A new generalised model for liquid film cooling in rocket combustion chambers

A one dimensional analytical model of liquid film cooling in rocket combustion chambers operating at subcritical conditions is developed. The approach followed involves the selection of a control volume for mass and energy balance. The coolant evaporation rate per area is obtained from this energy balance. The present model incorporates mass transfer via entrainment by adapting suitable correlations from literature pertaining to annular flow conditions. The model predicted favourably with the experimental data available in open literature and produced superior results compared to all existing models. Results are presented for a mixed gas–water system under different conditions. Results indicate that convection dominates the heat transfer at the gas–liquid interface. Effects of gas Reynolds number, coolant inlet temperature, combustion chamber pressure, mass flow ratio of the liquid coolant to the free stream and the free stream turbulence on the liquid film length are presented in detail.     

Theoretical and experimental studies of water injection scroll compressor in automotive fuel cell systems

A water injection scroll compressor to supply clean compressed air to an automotive fuel cell system is researched. The water is used as both the lubricant and coolant in the compressor. A thermodynamic model of the water injection scroll compressor considering leakage and heat exchange for use with an automotive fuel cell system was developed using the conservation of energy and mass equations and the equation of state. The results show that the scroll compressor has nearly isothermal compression when injecting water in it. Increasing the compressor rotation speed increases the discharge loss and the volumetric efficiency of the scroll compressor. The difference between the calculated power and the isothermal power increases as the compressor rotation speed rises, which means the efficiency of the compressor decreases. Increasing the flow rate of water injected increases the indicated isothermal efficiency and decreases the discharge temperature. Under the condition studied, the mass flow rate of water has the greatest effect on the discharge temperature.     

Modelling and validation of a gas engine heat pump working with R410A for cooling applications

Gas engine heat pumps play an important role in energy saving and environment protection in both cooling and heating applications. In the present work, a thermal modelling of the gas engine driven heat pump in cooling mode is performed and system main parameters such as cooling capacity, gas engine energy consumption and primary energy ratio (PER) are computed. The modelling of the gas engine heat pump includes modelling of the scroll compressor, the plate evaporator and the gas engine. Discharged refrigerant mass flow rate and compressor power represent the main output parameters of the compressor semi-empirical model. Using the discharged refrigerant mass flow rates along with the available evaporation heat transfer correlations, the system cooling capacity is deduced. Based on the present experimental data, a correlation of gas engine energy consumption as function of compressor power, engine speed and ambient air temperature is obtained. Furthermore, the gas engine heat pump model is validated by comparing experimental and simulation data. The model error percentages to predict the cooling capacity, the gas engine energy consumption and the PER are 7%, 5%, 6% respectively.     

MAT, a novel, open cycle gas turbine for power augmentation

A Moisture Air Turbine (MAT) cycle is proposed for improving the characteristics of land-based gas turbines by injecting atomized water through an inlet into a compressor. Compressor work of isentropic compression for moist air mixtures with phase change is theoretically considered, which has revealed that water evaporation may reduce compressor work. An experiment using a 15 MW class axial flow load compressor has also verified the theory. Realistic cycle model calculations predict that a 10% power increment by a ratio of 1% water to compressor intake air is expected and also that the amount of water consumption is much less than that of conventional inlet air cooling systems, used for heat rejection at the cooling tower. In addition, thermal efficiency is anticipated to be improved mainly due to the reduction of compressor work. Contrary to the conventional evaporative cooler, a MAT cycle could provide power output at a desired value within its capability regardless of ambient humidity condition.     

Three-dimensional multi-phase numerical study for the effect of coolant flow field designs on water and thermal management for the large-scale PEMFCs

The multi-phase numerical study is performed for the large-scale proton exchange membrane fuel cells (PEMFCs) regarding coolant flow field design. In this study, three coolant flow fields were designed to explore the effect of different temperature distributions on the water management of the PEMFCs. The numerical results show that increasing the temperature gradient along the gas flow direction and improving the temperature uniformity perpendicular to the gas flow direction enhances PEMFC performance and makes the liquid water distribution in the gas diffusion layers more reasonable. The co-flow for the cathode gas stream and the coolant flow is beneficial to raise the temperature along the cathode gas flow direction and reduce the risk of flooding near the cathode outlet. Then, it is noted that the coolant flow field design is not necessary to keep the temperature absolutely uniform for the PEMFCs. Although increasing the coolant volume flow rate will reduce the IUT, it dramatically increases the risk of flooding near the cathode outlet. Therefore, the moderate volume flow rate is preferred. Finally, the effect of the coolant manifold on the volume flow rate uniformity in the coolant channels is investigated, and it is found that reducing the number of coolant channels is the best strategy to improve volume flow rate uniformity and thermal management performance.     

Power and efficiency optimization for combined Brayton and inverse Brayton cycles

A thermodynamic model for open combined Brayton and inverse Brayton cycles is established considering the pressure drops of the working fluid along the flow processes and the size constraints of the real power plant using finite time thermodynamics in this paper. There are 11 flow resistances encountered by the gas stream for the combined Brayton and inverse Brayton cycles. Four of these, the friction through the blades and vanes of the compressors and the turbines, are related to the isentropic efficiencies. The remaining flow resistances are always present because of the changes in flow cross-section at the compressor inlet of the top cycle, combustion inlet and outlet, turbine outlet of the top cycle, turbine outlet of the bottom cycle, heat exchanger inlet, and compressor inlet of the bottom cycle. These resistances control the air flow rate and the net power output. The relative pressure drops associated with the flow through various cross-sectional areas are derived as functions of the compressor inlet relative pressure drop of the top cycle. The analytical formulae about the relations between power output, thermal conversion efficiency, and the compressor pressure ratio of the top cycle are derived with the 11 pressure drop losses in the intake, compression, combustion, expansion, and flow process in the piping, the heat transfer loss to the ambient, the irreversible compression and expansion losses in the compressors and the turbines, and the irreversible combustion loss in the combustion chamber. The performance of the model cycle is optimized by adjusting the compressor inlet pressure of the bottom cycle, the air mass flow rate and the distribution of pressure losses along the flow path. It is shown that the power output has a maximum with respect to the compressor inlet pressure of the bottom cycle, the air mass flow rate or any of the overall pressure drops, and the maximized power output has an additional maximum with respect to the compressor pressure ratio of the top cycle. When the optimization is performed with the constraints of a fixed fuel flow rate and the power plant size, the power output and efficiency can be maximized again by properly allocating the fixed overall flow area among the compressor inlet of the top cycle and the turbine outlet of the bottom cycle.     

Development of an integrated membrane condenser system with LNG cold energy for water recovery from humid flue gases in power plants

This paper investigates a detailed thermodynamic analysis of a modular-type membrane condenser system where a cooler or condenser is connected in series upstream of the membrane condenser module. A coolant circulates inside the cooler/condenser to cool down the industrial flue gas up to saturation conditions. The analysis covers water recovery rate and energy requirement for different combinations of flue gas humidity, flow rate, and temperature. Additionally, a case study is included which considers a practical industrial exhaust flue gas where the constituents of the flue gas with volumetric ratio and the feed parameters are referred from the literature. The case study investigated the utilization of cold energy obtained by LNG regasification facility as a cooling power source for the water vapor recovery process. A detailed heat transfer analysis based on the heat exchanger model is performed to determine the required mass flow rate of cooling water and natural gas. It is concluded that, the water self-sufficiency of a power plant can be achieved if the mass flow rate of the −50 °C natural gas which is entering the membrane condenser is kept around 0.3 kg s⁻¹ for every 1  kg s⁻¹ flow rate of the 168 °C flue gas.     

Comparative performance analysis of cogeneration gas turbine cycle for different blade cooling means

The paper compares the thermodynamic performance of MS9001 gas turbine based cogeneration cycle having a two-pressure heat recovery steam generator (HRSG) for different blade cooling means. The HRSG has a steam drum generating steam to meet coolant requirement, and a second steam drum generates steam for process heating. Gas turbine stage cooling uses open loop cooling or closed loop cooling schemes. Internal convection cooling, film cooling and transpiration cooling techniques employing steam or air as coolants are considered for the performance evaluation of the cycle. Cogeneration cycle performance is evaluated using coolant flow requirements, plant specific work, fuel utilisation efficiency, power-to-heat-ratio, which are function of compressor pressure ratio and turbine inlet temperature, and process steam drum pressure. The maximum and minimum values of power-to-heat ratio are found with steam internal convection cooling and air internal convection cooling respectively whereas maximum and minimum values of fuel utilisation efficiency are found with steam internal convection cooling and closed loop steam cooling. The analysis is useful for power plant designers to select the optimum compressor pressure ratio, turbine inlet temperature, fuel utilisation efficiency, power-to-heat ratio, and appropriate cooling means for a specified value of plant specific work and process heating requirement.     

Numerical Study of Film and Regenerative Cooling in a Thrust Chamber at High Pressure

Numerical study of coupled heat transfer of gas flow with film cooling, chamber wall conduction, and regeneration coolant cooling in the thrust chamber of a liquid rocket engine was performed. A one-dimensional model was adopted for regeneration cooling to couple two-dimensional model simulation in the thrust camber. Numerical results show that the method adopted can simulate the gas flow field well, and can calculate the heat flux through the wall, the wall temperature, and the temperature increase of the coolant quickly. In addition, liquid film cooling can reduce the wall temperature greatly, and decrease the heat flux transferred from the hot gas to the chamber wall.     

Analysis of staggered tube bundle heat transfer to vertical foam flow

In general heat transfer intensity between solid surface and coolant (fluid) depends on three main parameters: heat transfer coefficient, size of heat exchange surface and temperature difference between surface and fluid. Sometimes the last two parameters (surface size and temperature difference) are strictly limited due to the process or technological requirements, and only increase of heat transfer coefficient is allowed. Simplest way offering sufficient increase in heat transfer rate (heat transfer coefficient as well) is to go from the laminar fluid flow regime to the turbulent one by increasing flow velocity. In many cases it helps despite such disadvantages like more complicated fluid supply system, rise of fluid flow mass rate and growth of energy usage for pumping. But in some cases, for example, in space application, in nuclear engineering, etc. there is not allowed to use high flow velocity of coolant – gas (due to vibration danger) or to apply high mass rate of coolant – liquid (due to limitation concerning weight or mass). One of the possible solutions of that problem could be the usage of two-phase flow as a coolant. An idea to use such two-phase coolant for heat removal from the solid surface is not new. Boiling liquid (water especially), gas flow with liquid droplets and other two-phase systems are widely used for heat and mass transfer purposes in various industries like food, chemical, oil, etc. An application of such two-phase coolants has lot advantages; high value of heat transfer coefficient is one of the most important. Unfortunately nothing is ideal on the Earth. Restrictions on vibration, on coolant weight (or mass rate); necessity to generate two-phase flow separately from the heat removal place; requirements on very low coolant velocities and other constraints do not allow using such type of two-phase coolant for purposes which were mentioned above (space application especially). As a possible way out can be usage of the statically stable foam flow produced from gas (air) and surfactant solutions in liquid (water). Our previous investigations [J. Gylys, Hydrodynamics and Heat Transfer under the Cellular Foam Systems, Technologija, Kaunas, 1998] showed the solid advantages of that type of two-phase coolant, including high values of heat transfer coefficient (up to 1000 W/m² K and more), low flow velocities (less than 1.0 m/s), small coolant density (less than 4 kg/m³), possibility to generate foam flow apart from the heat removal place, etc.This article is devoted to the experimental investigation of the staggered tube bundle heat transfer to the vertical upward and downward statically stable foam flow. The investigations were provided within the laminar regime of foam flow. The dependency of the tube bundle heat transfer on the foam flow velocity, flow direction and volumetric void fraction were analyzed. In addition to this, the influence of tube position in the bundle was investigated also. Investigation shows that the regularities of the tube bundle heat transfer to the vertical foam flow differ from the one-phase (gas or liquid) flow heat transfer peculiarities. It was showed that the heat transfer intensity of the staggered tube bundle to the foam flow is much higher (from 25 to 100 times) than that for the one-phase airflow under the same conditions (flow velocity). The results of the investigations were generalized using criterion equations, which can be applied for the calculation and design of the statically stable foam heat exchangers with the staggered tube bundles.     

不同冷气/燃气温比下高温涡轮叶片旋流冷却流固耦合特性研究

采用流固耦合方法对燃气轮机高温涡轮叶片旋流冷却结构进行数值模拟分析。探究了不同冷气/燃气温度比条件下旋流冷却的流动与传热特性、叶片前缘区域固体温度、热应力以及热应变分布。研究表明：在进气腔入口雷诺数固定的条件下，随着温度比升高，冷气密度降低，冷气流速逐渐提升，同时湍动能升高，靶面努塞尔数逐渐升高；当温度比较低时冷气的流速较低、单位时间冷气带走的热量较少，当温度比较高时冷气温度较高、单位质量冷气所能吸收的热量有限，靶面处热流密度先升高后降低。受靶面热流密度分布影响，随着温度比升高，叶片前缘固体的温度、热应力以及热应变先降低后升高。     

Pumpless thermal management of water-cooled high-temperature proton exchange membrane fuel cells

Proton exchange membrane fuel cells (PEMFCs) have been considered for combined heat and power (CHP) applications, but cost reduction has remained an issue for commercialization. Among various types of PEMFC, the high-temperature (HT) PEMFC is gaining more attention due to the simplicity of the system, that will make the total system cost lower. A pumpless cooling concept is introduced to reduce the number of components of a HT PEMFC system even further and also decrease the parasitic power required for operating the system. In this concept, water is used as the coolant, and the buoyancy force caused by the density difference between vapour and liquid when operated above boiling temperate is utilized to circulate the coolant between the stack and the cooling device. In this study, the basic parameters required to design the cooling device are discussed, and the stable operation of the HT PEMFC stack in both the steady-state and during transient periods is demonstrated. It found that the pumpless cooling method provides more uniform temperature distribution within the stack, regardless of the direction of coolant flow.     

A combined power cycle with absorption air conditioning

A cogeneration scheme comprising a combined cycle power plant (CCPP) with an absorption chiller used for space cooling is studied. A parametric study investigating the effect of different parameters, such as steam to gas mass flow rate ratio, fraction of turbine steam extraction, ambient temperature, inlet steam turbine temperature, compressor pressure ratio, and gas turbine (GT) combustion efficiency on the performance of the system has been made. In another aspect of the study, the relative advantage of using CCPP with absorption cooling over thermally equivalent mechanical vapor compression (MVC) cooling is also demonstrated.     

The extraction of power from a hot stream

The solution to the problem of maximizing the extraction of exergy from a stream of hot gas showed that the hot stream must be cooled in a counterflow heat exchanger with optimal imbalance of capacity rates, i.e. with an optimal capacity rate on the cold side. This paper outlines the first few steps toward making this solution practical, by combining the optimized counterflow with conventional components for compressing and expanding the cold stream. In the first part of the paper, the cold stream is compressed in an isothermal compressor, expanded in an adiabatic turbine, and discharged into the ambient. In the second part, the cold stream is compressed in an adiabatic compressor. Both designs are optimized with respect to two degrees of freedom, the capacity‐rate imbalance of the counterflow, and the pressure ratio maintained by the compressor. The effect of other constraints is documented, e.g. heat transfer area size, hot gas initial temperature and compressor and turbine efficiencies. This study shows the tradeoff between simplicity and increased performance, and outlines the path for further conceptual work on the extraction of exergy from a hot stream that is being cooled gradually. Copyright © 2001 John Wiley & Sons, Ltd.     

Liquid cooling in the mini-rectangular fin heat sink with and without thermoelectric for CPU

In the present study, the liquid cooling in the mini-rectangular fin heat sink with and without thermoelectric for CPU is studied. Six mini-rectangular fin heat sinks with two different material types and three different channel widths are fabricated from the copper or aluminum with the length, the width and the base thickness of 37, 37, 5 mm, respectively. The de-ionized water is used as coolant. Effects of channel width, coolant flow rate, material type of heat sink and run condition of PC on the CPU temperature are considered. The liquid cooling in mini-rectangular fin heat sink with thermoelectric is compared with the other cooling techniques. The thermoelectric has a significant effect on the CPU cooling of PC. However, energy consumption is also increased. The results of this study are expected to lead to guidelines that will allow the design of the cooling system with improved heat transfer performance of the electronic equipments.     

150单缸机试验台冷却系统流动与传热计算分析

基于Flowmaster软件建立了150单缸柴油机试验台冷却系统流动与传热模型,并在某大功率发动机上进行了验证。在此基础上分析得到了冷却水温度和流量、气缸套和气缸盖温度变化对冷却水总传热流量的影响规律,以及管道尺寸、壁面粗糙度、冷却水流量对冷却水流动总阻力的影响规律。     

Heat transfer from multiple row arrays of low aspect ratio pin fins

Pin fin arrays are used in many applications to enhance heat transfer. In modern gas turbines, for example, airfoils are designed with sophisticated internal and external cooling techniques. One method for cooling is routing air from the compressor through intricate cooling channels embedded in turbine airfoils. Heat transfer from the blade to the coolant air can be increased by installing arrays of cylindrical pedestals often referred to as pin fins. Pin fin arrays increase heat transfer by increasing the flow turbulence and surface area of the airfoil exposed to the coolant.For the current study, experiments were conducted to determine the effects of pin spacing on heat transfer and pressure loss through pin fin arrays for a range of Reynolds numbers between 5000 and 30,000. Results showed that spanwise pin spacing had a larger effect than streamwise spacing on array pressure loss while streamwise spacing had a larger effect than spanwise spacing on array heat transfer.     

Transpiration cooling of a nose cone by various foreign gases

The transpiration cooling mechanisms used for thermal protection of a nose cone was investigated experimentally and numerically for various cooling gases. The effects of injection rates, model geometry, inlet temperature and Reynolds number of the main stream were studied for air, nitrogen, argon, carbon dioxide and helium. The experiments used a hot gas wind tunnel with T_∞ = 375 K and 425 K and Re_∞ = 4630–10,000. The experimental results indicated that even a small amount of coolant injection drastically reduced the heat transfer from the hot gases with the cooling effectiveness increasing with increasing injection rate, although the increases became smaller as the gas injection rate was further increased. The temperature and cooling effectiveness distribution along the transpiration surface of the nose cone model exhibited similar tendencies for all the coolants employed in present experimental research. The temperature decreased from the stagnation point towards the downstream region, then increased because of the non-uniform mass flow distribution of the coolant and thermal conduction from the metal backplane, whereas the cooling effectiveness variation was the reverse. The local cooling effectivenesses and thermal capacities were found to depend on the coolant thermophysical properties. Two-dimensional numerical simulations using the RNG κ?ε turbulence model for the main stream flow and the Darcy–Brinkman–Forchheimer momentum equations and thermal equilibrium model for the porous zone compared well with the general features in the experiments.     

Experimental investigation of thermoelectric power generation versus coolant pumping power in a microchannel heat sink

The coolant heat sinks in thermoelectric generators (TEG) play an important role in order to power generation in the energy systems. This paper explores the effective pumping power required for the TEGs cooling at five temperature difference of the hot and cold sides of the TEG. In addition, the temperature distribution and the pressure drop in sample microchannels are considered at four sample coolant flow rates. The heat sink contains twenty plate-fin microchannels with hydraulic diameter equal to 0.93 mm. The experimental results show that there is a unique flow rate that gives maximum net-power in the system at the each temperature difference.     

Blade cooling optimisation in humid-air and steam-injected gas turbines

Humidified gas turbine cycles such as the humidified air turbine (HAT) and the steam-injected gas turbine (STIG) present exciting new prospects for industrial gas turbine technology, potentially offering greatly increased work outputs and cycle efficiencies at moderate costs. The availability of humidified air or steam in such cycles also presents new opportunities in blade and disk cooling architecture. Here, the blade cooling optimisation of a HAT cycle and a STIG cycle is considered, first by optimising the choice of coolant bleeds for a reference cycle, then by a full parametric optimisation of the cycle to consider a range of optimised designs. It was found that the coolant demand reductions which can be achieved in the HAT cycle using humidified or post-aftercooled coolant are compromised by the increase in the required compression work. Furthermore, full parametric optimisation showed that higher water flow-rates were required to prevent boiling within the system. This corresponded to higher work outputs, but lower cycle efficiencies. When optimising the choice of coolant bleeds in the STIG cycle, it was found that bleeding steam for cooling purposes reduced the steam available for power augmentation and thus compromised work output, but that this could largely be overcome by reducing the steam superheat to give useful cycle efficiency gains.