Thermophysical Parameters of a Semi-Finished Watermelon Product as an Object of Dehumidification

Introduction. Pectin-based protective coatings can produce a perfect biodegradable edible film. Secondary watermelon raw materials are a promising resource for this type of food coating as it contains 13.4% of pectin components, of which 8.1% is protopectin. The present research objective was to find the density and thermophysical characteristics of the pectin extract in order to optimize the drying process. Study objects and methods. The research featured a pectin extract from watermelon rind. Its thermophysical properties were defined according to the thermocouple inertia method. The calorimetric method was used to change the aggregation state, while the pycnometric method was applied to calculate the density. The method of criterion equations helped to define the heat transfer coefficient. Results and discussion. The average density of the final film material was 652 kg/m3 and that of the liquid semi-finished product was 1,028 kg/m3. The research also revealed the dependence of physical density and humidity W, heat capacity, thermal diffusivity, and thermal conductivity. For different W, averaged were 3393, 3225, 3137, and 3113, respectively. The study also provided the criterion dependence for determining the heat transfer coefficient and modified α on the speed of the air coolant for artificial convection at conventional coolant temperature (≈ 100°C) in contact with the food product surface (≈ 80°C). Conclusion. The article introduces the thermophysical characteristics and physical density of watermelon gel for various humidity and thermal agent parameters, as well as a modified criterion dependence for determining the heat transfer coefficient. The research results can be used to design dehydration operations, other thermophysical processes, and their equipment.

Thermal studies of vacuum panels of cellular structure of a passenger car

Aluminum alloys and composite materials are used in the body structures of modern passenger railway cars, which required the use of new manufacturing technologies: extrusion, pultrusion, etc. The use of new materials and new production technologies is changing the design requirements of passenger rail cars. The use of computer-aided design systems, in particular, SolidWorks Simulation, allows you to optimize the profile of cellular panels used in the construction of the body of a passenger railway car and obtained by extrusion or 3-D printing. Purpose of this work is to optimize the design stage of the enclosing structures of the body of a passenger railway car made of cellular profile panels, which can significantly reduce the heat transfer coefficient of the body walls and their mass, as well as provide the necessary strength conditions. Optimal profile of the vacuum panel, consisting of two rows of hexagonal cells, provides, according to calculations, the value of the specific thermal resistance R = 2.922 (m2 K)/W, which is 16.5% more than that of the existing body structure of a passenger rail car.

Determination of the heat transfer coefficient of a rotary film evaporator with a heating film-forming element

A model of a rotary film evaporator with a film-forming element with a reflective heated surface has been developed. This will allow stabilizing the hydraulic movement of the cut wave flow due to the reflective surface of the geometric shape for the forced direction of the cut raw material to the heating surface. Autonomous heating of the reflective surface additionally provides a temperature effect in the conditions of movement of particles of raw materials after cutting. The analysis of the experimental and theoretical parameters of heat transfer made it possible to substantiate the criterion equation for determining the heat transfer coefficient of an evaporator with the proposed film-forming element and a reflective heated surface for calculating the coefficient from the working surface to the raw material. The resulting equation takes into account the influence of the vertical component of the motion of the raw material film, centrifugal movement during the rotation of the film-forming element, mixing of the boiling film of the raw material with steam bubbles, and the geometric characteristics of the film-forming blade on the hydrodynamic flow of the raw material. The calculation of the rotary-film evaporator was carried out using the criterion equation and the obtained useful heat exchange surface – 0.75 m2. The specific metal consumption in a rotary film evaporator with a film-forming element having a reflective surface is 57 kg/m2, compared to the vacuum evaporator traditionally used in canning industries (410 kg/m2), which is 7.1 times less. The duration of the temperature effect on the raw material is also reduced: a rotary film evaporator – 200 s and 3600 s in a traditional apparatus. The data obtained will be useful for the design of rotary-film devices of different geometric parameters using articulated blades with a reflective plate.

AERODYNAMICS AND HEAT EXCHANGE OF SINGLE END TUBE DURING EXTERNAL FLOW

In Ukraine, the safety of modern thermal power plants depends on the reliable operation of the equipment installed on them. Unfortunately, the technical condition of the chimneys is not properly maintained. Of course, the modernization of basic equipment (boilers, switching to another type of fuel) leads to a decrease in the temperature of the exhaust gases. An important aspect to maintain the condition of the chimneys is to maintain the moisture of the exhaust gases. An important feature of the external flow of chimneys are large Reynolds numbers Re = wd/n, which reach 106 and more. In the thermal calculation only the average heat transfer coefficient on the outer surface of the pipe is usually determined, and the features of aerodynamics and local heat transfer due to the conicity of the pipe are not taken into account. The work is devoted to the study of aerodynamics and heat transfer in the air flow of a single conical chimney. The method of computer modeling with numerical integration of equations of motion and energy was used in the research. At the first stage, the single pipe with the uniform flow profile is considered. Further, the influence of the surrounding infrastructure on the aerodynamics and heat transfer of a single conical tube is studied. The single conical vertical pipe with 40 m height, 1.7 m diameter at the base and 0.85 m in the mouth was used for the calculation. The computer model was calculated in the ANSYS2020-R1 program. The model is developed in a homogeneous area with the air environment. In order to obtain reliable results, the study was conducted to obtain the optimal set of the grid parameters for the heat transfer conditions. The grids with parameters that affect the distance of the first node from the cylinder wall (options a, b, c, d) and the rate of increase in the size of the elements as they move away from the area of interest (Growth rate GR) were studied. The type of the cylindrical pipe with constant diameter of 1.7 m has been chosen to analyze the sensitivity and to check the grid. The turbulence model has been choosen as the following: RNG k-ε model which is common for the tasks of this class, the Enhanced Wall Function, the solution algorithm for the connection of the velocity pressure in stable flows Simplex. It is determined that in case if the distance between the first node from the cylinder wall and the area of interest (Growth rate GR) is more than 8 mm, instability and deviation of the obtained data from the values of the average coefficient of more than 20% appears. As a result of the research, the parameter grid area matching to the “2d” option of table 1 has been selected, i.e.: GR = 1.1, h = 8 mm. In the study of aerodynamics and heat transfer, the conical tube is conventionally divided into 22 sections (with 1 m height each). The case of uniform flow velocity in front of the pipe has been considered. As seen, the maximum value of the heat transfer coefficient is in the Zone(21-22). The research shows that oncoming flow velocity of 25 m/s causes the average value of heat transfer coefficient of the conical pipe 62.5 W/m2K, and 61.1 W/m2K according to the known formula . This indicates a small effect of taper on the average heat transfer of the entire pipe. In the calculations, three types of surrounding areas are considered: A - open coasts of seas, lakes and reservoirs, rural areas, including buildings less than 10 m high; B - urban areas, forests and other areas, evenly covered with obstacles higher than 10 m; C - urban areas with dense buildings with buildings higher than 25 m. Thus, the wind speed profiles for different types of terrain are nonlinear. The wind speed profile in front of the pipe (type of terrain) has a significant effect on the heat transfer coefficient. This confirms the need to take into account the type of terrain and the velocity profile in front of the pipe for local heat transfer.

ANALISIS KINERJA CONDENSER SHELL AND TUBE UNIT 2 DI PT. PLN (PERSERO) SEKTOR ASAM-ASAM KALIMANTAN SELATAN

Theecondenser is a type of heat exchanger that functions to condense fluid. On steam powermsystems. Thevmain function ofmthe condenser is to convert steam into liquid. The purpose of this study is to determine the value and influence of heat balance, heat transfer coefficient, pressure drop and condenser efficiency.Thewresults offthissstudy indicate that in 2018 thee average heat balance (Q) was obtained at 356,017,533.46 Kj / hour while in 2019 the results of the average heat balance (Q) were 640,293,647,066 Kj / hour, fouling factor was not affect the balance sheet. The average gross heat transfer coefficient (UD) in 2018 amounted to 204,274.25 Kj / hour.m2. C and the average net heat transfer coefficient (UC) was 206,378 Kj / hr.m2. ° C whereas in 2019 the average heat transfer coefficient is obtained by the average gross heat transfer coefficient (UD) of 366,544.07 Kj / jam.m2. ° C and the Clean heat transfer coefficient (UC) is 448,554 Kj / h.m2. ° C.Fouling factor is very influential onnthe heatwtransfer coefficient because the greater the fouling in the tube will result in the inhibition of theeheat transfer rate in the tube, so that the heat transfer coefficient decreases. The pressure drop in 2018 is still within the permissible limits, with an average of 504.28 bars and 2019 of 513.03 bars. The effectiveness of the condenser in 2018 is an average of 23.330 after maintenance has been obtained, the average effectiveness of the condenser in 2019 is 40.743

Influence of the heat transfer coefficient on the level of residual stress after heat treatment of the VVER-1000 reactor baffle

Background. Improvement of the methodology for the computational analysis of residual stresses in the structural elements of the reactor is an integral part of the work when extending the service life of NPP power units. Objective. Determine the value of residual technological stress arising in the baffle of a VVER-1000 reactor during welding and postweld heat treatment according to the austenitizing mode. To evaluate the effect of considering the dependence of the heat transfer coefficient on the temperature of the baffle surface at cooling in air during heat treatment. Methods. Numerical modeling of the stress-strain state of the baffle during welding and postweld heat treatment was carried out using the finite element method. Results. It was determined that in the process of heat treatment according to the austenitizing mode, the residual welding stress in the baffle are almost completely relaxed. Due to the high temperature gradient during rapid cooling in air after heating in the process of austenitization, new rather high residual stresses are formed in the zones of the baffle with the greatest metal thickness. Conclusions. Based on the results of the investigation, a high level of residual technological stress was determined, which should be considered when calculating the justification for extending the service life of the VVER-1000 reactor baffle.

Nanoparticle aggregation kinematics on the quadratic convective magnetohydrodynamic flow of nanomaterial past an inclined flat plate with sensitivity analysis

The study focuses on the aggregation kinematics in the quadratic convective magneto-hydrodynamics of ethylene glycol-titania ([Formula: see text]) nanofluid flowing through an inclined flat plate. The modified Krieger-Dougherty and Maxwell-Bruggeman models are used for the effective viscosity and thermal conductivity to account for the aggregation aspect. The effects of an exponential space-dependent heat source and thermal radiation are incorporated. The impact of pertinent parameters on the heat transfer coefficient is explored by using the Response Surface Methodology and Sensitivity Analysis. The effects of several parameters on the skin friction and heat transfer coefficient at the plate are displayed via surface graphs. The velocity and thermal profiles are compared for two physical scenarios: flow over a vertical plate and flow over an inclined plate. The nonlinear problem is solved using the Runge–Kutta-based shooting technique. It was found that the velocity profile significantly decreased as the inclination of the plate increased on the other hand the temperature profile improved. The heat transfer coefficient decreased due to the increase in the Hartmann number. The exponential heat source has a decreasing effect on the heat flux and the angle of inclination is more sensitive to the heat transfer coefficient than other variables. Further, when radiation is incremented, the sensitivity of the heat flux toward the inclination angle augments at the rate 0.5094% and the sensitivity toward the exponential heat source augments at the rate 0.0925%. In addition, 41.1388% decrement in wall shear stress is observed when the plate inclination is incremented from [Formula: see text] to [Formula: see text].

Estimation of Shutdown Schedule to Remove Fouling Layers of Heat Exchangers Using Risk-Based Inspection (RBI)

Oil and Gas plants consist of a set of heat exchangers, which are used in recovering the waste heat from product streams to preheat the oil. The heat transfer coefficient of exchangers declines considerably during the operation period due to fouling. Fouling in heat exchangers is a complex phenomenon due to the acceleration of many layers of chemical substances across tubes of heat exchangers resulting from chemical reactions and surface roughness. In this paper, the fouling process was determined as a critical failure in the heat exchanger. Failure is an accelerated fouling layer across the heat exchanger tubes, which can be the reason for the clogging of tubes. Hence, a risk assessment was conducted using the Risk-Based Inspection (RBI) approach to estimate the probability of fouling in heat exchangers. The results showed that the RBI approach can be used successfully to predict the suitable time to shut down the plant and conduct the fouling cleaning process.

Effect of Tube Expansion on Heat Transfer and Pressure Drop Characteristics During Condensation in Micro-Fin Tubes

Despite of the large number of research dedicated to condensation heat transfer and pressure drop characteristics in pristine micro-fin tubes, experimental investigation on effects of tube expansion have not been reported in the open literature. The paper reports measured cross-sectional dimensions, condensation heat transfer and pressure drop data of R1234ze(E) in pristine (5.10 mm OD) and expanded (5.26 mm OD) micro-fin tubes with mass fluxes from 100 to 300 kg/(m2·s). Effects of mass flux, vapor quality and tube expansion on the heat transfer coefficients and friction pressure gradients were investigated in the study. When the mass flux is 100 kg/(m2·s), the heat transfer coefficient and pressure drop of R1234ze(E) decrease after tube expansion. However, when the mass fluxes are 200 and 300 kg/(m2·s), tube expansion effects on the heat transfer coefficient and pressure drop are not notable. In addition, the experimental results are analyzed based on the existing condensation heat transfer and pressure drop correlations.