Experimental Investigation of the Effect of Turbulator Geometry on the Thermal Performance of Gas-Fired Boilers

Experimental investigation, using 3D digital image correlation, into the effect of component geometry on the wrinkling behaviour and the wrinkling mechanisms of a biaxial NCF during preforming

Effect of geometry and thermal mass of Direct-Metal-Laser-Sintered aluminium Heat Exchangers filled with phase change materials on Lithium-Ion cells’ passive cooling

The pressures and loads induced on the center of the end-wall of a shock tube by a shock wave that passes through different types of obstacles are investigated. Efforts have been made to understand the effect of the obstacle geometry on the load development. The experiments were conducted in a shock tube apparatus in which a modular test section was implemented. It is found that for a single-obstacle setup, the effect of the geometry becomes dominant when the blockage ratio (i.e., the ratio of the non-open area to the overall cross section) is large. It is also found that the attenuation effect is more pronounced for general geometries, which form diverging-like nozzle. In the case of multi-obstacles geometry, the same sensitivity to the blockage ratio as in the single-obstacle case is found. However, amplification or attenuation of the shock-wave load on the center of the end-wall of a shock tube is observed when the number of the obstacles is increased. This is due to different trapping effects of the shock wave between the obstacle and the end-wall.

This work addresses an experimental investigation on the cleavage fracture behavior of an ASTM A572 high strength, low alloy structural steel using standard and non-standard SE(B) specimens, including a non-standard PCVN configuration. One purpose of this study is to develop a fracture toughness test procedure applicable to bend geometries with varying specimen span over width ratio (a/W) and loaded under 3-point and 4-point flexural configuration. We provide a new set of plastic η-factors applicable to these non-standard bend geometries which serve to estimate the experimentally measured toughness values in terms of load-displacement records. Another purpose is to investigate the effects of geometry and loading mode in fracture tests using non-standard bend specimens. Fracture toughness testing conducted on various bend specimen geometries extracted from an A572 Grade 50 steel plate provides the cleavage fracture resistance data in terms of the J-integral at cleavage instability, Jc. The experimental results show a potential effect of specimen geometry and loading mode on Jc-values which can help mitigating the effects of constraint loss often observed in smaller fracture specimens. An exploratory application to determine the reference temperature, T0, derived from the Master Curve methodology also provides additional support for using non-standard bend specimens in routine fracture applications.

Numerical and experimental investigation of the effect of geometry on combustion characteristics of solid-fuel ramjet

Experiments have been conducted to investigate the overall thermal performance of a rectangular channel implemented with an elongated pedestal array. The staggered pedestals were elongated in the spanwise direction in order that the jet flow from between the pedestals impinges at the centre of the pedestals in the downstream row. The average heat transfer coefficient of the pedestal and the local heat transfer coefficient distribution of the bottom channel wall were investigated for different geometrical arrangements. The pressure drop across the pedestal bank was measured. The transient liquid crystal method was used to obtain the local heat transfer coefficient distribution on the bottom channel wall and the lumped capacitance method was used to measure the average heat transfer coefficient of the pedestals in the last two rows of the bank. Five pressure taps were arranged on the centerline of each gap between two pedestal rows to measure the pressure drop. The heat transfer coefficients were measured over the Reynolds number range from 10,000 to 30,000. The minimum flow area to the channel cross-section flow area ratio ranged from 0.149 to 0.333. The effects of pedestal geometry and array distribution were investigated in detail showing the relationship between the pedestal array geometry, heat transfer enhancement and pressure drop. Conclusions were drawn on the effects of geometry and flow conditions on overall thermal performance of the respective channels.

Machining of WC material presents a challenge due to its specific properties, particularly high hardness and brittleness. The Electrical Discharge Drilling (EDD) process is preferred for the production of small-diameter holes on difficult-to-cut materials. This study presents an experimental investigation of the effects of tool electrode geometry and material on the drilling performance and hole accuracy of WC-26%Co. Blind holes were produced under specific process conditions using tubular electrodes made of brass and copper, featuring single and multiple channels. The Material Removal Rate (MRR) and Electrode Wear Rate (EWR) were measured as process outputs to evaluate the impact of electrode material and geometry on drilling performance. Hole accuracy was also assessed based on the shape of drilled holes as well as enlargement in hole diameter, referred to as Overcut (OC). The set of experiments with utilization of each geometry and channel configuration of tool electrode were repeated for three times, and the results indicated good reliability. Compared to the single-channel electrode, the central protrusion at the hole center was significantly eliminated with the use of the multi-channel electrode, resulting in improved drilling performance as well as the achievement of an accurate hole shape. Among the average values of results from all sets of experiments, the multi-channel brass electrode provided the highest MRR (74.31 mg min−1), EWR (30.57 mg min−1), and OC (20.60%) with an accurate shape. Furthermore, the surfaces of holes drilled by multi-channel electrodes are relatively cleaner and more uniform due to less pronounced surface anomalies.

The effect of geometry on the performance of the closed tube thermosyphon at low Rayleigh numbers

Influence of Shoulder Geometry and Coating of the Tool on the Friction Stir Welding of Aluminium Alloy Plates

Indirect two-phase cooling with refrigerants allows management of CPU/GPU heat loads well in excess of those that can be managed with water cooling. Two-phase mini channel boilers are at the heart of such systems. Similar to single-phase cold plates, the performance of mini-channel boilers depends on proper selection of design parameters such as fin pitch, thickness and total surface area that ultimately dictates the number of fins. But unlike single-phase cold plates, two-phase cold plates must also take into account ancillary issues such as boiling flow instabilities, vapor generation and potential loss of coolant that severely affect thermal performance. The traditional metric used in assessing the thermal performance of boilers is thermal resistance, which can be used for comparative studies but does not offer a true assessment of cooling limits. In this paper, we introduce a new definition of heat exchanger effectiveness for two-phase boilers that can be used to compare actual performance to maximum performance and by its definition can also establish cooling limits. We show that the thermal resistance is directly related to the effectiveness. By first maximizing effectiveness, the design thermal resistance can be achieved by the proper sizing of an optimized heat exchanger core. The methodology is first validated for single-phase liquid cold plates by comparing the thermal resistance obtained from the proposed approach to that obtained from the commonly used definition. The proposed approach is demonstrated on experimentally characterized boilers found in the literature. The experimentally determined effectiveness for these test boilers demonstrate s the utility o f the technique.

The current models of boilers and furnaces which are used in HVAC system simulation programs are primarily concerned with calculating the heat output of the device and its fuel consumption. The formulation of the models relies heavily on empirical terms that are derived from manufacturers' data or testing programs. This paper describes a one-dimensional modeling approach that enables the emissions of NOx, CO, and SOx to be calculated together with the thermal performance of the boiler derived from basic heat transfer relationships. The model was developed for boilers with outputs in the range 100 kW to 3 MW. It provides good prediction of heat transfer performance and reproduces the values and trends of emissions throughout the operating range of the device. The use of the model in its intended mode is shown by its incorporation in a TRNSYS system simulation.

The seasonal operating cost of a small oil or gas-fired boiler or furnace depends upon the intrinsic merits of the device itself, the appropriateness of its capacity and cycle characteristics to the imposed load conditions, the weather characteristics and heat loss characteristics of the building being heated, and the control philosophy employed. The current study provides the bases for comparing quantitatively the seasonal operating costs of various specific space heating and/or domestic hot water systems, as influenced by the device specifics and device interaction with the space conditioned system that it serves. The resulting formalism is applied to various space-heating systems. Quantitative cost comparisons are presented.

The effects of hydrogen fraction (HF: volumetric fraction of H2 in the fuel mixture of CH4 + H2) from 0% to 100% by volume, on the thermal and environmental performance of a 207-MW industrial water tube boiler, are investigated numerically at a fixed excess air factor, λ = 1.15. This study aims to determine the hardware modifications required for boilers to be retrofitted for pure hydrogen operation and investigates how NOx emissions are affected by hydrogen enrichment. The results showed insignificant increases in maximum combustion temperature with increasing the HF, though the distributions of temperature profiles are distinct. In reference to the basic methane combustion, H2 flames resulted in a positive temperature rise in the vicinity of the burner. Increasing the HF from 0% to 2% resulted in higher average thermal NOx emissions at the boiler exit section from 37 up to 1284 ppm, then it decreased to 1136 ppm at HF = 30%, and later it leveled up to 1474 ppm at HF = 100%. The spots for higher differences in NO formation compared to the reference case are shifted downstream at higher HFs. The effect of hydrogen enrichment on CO2 and H2O as radiation sources, as well as the volumetric absorption radiation of the furnace wall and the heat flux at furnace surfaces, has all been presented in relation to the effect of hydrogen addition on boiler performance.

Efficiency and emissions of gas-fired industrial boiler fueled with hydrogen-enriched nature gas: A case study of 108 t/h steam boiler

This study is a three-dimensional research on the heat and fluid flow within the domestic cast-iron sectional boilers (CIBs). Considerations are focused on the shape effects of the hot gas passages on the boiler performance. For this purpose, various hot gas passage shapes such as the circle (Case-1), hexagon (Case-2), square (Case-3), and ellipse (with a constant aspect ratio of 2, Case-4) have been examined and compared with each other. Computations are performed under two practical water flow rates of 0.015 and 0.030 kg/s. For enhanced visualization, several results have been demonstrated in the present study. It is found that the shape of the hot gas passage in a domestic CIB affects the heat and fluid flow within the section, strongly. On the other hand, it is revealed that among the cases under consideration, the square shape (Case-3) for the hot gas passage has the best thermal performance with minimum pressure drop in a sectional CIB. It was hoped the obtained results arouse interest among the boiler designers.