Granular Flow and Heat-Transfer Study in a Near-Blackbody Enclosed Particle Receiver

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Janna Martinek ◽  
Zhiwen Ma
Keyword(s):  
Heat Transfer ◽  
Granular Flow ◽  
High Efficiency ◽  
Flow Instability ◽  
Solid Particles ◽  
Particle Flow ◽  
Outlet Temperature ◽  
Conductive Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Concentrating solar power (CSP) is an effective means of converting solar energy into electricity with an energy storage capability for continuous, dispatchable, renewable power generation. However, challenges with current CSP systems include high initial capital cost and electricity price, and advances are needed to increase outlet temperature to drive high-efficiency power cycles while simultaneously maintaining stability of the heat-transfer medium and thermal performance of the receiver. Solid-particle-based CSP systems are one alternative projected to have significant cost and performance advantages over current nitrate-based molten salt systems. NREL is developing a design that uses gas/solid, two-phase flow as the heat-transfer fluid (HTF) and separated solid particles as the storage medium. A critical component in the system is a novel near-blackbody (NBB) enclosed particle receiver that uses an array of absorber tubes with a granular medium flowing downward through channels between tubes. Development of the NBB enclosed particle receiver necessitates detailed investigation of the dimensions of the receiver, particle-flow conditions, and heat-transfer coefficients. This study focuses on simulation and analysis of granular flow patterns and the resulting convective and conductive heat transfer to the particulate phase using Eulerian–Eulerian two-fluid modeling techniques. Heat-transfer coefficients in regions with good particle/wall contact are predicted to exceed 1000 W/m2 K. However, simulations predict particle/wall separation in vertical flow channels and a resultant reduction in heat transfer. Particle-flow visualization experiments confirm particle/wall separation, but also exhibit complex periodic behavior and flow instability that create intermittent side-wall contact and enhance heat transfer above that predicted by the theoretical simulations.

Granular Flow and Heat Transfer Study in a Near-Blackbody Enclosed Particle Receiver

2014 ◽  
Author(s):  
Janna Martinek ◽  
Zhiwen Ma
Keyword(s):  
Heat Transfer ◽  
Granular Flow ◽  
Effective Means ◽  
Solid Particles ◽  
Particle Flow ◽  
Heat Transfer Fluid ◽  
Conductive Heat ◽  
Transfer Coefficients ◽  
Performance Development ◽  
And Performance

Concentrating solar power (CSP) is an effective means of converting solar energy into electricity with an energy-storage capability for continuous, dispatchable, renewable power generation. However, challenges with current CSP systems include high initial capital cost and electricity price. The U.S. Department of Energy’s (DOE) SunShot program aims to reduce cost and improve performance of CSP technology. To this end, NREL is developing a solid-particle based CSP system projected to have significant cost and performance advantages over current nitrate-based molten salt systems. The design uses gas/solid, two-phase flow as the heat transfer fluid and separated solid particles as the storage medium. A critical component in the system is a novel near-blackbody (NBB) enclosed particle receiver with high-temperature capability developed with the goal of meeting DOE’s SunShot targets for receiver cost and performance. Development of the NBB enclosed particle receiver necessitates detailed study of the dimensions of the receiver, particle flow conditions, and heat transfer coefficients. The receiver utilizes an array of absorber tubes with a granular medium flowing downward through channels between tubes. The current study focuses on simulation and analysis of granular flow patterns and the resulting convective and conductive heat transfer to the particulate phase. This paper introduces modeling methods for the granular flow through the receiver module and compares the results with an in-situ particle flow test.

scholarly journals Heat Transfer and Fluid Dynamics Measurements in the Expansion Space of a Stirling Cycle Engine

2006 ◽  
Author(s):  
Nan Jiang ◽  
Terrence W. Simon
Keyword(s):  
Heat Transfer ◽  
High Efficiency ◽  
Stirling Engine ◽  
Transfer Coefficients ◽  
Head Region ◽  
Heat Transfer Coefficients ◽  
Flow And Heat Transfer ◽  
Engine Design ◽  
Region Flow ◽  
Design Calculations

The heater (or acceptor) of a Stirling engine, where most of the thermal energy is accepted into the engine by heat transfer, is the hottest part of the engine. Almost as hot is the adjacent expansion space of the engine. In the expansion space, the flow is oscillatory, impinging on a two-dimensional concavely-curved surface. Knowing the heat transfer on the inside surface of the engine head is critical to the engine design for efficiency and reliability. However, the flow in this region is not well understood and support is required to develop the CFD codes needed to design modern Stirling engines of high efficiency and power output. The present project is to experimentally investigate the flow and heat transfer in the heater head region. Flow fields and heat transfer coefficients are measured to characterize the oscillatory flow as well as to supply experimental validation for the CFD Stirling engine design codes. Presented also is a discussion of how these results might be used for heater head and acceptor region design calculations.

An Experiment of Natural Circulation Flow and Heat Transfer With Supercritical Water in Parallel Channels

2016 ◽  
Vol 2 (3) ◽  
Author(s):  
Yuzhou Chen ◽  
Chunsheng Yang ◽  
Minfu Zhao ◽  
Keming Bi ◽  
Kaiwen Du
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Rate ◽  
Supercritical Water ◽  
Dynamic Instability ◽  
Flow Instability ◽  
Natural Circulation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Parallel Channels

An experiment of natural circulation of supercritical water in parallel channels was performed in bare tubes of inner diameter 7.98 mm and heated length 1.3 m, covering the ranges of pressure of 24.7–25.5 MPa, mass flux of 400–1000  kg/m2 s, and heat flux of up to 1.83  MW/m2. When the heat flux reached 1.12  MW/m2, the outlet water temperature jumped from 325°C to 360°C, associated with a decrease in the flow rate and an initiation of dynamic instability. When the heat flux exceeded 1.39  MW/m2, the flow instability was stronger, and the flow rate increased in one channel and decreased in another one. Until the heat flux reached 1.61  MW/m2, the outlet water temperatures of two channels reached the pseudocritical point, and the flow rates of two channels tended to close each other. The experiment with a single heated channel was also performed for comparison. The measurements on the heat-transfer coefficients (HTCs) were compared to the calculations by the Bishop et al., Jackson’s, and Mokry et al. correlations, showing different agreements within various conditions.

scholarly journals Effects of Dissolved Air on Subcooled Flow Boiling of a Dielectric Coolant in a Microchannel Heat Sink

2005 ◽  
Author(s):  
Tailian Chen ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Flow Instability ◽  
Flow Boiling ◽  
Microchannel Heat Sink ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Boiling Process ◽  
Dissolved Air

The effects of dissolved air in the dielectric liquid FC-77 on flow boiling in a microchannel heat sink containing 10 parallel channels, each 500 μm wide and 2.5 mm deep, were experimentally investigated. Experiments were conducted before and after degassing, at three flow rates in the range of 30 to 50 ml/min. The dissolved air resulted in a significant reduction in wall temperature at which bubbles were first observed in the microchannels. Analysis of the results suggests that the bubbles observed initially in the undegassed liquid were most likely air bubbles. Once the boiling process is initiated, the wall temperature continues to increase for the undegassed liquid, while it remains relatively unchanged in the case of the degassed liquid. Prior to the inception of boiling in the degassed liquid, the heat transfer coefficients with the undegassed liquid were 300–500% higher than for degassed liquid, depending on the flow rate. The heat transfer coefficients for both cases reach similar values at high heat fluxes (over 120 kW/m2) once the boiling process with the degassed liquid was well established. The boiling process induced a significant increase in pressure drop relative to single-phase flow; the pressure drop for undegassed liquid was measured to be higher than for degassed liquid once the boiling process became well established in both cases. Flow instabilities were induced by the boiling process, and the magnitude of the instability was quantified using the standard deviation of the measured pressure drop at a given heat flux. It was found that the magnitude of flow instability increased with increasing heat flux in both the undegassed and degassed liquids, with greater flow instability noted in the undegassed liquid.

scholarly journals Cooling Temperature and Heat Transfer Coefficients in Cylindrical Heat Exchangers

2021 ◽  
Vol 15 ◽  
pp. 254-259
Author(s):  
Enrique Torres Tamayo ◽  
José W. Morales ◽  
Mauro D. Albarracín ◽  
Héctor L. Laurencio ◽  
Israel P. Pachacama ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Outlet Temperature ◽  
Cooling Zone ◽  
Cooling Process ◽  
Transfer Coefficients ◽  
Cooling Temperature ◽  
Heat Transfer Coefficients ◽  
Temperature Heat ◽  
Temperature Water

The parameters behavior that characterize the process was carried out through an experimental investigation to obtain the cooling temperature, heat transfer coefficients and the heat flow in mineral coolers. The values of water temperature, water flow and mineral temperature were recorded at the inlet and outlet of the cylindrical cooler. Experiments were carried out with five values of the mass flow, keeping the cylinder revolutions constant. The calculation procedure for the system was obtained, in the mineral coolers the heat transfer by conduction, convection and evaporation predominates as a function of the cooling zone. A reduction in temperature is shown with increasing length, the lowest temperature values were obtained for a mass flow of 8 kg/s. The mineral outlet temperature should not exceed 200 oC, therefore it is recommended to work with the mass flow less than 10 kg/s that guarantees the cooling process.

scholarly journals Experimental determination of correlations for mean heat transfer coefficients in plate fin and tube heat exchangers

2012 ◽  
Vol 33 (3) ◽  
pp. 1-24 ◽  
Author(s):  
Dawid Taler
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Cross Flow ◽  
Correlation Coefficients ◽  
Outlet Temperature ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nonlinear Regression Method ◽  
Propagation Rule

Abstract This paper presents a numerical method for determining heat transfer coefficients in cross-flow heat exchangers with extended heat exchange surfaces. Coefficients in the correlations defining heat transfer on the liquid- and air-side were determined using a nonlinear regression method. Correlation coefficients were determined from the condition that the sum of squared liquid and air temperature differences at the heat exchanger outlet, obtained by measurements and those calculated, achieved minimum. Minimum of the sum of the squares was found using the Levenberg-Marquardt method. The uncertainty in estimated parameters was determined using the error propagation rule by Gauss. The outlet temperature of the liquid and air leaving the heat exchanger was calculated using the analytical model of the heat exchanger.

Computational Fluid Dynamics Modeling of Gas-Particle Flow Within a Solid-Particle Solar Receiver

2006 ◽  
Vol 129 (2) ◽  
pp. 160-170 ◽  
Author(s):  
Huajun Chen ◽  
Yitung Chen ◽  
Hsuan-Tsung Hsieh ◽  
Nathan Siegel
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Solar Radiation ◽  
Solid Particle ◽  
Operating Conditions ◽  
Solid Particles ◽  
Particle Flow ◽  
Outlet Temperature ◽  
Solar Receiver

A detailed three-dimensional computational fluid dynamics (CFD) analysis on gas-particle flow and heat transfer inside a solid-particle solar receiver, which utilizes free-falling particles for direct absorption of concentrated solar radiation, is presented. The two-way coupled Euler-Lagrange method is implemented and includes the exchange of heat and momentum between the gas phase and solid particles. A two-band discrete ordinate method is included to investigate radiation heat transfer within the particle cloud and between the cloud and the internal surfaces of the receiver. The direct illumination energy source that results from incident solar radiation was predicted by a solar load model using a solar ray-tracing algorithm. Two kinds of solid-particle receivers, each having a different exit condition for the solid particles, are modeled to evaluate the thermal performance of the receiver. Parametric studies, where the particle size and mass flow rate are varied, are made to determine the optimal operating conditions. The results also include detailed information for the gas velocity, temperature, particle solid volume fraction, particle outlet temperature, and cavity efficiency.

scholarly journals Effects of Dissolved Air on Subcooled Flow Boiling of a Dielectric Coolant in a Microchannel Heat Sink

2006 ◽  
Vol 128 (4) ◽  
pp. 398-404 ◽  
Author(s):  
Tailian Chen ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Flow Instability ◽  
Flow Boiling ◽  
Microchannel Heat Sink ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Boiling Process ◽  
Dissolved Air

The effects of dissolved air in the dielectric liquid FC-77 on flow boiling in a microchannel heat sink containing ten parallel channels, each 500μm wide and 2.5mm deep, were experimentally investigated. Experiments were conducted before and after degassing, at three flow rates in the range of 30-50ml∕min. The dissolved air resulted in a significant reduction in wall temperature at which bubbles were first observed in the microchannels. Analysis of the results suggests that the bubbles observed initially in the undegassed liquid were most likely air bubbles. Once the boiling process is initiated, the wall temperature continues to increase for the undegassed liquid, whereas it remains relatively unchanged in the case of the degassed liquid. Prior to the inception of boiling in the degassed liquid, the heat transfer coefficients with the undegassed liquid were 300-500% higher than for degassed liquid, depending on the flow rate. The heat transfer coefficients for both cases reach similar values at high heat fluxes (>120kW∕m2) once the boiling process with the degassed liquid was well established. The boiling process induced a significant increase in pressure drop relative to single-phase flow; the pressure drop for undegassed liquid was measured to be higher than for degassed liquid once the boiling process became well established in both cases. Flow instabilities were induced by the boiling process, and the magnitude of the instability was quantified using the standard deviation of the measured pressure drop at a given heat flux. It was found that the magnitude of flow instability increased with increasing heat flux in both the undegassed and degassed liquids, with greater flow instability noted in the undegassed liquid.

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