scholarly journals A Compact Thermally Driven Cooling System Based on Metal Hydrides

Energies ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2482 ◽  
Author(s):  
Christoph Weckerle ◽  
Marius Dörr ◽  
Marc Linder ◽  
Inga Bürger
Keyword(s):  
Internal Combustion Engines ◽  
Cooling System ◽  
Heating System ◽  
Operating Conditions ◽  
Specific Power ◽  
Working Fluid ◽  
Cooling Power ◽  
Half Cycle ◽  
Exhaust Heat ◽  
Thermally Driven

Independent of the actual power train, efficiency and a high driving range in any weather conditions are two key requirements for future vehicles. Especially during summertime, thermally driven air conditioning systems can contribute to this goal as they can turn the exhaust heat of internal combustion engines, fuel cells or of any additional fuel-based heating system into a cooling effect. Amongst these, metal hydride cooling systems (MHCSs) promise very high specific power densities due to the short reaction times as well as high reaction enthalpies. Additionally, the working fluid hydrogen has a very low global warming potential. In this study, the experimental results of a compact and modular MHCS with a specific cooling power of up to 585 W kg MH − 1 referred to one cold generating MH are presented, while reactor and MH weight in total is less than 30 kg and require a volume < 20 dm3. The system is driven by an auxiliary fuel heating system and its performance is evaluated for different operating conditions, e.g., temperature levels and half-cycle times. Additionally, a novel operation optimization of time-shifted valve switching to increase the cooling power is implemented and investigated in detail.

A Parametric Examination of the Factors Affecting the Performance of a Diffusion Absorption Refrigeration System

2021 ◽  
pp. 1-38
Author(s):  
Noman Yousuf ◽  
Timothy Anderson ◽  
Roy Nates
Keyword(s):  
Waste Heat ◽  
Operating Conditions ◽  
Design Parameters ◽  
Working Fluid ◽  
Low Grade ◽  
Absorption Refrigeration ◽  
Factors Affecting ◽  
Thermally Driven ◽  
Mass Flowrate ◽  
Diffusion Absorption

Abstract Despite being identified nearly a century ago, the diffusion absorption refrigeration (DAR) cycle has received relatively little attention. One of the strongest attractions of the DAR cycle lies in the fact that it is thermally driven and does not require high value work. This makes it a prime candidate for harnessing low grade heat from solar collectors, or the waste heat from stationary generators, to produce cooling. However, to realize the benefits of the DAR cycle, there is a need to develop an improved understanding of how design parameters influence its performance. In this vein, this work developed a new parametric model that can be used to examine the performance of the DAR cycle for a range of operating conditions. The results showed that the cycle's performance was particularly sensitive to several factors: the rate of heat added and the temperature of the generator, the effectiveness of the gas and solution heat exchangers, the mass flowrate of the refrigerant and the type of the working fluid. It was shown that can deliver good performance at low generator temperatures if the refrigerant mass fraction in the strong solution is made as high as possible. Moreover, it was shown that a H2O-LiBr working pair could be useful for achieving cooling at low generator temperatures.

The Effects of Spraying Parameters on Spray Cooling Heat Transfer Performance in the Non-Boiling Regime

2017 ◽  
Author(s):  
Azzam S. Salman ◽  
Jamil A. Khan
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Target Surface ◽  
Spray Cooling ◽  
Operating Conditions ◽  
Droplet Velocity ◽  
Inlet Pressure ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Spraying Parameters

Experiments were conducted in a closed loop spray cooling system working with deionized water as a working fluid. This study was performed to investigate the effect of the spraying parameters, such as Sauter mean diameter (SMD), the droplet velocity, and the residual velocity on the spray cooling heat transfer in the non-boiling region. Thermal effects on plain and modified surfaces with circular grooves were examined under different operating conditions. The inlet pressure of the working fluid was varied from 78.6 kPa to 183.515kPa, and the inlet temperature was kept between 21–22 °C. The distance between the nozzle and the target surface 10 mm. The results showed that increasing the coolant inlet pressure increases the droplet velocity and the number of droplets produced while decreasing the droplet size. As a consequence of these changes, increasing inlet pressure improved the heat transfer characteristics of both surfaces.

The Heat Transfer Performance of Porous Gas Turbine Blades

1968 ◽  
Vol 72 (696) ◽  
pp. 1087-1094 ◽  
Author(s):  
F. J. Bayley ◽  
A. B. Turner
Keyword(s):  
Gas Turbine ◽  
Turbine Blades ◽  
Engine Performance ◽  
Operating Conditions ◽  
Maximum Temperature ◽  
Specific Power ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Turbine Inlet ◽  
Compression And Expansion

It is well known that the performance of the practical gas turbine cycle, in which compression and expansion are non-isentropic, is critically dependent upon the maximum temperature of the working fluid. In engines in which shaft-power is produced the thermal efficiency and the specific power output rise steadily as the turbine inlet temperature is increased. In jet engines, in which the gas turbine has so far found its greatest success, similar advantages of high temperature operation accrue, more particularly as aircraft speeds increase to utilise the higher resultant jet velocities. Even in high by-pass ratio engines, designed specifically to reduce jet efflux velocities for application to lower speed aircraft, overall engine performance responds very favourably to increased turbine inlet temperatures, in which, moreover, these more severe operating conditions apply continuously during flight, and not only at maximum power as with more conventional cycles.

scholarly journals Unified Methodology to Identify the Potential Application of Seasonal Sorption Storage Technology

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1037 ◽  
Author(s):  
Andrea Frazzica ◽  
Vincenza Brancato ◽  
Belal Dawoud
Keyword(s):  
Distribution Systems ◽  
Heating System ◽  
Climatic Conditions ◽  
Operating Conditions ◽  
Working Fluid ◽  
Space Heating ◽  
Preliminary Evaluation ◽  
Multi Wall Carbon Nanotubes ◽  
Sorbent Materials ◽  
Definition Of

In this study, the definition of a new methodology for a preliminary evaluation of the working boundary conditions under which a seasonal thermal energy storage (STES) system operates is described. The approach starts by considering the building features as well as the reference heating system in terms of solar thermal collectors’ technology, ambient heat sinks/source, and space heating distribution systems employed. Furthermore, it is based on a deep climatic analysis of the place where the STES needs to be installed, to identify both winter and summer operating conditions. In particular, the STES energy density is evaluated considering different space heating demands covered by the STES (ranging from 10% up to 60%). The obtained results demonstrate that this approach allows for the careful estimation of the achievable STES density, which is varies significantly both with the space heating coverage guaranteed by the STES as well as with the ambient heat source/sink that is employed in the system. This confirms the need for careful preliminary analysis to avoid the overestimation of the STES material volume. The proposed approach was then applied for different climatic conditions (e.g., Germany and Sweden) and the volume of one of the most attractive composite sorbent materials reported in the literature, i.e., multi-wall carbon nanotubes (MWCNT)-LiCl, using water as the working fluid, needed for covering the variable space heating demand in a Nearly Zero Energy Building (NZEB) was calculated. In the case of Swedish buildings, it ranges from about 3.5 m3 when 10% of the space heating demand is provided by the STES, up to 11.1 m3 when 30% of the space heating demand is provided by the STES.

Organic Rankine Cycle for Waste Heat Recovery in a Hybrid Vehicle

2010 ◽  
Author(s):  
Quazi E. Hussain ◽  
David R. Brigham
Keyword(s):  
Fuel Economy ◽  
Heat Recovery ◽  
Waste Heat Recovery ◽  
Waste Heat ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Operating Conditions ◽  
Working Fluid ◽  
Drive Cycle ◽  
Exhaust Heat

The Rankine cycle is used commercially to generate power in stationary power plants using water as the working fluid. For waste heat recovery applications, where the temperature is lower, water is typically replaced by a carefully selected organic fluid. This work is based on using the waste heat in an automobile to generate electricity using the Organic Rankine cycle (ORC) with R245fa (1, 1, 1, 3, 3 penta-fluoropropane) as the working fluid. The electricity thus generated can be used to drive the accessory load or charge the battery which in any case helps improve the fuel economy. A simple transient numerical model has been developed that is capable of capturing the main effects of this cycle. Results show that exhaust heat alone can generate enough electricity that is capable of bringing about an improvement to the fuel economy under transient drive cycle conditions. Power output during EPA Highway drive cycle is much higher than EPA City due to higher exhaust mass flow rate and temperature. Time needed to reach operating conditions or in other words, the warm-up time plays an important role in the overall drive cycle output. Performance is found to improve significantly when coolant waste heat is used in conjunction with the residual exhaust heat to pre-heat the liquid. A sizing study is also performed to keep the cost, weight, and packaging requirement down without sacrificing too much power. With careful selection of heat exchanger design parameters, it has been demonstrated that the backpressure on the engine can be actually lowered by cooling off the exhaust gas. This lower backpressure will further boost the fuel economy gained by the electricity produced by the Rankine bottoming cycle.

Performance Assessment of Semi-Closed Chemically Recuperated Gas Turbine Systems

2000 ◽  
Author(s):  
Giorgio Cau ◽  
Daniele Cocco
Keyword(s):  
Gas Turbine ◽  
System Analysis ◽  
Combustion Process ◽  
Pure Oxygen ◽  
Specific Power ◽  
Working Fluid ◽  
Exhaust Heat ◽  
And Performance ◽  
Polluting Emissions ◽  
Cycle Efficiency

The paper is concerned with thermochemical recuperation in semi-closed gas turbine systems. Semi-closed turbines use CO2 as the main working fluid and the combustion process takes place with pure oxygen, allowing the CO2 produced to be easily removed. On the other hand, the exhaust heat recovery through thermochemical recuperation offers interesting capabilities in terms of high conversion efficiency and low polluting emissions. System analysis and performance evaluation of the semi-closed, chemically recuperated gas turbine systems has been conducted and their performance assessed. A comparative analysis of semi-closed and open gas turbine cycles, with and without thermochemical recuperation, has been also carried out. The results of the analysis show that thermochemical recuperation in semi-closed gas turbine systems can allow to remove the CO2 with high cycle efficiency and specific power.

A Computational Investigation of Non-Premixed Combustion of Natural Gas Injected Into Mixture of Argon and Oxygen

2018 ◽  
Author(s):  
Martia Shahsavan ◽  
Mohammadrasool Morovatiyan ◽  
J. Hunter Mack
Keyword(s):  
Natural Gas ◽  
Internal Combustion Engines ◽  
Numerical Study ◽  
Direct Injection ◽  
Dynamic Structure ◽  
Operating Conditions ◽  
Working Fluid ◽  
Thermodynamic Efficiency ◽  
Transient Model ◽  
Large Eddy Simulation Model

Natural gas is traditionally considered as a promising fuel in comparison to gasoline due to the potential of lower emissions and significant domestic reserves. These emissions can be further diminished by using noble gases, such as argon, instead of nitrogen as the working fluid in internal combustion engines. Furthermore, the use of argon as the working fluid can increase the thermodynamic efficiency due to its higher specific heat ratio. In comparison to pre-mixed operation, the direct injection of natural gas enables the engine to reach higher compression ratios while avoiding knock. Using argon as the working fluid increases the in-cylinder temperature at top dead center and enables the compression ignition of natural gas. In this numerical study, the combustion quality and ignition behavior of methane injected into a mixture of oxygen and argon has been investigated using a three-dimensional transient model of a constant volume combustion chamber. A dynamic structure large eddy simulation model has been utilized to capture the behavior of the non-premixed turbulent gaseous jet. A reduced mechanism consists of 22-species and 104-reactions were coupled with the CFD solver. The simulation results show that the methane jet ignites at engine-relevant conditions when nitrogen is replaced by argon as the working fluid. Ignition delay times are compared across a variety of operating conditions to show how mixing affects jet development and flame characteristics.

A Computational Investigation of Nonpremixed Combustion of Natural Gas Injected Into Mixture of Argon and Oxygen

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Martia Shahsavan ◽  
Mohammadrasool Morovatiyan ◽  
J. Hunter Mack
Keyword(s):  
Natural Gas ◽  
Internal Combustion Engines ◽  
Numerical Study ◽  
Direct Injection ◽  
Three Dimensional ◽  
Dynamic Structure ◽  
Operating Conditions ◽  
Working Fluid ◽  
Thermodynamic Efficiency ◽  
Transient Model

Natural gas is traditionally considered as a promising fuel in comparison with gasoline due to the potential of lower emissions and significant domestic reserves. These emissions can be further diminished by using noble gases, such as argon, instead of nitrogen as the working fluid in internal combustion engines. Furthermore, the use of argon as the working fluid can increase the thermodynamic efficiency due to its higher specific heat ratio. In comparison with premixed operation, the direct injection of natural gas enables the engine to reach higher compression ratios while avoiding knock. Using argon as the working fluid increases the in-cylinder temperature at top dead center (TDC) and enables the compression ignition (CI) of natural gas. In this numerical study, the combustion quality and ignition behavior of methane injected into a mixture of oxygen and argon have been investigated using a three-dimensional transient model of a constant volume combustion chamber (CVCC). A dynamic structure large eddy simulation (LES) model has been utilized to capture the behavior of the nonpremixed turbulent gaseous jet. A reduced mechanism consists of 22-species, and 104-reactions were coupled with the CFD solver. The simulation results show that the methane jet ignites at engine-relevant conditions when nitrogen is replaced by argon as the working fluid. Ignition delay times are compared across a variety of operating conditions to show how mixing affects jet development and flame characteristics.

Novel Air-Cooled Thermosyphon Cooling System for Desktop Computers

2021 ◽  
Author(s):  
Filippo Cataldo ◽  
Raffaele L. Amalfi ◽  
Jackson B. Marcinichen ◽  
John R. Thome
Keyword(s):  
Power Consumption ◽  
Cooling System ◽  
Electronics Cooling ◽  
Operating Conditions ◽  
Working Fluid ◽  
Maximum Heat ◽  
Desktop Computers ◽  
Fan Speed ◽  
Conventional Cooling ◽  
Power Densities

Abstract The trade-off between efficient cooling and low power consumption is a goal that has always been very desirable in electronics cooling, especially nowadays that power densities of processing units are increasing. Conventional cooling solutions do not have the necessary cooling capacities for these power densities or require significant power consumption. In this study, a novel air-cooled thermosyphon cooling system for desktop computers is presented and experimentally tested. The thermosyphon comprises a vertical micro-channel cold plate as the evaporator and a horizontal air-cooled multiport coil as the condenser. The thermosyphon has a total height of 12 cm and operates with a fan speed of 1700 RPM. The working fluid selected for the thermosyphon loop is R1234ze(E), chosen for its advantageous thermophysical properties and nearly zero-GWP (Global Warming Potential). The test results presented in this paper aim to analyze thermosyphon’s thermal and hydraulic performance by studying the trends of thermal resistance and mass flow rate as a function of different operating conditions. The maximum heat rejection under safe conditions is 250 W, corresponding to a heat flux of about 18 W/cm2.

Flow and heat transfer in a closed loop thermosyphon Part II – experimental simulation

2007 ◽  
Vol 18 (4) ◽  
pp. 41-48 ◽  
Author(s):  
J.C. Ruppersberg ◽  
R.T. Dobson
Keyword(s):  
Heat Transfer ◽  
Closed Loop ◽  
Cooling System ◽  
Operating Conditions ◽  
Experimental Simulation ◽  
Theoretical Modelling ◽  
Working Fluid ◽  
Small Scale ◽  
System A ◽  
Test Loop

A closed loop thermosyphon is an energy transfer device that employs thermally induced density gra-dients to induce circulation of the working fluid thereby obviating the need for any mechanical moving parts such as pumps and pump controls. This increases the reliability and safety of the cool-ing system and reduces installation, operation and maintenance costs. These characteristics make it a particularly attractive option for the cavity cooling system of the Pebble Bed Modular Reactor (PBMR). Loop thermosyphons are however, known to become unstable under certain initial and operating conditions. It is therefore necessary to conduct an experimental and theoretical study of the start-up and transient behaviour of such a system. A small scale test loop was built representing a section of a concept cooling system. A number of representative yet typical experimental temperature and flow rate curves for a range of initial and boundary condi-tions were generated, plotted and are given as a function of time. These curves show that oscillatory temperature and flow occurred that was dependent on the differing design and operating conditions. A number of theoretical modelling and actual cooling system design problem areas were identified. These problem areas need to be addressed if more accu-racy is required to capture the erratic and ostensibly chaotic heat transfer behaviour of the loop.

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