Some aspects of plate number estimation of plate heat exchangers (PHEs). A case study

For the proper estimation of the plate number (N) of a plate heat exchanger (PHE) – in addition to the flow rates and thermophysical properties of fluids –, an appropriate correlation is needed for convective heat transfer coefficient (α) calculation. When one does not have a criterial equation for the corresponding plate shape, we propose a selecting method for α. With the suggested relationships from literature, we calculate the plate number of a geometrically known, similar heat duty PHE and choose those relationships that give the same plate number with the known heat exchanger. In our case study, the plate number determined by any of the screened equations for whole milk preheating has almost the same value (n = 10 ± 1) regardless of the method used to solve the PHE model (plate efficiency and Nconverg or Kconverg convergence methods). For liquids’ thermophysical property estimation, we recommend averaging the values given by equations from literature, followed by equation fitting.

Determination of heat transfer criterial equation when cooling aluminum ingots

A big problem when casting aluminum ingots is the uneven structure formation, which leads to an increased rejection of products. Nonequilibrium structure elimination is carried out by heat treatment. To obtain the required aluminum ingots’ physicochemical properties, it is necessary to know the conditions of heat transfer between the ingots and the cooling air, i.e. a mathematical model of conjugate heat transfer is needed. The mathematical model obtained by the authors makes it possible to analytically investigate the ingots temperature and cooling air during heat treatment. This mathematical model assumes the heat transfer coefficient calculation. The existing criterion equations for determining the heat transfer coefficient have a drawback - the heat transfer coefficient according to these equations is calculated in circular channels, while heat transfer between aluminum ingots and air occurs in rectangular channels. The article describes the criterion equation identification for heat transfer, used in the analytical study, by the data of the experimental study.

Substantiation of regime parameters of vibrating conveyor infrared dryers

The analysis of constructive-technological schemes of vibrating conveyor machines for heat-exchange processing of bulk technological masses in the current mode is carried out, which allowed to substantiate the effectiveness of using a new modification of infrared dryers of vibration-wave execution with a flexible transporting body. For this scheme, a vibrating system is developed which mathematical modelling allowed to determine and substantiate the main parameters of the operating mode of the drive mechanism of the projected device. The experiments, using the developed research model, confirm and refine the results of theoretical analysis, energy efficiency and comparatively low metal consumption of the design structure. The difficulty of working with such a large number of factors led to the application of the second similarity theorem and the introduction of a mathematical model of the criteria of Stanton, Froude, Burdo, whose magnitudes are reflected through the main factors of influence and were found experimentally. After using the "dimension theory" and graph-analytic analysis of power functions, a criterial equation of the investigated process was obtained. This allows recommending the regime parameters and the design series of projected thermo-radiation dryers with vibration-wave transport of products when varying the main factors of influence.

Experimental Research of Valve Tightness at Different Closure Forces

Power valves are installed on almost all the pipelines of nuclear power plants performing the functions of regulation and shutting off the flow, so its failure often leads to emergencies. A particularly large number of failures is observed in motor-operated valves. Incorrect setting of the limiting clutch leads either to incomplete closure of the valve or to rod failure. Therefore, the valves are equipment of a nuclear power plant, which often falls into repair shops. Failures leading to an increase of valve leakage are especially dangerous for nuclear power plants. In this case, leakage of high-pressure valves leads to erosion of the sealing surfaces, which only increases the leakage. Thus, it is very important to determine the optimum rotational value when the valve is closed. The lack of conditions for closure force in the standards for valve leakage complicates the issue. A bench that allows working in the air with a pressure up to 3.5 MPa was developed on valve rod to study dependence of valve leakage on the rotational moment. Four independent parameters were measured: air pressure in front of the valve under study, closure force of the valve, volume of air loss through the valve and leakage time. A standard stop valve with a nominal diameter of 15 mm and a nominal pressure of 64 atm was used for the study. The determined dependence of the leakage on torque value allows recommending a gentler mode of valve closure without significantly reducing its tightness. As a result of experimental data processing, a criterial equation is obtained linking a leakage rate, pressure drop on the valve and a rotational moment value. The received criterial equation will allow defining the compromise between valve closure force and permissible leak level according to regulatory requirements. The analysis of the “leakage/rotational moment” diagram showed the possibility to reveal the damaged valves. This possibility may be used during the incoming inspection of the valves supplied to NPP, which should significantly improve the reliability of their operation.

ОБГРУНТУВАННЯ ПАРАМЕТРІВ ПРОЦЕСУ ІНФРАЧЕРВОНОГО СУШІННЯ ЗЕРНОВОЇ ПРОДУКЦІЇ З ВІБРОХВИЛЬОВИМ КОНВЕЄРОМ

Проведений аналіз конвеєрних апаратів для забезпечення необхідного вологовидалення сипкої сільськогосподарської сировини дозволив обґрунтувати ефективність вібраційних конвеєрних схем. Класичні віброконвеєрні машини базуються на електромагнітному віброзбудженні та використанні жорсткого вантажонесучого органу, що вимагає значних витрат енергії та матеріалу. Дана проблема вирішується за рахунок використання механічного віброзбудження та недеформувального транспортуючого елементу, що притаманні віброхвильвим конвеєрним апаратам. Представлена принципова схема віброхвильової терморадіаційної сушарки, яка дозволяє ефективно вирішити проблеми достатньо інтенсивної та рівномірної обробки при мінімізації енерго- та матеріаловитрат, поміроного термічного навантаження на шари продукції та максимального збереження її вихідних властивостей. На основі експериментальних досліджень розробленої дослідної моделі даної сушарки було складено критеріальне рівняння тепломасобміну, що дозволяє проектувати сушарки із заданими параметрами процесу. The analysis of conveyor devices to ensure the necessary moisture removal of loose agricultural raw materials allowed to substantiate the effectiveness of vibration conveyor circuits. Classic vibroconveyor machines are based on electromagnetic vibroexcitation and the use of a rigid carrier, which requires significant energy and material costs. This problem is solved by the use of mechanical vibration and undetectable transporter element inherent in vibrating conveyor devices. Mechanical vibrators are aggregated in the support bundles of the tape mechanism, providing with sufficiently compact performance of the standing or running wave on the surface of the deformation carrier body. Necessary parameters of this wave for the appropriate promotion of bulk masses of grain products with a given speed are determined from experimental studies in the variation of angular frequencies and amplitudes of the oscillations of the drive shafts of the designated vibroscuders. The required speed of movement of products processed on a projected wave conveyor is determined by the condition of achieving the desired level of moisture content of the raw material during its single passage along the processing zone, which ensures the continuity of the dehydration cycle and the sufficiently high productivity of the dryer. The principal scheme of the vibratory thermo-radiation dryer is presented, which allows to effectively solve the problems of sufficiently intensive and uniform treatment with minimization of energy and material costs, the moderate thermal load on the product layers and maximal preservation of its initial properties. On the basis of experimental researches of the developed experimental model of this dryer, a criterial equation of the heat capacity was compiled, which allows the design of driers with the given parameters of the process. Among such parameters, the characteristics of the oscillation processes, which lead to the appearance of a wave on the surface of the tape, were used. This approach allows us to maximally approximate the results of mathematical modeling of this drying process to real conditions.

Possibility of Using Fourier’s Differential Equation in Cooling Process of Meat Steaks

Summary: In this paper, based on derived differential equation for the heat transfer and a suitable boundary condition (equation of heat exchange), the appropriate model of cooling of meat stakes in the form of a flat plate is set up. By using theory of similarity, Fourier and Biot criterion is defined, which allowed setting criterial equation of temperature field which included an unnamed temperature and geometric criterion. For solving the obtained criterial equation, existing diagrams of temperature functions were utilized, which were specified by analytical method for the core, the surface and the interior of the observed model. The proposed model is used for analytical solving of a number of practical problems in the cooling process of meat steaks in a gaseous environment. Particular focus has been on the temperature of the surface and core of steak as well as ambient temperature and cooling time. Also, it was shown that proposed model can be used to define temperatures or temperature field along the thickness of steak, depending on the distance from the central plane. Special possibility of applying the model is for the case of preventing freezing steaks, when their temperature is maintained within specified limits.

Measuring the Effective Mass Transfer Area of a Structured Packing by a Chemical Method

The effective mass transfer area of a Mellapak 750 Y structured packing was measured in a bench- scale plant with a column having an internal diameter of 100mm, and a packing height of 518 mm, using a broad range of gas and liquid flow rates. The absorption of carbon dioxide into natrium hydroxide aqueous solutions of 0.5 and 1.0 mol/L has been employed as test reaction. The validity of data obtained was tested by checking the two conditions of fast pseudo first order irreversible reaction. The data have been correlated by a criterial equation giving the ratio between the effective and the geometric areas versus the Reynolds number of the liquid phase. The coefficients of the equation have been identified by regression.