Indirect Heat Exchanger Research Articles

Experimental Investigation of R404A Indirect Refrigeration System Applied Internal Heat Exchanger: Part 2—Exergy Characteristics

Although the R404A indirect refrigeration system (IRS) with an internal heat exchanger (IHX) and R744 as the secondary fluid has potential applications in supermarkets and hypermarkets, the exergy characteristics of this IRS have not been extensively investigated. In this study, the factors affecting the R744 exergy characteristics (degree of subcooling (DSB) and degree of superheating (DSP) of the R404A cycle, DSP of the R744 cycle, condensation temperature (CT) and cascade evaporation temperature (CET), and IHX efficiency) were experimentally evaluated to obtain basic data for the design of R404A IRS with R744 as the optimal secondary fluid. The main results can be summarized as follows: (1) Under given conditions, the smallest change in the system exergy destruction rate (EDR) according to the change in each parameter is the DSP of the R744 cycle (0.3–1%), followed by the DSB of the R404A cycle (6.1–8.8%), the IHX efficiency of the R404A cycle (3.8–14.3%), the DSP of the R404A cycle (11.7–15.9%), the CET (29.4–41.9%), and the CT (35–47%). (2) Also, in terms of the exergy efficiency of system (EES), the largest value was obtained for the DSP of the R404A cycle (2.4–12.7%), followed by the IHX efficiency of the R404A cycle (3–10.2%), the CET (2.2–8.7%), the CT (4–6.9%), the DSB of the R404A cycle (2.7–6.2%), and the DSP of the R744 cycle (0.04–1.2%). (3) In order to lower the system EDR, DSP, DSB, and IHX efficiency of the R404A cycle, the CET must be increased to the maximum, and to lower the DSP of the R744 cycle, the CT must be reduced to the minimum.

Experimental Investigation of R404A Indirect Refrigeration System Applied Internal Heat Exchanger: Part 1—Coefficient of Performance Characteristics

In this study, the performance characteristics of an R404A indirect refrigeration system (IRS) applied to an internal heat exchanger (IHX) is evaluated for supermarkets and hypermarkets. In a direct expansion system, R404A is the primary refrigerant and R744, a brine, is the secondary fluid. While there are abundant studies analyzing the theoretical performance of IRS, experimental research on IRS is lacking, and there are no papers that address the results of changes in the IHX in detail. In this study, the results achieved by modifying various parameters are experimentally evaluated to provide fundamental data for designing the optimal IRS. In the main results, looking at the trend of the increase in IHX efficiency, the change is very minimal when the efficiency is above 50%, so it is ideal to apply an IHX efficiency of about 50% considering economics and COP, etc. Applying the results in this study enables the operation and maintenance of IRSs as an eco-friendly system by achieving energy efficiency through optimizing the system coefficient of performance and securing economic feasibility by minimizing the R404A charging amount of the refrigeration cycle. To serve supermarkets and hypermarkets, R744 as a secondary fluid may help to realize an ecologically friendly, compact IRS system with a high heat transfer coefficient that can operate at low temperatures (−35 to 5 °C).

Comparative analysis of zero-carbon supply solutions for mid-to-low temperature process heat using nuclear energy

Energy consumption and carbon emissions from industrial heating processes constitute a significant and indispensable proportion of industrial production. Therefore, advancing the decarbonization of industrial production, particularly to optimize industrial heating processes, is of considerable importance in achieving global environmental sustainability. This study evaluates long-distance steam transport (LDST) and long-distance hot water transport (LDHWT) as zero-carbon supply schemes for mid-to-low temperature process heat. The heat is sourced from the existing Hainan Nuclear Power Plant using indirect heat exchange, ensuring safety for the long-distance transport medium. The schemes were applied in the Yangpu Industrial Park and comparatively analyzed based on energy efficiency and economic viability. The results indicate that both schemes exhibit comparable energy efficiencies, with LDHWT offering a slight economic advantage. However, beyond this case study, LDHWT becomes increasingly advantageous with longer transport distances and encourages factories to lower their required temperatures through technological modifications. By evaluating these schemes, this study aimed to inform future sustainable process heat decisions and contribute to reducing carbon emissions in global industrial operations.

Techno-economic evaluation of a seawater source heat pump system with auxiliary heat source in cold region of China

The utilizing of renewable seawater energy through seawater source heat pumps (SWHPs) in coastal areas is considered as a sustainable technology with minimal environment impact. Promotion of this technology needs clear understanding of its techno-economic performance but there are limited relevant studies. An empirical study was conducted in Qingdao, China, based on a practical installation comprising SWHPs supplemented by electric boilers. On-site measurements revealed considerable COP of 3.81 for SWHP and COPs of 2.87 for the whole system, implying SWHP as a viable and efficient solution for space heating in mild winter in this region. Results from TRNSYS simulations showed SWHP with auxiliary gas boilers (SWHP-GB) achieved the lowest annual primary energy demand and best economic and environmental benefits compared with other three schemes, namely SWHP with electric boilers (SWHP-EB), chillers with gas boilers (Chiller-GB) and air source heat pumps with gas boilers (ASHP-GB). SWHP played important roles in energy efficiency of the whole system with a considerable seasonal COP of 3.72 and 3.22 respectively for heating and cooling. Annual primary energy demand of SWHP-GB accounted for 55 %, 78 % and 56 % of SWHP-EB, Chiller-GB and ASHP-GB, respectively. SWHP-GB achieved the lowest life cycle costs and a rapid payback period of 10.9 years. Moreover, using direct or indirect heat exchange with seawater was found with limited impact on techno-economic performance of the system. To conclude, SWHP-GB could be used as an efficient solution for building heating and cooling in northern coastal cities in China.

Review on Factors Affecting Efficiency of Shell and Tube Heat Exchanger

Heat exchanger is one amongst promising thermal device in which heat transfer takes place between hot fluid and cold fluid. Among various classifications of warmth exchangers, the main focus was shown by researchers on indirect contact type compact heat exchangers. Among them the shell and tube device belongs to fluid to fluid type heat transfer device. Main applications of shell and tube device feed device in process industries, refineries, chemical plants and power plants. Usually the analysis of shell and tube heat exchangers are divided into two parts namely shell side and tube side analysis. Shell side analysis is easy and doesn't involve much modification. Whereas the tube side analysis is complex and it's done by varying baffle design and elevation with regard to arrangements of tubes. The most disadvantage of shell and tube device is pressure drop which occur at the end of tubes. To overcome this problem, drilled cylindrical copper block has been introduced to switch the tube part through which the new fluid flows and therefore the cold fluid is circulated through the shell. With this design modification, the effectiveness, mass rate, overall heat transfer co efficient are simulated and analysed.

Effective waste heat recovery from industrial cohesive granular materials: A moving bed indirect heat exchanger with special flow control

Particle-based moving bed heat exchangers are increasingly playing a significant role in industrial energy conservation and solar energy utilization. However, the moving bed heat exchanger used for cohesive granular materials still needs to be developed. This paper investigates the feasibility of indirect heat transfer of cohesive granular materials through a moving bed heat exchanger. A vibrating moving bed heat exchanger is developed for the metallurgical slag of vanadium-titanium (MSVT) from industry. The experiment demonstrates that the vibrating moving bed heat exchanger can establish an approximate mass flow regime of MSVT in the experimental section. The vibration device designed for the experimental and discharge section effectively resolves bridging and the intermittent collapse of arching in cohesive granular materials. The outer side of the tube is tightly wrapped by MSVT with vibration. Significant differences are observed in the flow and heat transfer behavior of MSVT between the aligned and staggered tubes. The local heat transfer coefficient at the top and bottom of the aligned tubes exhibits much lower sensitivity to flow velocity compared to the staggered tubes. The relationship between Nu−1 and Pe−0.5 or MSVT around the aligned and staggered tubes follows a linear correlation. Compared to aligned tubes, Nu−1 for MSVT in staggered tubes shows an average reduction of 28%.

A novel two-step approach for multi-plant indirect HENs design

Implementing interplant heat integration indirectly via intermediate fluid circuits is a reliable and promising means of enhancing the overall energy efficiency and reducing the carbon emissions of a chemical industrial zone. Although optimization-based sequential and simultaneous synthesis methods have been developed for interplant heat integration, obtaining optimal multi-plant indirect heat exchanger networks (HENs) remains a challenge due to the problem's size and complexity. Under this content, a two-step method is proposed based on the decomposable structural features of the HENs. In the first step, a mathematical model incorporating superstructure representation and pinch location technique is developed to optimize interplant intermediate stream allocation, by which the optimal configuration of intermediate fluids is determined by balancing utility targets and intermediate stream cost with pumps and pipelines. This approach enables multiple HENs synthesis to become independent, and in the second step, a compact MINLP model is proposed for the cost-optimal HEN design in each plant. The effectiveness and advantages of the proposed method are demonstrated by the better results obtained within reasonable computing times for three literature examples, particularly an industrial-scale problem.

Performance evaluation of an indirect–direct evaporative cooler using aluminum oxide-based nanofluid

Indoor comfort has become a necessity in recent times with the advancement of science and technology. The usage of direct type air coolers increases the humidity of the closed room, and this increase in humidity is unfavorable. The present work deals with the study related to the combination of direct and indirect type air cooler to increase the performance. A set of mild steel plates have been arranged to form a cross flow heat exchanger to exchange the heat between cold nanofluid and warm air forms the indirect heat exchanger. Al2O3-based nanoparticles have been blended with pure water and used in indirect air coolers. Celdek pad 7090 is used as the cooling pad in the direct type of air cooling. Experiments are performed by varying the flow rates of water from 1 to 4 lpm, by varying the air velocities from 3 to 6 ms−1, and by varying the concentration of nanoparticles in the water from 0 to 0.2.5%. Performance parameters such as change in temperature, change in Relative humidity (RH), cooling efficiency and coefficient of performance (COP) are determined. It was found that by adding the nanoparticles, the performance of the cooler has been enhanced. Chane in dry bulb temperature (ΔDBT), cooling efficiency increased by 13.1%, 14% as compared to the indirect method without using the nanoparticles and 39.2% and 21% as compared to the only direct type. Similarly, ΔRH reduced by 27% when compared to only direct evaporative cooler. 3 LPM showed the best performance with the highest humidification efficiency and COP of 96% and 5.9, respectively. When the air velocity is increased from 3 to 6 ms−1, energy consumption increases by 49%. Combination of indirect–direct techniques with the use of nanofluid has shown the potential of greater reduction in the exit DBT with simultaneously without appreciably increasing the exit RH.

Numerical insight into heat transfer enhancement by granules inner-migration in a moving bed: A performance comparison between slanted-stick and plow-shaped agitator

Waste heat recovery of high-temperature granules is one of the most promising sustainable energy supply and carbon reduction ways for industry. A moving bed indirect heat exchanger (MBIHE) with inner-migration was proposed for granular heat recovery. Granule migration and the enhanced heat transfer induced by two types of agitators (i.e., agitator with slanted stick As and with plow-shaped surface Ap) in the MBIHE are analyzed based on DEM coupled with CFD. Owing to the effective agitation, the average heat transfer coefficient in the granule side is enhanced to ∼3 times compared to that without agitation. The heat recovery efficiency in the moving bed reached more than 70% with the agitations of either As or Ap. The heat efficiency of As is ∼7% higher than that of Ap, but with at least 60% greater rotational torque. To ensure reliable agitation, the Ap is suggested to be adopted in the MBIHE to induce granule migration.

Response to “‘Isochoric freezing’: Ambitions and reality”

The study aims at comparing the environmental performances of the indirect heat exchanger and the ohmic heater for foodstuff decontamination. By means of a Life Cycle Assessment, adopting ReCiPe 2016 midpoint (H) method, applied to the sterilization of diced tomatoes and to the pasteurization of diced peaches for a standard company respectively in Italy and in Australia, it emerged that environmental impact of ohmic heating is higher than the indirect one. Having the ohmic heater the electric energy as the main contributor, a sensitivity analysis is added to investigate the impact of the mix of primary sources. Relevant savings in global warming potential are achieved when the French energy mix is used (77.1% on tomatoes and 87.7% on peaches) or when 100% of the energy source comes from photovoltaic panels (79.7% and 88.5% respectively). Finally, the combined use of the two technologies has been investigated, resulting to be an intermediate solution compared to the others.

Evolution and Parametric Analysis of Concrete Temperature Field Induced by Electric Heating Curing in Winter

Electric heat treatment is a widely used concrete curing method during the winter. Through direct and indirect heat exchange, the electric heating system tracks and controls the temperature of the heating medium based on a positive temperature coefficient (PTC) effect. In this study, to standardize the application of this treatment in the winter curing of concrete, the thermal energy conversion of an electric heating system and the heat-transfer characteristics of concrete have been studied. Based on the theoretical derivation, a calculation model of the relationship between the thermal energy of the electric heating system and the temperature of the concrete is established. The model is verified using the concrete heating and curing test results. The numerical analysis program COMSOL is used to analyze the effects of various factors on the concrete temperature field, including the electric heating power (e.g., the surface temperature of the electric heating system), concrete casting temperature, thermal conductivity, and heat release coefficient. The results show that decreasing the surface exothermic coefficient and increasing the heating temperature will significantly increase the peak temperature of the concrete. When the heat source temperature increases by 20 °C, the peak temperature could increase by approximately 13 °C. When the heating stops, the concrete volume increases temporarily, particularly in the region where the heating cable is buried. Consequently, an excessive heating power increase may cause cracks on the concrete surface. Compared with the factors of thermal conductivity and surface exothermic coefficient, the ambient temperature has the most significant effect on the concrete cooling rate when the heating stops. When the ambient temperature decreases by −20 °C, the cooling rate of concrete increases by 0.72 °C/h. The role of concrete insulation materials needs to be strengthened to reduce cooling rates during power outages and form removal. The findings from the study provide industry practitioners with a comprehensive guide regarding the specific applications of the electric heating system in early-age concrete curing.

Heat transfer enhancement of moving bed indirect heat exchanger through directional granule migration in 3-D shell enclosure

A huge amount of waste heat is emitted with industrial high-temperature granules. Although the waste heat can be recovered by Moving Bed Indirect Heat Exchanger (MBIHE), the recovery efficiency is limited by extremely large thermal resistance in MBIHE granule side. In order to enhance the heat transfer efficiency, directional granule migration is induced by an optimized agitator to take heat to the Heat Transfer Surface (HTS). The optimized agitator is designed with plow-shaped surface (Ap), which can double the granule migrativity compared to slanted-stick agitator. To further take full advantage of granule migration in 3-directions, a heat exchanger with spherical HTS and embedded Ap is created, and the comprehensive heat transfer coefficient (Kcom) in granule side is significantly enhanced by 383% than conventional MBIHE. The Kcom is immediately increased by ∼75% at agitator start-up and gradually decreased, and the variation of Kcom is closely related to the change rate of migrativity (αc). To achieve cost-effective enhancement for Kcom, the Ap agitation is changed from consecutively to intermittently (50 s agitation with 50 s interval), where the αc is converted from constant to periodic variation, and the energy consumption of Ap can be effectively cut down by 50%.

Experimental investigation of presence of air on performance of steam heating process

A Presence of air and other non-condensable gasses poses a serious nuisance for the steam network in a process industry. From a reduction in the process throughput to an acceleration in corrosion effects, presence of air & non-condensable can hamper the productivity as well as life of a process plant. For instance, the thermal conductivity (in W/mk) of air is 0.000049; in contrast with 0.002 for water, 0.20 for iron, and 0.96 for copper. Thus, even a thin layer of air can increase the resistance to heat flow significantly. Even the convective heat transfer coefficient for air is quite low (∼15 W/m2K) as compared to condensing steam (∼2000 W/m2K); so that even if the air convicts heat, it is likely to do so poorly.The objective of this paper is to show experimentally, how air affects the heat transfer process. We investigate the heat transfer performance in terms of the rate of temperature rise (ΔT/Δt) for a water-bath-type indirect heat exchanger. The bath is filled with 100 Litre of water each time and heated with steam; where an air vent is bypassed or taken in-line alternatively, while maintaining the initial conditions constant as far as feasible. The water bath is heated from 25 to 30℃ (room temperature) to 90-95℃ and the time taken for heating is noted in each case. The experimental set-up is equipped with electronic sensors for various temperatures, pressures, steam flow rates etc. Over a set of 10 such experiments, we have found that the presence of the air vent in the steam line consistently improves the rate of temperature rise (ΔT/Δt) with uniform heating in all sections of the heat exchanger. Furthermore, when the air vent is bypassed, the different sections of the heat exchanger are heated at different rates leading to distinct hot & cold spots in the heat exchanger sections.

Prospective life cycle assessment for designing mobile thermal energy storage system utilizing zeolite

The decarbonization of industrial heat, especially utilization process heat over 100 °C, is important for the transition to a sustainable society, including climate change mitigation and the transition to a circular economy . This study focused on a mobile thermal energy storage system for industrial use using a zeolite water vapor adsorption and desorption cycle that can utilize waste heat not only in space but also over time, and a prospective life cycle assessment (LCA) to design the system and provide feedback for further development. A numerical model was developed to predict the performance of the system using a moving bed indirect heat exchange system as the heat-discharging system and a moving bed countercurrent contact system as the heat-charging system, coupled with mass, energy, and momentum conservation equations for obtaining the foreground data for the prospective LCA. A prospective LCA was conducted to calculate greenhouse gas emissions (GHG) and resource consumption. The results showed that the m-TES reduces lifecycle GHG, and there are conditions for zeolite flow rates that minimize GHG emissions. It was also found that the resource consumption of m-TES increases as the system size increases, but is less than that of batteries. The hot spots are the fuel-saving effect at the heat-discharging side, auxiliary power at the heat-charging side, and the zeolite manufacturing stage. • A mobile thermal energy storage using zeolite was designed by numerical analysis. • A prospective LCA provides feedbacks to further development required. • There are conditions for zeolite flow rates that minimize lifecycle greenhouse gas. • Abiotic resource consumption is lower than other energy storage.

Simultaneous retrofit of direct and indirect Heat Exchanger Storage Network (HESN) via individual batch process stream mapping

This paper proposed a novel methodology to retrofit Heat Exchanger Storage Networks (HESN) of batch processes using a modified graphical retrofit tool, namely batch Stream Temperature Enthalpy Plot (batch STEP). Unlike other graphical retrofit tools, batch STEP maintains individual characteristic of process streams as well as serves as the one-stop retrofit tool to retrofit direct and indirect HESN simultaneously. The conventional batch heat integration typically aimed to synthesise new Heat Recovery Loops (HRLs) for heat recovery enhancement without exploiting the benefits of reusing existing HRLs in saving the additional volume of heat storage units (HSUs) and space allocated for retrofit. Thus, this paper extends the STEP continuous retrofit methodology to batch processes by introducing a batch STEP diagram for identification of the potential process streams to be integrated into existing HRLs and potential modifications of existing HRLs operating temperature. The methodology also introduces HRL– problem table algorithm (HRL-PTA) and heuristics to target the maximum indirect heat recovery and integrate process streams into the existing HRLs systematically. The methodology proposed achieves plant savings of 23.9%–60.0% for hot utility, 25.9%–42.2% for cold utility and a reduction of 6.3%–8.1% for additional volume of HSUs required in two illustrative case studies.

Performance Enhancement of a Ventilation System in Hot and Dry Climate Using Air-PCM Heat Exchanger

The building projects' power consumption and CO2 emissions are 40% and 33%, respectively. It is a viable strategy to use phase change material in energy storage to provide free cooling. There are few studies on free cooling in hot climates, so the proposed system uses paraffin as a thermal storage material for free cooling and ventilation. The project contains a cooling tower, a horizontal slab heat exchanger between air and phase change material, and an indirect compact heat exchanger between air and water. The energy equation is computed using Engineering Equation Solver software to assess the overall system perform properly. The model investigated the parameters that affect the system's performance under various climate conditions. The system has improved indoor air quality by providing ventilation and extending the period of thermal comfort. The system's performance is determined by the cooling tower's performance and the Air to PCM and Air to water heat exchangers. The Air to PCM heat exchanger reduces supply temperature by 2°C with a slight pressure drop < 20Pa and does not affect system power consumption.

SIMULATION OF HEAT AND MASS EXCHANGE PROCESS HEAT EXCHANGER OF SIDE-EVAPORATIVE TYPE

It is known that the share of influence of the microclimate on the productivity of animals is about 20-25%. In the process of life, animals emit a large amount of heat, moisture, harmful gases, including carbon dioxide, ammonia and hydrogen sulfide. If the ventilation system does not work satisfactorily, the concentration of water vapor and harmful gases may exceed the standards, as a result of which animals drastically reduce productivity and may die. Currently, when creating livestock enterprises, it is necessary to resolve issues related to the reduction of investments, 40% of which is equipment. More than 20% of the cost of equipment falls on the heating and ventilation system; it is on it that they most often try to save money. Disagreements often arise between specialists on the deviation of microclimate parameters from optimal values for the productive qualities of farm animals. The article presents the physical and mathematical apparatus and methods for simulating the process of heat and mass transfer in an indirect-evaporative type heat exchanger for livestock buildings. The description of the process of heat and mass transfer in the heat exchanger of the indirect evaporative type of the Maisotsenko cycle is complex and requires the solution of many important mathematical problems (for example, the algorithmic solution of the combined heat and mass transfer on the surface with existing walls). Of particular importance is the development of an efficient algorithm that allows one to calculate differential equations of heat and mass transfer in partial derivatives. Therefore, the aim of the research is to describe the physical and mathematical apparatus and simulation technique (numerical simulation) of the heat and mass transfer process in an indirect evaporative type heat exchanger. As a result of analytical studies, the physico-mathematical apparatus of the process of heat and mass transfer in the heat exchanger of the indirect evaporative type of the Maisotsenko cycle was compiled, including the energy balance equation, taking into account sensitive and latent heat transfer on the surface of the wall of the wet and dry channels. The initial and limiting conditions of the heat and mass transfer model in the working part of the evaporative cooler under study are determined, which form the basis of numerical simulation in the Star CCM+ software package. A simulation technique (numerical modeling) has been developed and preliminary studies of the heat and mass transfer process in the heat exchanger of the indirect evaporative type of the Maysocenka cycle have been carried out. As a result of numerical simulation, the distributions of the temperature field, the vector field of velocities and the absolute humidity of the air flow in the heat exchanger of the indirect evaporative type of the Maysocenka cycle were obtained.

Efficient District Heating in a Decarbonisation Perspective: A Case Study in Italy

The European and national regulations in the decarbonisation path towards 2050 promote district heating in achieving the goals of efficiency, energy sustainability, use of renewables, and reduction of fossil fuel use. Improved management and optimisation, use of RES, and waste heat/cold sources decrease the overall demand for primary energy, a condition that is further supported by building renovations and new construction of under (almost) zero energy buildings, with a foreseeable decrease in the temperature of domestic heating systems. Models for the simulation of efficient thermal networks were implemented and described in this paper, together with results from a real case study in Italy, i.e., University Campus of Parma. Activities include the creation and validation of calculation codes and specific models in the Modelica language (Dymola software), aimed at investigating stationary regimes and dynamic behaviour as well. An indirect heat exchange substation was coupled with a resistive-capacitive model, which describes the building behaviour and the thermal exchanges by the use of thermos-physical parameters. To optimise indoor comfort conditions and minimise consumption, dynamic simulations were carried out for different operating sets: modulating the supply temperature in the plant depending on external conditions (Scenario 4) decreases the supplied thermal energy (−2.34%) and heat losses (−8.91%), even if a lower temperature level results in higher electricity consumption for pumping (+12.96%), the total energy consumption is reduced by 1.41%. A simulation of the entire heating season was performed for the optimised scenario, combining benefits from turning off the supply in the case of no thermal demand (Scenario 3) and from the modulation of the supply temperature (Scenario 4), resulting in lower energy consumption (the thermal energy supplied by the power plant −3.54%, pumping +7.76%), operating costs (−2.40), and emissions (−3.02%). The energy balance ex-ante and ex-post deep renovation in a single user was then assessed, showing how lowering the network operating temperature at 55 °C decreases the supplied thermal energy (−22.38%) and heat losses (−22.11%) with a slightly higher pumping consumption (+3.28%), while maintaining good comfort conditions. These promising results are useful for evaluating the application of low-temperature operations to the existing district heating networks, especially for large interventions of building renovation, and confirm their potential contribution to the energy efficiency targets.

Study on the influence of residence time on the componential evolution of biomass pyrolysis vapors during indirect heat exchange process through a combining method of bio-oil composition inversion and function fitting

A novel and effective experimental method for describing the evolution curves and hot maps of biomass pyrolysis vapors with the adjustment of sweeping gas flow rate was developed during condensation. The composition proportion of pyrolysis vapors was inverted from the composition quantification of segmental bio-oil recovered by the specific condenser with two flumes. The mathematical relationship between location and vapor composition was fitted by Slogistic function. The condensable proportion of water decreased from 85% to 60% as N2 flow rate increased from 100 mL/min to 500 mL/min under 340 K water bath. But 500 mL/min N2 flow rate accelerated the disturbance of condensing field and improved the recoveries of components with stronger condensing abilities than water. The condensable proportion of guaiacol and its derivatives decreased from 60% to 40% under 300 mL/min but increased to 55% under 500 mL/min. Furthermore, the evolution difference between high-proportion and low-proportion components in pyrolysis vapors in the condensing field was also discussed as well as the unique evolution of components with azeotrope phenomenon or special solubility. For the first time, the adjustment mechanism of constant non-condensable components on the evolution of condensable components was clarified during water bath condensation, which would remarkably improve the comprehension for the complex phase transition process during the selective condensation of biomass pyrolysis vapors.

Study on soil heat storage performance and operation strategy of new integrated HST-GSHP system in different cold regions

Heat source tower (HST) can absorb and transfer the total heat of air into soil through borehole heat exchanger (BHE) in summer, which is a potential and effective method to eliminate soil thermal imbalance of ground source heat pump (GSHP) in cold regions. In this paper, a new integrated system of HST and GSHP (HST-GSHP system) and its operating modes were proposed for soil heat storage in non heating season. Based on modeling and calculation, soil heat storage performance, operating strategy and economy analysis of the HST-GSHP system were studied. The results show that the soil heat storage of the system is concentrated in the middle of non heating season, and only from HST-BHE mode in Mohe and mainly from HST-BHE&GSHP mode in Changchun and Lanzhou. The air energy absorbed by HST accounts for 100%, 59.7% and 33.2% of the total soil heat storage in Mohe, Changchun and Lanzhou respectively. The optimal operating periods of the system are from May 30 to September 4 in Mohe and from May 30 to September 11 in Changchun, and from May 29 to June 5, from June 21 to September 4 in Lanzhou. The HST can be used for soil heat storage in Mohe and Changchun effectively, while indirect heat exchanger is more suitable for soil heat storage in Lanzhou and the optimal operating periods are from April 28 to May 4 and from May 8 to September 10. Compared with the boiler and split air conditioner system and air source heat compensator integrated with GSHP system, the energy-saving rate of the HST-GSHP system is 47.6% and 31.2% respectively and the HST-GSHP system is more economical in most cases.