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The hydraulic system is the backbone of industrial, construction, and agricultural machines. Its high-power density and efficiency execution make it the preferred choice for high-energy applications. This manuscript presents the evidence against the statement, Whenever the system runs to its full capacity, hydraulic oil heats up more as compared to partial loads.“ Our experimental study on Injection Molding Machine (IMM) hydraulic system tries to reshape the above statement by presenting the fact where we came across that lower system loading case is causing higher hydraulic oil temperatures than full loading.” The concern started when the machine at lower speeds results in frequent shutdowns due to increasing operating temperature high alarm!“ This article presents the study to resolve the stated issue completely. For the design evolution, a systematic diagnostic approach is displayed based on the six-sigma and the associated mathematical model. Our study concludes with an approach to find the self-balancing system for the case where the temperature increase is must be due to the higher rate of heat addition than the rate of heat rejection. Presented learning can be equally extended for the other fields of interest, as care should be taken to understand the passive system losses, which can result in elevated temperatures due to lower cooling capabilities.

Transcritical CO2 plants combined with subcooling systems are the focus of several researches in the last years with the objective of improving their performance. Among the subcooling systems, the Dedicated Mechanical Subcooling system (DMS) is one of the most interesting because it greatly improves the overall COP and the cooling capacity of the system. This work presents the experimental study of a transcritical CO2 plant working with an R-152a DMS. The plant was tested at different pressure and subcooling conditions in order to determine the working conditions where the COP of the plant is maximum. The optimal operation conditions are determined for three ambient temperatures 25.0 °C, 30.4 °C and 35.1 °C and three cold sink temperatures (-1.3 °C, 3.8 °C and 10.0 °C). The measured values go from 6.5 kW to 7.3 kW for glycol inlet temperature -1.3 °C, from 7.6 kW to 8.4 kW for 3.8 °C and from 8.8 kW to 9.8 kW for 10.0 °C. Optimum COP goes from 1.51 to 1.95 for -1.3 °C, from 1.69 to 2.21 for 3.8 °C and from 1.86 to 2.52 for 10.0 °C. Optimum gas-cooler pressure has a higher dependence on the heat rejection level, being higher when higher the heat rejection level is, but it slightly depends on the evaporation level. Optimum subcooling degree is both dependent on the water inlet temperature and on the glycol inlet temperature. Two correlations are proposed to determine the optimal pressure and subcooling degree for the CO2 plants working with DMS as a function of the gas-cooler outlet temperature and the evaporation level.

Interest towards adsorption heat storage, especially for long-term (seasonal) applications, is growing. The previous studies have always treated the heat storage cycle as a fully temperature-initiated process, similarly to common adsorption cooling and heating cycles. However, in long term storage applications, the discharge stage of the cycle is initiated by a jump of pressure rather than by a traditional drop of temperature. This requires specific investigations on the useful heat recoverable as well as on the adsorption dynamics.In the present paper, an appropriate experimental methodology was applied for studying the heat discharge stage. Three well known adsorbents (Mitsubishi AQSOA FAM-Z02, silica Siogel and composite LiCl/silica) were experimentally tested in a lab-scale heat storage unit, evaluating the effect of cycle operating parameters. The results, elaborated in terms of useful heat recoverable from the charged adsorbent, highlighted that the evaporation temperature and the flow rate of heat transfer fluid have a great influence on the adsorption dynamics and the useful heat. For the silica gel and FAM Z02, the maximum heat storage capacity 450 kJ/kg is reached at the evaporation temperature of 25 degrees C. The composite performs better at low evaporation temperatures, allowing heat upgrade even at 5 degrees C. The flow rate of the heat transfer fluid has a more significant effect on FAM Z02 than on the other adsorbents, for which an optimal flow rate of 1.2 kg/min was found.

Numerical simulation of a mini-channel, flat-tube, louvered fin, automotive condenser is performed to study the heat rejection rate, pressure drop and performance of the heat exchanger. The simulation study is carried out for the refrigerant R1234yf. The properties of R1234y are obtained from REFPROP software. The moist air properties are calculated from those of dry air and water vapor using suitable correlations. To select the input data, the cycle performance is carried out for a standard vapor compression refrigeration system working with R1234yf between the temperature limits of [Formula: see text]C on the low-pressure side and [Formula: see text]C on the high-pressure side. The condensation process is taken into account in three sections, namely, the superheated, two-phase and the subcooled regions. A custom code is prepared in MATLAB to solve the simultaneous equations of heat transfer from refrigerant to inside tube wall, inside tube wall to outside tube wall and outside tube wall to moist air. The simulation results show the sensible heat transfer during desuper heating to be very small compared to the condensing region. Results are reported for the pressure variation along the refrigerant flow passage in the desuper heating, two-phase and subcooling regions. The heat-transfer coefficient is found to be the highest in the two-phase region for higher dryness fractions. The effect of inlet air velocity is less compared to that of the inlet air temperature on the heat rejection rate.

Use of zeotropic blends in the dedicated mechanical subcooling system of a CO2 refrigeration system was suggested as a possible improvement due to matching of evaporating temperature with CO2 temperature profile during subcooling. This work has verified this possibility and has determined theoretically the best performing compositions of R-600, R-32 and CO2 with the base fluid R-152a. Then, the mixtures have been tested experimentally in a lab-test bench for constant heat load temperature for three heat rejection temperatures (25.1, 30.3 and 35.1°C). Optimum conditions are measured (subcooling degree and heat rejection) and a COP increase of 1.4% has been obtained. The work, for the optimum conditions, analyses the operating parameters of the cycles and focus specially on the thermal parameters of the subcooler. It has been verified that the use of zeotropic mixtures allows to reduce irreversibilities in the cycle, as pointed out theoretically by Dai et al. (2018). Funding for open access charge: CRUE-Universitat Jaume I

The paper presents the design of a novel heat rejection system suitable for desert climates where daytime temperatures are typically high, nighttime cooling through sky radiation exchange is highly effective, and freshwater is scarce. Desert climates also feature high solar energy intensities during daytime, which can be exploited to power thermodynamic cycles. However, such cycles reject heat during operation, and daytime temperatures are too high for employing air cooling whereas scarcity of freshwater limits the applicability of evaporative cooling. We propose a system that defers dissipation of heat rejected during daytime operation to nighttime when ambient conditions are much more favorable for heat dissipation to the atmosphere. The paper presents the proposed design, its method of operation, and its implementation in a solar-driven ice-making plant in Upper Egypt. A mathematical model was developed to predict system performance and support decision-making over equipment sizing. It was used to simulate the performance of the deferred cooling system over a week. Using weather data collected at New Cairo (30.02 °N latitude, 31.5 °E longitude) in April 2017, the model demonstrated that the system could achieve a maximum temperature drop of 16 °C, which corresponds to a cooling of 47 MJ/m2/night.

The aim of this numerical investigation is to analyze the performance of a building integrated photovoltaic/thermal (BIPV/T) system from exergoeconomic and enviroeconomic points of view for Kermanshah, Iran climatic condition. In the proposed system, the cooling potential of supply air and exhaust air is used for cooling the PV panels as well as heating the supply air by heat rejection of the panels. The results showed that the yearly total amount of 3038.83 kWh thermal energy, 2259.64 kWh electrical energy, and 19.97 kWh useful exergy could be saved by using the studied BIPV/T system. Furthermore, the annual reduction of 5.94 tons of CO2 emission was achieved by using the proposed BIPV/T system. Finally, it was revealed that proposed system provides 32.52% of the required heating load for ventilation air on the average basis.

The International Fusion Material Irradiation Facility (IFMIF) aims at qualifying and characterizing materials capable to withstand the intense neutron flux originated in the D-T reactions of future fusion reactors by a neutron flux with a broad peak at 14 MeV, capable to provide >20 dpa/fpy on small specimens, also qualified in this engineering validation engineering design activity (EVEDA) phase. Its broad mandate has been successfully achieved, only pending the validation of its accelerator with its conventional facilities. The validation of the IFMIF’s accelerators will be achieved in this on-going phase, until December 2019, with the operation of a deuteron accelerator at 125 mA CW mode and 9 MeV, which is presently under installation and commissioning in Rokkasho (Japan). The target availability of the IFMIF facility, 70%, is one of its main challenges because it demands an extraordinary individual availability of the sub-systems, such as the accelerator, with 87%. The linear IFMIF prototype accelerator (LIPAc) presents a broad spectrum of ancillary equipment to optimize its operational beam time. A description of the nuclear HVAC of IFMIF has already been reported (Pruneri et al., 2016) [1] . The present paper describes the design of the conventional systems of LIPAc, among which we address the electrical power supply, the heating, ventilation, and air conditioning (HVAC), the heat rejection system (HRS), the service water system (SWS), the service gas system (SGS), the cryoplant system (Cryo), and the fire protection system (FPS).

This paper presents the experimental testing results of a novel triple-state sorption chiller with integrated cold storage. The performance of the chiller was measured for hot water inlet temperatures between 65 °C and 95 °C, heat rejection inlet temperatures between 15 °C and 35 °C, and chilled water inlet temperatures between 10 °C and 25 °C. An empirical model was developed for implementation in the TRaNsient SYstem Simulation (TRNSYS) software. To validate the model, a five-hour experimental charge test was conducted during which the hot water and heat rejection inlet temperatures were continuously varied. The model was able to predict the total heat input and heat rejection energy to within 0.7% and 1.3% of the experimentally measured values, respectively.

Spray ponds offer significant advantages over mechanical draft cooling towers (MDCT) including superior simplicity and operability, lower preferred power requirements, and lower capital and maintenance costs. Unlike a conventional spray pond in which spray nozzles are arranged in a flat bed and water is sprayed upward, the Oriented Spray Cooling System (OSCS) is an evolutionary spray pond design in which nozzles are mounted on spray trees arranged in a circle and are tilted at an angle oriented towards the center of the circle. As a result, each nozzle is exposed to essentially ambient air as water droplets drag air into the spray region while the warm air concentrated in the center of the circle rises. Both of these effects work together to increase air flow through the spray region. Increased air flow reduces the local wet-bulb temperature (LWBT) of the air in the spray pattern, promoting heat transfer and more efficient cooling. The authors have developed analytical models to predict the thermal performance of the OSCS that are based on classical heat and mass transfer and kinetic vector relationships for spherical water droplets that rely only on generic experimental thermal performance data. Therefore, the model is not limited in application with regard to spray pressure or nozzle spacing or orientation and is not limited by droplet size considerations. This paper describes specific details such as nozzle type, orientation, and drop spectrum and details on the analytical model never before published that are used to predict the OSCS performance. The paper compares the predicted performance of the OSCS with the rigorous full-scale field test results that were measured in compliance with Nuclear Regulatory Commission requirements at the Columbia Generating Station (CGS) where the ultimate heat sink (UHS) is two OSCS.

Oil-coolers are necessary components in high performance diesel engines. The heat removed by the cooler is a component in the total heat rejection via the engine coolant. Oil-cooler absorbs the heat rejected during the piston cooling and engine rubbing friction power loss. During flows of both coolant and engine oil via the oil-cooler, some flow resistances occur. The aim of the study is to determine values of the flow resistance coefficient for oil going through the cooler at various temperatures. The test stand was developed to determine time needed to empty tanks from liquids flowing through oil-cooler. The flow model was elaborated to study the mentioned flow resistance coefficient with respect to changing liquid temperature. The 20 °C increase in liquid temperature resulted in a flow resistance coefficient decrease of 30% for coolant and of the much more for engine oil. It was found that better results would be achieved with flows forced by means of pumps instead of using gravitational forces on the test stand.

With the introduction of PCM-based heat sinks, the cooling of the electronic components in transient applications has been developed. The PCM-based heat sink effectiveness is acceptable only within the melting time, so that in the post-melting stage, the electronic component temperature increases significantly. In this study, a novel hybrid heat sink filled with PCM and air was introduced. This heat sink uses the PCM and air potentials simultaneously to neutralize the effects of the incoming heat flux to keep low the electronic device temperature. Incorporation of air into the PCM-based heat sink leads to acceleration in the heat rejection to the ambient (positive effect) and reduces the PCM volume fraction (negative effect). Based on the results, the positive effect outweighed the negative one and consequently, the cooling ability of the novel heat sink was better than the PCM-based as well as air-cooled heat sinks. As the convective coefficient increases, the positive effect strengthened and hybrid heat sink effectiveness become more apparent. It was found that the novel heat sink (with 50 W.m−2.K−1 ) can compete with air-cooled heat sinks with much higher convective heat transfer coefficient (100 W.m−2.K−1 ) .

Practical long-lived exploration systems on and near the surface of Saturn’s moon Titan likely would require radioisotope power systems and could usefully exploit the waste heat from such systems to maintain benign internal operating temperatures. However, the heat must still be rejected, and the understanding of heat transfer conditions to the atmosphere, as well as to liquid and solid surfaces, is summarized. This waste heat may perturb the environment in several ways that would compromise scientific measurements. The potential meteorological disturbances introduced by various power levels are discussed, and the effects of heat flux on surface materials are assessed. It is found that a heat output of ∼2 kW or higher requires a mast of 1 m or more be deployed away from a lander to avoid significant wind measurement perturbations. Even heat leaks of only 100 W·m−2 through the hull of a vehicle immersed in Titan’s liquid hydrocarbon seas may cause significant effervescence and fog generation.

Miniature condensers utilizing mini/micro-channel has been recognized as one effective technique for designing a compact heat rejection device. However, because of the complex behaviors in phase-change systems like flow condensation, accurately predicting heat transfer coefficients can be a challenging task. In this study, a large database is utilized to develop machine-learning based models for predicting condensation heat transfer coefficients in mini/micro-channels. A consolidated database of 4,882 data points for flow condensation heat transfer in mini/micro-channels is amassed from 37 sources that includes 17 working fluid, reduced pressures of 0.039 – 0.916, hydraulic diameters of 0.424 mm – 6.52 mm, mass velocities of 50

The actual value of the heat rejection through the cooling towers from the air-conditioning system of the typical large-scale office building is measured in the tropical summer climate of Shenzhen. The daily average measured value of the total heat rejection per unit building area is 82.75 W/m 2 during weekdays. During the weekend, this value is only 20.24 W/m 2 , i.e., about 1/4 of that found for the weekdays, which is attributable to the less activity of building. The proportion of the sensible heat rejection is only 1.15%, and even attains a negative value when the inlet water temperature is lower than the inlet air temperature of the cooling towers. To evaluate quantitatively the effect of the heat rejection from the air-conditioning system on the urban thermal climate, the heat-rejection efficiency ratio (HRER) is presented in this study, for which the average measured value during weekdays is 1.35. In addition, a heat-rejection numerical model is developed, and the heat-rejection simulation results generally agree well with the field test data. The results indicate that the hot and humid climatic conditions impair the heat and the mass transfer efficiency of the cooling towers, and ultimately reduce the heat rejection from the building air-conditioning system.

CO2 has low critical pressure and temperature. This gives an opportunity CO2 cycles to work in a transcritical nature where heat rejection and absorption are done at supercritical and subcritical conditions, respectively. However, this characteristic posed some performance issues for CO2 refrigeration cycle such as the pressure and temperature of CO2 becomes independent of one another above the critical point thus specifying the operating conditions would be tough. It is also important to identify the optimum cooler pressure and control it; in order to get high cycle coefficient of performance (COP). Thus, the objective of this paper is to investigate the performance of a transcritical CO2 compression refrigeration cycle for different parameters and evaluate its COP. To achieve that, a refrigeration cycle was modeled using thermodynamic concepts. Then, the model was simulated for various parameters that were manipulated to investigate the cycle performance. Maintaining other operating parameters constant the highest COP was 3.24 at 10MPa gas cooler pressure. It was also observed that the cycle is suitable for air-condition application than refrigeration cycle, as COP increases when the evaporator temperature increases. Simulations were conducted using EXCEL developed program. The results can be used in the design of CO2 refrigeration cycle.

Carbon dioxide (CO2) is one of the replacements of the synthetic refrigerants whose properties are good as a refrigerant with no ozone depletion and a very little global warming effect. However, its low critical temperature makes a CO2 refrigeration system to form trans-critical cycle and determination of an optimal heat rejection pressure becomes an important problem for the best performance. Until now, number of studies have been published which correlate preliminarily obtained data map with some major operating parameters. In this study, a generally usable real time optimal control method is introduced. This real time optimal control method does not require preliminarily obtained correlations and makes the system operate in a nearly optimal region. Additionally, its limitations which produce undesirable errors and bias of controlled value were also treated in this paper. Three causes of errors were discussed and it is helpful to improve the control method.

In this study, a hybrid ground-source heat pump (GSHP) system with surface water heat exchangers is employed in an exhibition building in Shanghai to provide with high-efficiency energy for space cooling and heating and also solve the problem of thermal imbalance of the soil because of a significant imbalance between the annual heat rejection to the ground and the annual heat extraction from the ground. The operation strategies were put forward based on the annual building hourly load to make the hybrid GSHP system in a high-efficiency status during the long-term operation. The results show that the hybrid GSHP system can effectively solve the heat accumulation problem and decrease in system performance for the ten-year long run.

The use of air-conditioning, the largest energy demand for buildings in the tropics, is increasing as regional population and affluence grow. The majority of installed systems are split type air-conditioners. While the performance of new equipment is much better, the influence of the microclimate where the condensing units are installed is often overlooked. Several studies have used CFD simulations to analyse the stack effect, a buoyancy-driven airflow induced by heat rejected from condensing units. This leads to higher on-coil temperatures, deteriorating the performance of the air-conditioners. We present the first field measurements from a 24-storey building in Singapore. A network of wireless temperature sensors measured the temperature around the stack of condensing units. We found that the temperatures in the void space increased continuously along the height of the building by 10–13 °C, showing a significant stack effect from the rejected heat from condensing units. We also found that hot air gets stuck behind louvres, built as aesthetic barriers, which increases the temperature another 9 °C. Temperatures of around 50 °C at the inlet of the condensing units for floors 10 and above are the combined result, reducing the unit efficiency by 32% compared to the undisturbed design case. This significant effect is completely neglected in building design and performance evaluation, and only with an integrated design process can truly efficient solutions be realised., Energy and Buildings, 71, ISSN:0378-7788, ISSN:1872-6178

We analyzed of heat transmission across three roof structures ; bare RCC (reinforced cement concrete) roof, RCC roof with weathering coarse and RCC roof with PCM (phase change material) above RCC. A transient numerical procedure was developed. ANSYS-Fluent 12 finite volume method based software was used for solving the problem. The numerical procedure was validated against the available experimental data. The simulation was carried out on 365 days of the year for these three roofs. The PCM melted from 8 h to 18 h and solidified during the rest of the day. From March to August, the net heat entering into the room per day is positive, thus more and more PCM melts and becomes liquid. The liquid portion of PCM increases from March to August, during September to February, there is a net heat rejection per day, thus the melted PCM becomes solid progressively, and at the end of February, almost all PCM has become solid. Thus there is a melting cycle on a daily basis and over the year. It takes care of all the external climatic variations and keeps the roof bottom surface temperature almost constant and close to room air temperature. On yearly basis, about 56% reduction in heat transmission into the room is obtained with PCM roof when compared to the conventional weathering coarse laid roof.

The geographical contradictions between plenty of water and high solar radiation constitute are hindering the development of concentrated solar power (CSP) plants, dry cooling systems are compelled to adopt to solve the contradictions for the CSP plants. This paper analysis the feasibility of a novel indirect air cooling with compound refrigerating cycle (CRC-IAC) system used in CSP plants. The solar field and power block in the analysis are modeled using NREL’s Solar Advisor Model (SAM), excluding heat rejection system. Thermodynamic simulations and optimizations for operation exhaust pressure with the changes of ambient dry-bulb temperature are presented. The ideal cycle performance for CRC-IAC system is evaluated and quantified. Moreover, the system was compared with circulating wet cooling (CWC) and air cooling condenser (ACC) in terms of electricity generation and levelized electricity cost (LEC). The results show that the LEC of CRC-IAC is increased by 6.44% and reduced by 5.38%.

Recently, interest in chemical-looping combustion (CLC) has grown because it is a technique that could allow cost-effective carbon capture and storage. Recently, the chemical-looping process was also proposed for the production of hydrogen. Chemical-looping hydrogen (CLH) generation, which is a derivation of CLC, is a water-splitting process that involves the reduction–oxidation of a metal oxide. CLC and CLH can reduce the irreversibility and the extent of heat rejection, thereby improving the cycle efficiency. The current paper presents a thermodynamic analysis of CLH to illustrate its potential for improved efficiency. A methodology for selecting oxygen carriers based on their thermodynamic properties is developed, and several candidate materials are reviewed. From a thermodynamic perspective, metals such as Ni and Fe are more suitable for CLH, whereas metals such as Ca and Cd can provide higher efficiency for CLC. Finally, comments on the practical implementations of CLH in power plants are presented.

Conventional modeling of condensers typically assumes three zones: de-superheating, condensation, and subcooling zone, even though it is clear that condensation occurs in the de-superheating zone at some conditions and subcooling occurs during condensation. This article discusses the actual situation and provides experimental validation of the hypothesis. The experimental results show heat transfer coefficients (HTC) of CO2 and R410A at mass fluxes from 100 to 240 kg m−2 s−1, heat fluxes from 3 to 25 kW m−2, and reduced pressures from 0.68 to 1.00 in a horizontal smooth tube of 6.1 mm inner diameter. Data are compared to correlations proposed for other working fluids or other conditions. Results show much higher values of HTC than the correlation proposed for single-phase turbulent flow in the superheat zone. The occurrence of condensation in the superheat zone is evident when tube wall temperature is below saturation temperature. The results suggest that simplified calculations of heat rejection in a sup...

The present work aims to investigate the potential advantages in using a novel wet and dry configuration for heat rejection units in ORC power plants. The reference case is a geothermal power plant that exploits a medium temperature brine and uses a closed loop of cooling water to release the condensation heat. In the calculations, the off-design operation of the whole plant is optimized by a techno-economic point of view with a realistic part-load behaviour for the ORC and the use of experimentally validated correlations for the heat rejection section. The performance attainable with the novel LU-VE Emeritus ® unit equipped with a water spray system and adiabatic panels is compared with those achievable with the same unit in dry operation. Final results show a marked increase of revenues with Emeritus ® units with respect to a dry unit.

The evaporative cooling is an energy saving technology and for this reason is widely used both in industrial and civil fields. The heat and mass transfer phenomena occurring inside their tube banks are hard to study and even if many researchers have faced them, further activities need to be carried out. For this reason, this work aims at investigating with an experimental approach the evaporative condensers performance at the tube scale, focusing on the air side where more complex physical interactions occur. A test rig has been set up made of a rectangular transparent channel where electrical heaters simulate the refrigerant side and embedded Pt100 Resistance Temperature Detectors controlled by a PID set and keep constant a given outer surface temperature. Water and air operating conditions are controlled as well, and this allows to carry out a sensitivity analysis depending on all the parameters influencing those thermo-fluid dynamic phenomena. The results show that the cooling rate decreases with the air relative humidity and dry bulb temperature, while increases with water flow rate and temperature. For the testing cases the maximum improvements deriving from increasing water flow rate and temperature are of 37 % and 14 % respectively.

Analysis of heat transmission across three roof structures, namely, bare reinforced cement concrete roof, reinforced cement concrete roof with weathering coarse and reinforced cement concrete roof with phase change material above reinforced cement concrete are analysed. A transient numerical procedure is developed. The numerical procedure is validated against the available experimental data. The simulation is carried out on 365 days of year for these three roofs. The phase change material melts from 8 to 18 h and solidifies during the rest of the day. From March to August, the net heat entering into the room per day is positive, thus more and more phase change material melts and becomes liquid. The liquid portion of phase change material increases from March to August. During September to February, there is a net heat rejection per day, thus the melted phase change material becomes solid progressively, and at the end of February, almost all phase change material has become solid. Thus, there is melting cycle on daily basis and over the year. It takes care of all the external climatic variations and keeps the roof bottom surface temperature almost constant and closes to room air temperature. On yearly basis, about 56% reduction in heat transmission into the room is obtained with phase change material roof when compared to the conventional weathering coarse laid roof.

A building integrated photovoltaic-thermal (BIPVT) setup has been developed for using the cooling potential of ventilation and exhaust airs in buildings for cooling the photovoltaic (PV) panels and also heating the ventilation air by heat rejection of PV panels. The setup has been tested numerically for the Kerman city located in Kerman province in the south of Iran. Results showed that, the exhaust and ventilation airs in heating ventilating air conditioning systems can be used as the cooling fluid of the PV panels and increase their efficiency. On the other hand, the heat rejection of the PV panels could provide some part of the ventilation air heating load.

In this study, it was aimed to investigate the effect of ceramic coating on a turbocharged diesel engine performance and energy balance. For this purpose, cylinder head, valves and pistons of the engine were coated with yttria stabilized zirconia layer with a thickness of 0.35 mm nickel-chromium- aluminium bond coat, as well as the atmospheric plasma spray coating method with a thickness of 0.15 mm. Then, the engines were tested for full load. The heating values of the diesel fuel and ethanol were 46.2 and 25.182 MJ/kg, respectively. Because of the lower heating values of the ethanol, compared with the diesel fuel, it appears to have lower following to engine power, torque and SFC. Compare to engine power of SDE, LHRe has increased about 2%, LHReth has decreased about 22% at all engine speed. Compare to engine torque of SDE, LHRe has increased about 2.5%, LHReth has decreased about 23 % at all engine speeds. Compare to SFC of SDE, LHRe has decreased about 1.1 %, LHReth has increased about 54 % at all engine speeds. Compare to exhaust turbine inlet temperature of SDE, LHRe has increased about 15 %, LHReth has decreased about 17 % at all engine speeds.

In order to investigate the operation performance of ground-coupled heat-pump (GCHP) system, an analytical simulation model of GCHP system on short time-step basis and a computer program based on this model to predict system operating parameters are developed in this study. Besides, detailed on-site experiments on GCHP test rig installed in a temperate region of China are carried out. The temperature distributions of borehole as well as ground around borehole at different depths are evaluated. Operation parameters of GCHP system such as circulating water temperature, heat rejection into ground and system power consumption when the system operated in intermittent and continuous modes are investigated. The accuracy of proposed simulation model is validated by experimental data. The advantage of GCHP technology in energy efficiency over other conventional air-conditioning systems is proved to be obvious and the performance of GCHP system is found to be affected by its operation modes. Copyright The Author 2010. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com, Oxford University Press.

The solid-core Submersion-Subcritical Safe Space (S 4 ) reactor is cooled with He-28% Xe gas (molecular weight of 40 g/mole) and nominally generates 471 kWth for at least 7 years. To avoid single point failures in reactor cooling and energy conversion, the S 4 reactor core is divided into three hydraulically independent, but neutronically and thermally coupled sectors. Each sector feeds a separate Closed Brayton Cycle (CBC) power conversion loop with separate heat rejection radiator panels. Detailed thermal-hydraulic analyses of the S 4 reactor core are performed to ensure that the maximum fuel temperature during nominal operation stays below 1300 K. In addition, a neutronics analysis performed using MCNP 5 confirms that the S 4 reactor satisfies the design reactivity requirements. These are at least $ 4 of cold clean excess reactivity, at least $ 2.25 of shutdown margin, and at least $ 1 subcritical in the worst-case of submersion and flooding, following a launch abort accident. Mass estimates of the S 4 reactor design that meets both the thermal and the reactivity requirements are provided.

Recent studies indicate carbon dioxide (R744) as a valid alternative to classical substances such as HFCs used in vapour compression plants. However a transcritical refrigeration cycle is needed because the critical temperature of carbon dioxide is usually near the ambient temperature. Consequently the carbon dioxide refrigerator performances are significantly influenced by the heat rejection pressure. In this paper an experimental investigation on working optimization for a “split-system” to cool air in residential applications is presented: by varying the heat rejection pressure an optimum working condition has been found at different ambient temperatures. Furthermore a simplified model to predict the optimum heat rejection pressure is shown and a comparison with experimental results is carried out. Both the model validation and the experimental results suggest that the heat rejection pressure optimization is an convenient method to improve the performance of a carbon dioxide split system. Finally an algorithm based on the aforementioned model has been proposed in order to control an electronic back pressure valve by means of a PLC.

During an ExtraVehicular Activity (EVA), both the heat generated by the astronaut s metabolism and that produced by the Portable Life Support System (PLSS) must be rejected to space. The heat sources include the heat of adsorption of metabolic CO2, the heat of condensation of water, the heat removed from the body by the liquid cooling garment and the load from the electrical components. Although the sublimator hardware to reject this load weighs only 1.58 kg (3.48 lbm), an additional 3.6 kg (8 lbm) of water are loaded into the unit, most of which is sublimated and lost to space, thus becoming the single largest expendable during an eight-hour EVA. Using a radiator to reject heat from the astronaut during an EVA can reduce the amount of expendable water consumed in the sublimator. Radiators have no moving parts and are thus highly reliable. Past freezable radiators have been too heavy, but the weight can be greatly reduced by placing a small and freeze tolerant heat exchanger between the astronaut and radiator, instead of making the very large radiator freeze tolerant. Therefore, the key technological innovation to improve space suit radiator performance was the development of a lightweight and freezable heat exchanger that accommodates the variable heat load generated by the astronaut. Herein, we present the heat transfer performance of a newly designed heat exchanger that endured several freeze / thaw cycles without any apparent damage. The heat exchanger was also able to continuously turn down or turn up the heat rejection to follow the variable load.

Energy conservation and efficiency have always been the quest of engineers concerned with internal combustion (IC) engines. A diesel engine generally offers better fuel economy than its counter part petrol engines. It rejects about two-third of heat energy of the fuel to the coolant and one-third to the exhaust, leaving only about one-third as useful power output. Theoretically if the heat rejected could be reduced, then thermal efficiency would improve, at least up to the limits set by the second law of thermodynamics. The main objective of low heat rejection (LHR) engines is to improve the thermal efficiency by reducing the heat lost to the coolant. Diesel engines with their combustion chamber walls insulated by ceramics are referred to as LHR engines. To meet increasing energy requirements, there has been growing interest in alternative fuels like biodiesels derived from vegetable oils to provide a suitable diesel oil substitute for IC engines. Vegetable oils present a very promising alternative to diesel oil since they are renewable and have similar properties. Vegetable oils offer almost the same power output with slightly lower thermal efficiency when used in a diesel engine. In view of this, Honge oil, being non-edible, could be regarded as an alternative fuel for compression ignition (CI) engine applications. The viscosity of Honge oil is reduced by transesterification to obtain Honge oil methyl ester (HOME). In the present work, an attempt has been made to utilize the low volatile Honge oil and HOME in a CI engine to study the performance, combustion, and emission characteristics with a ceramic coating of partially stabilized Zirconium (PSZ) on combustion chamber elements. Initial experiments were conducted on a single cylinder, direct injection, four stroke, water-cooled CI engine without LHR using diesel, Honge oil and HOME to determine optimum injection timings and injection pressures. The optimum values of injection timings were found to be 23° before top dead centre (BTDC) for diesel and 19° BTDC for Honge oil and HOME. Optimum injection pressures were 260 and 205 bar for Honge oil and HOME, respectively. The results obtained showed decrease in brake thermal efficiency and increase in emissions for Honge oil operation compared with conventional diesel engine operation. However, with HOME marginal improvement in brake thermal efficiency and reduction in emissions were observed when compared with Honge oil operation. Further tests were conducted on the CI engine for Honge oil and HOME with ceramic coating on combustion chamber surfaces. The results obtained showed improvement in brake thermal efficiency and reduction in emissions. The effect of injection timings/injection pressures on combustion, rate of heat transfer, cumulative heat transfer, combustion duration and delay period have been considered and analysed for the overall performance of LHR and conventional diesel engines for different fuels tested. However, results obtained with optimum injection timing and injection pressure have only been presented.

Taipei City, located in the subtropical zone, has a basin landform. The summer is always hot and humid and the air temperature right after sunset is typically higher than 30 °C. Heat rejection from residential buildings in urban area, equipped with lots of the window type air conditioners, not only increases the air temperature outside, but also burdens the cooling load. Based on the time schedule of air conditioner use of Taipei citizens, the heat rejection/building energy use and the air temperature distribution were evaluated, and finally the additional electric consumption of air conditioners was predicted. Two software, EnergyPlus (building energy program) and Windperfect (CFD, computational fluid dynamics software) were employed in this study. In the CFD simulation, the geometry of buildings that covers 700 m in diameter was created with GIS (geographical information system) and the total mesh number was more than 3 millions. Three specified temperatures (Tam, Tbu and Tac) were used to describe the temperature distribution within the urban canopy by hourly time variation and spatial distribution with height and horizontal profile. The results revealed that the temperature gradually increased with height and the temperature next to the buildings was always higher than the ambient air. The feedback (penalty) of heat rejection to cooling load was found 10.7% during 19:01 to 02:00 h on the following day.

Mechanical power production by a dynamic micro heat engine with integrated thermal switch is demonstrated. A microengine operated from a constant heat source of 60 °C is shown to produce 350 µW of mechanical power. Employing an active thermal switch to control heat rejection from the microengine enables power to be increased to 2500 µW. Power consumption by the thermal switch is shown to be minimized by operating the cantilever switch at its resonant frequency. Thermal switch power requirements can be reduced to less than 20 µW for operational speeds up to 100 Hz.

Passive cooling of electronic components by natural convection heat transfer is the least expensive, quietest and most reliable method of heat rejection. However, some characteristics intrinsic to the phenomenon, such as a non-linear interaction between heat sources difficult its practical application. The objective of this work is to study the natural convection heat transfer optimization through genetic algorithms. Four cases were studied: one heat source, two heat sources with same dissipation rate, and two heat sources with different dissipation rates on a vertical wall. The results showed good agreement with literature and confirmed the methodology as computationally feasible for the optimal location of heat sources in a vertical wall.

LiPb auxiliary system is an important external loop equipment of test blanket module (TBM) for liquid LiPb blanket design. According to the requirement of testing strategy of DFLL (dual functional lithium lead) TBM, which could demonstrate the technology of the SLL (single-coolant lithium lead) and the DLL (dual-coolant lithium lead) blankets, a conceptual design of the LiPb ancillary system is done, which could serve to achieve the dual functions. The auxiliary system can be used to achieve the recovery of tritium, heat rejection, monitoring of impurity in LiPb, LiPb purification and so on. It consists of detritiation unit, LiPb to He heat exchanger, plugging indicator, LiPb purification system and pumping system, etc.

Theoretical study of triangular cycle with cooling and heating at variable temperatures is investigated in this study. Simple approximated correlations for COP are obtained. By implementation of the cooling and heating using multistage machines, single-compressor machines accompanying with refrigerants mixtures, semiconductor thermopiles, and the supercritical cycles with variable temperature of heat rejection, the “triangular” cycle shows promising interesting features.

The real challenge in the processes of heat transfer by heat rejection from a constrained small space is a well known issue in the process of cooling small areas. Past research in this area covered numerous theoretical and experimental studies; however in-depth investigation of the nano-fluid flow is still insufficient. In recent years the tried researchers fill the gaps on this subject matter; the aim of this paper is to know the idea enhancing the performance of the heat transfer from literatures.

This study summarizes the cooling performance of a ground-source heat pump system which was installed in a 65-m2 room in the Solar Energy Institute, Ege University, Izmir (568 degree-days cooling, base: 22°C; 1226 degree-days heating, base: 18°C) Turkey. The institute, built in 1986, has a liveable floor area of 3000 m2, and uses passive solar techniques. The heating and cooling loads of the room were, respectively, 3.8 and 4.2 kW at design conditions. The system was commissioned in May 2000 and the performance tests have been carried out since then. Based upon the measurements, the heat rejection rate to the soil with an average thermal diffusivity of 0.00375 m2h−1 in the cooling mode was found to be in average 51 W m−1 of bore depth, while the maximum entering water temperature to the unit was recorded as 35.9°C. The cooling coefficient of performance of the heat pump and the whole system was relatively low when compared to other heat pumps operating under conditions at or near design values. The primary reasons for this were discussed in detail and the potential for performance improvements was also suggested. Copyright © 2002 John Wiley & Sons, Ltd.

This charge air cooler is extensively used in diesel engine mostly for marine applications. The main purpose of a charge air cooler is to cool the engine air, ensuring efficient performance. The main objective of the charge air cooler is to increase the heat dissipation capacity and to reduce the outlet temperature. In this paper, the charge air cooler was designed, simulated and developed in MAHLE Behr India Private Limited, Pune. Based on the simulation results it is observed that heat rejection and outlet temperature were matched with the requirement and tested values.

In this paper, a detailed thermodynamic performance analysis of a transcritical condensing (TC) cycle is performed with pure CO2 and a blend of 48.5 % propane with 51.5 % CO2 as working fluids. A realistic thermodynamic model is used incorporating irreversibilities in turbo-machineries and heat exchangers. The Key finding is that the addition of propane elevates the heat rejection temperature, but does not impair any of the performance indicators. Such a fluid may be useful for power generation in concentrated solar power applications by using which a hike of up to 2 % can be realized in the thermal efficiency of a power plant.

A mathematical model of a low-gravity reflux boiler system for lunar-surface heat rejection, including the performance of a single tube and a linear array of tubes, is described. Model verification is demonstrated throughcorrelation with NASA vacuum chamber test data. Performance comparisons are made between three manufactured configurations of the tubes for similar environmental conditions and with the tube dimensions normalized with respect to one another. Finally, the optimization of a linear array of composite tubes for operation in a worstcase lunar surface thermal environment is presented. A pitch-to-diameter ratio of between 4 and 5 is recommended because that choice provides over 95% of the maximum heat transfer with a more logistically feasible array.

In order to evaluate the validity of a low heat rejection engine proposed for the reduction of heat loss, a thin film thermocouple was developed for accurate measurement of the instantaneous heat flux flowing into the ceramic combustion chamber wall. The thin film thermocouple is the pair-wire type construction without effects of the material of the thermocouple and the instantaneous heat flux, which was confirmed by finite element analysis. This paper also shows examples of measurements conducted on the instantaneous heat flux flowing into the ceramic combustion chamber, using the pairwire type thin film thermocouple made of ceramic base material.