Papers by Keyword: Compact Heat Exchanger

Abstract: The article contains the results of a research in constructing of modern heat exchangers form of heat exchanging surfaces and modes of heat media flux, providing minimum area (size) of heat exchanging apparatus. Decreasing of heat-transferring area is achieved by using different techniques of intensification of convective heat exchange. Intensification of the heat exchange is accompanied by increasing of energy consumption for pumping the coolant. It is concluded that under the conditions of turbulent flow, the transport mechanism does not strongly depend on the shape of the perturbations introduced into the flow, while the tendency to approach the dependences is common to the curves for the considered surfaces, and the experimental data obtained on pipes with a periodic section of the flow cross-section along the length. Using surfaces creating channels with a greater coefficient of hydraulic resistance when creating a compact heat exchangers, which corresponds to surfaces for which the principle of trans-verse flow is realized.

Abstract: Every technological process developed since the beginning of humanity to the present day always involves some kind of energy use, either mechanical energy of the body or energy from burning fuel or the solar energy obtained from the sun. To manipulate and use that energy, the man always developed resources and equipment to allow it. Among the wide range of equipment, heat exchangers, designed to transfer heat from one fluid to another, will be analyzed in this work. To do this analysis, are used computational fluid dynamics (CFD) techniques to analyze the flow behavior of a compact heat exchanger, of tube and louvered fins type. After this step that aims to pull the parameters of efficiency, optimization features will be used to be able to propose a model for more efficient fin.

Abstract: This paper presents the heat transfer and friction coefficient correlations for triangular plain fin surfaces of plate fin compact heat exchanger. It will be prohibitively expensive and time consuming to fabricate heat exchanger cores and conduct experiments over reasonable ranges of all the geometric variables. In contrast, it is relatively easy and cost effective to carry out a parametric study through numerical simulation and derive acceptable correlations for use in industry. A numerical model has been developed for the triangular plain fin of plate fin heat exchanger. The CFD analysis is carried out using FLUENT 12.1, Colburn factor j and fanning friction factor f are calculated for different Reynolds numbers. These values are compared with the available literature data of j and f factors. The correlations have been expressed in terms of two separate equations over the low and high Re regions along with dimensionless geometric parameters.

Abstract: Experimental works were conducted to investigate the effect of Al2O3 sizes and volumeconcentration on the rate of nanofluids heat transfer in a compact heat exchanger. Two sizes ofAl2O3 nanoparticle, 40 nm and 100 nm, were mixed with demineralized water at 2% and 10%volume concentrations. Sodium Lauryl Sulphate (SLS) powder was added to enhance the mixingprocess and stabilize the dispersion of the nanofluids. A custom-made closed loop test rig weredesigned, fabricated and tested for these experiments. The test rig was set-up to represent the actualapplication of the nanofluids in cooling of a compact heat exchanger. Experimental runs wereconducted which include the runs for water, 40 nm Al2O3-water and 100 nm Al2O3-water. Theresults indicate that Al2O3-water gave better heat transfer performance than water alone. Nanofluidswith 40 nm- Al2O3 gives better heat transfer performance as compared to 100 nm- Al2O3 nanofluids.The results of the current work generally indicate that nanofluids have the potential to enhance theheat transfer of a compact heat exchanger if properly designed. This superior performance of thenanofluids would only be produced if smaller diameter of nanoparticles were used (less than 100nm). No enhancement in heat transfer can be observed by using nanofluids with particle size of 100nm or at higher volume loading (more than 5%).

Abstract: In this communication we present a new active method to modify two-phase flow distribution in a heat exchanger, when it is in operation, by using ultrasound generators which can be activated when necessary. An experimental study has been carried out to validate the concept and to evaluate the effects of ultrasound on the flow distribution. An experimental test rig was built to measure the flow distribution in realistic manifold and parallel channel geometry. The test section is composed of a manifold feeding 10 channels with air-water mixture. In front of each channel a piezoelectric generator is placed to emit ultrasonic waves which can interact with liquid flows. Comparison was made between two-phase flows with and without ultrasound. It was demonstrated that, in most cases, uneven distribution was improved by using ultrasound.

Abstract: In the present work, laminar cross flow forced convective heat transfer of nanofluid over tube banks with various geometry under constant wall temperature condition is investigated numerically. We used nanofluid instead of pure fluid ,as external cross flow, because of its potential to increase heat transfer of system. The effect of the nanofluid on the compact heat exchanger performance was studied and compared to that of a conventional fluid.The two-dimensional steady state Navier-Stokes equations and the energy equation governing laminar incompressible flow are solved using a Finite volume method for the case of flow across an in-line bundle of tube banks as commercial compact heat exchanger. The nanofluid used was alumina-water 4% and the performance was compared with water. In this paper, the effect of parameters such as various tube shapes ( flat, circle, elliptic), and heat transfer comparison between nanofluid and pure fluid is studied. Temperature profile, heat transfer coefficient and pressure profile were obtained from the simulations and the performance was discussed in terms of heat transfer rate and performance index. Results indicated enhanced performance in the use of a nanofluid, and slight penalty in pressure drop. The increase in Reynolds number caused an increase in the heat transfer rate and a decrease in the overall bulk temperature of the cold fluid. The results show that, for a given heat duty, a mas flow rate required of the nanofluid is lower than that of water causing lower pressure drop. Consequently, smaller equipment and less pumping power are required.

Abstract: The recent interest in boiling heat transfer in small diameter tubes has led to the study of boiling heat transfer outside a compact tube bundle of diameter 3mm. The bank comprised 3 columns each of 10 stainless steel electrically heated tubes of 3mm outside diameter, with pitch to diameter ratio of 1.5 in an in-line arrangement. These tests were carried out using distilled water and R113 at nominal atmospheric pressure over a range of heat fluxes between 4-21 kW/m2 for mass fluxes from G=5.6 - 32.8 kg/m2s. The recent three-zone evaporation model developed by Thome, Dupont and Jacobi for boiling inside micro channels was used to compare with experimental results as photographic study showed that bubbles confined within the bundle were responsible for the heat transfer enhancement observed. It was observed that the three state model was promising in its application to the bundle arrangement as the confinement number Co for bundle has been shown to be in the order of 0.63

Abstract: This numerical study focuses on the determination of macroscopic (effective) properties from pore scale calculation. These results will be applied to heat exchangers design. The computational domain -representative of heat exchanger section- is a parallelepiped filled with metallic foam, heated on one face and crossed by a forced fluid flow. Conjugate heat transfer and fluid flow are computed using finite volume approach on the actual solid matrix and pore space topology obtained from X-ray tomograms. Calculated heat transfer coefficient and flow law parameters are in good agreement with literature data. An active foam length is defined and measured in order to provide optimal design characteristic for foamed heat exchanger.