Fouling Thermal Resistance Research Articles

Novel methods of oil fouling inhibition on surface of plate heat exchanger in simulated oilfield geothermal water

Crude oil fouling on heat transfer surface (HTS) is a very troublesome problem for the utilization of oilfield geothermal water in which slight crude oil exists. The deposition of crude oil on HTS will decrease heat transfer efficiency, increase the pressure drop of fluid flow, and even block flow channel. In this study, surface hydrophilization via anodization, flow velocity enhancement and chemical addition three measures were adopted to solve the problem of crude oil soiling via weakening the adhesion force between crude oil and HTS as well as intensifying the interaction between water and crude oil. Contact angle measurement and microscopic morphology study were conducted on the highly-hydrophilic surface fabricated via anodization. Oil-soiling experiments accompanied with three mentioned techniques were carried out in plate heat exchanger (PHE) apparatus, and obvious oil-fouling inhibition effects were presented. The effect was reflected by the decrease of fouling thermal resistance. For 110°C simulated oilfield geothermal water, which contained approximate 1vol.% crude oil soiling, with 0.24m/s flow velocity, the fouling induction period extended to 500min from 0min when surface hydrophilization was applied through anodization. In anodized PHE with titanium plates, the value of fouling thermal resistance decreased by about 77.8% when the flow velocity of 110°C hot fluid without chemical additive increased from 0.24m/s to 0.72m/s, and the value could be reduced by around 62.5% after the addition of 0.29g/L chemical additive LIUXU-10 mainly composed of sodium dodecyl sulfonate (SDS), when the flow velocity of 110°C hot fluid was 0.12m/s. Compared with PHE with titanium plates (Ti-PHE) at 0.24m/s hot fluid flow velocity, the fouling thermal resistance decreased by approximate 93.3% when the Ti-PHE was anodized to be highly hydrophilic, the hot fluid flow velocity increased to 0.6m/s and 0.87g/L chemical additive was added.

Fouling formation and thermal performance of aqueous carbon nanotube nanofluid in a heat sink with rectangular parallel microchannel

Experimental investigation is performed on the thermal performance of a copper-made heat sink with rectangular microchannel. Carbon nano tube aqueous nanofluid is used as a coolant inside the microchannel at mass concentrations of 0.05–0.1%. Influence of different operating parameters including applied heat flux, fluid flow rate and mass concentration of nanofluid on the local and average heat transfer coefficients, fouling thermal resistance, overall thermal resistance and local (axial) temperature profile is investigated. Results showed the higher heat transfer coefficient and lower temperature profile inside the heat sink in comparison with the base fluid (water). Fluid flow rate and mass concentrations were found to increase the heat transfer coefficient significantly, while slight improvement was seen when higher heat fluxes were applied into the microchannel heat sink. Fouling thermal resistance was found to asymptotically increase with an increase in operating time and strongly depends on the concentration of nanofluid such that the required operating time to reach a constant value was different. The higher the mass concentration, the lower operating time is required to reach the constant fouling thermal resistance. However, overall thermal resistance of the microchannel (without considering the fouling effect) was found to linearly decrease with the mass concentration of nanofluid.

A novel fouling measurement system: Part I. design evaluation and description

The enhanced tube is being used more often in water-chiller condensers because of their superior performance in heat transfer. Both the predicted and real-world performance of these heat exchangers is affected by the fouling build-up on the heat transfer surfaces. Thus, accurate quantification of fouling thermal resistance is required to address the correlation between the fouling resistance of heat transfer tubes and operation conditions. A newly developed Fouling Measurement System (FMS) supports research on the relationships between fouling development and operation condition by measuring fouling thermal resistance on the heat transfer surface. Part I of this two-part series describes the design and evaluation of FMS. An uncertainty analysis of fouling thermal resistance was conducted to identify measurement component contributions to the uncertainty of final results and guide component selection. In Part II, FMS commissioning was performed, and a primary fouling test and analysis on cooling water quality were conducted. The FMS consists of three subsystems: heat pump subsystem, cooling/chilled water subsystem and control and data acquisition (DAQ) subsystem. The FMS has three heat pumps individually installed with a shell-and-tube condenser and separately equipped with a cooling/chilled water supply loop. In the cooling/chilled water subsystem, these three heat pumps share the same cooling water pool and chilled water pool, which ensures that the cooling/chilled water supplied to each heat pump is uniform. A cooling water tower was installed outside the Air Quality Lab in University of Illinois at Urbana-Champaign to cool down the cooling water of the FMS, and to evaporate water and keep the cooling water at the required range. In the control and DAQ subsystem, the control of water temperature, water quality, water velocity, and refrigerant saturation temperature are described.

Boiling Heat Transfer of Alumina Nano-Fluids: Role of Nanoparticle Deposition on the Boiling Heat Transfer Coefficient

This paper focuses on the thermal performance of alumina nano-fluids during the quenching process of a surface at the boiling condition, which can be a good answer to the controversial results available in the nano-fluid related literature. For this purpose, an experimental study is conducted to investigate the potential application of alumina/water nano-fluid for cooling a stainless steel rod under the flow boiling heat transfer mechanism. Nano-fluids are prepared by dispersing the 5, 50 and 80nm alumina nanoparticles into the deionized water. The experimental facility provides conditions to quantify the heat transfer coefficient in forced convection and nucleate boiling heat transfer domains at different operating conditions. In terms of operating time, the experiments are divided into two domains namely short time study and extended time study. For the short time study (0-60 minutes of study with neglecting the role of time on the deposition of nanoparticles) enhancement of heat transfer coefficient is reported for all nano-fluids, however for nano-fluid with smaller nanoparticle size, higher thermal performance is registered. In extended time study (60-1000 minutes) heat transfer coefficient is found to be considerably deteriorated for all nano-fluids. This work demonstrates that the reason for deterioration of heat transfer coefficient is referred to the surface roughness, nanoparticle size, static contact angle and thermal fouling resistance parameters. These four parameters are simultaneously determinative factors, which strongly control the thermal behaviour of nano-fluids over the extended time and are the exact reasons for the controversies raised in the literature.

The influence of fouling on the dynamic behavior of PID-controlled heat exchangers

The influence of fouling build-up on the dynamic behavior of PID-controlled shell-and-tube heat exchangers was studied. A mathematical model was proposed in which heat exchanger is considered as an array of cells where the exchange of heat is modelled using lumped-parameter approach. The model was implemented employing Simulink/MATLAB software and validated using real-life data records acquired during 3years of operation of a heat exchanger network coupled with a crude distillation unit. Using the validated dynamic model, a simulation study was carried out on selected PID-controlled exchangers operated in the mentioned network. For different periods of uninterrupted exchanger operation, that is, at different values of the thermal resistance of fouling, suitable controller tuning parameters were studied. The results proved that at changed thermal resistance of fouling, the values of tuning parameters should be changed too.

Tuning Parameters of Pid Controllers for the Operation of Heat Exchangers Under Fouling Conditions

The present paper is an extension of the work presented by authors at SDEWES2015 conference, where changes in the dynamic behaviour of shell-and-tube heat exchangers induced by fouling build-up were studied. A mathematical model was proposed of transient heat exchange with the influence of thermal resistance of fouling taken into account. Next a mathematical model of the entire heat exchanger was implemented and simulations were carried out using Simulink in MATLAB environment. The model was validated using data records acquired during 3 years of operation of a heat exchanger network coupled with a Crude Distillation Unit (CDU). Using the validated dynamic model, one can simulate the behaviour of a heat exchanger together with its PID control loop and investigate the influence of fouling build-up on specific indexes of quality of operation. A simulation study was carried out on selected PID-controlled exchangers operated in a heat exchanger network coupled with a CDU rated 220 kg/s crude oil. For different periods of uninterrupted exchanger operation, that is, at different values of the thermal resistance of fouling, tuning parameters were determined using the Ziegler-Nichols method. It was found that the optimal values of tuning parameters changed when the thermal resistance of fouling was changed. However, oscillations remained in the characteristics of some controlled exchangers indicating that the new values of tuning parameters determined by the simple Ziegler–Nichols method were ineffective. In the present work, to improve the quality indices of the exchangers control under fouling conditions, a more advanced method of the optimization of controller tuning is presented using Signal Constraint block in MATLAB/SIMULINK.

An experimental study on the thermal and fouling characteristics in a washable shell and helically coiled heat exchanger by the Wilson plot method

Brazed plate heat exchangers (BPHEX) are broadly used in water source heat pump systems for their large heat transfer capacity. Despite their high heat transfer rate, their high-performance rate tends to decrease sharply, due to fouling and they cannot be cleaned. So the thermal and fouling resistances of washable Shell and helically coiled tube heat exchangers (SCHEX) are designed and experimentally investigated in this study. Heat exchangers with two different tube types are studied and compared with a brazed plate heat exchanger. The overall thermal resistance coefficient of the heat exchangers as determined by using Wilson plots is 38% lower than that of the brazed plate heat exchanger at a Reynolds number of 2460. Fouling test results revealed that regular maintenance and physical cleaning can be used to maintain the thermal resistance of fouling of the washable heat exchanger at a level equal to or less than that of the brazed plate heat exchanger.

Optimal design of tests for heat exchanger fouling identification

Particulate fouling in plate fin heat exchangers of aircraft environmental control systems is a recurring issue in environments rich in foreign object debris. Heat exchanger fouling detection, in terms of quantification of its severity, is critical for aircraft maintenance scheduling and safe operation. In this work, we focus on methods for offline fouling detection during aircraft ground handling, where the allowable variability range of admissible inputs is wider. We explore methods of optimal experimental design to estimate heat exchanger inputs and input trajectories that maximize the identifiability of fouling. In particular, we present a methodology in which D-optimality is used as a criterion for statistically significant inference of heat exchanger fouling in uncertain environments. The optimal tests are designed on the basis of a heat exchanger model of the inherent mass, energy and momentum balances, validated against literature data. The model is then used to infer sensitivities of the heat exchanger outputs with respect to fouling metrics and maximize them by manipulating input trajectories; thus enhancing the accuracy in quantifying the fouling extent. The proposed methodology is evaluated with statistical indices of the confidence in estimating thermal fouling resistance at uncertain operating conditions, explored in a series of case studies.

Comparatively experimental study on the boiling thermal performance of metal oxide and multi-walled carbon nanotube nanofluids

This work aims to focus on the flow boiling heat transfer characteristics of metal oxide and multi-walled carbon nanotube nanofluids inside an annulus heat exchanger. The flow boiling heat transfer coefficient and thermal fouling resistance parameter is experimentally quantified at different operating conditions including different heat and mass fluxes, mass concentration of nanofluid, and bulk temperature of nanofluid. In order to prepare the nanofluids, multi-walled carbon nanotubes (MWCNT), alumina and copper oxide nanoparticles were dispersed into deionized water. Based on the type of nanoparticle, different techniques were implemented for stabilizing the nanofluids such as functionalizing process for MWCNT, pH setting, ultra-sonic dispersion and adding the surfactant for metal oxide nanofluids. Results of time-Settlement experiments showed that functionalizing process can provide longer and reliable stability for MWCNT nanofluid. As a continuation, thermal conductivity of nanofluids was experimentally measured and compared to those of available in the literature. Then, experiments were carried out on the upward flow boiling heat transfer characteristics of nanofluids. According to the results, MWCNT/water nanofluid had higher thermal conductivity, higher boiling thermal performance and lower thermal fouling resistance value in comparison with other nanofluids. Likewise, boiling thermal performance of MWCNT nanofluids was found to be intensified, when heat and mass flux and concentration of nanofluids increased. The experimental heat transfer coefficients were also validated by comparing to the well-known correlations and available data in the literature.

The fouling in the tubular heat exchanger of Algiers refinery

Crude oil fouling in refinery preheat exchangers is a chronic operational problem that compromises energy recovery in these systems. Progress is hindered by the lack of quantitative knowledge of the dynamic effects of fouling on heat exchanger transfer and pressure drops. In subject of this work is an experimental determination of the thermal fouling resistance in the tubular heat exchanger of the crude oil preheats trains installed in an Algiers refinery. By measuring the inlet and outlet temperatures and mass flows of the two fluids, the overall heat transfer coefficient has been determined. Determining the overall heat transfer coefficient for the heat exchanger with clean and fouled surfaces, the fouling resistance was calculated. The results obtained from the two cells of exchangers studies, showed that the fouling resistance increased with time presented an exponential evolution in agreement with the model suggested by Kern and Seaton, with the existence of fluctuation caused by the instability of the flow rate and the impact between the particles. The bad cleaning of the heat exchangers involved the absence of the induction period and caused consequently, high values of the fouling resistance in a relatively short period of time.

Uncertainty analysis: Design of a fouling test device for the liquid-to-refrigerant heat exchangers

Fouling usually builds up on the waterside heat transfer surface of heat exchangers after long-term operation due to the impurity of the working water. Fouling research is important in the HVAC&R and chemical industries in order to develop fouling mitigation strategies and to direct manufacturers and designers for producing better heat exchangers. Fouling thermal resistance was studied using a heat exchanger installed in a testing system, which should have a high accuracy. Many operation parameters could affect the fouling test, thus a thorough design of the testing system is necessary to get reliable and robust data. This paper analyzes the effect of different operating parameters on the uncertainty of the fouling test results (fouling thermal resistance), including the length of the test tube, the surface heat transfer coefficient, the heat flux, the water velocity, and the fouling thermal resistance. Results show that the fouling test on tubes with higher surface heat transfer coefficient has a higher accuracy; Longer tube, higher heat flux, and lower water velocity can reduce the test uncertainty; When the fouling resistance is lower than 1E-5 m2K/W, the uncertainty is very high. The work in this paper is intended to help other fouling researchers to build a reliable test set-up so as to achieve accurate and comparable results.

Modeling CaCO3 crystallization fouling on a heat exchanger surface – Definition of fouling layer properties and model parameters

Crystallization fouling occurs when dissolved salts precipitate from an aqueous solution to the walls of process equipment. In the case of inversely soluble salts, like CaCO3, this may lead to crystal growth on heated surfaces. In this study, crystallization fouling of CaCO3 on a flat-plate heat exchanger surface is studied. The mass deposition rates are determined from the measurements of the fouling thermal resistance and the properties of the porous fouling layer. The uncertainty of the fouling layer properties and the mass depositions rate are quantified with a detailed uncertainty analysis, which shows that the proposed method and experimental analysis provide values that are reasonably defined and acceptable. The obtained mass deposition rates are used to determine the kinetic parameters of different fouling models using a regression analysis. The validation of the models against the experimental data shows that the closest correspondence between the experimental and modeled results occurs when the crystallization fouling is described by the surface integration model including the time scaling factor which depends on the flow velocity.

Key Problem Analysis and Solution on Intake Water and Heat Transfer of Sewage-Source Heat Pump System

Changing "high consumption energy, low temperature heat to the indoor, waste heat to the environment", and turning the HVAC harmoniously into the natural ecological cycle, conform to the trend of the development of ecological architecture. Heat pump technology is a way of HVAC energy saving the most practical. Although low heat and cold source of the city sewage is ideal, but the quality is very unstable, can not meet the operation requirements of heat exchange equipment. This paper analyzes the key problems of the sewage side in sewage source heat pump technology application in the present: hair dirt clog sewage heat exchanger; fouling in heat surface reduces the heat transfer performance, and results in large heat-transfer equipment in the practical application. According to the key problems of sewage side, this paper prevents hair clogged with large tube heat exchanger; reduces the fouling thermal resistance, and enhances heat transfer process using the heat exchanging technology of circulating fluidized bed.

Effect of Fouling on the Thermal Performance of Condensers and on the Water Consumption in Cooling Tower Systems

Circulating water in cooling tower systems contains an excess of amount of mineral ions. When this hard water is heated inside condensers, these minerals precipitate and the deposition of unwanted material on the heat transfer surface reduces the overall heat transfer performance and increases the pressure drop. Fresh water is often used to mitigate fouling but then water conservation might become a concern. This paper focuses on fouling effects on the thermal and hydraulic performance of refrigerant condensers and on the water consumption of cooling tower systems. Two brazed plate heat exchangers and a smooth tube-in-tube heat exchanger were experimentally investigated under fouling operating conditions. A model for the mineral species dissociation and mineral precipitation on the heat transfer surfaces was developed. A new semiempirical correlation for the fouling deposition strength factor was also developed and the simulation results predicted the fouling thermal resistance with an error of 30%. The daily ions concentration in the water stream is a key input to the model, but unfortunately this information is not always readily available for long periods of operation with water in fouling conditions. The fouling model limitations and potential improvements are discussed.

Modeling Fouling Factors for Microscale Heat Exchangers

This article presents an approach to the modeling of CaCO3 fouling and cleaning in a microscale cross-flow heat exchanger. The fouling progress was detected by thermal, fluid dynamical, and optical measures. In general, the observed fouling phenomena at microscale were comparable to those at macroscale. The detected thermal fouling resistance was between 10− 6 and 10− 3 m− 2 K− 1. As expected, crystallization fouling strongly depends on the surface temperature. In addition, the surface coverage can be a useful measure for both processes—fouling and cleaning. An extended approach to derive a reasonable fouling allowance was formulated through a fractional fouling resistance.

Study on Scale Inhibition Performance of Modified Polyaspartic Acid

Static and dynamic experiments were used to evaluate scale inhibition performance of modified polyaspartic acid (PASP-ASP). The static experiments showed that the PASP-ASP had good scale inhibition performance and the scale inhibition rate exceeded 98% when the PASP-ASP was 2 mg·L-1 and the solution temperature was 40 OC. In the dynamic experiments, almost no scale was formed on the heat transfer surface and the fouling thermal resistance decreases extraordinarily with PASP-ASP treatment experiment compared with the experiment without treatment. The PASP-ASP could be used in industrial cooling water systems.

On-line cleaning technique for mitigation of biofouling in heat exchangers: A case study of a hydroelectric power plant in Brazil

An experimental methodology was developed to assess an on-line cleaning technique to mitigate biofouling in plate heat exchangers. The exchangers are used in the cooling system of the journal bearings of hydro-generators of a power plant. The cleaning technology tested consisted of a non-intrusive electronic device wrapped around the water cooling piping that generated an electric field to inhibit the growth of micro-organisms on the heat transfer surfaces. Limnology studies explained the phenomenon of biofouling formation caused by limnophilous microorganisms present in the deepest parts of the reservoir manage to survive in hostile environments under anoxic conditions. Two criteria were adopted to assess the performance of the antifouling technology: a hydrodynamic criterion based on Kakaç’s pressure drop equation for plate heat exchangers and a thermal criterion (index of fouling) that takes into account the heat transfer effectiveness under the clean and fouled conditions of operation. The position of the antifouling device produced better results when installed in the primary cooling circuit. For the conditions studied, the cleaning technique mitigated biofouling but did not eliminate it completely. Excitation of the flow by an electric field diminishes the pressure drop and the index of fouling when compared to the unexcited flow condition. Control and reduction of the fouling thermal resistance is highly desired as it drastically lessens mechanical pumping costs and increases heat transfer performance.

Experimental investigations of fouling reduction in an ultrasonically-assisted heat exchanger

The aim of this study is to investigate the potential use of ultrasonic waves directly applied to a heat exchanger structure in order to clean some fouling layers. The heat exchanger is a double pipe configuration where the central pipe is removable. Glass and stainless steel central pipes were tested after being painted with spraying paint to simulate some fouling layers. The fouling reduction, or paint removal, can be illustrated visually or by plotting the evolution of either the overall heat transfer coefficient or the fouling thermal resistance with time as the paint is removed. Results are very encouraging since the fouling layers can be removed both from the external side of the pipe and, with more difficulties, from the internal side. Therefore, the overall heat transfer coefficient, previously decreased by the thermal resistance of the paint thickness, can be found again up to its initial value, corresponding to that of a clean tube.

Study on Scale Inhibition Performance of Polyaspartic Acid Derivative

Static and dynamic experiments were used to evaluate scale inhibition performance of polyaspartic acid derivative (PASP-SEA-ASP). The static experiments showed that the PASP-SEA-ASP had good scale inhibition performance and the scale inhibition rate exceeded 80% when the PASP-SEA-ASP was 2 mg•L-1 and the solution temperature was 40 OC. In the dynamic experiments, almost no scale formed on the heat transfer surface and the fouling thermal resistance decreases extraordinarily with PASP-SEA-ASP treatment experiment compared with the experiment without treatment. The PASP-SEA-ASP could be used in industrial cooling water systems.

A pilot-scale investigation of ash and deposition formation during oil-palm empty-fruit-bunch (EFB) combustion

In Thailand, oil-palm empty-fruit-bunch (EFB) a by-product of the crude-palm-oil milling process is currently one of the most promising potential energy resources. However, the ash-forming potassium, chlorine, silicon, and calcium constituents of EFB fuel can cause severe fouling, slagging, and ash meltdown, during combustion. This study is aimed to investigate EFB firing in a pilot-scale reciprocating grate-fired combustor with a 150kWth capacity. The study included chemical analyses of fuel and fuel ash, and samples of bottom ash, fly ash, and deposits derived from laboratory combustion tests. Experiments were conducted at temperatures of ≈800°C (low-temperature) and 900–950°C (high-temperature).Deposits mainly formed on the upstream side of the probe, and comprised two distinct layers, i.e., a thin white inner layer, and a gray outer layer. A swift growth of deposits on the cooled deposit probe, simulating superheater conditions, was evident, with significant retardation of heat transfer. Heat uptake by the probe appeared to reduce to 70% of the initial value within a 19-h period. The deposit mass flux was 167g/m2h, which corresponded with a fouling thermal resistance of 0.023m2·K/W. Following initial deposit formation of KCl condensate, particle impaction entailed deposit formation for incorporating Si- and Ca-rich fly ash particles into the deposits. XRF (X-ray fluorescence spectrometer) and SEM/EDX (scanning electron microscopy/energy dispersive X-ray) analyses revealed that not only did KCl mainly exist in the inner deposit layer, but also dominated the entire deposit mass (60–80wt.%), suggesting a crucial role for alkali condensation in deposit formation. If the bulk flue gases were sufficiently cooled, the KCl deposited on the probe by the transport of small solidified KCl particles. Corrosion attack was apparent near the metal surface and involved the deposition of KCl. SEM–EDX mapping exhibited that silica in combination with potassium led to the formation of low-melting-point compounds, which readily melted at high-temperature combustion. ICP-AES (inductively coupled plasma-atomic emission spectroscopy) analysis indicated that the potassium in the deposits had high mobility; the results were consistent with the XRF and SEM–EDX analyses.