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A Simple Method to Evaluate Heat Exchanger Performance

In this post, I want to share a simple method to evaluate heat exchanger performance. One of the most helpful ways to evaluate the performance of heat exchanger is to determine its effectiveness by comparing the actual heat transfer rate to the maximum rate that is thermodynamically feasible. The simple formula is expressed below.


η        = effectiveness

Q       = actual heat transfer rate

Qmax    = heat transfer rate which would be achieved if it were possible to bring the exit temperature of the stream with the lower heat capacity, to the inlet temperature of the other stream. Read More

How to Estimate Time Required for Heating or Cooling

In this post, I want to share how to estimate time required for heating and cooling.

The contents of a large batch reactor or storage tank frequently need to be heated or cooled. In this circumstance, the physical properties of the liquor may change throughout the process, as well as the overall transfer coefficient. When estimating the amount of time needed to heat or cool a batch of liquid, it is frequently possible to assume an average value for the transfer coefficient. Steam condensing, either in a coil or some type of hairpin tube heater, is a common method for heating the content of storage tank.

It is reasonable to assume that the overall transfer coefficient U is constant in the context of a storage tank filled with liquor having mass m and specific heat Cp and heated by steam condensing in a helical coil. The rate of heat transfer is given by: If T s is the temperature of the condensing steam, T1 and T2 are the initial and final temperatures of the liquor, A is the area of the heat transfer surface, and T is the temperature of the liquor at any time t, then:

The time t for heating from T1 to T2 can be determined using this equation. If the steam condenses in a reaction vessel’s jacket, the same analysis may be applied.

Heat losses during the heating or, for that matter, cooling operation are not considered in this analysis. The heat losses increase naturally as the temperature of the vessel’s contents rises, and at a certain point, the heat supplied to the vessel equals the heat losses, making further increases in the temperature of the vessel’s contents impossible.

By increasing the rate of heat transfer to the fluid, for example, by agitating the fluid, and by minimizing heat losses from the vessel by insulation, the heating-up time can be shortened.

The amount of agitation that can be achieved in a large vessel is constrained, thus one attractive alternative is to circulate the fluid through an external heat exchanger.

Let’s see example below on how to estimate time required for heating or cooling. Read More

Example How to Design Thin-Walled Vessel under Internal Pressure

In this post, I want to share a simple example on how to design thin-walled vessel under internal pressure. Please check my previous post about the method on how to estimate minimum thickness of vessel component (shell, flat end closures, domed head closures).


Estimate the thickness required for the component parts of the vessel shown in the diagram.

How to Design Thin-Walled Vessel under Internal PressureThe vessel is to operate at a pressure of 16 bar (absolute) and design temperature of 300oC. The material of construction will be plain carbon steel. Welds will be fully radiographed. A corrosion allowance of 2 mm should be used. Read More

How to Design Thin-Walled Vessel under Internal Pressure

In this post, I want to share how to design thin-walled vessel under internal pressure. I will also share a simple example about the application in the next post.

For information, I do not have any experience of the calculation in my whole career until posted this post. The design of thin-walled vessel under internal pressure is usually job of mechanical engineer. But it is good for process engineers to understand it in general.

The design of thin-walled vessel under internal pressure, in general, will be divided into two parts: design of cylinder and spherical shells and design of heads and closures. Read More

Types of Liquid-Solid Separation

Most process industries require the separation of solid and liquid phases, and several techniques are utilized to accomplish this. Figure below shows several types of liquid-solid separation techniques.

Liquid-solid separation methods
Liquid-solid separation methods

Gravity or centrifugal force can be used to separate materials based on their different densities, or in the case of filtration, the particle size and shape. The best method to apply will be specified by the solids concentration, feed rate, size, composition of the solid particles, the objective of separation (clear liquid or solid product), and degree of dryness of the solid required. Read More

How Air-Diaphragm Pumps Work

Air-diaphragm pumps (double diaphragm pumps) are one type of positive displacement pump. Their main applications are to transfer fluid, low pressure spray, and other low-pressure applications requiring less than 120 psig. They do not meet either ANSI or API standards and are most often used because of their profitability and ability to run on compressed air.

Air-diaphragm valves
Air-diaphragm valves

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General Selection Guidelines of Rotary Pumps

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

Basic Filtration Equation

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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Many Types of Cake Filters

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