KESTNER EVAPORATOR PDF

Apart from the heating tube dimensions, it is very important to choose a suitable distribution device to achieve full wetting. Due to the low liquid content and high flow velocity in the heating tubes, the residence time of the product is very short. This not only reduces heat injury to the juice but also scaling intensity is reduced. Wetting rate is also known as juice loading per unit area of perimeter.

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Apart from the heating tube dimensions, it is very important to choose a suitable distribution device to achieve full wetting. Due to the low liquid content and high flow velocity in the heating tubes, the residence time of the product is very short. This not only reduces heat injury to the juice but also scaling intensity is reduced. Wetting rate is also known as juice loading per unit area of perimeter.

This rate is easily attained for the first vessel, but not for the later ones. Where it is not reached, it is necessary to provide for recycling juice between the outlet and the inlet of the vessel, in order to assure complete wetting of the tubes and avoiding periods of operation with partly dry tubes at times of low juice flow.

In some cases a recirculation line is installed on Kestner to achieve these rates However, in Robert and Kestner and evaporators, there is no need for any control systems to keep the tubes wetted. Wetting rate for Falling Film Evaporators : In Falling Film Evaporators require uniform and adequate wetting of the tubes and so need the complication of juice recirculation and a distribution system feeding equal quantities of juice to every tube.

An emergency water feed to the evaporator is also required, in case the juice supply fails; the absence of adequate feed even for a short time can lead to severe fouling of the tubes. The main problem, with a descending-film evaporator, is the distribution of juice on the upper tube plate.

It is necessary that all tubes from this plate, or from one section of the tube plate, should receive the required volume of juice so that the juice is distributed only in a thin layer around the tube, and that no section of tube remains dry at any moment. As per E. This requires a level of liquid held in the sump of the vessel and a control system to ensure that the required liquid flow to the distributor is achieved.

The falling film plate evaporators need a similar system, although the wetting rate required is lower. Good juice distribution is the key to good performance from falling film evaporators. Wetting rate calculation The constant wetting of the heating tubes with juice is of great importance for a trouble-free operation of a falling film evaporator.

According to that we can calculate capacity of circulation pump.

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Semi-Kestner / Evaporator

Thi is the hot fluid inlet temperature Tho is the hot fluid outlet temperature Tci is the cold fluid inlet temperature Tco is the cold fluid outlet temperature The hot fluid in the case of the rising film evaporator would be the steam in the shell side and the cold fluid would be the liquid inside the long tubes. In relation to the overall heat transfer rate, there are several key parameters that affect this characteristic specifically in terms of a rising film evaporator. Heat transfer coefficients[ edit ] For a rising film evaporator, the main paths of heat transfer are conduction and convection. These occur as the steam in the shell side heats up the tube and as the tube heats up the liquid and vapour within.

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Cail & Fletcher Roberts and Kestner evaporator

The rising film which is formed due to the pressure of the vapor within the vertical tubes greatly influences the efficiency of kesnter heat transfer. Semi Kestner Evaporator As more vapour is formed, the centre of the tube will have a higher velocity which forces the remaining liquid against the tube wall forming a thin film which moves upwards. Despite that, increasing the area of the heat transfer may include complications in terms of increasing the different dimensions of the evaporator which in results increases eevaporator cost of construction in addition to being subject to other limitations such as space and design constraints. Nonetheless, while weighing in the cost of the construction against the requirement, the size can be always adjusted and customized depending on the required application in producing the desired products. Email to friends Share on Facebook — opens in a new window or tab Share on Twitter — opens in a new window or tab Share on Pinterest — opens in a new window or tab. As more vapour is formed, the centre of the tube will have a higher velocity which forces the remaining liquid against the tube wall forming a thin film which moves upwards.

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