Thermoeconomic analysis of spiral heat exchanger with constant wall temperature

Thermoeconomic analysis of spiral heat exchanger is conducted. Different geometrical parameters, such as outer diameter, plate height, passage gap, etc. are used and varied in a wide range. Detailed thermal and total costs analyses were performed for two spiral heat exchanger with different process fluids (water and thermal oil) with temperature changes, while the wall temperature was kept constant (condensation). The results were shown graphically. It is determined that optimum values of number of entropy generation units correspond to minimum total annual cost. The optimal solution could be found in the recommended range of geometric sizes for defined inlet and outlet temperatures and process fluid-flow rate

HEAT TRANSFER AND MOISTURE LOSS FROM F ROZEN SURFACE - AN ENGINEERING APPROACH

This paper presents an analysis of convective heat load of frozen surfaces. A mathematical model for determination of "dry" and "wet" heat loads has been formed. The mass heat transfer coefficient σ i s estimated by the Chilton -Colburn's analogy . T he impact of re levant parameters of convective loads (flow velocity and relative humidity over ice, the surface temperature of the ice rink and the characteristic length of ice rink ) has been analyzed . Finally, measures for improv ing the energy efficiency of the system has been highlighted

PARAMETRIC ANALYSIS OF HEAT PUMP OPERATION FOR SUGAR STORAGE VENTILATION

This paper presents influence of relevant operating parameters to performances of refrigeration devices as part of the technical systems intended for ventilating of industrial storage of refined sugar . For the designed technical ventilation system , using the method of "coupling of performances characteristics of refrigeration plant components ", the effect of evaporation and condensation temperature , as well as temperature and relative humidity of the treated air are analyzed . It was also found quantifiable impact of some relevant parameters on energy consumption

Thermoeconomic analysis of spiral heat exchanger with constant wall temperature

Thermoeconomic analysis of spiral heat exchanger is conducted. Different geometrical parameters, such as outer diameter, plate height, passage gap, etc. are used and varied in a wide range. Detailed thermal and total costs analyses were performed for two spiral heat exchanger with different process fluids (water and thermal oil) with temperature changes, while the wall temperature was kept constant (condensation). The results were shown graphically. It is determined that optimum values of number of entropy generation units correspond to minimum total annual cost. The optimal solution could be found in the recommended range of geometric sizes for defined inlet and outlet temperatures and process fluid-flow rate

COMPARATIVE ANALYSIS OF THREE GENERATIONS OF TRANSCRITICAL CO2 SYSTEMS

The paper analyzed three generations of R744 systems: the basic booster system, the booster system with parallel compression, and the multi ejector system. The aim was to compare these systems from the point of view of efficiency and electricity consumption. The analysis is based on the model with two temperature levels of evaporators –30 °C and –10 °C, and with a total cooling capacity of 250 kW and 150 kW, respectively. The analysis was carried out for the climatic conditions of the city of Belgrade in the summer period when the greatest differences in operation are expected. The results showed that the next system generations achieve savings in electricity consumption for the considered period

Storing apples in ULO atmosphere controlled cold storage

Fruit has a significant place in the total value of agricultural production in Serbia and an increasing amount of fresh fruits has been exported recently. For a more significant placement of fresh food on foreign markets, it is necessary to provide quality protection during transport and storage. Postharvest losses of fresh fruits and vegetables are very high, especially in undeveloped countries. Therefore, modern postharvest technologies, such as modified and controlled atmosphere, are increasingly used to prolong storage life of fresh fruits. ULO (Ultra Low Oxygen) controlled atmosphere has suppressed all other solutions in terms of quality and prolonged storage life (up to 300 days) of apples. In this paper, the optimum conditions and recommended storage regimes for different apple varieties in ULO atmosphere have been reported

Effect of freezing in the industrial conditions on quality of strawberry fruits

Freezing is the method usually used for preserving delicate fruit, because the product tends to maintain its original attributes, i.e., keeping its nutritional properties as close as possible to those of fresh fruit. Strawberry is a widespread and highly demanded fruit, but the fresh fruits are available in a short period of time and the largest amount of strawberry is processed by freezing. The aim of the paper is to determine the effect of process of freezing in the industrial conditions, with precooling, on the relevant parameters of the strawberry quality. The fruits were frozen in the conventional freezing tunnel by cold air temperature of –33 °C until reaching a temperature of –15 °C in the thermal center of the fruits. Packaged frozen fruits were stored in the chamber at –18 °C. In order to determine the changes in strawberry quality, the content of dry matter, total sugars and acids, pH, vitamin C, and sensory quality characteristics were analyzed. Also, quality index of the fresh and frozen strawberry is determined by calculation. The obtained results showed that there were no significant changes in the physicochemical parameters of quality after the freezing of the strawberry fruits. Significant changes are found in the sensory characteristics and the most remarkable is the loss of consistency and firmness of the frozen strawberry. Also, some modified color, taste and aroma of the strawberry fruit have been noticed after freezing in the industrial conditions

THE EFFECT OF FREEZING ON THE QUALITY OF BERRY FRUITS

Berries are a large and economically very important group of fruit. Serbia is not at the top in the production of this fruit, but is at the top in exported quantities of berries. Almost the total amount of berries are exported i n frozen condition. The aim of this study was to analyze the influence of freezing process on the quality and sensory characteristics of berry fruit. Investigation were carried out with the strawberry, raspberry and blackberry fruits. Within the sensory qu ality analysis, special emphasis is placed on maintaining the strength and color of these delicate fruits. As quality parameters, content of total sugar and acid, dry matter content and pH value s of berry fruits were analysed. The content of vitamin C in t he berries, before and after process of freezing, were determined. The obtained results showed that there was no significant changes in chemical quality parameters. Somewhat larger changes was in sensory characteristics, as determined by the loss of streng th and consistency, especially in strawberry fruit