What Is Heat Transfer

[caption id="attachment_198" align="alignright" width="300" caption="what is heat transfer"][/caption]

Heat transfer is considered as one of the most basic discipline of chemical engineering & technology. It generally concerns with generation, consumption and conversion of heat energy in the system. Heat transfer; it self plays a very important role in process industries, and it is always better for the process industries, to optimize their heat transfer processes [may include furnaces, evaporators, distillation units, dryers, reaction vessels etc] by the selection of proper heat exchangers, preventing heat losses and controlling the heat flow rate.

Heat transfer under normal conditions always flows from a hotter region to a cooler region, i.e. heat transfer follows the temperature gradient between the two systems [or system and surrounding], until a thermal equilibrium is maintained between the two systems.  However, according to the “Clausius statement of second law of thermodynamics”, if the work is done on the system, the heat can flow from a colder region to a hotter region. This Clausius statement is the basic principle behind the working of refrigerators.

Now how to calculate heat transfer :

\[Q=UAΔT\]

Where,

Q = transfer of heat per unit time
A = heat transfer area
ΔT = temperature difference between two systems

This is the most basic expression to define heat transfer, there are several other heat transfer formulas derived from this expression. Picture at the right side is taken from images by dan.

There are three forms of heat transfer:

1) Conduction

Conduction is generally considered as the heat transfer phenomena for the solids, however conduction can also occur in fluids too [in microscopic level, like diffusion phenomena]. In solids, Conduction is the result of transfer of vibration energy from one molecule to other, while in fluids, it occurs in addition as a result of transfer of kinetic energy. Conduction follows the Fourier Law of Heat Conduction:

\[Q=-kAΔT\]

Where,

Q = transfer of heat per unit time
k = conductive heat transfer coefficient
A  = heat transfer area
ΔT = temperature difference between two systems

  The thermal conductivity units in SI system is W/mK.

2) Convection

Convective heat transfer occurs when the heat is transferred from a solid surface to a moving fluid owing to the temperature difference between the solid and the fluid. Convection follows the Newton’s Cooling Law of Heat Convection:

\[Q=hA(T-T_{'})\]

Where,

Q = transfer of heat per unit time
h = convection heat transfer coefficient
A  = heat transfer area
T = temperature of fluid
T'= temperature of solid

3) Radiation

All materials radiate thermal energy in the form of electromagnetic waves. So radiation is the transfer of heat by the emission of electromagnetic waves. When they fall on the body, they may partially be reflected, transmitted or absorbed. Radiation is that fraction which falls and absorbed by the body.

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What Is Heat Transfer

Heat transfer is considered as one of the most basic discipline of chemical engineering & technology. It generally concerns with generation, consumption and conversion of heat energy in the system. Heat transfer; it self plays a very important role in process industries, and it is always better for the process industries, to optimize their heat transfer processes (may include furnaces, evaporators, distillation units, dryers, reaction vessels etc) by the selection of proper heat exchangers, preventing heat losses and controlling the heat flow rate.

Heat transfer under normal conditions always flows from a hotter region to a cooler region, i.e. heat transfer follows the temperature gradient between the two systems (or system and surrounding), until a thermal equilibrium is maintained between the two systems.  However, according to the “Clausius statement of second law of thermodynamics”, if the work is done on the system, the heat can flow from a colder region to a hotter region. This Clausius statement is the basic principle behind the working of refrigerators.

Now how to calculate heat transfer :
                                                           Q = UAΔT

Where,
  Q = transfer of heat per unit time
  A = heat transfer area
  ΔT = temperature difference between two systems

This is the most basic expression to define heat transfer, there are several other heat transfer formulas derived from this expression.

There are three forms of heat transfer:

1) Conduction

Conduction is generally considered as the heat transfer phenomena for the solids, however conduction can also occur in fluids too(in microscopic level, like diffusion phenomena). In solids, Conduction is the result of transfer of vibration energy from one molecule to other, while in fluids, it occurs in addition as a result of transfer of kinetic energy.

Conduction follows the Fourier Law of Heat Conduction:

                                                          Q = -kAΔT

Where,
  Q = transfer of heat per unit time
   k = conductive heat transfer coefficient
  A  = heat transfer area
 ΔT = temperature difference between two systems

  The thermal conductivity units in SI system is W/mK.

2) Convection

Convective heat transfer occurs when the heat is transferred from a solid surface to a moving fluid owing to the temperature difference between the solid and the fluid.

Convection follows the Newton’s Cooling Law of Heat Convection:

                                                        Q = hA(T – T')
Where,
  Q = transfer of heat per unit time
   h = convection heat transfer coefficient
  A  = heat transfer area
  T = temperature of fluid
  T'= temperature of solid

3) Radiation

All materials radiate thermal energy in the form of electromagnetic waves. So radiation is the transfer of heat by the emission of electromagnetic waves. When they fall on the body, they may partially be reflected, transmitted or absorbed. Radiation is that fraction which falls and absorbed by the body.

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What Are Fertilizers

[caption id="attachment_217" align="alignright" width="300" caption="what are fertilizers"][/caption]

Fertilizer industry is one of the most important industries. To study that what are fertilizers, the basics of chemical engineering are required. Types of fertilizer depend on the thorough study of the nature of the soil, and the type of the plants. So first, it is important to review the plants physiology and needs then we can move on to what are fertilizers.

.

Plants have the natural ability to convert carbon dioxide from the atmosphere and inorganic components of the earth directly into the fats, proteins and high energy carbohydrates. So the plants are the essential elements for the nutrition and growth of humans as well as the animals too. For a plant to grow properly, it needs sun light, air, water and minerals. As discussed above, the plant takes these minerals from the earth, but some times the soil has the deficiency of the certain minerals so these minerals are added manually, and are named as fertilizers. So,

.

“The fertilizers are the minerals [nutrients], which are added to soil to improve its fertility”.

Some decades before, the agriculture was totally based on the empirically developed agricultural practices. But now, the plant physiology, and its nutrition involves a general process engineering knowledge, as scientific study leads a chemical engineer to required fertilization or photosynthesis level.

The plant needs approximately 22 different chemical elements for proper growth. The three primary nutrients of fertilizers are nitrogen [N – helps in the growth of plants], phosphorous [P – encourages blooming, rooting and fruit production], or potassium [K – resists plant diseases and resist in winter hardness, the 3 secondary nutrients are Magnesium (Mg) , Calcium (Ca) and Sulfur (S), while the 3 essential elements are Carbon (C), Hydrogen (H) and Oxygen (O). Plants obtain these elements from carbon dioxide (CO_2) and water (H_2O).

Types Of Fertilizers

The types of fertilizer are:

1) Organic/natural fertilizers

These fertilizers are derived from the organic / naturally occurring sources. The human or animal wastes, slurry [needs to be metal free], bones, fish meal, blood and similar substances are the main content of the fertilizer. Normally these types of nutrients are not chemically treated. The mineral content of these fertilizers is comparatively lower than the synthetic one, but has the benefit of being natural, increase biological and physical nutrient storage of the soil; increases soil moisture content, and also mitigate the risk of over fertilization.

2) Synthetic fertilizer

These fertilizers are composed of synthetic minerals or chemicals, so these are also named as synthetic fertilizer or inorganic fertilizers. As all the minerals used for the production of these fertilizers are synthetic, so we use several other processes to prepare the raw materials. A process engineer normally recommends using the Haber-Bosch process for the production of synthetic ammonia. This synthetic ammonia is generally used in other nitrogen fertilizers like urea or anhydrous ammonium nitrate. These synthetic fertilizers are generally used to treat maze, barley, soy, sunflower fields. Also the studies show that nitrogen fertilizers can increase the bio mass of these crops, along with the beneficial effect on the nitrogen level of the soil. Unlike the organic fertilizers, they don’t take too much time for the growth of the plant, but synthetic fertilizer provides the appropriate actions for plant growth in required time frame.

Forms Of Fertilizers:

Mostly, fertilizers are used in the granular [powder] form, however liquid fertilizers are also widely produced and used.

Environmental Concerns Of Fertilizers

There are several environmental concerns with the poor handling of fertilizers. The general environmental problems are

Eutrophication – i.e. Phosphorous is contaminated on the soil, is bound to soil particles and can not be washed out. It indirectly stimulates the growth of algae. These types of algae die, decompose and remove oxygen from the water causing harm to water life.

Contamination of water with phosphates and nitrates. The general process engineering practice describes that the higher level of nitrates in drinking water is hazardous for human health.

Nitrogen remaining in the soil is converted into nitrates by bacteria. These nitrates can be washed out from the surface into river streams, or can be leached into the ground water.

Read More

What Are Fertilizers

Fertilizer industry is one of the most important industries. To study that what are fertilizers, the basics of chemical engineering are required. Types of fertilizer depend on the thorough study of the nature of the soil, and the type of the plants. So first, it is important to review the plants physiology and needs then we can move on to what are fertilizers.

Plants have the natural ability to convert carbon dioxide from the atmosphere and inorganic components of the earth directly into the fats, proteins and high energy carbohydrates. So the plants are the essential elements for the nutrition and growth of humans as well as the animals too. For a plant to grow properly, it needs sun light, air, water and minerals. As discussed above, the plant takes these minerals from the earth, but some times the soil has the deficiency of the certain minerals so these minerals are added manually, and are named as fertilizers. So,

           “The fertilizers are the minerals (nutrients), which are added to soil to improve its fertility”.

Some decades before, the agriculture was totally based on the empirically developed agricultural practices. But now, the plant physiology, and its nutrition involves a general process engineering knowledge, as scientific study leads a chemical engineer to required fertilization or photosynthesis level.

The plant needs approximately 22 different chemical elements for proper growth. The three primary nutrients of fertilizers are nitrogen (N – helps in the growth of plants), phosphorous (P – encourages blooming, rooting and fruit production), or potassium (K – resists plant diseases and resist in winter hardness, the 3 secondary nutrients are Magnesium (Mg) , Calcium (Ca) and Sulfur (S), while the 3 essential elements are Carbon (C), Hydrogen (H) and Oxygen (O). Plants obtain these elements from carbon dioxide (CO2) and water (H2O).

The types of fertilizer are:

1) organic/natural fertilizers

These fertilizers are derived from the organic / naturally occurring sources. The human or animal wastes, slurry (needs to be metal free), bones, fish meal, blood and similar substances are the main content of the fertilizer. Normally these types of nutrients are not chemically treated. The mineral content of these fertilizers is comparatively lower then the synthetic one, but has the benefit of being natural, increase biological and physical nutrient storage of the soil; increases soil moisture content, and also mitigate the risk of over fertilization.

2) Synthetic fertilizer

These fertilizers are composed of synthetic minerals or chemicals, so these are also named as synthetic fertilizer or inorganic fertilizers. As all the minerals used for the production of these fertilizers are synthetic, so we use several other processes to prepare the raw materials. A process engineer normally recommends using the Haber-Bosch process for the production of synthetic ammonia. This synthetic ammonia is generally used in other nitrogen fertilizers like urea or anhydrous ammonium nitrate. These synthetic fertilizers are generally used to treat maze, barley, soy, sunflower fields. Also the studies show that nitrogen fertilizers can increase the bio mass of these crops, along with the beneficial effect on the nitrogen level of the soil. Unlike the organic fertilizers, they don’t take too much time for the growth of the plant, but synthetic fertilizer provides the appropriate actions for plant growth in required time frame.

Forms Of Fertilizers:

Mostly, fertilizers are used in the granular (powder) form, however liquid fertilizers are also widely produced and used.

Environmental Concerns Of Fertilizers

There are several environmental concerns with the poor handling of fertilizers. The general environmental problems are

Eutrophication – i.e. Phosphorous is contaminated on the soil, is bound to soil particles and can not be washed out. It indirectly stimulates the growth of algae. These types of algae die, decompose and remove oxygen from the water causing harm to water life.

Contamination of water with phosphates and nitrates. The general process engineering practice describes that the higher level of nitrates in drinking water is hazardous for human health.

Nitrogen remaining in the soil is converted into nitrates by bacteria. These nitrates can be washed out from the surface into river streams, or can be leached into the ground water.

Read More

Types of catalysis

In my last post, I have discussed about the general catalysis phenomena, and its most basic types. But the homogeneous and heterogeneous catalysis are not the only types of the catalysis. The chemical engineer also classifies catalysis on the basis of the nature of species responsible for the catalytic activity. These types are mostly inter-related with other types of the same nature. E.g. molecular catalysts can be used as homogeneous, as well as heterogeneous catalysts, Surface catalysts are heterogeneous catalysts etc. Some of the types are:

1) Molecular Catalysis:

This term is used for the systems, where identical molecular species are the catalytic entity. Many of these catalysts are used as homogeneous catalysts, but these can also be used in heterogeneous (multi-phase) catalysis.

2) Surface Catalysis:

Surface catalysis takes place on the surface atoms of the extended solid. It depends on the different properties of the surface atoms, and different types of the molecular sites. Surface catalysts are solid, so these are heterogeneous catalysts by nature.

3) Enzyme Catalysis:

Enzymes are proteins, polymers of amino acids, so this type of catalysis is used to catalyze reactions in living organism, biological and biochemical reactions. The enzyme catalysis is usually molecular catalysis.

4) Auto Catalysis:

In autocatalysis, there is no need to use a separate catalysis, but in a reaction one of the products acts as a catalyst it self. Some biochemical reactions are experimentally observed as the auto catalysis reactions.

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Types of catalysis

In my last post, I have discussed about the general catalysis phenomena, and its most basic types. But the homogeneous and heterogeneous catalysis are not the only types of the catalysis. The chemical engineer also classifies catalysis on the basis of the nature of species responsible for the catalytic activity. These types are mostly inter-related with other types of the same nature. E.g. molecular catalysts can be used as homogeneous, as well as heterogeneous catalysts, Surface catalysts are heterogeneous catalysts etc. Some of the types are:

1) Molecular Catalysis:

This term is used for the systems, where identical molecular species are the catalytic entity. Many of these catalysts are used as homogeneous catalysts, but these can also be used in heterogeneous (multi-phase) catalysis.

2) Surface Catalysis:

Surface catalysis takes place on the surface atoms of the extended solid. It depends on the different properties of the surface atoms, and different types of the molecular sites. Surface catalysts are solid, so these are heterogeneous catalysts by nature.

3) Enzyme Catalysis:

Enzymes are proteins, polymers of amino acids, so this type of catalysis is used to catalyze reactions in living organism, biological and biochemical reactions. The enzyme catalysis is usually molecular catalysis.

4) Auto Catalysis:

In autocatalysis, there is no need to use a separate catalysis, but in a reaction one of the products acts as a catalyst it self. Some biochemical reactions are experimentally observed as the auto catalysis reactions.

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Catalysis

Catalysis is the key to optimized and efficient process engineering. Catalysis is the major problem for the chemical engineer while understanding the basic chemical reaction engineering. Catalysis is used in most of the industrial and biological processes, and the products of these processes include food, drugs, clothing, plastics, fuels or detergents.

To understand the phenomena of the catalysis, a chemical engineer must understand that what is catalyst? Catalyst is the substance, which changes the rate of the chemical reaction, with out being consumed in the reaction it self. But practically after the completion of the process, the catalyst transforms (not consumed), so mostly, the catalysts needed to be regenerated and can be used again.

These catalysts may be in any state of matter, i.e. liquid, gas or solids. There can be two types of a catalyst:

• positive catalysts : increases the rate of the reaction.

• negative catalysts : decreases the rate of the reaction. These are also called as inhibitors.

Catalysis is the phenomena of change in the rate of a chemical reaction in presence of a catalyst. There can be two types of the catalysis.

1) Homogeneous catalysis:

The catalysts are in the same phase as the reactants are. I.e. the homogeneous catalysts are co-dissolved substances in the solvent, with the reagents. The acid catalysis can be taken as an example of the homogeneous catalysis. In which the water, after self ionization forms protons (most penetrating homogeneous catalyst).

2) Heterogeneous catalysis:

The catalysts are in different phase, as that of the reactants. Most heterogeneous catalysts are solids (in a liquid or gaseous reaction mixture). But as the surface area of the catalyst (especially in solid catalyst case) has important effect on the rate of reaction. So the catalysts are generally crushed into the smaller particle size, as the smaller the particle size, the more will be the surface area of the catalyst.

Read More

Catalysis

Catalysis is the key to optimized and efficient process engineering. Catalysis is the major problem for the chemical engineer while understanding the basic chemical reaction engineering. Catalysis is used in most of the industrial and biological processes, and the products of these processes include food, drugs, clothing, plastics, fuels or detergents.

To understand the phenomena of the catalysis, a chemical engineer must understand that what is catalyst? Catalyst is the substance, which changes the rate of the chemical reaction, with out being consumed in the reaction it self. But practically after the completion of the process, the catalyst transforms (not consumed), so mostly, the catalysts needed to be regenerated and can be used again.

These catalysts may be in any state of matter, i.e. liquid, gas or solids. There can be two types of a catalyst:

• positive catalysts : increases the rate of the reaction.

• negative catalysts : decreases the rate of the reaction. These are also called as inhibitors.

Catalysis is the phenomena of change in the rate of a chemical reaction in presence of a catalyst. There can be two types of the catalysis.

1) Homogeneous catalysis:

The catalysts are in the same phase as the reactants are. I.e. the homogeneous catalysts are co-dissolved substances in the solvent, with the reagents. The acid catalysis can be taken as an example of the homogeneous catalysis. In which the water, after self ionization forms protons (most penetrating homogeneous catalyst).

2) Heterogeneous catalysis:

The catalysts are in different phase, as that of the reactants. Most heterogeneous catalysts are solids (in a liquid or gaseous reaction mixture). But as the surface area of the catalyst (especially in solid catalyst case) has important effect on the rate of reaction. So the catalysts are generally crushed into the smaller particle size, as the smaller the particle size, the more will be the surface area of the catalyst.

Read More