Pressure Drop Of Water Flow Research Articles

Heat transfer coefficient and pressure drop of water flow boiling in porous open microchannels heat sink

• Porous open microchannels (POM) heat sink was proposed and fabricated. • Heat transfer coefficient was greatly improved by porous wall at high heat fluxes. • Periodic slug-stratified flow was newly observed in POM heat sink. • No local dryout was noted due to the enhanced capillary actions in porous wall. • Two-phase flow could maintain stable under all operating conditions tested. The open microchannel is attracting more attention due to the reduced pressure drop and the improved flow stability, but the local dryout easily occurs at the downstream of the microchannels and subsequently deteriorates the flow boiling heat transfer performance. In this study, two open microchannels heat sinks were fabricated utilizing solid copper substrate and the porous substrate sintered by copper powder particles, respectively. Flow boiling experiments were conducted using deionized water as the working fluid with the inlet temperate of 87 °C at different mass fluxes ranging from 151.5 to 551.1 kg/m 2 s over a heat flux range of 29.6-1871.1 kW/m 2 in the porous open microchannels (POM) and the solid copper open microchannels (SOM). Experimental results showed that the heat transfer coefficients (HTC) were greatly improved in POM compared with that in SOM at moderate (300 kW/m 2 < q eff < 600 kW/m 2 ) and high ( q eff > 600 kW/m 2 ) heat fluxes. No local dryout was observed even at the highest heat fluxes in POM heat sink. Therefore, the flow boiling HTC in POM no longer deteriorated with increment in heat flux at high heat flux region, unlike in SOM. A new periodic flow pattern named slug-stratified flow was found in POM heat sink during which the slug flow and the stratified flow alternated temporally and spatially. Besides, although the two-phase pressure drop of POM was larger than that of SOM due to the increased friction and acceleration loss, the flow could still maintain stable under all operating conditions tested here.

Experimental investigation of pressure drop of water flow in a double vertical coils and shell heat exchanger induced by 28 kHz ultrasound

This research experimentally investigated the pressure drop characteristics induced by 28 kHz ultrasound in a double vertical coils and shell heat exchanger, typically used in 3 – 10 tons water chiller. Also, the water inlet was positioning as 3 configurations, including 1: configuration 1 is the original model from a commercial type (2 ports to the coil center), 2: configuration 2 is the modified model to make a swirl in the heat exchanger (4 ports on 4 side walls), and 3: configuration 3 is the modified model that vertically injects water to the coil (4 ports on a top wall). The results showed that the pressure drop increased in accordance with the flow rate from 0.25 to 0.75 l/s. The second inlet configuration was found to be a promising setup due to its lowest occurring flow friction. Especially in the operation under ultrasonic waves, this configuration provided a lower pressure drop of approximately 20%. Therefore, the maximum reduction of pressure drop was at 86.6% from the original configuration at the lowest flow rate. These results lead to the better design of the heat exchanger and the consequence of higher efficiency water chiller in the future.

Heat transfer and fluid flow characteristics in a plate heat exchanger filled with copper foam

A small plate heat exchanger filled with copper foam which can be applied for small scale electronic cooling is presented. The heat transfer coefficient and pressure drop of water flow inside a plate heat exchanger filled with copper foam (PHECF) are experimentally studied. The effect of copper foam pore density and water velocity on the optimum thermal performance is also presented. The experiment is performed with a Reynolds number ranging from 1200 to 2000 and copper foam pore density ranging from 30 to 50 pores per inch (PPI). The results show that the heat transfer coefficient and pressure drop increased when the water velocity and pore density increased. The heat transfer coefficient is enhanced by 20.23%, 29.37%, and 40.28% for PHECF with a pore density of 30 PPI, 40 PPI, and 50 PPI as compared to a plate heat exchanger. The total pressure drop of water flow inside PHECF is dominated by inertial drag pressure drop. Thermal performance of PHECF with 50 PPI is highest with the average thermal performance factor of 1.21. The Nusselt number and friction factor correlation of water flow inside plate heat exchanger filled with copper foam are also proposed for practical applications.

Artificial neural network model development for prediction of nonlinear flow in porous media

To explore non-linear flow behaviour in porous media, e.g., packed bed of particles, this study focuses on the prediction of pressure drop/gradient by establishing empirical relations for Forchheimer coefficients based on artificial neural network (ANN) development. To facilitate this process, a large set of experimental data for pressure drop of water flow in various porous media is collected: part from the present experiment and other from those available in the literature. The newly generated ANN model is developed by considering the key influencing factors such as particle density, diameter, and shape, and column porosity. The new model shows excellent performance on the prediction of flow behaviour over previous empirical formula, which is attributed to the ANN's advantages on considering the inter-factor connections and their influences on the results. This proposed approach can provide a new means for analysing the nonlinear flow regime through porous media based on limited dataset.

Developing predictive models for analysis the heat transfer in sinusoidal wavy channels

In this work, empirical correlations were proposed to accurately estimate the heat transfer and pressure drop for water flow in sinusoidal wavy channels. The artificial intelligence techniques such as artificial neural network (ANN) and genetic algorithm (GA) were applied to develop the correlations. The experimental data related to the Nusselt number (Nu) and pressure drop (ΔP) in the wavy channels with various geometries were collected for the modeling. The independent variables are Reynolds number (Re) and main geometrical parameters including amplitude ratio (b/H), phase shift (φ), and number of waves (Nw). The results indicate that the ANN is a suitable technique to develop correlations for predicting thermal and flow characteristics in heat exchangers with wavy channels.

Heat transfer and pressure drop performance of solar glycol/activated carbon based nanofluids in shot peened double pipe heat exchanger

The present study aims at analyzing the heat transfer and pressure drop characteristics the by determination of improved Nusselt number in a double pipe heat exchanger, whose outer surface of the inner tube is modified through the shot peening process. The attained convective heat transfer coefficient (CHTC) and pressure drop of water flow in the heat exchanger with this modified surface are first measured and compared with a high conductivity copper tube construction. The study is to analyze the variations in CHTC and the pressure drop of the activated carbon (AC) - solar glycol (SG) based nanofluid. The experiments stimulated nanomaterials volume concentrations of the nanofluids such as 0.2%, 0.4% and 0.6%. The Nusselt numbers at mass flow variation rates in the range of 0.04, 0.055 and 0.08 kg/sec with shot peened heat exchanger. The presence of AC nanomaterials in the SG enhances the Nusselt number by 26.25%, 40.79%, and 57.06% for 0.2, 0.4 and 0.6% volume concentrations respectively, at a mass flow rate of 0.04 kg/sec in the shot peened heat exchanger. The average CHTC of the nanofluid containing 0.6% of AC nanomaterials is noted to be augmented to a maximum of 71% at 0.04 kg/sec.

Simulation of the water controlling ability of an adaptive inflow control device

Traditional adaptive inflow control device (AICD) has low water control efficiency. Based on adaptive inflow control device, numerical simulation method is used to analyze the internal flow of the device. Influence of relevant design parameters on its water control capacity is studied. Internal structure of AICD is optimized to change internal flow and the flow path of oil flow in the restrictor. Purpose of controlling the flow of oil by using different viscosities of two flow states is achieved. Results show that setting the baffle to distinguish the annular passage and control chamber can improve pressure drop of water flow. The direction and number of flow channels have significant influence on AICD water control ability. Optimizing the shape of flow channel can change entrance speed and entrance angle, improving the water control capacity of inflow controlling device. The AICD achieves the optimal control capacity when it adopts the one transitional flow channel with 45°A angle.

Experimental investigation on heat transfer and pressure drop of MWCNT - Solar glycol based nanofluids in shot peened double pipe heat exchanger

The present work aims at analyzing the heat transfer, pressure drop characteristics and determination of Nusselt number in a double pipe heat exchanger, who's inner surface is modified through the shot peening process. The effects of shot peening on the fluid flow and heat transfer in the annulus are studied in detail and the results are reported. First, the convective heat transfer coefficient (CHTC) and pressure drop of water flow in the heat exchanger with a modified/roughened surface was measured and compared with a smooth tube. Later, the study is extended to analyze the variations in CHTC, the pressure drop of the nanofluid multi-walled carbon nanotubes (MWCNT-Solar glycol). The experiments were carried out at different volume concentrations (0.2%, 0.4%, and 0.6%) of the nanofluids. Experimental results showed that shot peening in tube surfaces has an appreciable effect on the performance of flow behavior and heat transfer. The CHTC of the nanofluid containing 0.6% of MWCNT nanomaterials is improved to a maximum of ~115% at a mass flow rate of 0.04 kg/s. Enhancement in thermal conductivity up to 30.59% was achieved with the MWCNT volume concentration of 0.6% and a temperature range from 30 to 50 °C. Pressure drop increased with an increase in mass flow rate, and volume concentrations of MWCNT nanoparticles. The augmentation in pressure drop for 0.6% volume concentration of MWCNT– solar glycol nanofluid is 1.56 times for a mass flow rate of 0.08 kg/s. The experimental results show that the combination of shot peening and nanofluids in the heat exchanger increases its heat transfer rate as well as its thermo-hydraulic performance.

Experimental study on single-phase frictional pressure drop for water flow under high heat fluxes

Pressure drop is one basic issue for the heat-removal systems for high heat flux components, such as the ITER divertors in fusion reactors, in which an accurate knowledge of single-phase frictional pressure drop is fundamental for further calculation of two-phase frictional pressure drop. However, the single-phase frictional pressure drop is still not well examined under high heat fluxes. In this study, experiments were conducted on the single-phase frictional pressure drop of water flow in circular tubes within the range of q = 5–10 MW/m2, G = 6000–10,000 kg/m2 s and p = 3–5 MPa (typical operating parameters for water-cooled divertors). The data were correlated using the equation of f/fad =(μw/μb)m, in which m is an empirical exponent. It is found that the exponent m is affected by the length-to-diameter ratio of flow channel, while the effects of mass flux and heat flux are insignificant. In addition, a number of existing correlations for single-phase friction factor were compared with our data. The results indicate that these correlations cannot well capture part of the data. Therefore, a modified correlation is proposed to calculate the single-phase friction factor under high heat fluxes, in which the effect of length-to-diameter ratio is taken into account. The new correlation has an improved performance compared with the existing correlations.

Effect of hydrophobicity on the water flow in carbon nanotube—A molecular dynamics study

ABSTRACT This work focuses on the study of the effect of hydrophobicity on the water flow in carbon nanotubes (CNTs) using a molecular dynamics (MD) approach for a wide range of potential applications such as water purification and high efficiency of nanofluid energy absorption systems (NEAS). The hydrophobicity between liquid water and surface of CNTs was characterized by interaction-energy-coefficient (IEC)—a parameter describing the energy interaction strength between water molecules and carbon atoms. It is shown that the static contact angles between water and carbon surface decrease from 155° to 44° when the values of IEC increase from 0.042 kJ/mol to 2.196 kJ/mol. In addition, the pressure drops in CNT became independent of IEC when the IEC value was higher than 1.192 kJ/mol for a given flow rate. It was found that the hydrophobicity of CNT surface has a significant impact on the pressure drop of water flow in the CNTs and MD method provides a quantitative evaluation of the impact.

Thermal-hydraulic effects of inserts in a fast reactor fuel bundle

The efficacy of inserts in the peripheral sub channels of a model fast reactor pin bundle with helical spacer wire has been investigated by 3 dimensional computational fluid dynamics (CFD) simulations as well as water experiments. Three different types of inserts, viz., triangular, semicircular and circular inserts have been considered along with a bundle without any insert. Sub channel sodium temperature, axial and circumferential temperature distributions of clad among the pins, Nusselt number and friction factor are the parameters targeted for the investigation. The CFD model has been validated by comparing the predicted pressure drop against measured pressure drop for water flow, for the cases of bundle with circular inserts and bundle without inserts. Thermal part of the CFD model has been validated against published Nusselt number for bundles without any insert. The inserts are found to reduce flow bypass in the peripheral sub channels and promote increase in central sub channel flow. As a consequence of this, the clad temperature with inserts was found to be lower than the bundle without any inserts. However, inserts were found to increase the friction factor. The increase in Nusselt number and friction factor for circular inserts are 86% and 17% more than that of a bundle without inserts. To find the optimum insert type, a Performance Enhancement Criterion (PEC) factor has been defined. This factor is found to be the maximum for circular inserts.

Experimental investigation on the thermal performance of a double pipe heat exchanger with segmental perforated baffles

This work experimentally investigates the characteristics of convective heat transfer and pressure drop of water flow in the annulus-side of horizontal double pipe heat exchangers. Twelve heat exchangers of counter-flow configurations are constructed with/without Single Segmental Perforated Baffles (SSPBs), which are fabricated with different holes spacing, void, cut, pitch ratios and inclination angle. The experiments are performed for annulus-side Reynolds number from 1380 to 5700, and for Prandtl number from 5.82 to 7.86. The results revealed that increasing SSPBs holes spacing and void ratios and inclination angle and decreasing SSPBs cut and pitch ratios increase the annulus average Nusselt number (Nu¯an) as well as friction factor (fan). The thermal performance index (TPI) is calculated to compare the thermal performance of perforated baffled double pipe heat exchangers with un-baffled one. It is observed that increasing SSPBs holes spacing ratio and inclination angle, and decreasing SSPBs void ratio, cut ratio and pitch ratio enhances the thermal performance index. Finally, correlations for Nu¯an in addition to fan for concentric tube heat exchangers with SSPBs as a function of the investigated parameters are obtained.

Experimental hydrodynamics of high-porosity metal foam: Effect of pore density

Commercial open-cell metal foam has very high porosity (often greater than 90%) and a large surface area density. The open flow area is copious compared to the ligament size. These properties are exploited in many applications, e.g., heat exchanger, reactors and filters. Pressure drop, flow regimes, and transition from one to another, are indispensable for any application involving flow of a fluid through the foam, and for heat transfer rates or reaction paces. These topics are not well-agreed on for foam-like porous media such as metal, graphite and polymeric foams. Pressure drop parameters such as permeability and form/inertial drag coefficients are very divergent for metal foam; the same can be said about flow regime boundaries. This paper presents experimental data for pressure drop for water flow in two commercial open-cell aluminium foams having 10 and 40 pores per inch (ppi). The two foams have similar porosities (88.5%). The wide range of flow Reynolds number covered all known flow regimes in porous media: pre-Darcy, Darcy, Forchheimer and turbulent. Flow regimes and transition between them were identified and compared. The friction factor based on the square root of permeability (measured in the Darcy regime) and the Reynolds number based on the same characteristic length were used. It is shown that the same foam exhibits different values of its permeability and Forchheimer coefficient in different flow regimes. A previously-tested foam having 20 pores per inch and a porosity of 87.6% was included in the comparisons. The basic finding of this study will inform numerical and analytical work concerning flow and heat transfer in foam-like highly-porous porous media.

Toward a generalized correlation for liquid–vapor two-phase frictional pressure drop across staggered micro-pin-fin arrays

In a previous study by the corresponding author and co-worker Mita and Qu (2015) (J. Mita, W. Qu, Pressure drop of water flow across a micro-pin-fin array part 2: adiabatic liquid–vapor two-phase flow, International Journal of Heat and Mass Transfer 89 (2015) 1007–1015), a modified Martinelli–Chisholm type correlation was developed to predict adiabatic water liquid–vapor two-phase frictional pressure drop across an array of staggered circular micro-pin-fins. This work expands on the study in ref. Mita and Qu (2015) and examines whether the correlation is geometry specific or it can be extended to describe a different array configuration. A square micro-pin-fin array were prepared, and adiabatic water liquid–vapor two-phase frictional pressure drop across the array was experimentally investigated. The square pin-fins were 200 microns in side length, 670 microns in height, and 400 microns in both longitudinal and transverse pitches. Two-phase friction multiplier and Martinelli parameter were calculated based on the measured pressure drop as well as a single-phase friction factor correlation developed for the same square array. An excellent agreement was found between the experimental data and correlation predictions despite the distinctive geometrical features possessed by the two sets of micro-pin-fin arrays. The result points to the possibility of establishing the correlation as a generalized one applicable to a broad range of staggered micro-pin-fin array configurations.

Thermal performance and pressure drop of spiral-tube ground heat exchangers for ground-source heat pump

Thermal performance and pressure drop of the spiral-tube GHE were evaluated in this present work. A numerical simulation tool was used to carry out this research. The heat exchange rates per meter borehole depth of the spiral-tube GHE with various pitches and their pressure drops were compared with that of the U-tube GHE. Furthermore, a comparative analysis between a spiral pipe and straight pipe was performed. In comparison with the straight pipe, using the spiral pipe in the borehole increased the heat exchange rate to the ground per meter borehole depth. However, the pressure drop of water flow also increased due to increasing the length of pipe per meter borehole depth and its spiral geometry. The accuracy of the numerical model was verified for its pressure drop with some pressure drop correlations. The heat exchange rate and pressure drop of the GHEs are presented. As an example, the heat exchange rate per meter borehole depth of spiral pipe with 0.05 m pitch in the turbulent flow increased of 1.5 times. Its pressure drop also increased of 6 times. However, from the view point of energy efficiency, using the spiral pipe in the ground-source heat pump system gives a better performance than using the straight pipe. The heat exchange rate and pressure drop are important parameter in design of the ground-source heat pump (GSHP) system.

Pressure drop of water flow across a micro-pin–fin array part 1: Isothermal liquid single-phase flow

This is part one of a two-part study that investigates water single-phase and two-phase pressure drop across a staggered array of circular micro-pin–fins. This paper presents results of isothermal liquid single-phase flow, and part two adiabatic liquid–vapor two-phase flow. The micro-pin–fins are 180μm in diameter, 683μm in height, and 399μm in both longitudinal and transverse pitches. Seven temperature levels from 23 to 80°C, and seventeen maximum mass velocities for each temperature, ranging from 133 to 1538kg/m2s, were tested. The resulting Reynolds number ranged from 26 to 776. Pressure drop across the micro-pin–fin array was measured, and friction factor calculated. The existing friction factor correlations for micro-pin–fin arrays, conventional-size pin–fin arrays, and tube banks were examined and found unable to predict the data. A numerical simulation was performed, and a good agreement was found between the experimental data and numerical results. A new friction factor correlation was developed that is used in part two of the study on calculating liquid–vapor two-phase pressure drop.

Pressure drop of water flow across a micro-pin–fin array part 2: Adiabatic liquid–vapor two-phase flow

This is part two of a two-part study that investigates water pressure drop across a staggered array of circular micro-pin–fins. This paper reports results of adiabatic liquid–vapor two-phase flow, and part one isothermal liquid single-phase flow. The micro-pin–fins are 180μm in diameter, 683μm in height, and 399μm in both longitudinal and transverse pitches. Seven maximum mass velocities from 171 to 491kg/m2s, and sixteen vapor qualities for each maximum mass velocity were tested. Two-phase pressure drop across the micro-pin–fin array was measured, and two-phase friction multiplier and Martinelli parameter calculated. It was revealed that a unique functional relationship exists between the two-phase friction multiplier and Martinelli parameter, which proved that the generalized procedure developed by Lockhart and Martinelli could be applied to describe two-phase pressure drop across the micro-pin–fin array. The existing Martinelli–Chisholm type correlations for staggered micro-pin–fin arrays and tube banks were unable to predict the data, and a new correlation was developed.

Experimental study of single-phase heat transfer and pressure drop inside a plate heat exchanger with a rough surface

Experimental data regarding heat transfer coefficient and pressure drop of water flow inside a plate heat exchanger with a rough surface is investigated and compared with that obtained from a smooth surface. Three commercial stainless steel corrugated plates with symmetrical chevron angle of 25° are used. The water flow inside the plate heat exchanger is arranged for a single pass and counter flow. The test runs are performed at Reynolds numbers ranging between 1300 and 3200 and plate surface roughness ranging between 0.936μm and 3.312μm. The experimental results show that increase in surface roughness yields an increase in heat transfer coefficient between 4.46% and 17.95% and an increase in pressure drop between 3.90% and 19.24% with respect to a smooth surface. The correlations for predicting the Nusselt number and friction factor of water flow inside a plate heat exchanger with a rough surface are proposed.

Investigation of heat transfer and pressure drop in an annular channel with heat transfer intensifiers

Results from systematic investigations of heat transfer and pressure drop for water flow in an annular channel using an efficient method for enhancing heat transfer on a convex heating surface are presented. The main technical data of the thermal-hydraulic experimental setup are given together with a brief description of the control, monitoring, and physical parameters measurement and recording systems, as well as primary experimental data processing and storage system. The test section, the enhancement method based on setting up swirl flows, the geometrical characteristics of intensifiers, their schematic design, and installation technology are described. The experimental data are obtained in a wide range of coolant flow parameters under the conditions of single-phase convection with using intensifiers having different shapes. The test measurements carried out on a smooth annular channel showed good agreement with the classic correlations both for heat transfer and pressure drop, thereby confirming reliability of the experimental data. A considerable improvement in heat removal efficiency on the convex heating surface is obtained. The value of heat transfer coefficient is a factor of 1.8 higher than it is for smooth annular channels. The region of the values of intensifier geometrical characteristics and Reynolds numbers for which the growth of heat transfer prevails over the growth of pressure drop is established. It is shown that the maximums of heat transfer and pressure drop are observed at quite definite values of intensifier geometrical characteristics. The primary experimental data are processed and presented as a dependence of the Nusselt number on the Reynolds number for different values of the intensifier’s relative fin height Ḣ. The value of Ḣ at which heat transfer reaches its maximum is found. The experiments were carried out in the pressure range p = 3.0–10.0 MPa and at the constant temperature of liquid at the test section inlet equal to 100°C. The influence of peripheral liquid flow swirling pitch on heat transfer and pressure drop is studied. An empirical correlation describing the dependence of heat transfer on the intensifier geometrical characteristics is obtained.

Effect of chamfer geometry on the pressure drop of perforated plates with thin orifices

Perforated plates with thin orifices is one of the options under considerations to be used in the debris filtering bottom end pieces for the next generation of fuel assemblies for the Brazilian nuclear plants. The increase in pressure drop can be drastically reduced by optimizing the chamfer geometries. This paper describes the development and validation of a procedure devised to use Computational Fluid Dynamics (CFD) to accurately estimate the pressure drop of water flow through perforated plates with chamfered thin orifices. The procedure comprises a scaled down calculation domain, grid configuration and a set of numerical solution parameters. The validation was performed against experiments with a set of plates with different chamfer geometric features like position (inlet, outlet and both sides), angles and sizes. Three turbulence models were evaluated with the standard k–ɛ giving the best result. For the range of parameters evaluated here the pressure drop decrease of a two sided chamfer plate can be estimated as a sum of both inlet and outlet chamfers individually. In both cases the pressure drop decreases rapidly for small chamfers and more slowly for larger chamfers. In the flat regions the chamfer angle has little influence at the inlet and is more important at outlet