## What is Convection and Its Problem Example

In previous post we learned what is conduction and its example on heat loss through a pipe wall with insulation. In this post, I want to share what is convection and its problem example.

Convection is heat transfer between a solid and an adjacent fluids develops as a result of fluid molecular movement. Cold molecules replace hot molecules as they leave the solid surface. A thin layer or film next to the solid surface is where most of the resistance to this type of heat transfer occurs. Even though the bulk fluid flow is extremely turbulent, this layer still exists.

Convective heat transport is governed by Newton’s law of cooling.

Q = h ∙A∙ ∆T

Where:

Q = heat transfer (Btu/hr)

h = heat transfer coefficient [Btu/(hr∙ ft2oF)]

A = area (ft2)

∆T = temperature difference (oF)

Convective heat transfer is divided into two types, natural or free convection and forced convection. Read More

## What is Conduction and Its Problem Example

In this post I want to share what is conduction and its problem example.

In contrast to general molecular motion or mixing, conduction describes the rate of heat transfer through materials as a function of vibrations and interactions between nearby molecules. Conduction always applies to solids and rarely to fluids.

There are several fundamental equations for steady heat conduction through some basic solid shapes, neglecting conditions of border:

## Sweep or Purge Gas Requirement for Flare

In many gas plant, flares are always installed to burn waste gases containing combustible components, such as methane, carbon monoxide, and hydrogen. The waste gases are piped to a remote, usually elevated location, and burned in open flame in ambient air using a specially designed burner tip, auxiliary fuel, and in some cases, assist gases like steam or air to promote mixing for nearly complete.

As mentioned in several posts, combustion requires three ingredients: fuel, an oxidizing agent (typically oxygen in air), and heat (or ignition source).

# Flare Purge Gas and Flare Sweep Gas

In flare system, a pipe connection for purging or sweeping purpose is usually installed. Flare purge gas means gas introduced between a flare header’s water seal and the flare tip to prevent oxygen infiltration (backflow) into the flare tip. For a flare with no water seal, the function of flare purge gas is performed by flare sweep gas.

Flare sweep gas means the gas intentionally introduced into the flare header system to maintain constant flow of gas through the flare header to prevent oxygen build up in the flare header. Read More

## Sizing and Horse Power Estimation of Counterflow Induced-Draft Cooling Tower

In this post I want to share to you how to do preliminary sizing and horse power estimation for counterflow induced-draft cooling tower. Calculation in this post parallel or cross-flow cooling tower. Also they do not apply when the approach to cold water temperature is less than 5oF (2.8oC).

Approach temperature is the temperature of the water leaving the cooling tower minus ambient wet bulb temperature.

[Read more: Assessment of Cooling Tower Performance]

To do this, we need this data:

• Hot water temperature
• Cold water temperature
• Wet-bulb temperature
• Water rate

Let’s start sizing the estimation. Let say we have cooling tower with the following process data:

• Hot water temperature = 102oF
• Cold water temperature = 78oF
• Wet-bulb temperature = 70oF
• Water rate = 1000 gallon per minute

Step 1: Find water concentration by using chart

Chart below is used to find water concentration, which is expressed in gallon per minute per square feet (gal/(min.ft2)).

When hot water temperature is 102oF and cold water temperature is 78oF, we get water concentration at around 2.8 gal/(min.ft2).

Step 2: Calculate required area of cooling tower

Required area of cooling tower is quantity of water circulated divided by water concentration = 1000/2.8 = 357.14 ft2.

Step 3: Find horsepower per area of cooling tower

Horsepower per area of cooling tower is estimated by using the following chart. Connecting the point representing 100 percent of standard tower performance with the turning point and extending this straight line to the horsepower scale show that it will give around 0.04 hp/ft2 of actual effective tower area. For a tower 357.14 ft2 (see Step 2), 14.6 hp is required to perform the necessary cooling.

Step 4: Check if commercial tower size is less than required area

Suppose the actual commercial tower size has an area of only 300 ft2. Within reasonable limit, the shortage of actual area can be compensated by increasing air velocity through the tower. This requires boosting fan horsepower to achieve 110 percent of standard tower performance. From chart in Step 3, we found the fan horse power is 0.057 hp/ft2 of actual area, or 0.057 x 300 = 17.1 hp.

Step 5: Check if commercial tower size is more than required area

On the other hand, if the actual commercial tower size is 370 ft2, the cooling equivalent to 357.14 ft2 of standard tower area can be accomplished with less air and less fan horsepower. From figure in Step 3, the fan horsepower for a tower operating at 90 percent of standard performance is 0.028 hp/ft2 of actual tower area, or 370 x 0.028 = 10.4 hp.

Reference:

Perry’s Chemical Engineers’ Handbook.

## Preliminary Sizing of Compressed Air Receiver

As a continuation of the post, I want to share you how to size capacity of compressed air receiver.

Compressed air receiver is used as buffer and storage medium between the compressor and air consumers.

A common formula used to size compressed air receiver is as followed: Read More

## Primary Treatment of Wastewater

Aims of primary treatment of wastewater is to separate suspended solids and greases from wastewater. What does primary treatment of wastewater remove? Sedimentation remove both organic and inorganic suspended solids. In addition, skimming, as part of sedimentation tank, remove grease, oil, scum, and floating solids.

Primary treatment of wastewater includes primary sedimentation (also called clarification), microscreen, Imhoff tanks. In most facilities, primary treatment is used as preliminary step ahead of biological treatment. Read More

## Wastewater Treatment – How Wastewater is Treated

In earlier posts, we learned sources of wastewater, which are domestic wastewater, industrial wastewater, and infiltration/inflow. In this post, I want to share to you how wastewater is treated.

Wastewater is treated at wastewater treatment plants before it is permitted to be discharged to the environment/water bodies. Basic function of wastewater treatment is to speed up the natural processes of water purification. Read More

## Where Does Wastewater Come From

Where does wastewater come? This basic question shall be answered if we want to design a wastewater treatment system. Source of wastewater, its characteristics, and its flow rate, will influence the type of technology to treat the wastewater.

Components that make up the wastewater depend on the type of collection systems. Urban wastewater that contribute to a wastewater treatment is originated from the following three main resources:

• Domestic (also called sanitary) wastewater. This type of wastewater is discharged from residential districts, commercial districts, institutional facilities, or recreational facilities.
• Industrial wastewater. Wastewater which predominantly consists of industrial waste.
• Infiltration/inflow.
• Infiltration is water entering a sewer system including service connections, defective pipes, pipe joints or manhole walls.
• Inflow is the water discharged into a sewer system from roof leader, cellar, yard and area drains, foundation drains, cooling water discharges, drains from springs and swampy area, manhole covers, cross connections from storm and combined sewers.

## What Is Wastewater Treatment

After a quite long absence of updating this blog, I want to begin this March’s post with refreshing our knowledge about wastewater treatment. Let’s begin with one fundamental question: what is wastewater treatment?

In general, wastewater treatment is a process converting wastewater into effluent that can be discharged back into the environment. This terms contains at least four keywords, which are wastewater, effluent, converting process, and environment.

## Sizing and Horse Power Estimation of Counterflow Induced-Draft Cooling Tower

In this post I want to share to you how to do preliminary sizing and horse power estimation for counterflow induced-draft cooling tower. Calculation in this post do not apply to counterflow cooling tower. Also they do not apply when the approach to cold water temperature is less than 5oF (2.8oC). Read More