Minimizing Environmental Impacts of Geothermal Energy


Geothermal energy is categorized as a “green energy”, with low emission of approximately 5% of carbon dioxide, 1% H2S, 1% sulfur dioxide and less than 1% of the nitrous oxide of an equal sized fossil or coal power plant. Concentrations of each environmentally disruptive gases are controlled by temperature, composition of fluid, and geological setting. Although most of the geothermal emissions commonly come from existing geothermal resource gas, some percentage of the emission also comes from various processes of the energy conversion process. Non-condensable gases are also emitted as a part of high temperature process of geothermal energy conversion.

According to various studies, the type of geothermal power plant design would really impact the production rate of the mentioned gasses. The selection between open-loop and closed (binary)-loop system is essential while taking into consideration air emission. Geothermal plants to this date are commonly separated into three main cycle design: dry-steam, flash-steam or binary –the first two extensively generate more greenhouse gasses (GHGs) compared to the last. In a binary loop system, gases which are removed from the system will not be transferred to the open atmosphere, instead, after transferring the heat gasses will be run through back to the ground, and result in minimal air pollution. In contrary, open-loop system emits all of the emission gas contained such as hydrogen sulfide, carbon dioxide and many more. There are also different factors which cause the technology to emits gases that are naturally present in the fluid such as fluid chemistry/composition, fluid phase, and geological setting to temperature.

The main types of air emission or contamination within the application of geothermal energy are commonly found to be carbon dioxide and hydrogen sulfide. Hydrogen sulfide reacts to produce SO2 once touched with the atmosphere. SO2 is known for its hazardous nature to health and environment, causing acid rain and respiration problem. Even though the concentration of this gas emission is significantly smaller than a conventional fuel power plant, reduction of hydrogen sulfide emission is still desirable for any conditions. Types of condensers installed to the design determines the ratio between the condensable and non-condensable gas. Consequently, with the right selection of condenser as well as implementing other reduction plans such as installation of adsorption tower, etc, hydrogen sulfide emission could be minimized.


A Reasonable Approach to Pump Design While Avoiding Resonance

For the majority of pump application, the growing use of variable speed operation has increased the likelihood of resonance conditions that can cause excessive vibration levels, which can negatively impact pump performance and reliability. Mechanical resonance is the tendency of a mechanical system to absorb more energy when the frequency of its oscillations (external excitation source) matches the system’s natural frequency of vibration more than it does at other frequencies. To avoid vibration issues, potential complications must be properly addressed and mitigated during the design phase.

Some of the factors that may cause excitation of a natural frequency include rotational balance, impeller exit pressure pulsations, and gear couplings misalignment. The effect of the resonance can be determined by evaluating the pumping machinery construction. All aspects of the installation such as the discharge head, mounting structure, piping and drive system will affect lateral, torsional and structural frequencies of the pumping system. It is advised that the analysis be conducted during the initial design phase to reduce the probability of reliability problems and the time and expense associated.

Natural frequencies of a pump and motor can be calculated by performing a modal analysis using the Finite Element Method Analysis (FEA). The finite element modelling and analysis techniques provide an understanding of the mechanical system behaviour, including the natural frequency values during design phase.

Understanding the predicted natural frequency values allows an evaluation of the expected separation between the pump natural frequency and excitation frequencies, such as pump operation speed. The separation is established by the pump manufacturer to avoid mechanical resonance.

The boundary conditions assumed during FEA are essential to the accuracy of predicted results. In some cases, the final as-built conditions (such as foundation stiffness) significantly affect the analysis accuracy if they differ from those conditions assumed during the analysis. In such case a pump test is recommended. Tests like that indicate that increasing the natural frequency of the system is the best solution. This increase in natural frequency could be accomplished by modifying two of the pump system’s physical characteristics, reducing mass or increasing stiffness of the system.

It is therefore important to know the type of acceptable solution that will provide the best pump operation. And this is where AxSTREAM adds significant value at the design process. Using SoftInWay fully integrated engineering platform the customers are able to optimize the pumping machine, and next to perform all the necessary structural analysis using AxSTRESS, our express structural, modal and harmonic analysis FEM solver with a customizable, automatic turbomachinery-specific mesh generation.


Development of Molten Salt Energy Storage

Over the past couple of years, energy storage technology has significantly evolved to meet engineering demand and political regulations. This wasn’t initially looked as a desirable investment due to the high production cost, however over time, exploration of such technology by bigger companies has driven down the manufacturing cost and generated more demand. With occurrences such as rapid capital raise of smaller start-up companies, to the acquisition of Solar City by Tesla, the market of energy storage is predicted to continue growing. The technology allows for collection of energy produced to be used at a later time. Energy storage systems have wide technology variation to manage power supply – from thermal, compressed air to everyday batteries.

blog-post-2-image-1Molten Salt Usage

The usage of molten salt in thermal energy storage applications has become more common. In commercial solar energy storage, molten salt (from potassium nitrate, lithium nitrate and more) is used in conjunction with concentrated solar energy for power generation. Molten salts are able to absorb and keep heat energy transferred from the fluid mediator, then to transfer it again when it’s needed. In the liquid state, molten salt has a similar state to water. It also has the capacity to retain temperatures of  1000 Fahrenheit. Though efficiency is known to be lower than other storage media such as batteries, (70% vs 90%), the main advantage of the usage of molten salt is lower costs which allows the technology to be implemented in a higher volume production.

How Molten Salt Energy Storage Works

Using solar energy as the main source of energy, heliostats (mirrors used to track sun/solar heat) are used to reflect the solar radiation into an energy receiver at the power plant. Molten salt then is used to collect this heat energy from the concentrated pool. The molten salt will later be stored. When power is needed, hot molten salt is transferred to a HX (or steam generator) to produce steam at a high pressure and temperature. The steam then will be used for electricity generation as the live steam in a conventional steam power plant. After exiting the generator, molten salt will then be transferred back to the thermal storage tank to again absorb energy.

The Benefits of Molten Salt Energy

There are three main benefits of molten salt energy storage – reliability, economic savings and environmental friendliness. While in a liquid state, molten salt improves long term reliability as well as reduces operation and maintenance cost. The capital cost of the material itself is also relatively cheap and easily accessible. Molten salt is also known as a non-toxic compound, thus completely green and comparable to fertilizer.


Interested in designing and optimizing your molten salt energy storage? Check out AxCYCLE!

Impeller Design Challenges on Integrally Geared Centrifugal Compressors

The integrally geared compressor, also known as a multi-shaft compressor, is a technology that has been around since the 1960s, but remains underdeveloped.  Usually seen in applications in the industrial gases industry, integrally geared compressors (IGCs) can range in size from small product machines to steam turbine driven high-horsepower, high-flow compressors for air separation plants.  These compressors modular construction principle, consisting of as many as eight different stages, allows for implementation in a large number of varied customer processes.  The main advantages of IGCs in the industrial gases industry is the compact design and smaller installation footprint, efficiency increases due to the use of multiple speeds for separate impellers, and overall lower operational and installation costs.

Figure 1 – Semi-Open Impeller

One of the key design differences between the standard inline compressors and the IGCs is that the integrally geared compressor makes use of both closed AND semi-open impellers.  The reason for the use of open impellers in IGCs are the higher strengths due to better manufacturing techniques, speed of manufacture, and the inherent lower costs.  However, the main drawback to having an open impeller in your system is that in the event of impeller rub, the damage to the compressor would be significantly worse than with a closed impeller.

Engineers have introduced several techniques in order to minimize this risk.  Axial position monitoring of the pinions as well as the use of high-speed thrust bearings can result in an improvement against this rub phenomenon.  However, even with these innovative solutions, open impellers still have a much larger tip clearance (clearance / blade height) then its closed impeller counterparts.  It is very important to realize the efficiency decrease present in compressors with varying tip clearances.

In SoftInWay’s latest update for its turbomachinery design and analysis software, AxSTREAM™, calculating models were improved for centrifugal compressors with large tip clearances.  By taking into account the additional flow deviation from the direction of the blade’s tail as well as the flow recirculation in the meridional direction, better estimates for the flow models can be identified on compressors with tip clearances greater than 0.1.

Figure 2 – Flow Characteristic on a Compressor with Large Tip Clearance

Although integrally geared compressors present several elegant solutions in the industrial gases industry and overall show higher efficiencies than single rotor compressors, many different challenges arise when working with them.  Among them are the impeller blade design challenges mentioned above as well as numerous additional challenges to rotor dynamics that these intricate gearing designs introduce.  SoftInWay has worked alongside MAN Diesel & Turbo since 2005 to solve these problems and many others. To learn more about designing integrally geared compressors or for an in-depth look into our rotor dynamics software please explore the links below.

Integrally Geared Compressors 

AxSTREAM for Rotor Dynamics




The Balancing Act – Rotor Stability

When designing rotating equipment, it is extremely important to take into account the types of unbalance that can occur. Forgetting this step can result in vibrations that lead to damage of the rotating parts, increasing maintenance costs and lowering efficiency. Currently, if a rotating part already vibrates or makes any noises, maintenance engineers rely on OEMs (Original Equipment Manufacturer) or third parties services companies to conduct balancing services.

Types of Unbalances

Figure 1: Static and Couple Forms of Unbalance

The three types of unbalances to consider are static, couple and dynamic. Static unbalance (Figure 1) occurs when a mass at a certain radius from the axis of rotation causes a shift in the inertia axis. Couple unbalance, usually found in cylindrical shapes, occurs when two equal masses positioned at 180 degrees from each other cause a shift in the inertia axis, leading to vibration effects on the bearings. Lastly and most common, dynamic unbalance occurs when you have a combination of both static and couple unbalance.

Balancing Methods used Today

Figure 2 High-Speed Balance

Two of the most popular balancing methods that are performed on existing turbine rotors are low-speed balancing and high-speed balancing methods. A low-speed balance helps determine wear and tear on rotor under minimum speed conditions. This method is generally used by companies who lack access to a high-speed balance cell. A high-speed balance (Figure 2) allows the test be run at or passed operating speed, and even though it is more expensive, it tends to be a more accurate method of testing. The primary reason why  more end users are opting for this type of balance, for both turbine rotors and power generator fields, is that all major components can be tested under rigorous conditions. By doing this, the full operating lives of these components can accurately be determined.

Want to make sure you’re taking into account unbalances when designing rotors in rotating equipment? Look into our rotordynamics software capabilities 


Reciprocating Machinery Dynamics by Abdulla S. Rangwala – Chapter 9

The Importance of Turbulence Modelling

What is the importance of turbulence modelling in capturing accurate 3D secondary flow and mixing losses in turbomachinery? An investigation on the effect of return channel (RCH) dimensions of a centrifugal compressor stage on the aerodynamic performance was studied to answer this question by A. Hildebrandt and F. Schilling as an effort to push turbomachinery one step further.

W. Fister was among the first to investigate the return channel flow using 3D-CFD. At that time the capability of commercial software was not extended and any computational effort was limited by the CPU-capacity. Therefore, only simplified calculations that included constant density without a turbulence model (based on the Prandtl mixing length hypothesis) embedded in in-house code, were performed.

Although separated flow without a predominant flow direction could not have been calculated, the method indicated separated flow regions with relatively accurate precision, and it predicted the magnitude of loss coefficients to a higher degree than experimental data. The study was further
simplified using incompressible flow, and an axial U-turn inlet flow.AxCFD

The biggest drawback of using inverse methods for return channel design refers to the question of appropriate flow distribution across the RCH surface. Furthermore, flow separation cannot be predicted with the help of singularity methods. In order to circumvent the problem of predicting flow separation, nowadays compressible viscous 3D-CFD applied with different highly complex turbulence modeling is the state of the art even at the conceptual stage of the design.

Hildebrandt and F. Schilling analyzed three different centrifugal stages regarding the return channel system performance. All three stages featured the same impeller type, two of them being applied with a 3D-RCH at different flow coefficient and one impeller being applied with a 2D-RCH system. The 3D-RCH stage featured both CFD calculated and measured superior aerodynamics over the 2D-RCH stage regarding the overall performance as well as regarding the outlet flow angle. The comparison between the measured and the CFD-predicted performance showed agreement both when it comes to overall performance (efficiency, pressure rise coefficient) and also regarding detailed flow field (outlet flow field). The 3D secondary flow and mixing losses of the entire domain downstream the vaneless diffuser were either underestimated or overestimated by the CFD-calculations, depending on the turbulence modeling and the impeller fillet radii-modeling which affects the RCH-inlet flow conditions. The effect of fillet radii-modeling on the RCH-exit flow angle spanwise distribution was found to be significant in order to better match the experimental results.

It is worth noting that the rather simple Spalart–Allmaras turbulence model provided better agreement with the measured RCH-exit flow angle distribution than the more sophisticated k-epsilon model, which on the other hand, outputted a closer fit with the measured surface vane pressure distribution. Regarding the RCH total pressure loss distribution, none of the models showed a perfect agreement with the measurement data.

Moreover, the incident losses of the 3D-RCH system seemed to play a minor role within the overall RCH-loss which is significantly dominated by the 3D-secondary losses.

Interested in learning more? Check out AxSTREAM and AxCFD!

[1] A. Hildebrandt and F. Schilling, 2017 “Numerical and Experimental Investigation of Return Channel Vane Aerodynamics With Two-Dimensional and Three-Dimensional Vanes”, Journal of Turbomachinery Vol. 139 / 011010-1

[2] Fister, W., Zahn, G., and Tasche, J., 1982, “Theoretical and Experimental Investigations About Vaneless Return Channels of Multi-Stage Radial Flow Turbomachines,” ASME Paper No. 82-GT-209.

The Future of Turbocharger Technology

­One of the main setbacks in scaling different turbochargers for diesel, petrol, and gas engines is the inherit variability that different turbochargers would exhibit at low or high RPMs. In order to understand this further, a common term used to describe a flow characteristic of these machines is the A/R ratio.  Technically, this ratio is defined as the inlet cross-sectional area divided by the radius from the turbo center to the centroid of that area (Figure 1).  This ratio is essentially a metric for the amount of air that is allowed into the turbine section of the turbocharger.

Ratio visualization
Figure 1 – A/R Ratio Visualization

For smaller turbochargers, lower A/R ratios allow the fast exhaust velocities to drive the turbine at lower speeds.  This results in a more responsive engine and overall higher boosts at lower RPMs.  However, once a vehicle starts to navigate at a higher RPM, smaller turbochargers experience a significant reduction in performance due to the high backpressure present in the system.  This occurs because of the low A/R ratio limits the flow capacity and does not allow a sufficient amount of air to feed into the turbine.  The same effect is present for larger turbochargers, only in reverse.  They will perform most efficiently at higher RPMs, but in turn exhibit a significant reduction in performance at lower RPMs.

In order to overcome this phenomenon, many engineers have developed more complex turbocharger systems over the years, which attempt to leverage the benefits of each type of turbo.  One of the first solutions to this dilemma was the twin turbo: simply comprised of two separate turbochargers operating in the system in parallel or in series.  The problem with this system is that it disproportionately increases the cost, complexity, and space necessary for implementation.

Other technologies are very common for overcoming this problem without the use of two separate turbos.  One design is the twin-scroll turbocharger, which works like a pair of turbochargers connected in parallel.  Instead of using two separately sized turbochargers, the twin-scroll design has two exhaust-gas inlets and two nozzles feeding into a single turbocharger.  Another design, the variable geometry turbocharger, uses internal vanes within the turbocharger to dynamically alter the A/R ratio of the system at different rev levels.  The variable geometry turbocharger (VGT) displays exceptional performance at the low and high RPM ranges, however, it requires the use several moving parts and exotic materials in order to handle the high exhaust temperatures present in petroleum engines.  For this reason, the variable geometry turbocharger is generally only used in diesel engines due to the relatively low exhaust temperatures in comparison.  Twin-scroll turbochargers, while more commonly used in gasoline applications, do not have the variability of the VGT and are not as efficient over the full rev range of the vehicle.

Figure 2 – BorgWarner Twin-Scroll Variable Geometry Turbocharger Concept

BorgWarner has recently showcased a new turbocharger concept that makes use of both technologies discussed above.  The “Twin-Scroll Variable Geometry Turbocharger” has a valve that can redirect airflow from just a single scroll to an airflow completely split between two scrolls.  It allows for the any range in between these extremes much like the VGT; however, it only uses only one valve as opposed to the several vanes needed in the VGT.  It derives the same exhaust separation idea as the twin-scroll while allowing for the variability of the VGT.  With all the new emissions regulations calling for increases in efficiency, it will be interesting to see if this new technology can find its way into the market.


Optimizing the Cooling Holes in Gas Turbine Blades

To increase the overall performance of the engine and reduce the specific fuel consumption, modern gas turbines operate at very high temperatures. However, the high temperature level of the cycle is limited by the melting point of the materials. Therefore, turbine blade cooling is necessary to reduce the blade metal temperature to increasing the thermal capability of the engine. Due to the contribution and development of turbine cooling systems, the turbine inlet temperature has doubled over the last 60 years.

Figure 1: Variations of Thermal Efficiency with TIT [1]
The cooling flow has a significant effect on the efficiency of the gas turbine. It has been found that the thermal efficiency of the cooled gas turbine is less than the uncooled gas turbine for the same input conditions (see figure 1). The reason for this is that the temperature at the inlet of turbine is decreased due to cooling and therefore, work produced by the turbine is slightly decreased. It is also known that the power consumption of the cool inlet air is of considerable concern since it decreases the net power output of  the gas turbine.

With this in mind, during  the design phase of gas turbine it is very important to optimize the cooling flow if you are considering both the performance and reliability. Cooled Gas turbine design is quite complicated and requires not only the right methodology, but also the most appropriate design tools, powerful enough to predict the results accurately from thermodynamics cycle to aerothermal design, ultimately generating the 3D blade.

Different cooling methods that are employed depend on the extent of the cooling required. The cooling flow passes through several loops internally and is then ejected over the blade surface to mix with the main flow. The mixing of the cooling flow with the main flow alters the aerodynamics of the flow within the turbine cascade. The cooling flow that is injected into the main flow needs to be optimized, not only in terms of thermodynamic parameters, but also  in terms of the locations to ensure the turbine vanes and blade surfaces are maintained well below the melting surface. The spacing between the holes, both in horizontal and vertical direction, affects not only the surface temperature of the blade, but also the strength of the blade and its overall life.

Performing a 3D analysis for optimizing the flow, spacing, and location of cooling flow is computationally expensive. A 1D flow and heat network simplifies the task of not only arriving at the optimal configuration of cooling holes and location, but also in aerothermal design of the gas turbine flow path and generation


of the optimized 3D blades with reduced overall design cycle time. Designers are faced with the challenge of simplifying the complex 3D cooled blade and accurately modelling it. AxNET, the module for 1-dimensional flow and heat transfer provides designers options to not only use the different components and models inbuilt in the module but also customize to represent the 3D blade as accurately as possible in a simplified approach


To learn more about how AxSTREAM Net can help you optimize the cooling holes in gas turbine blades, please contact us at or


[1] Amjed Ahmed Jasim Al-Luhaibi and Mohammad Tariq, “Thermal Analysis of cooling effect on gas turbine blade” International Journal of Research in Engineering and Technology, eISSN: 2319-1163, pISSN:2321-7308

Exotic Turbomachinery – Viscous Disc Pumps

Turbomachinery can be divided into two main groups. Group one consists of machines that perform work on the fluid, requiring energy and increasing its pressure, such as compressors, pumps, and fans. Group two consists of those that extracts energy from the fluid flowing through it – for example, wind, hydro, steam, and gas turbines.

Pumps specifically are devices whose purpose is to move fluid at a constant density, increasing its kinetic energy and its pressure while consuming energy in the process. We are quite used to seeing centrifugal and axial pumps, as they are the most common configurations.  However, more exotic designs have been tested and developed throughout the history of fluid machinery.

VTeslaiscous disk pumps are one such design – inspired by the concept of Tesla Disc Turbine, and conceived and developed in 1913. The key feature of these turbines is the bladeless design, consisting of multiple parallel rotating discs within a casing. Additionally, its operating principle is based in the so-called boundary layer effect. The main difference from a conventional turbine design is that there is no impingement of the rotating parts on the fluid.

As shown in figure 1, the nozzle is inserting the fluid to the discs’ edge, which is dragged by the moving fluid through its viscosity and fluid adherence to the discs’ surface. After energy is transferred to the discs, the fluid gets extracted by the center exhaust.

The same set of discs and a slightly different shape of casing/volute can be used as a pumping device, which is also called a boundary layer disc pump.

Even if Tesla’s turbine design didn’t undergo further development, the disc pump design found its purpose in highly demanding pumping applications.


In the last 30 years this type of pump has found its niche in high viscosity fluids and low Reynolds number flows. For instance, common applications include the pumping of crude oil, sludge, food pulps and wastewaters. They offer excellent pumping capacity for fluids with enthralled gases or delicate solid particles.

Due to its operating principles, flow is similar to an ordinary pipe with parabolic velocity profiles and stationary layers of fluid (relative to the rotating discs). This allows enthralled gases or solid particles to remain located in the core of the flow with no contact to the discs. As such, the reliability and lifetime for these pumps is very high, as the moving parts show little to no deterioration and require minimal maintenance.


In these conditions, viscous pumps show much higher efficiency despite the lower level of complexity when compared to their conventional counterparts with centrifugal design. Less complexity means lower maintenance and lower costs.

Simplicity of the design in these pumps also shows promising application in microfluidics with different miniaturized designs for drugs transportation and biomedical applications, such as blood transportation with no damage to plasma particles. Also in these operating conditions with low Reynolds flow, disc pumps have shown efficiencies as high as 95%, much higher than a centrifugal or displacement counterpart. Different designs have been investigated and proposed, involving 1, 2 or more bladed discs, depending on the application and size.

Despite of the advancements in the design of turbomachinery, and the increase in computing power allowing more and more complex fluid dynamics analyses, viscous disc pumps remain a unique case that shows that complexity and over-development do not necessarily equal higher efficiency and performance.


“Single-Disk and Double-Disk Viscous Micropump” – D. Blanchard, P. Ligrani and B. Gal – Sensors  and Actuators A-Physical, 122, 149-158, 2005

“Analytical and experimental modeling of a viscous disc pump for MEMS applications” – Marco D. C. Oliveira and José C. Páscoa

The Origin of Rotordynamics

Rotordynamics, the study of vibrational energy in rotors, has a rich history dating back to North America during the 1750’s. This branch of applied mechanics began with theories, but advanced quickly due to practices – starting with Mr. W.J.M Rankine in 1869 and his spinning shaft experiment. Now, decades later, we have strengthened our understanding of rotordynamics and created leading software tools, including AxSTREAM, that are able to simulate analyses to stabilize and increase the reliability of a turbomachinery.

W.J.M Rankine

Not only was W.J.M Rankine a prestigious theoretical scientist and educator, he was a main contributor in the development of rotordynamics and he contributed to thermodynamics and the development of heat engines throughout his lifetime. During his spinning shaft experiment, he concluded that beyond the shaft’s first critical speed, the shaft would be unstable simply because its shape had been bent. By not taking into consideration support damping and Coriolis force in his analysis, many engineers were left confused for almost two centuries, until Gustaf de Laval, a Swedish engineer, ran a steam turbine to supercritical speeds in the late 1880’s. Laval also introduced the use of bearings to oppose absolute motion in his machinery. As the years went by, many other engineers discovered and investigated additional phenomenons (FEM for example) that have an influence in today’s practices.
It is because of these previous innovators that companies like SoftInWay have been able to develop the advanced  rotodynamics modules that we use today.

AxSTREAM, for example is a prime example of this. The software tool saves engineering time and cost and it ensures that no destructive rotor dynamicsvibration will occur in the rotor-bearing system. It is able to perform many analyses like Static Gravity Deflection, Critical Speeds, Damped Unbalance Response, Modal and Transient. It is because of the rich history of rotordynamic development that software platforms like AxSTREAM are able to ensure the best design and performance for your turbomachinery.

Figure 2: Demostration of AxSTREAM RotorDynamics