Computational and Experimental Investigation of Heat Transfer Within a Column Photobioreactor

2011 ◽  
Author(s):  
S. M. Mortuza ◽  
Stephen P. Gent ◽  
Anil Kommareddy ◽  
Gary A. Anderson
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
High Speed ◽  
Bubble Formation ◽  
Heat Transfer Process ◽  
Mass Force ◽  
Transfer Coefficients ◽  
Transfer Effects ◽  
Two Phase ◽  
Heat Transfer Effects

The goal of this research is to investigate heat transfer effects of two phase gas-liquid flows in a column photobioreactor (PBR) experimentally as well as computationally using Computational Fluid Dynamics (CFD). The authors have completed a preliminary study on bubble formation, rise and resulting circulation patterns using lab-scale experiments and CFD simulations. This study extends on this previous work by investigating the relationships of bubble drag coefficient and bubble Reynolds number with superficial gas velocity and a study of heat transfer within the PBR. It is hypothesized that a greater understanding the bubble movement patterns will aid in predicting heat transfer rates within the PBR. Dispersed gas–liquid flow in the rectangular column PBR are modeled using the Eulerian–Lagrangian approach. The heat transfer process has been considered for the case of a steady state three dimensional PBR. A low Reynolds number k–epsilon CFD model is used for the description of flow pattern near the wall. The velocity profiles and eddy diffusivity obtained by the model are utilized to predict heat transfer coefficients for different superficial gas velocities. The information on heat transfer effects between cooling or heating surfaces and a gas-liquid dispersed bed is essential for designing a PBR. Carbon dioxide, which is necessary for photosynthetic microalgae growth, is added to the system. Bubble size distribution measurements are carried out using a high-speed digital camera. The main interaction forces, i.e. the drag force, the added mass force, and lift force are considered. Heat transfer and internal hydrodynamics of a column reactor are studied and the numerical simulations results are presented for heat transfer and hydrodynamics in column PBRs. The results are validated with experimental data and with data from current literature.

Darryl E. Metzger Memorial Session Paper: Comparison of Calculated and Measured Heat Transfer Coefficients for Transonic and Supersonic Boundary-Layer Flows

1995 ◽  
Vol 117 (2) ◽  
pp. 248-254 ◽  
Author(s):  
C. Hu¨rst ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
High Speed ◽  
Three Dimensional ◽  
Supersonic Boundary Layer ◽  
Nozzle Wall ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Three Dimensional Finite Element

The present study compares measured and computed heat transfer coefficients for high-speed boundary layer nozzle flows under engine Reynolds number conditions (U∞=230 ÷ 880 m/s, Re* = 0.37 ÷ 1.07 × 106). Experimental data have been obtained by heat transfer measurements in a two-dimensional, nonsymmetric, convergent–divergent nozzle. The nozzle wall is convectively cooled using water passages. The coolant heat transfer data and nozzle surface temperatures are used as boundary conditions for a three-dimensional finite-element code, which is employed to calculate the temperature distribution inside the nozzle wall. Heat transfer coefficients along the hot gas nozzle wall are derived from the temperature gradients normal to the surface. The results are compared with numerical heat transfer predictions using the low-Reynolds-number k–ε turbulence model by Lam and Bremhorst. Influence of compressibility in the transport equations for the turbulence properties is taken into account by using the local averaged density. The results confirm that this simplification leads to good results for transonic and low supersonic flows.

Two-Phase Wakes in Adiabatic Liquid-Gas Flow Around a Cylinder

2020 ◽  
Author(s):  
Dohwan Kim ◽  
Matthew J. Rau
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
High Speed ◽  
Gas Flow ◽  
Two Phase Flow ◽  
Water Channel ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Around A Cylinder ◽  
High Heat Transfer

Abstract Small tubes and fins have long been used as methods to increase surface area for convective heat transfer in single-phase flow applications. As demands for high heat transfer effectiveness has increased, implementing evaporative phase-change heat transfer in conjunction with small fins, tubes, and surface structures in advanced heat exchanger and heat sink designs has become increasingly attractive. The complex two-phase flow that results from these configurations is poorly understood, particularly in how the gas phase interacts with the flow structure of the wake created by these bluff bodies. An experimental study of liquid-gas bubbly flow around a cylinder was performed to understand these complex flow physics. A 9.5 mm diameter cylinder was installed horizontally within a vertical water channel facility. A high-speed camera captured the movement of the liquid-gas mixture around the cylinder for a range of bubble sizes. Liquid Reynolds number, calculated based on the cylinder diameter, was varied approximately from 100 to 3000. Time-averaged probability of bubble presence was calculated to characterize the cylinder wake and its effects on the bubble motion. The influence of the liquid Reynolds number, superficial air velocity, and bubble size is discussed in the context of the observed two-phase flow patterns.

scholarly journals Hall Currents and Heat Transfer Effects on Peristaltic Transport in a Vertical Asymmetric Channel through a Porous Medium

2012 ◽  
Vol 2012 ◽  
pp. 1-23 ◽  
Author(s):  
E. Abo-Eldahab ◽  
E. Barakat ◽  
Kh. Nowar
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Porous Medium ◽  
Frame Of Reference ◽  
Peristaltic Transport ◽  
Shear Stresses ◽  
Asymmetric Channel ◽  
Transfer Effects ◽  
Long Wavelength ◽  
Heat Transfer Effects

The influences of Hall currents and heat transfer on peristaltic transport of a Newtonian fluid in a vertical asymmetric channel through a porous medium are investigated theoretically and graphically under assumptions of low Reynolds number and long wavelength. The flow is investigated in a wave frame of reference moving with the velocity of the wave. Analytical solutions have been obtained for temperature, axial velocity, stream function, pressure gradient, and shear stresses. The trapping phenomenon is discussed. Graphical results are sketched for various embedded parameters and interpreted.

Comparison of Calculated and Measured Heat Transfer Coefficients for Transonic and Supersonic Boundary-Layer Flows

1994 ◽  
Author(s):  
C. Hürst ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
High Speed ◽  
Three Dimensional ◽  
Supersonic Boundary Layer ◽  
Nozzle Wall ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Three Dimensional Finite Element

The present study compares measured and computed heat transfer coefficients for high speed boundary layer nozzle flows under engine Reynolds-number conditions (U∞ = 230 ÷ 880 m/s, Re* = 0.37 ÷ 1.07 · 106). Experimental data have been obtained by heat transfer measurements in a two-dimensional, non-symmetric, convergent-divergent nozzle. The nozzle wall is convectively cooled using water passages. The coolant heat transfer data and nozzle surface temperatures are used as boundary conditions for a three-dimensional finite-element code which is employed to calculate the temperature distribution inside the nozzle wall. Heat transfer coefficients along the hot gas nozzle wall are derived from the temperature gradients normal to the surface. The results are compared with numerical heat transfer predictions using the low Reynolds-number k-ε turbulence model by Lam and Bremhorst. Influence of compressibility in the transport equations for the turbulence properties is taken into account by using the local averaged density. The results confirm that this simplification leads to good results for transonic and low supersonic flows.

Heat Transfer Measurements and Correlations for Air-Water Two-Phase Slug Flow in a Horizontal Pipe

Volume 3 ◽  
2004 ◽  
Author(s):  
Afshin J. Ghajar ◽  
Kapil Malhotra ◽  
Jae-Yong Kim ◽  
Steve A. Trimble
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Slug Flow ◽  
Reynolds Numbers ◽  
Mean Deviation ◽  
Heat Transfer Correlation ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Transfer Data ◽  
Heat Transfer Coefficients

Local heat transfer coefficients and flow parameters were measured for air-water slug flow in a horizontal 25.4 mm stainless steel schedule 10S pipe with a length to diameter ratio of 100. For this systematic study, a total of 83 data points were taken by carefully coordinating the liquid and gas superficial Reynolds number combinations. The heat transfer data were measured under a uniform wall heat flux boundary condition ranging from about 3800 to 16000 W/m2. The superficial Reynolds numbers ranged from about 3160 to 30290 for water and from about 1480 to 5840 for air. Comparison of heat transfer data for slug flow revealed that the heat transfer results were significantly dependent on the liquid and gas superficial Reynolds numbers. Overall, the experimental heat transfer data showed that the liquid phase dominated the heat transfer. However, it was found that the heat transfer data having a fixed liquid superficial Reynolds number showed that the heat transfer coefficients decreased as the gas superficial Reynolds number increased. A general heat transfer correlation for two-phase gas-liquid flow was fitted to our experimental horizontal slug flow heat transfer data with a mean deviation of −2.77% and an RMS deviation of 9.92%. Furthermore, a simplified heat transfer correlation for slug flow was developed based on the trends of heat transfer coefficient over the superficial liquid and gas Reynolds numbers. The proposed correlation predicted the experimental data with a mean deviation of −1.44% and an RMS deviation of 5.15%.

Two-Phase Heat Transfer and Flow Regimes in Pin Fin-Enhanced Microgaps—Effect of Pin Spacing

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Pouya Asrar ◽  
S. Mostafa Ghiaasiaan ◽  
Yogendra K. Joshi
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Flow Boiling ◽  
Frame Rate ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Pin Fin ◽  
Speed Flow ◽  
Wide Range ◽  
Two Phase Heat Transfer

Abstract An experimental investigation of the flow boiling of dielectric refrigerant R245fa is conducted in microgaps with enhancement features. A silicon microgap of height 200 μm populated with pin fin arrays of diameter 150 μm with spacing 200 μm in both horizontal and vertical directions is examined. For five different test conditions and in a wide range of mass flux from 781 to 5210 kg/m2s, and inlet temperatures in the range of 13–18 °C, average single-phase and two-phase heat transfer coefficients, pressure drop, and exit vapor quality are reported. Three major flow patterns are observed in the pin finned area using high-speed flow visualization at frame rate of 2229 fps: foggy, bubbly, and slug flow. Based on the experimental data, a flow regime map is constructed.

Whole Field Measurements to Understand the Role of Varying Depths of Nucleation Site on Vapor Bubble Dynamics and Heat Transfer Rates

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Surya Narayan L ◽  
Pasi Vijaykumar ◽  
Atul Srivastava
Keyword(s):  
Heat Transfer ◽  
Vapor Bubble ◽  
High Speed ◽  
Bubble Formation ◽  
Nucleation Site ◽  
Heat Transfer Process ◽  
Cavity Depth ◽  
Bulk Fluid ◽  
Transfer Rates ◽  
Transfer Processes

Abstract This work studies the possible effects of varying depths of cavity on bubbling features and the associated heat transfer rates in nucleate pool boiling regime. A single vapor bubble has been generated on a substrate with a cylindrical cavity at its center that acts as the nucleation site. Experiments have been conducted for three cavity depths (250, 500, and 1000 μm), while keeping its throat diameter constant at 200 μm. With the bulk fluid maintained under saturated conditions, for each cavity depth, surface superheat level has been varied in the range of ΔTsuperheat = 8, 10 and 12 °C. A gradient-based visualization technique, coupled with a high speed camera, has been employed to simultaneously map the changes in thermal gradients during the formation of the vapor bubble as well as bubble dynamic parameters. The image sequence obtained has been qualitatively and quantitatively analyzed to elucidate the dependence of bubbling features and various heat transfer processes on cavity depth. With an increase in the depth of cavity, the net effect of reduction in the available thermal energy due to the increased convection effects and significant depletion of superheated layer are identified as the dominant heat transfer processes that influence the bubbling features. Furthermore, based on the statistics of bubble departure characteristics, the cavity with higher depth (1000 μm) showed a much stable bubble formation with minimal variation in the bubble departure frequency as compared to the bubbling features from a cavity with smaller depth (250 μm). Evaporative heat transfer process has been identified as the primary cause for increased inconsistency of bubbling features at high superheat conditions for experiments performed for low cavity depths.

Two-Phase Heat Transfer and Bubble Characteristics in a Microchannel Array

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
T. P. Lagus ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Bubbly Flow ◽  
Bubble Diameter ◽  
Bubble Formation ◽  
Uniform Heat Flux ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Microchannel Array ◽  
Two Phase Heat Transfer

Heat transfer coefficients and bubble motion characteristics are reported for two-phase water flow in an array of 13 equally spaced microchannels over an area of 1 cm2. Each channel has Dh = 451 ± 38 μm, W/H = 0.8, and L/Dh = 22.2. Uniform heat flux is applied through the base, and wall temperatures are determined from the thermocouple readings corrected for heat conduction effects. The upper surface is insulated and transparent. Single-phase heat transfer coefficients are in a good agreement with comparable trends of existing correlations for developing flow and heat transfer, although a difference is seen due to the insulated upper surface. Two-phase heat transfer coefficients and flow characteristics are determined for 221 < G < 466 kg/m2s and 250 < q < 1780 kW/m2. Heat transfer coefficients normalized with mass flux exhibit a trend comparable to that of available studies that use similar thermal boundary conditions. Flow visualization shows expanding vapor slug flow as the primary flow regime with nucleation and bubbly flow as the precursors. Analysis of bubble dynamics reveals ∼t1/3 dependence for bubble growth. Flow reversal is observed and quantified, and different speeds of the vapor phase fronts are quantified at the leading and trailing edges of vapor slugs once the bubble diameter equals the channel width. Bubble formation, growth, coalescence, and detachment at the outlet of the array are best characterized by the Weber number.

scholarly journals Effect of Integrating Metal Wire Mesh with Spray Injection for Liquid Piston Gas Compression

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3723
Author(s):  
Barah Ahn ◽  
Vikram C. Patil ◽  
Paul I. Ro
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Metal Wire ◽  
Wire Mesh ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Gas Compression ◽  
Liquid Piston

Heat transfer enhancement techniques used in liquid piston gas compression can contribute to improving the efficiency of compressed air energy storage systems by achieving a near-isothermal compression process. This work examines the effectiveness of a simultaneous use of two proven heat transfer enhancement techniques, metal wire mesh inserts and spray injection methods, in liquid piston gas compression. By varying the dimension of the inserts and the pressure of the spray, a comparative study was performed to explore the plausibility of additional improvement. The addition of an insert can help abating the temperature rise when the insert does not take much space or when the spray flowrate is low. At higher pressure, however, the addition of spacious inserts can lead to less efficient temperature abatement. This is because inserts can distract the free-fall of droplets and hinder their speed. In order to analytically account for the compromised cooling effects of droplets, Reynolds number, Nusselt number, and heat transfer coefficients of droplets are estimated under the test conditions. Reynolds number of a free-falling droplet can be more than 1000 times that of a stationary droplet, which results in 3.95 to 4.22 times differences in heat transfer coefficients.

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