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# Read PDF Food engineering, principles and selected applications

Eulerian: - Describes the flow field velocity, acceleration, pressure, temperature, etc. In this method the motion of single particle is not considered but we considered the motion of all fluid particles that pass through a fix point during a passage of its flow. This is the Eulerian description. It is a field description. A probe fixed at a point is an example of an Eulerian measuring device. First type of fluid flow:- 1. Laminar Flow: - laminar flow or streamline flow occurs when a fluid flows in parallel layers, with no disruption between the layers.

Laminar flow generally happen when dealing with small pipes and low flow velocities. Laminar flow can be regarded as a series of liquid cylinders in the pipe where the innermost parts flow the fastest. Shear stress depends almost only on the viscosity-u-and in the independent of density.

Reynolds number for flow is 0 to Turbulent Flow:-In this flow type of fluid gas or liquid flow the fluid undergoes irregular fluctuations, or mixing. In turbulent flow the speed of the fluid at a point is continuously undergoing changes in both magnitude and direction. The flow of Transitional Flow: - On applying external disturbance we find there are irregular fluctuations. It is a mixture of laminar and turbulent flow with turbulence in the center edges.

Second type of fluid flow Change in space 1. Uniform Flow constant with space : - This flow is uniform in the nature if the flow of parameter like pressure, velocity temperature and dentistry remain constant throughout the flow of fluid at any given time. Non — Uniform Flow changes over space : - This flow is non —uniform if there is a change flow in parameter from one selection to another.

Third type of flow:- Change in time 1. Steady State constant with time : - Fluid motion is said to be steady when the fluid parameter at any point in flow field remain constant with regard to time. Example of steady uniform flow is the flow of water in a pipe of constant diameter at constant velocity. Unsteady State changes with time : - The flow is unsteady when parameter changes with regarded to time. Fourth type of fluid flow:- 1.

Compressible flow: - Flow is compressible if the density change due to temperature pressure variation. The gases are compressible fluid. Gases are mainly having compressible flow. Incompressible flow; - Flow is incompressible if the density change in very less with the change of pressure and temperature. All the liquid are regarded as incompressible. Fifth type of fluid flow:- 1. Ideal flow: - In ideal flow no friction exit between two fluid layers and the boundary wall.

Such a flow is imaginary but for all theoretical wall fluid may be assume to ideal. Real flow: - In real flow the resistance due to viscosity exists. Sixth type of fluid flow:- 1. Rotational flow: - A rotational flow exist when the fluid particle rotate about their center of gravity while moving along the steam line. In a rotational flow if a match stick is thrown on the surface of the moving fluid, it will rotate about its own axes 2. Irrotational flow: - The flow is irrotational when the fluid particles do not rotate about their center of gravity while moving along its steam line.

Seventh type of fluid flow:- Term one, two or three dimensional flow refers to the number of space coordinated required to describe a flow. It appears that any physical flow is generally three-dimensional. One dimensional: - In one dimensional flow the fluid parameter remain constant throughout any cross sectional area perpendicular to the flow direction. In reality, flow is never one-dimensional because viscosity causes the velocity to decrease to zero at the solid boundaries.

Example — Flow between parallel plates. Two dimensional:-In two dimensional flows the flow velocity and other parameter varies along two directions. Example- viscous flow between parallel plates. Three dimensional:-In three dimensional flow the flow parameter is varies in all the three direction.

Example — flow in a river. So the pump is a device which is used to pressure increase of a fluid. Or A pump is a device that moves fluids liquids or gases , or sometimes slurries, by mechanical action. Pumps are basically used for situation where gravity cannot be used to move liquid products and mechanical energy is required.

This mechanical energy is provided by pumps. A wide range of pump types is available to meet the many needs of individual water supply systems and special fluids handling systems. Most common pump used in food industry are centrifugal, positive displacement, peristaltic, turbine, gear, deep well, shallow well, jet, etc. Applications of pumps -: 1. In agriculture workers. Municipal water workers and drainage system. Condensing water, boiler feed and such other application in stream power plant.

Oil pumping. Transfer of raw materials. Most centrifugal pumps used in food industry use two vane impellers. Impellers with three or four vanes are available and may be used in some application. Centrifugal pumps are most efficient with low viscosity liquid such as milk or fruit juice. Where flow rate are high and pressure requirement are moderate. The discharge flow from centrifugal pump is steady. Centrifugal pumps are well suited for water handling as well as many other fluids-handling systems.

Principle:- This created centrifugal heat of water in the pressure. A particle vacuum created at the center due to which liquid is drawn through suction pipe. Working:- In these pumps the amount of liquid delivered will vary with the height to which liquid to be lifted.

Like most pumps, a centrifugal pump converts mechanical energy from a motor to kinetic energy of the fluid.

Fluid enters through eye of the casing, is caught up in the impeller blades. Now fluid is whirled tangentially and radially discharged from the casing to discharge pipe. The fluid gains both velocity and pressure while passing through the impeller. Positive DisplacementPumps A positive displacement pump makes a fluid move by trapping a fixed amount and forcing displacing that trapped volume into the discharge pipe.

Positive displacement types A positive displacement pump can be classified according to the mechanism used to move the fluid: Rotary-type positive displacement: - Rotary pumps include sliding vane lobe type internal gear and gear type pump. The rotary pump has the capability to rivers flow direction by reversing the direction of rotor rotation. Principle:-A centrifugal pump operates on the principle of centrifugal action of rotation but a rotary pump is a positive displacement pump. The liquid is discharged by a positive pressure. These pumps are priming use as power source in the hydraulic control system and to supply pressure oil for lubricating of turbine and machine tools.

Rotary positive displacement pumps fall into three main types: 1. Gear pumps - a simple type of rotary pump where the liquid is pushed between two gears. Gear pump uses rotating gears to force the pumped fluid through the pump. Several variations in design are possible. Close tolerances and associated high wear rates are a characteristic of these pumps. They are more appropriately used for special fluids handling applications than for water systems. Screw pumps - the shape of the internals of this pump is usually two screws turning against each other to pump the liquid.

Several different types of screw pumps exist. The differences between the various types are the number of intermeshing screws and the pitch of the screws. The pump is similar to a gear pump but uses helical gears or screws to move the fluid. As the screw turns, vacuum forms at the inlet.

Atmospheric pressure then pushes fluid into the cavities and the fluid moves to the outlet. This pump has very smooth flow -- without the pulses produced by the other positive-displacement pumps in this manual. Flow from the outlet is smooth and continuous. However, screw pumps are not highly efficient. This design pump often is used to supercharge other pumps, as a filter pump, or a transfer pump at low. High pressures can be attained in this type of pump.

The screw pump is commonly used in the food industry. Rotary vane pumps - similar to scroll compressors, these have a cylindrical rotor encased in a similarly shaped housing. As the rotor orbits, the vanes trap fluid between the rotor and the casing, drawing the fluid through the pump. Advantages: Rotary pumps are very efficient because they naturally remove air from the lines, eliminating the need to bleed the air from the lines manually. Drawbacks: The nature of the pump demands very close clearances between the rotating pump and the outer edge, making it rotate at a slow, steady speed.

If rotary pumps are operated at high speeds, the fluids because erosion, which eventually causes enlarged clearances that liquid can pass through, this reduces efficiency. Typical reciprocating pumps are: 1. Plunger pumps - A plunger pump is a type of positive displacement pump where the high-pressure seal is stationary and a smooth cylindrical plunger slides through the seal. This makes them different from piston pumps and allows them to be used at higher pressures. This type of pump is often used to transfer municipal and industrial sewage.

What is a Plunger Pump? Plunger pumps share the same operating principles of the piston pumps but use a plunger instead of a piston in the cylinder cavity. However, the plunger pumps can provide higher pressure conditions than the piston pumps ranging up to MPa. What is the difference between Piston and Plunger Pump? Piston pumps- Piston pumps and plunger pumps use a mechanism typically rotational to create a reciprocating motion along an axis, which then builds pressure in a cylinder to force gas or fluid through the pump.

The pressure in the chamber actuates the valves at both the suction and discharge points. The suction and discharge valves are mounted in the head of the cylinder. The common example of the piston pump is hand pump.

## Rheology of Fluid and Semisolid Foods: Principles and Applications (Food Engineering Series)

Although hand pumps are now relatively rare, piston pumps operated by electric motors are still in use. Except for limited applications, however, the piston pump has been replaced by the centrifugal pump in distribution systems for water and other fluids. The common hand soap dispenser is such a pump. Principle: - The piston closely fitted in the cylinder. During backward motion of the piston a partial vacuum is created behind the piston, opening the suction pipe from the tank or well into the cylinder.

During the forward motion of the piston, the suction valve closes, the delivery valve open and the fluid is pumped up the delivery pipe to the desired delivery tank. Operating Principle of a Piston Pump When the Motor is started, the piston first moves forward inside the cylinder. In the forward stroke the plunger pushes the liquid out of the discharge valve. Then when the Piston returns back, it creates an empty space where there will be a vacuum that will pull the suction valve, through this valve fluid come into the Cylinder.

When the piston again comes back into its previous position discharge plate opens up and the fluid discharge with high pressure. The same process is repeated and for every suction and discharge stroke a particular quantity of Fluid flows out. Two types of pumps: - Single acting pumps have one valve on each end, where suction and discharge take place in opposite directions. Single acting plunger pumps have only one cylinder in; the fluid flow varies between maximum flow when the plunger moves through the middle positions and zero flow when the plunger is at the end positions.

A lot of energy is wasted when the fluid is accelerated in the piping system. Vibration and water hammer may be a serious problem. In general the problems are compensated for by Double acting pumps using two or more cylinders not working in phase with each other, allowing suction and discharge in both directions.

But by proper alignment and maintenance the failure rate can be reduced. Diaphragm pumps — A diaphragm pump also known as a Membrane pump, Air Operated Double Diaphragm Pump AODD or Pneumatic Diaphragm Pump is a positive displacement pump that uses a combination of the reciprocating action of a rubber, thermoplastic or Teflon diaphragm and suitable valves on either side of the diaphragm check valve, butterfly valves, flap valves, or any other form of shut-off valves to pump a fluid.

Diaphragm valves are used to pump hazardous and toxic. Modes of heat transfer i. Heat is defined as thermal energy in transit. The kinetic energy due to the random motion of the molecules of a substance is known as its heat energy What is Heat Transfer Thermal energy is related to the temperature of matter. Heat transfer is a study of the exchange of thermal energy through a body or between bodies which occurs when there is a temperature difference.

When two bodies are at different temperatures, thermal energy transfers from the one with higher temperature to the one with lower temperature. Heat always transfers from hot to cold. The common SI and English units and conversion factors used for heat and heat transfer rates. Heat is typically given the symbol Q, and is expressed in joules J in SI units.

The rate of heat transfer is measured in watts W , equal to joules per second, and is denoted by q. Any energy exchange between bodies occurs through one of these modes or a combination of them. Conduction is the transfer of heat through solids or stationery fluids.

Convection uses the movement of fluids to transfer heat. Radiation does not require a medium for transferring heat; this mode uses the electromagnetic radiation emitted by an object for exchanging heat. Vibrational energy is transferred between atoms or molecules that do not themselves move. It is the basic transfer mechanism for heat transfer in solids when you touch a hot object, the heat you feel is transferred through your skin by conduction. In solids, atoms are bound to each other by a series of bonds. When there is a temperature difference in the solid, the hot side of the solid experiences more vigorous atomic movements.

The vibrations are transmitted through the springs to the cooler side of the solid. Eventually, they reach equilibrium, where all the atoms are vibrating with the same energy. Solids, especially metals, have free electrons, which are not bound to any particular atom and can freely move about the solid. The electrons in the hot side of the solid move faster than those on the cooler side. As the electrons undergo a series of collisions, the faster electrons give off some of their energy to the slower electrons.

Conduction through electron collision is more effective than through lattice vibration; this is why metals generally are better heat conductors than ceramic materials, which do not have many free electrons. Figure 1. The mechanism is identical to the electron collisions in metals. A good conductor, such as copper, has a high conductivity; a poor conductor, or an insulator, has a low conductivity.

In heat transfer, a positive q means that heat is flowing into the body, and a negative q represents heat leaving the body. In a typical convective heat transfer, a hot surface heats the surrounding fluid, which is then carried away by fluid movement such as wind. The warm fluid is replaced by cooler fluid, which can draw more heat away from the surface. Since the heated fluid is constantly replaced by cooler fluid, the rate of heat transfer is enhanced. Natural convection or free convection refers to a case where the fluid movement is created by the warm fluid itself.

The density of fluid decrease as it is heated; thus, hot fluids are lighter than cool fluids. Warm fluids surrounding a hot object rises, and are replaced by cooler fluid. The result is a circulation of air above the warm surface, Natural convection Forced convection uses external means of producing fluid movement. Forced convection is what makes a windy, winter day feel much colder than a calm day with same temperature. The heat loss from your body is increased due to the constant replenishment of cold air by the wind.

Natural wind and fans are the two most common sources of forced convection. Convection coefficient, h, is the measure of how effectively a fluid transfers heat by convection. Wind blowing at 5 mph has a lower h than wind at the same temperature blowing at 30 mph. Radiative heat transfer occurs when the emitted radiation strikes another body and is absorbed. We all experience radiative heat transfer everyday; solar radiation, absorbed by our skin, is why we feel warmer in the sun than in the shade.

The electromagnetic spectrum classifies radiation according to wavelengths of the radiation. Main types of radiation are from short to long wavelengths : gamma rays, x-rays, ultraviolet UV , visible light, infrared IR , microwaves, and radio waves. A radiation with shorter wavelengths is more energetic and contains more heat. A second characteristic which will become important later is that radiation with longer wavelengths generally can penetrate through thicker solids. Most "hot" objects, from a cooking standpoint, emit infrared radiation. Heat exchanger A heat exchanger is a device that is used to transfer thermal energy enthalpy between two or more fluids, between a solid surface and a fluid, or between solid particulates and a fluid, at different temperatures and in thermal contact.

Or A heat exchanger is a component that allows the transfer of heat from one fluid liquid or gas to another fluid. Reasons for heat transfer include the following: 1. To heat a cooler fluid by means of a hotter fluid 2. To reduce the temperature of a hot fluid by means of a cooler fluid 3. To boil a liquid by means of a hotter fluid 4. To condense a gaseous fluid by means of a cooler fluid 5.

To boil a liquid while condensing a hotter gaseous fluid A variety of heat exchangers are used in industry and in their products. Heat exchangers are classified according to transfer processes, number of fluids, degree of surface compactness, construction features, flow arrangements, and heat transfer mechanisms. Designed and construction 2. Operating principle 3. These arrangements have one disadvantage that it makes lanes between tubes which becomes difficult for us to do mechanical cleaning.

Due to this reason, we can do only chemical cleaning or water jet cleaning. In this arrangement the gap between the tubes is more, so less number of tubes can be installed in given area. In this type of heat exchanger one of the fluids flows through the inside of the shell and the other fluid flows through tubes passing through the inside of the shell, thereby enabling heat transfer between the two fluids. Baffles are added to enhance the convection coefficient, which increases heat transfer between the two fluids.

One shell one tube It is sometimes referred to as the Stationary Header. The purpose of longitudinal baffles is to control the overall flow direction of the shell fluid such that a desired overall flow arrangement of the two fluid streams is achieved. Baffles serve three functions: 1 support the tube; 2 maintain the tube spacing; and 3 direct the flow of fluid in the desired pattern through the shell side.

Heat transfer takes place from the primary fluid steam to the secondary process fluid in adjacent channels across the plate. A corrugated pattern of ridges increases the rigidity of the plates and provides greater support against differential pressures. This pattern also creates turbulent flow in the channels, improving heat transfer efficiency, which tends to It requires lower surface area than shell and tube exchangers. These exchangers can be used for highly viscous fluids at low, medium pressures.

In this type of heat exchanger the outside area of the tube is increased or extended by fins. Example auto mobile radiators Shell and Coil type heat exchanger-The shell and coil tube series are manufactured as a singe unit with no removable parts. The coiled tube bundles are welded to a compact tube sheet located within the entry and exit connections. The cylindrical shell is terminated by hemi-spherical heads. They are simple in construction and less expensive in fabrication.

Scraped surface heat exchanger contains large center tube of two of to mm in diameter jacketed with steam or cooling liquid. The inside of central tube is scraped continuously with two or more blades mounting on rotating shaft. Thus, ideally, there is no direct contact between thermally interacting fluids.

This type of heat exchanger also referred to as a surface heat exchanger, can be further classified into direct-transfer type, storage type, and fluidized-bed exchangers. Where mixing between the fluids is either harmless Common applications of a direct-contact exchanger involve mass transfer in addition to heat transfer, such as in evaporative cooling and rectification. Compared to indirect contact recuperates and regenerators, in direct-contact heat exchangers are: Very high heat transfer rates are achievable 2. The exchanger construction is relatively inexpensive 3.

The fouling problem is generally nonexistent, due to the absence of a heat transfer surface wall between the two fluids. However, the applications are limited because where a direct contact of two fluid streams is permissible.

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To accomplish this hot fluid is brought into contact with the heat storage medium, and then the fluid is displaced with the cold fluid, which absorbs the heat. It was later used in glass and steel making, in high pressure boilers and chemical and other applications, where it continues to be important today. Rotary regenerators the matrix rotates continuously through two counter-flowing streams of fluid. In this way, the two streams are mostly separated but the seals are generally not perfect. Only one stream flows through each section of the matrix at a time; however, over the course of a rotation, both streams eventually flow through all sections of the matrix in succession.

Each portion of the matrix will be nearly isothermal, since the rotation is perpendicular to both the temperature gradient and flow direction, and not through them.

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The two fluid streams flow counter-current. The fluid temperatures vary across the flow area; however the local stream temperatures are not a function of time. In a fixed matrix regenerator, a single fluid stream has cyclical, reversible flow; it is said to flow "counter-current". This regenerator may be part of a valve less system, such as a Stirling engine. In another configuration, the fluid is ducted through valves to different matrices in alternate operating periods In this case, the two fluids enter the heat exchanger from the same end with a large temperature difference.

As the fluids transfer heat, hotter to cooler, the temperatures of the two fluids approach each other. Note that the hottest cold-fluid temperature is always less than the coldest hot-fluid temperature. Each of the fluids enters the heat exchanger at opposite ends. Because the cooler fluid exits the counter flow heat exchanger at the end where the hot fluid enters the heat exchanger, the cooler fluid will approach the inlet temperature of the hot fluid. Counter flow heat exchangers are the most efficient of the three types. In contrast to the parallel flow heat exchanger, the counter flow heat exchanger can have the hottest cold-fluid temperature greater than the coldest hot-fluid temperature.

Cross flow heat exchangers are usually found in applications where one of the fluids changes state 2-phase flow. An example is a steam system's condenser, in which the steam exiting the turbine enters the condenser shell side, and the cool water flowing in the tubes absorbs the heat from the steam, condensing it into water. Large volumes of vapor may be condensed using this type of heat exchanger flow. It should be evident that a basic understanding of the mechanism of heat transfer both food and the materials used in construction of food processing equipment is necessary before we can design or evaluate any heat exchanger equipment.

A wide variety of food products is processed using heat exchanger. The following points are considered for the selection of heat exchanger 1. Thermal properties :- properties such as specific heat thermal conductivity and thermal diffusivity of food and equipment material plat an important role in determining the rate of heat transfer 2. Mode of heat transfer:- A mathematical description of the actual mode of heat transfer, such as conduction, convection, and radiation is necessary to determine quantity such as total amount of heat transfer from heating or cooling medium to the product Specifications of various types heat exchanger are:- 1.

The maintaince of these heat exchanger should be simple so that, they can be easily and quickly removed for product surface inspection 2. The plate heat exchanger have a hygienic design for food application 3. Their capacity can be easily increased by adding more relaters to the frame 4. The heat exchanger should be such that the energy conservation by regeneration possible. Principle of mass transfer, diffusion Mass transfer plays a very important role in basic unit operations of food processing, such as drying, extraction, distillation, and absorption.

Mass transfer is the net movement of mass from one location, usually meaning a stream, phase, fraction or component, to another. To study mass transfer in food systems, it is important that we understand the term mass transfer. We have a bulk flow of a fluid from one location to another, there is a movement of the fluid of a certain mass , but the process is not mass transfer, according to the context being used. Our use of the term mass transfer is restricted to the migration of a constituent of a fluid or a component of a mixture.

The migration occurs because of changes in the physical equilibrium of the system caused by the concentration differences.

If the air is stationary, the transfer occurs as a result of random motion of the acetone molecules. If a fan or any other external means are used to cause air turbulence, the eddy currents will enhance the transfer of acetone molecules to distant regions in the room. All three of the molecular transport processes - momentum, heat, and mass-are characterized by the general type of equation, In mass transfer, mass is transferred under the driving force provided by a partial pressure or concentration difference.

The rate of mass transfer is proportional to the potential pressure or concentration difference and to the properties of the transfer system characterized by a mass-transfer coefficient. Types of mass transfer :- Mass transfer involves both mass diffusion occurring at a molecular scale and bulk transport of mass due to convection flow. Diffusion mass transfer 2. Convection mass transfer 1. It is the transfer of matter on a microscopic level from a region of higher conc. Molecular diffusion is four types:- 1. Ordinary diffusion: - Result from the conc.

The diffusion sub-stance to moves from a position of lower conc. Thermal diffusion: - Due to different in temperature from one part to another in the system. A temperature gradient will develop which cause diffusion. Pressure diffusion: - Resulting from the atmospheric pressure differences that provide the driving potential to the mass transfer. Forced diffusion: - This is result due to external force. The zig —zag motion of one fluid greatly the speed of mass transfer.

Convection mass transfer: - Mass transfer involves bulk transport of mass due to convection flow. When the transport of a component due to a concentration gradient is enhanced by convection, the mass flux of the component will be higher than would occur by molecular diffusion. Convective mass transfer will occur in liquids and gases, and within the structure of a porous solid.

The relative contributions of molecular diffusion and convective mass transfer will depend on the magnitude of convective currents within the liquid or gas. The convective mass transfer coefficient k m is defined as the rate of mass transfer per unit area per unit concentration difference. The coefficient represents the volume m3 of component B transported across a boundary of one square meter per second. Fick's Law for Molecular Diffusion Fick's laws of diffusion describe diffusion and were derived by Adolf Fick in Molecular diffusion or molecular transport can be defined as the transfer or movement of individual molecules through a fluid by means of the random, individual movements of the molecules.

Consider a box which is initially divided into two parts, as shown in Figure. Each side of the box has a height and depth of 1 unit, and a width of length. At some instant in time, the partition is removed, and B and E diffuse in opposite directions as a result of the concentration gradients. We will check the box and count the molecules on each side. Thus, we obtain Fick's Law: Or Where J is the "diffusion flux" amount of substance per unit area per unit time]. J measures the amount of substance that will flow through a small area during a small time interval.

Pasteurizer In the food industry, we refer to the processing steps required to eliminate the potential for food borne illness or preservation process. Pasteurization is a process of heat treatment used to inactivate enzymes and to kill relatively heat-sensitive microorganisms that cause spoilage with minimal changes in food properties e.

It is also defined as mild heat treatment for avoiding microbial and enzymatic spoilage. The primary objective of pasteurization is to free the food of any microorganisms that might cause deterioration the consumer's health. Below pH 4. Pasteurization does not aim at killing spore-bearing organisms, such as the thermophilic Bacillus subtilis, but these organisms and most other spore-bearing bacteria cannot grow in acidic fruit juices. Pasteurization of carbonated juices done for destroying yeasts and molds. Types of Pasteurization there are several types of pasteurization: 1.

In-package pasteurization: Inside packages, heating to the level of sterility is not required. A gradual change in temperature is preferred in some containers 2. Pasteurization prior to packaging: Preheating is good for foods that are sensitive to high temperature gradients. Batch pasteurization or LTLT Low temperature long time is suitable for small quantities ranging from litre requiring low initial cost of production.

Here fluid foods like milk are held in a tank where they are heated to A batch pasteurizer consists of a steam-jacketed kettle or a tank equipped with steam coils in which the juice or milk is heated to the desired temperature. The complete process of preheating, heating, holding, pre-cooling and chilling is completed in a plate type heat exchanger: Foods like milk are subjected to In continuous pasteurization generally plate heat exchanger, tubular heat exchanger, scraped surface heat exchanger are used depending on the viscosity of the fluid food material.

The heating medium is usually steam or water. Ultra high temperature UHT : In ultra high temperature pasteurizer food product are heated at very high temperature Above boiling temperature for a fraction of second or for a few second. UHT is most commonly used in milk production, but the process is also used for fruit juices, cream, soy milk, yogurt, wine, soups, honey, and stews.

UHT milk was invented in the s, and became generally available for consumption in the s. High heat during the UHT process can cause Maillard browning and change the taste and smell of dairy products. UHT milk has a typical shelf life of six to nine months, until opened. Most pasteurization systems are designed for liquid foods, and with specific attention to achieving a specific time—temperature process. Mostly plate heat exchangers are used to heat the product to the desired temperature. The heating medium may be hot water or steam, and a regeneration section is used to increase efficiency of the process.

In this section, hot product becomes the heating medium. Cold water is the cooling medium in a separate section of the heat exchanger. The holding tube is an important component of the pasteurization system. Although lethality accumulates in the heating, holding, and cooling sections, the Food and Drug Administration FDA will consider only the lethality accumulating in the holding section.

It follows that the design of the holding tube is crucial to achieve a uniform and sufficient thermal process. A metering pump, located upstream from the holding tube, is used to maintain the required product flow rate. Usually a positive displacement pump is used for this application. Centrifugal pumps are more sensitive to pressure drop and should be used only for clean-in-place CIP applications. An important control point in any pasteurization system is the flow diversion valve FDV. This remotely activated valve is located downstream from the holding tube.

A temperature sensor located at the exit to the holding tube activates the FDV; when the temperature is above the established pasteurization temperature, the valve is maintained in a f o r w a r d f l o w position. If the product temperature drops below the desired pasteurization temperature, the FDV diverts the product flow to the unheated product inlet to the system.

The valve and sensor prevent product that has not received the established time—temperature treatment from reaching the product packing system. Or An autoclave Fig. Who invented autoclaves? He realizes that heating things to kill germs can prevent diseases and extend the life of foodstuffs which leads him to the invention of pasteurization. Theory of operation An autoclave is a large pressure cooker; it operates by using steam under pressure as the sterilizing agent. High pressures help steam to reach high temperatures, thus increasing its heat content and killing power.

Achieving high and even moisture content in the steam-air environment is important for effective autoclaving. The ability of air to carry heat is directly related to the amount of moisture present in the air. The more moisture present, the more heat can be carried, so steam is one of the most effective carriers of heat. Moist heat is kill microorganisms by causing coagulation of essential proteins. Thus, it critical to understand what are the different engineering unit operations, how are used in making different food process operations work, underlying physics behind these processes, and their advantage and limitation.

It is important to understand the process and packaging parameters that make the food safe and preserve food quality. Hopefully, our journey during the semester will help you to better appreciate the importance and benefits of integrating knowledge from engineering, chemistry and microbiology for controlling different food process. The material covered during lecture and recitation will come from several sources including the following books. In addition, you may find journal articles as additional valuable resources. Class notes posted through Carmen website.