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Why saturated steam is used for processWhile superheated steam not?
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Why saturated steam is used in exchangers frequently rather then superheated?
The heat transfer coefficient of superheated steam is poor. Saturated steam has a better heat transfer coefficient, and also most of the heat transferred from steam occurs because of the condensation phase change.
What is the difference between saturated steam and Superheated steam?
Saturated steam occurs when steam and water are in equilibrium. If you have a closed container of water and heat it, above 100 celsius the steam pressure will start to rise, and as the temperature continues to rise, the pressure will go on rising. What is happening is that steam is being evolved to match the temperature (steam tables will give this relation) and the steam conditions are said to be saturated because if the pressure is raised by external means, some of the steam will start to condense back to water.If the steam pressure is held at a lower level than that achieved at saturation, by taking steam off to feed a turbine or other steam usage, there is effectively an excess temperature for that pressure, and the steam is said to be superheated. It in fact then becomes dry, and behaves as a gas. The amount of superheat can be quantified as so many degrees of superheat (celsius or fahrenheit).Turbine designers want steam to be superheated before reaching the turbine, to avoid condensation causing blade erosion, and steam producing boilers in power plants are designed to produce superheated steam. In plants where no turbines are used, only satured steam is normally generated.In heating applications, saturated steam is preferable, because it has a better energy exchange capacity. Superheated steam must cool down, and become saturated steam, before condensing in a heat exchanger. Also, superheated steam is a thermal insulator, like air.That is why it is necessary to direct superheated steam through a desuperheater before using the steam in heating applications.
Why is heat trasnfer coefficient of saturated steam is higher than superheated steam?
when steam is at its saturation point for a given pressure, any heat removed will cause liquid water to form. So when saturated steam is used to heat something else, the heated object/substance receives the condensation heat of the steam. The latent heat of condensation/evaporation is 970 But/lb @ 0 psig. On the other, superheated steam only gives up about 10 BTU/lb if it is cooled 20 degrees F. That means that much more steam would be used to transfer the equivalent amount of heat. The liquid water interface also improves the heat transfer.
What is the function of a superheater?
It is used to convert saturated or wet steam into dry steam for use in steam turbines, which are used for marine propulsion and the generation of electricity. +++ Also used for steam feeding reciprocating engines such as railway locomotives. It is not just a matter of dryness. Superheating allows the steam to work as a gas for longer during its passage through the turbine or cylinder, hence increasing the thermal efficiency of the whole plant.
Is thermodynamics a type of mechanical engineering?
Thermodynamics is a branch of physics that was started after there was a need to understand the energy in superheated steam, so that steam engines could be made as efficient as possible. So thermodynamic is definitely part of mechanical engineering because it is now used in the design of all kinds of engines, piston engines, turbines etc.
Why saturated steam is used in exchangers frequently rather then superheated?
The heat transfer coefficient of superheated steam is poor. Saturated steam has a better heat transfer coefficient, and also most of the heat transferred from steam occurs because of the condensation phase change.
Is superheated steam suitable for air heaters instead of saturated steam?
No, superheated steam gives off little energy. Most of the heat given off by steam is the latent heat of condensation as it undergoes a phase change from vapor to liquid. Superheated steam could first be "desuperheated" by adding water until it reaches the saturation point, then used for heat transfer processes.
What is the difference between saturated steam and Superheated steam?
Saturated steam occurs when steam and water are in equilibrium. If you have a closed container of water and heat it, above 100 celsius the steam pressure will start to rise, and as the temperature continues to rise, the pressure will go on rising. What is happening is that steam is being evolved to match the temperature (steam tables will give this relation) and the steam conditions are said to be saturated because if the pressure is raised by external means, some of the steam will start to condense back to water.If the steam pressure is held at a lower level than that achieved at saturation, by taking steam off to feed a turbine or other steam usage, there is effectively an excess temperature for that pressure, and the steam is said to be superheated. It in fact then becomes dry, and behaves as a gas. The amount of superheat can be quantified as so many degrees of superheat (celsius or fahrenheit).Turbine designers want steam to be superheated before reaching the turbine, to avoid condensation causing blade erosion, and steam producing boilers in power plants are designed to produce superheated steam. In plants where no turbines are used, only satured steam is normally generated.In heating applications, saturated steam is preferable, because it has a better energy exchange capacity. Superheated steam must cool down, and become saturated steam, before condensing in a heat exchanger. Also, superheated steam is a thermal insulator, like air.That is why it is necessary to direct superheated steam through a desuperheater before using the steam in heating applications.
Why is superheated steam used in power plant?
because if the steam is not superheated the remaining water droplets reduce efficiency and can cause corrosion and pitting. +++ Nearly! Saturated steam, as non-superheated steam is called, is really only steam at the pressure and temperature in the boiler. Once it starts to expand as a gas in doing its work, the pressure and temperature fall and condensation will set in, leaving less and less useful water-vapour to act as a gas. Hence, as you say, the efficiency falls.
What the device used to increase the temperature of the saturated steam without increasing its pressure is called?
There is a small problem with the question: if you increase the temperature of saturated steam without increasing pressure, it will no longer be saturated - it will be superheated. With this in mind, it should be no surprise that the device that does this is normally called a "superheater". The picture accompanying this question is an example of a superheater.
How much energy is used per kilogram of steam?
That would depend on if the steam is superheated dry steam or not and if superheated dry steam its temperature. It should be possible to google "boiler equations" or "boiler design" to get details.
Why is heat trasnfer coefficient of saturated steam is higher than superheated steam?
when steam is at its saturation point for a given pressure, any heat removed will cause liquid water to form. So when saturated steam is used to heat something else, the heated object/substance receives the condensation heat of the steam. The latent heat of condensation/evaporation is 970 But/lb @ 0 psig. On the other, superheated steam only gives up about 10 BTU/lb if it is cooled 20 degrees F. That means that much more steam would be used to transfer the equivalent amount of heat. The liquid water interface also improves the heat transfer.
Why not super heated steam used in nuclear power plant?
Actually, superheated steam is used in nuclear power plants. It is part of the goal of extracting the most energy possible from the steam cycle.
How steam required for steam tracing of jacketed lines is calculated how much steam required for sulfur melting?
The steam required for steam tracing is calculated on the basis of the amount of heat transfer that is required or the temperature that you want to maintain with the help of steam. It also depends on the pipe material through which the steam is passing,the condition of the steam that whether it is saturated or superheated etc. Overall heat transfer cofficient is calculated considering all the factors like fouling or scaling,inside and outside dia. , surface area etc. After calculating the amount of heat to be transferred, the requirement of rate of steam is calculated. Generally, Low pressure steam is used as it has got more latent/Sensible heat as compared to MP or Superheated steam.
How can you use superheated steam to grow plants?
steam will kill just about any plant and superheat steam even more so. they are used for cleaning and disinfecting greenhouses and soil.
How atomic energy convert electric energy?
It is converted to heat first; this heat is then used to produce superheated steam. The pressure of the steam is what drives the electric generators.
What is meant by desuperheating vapor?
Basic steam desuperheatingDesuperheating is the process by which superheated steam is restored to its saturated state, or the superheat temperature is reduced. Most desuperheaters used to restore the saturated state produce discharge temperatures approaching saturation (typically to within 3°C of the saturation temperature as a minimum).Designs for discharge temperatures in excess of 3°C above saturation are also possible and often used.There are basically two broad types of desuperheater:Indirect contact type - The medium used to cool the superheated steam does not come into direct contact with it. A cooler liquid or gas may be employed as the cooling medium, for example, the surrounding air. Examples of this type of desuperheater are shell and tube heat exchangers. Here the superheated steam is supplied to one side of the heat exchanger and a cooler medium is supplied to the other side. As the superheated steam passes through the heat exchanger, heat is lost from the steam, and gained by the cooling medium. The temperature of the desuperheated steam could be controlled by either the inlet superheated steam pressure or the flowrate of the cooling water. Control of the superheated steam flow for this purpose is not normally practical and most systems adjust the flow of the cooling medium.Direct contact type - The medium used to cool the superheated steam comes into direct contact with it. In most cases, the cooling medium is the same fluid as the vapour to be desuperheated, but in the liquid state. For example, in the case of steam desuperheaters, water is used. A typical direct contact desuperheating station is shown in Figure 15.1.3. When the desuperheater is operational, a measured amount of water is added to the superheated steam via a mixing arrangement within the desuperheater. As it enters the desuperheater, the cooling water evaporates by absorbing heat from the superheated steam. Consequently, the temperature of the steam is reduced.Control of the amount of water to be added is usually achieved by measuring the temperature of the steam downstream of the desuperheater. The set temperature of the desuperheated steam would typically be 3°C above that at saturation. Therefore, in such arrangements the inlet pressure of the superheated steam should be kept constant.Desuperheating calculationsThe amount of water added must be sufficient to cool the steam to the desired temperature; too little water and the steam will not have been cooled enough, too much and wet saturated steam will be produced which will require drying through a separator. Using Equation 15.1.1, which is based on the conservation of energy, the cooling liquid requirement can be easily and quickly determined:Equation 15.1.1Where:cw=Mass flowrate of cooling water (kg / h)s=Mass flowrate of superheated steam (kg / h)hs=Enthalpy at superheat condition (kJ / kg)hd=Enthalpy at desuperheated condition (kJ / kg)hcw=Enthalpy of cooling water at inlet connection (kJ / kg)Example 15.1.1Determine the required cooling water flowrate for the conditions in the following Table:Solution:The necessary information can be obtained or interpolated from hard copy steam tables; the relevant extracts are shown in Table 15.1.1 and Table 15.1.2. Alternatively, the Spirax Sarco online steam tables can be used.Table 15.1.1 Extract from steam tables - Saturated water and steamTable 15.1.2 Extract from steam tables - Superheated steamThe information required to satisfy Equation 15.1.1 is therefore:s=Mass flowrate of superheated steam = 10 000 kg / hhs=Enthalpy at superheat condition (From steam tables 300°C at 10 bar a) = 3 052 kJ / kghcw=Enthalpy of the cooling liquid = 4.2 kJ / kg°C x 150°C =630 kJ / kgDetermining the enthalpy at the desuperheated condition, hd:From steam tables, the saturation temperature (T s) at 10 bar a is 180°C, therefore at the required desuperheated condition, the temperature will be:Ts + 5°C = 185°CInterpolating between the enthalpy of steam at 10 bar a and its saturation temperature, and at 10 bar a and 200°C:Enthalpy at 10 bar a, T s (saturated steam tables) = 2 778 kJ / kgEnthalpy at 10 bar a, 200°C (superheated steam tables) = 2 829 kJ/kgInterpolating for enthalpy at 10 bar a and 185°C:Finally, applying Equation 15.1.1:Equation 15.1.1Note that the desuperheated steam is supplied at a rate of:10 000 + 1 208 kg / h = 11 208 kg / hHad the requirement been for 10 000 kg / h of the desuperheated steam, the initial superheated steam flowrate can be determined using a simple proportional method:
