Water Volumetric Flow Rate Research Articles

Conceptual design of a two-step solar hydrogen thermochemical cycle with thermal storage in a reaction intermediate

This paper presents the conceptual design for a two-step thermochemical cycle producing hydrogen continuously, even off-sun, with the concentrated solar energy as the heat source. For a case study, the two-step iron oxide cycle (Fe3O4/FeO) is selected to illustrate the design concept. Two reactors, one storage tank and the solar collector comprise the system. Molten wustite (FeO) is accumulated in the storage tank on-sun. The FeO is not only involved in the reactions but also acts as the heat transfer medium, obtaining the energy from the solar insolation and delivering energy to support the thermal decomposition of magnetite (Fe3O4). In this way, the temperature limitation (<800 K) of molten salt is solved, and the intermittency problem of variable insolation is circumvented. A simple feedback scheme is used to control the flow rate between the storage tank and the reactors in order to minimize the temperature fluctuations. For the wustite hydrolysis reaction, the volumetric flow rate of water is regulated to control the temperature in the reactor. We derived the kinetics of the two-step iron oxide cycle from previous experimental reports. We simulated the dynamics of the system over 50 days with mass and energy balances. The simulation results show that the storage tank temperature will be stationary at 2250 K. After five days, the decomposition temperature at 2100 K, and the hydrogen production stabilized at 7 kg/min. Admitting the difficulty of high temperature operation, this design is still promising due to the high efficiency of two-step cycle itself, the process intensification of the FeO acting as the reactant/product/heat transfer medium (no need of heat exchangers), and the continuous operation/production of hydrogen.

Theoretical estimation of the optimum glass cover water film cooling parameters combinations of a stepped solar still

In the present work, theoretical performance evaluation of a stepped solar still using water film cooling over the glass cover is investigated. The effect of film cooling thickness, flow rate, inlet temperature, and air wind speed on the stepped solar still daily productivity is studied. To increase the performance of the stepped solar still outlet water film cooling is recycled as a makeup water. It was found that film cooling thickness, volumetric flow rate, and water film inlet temperature have a significant effect on the daily distillate productivity. The presence of the glass cover water film cooling may increase the stepped still daily productivity by about 8.2% but the value of this percentage mainly depends on the combinations of film cooling parameters. On the other hand, the presence of the film cooling neutralized the effect of air wind speed on the still distillate productivity. Moreover, it was found that the proper combinations of film cooling parameters have a great influence on stepped still productivity and the best combination was: film thickness from 2.5 × 10−4 to 5.5 × 10−4 m, cooling water volumetric flow rate from 4 × 10−5 to 8.5 × 10−5 m3/s, and glass cover length from 2 to 2.8 m. Finally a good agreement between the present theoretical work and previous experimental result has been obtained.

Water cooled minichannel heat sinks for microprocessor cooling: Effect of fin spacing

For effective thermal management of high heat generating microprocessors, five different heat sinks with fin spacings of 0.2 mm, 0.5 mm, 1.0 mm, and 1.5 mm along with a flat plate heat sink were investigated. Microprocessor heat was simulated by a heated copper block with water as a coolant. At a heater power of 325 W, the lowest heat sink base temperature of 40.5°C was achieved by using a heat sink of 0.2 mm fin spacing which was about 9% lower than the best reported base temperature of 44°C using a nanofluid with commercial heat sink in the open literature. The base temperature and thermal resistance of the heat sinks were found to drop by decreasing the fin spacing and by increasing volumetric flow rate of water circulating through the heat sink. For a flat plate heat sink, the maximum thermal resistance was 0.216 K/W that was reduced to as little as 0.03 K/W by using a heat sink of 0.2 mm fin spacing. The overall heat transfer coefficient was found to be 1297 W/m2K and 2156 W/m2K for the case of a flat plat and 0.2 mm fin spacing heat sinks, respectively, the latter showed about two-folds enhancement compared to the former.

Evaluation of elliptical finned-tube heat exchanger performance using CFD and response surface methodology

The elliptical tube has long been considered as an alternative of the circular tube in finned-tube heat exchangers (FTHE). Most of the previous studies evaluated the two tube shapes only based on the air-side performance of FTHE, and did not consider any interaction effect of the axis ratio with other parameters. We proposed a numerical model to simultaneously predict the fluid flow and heat transfer on both air-side and water-side of elliptical FTHE. The numerical results agree well with the reported experimental data. Response surface methodology was applied to understand the interactions among seven design factors including number of rows, axis ratio, transversal tube pitch, longitudinal tube pitch, fin pitch, air velocity, water volumetric flow rate. Response surface analysis was used to evaluate the axis ratio effect on the overall thermal–hydraulic performance which was quantified by the heat transfer rate per unit power consumption. The results indicate that the axis ratio strongly interacts with air velocity and water volumetric flow rate. The increase of axis ratio improves the overall thermal–hydraulic performance at higher air velocity or lower water volumetric flow rate, but the opposite effect is observed at lower air velocity or higher water volumetric flow rate.

Large probe arrays for measuring mean and time dependent local oil volume fraction and local oil velocity component distributions in inclined oil-in-water flows

Arrays of dual-sensor and four-sensor needle conductance probes have been used to measure the mean and time dependent local properties of upward inclined, bubbly oil-in-water flows (also known as dispersed oil-in-water flows) in a 153mm diameter pipe. The flow properties that were measured were (i) the local in-situ oil volume fraction α; (ii) the local oil velocity uo in the axial direction of the pipe (the Z direction); and (iii) the local oil velocity uY in the direction from the lower side of the inclined pipe to its upper side (the Y direction). Oil velocities in the X direction (orthogonal to the Y and Z directions) were found to be negligible. For all of the flow conditions investigated it was found that the mean value of α varied from a maximum value at the upper side of the inclined pipe to a minimum value at the lower side, and that the rate of decrease of this mean value of α with distance in the −Y direction became greater as the pipe inclination angle θ from the vertical was increased. It was also found that the mean value of uo was greatest at the upper side of the inclined pipe and decreased towards the lower side of the inclined pipe, the rate of decrease with distance in the −Y direction again becoming greater as θ was increased. For θ=45o, a water volumetric flow rate Qw=16.38m3h−1, an oil volumetric flow rate Qo=6.0m3h−1 and using a sampling period T=0.05s over a total time interval of 60s, it was found that at the upper side of the inclined pipe the standard deviation in uo was 31.6% of the mean value of uo. Furthermore for T=0.05s, θ=30o, Qw=16.38m3h−1 and Qo=6.0m3h−1 it was found that the standard deviation in the cross-pipe oil velocity component uY was approximately equal to the standard deviation in the axial velocity component uo. These large temporal variations in the local flow properties have been attributed to the presence of large scale Kelvin–Helmholtz waves which intermittently appear in the flow. It is believed that the techniques outlined in this paper for measuring the standard deviation of local flow properties as a function of the sampling period T will be of considerable value in validating mathematical models of time dependent oil–water flows. It should be noted that the principal focus of this paper is on the measurement techniques that were used and the methods of data analysis rather than the presentation of exhaustive experimental results at numerous different flow conditions.

Experimental performance analysis of an improved multifunctional heat pump system

An improved multifunctional heat pump (MFHP) system that integrates an air-source evaporator and a water–water heat exchanger was developed. An experimental set-up and a mathematical model were constructed to evaluate the performance of the MFHP system. Some characteristics of the system, such as the effects of water–water heat exchanger, hot water outlet temperature, and cooling capacities of the air-source and water-source evaporators, were discussed based on experimental data. Experimental results show that the MFHP system could simultaneously supply hot water for bathing and cold air for air conditioning. In addition, the coefficient of heating performance (COPh) varied from 3.69 to 5.70. Analysis results show that the COPh and the hot water volumetric flow rate of the MFHP system were closely related to the inlet and outlet temperature of hot water and wastewater. Empirical models of COPh and hot-water flow rate were proposed to predict the heating performance of the MFHP system. The improved MFHP system is shown to have satisfactory energy saving performance.

An experimental and numerical study on hydrodynamic characteristics of horizontal annular type water-air ejector

A water-driven annular type ejector loop is designed and constructed for air absorption. Fabricated ejector unit is horizontally installed in the loop, and annular water jet at the throat entrained atmospheric air through the circular pipe placed at the center of the ejector. The tested range of water flow rate is 160 L/min to 320 L/min and volumetric flow rate of water and air and local pressure are quantitatively measured using LabVIEW signal express program. For the quantitative measurement of bubble velocity, cinematic PIV technique using a high speed camera is adapted. In post processing, each bubble is used as seeding particles and ensemble averaged bubble velocity field at vertical plane of the ejector system is finally acquired. In the range of experiment, the bubble size distribution at downstream of the ejector seems to be quite uniform so that the flow can be classified as a homogeneous bubbly flow. In case of low range of water flow rate, the transition from bubbly flow to stratified flow occurs at the atmospheric outlet condition. As a comparative study, a numerical simulation on the same ejector shape is performed to understand the more detail hydrodynamic characteristics in the annular type ejector system. Homogeneous bubbly flow regime is used as default two-phase flow regime, and void fraction at the vertical plane of the ejector system is qualitatively compared with that of experiment. In volume flow rate comparison, numerical prediction agrees well with that of experiment where the homogeneous bubbly flow is maintained.

Urea separation in flat-plate microchannel hemodialyzer; experiment and modeling

Two flat-plate microchannel hemodialyzers were constructed consisting of two identical laminae separated by a 20[μm] thick ultrafiltration membrane (Gambro AN69). Each lamina contains a parallel array of microchannels 100[μm] deep, 200[μm] wide, and 5.6[cm] or 9.9[cm] in length respectively. Urea was removed from the aqueous stream containing 1.0[g] urea per liter de-ionized water in the blood side, by countercurrent contact with pure de-ionized water in the dialysate side of the flat-plate hemodialyzer. In all cases volumetric flow rate of water in the dialysate side was equal or less than the volumetric flow rate in the blood side, which is in large contrast to commercial applications of hollow-fiber hemodialyzers where dialysate flow is severalfold larger than blood flow rate. A three-dimensional finite volume mass transport model, built entirely from the first principles with no adjustable parameters, was written in FORTRAN. The results of the mathematical model excellently predict experimental results. The fractional removals of urea predicted by the model are within 2.7%-11% of experimentally obtained values for different blood and dialysate velocities/flow rates in microchannels, and for different transmembrane pressures. The overall mass transfer coefficient was calculated using the urea outlet concentrations obtained at various average velocities (1.0-5.0[cm/s]) in the blood and dialysate, and two nominal transmembrane pressures (∆P(tm) = 0 and 10,000.[Pa]). Overall mass transfer coefficients obtained experimentally ranged from 0.068 to 0.14 [cm/min]. The numerical model predicted an average overall mass transfer coefficient of 0.08 [cm/min]. This value is 60% higher than those found in commercial dialyzers (~0.05[cm/min]).

Inverse heat transfer problem in digital temperature control in plate fin and tube heat exchangers

Inverse heat transfer problem in digital temperature control in plate fin and tube heat exchangersThe aim of the paper is a steady-state inverse heat transfer problem for plate-fin and tube heat exchangers. The objective of the process control is to adjust the number of fan revolutions per minute so that the water temperature at the heat exchanger outlet is equal to a preset value. Two control techniques were developed. The first is based on the presented mathematical model of the heat exchanger while the second is a digital proportional-integral-derivative (PID) control. The first procedure is very stable. The digital PID controller becomes unstable if the water volumetric flow rate changes significantly. The developed techniques were implemented in digital control system of the water exit temperature in a plate fin and tube heat exchanger. The measured exit temperature of the water was very close to the set value of the temperature if the first method was used. The experiments showed that the PID controller works also well but becomes frequently unstable.

Results of participation of Russian standards in key comparisons conducted by the Regional Metrological Organization for countries of the Asia-Pacific Region in the field of liquid and gas flow rate parameter measurement

Results of international key comparisons of the national standard for air flow rate and the working standard for water volumetric and mass flow rate are provided. Comparisons were made in 2009 within the framework of the Asia-Pacific Metrological Program (APMP) international organization. Russia was represented by state special standard for the unit of air flow rate (GET 150–85) and the highest accuracy working standard for the unit of water volumetric mass flow rate (RE VT 6–98). Results of comparison point to conformity of the metrological properties of these standards to the world level.

Thermochemical water-splitting for H 2 generation using sol-gel derived Mn-ferrite in a packed bed reactor

This paper reports synthesis of Mn-ferrite using sol-gel technique, which involved the addition of Mn and Fe salts in ethanol followed by gelation using propylene oxide (PO). As-prepared gels were aged, dried and calcined rapidly upto different temperatures of 600 °C–900 °C and quenched in air. Calcined powders obtained were analyzed using x-ray diffraction, BET surface area analyzer, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The gels calcined rapidly upto 600 °C and quenched in air resulted into a phase pure Mn-ferrite with porous/nanoparticle morphology and higher SSA. The H 2 generation ability of the calcined powder was investigated by performing multiple thermochemical cycles in the Inconel packed bed reactor. In addition, the effects of several process parameters such as water-splitting temperature (T ws), regeneration temperature (T reg), regeneration time (t reg) and volumetric flow rate of water (v o) on H 2 generation ability of Mn-ferrite were investigated in detail.

Optimization of Methanol Yield from a Lurgi Reactor

AbstractMethanol is an important chemical with the potential to become an alternative fuel. An optimization study was performed for a Lurgi methanol synthesis reactor using the commercial process simulator Aspen Plus. The optimization routine is coupled with a steady‐state model of the methanol synthesis reactor. Syngas inlet temperature, steam drum pressure, and cooling water volumetric flow rate were optimized so that methanol production in the reactor outlet was maximized. The methanol yield increased by 7.04 %.

Morphological instability of the solid-liquid interface in crystal growth under supercooled liquid film flow and natural convection airflow

Ringlike ripples on the surface of icicles are an example of morphological instability of the ice-water interface during ice growth under supercooled water film flow. The surface of icicles is typically covered with ripples of about 1 cm in wavelength, and the wavelength appears to be almost independent of external temperature, icicle radius, and volumetric water flow rate. One side of the water layer consists of the water-air surface and growing ice is the other. This is one of the more complicated moving phase boundary problems with two interfaces. A recent theoretical work [K. Ueno, Phys. Rev. E 68, 021603 (2003)] to address the underlying instability that produces ripples is based on the assumption of the absence of airflow around icicles. In this paper, we extend the previous theoretical framework to include a natural convection airflow ahead of the water-air surface and consider whether the effect of natural convection airflow on the wavelength of ripples produced on an ice surface is essential or not.

Experimental Studies on Thermal Performance and Flow Resistance of Heat Exchangers with Helical Baffles

In this study, the shell-side heat transfer performance and flow resistance of the shell-and-tube heat exchangers with third-symmetrical, quarter-symmetrical, quarter-unsymmetrical helical baffles and segmental baffles were experimentally obtained. Except for the baffles, these heat exchangers had the same geometrical configuration and number of tubes. Cold and hot water were used as working fluids in the shell and the tube side, respectively. The experiments were done with the cold water volumetric flow rate ranging between 3 and 7 m3/h and the hot water volumetric flow rate constant at 5.5 m3/h. The results show that the heat exchanger with segmental baffles has higher shell-side heat transfer performance and flow resistance than those with helical baffles. Among the three helical baffles used, the third-symmetrical helical baffle offers the highest shell-side heat transfer performance and flow resistance. The quarter-unsymmetrical helical baffle offers the lowest shell-side flow resistance. Its performance of shell-side heat transfer is also the lowest one but close to that of the quarter-symmetrical helical baffle, so the quarter-unsymmetrical helical baffle provides the best conversion efficiency in all heat exchangers mentioned. Compared with the segmental baffle, the shell-side Nusselt numbers that the third-symmetrical, the quarter-symmetrical, and the quarter-unsymmetrical helical baffle offer decrease on the average by about 26%, 37%, and 38%, respectively, and the corresponding shell-side Euler numbers they provide decrease on the average by about 33%, 49%, and 55%, respectively. Thus, the relative shell-side conversion efficiencies increase by about 9%, 25%, and 39% on the average, respectively.

Theoretical modeling and experimental analysis of direct contact membrane distillation

A two-dimensional mathematical model was theoretically developed to predict the temperature polarization profile of direct contact membrane distillation (DCMD) processes. A concurrent flat-plate device was designed to verify the theoretical prediction of pure water productivity on saline water desalination. The numerical results from the temperature polarization profile were obtained using the finite difference technique to reduce the two-dimensional partial differential equations into an ordinary differential equations system. The resultant simultaneous linear equations system was solved with the fourth-order Runge-Kutta method. The results show theoretical prediction agreement with the measured values from the experimental runs. A combination of the Knudsen flow and Poiseuille flow models in the present mathematical formulation for membrane coefficient estimation was used to establish theoretical agreement. The influence of the inlet saline water temperature and volumetric flow rate on the pure water productivity as well as the hydraulic dissipated energy are also delineated.

Subcritical water extraction of polyphenolic compounds from Terminalia chebula Retz. fruits

This study investigated subcritical water extraction (SWE) of polyphenolic compounds such as gallic acid (GA), ellagic acid (EA), and corilagin (CG) from Terminalia chebula Retz . The effects of extraction temperatures (120–220 °C) and water flow rates (2–4 ml/min) at the pressure of 4 MPa were examined on the amounts of compounds extracted. In addition, the total phenolic contents and antioxidant activities of the extracts were analyzed and compared to those obtained by hot water extraction and Soxhlet extraction with ethanol at ambient pressure. The amounts of extracted GA and EA increased with an increase in subcritical water temperature up to 180 °C, while the highest amount of CG was recovered at 120 °C. Water volumetric flow rate was found to affect the extraction behavior and the suitable flow rate for extraction of total phenolic compounds was 4 ml/min. Compared to other extraction methods, SWE of T. chebula effectively resulted in considerable amount of phenolic compounds with high antioxidant activity.

Morphological Change in the Tessellated Darter (Etheostoma olmstedi) Following the Introduction of the Banded Darter (E. zonale) to the Susquehanna River Drainage

Abstract The strong connection between ecology and morphology in fishes predicts that ecologically relevant morphological features will change in concert with changes in habitat use and feeding ecology even over relatively short timescales following species introduction. Here, this hypothesis is tested by examining the trophic morphology of specimens of the native Tessellated Darter, Etheostoma olmstedi, collected at Catatonk Creek, Candor, Tioga Co., NY, USA, between 1961 and 2002. The collections of E. olmstedi bracket a 1980 range expansion by the non-native Banded Darter, E. zonale. Examination of the E. olmstedi specimens revealed that the length of the buccal cavity relative to body size increased following the invasion of Catatonk Creek by E. zonale. An increase in buccal cavity length (BCL) is expected to result in higher suction feeding performance measured as volumetric flow rate of water through the mouth. Such an increase in BCL may enable E. olmstedi to exert greater suction forces on prey an...

CFD and experimental study on methane hydrate dissociation Part I. Dissociation under water flow

AbstractDissociation processes of methane hydrate under water flow conditions were investigated by a combination of experimental observations and numerical simulations using computational fluid dynamics (CFD). In Part I of this study, the dissociation process induced by water flow at pressures above the three‐phase [hydrate (H)–liquid water (Lw)–vapor (V)] boundary in an isothermal x–P phase diagram is discussed. Dissociation experiments were carried out with a methane hydrate ball (diameter ≅ 10 mm) suspended in a flow cell, and the overall dissociation rate of methane hydrate without bubble formation was measured under various conditions of pressure, temperature, and volumetric flow rate of water. A linear phenomenological rate equation in the form of the product of the dissociation rate constant kbl and the molar Gibbs free energy difference ΔG, between the hydrate phase and the ambient aqueous phase, was derived by considering the Gibbs free energy difference as the driving force for the dissociation. The molar Gibbs free energy difference was expressed by the logarithm of the ratio of the concentration of methane dissolved in water at the hydrate surface to the solubility of methane in the aqueous solution in equilibrium with the hydrate. The dissociation rate constant kbl was determined from the experimental results of the overall dissociation rate combined with the numerical simulation results of the concentration profile of methane by the CFD method. The obtained dissociation rate constant was found to be independent of the ambient water flow rate, indicating that the rate constant is intrinsic for the hydrate dissociation within the conditions examined in this study. The rate constant was independent of the pressure, whereas the temperature dependency was described by an Arrhenius‐type equation with the apparent activation energy of 98.3 kJ/mol. © 2006 American Institute of Chemical Engineers AIChE J, 2007

Integration of biaxial planar gradient coils and an RF microcoil for NMR flow imaging

A package of two planar gradient coils combined with an RF coil was microfabricated for low-field MRI measurements of velocity flow profiles. The package generates orthogonal gradients in the radial and velocity encoding directions for standard flow imaging experiments. A commercial 0.6 T superconductive magnet was used to test coil performance. For comparison flow imaging was also performed using a commercial set of gradient coils. Velocity profiles were obtained for several volumetric flow rates of water in tubes with inner diameters of 1.02 mm and 1.4 mm. Velocity resolution was 0.13 mm s−1, comparable to that achieved with commercial gradient coils. The quality of the velocity profile was sufficient for viscosity calculations, and thus permits future utilization of this coil package in the design of a portable MRI viscometer.

Effect of fin thickness on air-side performance of herringbone wavy fin-and-tube heat exchangers

In the present study, the effects of fin thickness on the heat transfer and friction characteristics of fin-and-tube heat exchangers having herringbone wavy fin configuration are experimentally investigated. The experimental apparatus consists essentially of a well insulated open wind tunnel and herringbone wavy fin-and-tube heat exchangers made from aluminium plate finned, copper tube. Air and water are used to be working fluids in air-side and tube-side, respectively. A total of 10 samples of the fin-and-tube heat exchangers are tested. The experimental procedures are conducted by keeping the inlet water temperature at a pre-selected value, adjusting the water volumetric flow rate at a specific value and varying the air velocity. The results are presented as plots of the Colburn factor and friction factor against the Reynolds number based on the fin collar outside diameter (ReDc). From the results, it is found that for number of tube rows (N) = 2, the Colburn factor increases with increasing fin thickness. For N ≥ 4, the Colburn factor decreases with increasing fin thickness when ReDc 2500. The friction factor increases with increasing fin thickness when fin pitch (Fp) ≤ 1.81 mm.