Heat transfer parameters of a parallel plate heat exchanger

Performance of Counterflow, Parallel Plate Heat Exchangers under Laminar Flow Conditions

Abstract: Multilayered heat exchangers were analyzed theoretically and their heat transfer characteristics were clarified. The problem was treated as a two-dimensional, conjugated one with three phases-two fully developed laminar flows and the exchanger wall. From numerical results, the exchanger effectiveness was found to be definitely influenced by the following parameters: Graetz number, heat capacity flow rate ratio, dimensionless wall thickness, and conductance ratios between fluid and wall and between both fluids. Examination of mixed-mean temperature distributions in the exchanger showed that longitudinal wall conduction significantly reduces exchanger effectiveness in the low-Graetz-number region. Experimental results were in fairly good agreement with theoretical predictions.

Counterflow double-pipe heat exchanger analysis using a mixed lumped-differential formulation

Abstract: An analysis is made of double-pipe heat exchangers under a thermally developing countercurrent flow condition. A lumped-differential mixed formulation is employed, by radially lumping the temperature field in the outer channel, which results in a more involved boundary condition for the inner differential system, involving the axially varying outer channel bulk temperature. The generalized integral transform technique is utilized to provide a reliable and straightforward analytical solution to this class of problems. Numerical results for heat transfer quantities are presented in terms of the dimensionless governing parameters along the thermal entry region, allowing for critical comparisons against the concurrent flow situation, limiting solutions and engineering-type correlations.

Lumped-differential analysis of concurrent flow double-pipe heat exchanger

Abstract: A mixed lumped-differential formulation for double-pipe heat exchangers is presented that radially lumps the temperature distribution in the outer channel, providing a differential problem for the inner channel that involves a more general type of boundary condition for the wall temperature. The generalized integral transform technique is extended to allow for the analytical solution of this class of problems. Applicability limits for the simplified model are then established in terms of related parameters, based on numerical results obtained for bulk temperatures and Nusselt numbers, as compared to more involved approaches for the complete differential model. Une formulation mixte differentielle-globale est presentee pour les echangeurs de chaleur a double conduite; cette formulation basee sur une valeur moyenne de la distribution radiale de temperature dans le canal exterieur permet d'etablir une equation differentielle pour le canal interieur qui necessite un type de conditions limites plus general pour la temperature aux parois. La technique des transformees integrales generalisees est etendue de facon a permettre la resolution analytique de cette categorie de problemes. Les limites d'applicabilite pour le modele simplifie sont ensuite etablies en termes de parametres connexes, a partir des resultats obtenus pour les temperatures et les nombres de Nusselt en masse, par comparaison a des techniques plus complexes pour le modele differentiel complet.

Heat transfer in a pipe with turbulent flow and arbitrary wall-temperature distribution

Abstract: The first three eigenvalues and constants for the problem of heat flow to a constant property fluid in established turbulent flow in a round pipe are presented for all important values of Reynolds and Prandtl Moduli. These results permit one to compute heat transfer from nonisothermal pipe walls. Comparisons with experiment are good for all fluids from oils to liquid metals. The thermal entry length and rate of heat transfer for low Prandtl Moduli are shown to depend markedly on the wall-temperature profile.

Liquid Metal Heat Transfer

Abstract: Publisher Summary This chapter focuses on certain fundamental aspects of forced convection heat transfer in symmetrical ducts that are of special interest when the fluid is a liquid metal. Compared to the nonmetallic liquids, the combination of large thermal conductivity, small vapor pressure, and extensive temperature range over which they remain in the liquid phase make the liquid metals desirable for certain important technological applications. The most familiar of these applications is their use as coolants in nuclear reactors. The categories of liquid metal heat transfer research are provided in a tabulated form. Some of these categories include turbulent forced convection, convection with “small” Reynolds number, and condensation. The turbulent forced convection in symmetrical ducts is discussed in detail. One of the important consequences of the difference between liquid metals and nonmetallic fluids in turbulent flow is that the temperature distributions in the latter are relatively insensitive to local changes at the duct walls and thus to boundary conditions and to duct shape. This relative sensitivity is illustrated to boundary conditions by comparing computed fully developed heat transfer coefficients for a circular tube for uniform wall flux with those for uniform wall temperature.

Comparison of Turbulent Heat-Transfer Results for Uniform Wall Heat Flux and Uniform Wall Temperature

Abstract: The purpose of this note is to examine in a more precise way how the Nusselt numbers for turbulent heat transfer in both the fully developed and thermal entrance regions of a circular tube are affected by two different wall boundary conditions. The comparisons are made for: (a) Uniform wall temperature (UWT); and (b) uniform wall heat flux (UHF). Several papers which have been concerned with the turbulent thermal entrance region problem are given. 1 Although these analyses have all utilized an eigenvalue formulation for the thermal entrance region there were differences in the choices of eddy diffusivity expressions, velocity distributions, and methods for carrying out the numerical solutions. These differences were also found in the fully developed analyses. Hence when making a comparison of the analytical results for uniform wall temperature and uniform wall heat flux, it was not known if differences in the Nusselt numbers could be wholly attributed to the difference in wall boundary conditions, since all the analytical results were not obtained in a consistent way. To have results which could be directly compared, computations were carried out for the uniform wall temperature case, using the same eddy diffusivity, velocity distribution, and digital computer program employed for uniform wall heat flux. In addition, the previous work was extended to a lower Reynolds number range so that comparisons could be made over a wide range of both Reynolds and Prandtl numbers.