Condensing steams heat transfer coefficient

An organic liquid is boiling at 340 K on the inside of a metal surface of thermal conductivity 42 W/m K and thickness 3 mm. The outside of the surface is heated by condensing steam. Assuming that the heat transfer coefficient from steam to the outer metal surface is constant at 11 kW/m2 K, irrespective of the steam temperature, find the value of the steam temperature to give a maximum rate of evaporation. 

Estimate the heat-transfer coefficient for steam condensing on the outside, and on the inside, of a 25 mm o.d., 21 mm i.d. vertical tube 3.66 m long. The steam condensate rate... 

The correct heat-transfer coefficient for a clean surface condenser, with a water-side velocity of 6 ft/s, is about 200 to 240. Including an allowance for fouling, we suggest you use 140 to 160 overall heat-transfer coefficient, for steam surface condensers. 

It can be seen from Fig. 7.17 that the condensing heat-transfer coefficient for a fluid with a Prandtl number of approximately 2 (for instance, steam) is not strongly dependent on flow rate or Reynolds number. For this reason, heat-transfer coefficients for steam condensing on vertical tubes are frequently not calculated, but are assigned a value of 1500 to 2000Btu/(h)(ft2)(°F) [8500 to 11,340 W/(m2)(K)]. 

FIGURE 14.2 The influence of surface material and operating pressure on the dropwise condensation heat transfer coefficient of steam. (Adapted from Ref 1 and printed with permission from Academic Press, Inc., Orlando, FL.)... 

Mechanisms of condensation. Condensation of a vapor to a liquid and vaporization of a liquid to a vapor both involve a change of phase of a fluid with large heat-transfer coefficients. Condensation occurs when a saturated vapor such as steam comes in contact with a solid whose surface temperature is below the saturation temperature, to form a liquid such as water. 

Steam. The steam system serves as the integrating energy system in most chemical process plants. Steam holds this unique position because it is an exceUent heat-transfer medium over a wide range of temperatures. Water gives high heat-transfer coefficients whether in Hquid phase, boiling, or in condensation. In addition, water is safe, nonpolluting, and if proper water treatment is maintained, noncorrosive to carbon steel. 

For steam side noncondensibles, a proper vent is required. A small amount of noncondensibles can greatly lower the steam side heat transfer coefficient. The improper removal of condensate is another way to reduce... 

In water-cooled tube-and-shell condensers with shell side condensation, overall heat transfer coefficients for essentially pure steam range from 200 to 800 Btu per hour per square foot per °F. 

A stirred reactor contains a batch of 700 kg reactants of specific heat 3.8 kJ/kg K initially at 290 K, which is heated by dry saturated steam at 170 kN/m2 fed to a helical coil. During the heating period the steam supply rate is constant at 0.1 kg/s and condensate leaves at the temperature of the steam. If heat losses arc neglected, calculate the true temperature of the reactants when a thermometer immersed in the material reads 360 K. The bulb of the thermometer is approximately cylindrical and is 100 mm long by 10 mm diameter with a water equivalent of 15 g, and the overall heat transfer coefficient to the thermometer is 300 W/m2 K. What would a thermometer with a similar bulb of half the length and half the heat capacity indicate under these conditions ... 

Assume that the film heat transfer coefficient for the liquid in the tubes is proportional to the 0.8 power of the. velocity, the transfer coefficient for the condensing steam remains constant at 3.4 kW/m- K and that the resistance of the tube wall and scale can be neglected. 

Example 17.2 For the process in Figure 16.2, calculate the target for network heat transfer area for ATmi = 10°C. Steam at 240°C and condensing to 239°C is to be used for hot utility. Cooling water at 20°C and returning to the cooling tower at 30°C is to be used for cold utility. Table 17.1 presents the stream data, together with utility data and stream heat transfer coefficients. 

A single-effect evaporator is used to concentrate 7 kg/s of a solution from 10 to 50 per cent of solids. Steam is available at 205 kN/m2 and evaporation takes place at 13.5 kN/m2. If the overall heat transfer coefficient is 3 kW/m2 K, calculate the heating surface required and the amount of steam used if the feed to the evaporator is at 294 K and the condensate leaves the heating space at 352.7 K. The specific heat capacity of a 10 per cent solution is 3.76 kJ/kgK, the specific heat capacity of a 50 per cent solution is 3.14 kJ/kgK. 

A triple-effect evaporator is fed with 5 kg/s of a liquor containing 15 per cent solids. The concentration in the last effect, which operates at 13.5 kN/m2, is 60 per cent solids. If the overall heat transfer coefficients in the three effects are 2.5, 2.0, and 1.1 kW/m2K, respectively, and the steam is fed at 388 K to the first effect, determine the temperature distribution and the area of heating surface required in each effect The calandrias are identical. What is the economy and what is the heat load on the condenser ... 

A double-effect forward-feed evaporator is required to give a product which contains 50 per cent by mass of solids. Each effect has 10 m2 of heating surface and the heat transfer coefficients are 2.8 and 1.7 kW/m2 K in the first and second effects respectively. Dry and saturated steam is available at 375 kN/m2 and the condenser operates at 13.5 kN/m2. The concentrated solution exhibits a boiling-point rise of 3 deg K. What is the maximum permissible feed rate if the feed contains 10 per cent solids and is at 310 K The latent heat is 2330 kJ/kg and the specific heat capacity is 4.18 kJ/kg under all the above conditions. 

A salt solution at 293 K is fed at the rate of 6.3 kg/s to a forward-feed triple-effect evaporator and is concentrated from 2 per cent to 10 per cent of solids. Saturated steam at 170 kN/m2 is introduced into the calandria of the first effect and a pressure of 34 kN/m2 is maintained in the last effect. If the heat transfer coefficients in the three effects are 1.7, 1.4 and 1.1 kW/m2K respectively and the specific heat capacity of the liquid is approximately 4 kJ/kgK, what area is required if each effect is identical Condensate may be assumed to leave at the vapour temperature at each stage, and the effects of boiling point rise may be neglected. The latent heat of vaporisation may be taken as constant throughout. 

Overall heat transfer coefficients for any form of evaporator depend on the value of the film coefficients on the heating side and for the liquor, together with allowances for scale deposits and the tube wall. For condensing steam, which is a common heating medium, film coefficients are approximately 6 kW/m2 K. There is no entirely satisfactory... 

An evaporator, working at atmospheric pressure, is to concentrate a solution from 5 per cent to 20 per cent solids at the rate of 1.25 kg/s. The solution, which has a specific heat capacity of 4.18 kJ/kg K, is fed to the evaporator at 295 K and boils at 380 K. Dry saturated steam at 240 kN/m2 is fed to the calandria, and the condensate leaves at the temperature of the condensing stream. If the heat transfer coefficient is 2.3 kW/m2 K, what is the required area of heat transfer surface and how much steam is required The latent heat of vaporisation of the solution may be taken as being equal to that of water. 

The condensing temperature of the steam is 300°F. The process into which the heat is transferred is at a constant temperature of 20O°F. The overall heat transfer coefficient is 300 Btu/h °F ft. The reboiler has S09 tubes that arc 10 feet long and 1 inch inside diameter. The steam and condensate are inside the tubes. The density of the condensate is 62,4 Ib ft and the latent heat of condensation of the steam is 900 Btu/lb . Neglect any sensible heat transfer. 

In a retort which uses condensing steam the heat transfer coefficient to the can is of the order of 5000-10 000 and therefore the... 

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