.The Spray Condenser. The coolant is sprayed, using nozzles, into a vessel to which the vapor is supplied.
This is shown schematically in. It is important that the spray nozzles and vessel are designed to produce a fine spray of liquid (to give a large interfacial area for heat transfer), and a long enough residence time of liquid droplets in the vessel.The Baffled Column. This is similar to the spray condenser, except that the coolant is directed to flow over a series of trays in a column (see ). The vapor is supplied to the bottom of the column. It has the advantage of countercurrent flow of vapor and coolant, though care must be taken to avoid flooding. (Flooding is an unstable condition when the vapor flow is such that the downward flow of condensate is interrupted and held up.).The Packed Column.
A packed column may consist of tightly-packed metal rings to increase the interfacial area for heat transfer. Liquid is supplied to the top of the column and vapor is supplied to the bottom. The disadvantage of this type of condenser is that the pressure drop is higher than in other types of direct-contact condenser.The Jet Condenser. This is a device in which a jet of liquid is directed into a vapor stream, usually with the objective of desuperheating the vapor. A jet of liquid is injected into a pipeline carrying vapor via a small bore pipe and a nozzle located at the center line. The liquid is usually injected in counterflow to the vapor.The Sparge Pipe.
The sparge pipe consists of a pipe with holes for injecting bubbles of vapor into a pool of liquid. This is a simple method of condensing a vapor, but there are practical problems associated with generating a good distribution of bubbles of small size, which are required for efficient heat transfer. Crossflow shell-side condenserThe crossflow condenser is similar to the surface condenser. It consists of a shell containing tubes through which the coolant flows. The shell-side flow path is designed such that the vapor flows mainly in crossflow direction to the tubes. The crossflow condenser is typically used for low-pressure applications, in which there is a large volume flow of vapor and a low-pressure drop is required.The tubes are supported at intervals by plates to prevent sagging of the tubes and to avoid vibration.The vapor enters at the top of the shell.
Often, more than one nozzle is used to minimise pressure loss and promote good distribution.It is particularly important to ensure that the crossflow condenser is properly vented. Tube-side condensersCondensation on the tube-side is preferred when the coolant is a gas, such as air. It may also be preferred if the condensing fluid is at a higher pressure than the coolant, since it is usually less expensive to contain a higher pressure inside tubes than inside a shell. An air-cooled condenser is typical of a tube-side condenser. It consists of a tube bundle, normally with finned tubes, over which air flows in crossflow.
The air flow is driven by fans, either in forced- or induced-draft mode. A typical forced-draft, air-cooled condenser is depicted in. Area calculation.In condensation of a single pure vapor, provided that the pressure drop is small compared to the absolute pressure, the temperature of the condensing stream is a constant value determined by the saturation pressure.If the coolant is single-phase, and if the overall heat transfer coefficient is reasonably constant, then the assumptions underlying the “logarithmic mean temperature difference (LMTD)” are valid. (See.) This means that the surface area requirement, A, of the condenser can be determined from. Where Q T is the total heat load and U is the mean overall heat transfer coefficient.In condensation from mixtures, with or without a noncondensing gas, the variation of the equilibrium temperature with enthalpy can be highly nonlinear. Also, the heat transfer coefficient of the condensing stream can vary by an order of magnitude over the condensing path.
This means that it is not possible to assign a single representative temperature difference and overall heat transfer coefficient to the exchanger, and that a zonal or stepwise calculation of the surface area is required.The thermal design of condenser is therefore considerably more complicated than that of a single-phase heat exchanger.shows a typical temperature/enthalpy relationship for a mixture which is superheated at entry. This relationship, and the corresponding physical properties, are normally obtained from specialist computer programs which perform vapor-liquid equilibrium calculations and determine the compositions of the vapor and liquid phases along the condensing path.
Contents.Condenser system and vacuum equipment are common to evaporators and vacuum pans. Nearly all these vessels use direct contact condensers, where the cooling water comes into direct contact with the vapour to be condensed. Creation of Vacuum:. In a condenser, we condense large volume of vapour and it will only produce a comparatively small volume of wateror (condensate) and this water runs out through the bottom of the condenser down the barometric leg with the waste water. Therefore if we have condensed the large volume of vapor into small volume of water in a condenser, the remaining volume or area must be a vacuum(reduced).
Thus we have created a vacuum. With the aid of an air pump or other, vacuum is produced in an enclosed vessel called a condenser, which communicates with the vessels to be maintained under vacuum. Cold water is pumped in to the condenser to ensure condensation of vapour coming from pan or multiple effect evaporator.
The Condenser is placed at a height that the water after condensation flow out by gravity together with condensed vapours. A = coefficient depending on the length of the pipe, its bends, valves and other obstructions to flow. In general, ” a ” is of the order of 5g = 9.8 m/sec 2h = head of cold water, at entry to condenser, in mtr (h = pressure Of water at inlet X head at mean sea level) Multi Jet Condensers ( Wet air barometric condensers):Principle:Jet condensers were first placed on the market by Schutte – Koerting about 1930. They are based on the dynamic effect of jets of water which, penetrating into the body of water in the barometric column, enter with them, by friction, the air contained in the condenser.
If the cross-section of the barometric column is small enough to ensure a suitable velocity, the bubbles of air do not rise into the condenser and are evacuated to the well at the foot of the column. The main difference with the Multi Jet condenser is that, it does not require air pump, and although it requires more water than the dry air type condenser, it is more economical to operate and maintain.
This type of condenser has high pressure water jet nozzles fitted in the lower section of the condenser, directed straight at the outlet or barometric leg. The vapor inlet to the condenser is from the top of the condenser much above the level of the jet.
The nozzles are called as jet nozzles and they create vacuum in the system. The jet is given such manner, that the jet of water will flow exactly through the center of the tailpipe. On the top portion of the jet box another set of nozzles is fitted circumferential through which the flow of pressurized water is flowing towards the center of the box. This part of water is responsible for the condensation of vapour, which is called as spray nozzles. As against the dry air type, the Multi Jet differs (wet type) in principle that due to the high velocity of water passing down the barometric leg, air or gas bubbles will not rise but instead it will be drawn away through the outlet with the waste water. The pressure of water in both the parts to be employed as between 0.5 to 0.7 kg/cm2 for observing the pressure the gauges are fitted to inlet pipes.
The proportion of the quantity of water is in ratio of 40% water to jet and 60% to spray.Diameter of spray nozzle (Ds)Ds =As (area of the each spray nozzle ) = Qs / VsQs = Quantity of water per each spray nozzle in M 3/Sec = Quantity of water / No. Of spray nozzlesVs = Velocity of water at nozzle in m/sec =h = Pressure of water at spray nozzle in kg/cm 2 x head at mean sea level Diameter of jet nozzle (Dj ):Dj =Aj (area of the each jet nozzle) = Qj / VjQj = Quantity of water per each jet nozzle in M 3/Sec = Quantity of water / No. Of jet nozzlesVj = Velocity of water at nozzle in m/sec =h = Pressure of water at jet nozzle in kg/cm 2 x head at mean sea level Condenser Vapour pipe dia:Quantity of vapour to condensed (Q) = Heating surface of the equipment x Evaporation rate.Cross sectional area of the vapour pipe = Quantity of vapour in M 3/sec / Velocity of vapour in m/sec.
Condenser Design Calculation
Condenser Diameter:Cross sectional area of the condenser =( Quantity of vapour in M 3/sec + Quantity of inlet water to the condenser in M 3/sec) / Velocity of vapour in m/sec. Single Entry Condenser:. Single entry condensers are having only one water distributing box for spray and jet nozzles. Out of total water about 60 to 80% water is used at Spray nozzles and 20 to 40% water for jet nozzles. Vapours are condensed by forming fine mist inside the condenser, increasing surface area of contact and finally minimum requirement of water. The difference between approach temperature ( difference between vapour temp.
And condenser water tail pipe temp) does not exceed 5 to 6 0C. The Specially designed high efficiency centrifugal spray nozzles fitted on the jet box create micro fine atomized spray, resulting into wider surface contact with incoming vapours. The difference between water outlet temperature and inlet temperature of 10°C is achieved. Under automation the difference can achieved upto 15°C. Single entry and Multi jet condensers are of Parallel flow type wet air condenser.
The Single entry condenser requires less water than conventional Multijet condenser due to the following reason. In the single entry condenser design the spray nozzles are fitted in nozzle box which fitted at the center of the condenser. Thus the spray water covers all the available area inside the condenser hence the spray water particles contact area for the vapour condensation is more than the multi-jet condenser system. Another impotent parameter in this design tail pipe diameter and velocity of water in the tail pipe.
Condenser Design Calculation Pdf Reader Pdf
The nozzles dia calculation same as multijet condenser. The velocity of warm water (outlet water ) goes upto 4 to 5 m/sec. The design of bottom cone, its reducer and venture were placed important role.Condenser Water RequirementIn a condenser the vapours entering, transfer heat to the cold injection water, the heat transmission depending on the temperature and quantity of water.