The Use of SCO2 in Power Generation

Lab imageGlobal warming and the growing demand for energy are two primary problems rising in the power generation industry. A simple solution to these problems has been researched for a number of years. The SCO2 Brayton cycle is often looked into as an alternative working fluid for power generation cycles due to its compactness, high efficiency and small environmental footprint. The usage of SCO2 in nuclear reactors has been studied since the early 2000s in development of Generation IV nuclear reactors, but the idea itself can be traced back to the 1940s. During this time however, no one really looked into the potential of supercritical CO2 since steam was found to be efficient enough, not to mention it was the more understood technology when compared to SCO2. In modern times though, demand of more efficient energy continues to rise and with it, the need for SCO2.

The potential of supercritical CO2 implementation is vast across power generation applications spanning nuclear, geothermal and even fossil fuel.  The cycle envisioned is a non-condensing closed loop Brayton cycle with heat addition and rejection inside the expander to indirectly heat up the carbon dioxide working fluid.
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Gas Turbine Cooling Technology

Turbine Cooling Scheme Designed in AxSTREAM NET
Figure 1. Turbine Cooling Scheme Designed in AxSTREAM NET

People are pushing turbine inlet temperature to extremes to achieve higher power and efficiency. Material scientists have contributed a lot to developing the most durable material under high temperatures such as special steels, titanium alloys and superalloys. However, turbine inlet temperature can be as high as 1700˚C [1] and cooling has to be integrated to the system to prolong blade life, secure operation and achieve economic viability.

A high pressure turbine can use up to 30% of the compressor air for cooling, purge, and leakage flows, which is a huge loss for efficiency. It is worth it only if the gain of turbine inlet temperature can outweigh the loss of cooling. This applies to both aviation engines and land based gas turbines.

The history of turbine cooling goes back 50 years and has evolved to fit different environments. The diversity of turbine cooling technology we see today is just the tip of the iceberg. As time goes on and technology advances, people are able to achieve higher cooling efficiency at lower coolant usages. For different goals and needs, different constructs can be applied but the detailed cooling design must balance with the whole system and make the most of technological advances in the areas. For example, if the flow path is optimized, mechanical design is modified, or if new material is employed, the cooling design needs to change accordingly. One thing worth mentioning is that manufacturing of hot section components and turbine cooling design have an interdependent cause and effect, outpacing and leading each other to new levels. Merging of disciplines and additive manufacturing will, in the future, bring more flexibility to turbine cooling design.

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Leveraging AxSLICE for Centrifugal Pump Upgrades and Retrofits

Often, service companies are faced with the challenge of redesigning existing pumps that have failed in the field with extremely quick turnaround times. While there are quick-fix methods to return these pumps into operation, other more complex problems may require taking a step back and analyzing how this particular pump could be redesigned based on its current operation.  These engineering upgrades could solve recurring issues with failure modes of a certain machine, and they could also solve new capacity demands that are imposed by a customer based on their system’s upstream or downstream changes. While efficiency increases could be beneficial to the overall system, many times it is more important to solve capacity requirements and increase the life of the pump by decreasing the Net Positive Suction Head Required (NPSHr).

In this blog post, we will investigate how to move an existing centrifugal pump through the AxSTREAM platform in order to solve engineering challenges seen on common OEM pump upgrades.  With the use of AxSTREAM’s integrated platform and reverse engineering module, many of the CAE tasks that are common in an analysis such as this one can be realized in record speed. The first step of the reverse engineering process occurs in obtaining the necessary geometrical information for the desired pump. Through AxSLICE, the user can take an STL, IGES, CURVE file, or a generated cloud of points and properly transform this 3D profile into a workable geometry inside the AxSTREAM platform. In a matter of minutes, the user can outline the hub and shroud and transform a blank 3D profile into a profile defined by a series of segments.  Seen in Figure 1, the centrifugal pump is now defined by a hub, shroud, and intermediate section.

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Identifying Compressor Problems

Centrifugal Compressor for Refrigeration Because the most vital part of a refrigeration and HVAC system is to function optimally, compressors are used to raise the temperature and pressure of the low superheated gas to move fluid into the condenser. Consequently, refrigeration compressors must be properly maintained through regular maintenance, testing and inspection. There are a couple conditions which would indicate compressor problem or failures. However, with the right supervision it is possible to avoid further damage. Through this post we will identify and discuss some of these conditions:
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Helicopter Engines – Understanding the Constant Threats and Analyzing their Effects with AxSTREAM

Helicopter landing on a desert
Figure 1: Helicopter landing on a desert – burnout threat

The helicopter is a sophisticated, versatile and reliable aircraft of extraordinary capabilities. Its contribution to civil and military operations due to its high versatility is significant and is the reason for further research on the enhancement of its performance. The complexity of helicopter operations does not allow  priority to be given for any of its components. However, the main engine is key for a successful flight. In case of engine failure, the helicopter can still land safely if it enters autorotation, but this is dictated by particular flight conditions. This article will focus on the possible threats that can cause engine failure or deteriorate its performance.

When a helicopter is operating at a desert or above coasts, the dust and the sand can challenge the performance of the engine by causing erosion of the rotating components, especially the compressor blades. Moreover, the cooling passages of the turbine blade can be blocked and the dust can be accumulated in the inner shaft causing imbalance and unwanted vibration. The most common threat of this kind is the brownout which is caused by the helicopter rotorwash as it kicks up a cloud of dust during landing.

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The Benefits of a Variable Frequency Drive

Variable Frequency Drive is found to be very effective in assisting with energy management for HVAC systems. The main objective of this technology is to ensure that the motor only generates enough energy to power the compressor and no more. VFD provides constant load-matching capacity which results in the elimination of over-capacity running. Recently studied, current variable frequency drive benefits goes beyond the advantage of energy savings or energy efficiency. In conventional common application, the installation of variable frequency drive saves about 35% to 50% energy used by matching system capacity to the actual load.

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Demystifying S1-S2 Optimization in Turbomachinery

  1. Historically turbomachinery development began with empirical rules postulated by early pioneers. With the need for jet engine for aircraft propulsion, dimensionless analysis became popular, followed by the 1 D mean line design and 2D meridional methods. Today 2D meridional methods with 3D blade to blade CFD/FEA methods are a necessity as efficiency and reliability requirements are further pushed.

 

  1. One key aspect of 2D meridional design is S1-S2 optimization, which is a time consuming, laborious task and hence subject to human errors. S1-S2 optimization is a task of reviewing, adjusting and optimizing the flow path in the Tangential (S1 or blade-to-blade or pitchwise) and the Meridional (S2 or span wise) planes. The main purpose is to:
  • Fit the flow path to specific meridional dimensional constraints
  • Adjust blade-to-blade parameters while taking into account structural constraints.

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What Happened to R22?

R-22Freon (brand name by DuPont) used to be the regulated and most used refrigerant in the HVAC market. The chemical (R-22) was introduced to the refrigerant system in 1920. It consisted of hydrogen, carbon, fluorine and chlorine. HCFC was used in replacement to CFC or chloro-fluoro-carbon which is considered more dangerous. Within a few years, HCFC took over CFC’s role as the safer option.

Even though it was found to be safer than the alternative at the time, various recent studies state that R-22 is detrimental to the environment as it is a substantial ozone depleting substance that leads to greenhouse effects. Since January 2015, the maintenance or servicing of existing refrigeration, air condition and heat pump equipment using R22 has been prohibited by the EPA (Environmental Protection Agency) and related international agencies. Based on the Montreal Protocol, which prevents more damage to the ozone layer by banning all ozone deteriorating substances, R22 can no longer be used in any kind of application.

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History of Refrigeration

RefrigerationIn its natural state, heat flows from higher to lower temperature regions. Refrigeration cycles are utilized to modify or reverse this cycle, using work obliging heat to flow with the direction that is desired, and align with increasing temperature from low temperature region to higher.

During the earliest records of the “cooling” process being invented, people harvested ice to refrigerate, cool and conserve food. As time progressed, humanity’s basic needs changed and new ways to manipulate temperature started being explored. Major research into refrigeration began with the creation of pup to create a partial vacuum container which absorbs heat from the air. That being said, while the experiment was successful it did not have any practical applications.

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Design Process with AxSTREAM

Step 1: Basic inputs

– Input a set of boundary conditions, geometrical parameters and constraints that are known to the user.

Step 2: Design space generation

– Thousands of machine flow path designs can be generated from scratch
–  Explore a set of design solution points using the Design Space Explorer
–  Adjusting geometric parameters while retaining the desired boundary conditions is also possible

Preliminary Design
Figure 1: Design space
Post design geo modification B
Figure 2:  Post design geometry modification

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