Surface Heat Transfer Research Articles

Seawater Corrosion of the Anodized A1050 Aluminum Plate for Heat Exchangers

To confirm the suitability of aluminum for the heat transfer surfaces as a heat exchanger material for ocean thermal energy conversion, the seawater corrosion resistance of aluminum plates in a plate heat exchanger was experimentally investigated. In this study, four different surface shapes with chevron angles of 45° and 60° and different treatment types of A1050 aluminum heat transfer surfaces were processed into herringbone patterns. Additionally, the surfaces of the test plates were either anodized or untreated. In continuously flowing deep ocean water, the surface conditions of the test plates were observed at 1, 3, 6, and 12 months using mass measurements, visual inspection, laser microscopy, and SEM. For the anodized A1050 plates, regardless of the surface shape, there was almost no change in the mass, laser microscopy, or SEM results even after 12 months. In contrast, the untreated plate mass decreased in the samples after 3 months or later, and the mass reduction rate was approximately 2–7%. In conclusion, untreated aluminum is not suitable for use in seawater and an anodizing treatment is necessary for its use in heat exchangers for ocean thermal energy conversion.

Research into Deposits Accumulating on Heat Exchange Surfaces Due to the Thermal Degradation of Heat Exchange Apparatus in Steam Power Plants: A Study of Model Deposits

Abstract Deposits gathering on heat transfer surfaces can cause an increase in thermal resistance, which leads to thermal degradation. As a result, it causes a decrease in the efficiency of the entire thermal system, which translates into an increase in energy conversion costs, as well as an increase in environmental degradation. These deposits are characterised by the diverse geometric structure of the surface layer, which can be described using roughness parameters. The paper presents an original method for fabricating model deposits with diverse irregularities in their surface layers. The model deposits fabricated in this way can be dedicated as model research material for studies on the description of thermal degradation phenomena of heat exchangers within steam power plants, particularly condensers and regenerative heat exchangers. The physical characteristics of the model deposits and an original geometric model of their disposition onto the heat transfer area are presented in the paper, as well as the concept of a texture parameter defining the irregularity for the surface layer of these deposits.

Effect of heat flux on the passive film and passive/active transition behavior of heat transfer surface of 304 SS in 0.5 M H2SO4 solution

Effect of heat flux on the passive film and passive/active transition behavior of heat transfer surface of 304 SS in 0.5 M H2SO4 solution

Key factors affecting the boiling heat transfer coefficient of FC-72 in saturated pool boiling using lotus-type porous copper

Key factors affecting the boiling heat transfer coefficient of FC-72 in saturated pool boiling using lotus-type porous copper

Palm Oil as a Heat Transfer Medium

Palm oil plants are abundantly available in Malaysia and are harvested commercially to either be exported in their crude form or used as a base for products such as soap and cooking oil. However, palm oil has also invoked interest in being used as a coolant. As opposed to conventional coolants, vegetable-based coolants such as palm oil offer several advantages, such as being more environmentally friendly upon disposal and safer for users as they are less chemically reactive. It is an accepted hypothesis that the inclusion of nanoparticles would generally increase the heat transfer rate of most fluids as these nanoparticles contribute to a rise in the heat transfer area. This paper presents a numerical study on using palm oil as a medium for heat transfer in machining operations, with and without the use of nanoparticles. It presents heat transfer comparisons between palm oil, conventional water and mineral oil coolants. It was found that the inclusion of nanoparticles increases the heat transfer capability of mineral oil and palm oil with palm oil being more positively affected. However, there is no apparent trend or correlation that can be made between concentration and heat transfer as the percentage increase of the surface heat flux and heat transfer coefficient are inconsistent with the 2% concentration showing a higher percentage increase compared to the 1% and 3% concentrations. Considering the results of this preliminary study, it can be concluded that palm oil together with nanoparticles does present a promising prospect as a coolant.

Phase change material infused surfaces for thermo-responsive condensation heat transfer for effective thermal management

Phase change material infused surfaces for thermo-responsive condensation heat transfer for effective thermal management

Analysis of Casson ternary nanofluid integration under various thermal physical impacts with Cattaneo-Christov model: Exploring magnified heat transfer in stretchy surface

Analysis of Casson ternary nanofluid integration under various thermal physical impacts with Cattaneo-Christov model: Exploring magnified heat transfer in stretchy surface

Heat transfer augmentation, endothermic pyrolysis and surface coking of hydrocarbon fuel in manifold microchannels at a supercritical pressure

Heat transfer augmentation, endothermic pyrolysis and surface coking of hydrocarbon fuel in manifold microchannels at a supercritical pressure

International inter-laboratory comparison of solar heat gain coefficient of building-integrated photovoltaic modules results of tests with or without power generation and tests with PV cell coverage ratios

International inter-laboratory comparison of solar heat gain coefficient of building-integrated photovoltaic modules results of tests with or without power generation and tests with PV cell coverage ratios

Acoustic State Sensing of Subcooled Boiling Heat Transfer on a CuCrZr Surface Using a Deep Neural Network for Divertor Application

In the cooling systems of a nuclear fusion reactor (NFR), anomaly events may occur where the flow of coolant unexpectedly decreases, such as in a loss-of-flow accident (LOFA). From the viewpoint of reactor safety design, ITER should be capable of handling subcooled boiling in coolant duct lines due to a sudden LOFA under severe operating conditions where the reactor’s divertor is under a steady-state massive heat load of 10 MW / m 2 . To detect anomaly events, we performed a proof-of-concept (PoC) experiment and propose a novel method of state sensing of the coolant duct line based on sound emitted from boiling. In the PoC pool boiling experiment, using a hydrophone, we acquired sound from water boiling where the heat transfer surface was made of a divertor alloy [copper-chromium-zirconium (CuCrZr)] or copper (Cu) as the reference material. Notably, microbubble emission boiling (MEB) occurred at the highest heat flux in the case of CuCrZr alloy as well as Cu. This indicates that MEB can also occur in an actual NFR. In this study, we developed deep neural network (DNN) models to identify boiling states from acquired sound. Our well-trained DNN models could distinguish between the boiling sound of Cu and the CuCrZr alloy of the heat transfer surface material. The regression DNN models achieved a coefficient of determination R 2 of approximately 99%. Based on the PoC study, we have demonstrated that DNN models of boiling acoustics have the potential to identify boiling states inside coolant duct lines in the NFR, where the heat flux ranges from the low region to the high region with MEB occurrence.

Numerical Analysis of the Influence of Frost Layers on the Heat Transfer Characteristics of Cryogenic Valves for Polar LNG Ships

To investigate the impact of frost-layer formation on the heat transfer characteristics of cryogenic valves in LNG vessels, this study derived the temporal variation in the valve’s temperature field based on the thermodynamic characteristic parameters of the low-temperature valve. Additionally, a frost formation model was developed for the drip tray. This considered the physical model characteristics of the tray, and the frost thickness was calculated for different times. The morphology of the calculated frost layer was coupled with the low-temperature valve model for heat transfer calculations to explore the influence of the frost layer on valve heat transfer characteristics. The results show that, in the initial stage of frost formation, the frost layer acts similarly to a finned heat sink, enhancing the thermal exchange efficiency at the surface of the drip tray, which results in a temperature increase in the drip tray and stuffing box compared to the frost-free condition. However, as the frost layer grows on the surface of the drip tray, the surface heat transfer resistance increases, gradually diminishing the enhancing effect of the frost layer on the heat dissipation of the drip tray. The results validate the dual role of the frost layer in the heat transfer process of low-temperature valves, providing important insights for the design and optimization of such valves.

Machining Path Optimization of Inductively Coupled Plasma Based on Surface Heat Transfer Model.

Inductively coupled plasma (ICP), a non-contact optical processing method, has been widely used in the preparation of fused quartz. However, the thermal effect during processing inevitably affects the stability of the removal rate, reduces the processing accuracy, and restricts the further development of plasma processing. This paper analyzes the critical temperature that affects the changes in plasma removal depth, establishes a heat transfer model for plasma jet processing through simulations, derives the heat conduction equation during processing, and obtains the critical radius corresponding to the critical temperature related to the processing speed. Additionally, this work analyzes the path temperature of the grating track used in processing and obtains the path temperature variation curve. Based on the critical radius, a staggered grating track was proposed, which verified that this track can effectively control the path temperature, thereby suppressing the error caused by the thermal effect of processing. This study not only helps to gain a deeper understanding of the heat transfer process in plasma machining, but also provides a basis for achieving high-precision plasma machining path optimization schemes.

Numerical Enhancement of Forced Convection Heat Transfer Characteristics for Skewed Wavy Channel Partially Inserted With Copper Metal Foam

ABSTRACTIn this paper, the convective heat transfer (HT) and airflow characteristics are numerically examined for skewed wavy rectangular channels inserted partially with copper metal foam. Calculations were performed using ANSYS Fluent 19.2 at the airflow with a laminar range of Reynolds number from 700 to 1700. The thermohydraulic performance (THP), friction factor (f), and average Nusselt number (Nuavg) variation with Re for foam heights of hmf = 0.2–0.3H and foam pore densities of 10, 20, 30 and 40 pores per inch (PPI) have been examined for the tested channels. The results indicated that partial metal foam inserts enhance temperature distribution and increase the HT rate inside the channel due to the large HT surface area, high‐thermal conductivity of copper, and increased flow resistance, which increases the velocity of the fluid passing through the heat exchange system. Also, increasing hmf, PPI, and Re improves the HT rate in the channel, leading to an increase in both Nuavg and f due to decreased permeability. In addition, under constant hmf conditions, the THP exhibited a rise when the PPI and Re increased. Furthermore, at constant PPI and Re, the THP value lowers when the hmf grows due high increase in flow restriction. At hmf = 0.2H, 40 PPI, and Re = 1700, the THP reaches a maximum value of 1.51.

Research on surface characteristics and heat transfer performance of nanocoatings for heat exchange surfaces

Research on surface characteristics and heat transfer performance of nanocoatings for heat exchange surfaces

Study on acoustic streaming characteristics around elliptical heat exchanger tubes at different angles of attack

The distribution of acoustic streaming outside the tube in a planar standing wave field is calculated by numerical simulation using an elliptical heat exchanger tube at the low-temperature heating surface of a 600 MW unit as an example. The study discusses the impact of angle of attack (AOA), Strouhal number (St0), and Reynolds number (Re0) on the external acoustic streaming characteristics of the tube from structural, intensity, and scale perspectives. The results indicate that the strong nonlinearity of the second-order acoustic streaming in the Stokes boundary layer is driven by the first-order acoustic field. As the AOA increases, the external acoustic streaming vortices exhibit a phenomenon of inner and external vortex merging. Along the direction of the inner vortex center, the acoustic streaming velocity shows peak and valley fluctuations influenced by the vortices. In the normal direction, the acoustic streaming is significantly weakened, and the velocity distribution characteristics vary at different distances s. The inner vortices i = 1 and 2 achieve maximum and minimum values around AOA = 60° and 30°, respectively. The relative Nusselt number NU and relative shear rate SH quantify heat transfer and ash removal effects, respectively. Both small St0 and large Re0 enhance the heat transfer effectiveness. The SH shows a similar variation pattern to the scale of the acoustic streaming under the corresponding cases. The conclusion aligns well with the requirements of enhanced heat transfer and ash resistance for low-temperature heating surfaces, providing important reference for the selection of AOA for elliptical heat exchange tubes.

Features of the operation of the heat exchanger-condenser of modern passenger aircraft

This paper presents a description of the design problems of the heat exchanger-condenser of modern aviation air conditioning systems (ACS) of passenger aircraft. The purpose of the work is to study known design methods and explore an alternative option. The paper presents a description of the problems of operating an ACS heat exchanger-condenser: freezing of the heat transfer surface along the cold and hot paths, as well as known methods of anti-icing systems (AIS) for it. The features of the calculation and design of the design variant under study are described. The results of computer simulation of heat transfer processes for various configuration options of the heat exchanger-condenser are presented. The most effective ways to prevent surface freezing are shown. The work is based on original copyright materials obtained at the Department of Technical Thermophysics of NSTU.

Numerical Investigation on PCM-Based Enclosure: Effect of Pin Height and Count

One of the challenges in energy storage is the reduced thermal conductivity coefficient of phase-change materials (PCMs), which presents a barrier to efficient energy storage. Fins can be used as thermal conductivity enhancers to help overcome this problem. The PCM is meant to melt by heat transfer from high-temperature water, and this numerical study examined the impacts of pin-fin height and number on the heat transfer rate and melting time. The PCM enclosure had dimensions of 480×240×60 mm. It was equipped with four sets containing 21, 35, 49, and 63 cylindrical pin fins, each with a diameter of 10 mm. The fins were arranged at heights of 30, 42, and 56 mm. The material for the pin fins and the plate between the water and PCM on which the pin fins are mounted is St37. The findings show that, compared to the design without fins, installing pin fins at a height of 56 mm and with a count of 63 may enhance the heat transfer rate from water to PCM by 59.65%. Additionally, it decreases the melting time by 36.6% for 1 kg of PCM. Increasing the number of pin fins was shown to reduce the melting time more effectively than increasing the fin height. It was shown that the larger heat transfer surface area and improved natural convection from flow vortices inside the PCM enclosure account for the higher heat transfer rate in designs with pin fins compared to those without.

Experimental & Modelling Studies on Novel Scraped Surface Falling Film Crystallizer for Freeze Desalination

Experimental & Modelling Studies on Novel Scraped Surface Falling Film Crystallizer for Freeze Desalination

Effects of magnetism on porous rectangular fins with convection and radiation

A fin is an extended surface used to enhance the surface area of a heat transfer surface between a hot source and the outside environment. To maximise the rate of heat transportation, the exterior surface of heated equipment is equipped with fins of various geometries. Heat is exchanged using fins in radiators, refrigeration systems, superheaters, combustion engines, electrical equipment, electric transformers, space vehicles, and aircraft engines. Reflecting these applications, we analyse the effect of a magnetic field on the thermal properties of radiating porous rectangular fins. The proposed model is numerically analysed using the shooting method under the influence of radiation and convection, then compared with the DTM solution and both the solution found closer to each other. The effect of various dimensionless parameters on temperature transmission in magnetized rectangular-shaped porous fins is revealed using numerical results. It is revealed that, when the Raleigh, Hartmann, Peclet numbers, convective and radiative parameters increase, the fin?s thermal profile decreases, whereas the thermal profile increases with an increase in surface temperature, porosity, and ambient temperature. It is observed that the magnetic effect increases the heat transfer rate from porous rectangular fin surfaces. Accordingly, efficiency increases as Hartmann number, Raleigh number, and radiative parameter rise. Increasing Peclet number, surface temperature, and ambient temperature leads to a reduction in efficiency.

Leveraging CFD simulation to optimize the flow of cleaning artifacts to remove scale from heat transfer surfaces of heat exchangers

Leveraging CFD simulation to optimize the flow of cleaning artifacts to remove scale from heat transfer surfaces of heat exchangers