HYDRODYNAMICS, DISTRIBUTION OF FLOWS AND THERMAL EFFICIENCY OF COIL HEAT EXCHANGERS IN UNITS OF HEAT-USING APPARATUS OF TUBE FURNACES

The theoretical foundations of construction, mathematical description and engineering calculation of heat exchangers of the serpentine type in blocks of heat-using equipment of tube furnaces and other types of reactors designed for carrying out endothermic reactions (in particular, reforming of natural gas with water vapor) are considered. It is shown that the thermal efficiency of heat exchangers of the coil type is significantly affected by the correct choice of parameters ensuring a uniform distribution of energy flows over the surface of heat-resistant heat exchange tubes. This technological problem is solved by compiling the heat balance and selecting the system of the corresponding equations, which allows to calculate the temperature contour of the coil heat exchanger, its hydrodynamic characteristics and the distribution of mass and heat flows through the heat exchange tubes. The use of the tensor form of the Boussinesq hypothesis is considered, with which the Reynolds equation describing a turbulent flow is transformed to a partial differential equation for a single unknown function and its averaged form is obtained. In relation to the problem under consideration, the correctness of the chosen approach was confirmed both theoretically and experimentally. It is shown that in the core of a turbulent flow with an intense suction or injection, the liquid behaves almost as ideal and the well-known Helmholtz – Friedmann theorem holds with the necessary accuracy. From the aforementioned averaged equation, expressions are obtained that are suitable for describing heat fluxes in channels with suction or injection. According to this theoretical model, thermal calculations of coil-type heat exchangers were carried out, a more accurate assessment of the temperature of the heated medium in each coil tube was made, and the temperature gradient of the external heat carrier over the cross section of the gas duct was found. For the first time in the practice of calculations when choosing the parameters of coils, a number of boundary conditions were taken into account, such as the condition of the coil layout, the necessary heat exchange surface, permissible restrictions on hydraulic resistance, etc.

Discussion: “Convection Heat Transfer of Power-Law Fluids Along the Inclined Nonuniformly Heated Plate With Suction or Injection” [Sui, J., Zheng, L., and Zhang, X., 2016, ASME J. Heat Transfer, 138(2), p. 021701]

The present comment concerns some doubtful results in the above paper.

New exact and numerical solutions for the effect of suction or injection on flow of nanofluids past a stretching sheet

The flow of nanofluids past a stretching sheet has attracted much attention due to its wide applications in industry and engineering. Theoretical and numerical solutions have been discussed in this paper for studying the effect of suction or injection on flow of nanofluids past a stretching sheet. In the absence of thermophoresis the analytical exact solution of the stream function was obtained in terms of exponential function, while the exact solutions for temperature and nanoparticle volume fraction were obtained in terms of the generalized incomplete gamma function. In addition, in the presence of thermophoresis, the exact solutions are not available. Therefore, the numerical results, carried out by using Chebyshev collocation method (ChCM). It is found that a good agreement exists between the present results and with those published works. Useful results for temperature profile, concentration profile, reduced Nusselt number and reduced Sherwood number are discussed in details graphically. It was also demonstrated that both temperature and concentration profiles decrease by an increase from injection to suction. Finally, the present results showed that increase of the wall mass transfer from injection to suction decreased both reduced Nusselt number and the reduced Sherwood number when Brownian motion parameter and Lewis number increased.

Unsteady Stokes Flow through Porous Channel with Periodic Suction and Injection with Slip Conditions

This work is concerned with the influence of slip conditions on unsteady stokes flow between parallel porous plates with periodic suction and injection. The obtained unsteady governing equations are solved analytically by similarity method. The characteristics of complex axial velocity and complex radial velocity for different values of parameters are analyzed. Graphical results for slip parameter reveal that it has significant influence on the axial and radial velocity profiles. The effects of suction or injection are also observed. The problem of unsteady stokes flow through porous plates with no slip is recovered as a special case of our problem.