Numerical Design of a Planar High-Flux Microchannel Solar Receiver

2014 ◽  
Author(s):  
Charles J. Rymal ◽  
Sourabh V. Apte ◽  
Vinod Narayanan ◽  
Kevin Drost
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Pressure Drop ◽  
Molten Salt ◽  
Thermal Stresses ◽  
Maximum Pressure ◽  
Operating Pressure ◽  
Design Features ◽  
Power Cycles ◽  
Solar Receiver

This paper discuses the design of several micro-channel solar receiver devices. Due to enhanced heat transfer in micro-channels, these devices can achieve a higher surface efficiency than current receiver technology, leading to an increase in overall plant efficiency. The goal is to design an efficient solar receiver based on use of super-critical carbon-dioxide and molten salt as heat-transfer fluids. The super-critical Brayton cycle has shown potential for a higher efficiency than current power cycles used in CSP. Molten salt has been used in CSP applications in the past. The required inlet and outlet temperatures of the fluid are 773.15 K and 923.15 K for carbon-dioxide and 573.15 K and 873.15 K for molten salt. These temperature values are determined by the power cycles the devices are designed to operate in. The required maximum pressure drop is 0.35 bar for carbon-dioxide and 1 bar for molten salt. These pressure values are intended to be a practical goal for maximum pressure drop. The super-critical carbon-dioxide power cycle requires an operating pressure of is 120 bar. Finally, each device must withstand any mechanical and thermal stresses that may exist. Devices presented range in size from 1 cm2 to 4 cm2 and in heat transfer rates from 200 W to 400 W. The size of the device is based on the output capacity of the solar simulator which will be used for testing. For carbon-dioxide, three designs were developed with varying manufacturability. The low risk design features machined and welded parts and straight parallel channels. The medium risk design features machined and diffusion bonded parts and straight parallel channels. The high risk design features a circular micro-pin-fin array created using EDM and is constructed using diffusion bonding. The absence of high operating pressure for molten salt made structural design much easier than for carbon-dioxide. Conjugate heat-transfer simulations of each design were used to evaluate pressure drop, receiver efficiency, and flow distribution. Two and three dimensional structural analyses were used to ensure that the devices would withstand the mechanical and thermal stresses. Based on the numerical analyses, a receiver efficiency of 89.7% with a pressure drop of 0.2 bar were achieved for carbon-dioxide. The design was found to have a structural safety factor of 1.3 based maximum mechanical stress occurring in the headers. For molten salt, an efficiency of 92.1% was achieved with a pressure drop of 0.5 bar.

Numerical Design of a High-Flux Microchannel Solar Receiver

2013 ◽  
Author(s):  
Charles J. Rymal ◽  
Sourabh V. Apte ◽  
Vinod Narayanan ◽  
Kevin Drost
Keyword(s):  
Pressure Drop ◽  
Cross Section ◽  
Thermal Stresses ◽  
Computational Study ◽  
Rectangular Cross Section ◽  
Working Fluid ◽  
Operating Pressure ◽  
Pin Fin ◽  
Fin Design ◽  
Solar Receiver

This computational study investigates design of microchannel based solar receiver for use in concentrated solar power. A design consisting of a planar array of channels with solar flux incident on one side and using supercritical carbon dioxide as the working fluid is sought. Use of microchannels is investigated as they offer enhanced heat transfer in solar receivers and have the potential to dramatically reduce the size and increase the performance. Designs are investigated for an incident heat flux of 1 MW/m2, up to 3.3 times that of current solar receivers [1], resulting in significant reduction of size and cost. The goal is to design a microchannel receiver with inlet and outlet temperatures of the working fluid of 500°C and 650°C, operating pressure of 100 bar, pressure drop less than 0.35 bar and surface efficiency greater than 90% defined by radiation and convection losses to the environment. Three micro-channel designs are considered: rectangular cross section with high and low aspect ratio (designs A and B) and rectangular cross section with an array of micro pin-fins of various shape spanning the height of the channel (design C). Numerical simulations are performed on individual channels and on a unit cell of the pin-fin design. Structural analysis is performed to ensure that the design can withstand the operating pressure and thermal stresses. The effects of flow maldistribution and header system in an array of channels are also investigated. Preliminary results show that all three designs are capable of meeting the requirements, with the pin-fin design having the lowest pressure drop and highest efficiency.

Conceptual design of porous volumetric solar receiver using molten salt as heat transfer fluid

2021 ◽  
Vol 301 ◽  
pp. 117400
Author(s):  
Shen Du ◽  
Ming-Jia Li ◽  
Ya-Ling He ◽  
Sheng Shen
Keyword(s):  
Heat Transfer ◽  
Molten Salt ◽  
Conceptual Design ◽  
Heat Transfer Fluid ◽  
Solar Receiver

Application of Supercritical Fluids in Thermal- and Nuclear-Power Engineering

2021 ◽  
pp. 601-658
Author(s):  
Igor L. Pioro
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Supercritical Fluids ◽  
Nuclear Power ◽  
Power Plants ◽  
Thermal Power ◽  
Rankine Cycle ◽  
Working Fluid ◽  
Thermal Power Plants ◽  
Power Cycles

Supercritical Fluids (SCFs) have unique thermophyscial properties and heat-transfer characteristics, which make them very attractive for use in power industry. In this chapter, specifics of thermophysical properties and heat transfer of SCFs such as water, carbon dioxide, and helium are considered and discussed. Also, particularities of heat transfer at Supercritical Pressures (SCPs) are presented, and the most accurate heat-transfer correlations are listed. Supercritical Water (SCW) is widely used as the working fluid in the SCP Rankine “steam”-turbine cycle in fossil-fuel thermal power plants. This increase in thermal efficiency is possible by application of high-temperature reactors and power cycles. Currently, six concepts of Generation-IV reactors are being developed, with coolant outlet temperatures of 500°C~1000°C. SCFs will be used as coolants (helium in GFRs and VHTRs, and SCW in SCWRs) and/or working fluids in power cycles (helium, mixture of nitrogen (80%) and helium (20%), nitrogen and carbon dioxide in Brayton gas-turbine cycles, and SCW/“steam” in Rankine cycle).

scholarly journals Modelling and Evaluation of the Thermohydraulic Performance of Finned-Tube Supercritical Carbon Dioxide Gas Coolers

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1031 ◽  
Author(s):  
Lei Chai ◽  
Konstantinos M. Tsamos ◽  
Savvas A. Tassou
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Pressure Drop ◽  
Supercritical Carbon Dioxide ◽  
Heat Pump ◽  
Life Cycle Cost ◽  
Flow Direction ◽  
Finned Tube ◽  
Distributed Modelling ◽  
Supercritical Carbon

This paper investigates the thermohydraulic performance of finned-tube supercritical carbon dioxide (sCO2) gas coolers operating with refrigerant pressures near the critical point. A distributed modelling approach combined with the ε-NTU method has been developed for the simulation of the gas cooler. The heat transfer and pressure drop for each evenly divided segment are calculated using empirical correlations for Nusselt number and friction factor. The model was validated against test results and then used to investigate the influence of design and operating parameters on local and overall gas cooler performance. The results show that the refrigerant heat-transfer coefficient increases with decreasing temperature and reaches its maximum close to the pseudocritical temperature before beginning to decrease. The pressure drop increases along the flow direction with decreasing temperature. Overall performance results illustrate that higher refrigerant mass flow rate and decreasing finned-tube diameter lead to improved heat-transfer rates but also increased pressure drops. Design optimization of gas coolers should take into consideration their impact on overall refrigeration performance and life cycle cost. This is important in the drive to reduce the footprint of components, energy consumption, and environmental impacts of refrigeration and heat-pump systems. The present work provides practical guidance to the design of finned-tube gas coolers and can be used as the basis for the modelling of integrated sCO2 refrigeration and heat-pump systems.

Effect of Pressure Drop and Reheating on Thermal and Exergetic Performance of Supercritical Carbon Dioxide Brayton Cycles Integrated With a Solar Central Receiver

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Ricardo Vasquez Padilla ◽  
Yen Chean Soo Too ◽  
Andrew Beath ◽  
Robbie McNaughton ◽  
Wes Stein
Keyword(s):  
Carbon Dioxide ◽  
Pressure Drop ◽  
Supercritical Carbon Dioxide ◽  
Surface Temperature ◽  
Brayton Cycle ◽  
Pressure Drops ◽  
Central Receiver ◽  
Maximum Value ◽  
Solar Receiver ◽  
Exergy Performance

Concentrated solar power using supercritical carbon dioxide (S-CO2) Brayton cycles offers advantages of similar or higher overall thermal efficiencies than conventional Rankine cycles using superheated or supercritical steam. The high efficiency and compactness of S-CO2, as compared with steam Rankine cycles operating at the same temperature, make this cycle attractive for solar central receiver applications. In this paper, S-CO2 Brayton cycle is integrated with a solar central receiver that provides heat input to the power cycle. Three configurations were analyzed: simple, recompression (RC), and recompression with main intercooling (MC). The effect of pressure drop in heat exchangers and solar receiver and solar receiver surface temperature on the thermal and exergetic performance of the CO2 Brayton cycle with and without reheat condition was studied. Energy, exergy, and mass balance were carried out for each component and the cycle first law and exergy efficiencies were calculated. In order to obtain optimal operating conditions, optimum pressure ratios were obtained by maximizing the cycle thermal efficiency under different pressure drops and solar receiver temperature conditions. Optimization of the cycle first law efficiency was carried out in python 2.7 by using sequential least squares programing (SLSQP). The results showed that under low pressure drops, adding reheat to the S-CO2 Brayton cycle has a favorable effect on the thermal and exergy efficiencies. Increasing pressure drop reduces the gap between efficiencies for reheat and no reheat configuration, and for pressure drop factors in the solar receiver above 2.5%, reheat has a negligible or detrimental effect on thermal and exergy performance of S-CO2 Brayton cycles. Additionally, the results showed that the overall exergy efficiency has a bell shape, reaching a maximum value between 18.3% and 25.1% at turbine inlet temperatures in the range of 666–827 °C for different configurations. This maximum value is highly dependent on the solar receiver surface temperature, the thermal performance of the solar receiver, and the solar field efficiency. As the solar receiver surface temperature increases, more exergy destruction associated with heat transfer losses to the environment takes place in the solar receiver and therefore the overall exergy efficiency decreases. Recompression with main intercooling (MC) showed the best thermal (ηI,cycle > 47% at Tin,turbine > 700 °C) and exergy performance followed by RC configuration.

Enhanced heat transfer in a parabolic trough solar receiver by inserting rods and using molten salt as heat transfer fluid

2018 ◽  
Vol 220 ◽  
pp. 337-350 ◽  
Author(s):  
Chun Chang ◽  
Adriano Sciacovelli ◽  
Zhiyong Wu ◽  
Xin Li ◽  
Yongliang Li ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Molten Salt ◽  
Heat Transfer Fluid ◽  
Parabolic Trough ◽  
Enhanced Heat Transfer ◽  
Solar Receiver

Investigation of Heat Transfer Characteristics of Supercritical Carbon Dioxide at Microchannels

2019 ◽  
Author(s):  
Mostafa Asadzadeh ◽  
Anatoly Parahovnik ◽  
Stephen Adeoye ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Supercritical Co2 ◽  
Local Heat Transfer ◽  
Local Heat ◽  
System Pressure ◽  
Micro Channels

Abstract Carbon Dioxide (SCO2) can revolutionize the thermal management landscape due to a dramatic increase in enthalpy and a specific heat near supercritical state, particularly along the pseudocritical line, which correspond to much lower temperatures and pressures than water and other refrigerants. This study is conducted to assess the capability of supercritical CO2 in heat transfer applications. The heat transfer coefficient of carbon dioxide near the pseudocritical conditions was experimentally studied at the micro scale. Devices with 20 micro channels were fabricated to measure local and average heat transfer coefficient as well as system pressure drop. The experimental results showed a significant increase up to 72000 W/m2.k in local heat transfer coefficient and large pressure drop up to 3 MPa at microscale with supercritical CO2.

Heat Transfer Performance of Supercritical Carbon Dioxide in Microchannels

2015 ◽  
Author(s):  
Chien-Yuh Yang ◽  
Kun-Chieh Liao
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Pressure Drop ◽  
Critical Point ◽  
Test Section ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Test Results ◽  
Test Conditions ◽  
Critical Carbon Dioxide

This paper provides an experimental investigation of heat transfer performance and pressure drop of supercritical carbon dioxide cooling in microchannel heat exchanger. An extruded flat aluminum tube with 37 parallel channels and each channel of 0.5 mm × 0.5 mm cross section was used as the test section. Super critical carbon dioxide at pressure of 7.5 MPa and inlet temperature varied from 55 to 25 °C was tested. The temperature drops of CO2 cooled inside the test section was controlled at 2, 4 and 8 °C separately for each test to investigate the effect of properties change on the friction and heat transfer performance at various temperature cooling ranges near the critical point. The test results showed that while the test conditions were away from (approximately 5 °C higher or lower) the critical point, both heat transfer and pressure drop performance agreed very well with those predicted by convention correlations. However, while the test conditions near the critical point, the difference between the present test results and the prediction values is very high. From the experiment results of various temperature change range inside the test section, we can find that both heat transfer and pressure drop were strongly affected by the temperature cooling ranges near the critical point. Since there is a drastic peak of the properties change near the critical point, neither fluid properties at the average temperature nor the average properties at the inlet and exit temperatures may appropriately present the actual properties change in the test process. If we use the properties integrated but not averaged from inlet to the exit temperatures, we may obtain the results that agree well with the values predicted by conventional correlations. The heat transfer and pressure drop performance of super critical carbon dioxide are indeed similar to these at normal conditions if its properties were appropriately evaluated.

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