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Case Study — Phthalic Anhydride After-Cooler Design
Published in Martyn S. Ray, Martin G. Sneesby, Chemical Engineering Design Project, 2020
Martyn S. Ray, Martin G. Sneesby
The computer model of the after-cooler was used to optimise the exchanger configuration and to minimise the coolant flow rate. A provisional design was developed to estimate an appropriate starting point for the optimisation of the design using the computer simulation model. This design is detailed in Appendix E at the end of this chapter. This design was based on several key assumptions: standard tube dimensions (25.4 mm o.d., 14 BWG, 6.0 m long); standard tube pitch (32 mm); log mean temperature difference (LMTD) of 10°C; heat transfer coefficient of 800W/m2/°C; basic exchanger configuration with two tube-side passes and one internal shell-side baffle; coolant inlet temperature of 120°C; film temperature that was relatively close to the exchanger outlet temperature (already fixed at 136°C through optimisation of the process layout and PFD); and a tube-side velocity of 1.5 m/s. The film temperature is important to prevent solidification on the tubes which would significantly reduce the heat transfer rate.
Liquid Crystal Thermography Techniques
Published in Je-Chin Han, Lesley M. Wright, Experimental Methods in Heat Transfer and Fluid Mechanics, 2020
The value of η falls between 0 and 1. η = 0 represents no film coverage, the film temperature, Tf, equals the mainstream temperature, Tm. η = 1 represents highest effectiveness, the film temperature, Tf, equals the coolant temperature, Tc. When film cooling takes place, the driving temperature for the convective heat transfer becomes the film temperature, instead of the mainstream temperature. Thus, Tm in Equation (7.3) is replaced with the film temperature, Tf. The governing equation becomes: () Tw−Ti=[1−exp(h2αtk2)erfc(hαtk)]⋅[ηTc+(1−η)Tm−Ti]
Convection Heat Transfer in Flows Past Immersed Bodies
Published in William S. Janna, Engineering Heat Transfer, 2018
The preceding equations for the constant-wall-flux case apply to laminar flow of a Newtonian fluid, in which properties are evaluated at the film temperature Tf = (Tw + T∞)/2.
Presentation of Farahbod-Karazhian equation as an accurate mathematical model based on thermodynamics and fluid flow with the aim of predicting the deposition rate of oil heavy compounds in heat exchangers
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2021
Farshad Farahbod, Neda Karazhian
In fact, Table 5 shows the effect of four essential parameters on the main response of the proposed equation or predicting the rate of asphaltene deposition. The film temperature variable indicates the ability of heat to pass between the fluid and the heat exchanger. The shear stress parameter indicates the amount of created stress in the deposition process. The velocity variable indicates the movement of fluid molecules as they pass through the tube. Also, the pressure is considered as the main variable in the study of applied forces to the fluid passing through the pipe. As can be seen in Table 5, the sensitivity of each of the variables and their effect on predicting the amount of sediment or the main response of the proposed model have been calculated. The presented results in Table 5 show that the proposed model can obtain the necessary permits from four areas of heat transfer, fluid mechanics, stress, and kinematics. Finally, the response accuracy of the proposed model and the accuracy of the equation in predicting the deposition rate of heavy compounds in plain tubes of heat exchanger have been calculated.
Fouling in a Steam Cracker Convection Section Part 2: Coupled Tube Bank Simulation using an Improved Hybrid CFD-1D Model
Published in Heat Transfer Engineering, 2020
Shekhar R. Kulkarni, Pieter Verhees, Abdul R. Akhras, Kevin M. Van Geem, Geraldine J. Heynderickx
The first contribution to the thermal resistance increase, i.e., the formation of the fouling layer, highly depends on the film temperature of the liquid, Tf. The film temperature is known to be largely related to the tube wall temperature. The second contribution, i.e., the removal of coke particles, depends on the shear stress of the liquid at the fouling layer. The drawback of the model is that the major parameters determining the extent of production and removal (αfo, βfo, Ea, and γfo) have to be obtained by fitting to experimental or industrial data. Correct quantification of the fouling layer buildup can only be obtained when accurate tube wall temperature profiles are available. Hence, determining tube wall temperature profiles is the first step in a more fundamental fouling study.
Numerical studies on the thermal regimes of the horizontal tube falling film evaporation under varying feeder height
Published in International Journal of Green Energy, 2020
D. Balaji, R. Velraj, M.V. Ramana Murthy
It is observed from the Table 3 that the heat transfer co-efficient values in the stagnation region found to be the highest followed closely by the HTC values in impingement region. The percentage of deviation between the simulation results and correlation values varies between 10 and 16%. The heat transfer co-efficient values obtained from the correlation are found to be higher compared to the simulation results. This could be due to the fact that the operating condition under which these correlations developed are different from the present study. However the working principle remains the same. It is also observed from the Table 3 that the increase of the feeder height lead to increase in the heat transfer co-efficient values in the stagnation region and impingement region due to the increased velocity of liquid flow on these region and decreased liquid film thickness caused by the increased feeder height and the heat flux. Increase in heat flux resulted in increase in the wall temperature of the tube surface that in turn heats the liquid film. When the liquid film temperature increases, the property such as liquid viscosity and surface tension decreases which resulted in the increased wettability of the liquid film on the tube surface and hence the enhanced heat transfer co-efficient. It is also observed from the Table 3 that the HTC values of the 9 mm and 11 mm feeder height is higher than the 5 mm and 7 mm feeder height by 1.5–2.5 times. The highest heat transfer value is obtained for the 11 mm feeder height and this could be because of the impinging effect where the liquid film thickness drastically reduces and paves way for the increment in the heat transfer co-efficient value.