. The simulation results show that peak values of the water production and gained-output-ratio (GOR) are obtained as 84.60 kg h−1 and 1.44 at the balance condition of the dehumidifier. The total cost for all the heat and mass transfer areas rises from 470.81$ to 701.46$ when the mass flow rate of the dry air increases from 0.1 kg s−1 at to 0.5 kg s−1, while the unit cost of water production (UCWP) ascends from 6.20$ kg−1 h to 13.41$ kg−1 h. Furthermore, raising the effectiveness, reducing the spraying temperature into the humidifier is always effective to cut the unit cost of water production, while it is only useful within a limited range of air mass flow rate for a higher ambient temperature.

Thermodynamic performance comparison of Organic Rankine Cycle between zeotropic mixtures and pure fluids under open heat source

Zeotropic mixtures have been widely investigated for the development of Organic Rankine Cycle (ORC) as an alternative option for pure fluids. However, few zeotropic mixtures have been applied to the ORC in practical engineering. Therefore, a nature question is that whether zeotropic mixture has better thermodynamic performance of ORC than pure fluid. In this contribution, a comprehensive performance comparison between zeotropic mixtures and pure fluids is conducted via cycle simulation for the basic ORC and recuperative ORC driven by open heat source. In the simulation, a certain range of mass flow rate of cooling water is considered as the condition of heat sink, and mixtures R600a/R601a, R600a/R227ea are employed. Performances of these mixtures are optimized and compared with those of their constituents from the points of first and second laws. It can be concluded that zeotropic mixture may have lower cycle performance than pure fluid. For the optimal mixture R600a/R601a (0.1/0.9, mass fraction) with the highest net power of basic ORC, the cycle efficiency 8.18% is lower than that of R601a 8.24%. Although zeotropic mixture generally has lower temperature differences in the evaporator and condenser, the exergy losses of these heat exchangers are not certain to be reduced. In the basic ORC, the exergy efficiency 34.61% of optimal R600a/R227ea (0.2/0.8, mass fraction) is lower than that of R227ea 35.68%. Furthermore, the introduction of internal heat exchanger (IHE) can enhance the output work and cycle efficiency. The exergy loss in the evaporator and condenser can be reduced by IHE. The mixture with a larger temperature glide can generally recover more heat in the IHE.

Thermodynamic analysis of a novel evaporation and crystallization system based on humidification processes at ambient temperature

Power consumption in the field of evaporation and crystallization has attracted extensive attentions all over the world. In this paper, humidification and cooling crystallization methods are involved simultaneously to constitute a novel evaporation and crystallization configuration. In light of the thermal processes included, mathematical models based on the mass and energy equilibrium are established. The characteristics of the adopted evaporation and crystallization system (ECS) at the designed parameters are first simulated and analyzed, and the corresponding influence laws from the appointed key parameters are analyzed. Furthermore, a scale and economic analysis is also achieved to explore the application prospect of the evaporation crystallization system. The practicability of the novel evaporation and crystallization system at ambient temperature is verified, with a descent amplitude of 52.88% for the energy consumption of evaporated water within the prescribed range of the air mass flow rate. The simulation results indicate variation of the inlet air parameters, including the relative humidity and temperature, is not effective to improve the thermal efficiency of the evaporation and crystallization system, while an evident reduction for the energy consumption of evaporated water (ECEW) as 45.08 kWht−1 is achieved in response to the volume growth of the packings from 15 m3 to 30 m3. Finally, it is also found that the cost of heat and mass transfer areas will rise significantly with the increase of the volume although the energy conversion is improved.

Material Selection for Microchannel Heatsink: Conjugate Heat Transfer Simulation

Heat dissipation during the operation of electronic devices causes rise in temperature, which demands an effective thermal management for their performance, life and reliability. Single phase liquid cooling in microchannels is an effective and proven technology for electronics cooling. However, due to the ongoing trends of miniaturization and developments in the microelectronics technology, the future needs of heat flux dissipation rate are expected to rise to 1 kW/cm2. Air cooled systems are unable to meet this demand. Hence, liquid cooled heatsinks are preferred. This paper presents conjugate heat transfer simulation of single phase flow in microchannels with application to electronic cooling. The numerical model is simulated for different materials: copper, aluminium and silicon as solid and water as liquid coolant. The performances of microchannel heatsink are analysed for mass flow rate range of 20-40 ml/min. The investigation has been carried out on same size of electronic chip and heat flux in order to have comparative study of different materials. This paper is divided into two sections: fabrication techniques and numerical simulation for different materials. In the first part, a brief discussion of fabrication techniques of microchannel heatsink have been presented. The second section presents conjugate heat transfer simulation and parametric investigation for different material microchannel heatsink. The presented study and findings are useful for selection of materials for microchannel heatsink.

Understanding the plume dynamics of explosive super-eruptions

Explosive super-eruptions can erupt up to thousands of km3 of magma with extremely high mass flow rates (MFR). The plume dynamics of these super-eruptions are still poorly understood. To understand the processes operating in these plumes we used a fluid-dynamical model to simulate what happens at a range of MFR, from values generating intense Plinian columns, as did the 1991 Pinatubo eruption, to upper end-members resulting in co-ignimbrite plumes like Toba super-eruption. Here, we show that simple extrapolations of integral models for Plinian columns to those of super-eruption plumes are not valid and their dynamics diverge from current ideas of how volcanic plumes operate. The different regimes of air entrainment lead to different shaped plumes. For the upper end-members can generate local up-lifts above the main plume (over-plumes). These over-plumes can extend up to the mesosphere. Injecting volatiles into such heights would amplify their impact on Earth climate and ecosystems.

Experimental and numerical studies of helium-cooled modular divertors with multiple jets

As part of the US-Japan PHENIX program, the helium-cooled modular divertor with multiple jets (HEMJ) and a simpler “flat” variant were experimentally studied in a closed helium loop with a redesigned test chamber at coolant inlet temperatures as great as 425 °C, incident heat fluxes as great as 2.2 MW/m2 and prototypical inlet pressures of ∼10 MPa. The data were used to develop correlations for the average Nusselt number and loss coefficient for a range of mass flow rates; these correlations were used in turn to predict the thermal-hydraulic performance of a single divertor module at prototypical conditions.The experimental results suggest that a flat jet array with six holes surrounding one central hole, all of the same diameter, can provide similar average heat transfer coefficients as the HEMJ divertor, albeit with higher pumping power requirements. Because of its smaller cooled surface area, however, this design has lower maximum allowable heat fluxes compared with the HEMJ divertor. Nevertheless, the flat variant could potentially simplify manufacturing and reduce the costs required to fabricate O(106) “finger” modules.

Numerical Analysis of Heat transfer Enhancement in a double pipe heat exchanger with a holed twisted tape

In the present study numerical analysis of enhancement in heat transfer characteristics in a double pipe heat exchanger is studied using a holed twisted tape.The twisted tape with a constant twist ratio is inserted in a double pipe heat exchanger. Holes of diameter 1mm, 3 mm and 5 mm were drilled at regular pitch throughout the length of the tape. Numerical modeling of a double pipe heat exchanger with the holed twisted tape was constructed considering hot fluid flowing in the inner pipe and cold fluid through the annulus.Simulation was done for varied mass flow rates of hot fluid in the turbulent condition keeping the mass flow rate of cold fluid being constant. Thermal properties like Outlet temperatures, Nusselt number, overall heat transfer coefficient, heat transfer rate and pressure drop were determined for all the cases. Results indicated that normaltwisted tape without holes performed better than the bare tube. In the tested range of mass flow rates the average Nusselt number and heat transfer rate were increased by 85% and 34% respectively. Performance of Twisted tape with holes was slightly reduced than the normal twisted tape and it deteriorated further for higher values hole diameter. Pressure drop was found to be higher for the holed twisted tape than the normal tape.

Numerical Analysis of Heat transfer Enhancement in a double pipe heat exchanger with a holed twisted tape

In the present study numerical analysis of enhancement in heat transfer characteristics in a double pipe heat exchanger is studied using a holed twisted tape.The twisted tape with a constant twist ratio is inserted in a double pipe heat exchanger. Holes of diameter 1mm, 3 mm and 5 mm were drilled at regular pitch throughout the length of the tape. Numerical modeling of a double pipe heat exchanger with the holed twisted tape was constructed considering hot fluid flowing in the inner pipe and cold fluid through the annulus.Simulation was done for varied mass flow rates of hot fluid in the turbulent condition keeping the mass flow rate of cold fluid being constant. Thermal properties like Outlet temperatures, Nusselt number, overall heat transfer coefficient, heat transfer rate and pressure drop were determined for all the cases. Results indicated that normaltwisted tape without holes performed better than the bare tube. In the tested range of mass flow rates the average Nusselt number and heat transfer rate were increased by 85% and 34% respectively. Performance of Twisted tape with holes was slightly reduced than the normal twisted tape and it deteriorated further for higher values hole diameter. Pressure drop was found to be higher for the holed twisted tape than the normal tape.

Fourier and wavelet analyses of intermittent and resonant pressure components in a slot burner

In laboratory-scale burner it has been observed that the acoustic excitations change the flame topology inducing asymmetry and oscillations. Hence, an acoustic and aeroacoustic study in non reactive condition is of primary importance during the design stage of a new burner in order to avoid the development of standing waves which can force the flame. So wall pressure fluctuations inside and outside of a novel slot burner have been studied experimentally and numerically for a broad range of geometrical parameters and mass flow rates. Wall pressure fluctuations have been measured through cavity-mounted microphones, providing uni- and multi-variate pressure statistics in both the time and frequency domains. Furthermore, since the onset of combustion-driven oscillations is always presaged by intermittent bursts of high amplitude, a wavelet-based conditional sampling procedure was applied to the database in order to detect coherent signatures embedded in the pressure time signals. Since for a particular case the coherent structures identified have a multi-scale signature, a wavelet-based decomposition technique was proposed as well to separate the contribution of the large- and small-scale flow structures to the pressure fluctuation field. As a main outcome of the activity no coupling between standing waves and velocity fluctuations was observed, but only well localized pressure signatures with shape strongly affected by the neighbouring flow physics.

Experimental investigation on flow condensation in horizontal tubes filled with annular metal foam

This work studies the heat transfer and pressure drop of water vapor flow condensation in horizontal tubes filled with annular metal foam of three different sizes (10, 15 and 20PPI). The range of vapor mass flow rate is 20–100kg/h and cooling water flow rate is 1–3m3/h. The flow condensation characteristic in metal foam tubes is presented and compared with corresponding micro-fin tubes by using unit mass efficiency coefficient method. The effects of metal foam size, inlet vapor pressure, vapor mass flow rate, and cooling water temperature on heat transfer and pressure drop are examined and analyzed. Heat transfer and pressure drop correlations for horizontal tubes with annular metal foam are obtained by curve-fitting of the experimental values. The results indicate that the introduction of metal foam enhances the heat transfer although resulting in a larger pressure drop. Metal foam of 10PPI size exhibits the superior performance. The average heat transfer coefficient is also observed to increase with higher inlet vapor pressure, higher vapor mass flow rate and higher cooling water temperature.

Evolution of steam-water flow structure under subcooled water boiling at smooth and structured heating surfaces

Experimentally studying of subcooled water boiling in rectangular channel electrically heated from one side was conducted. Flat surfaces, both smooth and coated by microarc oxidation technology, were used as heating surfaces. The tests were conducted at atmospheric pressure in the range of mass flow rate from 650 to 1300 kg/(m2 s) and water subcooling relative to saturation temperature from 23 to 75 °C.Using high-speed filming a change in the two-phase flow structure and its statistic characteristics (nucleation sites density, vapor bubble distribution by size, etc.) were studied. With an increase in the heat flux density (with the mass flow rate and subcooling being the same) and amount and size of the vapor bubbles increased also. At a relatively high heat flux density, non-spherical vapor agglomerates appeared at the heating surface as a result of coalescence of small bubbles. They originated in chaotic manner in arbitrary points of the heating surface and then after random evolution in form and size collapsed. The agglomerate size reached several millimeters and their duration of life was several milliseconds. After formation of large vapor agglomerates, with a further small increase in heat flux density a burnout of the heating surface occurred. In most cases the same effect took place if the large agglomerates were retained for several minutes.

EDU liquid acquisition device outflow tests in liquid hydrogen: Experiments and analytical modeling

This paper presents experiments and modeling of the most recent set of liquid acquisition device (LAD) vertical outflow tests conducted in liquid hydrogen. The Engineering Development Unit (EDU) was a relatively large tank (4.25m3) used to mimic a storage tank for a cryogenic storage and transfer flight demonstration test. Six 1-g propellant tank outflow tests were conducted with a standard 325×2300 rectangular cross-section curved LAD channel conformal to the tank walls over a range of tank pressure (158–221kPa), ullage temperature (22–39K), and mass flow rate (0.0103–0.0187kg/s) per arm. An analytical LAD channel solver, an exact solution to the Navier-Stokes equations, is used to model propellant outflow for the LAD channel. Results shows that the breakdown height of the LAD is dominated by liquid and ullage gas temperatures, with a secondary effect of flow rate. The best performance is always obtained by exposing the channel to cold pressurant gas and low flow rates, consistent with the cryogenic bubble point model. The model tracks the trends in the data and shows that the contribution of flow-through-screen pressure drop is minimized for bottom outflow in 1-g, versus the standard inverted outflow.

A Comparative Investigation of Two Types of MHPA Flat-Plate Solar Air Collector Based on Exergy Analysis

In this study, a comparative investigation of two types of microheat pipe array (MHPA) flat-plate solar air collectors (FPSAC) based on exergy analysis has been conducted. The thermal performance of MHPA-type solar air collectors (SACs) with two different shaped fins is experimentally evaluated. A detailed parametric study is also conducted to examine the effects of various fins, operation parameters, and inlet air temperature at different mass flow rates on thermal and exergy efficiencies. Results indicated that using V-shaped slotted fins at the specified range of mass flow rates can enhance exergy efficiency. Exergy efficiency can be considered as the main criterion to evaluate the performance of MHPA FPSACs. Attaching V-shaped slotted fins on the condenser section of MHPA is more effective than attaching rectangular fins at high mass flow rates. By contrast, the latter is more effective than the former at low mass flow rates.

Investigation into the efficiency of a fin and wound wire intensifier

The work continues the experimental investigations into heat transfer enhancement carried out at NIU MPEI. To verify the obtained results and extend the range of geometric characteristics of the intensifier, additional systematic experiments were performed. The investigations were carried out under the program of improvement of existing water-cooled water-moderated reactors to create a base of reliable experimental data and design correlations that could be required in developing reactors of the fourth generation. Among the methods for improving the safety of the core and of the overall reactor is the replacement of conventional fuel rods in fuel assemblies with tubular ones and development of spacers that best suit fuel assemblies. A design of an intensifier that can be used in a spacer grid is examined. A brief description of the test section and the design of developed intensifiers with a list of their basic geometric characteristics are presented. New systematic experimental data are given on hydraulic resistance factors and heat transfer coefficients for single-phase convection with the use of a fin-and-wound wire intensifier. This investigation extends the range of intensifier geometric characteristics and operating conditions: the mass flow rate range was ρw = 1000–4000 kg/(m2 s), the pressure range was p = 3.0–7.0 MPa, the coolant temperature at the test section inlet was 100°C, and the heat flux range was q = 0.23–0.70 MW/m2. The experiments revealed a considerable increase in the heat transfer coefficient on the convex heated surface and dependence of the hydraulic resistance factors and the heat transfer coefficients on the wire winding pitch. The relative pin heights offering a higher increase in heat transfer as compared with an increase in hydraulic resistance were established. Empirical correlations for predicting the heat transfer coefficients and the hydraulic resistance factors as a function of the intensifier geometric characteristics are proposed.

Heat transfer performance of wavy-channeled PCHEs and the effects of waviness factors

The printed circuit heat exchanger (PCHE) is a key component in the future compact energy cycles due to its high heat transfer performance and structural rigidity. In this study, the thermal performance of wavy-channeled PCHEs, and the effects of the waviness factors: the amplitude and the period, on the thermal performance of the PCHE are investigated numerically. The thermal performance of the wavy-channeled PCHEs is compared with that of conventional PCHEs with straight channels. Based on the numerical results, it has been shown that the wavy-channeled PCHEs can have significantly higher thermal performance than the conventional straight-channeled PCHEs due to the increased area for heat transfer. The effect of recirculating flow induced by the waviness is estimated to be negligible for the typical range of CO2 mass flow rate of compact power generations. It has been shown that the performance enhancement can be predicted using a sole nondimensional parameter: the ratio between amplitude and period, and has linear relationship with this nondimensional parameter.