Hot Water Flow Rate Research Articles

Off-design performance optimization for steam-water dual heat source ORC systems

High-pressure steam and hot water often coexist as industrial waste heat. In this study, dual loop and single loop ORC systems are designed for 700 kPa, 4.1 kg/s steam, and 90 ℃, 122.36 kg/s hot water conditions to study the off-design performance when steam or hot water conditions change. To maximize net output power, we employ a particle swarm optimization algorithm to optimize the evaporation and condensation temperatures. The results show that within the specified hot water conditions, the evaporation and condensation temperatures of D-ORC's low-pressure loop and S-ORC increase with rising hot water inlet temperature and flow rate. The S-ORC demonstrates a higher net output power growth rate as hot water flow rate and temperature rise. Under specific steam conditions, when the steam outlet is in a gas-liquid two-phase state, D-ORC's maximum net output power is 1.7 % higher than that of the S-ORC, with little variation in optimal evaporation and condensation temperatures with respect to steam inlet pressure. At a 3.5 kg/s steam flow rate, the D-ORC's high-pressure loop becomes ineffective, whereas S-ORC efficiently adjusts heat exchange capacity under diverse steam-water conditions, Consequently, the D-ORC's average net output power is 34.2 % lower than that of the S-ORC.

Preparation of dodecahydrate disodium hydrogen phosphate shape-stabilized composite phase change materials and their experimental investigation in solar thermal storage and exothermic systems

To alleviate the mismatch between energy supply and demand caused by the spatial and temporal distribution mismatch and weather uncertainty during solar energy utilization, solar energy is combined with phase change thermal storage technology to improve the performance of solar thermal storage systems. In this study, a shape-stabilized composite phase change material with a highly absorbent resin structure is proposed as thermal storage material. This material exhibits a latent heat of phase change of 246.5 J/g, a thermal conductivity of 1.968 W/(m·K), and maintains good stability after 200 thermal cycles. Subsequently, a detachable experimental setup integrating solar energy with a phase change thermal storage tank was designed and constructed. The effects of inlet and outlet hot water flow rates and heat source temperature on heat storage time and the amount of stored water were investigated separately. The experiments show that increasing the heat source temperature during storage effectively shortens the storage time, and that the largest effective amount of hot water is obtained when the exothermic flow rate is 300 L/h. The study's results are significant for broadening solar energy utilization, alleviating the mismatch between solar energy supply and demand, and evaluating the thermal performance of latent heat storage systems.

Effective design of sustainable energy productivity based on the experimental investigation of the humidification-dehumidification-desalination system using hybrid optimization

Reliable and cost-effective industrial-based sustainable desalination technologies are crucial for efficient and effective desalination of saline water. Seawater desalination emerges as a vital treatment, with humidification-dehumidification identified as a promising technology due to its simple, low-maintenance design and compatibility with renewable energy sources. The present work was developed using a large-scale experimental test rig based on the performance of a humidification-dehumidification system operated by the heat pump. As such, the study presents an advanced approach for optimizing humidification-dehumidification desalination systems using hybrid machine learning optimization techniques. The effectiveness of a neuro-fuzzy model, a decision algorithm based on a boosted tree, and a simple averaging ensemble in enhancing the performance of humidification-dehumidification systems were investigated. Experimental data includes cold water flowrate (L/min), hot water flowrate (L/min), inlet air temperature (°C), inlet cold water temperature (°C), inlet hot water temperature (°C), and inlet air relative humidity (%) as input variables combination and freshwater productivity (L/h), recovery ratio (%) as target variables. Several statistical indicators were used to evaluate the models’ prediction skills; similarly, a 2-dimensional Taylor diagram and error-radial plot were also utilized. In the calibration phase, boosted tree models slightly outperform neuro-fuzzy models, particularly for recovery ratio, demonstrating high accuracy and low bias. However, all models exhibit robust predictive accuracy in the verification phase, especially for recovery ratio, emphasizing their potential in generalizing to unseen data. The result indicated that the boosted tree outperformed others with Nash–Sutcliffe Efficiency = 94 % and 88 % for recovery ratio and freshwater productivity, respectively. The simple averaging ensemble shows marginal improvement with 95 % accuracy for the recovery ratio. Integrating hybrid artificial intelligence optimization with humidification-dehumidification desalination systems marks a transformative step in addressing freshwater shortages. By utilizing cutting-edge machine learning techniques, we achieve a more efficient, accurate, and reliable prediction of desalination performance.

Effect of the surface form of the herringbone aluminum plate in a plate heat exchanger on the boiling heat transfer performance of ammonia

In this study, ammonia boiling heat transfer coefficient and the overall heat transfer were measured in a plate evaporator for an ocean thermal energy conversion (OTEC) system using aluminum plates. The OTEC system used ammonia as the working and a plate heat exchanger (PHE) that combined titanium plates. In this study, we used an anodized aluminum herringbone plate with two chevron angles of 45 and 60° installed in a PHE and measured the boiling heat transfer coefficients of ammonia and overall heat transfer coefficients for both plates to compare their heat transfer performances. The experimental conditions included a hot water flow rate of 1 – 12 L/min, a working fluid mass flux of 7 – 30 kg/m2s, a hot water inlet temperature of 30 – 40 °C, and a system pressure of 700 kPa.It was observed that anodized aluminum can be used as a heat-transfer plate for the PHE. In addition, the maximum overall heat transfer coefficient of chevron angle of 45° was 4 kW/m2K, and that of 60° was 3.5 kW/m2K, respectively. The maximum ammonia boiling heat transfer coefficient of 45° was 12.5 kW/m2K, and that of 60° was 13 kW/m2K, respectively. The heat transfer coefficient values are similar. Additionally, the correlation between the nondimensional heat transfer and the Lockhart-Martinelli parameter of aluminum plates was also clarified for comparison with the previous ammonia plate heat transfer in a flat plate. By comparing the correlation equations, the aluminum plate exhibited a value twice that of the flat plate.

Experimental study of the optimal mixing ratio of metallic additives for improving the performance of the solar activated carbon-methanol adsorption refrigeration system

An activated carbon–methanol system can run on low heat (70–100°C). Methanol is dependable and works well with activated carbon because of several benefits, including an appropriate latent heat of evaporation, a low freezing point, and negligible copper corrosion and steel at temperatures below 100 °C. An experimental study of the thermal performance by increasing the adsorption bed thermal conductivity was conducted. Using0 10 % 20 and %30 % of metallic copper powder with activated carbon to improve the bed thermal conductivity. A sample is prepared with 20 % copper powder to find out the improvement of heat transfer characteristics to the cooling effect. The temperature gradient has been tested with two flow rates to examine the coolant performance and increase. Solar energy can be effectively utilized based on low-grade temperature consumption in such systems. This work aims to make an experimental investigation of the thermal performance of an activated carbon-methanol adsorption refrigeration system to study the effect of the enhanced thermal conductivity of the adsorbing bed. Using 0 %, 10 %, 20 %, 30 % of metallic copper powder with activated carbon to enhance the thermal conductivity of the bed, providing a significant improvement in the system efficiency, specific cooling power (SCP), and coefficient of performance of adsorption cooling. It is found that copper filing with a mass concentration of 20 % are appeared the optimal ratio metallic additive to enhance the thermal performance of the system. Moreover, the effect of the hot water flow rate is studied. Results indicated that the addition of 20 % metallic copper filings to the activated carbon lowered the evaporator temperature to reach -5 and -10 °C for heating water flow rates 3 and 2 LPM, respectively. Also, the addition of copper filing enhances the cycle COP of the system by 49 % and 46 % at hot water flow rates of 2and 3 LPM, respectively. The highest cycle COP of the current system reached was 0.92 for the condition 20 % additives at 3 LPM hot water flow rate. Owning the feature of great solar energy availability and the long daily sunny hours, solar-powered adsorption cooling systems have promising potential applications in Egypt. A mathematical model of the system performance is also studied.

Optimal refrigerant selection and parameter analysis of a wastewater heat pump using CO2 zeotropic mixtures

Heat pump technology can effectively recover waste heat from low-grade wastewater, which is crucial for energy conservation and carbon emission reduction in buildings. In this study, zeotropic mixtures were used to recover heat from low-grade wastewater and produce high-temperature water in a heat pump. The deep recovery of waste heat was realized by using a CO2 zeotropic mixture with a large glide temperature. Furthermore, this method ensures an excellent temperature matching between the heat transfer fluids and effectively reduces irreversible losses. To obtain an optimal zeotropic mixture, a method based on heuristic screening of the optimal CO2 zeotropic mixture was proposed. Furthermore, a model of a CO2 zeotropic mixture heat pump was established and experimentally validated. Based on the validated model, a sensitivity analysis of the various operating parameters of the heat pump was conducted. The results show that the zeotropic mixture CO2/R1234yf with a mass fraction of 0.17/0.83 is selected as the optimal refrigerant for the heat pump with the coefficient of performance, exergy efficiency and volumetric heating capacity of 7.46, 0.37, and 7978 kJ⋅m−3, respectively. The sensitivity analysis of operating parameters shows that the inlet temperature of hot water has more crucial influence on the coefficient of performance and exergy efficiency than various operating parameters, with sensitivity coefficients of −0.3868 and 0.2157, respectively. The volumetric heating capacity and system total exergy destruction per heating capacity unit are most sensitive to the flow rate of wastewater and hot water, with sensitivity coefficients of 0.1121 and −0.4985, respectively. These results provide a foundation for the design and optimization of a CO2 zeotropic mixture heat pump system.

Multi-objective optimization of solar-driven hollow fiber membrane dehumidification system based on MOPSO

The solar-driven hollow fiber membrane dehumidification (SHFMD) system is a renewable, energy-saving, and highly effective dehumidification system. It provides an effective solution to the problem of air-entrained liquid droplets during the traditional solution dehumidification process. The system's mathematical model was established and the reliability of the mathematical model was verified by experimental data. To enhance the comprehensive performance of the system, the multi-objective particle swarm optimization (MOPSO) algorithm is used in this paper to optimize the multi-objective parameters of the system. The objective function is the total exergy destruction of the system and the dehumidification capacity of the system. The optimization variables are cold water temperature, cold water flow rate, solution flow rate, air flow rate, and hot water flow rate. The optimization is performed using the multi-objective particle swarm optimization (MOPSO) algorithm to obtain the Pareto front, and the points of the Pareto front are normalized. Finally, the optimal trade-off point of the Pareto frontier is obtained. Each operating parameter of the optimal point of the Pareto front is also analyzed. The results show that the air flow rate and cold water flow rate have the most influence on the conflict between the total exergy destruction of the system and the dehumidification capacity of the system.

Innovative Heat Transfer Enhancement in Tubular Heat Exchanger: An Experimental Investigation with Minijet Impingement

This paper investigates heat transfer in a horizontally oriented tubular heat exchanger through a comprehensive examination of both numerical simulations and experimental analyses. The primary focus is on copper as the material of interest, specifically examining an inner tube with a 14 mm internal diameter and 1 mm thickness, as well as an outer tube with a 29 mm external diameter and 1 mm thickness. In addition to these components, two perforated pipes with internal diameters of 11 mm and 20 mm are incorporated; contributing to an overall length of the heat exchanger measuring 281 mm. Notably, the perforation pipe features a 5 mm diameter hole on its periphery. A comprehensive assessment was conducted to appraise heat transfer and coefficients within a straightforward tubular heat exchanger. The mass flow rate of chilled water in the annular space fluctuated between 0.01 kg/sec and 0.11 kg/sec, while the steady flow rate of hot water within the inner tube remained constant at 0.11 kg/sec. Inlet temperatures for the hot water were established at 55 °C, 75 °C, and 85 °C, with the cold water maintaining a consistent inlet temperature of 29 °C throughout the experiment.

Experimental investigation of two-bed adsorption thermophysical battery with mass recovery technology

This paper developed a novel semi-continuous two-bed Adsorption Thermophysical Battery (ATB), utilizing silica gel RD/water as the adsorption pair. The Absorber Bed Unit (ABU) was designed and manufactured using finned tubes, while the condenser and evaporator are incorporated under a single Evaporator-Condenser Unit (ECU). The study investigated the impact of mass recovery, hot and cooled water temperature, and the chilled, cooled, and hot water flow rate on the system performance. The results of the study revealed that the ATBwith mass recovery demonstrated a higher Coefficient of Performance (COP) and Refrigeration Capacity (RC) in comparison to the system without mass recovery. The average COP for the cycles with and without mass recovery were 0.228 and 0.2, respectively. The present study determined that the most favorable duration for mass recovery was 60 s. A substantial reduction in the COP can be observed as the hot and cooled water temperature increases. Also, the COP of the ATB was found to be directly related to the flow rates of chilled and cooled water but not to the flow rates of hot water. In addition, the COP of the two-bed ATB with mass recovery was improved by 14 % compared with the single-bed ATB. Finally, the adsorption uptake rose by 24 % when the cooled temperature was decreased from 313 K to 303 K.

Experimental study of a novel in-tube spray evaporative condenser for geothermal power generation

To enhance the efficiency of medium to low-temperature geothermal power systems, we designed a novel in-tube spray evaporative condenser. Experimental setups for single-tube heat exchange were devised, examining both water-water and working fluid-water configurations. The study analyzed the impact of air volume and hot water flow rate on heat transfer. Economic comparisons were made in laboratory conditions among the novel evaporative condenser, traditional evaporative condenser, water-cooled condenser, and air-cooled condenser. Results indicated: (1) The novel evaporative condenser exhibited 1.5–1.7 times higher heat flux density and 2.0–2.7 times higher mass transfer coefficient, indicating superior heat transfer performance compared to the traditional one. (2) Variations in hot water flow rate within a certain range had minimal impact on condenser performance when the condenser size was constant, providing valuable insights for condenser selection and structural design. (3) Both total power and water consumption of the novel evaporative condenser were lower than the other three types. Its daily operating cost was approximately 3/4 of the traditional evaporative condenser, 1/2 of the air-cooled condenser, and 1/4 of the water-cooled condenser, demonstrating superior economic feasibility.

Case study of design and construction of dehydration for paddy by heat exchanger rectangular two-phase closed thermosyphon(DP-HE/RTPCT)

The purpose of this research was to design and produce a dehydration system for paddy using a heat exchanger rectangular two-phase closed thermosyphon (DP-HE/RTPCT), which is a modified version of the rectangular two-phase closed thermosyphon (RTPCT). The working fluids used in this study were R11 and methanol at 50% addition rate of the evaporator volume while evaporator temperatures of DP-HE/RTPCT were set at 60 and 80 °C. The evaporator and condenser of the DP-HE/RTPCT were of equal length, the hot water flow rate into the evaporator was 1.5 L/min whereas the initial moisture content of the paddy was 21.50% of the wet basis. Using methanol as a working fluid at the evaporator temperature of 80 °C reduced the moisture content of the paddy to 14% of the wet basis in 390 min, which yielded the highest DP-HE/RTPCT efficiency of 0.62. This was the shortest time in all cases while the internal heat of the paddy pile peaked at A-depth and decreased at B-depth and C-depth, respectively. Paddy germination rate was 90% in the DP-HE/RTPCT that used R11 as the working fluid, at the evaporator temperature of 60 °C. The design and construction of DP-HE/RTPCT demonstrated a novel application of thermosyphons with a modified cross-sectional area. This study could serve as a foundation for future research on heat exchangers.

Thermodynamic condition of cylinder diesel group for infrastructure objects under high temperatures

The article presents the results of research on the influence of ambient temperature on the thermal state of cylinder-piston groups of diesel engines, carried out by the experimental-calculation method on diesel engines 12ChN 18/20 (M787B) and 8ChN 13/14 (YAMZ-7511.10) of autonomous sources on factory test benches. In the experimental study of the effect of temperature change on the thermal state of cylinder-piston groups, the diesels were equipped with a special water-air heat exchanger for heating the air at the suction to the compressor, and the temperature of the suction air was regulated by changing the flow rate of hot water through the water-air heat exchanger. In the experimental study, along with the thermometry of parts of cylinder-piston groups, the engine operating process was indicated, the heat balance was taken, etc.; and the experimental data of other researchers were analyzed. The results of this experimental study, as well as analyzing the results of earlier work on the effect of temperature on the thermal state of cylinder-piston groups allowed to obtain empirical dependencies of local temperatures of the walls of their parts, the distinguishing feature of which is that as variables are considered their relative (dimensionless) values, which increases the degree of experimental data. The results of the performed research can be used for the calculated estimation of the temperature level in the walls of parts of cylinder-piston groups of diesel engines of a wide class of both stationary and transport diesel engines, while providing satisfactory convergence of the calculation results with the experimental data.

Peak loads vs. cold showers: the impact of existing and emerging hot water controllers on load management

ABSTRACT Electric Hot Water Cylinders (HWCs) offer considerable Demand Side Management in Aotearoa New Zealand, which can provide load management and increase integration of renewable electricity. In this work, scenario analyses are conducted to simulate the impact on Low Voltage transformer load and demand fulfilment of four HWC controller types: setpoint (the default in Aotearoa New Zealand), ripple, smart-power, and smart-thermostat. All controllers reduce peak electricity demand by 14-34% from setpoint, where 34% is the maximum possible reduction with hot water control. Unmet demand, which indicates insufficient hot water and can lead to negative outcomes such as cold showers, is increased by 120% and 12-69% by ripple and smart-power control, respectively, and decreased by 7-31% by smart-thermostat control. Average thermal losses are 2.25 kWh/day for the setpoint controller, and between 2.20-2.76 kWh/day for other controllers. Smart-power controllers demonstrate demand deferral, shifting peak electricity loads to shoulder loads, while smart-thermostat controllers demonstrate demand deferral and valley filling, shifting peak loads to times of lowest demand and smoothing load distribution. Overall, smart controllers improve load management performance with little-to-no increase in unmet demand or thermal losses. Thus, smart controllers are a viable option for Demand Side Management in Aotearoa New Zealand. Abbreviations and Nomenclature: DHW: Domestic Hot Water; DLC: Dynamic Load Control; DSM: Demand Side Management; EV: Electric Vehicle; GHG: Green House Gas; HV: High Voltage; HWC: Hot Water Cylinder; LDC: Load Duration Curve; LV: Low Voltage; MV: Medium Voltage; NZD: New Zealand Dollar; PV: PhotoVoltaic; TOU: Time Of Use; UD: Unmet Demand; WTP: Willingness To Pay; A: WTP function coefficient; B: WTP function coefficient; Cp: specific heat of water [J/kg/K]; Ctrans: cost imposed by the transformer; HWsuff: ratio of hot water sufficiency; Kloss,h: thermal losses for cylinder h [W/K]; Kmix: thermostatic mixing valve factor; m: WTP function coefficient; Ptotal: transformer power demand [W]; Pcap: transformer capacity [W]; Ph: Household power demand [W].; PHWC: heater element power [W]; Pop: Transformer limit for Type3 controller [W]; QDHW: heat loss from DHW use [W]; Qloss: heat loss from standing losses [W]; th: time horizon [s]; Tamb: ambient temperature [K]; THWC: temperature of the HWC [K]; Tin: water inlet temperature [K]; Tmin: minimum temperature before fulfilment failure; Tout: water outlet temperature [K].; Tset: temperature setpoint of the HWC controller [K]; V ˙ : flow rate of hot water from the HWC [L/s]; Vavail: available DHW in the HWC [L]; VDHW: volume of hot water draw [L]; VDHW,expected: expected time weighted demand; VDHW,expected,max: maximum expected DHW demand; VHWC: volume of the HWC [L]; wf: time weighting function; ρ: density of water [kg/m3].

An Analysis Of Flow Capacity Variation and Distance Between Louvered Strip Constant Angle 25o Of Heat Transfer and Pressure Decrease On The Heat Exchanger

This study aims to determine the effect of variations in flow rate and the louvered strip inclination angle on heat transfer in a double-pipe heat exchanger and the impact of variations in flow rate and inclination angle of the louvered strip on the inner tube pressure drop in a double-pipe heat exchanger. Three pieces of louvered strips at 50 mm, 70 mm, 90 mm are inserted into the inner tube of the heat exchanger with a constant tilt angle of 25°. Cold and hot water are used at a constant value where the cold-water flow rate is 600 liters/hour and V = 900 liters/hour, while the hot water flow rate is 1200 liters/hour. The inlet and outlet temperatures of both hot and cold water are measured, and the heat transfer characteristics of the heat exchanger are calculated as a result of the pressure drop that occurs in the inner tube due to the difference in height on the U-tube manometer used.

Numerical analysis of two-bed adsorption thermophysical battery

Air conditioning systems powered by waste energy sources, such as solar-driven adsorption air conditioning systems, hold significant importance. The present study delves into the performance assessment of a silica gel-based adsorption thermophysical battery (ATB) under varying operational conditions. Advanced cycles featuring a two-bed configuration have been devised to enable semi-continuous operation and refrigeration. This novel design presents a compact ATB that integrates the evaporator and condenser within a single heat exchanger, referred to as the Evaporator-Condenser Unit (ECU), thereby reducing the overall size and cost of the ATB system. The operating and design characteristics of the two-bed adsorption system were thoroughly explored using a theoretical model developed through MATLAB software. Evaluations were conducted on various performance metrics of the ATB, encompassing the coefficient of performance (COP), cooling capacity, specific cooling power, adsorption isotherm, and kinetics. A theoretical approach was formulated using the lumped parameter (LPM) and modified Freundlich adsorption equations. It can be deduced that the inlet temperature of the hot coolant exhibited a direct proportion with both refrigeration effect (RE) and specific cooling power (SCP) while inversely affecting the coefficient of performance (COP). A decrease in coolant temperature from 313 to 303 K resulted in a noteworthy 13.4 %. Furthermore, it was observed that COP exhibited a direct proportionality with the flow rate of chilled and cooled water while inversely relating to the flow rate of hot water.

Matching Characteristics of CTHP Circulation Systems

Cogeneration can not only reduce the use of primary energy, but also reduce the pollution to the environment; the article selects a 1200kW low-pressure stage turbine as an example to give an analysis, calculates the variation of parameters such as heat production, heat production coefficient, flow rate of cold water and hot water of this turbine, and proposes and analyzes the circulation characteristics of the CTHP system, determines the matching relationship between the steam engine driven heat pump that the system needs to meet, and fits the relationship between the steam engine efficiency and power of the heat pump. The correlation equation of steam engine efficiency and power is regressed, and the relationship of circulating cooling water flow rate with turbine discharge temperature is fitted. It is found that the heat production performance coefficients of the high and low pressure stages of the heat pump increase by 27.6% and 29.3% respectively when the discharge temperature increases from 160°C to 220°C, and the system can realize better economic and social benefits compared with the conventional CHP system.

Regulation of electrically responsive shape recovery behavior of 4D printed polymers for application in actuators

Four-dimensional (4D) printing, an additive manufacturing technology for intelligent materials and structures, has received increasing scholarly attention for its ability to achieve variable shapes, properties and functions. However, recent research has primarily focused on developing new materials and structures, neglecting the regulation of deformation behavior. We hereby propose a novel photocuring 4D printing strategy for electrically responsive shape memory polymers (E-SMPs) actuators embedded with a dual-layered electrothermal layer (ETL) and channel. One way to achieve tunable shape recovery behavior in E-SMPs is to regulate the heat generation behavior of ETL by introducing a coolant into the channel. The electric heating and water cooling were sequentially and simultaneously activated to achieve suspension of the shape recovery process and reduction in the shape recovery rate, respectively. E-SMPs embedded with single and double ETLs were utilized to evaluate their electrically-induced heating behavior, electrically responsive shape recovery behavior, and shape recovery force. Additionally, sequential shape recovery behavior was achieved by serially interconnecting three (3) ETLs with varying thicknesses. Furthermore, the channel integrated within the SMPs were employed to realize remote thermally responsive shape recovery (T-SMPs), for which the shape recovery rate was regulated by adjusting the flow rate of hot water and channel dimensions. This strategy was successfully demonstrated for manufacturing E-SMPs actuators with adjustable shape recovery rate, sequential recovery behavior, and high-load deformation capability.

Comparative Experimental Study on Effect of Copper Wire Helical Wound Steel Tube with 2.5” Full Length Insert on Performance of Double Pipe Steel Tube Heat Exchanger

Abstract: A comparative experimental study was conducted to explore the hydrothermal behavior of a double tube heat exchanger with copper wire helical wound steel tubes and plane steel tubes with and without twisted tap inserts of pitch length 2.5 inches. In comparison to helical tubes, corrugated tubes, and many other more compact tube type heat exchangers, straight tube heat exchangers offer advantages since the construction of the heat exchanger tubes is easier. In the current work, the fluid-to-fluid heat exchange is considered, with a flow rate ranging from 15 to 75 liters/hour. Constant wall temperature or constant heat flux ideas are used in the majority of investigations on heat transfer coefficients. The efficiency, overall heat transfer coefficient, and impact of hot water flow rate with constant cold water flow rate for straight steel tube and copper wire helical wrapped steel tube heat exchangers in parallel flow and counter flow configurations were investigated and compared. Utilizing a 2.5" full length clockwise twisted tape insert, both layouts were created. The measurements were carried out in a constant state. When the hot water flow rate is increased while maintaining the cold water flow rate constant, the efficiency of the heat exchanger drops for both the straight steel and the copper wire helical wound steel tube. Compared to a plane steel tube heat exchanger, the copper wire helical wound steel tube heat exchanger has a better efficiency. The test findings demonstrate that inserting inserts causes pressure drop. With 2.5" clockwise twisted tape inserts wrapped in helical copper wire, steel tube was able to transmit heat more quickly than other arrangements.

The Numerical Investigations of Heat Transfer and Bubble Behaviors of R22 in Subcooled Flow Boiling in Casing Tubes

Amidst the background of “double carbon”, energy saving and emission reduction is a popular direction in the current refrigeration industry. Therefore, the research on the boiling heat transfer of gas–liquid two-phase flow is helpful to strengthen the heat transfer and design a more efficient heat exchanger. In this paper, a research method combining numerical simulation and experimental verification is adopted. Firstly, an experimental platform used for the subcooled flow boiling of refrigerant in casing tubes is introduced and experiments are carried out to obtain experimental data, which provides a theoretical basis for the development of numerical simulation and verifies the feasibility of numerical simulation. A numerical model of subcooled flow boiling in R22 was established and the grid independence test was carried out. Based on the simulation results, three factors affecting the boiling heat transfer of R22 are analyzed: First, the boiling heat transfer coefficient of R22 increases with the increase of the mass flow rate of R22, but the increase decreases when the mass flow rate increases from 0.018 kg/s to 0.020 kg/s. Second, the boiling heat transfer coefficient of R22 increases significantly with the increase of hot water flow rate. Third, the influence of R22 subcooling on boiling heat transfer is more complex. When the subcooling is 5 °C and 1 °C, heat transfer can be enhanced; high subcooling at 5 °C can enhance convective heat transfer and low subcooling at 1 °C can accelerate the arrival of saturated boiling. In this paper, three kinds of bubble behaviors affecting heat transfer in supercooled flow boiling, including sliding, polymerization, and bounce are also studied, which provides a basis for further research on heat transfer mechanism of supercooled flow boiling.

Design of Performance Test System for Water-Water and Carbon Dioxide Compressed Air Microchannel Heat Exchanger

As a new type of heat exchanger with compact structure and efficient performance, microchannel heat exchangers have good application prospects in industries with strict requirements such as energy and power, petrochemical, aerospace, and other industries. Therefore, exploring the performance and heat transfer characteristics of microchannel heat exchangers is of great significance. This article designs a performance testing system that can simultaneously explore the enhanced heat transfer inside the pipeline of water water and carbon dioxide compressed air microchannel heat exchangers. The variable working fluid circuit design is used to analyze the factors that affect the enhanced heat transfer. The Control variates is used to control the heat transfer conditions, explore the difference of heat transfer performance between different working fluids under different flow rates, inlet temperatures and other conditions, and analyze the heat transfer performance of different channel types by comparison method. The results indicate that when the hot water flow rate range is 2.063×10-5~2.556×10-5m3/s, Re<2320, and under the same flow rate conditions, the Nu of the 3.6 mm inner diameter microchannel is significantly higher than that of the 6.6 mm inner diameter microchannel. When the inlet flow range is 2.063×10-5~2.556 ×10-5m3/s, the Reynolds number and Nusselt number in the pipeline increase with the increase of inlet flow. In the carbon dioxide compressed air heat transfer experiment, when the flow rate range is 2.810×10-4~3.182×10-4m3/s, the Nusselt number and convective heat transfer coefficient of the 3.6mm inner diameter microchannel are always greater than the Nusselt number and convective heat transfer coefficient of 6.6mm. When the pipe diameter is the same, the water water microchannel heat exchanger has better heat transfer performance and smaller pressure drop compared to the carbon dioxide compressed air microchannel heat exchanger.