Exchanger Unit Research Articles

Experimental Study on Flow and Heat Transfer Characteristics of Jet Array Impingement Combined with Kagome Truss Structures with/without Cross-flow

Jet array impingement providing high heat transfer are widely used in heat exchangers. However, the target plate is easily damaged impinged by high-speed air flow constantly. To solve this issue, Kagome truss structure is combined with jet array impingement to improve cooling performance in this paper. The flow and heat transfer characteristics of this composite structure in a heat exchanger unit with/without cross-flow were experimentally studied. Additionally, Kagome truss structures of circular and water-drop-shaped rods were used respectively in jet space and the results showed that the latter was beyond 7% higher than the former for the comprehensive thermal performance. When cross-flow was not added, the comprehensive thermal performance factor of the latter reached to a maximum of 1.656 at the Reynolds number of 5000. When cross-flow was added, the comprehensive thermal performance got worse at the cross-flow-to-jet velocity ratio of 1.0, while the best comprehensive thermal performances were found at the cross-flow-to-jet velocity ratio of 0.6 and at the mass flow rate proportion of cross-flow of 0.5, respectively. These results can provide a basic experimental data as a reference for designing new structures in advanced heat exchanger.

Effects of thermophysical properties on optimal selection of phase change material for a triple tube heat exchanger unit at different time scales

The multi-criteria decision making (MCDM) method has been widely applied to select phase change material (PCM) for various applications. However, the relationship between the thermophysical properties of a PCM and the optimization objective, as well as the effect on different time scales for specific applications, has not been addressed in the selection process of the optimum PCM. In this study, to solve the above two issues, first, an orthogonal experiment with five factors and four levels is designed to explore the effect of the thermophysical properties of PCMs on the heat storage ratio of a triple tube heat exchanger (TTHX) unit based on a numerical simulation. Then, the criteria weights are determined based on the range analysis at different time scales, and finally, the technique for order performance by similarity to an ideal solution (TOPSIS) method is employed to perform the ranking and selection. The results indicated that the thermophysical properties have a significant influence on the heat storage rate. When the melting time was 20 min, the PCM density and thermal conductivity had higher weights and PlusICE-S117 was selected as the optimal PCM. However, when the melting time was 150 or 250 min, the PCM density and melting enthalpy were the primary criteria to consider, and the best choice was Urea-NaCl. Furthermore, the reliability and effectiveness of the proposed PCM selection method were verified through a comparison with the TOPSIS-entropy method.

Experimental Approach for Enhancing the Natural Convection Heat Transfer by Nanofluid in a Porous Heat Exchanger Unit

Natural convection heat transfer is a significant component in the energy transfer mechanism and plays an essential role in a wide range of scientific and industrial technologies. This research seeks to enhance the energy transfer by nanofluid, which is compatible with some applications, such as heat exchanger thermal energy storage (HXTES). For this purpose, a triplex tube heat exchanger (TTHX) is designed to receive the hot and cold flow by two pumps from two thermal baths, respectively. Samples of the Copper (Cu) nanoparticles were then carefully selected in a volume concentration range of 0.05 ≤ ∅ ≤ 0.5 to promote the thermal conductivity of the base fluid, which consists of 55% water and 35% ethylene glycol (EG), and to form nanofluid. On the other side, the effect of the porous medium of glass spheres inside a TTHX is considered. Experimentally, and after preparing the nanofluid, temperature readings of six various thermocouples locations have been investigated. The effects of Cu volume concentrations under different temperatures of 20 °C, 30 °C and 50 °C on nanofluid heat transfer are evaluated, respectively. One more result: the yields in the heat transfer coefficient of the hot tube were higher compared to those of the cold tube under Reynolds number (Re) between 200 and 7000. The efficiency of transition and turbulent flow through TTHX is clearly appointed. Overall, these findings support the supposition that the heat transfer enhancement is optimized by 0.05% nanoparticle volume concentration due to increasing thermal conductivity and fluid movement effectiveness. Ultimately, a natural progression of this work is to analyze more convective form using controlled trial applications, such as solar collectors.

Dynamic numerical investigation of the long-term performance of a GSHP system considering groundwater seepage and layered subsurface coupling conditions

This study presents a novel analytical model for ground source heat pump (GSHP) which comprehensively considers the dynamic interaction between building load, borehole heat exchanger (BHE) and heat pump unit, and the BHE under groundwater seepage and layered subsurface coupling conditions, as well as the impact of seasonal ground temperature fluctuation. The model achieved comprehensively reflect the influence of complex geological condition, interaction of unit system and seasonal fluctuation on GHSP performance. The model is utilized to simulate and analyze the long-term dynamic performance and the evaluation index (SCOP) is introduced to evaluate it, the results indicate that, after the 20 years of operation, the SCOP decreases by 9.1% from 4.81 to 4.37. Moreover, by analyzing the influence of load variation on outlet liquid temperature, it can find that the maximum value of the outlet temperature of the circulating fluid and the building cooling load appear at different times, with a difference of 44 days. Finally, the effect of seepage and seasonal ground temperature fluctuates on GSHP performance is investigated, the results reveal that the seepage effect is beneficial to it, and the seasonal ground temperature fluctuate will have an adverse effect on it.

Thermo-mechanical behaviour of energy piles in overconsolidated clay under various mechanical loading levels and thermal cycles

Energy pile foundations play the dual role of providing structural support to buildings and acting as heat exchanger units. Thus, they are subjected to different mechanical loads from the buildings and the cyclic temperature changes encountered in optimized hybrid systems. However, the effects of mechanical loading levels on the thermo-mechanical behaviour of energy piles under cyclic temperature changes are still to be investigated fully. This paper fills this knowledge gap through a series of model scale tests where the effects of different mechanical loading levels were investigated over multiple cooling-heating cycles in over-consolidated saturated clay. In this respect, ten cooling-heating cycles were applied while the pile's head load was maintained at 0, 25%, and 50% of the pile's ultimate bearing capacity, respectively. After ten thermal cycles, the pile's normalized settlement reached 0.05%, 0.37%, and 1.19%, respectively. The ultimate bearing capacity was 555 N, 535 N, and 520 N, respectively. The results indicate that the increase in load levels exacerbates the irreversible settlement while reducing the bearing capacity of the piles. Moreover, it also affects the stress distribution within the pile and further develops internal tension. The results from this study can be used for qualitative analysis of energy pile design.

Thermal performance analysis of a mixed-flow indirect evaporative cooler

This study experimentally investigates the performance of an indirect evaporative cooler based on the Maisotsenko cycle. It consists of a heat and mass exchanger (HMX) with a novel mixed-flow configuration. The de-sized cellulose rich cotton fabric is used as water-absorbing material, and aluminum sheets are used to fabricate the heat mass exchanger unit. The cooling performance indices of the system, namely dew point effectiveness (DPE), wet bulb effectiveness (WBE), and the coefficient of performance (COP), are evaluated at different inlet air temperatures (24 to 35 °C), volumetric flow rates (600 to 1050 m 3 /h), relative humidity (35 to 65%) and the extraction ratio (0.1 to 0.6). The results of the experimental study show that at a relative humidity of 35%, and inlet air temperature of 35 °C, the magnitude of the wet bulb and dew point effectiveness are highest and higher dew point and wet bulb effectiveness are observed at lower mass flow rates. The best cooling capacity and COP were obtained at an extraction ratio of 0.3 and are found to be highest at DBT of 35 °C. The maximum magnitude of CC was 2 kW with a COP of 16. Additionally, the convective heat transfer coefficient is calculated theoretically and compared with the experimental value. Further, a comparison of the obtained results for the mixed flow configuration considered in this study with those for other configurations reported in the literature reveals that the indirect evaporative cooler with mixed-flow configuration yields comparably good effectiveness. • Performance of indirect mixed flow evaporative cooler evaluated experimentally. • Effect of temperature, flow rate, relative humidity and extraction ratio are studied. • The optimum extraction ratio is observed to be 0.30. • Better performance is at higher inlet air temperature with lower humidity. • The maximum COP of 16 was observed at 35 °C with 35% relative humidity.

Thermo-Hydraulic Optimization of Shell and Externally Finned Tubes Heat Exchanger by the Thermal Efficiency Method and Second Law of Thermodynamics

The application aims to determine the thermal and hydraulic performance of externally finned, counter-flow, Shell, and Tube Heat Exchangers (STHE). The application refers to the cooling of machine oil flowing in the annular region, including non-spherical cylindrical nanoparticles of Boehmite Alumina. The oil inlet temperature is equal to 80 °C. Sea water is a coolant with an inlet temperature of 20°C. The main parameter in the optimization process is the number of finned tubes used for oil cooling. Another optimization factor is the number of heat exchanger units connected by hairpin. The number of fins per tube is fixed, equal to 34. The oil flow is set and equal to 4.0 kg/s. The inlet water flow varies, with a maximum flow of 5.0 kg/s. The quantities determined for analysis are: the thermal effectiveness, the actual and maximum heat transfer rates, the pressure drops caused in the tubes and by the flow in the annular region and fin system, the thermal and viscous irreversibilities, and the fluid outlet temperatures, and the thermodynamic Bejan number. It was determined that increasing the number of finned tubes from two to six tubes leads to better thermal and hydrodynamic performance. That is, it produces a favorable cost-benefit, to the detriment of the high viscous dissipation caused by the oil in the annular region. As an object of analysis, the inclusion of nanoparticles showed a significant improvement in thermal performance and an increase in viscous dissipation, with a slight decline in the Bejan number.

Performance assessment of annular fins and cellulose cooling pad on heat transfer enhancement of evaporative heat exchangers using volumetric heat and mass transfer coefficients

In the present work, a test facility has been built to assess the performance of evaporative heat exchangers. The experimental set-up consists of Fan-Cooling pad-Water spray-Heat exchanger (FCWHX) unit with four different configurations namely a) plain tube heat exchanger and b) finned tube heat exchanger with water spray arrangement on their top and without cooling pad, c) plain tube heat exchanger and d) finned tube heat exchanger with cooling pad and water spray arrangement on the top of cooling pad. Experiments are conducted during various durations with climatic conditions in the range of 27 °C–31 °C DBT and 45%–65% RH. While testing the FCWHX unit with and without cellulose pad, exit temperature and humidity of air, exit temperature of spray water and exit temperature of hot water from heat exchanger were continuously monitored. The performance parameters namely heat exchanger duty, evaporative cooling rate and evaporation rate of spray water, volumetric heat and mass transfer coefficients have been determined. Correlations for Nusselt and Sherwood number for all four configurations of FCWHX unit have been presented from these studies, with a maximum of ±10% error band.

Efisiensi Heat Exchanger (HE-002) Pada Crude Distillation Unit di Pusat Pengembangan Sumber Daya Manusia Minyak dan Gas Bumi (PPSDM Migas)

PPSDM Migas Cepu processes crude oil from PT.  Pertamina EP Asset 4 Cepu Field becomes Pertasol CA, Pertasol CB, Pertasol CC, Solar and Residue, through the Crude Distillation Unit (CDU) process in the refinery unit.  In the early stages of the process, the raw material in the form of crude oil is heated in a heat exchanger and then reheated in the furnace until it reaches a certain temperature to flow to the next stages.  A heat exchanger is a heat transfer device between a hot fluid and a cold fluid, without the need to mix the two fluids.  HE-002 shell and tube type is one of five heat exchanger units owned by the PPSDM Migas Refinery unit.  HE-002 plays a role in heating the cold fluid in the form of crude oil which is placed in the tube and flows the hot fluid in the form of diesel fuel through the shell.  Heat transfer can occur due to temperature differences between fluids.  However, in actual conditions, the amount of heat released by diesel and the heat received by crude oil is not of the same value.  This study aims to determine the heat transfer efficiency on the HE-002 by comparing the heat changes in the hot fluid and cold fluid.  After data collection and calculations, the efficiency of the HE-002 PPSDM Migas Refinery unit was 94.463% with a heat loss percentage of 4.753%.

Heat transfer and field synergy characteristics in a rectangular unit channel under mechanical vibration

The internal heat exchangers of a vehicle in driving are excited by forced vibration due to road bumps. But the effect of this phenomenon on the thermal-hydraulic performance of the heat exchanger has not been systematically studied. To investigate the influence of this vibration on the heat transfer characteristics, a numerical model of the rectangular heat exchanger unit channel under vibration excitation was established and verified by experiments. It is found that compared to frequency, amplitude of vibration has a greater effect in enhancing heat transfer but when it is more than 4 mm, which leads to a rapid increase in the friction factor f. An index (j/js)/(f/fs) and a thermal-vibration performance factor (TVPF) considering the frequency and amplitude are proposed to evaluate the effect of vibration on the heat transfer, and it is indicated that for real vehicle operation, an amplitude of 2 mm and frequency of 25 Hz can effectively enhance heat transfer. Besides, it was found that the velocity gradient field perpendicular to the main flow direction caused by vibration synergizes with the temperature gradient field. This work is meaningful and of significance to the practical design of the actual heat exchangers in the automotive application.

Fluid–Rock Interactions in Geothermal Reservoirs, Germany: Thermal Autoclave Experiments Using Sandstones and Natural Hydrothermal Brines

As renewable energy, geothermal can contribute substantially to the energy transition. To generate electricity or to harvest heat, high-saline fluids are tapped by wells of a few kilometres and extracted from hydrothermal reservoirs. After the heat exchanger units have been passed by, these fluids are reinjected into the reservoir. Due to the pressure and temperature differences between the subsurface and the surface, as well as the cooling of the fluids in the power plant, unwanted chemical reactions can occur within the reservoir, in the borehole, and within the power plant itself. This can reduce the permeability of the reservoir as well as the output of the geothermal power plant. This study aims to simulate real subsurface reactions using batch and leaching experiments with sandstone or sandstone powder as solid phase, and deionised water or natural brine as liquid phase. It is demonstrated that fluid composition changes after only a few days. In particular, calcite, aragonite, clay minerals, and zinc phases precipitate from the natural brine. In contrast, in particular minerals containing potassium, arsenic, barium, and silica are dissolved. Due to the experimental set-up, these mineral reactions mainly took place on the surface of the samples, which is why no substantial changes in petrophysical properties could be observed. However, it is assumed that the observed reactions on the reservoir scale have a relevant influence on parameters such as permeability.

Thermoelectric Generator as the Waste Heat Recovery Unit of Proton Exchange Membrane Fuel Cell: A Numerical Study

The proton exchange membrane fuel cell (PEMFC) is a prominent environmentally friendly alternative candidate to internal combustion engines in automotive applications. The recovery of the waste heat of light-duty diesel engines has been investigated recently, which is similarly relevant for PEMFCs. Thermoelectric generators (TEG) applied on the stack’s walls have been already proposed and tested as a cooling method for small scale applications of the PEMFC. For the medium scale usages of the PEMFC stack, TEG technology may be further used to recover heat lost through the cooling water required for stack thermal management, which was the focus of the present study. Using an agglomerate model for the PEMFC and a computational fluid dynamic (CFD) thermal model for the TEG heat exchanger unit, the operation and performance of the PEMFC stack and heat recovery unit were simulated, respectively. After validation, results indicated that the transferred heat from the PEMFC to the cooling channel increased the temperature of the coolant from room temperature to 330.5 K at the current density of 0.8 A/cm2. CFD analysis revealed that 37.7 W of the heated wasted by the PEMFC stack could be recovered by the currently available TEG material and geometry.

An investigation on simultaneous freshwater production and CO2 capture using flue gas of a power plant

AbstractThis paper presents an investigation on simultaneous freshwater production and CO2 capture using the flue gases of a 500 MWe coal‐fired power plant. Generally, a fan/cooler is used to reduce the temperature of flue gas before flowing into the absorber column of a CO2 capture unit. It has been replaced with a heat exchanger in this study. Seawater and flue gas were passed through the heat exchanger to raise the temperature of seawater and reduce the temperature of flue gas. The high‐temperature seawater was subsequently fed into a membrane distillation (MD) unit for freshwater production. The cold flue gas was directed to the CO2 capture unit. The heat exchanger and CO2 capture unit were modeled with Aspen Plus software. Whereas MATLAB software was used to develop and solve the MD mathematical model software for freshwater production. The seawater flow rate was varied from 4000 L/min to 7000 L/min in the heat exchanger. As a result, the flue gas (flow rate 781.6 t/h) and the outlet seawater temperatures were reduced from 27.498 to 22.360°C and 73.384 to 52.670°C, respectively. However, higher inlet seawater temperature in the MD unit produced more freshwater. An increase in inlet seawater feed temperature in the MD unit from 52.670 to 73.384°C increased the freshwater production from 211,956.5 to 299,244 L/day. Furthermore, the CO2 capture process has been analyzed by varying the methyldiethanolamine (MDEA) and piperazine (PZ) concentrations in weight% (45 and 5, 40 and 10, 35 and 15, and 30 and 20, respectively). It was observed that the energy requirement reduced from 3.55 to 3.26 MJ/kg CO2 by increasing the PZ content from 5 to 20 wt.%. At 15 and 20 wt.% of PZ content in the blended solution of MDEA/PZ, the energy required to regenerate the solvent was 3.31 and 3.26 MJ/kg CO2, respectively. PZ emissions from the absorber were also increased with the raising of PZ content in the blended solution. The energy requirement was not much higher at 15 wt.% than 20 wt.%. Therefore, MDEA/PZ solution (15/35 wt.%) was considered an optimal concentration. The reboiler duty was reduced up to 3.25 MJ/kg CO2 at 15/35 wt.% concentration with stripper pressure of 2.3 bar. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Automated and Dynamic Control of Chemical Content in Droplets for Scalable Screens of Small Animals (Small 17/2022)

Small Animal Screening In article number 2200319, Hang Lu and co-workers develop a droplet-based microfluidic platform for the screening of dynamic phenotypes in small animals. The microfluidic liquid exchanger unit illustrated here allows switching of the chemical environment of an animal encapsulated in a droplet. This method represents an efficient way of altering the chemical or biological environment of an animal (here C. elegans) and monitoring its dynamic response. Integrated with an encapsulation unit and chemical dispensers, this system leads to a powerful technology that will help bridge the gap between the environment, genotype, and phenotype.

Automated and Dynamic Control of Chemical Content in Droplets for Scalable Screens of Small Animals.

Screening functional phenotypes in small animals is important for genetics and drug discovery. Multiphase microfluidics has great potential for enhancing throughput but has been hampered by inefficient animal encapsulation and limited control over the animal's environment in droplets. Here, a highly efficient single-animal encapsulation unit, a liquid exchanger system for controlling the droplet chemical environment dynamically, and an automation scheme for the programming and robust execution of complex protocols are demonstrated. By careful use of interfacial forces, the liquid exchanger unit allows for adding and removing chemicals from a droplet and, therefore, generating chemical gradients inaccessible in previous multiphase systems. Using Caenorhabditis elegans as an example, it is demonstrated that these advances can serve to analyze dynamic phenotyping, such as behavior and neuronal activity, perform forward genetic screen, and are scalable to manipulate animals of different sizes. This platform paves the way for large-scale screens of complex dynamic phenotypes in small animals.

Model predictive controller for a retrofitted heat exchanger temperature control laboratory experiment

This paper aims to demonstrate the practical aspects of process control theory for undergraduate students at the Department of Chemical Engineering at the University of Bahrain. Both, the ubiquitous proportional integral derivative (PID) as well as model predictive control (MPC) and their auxiliaries were designed and implemented in a real-time framework. The latter was realized through retrofitting an existing plate-and-frame heat exchanger unit that has been operated using an analog PID temperature controller. The upgraded control system consists of a personal computer (PC), low-cost interface using X-transposed-region (XTR) converter, national instruments USB 6008 data acquisition card, and LabVIEW software. LabVIEW control design and simulation modules were used to design and implement the PID and MPC controllers. The performance of the designed controllers was evaluated while controlling the outlet temperature of the retrofitted plate-and-frame heat exchanger. The distinguished feature of the MPC controller in handling input and output constraints was perceived in real-time. From a pedagogical point of view, realizing the theory of process control through practical implementation was substantial in enhancing the student’s learning and the instructor’s teaching experience

A hybrid TEG/evacuated tube solar collectors for electric power generation and space heating

The present work aimed to examine the performance of a thermoelectric generator (TEG) augmented with a hydronic evacuated tube solar collector heat exchanger used to heat a cold zone. TEGs were operated on the temperature difference between hot water circulated through the heat exchanger and the cold temperature of the surrounding space. The setup model of a heat exchanger with TEGs installed on the outer surface was examined numerically under steady state conditions for natural and forced convection modes. The results obtained show that 1.03 W of electricity could be produced when the temperature differences across the TEG and air velocity are 60 °C and 0.5 m/s, respectively. Also, an increase of 17.47% of TEG power was achieved for each 5 °C drop in surrounding space temperature and by 11% for each 5 °C rise in circulated hot water temperature. Besides the importance of improving TEG efficiencies, the amount of generated electricity may be valuable when large-surface area heat exchanger units are installed in large systems.

Thermal and acoustic performance of silencing heat exchanger for engine waste heat recovery

The integrated design of gas heat exchanger and after-treatment unit can reduce the size and weight of the engine waste heat recovery system, releasing the back pressure of exhaust gas and enhancing net benefit of the waste heat recovery system. In this study, we propose a silencing heat exchanger that integrates an exhaust heat exchanger with an impedance composite muffler in the post-treatment system, using metal foam material instead of the sound absorbing material in the impedance composite muffler. By adapting ANSYS Fluent and LMS Virtual.Lab, thermal simulation and acoustic simulation of the silencing heat exchanger were realized, and comparative analysis of the modified structure and the basic structure was carried out. The modified silencing heat exchanger was then designed and fabricated, and the thermal and acoustic performance were tested. The results show that the modified silencing heat exchanger can achieve improved heat transfer and flow performance, and more uniform temperature distribution at the hot side, simultaneously resulting in an 8.4% reduction in exhaust pressure drop. Even more, the improvement of silence effect in the middle and high frequency band is fairly obvious, and the overall transmission loss is 44.4% higher than that of the basic structure.

Effects of Mechanical Vibration on the Heat Transfer Performance of Shell-Tube Heat Exchanger Units During Charging Process

Effects of Mechanical Vibration on the Heat Transfer Performance of Shell-Tube Heat Exchanger Units During Charging Process

Control allocation based fault tolerant control of descriptor system with actuator saturation

This paper deals with the design of active fault-tolerant control (FTC) system based on control allocation (CA) technique for the uncertain descriptor system (DS) with actuator saturation. This work assumes that a fault detection unit is available to estimate the actuator fault. The proposed CA technique is responsible to redistribute the control effort to the healthy actuators taking the advantage of actuator redundancy of the DS. The so-called virtual control law is designed based on a variable gain super twisting sliding mode algorithm (VGSTSMA) to meet the admissibility criteria of continuous control input for the DS. This VGSTSMA based control strategy is designed based on the generalized regular form (GRF) of DS ensuring the robustness against the actuator faults, error in the fault estimation, and the external uncertainties. The CA scheme developed here is applicable to the DS even with a full rank input matrix which is different from the traditional design where it generally deals with the system with rank deficient input matrix. Furthermore, a static control redistribution mechanism is introduced to handle the actuator saturation which is responsible to re-allocate the excess control efforts to the available healthy actuators in the face of actuator saturation. Finally, a dual-pipe heat exchanger unit, modeled as DS, is simulated with proposed CA-based FTC such that the system can follow the time varying and constant reference trajectories in a situation of actuator faults and saturation. The simulation results are compared with the CA-based FTC where virtual control is designed based on super-twisting algorithm (STA) and with the traditional pseudo inverse-CA-based FTC to establish the superiority of the proposed scheme.