#### Radial versus Diagonal Diffusion in Multi-Stage Pumps

Although crossover design has only a secondary effect on pump efficiency, it too should use every available trick to achieve the best possible results.

This picture (left and below) shows short and long configurations of the two basic types of crossovers normally used on multi-stage pumps. Both have been tested by the West Coast pump companies and the results of these tests indicate that the radial diffusion type is approximately one point more efficient than the diagonal diffusion type. Here’s why: Continue reading “Radial versus Diagonal Diffusion in Multi-Stage Pumps”

#### Cavitation Problems

Cavitation is not welcome in pumps. One of the most problematic effects of cavitation is the reduction in performance, but this is not the only problem! Cavitation can also cause damage to blades and create noise while the pump is working.

Perhaps, the most universal problem caused by cavitation is the material damage that bubbles can cause when they collapse in the vicinity of a solid surface. The problem is complex because it involves the details of a complicated unsteady flow combined with the reaction of the particular blade material. Continue reading “Cavitation Problems”

#### Axial and Mixed Pump Theory

Unlike the centrifugal pump, the performance in axial machines is a function of the action of the blade profiles. Because of this, the main approach in design of axial pumps is focused on blade performance.

Impeller blades of axial flow pumps have a double curvature form at the inlet and at the outlet due to the change in diameter from hub to periphery. Absolute flow before and after the impeller and relative flow along the impeller passage are axisymmetric and potential. There is no radial mixing. Under this condition, each streamline is parallel to the axis of the pump. Fluid passes parallel to the pump axis i.e., along the streamline. Continue reading “Axial and Mixed Pump Theory”

#### Criteria for Selecting Pumps – Specific Speed

We had a great week last week with our Steam and Gas Turbine Design workshop and we thank all of our participants who joined us in Boston and Zug, Switzerland! But like any rotating turbomachinery company, we’re rotating right along into another topic, pumps.

As with any turbomachine, when you’re in the process of selection, you should take into account a few factors depending on the application.

The specific speed should be the first parameter to take into account when designing and installing a new pump. Continue reading “Criteria for Selecting Pumps – Specific Speed”

#### Working Fluid in Organic Rankine Cycles

The choice of the working fluid for any given application is a key issue and should be done based on specific applications to achieve maximal efficiency. For working fluids in ORC, a green energy alternative, there are some requirements to keep in mind:

•Thermodynamic performance
Low pump consumption and high critical point

•Positive or isentropic saturation vapor curve
Avoid wetness in flow path, i.e. avoid damages of flow path elements

•High vapor density
Decrease sizes of equipment (expander and condenser)

•Acceptable pressures
High pressures usually lead to higher investment cost and increasing complexity

•High stability temperature
Prevent from chemical deterioration and decomposition at high temperatures

•Low environmental impact and safety level
•Good availability and low cost Continue reading “Working Fluid in Organic Rankine Cycles”

#### What’s An Ideal Heat Engine Cycle?

The Carnot cycle is the most efficient cycle possible for converting a given amount of thermal energy into work or, conversely, for using a given amount of work for refrigeration purposes.

Every thermodynamic system exists in a particular state. A thermodynamic cycle occurs when a system is taken through a series of different states, and finally returned to its initial state. In the process of going through this cycle, the system may perform work on its surroundings, thereby acting as a heat engine. Continue reading “What’s An Ideal Heat Engine Cycle?”