Heat Exchange Section Research Articles

Thermodynamic Optimization of the HAT Cycle Plant Structure—Part I: Optimization of the “Basic Plant Configuration”

A method for the thermodynamic optimization of the humid air turbine cycle plant structure is presented here. The method is based on the optimization of a “basic configuration of the plant” including “basic components” (compressor, turbine, combustion chamber, regenerator, and saturator), always present and connected in the same way in the plant structure and a heat exchange section which is viewed as a “black-box” where the heat transfer between hot and cold thermal flows occurs regardless of how many heat exchangers there are and of how they are interconnected. The optimal boundary conditions between the basic components and black-box are determined by calculating the conditions of maximum heat transfer in the black-box independently of the structure of the heat exchanger network. This is done by defining optimal composite curves in a Fortran routine at each step in the main optimization procedure. Once the structure of the heat exchanger networks that fulfill the optimal boundary conditions have been found, the optimal structure of the whole plant is obtained (see Section 2). The method is useful in a general sense as it can be applied to highly integrated energy systems in which it is difficult to define the optimal structure of the heat exchanger network in advance.

Thermodynamic Optimization of the HAT Cycle Plant Structure—Part II: Structure of the Heat Exchanger Network

In Part I of the paper a thermodynamic optimization methodology was presented for the “basic” configuration of a humid air turbine cycle plant in which the heat exchange section is viewed as a black-box separated from the rest of the plant (basic components), having a fixed structure. The results of the optimization apply to all the heat exchanger networks that fulfill the optimal boundary conditions between the black-box and the rest of the plant. The aim of this part is to define these heat exchanger networks using a combination of Pinch Technology and Second Law insights. The possibility of a further reduction in the number of heat exchangers is then investigated in order to achieve the best compromise between high performances and structural simplicity.

Denaturation of β-lactoglobulin and native enzymes in the plate exchanger and holding tube section during continuous flow pasteurization of milk

The denaturation of β-lactoglobulin, alkaline phosphatase and lactoperoxidase and changes in the proteolytic activity, were studied at the heating and holding sections of a plate heat-exchanger, during treatment of milk under different conditions of temperature and flow rate. The heating rate contributed considerably to the heat-induced changes in the milk components during continuous flow pasteurization, whereas these indicators were less susceptible to differences in the holding times. Information gained in such studies on the denaturation effects occurring in the different sections could be useful in the design of heat exchangers and holding tubes.

Russian Doll Type Cryogenic Traps: Improved Design and Isotope Separation Effects

An improved cryogenic trap for removing micromole quantities of condensables from gas mixtures is described. It is based on the so-called Russian doll design, with which extraordinary trapping efficiencies at flow rates of up to 10 L/min are obtained. The active element consists of one or more nested glass fiber thimbles. Despite the large fiber area, quantitative retrieval of condensed CO(2) is obtained. The new design is demountable and incorporates a heat exchange section; trapping efficiency depends little on the level of coolant, as has been tested for CO(2). When fractionation is induced by incomplete trapping, a small isotopic enrichment in (13)C occurs. It also has been discovered that when He is used as carrier gas, a gas chromatographic effect for CO occurs in Russian doll traps, accompanied by a large isotope separation, in which the elution sequence corresponds to the vapor pressure ratios of the isotopomers.

Modular thermoacoustic refrigerator

A thermoacoustic refrigerator was built to explore scaling to large heat flux. The refrigerator was constructed according to a modular design so that various stack, heat exchanger, and resonator sections are easily interchangeable. The resonator is driven by a commercial 10‐in. woofer. Initial tests, using pure helium gas as the working fluid and steel honeycomb (0.8‐mm cell) for the stack, pumped 60 W of heat against a 10 °C temperature gradient. Measurements of heat flux and efficiency will be reported as functions of stack structure (e.g., pore size and shape) and will be compared with theoretical predictions.

Dynamic modelling of industrial so 2 oxidation reactors part I. model of 'hot' and 'cold'start-ups of the plant

The paper describes a comparison of some results computed using a mathematical dynamic model of a single reactor bed with real temperature unsteady state transients, measured in a large industrial scale SO 2 oxidation reactor. Problems of the dynamic modelling of complete oxidation plants, including a heat exchange section and a start-up installation are discussed in the next section of the paper. As a basis for comparison some start-up dynamic transients were analysed. The analysis shows that the model (two-phase model for heat transfer and homogeneous model for mass transfer) is sufficient for qualitative analysis of the problem. The problems of obtaining reliable parameters for simulation as well as parameter sensivity of the model are also described. The plant is modelled using the dynamic flowsheeting simulator DYNAM, whose algorithm is presented against a background of similar simulators known from the literature. The major part of the paper presents the results of the identification of the model based on an actual industrial plant, together with the start-up analysis concerning the SO 2 oxidation plant. The analysis has been aimed at minimizing both the emission of SO 2 during start-up and its duration. The results are given for the various modes of the start-up operation.

Optimization of air conditioning air-cooler installation parameters in mines

1. The investigations performed showed that the structural parameters of ARVE air coolers being exploited in mine air-conditioning systems are not optimal. 2. On the basis of an analysis of an AC structure as a MACI with the probabilistic nature of the initial data taken into account, a method is developed for optimizing the AC structural parameters and a new series of optimal standard-size AC is obtained on the basis of standard heat-exchanger sections for working depths from 900–1500 m. 3. Utilization of a systems approach to determining the optimal AC parameters permits reducing the referred expenditures on air conditioning. 4. The method developed permits solving a number of problems for the design and exploitation of AC in MACI.

THERMAL DEATH KINETICS of B. STEAROTHERMOPHILUS IN THIN FILM SCRAPED SURFACE HEAT EXCHANGER

A cascade thin film scraped surface heat exchanger, having sterilizer, regenerator and cooler sections was tested for thermal death kinetics of B. stearothermophilus spores in milk. A sterilizing effect of 6.15 was obtained at 152°:C for a holding time of 1.25 s. D values of 1.18, 0.75, 0.25 and 0.20 s were obtained for B. stearothermophilus at 143, 145, 150 and 152°C, respectively. the Z-value obtained was 10.1°C.

A theoretical model for the calculation of large transients in nuclear natural-circulation U-tube steam generators (Digital code UTSG)

A newly developed nonlinear transient model for the calculation of the dynamic behaviour of a vertical natural-circulation U-tube steam generator together with its steam removal system is presented. The steam generator is considered to consist of a heat exchange section, a top plenum, a downcomer region and a steam removal system with a sequence of relief and/or safety valves, isolation, bypass, turbine-trip and turbine-control valves and a steam turbine. Possible perturbations from outside can be: inlet water temperature, inlet water mass flow and system pressure on the primary side, feed water temperature, feed water mass flow and outlet steam mass flow disturbed by actions of the different valves within the steam removal system on the secondary side. Based on this theoretical model the digital code UTSG has been established. Post-calculations of start-up tests at a PWR nuclear power plant simulating perturbations both on the primary and secondary side of the steam generator and similar calculations for the corresponding ATWS-cases will show the efficiency of the code UTSG and the underlying theoretical model.

Effect of natural convection on stability of flow in a vertical pipe

If water is heated or cooled while flowing through a vertical pipe with a laminar motion, the velocity profile will differ from the parabolic shape for isothermal flow due to density variations in the fluid. If a constant heat flux is used at the wall and if the changes in temperature affect only the density appearing in the gravity term of the equations of motion, a condition is attained far downstream in the heat-transfer section such that there is no further change in the velocity profile. The shape of this fully developed velocity profile depends on the ratio of the heat flux to the flow rate. The stability of flow in an electrically heated pipe 762 diameters long was studied by detecting temperature fluctuations in the effluent. By use of a carefully designed entry and a long isothermal section prior to the heat exchange section, inlet disturbances were eliminated and transition to an unsteady flow resulted from a natural instability of the distorted profiles. It was found that the stability depends primarily on the shape of the velocity profile and only secondarily on the value of the Reynolds number, if at all. For upflow heating the flow first becomes unstable when the velocity profiles develop points of inflexion. Transition to an unsteady flow involves the gradual growth of small disturbances and therefore it is quite possible to have unstable flows without observing transition because the pipe is not long enough for the disturbances to attain a measurable amplitude. For downflow heating the flow instability is associated with separation at the wall. Transition to an unsteady flow is sudden and therefore transition occurs shortly after an unstable flow occurs. It is suggested that a change from a steady symmetrical to a steady unsymmetrical flow occurs in downflow when the profile develops points of inflexion.