Thermodynamics deals with irreversible transformations of substances. Every thermodynamic property of a substance, as a function of two parameters describing its state, can be illustrated as a simply connected manifold. The term manifold stands for the Methods of Geometrical Representation of Thermodynamic Properties of Substances by Means of Surfaces. Generally, every transformation of a substance changes its energy (or enthalpy) by heat transfer and work done on it. All such changes (transformations) are considered to be irreversible and can be described using appropriate manifolds. Studies show that every transformation is associated with the degradation of energy. Such relations (between heat, work and other forms of energy or enthalpy) can be described by the Pfaff formulas and their integrations.

This article discusses the issue of irreversible energy degradation in heat transfer between two fluids. Irreversible heat transfer between separated fluids most often occurs through surface heat exchangers. All such processes are determined by convective heat transfer in thermal boundary layers and conduction through the wall. Consequently, entropy changes of fluids in heat and mass transfer can be observed in these layers. While the entropy rate of the heating fluid is negative and that of the heated medium is positive, the sum of entropy changes of all substances involved in the heat transfer process is always positive. These sums, known as entropy increase (entropy generation), can be interpreted as the measure of irreversible degradation of energy in heat transfer processes. The consequence of this degradation is that an arbitrary engine powered by the degraded (lower-temperature) heat flux will operate at a lower efficiency. The significance of this discussion relates especially to cases in power plants and cooling systems where surface heat exchangers are used. In the discussion proposed is the entropy increase as a criterion of irreversible energy degradation in heat transfer. Such introduced measure of effectiveness leads to an analysis of local overall heat transfer coefficient optimization on the cone-shaped manifold.

The paper deals with a study of the effect of regulating elements on local values of heat transfer coefficients along shaped heat exchange surfaces with forced air convection. The use of combined methods of heat transfer intensification, i.e. a combination of regulating elements with appropriately shaped heat exchange areas seems to be highly effective. The study focused on the analysis of local values of heat transfer coefficients in indicated cuts, in distances expressed as a ratio x/s for 0; 0.33; 0.66 and 1. As can be seen from our findings, in given conditions the regulating elements can increase the values of local heat transfer coefficients along shaped heat exchange surfaces. An optical method of holographic interferometry was used for the experimental research into temperature fields in the vicinity of heat exchange surfaces. The obtained values correspond very well with those of local heat transfer coefficients αx, recorded in a CFD simulation.

In order to provide sufficient cooling capacity for working and heading faces of the coal mine, chilled water is often transported a long distance along pipelines in deep mine, which inevitably results in its temperature rising owing to heat transfer through pipe wall and the friction heat for flow resistance. Through theoretical models for temperature increasing of the chilled water were built. It is pointed out that the temperature rising of the chilled water should be considered as a result of the synergy effects of the heat transfer and the friction heat, but theoretical analysis shows that within engineering permitting error range, the temperature increasing can be regarded as the sum caused by heat transfer and fraction heat respectively, and the calculation is simplified. The calculation analysis of the above two methods was made by taking two type of pipe whose diameters are De273 × 7 mm and De377 × 10 mm, with 15 km length in coal mine as an example, which shows that the error between the two methods is not over 0.04°C within the allowable error range. Aims at the commonly used chilled water diameter pipe, it is proposed that if the specific frictional head loss is limited between 100 Pa/m and 400 Pa/m, the proportion of the frictional temperature rising is about 24%~81% of the total, and it will increase with high flow velocity and the thin of the pipe. As a result, the friction temperature rising must not be ignored and should be paid enough attention in calculation of the chilled water temperature rising along pipe.

The authors present a numerical study of a start-up of a boiler with a thick-walled element subjected to thermomechanical loading. The significance of calculations of real heat transfer coefficients has been demonstrated. Fluid dynamics, mechanical transient thermal and static structural calculations have been conducted in both separate and coupled modes. Strain-stress analyses prove that the effect of the heat transfer coefficient changing in time and place in comparison with a constant one as recommended by standards is the key factor of fatigue calculations.

This work discusses the heat transfer aspects of the neonate’s brain cooling process carried out by the the device to treat hypoxic-ischemic encephalopathy. This kind of hypothermic therapy is undertaken in case of improper blood circulation during delivery which causes insufficient transport of oxygen to the brain and insufficient cooling of the brain by circulating blood. The experimental setup discussed in this manuscript consists of a special water flow meter and two temperature sensors allowing to measure inlet and outlet water temperatures. Collected results of the measurements allowed to determine time histories of the heat transfer rate transferred from brain to the cooling water for three patients. These results are then analysed and compared among themselves.

Plate fin-tube heat exchangers fins are bonded with tubes by means of brazing or by mechanical expansion of tubes. Various errors made in the process of expansion can result in formation of an air gap between tube and fin. A number of numerical simulations was carried out for symmetric section of plate fin-tube heat exchanger to study the influence of air gap on heat transfer in forced convection conditions. Different locations of air gap spanning 1/2 circumference of the tube were considered, relatively to air flow direction. Inlet velocities were a variable parameter in the simulations (1– 5 m/s). Velocity and temperature fields for cases with air gap were compared with cases without it (ideal thermal contact). For the case of gap in the back of the tube (in recirculation zone) the lowest reduction (relatively to the case without gap) of heat transfer rate was obtained (average of 11%). The worst performance was obtained for the gap in the front (reduction relatively to full thermal contact in the average of 16%).

Falling film, shell-tube type evaporators are commonly used heat exchangers for the production of fruit juice concentrate. The main problem in the design of the exchanger is a reliable estimation of wall heat transfer coefficients for all effects in real operating conditions. Most literature sources for the overall heat transfer coefficients are based on laboratory measurements, where the tubes are usually short, no fouling exists and the flow rate is carefully adjusted. This paper shows the heat transfer estimated in real industrial operating conditions, compared to literature sources. Paper is based on the author’s own experience in designing and launching several evaporators for juice concentrate production into operation. As a summary, the design heat transfer coefficients are provided with relation to sugar content in juice concentrate.

The paper describes experimental research on a resistojet type rocket thruster which was built as an actuator in the Attitude Control System of a model space robotic platform. A key element of the thruster is the heater responsible for increasing the temperature of the working medium in the thruster chamber and hence the specific impulse. This parameter describes the performance of the thruster, increases providing – for lower propellant consumption – the same propulsion effect (thrust). A high performance thruster means either total launch mass can be reduced or satellite lifetime increased, which are key commercial factors. During the first phase of the project, 7 different heating chamber designs were examined. The heater is made of resistive wire with resistivity of 9Ω/m. Power is delivered by a dedicated supply system based on supercapacitors with output voltage regulated in the range of 20–70 V. The experimental phase was followed by designing the chamber geometry and the heating element able to deliver both: maximum increase of gas temperature and minimum construction dimensions. Experiments with the optimal design show an increase in temperature of the working gas (air) by about 300 ◦C giving a 40% increase in specific impulse. The final effect of that is a 40% reduction in mass flow rate while retaining thrust at a nominal level of 1 N.

Construction elements of supercritical power plants are subjected to high working pressures and high temperatures while operating. Under these conditions high stresses in the construction are created. In order to operate safely, it is important to monitor stresses, especially during start-up and shut-down processes. The maximum stresses in the construction elements should not exceed the allowable stress limit. The goal is to find optimum operating parameters that can assure safe heating and cooling processes [1-5]. The optimum parameters should guarantee that the allowable stresses are not exceeded and the entire process is conducted in the shortest time. In this work new numerical method for determining optimum working parameters is presented. Based on these parameters heating operations were conducted. Stresses were monitored during the entire processes. The results obtained were compared with the German boiler regulations - Technische Regeln für Dampfkessel 301.

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.