A Numerical Study on Fully Developed Fluid Flow and Heat Transfer in a Spiral Finned Tube

In this paper, the standard k-ε two-equation model is adopted to numerically simulate fully developed fluid flow and heat transfer in a spiral finned tube within a cracking furnace for ethylene manufacturing. By variable transformation, the original 3-D problem is converted into a 2-D problem in spiral coordinates. The algorithm of SIMPLEC is used to study the fully developed fluid flow and heat transfer in the spiral finned tube at constant periphery temperature and constant axial heat flux. The computed results agree pretty well with the experimental data obtained from the industry. Further studies on the fluid flows and temperature profiles at different Reynolds numbers within straight and spiral finned tubes are conducted and the mechanisms involved are explored. It is found that with the spiral finned tube, pressure drop increases to a great extent whereas heat transfer tends to be decreased.

Parametric study of natural convection over horizontal annular finned tube

Natural convection heat transfer from annular finned tubes was studied numerically. Effects of fin spacing, temperature difference and tube diameter on flow pathlines and local heat transfer were also studied. It was shown that pathlines remain mostly circular for different geometries. Moreover, the contributions of fin periphery, fin side and bare tube to heat transfer were specified. It was shown that the heat transfer per unit area of fin periphery can be several times that of other parts. Moreover, in higher finspacing, the heat transfer from the bare tube can be more important than fin sides.

Theoretical Analysis of Annular Elliptic Finned Tube Evaporative Condenser Based on Field Measurement

In this article,a new evaporative condenser with an annular elliptic firmed tube heat exchanger that includes a round inner tube and elliptic outer finned tube was designed and analyzed.The refrigerant flows between the round inner tube and the elliptic outer tube,and it simultaneously exchanges heat with the cooling water in the inner tube,the spray water,and the cooling air flowing past the outer tube.Using field measurement for the traditional round finned tube evaporative condenser in the Futong Metro Station of Line 14 in Beijing,China,the theoretical heat transfer performance of the annular elliptic finned tube evaporative condenser was analyzed and simulated.Compared with a round finned tube heat exchanger,the heat exchange capacity of the annular elliptic finned tube increased by 2.34%to 9.28%;the total heat transfer coefficient increased by 47.42%,and the power consumption of the fan in the air-conditioning system with an annular elliptic finned tube heat exchanger decreased by 11.18%to 14.65%.Therefore,the energy-saving performance and the heat transfer performance of the new annular elliptic finned tube heat exchanger were enhanced compared to the round finned tube heat exchanger.

Study on Thermo-Conductive Plastic Finned TubeRadiators

This paper discusses thermo-conductive plastic finned tube radiators used in water saving type powerstations. First, the development of thermo-conductive plastics is introduced. Second, in order todetermine the rational geometric dimensions of thermo-conductive plastic finned tubes, an objectivefunction which takes the minimum volume of the consumed material for making finned tubes as an ob-ject is introduced. On the basis of the function, the economy comparison between thermaxonductiveplastic finned tubes and metal finned tubes is conducted.

EXPERIMENTAL STUDY ON ENHANCED HEAT TRANSFER WITH NI-BASED IMPLANTED SPIRAL FINNED TUBES

The new type of heat exchanger elements-Ni-based Implanted Spiral FinnedTurbes (NISFT) was studied and tested, which can contribute to increase the efficiency andreliability. The relation of Nu, Eu and Re with different fin pitch, fin height, transverse pitchand longitudinal pitch were gained, which constituted the basic foundation for the engineeringapplication of NISFT.

Surface treatment of 3D outside serrated integral-fin tube manufactured by rolling and extrusion

The outside serrated integral-fin tubes fabricated by rolling-plowing-extrusion processing were surface-treated through different processes of annealing in hydrogen atmosphere,electrochemical corrosion or sandblasting.The purpose was to eliminate residual stress,clear secondary micro-fins and enhance heat transfer performance.By comparing the surface characteristics,it is found that the finned tubes treated by electrochemical corrosion have the most glabrous surfaces where the fins are almost perfectly reserved.Clear layer cracks can be observed on the top of the fins.These structures are effective in enhancing heat transfer performance when being applied to flow heat exchange.Therefore,the finned tubes treated by electrochemical corrosion are proper for the tubular exchanger with water coolant.The finned tubes treated by sandblasting have rougher surfaces with layer cracks and micro gaps removed.As these structures are useful to clearing adhesive feculence,the tubes are more suitable for the tubular heat exchanger with oil coolant.

Fin formation model during pre-roll ploughing of copper 3D outside fin tube

The mechanism of pre roll ploughing for 3D fins on the outside surface of copper tube was studied systematically, and especially the process and conditions of 3D fin formation were analyzed. The right mathematical model was also established. Based on the volume of fin ploughed out is equal to the volume of the metal extruded up by the extruding face of the tool, the relations between fin height, pre roll ploughing feed and pre roll ploughing depth have been achieved. With the increase of pre roll ploughing depth which must be equal to groove depth, the fin height gradually becomes larger. There are different critical feeds with the various depths of pre roll ploughing. The pre roll ploughing feed is the critical one, the height of fin is largest. And when the feed is above the critical one, the fin height will reduce with the increase of feed. The theoretical analysis basically accords with experimental results.

Numerical analysis of heat transfer enhancement on steam condensation in the presence of air outside the tube

In loss-of-coolant accidents,a passive containment heat removal system protects the integrity of the containment by condensing steam.As a large amount of air exists in the containment,the steam condensation heat transfer can be significantly reduced.Based on previous research,traditional methods for enhancing pure steam condensation may not be applicable to steam–air condensation.In the present study,new methods of enhancing condensation heat transfer were adopted and several potentially enhanced heat transfer tubes,including corrugated tubes,spiral fin tubes,and ring fin tubes were designed.STAR-CCM+was used to determine the effect of enhanced heat transfer tubes on the steam condensation heat transfer.According to the calculations,the gas pressure ranged from 0.2 to 1.6 MPa,and air mass fraction ranged from 0.1 to 0.9.The effective perturbation of the high-concentration air layer was identified as the key factor for enhancing steam–air condensation heat transfer.Further,the designed corrugated tube performed well at atmospheric pressure,with a maximum enhancement of 27.4%,and performed poorly at high pressures.In the design of spiral fin tubes,special attention should be paid to the locations that may accumulate high-concentration air.Nonetheless,the ring-fin tubes generally displayed good performance under all conditions of interest,with a maximum enhancement of 24.2%.

Decoupled thermal–hydraulic analysis of an air-cooled separated heat pipe for spent fuel pools under natural convection

An investigation of the decoupled thermal–hydraulic analysis of a separated heat pipe spent fuel pool passive cooling system(SFS)is essential for practical engineering applications.Based on the principles of thermal and mass balance,this study decoupled the heat transfer processes in the SFS.In accordance with the decoupling conditions,we modeled the spent fuel pool of the CAP1400 pressurized water reactor in Weihai and used computational fluid dynamics to explore the heat dissipation capacity of the SFS under different air temperatures and wind speeds.The results show that the air-cooled separated heat pipe radiator achieved optimal performance at an air temperature of 10℃ or wind speed of 8 m/s.Fitted equations for the equivalent thermal conductivity of the separated heat pipes with the wind speed and air temperature we obtained according to the thermal resistance network model.This study is instructive for the actual operation of an SFS.

Heat Transfer Characteristics of Laminar Flow in Internally Finned Tubes under Various Boundary Conditions

Numerical solutions for fully developed laminar flow in internally finned tubes with trapezoidal and triangular fin profiles were given with Finite Element Method (FEM): The heat transfer characteristics were obtained and compared under the boundary conditions of uniform heat flux, uniform wall temperature, and the third boundary condition with finite wall thermal conductivity considered. The numerical results show that boundary conditions have pronounced effects on the temperature field.Furthermore, a new mechanism on the heat transfer augmentation of internally finned tubes is proposed.

A Prediction Model for Condensation on Single Horizontal Rectangular Fin Tube

A model was established to predict condensation heat transfer coefficient on horizontal rectangular-finned tube. Drop-Off zone at the tube bottom was considered and determined, the known Honda(and owen) expression of retention angle was also modified as a result of considering drop-off zone.Heat flux on fin tips in the unflooded region, fin fianks, fin spacings and fin tips in the flooded regionwere analyzed respectively. Condensation on fin tips is emphasized by considering the variation of filmthickness along circumference as well as horizootally. Fin efficiency was considered in calculation. Theprediction results were compared with several researchers’ experimental data for three kinds of workingfluids on seven different tube geometries and for various temperature differences. These data underabout 60 test conditions were predicted with discrepancy of ±10%. Prediction by the present modelfor steam and R-113 condensation were compared with previous models.

Effects of Working Fluid,Tubeside Enhancement and Bundle Depth on the Optimized Fin Geometry of a Horizontal Condenser Tube

A theoretical study has been made to optimize the fin geometry of a horizontal finned tube which is to be used for condensers that handle the vapor load of a liquid phase change cooling module.Systematic numerical calcu- lations of the vapor to coolant heat transfer have been performed for parametric values of fin height,fin spacing, vertical bundle depth and tubeside heat transfer coefficient.Three dielectric fluids (R-113,FC-72,and FC-87) at atmospheric pressure were selected as the working fluids.For a single tube with optimized fin geometry,the average heat flux increased in the order of FC-87,R-113 and FC-72.Both the optimum fin height and optimum fin spacing increased with increasing vertical bundle depth.

Mechanism of Tonal Noise Generation from Circular Cylinder with Spiral Fin

The pitch of the spiral finned tube influences seriously to the acoustic resonance in the heat exchanger.In this research,the flow characteristics in relating to the aeolian tone from the finned cylinder are studied by the numerical simulation.It is observed that the tonal noise generated from the finned tube at two pitch spaces.The ratio of the fin pitch to the cylinder diameter is changed at 0.11 and 0.27.The tone level increases and the frequency decreases with the pitch shorter.The separation flow from the cylinder generates the span-wise vortices,Karman vortices,and the separation flow from the fin generates the stream-wise vortices.When the fin pitch ratio is small,the stream-wise vortices line up to span-wise and become weak rapidly.Only the Karman vortices are remained and integrate in span.So the Karman vortex became large.This causes the low frequency and the large aeolian tone.

A Lightweight Compact Lithium-Ion Battery Thermal Management System Integratable Directly with EV Air Conditioning Systems

This paper discusses an improved thermal management system to ameliorate the performance of lithium-ion battery storage systems for electric vehicles(EVs) applications. A compact and lightweight cold plate is designed and fabricated to fit 18650-type lithium-ion batteries, using aluminum-finned copper tubes. A dynamic temperature PID(proportional, integral, differential) control algorithm for electronic expansion valves is developed to study using EV air conditioning refrigerant, R134a, to control battery modules’ temperature with this compact and lightweight thermal management system. The experimental results show that the proposed battery thermal management system can effectively control the battery module’s temperature. In addition, during 1C discharge, when the PID temperature algorithm control scheme is used, the maximum temperature difference across the battery module peaks at less than 4℃, and the maximum temperature within the battery module is less than 36℃.