Thermohydraulic Behavior of the Liquid–Vapor Flow in the Receiver Tube of a Solar Parabolic Trough Collector

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Sara Sallam ◽  
Mohamed Taqi
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Vapor Flow ◽  
High Heat Flux ◽  
Parabolic Trough ◽  
Convective Boiling ◽  
Flow Rates ◽  
Pressure Drops ◽  
Inlet Conditions ◽  
Liquid Vapor

Abstract Liquid–vapor flows are present in many industrial applications. In particular, in the solar field, these flows are encountered in the new generations of solar parabolic trough collectors with direct steam generation (PTCs-DSG). In this technical brief, we compare the two-phase convective transfer and the pressure drop models in the PTC-DSG. The results show that the heat exchange coefficients estimated by Chen–Cooper, Shah, Gungor–Winterton, and Kandlikar models have same trend with difference between them. However, the models of Liu–Winterton and Steiner–Taborek seem inappropriate due to the decrease in the exchange coefficient for moderate and high steam qualities. In addition, a comparison of the models describing pressure drops with experimental data of literature was carried out. The results show that the pressure decreases as the steam quality increases and the differences between these models remain small. Friedel's model is the closest to the experiment for high inlet pressures and flow rates, while Chisholm's model gives the best prediction of the pressure drop for low inlet conditions. Effect analysis of inlet conditions shows that the increase in inlet water mass flow and decrease in pressure favor convective heat transfer. The variation of heat flux on tube wall does not affect the convective boiling heat coefficient evaluated by the Chen–Copper model, whereas it influences the calculating coefficient by Gungor–Winterton model for high heat flux and particularly for low steam qualities. Pressure drops are higher at high flow rates and low pressures.

scholarly journals Parametric Analysis of Parasitic Pressure Drop and Heat Losses for a Parabolic Trough With Considerations of Varying Aperture Sizes and Receiver Sizes

2011 ◽  
Author(s):  
Kyle W. Glenn ◽  
Clifford K. Ho ◽  
Gregory J. Kolb
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Heat Loss ◽  
Heat Losses ◽  
Heat Transfer Fluid ◽  
Aperture Size ◽  
Parabolic Trough ◽  
Pressure Drops ◽  
Loss Efficiency

The collector aperture and diameter of the receiver of a parabolic trough were studied to investigate the relative impacts of parasitic pressure drop, heat losses, and heat flux intercepted by the receiver tube. The configuration of an LS-2 parabolic trough was used as the baseline, and the size of the HCE and collector aperture were parametrically varied using values between the baseline and twice their original size. A Matlab computer model was created to determine the flux on the receiver, heat loss from the HCE, and pressure drop within the heat transfer fluid (HTF) at each combination of aperture size and receiver diameter. Flux on the receiver is calculated for each geometry assuming a Gaussian flux distribution. Based on pressure data from SEGS VII, the standard Darcy-Weisbach equation for the pressure drop was modified to include the contribution that connective joints of varying quantities and types have on the pressure drop within the HTF. The model employs the Sandia thermal resistive network and iteratively solves for the temperatures accounting for various heat transfer modes that contribute to the heat lost by the HCE. The Matlab model expresses pressure drop and heat losses in terms of electric power. It does this by calculating both the power required to pump the HTF for varying pressure drops and the power that could have been produced if heat was not lost to the environment. The Matlab model displays the results in the form of surface plots that represent the values of heat loss, efficiency, pumping power, etc. as a function of aperture size and receiver diameter. The combined effects of pressure drop, heat loss, and heat flux intercepted by the receiver tube were evaluated, and results show that configurations with receiver diameters ranging from 85–90 millimeters and large (up to 10 meter) aperture sizes minimize the overall power consumption and maximize the efficiency of a single loop. Structural effects, wind and gravity loads, and factors associated with the balance of plant were not considered.

Flow Patterns and CHF in a Locally Heated Liquid Film Shear-Driven in a Minichannel

2010 ◽  
Author(s):  
D. V. Zaitsev ◽  
O. A. Kabov
Keyword(s):  
Heat Flux ◽  
Liquid Film ◽  
Gas Flow ◽  
Liquid Films ◽  
Vapor Flow ◽  
High Heat Flux ◽  
Film Rupture ◽  
Space Applications ◽  
Flow Rates ◽  
Wide Range

Thin and very thin (less than 10 μm) liquid films driven by a forced gas/vapor flow (stratified or annular flows), i.e. shear-driven liquid films in a narrow channel is a promising candidate for the thermal management of advanced semiconductor devices in earth and space applications. Development of such technology requires significant advances in fundamental research, since the stability of joint flow of locally heated liquid film and gas is a rather complex problem. The paper focuses on the recent progress that has been achieved by the authors through conducting experiments. Experiments with water in flat channels with height of H = 1.2–2.0 mm (mini-scale) show that a liquid film driven by the action of a gas flow is stable in a wide range of liquid/gas flow rates. Map of isothermal flow regime was plotted and the length of smooth region was measured. Even for sufficiently high gas flow rates an important thermocapillary effect on film dynamics occurs. Scenario of film rupture differs widely for different flow regimes. It is found that the critical heat flux for a shear driven film can be 10 times higher than that for a falling liquid film, and exceeds 400 W/cm2 in experiments with water for moderate liquid flow rates. This fact makes use of shear-driven liquid films promising in high heat flux chip cooling applications.

Microgap Cooling Technique Based on Evaporation of Thin Liquid Films

2009 ◽  
Author(s):  
D. V. Zaitsev ◽  
O. A. Kabov
Keyword(s):  
Heat Flux ◽  
Liquid Film ◽  
Gas Flow ◽  
Liquid Films ◽  
Vapor Flow ◽  
High Heat Flux ◽  
Film Rupture ◽  
Space Applications ◽  
Flow Rates ◽  
Wide Range

Thin and very thin (less than 10 μm) liquid films driven by a forced gas/vapor flow (stratified or annular flows), i.e. shear-driven liquid films in a narrow channel is a promising candidate for the thermal management of advanced semiconductor devices in earth and space applications. Development of such technology requires significant advances in fundamental research, since the stability of joint flow of locally heated liquid film and gas is a rather complex problem. The paper focuses on the recent progress that has been achieved by the authors through conducting experiments. Experiments with water in flat channels with height of H = 1.2–2.0 mm show that a liquid film driven by the action of a gas flow is stable in a wide range of liquid/gas flow rates. Map of isothermal flow regime was plotted and the length of smooth region was measured. Even for sufficiently high gas flow rates an important thermocapillary effect on film dynamics occurs. Scenario of film rupture differs widely for different flow regimes. It is found that the critical heat flux for a shear driven film can be 10 times higher than that for a falling liquid film, and exceeds 400 W/cm2 in experiments with water for moderate liquid flow rates. This fact makes use of shear-driven liquid films promising in high heat flux chip cooling applications.

Modeling In-Situ Vapor Extraction During Convective Boiling

2009 ◽  
Author(s):  
Saran Salakij ◽  
James A. Liburdy ◽  
Deborah V. Pence
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Flow Rate ◽  
Porous Membrane ◽  
High Heat Flux ◽  
Vapor Extraction ◽  
Convective Boiling ◽  
Inlet Flow ◽  
Inlet Flow Rate ◽  
Boiling Flow

The pressure drop of convective boiling flow may be reduced by extracting vapor locally since the entire generated vapor does not have to travel through the entire channel length. In this study, the theoretical model was developed to simulate a convective boiling flow through a fractal-like branching microchannel network with vapor extraction. The fractal-like branching microchannel network has a porous membrane forming one wall of the channels. Vapor extraction occurs by applying a vacuum across the membrane. Sample predictive local conditions and global results are presented and discussed. The predicting results are classified into two groups: low inlet flow rate-low heat flux and high inlet flow rate-high heat flux. The results show that to increase extracted vapor mass flow rate, either decreasing supplying extracting pressure or increasing permeability of the porous membrane must be applied. As the amount of vapor extracting increases, the reduction in pressure drop across the channel and the exit vapor quality is achieved.

Innovative Realizations of High Heat-Flux Boiling and Condensing Flows for Milli-Meter and Micro-Meter Scale Applications

2014 ◽  
Author(s):  
Michael Kivisalu ◽  
Amitabh Narain ◽  
Patcharapol Gorgitrattanagul ◽  
Ranjeeth Naik
Keyword(s):  
Heat Flux ◽  
Heat Load ◽  
High Heat ◽  
Electronic Cooling ◽  
System Level ◽  
High Heat Flux ◽  
Zero Gravity ◽  
Pressure Drops ◽  
Condensing Flows ◽  
High Heat Load

For shear driven mm-scale flows, the traditional boiler and condenser operations pose serious problems of degraded performance (low heat-flux values, high pressure drops, and device-and-system level instabilities). The innovative devices are introduced for functionality and high heat load capabilities needed for shear dominated electronic cooling situations that arise in milli-meter scale operations, certain gravity-insensitive avionics-cooling and zero-gravity applications.

Numerical Study of Turbulent Heat Transfer and Pressure Drop Characteristics in a Water-Cooled Minichannel Heat Sink

2006 ◽  
Vol 129 (3) ◽  
pp. 247-255 ◽  
Author(s):  
X. L. Xie ◽  
W. Q. Tao ◽  
Y. L. He
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Wall Thickness ◽  
Heat Sink ◽  
Channel Wall ◽  
High Heat ◽  
Coolant Fluid ◽  
High Heat Flux ◽  
It Industry

With the rapid development of the Information Technology (IT) industry, the heat flux in integrated circuit (IC) chips cooled by air has almost reached its limit at about 100W∕cm2. Some applications in high technology industries require heat fluxes well beyond such a limitation. Therefore, the search for a more efficient cooling technology becomes one of the bottleneck problems of the further development of the IT industry. The microchannel flow geometry offers a large surface area of heat transfer and a high convective heat transfer coefficient. However, it has been hard to implement because of its very high pressure head required to pump the coolant fluid through the channels. A normal channel size could not give high heat flux, although the pressure drop is very small. A minichannel can be used in a heat sink with quite a high heat flux and a mild pressure loss. A minichannel heat sink with bottom size of 20mm×20mm is analyzed numerically for the single-phase turbulent flow of water as a coolant through small hydraulic diameters. A constant heat flux boundary condition is assumed. The effect of channel dimensions, channel wall thickness, bottom thickness, and inlet velocity on the pressure drop, temperature difference, and maximum allowable heat flux are presented. The results indicate that a narrow and deep channel with thin bottom thickness and relatively thin channel wall thickness results in improved heat transfer performance with a relatively high but acceptable pressure drop. A nearly optimized structure of heat sink is found that can cool a chip with heat flux of 350W∕cm2 at a pumping power of 0.314W.

Effects of Taper Configurations on Heat Transfer and Pressure Drop in Single-Phase Flows in Microgaps

2020 ◽  
Author(s):  
Debora C. Moreira ◽  
Gherhardt Ribatski ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Single Phase ◽  
Bubble Nucleation ◽  
Low Flow ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Inlet Section ◽  
Flow Rates

Abstract This paper presents a comparison of heat transfer and pressure drop during single-phase flows inside diverging, converging, and uniform microgaps using distilled water as the working fluid. The microgaps were created on a plain heated copper surface with a polysulfone cover that was either uniform or tapered with an angle of 3.4°. The average gap height was 400 microns and the length and width dimensions were 10 mm × 10 mm, resulting in an average hydraulic diameter of approximately 800 microns for all configurations. Experiments were conducted at atmospheric pressure and the inlet temperature was set to 30 °C. Heat transfer and pressure drop data were acquired for flow rates varying from 57 to 485 ml/min and the surface temperature was monitored not to exceed 90 °C to avoid bubble nucleation, so the heat flux varied from 35 to 153 W/cm2 depending on the flow rate. The uniform configuration resulted in the lowest pressure drop, and the diverging one showed slightly higher pressure drop values than the converging configuration, possibly because the flow is most constrained at the inlet section, where the fluid is colder and presents higher viscosity. In addition, a minor dependence of pressure drop with heat flux was observed due to temperature dependent properties. The best heat transfer performance was obtained with the converging configuration, which was especially significant at low flow rates. This behavior could be explained by an increase in the heat transfer coefficient due to flow acceleration in converging gaps, which compensates the decrease in temperature difference between the fluid and the surface due to fluid heating along the gap. Overall, the comparison between the three configurations shows that converging microgaps have better performance than uniform or diverging ones for single-phase flows, and such effect is more pronounced at lower flow rates, when the fluid experiences higher temperature changes.

scholarly journals Boiling Heat Transfer From an Array of Round Jets With Hybrid Surface Enhancements

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Matthew J. Rau ◽  
Suresh V. Garimella ◽  
Ercan M. Dede ◽  
Shailesh N. Joshi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Flat Surface ◽  
Microporous Layer ◽  
Maximum Heat ◽  
Flow Rates ◽  
Pin Fin ◽  
Pin Fins ◽  
Single Jet

The effect of a variety of surface enhancements on the heat transfer achieved with an array of impinging jets is experimentally investigated using the dielectric fluid HFE-7100 at different volumetric flow rates. The performance of a 5 × 5 array of jets, each 0.75 mm in diameter, is compared to that of a single 3.75 mm diameter jet with the same total open orifice area, in single-and two-phase operation. Four different target copper surfaces are evaluated: a baseline smooth flat surface, a flat surface coated with a microporous layer, a surface with macroscale area enhancement (extended square pin–fins), and a hybrid surface on which the pin–fins are coated with the microporous layer; area-averaged heat transfer and pressure drop measurements are reported. The array of jets enhances the single-phase heat transfer coefficients by 1.13–1.29 times and extends the critical heat flux (CHF) on all surfaces compared to the single jet at the same volumetric flow rates. Additionally, the array greatly enhances the heat flux dissipation capability of the hybrid coated pin–fin surface, extending CHF by 1.89–2.33 times compared to the single jet on this surface, with a minimal increase in pressure drop. The jet array coupled with the hybrid enhancement dissipates a maximum heat flux of 205.8 W/cm2 (heat input of 1.33 kW) at a flow rate of 1800 ml/min (corresponding to a jet diameter-based Reynolds number of 7800) with a pressure drop incurred of only 10.9 kPa. Compared to the single jet impinging on the smooth flat surface, the array of jets on the coated pin–fin enhanced surface increased CHF by a factor of over four at all flow rates.

Thick-Film Phenomenon in High-Heat-Flux Evaporation From Cylindrical Pores

1997 ◽  
Vol 119 (2) ◽  
pp. 272-278 ◽  
Author(s):  
D. Khrustalev ◽  
A. Faghri
Keyword(s):  
Thick Film ◽  
High Heat ◽  
Liquid Films ◽  
Momentum Conservation ◽  
Vapor Flow ◽  
High Heat Flux ◽  
Operational Conditions ◽  
Flux Evaporation ◽  
Cylindrical Pores ◽  
Liquid Vapor

A physical and mathematical model of the evaporating thick liquid film, attached to the liquid-vapor meniscus in a circular micropore, has been developed. The liquid flow has been coupled with the vapor flow along the liquid-vapor interface. The model includes quasi-one-dimensional compressible steady-state momentum conservation for the vapor and also a simplified description of the microfilm at the end of the thick film. The numerical results, obtained for water, demonstrate that formation of extended thick liquid films in micropores can take place due to high-velocity vapor flow under high rates of vaporization. The model has also predicted that the available capillary pressure significantly changes with the wall-vapor superheat and other operational conditions.

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