In the paper presented are experiences from operation of three different expansion devices for possible implementation in the domestic micro CHP. These were the modified scroll expander and two designs based on the variable working chamber volume pneumatic devices. Experiments showed the superiority of both "pneumatic devices" over the scroll expander, indicating the possible internal efficiencies in the range of 61 82Such efficiencies are very attractive, especially at the higher end of that range. The volume of these devices is much smaller than the scroll expander which makes it again more suitable for a domestic micro CHP. Small rotational velocities enable to conclude that connection to electricity grid will also be simpler in the case of "pneumatic devices". The "pneumatic devices" under scrutiny here could be an alternative to the typical vapour turbine in the ORC cycle, which is in the process of development at the IFFM.
The paper analyzes a new concept of integration of combined cycle with the installation of supplementary firing. The whole system was enclosed by thermodynamic analysis, which consists of a gas-steam unit with triple-pressure heat recovery steam generator. The system uses a determined model of the gas turbine and the assumptions relating to the construction features of steam-water part were made. The proposed conception involves building of supplementary firing installation only on part of the exhaust stream leaving the gas turbine. In the proposed solution superheater was divided into two sections, one of which was located on the exhaust gases leaving the installation of supplementary firing. The paper presents the results of the analyses of which the main aim was to demonstrate the superiority of the new thermodynamic concept of the supplementary firing over the classical one. For this purpose a model of a system was built, in which it was possible to carry out simulations of the gradual transition from a classically understood supplementary firing to the supplementary firing completely modified. For building of a model the GateCycle™ software was used.
The article describes the methodology for the determination of ambient temperature for thermovision measurements. The adopted methodology consists in the use of the technical blackbody model. Determining the value of the ambient temperature parameter makes it possible to enhance the accuracy of temperature measurement of objects exposed to strong irradiation using a thermovision camera.
The analysis of effectiveness of the gradient algorithm for the two-dimension steady state heat transfer problems is being performed. The three gradient algorithms - the BCG (biconjugate gradient algorithm), the BICGSTAB (biconjugate gradient stabilized algorithm), and the CGS (conjugate gradient squared algorithm) are implemented in a computer code. Because the first type boundary conditions are imposed, it is possible to compare the results with the analytical solution. Computations are carried out for different numerical grid densities. Therefore it is possible to investigate how the grid density influences the efficiency of the gradient algorithms. The total computational time, residual drop and the iteration time for the gradient algorithms are additionally compared with the performance of the SOR (successive over-relaxation) method.
In the present paper it is proposed to consider the computer cooling capacity using the thermosyphon loop. A closed thermosyphon loop consists of combined two heaters and a cooler connected to each other by tubes. The first heater may be a CPU processor located on the motherboard of the personal computer. The second heater may be a chip of a graphic card placed perpendicular to the motherboard of personal computer. The cooler can be placed above the heaters on the computer chassis. The thermosyphon cooling system on the use of computer can be modeled using the rectangular thermosyphon loop with minichannels heated at the bottom horizontal side and the bottom vertical side and cooled at the upper vertical side. The riser and a downcomer connect these parts. A one-dimensional model of two-phase flow and heat transfer in a closed thermosyphon loop is based on mass, momentum, and energy balances in the evaporators, rising tube, condenser and the falling tube. The separate two-phase flow model is used in calculations. A numerical investigation for the analysis of the mass flux rate and heat transfer coefficient in the steady state has been accomplished.
An analysis of energy efficiency for transcritical compression unit with CO2 (R744) as the refrigerant has been carried out using empirical operating characteristics for the two-phase ejector. The first stage of the refrigerant compression is carried out in the ejector. The criterion adopted for the estimation of energy efficiency for the cycle is the coefficient of performance COP. The analysis is performed for the heat pump and refrigeration systems. The results of COP for the systems with the ejector has been compared with the COPL values for the single stage Linde cycle.
Thermodynamic analysis of car air cooler is presented in this paper. Typical refrigerator cycles are studied. The first: with uncontrolled orifice and non controlled compressor and the second one with the thermostatic controlled expansion valve and externally controlled compressor. The influence of the refrigerant decrease and the change of the air temperature which gets to exchangers on the refrigeration efficiency of the system; was analysed. Also, its effectiveness and the power required to drive the compressor were investigated. The impact of improper refrigerant charge on the performance of air conditioning systems was also checked.
Szargut proposed the algorithm for determination of the influence of irreversibility of components of thermal process on the emission of CO2 . In the presented paper, basing on Szargut's proposal, the example of analysis of influence of operational parameters of coal fired power plant on the local increase of CO2 emission is presented. The influence of operational parameters on the local exergy losses appearing in components of investigated power plant are simulating making use of the semi-empirical model of power plant.
In the paper a heating system with a vapour compressor heat pump and vertical U-tube ground heat exchanger for small residential house is considered. A mathematical model of the system: heated object - vapour compressor heat pump - ground heat exchanger is presented shortly. The system investigated is equipped, apart from the heat pump, with the additional conventional source of heat. The processes taking place in the analyzed system are of unsteady character. The model consists of three elements; the first containing the calculation model of the space to be heated, the second - the vertical U-tube ground heat exchanger with the adjoining area of the ground. The equations for the elements of vapour compressor heat pump form the third element of the general model. The period of one heating season is taken into consideration. The results of calculations for two variants of the ground heat exchanger are presented and compared. These results concern variable in time parameters at particular points of the system and energy consumption during the heating season. This paper presents the mutual influence of the ground heat exchanger subsystem, elements of vapour compressor heat pump and heated space.
The present work is devoted to the problem of utilization of the waste heat contained in the exhaust gases having the temperature of 350 °C. Conversion of the waste heat into electricity using a power plant working with organic fluid cycles is considered. Three Organic Rankine Cycle (ORC) power plant solutions are analysed and compared: a solution with the basic, single thermodynamic conversion cycle, one with internal heat recuperation and one with external heat recuperation. It results from the analysis that it is the proper choice of the working fluid evaporation temperature that fundamentally affects the maximum of the ORC plant output power. Application of the internal heat recuperation in the plant basic cycle results in the output power increase of approx. 5%. Addition of the external heat recuperation to the plant basic cycle, in the form of a secondary supercritical ORC power cycle can rise the output power by approx. 2%.
Heat pipes, as passive elements show a high level of reliability when taking heat away and they can take away heat flows having a significantly higher density than systems with forced convection. A heat pipe is a hermetically closed duct, filled with working fluid. Transport of heat in heat pipes is procured by the change of state of the working fluid from liquid state to steam and vice versa and depends on the hydrodynamic and heat processes in the pipe. This study have been focused on observing the impact these processes have on the heat process, the transport of heat within the heat pipe with the help of thermovision. The experiment is oriented at scanning the changes in the surface temperatures of the basic structural types of capillary heat pipes in vertical position.
The work deals with experimental and numerical thermodynamic analyses of cross-flow finned tube heat exchangers of the gas-liquid type. The aim of the work is to determine an impact of the gas non-uniform inlet on the heat exchangers performance. The measurements have been carried out on a special testing rig and own numerical code has been used for numerical simulations. Analysis of the experimental and numerical results has shown that the range of the non-uniform air inlet to the considered heat exchangers may be significant and it can significantly affect the heat exchanger efficiency.
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