Pre-cooling Systems Research Articles

Pre-cooling systems in modern hydrogen liquefaction

The research work presents recommendations for choosing a circuit design for low-capacity hydrogen liquefaction plants with a production rate up to 20 kg/h or 0,48 tpd (ton per day). Main design criteria considered are specific energy cost, as well as capital costs and overall characteristics of the system. A review of theoretical and real hydrogen liquefaction cycles is presented. Mathematical models of different circuits are built up considering real parameters of the typical equipment. The advantages and disadvantages of certain solutions are identified, efficiency trends in terms of hydrogen liquefaction plants are analysed. According to the obtained results of the research main of the circuits for low-capacity hydrogen liquefaction plants are selected.

Performance analysis of precooling systems for cryogenic carbon capture: A comparative study of theoretical, numerical, and experimental methods

The urgency of addressing climate change has necessitated innovative and practical approaches to reducing greenhouse gas emissions. Cryogenic Carbon Capture (CCC) technology has emerged as a promising solution for capturing CO2 from industrial emissions. This study investigates a simplified design for a precooling system within CCC technology, focusing on optimizing the efficiency and reliability of the system while minimizing energy consumption. The research examines the effects of CO2 concentration in a gas mixture (simulated flue gas, nitrogen and carbon dioxide), cooling bath temperature, and gas mixture flow rate on the performance of heat exchangers in the precooling system. Theoretical, numerical, and experimental analyses were conducted to assess the system's performance. The use of liquid nitrogen at −196 °C in the cooling bath was found unsuitable due to CO2 freezing within the pipes. Instead, a mixture of dry ice and isopropyl alcohol at −78.5 °C proved effective in maintaining consistent temperature and pressure conditions without causing CO2 blockages. Numerical simulations highlighted the importance of optimizing pipe length to balance temperature control and pressure dynamics, with a 140 cm pipe length identified as optimal for heat exchanger design. Experimental results revealed that longer pipes enhance cooling performance due to increased heat exchange surface area, while higher CO2 compositions and flow rates result in higher outlet temperatures and pressures. The study emphasizes the need for further research and simulation work to refine heat exchanger designs for industrial applications, aiming to develop systems that maximize cooling efficiency while ensuring reliable operation.

Study of an integrated vortex tube used in hydrogen pre-cooling system

In hydrogen refueling stations, a hydrogen pre-cooling system is essential to protect the onboard hydrogen storage cylinder from high-temperature damage during refueling. To address the high power consumption of existing systems, this study proposes an integrated vortex tube hydrogen pre-cooling system. This system combines the vortex tube with a two-stage compression refrigeration cycle to create a new refrigeration device. The vortex tube component is numerically simulated using the standard k-ε turbulence model. Comparative analysis of power consumption and coefficient of performance (COP) is conducted between the new system, single-stage, and two-stage hydrogen pre-cooling systems. The results indicate that the vortex tube, as the pressure ratio increases from 1.5 to 20, reduces power consumption by 26.37%–41.52% compared to the single-stage system. Additionally, it improves the COP by 30.9%–53.8% compared to the single-stage system. Furthermore, compared to the two-stage system, the vortex tube achieves power savings of 4.08%–10.44% and COP improvements of 4.3%–11.7%.

Effect of dispersant on the performances of an ice slurry-wet precooling system

This study addresses the problem of prolonged precooling time and excessive weight loss of fruits and vegetables during postharvest processes. Ice slurry precooling system shows potential but faces challenges like low undercooling and ice blockage. Dispersants are introduced to optimize heat and moisture transfer as well as the flow characteristics of the ice slurry. This research investigates the effects of four dispersants on the performance of an ice slurry-based wet precooling system through experiments. Key parameters analyzed include temperature and humidity in the chamber, cooling rate, and weight loss rate of the tested load. Results show that the addition of dispersants effectively reduces the freezing temperature, enhancing the cooling rate in the system. Among the four dispersants tested, sodium diacetate yields the lowest freezing temperature of −6.4 °C and the highest cooling rate of 0.3 °C min−1. Furthermore, dispersants influence moisture transfer between ice slurry and circulating air, impacting the humidity within the precooling chamber. Notably, the addition of sodium diacetate results in the lowest weight loss rate of 2.74 %. This research shows the potential of using dispersants in ice slurry-based wet precooling systems to enhance the postharvest preservation of fruits and vegetables.

An optimization of a pre-cooling system for batch processes: A case study of the tubular ice production process

Mathematical models for predicting the thermal behavior of feed water precooling systems for tubular ice makers were developed. A commercial water chiller and plate type heat exchanger were used as the cooling source and heat exchanging device. The simulation results suggest that the system, in which the feed water is circulated through the heat exchanger, provides a higher effectiveness (ε) with a lower heat capacity rate ratio of the feed water to the chilled water (wr) for a certain number of transfer units (NTU). In the range of the ice maker capacities popularly used, at a NTU of unity, the optimum heat capacity rate ratio of the feed water to the chilled water (wr) could be estimated to be 0.48. The water chillers would operate in the range of their minimum specific power consumptions when the feed water temperature was higher than 11 °C. The system has the potential to reduce the energy consumption about 6.7–11.6%. In addition, it can improve the productivity. The system was tested with a conventional ice maker. The energy consumption can be reduced as predicted by the model. The results could be also applied to a precooling or preheating of any production process.

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.

Comparison of EMLA Cream versus Mucosal Vibration or Pre-cooling Systems as Topical Anesthetic Agents in Children

Comparison of EMLA Cream versus Mucosal Vibration or Pre-cooling Systems as Topical Anesthetic Agents in Children

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.

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.

An innovative integrated process for helium and NGL recovery and nitrogen removal

Raw natural gas is composed of several hydrocarbons, incombustible gases, such as nitrogen and helium, and impurities. While all the impurities are typically rejected at the beginning of the process, the removals of the two inert gases are postponed to last steps, where almost all the hydrocarbons except methane are already produced in an NGL recovery unit. Hence, NGL recovery, nitrogen removal and helium extraction steps are counted the most downstream units of the entire gas processing plant. This study investigates an integrated design and optimization of the three processes. In this paper, a novel process configuration, for co-production of sales gas, NGL and crude helium, is introduced. For this purpose, first we investigate and propose an efficient design to embed the helium extraction unit into a single-column nitrogen removal process. The proposed configuration is extended to an integrated process structure which combines nitrogen removal, NGL recovery and helium extraction units. The design reduces significantly the quantity of equipment as eliminating the need for the open refrigeration cycle and propane pre-cooling systems in NGL plants. High ethane and helium recovery, high nitrogen removal rate for different ranges of nitrogen, as well as the crude helium with high purity, are the outstanding potentials of the novel process. We finally optimize the key process parameters using the particle swarm optimization method to guarantee the minimum required work and present the economic evaluation of the new developed process.

Economic Analysis of Compressor Inlet Air Precooling Techniques of a Gas Turbine Operational in Nigerian Energy Utility Sector

Economic analysis of gas turbine compressor inlet air precooling is based on the economical evaluation (maintenance, operations and personnel costs) of the various precooling systems used to improve the performance of gas turbine operational in Nigeria energy utility sector. The precooling techniques studied are evaporative, vapour compression and vapour absorption precooling techniques. This study objectively compared the three precooling techniques taking into consideration the prevailing climatic conditions of Nigeria. The overall yearly cost for evaporative, vapour compression and vapour absorption precooling techniques are evaluated to be USD25501.31/KWh, USD69867.19/KWh and USD1184548.01/KWh respectively and the payback time is three years. The system profitability for evaporative, vapour compression and vapour absorption precooling systems are USD1785376.83/KWh, USD7198182.79/KWh and USD11103747.4/KWh respectively and the payback time is three and a half year. The Net Revenue of the systems is USD8782909.21/KWh, USD15888192.52/KWh and USD84947043.84/KWh respectively. In conclusion, it is recommended that evaporative precooling system should be used in dry and humid weather conditions (Northern region of Nigeria) but it must be ensured that water is in abundance and refrigeration precooling should be employed in the moderate climatic conditions (Southern Region of Nigeria).

THERMODYNAMIC ANALYSIS OF COMPRESSOR INLET AIR PRECOOLING TECHNIQUES OF A GAS TURBINE PLANT OPERATIONAL IN NIGERIA ENERGY UTILITY SECTOR

Thermodynamic analysis of inlet air pre-cooling techniques of compressor is among the methods for the enhancement of gas turbine performance. This study compared the effect of using evaporative cooling system pre-cooling method, vapour compression refrigeration precooling and vapour absorption refrigeration precooling techniques to the gas turbine Net Power Output, Thermal efficiency, Thermal Efficiency Change factor (TEC) and Power Gain Ratio (PGR) taking into recognition the prevalent weather and climatic conditions of Nigeria and as well as optimization parameters for the reference system (i.e. without precooling techniques). The results show that at air temperature of 311K, the reference system, evaporative precooling, vapour compression refrigeration and vapour absorption refrigeration precooling methods recorded Net power Outputs of 23.143MW, 25.39MW, 31.84MW and 34.90MW respectively. The Thermal Efficiency Change factor recorded by the precooling systems at an ambient temperature of 311K is 8.68%, 37.4% and 51% respectively.

Performance and design study of optimized LNG Mixed Fluid Cascade processes

Mixed Fluid Cascade (MFC) processes are often claimed to be one of the most efficient methods to liquefy natural gas. Their performance depends on both operating conditions such as ambient temperature, and system design parameters such as exchanger sizes. The performance of the standard MFC process can be further improved by modifying the design with additional equipment, such as liquid refrigerant expanders or additional pressure levels in the refrigerant cycles.This article presents a performance study of several modified MFC processes. Results are obtained using multivariable optimization algorithms in MATLAB and a process model developed in HYSYS. Constraints related to minimum internal temperature approach are used to model the main heat exchangers. The results illustrate the impact of ambient temperature on performance, and that modifications with either two-stage pre-cooling systems or liquid expanders reduce the power consumption by 3.0%–4.5%, translating into a 15%–30% reduction in the combined UA values of the main heat exchangers.

Prediction of cooling efficiency of forced-air precooling systems based on optimized differential evolution and improved BP neural network

This paper proposes an approach to predict the efficiency of forced-air cooling of fresh apples that combines the optimized differential evolution (DE) algorithm and the back-propagation (BP) neural network algorithm. First, to balance population diversity and fast convergence, the individual mutation operation of the basic DE algorithm was optimized by dividing the entire population into two equal parts according to the fitness value of individuals, and DE-best-1 and DE-current-to-rand-1 are used as individual mutation operations for the superior- and inferior-part individuals, respectively. Moreover, the selection operation of basic DE was also changed by using a crowding scheme, which helps maintain population diversity and discover more regions containing the global optima. Second, an optimized DE-BP neural network model was established by using the optimized DE to determine the initial weights and thresholds of the BP neural network to avoid being trapped in local minima, following which the effect of input parameters on the network output was subjected to a comprehensive sensitivity analysis based on the trained neural network. The results show that the optimized DE-BP model accurately predicts the efficiency with which apples are cooled. Furthermore, the airflow velocity and total opening area have a significant negative correlation with the average apple temperature and a positive correlation with the cooling rate of the apples. Finally, the most important factor influencing the cooling efficiency of the pre-cooling system is the total opening area of the ventilated packaging.

Extending the shelf life and qualities of baby cos lettuce using commercial precooling systems

Due to a limited shelf life, baby cos lettuce lasts for only a few days after arriving at a market destination. At the present time, no research is conducted on what impacts of commercial precooling systems have on physico-chemical qualities and ultrastructure of this crop. The study provides understanding of the cellular senescence, especially associated with chloroplast and vacuole which directly affect the produce’s greenness and freshness. This research was conducted to investigate the optimum parameters for vacuum cooling, and the effects of different commercial precooling systems (room cooling, forced-air cooling, and vacuum cooling) on the physico-chemical qualities, bioactive compounds and ultrastructure of baby cos lettuce during storage at 4 °C. Overall, vacuum cooling at 0.6 kPa holding pressure and 25 min holding time maintained significantly (P ≤ 0.05) better produce qualities than forced-air cooling at 1.4 m s−1 air velocity or room cooling at 0.65 m s−1. A significant increase in total phenolics content was detected in all samples, with antioxidant activity also increasing significantly until seven days of storage for samples precooled by vacuum cooling, and until nine days of storage for samples precooled by forced-air cooling, room cooling, and in the non-precooled sample, decreasing thereafter. However, both antioxidant activity and phenolics content were better retained during storage in samples precooled by vacuum cooling. Although gradual declines in ascorbic acid and total chlorophyll content were observed across all treatments, cells of baby cos lettuce precooled via forced-air or room cooling and those in the control sample exhibited chlorophyll degradation (according to TEM), resulting in a diminished green colour. This study thus demonstrates that vacuum cooling is effective in prolonging the shelf life of baby cos lettuce grown in Chiang Mai, Thailand from nine to sixteen days at 4 °C and 85% RH, increasing the produce market window.

The effect of different precooling rates and cold storage on milk microbiological quality and composition

The objective of this study was to measure the effect of different milk cooling rates, before entering the bulk tank, on the microbiological load and composition of the milk, as well as on energy usage. Three milk precooling treatments were applied before milk entered 3 identical bulk milk tanks: no plate cooler (NP), single-stage plate cooler (SP), and double-stage plate cooler (DP). These precooling treatments cooled the milk to 32.0 ± 1.4°C, 17.0 ± 2.8°C, and 6.0 ± 1.1°C, respectively. Milk was added to the bulk tank twice daily for 72 h, and the tank refrigeration temperature was set at 3°C. The blend temperature within each bulk tank was reduced after each milking event as the volume of milk at 3°C increased simultaneously. The bacterial counts of the milk volumes precooled at different rates did not differ significantly at 0 h of storage or at 24-h intervals thereafter. After 72 h of storage, the total bacterial count of the NP milk was 3.90 ± 0.09 log10 cfu/mL, whereas that of the precooled milk volumes were 3.77 ± 0.09 (SP) and 3.71 ± 0.09 (DP) log10 cfu/mL. The constant storage temperature (3°C) over 72 h helped to reduce bacterial growth rates in milk; consequently, milk composition was not affected and minimal, if any, proteolysis occurred. The DP treatment had the highest energy consumption (17.6 ± 0.5 Wh/L), followed by the NP (16.8 ± 2.7 Wh/L) and SP (10.6 ± 1.3 Wh/L) treatments. This study suggests that bacterial count and composition of milk are minimally affected when milk is stored at 3°C for 72 h, regardless of whether the milk is precooled; however, milk entering the tank should have good initial microbiological quality. Considering the numerical differences between bacterial counts, however, the use of the SP or DP precooling systems is recommended to maintain low levels of bacterial counts and reduce energy consumption.

Techno-economic and thermodynamic analysis of pre-cooling systems at gaseous hydrogen refueling stations

We conducted a techno-economic and thermodynamic analysis of precooling units (PCUs) at hydrogen refueling stations and developed a cost-minimizing design algorithm for the PCU observing the SAE J2601 refueling protocol for T40 stations (requiring −40 °C precooling temperature). In so doing, we identified major factors that affect PCU cost and energy use. The hydrogen precooling energy intensity depends strongly on the station utilization rate, but approaches 0.3 kWhe/kg-H2 at full utilization. In early fuel cell electric vehicle markets where utilization of the refueling capacity is low, the overhead cooling load (to keep the heat exchanger cold at −40 °C) results in significantly high PCU energy intensity because only a small amount of hydrogen is being dispensed. We developed a parameterized precooling energy intensity prediction formula as a function of the ambient temperature and station utilization rate. We also found that the Joule-Thomson effect of the flow control device introduces a significant increase in temperature upstream of the PCU's heat exchanger (HX), which impacts the PCU design capacity. An optimal PCU (per dispenser, at 35 °C HX inlet temperature) consists of a 13-kW refrigerator and a HX with 1400 kg of thermal mass (aluminum), which currently costs $70,000 (uninstalled). The total (installed) capital and operation cost of PCU at a fully utilized hydrogen refueling station adds $0.50/kg-H2.

Material performance of age-hardened beryllium–copper alloy, CDA-C17200, in a high-pressure, gaseous hydrogen environment

In order to develop safer and more energy-efficient, hydrogen pre-cooling systems for use in hydrogen refueling stations, it is necessary to identify a high-strength metallic material with greater thermal conductivity and lower susceptibility to hydrogen embrittlement, as compared with ordinary, stable austenitic stainless steels. To accomplish this task, the hydrogen compatibility of a precipitation-hardened, high-strength, copper-based alloy was investigated by slow-strain-rate tensile (SSRT), fatigue-life, fatigue-crack-growth (FCG) and fracture toughness tests in 115-MPa hydrogen gas at room temperature. The hydrogen solubility and diffusivity of the alloy were also determined. The hydrogen solubility of the alloy was two or three orders of magnitude lower than that of austenitic stainless steels. The alloy also demonstrated absolutely no hydrogen-induced degradation of its strength properties, a factor which could contribute to the reduction of costs related to the construction and maintenance of hydrogen refueling stations, owing to the downsizing and improved cooling performance of the pre-cooling systems.

Optimisation of expansion liquefaction processes using mixed refrigerant N2–CH4

An expansion process with a pre-cooling system is simulated and optimised by Aspen HYSYS and MATLAB™. Taking advantage of higher specific refrigeration effect of methane and easily reduced refrigeration temperature of nitrogen, the designed process adopts N2–CH4 as a mixed refrigerant. Based on the different thermodynamic properties and sensitivity difference of N2 and CH4 over the same heat transfer temperature range, this work proposes a novel method of matching refrigerant composition which aims at single-stage or multi-stage series expansion liquefaction processes with pre-cooling systems. This novel method is applied successfully in propane pre-cooled N2–CH4 expansion process, and the unit power consumption is reduced to 7.09 kWh/kmol, which is only 5.35% higher than the global optimised solutions obtained by genetic algorithm. This novel method can fulfil the accomplishments of low energy consumption and high liquefaction rate, and thus decreases the gap between the mixed refrigerant and expansion processes in energy consumption. Furthermore, the high exergy efficiency of the process indicates good adaptability to varying natural gas compositions.

Comparison of industrial precooling systems for minimally processed baby spinach

Leafy greens including baby spinach are particularly prone to rapid dehydration. After harvest, leafy greens should be refrigerated as soon as possible to remove the heat from the field in order to decrease respiration rate and increase shelf-life. Delays between harvest and cooling should be avoided, especially during warm weather to avoid water loss. There is a wide range of precooling systems available for using in fresh produce. However, the best precooling system for baby leaves as raw material for the fresh-cut industry has not been well established. The aim of this study was to compare four precooling systems including room cooling (RC), forced air cooling (FAC), hydro cooling (HC) and vacuum cooling (VC) for their effects on quality and shelf-life of baby spinach. Two separate trials, one in winter and another in spring were carried out. Leaf water content increased after cooling in HC and VC but more significantly in winter while in spring, differences among treatments were not significant. The colour measured as chroma was more vivid in HC and VC just after processing but after storage, no differences among precooling treatments were observed. In winter, there were no significant differences in the respiration rate among precooling systems. However, in spring, HC and VC decreased respiration rate and modified less the headspace gas composition of the packages. Pseudomonas counts significantly decreased in HC and VC due probably to the washing effect of the leaf surface without promoting the growth of spoilage microorganisms. Surprisingly, visual quality was significantly lower in VC compared with the rest of precooling treatments due to the higher degree and number of damaged leaves. In conclusion, selection of the precooling system is critical during warm weather because of the high temperature at harvest. Hydro cooling is a good precooling system for baby spinach in spring as it decreases rapidly leaf temperature, decreasing respiration rate and extending shelf life. However, in winter, precooling systems are not as critical because the temperature at harvest was similar to the temperature reached after precooling.