Experimental Test Rig Research Articles

Development of Nusselt number and friction factor correlations for double-pass solar air heater duct

A solar air heater exhibits a low heat transfer rate due to the formation of a laminar thermal boundary layer across the absorber plate. Furthermore, the artificial roughness contributes to the intensification of turbulence along the absorber plate, which interrupts and breaks the thermal boundary layer. Keeping in this view, a three-dimensional simulation is performed to investigate the heat transfer and frictional characteristics of a double-pass solar air heater with semicircular tubes and perforated baffles as artificial roughness. This numerical investigation is performed for the parameters considered in the study: tube amplitude ratios (a/H) from 0.2 to 0.5, baffle height ratios (e/H) from 0.4 to 0.8, open area ratios (β) from 13 % to 30 % and Reynolds number (Re) from 3000 to 19000. The experimental testing rig is designed to validate numerical results corresponding to e/H of 0.4, an open area ratio of 30 %, a/H of 0.3, and Reynolds number varying from 3000 to 15000. Numerical results are found to be in good agreement with the experimental results, with a maximum absolute percentage error of 1.82 % and 5.28 % for the Nusselt number (Nur) and friction factor (fr), respectively. The maximum Nusselt number is observed as 274.29 at Reynolds number of 19,000 and e/H of 0.8; however, the maximum friction factor is observed as 0.6290 at Reynolds number of 3000 and e/H of 0.8 at a constant value of open area ratio of 30 % and a/H of 0.3. Within the range parameters studied, the maximum THPP value is reported to be 2.51 at Reynolds number of 3000, β of 30 %, e/H of 0.4, and a/H of 0.3. Further, correlations for the Nusselt number and friction factor in the function of a/H, e/H, open area ratio, and Reynolds number have been derived based on simulation results.

Optimal Maximum Cyclostationary Blind Deconvolution for Bearing Fault Detection

Maximum cyclostationary blind deconvolution (CYCBD) is a newly presented blind deconvolution method for extracting faults in mechanical systems. The method presents two challenges, which mainly come from needing to set the cyclic frequency in advance and a defining suitable filter length. To address these issues, an optimal maximum CYCBD method is developed. First, the raw signals are processed by the noise subtraction method to remove the inference of inherent impulses and environmental noise. Furthermore, the cyclic frequency is estimated by calculating the autocorrelation of the envelope signals to reveal the fault-induced impulses. Second, to determine the filter length adaptively and automatically, the residual autocorrelation energy (RAE) ratio is employed as the objective function to optimize the filter length by the improved success–failure method. Finally, the proposed method is applied to extract fault features. The effectiveness of the proposed method is validated with data obtained from an open-access bearing dataset and experimental test rigs.

Failure diagnosis and physical interpretation of journal bearing for slurry liquid using long-term real vibration data

Pumps are important machines used in rivers, social infrastructure, and industrial facilities. During long-term operation, journal bearings that support the pump shaft are subject to wear and peeling caused by liquids, including slurry. Wear and peeling can change the characteristics of journal bearings and cause abnormal shaft vibration. If wear and peeling progress, it can severely damage the pump. Thus, periodic maintenance and replacement are required. However, the frequency of periodic maintenance should be reduced as much as possible from a cost standpoint. Therefore, it is desirable to monitor the condition of the machine and perform maintenance only when necessary. In this study, the long-term vibration of a submerged journal bearing with slurry-containing water was monitored and recorded to identify the features that are important for condition monitoring and diagnosis and to interpret their contributions. First, an experimental test rig for a rotating shaft system was developed and long-term vibration data and changes in wear were recorded. A machine learning model (support vector machine (SVM)) was trained to predict the wear and damage conditions of the bearings, and its effectiveness was verified. In addition, two important features were selected as major contributors to the wear and peeling phenomena of journal bearings. These important features were interpreted using partial dependence (PD), Individual Conditional Expectation (ICE), and SHapley Additive exPlanations (SHAP), and the degree of contribution and characteristics of these features were clarified. Later, a reduced SVM model was trained using only these important features, and its effectiveness was clarified using another bearing’s data of wear and peeling processes.

Selection and Performance Prediction of a Pump as a Turbine for Power Generation Applications

The high price of purpose-made turbines always represents an active challenge when utilizing pico- and micro-hydropower resources. Pumps as turbines (PATs) are a promising option to solve the problem. However, the selection of a suitable pump for a specific site and estimating its performance in the reverse mode are both major problems in the field. Therefore, this paper aims to develop generic mathematical correlations between the site and the pump hydraulic data, which can be used to select the optimal operation of the pump as a turbine. A statistical model and the Pearson correlation coefficient formula were employed to generate correlations between the flow rate and the head of the pumps with the sites. Then, Ansys CFX, coupled with SST k-ω and standard k-ε turbulence models, was used to analyze the performance of the PAT. The analysis was conducted in terms of flow rate, pressure head, efficiency, and power output. The numerical results were validated using an experimental test rig. The deviations of the proposed correlations from the statistical model were found to be in the range of −0.2% and 1.5% for the flow rate and ±3.3% for the pressure head. The obtained numerical outputs using the standard k-ε turbulence model strongly agreed with the experimental results, with variations of −1.82%, 2.94%, 2.88%, and 1.76% for the flow rate, head, power, and efficiency, respectively. The shear stress transport (SST) k-ω turbulence model showed relatively higher deviations when compared to standard k-ε. From the results, it can be concluded that the developed mathematical correlations significantly contribute to selecting the optimal operation of the pump for power-generating applications. The adopted numerical procedure, selected mesh type, turbulence model, and physics setup provided good agreement with the test result. Among the two turbulence models, the standard k-ε performs better in estimating the pressure head, output power, and efficiency of the PAT with less than 3% errors when compared to experimental results.

Investigation of wheel squeal noise under mode coupling using two-disk testrig experiments

Wheel squeal noise is a common problem that occurs in railway systems especially on curved tracks. These tonal noises are usually found at high frequency, typically over 1 kHz. The cause of the squeal noise remains unclear and could be different under varied conditions. Several mechanisms that could cause wheel squeal, including falling friction and mode coupling, have been proposed in literature. Most existing lab experimental investigations were focused on the squeal noise caused by falling friction with vertical contacts. As a result, the squeal noise generated by mode coupling could be missed due to the absence of a non-vertical contact angle. In this work, a two-wheel test rig has been designed with curved wheel profiles to achieve adjustable contact angles with lateral components. Experimental and numerical modal analysis of the two-disk system was conducted to determine the dynamic characteristics for exploration of mode coupling effects. Using a set of benchmark parameters predicted to be the cause of significant mode-coupled instability, squeal noise was found at frequencies higher than the existing falling friction experimental tests as reported in the literature. The frequency and amplitude measured in the experiments agreed with the predictions of the analytical mode coupling model. Further experiments varying control parameters, contact angle, angle of attack and direction of rotation were performed, confirming that the new squeal noise was caused by mode coupling.

Compound Heat Transfer Enhancement in Dimpled and Sinusoidal Metal Solar Wall Ducts Fitted with Wired Inserts

An improved Metal Solar Wall (MSW) with integrated thermal energy storage is presented in this research. The proposed MSW makes use of two, combined, enhanced heat transfer methods. One of the methods is characterized by filling the tested ducts with a commercially available copper Wired Inserts (WI), while the other one uses dimpled or sinusoidal shaped duct walls instead of plane walls. Ducts having square or semi-circular cross sectional areas are tested in this work.A developed numerical model for simulating the transported thermal energy in MSW is solved by finite difference method. The model is described by system of three governing energy equations. An experimental test rig has been built and six new duct configurations have been fabricated and tested. Air is passed through the six ducts with Reynolds numbers from 1825 to 7300.Six, new, correlations for Nusselt number and friction factor are developed to assess the benefits that are gained from using the WI and the dimpled and sine-wave duct walls. It is found that higher heat transfer rates are achieved using the Dimpled, semi–circular duct with Wired Inserts (DCWI). Also, it is found that Nusselt number and the pressure drop in the DCWI are respectively(44.2% -100%) and (101.27% - 172.8%) greater than those of the flat duct with WI. The improvement in Nusselt number for flat duct with WI is found to be (1.4 – 2) times the values for flat duct with no WI. The results demonstrated that DCWI provides enhancements efficiency value that is higher than those obtained from other types of ducts. The developed MSW ducts have added to local knowledge a better understanding of the compound heat transfer enhancement.

Experimental and Numerical Visualisation of Subsurface Rail Deformation in a Full-Scale Wheel–Rail Test Rig

To tackle the problem of various types of rail damage, such as rolling contact fatigue (RCF) or wear, a profound knowledge of the occurring mechanisms is necessary. This paper presents a newly developed full-scale test rig experiment that involves inserting softer pins into the rail head. These tests help deepen our understanding of shear deformation in rail steels. Furthermore, a finite element (FE) simulation approach is introduced that can be related to the test rig experiments. With these experiments, in combination with the FE simulation, valuable information regarding the plastic deformation can be obtained. This methodology allows predictions regarding a rail’s material behaviour during cyclic wheel loading. Moreover, it enables an effective and rapid qualitative material assessment, reducing the costs of expensive and time-consuming experiments.

Hydrodynamic and experimental characterization of pumps as turbines

To estimate the performance, efficacy, modes of operation, hydrodynamic instabilities, and methodologies for harnessing energy from the pump as turbine (PAT), it is necessary to characterize these hydraulic turbomachines in all their modes of operation using an experimental test rig that simulates actual operating conditions. In this process, the characteristic curve of four quadrants of a turbomachine is constructed, especially its five modes: pump mode, brake pump mode, turbine mode, brake turbine mode, and reverse pump mode. In addition, with dynamic sensors installed in the pump volute, it is possible to know the hydrodynamic phenomena within PAT, finding its average behavior and frequency response, which is a tool for diagnosing the machine’s condition.

A simplified opto-thermal assessment and economic study of parabolic dish solar concentrator pondering on the receiver position induced uncertainties

This paper investigates the opto-thermal and economic assessment of low-cost solar parabolic dish concentrators (PDC), focusing on the receiver position-induced uncertainties. An optical model of the proposed PDC system is developed in Tonatiuh optical simulation tool. The optical analysis is conducted by the Monte Carlo Ray Tracing method for different vertical and horizontal positions of the PDC’s receiver. In addition, An experimental test rig based on a locally manufactured PDC with a low-cost reflecting surface made of aluminium reflector foil is developed to achieve the purpose of this work. A cavity receiver made of a cylindrical-cone brass tube is used and tested under different positions of the focal point of the PDC. The impact of the uncertainties on the performance of the proposed PDC is experimentally estimated. A relatively simple mathematical model is utilized to evaluate the thermal and exergy performance for the different positions of the cavity receiver. The results showed that the proposed PDC could generate hot water at temperatures 77 °C, 64 °C, and 55 °C for the three focal point positions, respectively. The collector efficiency of the PDC-cavity receiver system in the receiver position 1, 2, and 3 were 70.2%, 53.2%, and 24 % while the average values of exergy efficiency for the PDC at the receiver positions were 4.7%, 2.3%, and 0.93% respectively. This clearly shows the effect of the receiver positions on the performance of the parabolic dish solar concentrator and justifies the requirement of appropriate positioning of the receiver for the parabolic dishes.

Numerical investigation of the air conditioning system performance assisted with energy storage of capsulated concave/convex phase change material

One of the highest energy drains in homes and businesses is the air conditioning (AC) system. Thus, any slight improvement in the AC system performance can result in considerable energy savings. This numerical study aims to boost the AC performance in hot environments via thermal energy storage. This is accomplished by directly cooling the AC condenser using capsulated phase change materials (PCM). The PCM is capsulated in a new design of concave/convex (CX) plates to reduce the lengthy PCM solidification time and also enhance the AC performance. The PCM is solidified during a relatively low nighttime temperature and then cools the AC condenser during daytime operation. The proposed encapsulated PCM design's impact on the AC performance is assessed and compared to those of used flat plates. Using ANSYS Fluent, a mathematical equations model is developed and solved and then validated via an experimental test rig of the PCM flat plates. The effects of varying the size and number of concave/convex configurations are investigated. It is found that concave/convex PCM plates greatly minimize the solidification/melting periods compared to flat plates, making them effective in AC system daily work. Rising the CX diameter and numbers enhances the PCM melting and solidification rates and decreases the air outlet temperature. Moreover, the saved percentage of the power rises with the ambient temperature and airflow rate rising. Further, the AC power usage by adopting PCM concave/convex plates is saved by a maximum value of about 16 % and 7.5 % when working for 120 and 300 min, respectively.

Theoretical and Experimental Investigation of Porous Tilting Pad Gas Bearings with Hermetic Squeeze Film Dampers Based on Multilayer Diaphragm Structure

A novel porous tilting pad gas bearing (PTPGB) with hermetic squeeze film dampers based on multilayer diaphragm structure (MLD-HSFD) is proposed for oil-free turbomachinery. A dynamic model of MLD-HSFDs including the frequency dependence effect is presented by considering the compressibility of the damper fluid. An experimental test rig was assembled to measure the performance of MLD-HSFDs. The model predicts well the test data, including the frequency dependence of force coefficients. A comprehensive theoretical model of PTPGBs with MLD-HSFDs is proposed based on the implementation of the isothermal compressible Reynolds equation coupled to a flexible support and porous models. The effects of thickness of diaphragms thickness, bearing clearance, and supply pressure on bearing performance are discussed.

Analysis of the Transmission Spectrum of Flat Glass from Near-infrared to the Ultraviolet

Contemporarily, glass windows have a great impact on human beings’ daily life. It is crucial to design a glass with a reasonable thickness with a high transmission of visible light as well as a high reflection of near infrared light. In general, reflection from the glass surface and absorption of light waves by the glass material are important features for transmission. Therefore, for UV-visible near-infrared light waves, the greater the thickness of the glass, the greater the light absorption loss and the lower the transmission rate. However, it is believed that there are multiple reflections of light waves in flat glass and that the losses caused by reflections should also be related to the refractive index of the glass and the wavelength of the incident light. On this basis, this study has developed theoretical models of transmittance versus incident light wavelength and glass thickness, refractive index and absorption coefficient. According to the theoretical analysis, the thickness of the glass has a significant effect on the transmission spectrum of sunlight. To experimentally verify this theoretically predicted anomaly, this paper designed the experimental and measurement route and built the experimental test rig. A variety of glass samples in the thickness range of 1mm-10mm were designed and prepared for this project, and the UV-Vis-NIR transmission of the glass was scanned and measured, while the final measurement results observed anomalies in the variation of transmission with thickness. The experimental results, therefore, provide valid support for the theoretical model of this paper.

A new experimental test rig for performance analysis of radial compressors inside innovative heat pumps

Electrification is playing a major role in the industrial and energy sector, with heat pump (HP) market expected to grow significantly in the next future in accordance with the current energy transition phase, which aims to reduce the utilization of fossil fuels for heat production sector. It is therefore of crucial importance to find new ways to increase heat pump performance and reliability, containing maintenance costs. The use of dynamic compressors in HPs makes it possible to combine good performance with high compactness and silent operation, but unlike the volumetric compressor, this equipment could undergo dangerous instability during operation, which can occur in closed-cycle configuration, quite unusual for dynamic compressors. The aim of this paper is to present a new test-rig for stable and unstable performance analysis of dynamic compressors for innovative heat pumps. An in-depth description of the plant and instrumentation system is provided. The performance of the compressor is analyzed for different operating points, with a particular focus on near-surge operation. Experimental uncertainties and their reduction through data reconciliation techniques is thoroughly investigated.

Experimental and numerical investigation on the dynamic behavior of two partially overlapped identical plates submerged in water

Partially overlapped plates submerged in water are of interest in some industrial applications such as in blade-adjustable hydraulic turbine runners, where the neighboring blades become closer and partially overlapped for certain operating conditions. To know the influence of partially overlapped structures on their dynamic behavior is of great importance to avoid resonances and therefore to extend their lifetime. In this paper, the dynamic behavior of two identical rectangular plates with a partially overlapped area in water has been studied experimentally and numerically. An experimental test rig has been constructed, which consists of two identical rectangular plates in a tank full of water. The distance and the overlapped area between the two plates can be changed to investigate their influence on the added mass, added damping and mode shapes. A finite element method model based on acoustic fluid-structure interaction was used to simulate the added mass effect of the plates from the surrounding water. A theoretical equation used to calculate the damping ratios of submerged structures has also been proposed. Theoretical, experimental and numerical results have been compared and analyzed.

Energetic performance evaluation of an automotive CO2 air conditioning system with a dual-evaporator configuration

Inefficient performance of CO2 refrigerant in hot climates has become a major obstacle to its wide application in electric vehicles. In this paper, the vacant heating core in cooling mode was exploited to increase the heat transfer area of evaporator and improve system performance. With the aid of a validated evaporator model and an experimental test rig, performance improvements brought by this added area were evaluated. Results indicated that this area is not suggested to be directly added to cooling core. This necessitates a dual-evaporator (D-E) configuration. For case I (small CO2 pressure drop), the growth rate in heat transfer rate brought by D-E configuration is 19∼20% and less sensitive to parallel or series operation. Nevertheless, this growth rate for case II (large CO2 pressure drop) is greatly affected, 30.6∼32.6% for parallel operation and 7.5∼17.6% for series operation. Specifically, it is around 17.5% and 7.5∼13.6% for series cross-parallel and cross-counter arrangements, respectively. By comprehensive consideration, the cross-parallel arrangement is recommended to be adopted. Experimental results indicated that the cross-parallel D-E configuration greatly increases the evaporation temperature and exhibits a slight impact on optimum high pressure within the transcritical cycle. The enhancement in COP brought by this configuration is around 6∼12% without additional cost, and it rises with the decreased air flowrate through evaporator and air velocity through gas cooler and the increased ambient temperature. This indicates that this configuration is an effective and economical technology to alleviate the efficiency degradation issue of transcritical CO2 automotive air-conditioners.

Cold welding adhesion for spacecraft repair: Experiment design and roadmap

Collisions with micrometeoroids and space debris can perforate spacecraft shields and hulls; in-situ repair or substitution of the damaged elements is currently considered a complex task, in particular the case of crewed modules with pressurized elements. In this context, cold-welding can overcome the current technological difficulties allowing fast and safe repairing procedures. To date, it has been shown that similar metallic materials can fuse or weld at ambient temperatures provided that there are sufficiently high contact forces. In the space environment this fusion is aided by the fact that the joint surfaces do not re-oxide after wear and, as a consequence, atomic diffusion of the metal occurs at lower contact forces. It has also been demonstrated that, even under terrestrial conditions, the action of a low fretting load can nearly double this adhesion force.In this paper, the suggested utilization of cold-welding phenomenon for spacecraft hull repair is described, as well as a verification road map to demonstrate its feasibility. It is proposed to develop an experimental test rig to apply custom repair patches of different materials to pre-damaged metallic structures and monitor the performance the adhered joint in low orbit and during re-entry. The test samples will include simple plates, Whipple shields, and sandwich panels that have been subjected to hypervelocity impacts. In the first phase, the cold-welding phenomena will be investigated in ground laboratories and validated in a vacuum chamber; afterwards, it is proposed to repeat the experiment in microgravity conditions, during a sounding rocket flight. Results will include an assessment of the contact forces necessary to apply the repair patch and an evaluation of the structural properties of the refurbished systems.

A numerical and experimental comparison of heat transfer in a quasi two-dimensional packed bed

Heat transfer plays a major role in many industrial processes taking place in packed beds. An accurate and reliable simulation of the heat exchange between particles is therefore crucial for a reliable operation and to optimize the processes in the bed. The discrete ordinates method (DOM) provides an established numerical technique to model radiative heat transfer in granular media that offers the possibility to consider the directional dependence of the radiation propagation. In this work, DOM is compared with Monte Carlo ray tracing, which provides an alternative method for heat transfer simulations. Geometrically simple configurations are used to investigate the influence of the angular discretization on the accuracy of the results and the computation time in both methods. The obtained insights are then transferred to a more complex configuration of a quasi two-dimensional test rig consisting of metal rods for which also experimental results are available. Our results show that both DOM and Monte Carlo ray tracing allow for an accurate simulation of heat transfer in packed beds. Monte Carlo ray tracing requires thereby computation times that are surprisingly competitive (although still somewhat slower) compared to DOM and allows for an easier computation of highly accurate reference solutions. In our preliminary comparison to the experimental test rig, Monte Carlo ray tracing also provides the advantage that it can more easily model highly specular materials such as stainless steel. Both methods are comparable for diffuse materials such as magnesium oxide.

Performance Evaluation of Small Scale Air-Conditioning System Using R22 and Alternative Refrigerants

A mathematical model has been formulated to predict the influence of high outdoor air temperature on the performance of small scale air - conditioning system using R22 and alternative refrigerants R290, R407C, R410A. All refrigerants were investigated in the cooling mode operation. The mathematical model results have been validated with experimental data extracted from split type air conditioner of 2 TR capacity. This entailed the construction of an experimental test rig which consists of four main parts. They are, the refrigeration system, psychrometric test facility, measuring instrumentation, and auxiliary systems. The conditioned air was maintained at 25 0C dry bulb and 19 0C wet bulb for all tests. The outdoor ambient air temperature was varied from 35 0C to 55 0C in 5 0C increments. The study showed that R290 is the better replacement for R22 when the air conditioning system works under high ambient temperature. It has better performance as a drop in refrigerant. R407C has the closest performance to R22, followed by R410A.

Experimental Investigation Techniques for Non-Ideal Compressible Fluid Dynamics

The rising number of applications of the organic Rankine cycle (ORC) or supercritical CO2 (sCO2) power systems have shaped a new branch of fluid mechanics called non-ideal compressible fluid dynamics (NICFD). This field of fluid mechanics is concerned with flows of vapors or gases, which are characterized by substantial deviations from the perfect gas model. In extreme cases, even non-classical gas dynamic phenomena could occur. Although these non-ideal compressible flows are the subject of sophisticated numerical simulation studies today, there is also a growing need for experimental data for validating purposes. In the last couple of years, new experimental test rigs designed for investigating non-ideal compressible fluid dynamics have been developed and commissioned. Classical practical measurement techniques are currently being re-developed and applied to non-ideal compressible flows. Despite its substantial relevance, information about these measurement techniques and their differences from conventional methods in the open literature is scarce. The present review article is an attempt to reduce that gap. After briefly discussing the thermodynamics and fluid dynamics of non-ideal compressible flows, the currently available test rigs and their utilized measurement techniques are reviewed. This review discusses schlieren optical investigations, pneumatic and laser-optical methods, and hot-wire anemometry for non-ideal compressible flows.

Experimental and Simulation Study of the Latest HFC/HFO and Blend of Refrigerants in Vapour Compression Refrigeration System as an Alternative of R134a

Experimental and simulation investigation of the performance and characteristics of different refrigerants and blends of refrigerants is carried out to replace the existing refrigerant R134a for a vapour compression refrigeration system. The performance of VCRS systems was improved by several researchers by introducing the concept of mixing the family of refrigerants with low GWP in the working circuit. This research paper presents the performance results of different refrigerants and blends of refrigerants that can replace the R134a it is also an attempt to cover the mechanism and possible combination of different blends of refrigerants to improve the effectiveness as well as efficiency of the refrigeration system. Detailed analysis of different parameters of heat transfer and predictions of low-GWP refrigerants, including the HFO (hydro fluoro-olefin) class and the HC (hydrocarbon) class through energy and exergy analysis of commercial refrigerants such as R134a is performed. Results are obtained by using an experimental test rig and the input parameters of the experiments are kept the same with the simulation software (CYCLE_D-HX 2.0) and validated with the results to replace R134a.