Riser Tube Research Articles

Analysis of thermal performance characteristics in variable header solar water heating system by a swirling effect of twisted tapes

ABSTRACT This present study experimentally investigates the hydrothermal performance of a variable header solar water heating system inserted with helix twists (HT) and helix twist with square-cut perforated (HTSCP). Experiments have been conducted between variable header inserted with simple helix and HTSCP with the Reynolds number range from 190 to 1245. From the experimentation, the Nusselt number, friction factor, and thermal performance factor for the twist ratios Y = 3and Y = 6 have been calculated. In general, the overall thermal performance of a solar water heater has been augmented by increasing the mass flow rate, this is achieved from commencing to end providing a uniform flow in all riser tubes by introducing variable header. The experiments have been performed for the ratio of Y = 3 and Y = 6 with square cut of depth ratio (DR) and width ratio (WR) of 0.27. The performance comparison between the HTSCP with the simple helix twists (HT) and plain tube collector proved that the HTSCP-3 significantly performs superior. The HTSCP-3 attained 2.46% higher Nusselt number than the other twists HT-3, HT-6, and HTSCP-6.

Electrodeposited black cobalt selective coatings for application in solar thermal collectors: Fabrication, characterization, and stability

We report on the electrodeposition of nickel/black cobalt selective coatings, and evaluate the performance stability as a function of the substrate material, the temperature of heat treatments, and under accelerated weathering conditions. The black cobalt absorber material is shown to be stable up to 750 °C, and the performance stability for a stainless steel substrate with a nickel/black cobalt selective coating after 200 h at 300 °C is demonstrated, with a solar absorptance of 95% and thermal emittance of 7% (at 100 °C). The galvanostatic electrodeposition process has been scaled up to collector size, and is demonstrated both for a flat plate and a tubular substrate. A copper flat plate of 193 cm × 12 cm connected to a riser tube was coated, and a single-fin solar thermal collector was evaluated under realistic outdoor conditions. The collector produced essentially the same amount of heat as an identical reference collector with a commercial TiNOX selective coating. In addition, the coating was applied to a copper tube for a 3 m parabolic trough collector . The selective coating is hydrophobic and withstands an accelerated weathering test, illustrating the viability of black cobalt electrodeposition for the fabrication of solar collectors for low and high temperature applications.

Performance Analysis of Alumina Nanofluids on Flat Plate Solar Collector by Using Computational Fluid Dynamics

It is essential to find more renewable, sustainable ways of generating energy as the global energy demand is expected to grow by 30% by 2040. This work is concerned with the numerical prediction of thermal performance of flat plate solar collector, professor by varying the diameter of riser tube and changing the working fluid. A solar collector for heating a volume of 10 liters of working fluid is designed and investigated. 3D CAD model of the collector consisting of a fluid zone and two solid zones is generated for solving this conjugate heat transfer problem. Numerical analysis is carried out on the solar collector systems and their performance is predicted. The thermal and flow properties obtained for the solar collector systems are compared with each other to identify the best performing model of the solar collector. It is found from the numerical results that 14 mm riser tube with nano fluids gives comparatively best performance in terms of absorbing solar energy.

Approximate Representation and Exposition of ISI Flat Plate Collector including Revised Flat Plate Collector : A Review

Cosmic power is one of the numerous renewable energy sources that can use in a Photovoltaic (PV) system or Thermal. Solar collectors play a crucial role in solar thermal systems. They convert solar radiation into heat and transfer the heat to working fluids Such as water or air. The Flat-plate collectors are the numerous common type of solar collectors and typically used as a water heater or air heater. These collectors have low efficiency and low outlet temperature. Recently, many scientists have attempted to improve the efficiency and performance of flat-plate collectors via different methods. This review paper describes the results of the experimentation carried out to study and compare the performance of the modified flat plate collector having increasing riser tube diameter and reducing riser tube length with the conventional ISI marked solar liquid flat plate collector. To study, the comparative performance characteristics of a modified flat plate collector with ISI flat plate collector operated under natural circulation mode. The suggested design found to be better than the existing ISI design of the absorber plate from an efficiency point of view. The actual useful heat gain (Qu) in the suggested design understudy found to be more by 30% than that in the case of ISI collector. However, the modified flat plate collector found to operate at a relatively lower exit temperature than the conventional ISI marked collector.

Experimental Analysis of the Condenser Design in a Thermosiphon System for Cooling of Telecommunication Electronics

Passive two-phase cooling systems are an efficient and viable alternative to conventional air-cooling schemes for thermal management of electronics due to their capability of dissipating higher power densities with lower power consumption and noise levels. This article aims to assess the performance of a novel two-phase air-cooled thermosyphon for cooling shelf-level telecommunications equipment that is designed with 18 line cards. In particular, the main objective is to investigate the effect of the condenser technology on the thermal-hydraulic performance of the cooling system. The thermosyphon consists of a multimicrochannel evaporator with 18 individual microchannel zones (one per card) connected to an air-cooled condenser via riser and downcomer tubes. The total height of the loop, from midevaporator to midcondenser, is approximately 50 cm. Two different condenser designs have been tested: a single-pass louvered-fin flat-tube condenser, and a multipass wavy-fin, circular-tube condenser. An extensive experimental campaign is performed to evaluate the performance of these two air-cooled condensers in a front-to-back airflow configuration. The experiments are carried out with R134a as the working fluid, varying filling ratios from 45% to 60%, and heat loads from 102 to 1023 W under uniform and nonuniform conditions. The influence of the air-side fan configuration is also investigated by varying the fans speed from 10 548 to 15 480 min−1 and by increasing the fan-tray height from 65 to 103 mm. The results demonstrate that the single-pass louvered-fin flat-tube condenser provides lower liquid-side frictional pressure drops and consequently higher refrigerant mass flow rate in the loop. This leads to a higher critical heat flux value, which is ideal for increasing power densities and limiting dry-out occurrence. On the other hand, the multiple-pass wavy-fin, condenser offers lower thermal resistances over a larger range of dissipated heat loads. This is mainly attributed to its lower air-side pressure drop.

Two-phase thermo-hydraulic model of a 210 MW thermal power plant boiler for designing the riser-downcomer circuit

In the present work, a natural circulation boiler of a typical 210 MW thermal power plant is investigated with an objective to provide the feasible, reliable, and safe design solution of the riser-downcomer circuit. A thermo-geometric analysis of a riser-downcomer circuit of a typical subcritical boiler is carried out for a specified steam generation rate, based on a two-phase flow model. The developed model is validated with the available experimental/numerical data, satisfactorily. The model takes care of a detailed flow regime map, is capable of identifying DNB and CHF points, and can estimate a typical temperature rise of riser tubes under any flow regimes. The safe and unsafe zones of operations of heated riser tubes have been identified quantitatively and accordingly a range of feasible design solutions are demonstrated in a tabular form. The tube numbers, lengths, and especially the diameters and thicknesses are provided in compliance with the ASME boiler code. We would like to emphasize that the objective of this work is not to select a single design, rather provide a number of flexible solutions, which can be utilized by researchers, manufacturers, and practicing engineers, according to their needs.

Effect of air bubble injection on the thermal performance of a flat plate solar collector

Air bubble injection has been proved to be a simple and effective heat transfer enhancement technique in liquid-to-liquid heat exchangers. This study aimed to investigate the technique experimentally as a possible method for augmenting the thermal performance of a flat plate solar collector in the climatic conditions of Najaf city, Iraq. Air was injected as small bubbles into the riser tubes of the solar collector with three different flow rates Qa=1,1.5and2LPM and was compared with no air injection Qa=0LPM. The flat plate solar collector had dimensions of 1000 × 2000 × 80 mm (length, width and thickness respectively) and contained seven riser tubes of 8 mm internal diameter and 0.6 mm thickness. A perforated silicon tube (with holes of 0.5 mm diameter) was used for the air injection. Tap water was used as a working fluid and the experiments were repeated three times for each air flow rate. The experimental results showed that the injected air significantly improved the thermal performance of the solar collector. Its efficiency was enhanced by about 16.5%, 69.2% and 68.8% for the injected air flow rates of 1 LPM, 1.5 LPM and 2 LPM respectively.

“Performance comparison of innovative spiral shaped solar collector design with conventional flat plate solar collector”

Flat plate solar collector is an essential device, which facilitate direct application of solar energy for water heating in household and industrial sector. Existing Flat plate solar collectors (FPSC) suffers from stagnant and comparatively low efficiency. Further research to improve efficiency of FPSC by inculcating innovative design is necessary. To fill the gap, the presented work is an experimental investigation of an innovative design and fabrication approach which deals with analysis of flat plate solar collector efficiency. Design modifications of solar collector always offer an important alternative to achieve significant effect on thermal efficiency. In this work single spiral shaped collector tube as compare to number of riser tubes connected with headers in conventional type flat plate solar collector has been developed. Keeping all other parameters similar to conventional design, it has been observed very encouraging outcomes in efficiencies of solar collector. Under forced mode of testing, enhancement in thermal efficiency achieved is, 21.94% compared to conventional flat plate collector design. Enhancement in exergy efficiency is 6.73%. Overall material saving is about ∼30% and cost of manufacturing and maintenance can be significantly reduced at equivalent performance of conventional collector.

Performance analysis of solar water heater by using TiO2 nanofluids

Abstract In the industrial sectors, heat must be transferred either to insert energy into the system or to remove the energy produced in the system. In this research work, the investigations on convection heat transfer and pressure drop characteristics of water and TiO2 nanofluids. TiO2 nanofluid of 0.3% volume concentration is used for experimentation. Copper rod of 3 mm diameter is used to prepare the riser tube of 2 m length. The maximum efficiency attained from the TiO2 nanofluids plane tube collector is 58%.

Operational behavior and heat transfer in a thermosiphon desorber at sub-atmospheric pressure. Part I: The model

The thermosiphon desorber or bubble pump is advantageous in absorption cooling devices, since the processes of refrigerant desorption and solution pumping is combined in one hermetical unit. This supersedes the necessity of a mechanical solution pump. In the application with NH3/H2O the thermosiphon desorber typically operates at a pressure of around 15 bar with a liquid vapor density ratio in the range of 102, which is in a well-known regime of two phase flow. Nevertheless, for the application of thermosiphon desorbers in H2O/LiBr absorption chillers, which are commonly operated at a pressure below 0.1 bar with the liquid vapor density ratio in the range of 104, there is a lack of heat transfer correlations for two-phase flow.First attempts to fill this gap of flow boiling heat transfer correlations in the thermosiphon desorber at sub-atmospheric pressures is presented in this paper. A model is formed by solving simultaneously the mass, energy, and momentum equations. The well-known correlations for predicting single-phase and two-phase flow heat transfer coefficient and frictional pressure drop have been reviewed to find a possibility for applying them to the thermosiphon desorber. The mass flow rate and heat transfer behavior with the different flow length of the riser tube and with changing the pressure has been theoretically studied in the model. For verification, the model has been compared to experimental data using pure water. This will be presented in the second part of the paper.

Investigation of a hybrid solar collector/nocturnal radiator for water heating/cooling in selected Nigerian cities

The present investigation presents a finite element analysis of the dynamic performance of a hybrid flat-plate solar collector/nocturnal radiator (SCONOR) for water heating and cooling in five Nigerian cities. Riser tubes for water conduit were welded to the SCONOR underneath and model equations were developed for heat transfer processes around the SCONOR-bond-tube-water region during the heating, cool down and nocturnal phases. Also, appropriate climatic models were developed to capture absorptions and emissions of energy from the sun and the sky during periods of solar heating and night sky cooling respectively. Results obtained showed that the maximum temperatures attained by the water during diurnal heating were 84.6 °C, 75.61 °C, 86.4 °C, 88.33 °C, and 93.67 °C while during the nocturnal cooling period, the minimum temperatures of water were 20.21 °C, 20.12 °C, 21.9 °C, 20.95 °C and 22.01 °C for Owerri, Portharcourt, Ikeja, Maiduguri and Sokoto respectively. The optimum bond thickness for best performance is 3.0 × 10−3 m at bond width of 0.26 m, tube spacing of 0.1 m and single polyethylene windscreen. For solar heating, Sokoto showed the best performance while for nocturnal cooling; Port Harcourt showed the best performance. Therefore, ambient energy possesses a great potential to ameliorate the energy security challenge and ensure a sustainably clean environment.

Numerical and Experimental Study of Flow Characteristics in Solar Collector Manifolds

The flow through a forced circulation Z-type flat plate solar collector was investigated by means of combined experimental measurements and numerical simulations. The efficient operation of such collectors depends on the uniformity of the flow rate distribution among their riser tubes, while low pumping power demand is also sought. Mass flow rate measurements in the riser tubes were performed, utilizing a specially adapted ultrasound instrument for various values of total flow rates in the collector. By means of a commercial Computational Fluid Dynamics (CFD) code, laminar and turbulent flow models in different computational grids were tested and validated against the experiments. Appropriate metrics were introduced to quantify flow rate distribution non-uniformity among the risers, and pressure drop through the manifold was calculated. Parametric studies for flow conditions outside the experimental window were performed utilizing the CFD method in order to assess the effect of the Reynolds number in the flow distribution among the riser tubes. Furthermore, aiming to enhance flow rate uniformity, a methodology based on modifying the diameter of each riser tube was applied and successfully demonstrated. The proposed method can be employed in large solar collector arrays, either as stand-alone systems or as belonging to hybrid alternative sources of energy (ASE) systems, aiming to optimize their overall efficiency.

Research on design and technology of aluminium alloy conductor low pressure casting die

Basic principles of aluminium alloy conductor low pressure casting are introduced in the paper. Casting die design and casting system are respectively introduced aiming at the low-pressure casting process of aluminium alloy conductor, the influence of cylindrical riser tube and cone riser tube on liquid rising pressure and liquid rising stability in liquid rising process are analysed in details. It is concluded that the liquid rising pressure for liquid rising process is relatively low during selection of cone liquid rising, and liquid rising process of cone riser tube is more stable. Therefore, cone riser tube is more suitable for liquid rising process of aluminium alloy conductor low pressure casting than cylindrical riser tube. Low pressure casting technological parameters of aluminium alloy conductors are summarized through analysis on low pressure casting technology, thereby providing reference for low pressure casting technique of aluminium alloy conductors.

Experimental Analysis of Solar Water Heater Using Porous Medium with Agitator

Abstract The objective of the work is to improve the thermal efficiency of the system by energy conversion processes from the solar collector to the working fluid. The experiment consists of solar collector with porous medium such as pebble stones as packed with the agitator. The collector having the riser tube, the basic purpose of agitator in the riser tube is to improve the heat transfer rate in the system. Here the pebble stones are used to absorb the heat energy and stored in the materials, then it will be gradually transmitted to the working fluids for long duration. The experiment has conducted with porous medium and without the porous medium. The temperature have noted for certain period of time interval and also noted the solar radiation. With respect to these available data and designed value of collector capacity, heat absorption and efficiency have been calculated. In which both factor is being considered and placing of agitator with pebble stones can increase convective heat transfer and reduce thermal loss thereby efficiency is increased gradually.

CFD modelling of different properties of nanofluids in header and riser tube of flat plate solar collector

This paper aimed to evaluate the state of three different flow parameters of nanofluids and hybrid nanofluids flowing through inside header and riser tube of flat plate solar collector. This research work studied with Computational fluid dynamics (CFD) modelling method using nanofluids (Al2O3, TiO2, ZnO) and hybrid nanofluids (Al2O3+TiO2, TiO2+ZnO, ZnO + Al2O3). The modelling was three dimensional under k-epsilon turbulence model, which was set with Standard and Standard Wall Functions. Besides, Absolute reference frame and calculative intensity percentage was fixed. The base fluid was water as well as volume fraction of nanofluids and hybrid nanofluids was 0.1%. Single-phase viscous model with energy equation used. Three types of design models (Model A, B and C) used with fixed inlet and outlet diameter. The number of header tubes fixed with two, but the number of riser tube varied such as two, seven and twelve. Maximum dynamic pressure increased in model B for both nanofluid and hybrid nanofluid of about 48% and 16% respectively. Velocity magnitude enhanced in maximal for both nanofluid and hybrid nanofluid in model B. Besides, highest turbulence kinetic energy achieved in model A (5.5%) for nanofluids and in model B (18%) for hybrid nanofluids. Model B perform better comparing with model A and model C.

Internal energy analysis with nanofluids in header and riser tube of flat plate solar collector by CFD modelling

In this study, Computational Fluid Dynamics (CFD) modelling of internal energy with different nanofluids (TiO2 and crystal nano cellulose) studied. The modelling was three dimensional under Viscous Laminar model. The base fluid for nanoparticles was 60% water+40% ethylene glycol along with individual water and ethylene glycol fluids. Volume fraction of nanofluids was 0.5% and single-phase model used. The diameter of inlet and outlet was fixed of individual model and three kinds of designing model used here. The diameter of both header and riser tubes varied whereas the number of tubes varied only for riser. The results revealed that diameter and number of tubes (riser) do not affect on the internal energy. Since internal energy only depends on different properties of the inside fluids.

Fluid – structure interaction study for the DIFIS System’s composite riser tube

DIFIS System was developed for oil recovery from shipwrecks and for the elimination of the pollution threat during EU FP-6 framework. The installation time’s reduction in cases of environmental pollution is a crucial factor for DIFIS system design. In the current work, the polyethylene riser tube parts (15 meter) of DIFIS System was replaced by a composite riser tube parts (30 meter) succeeding lower installation time for the DIFIS’s riser. The analysis and development of composite riser was based on the verified 2 – way fluid structure interaction (FSI) results from polyethylene riser. A methodology based on polyethylene riser’s normal modes (target values) was proposed and the composite riser’s structural integrity was investigated in order to reach these target values. The normal modes analysis and the 2 – way fluid structure interaction simulation were performed in ABAQUS software. The composite riser’s dynamic response under sea current is significant better than polyethylene riser (lower displacements in both axes, parallel and vertical to flow). In overall, the time reduction of the DIFIS’ risers installation by 40% was achieved, using longer riser parts.

Macro Flat-Plate Solar Thermal Collector With Rectangular Channels

A macro rectangular-channel flat-plate solar thermal collector is designed and examined in this study. It consists of a set of adjacent macro rectangular channels formed between the upper, lower, and fin-parts of an absorber plate, thus, overcoming the necessary welding between the absorber plate and riser tubes used in conventional flat-plate collectors. An optimization model is suggested and solved to obtain an optimal design of the proposed collector. After that, a detailed dynamic mathematical model of this collector is presented and numerical simulation is carried out using matlab. Furthermore, a comparison with a conventional sheet-and-tube solar thermal collector is investigated and parametric analysis is conducted under both steady-state and dynamic conditions. The results reveal that the designed collector yields an enhancement of 8% for integrated thermal efficiency under transient regime and an average improvement of 12% for steady-state efficiency when compared with the conventional collector. In addition, the influence of the variation of different parameters, such as the mass flow rate of the heat transfer fluid (HTF), the thickness of different parts of the absorber plate, and the number of channels, on the performance of the proposed collector is presented. From an economical perspective, the cost of materials composing the new collector is less than that of materials composing the conventional one.

Global hydrodynamic of hybrid external loop airlift reactor: Experiments and CFD modelling

In this study, the mixing and mass transfer of air-water system were characterized in hybrid external loop airlift reactor using the computational fluid dynamics (CFD). This hybrid configuration involves the advantages of both airlift and torus reactors. To predict the flow in hybrid geometry, an Eulerian-Eulerian approach has been adopted with per-phase interaction of the standard k–ε turbulence model. To simplify the solution, the bubbles were considered to have approximately the same size. The global flow characteristics were experimentally determined by a conductimetric method. Gassing-out method was applied to determine gas-liquid mass transfer coefficients. The findings highlighted a uniform gas flow distribution in the riser tube, despite the riser included two different sections. It was noticed that beyond the superficial gas velocity, 0.0253 m/s, the fine rotational bubbles were dragged away by the liquid recirculation in the downcomer section. The STD k–ε turbulence model with per-phase effect, estimated correctly the hydrodynamic of homogenous and transition regimes except for high superficial gas velocity, Ug = 0.0703 m/s. For superficial gas velocities ranging from 0.0253 to 0.0703 m/s, there was a good agreement between simulated and experimental values; the error was less than 6%. Optimal conception of this hybrid geometry and its industrial scale use need further research and testing.

Numerical Study on the Effect of Distribution Plates in the Manifolds on the Flow Distribution and Thermal Performance of a Flat Plate Solar Collector

Flow maldistribution represents a problem of particular interest in the engineering field for several thermal systems. In flat plate solar collectors, the thermal efficiency strongly depends on the flow distribution through the riser tubes, where a uniform distribution causes a uniform temperature distribution and therefore a higher efficiency. In this work, a Computational Fluid Dynamics (CFD) numerical analysis has been carried out using the commercial software FLUENT®, in order to determine the flow distribution, pressure drop and hence the thermal efficiency of a solar collector with distribution flow plates inside the manifolds. The obtained numerical solution for this type of thermal systems has been validated with experimental results available in literature for laminar and turbulent flow. Four distribution plate configurations were analyzed. Results show that using two distribution plates in each of both manifolds improves the flow uniformity up to 40% under the same operating conditions when distribution plates are not used. Besides, it is shown that there exists an increase in the overall pressure drop which is practically negligible for the tilt angles commonly employed in the installation of flat plate solar collectors in Mexico. The use of closed end distribution plates on the dividing and combining manifolds allows the thermal efficiency to become close to the ideal thermal efficiency which is obtained with a uniform flow distribution.