Plate Heat Transfer Research Articles

Semi-infinite solid heat transfer limitation

One-dimensional semi-infinite heat transfer solution is a common solution for transient heat transfer experiments. This solution is valid for a short certain amount of time before the semi-infinite solid became invalid. Crank Nicolson solution has been chosen to address this issue. This paper reports the time limitation for semi-infinite solid solution and justify the usability of Crank Nicolson solution given the same boundary conditions. The flat plate heat transfer experiment has been conducted. With the same boundary conditions, at Fourier number 0.1, the resultant heat transfer coefficient and adiabatic wall temperature have shown a good agreement between the semi-infinite solid solution and the Crank Nicolson solution. Beyond this Fourier number, both solutions have given inaccurate results. The inaccurate results are due to unsuitable boundary conditions. Future work will involve modification of the back face boundary conditions to address the time limitation of the one-dimensional semi-infinite solid heat transfer solution.

Synthesis of Cu-Al LDH nanofluid and its application in spray cooling heat transfer of a hot steel plate

In the current study, authors have synthesized Cu-Al Layered Double Hydroxide nanofluid at different molar ratios of Cu and Al by using co-precipitation technique and utilized this as a coolant in a pressure atomized spray to achieve high cooling rates in the temperature range of 900–600 °C for a 6 mm thick steel plate. The study initially focuses on the effect of Cu: Al molar ratio variation on thermal conductivity, stability as well as its heat transfer potential in steel quenching. Post thermal conductivity and stability analysis, spray cooling experiments were conducted in two parts. The first part involves optimization of Cu: Al molar ratio by varying the ratio (Cu: Al = 2:1, 4:1 and 6:1) at a fixed nanofluid concentration (120 ppm) to select the best Cu: Al molar ratio based on heat transfer results. The results show that the highest cooling rate and average heat flux were achieved at a Cu and Al molar ratio of 4:1 among all molar ratio combinations. Once, the optimized molar ratio is selected, the second part of the spray cooling experiments was performed to study the effect of nanofluid concentration variation (40–240 ppm, at an optimized molar ratio of Cu: Al = 4:1) on spray cooling results. With respect to concentration optimization, the maximum cooling rate of 168.6 °C/s was attained at a concentration of 160 ppm which is 26% higher than what was achieved by normal water spray. Results obtained from the spray cooling experiments were further verified by the thermal conductivity analysis where highest enhancement of 15.17% was also observed at 160 ppm nanofluid concentration.

On Problem of Mathematical Modelling of Thermo-Physical Processes in Regenerative Water-Evaporating Coolers

For cooling the air environment of industrial premises water-evaporating air, conditioners are being increasingly applied. The simplicity of their construction, ecological safety and low power consumption distinguish them from the coolers of other types. Cooling the processed air is due to the loss of energy for the evaporation of moisture from the surface of the water-wetted plates that form air channels. As a result of this process, cooled air is often saturated with moisture, which limits the possibilities for the operation of the coolers of this type. In these cases, more complex coolers of indirect principle without such drawback should be applied. The most effective modification of indirect cooling is the installation of recuperative principle units. The paper presents a mathematical model of heat-mass transfer in such water-evaporating coolers. The scheme of realization of this model based on an iterative algorithm of solution of the system of finite–difference linear equations that takes into account longitudinal and transverse thermal conductivity of the heat transfer plates is suggested. The possibility of obtaining the optimal values of the redistribution of the main and auxiliary air flows through the substantiation of the aerodynamic resistance of the output grid is proved. This allows refusing the inclusion in the additional system cooling fan unit for discharging an auxiliary stream of air.

Experimental study of the external forced convection heat transfer of flat plate

Experimental study of the external forced convection heat transfer of flat plate

The flow boiling heat transfer coefficient determination in a minichannel used the FEM combined with Trefftz functions

The method of solving the inverse heat conduction problem, by means of the FEM with Trefftz-type basis functions, during flow boiling in a minichannel was shown. This basis functions were constructed with using the Hermite interpolation and Trefftz functions. The aim of the numerical calculations was to determine the local heat transfer coefficient on the basis of experimental data in a horizontally oriented minichannel. The refrigerant flowing along the minichannel (HFE-649 or HFE-7100) was heated by a thin enhanced plate by vibration-assisted laser texturing. The temperature on an outer smooth side of the plate was detected by means of infrared thermography. On the heated wall–fluid contact surface in the minichannel the heat transfer coefficient was obtained from the Robin boundary condition. It was assumed that the temperature distribution in the heated plate was described by the Poisson equation. The unknown values of temperature and temperature derivatives at nodes were computed by minimizing the functional which describes the mean square error of the approximate solution on the boundary and along common edges of neighbouring elements. The results were presented as the heated plate temperature and heat transfer coefficient versus the minichannel length.

Numerical simulation of thermal property effect of heat transfer plate on bubble growth with microlayer evaporation during nucleate pool boiling

It is well known that during nucleate boiling, a large amount of energy can be transferred under relatively small temperature difference between the heat transfer surface and fluid, indicating that high efficiency of heat transfer can be achieved. However, the mechanism of nucleate boiling is still not well elucidated owing to the complexity of the phenomenon. The thermal properties of heat transfer plate, which is directly in contact with the microlayer, may have a significant impact on heat transfer and evaporation characteristics of the microlayer. A volume of fluid (VOF) method based algorithm, in which the experimentally measured microlayer structure was taken into account, has been developed to simulate microlayer evaporation and single bubble behavior. The influence of thermal conductivity of heat transfer plates on the contribution of microlayer evaporation was examined. It was concluded that more efficient heat supply to the heat transfer surface can be achieved for the heat transfer plate with higher thermal conductivity. Microlayer evaporation occupied approximately 30–70% of the bubble volume, indicating that microlayer evaporation is a principal mechanism of boiling heat transfer.

Prediction of fouling tendency in PHE by data of on-site monitoring. Case study at sugar factory

The fouling deposition on heat transfer surfaces can have significant detrimental effect on heat recuperation and jeopardise the efficiency of energy usage, increasing fossil fuels consumption and harmful environmental effects. The data of plate heat exchanger (PHE) thermal performance monitoring in fouling conditions are presented. PHE is installed at sugar factory for preheating purified thin juice before evaporation. The character of deposits on plate heat transfer surface is examined by opening PHE after the tests. It reviled the scaling and particulate fouling mechanism. Mathematical model for prediction of fouling deposition development in time is proposed, which accounts for shear stress at the channel walls and surface temperature. The model parameters are determined according to industrial tests data. The ways of fouling mitigation in PHE are discussed using the model predictions. It is shown that fouling mitigation in PHE is possible by increasing wall shear stress at the same pressure drop in heat exchanger. It requires to eliminate additional pressure loss in connections and to optimize the number of plates and their arrangement adding some plates with higher corrugation angle. These recommendations are discussed and some are implemented at the factory conditions. That allowed increase the operation time between stops for PHE cleaning maintenance. The proposed model can be directly used for design and maintenance scheduling at the specific factory. It can also be used asa preliminary guidance for energy saving reconstructions in other sugar factories. But the direct model application requires data of fouling formation monitoring to identify its parameters for work with specific media streams prone to fouling.

On-demand operation of a compact solar water heater based on U-pipe evacuated tube solar collector combined with phase change material

Abstract Space and weight requirements coupled with time delay between energy production and consumption represent great barriers toward further deployment of typical solar water heating systems in existing buildings with limited space. Therefore, a new compact U-pipe evacuated tube solar collector (ETC) integrated with paraffin wax (ALEX WAX 600) for energy storage is presented in the current study. The ALEX WAX 600 is an organic chemical-based phase change material (PCM) having an average melting temperature of 60 °C and a thermal conductivity of 0.21 W/m K. The key issue of the developed system is the elimination of entire systems components by storing the energy in the evacuated tube itself through the usage of paraffin wax. Due to the low thermal conductivity of paraffin wax, heat transfer plate (fin) with an area of 0.1251 m2 is integrated in the proposed system. The present study investigates the developed system under two configurations; un-finned and finned U-pipe evacuated tube solar collector side by side with a typical forced recirculation solar water heating system (FSWHS) under the same operation and weather conditions. The operation of the solar water heating systems is studied during the on-demand operation under a simultaneous operation and a real water consumption profile. The results clarify the favorable performance of the developed compact solar water over the typical FSWHS during different operation scenarios and weather conditions due to their low thermal inertia. Furthermore, the utilization of fin in the developed system has a substantial effect on improving the heat transfer characteristics of the PCM and enhances the overall system stability. During simultaneous operation tests, the total effective energy discharged for the un-finned system is higher than FSWHS by 35.8% under clear day weather conditions. However, the finned system is higher than FSWHS by 47.7%. The simultaneous long-term predictions based on regression modeling show that the average annual efficiency is 71.8%, 85.7% and 40.5% for the un-finned, finned and FSWHS systems, respectively. During real water consumption profile tests, the daily system efficiency is, 33%, 26% and 20% for the un-finned, finned and FSWHS systems.

On the coupled condensation-evaporation in pillow-plate condensers: Investigation of cooling medium evaporation

Pillow-plate heat exchangers (PPHE) represent a promising alternative to conventional equipment, e.g., in the process industries; however, the lack of published design methods still hinders their widespread application. The present work represents a first step towards investigation of a particular PPHE operation mode, which comprises process medium condensation between adjacent pillow plates and simultaneous cooling medium evaporation in the plates. An experimental set-up was built and used for heattransfer experiments, in which 1,1,1,2-tetrafluoroethane evaporated in both thermosyphon and forced-convection operation mode. The focus was on the investigation of heat transfer during the evaporation process in the wavy pillow-plate channel, and the (virtual) enthalpy of condensation was imitated using dissipation of electrical current in the walls of a single pillow plate. Along these lines, two-phase heat transfer coefficients for the evaporating fluid flow in the inner channels of the plates were determined. The results reveal a promising heat transfer performance, which can be utilised to increase energy efficiency in the process industries. A correlation proposed by Kandlikar for saturated two-phase flow boiling heat transfer inside tubes was found suitable for the prediction of heat transfer in pillow plates, with slight underestimation. The results of this study can further be applied for the description of a number of heating and cooling processes.

Development of a numerical analysis model using a flow network for a plate heat exchanger with consideration of the flow distribution

A numerical analysis model using a flow network approach is developed to evaluate the performance of a plate heat exchanger (PHE). In order to consider complex flows in PHEs in the model, the flow paths in the channels are represented by a flow network consisting of nodes and branches. This model is able to evaluate the node-average local properties of the working fluids of each channel in a PHE. Several empirical correlations for the pressure drop and the heat transfer are evaluated against various experimental data to implement the selected correlations into the numerical analysis model according to the flow conditions and geometry of the heat transfer plates used. The pressure drop and heat transfer capacity of a PHE were experimentally measured with a range of operating parameters and the measured values were then compared with the prediction by the numerical analysis model. The predictions of the heat transfer capacity are in good agreement with the experimental data within a discrepancy of 10%, whereas the prediction of the pressure drop significantly deviated from the experimental data. The analysis also demonstrates that the total heat transfer rate varies little whereas the pressure drop increases sharply as the maldistribution of the flow is intensified.

Surface heat transfer study of ultra heavy plate during quenching process of jet array impingement

Abstract Heat treatment is a key technology to improve the performance of ultra heavy plates with large fractured surface. Roller-type jet quenching test facility and multi-channel temperature tracking recorder dedicated for ultra heavy plate are developed in present work to measure the temperature drop curves of the plate with a thickness of 84 mm during quenching process when jet velocity, Re and water flow density are 3.39–26.8 m/s, 12,808–117,340 and 978.7–6751.5 L/(m 2 min), respectively. Effect of multi-beam round hole jet array on heat transfer of ultra heavy plate are analyzed. The results indicate that parameters such as jet velocity, water density affect the heat transfer mechanism of jet stagnation zone and parallel flow zone of plate surface, which further exerts influence on the maximum heat flux of different positions away from stagnation points. Mixed heat transfer and “heat flux shoulder” phenomena can be observed in surface parallel flow zone when jet velocity is relatively lower (3.39 m/s); film boiling heat transfer mechanism disappears with increasing jet velocity (11.16 → 26.8 m/s) and maximum heat flux moves towards superheat positions at lower surface. Relevant study would be beneficial for the temperature field computation and regulation of texture performance of ultra heavy plate during quenching process.

Structure and Lean Extinction of Premixed Flames Stabilized on Conductive Perforated Plates

The structure and lean extinction of premixed liquefied petroleum gas–air flames seated on conductive perforated plates were examined experimentally, with focus on the effects of plate material, thickness, and hole diameter. The lean extinction limit was determined by gradually reducing the fuel-flow rate for a given air-flow rate, until extinction occurred. Flame structure was quantified by mapping the local mean temperature and species concentrations and by imaging the average visual length of the flame plume. Pyrometer measurements of the temperature of the upper plate surface were made to estimate the heat transfer through the plate. It was found that the flames stabilized on plates with higher thermal conductivity were shorter and more stable (i.e., have lower lean extinction limits). This was attributed to preheating of fresh reactant mixture by greater heat transfer through the plate. Increasing the hole diameter (percentage open area) was found to enhance flame stability by reducing the reactant jet velocity for a given flow rate of reactant mixture. Heat transfer through the plate deteriorated with increasing hole size. However, the positive effect of smaller jet velocity on flame stability overpowered the negative effect of reduced heat transfer, and the net result was enhanced stability with larger hole sizes. Plate thickness, on the other hand, was found to have a weak effect on flame stability and structure. Thicker plates showed slightly better stability characteristics because of greater heat transfer through them. Nonetheless, plate heat transfer did not affect flame stability as significantly as jet velocity did.

Influence of filling ratio and working fluid thermal properties on starting up and heat transferring performance of closed loop plate oscillating heat pipe with parallel channels

Using ethanol or acetone as the working fluid, the performance of starting up and heat transfer of closed-loop plate oscillating heat pipe with parallel channels (POHP-PC) were experimentally investigated by varying filling ratio, inclination, working fluids and heating power. The performance of the tested pulsating heat pipe was mainly evaluated by thermal resistance and wall temperature. Heating copper block and cold water bath were adopted in the experimental investigations. It was found that oscillating heat pipe with filling ratio of 50% started up earlier than that with 70% when heating input was 159.4 W, however, it has similar starting up performance with filling ratio of 50% as compared to 70% on the condition of heat input of 205.4 W. And heat pipe with filling ratio of 10% could not start up but directly transit to dry burning. A reasonable filling ratio range of 35%‒70% was needed in order to achieve better performance, and there are different optimal filling ratios with different heating inputs - the more heating input, the higher optimal filling ratio, and vice versa. However, the dry burning appeared easily with low filling ratio, especially at very low filling ratio, such as 10%. And higher filling ratio, such as 70%, resulted in higher heat transfer ( dry burning ) limit. With filling ratio of 70% and inclination of 75°, oscillating heat pipe with acetone started up with heating input of just 24W, but for ethanol, it needed to be achieved 68 W, Furthermore, the start time with acetone was similar as compared to that with ethanol. For steady operating state, the heating input with acetone was about 80 W, but it transited to dry burning state when heating input was greater than 160 W. However, for ethanol, the heating input was in vicinity of 160 W. Furthermore, thermal resistance with acetone was lower than that with ethanol at the same heating input of 120 W.

Influence of Prandtl number on heat transfer of a flat vertical plate

Liquid metals, such as sodium (Na), lead (Pb), and lead-bismuth (Pb-Bi) eutectic (e), are considered as potential coolants for the fast spectrum nuclear reactors of the next generation. So the main objective of this paper is to study the heat transfer and fluid flow characteristics of liquid metal coolants flowing over a nuclear fuel element having uniform volumetric energy generation. Stream function vorticity formulation method was used to solve the full Navier Stokes equations governing the flow. The energy equation was solved using central finite difference method. For the two-dimensional steady state heat conduction and stream-function equation, the discretisation was done in the form suitable to solve using 'line-by-line Gauss-Seidel' solution technique whereas the discretisation of vorticity transport and energy equations was done using Alternating Direction Implicit (ADI) scheme. After discretisation the systems of algebraic equations were solved using 'Thomas algorithm'. The complete work was done by writing a well-validated indigenous computer code using C-language. The parameters considered for the study were: aspect ratio of fuel element, Ar, conduction-convection parameter Ncc, total energy generation parameter Qt, and flow Reynolds number ReH. The results obtained can be used to minimise the maximum temperature in the fuel element (hot spots) and prevent its melting.

Application of the method of weighted residuals for determining the distribution of temperatures and radiation creep strains in plates

The paper is devoted to the description of the Weighted Residuals Method in Galerkin form for solution of the non-stationary heat transfer and irradiation creep problems in rectangular plates. The basic methods and dependencies were used for the solution of these problems are considered. The non-stationary heat problem is derived to sequential decisions of the systems of linear algebraic equations for the coefficients in expansions of temperature function in series on the basis functions for the different time moments. The problem of rectangular plate’s bending with specified temperature drops in its sides is preliminary solved in order to obtain the solution of irradiation creep problem. The stress tensor components were found in the plate’s points, are used in associated flow rule for the obtaining the components of creep irradiation strain tensor. The non-stationary heat transfer problem in quadratic area with boundary conditions of Newton and Diriclet types is considered as well as the calculated temperature distributions on co-ordinates in plane and time are presented. The irradiation creep of rectangular plate made from high resistant steel 15Х1М1Ф is considered. Obtained distributions of irradiation creep strains for three regarded values of temperature drops allow us to evaluate the plate deformation and service ability at different time moments.

Influence of Prandtl number on heat transfer of a flat vertical plate

Influence of Prandtl number on heat transfer of a flat vertical plate

Modelling of conjugate heat transfer in barium titanate plates heated by the air flow

We present the results of simulation of conjugate heat transfer between the grid of barium titanate plates and the hot air flow. The air temperature undergoes rapid change and the thermal front propagation and heat exchange with the solid plates have been studied for several plate configurations. The results show that the air heat could be effectively absorbed by the plates during the time of thermal front propagation, making such configuration attractive for pyroelectric energy harvesting applications.

Experimental Research on the Heat and Mass Transfer Characteristics of Corrugated Plate Spray Humidification Air Coolers

This paper studies the heat and mass transfer characteristics of corrugated plate spray humidification air coolers as a new air cooling technology under wet working conditions. In terms of the air cooling effect, the spray cooling characteristics comparisons of the same nozzle under different layouts are made. The TF6 nozzle spray with a layout of 500 mmx500 mm is adopted as the optimal working condition for the heat and mass transfer characteristics. The experimental data under wet working conditions are fit on the basis of the corrugated plate heat exchanger resistance and heat transfer characteristics under dry working conditions. The results show that the spray increases the LMTD of the corrugated plate heat exchanger and significantly increases the air side heat transfer coefficient without jamming the air side runner or increasing the air resistance.

SOME FEATURES OF OPERATION AND THERMAL-HYDRAULIC TESTS OF PLATE HEAT EXCHANGERS

At present, plate heat exchangers (PHE) are used everywhere, starting from the housing and utilities sector to nuclear power. However, there are no standard methods for heat and hydraulic calculations for plate heat exchangers. That is why the manufacturer uses special software to select heat exchangers for a particular task. And often even engineers have no access to the code and algorithms of these programs. Thus, correctness of such calculations is questionable, especially for the unusual operating modes of heat exchangers. To solve these issues, it is necessary to carry out thermal-hydraulic tests of plate heat exchangers from diff erent companies, with subsequent comparative analysis and identifi cation of possible diffi culties in thermal-hydraulic calculations. In the course of this work, we proposed a test procedure for plate heat exchangers with the same fl ow rate along the circuits, simplifying the subsequent processing of the experimental data. This method is applicable for PHEs with an equal number of channels on their hot and cold sides. Using this method, 13 plate heat exchangers were tested at the KS10606 Complex test facility of JSC “NPO CKTI”. The results of experiments and analysis of the data provided by the PHE manufacturers showed no signifi cant diff erence in the thermal-hydraulic characteristics of plates of the same size of diff erent manufacturers. Presence of breathing eff ect in PHEs was confi rmed. Breathing eff ect is caused by elastic deformation of heat transfer plates in the presence of pressure diff erence between hot and cold sides of PHE. It is shown that this eff ect can signifi cantly aff ect the hydraulic resistance. The maximum observed diff erence between the hydraulic resistance coeffi cients in circuits with a lower and higher pressure was about 3.5 times. However, this eff ect is not typical of all plate heat exchangers.

Numerical study of mixed convection heat transfer of various fin arrangements in a horizontal channel

The mixed convection of a three-dimensional square duct with various arrangements of fins in both laminar and turbulent flow is numerically characterized and studied. This study focuses on the ability of fin arrangements to enhance a heat transfer while flow is incompressible and the fluid is air. In our models, the lower duct wall is defined with a constant heat flux condition while the two side walls and upper wall are insulated. The finite volume method with the SIMPLE (Semi Implicit Method for Pressure Linked Equations) algorithm is used for handling the pressure–velocity coupling. The numerical results are validated with experimental data and show good agreement. The computations confirm that fin arrangement significantly changes the temperature distribution and cooling performance of the fins. This study focuses on the new arrangements of the fins that are not presented in previous studies. These arrangements have 3 Models with two angles (30 and 45°). According to the results, heat transfer highly improves (approximately 40–50% in the laminar flow stream and 15–20% in turbulent flow in comparison to base plate heat transfer) as the simple fin arrangement is replaced by inclined fins. Moreover, the influence of limited heat flux on temperature distribution is extensively investigated. It is notable that the temperature of fins significantly reduces as the best arrangement of the fins is presented in the air flow stream. Therefore, an enhanced cooling zone occurs when the fin arrangement is adjusted according to the location of the source of the heat flux on the base plate.