Heat exchanger shell-side film coefficient

U-value The overall heat transfer coefficient for a heating or cooling system, such as a heat changer, and is a measure of the thermal efficiency of the heat transfer device. It is dependent on the tube and shell side film coefficients as well as the thermal conductivity of the material of the heat exchanger. The SI units are W m K. ... 

In evaluating the overall heat transfer coefficient for the exchanger tube-side film resistance and wall resistances were taken as constant at 0.00103 and 0.00022, respectively the shell side resistance was taken to be temperature dependent. Then by standard calculations the overall heat transfer coefficient is... 

The calculated value based on exchanger design specifications is less than the assumed design value consequently, the design is not successful and the heat exchanger is underspecified. The shell side film heat transfer coefficient should be increased so that the overall heat transfer coefficient is increased. Assuming baffle spacing, b IS 7 in. 

Double-Pipe Scrapea-Surface Crystallizer This type of equipment consists of a double-pipe heat exchanger with an internal agitator fitted with spring-loaded scrapers that wipe the wall of the inner pipe. The cooling hquid passes between the pipes, this annulus being dimensioned to permit reasonable shell-side velocities. The scrapers prevent the buildup of solids and maintain a good film coefficient of heat transfer. The equipment can be operated in a continuous or in a recirculating batch manner. 

For sheU-aiKl-l-ube heat exchangers with shell-side balile. die shell-side fluid flow is perpendicular to the tubes. In this arrangement, the outside film coefficient can be calculated from the following equation ... 

TWo tubular heat exchangers are available each with a 0.44 m i.d. shell fitted with 166 tubes, 19.0 mm o.d. and 15.0 mm i.d., each 5.0 m long. The tubes are arranged in two passes on 25 mm square pitch with a baffle spacing of 150 mm. There are two passes on the shell side and operation is to be countercurrent. With benzene passing through the tubes, the anticipated film coefficient on the tube side is 1000 W/m2K. 

The detailed allocation of fluids to tube-side or shell-side can only be made later in the heat exchanger network design. Also, the area targeting formula does not recognize fluids to be allocated to the tube-side or shell-side. Area targeting only recognizes the individual film heat transfer coefficients. All that can be done in network area targeting... 

PROGRAM CALCULATES HEAT-TRANSFER FILM COEFFICIENT IN THE SHELL SIDE (BARE-TUBE) AND THE OVERALL HEAT TRANSFER COEFFICIENT OF THE HEAT EXCHANGER... 

Heat Transfer Enhancements Heat transfer enhancements increase the film heat transfer coefficient, thus improving U and consequently heat tfansfer in the exchanger. In the case of the ubiquitous ST heat exchanger, heat transfer enhancement can be achieved on the shell and/or tube sides as required. Tube-side enhancements help in improving the film heat transfer coefficient on the tube side, and are useful if the exchanger involved has lower film heat transfer coefficient on the tube side. Tube-side enhancements include, but are not limited to, twisted-tape inserts, coiled-wire inserts and internal fins. Similarly, shell-side enhancements are used to improve the heat transfer coefficient on the shell side. They include helical baffles, external fins and Expanded Metal (EM) baffles. More details on heat transfer enhancements are available in Pan et al. (2013). 

The overall heat transfer coefficient of the designed heat exchanger must be calculated to be compared with the guessed corrected value for this purpose, the tube side h) and shell side (hj film heat transfer coefficient must be determined. The tube side film heat transfer coefficient h, is calculated using the following equation [6] ... 

The corrected overall heat transfer coefficient is within the design range (140-260 Btu/ft h °F). The assumed value should match U-value estimated from the heat exchanger design specifications that depends on the film heat transfer coefficient of tube side and shell side, fouling factor, and metal resistance. 

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