Local Heat Transfer Coefficient Research Articles

A fractal blade for cooling liquids: Experiments and simulations

The performance of a fractal geometry blade for cooling hot water by natural convection and evaporation was studied numerically and experimentally. The blade design includes a tree-like fractal pattern and the Sierpinski carpet. The fin is made up of a solid hollow structure whose core is embedded with a porous material through which liquid flows. For the experiments, temperature measurements were taken in the porous medium by holding the fin in a fixed vertical position while warmed water was fed through its flow inlet. Numerical simulations were performed using a two iteration scheme that first involves the calculation of the local convective heat transfer coefficients and then the estimation of the heat dissipated by evaporation. The behavior of the fractal blade was compared with that of a benchmark heat sink that does not include the Sierpinski pattern in its construction. The experimental and numerical results agree well with each other and show a better performance of the reference heat sink when cooling water. Although the windows in the Sierpinski pattern improve convective cooling, this effect is marginal compared to evaporative cooling, which is enhanced by the larger surface area of wet porous medium exposed to the environment in the benchmark fin.

Heat transfer enhancement of a slot-confined and submerged impinging jet utilizing lamina-shaped CoFe3O2/water nanofluid

Designing a cooling system is crucial for the thermal management of many different types of energy applications, such as fuel cells, solar panels, electronic cooling, and many more. A higher local heat transfer coefficient is attained by impinging jets, making them a viable cooling option. This study investigates a two-dimensional numerical study into the turbulent convective heat transfer in a confined slot and submerged impinging jet by using water and a nanofluid for Reynolds numbers between 6000 and 24000. The nanofluid of lamina-shaped CoFe3O2/water has been studied, with the volume concentration of nanoparticles ranging from 2.0% to 4.0%. Using a finite volume technique based on the SIMPLE algorithm, the governing momentum, continuity, and energy equations are solved. A presentation and discussion of the influence of the nanoparticle's volume fraction and the Reynolds number on the flow and thermal properties are provided. Increasing the volume fraction of nanoparticles is shown to enhance the Nusselt number and the Darcy friction factor. Entropy generation increases with the increase of the Reynolds number for all working fluids.

Heat transfer and gas dynamics numerical modelling of compact pipe bundles of new design

Weight and size characteristics, heat transfer efficiency across the surface, pressure losses in the flow paths for each heat transfer medium, and other parameters that characterise the heat exchanger play an important role in the development of new types of heat exchanger designs. This predefines the research relevance and the need for a solution. The research aims to develop and implement fundamentally new approaches to the design parameters of shell-and-tube heat exchangers, in which smooth-tube bundles are placed as compactly as possible in their crossflow. For this purpose, numerical modelling in the heat exchanger channels and studies of heat transfer and gas dynamics were carried out. The ANSYS Fluent software package was used to calculate the hydrodynamics and heat transfer in the tube bundle channels. Numerical modelling of hydrodynamics and heat transfer processes in the flow of a compact bundle of small-diameter pipes was carried out. The mathematical model includes the Navier-Stokes equation, the energy equation, and equations describing the turbulence of the external flow. The turbulence model was chosen as a model that describes turbulence in channels well. The results of numerical modelling showed a compact bundle of pipes at the outlet of the channels, with an average value of +20.1ºС. Notably, the local temperature values near the channel walls are close to +30 °C. The air velocity at certain points of the duct reaches 85.1 m/s. At the same time, the average air velocity in the cross-section of the channel is about 41.2 m/s at Re=21420. It is demonstrated that the maximum values of local heat transfer coefficients for pipes in a compact bundle are observed in the areas where the flow joins the pipe surface and at the beginning of the boundary layer formation. The maximum values of the heat transfer coefficient reach up to 1335.5 W/m2·ºС for the second and third rows, and at the front point of the first order, it is 1042.3 W/m2ºС. These results will improve the weight and dimensions of shell-and-tube heat exchangers and reduce their cost

Study of natural convection heat transfer for a cylindrical and semicylindrical heat transfer system geometry

The paper presents the experimental and numerical study of the heat transfer parameters for the heated tube bank and arc-shaped plate made up of four tubes and four arc protrusions arranged one above the other. To evaluate the local heat transfer coefficients, the holographic interferometry is used as the experimental method, while the numerical simulations are performed by the Ansys Fluent software. The tube bank supplemented by the fin of different thickness and the double arc-shaped plate is further considered to improve the heat transfer parameters and the numerical results are compared with the basic arrangements. Considering the natural convection, the Rayleigh numbers are specified in the range of 16,460 to 46,340. It is observed that the tube bank achieves a higher average Nusselt number in the range of 37%–82% compared with the other arrangements depending on the Rayleigh number. The tube bank with fins does not increase the heat transfer parameters; however, there is an increase in average heat flux compared to the tube bank without fins. The double arc-shaped plate arrangement slightly increases the heat transfer and markedly increases the average heat flux compared to the single one. The highest average heat flux is achieved for the double arc-shaped plate and tube bank with fins in the range of 27.430 Wm-2 to 126.139 Wm-2.

Flow and heat transfer in rotating smooth and ribbed multi-channel double-wall structure with multiple-jet impingement cooling

In this study, the heat transfer of multiple-jet impingement in rotating smooth and ribbed multichannel double-wall cooling structure with film extraction are investigated. The dimensionless jet-to-target spacing is 1, and the dimensionless jet-to-jet spacing is 3.55. In ribbed channel, the rib height is 1 mm and rib spacing is 8 mm. The experimental jet Reynolds number ranges from 2000 to 8000, and the maximum jet rotation number is 0.22. The test section contains five impingement channels. The local average convective heat transfer coefficient is measured by the “copper plate method”. The SST k-ω model is used to study the effect of rotation on the flow in channels. The results show that the heat transfer gap between high and low radius is more evident with an increase of the Roj. This is because the rotation effect increases and decreases the mass flow rate at high and low radius, respectively. Moreover, rotation can strengthen the impingement effect of the trailing side (TS) while weakening the effect of the leading side (LS) when the Roj is less than 0.06, Which causes differences in the heat transfer between the LS and TS of the impingement channel. Furthermore, affected by the ribs, the average heat transfer of ribbed target surface is improved. The area of high heat transfer region generated by impingement decreases, and an inverted butterfly-shaped high heat transfer region is generated near the film hole. Finally, the rib weakens the effect of rotation on the flow of target surface to some extent.

The effect of two main vortexes generator on heat transfer enhancement in mini rectangular ducts of airborne thermoelectric conversion system

To enhance the heat transfer process of supercritical pressure fluid in rectangular channels of the airborne thermoelectric conversion system, the combined effect of the Reynolds stress, properties variation and longitudinal fins on convective heat transfer process in ducts under supercritical pressure is investigated. Then, a method to induce the two main vortexes structure in rectangular ducts is proposed. Results show that, in smooth ducts, the two main vortexes structure is formed due to the effect of density variation. By comparing the flow and heat transfer process in the smooth duct and ridged duct with trapezoidal fins attached on the lower wall, it is found that, due to the effect of new vortexes induced by trapezoidal fins, the two main vortexes structure is inhibited, which makes local wall temperature increases about 50 K. Accordingly, the thermal performance enhancement factor of rectangular duct with trapezoidal fins is lower than 1. To enhance the two main vortexes structure, a method that using triangular fins to induce two main vortexes structure is proposed, and the duct with one triangular longitudinal fin attached on the upper wall is designed, which has better thermal performance than ducts with trapezoidal fins. Due to the effect of triangular fins, the dominant distance of two main vortexes structure increases by 416%. Accordingly, in ducts with triangular fins, local heat transfer coefficient is enhanced about 23.5%, and the maximum of thermal performance enhancement factor is about 1.29.

Study of flow boiling in a vertical mini-channel with surface structuring: Heat transfer analysis using inverse method

Using a boiling fluid to cool components is a very efficient process, which is often used in micro/mini channel flows. A proposed application is the direct contact liquid cooling of lithium-ion battery cells, where a dielectric fluid is required and where the effects a cell thermal runaway could be mitigated by a convective boiling flow between the cells. For such applications, better designs require both to understand confined convective boiling with coupled flow phenomena and to quantify the local heat transfer accurately. The present paper introduces new experimental results of flow boiling heat transfer of a dielectric fluid, the HFE-7100, in a vertical rectangular 1 mm deep, 30 mm wide and 120 mm long mini-channel. The test section is an aluminum block instrumented with three lines of five K-type thermocouples located all along the flow. The experiment mainly aims at determining the heat transfer coefficient and CHF and at characterizing both the flow regimes and the dry-out phenomenon. Measurements are carried out from start of boiling to dry-out, at different mass fluxes (140, 390 and 648 kg/(m2.s)) and at a pressure of 1.1 bar. These tests were performed on a reference unmodified surface and compared to two biphilic surfaces including coating techniques. The visualization of the flow is achieved through a glass pane with a high-speed camera to identify different flow patterns. The local heat transfer coefficient is calculated by a resolution of a 2D inverse heat conduction method. This approach uses a numerical Finite Difference Method (FDM) for the spatial discretization and a Tikhonov's method for regularization. The inverse 2D method permits to follow the evolution of the heat transfer coefficient along the channel with the visualized flow pattern. The experimental results show a small sensitivity of the mass flux on the heat transfer coefficient and a predominance of nucleate boiling. On the other hand, there is a significant sensitivity of the mass flux on the dry-out occurrence. Finally, the sensitivity of two techniques of biphilic surface coating on boiling and on the dry-out occurrence is quantified and discussed.

Case studies on local mixed convection heat transfer coefficients along a radiant heated wall subjected to displacement ventilation

Case studies on local mixed convection heat transfer coefficients along a radiant heated wall subjected to displacement ventilation

Experimental Analysis Of The Influential Factors On Mixed Convection Flow In Horizontal Pipes

Abstract It has been speculated that a forced pipe flow is always assisted by free convection owing to the dependency of fluid properties on its temperature. The purpose of the current study is to experimentally examine the effect of different-sized smooth horizontal pipes on mixed convection of water in internal flows under uniform heat flux wall conditions. Infra-red thermal imaging is used to measure outer surface temperature in axial and circumferential direction. Reynolds number range is taken between 1000 and 18000 on three test sections of the diameter of 8mm, 13.8 mm, and 17.8 mm. The outcome of varying tube diameter, mass flux, and heat flux on mixed flow characteristics is studied. The strength of free convection is illustrated by the ratio of top to bottom local heat transfer coefficient. It is found to be maximum at the tube outlet by 50% and 80% for 8mm and 13.8mm tube diameter than the inlet. The laminar Nusselt number is 3 to 6 times the analytical value of Nu=4.36 under UHF condition. The Nusselt number increases with the increase in the tube diameter. The temperature distribution in the turbulent regime remains constant from the top to the bottom point. However, it significantly differs in laminar flow. A suitable correlation is suggested for the variation of the Nusselt number under the laminar regime showing the emphasis of free convection on forced convection.

Effects of pressure side film cooling hole placement and condition on surface heat transfer coefficients along a transonic turbine blade tip

Considered is thermal performance for the squealer blade tip of four film cooling configurations, B1, B2, B3 and B4, with hole exits for each arrangement positioned along a different portion of the upper pressure side of a transonic turbine blade. Each upper pressure side configuration includes five film cooling holes, such that each hole has a compound angle of 45° with respect to the circumferential/axial plane, also with an angle orientation of 40° relative to the plane tangent to the exit cross sectional area of each hole. Results are given for blowing ratios ranging from 0.42 to 3.20 in the form of spatially-resolved and spatially-averaged surface distributions of heat transfer coefficients and heat transfer coefficient ratios. In regard to tip surface variations, surface heat transfer coefficient ratios distributions are a consequence of the manner in which the film coolant collects in a substantial manner along the pressure side rim and then advects above and across the squealer recess with little to no coolant collecting within the cavity, or along the recess surface, to then collect in a substantial manner further downstream along the suction side rim. Such flow characteristics affect heat transfer coefficient ratio variations for all four film cooling configurations, but are especially influential for the B3 arrangement. Considering local heat transfer coefficient ratio distributions along the upper pressure side surface, the most significant local variations in the vicinity of a film cooling hole exit locations. Here, heat transfer coefficient ratio distributions for the B1 and the B4 configurations, in particular, show evidence of a horseshoe-shaped vortex which forms around each emerging coolant concentration. The two downstream legs of each vortex are associated with a pair of locally augmented heat transfer coefficient streaks, often with a streak of locally-lower coefficient ratios positioned between. Local and line-averaged heat transfer coefficient ratios along the upper pressure side also vary significantly with blowing ratio, with additional periodic variations as the normalized circumferential/axial coordinate varies. Within the resulting distributions, local heat transfer coefficient ratio increases are associated with locally augmented mixing and turbulent transport, which are especially present near the exits of different film cooling hole locations.

Experimental Analysis of Local Condensation Heat Transfer Characteristics of CF3I Inside a Plate Heat Exchanger

Due to its low global warming potential (GWP) and good environmental properties, CF3I can be a suitable component of refrigerant mixtures in the field of refrigeration and air conditioning. In this work, the local condensation heat transfer characteristics of CF3I were experimentally investigated in a plate heat exchanger (PHE). The condensation heat transfer experiments were carried out under conditions of vapor qualities from 1.0 to 0.0, at saturation temperatures of 25–30 °C, mass fluxes of 20–50 kg/m2s, and heat fluxes of 10.4–13.7 kW/m2. Local heat transfer coefficients were found to vary in both the horizontal and vertical directions of the plate heat exchanger showing similar trends in all mass fluxes. In addition, the characteristics of local heat flux and wall temperature distribution as a function of distance from the inlet to the outlet of the refrigerant channel were explored in detail. The comparison of the experimental data of CF3I with that of R1234yf in the same test facility showed that the heat transfer coefficients of CF3I were comparable to R1234yf at a low vapor quality and a mass flux of 20 kg/m2s. However, R1234yf exhibited a transfer coefficient about 1.5 times higher at all vapor qualities and a mass flux of 50 kg/m2s. The newly developed correlation predicts well the experimentally obtained data for both CF3I and R1234yf within ±30%.

Heat transfer deterioration and circumferential wall temperature inhomogeneity in a helically coiled tube carrying supercritical water: An intensive numerical simulation

Analysis of the flow and heat transfer characteristics of supercritical water (SCW) become complicated by the extensive changes in the physical properties of SCW near its pseudo-critical line and by the secondary flow stemming from the buoyancy and centrifugal force in a helically coiled tube (HCT). To address the heat transfer deterioration (HTD) of SCW in HCTs, we investigated the distribution of circumferential wall temperatures and heat transfer coefficients of SCW in a vertical HCT under the HTD condition via numerical simulation. Wall temperature was highest on the inner side, and the local heat transfer coefficient was the lowest. With increasing heat flux, the wall temperature of each circumferential position around the tube rose, while the inner wall temperature rose the most. To explain the mechanism of HTD, the rapid decrease of the specific heat and thermal conductivity near the inner side played a certain role in deteriorating the heat transfer. Further, the buoyancy effect, and the thermal acceleration effect could be used to quantitatively assess the HTD condition. The threshold values of the dimensionless number Bu describing buoyancy effect and the dimensionless number Ac describing thermal acceleration effect were found to be 3.0 × 10−6 and 1.28 × 10−6, respectively. The concept of circumferential wall temperature inhomogeneity (CWTI) was used to quantify differences in local wall temperature around the HCT. CWTI significantly increased with increasing heat flux. At low heat flux levels (qw = 300–700 kW m−2), the CWTI decreased at first, and then increases. When the heat transfer deteriorated with increasing heat flux, the trend of CWTI reversed. These results indicated that differences in circumferential wall temperature became larger under HTD conditions. Increasing pressure reduced the physical property changes in the HCT, leading to more uniform wall temperatures and a smaller CWTI. Under a constant ratio of heat flux to mass velocity, increasing the mass velocity weakens the heat transfer and even triggers HTD. In contrast, increasing pressure suppresses HTD.

Local heat transfer characteristics of circular multiple air jet impinging on a semicircular concave surface

ABSTRACT The local heat transfer characteristics of circular multiple air jet impingement on semicircular concave surface were studied experimentally. For constant Reynolds number (Re = 9,000), the effect of jet to concave surface spacing (z/d = 1, 4.2, 6), ratio of curvature (D/d = 4.28, 6, 8.6), jet-to-jet spacing (s/d = 2.4, 4, 5.6), and number of jets were considered. The local heat transfer characteristics were determined by using infrared thermal camera and thin foil method. Lower curvature value ratio (D/d = 4.28) resulted higher average heat transfer coefficient due to broader spread of heat transfer distribution, whereas higher curvature ratio (D/d = 8.6) resulted in lower average heat transfer coefficient due to steeper heat transfer distribution in the stagnation area. At lower D/d, z/d, and s/d with seven jet configuration, the heat transfer coefficients were found effective as compared to other configurations due to broad heat transfer distribution and less interaction between the jets. At given D/d and s/d configuration, the stagnation Nu at θ = 0° do not coincide with jet hole center axis and this shift is more pronounced at higher z/d value. This could be due to additional push before jet impinging on concave surface. The secondary peaks were observed between two neighboring stagnation regions in Nu distribution along the center longitudinal line for lower z/d and higher s/d values. This resulted due to upwash that was obtained from jet interactions related to collisions with the wall jets. The correlations of stagnation line average Nu and overall average Nu were obtained. The coefficient of variance of local heat transfer coefficient for each configuration was determined, and correlation was proposed to analyze the degree of non-uniformity.

Numerical investigation of bed-to-tube heat transfer in a shallow fluidized bed containing mixed-size particles

Mixed-size particles with low processing cost have great potential to act as the absorbing media in the next-generation concentrated solar power plants. However, the research on the heat transfer from the particles to heated surfaces in gas–solid fluidized beds is limited. In this paper, the bed-to-tube heat transfer coefficient (HTC) in a shallow fluidized bed with immersed tubes is determined numerically. The Eulerian–Eulerian approach that incorporated the kinetic theory of granular flow has been implemented in a two-dimensional model. The distribution of the local HTC around the tube is investigated for various particle systems. The results show that the HTC reaches a maximum at the upper right (45°) and upper left (135°) of the tube, respectively, indicating a strong relation between the local HTC and solid volume fraction (SVF). The average HTC increases as the mean particle size gets smaller. For monosized particles, the HTC increases from 925 W/(m2·K) to 3033 W/(m2·K) as the particle size decreases from 300 to 100 µm. For binary particles, the growth in the HTC is nonlinear, with an increase in growth rate being observed as the small-size component becomes dominant. For mixed-size particles with the same mean size, a higher HTC can be achieved by enlarging the size difference between the components. A modified correlation for predicting the bed-to-tube HTC is established. Besides, the impacts of gas velocity and temperature, and heat radiation on the bed-to-tube HTC are discussed. It is found that an optimal gas velocity exists to maximize the average HTC and SVF simultaneously, while the gas temperature has a minor contribution. Due to the small heat transfer temperature difference, the effect of thermal radiation on the HTC can be neglected even though the bed temperature reaches 800 °C.

Heat transfer and pressure drop performance improvement using curved circular spines for flow through circular pipe

The heat transfer augmentation method of inserting curved circular spines increases the dwelling time of the fluid within the system by inducing swirling motion within the fluid. It is a promising passive heat transfer augmentation technique for improving average and local heat transfer coefficients in the flow across uniform & non-uniform cross-sectioned channels at a high Reynolds number. The spines of circular cross-sections can considerably enhance flow passages employed for various purposes. The heat transfer performance study of tubes mounted with curved circular spines is presented for turbulent fluid flow conditions for Reynolds numbers ranging from 10,000 to 50,000. The curved spines are placed in the inline arrangement at the inner wall of the circular tube, disturb the flow, and break the dominant thermal resistance close to the wall, improving the heat transfer to the flowing fluid. The heat transfer enhancement at the cost of a rise in the pressure drop is also studied. The overall performance factor, R3, at the same pumping power, is presented to account for cost-effectiveness. The numerical results show that the enhancement ratio, Nue/Nuo, and friction factor ratio, fe/fo, using curved spines are 1.5 to 3.6, and 2.0 to 20.0, respectively, compared with the smooth tube at similar flow conditions. The Nusselt number ratio, Nue/Nup, at the same pumping power of the equivalent smooth tube, is 0.8 to 1.6.

Thermal performance investigation of metal foam heat exchanger for micro-gas turbine

This study presents the experimental monitoring of heat transfer performance of metal foams in transient state. Micro gas turbines require a compact recuperator with high effectiveness to achieve higher thermal efficiency. Porous media such as metal and ceramic foams are characterised by high surface-to-volume ratio. They are known to increase heat transfer and potentially can be incorporated in recuperators. Their structure is ideal for thermal management of compact and lightweight applications. The idea is to combine excellent thermal properties of metal foams with turbine gases heat fluxes exploitation, in order to elevate the temperature of a different working fluid such as water or compressed air before it enters the combustor. A novel facility was designed and developed for monitoring heat transfer mechanisms that occur in metal foams. A copper cylinder is filled with metal foam which is heated in transient state by a sudden switch from cold to hot water flow whereas a cold stream cools the device in a crossflow configuration. The study demonstrates a method based on computerisation of true-colour analysis of digital images for surface temperature visualisation using thermochromic liquid crystals (TLC). Results of temperature as well as local and mean heat transfer coefficient were obtained showing that the hot flow inside the foam was more dominant in heat transfer than the cold flow in the empty channel. The method is promising for the evaluation of transient phenomena in a tube that is filled with porous media.

Boundary element method for contactless estimation of spatially varying internal heat transfer coefficient in circular pipes

In the present study it is proposed a solution approach of the Inverse Heat Conduction Problem (IHCP) intended at assessing the local heat transfer coefficient on the inner wall of a tube, under a forced convection problem. The estimation method is established on the Boundary Element Method (BEM) combined with the Truncated Singular Value Decomposition (TSVD) methodology, employed to manage the ill-conditioned nature of the problem. The numerical results of the direct problem, built by the BEM, are firstly validated, and consequently adopted as synthetic data inputs to resolve the IHCP and corroborate the whole assessment procedure. This approach is also tested with experimental data about forced convection problem in coiled pipes. In these geometries, the convective heat transfer coefficient changes considerably along the wall periphery and for this reason, it constitutes a perfect example to test the ability of the presented method to infer a spatially varying internal heat transfer coefficient distribution.

Computationally efficient methodology of 3D thermal-hydraulic analysis of Diagnostic Shielding Module #2 of ITER Equatorial Port #11

The process of design justification of Diagnostic Shielding Modules (DSMs) of port plugs of the International Thermonuclear Experimental Reactor (ITER) includes a stage of thermal-hydraulic computational analysis. The ITER tokamak operates in a pulsation mode that means the nuclear heating affecting DSMs is unsteady, and transient analysis is required. Three-dimensional (3D) approaches for fully coupled thermal-hydraulic analysis, which imply simultaneous computations for fluid and solid parts of a 3D DSM model, lead typically to “heavy” numerical models being very expensive from the computational point of view, especially for transient simulations. In order to significantly reduce the consumption of computational resources, the present 3D thermal-hydraulic analysis of DSM #2 of ITER Equatorial Port #11 was performed using one-way coupling. Firstly, steady-state CFD computations of turbulent flow were performed for the front part of DSM cooling system, which is a high-density network of channels of complex geometry. Obtained in CFD analysis map of wall shear stress on surface of channels was then converted into a map of local heat transfer coefficient using a simple and conservative approach based on known empirical correlations for turbulent flow in a circular pipe. For the back part of DSM cooling system, which basically consist of many relatively long channels, an individual (single) value of heat transfer coefficient for each of the channels was directly evaluated using empirical correlation. The heat transfer coefficient maps obtained for both parts of DSM cooling system were used finally as a boundary condition in transient thermal analysis of the solid part of the DSM model. Details and justifications of the described computationally-efficient methodology are presented.

Effect of jet plate thickness on the local heat transfer coefficient with multiple air jet impingement

For designing a multiple jet impingement cooling system, the thickness of jet plate (a passage through which jet comes out) is one of the important parameters. Considering the thermal point of view, the thickness of the plate should be chosen so that it would enhance the heat transfer rate. In this study, the effect of jet plate thickness on the local heat transfer coefficient on a flat plate with multiple impinging air jets is investigated. The thickness ratios (t/d) of 0.5, 1.0 and 2.67 are studied. Reynolds number is varied from 5000 to 20,000 and jet-to-plate distance (z/d) is varied from 1 to 5. Jet diameter (d) is chosen to be 6 mm. The jet-to-jet distance (p/d) is kept constant at 3.Steady-state thin metal foil technique, along with infrared thermography, is used to obtain the temperature distribution and thereby the heat transfer coefficient. Coefficient of discharge for each jet plate, central line velocity decay and pressure distribution on the target surface are measured. These measurements provided new insights to better understand the heat transfer results in this study. For lower jet-to-plate distances (t/d = 0.5 to 1), heat transfer decreases with the increase in the jet plate thickness ratio. However, heat transfer is not affected with the further increase in the jet plate thickness ratio i.e., t/d = 1 to 2.67. Therefore, smaller jet plate thickness ratio is suitable to obtained high heat transfer rate. This study presents a new correlation for the local Nusselt number distribution or different jet plate thickness.

Detailed Thermal Evaluation of Brazed Plate Heat Exchanger Using Infrared Thermography

AbstractInfrared thermography of brazed plate heat exchangers for evaporators and condensers recently was used to quantify maldistribution. With the knowledge of the secondary fluids heat transfer coefficient and a given secondary fluids distribution, the local heat transfer coefficient of the primary fluid (refrigerant) and its distribution to the channels can be calculated. A sensitivity analysis shows ± 10 % difference of the surface temperature to the wall center temperature at the expected ratios of heat transfer coefficients. The method is presented in this paper using an exemplary infrared picture.