Vertical Double-pipe Heat Exchanger Research Articles

Thermal and exergy analysis of air- nanofluid bubbly flow in a double-pipe heat exchanger

Heat exchangers are among the most applied energy systems and increasing their performance can contribute to resolving current energy and environmental issues. Of the active and passive methods of heat transfer enhancement, air bubble injection and using nanofluids, respectively, were selected for this research. Experiments were conducted to study energy, exergy and hydrodynamic performances of a vertical double pipe heat exchanger under the effects of the combined method applied in the annulus side. Finally, multi-objective optimization based on artificial neural network metamodeling and genetic algorithm was carried out to find the best performance on the basis of heat exchanger effectiveness and exergy performance. Results indicate a promising potential in performance enhancement of the combined method.

Performance Enhancement of the Vertical Double Pipe Heat Exchanger by Applying of Bubbling Generation on the Shell Side

Performance Enhancement of the Vertical Double Pipe Heat Exchanger by Applying of Bubbling Generation on the Shell Side

Numerical investigation on heat transfer to supercritical CO2 in rolling motion

The numerical calculations with and without rolling motions are conducted to investigate the effect of rolling motion on flow and heat transfer of supercritical CO2 in a vertical double-pipe heat exchanger. The purpose is to provide the detailed information on heat transfer behaviors for better understanding the abnormal heat transfer mechanism of supercritical fluid in rolling motion. It concludes that the effect of rolling motion on the supercritical CO2 is much more notable than that on conventional single-phase fluid. The rolling motion can cause the periodic oscillation of the local heat transfer coefficients and suppress the whole heat transfer deterioration. As supercritical CO2 temperature or mass flux increases, the influences of rolling motion and flow direction on the heat transfer decrease markedly. The secondary flow induced by the rolling motion for upward flow is stronger than that for downward flow, and the influence of rolling motion on the left and right sides of the tube is more obvious than on other locations. The heat transfer deterioration phenomenon weakens gradually as the rolling period decreasing or rolling amplitude increasing. It is important to note that the rolling motion may bring about the large wall temperature oscillation and the wall peak temperature increment to influence the safety of high-pressure pipeline.

Numerical investigation on conjugate cooling heat transfer to supercritical CO2 in vertical double-pipe heat exchangers

ABSTRACTConjugate cooling heat transfer to supercritical CO2 in a vertical double-pipe heat exchanger was numerically investigated in the present study. With the aim to better understand the conjugate cooling mechanism of supercritical fluid, detailed information on heat transfer behavior is provided. The results demonstrate that the numerical results predicted by the Abe, Kondoh, and Nagano (AKN) model show the best agreement with the experimental data. After validation, the influences of cooling water Re and temperature at the shell side, supercritical fluid Re at the tube side, flow direction, and pipe diameter on conjugate cooling heat transfer were investigated based on velocity fields. We conclude that cool water Re and temperature at the shell side have a significant effect on the cooling phenomenon at the tube side. Reduction in heat transfer could be avoided by either an increase in ReCO2 or a decrease in di. In addition, variations in density and cp are the most significant factors to determine the occurrence of abnormal heat transfer phenomena. In comparison with the heating process of supercritical CO2, the sharply increased viscosity noted would hinder the distortion of the flow field to ameliorate heat transfer deterioration during the cooling process.

Experimental Study and Numerical Simulation on Thermal Energy Storage Characteristics of Composite Phase Change Materials in Annular Space of Vertical Double-Pipe Heat Exchanger

Experimental system on thermal energy storage characteristics of phase change materials (PCMs) in annular space of a vertical double-pipe heat exchanger was set up. The thermal storage performance of paraffin and paraffin/expanded graphite composite PCM with the mass fraction of 70% paraffin was compared. The Fluent software was used to simulate the temperature field of the composite PCM during the thermal storage process. The results show that, for the paraffin, in the sensible heat storage phase, because the heat transfer process is controlled by the heat conduction, the temperature in paraffin gradually reduces from the inside to the outside of the annular space. But for the phase change thermal storage phase, solid-liquid phase change heat transfer is controlled by natural convection and the effect of buoyancy, the temperature in paraffin reduces from top to bottom, from the inside to the outside of the annular space. For the composite PCM, heat transfer is controlled only by the heat conduction process, both the sensible and latent heat storage process, the temperature in the composite PCM decreases from bottom to top, from inside to outside of the annular space. As the thermal conductivity of composite PCM is 15.65 times of paraffin, the thermal energy storage time is shortened by 86.6% than paraffin. The temperature fields of composite PCM in different time are obtained by numerical simulation method, the measured temperatures and simulation results are in good agreement.

Effect of advanced surfaces on the ammonia absorption process with NH3/LiNO3 in a tubular bubble absorber

An experimental study was conducted to investigate the effect of advanced surfaces on the ammonia absorption process in tubular bubble absorbers using NH3/LiNO3 as a working pair at operating conditions of interest for absorption chillers. The tubular bubble absorber is a vertical double-pipe heat exchanger in which absorption takes place in the inner tube. In order to compare the effect of surface enhancement, a smooth tube and an internally micro-finned tube were tested. The inner tube of the absorber is made of aluminium and has an outer diameter of 8.0mm and the micro-finned tube has internal helical micro-fins measuring 0.3mm in length. The effect of tube length on absorption was also studied using two tube lengths (1 and 3m) and two tube diameters (8 and 9.5mm).Our results show that the absorption rate achieved with the micro-finned tube is up to 1.7 times higher than with the smooth tube at a solution mass flow rate of 40kgh−1. We also found that absorption mass flux increases when tube diameter is reduced and decreases when tube length is increased.

EFFECTS OF BUOYANCY ON THE PERFORMANCE OF A VERTICAL DOUBLE-PIPE HEAT EXCHANGER

CFD simulations of heat transfer between two fluids in a parallel-flow vertical double-pipe heat exchanger, taking into consideration conduction in the walls, viscous dissipation, variable fluid properties, and axial diffusion in the fluids, illustrate the effects of buoyancy on the velocity and temperature profiles as well as on the Nusselt numbers and friction coefficients. In particular, the results show that flow reversal occurs at different positions depending on the flow direction. In the developing region, the fluid bulk temperatures, the wall temperature, and the local Nusselt numbers for both fluids depend on the flow direction. For the conditions under consideration, the Nusselt number for the fully developed flow in the inner pipe lies between the corresponding forced convection values for the constant heat flux and constant temperature conditions, while the one in the annulus is smaller than both these forced convection values. It is established that the flow and thermal fields in the inner cylinder and the annulus cannot be predicted correctly by studying each one separately since the thermal condition at the solid wall separating the two fluids depends on flow characteristics such as the Richardson number in the inner tube.

Modeling ice removal in fluidized‐bed freeze concentration of apple juice

AbstractStable operation of fluidized‐bed heat exchangers during freeze concentration is limited by the rate of ice removal from the cooling surfaces. Operation remains stable as long as the erosion rate caused by the fluidized particles is equal or greater then the ice growth rate. An empirical model has been devised to estimate the erosion rate at different operating conditions. 4 and 5 mm equilateral cylindrical particles made of stainless steel (SS304) were fluidized in the inside pipe of a vertical double pipe heat exchanger. Bed porosities of 0.94–0.76, and apple juice concentrations of 12, 16, 18, and 20 Brix were tested. The new erosion model was developed based on an analogy between erosion and heat‐transfer phenomenon. Experimental values of erosion rate were obtained for different operating conditions and compared with the values estimated by the model. © 2008 American Institute of Chemical Engineers AIChE J, 2008

Mixed convection in a vertical double pipe heat exchanger

A numerical study of steady state, simultaneously developing, laminar mixed convection in a vertical double pipe heat exchanger has been conducted for upward parallel flow. The model is elliptic and takes into account conduction in the solid walls as well as dissipation in the two streams. The viscosity and the density of the fluids depend on the temperature while all other thermophysical properties are constant. Results have been calculated for fixed inlet temperatures, a Richardson number equal to 1 for the annular space and three different values in the cylinder (4.85, 1 and 0.34). Flow reversal occurs in the warm fluid for Ri c ⩾ 1 and affects significantly the thermal and hydrodynamic fields. In particular, the temperature of the wall separating the two fluids varies considerably in the flow direction despite its high conductivity. The results include temperature and velocity profiles at different cross sections as well as the axial evolution of bulk and wall temperatures, Nusselt numbers and friction factors in the cylinder and the annular region. The effect of Ri c on the asymptotic values of the Nusselt numbers is analyzed.

Hydrodynamic and heat transfer studies on fluted tubes with drainage discs

A vertical double-pipe heat exchanger with steam condensing on the outside was used for heat transfer studies. The discs, equally located over the outer surface of the tubes. Experiments were performed both on smooth and on fluted tubes having different geometries with discs of variable separations. Film coefficients were determined both theoretically and experimentally. Optimum separations for different flute geometries were determined.

Hydrodynamic and heat transfer studies on fluted tubes with drainage discs

A vertical double-pipe heat exchanger with steam condensing on the outside was used for heat transfer studies. The discs, equally located over the outer surface of the tubes. Experiments were performed both on smooth and on fluted tubes having different geometries with discs of variable separations. Film coefficients were determined both theoretically and experimentally. Optimum separations for different flute geometries were determined.