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.

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.

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.

A Copper Microchannel Heat Exchanger for MEMS-Based Waste Heat Thermal Scavenging

2014 ◽  
Author(s):  
E. Borquist ◽  
A. Baniya ◽  
S. Thapa ◽  
D. Wood ◽  
L. Weiss
Keyword(s):  
Heat Exchanger ◽  
Thermal Energy ◽  
Waste Heat ◽  
Heated Surface ◽  
Copper Substrate ◽  
Working Fluid ◽  
Bottom Plate ◽  
Small Scale ◽  
Thermal Source ◽  
Micro Channels

The growing necessity for increased efficiency and sustainability in energy systems such as MEMS devices has driven research in waste heat scavenging. This approach uses thermal energy, which is typically rejected to the surrounding environment, transferred to a secondary device to produce useful power output. This paper investigates a MEMS-based micro-channel heat exchanger (MHE) designed to operate as part of a micro-scale thermal energy scavenging system. Fabrication and operation of the MHE is presented. MHE operation relies on capillary action which drives working fluid from surrounding reservoirs via micro-channels above a heated surface. Energy absorption by the MHE is increased through the use of a working fluid which undergoes phase change as a result of thermal input. In a real-world implementation, the efficiency at which the MHE operates contributes to the thermal efficiency of connected small-scale devices, such as those powered by thermoelectrics which require continual heat transfer. This full system can then more efficiently power MEMS-based sensors or other devices in diverse applications. In this work, the MHE and micro-channels are fabricated entirely of copper with 300μm width channels. Copper electro-deposition onto a copper substrate provides enhanced thermal conductivity when compared to other materials such as silicon or aluminum. The deposition process also increases the surface area of the channels due to porosity. Fabrication with copper produces a robust device, which is not limited to environments where fragility is a concern. The MHE operation has been designed for widespread use in varied environments. The exchanger working fluid is also non-specific, allowing for fluid flexibility for a range of temperatures, depending on the thermal source potential. In these tests, the exchanger shows approximately 8.7 kW/m2 of thermal absorption and 7.6 kW/m2 of thermal transfer for a dry MHE while the wetted MHE had an energy throughput of 8.3 kW/m2. The temperature gradient maintained across the MHE bottom plate and lid is approximately 30 °C for both the dry and wetted MHE tests though overall temperatures were lower for the wetted MHE.

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.

Sizing of an Innovative and Improved Meat Smoking System

2005 ◽  
Vol 1 (4) ◽  
Author(s):  
Denis M Bruneau ◽  
Patrick Sebastian ◽  
Jean-Yves Lecompte ◽  
Antoine Collignan ◽  
Vincent Rochery
Keyword(s):  
Mass Transfer ◽  
Heat Exchanger ◽  
Heat And Mass Transfer ◽  
Power Supply ◽  
Small Scale ◽  
Thermodynamic Efficiency ◽  
Recent Interest ◽  
Cold Source ◽  
Drying Kinetic

There has been recent interest in developing small-scale smoking technologies that respect French sanitary recommendations concerning benzo(a)pyrene deposition on food. The conceptual and embodiment phases of design, and the sizing of a smoker in which this deposition phenomenon is limited are reviewed in this paper. The conceptual phase of design has lead to a process based on the operations of smoking, heating and drying units, using cooled smoke, radiant plates and supplying flows of this cooled smoke directly to the product. For marketing reasons, the power supply is exclusively derived from the combustion of small logs and the smoke comes from sawdust pyrolysis, this smoke being cooled by flowing through a heat exchanger using ice as a cold source. The embodiment phase of design has lead to a versatile system in terms of smoking, heating and drying functionalities. The sizing of this system is based on knowing the drying kinetic of the product in a traditional smoke house (“boucan”); it was performed by estimating heat and mass transfer phenomena occurring between the product and its surroundings. It leads to a kiln having a thermodynamic efficiency close to 13%.

Dynamic Modelling of Small Scale and High Temperature ORC System Using Simulink and CoolProp

2020 ◽  
Author(s):  
Radheesh Dhanasegaran ◽  
Antti Uusitalo ◽  
Teemu Turunen-Saaresti
Keyword(s):  
High Temperature ◽  
Dynamic Model ◽  
High Speed ◽  
Waste Heat ◽  
Fluid Pressure ◽  
Dynamic Modelling ◽  
Working Fluid ◽  
Small Scale ◽  
Condensation Process ◽  
Feed Pump

Abstract In the present work, a dynamic model has been developed for the small-scale high-temperature ORC experimental test rig at the LUT University that utilizes waste heat from a heavy-duty diesel engine exhaust. The experimental facility consists of a high-speed Turbogenerator, heat exchanger components such as recuperator, condenser, and evaporator with a pre-feed pump to boost the working fluid pressure after the condensation process constituting a cycle. The turbogenerator consists of a supersonic radial-inflow turbine, a barske type main-feed pump, and a permanent magnet type generator components connected on a single shaft. Octamethyltrisiloxane (MDM) is the chosen organic working fluid in this cycle. Matlab-Simulink environment along with the open-source thermodynamic and transport database Cool-Prop has been chosen for calculating the thermodynamic properties of the dynamic model. A functional parameter approach has been followed for modeling each block component by predefined input and output parameters, aimed at modeling the performance characteristics with a limited number of inputs for both design and off-design operations of the cycle. The dynamic model is validated with the experimental data in addition to the investigation of exhaust gas mass flow regulation that establishes a control strategy for the dynamic model.

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