A universal NDT method for examination of low energy impact damage in CFRP with the use of TLC film

The article presents an attempt to use a sheet of laminated thermochromic liquid crystal film (TLC film) for non-destructive testing of the impact damage (energy values: 1J, 2J, 3J and 4J) in carbon fibre-reinforced polymer (CFRP). This is a new, alternative NDT approach based on the thermo-optical effect. The main advantages of this method are a) the low cost of TLC film, b) the low cost of recording devices due to the usage of conventional digital recording equipment and c) the low requirements for tests. The TLC film method was compared with two other conventional NDT methods: computer radiography (CR) and active thermography (thermographic camera). The scatter of results regarding the average crack length (TLC film and active thermography) was ±5% in relation to the CR method. The damage area (impact energy 2J to 4J) showed a similar shape (TLC film vs active thermography) and the scatter of results for the TLC film was ±2% in relation to the active thermography method. Only the CR detected the damage caused by 1J impact energy. The comparative studies have proven that the described method (TLC film) is a fullfledged and accurate tool for NDT method for the diagnosis of impact damage in CFRP.

Alternative cogeneration thermodynamic cycles for domestic ORC

The Organic Flash Cycle (OFC) is suggested as a vapor power cycle that could potentially improve the efficiency of utilization of the heat source. Low and medium temperature finite thermal sources are considered in the cycle. Additionally the OFC’s aim is to reduce temperature difference during heat addition. The study examines 2 different fluids. Comparisons are drawn between the OFC and an optimized basic Organic Rankine Cycle (ORC). Preliminary results show that ethanol and water are better suited for the ORC and OFC due to higher power output. Results also show that the single flash OFC achieves better efficiencies than the optimized basic ORC. Although the OFC improves the heat addition exergetic efficiency, this advantage was negated by irreversibility introduced during flash evaporation.

Comparison of predictive methods for flow boiling heat transfer in conventional channels and minichannels - the effect of reduced pressure

In the paper are presented the results of follow on studies from [1]–[3] using authors own model to predict heat transfer coefficient during flow boiling. The model has been tested against a large selection of experimental data collected from various researchers to investigate the sensitivity of the in-house developed model. The collected experimental data came from various studies from literature and were conducted for the full range of quality variation and a wide range of mass velocity and saturation temperatures. In the work are presented the results of calculations obtained using the in-house developed semi empirical model on selected experimental flow boiling data of the refrigerants: R134a, R1234yf, R600a, R290, NH3, CO2, R236fa, R245fa, R152a and HFE7000. In the present study the particular attention was focused on the influence of reduced pressure on the predictions of the theoretical model. The results of calculations were to test the sensitivity of the flow boiling model with respect to selection of the appropriate two-phase flow multiplier, which is one of thedistinctive elements of the in-house model. The main purpose of this paper however is to show the effect of the reduced pressure on the predictions of heat transfer during flow boiling.

COMPARISON OF PREDICTIVE METHODS FOR FLOW BOILING HEAT TRANSFER IN CONVENTIONAL CHANNELS AND MINICHANNELS – THE EFFECT OF REDUCED PRESSURE

In the paper are presented the results of follow on studies from [1]–[3] using authors own model to predict heat transfer coefficient during flow boiling. The model has been tested against a large selection of experimental data collected from various researchers to investigate the sensitivity of the in-house developed model. The collected experimental data came from various studies from literature and were conducted for the full range of quality variation and a wide range of mass velocity and saturation temperatures. In the work are presented the results of calculations obtained using the in-house developed semi empirical model on selected experimental flow boiling data of the following refrigerants: R134a, R1234yf, R600a, R290, NH 3 , CO 2 , R236fa, R245fa, R152a and HFE7000. In the case of the fluid HFE7000 authors own unpublished experimental results have also been presented. In the present study the particular attention was focused on the influence of reduced pressure on the predictions of the theoretical model. The results of calculations were to test the sensitivity of the flow boiling model with respect to selection of the appropriate two-phase flow multiplier, which is one of the distinctive elements of the in-house model. Four two-phase flow multiplier models were used for this purpose, i.e. due to Müller-Steinhagen and Heck and its in-house modification for applicability to minichannels, Friedel and Tran. The main purpose of this paper however is to show the effect of the reduced pressure on the predictions of heat transfer during flow boiling in minichannels.

Ekspertyza dotycząca przyczyn wybuchu zbiornika HAS 18-204 w oddziale placu drzewnego

Celem ekspertyzy było wyjaśnienie przyczyn wybuchu zbiornika kondensatu. W ramach pracy przeprowadzono obliczenia wytrzymałościowe oraz analizy cieplno-przepływowe zjawisk skutkujących awarią w instalacji.

High-temperature heat pumps – new devices for heat recovery and production of technological steam

In the paper, the original high temperature compressor based heat pump with a dry working fluid, i.e. the one in which the slope of saturated vapour line is positive, was presented. The objective of the paper is to investigate the possibility of preparation of technological steam with tempperature 120 C from the waste heat resource at temperature of 50 C. Single comppression cycles as well as cascade systems have been considered for that purpose for a number of working fluids.

Performance of the domestic micro ORC equipped with the shell-and-tube condenser with minichannels

In this paper, the original compact shell-and-tube heat exchanger with circular minichannels of in-house design and manufacturing is presented as the condenser for the domestic micro heat and power plant investigations as well as other future technical applications. The heat exchanger is equipped with turbulizing baffles inside the shell. The shell itself is made of a tubular sleeve having an inner diameter of 0.067 m and the length of 0.38 m. The tube bundle constitutes of 103 pipes arranged hexagonally with the active length equal to 0.31 m. The tubes inner diameter equals to 0.002 m and the wall thickness is 0.001 m. The calculations of the heat transfer coefficient for the condensation in the flow of the ethanol as a working fluid was done by means of several methods, among others the one developed in-house. That model accounts for the non-adiabatic effects in the convective heat transfer coefficient. The experimental validation of the prototype construction was accomplished. During the tests the condenser was cooled by water with ethanol as a working fluid. The obtained results are in a good consistency with the in-house model predictions.

Pressure drop related to flow maldistribution in a model minichannel plate heat exchanger

The paper describes the issues related to the pressure drop that accompanies the phenomenon of maldistribution of working fluid between the channels of a model minichannel plate heat exchanger. The research concerns a single exchanger's plate containing 51 (in every geometry) parallel rectangular minichannels of hydraulic diameters 461 µm, 571 µm, 750 µm and 823 µm. In addition, the more complex geometry has been investigated, equipped with additional diagonal channels (so called extended geometry). The moment of the liquid phase transition through the heat exchanger was recorded at the flow rates from 0.83 g/s to 13.33 g/s in the inlet manifold. The article discusses the total pressure drop as a function of the flow rate and the characteristic dimension of minichannels, as well as the pressure drop as a function of the time of the fluid passage through the main part of the measuring section in which measurements were done. The resulting profiles correlate with the images of the flow distribution between channels recorded using the fast shutter speed camera, that allows to draw a further conclusions about the specifics of the maldistribution process. The impact of the total pressure drop on the actual range of optimum operating conditions of the heat exchanger was analyzed.

The effect of reduced pressure on carbon dioxide flow boiling heat transfer in minichannels

. In the paper presented are the results of the study on the effect of reduced pressure on flow boiling heat transfer data in minichannels as well as conventional ones. That effect renders that most of heat transfer correlations fail to return appropriate results of predictions. Mostly they have been developed for the reduced pressures from the range 0.1-0.3. The special correction has been postulated to the in-house model of flow boiling and condensation which modifies the two-phase flow multiplier as well as the temperature gradient in pool boiling. Four two-phase flow multiplier models were tested for this purpose, i.e. due to Friedel, Tran, Müller-Steinhagen and Heck and finally its in-house modification for applicability to minichannels. The model has been tested against a large selection of experimental data collected from various researchers to investigate the sensitivity of the in-house developed model. The collected experimental data came from various studies from literature and were conducted for the full range of quality variation and a wide range of mass velocity and saturation temperatures. In the work are presented the results of calculations obtained using the in-house developed semi empirical model on selected experimental flow boiling data related to carbon dioxide.

A simplified energy dissipation based model of heat transfer for subcooled flow boiling

In the paper a model is presented based on energetic considerations for subcooled flow boiling heat transfer. The model is the extension of authors own model developed earlier for saturated flow boiling and condensation. In the former version of the model we used the heat transfer coefficient for the liquid single-phase as a reference level, due to the lack of the appropriate model for heat transfer coefficient for the subcooled flow boiling. That issue was a fundamental weakness of the that approach. The purpose of present investigation is to fulfil this drawback. Now the reference heat transfer coefficient for the saturated flow boiling in terms of the value taking into account the subcooled flow conditions. The wall heat flux is based on partitioning and constitutes of two principal components, namely the convective heat flux and partial evaporation heat flux of the liquid replacing the detached bubble. Both terms are accordingly modeled. The convective heat flux is regarding vapour bubbles travelling longitudinally and the liquid moving radially – liquid pumping. The results of calculations have been compared with some experimental data from literature showing a good consistency.