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Sunday, 7 July 2019

July 07, 2019

DIFFERENCE BETWEEN INWARD AND OUTWARD RADIAL FLOW REACTION TURBINE

We were discussing a new topic, in the subject of fluid mechanics and hydraulics machine, i.e. an introduction to hydraulic machinevarious types of hydraulic turbines and some important terminologies associated with a hydraulic turbine such as Gross head, Net head and efficiencies of a hydraulic turbine and also we have seen the fundamental of Pelton wheel or Pelton hydraulic turbine and basics of radial flow reaction turbines in our recent posts. 

Now we will focus here to understand the difference between inward radial flow reaction turbine and outward radial flow reaction turbine with the help of this post. 

So let us start here with the basics of inward radial flow reaction turbine and outward radial flow reaction turbine in order to understand the difference between both types of radial flow reaction turbines. 

First of all, let us recall the fundamentals of radial flow reaction turbine 

Let us first understand the meaning of radial here and then we will see the meaning of reaction in radial flow reaction turbines. 

Water will flow in radial direction in radial flow reaction turbines. Water may flow radially from outwards to inwards or from inwards to outwards. 

If water flows through the runner from outwards to inwards, turbines will be termed as inward radial flow turbine. 

If water flows through the runner from inwards to outwards, turbines will be termed as outward radial flow turbine. 

Inward radial flow reaction turbine 

If water flows through the runner from outwards to inwards, such turbines will be termed as inward radial flow turbines. 

Following figure shows the inward radial flow reaction turbine 

Water will enter in to the casing, from penstock, and from casing water will flow towards stationary guiding wheel. The guiding wheel will have guide vanes which will direct the water to enter the runner and turbine runner will have moving vanes. 

Water will flow over the moving vanes in the inward radial direction and water will be discharged at the inner diameter of the runner. 

Therefore the outer diameter of the runner will be considered as the inlet and inner diameter of the runner will be considered as the outlet. 

Outward radial flow reaction turbine 
If water flows through the runner from inwards to outwards, such turbines will be termed as outward radial flow turbines. 

Following figure shows the outward radial flow reaction turbine 

Water will enter, from casing, at the center of stationary guiding wheel. The guiding wheel will have guide vanes which will direct the water to enter the runner which is around the stationary guide wheel. 

Turbine runner will have moving vanes and water will flow over the moving vanes in the outward radial direction and water will be discharged at the outer diameter of the runner. 

Therefore the inlet diameter of the runner will be considered as the inlet and outer diameter of the runner will be considered as the outlet. 

Do you have any suggestions? Please write in comment box.  Further we will find out, in our next post, Francis turbine. 

Reference: 

Fluid mechanics, By R. K. Bansal 

Image courtesy: Google 

Also read  

Sunday, 30 June 2019

June 30, 2019

RADIAL FLOW REACTION TURBINE AND ITS COMPONENTS

We were discussing a new topic, in the subject of fluid mechanics and hydraulics machine, i.e. an introduction to hydraulic machinevarious types of hydraulic turbines and some important terminologies associated with a hydraulic turbine such as Gross head, Net head and efficiencies of a hydraulic turbine and also we have seen the fundamental of Pelton wheel or Pelton hydraulic turbine in our recent posts. 

Now we will focus here to understand the basics of Radial flow reaction turbines and we will also find out here the various parts of a radial flow reaction turbine with the help of this post. 

So let us start here with the basics of Radial flow reaction turbines 

Radial flow reaction turbines 

Do you have any idea about Radial flow reaction turbine? Why we have used word radial or reaction here? 

Let us first understand the meaning of radial here and then we will see the meaning of reaction in radial flow reaction turbines. 

Water will flow in radial direction in radial flow reaction turbines. Water may flow radially from outwards to inwards or from inwards to outwards. 

If water flows through the runner from outwards to inwards, turbines will be termed as inward radial flow turbine. 

If water flows through the runner from inwards to outwards, turbines will be termed as outward radial flow turbine. 

Now we will see here the meaning of reaction turbine. Reaction turbine means the water, at the inlet of turbine, will have kinetic energy and pressure energy. When water will flow through the runner, a part of pressure energy will be changing into kinetic energy. 

Water flowing through the runner will be under pressure. Runner will be completely enclosed in an air tight casing. Casing and runner will always be full of water. 

Main parts of a radial flow reaction turbine

There are following important parts of a radial flow reaction turbine.
  1. Casing
  2. Guide Mechanism
  3. Runner
  4. Draft-Tube

Casing 

As we have already discussed that in radial flow reaction turbine, casing and runner will always be full of water. Water will enter in to the casing from the penstock. Casing of a radial flow reaction turbine is displayed here in following figure. 

Casing of a radial flow reaction turbine will completely surrounds the runner of the turbine. Casing of a radial flow reaction turbine, as displayed above in figure, will be in spiral shape so that water may enter the runner at constant velocity throughout the circumference of the runner. 

Area of cross-section of the casing will be decreasing gradually. Material of casting of casing will be concrete, cast steel or plate steel. 

Guide Mechanism 

Guide mechanism will be basically a stationary circular wheel all around the turbine runner. There will be stationary guide vanes fixed on the guide mechanism and these guide vanes will allow the water to strike the vanes fixed on the turbine runner without shock at inlet. 

Width between two adjacent vanes of guide mechanism could be varied with the help of a mechanism in order to alter the amount of water striking the runner. 

Runner

Runner of a radial flow reaction turbine is basically a circular wheel on which a series of radial curved vanes will be fixed. Surface of these radial curved vanes will be made smooth in order to minimize the hydraulic losses. 

These radial curved vanes will be shaped in such a way that water may enter and leave the runner without shock. 

Runner will be fixed with the shaft with the key assembly. Material of casting of runner will be cast steel, cast iron and stainless steel. 

Draft-Tube

The pressure at the exit of the radial flow reaction turbine runner will be usually less than the atmospheric pressure and hence water at exit could not be directly discharged to the tail race. 

Therefore a tube or pipe of gradually increasing area will be used in order to discharge the water from the exit of turbine runner to the tail race. 

This tube or pipe of increasing area will be termed as draft tube. 

Do you have any suggestions? Please write in comment box.  

Further we will find out, in our next post, difference between inward and outward radial flow reaction turbine.  

Reference: 

Fluid mechanics, By R. K. Bansal 
Image courtesy: Google  

Also read  

June 30, 2019

GROSS HEAD NET HEAD AND EFFICIENCY OF TURBINE

We were discussing a new topic, in the subject of fluid mechanics and hydraulics machine, i.e. an introduction to hydraulic machine and various types of hydraulic turbines in our recent posts. 

Now we will focus here to understand some important terminologies associated with a hydraulic turbine such as Gross head, Net head and efficiencies of a hydraulic turbine with the help of this post. 

Will you be interested today to find out these important terminologies associated with a hydraulic turbine? 

So let us start here with the following important terminologies 

Gross Head 

Gross head is basically defined as the difference between the head race level and tail race level when water is not flowing. Gross head will be indicated by Hg as displayed here in following figure. 


Net Head 

Net head is basically defined as the head available at the inlet of the turbine. Net head is also simply called as effective head. 

When water will flow from head race to the turbine, there will be some losses of head due to friction between water and penstock. There will also be other losses of head such as loss of head due to bend, fitting, at entrance of penstock etc. We must note it here that these losses will be very less and could be neglected when we compare with head loss due to friction. 

Net head available at the inlet of turbine could be written as mentioned here. 

Net head, H = Gross head (Hg) – head loss due to friction (hf


Loss of head due to friction will be given by Darcy-Weisbach equation and we can find it here. 

Efficiencies of a turbine 

There are following important efficiencies that we will discuss here in this post.
  1. Hydraulic efficiency
  2. Mechanical Efficiency
  3. Volumetric efficiency
  4. Overall Efficiency 

Hydraulic efficiency 

Hydraulic efficiency is basically defined as the ratio of power given by water to the runner of turbine to the power supplied by the water at the inlet of the turbine. Hydraulic efficiency will be indicated by ηh

Runner is basically a rotating component of a turbine and buckets or vanes will be fixed at the circumference of the runner. 

Vanes or buckets fixed on the runner are not smooth and hence there will be hydraulic losses when water will flow through these vanes of the turbine. Therefore, power given by water to the runner of the turbine will be less than the power supplied by the water at the inlet of the turbine. 

Hydraulic efficiency of a turbine could be written as mentioned here

Hydraulic efficiency (ηh) = Power delivered to the runner of turbine / Power supplied at the inlet of turbine  Hydraulic efficiency (ηh) = R.P/ W.P

R.P = Power delivered to the runner of turbine
W.P = Power supplied at the inlet of turbine or water power 

Mechanical Efficiency 

Mechanical efficiency is basically defined as the ratio of power available at the shaft of the turbine to the power delivered to the runner of the turbine. Mechanical efficiency will be indicated by ηm.  

Power given by water to the runner of turbine will be transmitted to the shaft of the turbine. Power available at the shaft of the turbine will be less than the power delivered to the runner of the turbine due to mechanical losses. 

Mechanical efficiency of a turbine could be written as mentioned here

Mechanical efficiency (ηm) = Power available at the shaft of the turbine / Power delivered to the runner of the turbine
Mechanical efficiency (ηm) = S.P/ R.P

S.P = Power available at the shaft of the turbine
R.P = Power delivered to the runner of turbine 

Volumetric Efficiency 

The volume of the water striking the runner of a turbine will be slightly less than the volume of the water supplied to the turbine as some amount of water will be discharged to the tail race without striking the runner of the turbine. 

Volumetric efficiency is basically defined as the ratio of the volume of the water actually striking the runner of the turbine to the volume of water supplied to the turbine. Volumetric efficiency will be indicated by ηv

Volumetric efficiency of a turbine could be written as mentioned here  

Volumetric efficiency (ηv) = Volume of the water actually striking the runner of the turbine / Volume of water supplied to the turbine 


Overall Efficiency 

Overall efficiency is basically defined as the ratio of the power available at the shaft of the turbine to the power supplied by the water at the inlet of the turbine. Overall efficiency will be indicated by ηo.  

Overall efficiency, ηo = Power available at the shaft of the turbine / Power supplied by the water at the inlet of the turbine
Overall efficiency, ηo = S.P/W.P

Overall efficiency is also defined as the product of mechanical efficiency and hydraulic efficiency

Overall efficiency = Mechanical efficiency x Hydraulic efficiency
ηo = ηm x ηh

Do you have any suggestions? Please write in comment box. 

Further we will find out, in our next post, Pelton wheel turbine and its components.

Reference: 

Fluid mechanics, By R. K. Bansal 
Image courtesy: Google 

Also read  

Wednesday, 26 June 2019

June 26, 2019

PELTON WHEEL TURBINE AND ITS COMPONENTS

We were discussing a new topic, in the subject of fluid mechanics and hydraulics machine, i.e. an introduction to hydraulic machine, various types of hydraulic turbines and some important terminologies associated with a hydraulic turbine such as Gross head, Net head and efficiencies of a hydraulic turbine in our recent posts. 

Now we will focus here to understand the basics of Pelton wheel or Pelton hydraulic turbine and we will also find out here the various parts of Pelton wheel or pelton hydraulic turbine with the help of this post. 

So let us start here with the basics of Pelton wheel or Pelton hydraulic turbine

Pelton wheel or Pelton hydraulic turbines

Pelton wheel or Pelton hydraulic turbine is basically a tangential flow impulse turbine. In pelton wheel, water will strike the bucket along the tangent of the runner. 

Energy available at the inlet of the turbine will be kinetic energy. Pressure available at the inlet and outlet of the turbine will be atmospheric pressure. Pelton wheel or Pelton hydraulic turbuine is used for high heads. 

Following figure, displayed here, indicates the layout of hydroelectric power plant where pelton wheel hydraulic turbine is used to produce the electric energy. 

Water from the reservoir will flow through the penstock at the outlet of which there will be one nozzle. Nozzle, provided at the outlet of penstock, will increase the kinetic energy of the water flowing through the penstock. 

Water will come in the form of jet at the outlet of nozzle and this water jet will strike the bucket of the runner. 

Let us see here the main parts of the Pelton turbine

  1. Nozzle and flow regulating arrangement
  2. Runner and buckets
  3. Casing
  4. Breaking jet

Nozzle and flow regulating arrangement

The amount of water which will strike the buckets of the runner will be controlled by spear arrangement in the nozzle as displayed here in following figure. 

Spear is basically a conical needle which will be operated by hand wheel or automatically in the axial direction depending upon the size of the unit. 

In order to reduce the amount of water striking the buckets of the runner, spear will be moved forward into the nozzle. Similarly, in order to increase the amount of water striking the buckets of the runner, spear will be moved backward into the nozzle. 

Runner and buckets

Following figure, displayed here, indicates the runner of a Pelton wheel. It will have one circular disc and a number of buckets will be fixed evenly on the surface of periphery of this circular disc. 

The shape of the bucket will be a double hemispherical cup or bowl. Each bucket will be divided into two symmetrical parts by a dividing wall which is known as splitter. 

The jet of water will strike on the splitter and hence water jet will be divided in two parts by splitter and water jet will come out at the outer edge of the bucket. Buckets will be shaped in such a way that water jet will be deflected through 160 or 170 degree. 

Material selection of buckets will be based on the head at the inlet of the turbine. Buckets are usually made of cast iron, stainless steel or cast steel. 

Casing

Following figure indicates the casing of a Pelton wheel hydraulic turbine. 

There is no hydraulic function which will be performed by casing of pelton wheel turbine. Casing is basically used in order to prevent the splashing of the water and to discharge water to tail race. 

Casing also provides the safeguard against any accident. Material of casting of casing of pelton wheel turbine will be cast iron or fabricated steel plates. 

Breaking jet

As we have already discussed that in order to reduce the amount of water striking the buckets of the runner, spear will be moved forward into the nozzle. 

When the nozzle is completely closed by moving the spear in forward direction, the amount of water striking the buckets of the runner will be zero. 

But as we are quite aware that runner will keep moving for a long time due to its inertia and therefore a breaking jet will be provided to stop the runner in short interval of time. 

A nozzle is provided to direct the water jet on the back of vanes and this jet of water will be termed as breaking jet. 

Do you have any suggestions? Please write in comment box.  Further we will find out, in our next post, Radial flow reaction turbine

Reference: 

Fluid mechanics, By R. K. Bansal 
Image courtesy: Google 

Also read  

Wednesday, 15 May 2019

May 15, 2019

HYDRAULIC TURBINES AND THEIR CLASSIFICATION

We were discussing a new topic, in the subject of fluid mechanics and hydraulics machine, i.e. an introduction to hydraulic machine in our recent posts. 

Now we will focus here to understand the basics of hydraulic turbines and classification of hydraulic turbines with the help of this post. Further we will find out, in our next post, some important terminologies associated with a hydraulic turbine such as Gross head, Net head and efficiencies of a hydraulic turbine. 

So let us start here with the basics and classification of hydraulic turbines. 

Hydraulic turbines 

Hydraulic turbines are basically defined as the hydraulic machines which convert hydraulic energy in to mechanical energy and this mechanical energy will be given to a generator to produce electric energy.

Now there will be one question that how this mechanical energy will be given to electric generator. Electric generator will be directly coupled with the hydraulic turbine and therefore mechanical energy, developed by hydraulic turbines, will be transmitted to electric generator and hence mechanical energy will be converted in to electrical energy. 

Electric power developed from hydraulic energy will be considered as hydroelectric power. We have used here term i.e. hydraulic energy that indicates the energy of water. 

Classifications of hydraulic turbines 

Hydraulic turbines will be classified on the basis of the type of energy available at the inlet of the hydraulic turbine, direction of flow through the vanes, head at the inlet of the hydraulic turbine and specific speed of the hydraulic turbine. 

Let us find out here a brief classification of hydraulic turbines as mentioned here. 

According to the type of energy at the inlet of the turbine

  1. Impulse turbine
  2. Reaction turbine

Impulse turbine:

If the energy available at the inlet of the hydraulic turbine is only kinetic energy, the hydraulic turbine will be considered as Impulse turbine.

Reaction turbine:

If the energy available at the inlet of the hydraulic turbine is kinetic energy and pressure energy, the hydraulic turbine will be considered as Reaction turbine. 

According to the direction of flow through runner

  1. Tangential flow turbine
  2. Radial flow turbine
  3. Axial flow turbine
  4. Mixed flow turbine 

Tangential flow turbine:

If the water flows along the tangent of the runner, the hydraulic turbine will be considered as Tangential flow turbine.

Radial flow turbine:

If the water flows in radial direction through the runner, the hydraulic turbine will be considered as Radial flow turbine. 

If the water flows in radial direction through the runner from outwards to inwards, the hydraulic turbine will be considered as inward radial flow turbine. 

If the water flows in radial direction through the runner from inwards to outwards, the hydraulic turbine will be considered as outward radial flow turbine. 

Axial flow turbine:

If the water flows through the runner along the direction parallel to the axis of rotation of the runner, the hydraulic turbine will be considered as axial flow turbine. 

Mixed flow turbine:

If the water flows through the runner in the radial direction but leaves in the direction parallel to the axis of rotation of the runner, the hydraulic turbine will be considered as mixed flow turbine. 

According to the head at the inlet of the turbine

  1. High head turbine
  2. Medium head turbine
  3. Low head turbine 

According to the specific speed of the turbine

  1. Low specific speed turbine
  2. Medium specific speed turbine
  3. High specific speed turbine 

Do you have any suggestions? Please write in comment box. 

Further we will find out, in our next post, some important terminologies associated with a hydraulic turbine such as Gross head,Net head and efficiencies of a hydraulic turbine

Reference: 

Fluid mechanics, By R. K. Bansal 
Image courtesy: Google   

Also read  

Tuesday, 14 May 2019

May 14, 2019

INTRODUCTION TO HYDRAULIC MACHINES

We have seen various topics such as  force exerted by a jet on vertical flat plate,  force exerted by a jet on stationary inclined flat plateforce exerted by a jet on stationary curved plateforce exerted by a jet on a hinged plate,  force exerted by a jet on a curved plateforce exerted by a jet of water on a series of vanes,  force exerted by a jet of water on a series of radial curved vanes and basics of jet propulsion of ships in our recent posts. 

Now we will start here a new topic i.e. Hydraulic Machine with the help of this post. 

An introduction to hydraulic machine 

Let us first understand here the fundamental meaning of hydraulic machine. 

Hydraulic machines are basically defined as those machines which convert either hydraulic energy in to mechanical energy which will be further converted in to electrical energy or mechanical energy in to hydraulic energy. 

We can classify the hydraulic machines broadly in following two types as mentioned here

Hydraulic Turbine
Hydraulic Pump 

Hydraulic machines which convert hydraulic energy in to mechanical energy will be termed as hydraulic turbines. 

Let us see here Francis turbine as displayed here in following figure. 

Hydraulic machines which convert mechanical energy in to hydraulic energy will be termed as hydraulic pumps. 

Let us see here centrifugal pump as displayed here in following figure. 

Now we will be focused here and in our next post basically on the study of hydraulic turbines and hydraulic pumps. 

We will discuss hydraulic turbines in detail and further we will also find out the various types of hydraulic turbine such as Pelton turbine, Francis turbine and Kaplan turbine. 

Similarly, we will discuss hydraulic pumps in detail and further we will also find out the various types of hydraulic pumps such as reciprocating pumps and centrifugal pumps. 

Do you have any suggestions? Please write in comment box.  

Further, we will see hydraulic turbine and their classification, in the subject of fluid mechanics, with the help of our next post. 

Reference: 

Fluid mechanics, By R. K. Bansal 
Image courtesy: Google   

Also read