Need For Advanced Material Removal Processes

Advanced Material Removal Processes represent one of the technologies, which emerged after the second world war to cope up with the demands of sophisticated, more durable and cost competitive products. With the advent of new materials such as metal-matrix composites, super-alloys, ceramics, aluminates and high performance polymers etc. and the stringent requirements to machine complex geometrical shapes with high precision and accuracy, a strong need existed for the development of advanced material removal processes. The processes in this category differ from conventional processes in either utilization of energy in an innovative way or, in using forms of energy that were unused for the purpose of manufacturing. The conventional machining processes normally involve the use of energy from electric motors, hydraulics, gravity, etc. and rely on the physical contact between tools and work components. On the contrary, advanced material removal processes utilize energy from sources such as electrochemical reactions, high temperature plasma, high velocity jets and loose abrasives mixed in various carriers etc. Although these processes were originally developed to handle unique problems in aerospace industry (machining of very hard and tough alloys), today wide range of industries have adopted this technology in numerous manufacturing operations.

Why dry compressed air?

The air we breathe contains contamination in the form of water vapour and airborne particles. During the compression process an air compressor concentrates these contaminants and depending on the design and age will even add to the contamination in the form of oil carry over.

Modern air compressors generally have built in after coolers that reduce the discharge temperature of the compressed air and with the help of water separators, remove the bulk of liquid water.
In some applications this may be sufficient, but the remaining dirt and moisture content suspended in aerosol form, can, if not removed, damage the compressed air system and cause product spoilage.
Air Contaminants lead to increase down time and reduced productivity. it lead to corrosion , damaged Tools , poor finish to painting Jobs etc .

Compressors & Compressed Air Systems - Post 3

Rotary compressor

Rotary compressors have rotors in place of pistons and give a continuous pulsation free discharge. They operate at high speed and generally provide higher throughput than reciprocating compressors. Their capital costs are low, they are compact in size, have low weight, and are easy to maintain. For this reason they have gained popularity with industry. They are most commonly used in sizes from about 30 to 200 hp or 22 to 150 kW.

Types of rotary compressors include:
Lobe compressor (roots blower)
Screw compressor (rotary screw of helical-lobe,where mail and female screw rotors moving in opposite directions and trap air, which iscompressed as it moves forward,)
Rotary vane / sliding- vane, liquid-ring, and scroll-type
Rotary screw compressors may be air or water-cooled. Since the cooling takes place right inside the compressor, the working parts never experience extreme operating temperatures. The rotary compressor, therefore, is a continuous duty, air cooled or water cooled compressor package.
Because of the simple design and few wearing parts, rotary screw air compressors are easy to maintain, operate and provide great installation flexibility. Rotary air compressors can be installed on any sur face that will support the static weight.

Dynamic Compressors
The centrifugal air compressor is a dynamic compressor, which depends on transfer of energy from a rotating impeller to the air. The rotor accomplishes this by changing the momentum and pressure of the air. This momentum is converted to useful pressure by slowing the air down in a stationary diffuser. The centrifugal air compressor is an oil free compressor by design. The oil lubricated running gear is separated from the air by shaft seals and atmospheric vents.

COMPRESSORS AND COMPRESSED AIR SYSTEMS - Post 2

TYPES OF COMPRESSORS
There are two basic compressor types: positive-displacement and dynamic.

In the positive-displacement type, a given quantity of air or gas is trapped in a compression chamber and the volume it occupies is mechanically reduced, causing a corresponding rise in pressure prior to discharge. At constant speed, the air flow remains essentially constant with variations in discharge pressure.

Dynamic compressors impart velocity energy to continuously flowing air or gas by means of impellers rotating at very high speeds. The velocity energy is changed into pressure energy both by the impellers and the discharge volutes or diffusers.

Positive Displacement Compressor
two types: reciprocating and rotary.

Reciprocating compressor

In industry, reciprocating compressors are the most widely used type for both air and refrigerant compression. They work on the principles of a bicycle pump and are characterized by a flow output that remains nearly constant over a range of discharge pressures. Also, the compressor capacity is directly proportional to the speed
Reciprocating compressors are available in many configurations, the four most widely used are horizontal, vertical, horizontal balance-opposed and tandem. Vertical type reciprocating compressors are used in the capacity range of 50 – 150 cfm. Horizontal balance opposed compressors are used in the capacity range of 200 – 5000 cfm in multi-stage design and up to 10,000 cfm in single stage designs
The reciprocating air compressor is considered single acting when the compressing is accomplished using only one side of the piston. A compressor using both sides of the piston is considered double acting.
A compressor is considered to be single stage when the entire compression is accomplished with a single cylinder or a group of cylinders in parallel. Many applications involve conditions beyond the practical capability of a single compression stage. Too great a compression ratio (absolute discharge pressure/absolute intake pressure) may cause excessive discharge temperature or other design problems. Two stage machines are used for high pressures and are characterized by lower discharge temperature (140 to 160oC) compared to single-stage machines (205 to 240oC).
For practical purposes most plant air reciprocating air compressors over 100 horsepower are built as multi-stage units in which two or more steps of compression are grouped in series. The air is normally cooled between the stages to reduce the temperature and volume entering the following
Reciprocating air compressors are available either as air-cooled or water-cooled in lubricated and non- lubricated configurations, may be packaged, and provide a wide range of pressure and capacity selections.

COMPRESSORS AND COMPRESSED AIR SYSTEMS - Post 1

INTRODUCTION

Industrial plants use compressed air throughout their production operations, which is produced by compressed air units ranging from 5 horsepower (hp) to over 50,000 hp. The US Department of Energy (2003) reports that 70 to 90 percent of compressed air is lost in the form of unusable heat, friction, misuse and noise . For this reason, compressors and compressed air systems are important areas to improve energy efficiency at industrial plants.
It is worth noting that the running cost of a compressed air system is far higher than the cost of a compressor itself . Energy savings from system improvements can range from 20 to 50 percent or more of electricity consumption, resulting in thousands to hundreds of thousands of dollars. A properly managed compressed air system can save energy, reduce maintenance, decrease downtime, increase production throughput, and improve product quality

Compressed air systems consist of a supply side, which includes compressors and air treatment, and a demand side, which includes distribution and storage systems and end -use equipment. A properly managed supply side will result in clean, dry, stable air being delivered at the appropriate pressure in a dependable, cost-effective manner. A properly managed demand side minimizes wasted air and uses compressed air for appropriate applications. Improving and maintaining peak compressed air system performance requires addressing both the supply and demand sides of the system and how the two interact.

Main Components of Compressed Air Systems

Consist of the Following

Intake Air Filters : Prevent dust from entering a compressor; Dust causes sticking valves, scoured cylinders, excessive wear etc.
Inter-stage Coolers : Reduce the temperature of the air before it enters the next stage to reduce the work of compression and increase efficiency. They are normally water-cooled. After-Coolers: The objective is to remove the moisture in the air by reducing the temperature in a water-cooled heat exchanger.
Air-dryers : The remaining traces of moisture after after-cooler are removed using air dryers, as air for instrument and pneumatic equipment has to be relatively free of any moisture. The moisture is removed by using adsorbents like silica gel /activated carbon, or refrigerant dryers, or heat of compression dryers
Moisture Drain Traps: Moisture drain traps are used for removal of moisture in the compressed air. These traps resemble steam traps. Various types of traps used are manual drain cocks, timer based / automatic drain valves etc.
Receivers : Air receivers are provided as stora ge and smoothening pulsating air output - reducing pressure variations from the compressor

Design Consideration for Pools

Design Consideration for Pools & Spas Swimming Pools

According to ASHRAE (1999a) the desirable temperature for swimming pools is 27c , however this will vary from the culture by so much as 5 degree Celsius. .If the geothermal water is higher in temperature then some sort of mixing or cooling by aeration or in a holding pond is required to lower the temperature . If the geothermal water is used directly in the pool , then a flow through process is neccessary to replace the used water on regular basis. In many cases the pool water must be treated with chlorine , therefore it is more economical to used a closed loop system for treatment water and have geothermal water provide heat through heat ex changer . The Water Heating System should be installed in the return line to the pool. Acceptable water circulation level vary from eight hours to six hours for a complete change of water. Heat exchanger must be designed to resist the corrosive effect of the chlorine in the pool water and scaling or corrosion from the geothermal water. This often requires in the case of plate heat exchanger using titanium plates .

Four Factors determine the sizing of the system for temperature and flow rate . These are
i) Conduction through the pool walls
2) convection through the pool surface
3 ) Radiation from the pool surface
4) Evaporation from the pool surface

Conduction is Least significant unless the pool is above ground or in contact with the cold underground water
Convection losses depends on the temperature difference between the pool water and the surrounding air and the wind speed.this substantially low for indoor pool also pool with wind speed breakers.
Radiation losses are greater at night for the outdoor pools , however their will be gain in temperature during daytime. A Floating pool Covers can reduces both radiation and evaporation losses. Evaporation loss constitute the greatest heat loss from pools -50 to 60 % in most cases. The rate of which evaporation occurs is a function of air velocity and pressure difference between the pool water and the water vapor in the air .
As the temperature of the pool water is increased or the relative humidity of the air is decreased evaporation rate increase.

The required Gethermal heating output q can be determined by the following two equations
q1 = Density of Water * Pool heat up *pool Volume * ( Desired Temp - intial Temp ) * Pool heat up time

q2 = Surface heat Transfer Coefficient * pool Surface area * ( Pool Temp - ambient temp)

then Q= q1- q2

if there is no heat up time which is typical for geothermal pools then equations (1) will be zero and only equation 2 will apply. Equation 2 will assume a wind velocity of 5 to 8 Km/h . For Sheltered Pool wind velocity factor less than 5km/h

The neccessary Heat to increase and maintain the temperature of an outdoor pool can be expressed as

H( Total) = h (Surface) + h (heat up)

h (heat up) = Volume *8.34 (lbs/gal) * ( intial Temp - Final Temp) * 1.0 / 72

72 = time required to Rise the temp of pool

h (Surface) = ks * dtw* A

where

ks = surface heat loss factor

dtw = Temp Difference between the air and surface water in the pool

A = Surface area of the pool

Frequency Convertor

Frequency converters are used to change the frequency and magnitude of the constant grid voltage to a variable load voltage. Frequency converters are especially used in variable frequency AC motor drives.

Figure 1 shows the behavior of an induction motor with several motor input voltages. The bold blue curve represents the electrical torque as a function of rotor speed when the motor is connected directly to a constant supply network. The blue portion of the torque curve shows the nominal load region (-1…+1 [T/TN]), which is very steep, resulting in low slip and power losses. Similar motor torque behavior with other motor input frequencies can be achieved by feeding the induction motor with a frequency converter and keeping the ratio of the magnitude and frequency of the motor voltage constant. As a result, the shape of the torque curve remains unchanged below the nominal speed (constant-flux region -1…+1 [n/nN]). In the field weakening region the motor voltage is at its maximum and kept constant, resulting in the torque curves being flattened.
Frequency converters can be classified according to their DC circuit structure to voltage-source (Fig. 4), current-source (Fig. 3) and direct converters (Fig. 2). With a voltage-source converter the variable frequency and magnitude output voltage is produced by pulse-width modulating (PWM) the fixed DC voltage, whereas with a current-source converter the output voltage is produced by modulating the fixed DC current. With a direct frequency converter the variable output voltage is formed directly by modulating the constant input voltage. At low voltage applications (<1000 data-blogger-escaped-br="" data-blogger-escaped-is="" data-blogger-escaped-mainly="" data-blogger-escaped-the="" data-blogger-escaped-topology="" data-blogger-escaped-used.="" data-blogger-escaped-v="" data-blogger-escaped-voltage-source="">