Water-cooled Heat Exchanger Research Articles

Experimental Study on the Impact of Lubricant on the Performance of Gravity-Assisted Separated Heat Pipe

Gravity-assisted separation heat pipes (GSHPs) are extensively utilized in telecommunications base stations and data centers. To ensure year-round cooling, integrating GSHPs directly with a vapor compression refrigeration system is a viable solution. It is unavoidable that the refrigeration system’s lubricant will infiltrate the heat pipe loop, thereby affecting its thermal performance. This paper examines the performance of a GSHP, which features a water-cooled plate heat exchanger as the condenser and a finned-tube heat exchanger as the evaporator, when the working fluid (R134a) is contaminated with a lubricant (POE, Emkarate RL-46H). The findings are compared with those from a system free of lubricant. The experimental outcomes indicate that the presence of lubricant degrades the heat transfer efficiency, particularly when the filling ratio is adequate and no significant superheat is observed at the evaporator’s outlet. This results in a 3.86% increase in heat transfer resistance. When the charge of the working fluid is suboptimal, the average heat transfer resistance remains relatively constant at a 3% lubricant concentration yet increases to approximately 5.27% at a 4–6% lubricant concentration, and further to 12.32% at a 9% lubricant concentration. Concurrently, as the lubricant concentration fluctuates between 3% and 9%, the oil circulation ratio (OCR) varies from 0.02% to 0.11%.

Performance analysis of heat pump polygeneration system

A heat pump polygeneration system is a promising technology to meet daily needs such as drinking water, power, space cooling or heating, and hot water generation. This work is focused on integrating the solar heat pump and two-stage humidification–de-humidification with a minimum space requirement. In this integrated cycle, the desired outputs i.e. condenser heat and evaporator heat are used for maximizing hot water and desalinated water production with minimal thermal pollution. For warm or hot air generation, an air reheater device is used after the heat pump. By using the switching operation, the air reheater is used accordingly as per climatic conditions. So in this integrated cycle, a coconut coir-packed humidifier is used for the humidification process, and a water-cooled heat exchanger and heat pump evaporator are used for the dehumidification process to meet the desired outputs from the system. The MATLAB simulation tool is used to simulate the thermodynamic model of the integrated cycle, and it is focused on studying the effect of mass flow rate, atmospheric temperature, relative humidity, evaporator temperature, and hot/cold water temperature, on outputs, as well as the energy conversion factor of the plant and cycle. At 25°C ambient air temperature, the energy conversion factor of the plant and cycle are 0.866 and 2.2, respectively. Similarly, at 75% humid air and 35°C surrounding air temperature, the gained output ratio and coefficient of performance are 4.03 and 1.964, respectively. And also, the plant and cycle energy conversion factors are 0.903 and 2.4.

Performance of an Air-Cooled Heat Exchanger in a Separation Unit Based on Fouling Factor and Pressure Drop

Heat exchangers transfer heat from a high temperature to a low temperature in a fluid. Air-cooled heat exchangers are one of the most widely used types of heat exchangers, after shell and tube heat exchangers. Its performance is determined by calculating the fouling factor value and the pressure drop. The purpose of this case study is to evaluate the performance of a water-cooled heat exchanger in a plant that produces a thickening agent (CMC, or carboxymethylcellulose), which affects the amount of ethanol produced. Ethanol will cool from 79.347 to 54.133 oC, and air will cool from 31.333 to 59.667 oC as the cold fluid. The calculation results show that both reviews exceed the design threshold of 0.007056 h.ft2.oF/Btu. These heat exchangers require maintenance and repair. These results differ from the pressure drop values on the air side and pipe section, which are 1.2.10-3 inH2O and 0.647 psia, respectively. Both values remain outside the allowable limits. The performance evaluation of process equipment in the separation unit was aided by field data. The review of the data was able to predict a plant shut-down. This action was able to effect a partial or total plant shut-down due to fouling and scale exceeding design data thresholds.

Design and thermal performance of an innovative greenhouse

The study presents the design and thermal performance evaluation of a novel solar greenhouse with humidification-dehumidification unit, water-cooled heat exchanger and variable mixing ratio in the Mediterranean climate. The greenhouse is designed to provide proper microclimatic conditions for crops, produce fresh water through condensing water vapor released from the plants, and save energy using the semitransparent PV panels. Results showed that on a typical summer day, the solar greenhouse ensures proper microclimatic conditions all day long by reducing the temperature by 11.14 °C compared to conventional greenhouses, while maintaining acceptable values of relative humidity and producing 70 L of fresh water per day. An operation schedule was established based on varying return-to-fresh air ratio to ensure optimal system performance. The operation schedule showed that proper microclimatic conditions can be reached through ventilation for 13 h per day. To enhance the net-energy performance, the produced water can be used for irrigation and the return air can be used for cooling the PV panels.

A testbed for performance studies of gas–liquid thermoelectric generators for waste heat harvesting

We describe a unique test platform for performance studies of thermoelectric generators (TEGs) with gas/liquid heat exchangers. The designed stand allows to simulate the real working conditions of TEG prototypes. It provides accurate measurements of key operational parameters of these devices in high precision laboratory regime.The testbed consists of a hot-gas control unit (HGCU) for examination of the heat exchanger (HHX) of the TEG, a cooling liquid control unit (CLCU), an automated control system (ACS) that allows to precisely set the requested experimental conditions, and a data acquisition system (DAS) that gathers data on temperature, fluids flow, pressure drops and electrical parameters of the TEG.The HGCU unit is a source of hot air, with mass flows in the range of 0–550 m3/h, maximum heat power PH of 15 kW, and temperature range between 15 °C and 800 °C. The CLCU unit controls the flow and temperature of the liquid medium in the range from 10 °C to 110 °C and the mass flow of water ṁwater in the range of 0.006 – 1.2 m3/h. The designed testbed allows to evaluate the most important TEG performance parameters, such as: efficiencies of its TE converters, the effectiveness of heat exchangers, power losses due to pressure drops, and net power Pnet generated, as well as the statistical uncertainties of the determination of these parameters.The testbed has been used for tests of various TEG prototypes. As an application example, we show results for a prototypical TEG with nominal power of 168 W designed for heat recovery from an automobile exhaust system. The device is based on a hexagonal, internally finned HHX, 24 TEM converters and 24 water-cooled cold heat exchangers (CHXs).The constructed testbed allows for a direct determination of all the factors which may influence the conversion efficiency of the TEG, as well as its net and gross electrical power output under varying heat source and heat sink parameters. The device allows to estimate the performance of the entire thermoelectric generation system as a whole and to identify individual components within the TEG which potentially need to be improved. Such a holistic approach to TEG parameter characterization was not presented or discussed in the literature so far.

Experimental research on the performance of BIPV/T system with water-cooled wall

Solar photovoltaic/thermal building integrated power/heat technology (BIPV/T) can provide both electricity and heat to buildings, which is important for improving the efficiency of solar energy utilization and reducing building energy consumption. In this paper, a BIPV/T system with water-cooled wall is proposed. The water-cooled wall heat exchanger is not in direct contact with the PV module, and uses air to dissipate heat from the PV module, which in turn heats domestic water, and can provide hot water or hot air to the building as needed. This paper experimentally investigates the system’s ability to produce domestic hot water and power generation performance, with an average power generation efficiency of 12.6% for the whole day and providing 35 °C domestic hot water for more than 7 h. The results of this paper have some guiding significance for the efficient operation of BIPV/T.

Efficiency improvement of hybrid PV-TEG system based on an energy, exergy, energy-economic and environmental analysis; experimental, mathematical and numerical approaches

Nowadays, Photovoltaic panels are being used as effective devices to utilize solar free energy. However, they lose their efficiency when their temperature increases; consequently, a large portion of the solar energy is wasted. In this study, a hybrid system of polycrystalline Photovoltaic panel equipped with Thermoelectric generator modules and combined with water-cooled heat exchangers has been proposed to extract more power from the Photovoltaic meanwhile producing electricity by Thermoelectric generators and absorbing heat by water. Previous studies have been mostly based on a 24-hour simulation while not considering the long-term analysis of the system. This study includes a 24-hour analysis via experimental build testing, mathematical modelling, and finite element simulation, followed by a finite element simulation carried out for one year. This study considers the influence of varying irradiance and thermal resistance on the Photovoltaic, Thermoelectric hot and cold sides and outlet water temperatures on the daily and annual energy, exergy, environmental, and energy-economic outcomes. It was found that the averaged maximum Photovoltaic temperature for the experiment and simulations of the Photovoltaic-Thermoelectric hybrid system was 44.2°C at maximum irradiation. In comparison, it was 57.1°C for the stand-alone Photovoltaic. The electrical power production of the Photovoltaic-Thermoelectric hybrid system was 9.49W, which is noticeably higher than the 8.48W output of the stand-alone Photovoltaic meaning that the electrical efficiency and the exergy efficiency increased by 1.67%, and 1.72%, respectively. The environmental and energy-economic simulations show that the carbon payback period and the discounted payback period are 1.31 and 12.39 years, respectively.

Techno‐economic analysis of a hybrid solar‐geothermal power plant integrated with a desalination system

This paper proposes the use of a hybrid 5 MW power generation system combining concentrated solar thermal and solar photovoltaic technology where the efficiency of the power block is increased by taking advantage of hot water from a low-temperature geothermal source. Aiming at a case study for Winton in Queensland the pertinent meteorological data are used for our simulations. In addition, the paper analyzes the feasibility of including a thermal desalination technology that uses the waste heat from the power block for producing clean water from wastewater. Our design replaces the traditional dry cooling system with a water-cooled heat exchanger to remove the waste heat from the power block. Finally, this work explores the ratio of concentrated solar thermal and photovoltaic electricity production that optimizes the levelized cost of electricity and water production. the results indicate that the incorporation of the desalination system does not produce a significant increase in this value, and the optimal ratio of electricity production is obtained when the photovoltaic system contributes to 27.5% of the total electricity generation. Our water production cost can be as low as 40 ₵/m3 while for the combined system our minimum levelized cost of electricity figures out at 12.4 ₵/kWh to generate the base load with thermal storage.

Better thermoregulation of brain temperature using phase change material-mediated head cooling system

Regulation of the brain temperature is critical for managing heat stress related adverse events. It can be achieved by external cooling of the head. Head cooling systems that are lightweight, portable, and suitable for active work scenarios such as firefighting, mining, and construction work are currently unavailable in the market. This study proposes a novel active head cooling system that a) uses phase change material for thermal storage and b) can be designed for portability. The closed-loop bench-top system consists of two heat exchangers: a water cooled heat exchanger with an attached heater, mimicking heat generated from the head, and a helical tube heat exchanger surrounded with ice as heat sink. These heat exchanges are interconnected by tubing for water circulation. The system performance is assessed by cooling duration that depends on mass of ice used and heat transfer rate. The system was evaluated for different a) heat loads varying from rest to exercise conditions (20 W – 40 W) and b) flowrates (0.25 l/min – 0.65 l/min). The results show that the system can handle heat generation rate of 40 W from the head for 100 min (for the flowrate of 0.25 l/min), which is about 3 times the safe duration of firefighting drills. The cooling time increases linearly with decreasing heat load: 138 min for 30 W and 190 min for 20 W, an increase of 38% and 90%, respectively. It also increases with decreasing flowrate. The range of Nusselt number for helical coil flow is about 4.4 – 6.8 times higher when compared to that of a straight pipe flow. The helical design of heat exchanger led to enhanced heat transfer owing to the formation of Dean's vortical flow. The results suggest that the head cooling system, having possible features of being portable, cost-effective, light weight, and easy to use, can assist in the thermoregulation of brain temperature for workers during elevated thermal stress conditions.

Energy saving analysis of evaporative cooling composite air conditioning system for data centers

An evaporative cooling composite air conditioning system aimed at enhancing energy efficiency of data centers was proposed. Furthermore, the mathematical models on the base of the operation characteristics of the system were established. After verification by experiment, the energy saving performance of the system under different climatic conditions was investigated. The simulation results showed that the annual performance factor (APF) values are 5.31, 5.02, 4.75 and 4.50, respectively in severe cold zone-Shenyang (123.38E, 41.8N), cold zone-Beijing (116.30E, 39.9N), hot summer & cold winter zone-Nanjing (118.78E, 32.0N) and mild zone-Kunming (102.72E, 25.1N). The power usage effectiveness (PUE) values are below 1.40, the system has good energy saving advantages in different locations. After a water-cooled heat exchanger is used in the evaporative condenser, the APF values improve in all the four cities. The use of water-cooled heat exchanger is beneficial to further enhance energy saving of the system. A case study based on the system elaborates that it is feasible for energy saving of data centers in various climatic zones.

A RELAP5-3D/LSTM model for the analysis of drywell cooling fan failure

A RELAP5-3D/LSTM model was created to analyze the failures of two drywell cooling fans at a nuclear power plant. A total of four fan coil units (FCUs) each comprised of a water-cooled heat exchanger and a centrifugal fan located in the drywell provide cooling via a closed nitrogen loop to the primary containment of the boiling water reactor. A Reactor Excursion and Leak Analysis Program (RELAP5-3D) thermal hydraulic model was created to simulate the steady-state normal operation of the FCUs. Historical data from the plant Process Information (PI) system was synchronized in time for a total of 33 Plant Management Information System (PMIS) tags per FCU representing: (1) the temperatures at various locations within the drywell, (2) inlet, outlet, and dewpoint temperatures at the FCUs, (3) reactor power, and (4) water coolant flowrate and temperature. Because the inlet temperature sensor for the two fans that failed did not provide consistent data prior to the failures, a long short-term memory (LSTM) recurrent neural network was trained to predict the FCU inlet temperature history based upon the states of the other valid PMIS points. RELAP5-3D simulations were performed using the measured FCU inlet temperatures, as well as the LSTM-generated temperatures, and the resulting FCU outlet temperatures were compared. The simulation results using the measured and predicted FCU inlet temperature were shown to be within 7.35% and 5.16%, respectively, of the values reported by the PI system. Thus, a viable approach has been demonstrated to predict the expected FCU outlet temperature. By comparing real-time measurements of FCU outlet temperature with predictions such as those presented here, off-normal operation can be readily detected. The use of RELAP5-3D with the LSTM results was successfully implemented to prototype a physics-based anomaly detection model for the drywell FCUs.

Seismic Response Amplification Factors of Nuclear Power Plants for Seismic Performance Evaluation of Structures and Equipment due to High-frequency Earthquakes

Analysis of the 2016 Gyeongju earthquake and the 2017 Pohang earthquake showed the characteristics of a typical high-frequency earthquake with many high-frequency components, short time strong motion duration, and large peak ground acceleration relative to the magnitude of the earthquake. Domestic nuclear power plants were designed and evaluated based on NRC's Regulatory Guide 1.60 design response spectrum, which had a great deal of energy in the low-frequency range. Therefore, nuclear power plants should carry out seismic verification and seismic performance evaluation of systems, structures, and components by reflecting the domestic characteristics of earthquakes. In this study, high-frequency amplification factors that can be used for seismic verification and seismic performance evaluation of nuclear power plant systems, structures, and equipment were analyzed. In order to analyze the high-frequency amplification factor, five sets of seismic time history were generated, which were matched with the uniform hazard response spectrum to reflect the characteristics of domestic earthquake motion. The nuclear power plant was subjected to seismic analysis for the construction of the Korean standard nuclear power plant, OPR1000, which is a reactor building, an auxiliary building assembly, a component cooling water heat exchanger building, and an essential service water building. Based on the results of the seismic analysis, a high-frequency amplification factor was derived upon the calculation of the floor response spectrum of the important locations of nuclear power plants. The high-frequency amplification factor can be effectively used for the seismic verification and seismic performance evaluation of electric equipment which are sensitive to high-frequency earthquakes.

Experimental and numerical investigation on thermoelectric coolers for comparing air-to-water to air-to-air refrigerators

It has been determined that a significant portion of the total electrical energy is consumed for different cooling and refrigeration purposes at both domestic and industrial sectors. Moreover, cooling systems are employed in a wide range of critical fields such as food industry and pharmacy. In this study, experimental and numerical approach to evaluate two different modes of thermoelectric cooler efficiency is presented. Portable thermoelectric refrigerators operated by Peltier element have been constructed, and experiments are conducted to compare efficiency of air-to-water and air-to-air thermoelectric coolers. In air-to-air mode, the Peltier device was united with heat sinks and fans on both sides. However, in air-to-water mode, a water pump and suitable water-cooled heat exchanger were used to operate in the refrigerators made of styrofoam sheets. It was revealed that, in the laboratory conditions, air-to-water mode is more efficient than air-to-air mode and COP value of the air-to-water is approximately 30–50% higher than that of air-to-air refrigerator. Moreover, ANSYS Fluent 16.0 software has been used to analyze the problem closely in detail. The problem has been simulated, and CFD results were used to visualize flow structure and heat transfer characteristics inside refrigerator box.

The analysis of air-cooled heat exchanger for Reactor Cavity Cooling System (RCCS) on Experimental Power Reactor (RDE) design

The National Nuclear Energy Agency (BATAN) is designing the Experimental Power Reactor (RDE). The Reactor Cavity Cooling System (RCCS) is a new basic design in the nuclear power plant. It will be incorporated into High-Temperature Reactors (HTR), which is one proposed generation of IV reactors. While HTR has been designed and operated, the RCCS design is unique to the recent generation of gas-cooled reactors as a passive decay heat removal system. However, many aspects of the new air- or water-cooled design still need to be investigated on RCCS. The temperature, mass flow, configuration of the riser, and number of the risers on the water-cooled heat exchanger system which is used is a necessary test. The RCCS designs have not been studied for the RDE design. The heat-transfer and fluid-flow on the RCCS facility have not been investigated for the air-cooled cavity cooling system. The aim of this study is to examine the condition of the air-cooled heat exchanger of RCCS for RDE 10 MWth design. The pressure, temperature, and velocity with certain diameters of cooling pipes are computed with FLUENT 6.3 computational fluid dynamics (CFD) software package under a mass flow rate variation. The pressure, the flow velocity and delta temperature outlet were examined on the RCCS process. The air-cooled heat exchanger in RDE basic design was found to attain safe operation.

Hydrophilic silicone coatings as fouling release: Simple synthesis, comparison to commercial, marine coatings and application on fresh water-cooled heat exchangers

A synthesis route to hydrophilic, biocide-free fouling-release coatings by dispersing a polydimethyl siloxane (silicone, PDMS)-polyethylene glycol (PEG) copolymer in a PDMS coating is described. In comparison to known coatings including commercial fouling release for marine vessels, anti-fouling and fouling release performance was investigated by laboratory tests (contact angle, pseudo barnacle test and bacteria culture test applying Pseudomonas aeruginosa) and by application on fresh water-cooled surface condensers mimicking conditions of thermal power plants. A developmental silicone coating comprising PEG reduced fouling growth and adhesion in laboratory tests by more than a factor of ten compared to steel. In a freshwater exposure test, a comparative, commercial fouling release coating performed better than the developmental PEG-PDMS coating and is a promising candidate for applications on surface condensers of thermal power plants as it reduces fouling at a flow rate of just 1.6 m/s.

Numerical simulation of the fluid flow and heat transfer characteristics of microchannel heat exchangers with different reentrant cavities

PurposeWith the increasing heat dissipation of electronic devices, the cooling demand of electronic products is increasing gradually. A water-cooled microchannel heat exchanger is an effective cooling technology for electronic equipment. The structure of a microchannel has great impact on the heat transfer performance of a microchannel heat exchanger. The purpose of this paper is to analyze and compare the fluid flow and heat transfer characteristic of a microchannel heat exchanger with different reentrant cavities.Design/methodology/approachThe three-dimensional steady, laminar developing flow and conjugate heat transfer governing equations of a plate microchannel heat exchanger are solved using the finite volume method.FindingsAt the flow rate range studied in this paper, the microchannel heat exchangers with reentrant cavities present better heat transfer performance and smaller pressure drop. A microchannel heat exchanger with trapezoidal-shaped cavities has best heat transfer performance, and a microchannel heat exchanger with fan-shaped cavities has the smallest pressure drop.Research limitations/implicationsThe fluid is incompressible and the inlet temperature is constant.Practical implicationsIt is an effective way to enhance heat transfer and reduce pressure drop by adding cavities in microchannels and the data will be helpful as guidelines in the selection of reentrant cavities.Originality/valueThis paper provides the pressure drop and heat transfer performance analysis of microchannel heat exchangers with various reentrant cavities, which can provide reference for heat transfer augmentation of an existing microchannel heat exchanger in a thermal design.

Experimental investigation of condensation flows in circular cross-section channel

In this work, condensation flows of pure ethanol in a horizontal water-cooled circular cross-section heat exchanger were investigated for a mass velocity ranging between 30 and 100 kg m−2 s−1. The inner channel of condensation has inner and outer diameters of 4 mm and 10 mm, respectively, with a heat exchange length of 1020 mm. An adiabatic section consisted of a transparent circular cross-section channel, of 4 mm inner diameter and of 130 mm visible length, was placed downstream of the condenser in order to visualise the condensation flows by shadowgraph technique. Two main flow regimes were identified: the wavy-stratified regime and the wavy-annular regime. A flow regime map was developed and compared with flow regime maps available in the literature. Besides, the local vapour quality and internal heat transfer coefficient were determined and compared with prediction models of the literature. Finally, the total pressure drop in the condenser was determined.

Parametric resonance of a fluctuation fluid flow heat exchanger system

The tubes in a component-cooling water heat exchanger are frequently affected by shock waves that occur due to fluid flow in a nuclear power plant. Thus, the tubes often wear out. Such a fluid flow may alter the dynamic characteristics of a water heat exchanger and cause instability in it. In this study, the dynamics and instabilities in a component cooling water heat exchanger are examined. Because of the presence of fluid coupling between tubes, periodic tubes were used to realize a periodic coupling system. It is found that each tube is coupled to the adjacent tube through the fluid, and the system is weakly coupled. The dynamic equations of the heat exchanger system with consideration for the effect of fluid flow were derived using Galerkin method. Numerical results revealed that fluctuations in fluid flow may significantly affect the dynamics and instability of a component cooling water heat exchanger.

A single phase hybrid micro heat sink using impinging micro-jet arrays and microchannels

This work describes the development of a single phase water-cooled microfluidic heat exchanger for cooling very high heat flux electronics. The heat sink was designed so that it can be manufactured using the MICA Freeform process, which is an ultra-precision additive manufacturing method for millimeter-scale metallic parts with micron-scale features. The heat sink targets a heat flux of 1000 W/cm2 with an average base temperature constraint of 65 °C for a 4 mm × 3 mm heat source. The hydraulic constraints that were imposed on the design were that the pressure drop and flow rates could not exceed 100 kPa and 0.5 L/min respectively. The design was undertaken using Simulation-Driven Design whereby the commercial Computational Fluid Dynamics software ANSYS Fluent was utilized. The final embodiment of the design is a hybrid Microjet-Microchannel heat sink. The thermal performance is quite extraordinary, with a predicted effective thermal conductance of 400 kW/m2 K for a flow rate of 0.5 L/min. With such an exceptionally high thermal conductance, the heat sink is predicted to maintain an average base temperature of under 58 °C with a maximum variation about the mean of ±3 °C for an imposed heat flux of 1000 W/cm2.

Influence of the Water-Cooled Heat Exchanger on the Performance of a Pulse Tube Refrigerator

The water-cooled heat exchanger is one of the key components in a pulse tube refrigerator. Its heat exchange effectiveness directly influences the cooling performance of the refrigerator. However, effective heat exchange does not always result in a good performance, because excessively reinforced heat exchange can lead to additional flow loss. In this paper, seven different water-cooled heat exchangers were designed to explore the best configuration for a large-capacity pulse tube refrigerator. Results indicated that the heat exchanger invented by Hu always offered a better performance than that of finned and traditional shell-tube types. For a refrigerator with a working frequency of 50 Hz, the best hydraulic diameter is less than 1 mm.