Plate-fin Surfaces Research Articles

Flow and heat transfer performances of directly printed curved-rectangular vortex generators in a compact fin-tube heat exchanger

In this study, the flow and heat transfer characteristics of newly configured curved-rectangular vortex generators (VGs) in a compact fin-tube heat exchanger were numerically investigated. The proposed VGs were designed to be directly printed rather than being punched out from the plate fin surfaces. The influences of VGs on the overall flow structure and thermal mixing, and near-wall flow and thermal features were characterised in detail. The mechanisms of heat transfer enhancement were explored in terms of the secondary flow and field synergy theories. Results indicate two main mechanisms for the suppression of recirculation flows by applying VGs. The lowered local synergy angle rather than the enhanced local secondary flow intensity is the immediate mechanism for the enhanced heat transfer performance. Parametric analysis indicates that increasing VG height and radius increases both Nusselt number (Nu) and friction factor (f). An optimal VG configuration for the thermo-hydraulic performance is identified at the VG height ratio of 0.8 and radius ratio of 1.55, by which the obtained performance evaluation criterion (PEC) is about 1.3–1.5 times as that of the baseline over the tested Re range. Correlations are further developed to predict the Nu, f and PEC for future preliminary design purposes.

Thermohydraulic Engineering of Plate-Fin Surfaces for Heat Exchangers Subject to Required Dimensions

This paper presents a design approach for plate-fin heat exchangers, where secondary surfaces are engineered with the aim of achieving fixed block dimensions. Surface engineering refers to the determination of the surface geometrical parameters that produce a desired heat transfer and pressure drop performance. Through surface engineering, the exchanger dimensions, such as length, width and height, can be considered as a design objective in heat exchanger design along with the heat duty and the pressure drop. Simple secondary surfaces such as triangular and rectangular fins are considered in this work. The approach is demonstrated using a case study, and various scenarios are analysed.

Design of plate-fin surfaces for multi-fluid heat exchanger applications

Amidst the various design approaches available for the design of plate-fin heat exchangers for multi-fluid applications, are those based on the segmentation of the exchanger length into blocks that correspond to the enthalpy intervals in the Composite Curves. Such methods are characterized by three main features: identification of exchanger sections, surface selection from among the available types, and reconciliation of dimensions by pressure drop relaxation. The work presented in this paper introduces new concepts and removes some limitations in earlier approaches. In the first place, it reduces the number of block sections when the space between them is too short to fit intermediate headers along the length of the exchanger. Additionally, it introduces the concept of surface design as an aid to fulfil the heat transfer duties. Finally, it allows the design to meet fixed dimensions as design objective together with the heat duty within the limitations imposed by the pressure drop. The approach is demonstrated using a case study solved by different authors in the open literature. It is shown that the number of block sections is reduced from 3 to 2.

Investigation of the flow structure and heat transfer intensity of surfaces with split plate finning

The authors use CFD modeling to study three types of heat exchange surfaces, i.e. a basic plate fin surface and two modified split plate surfaces – without rotation and with rotation of the split sections at an angle of 30° against the incoming air flow. Thermal aerodynamic characteristics of the studied heat exchange surfaces are obtained and verified with experimental data. The flow patterns are presented in three sections along the height of the channels in the finned area. An explanation is offered for the intensification of heat transfer in the modified heat exchange surfaces. It is shown how geometrical and operating parameters influence the heat transfer intensity and aerodynamic resistance. The results can be useful in designing cooling systems for electronics, particularly microprocessor and microlaser devices, power amplifiers of transmitting modules for radar systems, promising energy-saving solid-state light sources, power electronics for electric vehicles, equipment for aviation and space-rocket electronics with heat pipes.

The Second Law Analysis of Thermodynamics for the Plate–Fin Surface Performance in a Cross Flow Heat Exchanger

In this paper, a particular heat exchanger is designed and analyzed by using second law of thermodynamics. The heat exchanger operates with the cross flow forced convection having cylindrical, square, and hexagonal pin fins (tubular router) placed in the rectangular duct. The pin fins are installed periodically at the top and bottom plates of the duct perpendicular to the flow direction, structured in-line, and staggered sheet layouts. The entropy generation in the flow domain of the channels is calculated to demonstrate the rate of irreversibilities. To obtain the efficiencies, irreversibility, thermal performance factor, and entropy generation number (EGN), the heat exchanger is operated at different temperatures and flow rates by using hot and cold fluids. Optimization of the design parameters and winglet geometry associated with the performance are determined by entropy generation minimization. The variation of the EGN with Reynolds number for various tubular routers is presented. The Reynolds number is determined according to the experimental plan and the performance is analyzed with the method of effectiveness—number of transfer unit (NTU). Based on particular designs, it was determined that the increment in fluid velocity enhances the heat transfer rate, which in turn decreases the heat transfer irreversibility.

P.1.l.016 - The role of C1473G polymorphism in mouse tryptophan hydroxylase-2 gene in the response of brain serotonergic system and behavior to short photoperiod

This chapter presents up-to-date theoretical results and correlations for the most important surfaces used in compact heat exchangers. Full-developed Nusselt numbers and friction factors are given for many continuous duct cross-sections, followed by a summary of entrance effects (developing flow), which give rise to increased Nusselt numbers and friction factors. Turbulent and transitional flow data for ducts are then given. Plate-fin surfaces, in a variety of forms, are by far the commonest of all compact types, being used for applications from oil refining to air conditioning; and some of the many semiempirical correlations are assessed. In particular, the offset strip fin (OSF) data and correlations are given critical attention, based on the theoretical results developed in previous. After a summary of the performance of perforated fins, a more in-depth assessment of louvered and offset convex louvered fins is presented. Pressed-plate surface performance correlations are then given, followed by considerations of the performance of printed circuit channels and microchannels. The chapter ends with a brief discussion of porous and sintered surfaces for which, it is argued that no consistent methodology is yet in place for performance assessment.

Experimental characterization of heat transfer in an additively manufactured polymer heat exchanger

In addition to their low cost and weight, polymer heat exchangers offer good anticorrosion and antifouling properties. In this work, a cost effective air-water polymer heat exchanger made of thin polymer sheets using layer-by-layer line welding with a laser through an additive manufacturing process was fabricated and experimentally tested. The flow channels were made of 150μm-thick high density polyethylene sheets, which were 15.5cm wide and 29cm long. The experimental results show that the overall heat transfer coefficient of 35–120W/m2K is achievable for an air-water fluid combination for air-side flow rate of 3–24L/s and water-side flow rate of 12.5mL/s. In addition, by fabricating a very thin wall heat exchanger (150μm), the wall thermal resistance, which usually becomes the limiting factor on polymer heat exchangers, was calculated to account for only 3% of the total thermal resistance. A comparison of the air-side heat transfer coefficient of the present polymer heat exchanger with some of the commercially available plain plate fin heat exchanger surfaces suggests that its performance in general is superior to that of common plain plate fin surfaces.

Analysis of the Fin Performance of Offset Strip Fins Used in Plate-Fin Heat Exchangers

As an important consideration in the design of plate-fin heat exchangers, the selection of plate-fin surfaces is associated with the estimation of the fin performance in many cases. The fin performance of offset strip fin (OSF) and plain fin is numerically investigated with well-validated 3D models in the present study. The comparative analysis shows that the conventional fin efficiency and fin effectiveness concepts provide an incomplete assessment of the fin performance of the fins, and lead to impractical suggestions of using OSF fin. Further investigation indicates that the idealization of uniform heat transfer coefficient over all the surfaces in fin channel, which runs through the conventional concepts, is untenable, and strongly restricts the fin performance analysis. An actual fin effectiveness is then proposed to measure the fin performance. It physically represents the ratio of the heat flux over the fin surfaces and that over the primary surfaces in the fin channel. With this method, the effects of the geometrical parameters of the OSF are discussed carefully. The results show that there exists a specific fin thickness-to-height ratio α and fin density γ, which contribute to the highest fin performance for a given mass flux, and the optimal γ (or α) increases (or decreases) as mass flux increases. The OSF fins with relatively large fin thickness-to-length ratio δ perform better in low Re region and the optimum δ decreases with the increasing Re number.

A novel trapezoid fin pattern applicable for air-cooled heat sink

The present study proposed a novel step or trapezoid surface design applicable to air-cooled heat sink under cross flow condition. A total of five heat sinks were made and tested, and the corresponding fin patterns are (a) plate fin; (b) step fin (step 1/3, 3 steps); (c) 2-step fin (step 1/2, 2 steps); (d) trapezoid fin (trap 1/3, cutting 1/3 length from the rear end) and (e) trapezoid fin (trap 1/2, cutting 1/2 length from the rear end). The design is based on the heat transfer augmentation via (1) longer perimeter of entrance region and (2) larger effective temperature difference at the rear part of the heat sink. From the test results, it is found that either step or trapezoid design can provide a higher heat transfer conductance and a lower pressure drop at a specified frontal velocity. The effective conductance of trap 1/3 design exceeds that of plate surface by approximately 38 % at a frontal velocity of 5 m s−1 while retains a lower pressure drop of 20 % with its surface area being reduced by 20.6 %. For comparisons exploiting the overall thermal resistance versus pumping power, the resultant thermal resistance of the proposed trapezoid design 1/3, still reveals a 10 % lower thermal resistance than the plate fin surface at a specified pumping power.

경계층 이론을 이용한 고효율 열교환기 설계를 위한 이론적 접근법

Abstract The objective of this study is theoretically to suggest the effective heat exchanger design method using boundary layer analysis. The boundary layer formation and interruption on rectangular plate and round plate fins are explained and the heat transfer coefficients showed with the variation of the velocity and temperature boundary layer. In addition, the flow pattern on one plate fin surface considered as external flow and flow pattern between fins considered as internal flow. As a result, theoretical method for the boundary layer interruption avoidance is suggested and the heat transfer coefficient of the round plate fin was higher than that of the rectangular plate fin because of the less thermal and velocity boundary layer thickness except the centerline. Key Words : Boundary layer, Heat exchanger, Heat transfer coefficient, Interruption, Plate fin 본 논문은 이 논문(작품)은 동아대학교 교내연구비 지원에 의하여 연구되었음. * Corresponding Author : Moo-Yeon Lee (Dong-A University)Tel: +82-10-5440-8421 email: mylee@dau.ac.krReceived September 18, 2012 Revised (1st September 27, 2012, 2nd October 12, 2012) Accepted December 12, 2012

Numerical optimization of a fin-tube gas to liquid heat exchanger

The influence of plate fin, fin tube and protrusion parameters on heat transfer and pressure drop characteristics of a finned tube gas to liquid heat exchanger is examined in this study. The optimization of plate fin, fin tube and protrusion dimensions as well as protrusion locations on plate fin surface is performed numerically using a computational fluid dynamics (CFD) program named “Fluent”. The dimensions of the plate fin of a commercially available combi boiler apparatus heat exchanger are taken as basic dimensions. As the first step, the best plate fin and fin tube geometry is determined. Secondly, the best dimensions for three different protrusions (balcony, winglet and imprint) and their most suitable locations on the plate fin surface are found. Finally, the cumulative effects of several combinations of these three protrusions on the plate fin surface are analyzed. The placement combinations of protrusions are decided according to the results obtained for the individual effect of each protrusion. The fin named as I5B2W3 is found to be the most efficient fin among the investigated cases. A comparison with a numerical and computational study is also performed to validate the numerical results of the present study.

Optimum Design of Two-Row Slotted Fin Surface with X-Shape Strip Arrangement Positioned by “Front Coarse and Rear Dense” Principle, Part II: Results and Discussion

In Part I of this article, design considerations for 15 slotted fin surfaces are introduced, and the physical/mathematical model and numerical methods are described. The strips in all slotted fin surface are designed according to two general guidelines: “front coarse and rear dense” and “X-shape arrangement.” In this article, the specific flow and heat transfer characteristics of the 15 slotted fin surfaces and their comparisons with the plain plate surface are presented. The major findings are as follows. For all 15 slotted fin surfaces, their j/f versus Re curves cross with the curve of the plain plate fin surface at some turning Reynolds number, beyond which the j/f ratio of slotted fin surfaces is higher than that of plain plate fin surfaces, and vice versa. The variation character of heat transfer rate versus Reynolds number under identical pumping power condition has the same feature, with its turning Reynolds number being appreciably lower than the former one. However, at the identical flow rate the heat transfer rates of all the slotted fin surfaces are higher than that of the plain plate fin, and the larger the velocity, the more significant the enhancement. Among the four techniques adopted—changing the number of strips, shortening the strip length, changing the location of the strips, and splitting one strip into two—the effect of strip location is the most and that of splitting one into two is the least. The field synergy principle analysis shows that the higher heat transfer rate of the slotted fin surfaces comes from their better synergy between velocity and temperature gradient. Two patterns of slotted fin are recommended for the two-row plate fin-and-tube surface.

Interpreting and Applying Experimental Data for Plate-Fin Surfaces: Problems with Power Law Correlation

The absence of reliable and theoretically consistent correlations for the prediction of the thermohydraulic performance of plate-fin surfaces from the definition of surface structure is placing a constraint upon plate-fin exchanger design. Many workers have made direct use of the experimental data without fully appreciating the limitations imposed by the way in which the experiments have been conducted. The dangers of such a practice are exposed. The data of Kays and London are then re-analyzed using established heat transfer theory. The comparison between the predicted and reported friction factor and j factor data is good. The predictions compare favorably with experimental measurements over laminar, transitional, and turbulent flow regimes. Predictions for heat transfer in the transitional flow regime can be improved if the transition occurs at a lower Reynolds number. The new equations can be used in design with greater confidence than the use of experimental data alone.

NUMERICAL DESIGN OF EFFICIENT SLOTTED FIN SURFACE BASED ON THE FIELD SYNERGY PRINCIPLE

In this article, a numerical investigation of the flow and heat transfer in a three-row finned-tube heat exchanger is conducted with a three-dimensional laminar conjugated model. Four types of fin surfaces are studied; one is the whole plain plate fin, and the other three are of slotted type, called slit 1, slit 2, and slit 3. All four fin surfaces have the same global geometry dimensions. The three slotted fin surfaces have the same numbers of strips, which protrude upward and downward alternatively and are positioned along the flow direction according to the rule of “front coarse and rear dense.” The difference in the three slotted fins is in the degree of “coarse” and “dense” along the flow direction. Numerical results show that, compared to the plain plate fin, the three types of slotted fin all have very good heat transfer performance in that the percentage increase in heat transfer is higher than that in the friction factor. Among the three slotted fin surfaces, slit 1 behaves the best, followed by slit 2 and slit 3 in order. Within the Reynolds number range compared ( from 2,100 to 13,500), the Nusselt number of slit 1 is about 112–48% higher than that of the plain plate fin surface under the identical pumping constraint. An analysis of the essence of heat transfer enhancement is conducted from the field synergy principle, which says that the reduction of the intersection angle between the velocity and the temperature gradient is the basic mechanism for enhancing convective heat transfer. It is found that for the three comparison constraints the domain-average synergy angle of slit 1 is always the smallest, while that of the plain plate fin is the largest, with slit 2 and slit 3 being somewhat in between. The results of the present study once again show the feasibility of the field synergy principle and are helpful to the development of new types of enhanced heat transfer surfaces.

Local heat transfer measurements of plate finned-tube heat exchangers by infrared thermography

An experimental study is performed using an infrared thermovision to monitor temperature distribution over a plate-fin surface inside the plate finned-tube heat exchangers. The differentiation of the temperature function is derived to determine the local convective heat transfer coefficients on the tested fin, using a local element lumped conduction equation included the convective effect on the boundaries with experimental data. It is disclosed that the infrared thermography is capable of rapidly detecting location and extent of transition and separation regions of the boundary layer over the whole surface of the tested models. Through the comparison of the test results on the strategy region of the in-line and staggered arrangements, it is more easy to understand or interpret the detailed dynamic phenomena of flow existed in the heat exchangers. In addition, the experimental results demonstrate that the averaged heat transfer coefficient of staggered configuration is 14–32% higher than that of in-lined configuration

Heat transfer and friction characteristics of fin-and-tube heat exchangers

An experimental study has been carried out to investigate the heat transfer and pressure drop characteristics of fin-and-tube exchangers with plate, wavy and louvered fin surfaces. In all, 36 samples of heat exchangers, including 12 plate-fin, 12 wavy-fin and 12 louvered-fin geometries, were tested. Results are presented as plots of friction factor f and Colburn j factor against Reynolds number in the range 300–2000. Additionally, the dimensional heat transfer coefficient and pressure drop are also presented against frontal air velocity. Finally, various comparison methods were adopted to evaluate the air side performance of the plate, wavy and louver fin heat exchangers.

Heat Transfer Performance of a Fin with Two Fences and Tube Heat Exchanger. Study in the Low Reynolds Number Range.

A three-dimensional steady numerical computation was made for a component model of fin and tube type of compact heat exchangers situated in a uniform flow. In this study, in order to find a clue to design high-efficient heat exchangers, numerical computation was made in the case where two fences are attached on the plate fin surface and their geometrical effects such as their locations, their heights and their attack angles on flow and heat transfer characteristics were investigated especially in the low Reynolds number range. The effect of a hole, open in the plate fin behind the fence, on heat transfer and flow structures was also examined. This hole simulates the hole of the plate fin to be produced in practical application, when a fence is produced by punching from the original plain fin plate. Two fences with holes were found to show several important effects on flow and heat transfer structures and to work well in heat transfer augmentation. They reduce the dead water area downstream the tube so that heat transfer enhancement was obtained there. Heat transfer enhancement was also attained on the fin surfaces around them. As a result, total heat transfer performance becomes 17% up compared to the normal plain fin case.

95/04053 From CFC-12 to HFC-134a — An analysis of a refrigerant retrofit project

This article is an in-depth look at the development of a refrigerant conversion plan and the actual refrigerant changeout at Sears Tower in Chicago. The design aspect deals with the initial considerations for refrigerant changeout at the onset of the recent project to completely refurbish the building's air handlers with new high-efficiency chilled water coils. First discussed in early 1991, the new replacement water coil study projected a substantial improvement in cooling capacity via an update to high-efficiency plate-fin surface in lieu of the spiral-fin design initially installed 20 years ago.

Experimental investigation of highly effective plate-fin heat exchanger surfaces

Results are presented of an experimental investigation of a new convective rational heat transfer augmentation law in plate-fin heat exchanger surfaces. This law is characterized by Nu/Nu sm ≥ ξ/ξ sm by comparing channels (heat transfer surfaces) with vortex promoters with similar smooth channels at equal Reynolds numbers. For experimental confirmation and investigation of this law, heat exchanger cores having three different plate-fin surfaces were developed and manufactured. Two surfaces are formed by short offset channels (interrupted surfaces) of equilateral triangular and rectangular cross sections. The third surface has channels of isosceles triangular cross sections, with transverse projections and grooves along the channel length direction. The experimental results and correlations are reported for the three surfaces. The experiments were conducted in a wind tunnel with specially developed precise instrumentation that ensured experimental uncertainties of δξ = ± 2.3% and δRe = 1.7% at a 0.997 confidence level. Analysis of the results indicated that the fundamental character and causes limiting rational heat transfer augmentation to Nu/Nu sm ≥ ξ/ξ sm depend upon the heat transfer surface configuration. This paper consolidates the author's research on the subject reported in the Russian language over the last 25 years.

Assessment of the efficiency of a plate-fin surface with discontinuous crossed fins

Assessment of the efficiency of a plate-fin surface with discontinuous crossed fins