Cold Water Flow Research Articles

Optimal operating conditions and economic analysis of the cold water phase change energy heat pump system for heating and cooling

The cold water phase change energy heat pump system has important economic value for supplying heating and cooling to office buildings. In this paper, the effect of ice thickness, cold water flow, evaporation and condensation temperatures on the system effective COP are analyzed to determine the optimal operating conditions of the system for heating and cooling of office buildings, the economics of the system are calculated, and an operation control scheme is proposed. The results show that the system performs best when the icing thickness is set to 8 mm, the cold water flow is set to 25 t/h during the icing period and the cold water flow is set to 45 t/h during the de-icing period; Under the optimal operating conditions, the winter operating cost of the project is USD 10363/Year and the summer operating cost is USD 2674/Year, with the return on investment of 14% and the payback period of 4 years; Regulating system operation according to year-round heating and cooling load requirements, the operating cost is reduced by 8% in winter and 2% in summer. This paper provides references to the best operating conditions and economic data for the application and promotion of the cold water phase change energy heat pump system.

Hollow fiber polytetrafluoroethylene membrane heat exchanger with anti-corrosion properties

Thin hollow polytetrafluoroethylene (PTFE) fibers (thickness: 200 μm; outer diameter: 1.3 mm; inner diameter: 0.9 mm) were produced by a specially designed die via stretching and sintering, and assembled into a shell-and-tube membrane heat exchanger. The effects of the flow velocities on the heat transfer performance and thermal resistance were studied in a water-water system. The maximum overall heat transfer coefficient (OHTC) was up to 391 W/(m2‧K) (flow velocities: 0.24 m/s for hot water; 0.11 m/s for cold water). The OHTC became larger (increased from 229 to 391 W/(m2‧K)) at a higher cold water flow velocity (increased from 0.02 to 0.11 m/s) on the shell side when maintaining the hot water flows on the tube side. The OHTC increased from 119 to 391 W/(m2‧K) first and then decreased to 298 W/(m2‧K) with the increase of the hot water flow velocities (from 0.08 to 0.40 m/s) on the tube side, while maintaining the cold water flow velocity on the shell side. The thermal resistance results showed that the increased flow velocity (0.11 m/s) on the shell side significantly reduced the thermal resistance to 2.56 × 10−3 K m2/W on the shell side. Furthermore, the flow turbulence on the tube side is favorable for the heat transfer, and the optimum flow velocity on the tube side was 0.24 m/s. The hollow PTFE fibers were extremely stable and durable in corrosive solutions, with less than 1% changes in bursting strength, tensile strength at break, and elongation at break. This work opens new opportunities for the fabrication and application of hollow fiber PTFE membrane heat exchangers to reuse waste heat in high temperature corrosive environments.

Microcontroller-based Sonar Ultrasonic Water Level Control System with Closed-loop Control Approach

This study proposes a microcontroller-based closed-loop water level control system that utilizes a sonar ultrasonic sensor to monitor and regulate water levels in a tank. The system operates by continuously checking the water level in the tank and adjusting the valve’s opening and closure times to maintain the desired water level. The closed-loop control approach employed by the system offers a precise water level control solution that can significantly reduce water waste in water pumping systems. The paper also assesses the theoretical and experimental response of an open-loop water level control system. The findings demonstrate that the closed-loop system outperforms the open-loop system, indicating the effectiveness of the proposed approach in maintaining water levels in a tank. The proposed system is not only applicable to water pumping systems but can also be used to manage the flow of hot and cold water from home water heaters. Additionally, the system can be utilized in various industries that require level or flow control, with particular emphasis on the production of distilled water, juice, and milk.

Experimental study on the bottom liquid cooling thermal management system for lithium-ion battery based on multichannel flat tube

Thermal management system (TMS) plays an important role in reducing the battery module’s temperature rise and ensuring temperature uniformity. In this study, a bottom liquid cooling (BLC) TMS based on multichannel flat tube (MCFT) is established. The temperature distribution of the battery module under the BLC method is analyzed through comparative experiments with the passive cooling method. Then, the influence of cold water flow rate and cold water inlet temperature variation on thermal management performance are studied. Results show that the BLC TMS based on MCFT can effectively reduce the temperature rise of the battery module without considerably reducing the temperature uniformity of the module. The increase in the cold water flow rate slightly influences the thermal management performance of the battery module, the change in the module’s maximum temperature is only 1.4%. However, the change in the cold water inlet temperature considerably influences the thermal management performance of the battery module. The temperature of the battery module can be maintained below 45 °C by decreasing the cold water inlet temperature, but the temperature difference of the battery and module levels are increased by 48.9% and 61.6%, respectively.

Operation and Multi-Objective Design Optimization of a Plate Heat Exchanger with Zigzag Flow Channel Geometry

The performance of a plate heat exchanger (PHE) using water as the working fluid with zigzag flow channels was optimized in the present study. The optimal operating conditions of the PHE are explored experimentally by the Taguchi method, with effectiveness as the objective function. The results are further verified by the analysis of variance (ANOVA). In addition, the zigzag flow channel geometry is optimized by the non-dominated sorting genetic algorithm-II (NSGA-II), in which the effectiveness and pressure drop of the PHE are considered the two objective functions in the multi-objective optimization process. The experimental results show that the ratio of flow rates is the most important factor affecting the effectiveness of the PHE. The optimal operating conditions are the temperatures of 95 °C and 10 °C at the inlets of hot and cold water flows, respectively, with a cold/hot flow rate ratio of 0.25. The resultant effectiveness is 0.945. Three geometric parameters of the zigzag flow channel are considered, including the entrance length, the bending angle, and the fillet radius. The sensitivity analysis of the parameters reveals that a conflict exists between the two objective functions, and multi-objective optimization is necessary for the zigzag flow channel geometry. The numerical simulations successfully obtain the Pareto optimal front for the two objective functions, which benefits the determination of the geometric design for the zigzag flow channel.

A Diagnostic Method Based on Active Thermography for the Degradation Assessment of Power Plant Boiler Tubes.

Proper maintenance management of power infrastructure requires inspections, in order to gather knowledge about the facility's current condition. For this purpose, periodic diagnostic tests are carried out, not only to determine the current state, but to also predict future conditions, and subsequently plan for the scope of necessary repair work. Currently, in the case of heat screens of power boilers, the diagnostic process takes many days, is very expensive, and usually does not cover the entire screen area. Therefore, it is necessary to develop new, noninvasive diagnostic methods. This study presents the concept and research for an alternative method of locating places with excessive energy boiler screen degradation that require replacement. It was assumed that the new method should be fast, require no scaffolding assembly, and permit checking of the entire screen surface; this is unlike the methods used currently, which require manual checking of selected screen tubes. The proposed method is based on active thermography, in which heat flux is forced by the liquid flowing inside the screen. Tests were carried out based on a model of an axial-symmetric system in the form of a tube, with controlled reductions in the wall thickness. An experiment was carried out many times by recording the pipe surface temperature in many characteristic places (different thicknesses of the tube walls) with a thermal imaging camera. A temperature change was forced by a controlled flow of hot or cold water. The methods of analysis were proposed and verified, allowing firstly, detection of places with a reduced wall thickness, and secondly, estimations of the wall thickness (i.e., excessive degradation). For the best-proposed model (one of the four analyzed), all of the thickness changes were detected, and the limit error of thickness obtained was 0.3 mm.

CFD simulation and optimization of an energy-efficient direct contact membrane distillation (DCMD) desalination system

In this paper, the CFD simulation and optimization of an energy-efficient direct contact membrane distillation (DCMD) desalination system in a counter-current flow mode are performed. Two-dimensional modeling was applied and the governing equations for momentum, heat, and mass transfer in the three regions i.e., feed channel, membrane, and permeate channel were solved and corresponding velocity, temperature, concentration fields, and the permeate water flux through the membrane was obtained. A two-step approach was considered to optimize the desalination system through the MD process. First, the model results were validated with the reported experimental data and good agreements were observed. The maximum deviation for the outlet concentration and hot stream outlet temperature with different feed velocities and temperatures was 0.33%. Then, the process was optimized for maximizing the permeate flux. Since the number of parameters was high, the response surface methodology (RSM) was used to find the optimum condition in order to obtain the maximum water flux. It was determined that the highest permeate water flux would be gained at the permeate temperature, the hot feed flow rate, the cold-water flow rate, the length and height of the channels of 35 °C, 20 lit/min, 10.25 lit/min, 20 cm, and 3 cm, respectively. At this optimum condition, a permeate flux of 53.5 kg/m2.h and a TPC of 0.82 are expected.

Heat Transfer Characteristics of Cold Water Phase-Change Heat Exchangers under Active Icing Conditions

Under active icing conditions, the heat transfer performance of the CPHE has a significant impact on the system’s efficiency and energy consumption. Using the enthalpy-porosity method for describing the solidification process of liquids, the simulation and analysis of the effects of different parameter changes on the CPHE heat transfer performance were conducted to clarify the effects of the changes in the intermediary side inlet water temperature, intermediate water flow rate, and cold water flow rate on the heat transfer process in the CPHE. According to our results, changing the intermediary inlet water temperature has a greater impact on the heat transfer process in the cold-water phase-change heat exchangers. For every decrease of 0.5 °C in the intermediary side inlet water temperature, the average heat transfer coefficient increases by approximately 50 W/m2-K. Changes in the intermediary water flow rate affect the cold water phase-change heat exchanger’s heat transfer process. By increasing the intermediary water flow rate, the average heat transfer coefficient of a cold water phase-change heat exchanger can be improved, but the growth decreases, and the maximum flow rate of the intermediary water should not exceed 0.5 m per second. A change in the cold water flow rate in the cold water phase-change heat exchanger’s heat transfer process has a small impact on the cold water flow rate, increasing by 0.02 m/s each, with the average heat transfer coefficient increasing by 20 W/m2-K.

Rotating thermal flow of water near its density inversion point in a vertical annulus: flow regime transition and heat transfer enhancement

Three-dimensional simulations are performed to identify the flow regimes of the rotating thermal flow of cold water near its density inversion point within a vertical annulus and evaluate the commensurate heat transfer abilities. The development of flow regimes and the variation in heat transfer behaviors in the special case with the density inversion parameter Θm=0.5 are explored over a wide range of parameters, with the Rayleigh number 104≤Ra≤106 and the Reynolds number Re≤150. The convection flow is radially separated into two layers by the density-maximum isosurface, with the inner and outer layers dominated by a positive and negative radial density gradient, respectively. Three axisymmetric and four non-axisymmetric basic flow regimes with different generation mechanisms are defined to describe the double-layer convection flow. Eleven flow regimes are identified, each of which consists of one, two or three basic flow regimes. The spatio-temporal features of the flow regimes depend on Ra and Re. The mixed convection parameter is demonstrated to be capable of qualitatively measuring the relative strength of the flow between the inner and outer layers in certain ranges of Ra. The mechanisms of both the flow regime transitions and the mode transitions between steady and oscillatory states are explored in terms of the combined action of density inversion effect, centrifugal effect and buoyancy effect. The heat transfer behaviors depend on the spatio-temporal features of flow regimes. The mechanism of heat transfer enhancement and that for the non-monotonic variation of heat transfer ability are revealed. The limitation of the axisymmetric assumption is quantified.

Study the Performance of a Novel Desiccant Heat Exchanger

Conserving energy and reducing emissions has become a global consensus. However, most air conditioning systems are highly energy-consuming, affecting global warming and the ozone layer because they use chlorine and fluorine refrigerating fluids. Evaporative cooling systems are one of the most important environmentally friendly air conditioning systems with low energy consumption. However, their performance is negatively affected by the high humidity of the inlet air. One of the solutions to control the relative humidity of the inlet air is using desiccant material. In this paper, a silica gel-coated heat exchanger was designed and constructed as a dehumidifying unit. The effect of airflow rate, hot water flow rate, cold water flow rate, and regeneration temperature on the system's performance has been studied. It was found that increasing the hot water flow rate improves the removing moisture from the desiccant. However, increasing the hot water flow rate has a negative effect on the thermal performance of the heat exchanger. The effectiveness of the heat exchanger was 53% in the regeneration phase and 52% in the cooling phase for the outside air temperature of 40 ºC, W=20 g/kg, and an airflow rate of 0.48 m³/s. From the results shown above, it was noticed that the system could work efficiently in hot and high humidity climates and be used in Iraqi weather.

Northeast Greenland: ice‐free shelf edge at 79.4°N around the Last Glacial Maximum 25.5–17.5 ka

The size of the last glacial ice sheet on the Northeast (NE) Greenland shelf and its interaction with ocean circulation have been the subject of debate. Here we provide insights into the extent of the ice sheet around the Last Glacial Maximum (LGM) and investigate timing and strength of changes in the flow of Atlantic Water. The study is based on a multiproxy investigation of a marine sediment core, gravity core DA17‐NG‐ST01‐019G, from 323‐m water depth at the NE Greenland shelf edge at 79.4°N. We present benthic and planktic foraminiferal distribution data, AMS‐14C dates, sedimentological (ice‐rafted debris (IRD) and grain sizes), and geochemical (XRF) data in combination with geophysical (sub‐bottom profiler) data. The oldest sediments at the study site are dated to 25.5–17.5 ka, encompassing the time frame from the beginning of the LGM to the early deglaciation. This part is overlain by sediments from the late deglaciation and Holocene. The deposits dating from the LGM are very rich in both planktic and benthic foraminifera and macrofossils of excellent preservation. The faunas show that the site generally was affected by a strong flow of relatively warm subsurface Atlantic Water during the LGM and Early Holocene. Conditions turned more polar with cold bottom water flow in the Middle–Late Holocene (c. 7.5 ka to Recent) with presence of mainly agglutinated benthic foraminiferal species. Our data from the LGM also indicate that the deposits were mixed by iceberg scouring, confirmed by the geophysical data showing extensive ploughing of the sediments on the outer shelf area. The results further indicate that the Greenland Ice Sheet did not reach to the edge of the NE Greenland shelf at 79.4°N during the LGM 24–18 ka.

Gain scheduling model predictive controller design for tankless gas water heaters with time-varying delay

• Thermal model with time-varying delay is developed for a tankless gas water heater. • Feedback, feedforward and model predictive controllers are designed. • Controllers are assessed for cold start and water flow rate sudden disturbances. • Impact of temperature overshoots and undershoots are diminished. • Gain scheduling MPC presents superior performance than classic controllers. One of the most significant drawbacks of tankless gas water heaters is the difficulty of controlling the outlet hot water temperature as changes in water demand cannot be predicted. These sudden changes in hot water flow rate, are associated with the system inhered delays, and are responsible for temperature overshoots and undershoots that severely affect the comfort perception of the user. In the present work, a linear model predictive controller (MPC) design is employed for the stabilization of a constrained nonlinear thermal process with time-varying delay, however, control performance degrades significantly when operating far from the linearization operating point. The idea is to design multiple linear MPC controllers, each with its linear state-space model and constant time delay, describing process dynamics at a specific level of operation. Gain scheduling MPC presents improved performance when compared with classic PID and combined feedforward-feedback controllers, reducing the settling time up to two thirds.

Analysis study of nano fluids and longitudinal fins on the heat transfer in the counter flow double pipe heat exchanger

In this paper, the heat transfer enhancement in a counter-flow double pipe heat exchanger with longitudinal rectangular fins on the outer surface of the inner tube was numerically investigated by ANSYS 20.R1 software using CFD package and finite volume method. Hot water flows in the inner tube at 60℃ while cold water flows in the outer tube at 25℃. The flow is laminar with five mass flow rates from 0.012kg/s to 0.02kg/s) for hot side and from 0.01kg/s to 0.03kg/s for cold side. Two types of nanoparticles Al₂O₃ and SiO₂ have been added to produce nanofluids as heat transfer fluid in the external channel (cold fluid flow) with four different concentrations from 0.04% to 1%. Results showed, as the concentration of Nanofluids increased, the heat transfer rate also increased. At 1% concentration, the maximum heat transfer coefficient was belonged to Al₂O₃/water nanofluid by 22.3% enhancement in comparison with distilled water, while the SiO₂/water nanofluid has enhancement of 19% in heat transfer coefficient in comparison with the distilled water. Both nanofluids show higher pressure drop compared with distilled water where the SiO₂/water nanofluid gives a higher drop of (33.2%), while the Al₂O₃/water nanofluid has (32.1%) of the pressure drop.

Performance of an air gap membrane distillation system and enhancement using a low-cost surface modification

ABSTRACT Water can be purified with a hydrophobic membrane in an air gap membrane distillation (AGMD) configuration. The present study presents experimental data for such a system and comparison with model predictions from simulations in a Matlab environment. The importance of the respective roles of feed water temperature and flow rate, cold water temperature and flow rate, and the extent of air gap on water production rate is studied, both from experiments and simulations. The comparison is found to be quite good, thus validating the choice of the mathematical model. In addition, possible improvements in the device performance are examined by using a surface modification of the hydrophobic membrane. In this respect, a layer of lead from a pencil is coated over the membrane. Evaporation rates through the pencil-coated membrane were measured in a solar simulator with 1 sun, 2 sun, and 3 sun settings. A distinct improvement in the evaporation rate was obtained when a pencil coated membrane was used. Following this observation, an augmented two-sided AGMD system is proposed, which carries a coated membrane exposed to solar radiation on one side and an uncoated membrane on the other.

Effectiveness Enhancement of the Double Tube Heat Exchanger Using ZnO Nanofluid

In this study, the effect of adding zinc oxide nanoparticles to the reversible effect double tube heat exchanger with a length of 1.5 meters, an outer diameter of 19.0 mm, is made of copper material that is used by Nano water as a cold liquid. Zinc solid nanoparticles with a volume concentration of 3% were used with water as the base liquid. The cold nanoscale water flows into the real tube with a volume of 4 L/min which enters into the heat exchanger at 16°C, where the hot water flows into the separator of the heat exchanger representing a blank volume of 6 L/min. The Reynolds number range and flowrate ranges are 10000 to 20000 and 5 to 15 respectively. The heat exchanger was introduced at a temperature of 65°C. An improvement in the performance of the exchanger was shown in the case of using water with the addition of nanoparticles

Inverse artificial neural network control design for a double tube heat exchanger

This work focused on a new developed and experimentally tested non-linear control approach to control a double tube heat exchanger's output cold water temperature. The control approach uses an inverse artificial neural network (ANNi) and an integral control law. The ANNi objective is to obtain the cold water flow considering as a reference the desidered output cold water temperature. The ANNi was built from a feedforward ANN with four inputs (input cold water temperature, input hot water temperature, cold water flow, hot water flow), a hidden layer with a neuron, and two outputs (output cold water and output hot water temperature). The integral control law is implemented to reduce the error between the setpoint and the ANNi estimate. As a result, the output cold water temperature regulation is achieved through a simple controller that does not need a complex ANN model and does not depend on the process parameters' exact value. The proposed control scheme (Inverse Artificial Neural Network with Integral Control (ICANNi)) showed good reference tracking, obtaining a root mean square error (RMSE) of 0.2025, standard deviation (SD) of 0.0410, establishment time of 23 s, and overshoots less than 2.7 °C. In addition, the ICANNi control has a settling time that is 1.91 times faster than the PID control and 1.5 times faster than the ANNi control.

CFD ANALYSIS FOR HEAT TRANSFER AND PRESSURE DROP IN TUBE BUNDLE OF CROSS-FLOW HEAT EXCHANGER

In the present work, the preliminary finding of possibilities of heat transfer and pressure drop is reported across the shell and tube arrangement cross-flow heat exchanger. The heat exchanger consists of cold-water flows through the bundle of circular tubes and hot air across the shell. Like in the conventional arrangement, the flow in adjacent rows of tubes is normal to the fluid flow in the shell in the cross-flow arrangement. The three-dimensional turbulent flow region is modelled by employing ANSYS FLUENT 21.0. The standard k-ε model is used to model the turbulence flow. A SIMPLE algorithm scheme is applied to link the pressure and velocity fields inside the domain for air fluids. The heat transfer in the water inside the tubes is represented by a convective boundary condition. The tube flow Reynolds number was fixed at 2200 and the shell flow Reynolds number was varied from 6000 to 10000 in the turbulent zone. The purpose of this paper is to determine temperature reduction and pressure drop across the tube bundle. The simulation will predict the temperature of the airstream at the heat exchanger exit and the pressure drop. The results indicated that there is a significant amount of temperature drop in the air that releases the heat due to forced convection and temperature drop continues in the turbulent region of the incoming fluid.

Optimization of the flow distribution in a gyrotron cavity using evolutionary CFD simulations driven by a genetic algorithm

The steadily increasing performance requested to gyrotrons, to comply with their function of heating and current drive in fusion reactors, put a progressively increasing burden on the heat removal from the interaction cavity, where the heat flux can easily reach 20 MW/m2 on its inner surface. The cavity is actively cooled by subcooled water in forced flow in an annular region, and the water flow typically enters and exits through a single inlet and outlet. The high-speed flow entering from the inlet potentially drives an inhomogeneous flow azimuthally in the cavity region, but helps in locally bursting the heat removal due to the impinging effect of the cold-water flow. Here a new design of the water inlet in the cavity region is performed through a simplified genetic algorithm, in such a way that the flow homogeneity in the gyrotron cavity is maximized, without reducing the beneficial cooling due to the impact of the water jet on the cavity wall. The presence of multiple holes feeding the cavity, with their azimuthal location driven by the genetic algorithm, is analyzed through Computational Fluid Dynamics (CFD) simulations. Once the multi-inlet location is optimized, the dimension of the inlet holes is tuned to burst the heat transfer effect, reaching a high level of temperature and flow homogeneity in the cavity.

Development of an innovative temperature control system in a fermenter: application to the case of the wine industry

Temperature is one of the most important parameters influencing the fermentation in wine making process. Indeed, its control during this phase is fundamental to obtain a high-quality product. Fermentation is an exothermic process and for this reason a good cooling system in fermenter tanks is required. The temperature control systems usually adopted are represented by an external cooling jacket in which cold water flows. This system is based on the water circulation which is activated only when a critical temperature in the fermenter is exceeded making the control less precise. In this paper an alternative solution based on heat pipe technology is designed and its feasibility is investigated through the application of its ideal variant. This innovative temperature control system has the advantage to work on continuous mode, thus keeping the temperature in the fermenter more uniform during the whole process. Moreover, the proposed system is fully passive reducing the costs of this process phase. The results of this work demonstrated that the device application could be feasible and that it represents a promising solution.

Analysis of a finned type concentric tube heat exchanger using different materials by applying CFD

Heat exchangers are equipment used to transfer heat from a high temperature fluid to a low temperature fluid without direct contact. Usually, the heat exchangers used for industrial applications are large in size. The objective of this study is to reduce the size of the heat exchanger and increasing the effectiveness by using suitable materials. The present study is carried out on a concentric tube heat exchanger with rectangular fins arranged around the circumference of the tube. The initial simulation is carried out to find the best material among aluminum bronze and Al 6061. The study is further continued to find the best inlet conditions by varying the mass flow rate from 0.25 kg/s to 3 kg/s in 0.25 kg/s increments and inlet temperature from 80°C to 90°C in 5°C increments. Cold water flow conditions, such as mass flow rate of 1.5 kg/s and inlet temperature of 30°C, are constant throughout the study. The heat exchanger was modeled in SOLIDWORKS 2020. The flow simulation and thermal analysis were carried out in SOLIDWORKS Flow Simulation 2020. The simulation results and the actual prototype results showed a variation of 4.2%.