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.

Small-Scale Thermal Energy Harvester With Copper Foams and Thermal Energy Storage

2015 ◽  
Author(s):  
S. Shrestha ◽  
A. Hays ◽  
S. Thapa ◽  
D. Wood ◽  
D. Bailey ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Heat Exchanger ◽  
Phase Change ◽  
Thermal Energy ◽  
Operating Temperature ◽  
Heat Pipes ◽  
Paraffin Wax ◽  
Working Fluid ◽  
Small Scale ◽  
Copper Tubing

This article investigates the use of advanced, high porosity thermally conductive foams and a thermal energy storage (TES) device for small scale thermal energy harvesting. In final application, it may be employed in various real world situations that include existing systems like thermoelectric generators (TEGs) and thermal scavenging systems that provide power output from freely available thermal sources. Experimental tests were conducted using various porosity metallic copper foams ranging from 85 % to 89 % porosity. Copper foams were selected to serve as the heat exchanger innards and examined for several key attributes. These included the ability of the foams to yield capillary action with working fluids like water or 3M™ HFE7200. Thermal energy absorption by the exchanger to the working fluid was also monitored. These results were compared to other exchangers based on capillary channel fabrication techniques as previously reported by the research team. Full characterization was based on operating temperature, measured thermal input, mass transfer rate, and heat transfer capability. Preliminary investigation of a matching, small-scale TES unit designed to integrate with the heat exchanger and a future thermoelectric for energy harvesting application was also conducted. Thermal storage was accomplished via solid-liquid phase change of a paraffin wax within the TES device forming a so-called “thermal battery.” In a final design, the TES includes what is defined by thermodynamics as heat pipes. The integrations of several heat pipes, made of copper tubing and filled with working fluid, mounted vertically and immersed in the wax medium will transfer heat to the wax by means of thermal conductivity and phase transition. This represents a first of its kind in this small-scale, thermal harvesting application. The specific tests performed in this initial work included one TES unit filled with a paraffin wax medium and a second that contained several copper vertically placed tubes surrounded by the paraffin wax. The overall thermal conductivity of the phase change medium (wax) was investigated for both constructions as was the ability of each to absorb thermal energy directly. Results indicated capillary action of the working fluid was possible via incorporation of copper foams within the heat exchanger. Maximum heat flux observed in exchanger tests was 0.27 kW/m2 given an operating temperature of 76.6 °C and 2.5W thermal input. Thermal storage tests indicated a maximum thermal capture rate of 0.91 W and phase change material thermal conductivity of 1.00 W/mK for the TES device constructed with copper tubing innards. This compared favorably to the baseline wax conductivity of approximately 0.32 W/mK. Future efforts will fully incorporate both the heat exchanger and matching TES device for a complete harvesting and thermal capture system. The ability of the exchanger to provide thermal energy for storage to the “thermal battery” will be monitored.

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.

scholarly journals Design and Operational Control Strategy for Optimum Off-Design Performance of an ORC Plant for Low-Grade Waste Heat Recovery

Energies ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 5846
Author(s):  
Fabio Fatigati ◽  
Diego Vittorini ◽  
Yaxiong Wang ◽  
Jian Song ◽  
Christos N. Markides ◽  
...  
Keyword(s):  
Power Unit ◽  
Control Strategy ◽  
Heat Recovery ◽  
Waste Heat Recovery ◽  
Waste Heat ◽  
Combustion Engine ◽  
Working Fluid ◽  
Thermal Source ◽  
Low Grade ◽  
Gear Pump

The applicability of organic Rankine cycle (ORC) technology to waste heat recovery (WHR) is currently experiencing growing interest and accelerated technological development. The utilization of low-to-medium grade thermal energy sources, especially in the presence of heat source intermittency in applications where the thermal source is characterized by highly variable thermodynamic conditions, requires a control strategy for off-design operation to achieve optimal ORC power-unit performance. This paper presents a validated comprehensive model for off-design analysis of an ORC power-unit, with R236fa as the working fluid, a gear pump, and a 1.5 kW sliding vane rotary expander (SVRE) for WHR from the exhaust gases of a light-duty internal combustion engine. Model validation is performed using data from an extensive experimental campaign on both the rotary equipment (pump, expander) and the remainder components of the plant, namely the heat recovery vapor generator (HRVH), condenser, reservoirs, and piping. Based on the validated computational platform, the benefits on the ORC plant net power output and efficiency of either a variable permeability expander or of sliding vane rotary pump optimization are assessed. The novelty introduced by this optimization strategy is that the evaluations are conducted by a numerical model, which reproduces the real features of the ORC plant. This approach ensures an analysis of the whole system both from a plant and cycle point of view, catching some real aspects that are otherwise undetectable. These optimization strategies are considered as a baseline ORC plant that suffers low expander efficiency (30%) and a large parasitic pumping power, with a backwork ratio (BWR) of up to 60%. It is found that the benefits on the expander power arising from a lower permeability combined with a lower energy demand by the pump (20% of BWR) for circulation of the working fluid allows a better recovery performance for the ORC plant with respect to the baseline case. Adopting the optimization strategies, the average efficiency and maximum generated power increase from 1.5% to 3.5% and from 400 to 1100 W, respectively. These performances are in accordance with the plant efficiencies found in the experimental works in the literature, which vary between 1.6% and 6.5% for similar applications. Nonetheless, there is still room for improvement regarding a proper design of rotary machines, which can be redesigned considering the indications resulting from the developed optimization analysis.

System and component modelling of a low temperature solar thermal energy conversion cycle

2013 ◽  
Vol 24 (4) ◽  
pp. 51-62
Author(s):  
Shadreck M. Situmbeko ◽  
Freddie L. Inambao
Keyword(s):  
Low Temperature ◽  
Solar Energy ◽  
Thermal Energy ◽  
Electrical Power ◽  
Solar Thermal ◽  
Working Fluid ◽  
Small Scale ◽  
Solar Thermal Energy ◽  
Solar Field ◽  
Conversion Technology

Solar thermal energy (STE) technology refers to the conversion of solar energy to readily usable energy forms. The most important component of a STE technology is the collectors; these absorb the shorter wavelength solar energy (400-700nm) and convert it into usable, longer wavelength (about 10 times as long) heat energy. Depending on the quality (temperature and intensity) of the resulting thermal energy, further conversions to other energy forms such as electrical power may follow. Currently some high temperature STE technologies for electricity production have attained technical maturity; technologies such as parabolic dish (commercially available), parabolic trough and power tower are only hindered by unfavourable market factors including high maintenance and operating costs. Low temperature STEs have so far been restricted to water and space heating; however, owing to their lower running costs and almost maintenance free operation, although operating at lower efficiencies, may hold a key to future wider usage of solar energy. Low temperature STE conversion technology typically uses flat plate and low concentrating collectors such as parabolic troughs to harness solar energy for conversion to mechanical and/or electrical energy. These collector systems are relatively cheaper, simpler in construction and easier to operate due to the absence of complex solar tracking equipment. Low temperature STEs operate within temperatures ranges below 300oC. This research work is geared towards developing feasible low temperature STE conversion technology for electrical power generation. Preliminary small-scale concept plants have been designed at 500Wp and 10KWp. Mathematical models of the plant systems have been developed and simulated on the EES (Engineering Equation Solver) platform. Fourteen candidate working fluids and three cycle configurations have been analysed with the models. The analyses included a logic model selector through which an optimal conversion cycle configuration and working fluid mix was established. This was followed by detailed plant component modelling; the detailed component model for the solar field was completed and was based on 2-dimensional segmented thermal network, heat transfer and thermo fluid dynamics analyses. Input data such as solar insolation, ambient temperature and wind speed were obtained from the national meteorology databases. Detailed models of the other cycle components are to follow in next stage of the research. This paper presents findings of the system and solar field component.

Sintering of Solid Particulates Under Elevated Temperature and Pressure in Large Storage Bins for Thermal Energy Storage

2014 ◽  
Author(s):  
R. C. Knott ◽  
D. L. Sadowski ◽  
S. M. Jeter ◽  
S. I. Abdel-Khalik ◽  
H. A. Al-Ansary ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Size Distribution ◽  
Thermal Energy ◽  
Solar Power ◽  
Physical Characteristics ◽  
Working Fluid ◽  
Concentrated Solar Power ◽  
Power Cycle ◽  
Solid Particulates ◽  
Storage Bins

This research is a part of the DOE-funded SunShot project on “High Temperature Falling Particle Receiver.” Storing thermal energy using solid particulates is a way to mitigate the time of day dependency of concentrated solar power. Small particles may be stored easily, and can be used as a heat transfer medium to transfer heat to the power cycle working fluid through a heat exchanger. This study examines the physical characteristics of solid particulates of different materials kept inside large storage containers. Particle behavior at the expected high temperatures of the concentrated solar power cycle combined with the elevated pressure experienced within the storage container must be evaluated to assess the impact on their physical properties and ensure that the particles would not sinter thereby impacting flow through the system components particularly the receiver and heat exchanger. Sintering is a process of fusing two or more particles together to form a larger agglomerate. In the proposed concentrated solar power tower design, particles will experience temperatures from 600°C to 1000°C. The increase in temperature changes the physical characteristics of the particle, along with any impurities that could form particle to particle bonds. In addition, the hydrostatic pressure exerted on particles stored inside a storage unit increases the probability of sintering. Thus, it is important to examine the characteristics of particles under elevated temperatures and pressures. The experimental procedure involves heating particulates of a known mass and size distribution to temperatures between 600°C and 1000°C inside a crucible. As the temperature is held constant, the particulate sample is pressed upon by a piston pushing into the crucible with a known constant pressure. This process is repeated for different temperatures and pressures for varying lengths of time. The resulting particulates are cooled, and their size distribution is measured to determine the extent of sintering, if any, during the experiment. The particulates tested include various types of sand, along with alumina particles. The data from this experiment will allow designers of storage bins for the solid particulates to determine when significant sintering is expected to occur.

Design and Optimization of Waste Heat Recovery Unit Using Carbon Dioxide as Cooling Fluid

2014 ◽  
Author(s):  
Geir Skaugen ◽  
Harald T. Walnum ◽  
Brede A. L. Hagen ◽  
Daniel P. Clos ◽  
Marit J. Mazzetti ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Heat Recovery ◽  
Waste Heat Recovery ◽  
Waste Heat ◽  
Working Fluid ◽  
Design And Optimization ◽  
Power Cycle ◽  
Turbine Efficiency ◽  
Recovery Unit ◽  
Process Simulations

This paper describes design and optimization of a Waste Heat Recovery Unit (WHRU) for a power cycle which uses CO2 as a working fluid. This system is designed for offshore installation to increase gas turbine efficiency by recovering waste heat from the exhaust for production of additional power. Due to severe constraints on weight and space in an offshore setting, it is essential to reduce size and weight of the equipment to a minimum. Process simulations are performed to optimize the geometry of the WHRU using different objective functions and thermal-hydraulic models. The underlying heat exchanger model used in the simulations is an in-house model that includes the calculation of weight and volume for frame and structure for the casing in addition to the thermal-hydraulic performance of the heat exchanger core. The results show that the for a set of given process constraints, optimization with respect to minimum total weight or minimum core weight shown similar results for the total installed weight, although the design of heat exchanger differs. The applied method also shows how the WHRU geometry can be optimized for different material combinations.

scholarly journals Análisis termodinámico del intercambiador de calor de un sistema ORC para el aprovechamiento de calor residual en procesos industriales

2019 ◽  
pp. 27-33
Author(s):  
Uzziel Caldiño-Herrera ◽  
Delfino Cornejo-Monroy ◽  
Shehret Tilvaldyev ◽  
José Omar Dávalos-Ramírez
Keyword(s):  
Energy Source ◽  
Heat Exchanger ◽  
Waste Heat ◽  
Organic Rankine Cycle ◽  
Industrial Process ◽  
Rankine Cycle ◽  
Energy System ◽  
Operating Conditions ◽  
Maximum Efficiency ◽  
Working Fluid

In this paper we present the implementation of a system based on organic Rankine cycle coupled to a heat discharge of an industrial process. Waste heat is used as an energy source input to the system, which uses this energy to evaporate an organic fluid and expand it in a turbine, where mechanical power is produced. The system consists of 4 processes and the heat exchanger is specially analyzed. According to the availability of heat energy, the heat exchanger was designed to achieve the maximum efficiency in the energy system. Likewise, the maximum thermal efficiency of the ORC system is calculated as a function of the available energy, the energy source temperature and the available mass flow rate. By these calculations, the working fluid and the suitable operating conditions were selected through a thermodynamic analysis.

scholarly journals Addressing Industrial Waste Heat Supply Variability With Organic Rankine Cycle Systems Incorporating Thermal Energy Storage

2021 ◽  
Author(s):  
Bipul Krishna Saha ◽  
Basab Chakraborty ◽  
Rohan Dutta
Keyword(s):  
Power Generation ◽  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Power Plants ◽  
Waste Heat ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Working Fluid ◽  
Low Grade

Abstract Industrial low-grade waste heat is lost, wasted and deposited in the atmosphere and is not put to any practical use. Different technologies are available to enable waste heat recovery, which can enhance system energy efficiency and reduce total energy consumption. Power plants are energy-intensive plants with low-grade waste heat. In the case of such plants, recovery of low-grade waste heat is gaining considerable interest. However, in such plants, power generation often varies based on market demand. Such variations may adversely influence any recovery system's performance and the economy, including the Organic Rankine Cycle (ORC). ORC technologies coupled with Cryogenic Energy Storage (CES) may be used for power generation by utilizing the waste heat from such power plants. The heat of compression in a CES may be stored in thermal energy storage systems and utilized in ORC or Regenerative ORC (RORC) for power generation during the system's discharge cycle. This may compensate for the variation of the waste heat from the power plant, and thereby, the ORC system may always work under-designed capacity. This paper presents the thermo-economic analysis of such an ORC system. In the analysis, a steady-state simulation of the ORC system has been developed in a commercial process simulator after validating the results with experimental data for a typical coke-oven plant. Forty-nine different working fluids were evaluated for power generation parameters, first law efficiencies, purchase equipment cost, and fixed investment payback period to identify the best working fluid.

A Microboiler: Waste Heat to Power Scavenging System

2014 ◽  
Author(s):  
S. Thapa ◽  
E. Borquist ◽  
A. Baniya ◽  
J. Fang ◽  
D. Wood ◽  
...  
Keyword(s):  
Waste Heat ◽  
Heated Surface ◽  
Electrical Power ◽  
Large Mass ◽  
Working Fluid ◽  
Thin Glass ◽  
Miniature Device ◽  
Useful Power ◽  
Power Inputs ◽  
Recovery Approach

This paper presents the detailed fabrication and baseline operational characterization of a miniature device capable of recovering waste heat for power. Waste heat to power is the process of scavenging heat from a large process as a result of mechanical inefficiencies and using that heat to generate useful power. To address this waste heat to power recovery approach, a MEMS based microboiler has been investigated in this work which is capable of capturing waste heat. The microboiler consists of a micro fabricated boilerplate and a steamdome. The boilerplate has been designed with capillary channels capable of driving fluid flow from the surrounding reservoirs to the heated surface, thus eliminating the need of an electrically powered flow pump. The working fluid undergoes phase change inside the enclosed central steamdome attached atop the boilerplate. This pressurized vapor can be made available to another MEMS device such as PZT membrane capable of generating mechanical or electrical power. In this way, the discarded heat from the larger process can be utilized to generate power output. In contrast to the previous work, a thick acrylic steamdome has been replaced with a thin glass steamdome to minimize premature condensation of vapor due to heat loss via large mass. The tests were performed on the microboiler with the input powers of 1.8 W and 2.7 W and the comparisons of the results were carried out using a simulation model. The average temperatures at the top of the boilerplate were 106° C and 144° C for the power inputs of 1.8 W and 2.7 W, respectively. The available powers at the top of the boilerplate via heat conduction were 1.14 W and 1.72 W for the power inputs of 1.8 W and 2.7 W for the supplied powers of 1.8 W and 2.7 W, respectively. With these known available power throughputs and the heat of vaporization of the future working fluid, the calculated maximum mass flow rates were 13.6 mg/s and 9.12 mg/s, respectively.

scholarly journals Experimental Investigation of a Small-Scale ORC Power Plant Using a Positive Displacement Expander with and without a Regenerator

Energies ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1452 ◽  
Author(s):  
Collings ◽  
Mckeown ◽  
Wang ◽  
Yu
Keyword(s):  
Heat Exchanger ◽  
Power Plants ◽  
Large Scale ◽  
Internal Heat ◽  
Expansion Ratio ◽  
Operating Conditions ◽  
Working Fluid ◽  
Small Scale ◽  
Regenerative Heat ◽  
Positive Displacement

While large-scale ORC power plants are a relatively mature technology, their application to small-scale power plants (i.e., below 10 kW) still encounters some technical challenges. Positive displacement expanders are mostly used for such small-scale applications. However, their built-in expansion ratios are often smaller than the expansion ratio required for the maximum utilisation of heat sources, leading to under expansion and consequently higher enthalpy at the outlet of the expander, and ultimately resulting in a lower thermal efficiency. In order to overcome this issue, one possible solution is to introduce an internal heat exchanger (i.e., the so-called regenerator) to recover the enthalpy exiting the expander and use it to pre-heat the liquid working fluid before it enters the evaporator. In this paper, a small-scale experimental rig (with 1-kW rated power) was designed and built that is capable of switching between regenerative and non-regenerative modes, using R245fa as the working fluid. It has been tested under various operating conditions, and the results reveal that the regenerative heat exchanger can recover a considerable amount of heat when under expansion occurs, increasing the cycle efficiency.

Sign in / Sign up

Export Citation Format

Share Document