# Complete vaporization time of water into superheated steam - DESUPERHEATER

• SimonTecnoil
In summary, the conversation discusses the problem of calculating the position and time of complete evaporation of a continuous water flow injected into a superheated steam flow. The position of a thermocouple is important for accurate temperature measurement, and the question of whether to use a continuous or discrete approach is raised. There is not enough information provided to suggest a reasonable approach, but it is recommended to consult a spray nozzle manufacturer or find a similar desuperheater system for guidance.
SimonTecnoil
Hi to all...i've a problem. i have to calculate the position and the time of complete evaporation of a continuous water flow which is injected trough a nozzle into a continuous flow of steam in superheated condition. The position (and than the time) at which I'm sure that there aren't water droplets is really important, 'cause I've to choose the position of a thermocouple which detects the effetc in temperature of the desuperheating stage. Clearly, the measurement of the thermocouple is wrong if is reached by water droplets.

I know all the macroscopic thermodynamic conditions of the system.

In your opinion, i have to consider the water flow according to a continuous or discrete approach? And if discrete...how i could manually calculate the diameter of the droplets of water?

I don't want to use CFD!

Could someone suggest a theoretic approach to the problem?

Last edited:
ping @Chestermiller , @jrmichler This is a spring cleaning post from 2010. It sounds like an interesting question. Thermo, but not thermo because it would have to do with drop size distribution and velocity.

Perhaps he could estimate the worst case with the largest drop moving at the highest velocity.

Whoops, ping @russ_watters also.

It seems to me that there is not enough information provided to suggest a reasonable approach to this. There isn't even an indication of whether the flow is horizontal or vertical, and whether the drops are large enough for gravity to play a role. There is also no indication of the ratio of the inlet flow rates or the degree of superheating and/or subcooling.

anorlunda
A desuperheater sprays water into a steam line to reduce the steam temperature down to somewhat above the saturation temperature. Typically (and ideally), the water is condensate at 90 to 100 deg C. Normally the steam velocity is high enough, and the droplet size small enough, to carry the water droplets in suspension. The water flow rate is controlled by the temperature of the desuperheated steam, hence the need to measure the steam temperature. The temperature sensor needs to be far enough downstream that the water is all evaporated, but not so far as to create a time lag in the control system. The desuperheater systems that I worked with had water flow rates from near zero with the steam turbine running, to quite high when the steam turbine was down.

If you really want to calculate droplet evaporation time, the spray nozzle manufacturer can supply droplet size information. The temperature difference will decrease as the droplets get smaller. The droplet size will change with water flow rate. Attempting to calculate the evaporation distance can easily turn into an exercise of paralysis by analysis because of the number of variables and unknowns.

A much easier approach is to find a desuperheater system of similar size and capacity, then ask how far downstream they put their temperature sensor. That approach will almost certainly give better results than a theoretical calculation.

anorlunda

## 1. How does a desuperheater work?

A desuperheater is a device that is used to reduce the temperature of superheated steam. It works by injecting a controlled amount of water into the steam, which then absorbs the heat and cools down the steam.

## 2. What is the purpose of a desuperheater?

The main purpose of a desuperheater is to control the temperature of superheated steam. This is important in industrial processes where precise temperature control is required. It also helps to prevent damage to equipment and ensure the safety of workers.

## 3. How long does it take for water to completely vaporize into superheated steam?

The time it takes for water to completely vaporize into superheated steam depends on several factors such as the temperature and pressure of the water and the surrounding environment. It can range from a few seconds to several minutes.

## 4. What are the benefits of using a desuperheater?

Using a desuperheater has several benefits, including precise temperature control, increased efficiency in industrial processes, and reduced wear and tear on equipment. It also helps to reduce energy consumption and costs.

## 5. How can the efficiency of a desuperheater be improved?

The efficiency of a desuperheater can be improved by using high-quality materials and regularly maintaining and calibrating the device. Proper installation and operation of the desuperheater can also help to increase its efficiency.

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