Thermal Hydraulic Efficiency Research Articles

Analysis of hydrodynamics and thermal–hydraulic performance of twisted angle fins within an annular conduit

AbstractThis paper investigated the influence of various twisted angles of fin inserts integrated on the inner heated pipe wall of a double-pipe heat exchanger by analysing the thermal–hydraulic performance through numerical simulations. Results showed twisted angle fin (TAF) induced turbulent fluid flow phenomena, generating transverse and longitudinal vortices, along with swirling flow. This collaboration between the vortices and swirling flow effectively prevents heat trapping and enhances heat transfer from the inner pipe wall through the intensive fluid mixing. Despite longitudinal swirling vortices and turbulence significantly enhance local and global heat transfer performance, they led to increased pressure drop. However, TAF twisting reduces pressure drop by streamlining flow. The performance evaluation criterion (PEC) value is a dimensionless quantity that facilitates the comprehensive evaluation of optimal configurations by comparing the increment in Nusselt number and the increment in friction factor. PEC values greater than 1 indicate that the increase in Nusselt number exceeded the increase in friction factor. Among tested configurations, the twisted fin angles of 60° (TAF60) exhibited the highest improvement in Nusselt number and friction factor, also achieving the highest PEC of 1.59712 at Reynolds number of 1194.71. TAF40 and TAF50 were identified as optimal configurations for enhancing the thermal–hydraulic efficiency, with average PEC values of 1.26893 and 1.27030, respectively. Overall, the study indicated a consistent enhancement trend with increasing twisted angles and emphasizes the significant thermal performance improvement of TAF configurations compared to the smooth conduit. Furthermore, the results showed a converging tendency across all TAF configurations in the percentage improvement in Nusselt number and friction factor, as well as PEC compared to the baseline No fin configuration with increasing Reynolds number, suggesting that future improvements in thermal–hydraulic performance are more dependent on geometric angles than fluid flow velocity.

Experience in Monitoring Brazed Aluminium Heat Exchanger, after Major Repairs

Brazed Aluminium Heat Exchangers are fundamental for a natural gas liquid recovery plant. Refrigeration at cryogenic temperatures and the liquefaction process take advantages from their thermal hydraulic efficiency and compactness characteristics, making such units economically feasible. These exchangers are proprietary design, with only a few manufacturers around the world and limited knowledge about their maintenance. After two failures in the same equipment with possible thermal fatigue contributions, occurring only nine months apart, two complex repair procedures had to be carried out. To ensure operational safety, online monitoring through Acoustic Emission Technique has been performed. This monitoring led to discoveries of systems and routine maneuverer that triggered damage mechanisms. This allowed for the implementation of adjustments to mitigate the propagation of damage, thereby increasing the equipment's lifespan. The procedure applied in this type of equipment constitutes an innovative approach using the Acoustic Emission technique, which has resulted in a successful strategy of condition monitoring.

Numerical analysis on the flow and heat transfer characteristics of heat exchanger with cruciform tube

The heat exchanger (HE) is widely used in energy and power industries, which has a vital impact on the stability and efficient operation of relevant industrial systems. Different shaped heat exchange tubes are often designed specially to improve the thermal–hydraulic efficiency of HEs. In the study, two new geometries named the cruciform twisted tube and cruciform straight tube are introduced, and the heat & mass transfer properties of liquid lead (Pb) and supercritical carbon dioxide (s-CO2) in the HEs are numerically studied to assess the thermal–hydraulic efficiency and application prospect of two kinds of cruciform tube HEs. The results demonstrate that the unique cross-section geometry of the cruciform tube improves the uniformity of the flow field, and the spiral structure of the cruciform twisted tube effectively improves the blending and turbulence of working fluid. The cruciform tube can improve the comprehensive performance of the HE by more than 12%.

Increasing the Economic Efficiency of Marine Power Plants Using Waste Heat Boilers with Controlled Flow Separation

Abstract Heat recovery of exhaust gases from main and auxiliary marine diesel engines is an effective way to improve the technical and economic parameters of marine power plants. Improvements in engine efficiency necessitate an increase in the weight-size parameters of the waste heat boilers, which makes it difficult to recover heat. Intensification of the heat transfer process is considered to be an effective way to reduce these indicators. By utilising mathematical modelling, this paper shows the effectiveness of using profiled heating surfaces of waste heat boilers for this purpose. The use of elliptical heating surfaces with a mechanism of controlled flow separation, in the form of a triangular notch, is proposed. This will reduce surface drag and increase the overall thermal-hydraulic efficiency of the heat transfer processes. It is shown that the use of such surfaces in waste heat boilers makes it possible to increase the efficiency of marine power plants in tankers with a deadweight of about 45,500 tons up to 1.5% absolute and container ships with a deadweight of about 122,000 tons up to 2.5% absolute.

Pseudo-transient flow path optimization of a solar tower receiver operating with supercritical carbon dioxide

Aiming to further promote the decarbonization of energy production processes, this article simulates and optimizes the pseudo-transient behavior of a cylindrical solar receiver subjected to a spatially varying concentrated heat flux. The model employed, which accounts for its thermal–hydraulic behavior, uses supercritical carbon dioxide (s-CO2) as the heat transfer fluid and is based on a literature-validated hybrid formulation that axially discretizes the tube of the receiver and simultaneously solves the 2-D temperature distribution within the cross-section of each node. The operational conditions imposed on the receiver were determined such that it can produce 10 MW in a recompression Brayton cycle. Also, the receiver’s surface was exposed to a spatially variable concentrated solar boundary condition based on the direct normal irradiance (DNI) of a representative day for each month of the year, which was selected from the typical meteorological year (TMY) in Seville (Spain). The results showed that the combined thermal–hydraulic efficiency of the receiver increases with the number of panels and that the mass flow flowing through each symmetrical side of the receiver should not necessarily be identical for achieving maximal efficiency. More importantly, the results showed that by simply changing the location of the s-CO2 inlet and outlet ports, one can increase the efficiency of the receiver by about 3 % while considering the exact same concentrated solar irradiation.

Heat Transfer and Flow Resistance in Crossflow over Corrugated Tube Banks

The engineering of tubes with surface corrugations is recognized as an effective method for enhancing heat transfer within the tube. Yet the impact of surface corrugation on the flow and heat transfer around the tube’s exterior remains inadequately explored. This study investigates the crossflow and heat transfer characteristics in banks of periodically inward-corrugated tubes using computational fluid dynamics. Numerical simulations were performed for both in-line and staggered tube arrangements, covering Reynolds numbers from 1000 to 10,000. The aim was to examine how various corrugation parameters affect heat transfer and flow dynamics in tube banks configured in both in-line and staggered layouts. The results show that the heat transfer and the pressure drop in crossflow across tube banks are substantially influenced by changes in corrugation parameters. Specifically, in the in-line arrangement, both the Nusselt number and Euler number decrease significantly as the corrugation height increases. In contrast, in the staggered arrangement, the Nusselt number and Euler number exhibit less variation in response to surface corrugation. A comparative analysis of performance criteria suggests that a staggered arrangement is more advantageous for improving thermal–hydraulic efficiency in crossflow through corrugated tube banks.

Hydrothermal performance assessment of a parabolic trough with proposed conical solar receiver

Parabolic Trough Collectors (PTCs) are commonly employed in both industrial and residential settings for the purpose of harnessing solar energy. Several techniques have been implemented to improve performance, such as altering the geometry of the absorber tube, enhancing the selective coatings of the receiver envelope, and utilizing nanofluids. This study proposes a new method for enhancing the thermal-hydraulic efficiency of PTCs through the utilization of non-uniform heat flux distribution on conical solar receiver. The effectiveness of this approach is evaluated through numerical simulations conducted using Ansys Fluent with the aid of optical simulation performed using TracePro. The geometry under consideration is assessed at various diameter ratios (DR) spanning from 1.25 to 2 and Reynolds number (Re) ranging from 20000 to 100000, with increments of 20000. This evaluation is conducted at three distinct inlet temperatures: 150 °C, 250 °C, and 350 °C. The studied parameters include-the Nusselt number (Nu), friction coefficient (f), thermal efficiency (ηth), exergetic efficiency (ηex), and thermal enhancement factor (TEF). Furthermore, a comparative analysis is conducted between the newly proposed geometric design and a traditional straight absorber and glass structure. The findings indicated that a conical receiver generally enhances system heat transfer by a minimum of 7 % and up to 65 %, resulting in improved thermal and exergetic efficiencies. Decreasing the pipe outlet diameter from DR = 1.25 to DR = 2 led to a significant exponential rise in the friction coefficient. The TEF demonstrated that a diameter ratio of 1.25 and 1.5 resulted in maximum values of 1.19 and 1.11, respectively, at high Re and an inlet temperature of 350 °C. The results suggested that incorporating conical receivers in PTCs can greatly improve their performance. To minimize the friction coefficient and associated pumping power, it is crucial to carefully evaluate the reduction of the diameter of the absorber outlet. The results offered valuable insights for the development and improvement of PTCs in both industrial and power generation settings, promoting the adoption of renewable energy and supporting long-term sustainability.

Flow in a channel with obstacles of different scales: A detached rib and a forward-facing step

A numerical study of the flow in a channel with a forward- facing step was carried out. A single disconnected rib 3 mm high served as a passive control element in the range of Reynolds numbers from 2700 to 16400. The rib was installed at a distance to the ledge from 1.6 to 0.8 calibers at a height of 0.2 to 1 caliber. The introduction of an edge transforms the flow in front of the step. A tear-off area is created behind the rib. In cases of a high-lying rib, the separation area behind the shoulder becomes larger than the unregulated case, which leads to a loss of total pressure and an increase in the hydraulic resistance of the channel. Thermal-hydraulic efficiency was assessed; installing the fin at a close distance from the wall showed the best result

Performance enhancement of fin and tube heat exchanger employing curved trapezoidal winglet vortex generator with circular punched holes

Vortex generation is a potential passive technology for increasing the heat transfer rate in the air side of fin and tube heat exchangers (FTHEs). This study proposes novel configurations of a curved trapezoidal winglet vortex generator (CTWVG) with and without circular holes to improve heat transfer in FTHEs. As per the literature, the streamlined form of the trapezoidal winglet demonstrates high heat transfer enhancement with low flow loss and pressure drop. But still, different design configurations are possible to augment the heat transfer characteristics of CTWVG further. The current study investigates the novel configurations of CTWVG (i.e., CTWVG without hole, CTWVG with 1 hole, CTWVG with 2 holes, CTWVG with 3 holes and CTWVG with 6 holes). A three-dimensional computational model is utilized to evaluate the thermal-hydraulic efficiency of FTHEs fitted with CTWVGs with or without circular holes for Reynolds numbers ranging from 400 to 2000. A common flow-down configuration of the CTWVG with circular tubes array is used to reduce the wake region. The thermo-hydraulic performance and flow structure of FTHE with four inline circular tube configurations are compared without VG and CTWVG with or without holes. Pressure drop (ΔP), Nusselt number (Nu), friction factor (f), Colburn factor (j), and London area goodness factor (j/f) are used for the thermal-hydraulic performance comparison. Results show that the number of punched holes has an impact on the FTHE performance, which is measured using a dimensionless number as performance evaluation criteria (i.e., (j/jo)/(f/fo)). CTWVGs with circular punched holes significantly increase the FTHE's thermo-hydraulic performance. The results indicate that the flow resistance is reduced in all cases (i.e., VG with no holes, VG with 6 holes, VG with 3 holes, VG with 2 holes, and VG with 1 hole) with a minor decrease in the Nusselt number. The CTWVG with six holes performs better than other CTWVG configurations. At Reynolds numbers 400 and 2000, the Nusselt number for CTWVG with six holes enhanced by 75.25% and 40.10%; pressure drop increased by 107.88% and 125.51%, respectively. On the other hand, friction is reduced by a factor of 8.1% in CTWVG with 6 holes compared to CTWVG without holes. The CTWVG with six holes performs better than other CTWVG configurations reported in the literature [48,54]. HTPF has increased by 30.96% (compared to rectangular winglet [48]) and 27.69% (compared to curved rectangular winglet [54]) with respect to values reported in the literature. The London area goodness factor (LAGF) has been increased by 275% compared to Modi et al. [48].

Improvement of thermal-hydraulic efficiency of mining power equipment through the application of porous freon steam generators with high heat conductivity

In the article, various areas of technical application of porous freon steam generators in mining power equipment are described, and explanations why freon coolants can provide a positive energy effect in such facilities are given. The paper presents results of calculations of thermal-hydraulic efficiency of the porous once-through tubular steam generators with freon-12 as a model working fluid in the the laminar flow area and with boundary conditions of the first kind. The smooth-wall cylindrical channels with different diameters were used as the reference surfaces to be compared. The following mode and design parameters were taken as a calculation base: the liquid temperature and pressure on the saturation line at the entry into the channel were: Ts0= 110 °С; P0s = 39,9·105 N/m2.; temperature heads, i.e. a difference between the wall temperature and temperature of the liquid at the entry into the channel were: ΔT=Tw-Ts0 = 1 °C; 2 °C; 3 °C; 4 °C; 5 °C; the Reynolds numbers at the entry into the channel were: Reo = 100; 200; 500; 1000; 2000; 2300; the channel porosities were: θ = 0.7; 0.75; 0.8; 0.85; 0.9. The porous material was metal felt with the copper fiber diameter of 200 microns. The channel diameters were: d =3·10-3 m; 4·10-3 m; 5·10-3 m; 6·10-3 m; 7·10-3 m. On the basis of the performed computational studies, it was concluded that for the conditions of the same mass flow rates of the coolant, with laminar flow, and the same channel diameters, it is possible to achieve a significant reduction in the length of the porous once-through steam generator in comparison with the length of the smooth-wall once-through steam generator. Due to the significantly shorter length, differential pressure for pumping the coolant can be several tens of percent less in porous evaporation channels than in the similar smooth-walled channels. This computational study also made it possible to establish main regularities in dynamics of the energy efficiency coefficients and their dependence on the model mode and design parameters. It was shown, that positive dynamics of the efficiency coefficients of porous steam generators occurs with decrease of the channel diameter and temperature head, as well as with increase of the Reynolds number in the investigated region of coolant laminar flow.

Hollow trapezoidal baffles in a rectangular channel: Thermal/hydraulic assessment with ANN numerical approach

In this study, thermal/hydraulic performance (THP) of a heated bottom surface channel, on which hollow straight, elliptic, and wavy top surface trapezoidal baffles are attached, have been investigated. Artificial neural network modeling (ANN) and 3D ANSYS numerical valuations are presented and validated using experimental data obtained by Sahin et al. (2019). Six parameters are studied: baffle height (H), baffle width (S), baffle length (L), corner angle (α), inclination angle (β), and Reynolds number (Re). This study is carried for both aligned and staggered baffles configuration. Air is considered to be the working fluid at a range of Reynolds number (5 × 103 ≤ Re ≤ 2.3 × 104). Backpropagation technique used to determine the optimal ANN size with the Bayesian regularization algorithm. Results show that the most effective parameters on THP are Re, α, and H. Based on the thermal hydraulic efficiency values, the optimum condition is obtained at α= 16°, β = 0°, and baffle dimensions of H = 20 mm, L = 25 mm, S = 26 mm. The average value of thermal enhancement factor (TEF) shows that the staggered arrangement is superior to aligned one for all baffle shapes at the optimum condition. The largest TEF is 1.2 which is captured for the case of the wavy top surface trapezoidal baffles in staggered arrangement at Re = 5000.

Two-stage thermal-hydraulic optimization for Pillow Plate Heat Exchanger with recirculation zone parameterization

• PPHE is a promising alternative to conventional heat exchangers. • A two-stage thermal-hydraulic optimization method is proposed. • The developed PPHE model is evaluated with existing experimental data. • Average PEC of the two-stage optimized PPHE is improved by 29.3%. Pillow plate heat exchanger (PPHE) has become a promising alternative to conventional heat exchangers due to their satisfactory heat transfer performance and geometric flexibility. Nevertheless, the presence of recirculation zone (RZ) greatly restricts its thermal-hydraulic efficiency. In this study, a two-stage thermal-hydraulic optimization method with RZ parameterization was proposed. At the first stage, a genetic particle swarm optimization algorithm was developed, which combines a genetic algorithm with particle swarm optimization to maximize the thermal-hydraulic performance of PPHE. While at the second stage, the optimization objective was refined to further enhance the heat transfer characteristics based on geometrical parameters of RZ. The developed CFD model of PPHE was evaluated against existing experimental data and found to be in satisfactory agreement in terms of hydraulic diameter, Nusselt coefficient and pressure drop. Compared to the baseline design, the average PEC of the two-stage optimized PPHE was improved by 29.3% over a Reynolds number ranging from roughly 4,000 to 8,000, while the heat transfer area of RZ was reduced by 25.3% in average. The results revealed that a decreased welding spot pitch ratio contributes to the flow mixing between mainstream and the stagnant fluid downstream of the RZ, while smaller welding spot can significantly improve the turbulent energy dissipation of the mainstream, and therefore enhance the overall heat transfer.

CFD analysis andheat transfer characteristics of printed circuit heat exchanger

This paper aims to investigate the cubical fins and the thermal-hydraulic characteristics in a Printed Circuit Heat Exchanger (PCHE). The working fluid is considered a supercritical LNG. The outcomes show that the thermal-hydraulic performance is enhanced using the cubical fins comparing it to the straight channel. The maximum and minimum difference of N_u/E_u between the cubical fins channel and the straight channel were 71.7 % and 64.8 % respectively. It is noticed that the pressure drop and Heat Transfer coefficient are increasedsimultaneously with increasing the mass flux.Using Ansys Fluent 15.0, numerical optimization isperformed to examine and analyzethe influence of the sparser staggered arrangement. The computed results show that this type of arrangement improves the thermal-hydraulic efficiency of the cubical fins in a PCHE. A comparison between the straight fins arrangement and the staggered fins arrangement is reported.It has been noticed that the velocity of the LNG flow in the cubical fins channel is increased along the length of the PCHE,and decreased byincreasing the vertical separationL_V. The side effect of the vertical separation L_V on the PCHE’s efficiency was more evident than that of the staggered arrangementL_S. Finally, afeasibility study is performed to inspect the power consumption of the new design.

Parametric CFD study for finding the optimal tube arrangement of a fin-and-tube heat exchanger with plain fins in a marine environment

In the past, fin-and tube heat exchanger (FTHE) tube pattern ratios have been largely based on ad-hoc design principles. Here, we investigate the optimal tube arrangements for a FTHE with plain fins in marine environments represented by two different air types; one for unfiltered air with high condensation rate and one for clean dry filtered air conditions. The thermal-hydraulic efficiency of the FTHE design is measured by comparing a modified ratio of Colburn j-factor and Fanning friction factor. The regression model generated from the CFD data is then used to identify the maximum efficiency for two design specific fin pitches separately. We identified two optimal tube patterns: one for a large fin pitch for unfiltered air, and another for a small fin pitch for filtered air. Manufacturing restrictions were found to significantly limit the maximum achievable efficiency of a tube pattern. By neglecting the related manufacturing restrictions, 4 % higher efficiency for a fin pitch of 1.5 mm and 23 % higher efficiency for a fin pitch of 3.5 mm is achieved. Without any application specific limitations or manufacturing restrictions the fin pitch 1.5 mm can have a 36 % increased efficiency than fin pitch 3.5 mm. These novel results show that development in manufacturing have potential for significant improvements in thermal-hydraulic efficiency. • Fin-and-tube heat exchanger is studied with open source conjugate CFD models. • The smaller fin pitch F p = 1 . 5 mm offers better JF performance than the F p = 3 . 5 mm. • A higher JF performance can be achieved by neglecting the manufacturing restrictions. • Unconventional tube arrangement ratio values P t / P l ≠ 1 . 1547 offer the best JF performance.

OPTIMIZATION OF INDIVIDUAL CONSTRUCTIONS OF A COMPACT SMALL DIAMETER PIPE BUNDLE USING CFD SIMULATION

Bundles of smooth cylindrical pipes with a checkerboard and corridor arrangement are widely used in various heat exchange devices and devices of power plants. Surfaces of this type, which are used in known designs of shell and tube heat exchangers, have a large mass and dimensions. The research proposed a new design of the shell-and-tube heat exchanger using compact bundles of small-diameter tubes, which significantly improved its mass-dimensional indicators. The location of the pipes in the pipe bundle was optimized using the ANSIS FLUENT software package. CFD model type planning was carried out using the "Latin Hypercube Sampling Design" method using ANSYS DesignXplorer software. The pipe offset (pipe diameter 8 mm, offset 1 to 5 mm) and the distance between adjacent rows of pipes (5 to 10 mm) were selected as variable parameters. The thermal-hydraulic efficiency of the beam was chosen as the optimal parameter. The MOGA method was used for optimization. The optimization results show that the greatest value of thermohydraulic efficiency has a pipe bundle for which the displacement of the tubes is 0.00101986 m, the distance between the tubes is 0.009937333 m. At the same time, the heat transfer coefficient is 100.019304 W/m2K, the pressure drop is 34.5701419 Pa, and thermohydraulic efficiency is equal to 312.101156. For an optimal bundle of pipes, the pressure drop in the channels of the bundle lies in the range from -47 to 130 Pa, and the flow speed in individual sections of the channel reaches 14 m/s.

CFD numerical investigation of Heat transfer characteristics of Y- shaped solar air heater

The numerical investigation of thermal hydraulic performance of Y-shaped rib rectangular solar air heater is observed by CFD tool of Ansys Fluent software. This paper explains the development of solar air heater technique that makes a suitable designed model for increasing heat transfer without increasing the global warming in environment. The rectangular solar air heater model is designed by Ansys fluent software. The Ansys fluent software is generally used for investigating heat energy by using RNG k-e model method for the fluid (air or liquid) and also has perfect information about flowing fluid (3000 ≤ Re ≤ 18,000) and then gives the perfect physical information relevant to design model. The Rectangular channel is (1500 × 200 × 30 mm) a station for two Y- shaped ribs which are placed on top and bottom sides of surface of the channel and total length of each Y-shaped rib is 50 mm. Y-shaped ribs are constructed with variants of angles between upper two parts (θ and relative roughness pitch, P/e = 6, 8, 10, and 12. In the paper, Y- shaped ribs roughness is used to increase heat transfer rate of SAH and observed maximum Thermal hydraulic efficiency ƞmax = 3.5992 at relative roughness pitch P/e = 10 mm, Re = 18000 and angle is taken θ = 90° between upper two parts of Y- shaped ribs.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ВИХРЕВЫХ ПОТОКОВ НА ЭЛЕМЕНТЫ ЯЭУ

The mechanisms of generation of stable large-scale eddies and flow swirling in complex channels of the 1st and 2nd circuits of transport nuclear power plants (NPP) are revealed. An analysis is given of the influence of vortex formation and flow swirling processes on failures in NPP systems. It is shown that with a complex geometry of the channels of the pipe systems of the thermohydraulic tract and the reactor plant (RP), the unauthorized swirl arising in certain dynamic modes can lead to the effect of blocking the flow caused by the swirl flow crisis. It has been established that the phenomenon of the crisis is accompanied by the generation of low-frequency acoustic vibrations and large pressure losses required to form a recirculation flow zone, which prevents the flow of fluids in complex channels of the nuclear power plant. In the presented work, the manifestation of a swirling flow crisis is considered by examples of modeling the processes of hydrodynamics and heat transfer in the channels of steam generators and the pressure compensation system of transport nuclear power plants. It is shown that the generation of stable vortex formations in the elements of the NPP equipment of the integral type can be directly related to the mechanism of excitation of hazardous vibroresonance effects. Methods for improving the design of pipe systems of steam generating plants are proposed to increase their thermal-hydraulic efficiency and vibration resistance.

Neural Network Modeling of Thermal-Hydraulic Efficiency of Promising Surface Heat Transfer Intensifiers

Neural Network Modeling of Thermal-Hydraulic Efficiency of Promising Surface Heat Transfer Intensifiers

An investigation on effects of blade angle and magnetic field on flow and heat transfer of non-Newtonian nanofluids: A numerical simulation

Effects of blade angle on thermal-hydraulic efficiency of two-phase non-Newtonian nanofluid flow in the presence of a magnetic field in a helical channel were studied numerically. The numerical 3D governing system of equations was resolved using the SIMPLEC technique-based control volume method to achieve the highest possible economic efficiency. The governing equations were also solved based on the Eulerian-Eulerian Two-Phase Model (TPM). The optimization was conducted to accomplish the most beneficial geometry in order to view the maximum Hydro-Thermal-Performance (HTP). The results showed that higher Reynolds numbers lead to an increase in velocities causing more heat transfer and higher Nusselt numbers. Moreover, velocities increase results in further formation of vortex and pressure drop. Besides, the higher magnetic field power, the higher heat transfer, pressure drop, friction factor and HTP index are expected. Based on the acquired results, the variation trend of Nu/Nu0 is similar for all studied corrugation angles and its ratio always reduces by increasing Reynolds number. For a configuration with α = 60°, the maximum values of Nu/Nu0 ratio are achieved regardless of the amount of all studied Reynolds numbers which is followed by configurations with α = 45° and α = 30°, respectively. The maximum values of the HTP index are achieved for all studied Reynolds numbers for the configuration with α = 60° which are followed by configurations with α = 30° and α = 45°.

Improvement of thermal-hydraulic performance of plate heat exchanger by electroless nickel, copper and silver plating

In this study, electroless plating of nickel, copper, and silver is applied to stainless steel 316 (SUS316) plate heat exchanger (PHE) to enhance thermal-hydraulic efficiency. The electroless plating experiment was first performed on small samples (30 × 30 × 1 mm) to determine optimum control parameters, i.e. solution concentration, current density, etching time prior to commercial PHE. The characteristics of the coating surfaces were indicated by static contact angle, thermal shock, roughness profile, Vickers hardness, SEM images, and EDS analysis. In order to research the effect of each electroless coating on PHE performance, a single-phase water flow heat transfer experiment was performed. The thermal-hydraulic efficiency was evaluated using the Overall Heat Transfer Coefficient (OHTC), Friction Factor, Number of Transfer Units (NTU), effectiveness and Performance of Evaluation Criterion (PEC). As a consequence, aqua regia solution with a volumetric ratio of 1HNO3: 2HCl: 75H2O, a current density of 0.1 A/cm2 and a 12-min etching were determined to be the optimum process parameters for optimizing surface area and minimizing mass loss. After electroless coating, the surface was completely changed from smooth to rough, resulting in a change from hydrophobicity to hydrophobicity, as well as a change in surface morphology. More significantly, all coated PHEs displayed a substantial increase in their performance, as shown by PEC ranging from 1.21 to 1.30 in the case of Silver-coated PHE, followed by 1.20–1.24 and 1.11–1.15 in the case of Copper and Nickel respectively.