Steam hammer

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As steam blow is referred to the sequence of implosionsartigen condensation of vapor - bubbles in a colder liquid.

Steam hammer occurs when steam is passed into a liquid that is at a lower temperature. The vapor bubbles condense through the heat transfer to the surrounding liquid and collapse suddenly (up to supersonic speed ). A vacuum is created , which is taken up by the liquid.

In contrast to the steam hammer, a water hammer is caused by a strongly accelerated volume of water that hits a wall.

Steam hammer in steam systems

Technically significant are steam hammer in steam systems such as steam boiler systems . With the targeted introduction of steam into liquids, e.g. B. for heating water, nozzle holders are chosen with a small cross-section in order to generate as many small-volume bubbles as possible. As a result, the pressure pulses that occur during condensation are evenly distributed over a large volume. The pressure waves generated by the individual bubbles are superimposed and there are no high stress amplitudes that affect the surrounding container wall.

Unintentional steam hammer occurs when condensate has not been adequately removed from equipment or pipes and hot steam flows into the cold liquid. In these cases the steam hammer is triggered by a very large volume of steam. The steam hammer can cause very serious damage, such as B. tearing off pipe supports or even tearing open a container. Steam hammer is one of the most common causes of serious accidents in steam power plants and steam boiler systems .

There is a particular risk from steam hammer in hot water systems or solar collectors that are operated at temperatures above 100 ° C. If the system pressure is higher than the saturated steam pressure at the maximum operating temperature due to external pressure maintenance (e.g. diaphragm expansion tank, dictation pumps) , no evaporation takes place in fault-free operation. If the pressure maintenance fails or if the heating temperature is too high, the water evaporates on the heating surfaces . In colder areas of the system, however, the steam condenses, so that steam hammer occurs there.

Steam hammer can also occur locally in the microscopic range and are then referred to as cavitation . The effect also occurs on a small, controlled scale in the milk frothers of fully automatic coffee machines . The characteristic screeching noise when the steam is introduced into the milk is caused by microscopic steam hammer.

Steam hammer in refrigeration systems

In refrigeration systems , steam hammer can occur in the refrigerant circuit when evaporators are periodically exposed to hot refrigerant steam to cool the room air below 0 ° C in order to defrost the ice jacket on the air side. If the liquid refrigerant has not yet completely evaporated and the superheated steam is then released too early, steam hammer occurs in the evaporator.

Individual evidence

  1. ↑ PIRAX SARCO GmbH (Ed.): Basics of steam and condensate technology. Konstanz 2014. Online (accessed August 2, 2018)
  2. ↑ Steam trap (accessed August 2, 2018)
  3. ^ Deutsches Kupferinstitut (Ed.): The professional installation of thermal solar systems. Online (accessed August 2, 2018)
  4. ↑ Dirk Bartel: Simulation of tribological systems. Basics and applications, Vieweg + Teubner Verlag, Wiesbaden 2010, ISBN 978-3-8348-1241-4 , p. 31.33.

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