Passive Heat Exchanger Anti-Fouling for Solar DHW Systems

Solar Energy ◽  
2005 ◽  
Author(s):  
Stephen J. Harrison
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Hot Water ◽  
Normal Operation ◽  
Mineral Deposits ◽  
Accelerated Tests ◽  
Mineral Salts ◽  
Potable Water Supply ◽  
External Power ◽  
User Intervention

The interior surfaces of heat exchangers used in domestic hot water systems are particularly prone to fouling or complete blockage due to the accumulation of sediments, scale and mineral deposits. In many locations, mineral salts and other impurities may be present in the potable water supply and fouling may occur if the heat exchanger is not routinely cleaned or flushed of accumulated matter. In small residential installations, however, this is not practical due to the associated costs. In response to this need, a passive back-flushing system was designed that allows heat exchangers to be routinely back-flushed many times a day. The action is a normal operation of the system and does not require user intervention, external power or controls to function. During back-flushing mineral deposits are washed out of the heat exchanger and flushed from the system. the operation of the device and documents the results of accelerated tests undertaken to verify its operation.

scholarly journals Simulation of the effectiveness of longitudinal rectangular fins on the efficiency of the double pipe heat exchanger

2019 ◽  
Vol 21 (4) ◽  
pp. 48-57
Author(s):  
N. F. Timerbaev ◽  
A. K. Ali ◽  
Omar Abdulhadi Mustafa Almohamed ◽  
A. R. Koryakin
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Cold Water ◽  
Tube Diameter ◽  
Hot Water ◽  
Outer Tube ◽  
Design Parameters ◽  
Double Pipe ◽  
Central Pipe ◽  
Pipe Heat

In this article, a mathematical simulation of a double pipe heat exchanger is carried out, having the longitudinal rectangular fins with the dimension of (2*3*1000) mm, mounted on the outer surface of the inner tube of the heat exchanger. In this paper, the advantage of using of that type of fins and its effect on the effectiveness of the heat exchanger are studied with the help of the computer program. The carried out research allowsmaking the calculation to find the optimum design parameters of heat exchangers. The outer tube diameter is (34.1mm) while the inner tube diameter is (16.05mm). The tubes wall thickness is (1.5mm) and the model length was (1 m). The hot water is flowing through the inner tube in parallel with the cold water that passing the outer tube. The hot and cold water temperature at the inlet is (75°C & 30°C) respectively. The mass flow rate inside the central pipe is (0.1 kg/s) while the annular pipe carrying (0.3 kg/s). In the present work, the program ANSYS Workbench 15.0 was used to find out the results of heat transfer as well as the behavior of liquids inside the heat exchangers.

scholarly journals Performance Analysis and Design Optimization of Shell and Tube Heat Exchangers

2021 ◽  
Author(s):  
praveen math
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Pressure Loss ◽  
Fluid Flows ◽  
Hot Water ◽  
Flow Conditions ◽  
Shell Side ◽  
Shell And Tube ◽  
Side Flow

Abstract Shell and Tube heat exchangers are having special importance in boilers, oil coolers, condensers, pre-heaters. They are also widely used in process applications as well as the refrigeration and air conditioning industry. The robustness and medium weighted shape of Shell and Tube heat exchangers make them well suited for high pressure operations. The aim of this study is to experiment, validate and to provide design suggestion to optimize the shell and tube heat exchanger (STHE). The heat exchanger is made of acrylic material with 2 baffles and 7 tubes made of stainless steel. Hot fluid flows inside the tube and cold fluid flows over the tube in the shell. 4 K-type thermocouples were used to read the hot and cold fluids inlet and outlet temperatures. Experiments were carried out for various combinations of hot and cold water flow rates with different hot water inlet temperatures. The flow conditions are limited to the lab size model of the experimental setup. A commercial CFD code was used to study the thermal and hydraulic flow field inside the shell and tubes. CFD methodology is developed to appropriately represent the flow physics and the procedure is validated with the experimental results. Turbulent flow in tube side is observed for all flow conditions, while the shell side has laminar flow except for extreme hot water temperatures. Hence transition k-kl-omega model was used to predict the flow better for transition cases. Realizable k- epsilon model with non-equilibrium wall function was used for turbulent cases. Temperature and velocity profiles are examined in detail and observed that the flow remains almost uniform to the tubes thus limiting heat transfer. Approximately 2/3 rd of the shell side flow does not surround the tubes due to biased flow contributing to reduced overall heat transfer and increased pressure loss. On the basis of these findings an attempt has been made to enhance the heat transfer by inducing turbulence in the shel l side flow. The two baffles were rotated in opposite direction to each other to achieve more circulation in the shell side flow and provide more contact with tube surface. Various positions of the baffles were simulated and studied using CFD analysis and th e results are summarized with respect to heat transfer and pressure loss.

Impact of an Anisotropic Fin Surface Design on the Thermal-Hydraulic Performance of a Plain-Fin-and-Tube Heat Exchanger

2011 ◽  
Author(s):  
Rong Yu ◽  
Andrew D. Sommers ◽  
Nicole C. Okamoto ◽  
Koushik Upadhyayula
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Heat Exchangers ◽  
Hydraulic Performance ◽  
Normal Operation ◽  
Surface Design ◽  
Tube Heat Exchanger ◽  
Silane Coating ◽  
Side Pressure

In this study, we have explored the effectiveness of heat exchangers constructed using anisotropic, micro-patterned aluminum fins to more completely drain the condensate that forms on the heat transfer surface during normal operation with the aim of improving the thermal-hydraulic performance of the heat exchanger. This study presents and critically evaluates the efficacy of full-scale heat exchangers constructed from these micro-grooved surfaces by measuring dry/wet air-side pressure drop and dry/wet air-side heat transfer data. The new fin surface design was shown to decrease the core pressure drop of the heat exchanger during wet operation from 9.3% to 52.7%. Furthermore, these prototype fin surfaces were shown to have a negligible effect on the heat transfer coefficient under both dry and wet conditions while at the same time reducing the wet airside pressure drop thereby decreasing fan power consumption. That is to say, this novel fin surface design has shown the ability, through improved condensate management, to enhance the thermal-hydraulic performance of plain-fin-and-tube heat exchangers used in air-conditioning applications. This paper also presents data pertaining to the durability of the alkyl silane coating.

Evaluation of Passive Anti-Fouling Technology Applied to CO2 Heat Pump Water Heaters

2014 ◽  
Author(s):  
Portia Murray ◽  
Stephen J. Harrison ◽  
Ben Stinson
Keyword(s):  
Heat Transfer ◽  
Water Supply ◽  
Heat Pump ◽  
Hot Water ◽  
Normal Operation ◽  
Mineral Deposits ◽  
Reverse Direction ◽  
Water Tank ◽  
Flow Rates ◽  
Water Heaters

Heat pump water heaters are increasing in popularity due to their increased energy efficiency and low environmental impact. This paper describes the experimental testing of a transcritical CO2 heat pump water heater at Queen’s University. A modified 4.5 kW Eco-Cute unit was studied. It sourced heat from a constant temperature water supply and rejected the heat to a 273 litre hot water tank through a gas-cooler. The high temperatures that occur in the gas-cooler of this unit make it ideally suited for natural convection, (i.e., thermosyphon) circulation on the potable water side. This has the potential to reduce pumping power, simplify system operation and design, and increase thermal stratification in the hot water storage tank. This configuration, however, is susceptible to the accumulation of sediments, scale and mineral deposits (i.e., fouling) in geographic regions where high mineral deposits may be present in the water supply. To counteract fouling in these cases, a passive back-flushing system was proposed to prevent the accumulation of deposits on the heat transfer surfaces of the gas-cooler. As hot water is drawn from the system, the cold “mains” supply water is directed through the gas-cooler in the reverse direction of normal operation, scouring the heat transfer surfaces and dissolving deposits of inverse-soluble salts which are a major contributor to fouling on hot heat transfer surfaces. The gas-cooler used was a specially designed unit that, although offering high performance in a compact unit, may be susceptible to the fouling and blockage of the heat transfer passages when used at thermosyphon flow rates. Experiments were conducted to evaluate the effects of the back-flush operation on heat pump performance (i.e., COP) and operation. These were conducted under controlled laboratory conditions, at a range of draw flow rates and temperatures, and are summarized in this paper.

scholarly journals Energy Conservation and the Promotion ofLegionella pneumophilaGrowth: The Probable Role of Heat Exchangers in a Nosocomial Outbreak

2016 ◽  
Vol 37 (12) ◽  
pp. 1475-1480 ◽  
Author(s):  
Emilie Bédard ◽  
Simon Lévesque ◽  
Philippe Martin ◽  
Linda Pinsonneault ◽  
Kiran Paranjape ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Water Samples ◽  
Heat Exchangers ◽  
Gel Electrophoresis ◽  
Water System ◽  
Pulsed Field Gel Electrophoresis ◽  
Hot Water ◽  
Nosocomial Outbreak ◽  
Hospital Acquired

OBJECTIVETo determine the source of aLegionella pneumophilaserogroup 5 nosocomial outbreak and the role of the heat exchanger installed on the hot water system within the previous year.SETTINGA 400-bed tertiary care university hospital in Sherbrooke, Canada.METHODSHot water samples were collected and cultured forL. pneumophilafrom 25 taps (baths and sinks) within wing A and 9 taps in wing B. Biofilm (5) and 2 L water samples (3) were collected within the heat exchangers forL. pneumophilaculture and detection of protists. Sequence-based typing was performed on strain DNA extracts and pulsed-field gel electrophoresis patterns were analyzed.RESULTSFollowing 2 cases of hospital-acquired legionellosis, the hot water system investigation revealed a large proportion ofL. pneumophilaserogroup 5 positive taps (22/25 in wing A and 5/9 in wing B). High positivity was also detected in the heat exchanger of wing A in water samples (3/3) and swabs from the heat exchanger (4/5). The outbreak genotyping investigation identified the hot water system as the source of infections. Genotyping results revealed that all isolated environmental strains harbored the same related pulsed-field gel electrophoresis pattern and sequence-based type.CONCLUSIONSTwo cases of hospital-acquired legionellosis occurred in the year following the installation of a heat exchanger to preheat hospital hot water. No cases were reported previously, although the sameL. pneumophilastrain was isolated from the hot water system in 1995. The heat exchanger promotedL. pneumophilagrowth and may have contributed to confirmed clinical cases.Infect. Control Hosp. Epidemiol.2016;1475–1480

Numerical Evaluation of Plate Heat Exchanger Performance in Geothermal District Heating Systems

1996 ◽  
Vol 210 (2) ◽  
pp. 139-147 ◽  
Author(s):  
T Karlsson
Keyword(s):  
Heat Exchanger ◽  
Mass Flow ◽  
Heat Exchangers ◽  
District Heating ◽  
Hot Water ◽  
Geothermal Systems ◽  
Geothermal Resources ◽  
Heating Systems ◽  
Plate Heat ◽  
Flow Approximation

This paper describes the performance of plate heat exchangers in residential water radiator heating systems receiving their heat from geothermal resources. Radiator theory is reviewed and determination of annual hot water requirements for space heating is discussed. Performance evaluation is made of plate heat exchangers and results obtained by means of two equations commonly used for this purpose, the Sieder–Tate and the Dittus–Boelter equations, compared to results obtained with a simplified equation where heat transfer in the heat exchanger is assumed to depend only on the fluid mass flow on both sides. It is found that for prevailing temperature ranges in Icelandic geothermal systems the mass flow approximation gives results very close to those determined by the more complicated conventional equations.

scholarly journals Fouling of Polymeric Hollow Fiber Heat Exchangers by Air Dust

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 4931
Author(s):  
Ilya Astrouski ◽  
Miroslav Raudensky ◽  
Tereza Kudelova ◽  
Tereza Kroulikova
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Transfer Rate ◽  
Hollow Fiber ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Hot Water ◽  
Hollow Fibers ◽  
Pressure Drops ◽  
Domestic Appliances

Currently, liquid-to-gas heat exchangers in buildings, domestic appliances and the automotive industry are mainly made of copper and aluminum. Using plastic instead of metal can be very beneficial from an economic and environmental point of view. However, it is required that a successful plastic design meets all the requirements of metal heat exchangers. The polymeric hollow fiber heat exchanger studied in this work is completive to common metal finned heat exchangers. Due to its unique design (the use of thousands of thin-walled microtubes connected in parallel), it achieves a high level of compactness and thermal performance, low pressure drops and high operation pressure. This paper focuses on an important aspect of heat exchanger operation—its fouling in conditions relevant to building and domestic application. In heating, ventilation and air conditioning (HVAC) and automotive and domestic appliances, outdoor and domestic dust are the main source of fouling. In this study, a heat exchanger made of polymeric hollow fibers was tested in conditions typical for indoor HVAC equipment, namely with the 20 °C room air flowing through the hot water coil (water inlet 50 °C) with air velocity of 1.5 m/s. ASHRAE test dust was used as a foulant to model domestic dust. A polymeric heat exchanger with fibers with an outer diameter of 0.6 mm (1960 fibers arranged into 14 layers in total) and a heat transfer area of 0.89 m2 was tested. It was proven that the smooth polypropylene surface of hollow fibers has a favorable antifouling characteristic. Fouling evolution on the metallic heat transfer surfaces of a similar surface density was about twice as quick as on the plastic one. The experimental results on the plastic heat exchanger showed a 38% decrease in the heat transfer rate and a 91% increase in pressure drops after eighteen days of the experiment when a total of 4000 g/m2 of the test dust had been injected into the air duct. The decrease in the heat transfer rate of the heat exchanger was influenced mainly by clogging in the frontal area because the first layers were fouled significantly more than the deeper layers.

scholarly journals Design and simulation of a new PCM heat exchanger for domestic hot water and air temperature control

2020 ◽  
Vol 172 ◽  
pp. 12006
Author(s):  
Jacques Robadey ◽  
Simon Rime ◽  
Dominique Voide
Keyword(s):  
Heat Exchanger ◽  
Air Temperature ◽  
Temperature Control ◽  
Heat Exchangers ◽  
Storage Capacity ◽  
Three Dimensional ◽  
Hot Water ◽  
Heat Extraction ◽  
Water Flows ◽  
Solidification Processes

Based on previous experiences which have proven the efficiency of PCM heat exchangers for air temperature control, we designed and simulated new PCM heat exchanger structures made of multiple PCM layers sandwiched between loading and discharge layers. By circulating air or water in the discharge circuit, these heat exchangers can be used for heating air or water, respectively. For both use cases, a three-dimensional analysis of the phase change and calculations of the charge/discharge powers were performed for the fusion and solidification processes. We obtained heating discharge powers ≥ 2.6 kW/m3 for 8 hours for air and ≥ 65 kW/m3 for 13 minutes for water with a respective total storage capacity of 28 kWh/m3 and 37 kWh/m3. The heat extraction of air and water flows and their time dependence are discussed according to the percentage of liquid PCM and the temperature profile of the discharge flow inside the heat exchanger.

Experimental Characterization of a Natural Convection Heat Exchanger for Solar Domestic Hot Water Systems

Solar Energy ◽  
2006 ◽  
Author(s):  
Cynthia A. Cruickshank ◽  
Stephen J. Harrison
Keyword(s):  
Natural Convection ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Computational Models ◽  
Operating Conditions ◽  
Hot Water ◽  
Test Method ◽  
Convection Flow ◽  
Convection Heat ◽  
Domestic Hot Water

To predict the long-term performance of solar domestic hot water (SDHW) systems requires computational models that can characterize the systems under a range of operating conditions. The development of detailed fundamental models that suitably describe the operation of systems with natural convection heat exchangers is, however, difficult and time consuming. The fact that the natural convection flow through the heat exchanger is intrinsically self-controlling and temperature dependent complicates the analysis. One approach to modeling this type of system is to use performance characteristics, empirically derived from experimental data, to predict the performance of the heat exchanger under typical operating conditions. Unfortunately, a significant number of tests may be required to characterize the full operation of the device. This paper presents a simplified test method that was developed to allow pre-configured SDHW systems that use natural convection heat exchangers, to be characterized. The results of this test method produce performance coefficients for simple empirical expressions that describe the fluid flow and heat transfer in the heat-exchange loop. These empirically derived coefficients are an input to a general simulation routine that allows overall system performance to be determined for various loads and climatic conditions. In this paper, data is presented for a typical heat exchanger under a range of operational conditions.

scholarly journals Heat Exchanger Design and System Balance of an Air Source Heat Pump/Chiller Using Brazed Plate Heat Exchangers

1997 ◽  
Author(s):  
Changiz Tolouee
Keyword(s):  
Heat Exchanger ◽  
Heat Pump ◽  
Heat Exchangers ◽  
Operating Conditions ◽  
Hot Water ◽  
Pump Efficiency ◽  
Plate Heat ◽  
Air Source Heat Pump ◽  
Water Side ◽  
Brazed Plate Heat Exchangers

Air Source heat pump/chiller is used to provide chilled water for cooling and hot water for heating purposes. This is one investment for both applications with no requirement for boiler and fuel with the advantage of heat pump efficiency. In this paper we are going to analyse both air side and water side heat exchangers used in air source heat pump/chiller with special attention and emphasis on brazed plate heat exchanger which is used in refrigerant to water side of this unit in order to achieve optimum performance in both the heat pump and chiller operations. Due to compactness of brazed plate heat exchangers it is very important to balance system volume in both operating conditions which will also be examined in this paper.

Sign in / Sign up

Export Citation Format

Share Document