Condenser Height Research Articles

Thermal performance analysis of heat pipe heat exchanger for effective waste heat recovery

The importance of waste heat recovery systems for various industrial processes has been growing steadily, driven by their potential to improve energy efficiency, reduce fuel consumption, and minimize environmental impacts. Heat exchangers are key components in these systems, facilitating the transfer of heat from waste sources to useful media. Among them, heat pipe heat exchangers (HPHX) have been widely employed in industries such as steel and ceramic as an energy-saving measure to cut carbon emissions. Previous studies have mainly focused on experimental analyses of HPHX thermal performance. However, due to the high cost of full-scale thermal tests, there is a lack of research investigating the effect of detailed geometrical and operational variations on HPHX thermal performance. This study addresses the existing gap by conducting a comprehensive conjugate numerical investigation to explore the influence of flow path structure and condenser area on the performance of an air-to-liquid HPHX. We first utilize a full-scale conjugate simulation to propose an optimized HPHX design that enhances both heat transfer rate and effectiveness through the variation of baffle configurations and condenser height. Subsequently, we experimentally validate the proposed design through a full-scale HPHX thermal test. Results revealed that the baffle design significantly improved the heat transfer rate and effectiveness by up to 36.3% and 36.0%, respectively. Conversely, increasing the condenser height by five times enhanced the heat transfer rate by only 3.5%, with the condenser area showing a minor impact owing to the higher heat capacity rate of water compared to air. The outcomes revealed remarkable energy-recovery capabilities, revealing a total thermal energy wastage recovery rate up to 19.7 kW. These findings demonstrate the potential and effectiveness of the proposed HPHX in waste heat recovery applications.

Thermal analysis of a heat pipe assisted passive cooling system for spent fuel pools

Passive cooling is a promising way to remove the decay heat and ensure the security of Spent Fuel Pool (SFP) at emergency conditions. A potential scheme of the passive cooling system consisting of bundles of large separate heat pipes is presented. A numerical model of the heat pipe is established. The model considered the pool boiling effect in the evaporator and self-adjusting of liquid column height in the downcomer. Influences of evaporator outlet vapor quality and corresponding flow resistance are studied. The model shows reasonable agreement with experimental data. Thermal performance and flow features with different working fluids, namely ammonia, water and R134a, under various conditions are analyzed. It is found that there is a minimum condenser height to activate the passive cooling system. Elevate the condenser helps to enhance the system performance when the downcomer is fully liquid filled. But when the downcomer is partially liquid filled, elevation of condenser provides little benefit. Besides, the cooling system functions well in a wide filling ratio range. Increase of filling ratio leads to growth of liquid column height in the downcomer. When the liquid column height comes to the maximum value, the cooling system shows the best heat transfer performance. In long distance heat transport applications, cooling system with water as the working fluid performs poorly. To balance between security and thermal performance, R134a is a better choice for the SFP passive cooling system than ammonia and water.

Performance investigation of a micro-channel flat separated loop heat pipe system for data centre cooling

Abstract This paper investigates a novel micro-channel flat separated loop heat pipe system for cooling the information technology equipment in the data centres through theoretical and experimental analysis and by assessing the impact of the inlet water temperature on system performance. A computer model is developed to simulate the steady-state performance of the micro-channel flat separated loop heat pipe system. After comparing the experimental and modelling results, the new and conventional system under the same working conditions, the model is validated yielding high accuracy in predicting the performance of the micro-channel flat separated loop heat pipe system with recorded error being limited to 2.16–8.97%. The new system has better performance than the conventional system. Under the operating conditions of heat load intensity of 1,000 W/m2, water flow rate of 0.28 m3/h, refrigerant filling rate of 30%, ambient air temperature of 26°C, and evaporator and condenser height difference of 0.8 m, the performance of the system has been explored at inlet temperature from 15 to 24°C with increments of 3°C. The system’s averaged heat transfer efficiency was found to decrease with the increase in inlet temperature. This research provides valuable insight into the data centre information technology equipment cooling, which is of great significance for energy saving and environmentally friendly operation of data centres.

A new heat transfer correlation for natural draft wire-on-tube condensers for a broad geometry span

Abstract This paper investigates the heat transfer performance of natural draft wire-on-tube condensers considering the geometric range of current designs adopted by the household refrigeration industry. Fifty-four samples with distinct geometries were manufactured and tested inside a standardized climate chamber that sets the air-side conditions, while a purpose-built apparatus was used to circulate hot brine through the coil with a strict control of the inlet temperature and mass flow rate. The results pointed out that the condenser height, and the wire and tube pitches are the key parameters affecting the heat transfer rate. An improved correlation was put forward to calculate the air-side heat transfer coefficient, being able to predict 90% of the experimental data within the ±10% error bounds. Also, it was noticed that the condenser design can be optimized by reducing the wires and tubes mass for a given heat duty.

Local heat transfer coefficient during stratified flow in large, flattened-tube steam condensers with non-uniform heat flux and wall temperature

Steam condensation heat transfer coefficient (HTC) in a large, flattened tube with non-uniform heat flux and wall temperature, and variable inclination angle is determined experimentally. The condenser tube is that typically used in an air-cooled condenser for power plants. The steel tube has an elongated-slot cross section with inner dimensions of 216 × 16 mm. Water vapor and liquid flow co-currently through a 5.7 m long air-cooled conditioning section, followed by a 0.12 m long water-cooled test section. The long conditioning section creates conditions in the test section that mimic the conditions in an operating condenser – allowing for the realistic development of flow regime and void fraction. HTC is then determined in the water-cooled section. The water-cooled section is designed as a crossflow heat exchanger to match the temperature and heat flux conditions of an air-cooled condenser. Visualization sections at the tube inlet and outlet allow determination of flow regime and void fraction. The flow is found to be stratified for all conditions. Tube inclination angle is varied from 0 to 38° downwards. Inlet quality in the water-cooled section ranges from 0 to 0.74. HTC is found to increase by more than 400% along the condenser height. In addition, inclination angle, wall-steam temperature difference, inlet water-steam temperature difference, water temperature glide and vapor quality are all found to affect the condensation HTC.

Parametric Study and Improvement of Phase Separation in Intermediate Headers of Microchannel Condensers

Abstract Phase separation has been proven to be beneficial to air-cooled parallel flow microchannel condensers for air conditioning systems. The inlet to the condenser with phase separation is at the middle of the condenser height. After the first pass, in the vertical second header of the condenser, refrigerant vapor separates from liquid mainly due to gravitational effects. In ideal case, vapor should go to the top exit and liquid to the bottom exit, resulting in increased heat transfer. Due to interaction between vapor and liquid, separation is not perfect, expressed through the separation efficiency. This paper presents a parametric study of phase separation efficiency in the intermediate headers, with the target to improve separation efficiency. Header prototypes which have two exits are made with transparent polyvinyl chloride (PVC) to simulate the real header and provide visual access. Using R-134a as a baseline, the measurement of separation efficiency and its general trend will be shown first. The experimental results are compared to the simulation of a mechanistic model based on flow regime and force balance analysis. Inlet mass flux in simulation is controlled at 87–311 kg · m−2 · s−1 and inlet quality at 0.05–0.25. The observed flow patterns in header are compared with the modeling results. Then, the header diameter is increased, which effectively improves the separation efficiency due to reduction of vapor velocity in header. Finally, R245fa and R32 are modeled in comparison with R-134a to discuss the effect of fluid properties on separation efficiency.

Research on the refrigerant column height in the downcomer of a two-phase loop thermosyphon

A two-phase loop thermosyphon (TPLT) is a highly efficient heat transfer device. It is a type of gravity-assisted heat pipe system. Therefore, there is a high refrigerant column height in the downcomer that supplies the driving force for the TPLT system. This study focused on the investigation of factors that influence the refrigerant column height in the downcomer of a TPLT system through an experiment and a numerical simulation. These factors were identified as the flow resistance, increased working pressure, and amount of liquid phase flow in the two-phase flow. In addition, the effect of the condenser height was considered. The extreme situation in which the condenser was filled with liquid refrigerant was analyzed through an experiment. The results indicated that a high refrigerant column height would occupy part of the condenser space and decrease the performance of the TPLT. In practical applications, the relationship between the condenser and refrigerant column height should be considered. These influencing factors of the column height in the downcomer should be considered when deciding the geometric parameters and filling ratio of a TPLT system.

A comparative study on the design of direct contact condenser for air and oxy-fuel combustion flue gas based on Callide Oxy-fuel Project

Direct contact condenser is widely used in oxy-fuel combustion capture systems. Unusually high content of water vapor in the flue gas requires rigorous sizing procedures for the condenser design. Non-linear differential equations for humidity, gas and liquid temperatures were set up to understand the evaporation/condensation process in the condenser. A Quasi-Newton method was adopted to simultaneously solve discrete equations to avoid difficulty in convergence.This model was firstly verified with reported experiments in a packed bed condenser. The significant impacts of L/G ratio on condenser height, packing volume, condenser diameter are identified. The optimum L/G range is obtained by the wet bulb temperature and minimal decrease on packing volume, and this results in the L/G range of 2.5–5.2 and 4.3–6.7 for air and oxy-fuel combustion respectively. The condenser diameter and packing volume corresponding to the optimum L/G range for air-fuel combustion are approximately twice and four times of these for oxy-fuel combustion. While the packing height for air-fuel combustion is slightly lower than that for oxy-fuel combustion.By economic analysis, normalized total capital and annual costs for air-fuel combustion are approximately four times and twice of these for oxy-fuel combustion. The decrease of L/G ratio reduces the normalized total capital and annual costs for both air and oxy-fuel combustion and more significant for air-fuel combustion. Therefore, the L/G ratio is preferably obtained by the wet bulb temperature. This paper sheds light on the rigorous design method and the optimization of design parameters for direct contact condenser.

Experimental Investigation of Condensation Heat Transfer in Ammonia Evaporative Condensers

This paper reports experimental data obtained for ammonia condensation heat transfer in an evaporative condenser. Experiments were carried out on a specially designed set-up equipped with both measuring and control devices, and a data acquisition system. Experiments were conducted for ammonia saturation temperature of 22°C to 40°C and condenser heat rejection rate ranging from 2000W to 6000W, during steady state condensation of ammonia. The experimental investigation aimed to determine thermal performances of the ammonia evaporative condenser under different operating conditions, namely as a function of: temperature difference between ammonia condensation and inlet air wet bulb temperature, cooling water mass flow rate and ammonia mass flow rate. Water film temperature distribution along the condenser's height has also been studied. Experimental results have been further compared to data in the open literature by authors with similar experimental investigations. The paper concluded that experimental results are in fairly good agreement with other authors work and consequently reliable. The paper also addresses the current ecological aspect implied by refrigerants, by using ammonia. Apart from its attractive thermo-physical properties, as compared to HFCs, ammonia is also an environment friendly natural refrigerant, known for its zero ozone depleting potential and zero global warming effect.

THE INFLUENCE FACTORS ON HEAT TRANSFER PERFORMANCE OF LOOP THERMOSYPHON SYSTEM

The influence factors on the heat transfer performance of a loop thermosyphon system, a passive cooling device, are studied systematically. The parameters investigated include types of enhanced boiling structure, the depth to width ratio of enhanced boiling structures, the gap of evaporator, the condenser height and the inclination of evaporator. The results show the depth to width ratio and the condenser height has positive influences on the heat transfer performance. An optimal channel gap of evaporator exists and possesses better heat transfer performance. The inclination effect of evaporator may not be favorable to heat transfer. Among those, the horizontal and 90° inclination of evaporator has better cooling performance.

Entropy generation analysis of a microchannel-condenser for use in a vapor compression refrigeration cycle

Dimensionless entropy generation number in the microchannel condenser of a vapor compression refrigeration cycle is investigated. An air cooled, brazed aluminum parallel flow heat exchanger is considered as the condenser with R-134a as the refrigerant. While the effects of the fin pitch, fin height, louver angle and the air mass flow rate are investigated for the air side, the effect of the channel diameter is examined for the refrigerant side. The analysis is performed segment by segment for the superheated, two phase and subcooled regions using well-established empirical correlations. A mapping study is presented for the variation of entropy generation number with the mentioned parameters. The optimum air mass flow rate interval is found to be between 0.055 and 0.1 kgs−1 for a given fin pitch interval of 1–1.6 mm. This range is within the operating limits of air fans in the market for this size. In this operating range, the optimal dimensions giving the minimum entropy generation numbers are presented. The entropy generation number distribution is given based on the pressure drop, heat transfer or the refrigerant state in the heat exchanger considering superheated, two phase, and subcooled regions. The entropy generation number due to pressure drop on the air side becomes dominant after a mass flow rate around 0.08 kgs−1. Hence, an optimum air mass flow rate generating the minimum entropy generation number is sought for different sizes of the condenser. The condenser length is variable in the range of 84.3–80.6 mm for the mentioned optimal air mass flow rate interval. The condenser height changes depending on desired operational conditions, and it is determined to be 112.5 mm for the fixed values given in the study. The study is unique in the literature in pursuing an entropy generation number mapping study for microchannel two-phase flow in air cooled heat exchangers.

On the adequacy of wall functions to predict condensation rates from steam-noncondensable gas mixtures

As one looks forward to applying CFD based methods to simulate turbulent flows in larger volumes up to containment scales, the mesh resolution, especially near the walls, becomes one of the main issues dictating the feasibility of the simulation. The wall-function approach is a natural choice to minimize the computational size of the problem and make it tractable. In the current investigation, we compare the wall-function to the fully resolved boundary layer approaches for the prediction of vapor condensation rates on cold walls in the presence of noncondensable gases. We simulate three sets of geometric configurations. The first two sets relate to domains which are small (height of 2m) and medium (height 4.8m), and for which experimental heat transfer data are available. In the third set, we look at a hypothetical large 2D rectangular domain in which the condenser height is comparable to that of typical NPP containments (20m).In the developing region of the boundary layer, it is found that the wall function treatment leads to substantial deviations from the wall resolved approach and available experimental data. Further downstream, however, when the boundary layer is fully developed, the discrepancy is greatly reduced.It is therefore concluded that the wall-function formulation is able to provide predictions of condensation rates that are similar to wall-resolved treatments in simple forced flows for which fully developed boundary layers can be assumed over most of the domain. Care must however be exercised to ensure the chosen wall functions relate to the flow regime under consideration.

Accident localization system with jet condensers for VVER 440-V 230 NPP at Jaslovské Bohunice

Compared to the current world standard, the operational safety of the V1 nuclear power plant (NPP) is unsatisfactory and it does not correspond to present requirements as to nuclear safety. Further NPP operation after 1995 is conditional on nuclear safety enhancement to a level comparable with that in West European countries. This aim should be achieved by a principal reconstruction involving in addition to others also backfitting the V1 NPP with technical facilities aimed at coping with a design basis accident (DBA). To cope with such an accident the Power Equipment Research Institute (VÚEZ) designed an accident localization system with jet condensers. This system consists of (a) an air trap (one for each unit, mutually interconnected) with an expansion bell enclosed within, placed on a plate with 200 pipes of jet condensers passing through, and (b) a connecting duct between the hermetic zone and the air trap. The vertical jet condenser is an essential element of the system designed for steam condensation. Apart from condensation it serves as a water seal separating units 1 and 2. Demonstration tests of the jet condenser (model 1:1) condensing functionw were carried out at the testing unit of the All-Union Research Institute for NPP Operation (VNIIAES), Moscow in Kashir, 11–22 September 1992. These experiments proved the jet condenser ability to ensure complete condensation of the steam produced. Experimental verification of the sealing function (model 1:1) was carried out at the testing unit of the VÜEZ Tlmače. These experiments concerning the dynamics and overpressure in the free space above the pool were close to the conditions in the air trap during DBA. The jet condenser height was proved to be sufficient to ensure the sealing function. Design and experimental work has been implemented in close cooperation with Russian experts Mr. V.N. Bulynin from the VNIIAES, Moscow, and Mr. M.V. Kuznecov from the Scientific and Engineering Center for Nuclear and Radiological Safety, Moscow.

Model of temperature profiles during condensation in a film in a molecular evaporator

The characteristics of the falling film of condensate flowing downwards along the condenser surface of a molecular evaporator are presented. They result from solving the mathematical model of glycerol vapour condensation. The significance of the film surface temperature of the condensate and of the effect of the process parameters determining film temperature such as evaporation rate, condenser temperature and condenser height are discussed. Measures for enhancing the vapour condensation efficiency are also treated.