Heat exchanger tube-side film coefficient

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... 

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. ... 

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] ... 

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 TUBE SIDE HEAT EXCHANGER... 

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). 

This U value is called as clean U value because fouling resistances (/ j, / o) are not taken into account in equation (6.2). The film coefficients, hi and h, can be calculated based on the fluids physical properties and the geometry of the heat exchanger. For example, for U-tube exchangers with streams all liquid or aU vapor (no boiling and condensing), the correlation (Dittus and Boelter, 1930) is used to estimate the tube side Nusselt... 

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. 

A standby air liquefaction plant uses a cold carbon dioxide gas to countercurrently precool a 20.2-MPa air stream from 300 to 260 K in an insulated concentric tube heat exchanger. The cold carbon dioxide gas enters the outer annulus at 220 K and exits at 280 K. The mass flow rate of the carbon dioxide gas is 1 kg/s. The outside diameter of the inner pipe is 80 mm, while the inside diameter of the outer pipe is 155 mm. Assuming comparable resistances to heat transfer through the carbon dioxide and air films, evaluate the heat transfer coefficient for the carbon dioxide side of the heat exchanger. At a mean film temperature of 257 K, carbon dioxide gas has the following properties /i= 1.28 x 10 kg/m s Cp = 795.7 J/kg K p = 2.11 kg/ml... 

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