scholarly journals Assessment and Evaluation of the Thermal Performance of Various Working Fluids in Parabolic Trough Collectors of Solar Thermal Power Plants under Non-Uniform Heat Flux Distribution Conditions

Energies ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 3776 ◽  
Author(s):  
Nabeel Abed ◽  
Imran Afgan ◽  
Andrea Cioncolini ◽  
Hector Iacovides ◽  
Adel Nasser
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Molten Salt ◽  
Thermal Performance ◽  
Thermal Efficiency ◽  
Thermal Stresses ◽  
The Other ◽  
Inlet Temperature ◽  
Parabolic Trough ◽  
Pure Fluids

Changing the heat transfer fluid (HTF) is a viable approach to study the corresponding effect on the thermal and hydraulic performances of parabolic trough collectors (PTC). Three categorized-types of pure fluids are used in this study; water, Therminol® VP-1 and molten salt. The parametric comparison between pure fluids is also studied considering the effect of various inlet fluid temperatures and different Reynolds ( R e ) numbers on the thermal performance. Two low-Reynolds turbulence models are used; Launder and Sharma (LS) k-epsilon and Shear Stress Transport (SST) k-omega models. In order to assess the performance of each fluid, a number of parameters are analyzed including average Nusselt ( N u ) number, specific pressure drop distributions, thermal losses, thermal stresses and overall thermal efficiency of the PTC system. Results confirmed that changing the working fluid in the PTC enhances the overall heat transfer thereby improving thermal efficiency. For a temperature-range of (320–500) K, the Therminol® VP-1 performed better than water, resulting in higher N u numbers, lower thermal stresses and higher thermal efficiencies. On the other hand, for the common temperature-range, both Therminol® VP-1 and molten salt preformed more or less the same with Therminol® VP-1 case depicting lower thermal stresses. The molten salt is thus the best choice for high operating temperatures (up to 873 K) as it does not depict any significant reduction in the overall thermal efficiency at high temperatures; this leads to a better performance for the Rankine cycle. For the highest tested Reynolds number for an inlet fluid temperature of 320 K, a comparison of heat transfer performance (Nusselt number) and the overall thermal efficiency between Therminol® VP-1 and water showed that Therminol® VP-1 is the best candidate, whereas the molten salt is the best choice for a higher inlet temperature of 600 K. For example, at an inlet temperature of 320 K, the Nusselt number and overall thermal efficiency of therminol VP-1 were 910 and 49% respectively as opposed to 443 and 38% for water. On the other hand, at the higher inlet temperature of 600 K, these two parameters (Nusselt number and overall thermal efficiency) were recorded as 614 and 41 % for molten salt and 500 and 39 % for Therminol® VP-1.

Numerical Analysis of Flow Structure and Heat Transfer Characteristics in Dimpled Channels With Secondary Protrusions

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Yonghui Xie ◽  
Zhongyang Shen ◽  
Di Zhang ◽  
Phillip Ligrani
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Numerical Analysis ◽  
Thermal Performance ◽  
The Other ◽  
Combination Effect ◽  
Enhancement Ratio ◽  
Heat Transfer Characteristics ◽  
Transfer Rates ◽  
Heat Transfer Augmentation

Dimple structure is an effective heat transfer augmentation approach on coolant channel due to its advantage on pressure penalty. The implication of secondary protrusion, which indicates protrusion with smaller dimension than dimple, will intensify the Nusselt number Nu inside dimple cavity without obvious extra pressure penalty. The objective of this study is to numerically analyze the combination effect of dimples and secondary protrusion. Different protrusion–dimple configurations including protrusion print-diameter Dp, protrusion–dimple gap P, and staggered angle α are investigated. From the results, it is concluded that the implication of secondary protrusion will considerably increase the heat transfer rates inside dimple cavity. Cases 4 and 6 possess the highest Nusselt number enhancement ratio Nu/Nu0 reaching up to 2.1–2.2. The additional pressure penalty brought by the protrusion is within 15% resulting in total friction ratio f/f0 among the range of 1.9–2.1. Dimpled channels with secondary protrusions possess higher thermal performance factor TP, defined as (Nu/Nu0)/(f/f0)1/3, among which cases 4 and 6 are the optimal structures. Besides this, the TP of protrusion–dimple channels are comparable to the other typical heat transfer devices, and higher TP can be speculated after a more optimal dimple shape or combination with ribs and fins.

Effect of nanofluids on heat transfer and cooling system of the photovoltaic/thermal performance

2019 ◽  
Vol 29 (6) ◽  
pp. 1920-1946 ◽  
Author(s):  
Rehena Nasrin ◽  
Md. Hasanuzzaman ◽  
N.A. Rahim
Keyword(s):  
Heat Transfer ◽  
Numerical Model ◽  
Thermal Performance ◽  
Thermal Efficiency ◽  
Volume Fraction ◽  
Cooling System ◽  
Solid Volume Fraction ◽  
Inlet Temperature ◽  
Content Type ◽  
Water Based

PurposeEffective cooling is one of the challenges for photovoltaic thermal (PVT) systems to maintain the PV operating temperature. One of the best ways to enhance rate of heat transfer of the PVT system is using advanced working fluids such as nanofluids. The purpose of this research is to develop a numerical model for designing different form of thermal collector systems with different materials. It is concluded that PVT system operated by nanofluid is more effective than water-based PVT system.Design/methodology/approachIn this research, a three-dimensional numerical model of PVT with new baffle-based thermal collector system has been developed and solved using finite element method-based COMSOL Multyphysics software. Water-based different nanofluids (Ag, Cu, Al, etc.), various solid volume fractions up to 3 per cent and variation of inlet temperature (20-40°C) have been applied to obtain high thermal efficiency of this system.FindingsThe numerical results show that increasing solid volume fraction increases the thermal performance of PVT system operated by nanofluids, and optimum solid concentration is 2 per cent. The thermal efficiency is enhanced approximately by 7.49, 7.08 and 4.97 per cent for PVT system operated by water/Ag, water/Cu and water/Al nanofluids, respectively, compared to water. The extracted thermal energy from the PVT system decreases by 53.13, 52.69, 42.37 and 38.99 W for water, water/Al, water/Cu and water/Ag nanofluids, respectively, due to each 1°C increase in inlet temperature. The heat transfer rate from heat exchanger to cooling fluid enhances by about 18.43, 27.45 and 31.37 per cent for the PVT system operated by water/Al, water/Cu, water/Ag, respectively, compared to water.Originality/valueThis study is original and is not being considered for publication elsewhere. This is also not currently under review with any other journal.

Thermal Performance of a Receiver Tube for a High Concentration Ratio Parabolic Trough System and Potential for Improved Performance With Syltherm800-CuO Nanofluid

2015 ◽  
Author(s):  
Aggrey Mwesigye ◽  
Zhongjie Huan ◽  
Josua P. Meyer
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Thermal Performance ◽  
Thermal Efficiency ◽  
Concentration Ratio ◽  
Low Flow ◽  
Fluid Temperature ◽  
Parabolic Trough ◽  
High Concentration ◽  
Flow Rates

In this paper, the thermal performance of a high concentration ratio parabolic trough system and the potential for improved thermal performance using Syltherm800-CuO nanofluid were investigated and presented. The parabolic trough system considered in this study has a concentration ratio of 113 compared with 82 in current commercial systems. The heat transfer fluid temperature was varied between 350 K and 650 K and volume fractions of nanoparticle were in the range 1–6%. Monte-Carlo ray tracing was used to obtain the actual heat flux on the receiver’s absorber tube. The obtained heat flux profiles were subsequently coupled with a computational fluid dynamics tool to investigate the thermal performance of the receiver. From the study, the results show that with increased concentration ratios, receiver thermal performance degrades, with both the receiver heat loss and the absorber tube circumferential temperature differences increasing, especially at low flow rates. The results further show that the use of nanofluids significantly improves receiver thermal performance. The heat transfer performance increases up to 38% while the thermal efficiency increases up to 15%. Significant improvements in receiver thermal efficiency exist at high inlet temperatures and low flow rates.

scholarly journals A Hybrid Nanofluid of Alumina and Tungsten Oxide for Performance Enhancement of a Parabolic Trough Collector under the Weather Conditions of Budapest

2021 ◽  
Vol 11 (11) ◽  
pp. 4946
Author(s):  
Otabeh Al-Oran ◽  
Ferenc Lezsovits
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Rate ◽  
Thermal Performance ◽  
Radiation Intensity ◽  
Hybrid Nanofluid ◽  
Intensity Level ◽  
Parabolic Trough

Recently, there has been significant interest in the thermal performance of parabolic trough collectors. They are capable of operating and generating highly variable temperature ranges, which can be used in various applications. This paper, therefore, addressed the thermal performance model of using a parabolic trough collector under the radiation intensity level found in Budapest city, as well as the effect of inserting a hybrid nanofluid as the thermal fluid. First, a new modified hybrid nanofluid of alumina and tungsten oxide-based Therminol VP1 is used to enhance the thermal properties of the thermal fluid to be more efficient to use. This enhancement is performed under various volume concentrations and has a volume fraction of 50:50. Second, in order to demonstrate the effectiveness of the thermal element, mathematical energy balance equations were solved and simulated using MATLAB Symbolic Tools. The simulation is presented for two cases: one under a constant radiation intensity and the other under the radiation intensity level of Budapest. For both cases, the results of the dimensionless Nusselt number, heat transfer coefficient, pressure drop, exergy efficiency, and energy efficiency are described. The major findings show that a volume concentration of 4% (Al2O3 and WO3) based Therminol VP1 was the most efficient volume concentrations in both cases. For the first case, the maximum enhancement of the Nusselt number and the heat transfer coefficient are 138% and 169%, respectively. These results enhanced the thermal and exergy efficiencies by 0.39% and 0.385% at a temperature 600 K, flow rate of 150 L/min, and radiation intensity of 1000 W/m2. For the second case, the maximum exergy and energy values are recorded at midday under Budapest’s summer climatic conditions and reach 32.728% and 71.255%, respectively, under the optimum temperature of 500 K and flow rate of 150 L/min. Accordingly, the mean improvement in thermal and exergy efficiencies approximately equal to 0.25% at a high concentration, regardless of the season (summer or winter).

Heat Transfer Performance of a Parabolic Trough Receiver Using SWCNTs-Therminol®VP-1 Nanofluids

2017 ◽  
Author(s):  
Aggrey Mwesigye ◽  
Josua P. Meyer
Keyword(s):  
Heat Transfer ◽  
Solar Energy ◽  
Thermal Performance ◽  
Thermal Efficiency ◽  
Concentration Ratio ◽  
Heat Transfer Performance ◽  
Energy System ◽  
Transfer Performance ◽  
Parabolic Trough ◽  
Flow Rates

In this paper, the potential for improved thermal performance of a high concentration ratio parabolic trough solar energy system working with high thermal conductivity single-walled carbon nanotubes (SWCNTs) and Therminol®VP-1 nanofluid is numerically investigated. In the numerical analysis, the practical heat flux profiles expected for parabolic trough receivers were obtained using Monte-Carlo ray tracing and coupled with a computational fluid dynamics tool using user defined functions to investigate the thermal performance of the parabolic trough solar energy system. A parabolic trough system with a concentration ratio of 113 was considered in this study and heat transfer fluid inlet temperatures between 400 K and 650 K were used. The volume fraction of SWCNTs in the base fluid was in the range 0% to 2.5% and the flow rates used were in the range 0.82 to 69.41 m3/h. Results show improvements in the convective heat transfer performance and receiver thermal efficiency as well as a considerable reduction of the receiver thermal losses with increasing volume fractions. The heat transfer performance increases up to 64% while the thermal efficiency increases by about 4.4%. Higher increments are observed at low flow rates and inlet temperatures. The receiver thermodynamic performance also increases significantly with the use of nanofluids. Entropy generation rates reduce by about 30% for the range of parameters considered.

Thermal performance of inserting hybrid nanofluid in parabolic trough collector

2021 ◽  
Author(s):  
Otabeh Al-Oran ◽  
Ferenc Lezsovits
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Thermal Performance ◽  
Hybrid Nanofluid ◽  
Heat Transfer Characteristics ◽  
Parabolic Trough ◽  
Transfer Coefficients ◽  
Parabolic Trough Collector ◽  
Heat Transfer Coefficients ◽  
Transfer Characteristics

AbstractIn this work, the thermal performance of using hybrid nanofluid of Ceria oxide and multi-walled carbon nanotube-based MOL 68 in the receiver tube of parabolic trough collector is simulated numerically. The influence of using this nanofluid under various volume concentrations and different Reynold numbers is solved numerically using computational fluid dynamics. The turbulent model's analysis is carried out based on k–ϵ re-normalization group and employed to find the Nusselt number and the heat transfer coefficients. The model results were validated with the previous correlation, which were used to evaluate the Nusselt number. The results showed that hybrid nanofluid enhances the heat transfer characteristics of the parabolic trough collector in comparison with the base fluid. Furthermore, even better heat transfer characteristics can be achieved with an increased volume concentration of the modified nanofluids.

Maximizing Heat Transfer Through Joint Fin Systems

2005 ◽  
Vol 128 (2) ◽  
pp. 203-206 ◽  
Author(s):  
A.-R. A. Khaled
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Performance ◽  
Critical Length ◽  
The Other ◽  
Rigid Fixation ◽  
Convection Coefficient ◽  
Heat Transfer Characteristics ◽  
Cold Side ◽  
Transfer Characteristics

Heat transfer through joint fins is modeled and analyzed analytically in this work. The terminology “joint fin systems” is used to refer to extending surfaces that are exposed to two different convective media from its both ends. It is found that heat transfer through joint fins is maximized at certain critical lengths of each portion (the receiver fin portion which faces the hot side and the sender fin portion that faces the cold side of the convective media). The critical length of each portion of joint fins is increased as the convection coefficient of the other fin portion increases. At a certain value of the thermal conductivity of the sender fin portion, the critical length for the receiver fin portion may be reduced while heat transfer is maximized. This value depends on the convection coefficient for both fin portions. Thermal performance of joint fins is increased as both thermal conductivity of the sender fin portion or its convection coefficient increases. This work shows that the design of machine components such as bolts, screws, and others can be improved to achieve favorable heat transfer characteristics in addition to its main functions such as rigid fixation properties.

Heat Transfer Enhancement in a Rectangular (AR = 3:1) Channel With V-Shaped Dimples

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
C. Neil Jordan ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Liquid Crystal ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Reduced Pressure

An alternative to ribs for internal heat transfer enhancement of gas turbine airfoils is dimpled depressions. Relative to ribs, dimples incur a reduced pressure drop, which can increase the overall thermal performance of the channel. This experimental investigation measures detailed Nusselt number ratio distributions obtained from an array of V-shaped dimples (δ/D = 0.30). Although the V-shaped dimple array is derived from a traditional hemispherical dimple array, the V-shaped dimples are arranged in an in-line pattern. The resulting spacing of the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. A single wide wall of a rectangular channel (AR = 3:1) is lined with V-shaped dimples. The channel Reynolds number ranges from 10,000–40,000. Detailed Nusselt number ratios are obtained using both a transient liquid crystal technique and a newly developed transient temperature sensitive paint (TSP) technique. Therefore, the TSP technique is not only validated against a baseline geometry (smooth channel), but it is also validated against a more established technique. Measurements indicate that the proposed V-shaped dimple design is a promising alternative to traditional ribs or hemispherical dimples. At lower Reynolds numbers, the V-shaped dimples display heat transfer and friction behavior similar to traditional dimples. However, as the Reynolds number increases to 30,000 and 40,000, secondary flows developed in the V-shaped concavities further enhance the heat transfer from the dimpled surface (similar to angled and V-shaped rib induced secondary flows). This additional enhancement is obtained with only a marginal increase in the pressure drop. Therefore, as the Reynolds number within the channel increases, the thermal performance also increases. While this trend has been confirmed with both the transient TSP and liquid crystal techniques, TSP is shown to have limited capabilities when acquiring highly resolved detailed heat transfer coefficient distributions.

Heat Transfer and Pressure Loss Characteristics of Pin-Fins With Different Shapes in a Wide Channel

2017 ◽  
Author(s):  
Jin Xu ◽  
Jiaxu Yao ◽  
Pengfei Su ◽  
Jiang Lei ◽  
Junmei Wu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Thermal Performance ◽  
Pressure Loss ◽  
Bottom Surface ◽  
Number Range ◽  
Pin Fin ◽  
Nominal Diameter ◽  
Pin Fins

Convective heat transfer enhancement and pressure loss characteristics in a wide rectangular channel (AR = 4) with staggered pin fin arrays are investigated experimentally. Six sets of pin fins with the same nominal diameter (Dn = 8mm) are tested, including: Circular, Elliptic, Oblong, Dropform, NACA and Lancet. The relative spanwise pitch (S/Dn = 2) and streamwise pitch (X/Dn = 4.5) are kept the same for all six sets. Same nominal diameter and arrangement guarantee the same blockage area in the channel for each set. Reynolds number based on channel hydraulic diameter is from 10000 to 70000 with an increment of 10000. Using thermochromic liquid crystal (R40C20W), heat transfer coefficients on bottom surface of the channel are achieved. The obtained friction factor, Nusselt number and overall thermal performance are compared with the previously published data from other groups. The averaged Nusselt number of Circular pin fins is the largest in these six pin fins under different Re. Though Elliptic has a moderate level of Nusselt number, its pressure loss is next to the lowest. Elliptic pin fins have pretty good overall thermal performance in the tested Reynolds number range. When Re>40000, Lancet has a same level of performance as Circular, but its pressure loss is much lower than Circular. These two types are both promising alternative configuration to Circular pin fin used in gas turbine blade.

scholarly journals Heat transfer studies in compact heat exchanger using ZnO and TiO2 nanofluids in ethylene glycol/water

2018 ◽  
Vol 24 (4) ◽  
pp. 309-318
Author(s):  
Srinivasan Manikandan ◽  
Rajoo Baskar
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Ethylene Glycol ◽  
Volume Fraction ◽  
Inlet Temperature ◽  
Percentage Increase ◽  
Cold Side ◽  
Volume Fractions ◽  
Experimental Values ◽  
Tio2 Nanofluids

This paper reports an experimental study on the heat transfer characteristics of a nanofluid consisting of ZnO/water/ethylene glycol (EG) and TiO2/water/ /ethylene glycol. In this study, the base fluids of ethylene glycol (EG):water (W) with volume fractions of 30:70, 40:60, and 50:50 were prepared, and 0.2 to 1.0 volume fractions of ZnO and TiO2 nanofluids were used as a cold side fluid. The prime objective of this study is to identify the effects of nanofluid concentration and three different hot fluid inlet temperatures viz., 55, 65 and 75?C C on the heat transfer enhancement of cold side fluid. The results are compared with base fluids and the percentage increase of the Nusselt number because of nanoparticle addition is noted both experimentally and theoretically. The results showed that at the hot fluid inlet temperature of 75?C, the increase in the Nusselt number is maximum with volume concentrations of 0.6 and 0.8% for ZnO and TiO2 nanofluids, respectively. The corresponding maximum Nusselt number enhancements are about 11.5 and 21.4%, respectively, for the base fluid volume fraction of 30:70 (EG:W). There is good agreement between the results calculated from experimental values and the correlation.

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