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General Selection Guidelines of Rotary Pumps

Rifka Aisyah

In this post, I want to share to you general selection guidelines of rotary pumps.

Rotary pumps are positive displacement pumps. However, they are different from reciprocating pumps because they have relatively steady and non-pulsating flow. Rotary pumps are generally selected to handle very high viscosity fluid or if the flow rate is too low to be handled economically by other pumps.

There are several common applications of rotary pumps:

  • Transferring gasoline, fuel oil, diesel fuel into tanks or day tanks
  • Supplying fuel oil to burners
  • Running lubricant through the bearings of process machinery, turbines, reduction gears, and engines.

Before we jump into the general selection guidelines of rotary pumps, I think we need to understand several terms that related to rotary pumps, such as slip, volumetric efficiency, and mechanical efficiency, and of course several types of rotary pumps. Read More

Efficiencies of Centrifugal and Axial-Flow Compressors

Rifka Aisyah

In this post, I want to share the approximate efficiencies of centrifugal compressors and axial-flow compressors. We may have already heard about these terms: polytropic efficiency and isentropic (adiabatic) efficiency. What are those?

Polytropic efficiency is frequently used in compressor evaluation. It is frequently referred to as small stage efficiency. The polytropic process is a modification of the adiabatic process, involving an efficiency to represent actual conditions more closely. The performance of centrifugal compressors is frequently compared using the polytropic compression method.

On the other hand, isentropic (adiabatic) efficiency compares actual compression to an ideal compression (adiabatic) in which no heat is exchanged with the environment and no losses are produced (no viscosity and reversible). It is isentropic because it is adiabatic and reversible. The adiabatic process that compresses with the least amount of work is hence the isentropic process. Read More

How To Calculate Sonic Velocity

Rifka Aisyah

In this post I want to share how to calculate sonic velocity. Before we jump into the equation, let’s review about sonic velocity briefly.

Sonic velocity or critical velocity is the maximum velocity that can be attained by a compressible fluid. We usually use this parameter in sizing pipe, control valve, and flare.

Sonic velocity is a function the following parameters:

  • Ratio of specific heats in the gas (k or Cp/Cv)
  • Temperature
  • Molecular weight of the gas

The molecular weight is expressed in absolute temperature, therefore we will use temperature unit of oR or oK. Read More

How to Check if a Horizontal Pipe Carrying Liquid is Full

Rifka Aisyah

In this post I want to share how to check if a horizontal pipe carrying liquid is full or partially full. We can use the following criteria to check:

  • The pipe is full if: Q/d5 ≥ 10.2
  • The pipe is partially full if: Q/d5 < 10.2

For partially full pipe, we need to do partially full flow analysis as follows.

x = ln (Q/d2.5)

Then we calculate height of liquid in the pipe using the following equation:

H/D = 0.446 + 0.272x + 0.0397x2 – 0.0153x3 – 0.003575x4 Read More

Basic Filtration Equation

Rifka Aisyah

Let’s learn the basic filtration equation which may be useful in sizing and evaluating many types of filtration unit. Disclaimer, this is also the first time in my working life learning about filtration equation, so if you find any mistakes, please feel free to comment below.

There are two terms in basic filtration equation. The first is, if the filtration occurs at constant pressure. And the second is, if the filtration occurs at constant flow rate. If the filtration occurs at constant pressure, then the flow rate will progressively diminished because the filter bed is steadily growing in thickness. Whereas, if the filtration occurs at constant flow rate, then the pressure must be gradually increased.


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Several Types of Clarifying Filtration

Rifka Aisyah

In previous post, I shared several types of filtration methods and more about cake filters. In this post, I want to share to you several types of clarifying filtration.

Read also: Introduction to Filtration

Read also: Many Types of Cake Filters

The main objective of clarifying filters is to remove small amounts of solids or liquid droplets from either liquids or gases. The liquid may be drinking water, wine, beer, oil, etc., and it is usually the liquid which is the valuable product.

In clarifying filters, the particles are trapped inside the filter medium or on its surfaces. Surface forces catch the particles and immobilize them on the surfaces or within the flow channels.

In general, clarifying filtration are categorized into liquid clarification and gas cleaning. Read More

A Simple calculation on How to Determine Time Required to Obtain Certain Volume of Filtrate

Rifka Aisyah 1 Comment

In this post, I want to share how to do a simple calculation on determination of time required to obtain certain amount of filtrate in a filtration test. We will still use basic equation as in previous post.

Read previous post: How to Determine Cake Resistance in Filtration Systems

For example, we have this case.

A filter press with a surface of 50 m2

C (weight of solid per volume of liquid) = 135 kg solid/m3 liquid

μ = 0.001 N sec/m2

α (specific resistance of the cake) = 1.1 (1011) m/kg

Rf (resistance of filter cloth) = 6.5 (1010) m-1 Read More

Many Types of Cake Filters

Rifka Aisyah 1 Comment

In previous post, there are three general types of filters, which are cake filters, clarifying filters, and crossflow filters. In this post, I want to share specifically about many types of cake filters.

When slurry enters cake filters, some solid particles enter the pores of the medium and are immobilized, but soon others begin to collect on the septum surface. A visible cake of significant thickness builds up on the surface and must be periodically removed. Cake filters are used almost entirely for liquid-solid separations.

Cake filters may operate with above-atmospheric pressure upstream from the filter medium or with vacuum applied downstream. Either type can be continuous or discontinuous, but most pressure filters are discontinuous.

Figure below shows many types of cake filters. Read More

How to Determine Cake Resistance in Filtration Systems

Rifka Aisyah 2 Comments

Purpose of this post is to determine cake resistance in filtration systems, as a function of operating pressure of filter. Before we jump into the calculation, let us learn first several basic calculation in filtration system.

As filtration proceeds, a porous cake of solid particles is built up on a porous medium, usually a supported cloth. The flow of liquid is laminar because of the fineness of the pores. Therefore, the following equation represented the phenomena:

Q = \frac{{dV}}{{dt}} = \frac{{A\Delta P}}{{\mu R}}

The resistance R is made up of filter cloth Rf and that of cake Rc which may be assumed proportional to the weight of the cake. Read More