An Integrated Design Support Environment for a Micro-Scale Portable Absorption Cooling System

2004 ◽  
Author(s):  
Brian J. Daniels ◽  
Ashutosh Ballal ◽  
Ping Ge ◽  
Kevin Drost
Keyword(s):  
Thermal Efficiency ◽  
Cooling System ◽  
Integrated Design ◽  
System Level ◽  
Cooling Systems ◽  
Design Support ◽  
Trade Off ◽  
Micro Scale ◽  
Study Results ◽  
Design Support Environment

Portable cooling systems play an important role in assisting human operations in unfriendly environments, such as soldiers continuously working in a desert area for long hours. Typical cooling system designs utilizing a vapor compression cycle driven by electrical power usually have high weights due to batteries and as a result, compromise the effectiveness of the portable cooling system. A self-contained absorption cycle cooling system design based on micro-scale thermal technology has demonstrated unique advantages in minimizing system weight while providing reasonable thermal efficiency. This system adopts a heat actuated absorption/desorption thermal cycle to raise the pressure of the refrigerant vapor without a heavy battery load. Design challenges exist: 1) multi-physics considerations when integrating the thermodynamic and transport models for the heat pump and peripheral component devices; 2) trade-off among multi-functional design requirements of system weight and thermal efficiency, using the inputs of cooling load, heat rejection temperature, and heat transfer characteristics based on the micro-channel geometry. No existing design automation tools are available on the market to directly support these design tasks. In this work, physics-based system-level models are developed and validated against state-of-the-art prototypes. The use of these models is demonstrated through the design of a 150-watt portable cooling system, typically used by the military in desert training. The system modeling methodology is implemented in Java as a part of an Integrated Design Support Environment, and has been used to generate trade-off study results. These results show that the current implementation is effective, and is a significant step toward a complete integrated design support environment to analyze and synthesize high-quality micro-scale portable cooling systems.

Relative Cooling: Part II — Design Considerations and Efficiency

2001 ◽  
Author(s):  
Sandu Constantin ◽  
Dan Brasoveanu
Keyword(s):  
Gas Turbine ◽  
Thermal Efficiency ◽  
Cooling System ◽  
High Reliability ◽  
Difficult Problem ◽  
Turbine Engines ◽  
Air Cooling ◽  
Gas Turbine Engines ◽  
Coolant Pump ◽  
Cooling Systems

Abstract Cooling systems with liquid for gas turbine engines that use the relative motion of the engine stator with respect to the rotor for actuating the coolant pump can be encapsulated within the engine rotor. In this manner, the difficult problem of sealing stator/rotor interfaces at high temperature, pressure and relative velocity is circumvented. A first generation of such cooling systems could be manufactured using existing technologies and would boost the thermal efficiency of gas turbine engines by more than 2% compared to recent designs that use advanced air-cooling methods. Later, relative cooling systems could increase the thermal efficiency of gas turbine engines by 8%–11% by boosting the temperatures at turbine inlet to stoichiometric levels and recovering most of the heat extracted from turbine during cooling. The appreciated high reliability of this cooling system will allow widespread use for aerospace propulsion.

Relative Cooling With Liquid for Gas Turbines: Part I — A Solution for Exceeding 2000 K at Turbine Inlet

2001 ◽  
Author(s):  
Sandu Constantin ◽  
Dan Brasoveanu
Keyword(s):  
Thermal Efficiency ◽  
Gas Turbines ◽  
Cooling System ◽  
Turbine Blades ◽  
Air Cooling ◽  
Liquid Cooling ◽  
Cooling Systems ◽  
Turbine Inlet ◽  
Cooling Methods ◽  
Current Operating

Abstract The thermal efficiency of gas turbines is critically dependent on the temperature of burnt gases at turbine inlet, the higher this temperature the higher the efficiency. Stochiometric combustion would provide maximum efficiency, but in the absence of an internal cooling system, turbine blades cannot tolerate gas temperatures that exceed 1300 K. Therefore, for this temperature, the thermal efficiency of turbine engine is 40% less than theoretical maximum. Conventional air-cooling techniques of turbine blades allow inlet temperatures of about 1500 K on current operating engines yielding thermal efficiency gains of about 6%. New designs, that incorporate advanced air-cooling methods allows inlet temperatures of 1750–1800 K, with a thermal efficiency gain of about 6% relative to current operating engines. This temperature is near the limit allowed by air-cooling systems. Turbine blades can be cooled with air taken from the compressor or with liquid. Cooling systems with air are easier to design but have a relatively low heat transfer capacity and reduce the efficiency of the engine. Some cooling systems with liquid rely on thermal gradients to promote re-circulation from the tip to the root of turbine blades. In this case, the flow and cooling of liquid are restricted. For best results, cooling systems with liquid should use a pump to re-circulate the coolant. In the past, designers tried to place this pump on the engine stator and therefore were unable to avoid high coolant losses because it is impossible to reliably seal the stator-rotor interface. Therefore it was assumed that cooling systems with liquid could not incorporate pumps. This is an unwarranted assumption as shown studying the system in a moving frame of reference that is linked to the rotor. Here is the crucial fact overlooked by previous designers. The relative motion of engine stator with respect to the rotor is sufficient to motivate a cooling pump. Both the pump and heat exchange system that is required to provide rapid cooling of liquid with cold ambient air, could be located within the rotor. Therefore, the entire cooling system can be encapsulated within the rotor and the sealing problem is circumvented. Compared to recent designs that use advanced air-cooling methods, such a liquid cooling system would increase the thermal efficiency by 8%–11% because the temperatures at turbine inlet can reach stoichiometric levels and most of the heat extracted from turbine during cooling is recuperated. The appreciated high reliability of the system will permit a large applicability in aerospace propulsion.

Exceeding 2000 K at Turbine Inlet: Relative Cooling With Liquid for Gas Turbines — Integrated Systems

2003 ◽  
Author(s):  
Sandu Constantin ◽  
Dan Brasoveanu
Keyword(s):  
Gas Turbine ◽  
Relative Motion ◽  
Thermal Efficiency ◽  
Gas Turbines ◽  
State Of The Art ◽  
Cooling System ◽  
Ambient Air ◽  
Air Cooling ◽  
Cooling Systems ◽  
Turbine Inlet

Thermal efficiency of gas turbines is critically dependent on temperature of burnt gases at turbine inlet, the higher this temperature the higher the efficiency. Stochiometric combustion would provide maximum efficiency, but in the absence of an internal cooling system, turbine blades cannot tolerate gas temperatures exceeding 1300 K. This temperature yields a low thermal efficiency, about 15% below the level provide by stoicthiometric combustion. Conventional engines rely on air for blade and disk cooling and limit temperature at turbine inlet to about 1500 K. These engines gain about 3% compared to non-cooled designs. Gas turbines with state of the art air-cooling systems reach up to 1700–1750 K, boosting thermal efficiency by another 2–3%. These temperatures are near the limit allowed by air-cooling systems. Cooling systems with air are easier to design, but air has a low heat transfer capacity, and compressor air bleeding lowers the overall efficiency of engines (less air remains available for combustion). In addition, these systems waste most of the heat extracted from turbine for cooling. In principle, gas turbines could be cooled with liquid. Half a century ago, designers tried to place the pump for coolant recirculation on the engine stator. Liquid was allowed to boil inside the turbine. Seals for parts in relative motion cannot prevent loss of superheated vapors, therefore these experiments failed. To circumvent this problem, another design relied on thermal gradients to promote recirculation from blade tip to root. Liquid flow and cooling capacity were minute. Therefore it was assumed that liquid couldn’t be used for gas turbine cooling. This is an unwarranted assumption. The relative motion between engine stator and rotor provides abundant power for pumps placed on the rotor. The heat exchanger needed for cooling the liquid with ambient air could also be embedded in the rotor. In fact, the entire cooling system can be encapsulated within the rotor. In this manner, the sealing problem is circumvented. Compared to state of the art air-cooling methods, such a cooling system would increase thermal efficiency of any gas turbine by 6%–8%, because stoichimoetric fuel-air mixtures would be used (maybe even with hydrogen fuel). In addition, these systems would recuperate most of the heat extracted from turbine for cooling, are expected to be highly reliable and to increase specific power of gas turbines by 400% to 500%.

Relative Cooling System: Design and Efficiency

2003 ◽  
Author(s):  
Sandu Constantin ◽  
Dan Brasoveanu
Keyword(s):  
Thermal Efficiency ◽  
Gas Turbines ◽  
First Generation ◽  
Cooling System ◽  
High Reliability ◽  
Weight Ratio ◽  
Difficult Problem ◽  
Air Cooling ◽  
Cooling Systems ◽  
Aerospace Applications

Cooling systems with liquid for gas turbines that use the relative motion of engine stator with respect to rotor have been called relative cooling systems. This motion actuates the pump for liquid recirculation and the system is encapsulated within the engine rotor. In this manner, the difficult problem of sealing stator/rotor interfaces at high temperature, pressure and relative velocity is circumvented. A first generation of such systems could be manufactured using existing technologies and would boost thermal efficiency of gas turbines by more than 3% compared to the most advanced air-cooling engines. In the end, relative systems would boost temperatures at turbine inlet to stoichiometric levels and therefore increase thermal efficiency of gas turbines by about 8%. Such systems would recover most heat extracted from turbine for cooling and increase the power to size and power to weight ratio of all gas turbines. The appreciated high reliability of this cooling relies on encapsulation within the rotor and will allow widespread use in both ground and aerospace applications.

Micro- and Nano- Technologies: Roadmap Enabling More Compact, Lightweight Thermoelectric Power Generation and Cooling Systems

2011 ◽  
Author(s):  
Terry J. Hendricks
Keyword(s):  
Heat Transfer ◽  
Power Generation ◽  
High Temperature ◽  
System Performance ◽  
Energy Recovery ◽  
Cooling System ◽  
System Level ◽  
Cooling Systems ◽  
Thermal Transfer ◽  
Micro Technology

Advanced thermoelectric (TE) energy recovery and cooling systems have critical benefits in transportation, industrial process, and military applications because of rising or uncertain energy costs and subsequent need for energy efficiency, geopolitical uncertainties impacting basic energy supplies worldwide, and the need for electrified, distributed cooling and heating systems in automotive applications. Advanced TE energy recovery and cooling technologies will require high-performance heat transfer characteristics to achieve system performance targets and requirements. However, TE energy recovery systems generally have high-temperature thermal transfer requirements (i.e., as high as 750–800 °C), while TE cooling systems require low temperature thermal transfer (i.e., 25 °C – 100 °C). Investigations have compared system power and cooling benefits and system thermal integration challenges of energy recovery and cooling systems using microchannel heat exchangers to provide high heat transfer performance in both high-temperature, high-enthalpy energy streams and low-temperature cooling streams. This work explores the roadmap and vision for using micro-technology solutions integrated with advanced thermoelectric materials in advanced TE power generation and cooling systems. Integrated system-level TE power generation and cooling system analyses demonstrate that inter-related system-level requirements on weight, volume, and performance lead to derived requirements for micro-technology solutions. Nano-technologies and micro-technologies will be presented that demonstrate where and how these technologies impact TE system designs. Of course, micro-technology manufacturing cost is critical in all energy recovery and cooling applications. Recent progress in microtechnology cost-modeling elucidates and quantifies key cost-manufacturing interdependencies, relationships, and sensitivities that will be explored in this presentation. This provides critical information on manufacturing processes, production volume dependence, material selections, and ultimately pathways forward leading to low-cost microtechnology heat and mass transfer devices that improve advanced TE energy recovery and cooling system performance (specifically including weight and volume impacts).

Power-Density vs Efficiency Trade-Off for a Recuperated Inside-Out Ceramic Turbine (ICT)

2019 ◽  
Author(s):  
B. Picard ◽  
A. L.-Blais ◽  
M. Picard ◽  
D. Rancourt
Keyword(s):  
Power Density ◽  
Thermal Efficiency ◽  
Gas Turbines ◽  
State Of The Art ◽  
Low Pressure ◽  
System Level ◽  
Specific Power ◽  
Inlet Temperature ◽  
Trade Off ◽  
Inside Out

Abstract Recuperated cycles can significantly increase the efficiency of small gas turbines that are today operating with low pressure ratios and uncooled or lightly cooled turbine blades. However, for mass-driven applications such as aeroengines, the efficiency benefit is typically outweighed by the increased weight associated with the heat exchanger (HX). Increase in specific power could overcome this penalty by reducing the mass flow through the system and therefore its weight and size. To do so, the Turbine Inlet Temperature (TIT) must be increased by ∼250 K over state-of-the-art small gas turbines. The Inside-out Ceramic Turbine (ICT) propose a new path to increase TIT of small turbines, where blade cooling schemes are impractical and costly. This new architecture increases the achievable TIT by using ceramic blades loaded in compression under centrifugal loads supported by an air-cooled rotating composite rim. This paper provides a system-level evaluation of the power-density to efficiency trade-off for the sub-megawatt class turbines using the ICT configuration. The numerical simulation includes 3 submodels to provide cycle efficiency and mass estimates for various cycle and HX design: (1) a station-based thermodynamic model; (2) a 1D-FEM HX model for a straight counterflow recuperator; and (3) a system-level mass model of the recuperated engine configured for a turboprop or turboshaft. At a TIT of 1550 K, the optimal ICT configuration provides a power density of 3 kW/kg and 40% thermal efficiency, which is 4 times lighter than recuperated turbines at 1300 K for the same efficiency level. Further increase in TIT to 1800 K would reach current state-of-the-art turboprop power densities (up to 5 kW/kg) while still achieving over 40% thermal efficiency or — for applications where power density can be traded for efficiency — up to 50% thermal efficiency while maintaining low pressure ratios and associated simplicity.

Assessment of thermal behavior of a cooling system to reduce thermal fatigue cracks in aluminum injection molds

2020 ◽  
pp. 75-86
Author(s):  
Sergio Antonio Camargo ◽  
Lauro Correa Romeiro ◽  
Carlos Alberto Mendes Moraes
Keyword(s):  
Thermal Fatigue ◽  
Cooling System ◽  
Fatigue Cracks ◽  
Cooling Water ◽  
Thermal Conditions ◽  
Thermal Gradients ◽  
Ansys Software ◽  
Cooling Systems ◽  
Thermal Fatigue Cracks ◽  
Number Of Cycles

The present article aimed to test changes in cooling water temperatures of males, present in aluminum injection molds, to reduce failures due to thermal fatigue. In order to carry out this work, cooling systems were studied, including their geometries, thermal gradients and the expected theoretical durability in relation to fatigue failure. The cooling system tests were developed with the aid of simulations in the ANSYS software and with fatigue calculations, using the method of Goodman. The study of the cooling system included its geometries, flow and temperature of this fluid. The results pointed to a significant increase in fatigue life of the mold component for the thermal conditions that were proposed, with a significant increase in the number of cycles, to happen failures due to thermal fatigue.

scholarly journals UNDERSTANDING THE EMBEDDED CARBON CHALLENGES OF BUILDING SERVICE SYSTEMS

2021 ◽  
Vol 1 ◽  
pp. 3279-3288
Author(s):  
Maria Hein ◽  
Darren Anthony Jones ◽  
Claudia Margot Eckert
Keyword(s):  
Energy Use ◽  
Cooling System ◽  
Current System ◽  
Energy Performance ◽  
Service Systems ◽  
Carbon Footprints ◽  
Embodied Carbon ◽  
Study Results ◽  
Operational Energy

AbstractEnergy consumed in buildings is a main contributor to CO2 emissions, there is therefore a need to improve the energy performance of buildings, particularly commercial buildings whereby building service systems are often substantially over-designed due to the application of excess margins during the design process.The cooling system of an NHS Hospital was studied and modelled in order to identify if the system was overdesigned, and to quantify the oversizing impact on the system operational and embodied carbon footprints. Looking at the operational energy use and environmental performance of the current system as well as an alternative optimised system through appropriate modelling and calculation, the case study results indicate significant environmental impacts are caused by the oversizing of cooling system.The study also established that it is currently more difficult to obtain an estimate of the embodied carbon footprint of building service systems. It is therefore the responsibility of the machine builders to provide information and data relating to the embodied carbon of their products, which in the longer term, this is likely to become a standard industry requirement.

Remote Heat Pipe Based Heat Exchanger Performance in Notebook Cooling

2005 ◽  
Author(s):  
Seyyed Khandani ◽  
Himanshu Pokharna ◽  
Sridhar Machiroutu ◽  
Eric DiStefano
Keyword(s):  
Heat Exchanger ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Cooling System ◽  
Temperature Drop ◽  
Operating Conditions ◽  
Cooling Systems ◽  
Temperature Variations ◽  
Non Linear ◽  
Condenser Temperature

Remote heat pipe based heat exchanger cooling systems are becoming increasingly popular in cooling of notebook computers. In such cooling systems, one or more heat pipes transfer the heat from the more populated area to a location with sufficient space allowing the use of a heat exchanger for removal of the heat from the system. In analsysis of such systems, the temperature drop in the condenser section of the heat pipe is assumed negligible due to the nature of the condensation process. However, in testing of various systems, non linear longitudinal temperature drops in the heat pipe in the range of 2 to 15 °C, for different processor power and heat exchanger airflow, have been measured. Such temperature drops could cause higher condenser thermal resistance and result in lower overall heat exchanger performance. In fact the application of the conventional method of estimating the thermal performance, which does not consider such a nonlinear temperature variations, results in inaccurate design of the cooling system and requires unnecessarily higher safety factors to compensate for this inaccuracy. To address the problem, this paper offers a new analytical approach for modeling the heat pipe based heat exchanger performance under various operating conditions. The method can be used with any arbitrary condenser temperature variations. The results of the model show significant increase in heat exchanger thermal resistance when considering a non linear condenser temperature drop. The experimental data also verifies the result of the model with sufficient accuracy and therefore validates the application of this model in estimating the performance of these systems.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.

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