FACTORS OF THE PVT-COLLECTOR EFFICIENCY FORMATION

Analytical researches of a hybrid solar collecting channel (PVT) are conducted by manufacture electric and thermal energy. The method of researches allows to analyse the following PVT-collector characteristics : a reheat temperature of an absorber and chilling liquid, as well as productivity depending on external and regime working conditions of the device. The work purpose is to work out of a method of calculation of opeating characteristics and definition of rational operating conditions of work of a hybrid solar collecting channel taking into account effective productivity. The complex mathematical model of the local analysis of processes of heat exchange and electrogeneration of a hybrid solar collecting channel for real conditions of a dynamic solar and climatic situation is used. The carried out analysis of heat exchange in alternative conditions showed that efficiency of a heat transport in a collecting channel integral cooling system ηT (a relationship of temperature of an absorber and final temperature of heat-transfer agent) is not a constant and considerably changes under the external and internal factors. It is influenced by intensity of insolation and the heat-transfer agent charge. With growth of these parametres ηT decreases. Existing dependence of electric power of a photo cell on the charge of a chilling liquid is characterised by presence of two expressed sections which are discriminated by rate of a variation of a function. The first of them, with low flux level of a liquid, differs considerable agency of functional parametres. The second one at high intensity differs asymptotic stabilisation of power. The limit values of the transition of the rate of decrease of the function correspond to the fluid flow rate of 0.08...0.085 l/(m2s). These values can be accepted for rationalisation of a refrigerating duty of the photobattery. Generalized dependences for determining the temperature of the liquid at the outlet of the device and the average temperature of the absorber are obtained. These dependences can be used to evaluate the efficiency of conversion of solar energy into electrical and thermal energy in regime optimization problems.

ВОЗБУЖДЕНИЕ ГАРМОНИЧЕСКИХ ТЕМПЕРАТУРНЫХ ВОЛН В ТВЕРДОМ ОБРАЗЦЕ МАТЕРИАЛА ПРИ КОНВЕКТИВНОМ НАГРЕВЕ

The article discusses the method and means of exciting harmonic temperature waves in a solid sample material during convective heating, it is typical for the working conditions of heat-stressed assemblies and parts in power plants systems. A supersonic jet of combustion products is used as a heat transfer agent. The scheme of power supply feed and control of the mode of operation of the gas generator is considered, which makes it possible to reliably regulate the modes of its operation and to obtain stable values of the heat transfer agent temperature. For determining the temperature of the heat transfer agent, the method of accounting for losses in the combustion chamber with using pulse coefficients is considered. To create a variable thermal effect, the property of the supersonic (barrel) section was used, consisting of the substantial non-uniformity of the distribution of gas-dynamic parameters along its length. The movement of the sample relative to the jet must be carried out at a variable speed. For determining this pattern, we analyzed the coordinates of the shock-wave structure in order to transform its linear coordinates into phase ones. The property of the logarithmic spiral is used. It is established that the growth coefficient of the logarithmic spiral for the first barrels from the nozzle exit varies slightly. The scheme of the device for the excitation of the temperature wave in the sample. The sample is placed on the worktable, which reciprocates relative to the jet (the section of the first half of the second barrel is used). The worktable drive carried out by a cam rotating at a constant speed. The cam profile is carried out along sections of the spiral branches (right and left), in this case, the pressure of the gas jet on the working surface changes according to a harmonic law. The heat transfer coefficient is proportional to the pressure. To determine the thermophysical characteristics of the material in the experiment, it is sufficient to measure the phase shift between the temperature oscillations of the second surface in the sample and the heat flow oscillations (gas pressure on the obstacle). The accuracy of such measurements is higher than when measuring parameters with continuous heating of the sample

UNSTEADY HEAT TRANSFER IN A HORIZONTAL GROUND HEAT EXCHANGER

By the three-dimensional model of heat transfer in the system "ground - horizontal ground heat exchanger - heat transfer agent", an analysis of the efficiency of the horizontal multi-loop heat exchanger, which is an element of the heat pump system, was carried out. Based on the results of numerical simulation, the time dependence of the heat transfer agent temperature at the outlet from the ground heat exchanger and the amount of heat extracted from the ground is determined. The results of calculations by the presented model are satisfactorily agree with the experimental data.

ABOUT ONE APPROACH TO CALCULATION OF PARAMETERS OF HEAT TRANSFER THROUGH WALL IN PRESENCE OF CONDENSING VAPOR

The article is dedicated to the study of heat exchangers operation. The main goal of the work was to improve a standard method for calculating a typical heat exchanger based on dependencies approved in engineering practice. The noted technique is presented in educational literature for chemical engineers and it is included in the educational process for the training of engineers. On the basis of practical recommendations stated in literature the working formulas of the process are taken in approximate form. Further, a correction is calculated, which, as calculations show, leads (together with the initial approximation) to an almost exact satisfaction of the initial equations. It is expedient because traditional equations of a heat transfer have not really high precision, which is determined by the processing of numerous experiments. These experiments are rather rough. It is reasonable that the accuracy of the analysis has to be consistent with the model accuracy. This factor justifies the need to simplify the models (use of various recommendations based on the experience of equipment operation, etc.). At the same time, it is desirable to simplify the mathematical model equation so that it is possible to calculate the corrections, i.e. to clarify the solution. We clarify the equation solution meaning more and more exact satisfaction with the initial equation of the mathematical model. In this direction, various variants of perturbation methods can be used. The search for analytical solutions is complicated by the fact that the equations of the mathematical model of energy transfer in a heat exchanger are nonlinear. The three-layer heat transfer problem in a stationary mode is considered. The first layer is the space of the heat exchanger where a phase transition (first heat transfer agent vapor condensation) occurs. The second layer is the space of the heat exchanger where convective movement of the second heat transfer agent takes place without phase transition. The third layer is a wall separating the heat transfer agent providing some resistance to the heat transfer process. As a result of the simplified model analysis, it became possible to obtain an analytical solution to the problem with such accuracy that the calculated correction turned out to be insignificant i.e. the correction is not appropriate to take into account. The solution found was almost exactly approximated by a simple analytic dependence.