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Chemical Engineering


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  1. 3 points
    Arun Gupta

    What is the Arrhenius equation used for?

    this explains well http://www.chemguide.co.uk/physical/basicrates/arrhenius.html
  2. 1 point
    Arun Gupta

    Why baffles are used in reactors?

    The ideal CSTR model assumes that the fluid in the reactor is perfectly mixed, and that there are no concentration gradients inside the reactor. However, in a real-world stirred tank reactor, you won't have perfect mixing and there will be concentration gradients present. The baffles contribute additional disturbance to the flow created by the mixer, and provide more effective mixing. So, including the baffles brings you closer to the ideal of perfect mixing
  3. 1 point
    Haris Shahid

    What is difference between fouling and scaling?

    Fouling is any particles that are able to "cling" to the surface of the plate, but can be removed relatively easily by mechanical means such as hydro blasting or scrubbing with a soft bristle brush. Fouling can usually be taken care of during a typical maintenance cycle. Scaling is a very different phenomenon from fouling. Scaling occurs when a mineral film coats the entire surface of a heat exchanger. The most common forms of scale are usually from calcium-based salts such as calcium sulfate or calcium carbonate. They belong to a family of salts referred to as "reverse soluble salts". Reverse soluble salts act in the opposite way. As temperature increases, their solubility decreases in water. So, when you heat a water-based stream containing these salts, the salts begin to plate out onto the heat transfer surfaces. Once this happens, the heat transfer performance of your heat exchanger will decrease quickly. Scale cannot be removed by hydro blasting or your typical scrubbing. The only reliable way to remove these types of scale is by acid cleaning the plates. The scale has to be dissolved and carried away from the plate surface.
  4. 1 point
    Outstanding properties of teflon:- Uses of Teflon and Properties 1. Chemicals includes ozone,chlorine,acetic acid ammonia,sulphuric acid and hydrochloric acid. The coatings are affected by molten alkali metals and highly reactive fluorinating agents. 2. It is weather and UV resistant Teflon 3. It has excellent optical properties 4. It is non stick Very few solid substances can permanently stick to a Teflon coating, where as tacky materials may show some adhesion, almost all substances release easily from the coating. 5. It has outstanding performance at extreme temperatures. Teflon can temporarily withstand temperatures of 260C and cryogenic temperatures of -240C and will then also have the same chemical properties.It has an initial melting point of 342C (+- 10C) temperature. 6. It has low coefficient of friction. Coefficient of friction is the ratio of the force required to make two surfaces slide over each other. A low coefficient of friction equals low resistance and smooth operation. Thus there is no difficulty in sliding one surface against another. The coefficient of friction of Teflon is generally in the range of 0.05 to 0.20, depending on the load, sliding speed, and type of Teflon coating used. 7. Teflon finishes are both hydrophobic and oleophobic, which makes cleanup easier and more thorough. 8. Over many different frequencies, low dissipation factor and high surface resistivity teflon has a high dielectric strength. The high voltage that the insulating material can withstand before it breaks down is its dielectric strength . In addition to it teflon has a low dissipation factor; that is the percentage of electrical energy absorbed and lost when current is applied to an insulating material. A low dissipation factor indicates that the absorbed energy dissipated as heat is low.The high surface resistivity indicates the electrical resistance between opposite edges of an unit square on the surface of an insulating material. Uses of Teflon:- The various market applications of Teflon include : Computer pin belt 1. In electronics industry it is used on account of its insulation property in wires and system components.Also used because of its outstanding electrical performance and durability. Uses for coating 2. Used for metal finishing, paints and coatings,as flour additives can be added to reduce the wear and tear on load-bearing surfaces. For example in inks and lithographic printing, thermoplastics and molded gears, protective industrial surfaces, lubricants to thicken, sterile packaging, etc. Uses as automobile air bags 3. In optical devices, as it can be used as clear coating, requiring a low refractive index and still perform in aggressive chemical environments over a wide range of use temperatures and light waves (UV-IR). For example, it is found in lightweight surgical lamps, photovoltaic cell glazing, etc. 4. In automobiles it finds its uses as airbag systems, fuel hose permeation barrier, fuel system, chassis, brake systems, oil filter, etc. 5. Used as nonstick coating on cooking devices like pans, oven , tawa as it is nonstick and exceptional performance at high temperatures.
  5. 1 point
    Pressurize in shell side and check in individual tubes for leakage
  6. 1 point
    Both equipment is based on phase change phenomenon . In heat exchanger use fast and stabilised the liquid to its general temperature but cooling tower use large section to exposed to liquid to gas phase phenomenon.
  7. 1 point
    Direct mixing and heat transfer take place in case of cooling tower while indirect mixing and heat transfer happens in heat exchangers.
  8. 1 point
    In HE heat transfer through conductions principle and in cooling tower heat transfer through convention principal.
  9. 1 point
    Jay Lokwani

    How can we measure entropy?

    You cannot measure entropy of any system at any point. You can only measure the change in entropy of system by determining the state of system. Only entropy known is the one given by third law of thermodynamics which says the entropy of perfectly crystalline solid at 0 K temperature is zero.
  10. 1 point
    In case of centrifugal pump the liquid would keep on revolving in side the pump and would heat up though Electric consumption would be low than if the discharge valve is open.

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