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In this study, the effects of adding pin-fins on heat sink effectiveness were investigated. To boost the pin-fin efficacy on heat rejection capability, four cross-sections were defined. Two arrange...

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.

El presente artículo científico trata el estudio y simulación de un radiador que se basa en un intercambiador de calor tubular de flujo cruzado, el cual tiene un propósito de refrigerar el procesador, tarjeta gráfica de una CPU o diversos hardware en los sistemas de computación. Se realizan diversas simulaciones en el programa ANSYS teniendo varias temperaturas de ingreso que van en rangos desde 75 °C hasta 90 °C y con flujos másicos diferentes. Los resultados muestran que, al aumentar la temperatura de ingreso del fluido a refrigerar, la salida de este fluido tambien aumenta. Sin embargo, cuando se aumenta el flujo másico existe una merma en el rechazo de calor en los dispositivos computacionales.

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.

Objective. The article deals with heat removal from computer processors in order to provide the necessary thermal conditions and temperature control of heat-generating components on integrated circuits.Methods. Methods for modeling heat exchange processes during heat transfer from a heated integral crystal to the environment are applied.Results. The power efficiency of heat rejection processors increases when using radiating thermoelectric semiconductor devices since heat is absorbed in some junctions, and instead of generating heat photons of the ultraviolet range are emitted to obtain better energy characteristics to ensure the necessary power removal from the heatgenerating components of radio-electronic circuits. This approach has a significant advantage as radiation has the maximum speed when transferring energy compared to convection and conduction, which allows for non-inertial heat removal from heat-generating components to the environment. This approach also allows increasing the efficiency of the cooling system and accelerating the transfer of heat from the heated areas to prevent heat breakdown.Conclusion. The conducted research allows concluding that light-emitting thermoelectric semiconductor devices can be used for cooling with high power efficiency, which can transfer large amounts of power to the environment with low inertia. An innovative cooling system for computer processors allows increasing the degree of integration by several orders of magnitude, which will increase the performance of computers and their speed.

On growing population leads to increasing the energy demand in the automotive sector. Many researchers are working for the substitute alternative for fossil fuel products to meet the huge energy ne...

In this investigation, the engine components were coated with metal matrix composite materials. Thus, a compression ignition (CI) was converted into low heat rejection (LHR) engine. Initially diese...

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 low temperature brine and uses a closed loop of cooling water to release the condensation heat to the ambient. In the calculations, the off-design operation of the whole plant is optimized from a techno-economic point of view with a realistic part-load behavior of 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 electricity production as well as of revenues with Emeritus® units with respect to a dry unit.

A second-law analysis of two types of MSF desalination plants (once-through OT and with heat rejection section HR) is conducted. Fixing the number of stages to 20, the HR configuration is found to present clearly less entropy generation but more specific area than the OT configuration. The detailed investigation showed that heat transfer is responsible of more than 65% of the irreversibility occurring in a stage. The 30% reduction of the entropy generation number when passing from OT to HR is totally due to the reduction of the heat-transfer irreversibility. The variation of the number of stages for OT configuration has no effect on the entropy generation. Besides, we noted that beyond 10 stages the specific area is not expected to vary noticeably. For the HR configuration, there is a continuous decrease of the entropy generation number accompanied by a continuous increase of the specific area. The comparison between the two plants showed that HR is not necessarily better than OT. The decision of which of them is the most competent depends on the number of stages and on the relative importance we attach to the irreversibility and to the specific area.

The thermodynamic analysis to improve the energetic performance of N2O transcritical cycle using dedicated mechanical subcooling is done for three different evaporator temperatures 5, −5 and −30 °C. The analysis is done for the environment temperature ranging from 30 to 40 °C. Propane is used as a refrigerant in mechanical subcooling cycle. It has been found that if combined cycle is used, the maximum increments in COP and specific cooling capacity (SCC) are 22% and 30%, respectively. It has also been found that using mechanical subcooling cycle, the reduction in optimum heat rejection pressure is higher at lower evaporator temperature, i.e. −30 °C and power consumption ratio is higher at higher evaporator temperature, i.e. 5 °C. Further, COP increment using different refrigerants in mechanical subcooling cycle has been presented, where no significant differences have been found. The increment indicates that this cycle is more efficient if the environment temperature is more than 30 °C.

They are various fuels being investigate as a potential substitute to the present extremely pollutants in diesel which is resulting from the withdrawing marketable sources. The vegetables oil is among the alternative fuel which can be directly use in C.I engine which having more cetane number and C.V. Though, the BTE of the vegetables oil is lesser to the diesel fuel. The custom of vegetables oil can causes to the more smokes, CO and HC emission. It be due to more viscosity and less volatility of the vegetables oil. The issue of more viscosity of vegetables oil is approach in various habits namely oil preheating, blending with other fuels, thermal cracking and transesterification. The main scope of project is to conduct an investigational analysis on the less heat rejection engine with help of raw Jatropha oil in the proportion 70:30 and diesel. The experiments conceded for the cylinder pressures when using the raw Jatropha oil and diesel. The results are obtained and specify the improved performances and emissions characteristics of engine with the Jatropha oil.

The disposal of waste plastic solids are becoming more than a crisis with respect to environmental safety. Proper disposal system may either be very expensive or leads to side effect. Hence researchers are looking for suitable methods to reuse them. Oils as substitute for petroleum products in internal combustion engines are gaining focus in India, because of its potential to generate large scale employment and relatively low environmental poverty. The present work aims at utilizing this waste plastic oil in a low heat rejection retarded timing engine whose combustion chamber surface is coated with partially stabilized zirconia (PSZ) ceramic. The influence of fuel injection timing was studied to completely understand the waste plastic oil performance in low heat rejection engine. The results revealed great improvement in performance, and emission characteristics. As a compensation, NOx formation was slightly increased. Overall performance of the low heat rejection engine with waste plastic oil fuel was better with 14⁰ bTDC retarded injection time.

To improve the energy efficiencies of building cooling systems, manufacturers are increasingly utilizing variable speed drive (VSD) motors in system components, e.g. compressors and condensers. While these technologies can provide significant energy savings, these benefits are only realized if these components operate as intended and under proper control. Undetected faults can foil efficiency gains. As such, it's imperative to monitor cooling system performance to both identify faulty conditions and to properly inform building or multi-building models used for predictive control and energy management. This paper presents nonintrusive load monitoring (NILM) based “mapping” techniques for tracking the performance of a building's central air conditioning from smart electrical meter or energy monitor data. Using a multivariate linear model, a first mapping disaggregates the air conditioner's power draw from that of the total building by exploiting the correlations between the building's line-current harmonics and the power consumption of the air conditioner's VSD motors. A second mapping then estimates the air conditioner's heat rejection performance using as inputs the estimated power draw of the first mapping, the building's zonal temperature, and the outside environmental temperature. The usefulness of these mapping techniques are demonstrated using data collected from a research facility building on the Masdar City Campus of Khalifa University. The mapping techniques combine to provide accurate estimates of the building's air conditioning performance when operating under normal conditions. These estimates could thus be used as feedback in building energy management controllers and can provide a performance baseline for detection of air conditioner underperformance.

This experimental analysis is carried out to investigate the performance, emission, and combustion characteristics of partially stabilized zirconia (PSZ) coated compression ignition engine using wa...

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.

In this work, waste cooking oil (WCO) was used as fuel in standard and low heat rejection (LHR) diesel engines. The experiments were conducted in standard and LHR engine to measure the performance,...

When placed in an outdoor environment, organic electronic devices (OEDs) can degrade on exposure to moisture, UV light, and heat, owing to the chemical sensitivity and decomposition of the organic materials. Therefore, to protect OEDs from outdoor environments, thin-film passivation, which can block harmful elements from reaching organic materials, is required. To meet the demands and trends in encapsulation technologies, in this study, we developed a low-temperature, simple, and effective gas diffusion multibarrier (GDM), which is UV and heat reflective as well as corrosion resistant. The designed UV- and heat-reflective GDM (UHGDM) has a multistacked structure in the form of a UV filter/Ag/gas diffusion barrier (GDB)/polymer based on a dielectric/metal/dielectric (DMD) configuration. First, the DMD structure was used as a heat mirror for infrared reflectance. Second, the bottom dielectric layer of the DMD structure was used as the UV filter, and it consisted of a ZnS/LiF multistacked structure with large differences in refractive indexes. Third, a nanolaminate-based GDB barrier with multi-interfacial and defect-decoupling systems, which achieved a water vapor transmission rate of 1.58 × 10

A cooling tower used in power plant or reactor is a heat rejection device, which extracts waste heat to the atmosphere though the cooling of a water stream to a lower temperature. Heat is generated in the primary loop and transferred to the secondary loop of a water reactor. Hence, fluid temperature in the secondary loop becomes very high which uses cooling tower to be cooled down. Therefore, an automated control system is necessary to develop for controlling this process since the operation of this stage is very sensitive and human interference is very risky. In this study a prototype of intelligent flow control system based on Fuzzy Logic Control (FLC) is developed which gives the possible solution for this problem. The system works based on the temperature difference of inlet and outlet and flow of the coolant. The inlet temperature is set to 37.8 °C while the outlet temperature is set to 25.4 °C with 5.08×10-4 m3/hr coolant flow rate at Normal Operation (NO). It is observed that the system works with its maximum efficiency in NO if the valve is opened at 75%. If the temperature difference deviates from NO then the corresponding coolant flow rate also varies automatically based on these parameters.

Present investigation is focused on the effect of thermal barrier coated piston on the performance and emission characteristics of diesel engine using diesel as a fuel. The piston crown top surface...

In this paper, an enhanced calculation method of a heat rejection system operating on the moon is presented. This was taken into consideration in the developed calculation method and in the propagation of heat fluxes with the radiation of the removed heat. The developed method made it possible to effectively evaluate the capabilities of various refrigerants and choose the radiator parameters and the refrigerant flow regime in a less time-consuming process and with minimal deviations (

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

In this contribution, a model predictive control algorithm is developed, which allows an increase of the solar operating hours of a solar cooling system without a negative impact on the auxiliary electricity demand, e.g., for heat rejection in a dry cooler. An improved method of the characteristic equations for single-effect H 2 O / LiBr absorption chillers is used in combination with a simple dry-cooler model to describe the part load behavior of both components. The aim of the control strategy is to find a cut-in and a cut-off condition for the solar heat operation (SHO) of an absorption chiller cooling assembly (i.e., including all the supply pumps and the dry cooler) under the constraint that the specific electricity demand during SHO is lower than the electricity demand of a reference cooling technology (e.g., a compression chiller cooling assembly). Especially for the cut-in condition, the model predictive control algorithm calculates a minimum driving temperature, which has to be reached by the solar collector and storage in order to cover the cooling load with a low cooling water temperature but restricted auxiliary electricity demand. Measurements at a solar cooling system for an IT center were used for the testing and a first evaluation of the control algorithm.

In this study, we enhance the understanding and design of a radiant cooling technology for outdoor comfort in tropical climates, originally proposed by R.N. Morse in 1963, in this journal. We inves...

Free piston Stirling convertors offer increased efficiency over radioisotope thermoelectric generators at the potential expense of increased risk to reliability and robustness. Steps in reducing that risk are system studies that integrate Stirling convertors into a generator. System integration of a Stirling convertor into a generator requires trade studies and in depth system analysis of a variety of subsystems. Subsystems focused upon here are the GPHS to convertor heating mechanism, convertor and system level heat rejection system, and the overall physical/mechanical configuration. An overview of several system design options and rationale for the down selection of the final configuration are presented. Included in the analysis is several off-nominal conditions and effects of failed convertors upon the system. Initial simulations showed a system efficiency of 21% and specific power of 3.9 W/kg, updated higher fidelity models and details indicate a system efficiency of 23% and a specific power of 3.0 W/kg for the reference condition are possible.

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.

A series of analysis has been conducted previously to analyze the finned heat sink thermal performance. The analysis is first performed to optimize the fin spacing of a vertical continuous finned heat sink. Both empirical and CFD methods are utilized to obtain the optimal fin spacing of a given heat sink. The results from both methods are in very good agreement. The analysis was then extended to optimize the fin configurations. Three types of fin configurations, namely continuous fins, staggered fins and in-line fins are under consideration. The results from the CFD analysis indicate that the continuous fin configuration is the most effective thermally. Later, the effects of the cover or shrouds at various distances on the heat sink thermal performance are also analyzed. The heat sink with the cover in a direct contact with the fin tips performs best in the heat rejection. For tower or poled mounted electronics, the heat sink weight is extremely important. Therefore, the extrusion fin heat sink is replaced by the plain fin heat sink for weight reduction. This study is aiming at the development of newly developed light weight finned heat sink and its thermal performance under natural convection for cooling of electronics.

Mist is increasingly applied to precool outdoor air in heat rejection. This study investigates how the coefficient of performance of an air-cooled chiller varies with a mist precooler at different levels of cooling effectiveness. A multi-variate regression model was developed to simulate the operating variables of an air-cooled chiller with mist precooling. The model was validated with typical performance data of an air-cooled centrifugal chiller. The coefficient of performance would increase by up to 30%, depending on the cooling effectiveness and the wet bulb depression – the difference between the dry bulb and wet bulb temperatures of outdoor air. At a large wet bulb depression, the percentage increase of coefficient of performance tended to correlate linearly with the chiller capacity. Yet at a small wet bulb depression, the dynamic control of condensing temperature resulted in a non-linear relationship between the percentage change of coefficient of performance and the cooling effectiveness. Further experimental work is required to optimize cooling effectiveness for the maximum coefficient of performance.

This paper presents a detailed thermodynamical exergy analysis of an optimized MSF distillation plant based on the latest published thermodynamics properties of water and seawater software of the Massachusetts Institute of Technology by using design and optimized plant operation data. Exergy flow rates are evaluated throughout the plant and the exergy flow diagram is prepared in both cases. The rates of exergy destruction and their percentages are indicated on the diagram so that the locations of each exergy destruction can easily be identified. The study concludes that as a result of an optimization, making the MSFD unit once-through cooling system to recirculating type by using cooling tower system, the unit's exergy destruction pattern changes meaningfully. Besides, in the three exist thermal desalination plants up to 53 percent of feed water, i.e.; 667 m3/h and the same amount of reject water can be conserved. Though, with this modification, the unit steam consumption has been increased up to 13 ton/h, about 50 percent of design. Moreover, the detail of the study showed that the exergy destruction can be reduced more than 39% in the pumps, and 30% in blowdown and around 29% in distillate streams. For brine heater, an enhance as small as 0.37% is also achieved. In the other hand, the rate of destruction of exergy increased around 25% in the cooling process and above 5% in the evaporators.

In tropical and sub-tropical regions, air-conditioning systems account for the greatest electricity consumption and high water use. Solar-driven absorption cooling systems can conveniently reduce electricity consumption at need. The performance of this cooling system depends on the system’s heat rejection. A simulation was performed for a 15 kW single effect ammonia-water absorption cooling system driven by low temperature thermal energy and with three different heat rejection methods (wet cooling, dry cooling, and hybrid cooling). This hybrid cooling system uses wet cooling on the absorber and dry cooling on the condenser. The system performance and economics of the chiller with these cooling methods were evaluated. The analysis showed that a wet cooling system has a higher system performance and water consumption compared to a dry cooling system, which has a high primary energy consumption with no water usage. In hot weather conditions and where there is scarcity of water, hybrid cooling can consume on average 41% less electrical energy than dry cooling and 49% less water than wet cooling and the payback period compared to a wet cooling system can be less than three years.

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).

The evaporative condensers operate at lower condensing temperatures with respect to dry condensing units and involve reduced water consumption if compared with water cooled condensers. A test rig to investigate the evaporative condenser at small scale has been designed and built up. The condensing refrigerant has been simulated by electrical heaters and an air handling unit provides air with dry bulb temperature and relative humidity set by the user. All the c affecting the evaporative condenser performance can be monitored and adjusted, in order to carry out either an extensive experimental campaign or a sensitivity analysis. The results, as expected, clearly show that the heat released to air increases with the outer surface temperature of electrical heaters and decreases with relative humidity. An increase of 37.5% of the air flow rate (at constant sprayed water) leads to a maximum reduction of the heat transfer rate of 50%. Different tubes arrangements have been compared, showing as a decrease of the transversal pitch involves worse performance.

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.

The performance of natural draft dry cooling towers (NDDCTs) can be improved by wetted-medium evaporative pre-cooling. However, the pre-cooling benefit is season dependent and is significantly affected by wetted media. To further investigate the effect of wetted medium type on pre-cooling performance, the current study simulates a pre-cooled NDDCT using two typical types of wetted media, i.e., film (Cellulose7060 and PVC1200) and trickle (Trickle125 and Trickle100). A MATLAB program was developed and was validated against published data. The model was then used to carry out case study of a 120 m-high NDDCT pre-cooled using the selected wetted media with fixed thickness of 300 mm. Both the medium performance and pre-cooled NDDCT performance were compared to recommend the characteristics of wetted media promising for evaporative pre-cooling. Simulation finds that the media with high or low cooling efficiencies and pressure drops are not promising for the studied pre-cooling case while those media with middle cooling efficiencies and pressure drops intend to produce much performance enhancement and Cellulose7060 is a representative of such kind of medium. For the 120 m-high NDDCT, the wetted-medium pre-cooling can raise the heat rejection rate of the tower without pre-cooling from 45 MW to 92 MW, 76 MW, 68 MW and 65 MW by Cellulose7060, PVC1200, Trickle125 and Trickle100, respectively at ambient temperature of 50 °C and humidity of 20%.

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.

The performance of air conditioning systems is highly dependent on the environmental conditions of the high pressure side, where heat is rejected to the environment. Air conditioning systems utilize dry cooling systems which often don’t provide adequate cooling during peak cooling periods, or wet cooling systems which consume a lot of water. In this study, a novel hybrid cooling system that can provide both wet and dry cooling was modelled in TRNSYS, and used to provide cooling to closed sorption air conditioning systems. The performance of these systems with the hybrid cooling system was compared to the performance of a standard vapor compression cooling system being cooled by a dry cooling system. The COPsol of the vapor compression cooling system exhibited a decrease of almost 26% during the summer period, whereas the COPsol of the sorption systems increased by around 30%. Similarly, the cooling capacity of the vapor compression cooling system dropped by almost 5%, and for the sorption systems, it increased by around 20% during the summer period.

Lithium-ion battery development is conventionally driven by energy and power density targets, yet the performance of a lithium-ion battery pack is often restricted by its heat rejection capabilities. It is therefore common to observe elevated cell temperatures and large internal thermal gradients which, given that impedance is a function of temperature, induce large current inhomogeneities and accelerate cell-level degradation. Battery thermal performance must be better quantified to resolve this limitation, but anisotropic thermal conductivity and uneven internal heat generation rates render conventional heat rejection measures, such as the Biot number, unsuitable. The Cell Cooling Coefficient (CCC) is introduced as a new metric which quantifies the rate of heat rejection. The CCC (units W.K−1) is constant for a given cell and thermal management method and is therefore ideal for comparing the thermal performance of different cell designs and form factors. By enhancing knowledge of pack-wide heat rejection, uptake of the CCC will also reduce the risk of thermal runaway. The CCC is presented as an essential tool to inform the cell down-selection process in the initial design phases, based solely on their thermal bottlenecks. This simple methodology has the potential to revolutionise the lithium-ion battery industry.

Since the 1960s there have been numerous development activities on high-impact material and device-level technologies that could be integrated into current or future radioisotope power systems (RPS) to enhance their performance. One recent concept study proposed cascading thermoelectrics to convert some of the waste heat from the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) into electrical power. The first-order evaluations of the concept study suggested that performance improvements to beginning-of-life (BOL) and end-of-design life (EODL) power could be achieved by integrating bismuth telluride (Bi 2 Te 3 ) thermoelectric modules into the MMRTG design. This paper discusses a proof of concept development approach to determine the BOL and EODL performance gains that could potentially be obtained by employing Bi 2 Te 3 thermoelectric modules in an RPS as a second stage in a cascaded architecture. The principal efforts embedded in this approach entail an iterative modeling and analytical process to arrive at a Stage 2 module design coupled with a heat rejection system design that enables the cascaded thermoelectric system to operate at satisfactory performance levels. This paper addresses some of the design considerations that will need to be addressed at the system level. For the purposes of this study the MMRTG characteristics and properties are employed as the basis for this paper.

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 rapid rates of urbanisation and significant improvements in construction technologies, the number of subsurface infrastructure projects has drastically increased in recent years. In addition to their primary functions, these structures have shown great potential as energy geo-structures, exchanging heat with the ground to heat and cool spaces. Given their large contact area with the ground, energy tunnels are proving to be a sustainable source of thermal energy for effectively heating under- and above-ground spaces. However, their efficiency in cooling-dominated conditions has not yet been adequately studied. This paper tackles one of the key challenges regarding transport tunnels: sustainable cooling of underground substations, by introducing an efficient and cost-effective cooling method. The method takes advantage of airflow in the tunnels and relatively stable ground temperatures and involves heat exchangers in the form of water-filled high-density polyethylene (HDPE) pipes being integrated into the tunnel space. The efficiency of the proposed system is numerically assessed by analysing the spatio-temporal variations of temperature in the ground, substation, tunnel air, tunnel structure and heat exchangers caused by continuous heat rejection from the substations. A detailed 3D finite element heat and mass transport model is used, and alternative placements of heat exchangers are investigated. Results show that heat exchangers placed on the tunnel lining, and hence exposed to the tunnel airflow, could efficiently supply a substation's cooling demand, without significantly increasing the temperature of the tunnel air or the ground. The substantial economic benefits of this cooling system compared to a conventional cooling system is also demonstrated.

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 ) .