Single-phase Flow Characteristics Research Articles

Experimental Investigation of Local Heat Transfer Coefficient in a Plate Heat Exchanger Using a Thin Heat Transfer Surface

Abstract This paper presents an experimental investigation of local heat transfer characteristics of single-phase flow in a plate heat exchanger (PHE). The local heat transfer coefficient is evaluated using a test section with PHE geometry for measuring wall temperature distribution. The test section of 1.5 mm thickness is employed to consider the heat conduction effect of the heat transfer plate. The results indicated that the local heat transfer coefficient is influenced by the development of the thermal boundary layer along the flow direction and the maldistribution of water flows along both the direction perpendicular to the flow and the stacking direction. The harmonic mean heat transfer coefficient calculated by the measured local heat transfer coefficient agrees with the average heat transfer coefficient evaluated by the modified Wilson plot method within ±25% and within ±16% for the hot side and the cold side, respectively.

Transient Pressure Interference during CO2 Injection in Saline Aquifers

Summary CO2 injection in subsurface geological formations (e.g., deep saline aquifers) causes pressure perturbations over a large area surrounding the injection well. Observation wells are widely considered in geologic CO2 storage (GCS) projects where the pressure perturbation induced by CO2 injection is measured. In this work, we use analytical and numerical modeling tools along with field data to examine the pressure behavior in GCS projects before and after CO2 arrival at an observation well. Before CO2 arrival, a baseline pressure trend is established which corresponds to single-phase brine flow across the observation well (approximated by the Theis solution). Therefore, analysis of early time pressure data is straightforward, provides the single-phase flow characteristics (mobility and storativity), and helps in establishing a baseline pressure change that can be extended beyond the single-phase flow period at the observation well. Upon CO2 arrival, a departure from this baseline trend is expected. For the pressure to detect the CO2 arrival at an observation well, the departure from baseline pressure behavior must be significant and well above the background noise levels. We use existing analytical models to determine the strength of the expected pressure departure signal from the baseline trend upon CO2 arrival. The strength of the expected pressure departure is found to be directly proportional to the change in the mobility upon CO2 arrival. Larger change in the flow mobility—compared with single-phase brine mobility—results in a stronger pressure departure signal. In addition, the departure is found to be upward (downward) from the baseline pressure trend when the mobility ratio is less (more) than unity. We present a pressure analysis approach through application to synthetic and field data and show the characteristic pressure behavior before and after CO2 arrival. We show that while generally the pressure can be either above or below the expected baseline pressure trend, it would be likely above the baseline upon CO2 arrival. This is because the mobility ratio becomes less than unity after CO2 arrival. We show that depending on the reservoir characteristics, changes in the pressure trend may or may not be sufficient to detect the CO2 arrival.

Thermal and hydrodynamic characteristics of single-phase flow in manifold microchannels with countercurrent regions

Manifold microchannel heat sink is promising to dissipate high heat fluxes for electronic devices due to its high surface to volume ratio. Traditional Z-type manifold encounters fluid flow maldistribution and a high temperature difference. In this work, two inlets and countercurrent flows are introduced into the manifold arrangement to alleviate these problems in the Z-type manifold microchannels. Six cases with different manifold arrangements are numerically investigated using single-phase HFE-7100 at mass flow rates ranging from 56.8 to 117.78 mg/s. The results show that the maximum temperature, average temperature, and temperature difference of the revised arrangements are all lower than these of the traditional Z-type manifold arrangement. The minimum temperature difference for an ideal multi inlet manifold arrangement can be less than 0.2 K, while the value is about 5.3 K for the traditional Z-type manifold arrangement. The revised arrangement can also improve the uniformity of mass flux distributions. The ratio of the maximum to the minimum mass flux within microchannels is 12.83 for the traditional Z-type manifold, while this value is about 5.82 for cases with two inlets and countercurrent zones. A longer flow path and a higher local pressure drop in the revised arrangements results in higher pressure drops than the traditional Z-type manifold microchannels. Compared with the traditional Z-type arrangement, heat transfer coefficients and performance evaluation criterion are higher for the improved cases. The presence of a countercurrent zone can improve the comprehensive performance of the manifold microchannel. New criterion based on the thermal resistance calculated at the maximum temperature is proposed to evaluate the cooling performance of electronics.

Experimental study on effect of structural parameters on pressure drop characteristics of multi-orifice plates

Owing to the advantages of rectification, low noise, low pressure loss, and more stable pressure drop signal compared with the characteristics of the conventional single-orifice plate, multi-orifice plates (MOPs) offer a wide range of application prospects in various industrial pipelines. However, owing to its various orifice shapes and orifice layouts, the pressure drop characteristics of MOPs are not fully understood. In this study, the pressure drop characteristics of single-phase flow across a multi-orifice plate, which implies a stable zone (turbulent flow) pressure loss coefficient and the minimum critical Reynolds number of the stable zone, are experimentally investigated in the Reynolds number range of 29,000–146,000 using water as the fluid. Nine MOPs with circular holes evenly arranged in an equilateral triangle are tested. Their structures differ in terms of the equivalent diameter ratio (0.30–0.60), orifice number (64–400), and relative orifice thickness (0.40–1.60). The results show that the minimum critical Reynolds number deceases as the equivalent diameter ratio decreases, the relative orifice thickness increases, and the orifice number increases, which allows an enlarged Reynolds number range for the stable zone. As the equivalent diameter ratio, orifice number, and relative orifice thickness increase, the stable zone pressure loss coefficient of MOPs initially decreases rapidly and gradually approaches a constant. Finally, based on the experimental results of this study, a correlation of the stable zone pressure loss coefficient of MOPs is proposed, which provides a reference for using MOPs in various industrial applications.

Transverse mixing characteristics of single-phase flow in the helical cruciform fuel assembly

The helical-cruciform fuel (HCF), with four-petalled twisted blades, is potential to improve the core power density while maintaining the safety margin for the current reactors. However, the transverse mixing characteristics of the HCF assembly were significantly different from these of traditional cylinder rod bundle due to the innovative geometry. In the current work, an experiment study based on the wire-mesh sensor measurement on the concentration transport of KCl was carried out to quantify the effective transverse mixing intensity. Furthermore, the CFD simulation was used to obtain the local flow field and lateral mixing characteristics based on a novel block-wise mesh generation method and the SST k-ω model. The local transverse flow intensity was high related to the local gap size, but independent from the Reynolds number. The inter-channel mixing in HCF rod bundle is dominated by the flow sweeping mixing and the turbulent mixing were insignificant.

CFD study on crossflow and heat transfer characteristics of single phase flow in rod bundle with spacer grid under rolling conditions

In order to study the thermal and hydraulic characteristics of nuclear reactors under ocean conditions and meet the urgent needs of the design of floating nuclear power plants, the crossflow and heat transfer characteristics of rod bundle with the spacer grid under rolling conditions are studied by using computational fluid dynamics (CFD) code. Firstly, revise and verify CFD codes suitable for rolling conditions. According to CFD results, the influence of heat flux on heat transfer coefficient is greater than that of pressure drops under this condition. And with the spacer grid, the total pressure drop between inlet and outlet is higher. Furthermore, the heat transfer coefficient is also higher due to the mixing effect of spacer grid. Under periodic inlet velocity, the fluctuation amplitude of total pressure, the temperature difference between inlet and outlet and heat transfer coefficient is increased obviously with the spacer grid. Under the condition of nonuniform heat flux, the variation law of crossflow with rolling motion will become more obvious and the spacer grid can enhance the crossflow mixing and improve the heat transfer capacity of the fluid under rolling conditions.

Investigation of Single-Phase Flow Characteristics in an Inline Pin-Fins Complex Geometry

In this guess investigation of concerns R113 heat transfer of pressure drop flow in single-phase flow in inline on the square shape of micro-channel of pin-fins own a (5×5 mm2) cross-area segment section via of (5 mm) heightly. Therefore, the inline square micro-channel of pin-fins complex geometry additionally owning (25) numbers of the pin-fins, total pin-fins channel dimension (50 mm × 50 mm). Subsequently. The liquid has (25°C) inlet temperature for the same inlet temperature six mass flow rates were applied, ranging from (0.0025 - 0.01 kg/sec), and heat apply ranged from (40-200 Watts). Guess single-phase heat transfer coefficients, guess liquid temperatures and guess wall temperatures were reported in this investigation.

Experimental investigation of pressure drop of air-water two-phase flow through open-cell metal foam

The thermal and hydraulic characteristics of single-phase flow through a porous media have long been studied, but knowledge of two-phase flow through porous media is limited. In this work, experiments were performed to measure the pressure drops of single-phase and two-phase flows through metal foams with various pore sizes. Some previous empirical correlations for single-phase flow showed good agreement with the experimental data, whereas a large discrepancy appeared between empirical correlations and experimental data for two-phase flow. Considering slip between two phases, a new two-phase multiplier correlation was developed to predict the pressure drop of a two-phase flow through porous media. The new correlation showed agreement with the present experimental data within a deviation of 9%. The new correlation also predicted a wider range of experimental data available in the open literature with less than 30% deviation.

Numerical investigation on the characteristics of flow and heat transfer enhancement by micro pin-fin array heat sink with fin-shaped strips

Targeted at improving microfluidic cooling for the use of micro heat sink in electronic chips, a novel fin-shaped pin-fin array heat sink is proposed. In this study, the mechanism of flow and heat transfer, the arrangements of pin-fin layout, the characteristics of single-phase flow and heat transfer among the micro cylinder pin-fin heat sink, micro fin-shaped pin-fin heat sink of A、B、C types are investigated. It’s showed that stagger micro fin-shaped A pin-fin (SMFAP) exhibits the best hydro-thermal performance. At high Reynolds number, the average Nusselt number of SMFAP reaches up to two times of the in-line micro cylinder pin-fin (IMCP). Moreover, the structure of fin-shaped pin-fin can enhance heat transfer by increasing Nu, while weaken heat transfer by large pressure drop. Therefore, the non-dimensional parameter PEC is adopted to evaluate the heat transfer performance of heat sink. When Re is 800, the PEC of SMFAP reaches to its maximum value of 1.4. SMFAP can effectively enhance heat transfer, while stagger micro fin-shaped B pin-fin(SMFBP) and stagger micro fin-shaped C pin-fin (SMFCP) are not obviously. It’s concluded that different structures of fin-shaped pin-fin will affect the separation point of flow, thus affecting the size of vortex behind the cylinder.

CFD Simulation of Single-phase Flow Characteristics and Pressure Drop in SiC Hollow-strut Foam Microchannel Reactors

Microchannel reactors (MCR) have received considerable attention by researchers in recent years. A novel hollow-strut ceramic foam microchannel reactor (HSCF-MCR) taking the material and structural advantages of SiC foam was proposed. The reactor could be used as a structural scaffold for continuous gas or liquid phase flow and reaction because all of its struts are hollow and interconnected with each other. The three-dimensional (3-D) microstructure of the SiC foam was characterized by SEM and micro-CT method. Based on the tetrakaidecahedron cell model, computational fluid dynamics (CFD) method was utilized to analyze the single-phase flow characteristics and pressure drop of HSCF-MCR. The 3-D interconnected structure can form the static mixing effect of the flow fields inside the foam microchannel and strengthen the mass transfer process. Both channel diameter D and cell size L of the foam play a vital role in the pressure drop gradient δ of the fluid flowing through HSCF-MCR. When the ratio of D to L is controlled as 0.1, δ is minimized. The CFD simulation results contribute to the structural optimization and energy saving of HSCF-MCR for its applications in the future.

A numerical investigation on single-phase flow characteristics and frictional pressure drop in helical pipes

Helical pipes have been widely applied in a vast range of industries owing to the remarkable characteristics. In practice, they still face the challenge of undesirable increased pressure resistance. The investigation on the flow characteristics in helix is essential to explore the pressure loss mechanism. In this paper, the k − ω model and k − ω SST model are utilized to investigate the flow characteristics in helical pipes with varying Reynolds number and geometry parameters including coil radius, pipe diameter and coil pitch. The influence of each variable on the flow field, especially axial and secondary velocity distribution, is thoroughly examined. The relationship between Darcy friction factor and different dimensionless variables is analyzed, which turns out to be positively dependent on radius ratio and inversely dependent on Reynolds number. The available correlations of friction factor in the laminar and turbulent regime in literature are presented and the prevailing forms are summarized, some in good accordance with simulation. Based on the results, new correlations are proposed and the coefficients are determined by virtue of non-linear data fitting, which could provide assistance for the design and optimization of helical pipes.

Experimental study on single phase flow characteristics in tight sandstone oil reservoirs

Tight oil resource is distributed worldwide and has great potential for exploration. As tight sandstone reservoirs have small pores and narrow throats, the liquid boundary layer has great influence on the seepage, inducing starting pressure gradient during fluid seepage. In this paper, flow characters of both single water and single oil phase is investigated. Results show that the curve of flow velocity vs. the pressure difference doesn’t pass through the origin. Extending the trend line will intersect the abscissa pressure difference, indicating it is non-Darcy flow for both single water and oil in tight sandstone cores. The permeability increases slowly with the increase of displacement pressure difference until basically stable.

Influence of inlet contraction ratios on the heat transfer and pressure drop characteristics of single-phase flow in smooth circular tubes in the transitional flow regime

An experimental investigation of the single-phase heat transfer and pressure drop characteristics in the transitional flow regime has been performed using flow-calming sections with different inlet geometries and section-to-tube inlet contraction ratios. Four different types of inlets were investigated namely a square-edged, re-entrant, a hydrodynamically fully developed inlet, and a 90° bend inlet. The contraction ratios for the squared-edged and re-entrant inlets were 5, 11, 15 and 33. For the hydrodynamically fully developed inlet and the 90° bend inlet, a contraction ratio of one was used. Experiments were conducted using a circular test section with an inner diameter of 5.1 mm, at a Reynolds number range of 1000–6000 to ensure that the laminar, transitional, quasi-turbulent and turbulent flow regimes were covered. Water was used as the working fluid and the test section was heated at constant wall heat fluxes of 4, 6 and 8 kW/m2. It was found that for a square-edged inlet geometry, the transition from the laminar to the turbulent flow regimes occurred earlier as the inlet contraction ratio increased, while for the re-entrant inlet, transition was delayed. The transitional flow regime was significantly affected by smaller contraction ratios and this effect increased with increasing heat flux. However, it was found that the critical Reynolds numbers were independent of inlet geometry for contraction ratios larger than 33. For the 90° bend inlet, transition occurred earlier than all the other inlet geometries and contraction ratios.

Interplay between developing flow length and bubble departure diameter during macroconvection enhanced pool boiling

Enhanced boiling structures based on the concept of separate liquid-vapor (L-V) pathways rely on the motion of the bubbles departing from the nucleating regions (NRs) to induce a macroconvective liquid jet impingement flow over adjacent non-boiling regions. Heat transfer in the non-boiling regions can be improved by incorporating microchannels which act as feeder channels (FCs) that also improve liquid directionality towards the NR. We hypothesize that the single-phase flow characteristics in the developing region of the FC contribute to the boiling enhancement and explore the interplay between the FC length, developing flow length, and departure bubble diameter. FC lengths shorter than the developing flow length benefit from the enhancement due to developing boundary layers over their entire length. However, FC lengths shorter than the departure bubble diameter suffer from bubble interference while FC lengths that are considerably longer than the developing flow length exhibit lower heat transfer rates in the fully developed region. This hypothesis was verified by conducting pool boiling experiments with four feeder channel lengths between 1 mm and 3 mm using HFE-7000, PP1, PP1C, and water. Three distinct regions: (i) interfering bubble, (ii) efficient L-V pathways, and (iii) diminished jet were identified to explain the boiling performance enhancement. This analysis will be beneficial in the pursuit to enhance critical heat flux (CHF) and heat transfer coefficient (HTC) on surfaces utilizing macroconvection mechanisms during boiling with different liquids.

Boiling pressure drop, local heat transfer distribution and critical heat flux in helical coils with R123

The objectives of the present work are to study the influence of curvature on local heat transfer coefficient, two-phase pressure drop and CHF in helical coils. The curvature of coil generates secondary flow of fluid which affects the mechanism inside helical coils. Very less information is available on the influence of curvature on flow boiling system. The present work investigates the characteristics of single phase flow and flow boiling in helical coils. Infra-red thermal imaging technique is used to measure the local wall temperature in the axial direction (along the length of coil) and in the circumferential direction. Experiments are performed with six helical coil test sections made of SS 304 circular tubes having three different tube diameters with two different coil diameters. The tube inner diameters are varying from 5.5 to 9.5 mm with wall thickness of 0.25 mm. The coil diameter to the tube diameter ratio ranges from 14 to 58 and coil pitch is 50 mm. The system pressure is varying from 1.1 bar to 3.6 bar. The analysis is performed for different heated lengths of test section. The experimental data of pressure drop and CHF are compared with available helical coil correlations. In fully developed flow boiling region, the circumferential averaged heat transfer coefficient in helical coils is same as in straight tubes. Correlations are suggested to predict local heat transfer coefficient in single phase and in flow boiling process, two-phase pressure drop and CHF in helical coils.

Experimental investigation on the friction characteristics of water–ethylene glycol mixture flow in internal helical finned horizontal tubes

Internal helical finned tubes are widely applied in the HVAC field because they enhance convective heat transfer. In this study, an experimental setup was built and used to investigate the single-phase flow characteristics of internal helical-rib roughness covering laminar and transition regimes. The single-phase flow characteristics of two internal helical finned tubes were also determined. The setup contained two test tubes, with nominal diameters of 22.48 and 16.662mm, number of fins of 60 and 38, helix angles of 45° and 60°, and relative roughness values of 0.022 and 0.053, respectively. The Prandtl number varied from 15 to 177, and the Reynolds number ranged from 200 to 36000. Friction factors were accurately measured under the adiabatic condition. Analysis results of the plain tube were in agreement with those obtained using the Filonenko equation. The first critical Reynolds numbers that judged the transition from laminar to transition regimes were 2160 for Tube-1 and 2070 for Tube-2. The second critical Reynolds numbers that judged the start of fully turbulent regime were 14300 for Tube-1 and 9500 for Tube-2. The entrance region influenced the friction factor of helical finned tubes. A correlation was developed to predict the friction factor in the transition regime of helical finned tubes for developing flow.

Experimental and numerical study on single-phase flow characteristics of natural circulation system with heated narrow rectangular channel under rolling motion condition

Effects of rolling motion on flow characteristics in a natural circulation system were investigated experimentally and numerically. The numerical results from validated code were mainly used to provide detailed information for the discussion and analysis of experimental results. The results indicate that under rolling motion condition, the phasic difference between flow rate and frictional pressure drop of narrow rectangular channel is negligible. Angular acceleration is the eigenvalue for the effects of rolling motion on flow rate under single-phase natural circulation condition. When angular acceleration is approximately equal, even though either the angle or the period of rolling motion is different, peak, trough and time-averaged values of flow rate are approximately equal. Under rolling motion and single-phase natural circulation conditions, the phenomenon that dimensionless time-averaged mass flow rate is smaller than that under steady state condition is controlled by the nonlinear relationship between mass flow rate and the resistance of loop. The factor also causes the result that the absolute difference of dimensionless flow rate between peak and steady state is smaller than that between trough and steady state. The startup model which is proposed in present paper can be used to predict the flow characteristics of single-phase natural circulation system at startup stage of rolling motion favorably. The self-developed code can simulate instantaneous flow characteristics of single-phase natural circulation system under rolling motion and steady state conditions correctly. The resistance correlations for steady state flow can be directly applied to calculate instantaneous resistance of narrow rectangular channel under rolling motion condition with satisfying agreement with experimental results.

Fractal analysis of single-phase water and polymer solution flow at high rates in open and horizontally displaced rough fractures

A study on the percolation characteristics of single-phase flow in rough fractures at high rates representing hydraulic fracturing conditions is presented. Two-dimensional transparent models of fractures obtained from different rock types (granite, marble and limestone) were reproduced by molding. To represent typical hydraulic fracturing fluids, water and polymeric solutions were injected at a constant flow rate. The inlet pressure was continuously monitored to correlate the permeability changes due to surface roughness of fractures. The fluid distributions were also mapped using the images acquired through the experiments. The surface roughness was quantified using three fractal methods (variogram, power spectral density, and triangular prism) and the ratio of total and planar areas, and these parameters were correlated to the percent wetted areas and pressure drop (i.e., permeability). This exercise was performed on joint type and horizontally displaced (sheared) model fractures.The percentage of planar flow wetted area representing invasion percolation and pressure drop changed remarkably with rock types. Both parameters were controlled by grain size and the surface roughness of fractures. Increasing degree of the roughness caused a decrease in permeability and area wetted by fluid. Models generated from bigger grain size rocks showed more channeling and a lower percentage of fluid wetted areas as well as lower pressure drop (higher permeability). The variogram fractal dimension showed better agreements among other methods for both fluid (water and polymeric solution) and fracture types (joint and horizontally displaced).

Experimental Study of Single-phase Pressure Drop Characteristics in Horizontal Internal Helical Finned Tubes

Due to the intense enhancement of the convective heat transfer, internal helical finned tubes are widely applied into the field of HVAC. An experimental setup was built for investigating single-phase flow characteristics of internal helical-rib roughness. The single-phase flow characteristics for water-ethylene glycol mixture in three internal finned tubes and a smooth tube were obtained. The nominal diameter of the two test tubes was 22.48mm and 16.662mm, the number of the fins was 60 and 38, the helix angle was 45 degrees and 60 degrees and the relative roughness was 0.022 and 0.053, respectively. The Prandtl number varied from 10.0 to 177 and the Reynolds number ranged from 185 to 40000. The friction factors were measured under the condition of thermal insulation. Experimental results showed that the smooth-tube results were compared to the Filonenko equation with satisfactory agreement. Transition for internal helical finned tubes occurred at lower Reynolds numbers than that of their smooth tube counterparts. The trend of the friction factor of the internal helical finned tube is remarkably different from that of plain tube in the transition regime. For Tube 2 and Tube 3, the flow turns into the fully turbulent flow at Re=14500, while Tube-4 at Re=9500, which is obviously different from that of the plain tube.

Single phase flow characteristics of FC-72 and ethanol in high aspect ratio rectangular mini- and micro-channels

Single phase flow friction factor of FC-72 and ethanol in mini-and micro-channels are experimentally investigated in the present study. High aspect ratio rectangular channels are selected, the hydraulic diameters of which are 571 µm, 762 µm and 1454 µm, and the aspect ratios are 20, 20 and 10 respectively. Degassed ethanol and FC-72 are used as working fluids. All the friction factors acquired in the 571 µm and 762 µm channels agree with the conventional friction theory within ±20%–±25%. In the 1454 µm channel, however, deviations from the conventional theory occur and a modified empirical correlation of friction factor as a function of Reynolds number is proposed. Early transition from laminar to transitional flow is captured. Besides, effects of liquid physical properties are discussed. Lower viscosity and higher liquid density are responsible for the higher friction factor of FC-72. The influence of liquid properties weakens as the Reynolds number increases.