Circulating Water Temperature Research Articles

Numerical study on heat and mass transfer performance of a natural draft wet cooling tower based on baffle optimization

In the natural draft wet cooling towers (NDWCTs), the resistance of the packing layer to air and the effect of the circular design of its cross-section, the air reaches the tower center area to overcome the maximum resistance. The air velocity in the center of the tower is low and the heat transfer is poor. To improve the performance of the cooling tower, the optimized design of the cooling tower distribution pipe surface with baffles is firstly investigated. Then, the three-dimensional numerical model of NDWCTs is developed and validated with power plant data. Finally, the effect of plates on cooling tower performance is analyzed through the influence of baffles on the cooling tower air field and combined with the circulating water temperature drop, evaporation, and ventilation. Results show that the air field uniformity inside the cooling tower is effectively improved by adding baffles. The cooling efficiency of the circulating water inside the cooling tower is improved. The air velocity in the packing zone is significantly increased by adding the a1a2 type baffle and the air temperature and circulating water in the central area of the tower decreases significantly and the a1a2 baffles performed best in terms of circulating water temperature drop in the packing zone and were able to significantly improve the cooling effect. The cooling tower with pro-wall baffles can cool the circulating water better than the conventional cooling tower. This study provides ideas for subsequent structural and energy efficiency studies.

Study on long-term operation characteristics of the medium-deep ground source heat pump system with solar heat storage

Long-term heating operation of the medium-deep ground source heat pump (MGSHP) system will cause the underground temperature around the mid-deep borehole heat exchanger (MBHE) significantly lower than its initial value, which will reduce the operating efficiency of the MGSHP system. In some cases, the temperature of the circulating water in MBHE even is lower than the lowest value required by the heat pump unit, which will lead to operation failure of the unit. Attenuating the ground temperature decrease by storing heat underground during non-heating seasons is an effect way to maintain the heat extraction capacity of the MBHE. In this paper, the influence of storing solar energy underground during non-heating seasons on the long-term operating characteristics of the MGSHP system is studied. The MBHE heat transfer model which considers the heat storage process is developed and embedded in the software of TRNSYS. Based on the numerical simulation model of solar assisted mid-deep ground source heat pump (SAMGSHP) system built by TRNSYS, the long-term characteristics including the variations of the fluid temperature of the MBHE, the ground temperature distribution and the COP of the heat pump unit of the MGSHP system with heat storage during non-heating seasons are analyzed and compared with the case without heat storage. The results show that storing solar energy underground during non-heating seasons can effectively improve the ground temperature, significantly slow down the decline of the circulating water temperature of the MBHE in heating seasons and apparently increase the COP of the heat pump unit. The results can serve as a reference for engineering applications of MGSHP systems, especially those cannot completely meet the original design heating load.

Effect Mechanism of Ambient Air Parameters on the Thermal Performance for Cooling Towers

Abstract As the volume of natural draft wet cooling towers (NDWCTs) continues to increase, the influence of ambient air on the thermal performance of the NDWCT is not clear. Therefore, the main parameters such as gas–water ratio, circulating water temperature difference, and heat transfer in each zone were calculated, and the temperature field and humidity field were also investigated. The results showed that the ambient temperature had the greatest influence on the cooling capacity of the NDWCT and the increase of ambient temperature led the circulating water temperature difference decreases the most, which was 7.63 °C (74.15%). The increase of relative humidity and atmospheric pressure led to an increase in convective heat transfer and the decrease in evaporative mass transfer, while both the convective heat transfer and evaporative mass transfer reduced with the decreasing temperature. This study establishes a theoretical foundation for optimizing of the thermal performance and energy-saving design of NDWCTs.

Suitable Analysis of Micro-Increased Capacity Model on Cold-End System of Nuclear Power Plant

The cold-end system of a nuclear power plant is a key complex node connecting the power generation system with the variable environmental conditions, and its operation, economy, and stability have become the main obstacles to further improving the performance of the first and second circuits. The current research on the interactions between the cold-end system and the thermal cycle of nuclear power mainly adopts the micropower model, while the existing condenser model does not take into account the influence of the turbine exhaust resistance and exhaust flow and other factors on the condenser vacuum change caused by the change in the circulating water flow rate and temperature in determining the optimal vacuum. This ignores the interactions between the equipment and the interconnections between the parameters, which results in the reduction of the model’s accuracy. This paper takes a nuclear power unit as an example, adopts the “constant flow calculation” method to calculate the heat balance of the two-loop thermal system of the nuclear power plant, and constructs an integrated simulation model of the reaction environment variables, the cold-end system, and the thermal cycle. Taking the circulating water temperature and flow rate as variables, the errors of the separate condenser model and the coupled model in circulating water parameter changes were obtained under the condition of satisfying the thermal system operation, and the circulating water temperature and flow rate change ranges applied by the separate condenser model were analyzed in order to reduce the amount of calculations when the unit power error was 1%. The results show that the circulating water temperature is 4 °C, the applicable range of the circulating water flow rate is 42 m3/s to the rated flow rate, the applicable range of the circulating water temperature is 20 °C, the applicable range of the circulating water flow rate is 32.12 m3/s to the rated flow rate, the applicable range of the circulating water temperature is 26 °C, the applicable range of the circulating water flow rate is 38.63 m3/s to the rated flow rate, the applicable range of the circulating water temperature is 30 °C, and the applicable range of the circulating water flow rate is 45 m3/s to the rated flow rate. At a circulating water temperature of 26 °C, the applicable range of the circulating water flow is between 38.63 m3/s and the rated flow; at a circulating water temperature of 30 °C, the applicable range of the circulating water flow is between 45.64 m3/s and the rated flow.

Evaluation of heating capacity of shallow ground heat exchangers in different Locations– A case study of two administrative districts of Xi'an

As a case study, two administrative districts of Xi'an are selected. Eight sites are drilled for shallow ground heat exchangers (SGHEs), and thermal response tests (TRTs) are conducted on the ground to investigate the heating capacity of SGHEs in different locations. The vertical distribution of initial ground temperature is identified using a temperature sensing system in TRTs. Simultaneously, the real-time inlet and outlet water temperatures of SGHEs are monitored by controlling heating power and buried pipe flow rate to be constant, and the thermophysical parameters of the ground are derived. A three-dimensional full-scale numerical model for buried pipe heat transfer is developed based on the results of TRTs. The heating capacity distribution of SGHEs is determined by clarifying the characteristics of buried pipe heat transfer at various locations and depths. The results showed that the maximum difference in geothermal gradient and ground thermal conductivity is 51.2 °C/km and 0.51 W/(m·K) respectively, indicating that the ground parameters vary significantly within the chosen places. The heat transfer intensity of SGHEs is directly related to buried pipe depth and mean circulating water temperature at the same locations. The same prediction formula can describe the heat transfer intensity of SGHEs at various locations.

Exploitation of drainage water heat: A novel solution experimented at the Brenner Base Tunnel

Deep tunnels in permeable fractured rock-masses and under high piezometric levels can drain notable volumes of warm water, which are collected under gravity in specific conduits towards the portals, where heat can be exploited. The utilization of this energy source is generally narrowed by the limited presence of end-users near the portals, while other promising heating and cooling needs can be found directly along the tunnel length. The work presents the design, construction and installation of a geothermal system prototype exploiting the drainage water heat directly inside the tunnel. The prototype was named Smart Flowing due to the peculiarity of its heat exchange process. The system was realized and installed inside the exploratory tunnel of the Brenner Base Tunnel, near the border between Italy and Austria. The Smart Flowing modules were built outside and later moved inside the tunnel, where they were placed and assembled concurrently to the advancement of the Tunnel Boring Machine. A design procedure was proposed and validated against a testing and monitoring campaign. The data from the experimental activity confirmed that the drainage water flow guarantees long-term stabilization of circulating water temperature and fast heat recovery afterwards, thus securing the considerable power and performance values of a water-water heat pump connected to the system. A sensitivity analysis allowed the reproduction of different working scenarios, in order to generalize the application of Smart Flowing beyond the specific installation context.

Humidification performance of hollow-fiber membrane humidifier for air-conditioning applications

In this research, a new humidification method is proposed, and the humidification performance of a single module is experimentally investigated. The humidification module was manufactured in a cylindrical structure, and the humidification performance was evaluated by supplying air to the feed side and circulating water to the permeate side. The humidification performance was evaluated according to two main operating variables, circulating water temperature and circulating water flow rate. Experimental results showed that the humidification rate of the proposed module was 0.59 ∼ 9.49 kg/s, and the humidification effectiveness was 11.8 ∼ 95.6% under various operating conditions. The temperature of the circulating water significantly affects the humidification performance, but the flow rate of the circulating water has an insignificant effect on the humidification performance. As a result, the proposed humidifier can supply humid air with a relative humidity of 80% to the room without a temperature change under standard conditions.

Thermodynamic investigation of a direct-expansion solar assisted heat pump with evacuated tube collector-evaporator

Direct-expansion solar-assisted heat pump (DX-SAHP) system has proven to be an effective energy-saving application. In view of the low output temperature and large radiant heat loss in the conventional flat plate type DX-SAHP, this paper proposed an evacuated tube type DX-SAHP system to realize performance enhancement. Then, an experimental prototype of the proposed system was originally designed and constructed in laboratory. Moreover, the thermodynamic performance of the system was thoroughly investigated and analyzed under different operating conditions. The results indicate that the thermodynamic performance of the proposed system is sensitive to the solar radiation intensity and collector area. About every 100 W m−2 increase of solar radiation intensity, the COP increases nearly 1.70% and the heat collection efficiency decreases nearly 8.44%. Increasing collector area (from 1.5 m2 to 3 m2) results in 8.81% increase of COP and 22.47% reduction of the system exergy efficiency. A higher circulating water temperature can effectively improve its exergy performance and higher ambient temperature can enhance its energetic performance. Additionally, the optimization of the evacuated tube collector-evaporator should be preferential to improve the system due to large exergy destruction and low exergy efficiency.

Design and optimization of thermal strategy to improve the thermal management of proton exchange membrane fuel cells

This paper briefly recommends the working principle of the cooling system of the fuel cell engine (PEMFC), studies the control strategy of the thermostat in the cooling system, which couples the electric heater to shorten the water temperature fluctuation and save time. Cooling PEMFC is a challenge due to the small temperature differences between the stack and the environment. The fluctuation of water temperature and time transformation will lead to the change of system power, and further impact on the system's dynamic performance, reliability and life. Firstly, the simulation and experimental verification of cooling system of 30 kW fuel cell engine are presented. The influence of mechanical paraffin thermostat and electronic thermostat with certain control logic on the outlet temperature of the engine system stack is contrasted. Severe water temperature fluctuations will decrease the life of the system. Furthermore, the PID control and fuzzy PID control of temperature control valve are adopted, and the control method of coupling electric heater is used to solve the temperature fluctuation when the water temperature at the outlet of the stack is mixed. The results indicate that compared with the paraffin thermostat and PID controller, the fuzzy PID controller can obviously decrease the temperature fluctuation during the mixing of water temperature. Further, in different external environments, the fuzzy PID control coupling electric heater can reduce the temperature difference fluctuation to 0.5 °C when the system mixes large and small circulating water temperatures. The optimized coupling control strategy can decrease the water temperature fluctuation of the cooling system, thereby optimizing the temperature management of the cooling system, and significantly extending the power and reliability of the system.

Impact mechanism of rhombus module on plume abatement and water saving of mechanical draft wet cooling tower

The wet cooling tower usually causes a large amount of water resource waste and generates visible plumes. To solve this problem, a new mechanical draft wet cooling tower with air channels and rhombus modules is proposed. The dry channel and wet channel are staggered in the rhombus module. A hot experiment of the cooling tower is constructed to analyze plume, water saving, and cooling performance. The main experiment variables include the dry bulb temperature, relative humidity, circulating water flow rate, circulating water temperature, crosswind velocity, and crosswind angle. Results show that the cooling tower with the rhombus module does not produce plume under studied conditions. With the increase of the dry bulb temperature, relative humidity, circulating water flow rate, and circulating water temperature, the water saving amount and rate are increased with the maximum value of 0.073 L/min and 24.2 %. As crosswind velocity rises, the water saving amount and rate are increased under the crosswind angle of 0°, and those are decreased under 90° and 180°. The water saving amount and rate can maximum reach 0.060 L/min and 21.2 % under crosswind. Meanwhile, the water temperature drop is decreased by 1.3 ℃ under windless and 1.2 ℃ under crosswind on average.

Comparative study on the thermal characteristics of natural draft wet cooling tower with internal and external auxiliary fans

Auxiliary ventilation is an innovative approach for strengthening the thermal performance of natural draft wet cooling towers, which can be implemented with internal and external fans. In this study, a three-dimensional numerical model for cooling tower with these fans is established, with consideration of the existence or absence of air deflectors. To comparatively study the thermal performance of the above cooling towers, some critical parameters such as the air mass flow rate and circulating water temperature drop are computed, and the airflow and water temperature field are also investigated. Results manifest that external fans can enhance the air mass flow rate greater than internal fans under various crosswind velocities, while they are more effective in increasing the water temperature drop under a lower and a higher crosswind velocity, with a maximum increment of 8.5% and 10.0%, respectively. The addition of air deflectors narrows the high-velocity area, thus improving the uniformity of air distribution. The positive effect of air deflectors enhances with the increase of crosswind velocity, which decreases the water temperature drop of cooling tower with internal fans and that with external fans by 10.3% and 5.6% at most, respectively. This study can promote the engineering applications of auxiliary fans.

Influence of layout pattern on thermal performance of mechanical draft wet cooling tower group

Mechanical draft wet cooling tower group is often arranged the back-to-back (back-to-back MCT group). However, the thermal performance of back-to-back MCT group will be weakened under crosswind. To resist the adverse effects of crosswind, an annular MCT group is proposed. A 3D model is established to compare the two types of MCT groups. The main research variables are ambient wind speed and direction. The results show that the outlet water temperature of the annular MCT group is lower than that of the back-to-back MCT group under windless or crosswind. The annular MCT group mainly improves the thermal performance of the leeward MCT, and the fluctuation range of outlet water temperature of each MCT in the annular MCT group is reduced. The water temperature drop of the annular MCT group is about 0.3 °C higher than that of the back-to-back MCT group under windless. Under crosswind, the improvement effect is most obvious under the crosswind angle of 45° with the increase of circulating water temperature drop of 0.8 °C on average. That is least under the crosswind angle of 90° with the increase of circulating water temperature drop of 0.3 °C on average.

An Esophageal Cooling Device During Radiofrequency Ablation for Atrial Fibrillation-A Comparison Between Reactive and Proactive Esophageal Cooling.

Esophageal thermal injury is one of the most feared risks of ablation of the posterior left atrium despite the various devices used to monitor esophageal temperature or deviate the esophagus. Reactive cooling, in which cold water is manually instilled into the esophagus via an orogastric tube in response to rises in luminal esophageal temperature (LET), has been used by operators, but the availability of a dedicated esophageal cooling device offers the ability to provide proactive esophageal cooling without having to react to individual temperature rises in the esophagus. The objective of this study was to evaluate the feasibility of using a commercially available esophageal cooling device to provide esophageal protection during left atrial catheter ablation, then to compare this approach to standard LET monitoring with reactive cooling via manual cold-water instillation. In this study, we randomized 6 patients undergoing catheter ablation for atrial fibrillation. Three patients received the standard of care for our site (use of a single-sensor temperature probe, with adjunct ice-water instillation for any temperature increases of >1°C). Three patients underwent standard ablation after placement of the esophageal cooling device at a circulating water temperature of 4°C, without the use of any esophageal temperature monitoring. All patients underwent transesophageal echocardiography and esophagogastroduodenoscopy on the day prior to the ablation, followed by a second esophagogastroduodenoscopy the day after. The 6 patients in this study were enrolled between March and August 2018. In the 3 control patients, 1 had no evidence of esophageal mucosal damage, 1 had diffuse sloughing of the esophageal mucosa and multiple ulcerations, and 1 had a superficial ulcer with a large clot. Both patients with lesions were classified as 2a cases using the Zargar grading scheme for caustic injury. In the 3 patients treated with the cooling device, 1 had no evidence of esophageal mucosal damage, 1 had esophageal erythema (Zargar grade 1), and 1 had a solitary Zargar grade 2a lesion. At 3 months of follow-up, 1 patient in each group had recurrence of atrial fibrillation. Although a number of subsequent studies have confirmed the reduction of esophageal injury with the use of proactive esophageal cooling, this study is the only one to date to compare reactive cooling (via manual cold-water instillation) and proactive cooling (via a dedicated esophageal cooling device). Moreover, this is the first study to support the feasibility of using a dedicated cooling device for this purpose and provides the basis for further investigation.

Numerical study on performance of hybrid mechanical draft wet cooling tower

To explore the operation mechanism of the hybrid mechanical draft wet cooling tower (hybrid MCT), a 3D model of the hybrid MCT is established. The plume, water saving, and cooling capacity of the hybrid MCT are discussed. The ambient dry bulb temperature, relative humidity, circulating water temperature, and circulating water flow rate are taken as the main variables. Results that the ambient dry bulb temperature and circulating water temperature have the larger impact on the plume abatement and water saving rate, and the relative humidity and circulating water flow rate have relatively small impact. As the ratio of circulating water flow rate in the dry part increases, the water saving rate and cooling capacity of hybrid MCT are enhanced. However, when the ratio of circulating water flow rate in the dry part exceeds 0.4, the variation of water saving rate is not obvious. Based on satisfied plume abatement, by adjusting the airflow resistance in the dry part, the water temperature drop of hybrid MCT can be increased by 0.4 °C.

Impact mechanism of the chip muffler on the cooling performance of super large-scale natural draft wet cooling tower under crosswind

• 3D numerical simulation on S-NDWCT with chip muffler is carried out. • The chip muffler enhances the cooling efficiency of S-NDWCT under crosswinds. • The positive effect of the chip muffler on the S-NDWCT varies with layout patterns. • The optimal pattern of chip muffler is proposed based on the tower performance. The noise attenuation of cooling towers mainly relies on the chip muffler, of which the layout pattern exerts a non-negligible impact on the cooling effect. This paper analyzes the impact mechanism of the chip muffler’s layout pattern on the cooling performance of a super large-scale natural draft wet cooling tower (S-NDWCT) through a three-dimensional numerical study. The layout patterns of chip muffler include three installation angles ( θ = 0°, 15° and 30°), three distances between the muffler and cooling tower ( L = 0.0 m, 2.5 m and 5.0 m), and two layout angles of the muffler ( α = 180° and 360°). Results manifest that the chip muffler can enhance the cooling performance of S-NDWCT by improving the airflow uniformity in the tower. The optimal layout pattern is L = 0.0 m, θ = 0° and α = 360°, under which the increment of circulating water temperature drop reaches a maximum of 1.04 ℃. The ventilation rate increases with the increase of L and the decrease of θ . The Merkel number increases with the decrease of L and θ . The circulating water temperature drop increases with the decrease of θ and shows little regularity with L . This paper can provide the reference for optimizing layout patterns and engineering applications of the chip muffler.

Long-Term Performance Analysis of Direct Photovoltaic Thermal-Assisted Heat Pump Water Heater Using Computational Model

The photovoltaic thermal system has a limitation in supplying hot water at the required temperature since it requires a supplementary heating system. One such system can be an air source heat pump operated by electricity from a PV/T system, which can be used to raise the temperature of the water preheated by PV/T to the required level. Such type system can also be called a hybrid PV/T-heat pump system, and it delivers thermal (hot water) and electrical energy. The performance of the hybrid PV/T-heat pump system was analyzed using the computational model for two Ethiopian cities, namely, Addis Ababa and Dire Dawa, which represent the highland and lowland regions, respectively. The simulation was conducted by inputting climatic data, daily hot water demand, and hourly hot water consumption patterns. Also, system design parameters such as PV/T area and peak Watt, PV/T warm water tank volume, air source heat pump water heater COP as a function of ambient temperature and circulating water temperature, and heat pump hot water tank volume. Besides, the effect of hot water consumption patterns (variability effect in three dissimilar cases constant, restaurant, and motel) on the system performance was examined. In addition, the effect of electric energy supply to the compressor of the heat pump using battery storage on the system performance was also investigated. In those diverse situations, the system in most of the cases generated hot water above 55°C and scored a COP of 3. The maximum value of hot water end-use efficiency of 66% was also obtained by making the hot water tank capacity about 50% of the daily hot water consumption size.

The research on plume abatement and water saving of mechanical draft wet cooling tower based on the rectangle module

To realize plume abatement and water saving of mechanical draft wet cooling tower (MCT), a rectangular module with plume abatement and water saving performance is proposed in this study. The plume, water saving, and thermal performance of MCT under different the environmental parameters, circulating water parameters, and crosswind conditions are analyzed. The result shows that, with the increase of relative humidity, circulating water temperature, and circulating water flow rate, the probability of plume generated increases. When the dry-bulb temperature increases, the probability of plume generated decreases. With the crosswind velocity increasing, the probability of plume generated decreases under the crosswind angle of 0°, and that increases under the crosswind angle of 90° and 180°. After using the rectangular module, the variation range of water saving amount is from 0.018 to 0.046 L/min, and the water saving rate is 4.3% ⁓ 16.2%. The plume can be abated, and the outlet water temperature is increased by about 2 °C in this study.

Experimental Investigation on the Cooling Performance of a Counterflow Dew Point Evaporative Cooler

In this study, an innovative indirect evaporative cooler is presented and experimentally analysed. A prototype was assembled for the experimental investigation of the system and tested in the laboratory environment under the conditions of constant air flow rate of 350 m3/h, circulating water temperatures of 15°C and 20°C, inlet air temperatures of 25°C and 30°C and lastly inlet air humidity of 9g/kg and 13g/kg, respectively. Based on the data obtained during the experiments, calculations were performed for the cooling capacity, cooling efficiency, energy efficiency and exergy efficiency of the system for each case. The findings showed that the highest wet bulb efficiency, dew point efficiency and EER of evaporative cooler were found to be 0.91, 0.62, and 0.77, respectively.

Response of energy pile-soil structure and pile group effect: An indoor similarity simulation study

Energy pile has dual functions of coupled heat transfer and load-bearing. The research on its bearing characteristics has attracted much attention. This research is based on the indoor scale model test of energy pile to simulate the thermo-mechanical response of single pile and pile group of spiral energy pile under summer and winter conditions. The thermal response of the middle part of the energy pile is the largest. Under the action of circulating water, additional tension is generated in the pile section in winter and additional pressure is generated in summer. Through comparative analysis, it is proved that when multiple piles are operated simultaneously, the heat transfer efficiency is almost the same as that of single pile in the initial operation, and the heat transfer efficiency of single pile is reduced in the long-term operation, the temperature response of soil between pile and pile is higher, and the quasi-steady state time is shortened. The axial force distribution of single pile and multiple piles is compared and analyzed. The results show that in the service process of multiple piles, when the upper load is 0.8 Pu in winter, the axial force in the middle of the pile group is reduced by 0.73 kN compared with that of single pile. In summer, when the upper load is 0.8 Pu, for example, the circulating water temperature is 35 °C, 45 °C and 55 °C, and the maximum axial force in the middle of the pile increases by 0.5 kN, 0.79 kN and 0.8 kN respectively. It is proved that the pile group effect does exist when the energy pile group works, which will reduce the heat exchange efficiency of single pile, advance the quasi steady state time, increase the single pile axial force in summer, reduce the single pile axial force in winter, and even generate tension in the pile section. The energy pile group effect should be fully considered in the design and application of energy pile.

New retrofit method to cooling capacity improvement of mechanical draft wet cooling tower group

The airflow distribution of the mechanical draft wet cooling tower group will become very uneven under crosswind conditions, and the cooling capacity of leeward towers can be seriously reduced. To strengthen the heat and mass transfer of the leeward tower and improve the cooling capacity of the tower group, a new retrofit method is proposed that removes the tower wall between the rain zone of the tower group. The airflow can enter the leeward tower from the windward tower, even flow out from the air inlet of the leeward tower under crosswind conditions, and the airflow distribution becomes more uniform in the tower group. A 3D numerical model of the mechanical cooling tower group is established and validated. The cooling capacity of the tower group is studied under variation crosswind velocities (0 m/s–12 m/s) and crosswind angles (0°–90°) by numerical calculation. The results show that the distribution of outlet water temperature in the retrofit tower group is more uniform. The retrofit tower group can increase the circulating water temperature drop of the leeward tower under the crosswind angle of 0° and 45°. Under the crosswind angle of 0°, the temperature drop of the circulating water increases 0.52 ℃ maximum and 0.31 ℃ on average. Under the crosswind angle of 45°, it increases 0.92 ℃ maximum and 0.59 ℃ on average. Under the crosswind angle of 90°, it increases 0.19 ℃ maximum and 0.09 ℃ on average.