Pre-cooling System Research Articles

Pre-cooling systems for hydrogen fueling stations: Techno-economic analysis for scaled enactment

Hydrogen fueling standards stipulates a sustainable cooling system technically and economically. Accordingly, the interior surface temperature of the on-board H2 storage tank in fuel cell electric vehicles must not exceed the maximum specified limit (358.15 K), and the fueling rate must be ≤ 42.86 sec / kg-H2, with T40 dispenser at 70 MPa. In this context, H2 refueling stations often employ double-tube and block heat exchangers for heat transfer. This study examines the H2 pre-cooling system for various loads and provides a comparative techno-economic analysis of double tube heat exchangers (DTHE) and microchannel heat exchangers (MCHE) under stipulated technical, operational, and outlet gas standards. For this purpose, thermal and hydraulic performances were simulated using ANSYS-CFX. Technical and cost models utilize manufacturer specifications and literature-based technical and economic characteristics to derive the minimum sustainable price, defined as the price to sustain the product. The results showed that the MCHE outperformed the DTHE for setups in mass manufacturing, improved effective heat transfer area, and predicted long term unit cost. The annual quantitative output affects manufacturing expenses and profit margins substantially. With high production rates, it is expected that the unit cost of the MCHE will decrease by up to 74%. In switching from DTHE to MCHE, general material requirements decreased by ∼60%, with scrap waste savings of ∼45% reflecting an appreciable footprint reduction.

A new heating system for the air pre-purification of air separation units

A new heating system is disclosed to reduce the regeneration heating electric consumption for air pre-purification of air separation units. The new heating system is of great energy-saving significance, as air separation units are energy-intensive installations that account for a considerable proportion (around 4.97 %) of China's total national electricity consumption. Unlike the traditional electric heater, the new heating system integrates components such as a compressor, a heat exchanger, and an expander to meet the heat requirement of the pre-purification unit, while also providing cooling capacity to reduce the refrigeration load of the pre-cooling system of an air separation unit, thereby realizing the efficient comprehensive utilization of electric energy. Furthermore, a regenerator is employed to enable the continuous operation and downsizing of the system. Mathematical models were established for each process in the new heating system, and then the simulation and calculation were carried out based on the field data of an industrial-scale air separation unit. Inlet and outlet parameters and power of the compressor, expander, and heat exchanger were obtained. The temperature and pressure bed profiles of the regenerator and the temperature history curves of the cold and hot ends of the regenerator were obtained. Then, the energy-saving effect of the new heating system relative to the traditional electric heater was obtained. In addition, an economic evaluation of the new heating system was conducted based on its energy-saving effect. The conclusions drawn are as follows: compared with a traditional electric heater, the new heating system can save about 55.5 % of electric energy, and the payback period of the new heating system retrofitted from a traditional electric heater is about 2.3 years.

A novel integrated hydrogen and natural gas liquefaction process utilizing a modified double mixed refrigerant process pre-cooling system

The hydrogen liquefaction process is energy-intensive due to the lower liquefaction temperature. To improve the energy efficiency of the hydrogen liquefaction process, a novel integrated liquefaction process employing a modified double mixed refrigerant process pre-cooling is proposed and analyzed. The three-stage adiabatic ortho–para hydrogen conversion makes the process compact. Furthermore, the particle swarm optimization algorithm is utilized to find the optimal decision variables. The result reveals that the total specific energy consumption (SEC) of the process is 6.5921 kWh/kgLH2-LNG, which is 15.83% lower than the base case. The SECs for the production of LNG and LH2 are 0.2445 kWh/kgLNG and 6.3476 kWh/kgLH2. Moreover, the exergy analysis and thermodynamic evaluation reveal that the exergy efficiency, coefficient of performance, and figure of merit of the process are 49.26%, 0.2306, and 0.49, exhibiting high thermodynamic performance. Finally, the sensitivity analysis indicates that the evaporation pressure of the sub-cooling refrigerant has the greatest impact on the performance of the process. The proposed process has an important reference value in the design of the combined production of LH2 and LNG from industrial by-products and the H2 liquefaction process.

Design and Analysis of Cryogenic Cooling System for Electric Propulsion System Using Liquid Hydrogen

As the demand for eco-friendly energy increases, hydrogen energy and liquid hydrogen storage technologies are being developed as an alternative. Hydrogen has a lower liquefaction point and higher thermal conductivity than nitrogen or neon used in general cryogenic systems. Therefore, the application of hydrogen to cryogenic systems can increase efficiency and stability. This paper describes the design and analysis of a cryogenic cooling system for an electric propulsion system using liquid hydrogen as a refrigerant and energy source. The proposed aviation propulsion system (APS) consists of a hydrogen fuel cell, a battery, a power distribution system, and a motor. For a lab-scale 5 kW superconducting motor using a 2G high-temperature superconducting (HTS) wire, the HTS motor and cooling system were analyzed for electromagnetic and thermal characteristics using a finite element method-based analysis program. The liquid hydrogen-based cooling system consists of a pre-cooling system, a hydrogen liquefaction system, and an HTS coil cooling system. Based on the thermal load analysis results of the HTS coil, the target temperature for hydrogen gas pre-cooling, the number of buffer layers, and the cryo-cooler capacity were selected to minimize the thermal load of the hydrogen liquefaction system. As a result, the hydrogen was stably liquefied, and the temperature of the HTS coil corresponding to the thermal load of the designed lab-scale HTS motor was maintained at 30 K.

Spray Effect on the Thermal Performances of a Dry Cooling Tower

Pre-cooling the inlet air of a dry cooling tower by means of a spray can improve the tower performance during periods of high temperature. To study the spray effect on the thermal performance of natural draft dry cooling towers (NDDCTs), in this study 3-D numerical simulations of such a process have been conducted using Fluent 16.2 (a two-way coupled Eulerian-Lagrangian approach). The considered NDDCT is 120 m high and only half system is simulated due to its structural symmetry. Three different spray strategies have been investigated at a typical crosswind speed of 4 m/s, which is the most frequent wind speed. The results have shown that: (1) The three implemented spray strategies can improve the thermal performance of the studied NDDCT with a varying degree of success. In one case, the heat rejection rate can be increased by 35.2%, and the tower outlet water temperature can be decreased by 2.1°C when compared with the no spray case; (2) To improve the thermal performance of the NDDCT using a small amount of water, the design of the spray pre-cooling system must include more nozzles on the windward and fewer or even no nozzles on the leeward sides of the NDDCT.

An efficient hydrogen liquefaction process integrated with a solar power tower and absorption precooling system

An efficient hydrogen liquefaction process integrated with a solar power tower and absorption precooling system

Investigation on the control mechanism of spray pre-cooling the inlet air of natural draft dry cooling tower

• A 3-D model of spray pre-cooled NDDCT was developed. • The control mechanism of nozzle spray was investigated from three aspects. • The highest modified cooling efficiency of 73.2% occurs in spray scheme 18. • The heat rejection rate of the NDDCT increases from 123.67 MW to 176.08 MW. • The regional regulation principle of spray water flowrate is proposed. Spray pre-cooling the inlet air can improve the thermal performance of natural draft dry cooling towers (NDDCTs). To achieve the purpose of good performance improvement with minor water consumption, it is necessary to investigate the control mechanism of spray pre-cooling system for NDDCT performance improvement. This paper developed a 3-D model of spray pre-cooled NDDCT using Fluent 16.2. The NDDCT was 120 m high and 1/12 NDDCT was simulated due to the symmetry. The control mechanism of nozzle spray was investigated from three aspects, i.e., the spray angles, arrangement of nozzles, and spray water flowrates. Simulation finds that: (1) To achieve the goal of maximal cooling performance improvement with benchmark spray water flowrate, the recommended scheme is 18, which consists of 1 upward nozzle at height of 3 m, 3 co-flow nozzles at height of 5 m, 3 nozzles with the spray angle of 45° at height of 5 m, 3 upward nozzles at height of 8 m, 3 nozzles with the spray angle of 45° at height of 11 m and 3 nozzles with the spray angle of 45° at height of 13 m. The heat rejection rate of the whole cooling tower increases from 123.67 MW to 176.08 MW because the natural convection is enhanced; (2) The highest modified cooling efficiency at the heat exchanger surface is 65.0 % when the spray water flowrate reduced to 75 % of benchmark spray water flowrate while it is 47.1 % with 50 % of benchmark spray water flowrate; (3) To achieve more uniform cooling, it is suggested that the nozzles should be arranged at the tower inner region in low-height zone while the nozzles should be arranged at the tower outer region in high-height zone. Besides, large spray water flowrate at high-height zone is recommended to achieve maximal cooling effect with low water consumption.

Numerical Simulation and Comparative Analysis of Three Boil-Off Gas Reliquefaction Systems

Abstract In view of the problem that the boil-off gas (BOG) generated by small liquefied natural gas (LNG) ships affects the transportation safety, three BOG reliquefaction systems are improved, which are as follows: case 1: serial nitrogen expansion reliquefaction system (N2-BOG); case 2: single mixed refrigerant reliquefaction system (SMR-BOG); and case 3: propane precooled mixed refrigerant reliquefaction system (C3MR-BOG). The basic process is simulated in aspen plus and combined with the mathematical model built up in matlab where the three cycles are optimized with the specific power consumption (SPC) as the objective function. The results show that the SPC of three cases are 0.8021 kWh/kg (LNG), 0.4150 kWh/kg (LNG), and 0.5063 kWh/kg (LNG); the coefficient of performance (COP) of cases 1, 2, and 3 are 0.20, 0.39, and 0.30; the exergy efficiency of 36.56%, 70.66%, and 57.93% along with the total product cost of 89.00 $/h, 55.73 $/h, and 77.54 $/h are achieved in Cases 1–3, respectively. In addition, the overall exergy destruction of the cycles and each equipment are discussed, and the matching of the cold and heat sources of the multistream heat exchanger in the three systems is analyzed. In conclusion, under the condition that the BOG mass flowrate is 350 kg/h, the improved SMR-BOG has advantages on thermodynamic performance and economic analysis, which makes it a better choice.

Influence of precooling systems on postharvest quality and shelf life of dragon fruits (Hylocereus polyrhizus)

Postharvest loss management has attained the main concern in the current world for the growing population and to ensure global food security. As a non-climacteric fruit, proper postharvest management is vital for dragon fruits in the context of decreasing postharvest losses and extending shelf life. A factorial experiment consisting of three locations (Tala, Dumuria, Keshobpur), and three precooling systems (without cooling, hydro cooling, CoolBot-AC cooling) was conducted to evaluate physico-chemical quality attributes of dragon fruits. The results showed that physico-chemical quality attributes were significantly influenced by precooling systems in which the CoolBot-AC cooling system significantly reduced weight loss by more than 9 % and extended shelf life by more than 2.5 days. Of the three-precooling system, the CoolBot-AC system significantly performed better resulting in higher flesh weight, flesh and pericarp ratio, edible portion, moisture, and dry matter content over other precooling systems. Similarly, CoolBot-AC precooling system performed pointedly better than other precooling systems and retained acceptable skin colour, firmness, high levels of TSS content, 12.03 % more anthocyanins, 30.73 % more flavonoid, 32.55 % more total phenols, 24.22 % more carotenoid, and high levels of ascorbic acid content. No statistical variation was documented among locations with a few exceptions. Therefore, the results indicated that CoolBot-AC precooling system could be an effective postharvest management strategy for prolonging shelf life and reducing postharvest losses of dragon fruit.

PV Pre-cooling system for the Engineers Association Branch in Latakia

This study presents pre-cooling technology using a solar photovoltaic energy system where the increasing in air-conditioning demand during summer results in a rise in the amount of electrical energy consumed from the electric network, as well as an increase in electricity bills. Air conditioners are operated in governmental facilities during official working hours, at the time of the peak demand for electricity, when electric costs are the highest. In order to shift the cooling demand out of the peak period into a lower electric cost period, reducing the energy consumption of the building and the value of the electricity bills, this study was conducted on the technology of pre-cooling using solar photovoltaic energy system. The Engineers Association Branch in Latakia was conducted as a case study. The results showed that applying the Photovoltaic (PV) pre-cooling system led to a significant decrease in the cooling demand during thek hours, and reduces the daily consumption of the electric power from the electric system, as the demand was decreased from 85 kWh to 21,250 kWh. Besides, the value of the electricity bills was decreased by 83%. Pre-cooling lowered the PV system capacity that was needed to operate the building's air conditioning equipment by 50%. A reduction of 42.5 kg of CO2 emissions per day could be achieved using PV-pre-cooling system.

Research on High-Pressure Hydrogen Pre-Cooling Based on CFD Technology in Fast Filling Process

In the fast filling process, in order to control the temperature of the vehicle-mounted storage tank not to exceed the upper limit of 85 °C, it is an effective method to add a hydrogen pre-cooling system upstream of the hydrogenation machine. In this paper, Fluent is used to simulate the heat transfer process of high-pressure hydrogen in a shell-and-tube heat exchanger and the phase change process of refrigerant R23. The accuracy of the model is proven by a comparison with the data in the references. Using this model, the temperature field and gas volume fraction in the heat transfer process are obtained, which is helpful to analyze the heat transfer mechanism. At the same time, the influence of hydrogen inlet temperature, hydrogen inlet pressure, and refrigerant flow rate on the refrigeration performance was studied. The current work shows that the model can be used to determine the best working parameters in the pre-cooling process and reduce the operating cost of the hydrogen refueling station.

Design of thermoelectric devices for extracting foreign objects from the human body by freezing

Objectives.The purpose of the article is to consider the designs of thermoelectric devices (TEC) for extracting foreign objects (IO) from the human body by freezing with various options for removing heat from the hot junctions of the thermoelectric module (TEM).Method. Modifications of thermoelectric devices are described for extracting the IO from the human body by freezing it to a special probe. Their technical design differs in the way of heat removal from the TEM hot junctions, for which air heat removal, melting working substances and preliminary cooling of the radiator are used. The basic relationships for calculating the technical means intended for the removal of heat from the hot junctions of the TEM are presented.Result. The graphs of the dependence of the temperature change of the TEM hot junctions in time are obtained for different values of its heat output when using an air heat removal system and the time of complete penetration of various working substances used in the device.Conclusion. The data obtained show that for the operating conditions of the TEC, the temperature of the hot junctions of the TEM with an air heat sink does not go beyond the permissible limits. With a module power of 8 W, 12 W and 16 W, the temperature of the hot junctions of thermoelements stabilizes rather quickly and takes the value of 308 K, 313 K and 318 K. maintaining their stable temperature is most preferred is nickel nitrate, less - elaidic acid and paraffin. Calculations of the design of a device with a pre-cooled radiator system also show the efficiency of heat removal from the hot junctions of the TEM for the duration of the entire procedure for removing the IO from the human body.

Experimental study on a wet precooling system for fruit and vegetables with ice slurry

Aiming at the application of fruit and vegetables precooling, an innovative wet precooling system with ice slurry as a cooling medium was proposed. A small wet precooling room performance test platform was built. With apples as the precooling subject, the temperature and relative humidity in precooling room, the cooling rate and weight loss of apples as indexes, by changing the weight concentration of ice slurry additives (0%-8%), the ice fraction (0%-10%) and the ice slurry flow rate (50-150 L h−1), the precooling experiments were carried out. The results showed that increasing the concentration of ice slurry additives (NaCl) could effectively reduce the equilibrium temperature in precooling room. For the ice slurry solution with the additive concentrations of 0%, 2%, 4%, 6% and 8%, the equilibrium temperature in precooling room were 4.3°C, 1.7°C, 0.4°C, 0.0°C and -0.7°C, respectively. When the ice fractions increased from 0% to 10%, the precooling time decreased from 165 min to 96 min, and the weight loss decreased from 2.11% to 0.42%. When the ice slurry flow rate increased, the relative humidity in precooling room increased, and the cooling rate of apples firstly increased rapidly and then leveled off. When the flow rate reached 100 L h−1, the relative humidity remained above 90%. The precooling system has a strong applicability, easy to realize the stable environment of low temperature and high relative humidity (0°C, >90%), so it has a large application space in the precooling and fresh-keeping of fruit and vegetables.

Performance of Solar-driven Ejector Refrigeration System (SERS) as pre-cooling system for air handling units in warm climates

Europe is encouraging new buildings to minimize their primary energy dependence to be considered, from 2021, Nearly Zero Energy Buildings (NZEB). In this regard, solar thermal energy is being extensively used as a renewable source to produce Domestic Hot Water (DHW). However, solar thermal energy fields may be oversized during the warmest season of the year, rejecting the waste heat to the ambient while increasing the air conditioning demand. The Solar-driven Ejector Refrigeration System (SERS) may be a solution for solar cooling. Nevertheless, the SERS performance is constrained when low to medium temperature solar thermal collectors, commonly installed for DHW production, are used in warm climates. Consequently, this paper reformulates the SERS application as a novel fresh air pre-cooling system for air handling units. Thereby, greater evaporating temperatures that enable the SERS adoption in NZEB are explored. In doing so, the seasonal performance under severe operating conditions is analyzed considering the two-phase flow ejector geometry, as well as refrigerants with low global warming potential. Main results demonstrate a maximum seasonal COP of 0.37 by using R717. Moreover, an average cooling capacity of 28.3 kW could be produced per kW of electricity if an optimized multi-ejector solution with R600 is adopted.

Comparison on cooling performance of pre-cooled natural draft dry cooling towers using nozzles spray and wet medium

Evaporative pre-cooling technology improves the cooling performance of natural draft dry cooling towers (NDDCTs) by introducing a certain amount of water into the air entrance. This paper compares the effects of different evaporative pre-cooling systems (i.e., normal wet-medium arrangement, A-frame wet-medium arrangement and nozzle spray) on the cooling performance of a 167 m high NDDCT. Based on the meteorological data of Naomao lake in Xinjiang in 2015, two MATLAB programs were developed for case studies. This study finds all the evaporative pre-cooling systems can improve the NDDCT's cooling performance in high temperature period. In non-high temperature period, the NDDCT's performance improvement is unremarkable, and the NDDCT's cooling performance even deteriorates in the case of evaporative pre-cooling using wet medium. In the hottest month of July, the water outlet temperatures of the NDDCT pre-cooled with normal wet-medium arrangement, A-frame wet-medium arrangement and nozzle spray drop 3.2 K, 3.5 K and 3.3 K, respectively when compared with no pre-cooling counterpart. The annual average water consumption values are 39.0 kg/s, 56.4 kg/s and 124.1 kg/s, respectively. Considering all the year around performance improvement, it is suggested to use nozzle spray pre-cooling system while intermittent operation or certain-time period operation should be considered to save water.

Energy saving potential of a fresh air pre-cooling system using radiative sky cooling

Energy saving potential of a fresh air pre-cooling system using radiative sky cooling

Energy reduction of split-type air conditioners using a pre-cooling system for the condenser

In the residential sector in Thailand, the largest source of energy consumption is air conditioning systems, particularly in summer as a reason of the high ambient temperatures. These high ambient temperatures affect condensers and result in low efficiency for the rejection of the heat out of the refrigerant. Moreover, air conditioning systems remove moisture from the air conditioning space due to the moisture in the air being condensed at the evaporator. This problem has led to a reduction in air conditioning systems using the condensed water to pre-cool the condenser. This study investigates the potential of reducing the energy of split-type air conditioners. We investigate the heat rejection from the condenser with a pre-cooling system compared to a traditional condenser. The result of the heat rejection from the condenser is extended to investigate the multiple linear regression model for future work. The pre-cooling system uses a wasted condenser coil to reduce the air temperature before entering the condenser. A commercial split-type air conditioner is used in this study since this type is the most used in Thailand. An ultrasonic humidifier is also installed to maintain the relative humidity at 70%RH in all testing conditions. The thermostat set points are 25, 26 and 27 ºC as the testing conditions. Each thermostat set point is tested using the pre-cooling system in the air conditioner and the traditional air conditioner. In total, six conditions are performed. The result shows that the pre-cooling system in the air conditioner can reduce the energy consumed by the air conditioner. The maximum energy reduction is 26.6% when used the pre-cooling system in the air conditioner is compared to the traditional air conditioner. The maximum heat rejection of the condenser using the pre-cooling system in the air conditioner is 74.3% higher than the traditional air conditioner. The multiple linear regression models and the coefficient of determination are reported. Finally, we conclude that the pre-cooling system in the air conditioner using removed condensed water to reduce the ambient air temperature before entering the condenser can reduce the energy consumed of split-type air conditioners and can be improved in future work.

Thermodynamic modeling of hydrogen fueling process from high-pressure storage tank to vehicle tank

This study develops a hydrogen fueling station (HFS) thermodynamic model that simulates the actual fueling process in which hydrogen is supplied from a high-pressure (HP) storage tank into a fuel cell electric vehicle (FCEV) tank. To make the model as accurate as possible, we use the same components and specifications as in actual HFSs, such as a pressure control valve, a pre-cooling system, and an FCEV tank. After the components and their specifications are set, pressure and temperature profiles are set as the HP tank supply conditions. Based on the pressure and temperature profiles, the model solves for the temperature, pressure, and mass flow rate of hydrogen at each downstream position, including the inside of the vehicle tank. The values predicted by the model are compared with experimental data, and we show that the developed model makes it possible to accurately simulate those values at any position during the fueling process.

Simulation Study of Forced Circulation Pre-cooling for Hydrogen

Due to the low boiling point for cryogenic propellant, the cryogenic rocket engine and delivery pipelines must be fully cooled before startup. Pre-cooling methods largely influence the complexity of the pre-launch rocket test procedure and the adaptability of delayed launch. Therefore, it is needed to comprehensively consider amounts of factors. In this paper, by comparing three pre-cooling methods in detail, selection principles are given. Finally, a model of the forced circulation pre-cooling system for hydrogen is developed with AMESim. According to the system characteristics, it is found that the tank pressure, the speed of the circulating pump and the pressure in the isolated cavity influence the cooling effect. The simulation results show that the pressure difference between the outlet pressure of the circulating pump and the pressure in the isolated cavity is the key factor, and the bigger, the better.

Investigation on Energy Consumption of an Olympic Ice Rink and Sports Facility

In these days, people spend 87% of their time indoors. Therefore, buildings are responsible for 36% of the total energy consumption and 40% of the CO2 emissions in the world. Besides, energy expenditures can be reduced, especially through improvements in public buildings used by many people. In this study, an annual energy consumption was conducted for an Olympic ice-skating rink and sports complex in Istanbul with a capacity of 900 spectators, was analyzed. Annual energy consumption of the building was 2 915 032 kWh electrical energy and 157 944 m3 natural gas. It was foreseen that 40 000kWh energy savings can be achieved annually with the evaporative pre-cooling system.