scholarly journals Design, simulation and optimization of a solar dish collector with spiral-coil thermal absorber

2016 ◽  
Vol 20 (4) ◽  
pp. 1387-1397 ◽  
Author(s):  
Sasa Pavlovic ◽  
Evangelos Bellos ◽  
Velimir Stefanovic ◽  
Christos Tzivanidis ◽  
Zoran Stamenkovic
Keyword(s):  
Heat Flux ◽  
Flow Simulation ◽  
Energetic Efficiency ◽  
Uniform Heat Flux ◽  
Inlet Temperature ◽  
Focal Distance ◽  
Optical Efficiency ◽  
Spiral Coil ◽  
Simulation And Optimization ◽  
Parabolic Dish

The efficient conversion of solar radiation into heat at high temperature levels requires the use of concentrating solar collectors. The goal of this paper is to present the optical and the thermal analysis of a parabolic dish concentrator with a spiral coil receiver. The parabolic dish reflector consists of 11 curvilinear trapezoidal reflective petals constructed by PMMA with silvered mirror layer and has a diameter of 3.8 m, while its focal distance is 2.26m. This collector is designed with commercial software SolidWorks and simulated, optically and thermally in its Flow Simulation Studio. The optical analysis proved that the ideal position of the absorber is at 2.1m from the reflector in order to maximize the optical efficiency and to create a relative uniform heat flux over the absorber. In thermal part of the analysis, the energetic efficiency was calculated approximately 65%, while the exergetic efficiency is varied from 4% to 15% according to the water inlet temperature. Moreover, other important parameters as the heat flux and temperature distribution over the absorber are presented. The pressure drop of the absorber coil is calculated at 0.07bar, an acceptable value.

Flow Resistance Characteristics of a Specific Fuel RP-3 in Helical Tubes at Supercritical Pressure With Uniform Heat Flux

2017 ◽  
Author(s):  
Nan Zhang ◽  
Yanchen Fu ◽  
Haoran Huang ◽  
Jie Wen ◽  
Nigeer Te
Keyword(s):  
Heat Flux ◽  
Friction Factor ◽  
Mass Flux ◽  
Flow Resistance ◽  
Flow Characteristics ◽  
Supercritical Pressure ◽  
Uniform Heat Flux ◽  
Inlet Temperature ◽  
Uniform Heat ◽  
Helical Tubes

The flow resistance characteristics of aviation kerosene RP-3 in horizontal helical tubes at the supercritical pressure under heating condition are investigated. Both pressure drop and friction factor were examined under uniform heat flux of 50kW/m2−300kW/m2, mass flux from 786kg/m2s to 1375kg/m2s, and helical diameter from 20mm to 40mm. The influence of viscous factors on the resistance is analyzed to explore flow characteristics in a helical tube and provide a reference for the design of heat exchangers. Friction factor decreases with the increase of heat flux at low inlet temperatures 323K and 423K. It is explained that the viscosity changes more dramatically than the density. When the fluid inlet temperature is 523K and the fluid mean temperature Tb is close to pseudo-critical temperature, frictional flow resistance becomes significantly larger Tpc due to huge variations in thermal properties in the radical direction. The effect of centrifugal force makes the friction factor decline slowly. The friction factor goes up with the enlargement of mass flux when Tb>0.81Tpc. This phenomenon is caused by the larger radial velocity gradient under the large mass flux. Different helical diameters play the leading roles for the bending flow in the tubes.

Development of an Experimental Facility for Investigating Critical Heat Flux of Saturated Flow Boiling of Refrigerant-123 in Microchannels

2005 ◽  
Author(s):  
Wai Keat Kuan ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Test Facility ◽  
Uniform Heat Flux ◽  
Inlet Temperature ◽  
Experimental Facility ◽  
Copper Block ◽  
Saturated Flow ◽  
Cartridge Heater

An experimental facility is developed to investigate critical heat flux (CHF) of saturated flow boiling of Refrigerant-123 (R-123) in microchannels. Six parallel Microchannels with cross sectional area of 0.2 mm × 0.2 mm are fabricated on a copper block, and a Polyvinyl Chloride (PVC) cover is then placed on top of the copper block to serve as a transparent cover through which flow patterns and boiling phenomena could be observed. A resistive cartridge heater is used to provide a uniform heat flux to the microchannels. The experimental test facility is designed to accommodate test sections with different microchannel geometries. The mass flow rate, inlet pressure, inlet temperature of Refrigerant-123, and the electric current supplied to the resistive cartridge heater are controlled to provide quantitative information near the CHF condition in microchannels. A high-speed camera is used to observe and interpret flow characteristics of CHF condition in microchannels.

Numerical and Experimental Investigation of Boiling Heat Transfer for Subcooled Water Flowing in a Small-Diameter Tube

2019 ◽  
Author(s):  
Makoto Shibahara ◽  
Qiusheng Liu ◽  
Koichi Hata ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Heat Flux ◽  
Exponential Function ◽  
Boiling Heat Transfer ◽  
Small Diameter ◽  
Uniform Heat Flux ◽  
Inlet Temperature ◽  
Simple Method ◽  
Subcooled Water

Abstract Numerical simulation of boiling heat transfer for subcooled water flowing in a small-diameter tube was conducted using the commercial computational fluid dynamics (CFD) code, PHOENICS ver. 2013. A small-diameter tube (d = 1.0–2.0 mm) was modeled in the simulation. A uniform heat flux with an exponential function was given at the inner tube wall as the boundary conditions. The inner wall boundary condition was set to a non-slip. The inlet temperature ranged from 302 to 312 K. The flow velocities of d = 1.0 mm and d = 2.0 mm are 9.29 m/s and 2.34 m/s, respectively. The transient analysis was carried out from the non-boiling region since the heat flux increased with time in the author’s experiments. The governing equations including the energy equation were discretized using the finite volume method in the PHOENICS code. The SIMPLE method was applied for the numerical simulation. For modeling boiling phenomena in the tube, the Eulerian-Eulerian two-fluid model was adopted using the interphase slip algorithm of PHOENICS code. In the experiment, a platinum tube was used as the experimental tube (d = 1.0–2.0 mm) to conduct joule heating by direct current. The distilled and deionized water was pressured by the pressurizer. The heat generation rate of the tube was controlled with the exponential function to obtain the transient heat transfer characteristics from the non-boiling region. The surface superheat increased as the heat flux increased in the experiment. The numerical simulation predicted the experimental data well. When the heat flux of the experiment was reached to the CHF point, the predicted value of heat transfer coefficient was approximately 3.5 % lower than that of the experiment.

scholarly journals Improvement in the Flux Uniformity of the Solar Dish Concentrator System through a Concave Quartz Window

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Du-zhong Nie ◽  
You-duo Peng ◽  
Jian Yan ◽  
Cheng-ji Mi ◽  
Yong-xiang Liu ◽  
...  
Keyword(s):  
Cylindrical Cavity ◽  
Peak Concentration ◽  
Concentration Ratio ◽  
Optimal Parameter ◽  
High Strength ◽  
Hyperbolic Tangent ◽  
Focal Distance ◽  
Optical Efficiency ◽  
Quartz Window ◽  
Parabolic Dish

A nonuniform and high-strength heat flux load would reduce the working efficiency, safety, and in-service life of a cavity receiver. Four types of concave quartz windows, including conical, spherical, sinusoidal, and hyperbolic tangent, were proposed to be used in the cylindrical cavity receiver of a solar dish concentrator system, which can improve the flux uniformity and reduce the peak concentration ratio of the receiver. For each concave quartz window, 36 structural schemes were offered. Based on the Monte Carlo ray-tracing method, the results showed that the nonuniformity coefficient of the receiver was 0.68 and the peak concentration ratio was 1320.21 by using a plane quartz window. At the same time, when the receiver is in the best optical performance, it is the receiver with sinusoidal, conical, spherical, and hyperbolic tangent quartz windows, respectively. The optical efficiency of the receiver with the above four types of quartz windows was basically the same as that of the receiver with the plane quartz window, but their nonuniformity coefficients were reduced to 0.31, 0.35, 0.36, and 0.39, respectively, and the peak concentration ratio was reduced to 806.82, 841.31, 853.23, and 875.89, respectively. Obviously, the concave quartz window was better than the plane quartz window in improving the flux uniformity. Finally, a further study on the sinusoidal quartz window scheme of all of the above optimal parameter schemes showed that when the installation position of the receiver relative to the dish concentrator was changed, the flux uniformity of the receiver could continue to improve. When the surface absorptivity of the receiver was reduced, the optical efficiency would be reduced. For the parabolic dish concentrator with different focal distance, the concave quartz window can also improve the uniformity of the flux distribution of the cylindrical cavity receiver.

Radiation heat transfer within a solar system considering nanofluid flow inside the absorber tube

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Zahra Ebrahimpour ◽  
Mohsen Sheikholeslami ◽  
Seyyed Ali Farshad ◽  
Ahmad Shafee
Keyword(s):  
Heat Flux ◽  
Thermal Treatment ◽  
Flux Distribution ◽  
Second Step ◽  
Inlet Temperature ◽  
Heat Flux Distribution ◽  
Optical Efficiency ◽  
Content Type ◽  
Carrier Fluid ◽  
Finite Volume Approach

Purpose This paper aims to model solar unit equipped with mirrors with numerical simulation. To augment the efficiency of system, absorber pipe was equipped with fins and nanomaterial was used as carrier fluid. Existence of secondary reflector results in better optical efficiency. Design/methodology/approach Finite volume approach is used for modeling which is done in two steps. The first one is done to achieve the heat flux distribution and second step to model turbulent flow inside the pipe. Verification has been presented for calculation of important functions (f and Nu). Outputs reveal the impacts of fin height (HF), number of fin (NF), inlet temperature (Tin) and velocity on irreversibility, thermal treatment. Findings Surface temperature decreases by 0.498, 0.07 and 0.017% with intensify of Re, HF and NF, respectively, when other factors were minimum. With augment of Tin, wall temperature increases about 9.87%. Given NF = 8, HF = 3 mmm, growth of Re makes Darcy factor to decrease about 28.28%, but it augments the Nu by 2.63%. Nu augments with rise of NF and HF about 2.63 and 7.66%. Irreversibility reduces about 29.5 and 11.65% with augment of NF and HF, respectively. Originality/value Numerical simulations for solar unit equipped with mirrors were reported in this modeling. To augment the efficiency of system, absorber pipe was equipped with fins and nanomaterial was used as carrier fluid. Existence of secondary reflector results in better optical efficiency. Finite volume approach is used for modeling which is done in two steps. The first one is done to achieve the heat flux distribution and second step to model turbulent flow inside the pipe. Verification has been presented for calculation of important functions (f and Nu). Outputs reveal the impacts of fin height (HF), number of fin (NF), inlet temperature (Tin) and velocity on irreversibility, thermal treatment.

Spray Cooling for Time Resolved Emission Measurements of ICs

2004 ◽  
Author(s):  
Rama R. Goruganthu ◽  
David Bethke ◽  
Shawn McBride ◽  
Tom Crawford ◽  
Jonathan Frank ◽  
...  
Keyword(s):  
Heat Flux ◽  
Thermal Performance ◽  
Flip Chip ◽  
Cooling System ◽  
Spray Cooling ◽  
Junction Temperature ◽  
Maximum Temperature ◽  
Uniform Heat Flux ◽  
High Heat Flux ◽  
Time Resolved

Abstract Spray cooling is implemented on an engineering tool for Time Resolved Emission measurements using a silicon solid immersion lens to achieve high spatial resolution and for probing high heat flux devices. Thermal performance is characterized using a thermal test vehicle consisting of a 4x3 array of cells each with a heater element and a thermal diode to monitor the temperature within the cell. The flip-chip packaged TTV is operated to achieve uniform heat flux across the die. The temperature distribution across the die is measured on the 4x3 grid of the die for various heat loads up to 180 W with corresponding heat flux of 204 W/cm2. Using water as coolant the maximum temperature differential across the die was about 30 °C while keeping the maximum junction temperature below 95 °C and at a heat flux of 200 W/cm2. Details of the thermal performance of spray cooling system as a function of flow rate, coolant

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