Evaluation of Heat and Mass Transfer Models for Sizing Low-Temperature Kalina Cycle Microchannel Condensers

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Brian M. Fronk ◽  
Kyle R. Zada
Keyword(s):  
Mass Transfer ◽  
Heat Exchanger ◽  
Low Temperature ◽  
Heat And Mass Transfer ◽  
Heat Exchangers ◽  
Waste Heat ◽  
Working Fluid ◽  
Kalina Cycle ◽  
Ammonia Water ◽  
Transfer Models

Waste heat driven ammonia/water Kalina cycles have shown promise for improving the efficiency of electricity production from low-temperature reservoirs (T < 150 °C). However, there has been limited application of these systems to utilize widely available, disperse, waste heat streams for smaller scale power production (1–10 kWe). Factors limiting increased deployment of these systems include large, costly heat exchangers, and concerns over safety of the working fluid. The use of mini- and microchannel (D < 1 mm) heat exchangers has the potential to decrease system size and material cost, while also reducing the working fluid inventory, enabling penetration of Kalina cycles into these new markets. However, accurate methods of predicting the heat and mass transfer in microscale geometries must be available for designing and optimizing these compact heat exchangers. In the present study, the effect of different heat and mass transfer models on the calculated Kalina cycle condenser size is investigated at representative system conditions. A detailed heat exchanger model for a liquid-coupled microchannel ammonia/water condenser is developed. The heat exchanger is sized using different predictive methods to provide the required heat transfer area for a 1 kWe Kalina system with a source and sink temperature of 150 °C and 20 °C, respectively. The results show that for the models considered, predicted heat exchanger size can vary by up to 58%. Based on prior experimental results, a nonequilibrium approach is recommended to provide the most accurate, economically sized ammonia/water condenser.

Application of Microchannel Condensers for Small Scale Kalina Waste Heat Recovery Systems

2015 ◽  
Author(s):  
Brian M. Fronk ◽  
Kyle R. Zada
Keyword(s):  
Mass Transfer ◽  
Heat Exchanger ◽  
Heat And Mass Transfer ◽  
Heat Exchangers ◽  
Waste Heat ◽  
Fluid Pressure ◽  
Working Fluid ◽  
Small Scale ◽  
Water Mixture ◽  
Ammonia Water

Thermally driven ammonia/water Kalina cycles have shown some promise for improving the efficiency of electricity production from low temperature reservoirs (T < 200°C). However, there has been limited application of these systems to exploiting widely available, disperse, waste heat streams for smaller scale power production (∼ 1 kWe). Factors limiting increased deployment of these systems include large, costly heat exchangers, and concerns over safety of the working fluid. The use of mini and microchannel (D < 1 mm) heat exchangers has the potential to decrease system size and cost, while also reducing the working fluid inventory, enabling penetration of Kalina cycles into these new markets. To demonstrate this potential, a detailed heat exchanger model for a liquid-coupled microchannel ammonia/water condenser is developed. The heat exchanger is sized to provide the required heat transfer area for a 1 kWe Kalina system with a source and sink temperature of 150° and 20°C, respectively. An additional constraint on heat exchanger size is that the fluid pressure loss is maintained below some threshold value. A parametric analysis is conducted to assess the effect of different correlations/models for predicting the underlying heat and mass transfer and pressure drop of the ammonia/water mixture on the calculated heat exchanger area. The results show that accurately minimizing the size of the overall system is dependent upon validated zeotropic heat and mass transfer models at low mass fluxes and in small channels.

A Fully Wet and Fully Dry Tiny Circular Fin Method for Heat and Mass Transfer Characteristics for Plain Fin-and-Tube Heat Exchangers Under Dehumidifying Conditions

2006 ◽  
Vol 129 (9) ◽  
pp. 1256-1267 ◽  
Author(s):  
Worachest Pirompugd ◽  
Chi-Chuan Wang ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Exchanger ◽  
Heat And Mass Transfer ◽  
Heat Exchangers ◽  
Heat Transfer Characteristic ◽  
Transfer Characteristic ◽  
Tube Heat Exchanger ◽  
Mass Transfer Characteristic ◽  
Transfer Characteristics

This study proposes a new method, namely the “fully wet and fully dry tiny circular fin method,” for analyzing the heat and mass transfer characteristics of plain fin-and-tube heat exchangers under dehumidifying conditions. The present method is developed from the tube-by-tube method proposed in the previous study by the same authors. The analysis of the fin-and-tube heat exchangers is carried out by dividing the heat exchanger into many tiny segments. A tiny segment will be assumed with fully wet or fully dry conditions. This method is capable of handling the plain fin-and-tube heat exchanger under fully wet and partially wet conditions. The heat and mass transfer characteristics are presented in dimensionless terms. The ratio of the heat transfer characteristic to mass transfer characteristic is also studied. Based on the reduced results, it is found that the heat transfer and mass transfer characteristics are insensitive to changes in fin spacing. The influence of the inlet relative humidity on the heat transfer characteristic is rather small. For one and two row configurations, a considerable increase of the mass transfer characteristic is encountered when partially wet conditions take place. The heat transfer characteristic is about the same in fully wet and partially wet conditions provided that the number of tube rows is equal to or greater than four. Correlations are proposed to describe the heat and mass characteristics for the present plain fin configuration.

scholarly journals The influence of airflow on the effectiveness of rotary heat exchangers operating under high-speed rotor conditions

2019 ◽  
Vol 116 ◽  
pp. 00032
Author(s):  
Paulina Kanaś ◽  
Andrzej Jedlikowski ◽  
Sergey Anisimov ◽  
Borys Vager
Keyword(s):  
Mass Transfer ◽  
Heat Exchanger ◽  
Heat And Mass Transfer ◽  
Heat Exchangers ◽  
Heat Recovery ◽  
High Speed ◽  
Airflow Rate ◽  
Sharp Drop ◽  
Transfer Processes ◽  
Mass Transfer Processes

The paper presents an analysis of heat and mass transfer processes occurring inside the rotary heat exchanger operating under high-speed rotor conditions for different values of the airflow rate. For this purpose the original mathematical α-model was used. Conducted computer simulations allowed to determine the influence of Number of Transfer Units (NTU) of airflow on the temperature effectiveness as well as on the distribution of different active heat and mass transfer zones: “dry”, “wet” and “frost”. It was found that the increase of the values of NTU strictly affects the increase of the effectiveness of heat recovery. Another issue emerging from this study is the fact that in the certain range of low values of NTU there is no “dry” area created. It was established that at low values of NTU (NTU≈1) “frost” area extremum and sharp drop in the “frost” area accumulation are observed.

Heat and mass transfer in low-temperature heat exchanger pipes

1972 ◽  
Vol 22 (5) ◽  
pp. 558-561
Author(s):  
L. L. Vasil'ev ◽  
L. P. Grakovich ◽  
S. V. Konev
Keyword(s):  
Mass Transfer ◽  
Heat Exchanger ◽  
Low Temperature ◽  
Heat And Mass Transfer ◽  
Temperature Heat

scholarly journals Investigation of effect of heat exchanger size on power output in low-temperature difference Stirling engines

2021 ◽  
Vol 313 ◽  
pp. 03002
Author(s):  
Linda Hasanovich ◽  
David Nobes
Keyword(s):  
Heat Exchanger ◽  
Low Temperature ◽  
Power Output ◽  
Heat Exchangers ◽  
Waste Heat ◽  
Significant Loss ◽  
Stirling Engine ◽  
Dead Volume ◽  
Optimal Geometry ◽  
Stirling Engines

The Stirling engine is capable of converting any source of thermal energy into kinetic energy, which makes it an attractive option for utilizing low-temperature sources such as geothermal or waste heat below 100 °C. However, at these low temperatures, the effects of losses are proportionally higher due to the lower thermal potential available. One such significant loss is excess dead volume, wherein a significant contributor is the heat exchangers. The heat exchangers must be selected to optimize power output by minimizing the dead volume loss while maximizing the heat transfer to and from the engine. To better understand what the optimal geometry of the heat exchanger components is, a Stirling engine is modelled using a third-order commercial modelling software (Sage) and trends of engine properties of power, temperature, and pressure for different heat exchanger geometries are observed. The results indicate that there is an optimum heat exchanger volume and geometry for low temperature Stirling engines. This optimum is also affected by other engine properties, such as regenerator size and engine speed. These results provide insight into the optimal geometry of these components for low-temperature Stirling engines, as well as providing design guidance for future engines to be built.

Influence of Pressure on the Performance of Heat Exchangers in Ammonia-Water Based Power Cycles

2012 ◽  
Vol 229-231 ◽  
pp. 1085-1089 ◽  
Author(s):  
Kyoung Hoon Kim ◽  
Chul Ho Han
Keyword(s):  
Power Generation ◽  
Heat Exchangers ◽  
Waste Heat ◽  
Inlet Pressure ◽  
Working Fluid ◽  
Pinch Point ◽  
Ammonia Water ◽  
Temperature Distributions ◽  
Turbine Inlet ◽  
Water Based

Recently the power generation systems using ammonia-water binary mixture as a working fluid have been attracted much attention for efficient conversion of low-temperature waste heat sources to useful energy forms. In this work, ammonia-water based Rankine (AWR) and regenerative Rankine (AWRR) power generation cycles are comparatively analyzed by investigating the effects of turbine inlet pressure on the performances of heat exchangers in AWR and AWRR systems. Temperature distributions of fluid streams in the heat exchanging devices are closely examined at different levels of turbine inlet pressure under the conditions that the minimum temperature difference of hot and cold streams reaches the prescribed pinch point. Results show that the position of pinch point and temperature distributions are sensitively affected by varying turbine inlet pressure, which might be the most important design consideration in the power systems using a binary working fluid.

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