Condensate outlet temperature, increase

The oldest, most direct method of pressure control is throttling on the cooling-water supply. This scheme is shown in Fig. 13.5. Closing the water valve to the tube side of the condenser increases the condenser outlet temperature. This makes the reflux drum hotter. The hotter liquid in the reflux drum creates a higher vapor pressure. The higher pressure in the reflux drum increases the pressure in the tower. The tower pressure is the pressure in the reflux drum, plus the pressure drop through the condenser. 

But not for long. After 15 min of operation, the turbine speed slipped back down. Once again, I had lost a lot of vacuum in the surface condenser. Once again, the vapor outlet temperature had dramatically increased. But this time, the condensate outlet temperature had also increased. What was my new problem ... 

The accumulator drum temperature equals the condenser outlet temperature. High circulating refrigerant rates increase the heat load on the condenser and raise the accumulator temperature. Hot weather has the same effect. 

On the same tower, a hot-vapor bypass around the condenser starts leaking. This puts a small amount of vapor into the reflux drum inlet. On mixing with the condenser outlet, the vapor condenses and increases the reflux drum temperature 3°F. For the contents of the reflux drum to remain at its bubble point, the condenser outlet temperature must drop an additional 3°F. Now, a total of 7.5°F subcooling is required. This is a lot of subcooling. 

Chilled-water temperature. As the chilled-water outlet temperature decreases, the ratio of steam/refrigeration effect decreases, thus increasing condensing temperatures and/or increasing the con-densing-water requirements. 

Water at 293 K is heated by passing through a 6.1 m coil of 25 mm internal diameter pipe. The thermal conductivity of the pipe wall is 20 W/m K and the wall thickness is 3.2 mm. The coil is heated by condensing steam at 373 K for which the film coefficient is 8 kW/m2 K. When the water velocity in the pipe is I tn/s, ils outlet temperature is 309 K. What will the outlet temperature be if the velocity is increased to 1.3 m/s, if the coefficient of heat transfer to the water in the tube is proportional to the velocity raised to the 0.8 power ... 

The temperature difference between inlet and outlet temperature at the coil(s) of the refrigerant should be smaller than 1 °C (AT < 1 °C), to ensure a uniform condensation on the total coil. On warmer areas no ice will condense until the temperature at the ice surface has increased to the warmer temperature on the coil. For large surfaces it is necessary to use several coils or plates in parallel, each of which must be separately temperature controlled. If the condenser is operated in an overflow mode, the weight of the liquid column should not change the boiling temperature of the liquid at the bottom of the column measurably. 

The next step wos to calculate the omount of dissolved water thot would be precipitated from the condensate as it is cooled in a pipeline shut-in situation and also the increase in gos-woter content for each 0.01 increose in free water content. These were calculated for a ronge of Production Cooler outlet temperatures. 

Let s say that the cooling-water outlet temperature from the condenser was 140°F. This is bad. The calcium carbonates in the cooling water will begin to deposit, as water-hardness deposits, inside the tubes. It is best to keep the cooling-water outlet temperature below 125°F, to retard such deposits. Increasing the pumparound heat removal will lower the cooling-water outlet temperature. 

The increase in the vapor outlet temperature from a condenser, as compared to a decrease in the temperature of the condensate from the same condenser, is a sure sign of condensate backup. The condensate is covering some of the tubes in the surface condenser. This subcools the condensate and does no harm. 

I now observed that the surface condenser cooling-water outlet temperature had increased from 100 to 135°F. This is a sign of loss of cooling-water flow. As none of the other water coolers in the plant had been affected, I concluded that the cooling-water inlet to my surface condenser was partly plugged. 

Determine the tube-side inlet and outlet temperatures on a scale with increasing heat transfer as the liquid condenses and the temperature decreases. This... 

Air-cooled heat exchangers are employed on large scale as condensers of distillation columns or process coolers. The approach temperature - the difference between process outlet temperature and dry-bulb air temperature - is typically of 8 to 14 °C above the temperature of the four consecutive warmest months. By air-humidification this difference can be reduced to 5 °C. Air cooled heat exchangers are manufactured from finned tubes. Typical ratio of extended to bare tube area is 15 1 to 20 1. Finned tubes are efficient when the heat transfer coefficient outside the tubes is much lower than inside the tubes. The only way to increase the heat transferred on the air-side is to extend the exchange area available. In this way the extended surface offered by fins increases significantly the heat duty. For example, the outside heat transfer coefficient increases from 10-15 W/m K for smooth tubes to 100-150 or more when finned tubes are used. Typical overall heat transfer coefficients are given in Table 16.10. The correction factor Ft for LMTD is about 0.8. 

Focus attention on exchanger duties which are calculated from small temperature differences (e.g., a condenser duty calculated from the inlet and outlet temperatures and cooling water flow, where the temperatures are less than 10°F apart). Often, the flow can be throttled to increase the temperatm-e difference if this is impractical, high-accuracy temperature indicators may be required. 

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