Values Of Temperature Difference Research Articles

Изучение параметров городских "островов тепла" на территории Иркутской области по данным дистанционного зондирования

The investigation is aimed to determine the boundaries and intensity of urban heat islands in the Irkutsk region and assess the change in these parameters over a long-term period. The formation of an urban heat island is an example of anthropogenic influence on the urban climate. Land surface temperature and its spatial and temporal variations can be used to study urban heat islands, since the difference between the land surface temperature within the city and its surroundings is the result of the transformation of the underlying surface, heat capacity and three-dimensional structure of urban buildings in the process of urbanization. In order to study the phenomenon of urban heat islands of cities of the Irkutsk region, the land surface temperature data reconstructed from AVHRR-based thermal infrared imagery for 1998-2019 was used. As a result of the study, multi-temporal maps showing the urban heat islands of the agglomeration of Irkutsk-Angarsk-Shelekhov and the city of Bratsk were obtained. The investigated heat islands are characterized by a significant diurnal dynamic, so the difference in temperature values between the city and the suburbs in summer daytime reached 8-10 °C, in the evening and at night in summer this parameter decreases to 3-5 °C. The dimensions of the urban heat islands of the cities under investigation in the daytime exceed the dimensions of these heat anomalies in the evening and at night. Interannual variability in the intensity of urban heat islands did not show statistically significant trends from 1998 to 2019, the areas of urban heat islands increased significantly over the study period. The observed increase in area was probably associated with the development of the cities under study, with the transformation of landscapes and a decrease in the density of vegetation in the suburbs. In order to assess the contribution of the lack of vegetation to the formation of the urban heat islands in summer daytime, the values of the land surface temperature were compared with the values of the vegetation index NDVI. An analysis of the relationships between these parameters found that daytime land surface temperature was in close inverse relationship with the NDVI value, while this relationship was less pronounced at night and in the evening.

Modeling and simulation of heat balance and internal heat recovery targets through a combination of stream specific minimum temperature difference and polynomial temperature coefficients of specific heat capacities using pinch analysis

Existing heat balancing and energy targeting model in Pinch Analysis rely on use of interpolated values of specific heat capacities and global values of minimum temperature difference ∆Tmin, respectively. Even though this model is useful in estimation of the maximum internally recoverable heat recoverable in processing plants, it does not adequately represent the actual state properties of industrial processes. Specific heat capacities of fluids are polynomial functions of temperature of material under processing. The values of ∆Tmin also vary depending on the nature of the process stream under analysis. In this study, improvement to the heat balancing and energy targeting processes of pinch analysis was proposed. The study combined the use of stream specific values of ∆Tmin and polynomial temperature functions of specific heat capacities for heat targeting model. This was coded and executed using a PHP program. The model performance was tested using data from three thermochemical plants, Plant A, B and C, which process linear alkyl benzene sulphonic acid, dairy products and ethanol, respectively. The proposed method for heat balancing computed more heating requirements for plant A, B and C by 0.37%, 0.65% and 0.72% respectively, compared to the traditional method of heat balancing. The cooling loads for Plant A and B were less by 2.23% and 32.52% respectively, while for Plant C, they were more by 0.64%. The computed internally recoverable heat targets were more by 1.5%, 4.5% and 2.2% for Plants A, B and C. Simulations of the proposed model were carried out over a range of temperature targets, for different process streams. For gaseous process streams, heating and cooling load requirements were less. Reverse behavior was observed in liquid and steam containing streams, where the heating and cooling load requirements were more.

Multy-year oscillations investigation of winter temperatures Prediction of integrated temperature difference during the heating period

To estimate possible deviations in fuel consumption for heating based on meteorological observations of previous years, the integrated temperature difference inside and outside the building during the heating season is used. When the heating period is divided into two subperiods relative to the considered date (for example, before and after December 1), the accumulated and residual integral temperature differences are obtained. The assumption about the presence of a statistical relationship between the accumulated and residual integral temperature difference is confirmed. A model for predicting the probability of the expected values of the integral temperature difference for the upcoming heating period is developed. The model is focused on obtaining matrices of conditional probabilities of observations from intervals of dividing the accumulated integral temperature differences into intervals of residual integral temperature differences.

Experimental Performance Evaluation of Thermoacoustic Refrigerator made up of Poly-Vinyl-Chloride for different Parallel Plate Stacks using Air as a working medium

Abstract Most of the experimental work carried out by fabricating Aluminium and other metallic resonator system in order to evaluate the performance of thermoacoustic refrigerator. In this experimental work, poly-vinyl-chloride has been used to fabricate all the structural parts including the resonator system to study the performance of thermoacoustic refrigerator for different operating conditions. Three parallel plate stacks are fabricated by using Aluminum and the Mylar sheet material of 0.12 mm thickness by considering three different porosity ratios. In this research work, only pure air is used as a working fluid. The experiments are conducted for the drive ratios ranging from 0.6% to 1.6% with an operating frequency varies from 200Hz to 600Hz with a step of 100 Hz. Also, the mean operating pressure and cooling load varies from 2 to 10 bar and 2 to 10 W respectively. In this work, Bruel and Kjaer data acquisition system and RTDs are used to measure and record the temperature difference between two heat exchangers. The effect of different parameters such as operating pressure, operating frequency, cooling load and drive ratios on the performance of thermoacoustic refrigerator in terms of temperature difference and coefficient of performance (COP) are studied.It is observed from experimental results that 1.23 oC is the lowest measured temperature at the cold heat exchanger by maintaining 32 oC at the hot heat exchanger. It is important to note that 30.77 oC is the highest value of temperature difference measured between two sides of stack, which is about 41% improvement in the temperature difference as compared to previous findings

Fabrication and experimental investigation of the bionic vapor chamber

With the rapid development of photoelectric products, their miniaturization and high integration have intensified the problem of heat dissipation. In this paper, a new type of bionic vapor chamber is designed and manufactured. The wick structure for the condenser combines the fractal network microchannels and copper foam, which are used to imitate the macroscopic leaf vein network and microscopic mesophyll tissue, respectively. Furthermore, the permeability gradient distribution between the leaf veins and mesophyll tissue is added, presented as the porosity gradient distribution of the copper foams around the fractal network microchannels. Then the fractal network microchannels on the wick are processed by laser engraving and mould coining, respectively. The wick structure for the evaporator is homogeneous copper foam. The minimum value of the maximum temperature difference on the upper surface of the condenser of the bionic vapor chamber is only 1.21 K and that of the overall thermal resistance of the bionic vapor chamber is only 0.094 K/W. Compared with the existing novel vapor chambers, when using deionized water as the working fluid, the maximum through-plane effective thermal conductivity and minimum in-plane effective thermal conductivity are 9.52 W/m·K and 10500 W/m·K, respectively, which are higher than most existing vapor chambers.

Simulation of temperature and moisture fields around a single borehole ground heat exchanger: effects of moisture migration and groundwater seepage

This paper aims to investigate the effects of moisture migration and groundwater seepage on the heat transfer capacity of ground heat exchangers in stratified soils. A three-dimensional unsteady groundwater flow and heat transport model was established using finite volume method. Sixteen cases with different model considerations and initial soil conditions were simulated based on the proposed model. A group of 8 cases considering only transverse moisture migration and another group considering both transverse and longitudinal moisture migration were compared. The heat and moisture fields after 30 days of operation reveal that considering the change of saturation caused by vertical moisture transfer, the soil temperature field will be affected, but borehole outlet temperature was less influenced. The absolute value of outlet temperature difference between corresponding cases in the two groups is only about 0.2 °C. The position of groundwater seepage and arrangement of unsaturated soil layers with different degrees of saturation on heat transfer capacity of vertical ground heat exchanger were further explored. The results show that the longitudinal moisture migration would be made more influential by the existence of seepage layer, because the average relative deviation of inlet and outlet temperature difference between the corresponding cases of Group 1 and Group 2 was 1.34% when setting seepage layer and was 0.44% when without seepage layer. Heat transfer performance of borehole heat exchanger is also affected by the location of seepage layer. The average relative deviation of inlet and outlet temperature difference between the reference case and cases with seepage in the top, middle and bottom layers is 34.18%, 25.08% and 16.82%, respectively. The arrangement of unsaturated soil layers also has a certain effect. When the soil layer with low degree of saturation is located in the upper layer of soil, heat transfer capacity is better.

Study on heat transfer performance of geothermal pile-foundation heat exchanger with 3-U pipe configuration

Targeting the heat transfer performance of geothermal pile-foundation heat exchanger in ground source heat pump system (GSHP), the physical models of 3-U pile-foundation heat exchanger and heat exchanger group were established. CFD software was used to simulate heat transfer processes and heat transfer performance was analyzed both in cooling and heating mode. The simulation results indicated that the higher thermal conductivity of pile-foundation heat exchanger contributed to the higher heat transfer efficiency than soil. Heat transfer flux per meter of the pile-foundation heat exchanger gradually decreased with time went on. After operating for ten years, the average soil temperature increased by 2.96 K in non-equilibrium condition and decreased by 0.61 K in equilibrium condition. The equilibrium condition of cooling and heating load was beneficial to operation system's safety and efficiency. The experimental values of temperature differences were 2.2 K, 2.5 K and 3.5 K, and the heat transfer flux were stable at 58.1 W·m − 1, 65.9 W·m − 1 and 46.2 W·m − 1 in three schemes separately. The maximum difference value was 8.4% for temperature difference between experiment and simulation. The simulation results corresponded well with experimental data, indicating the reliability of simulation. The study results were approximate to the actual situation and can be used as theoretical basis for design and application of pile-foundation heat exchanger in GSHP system.

An Experimental Investigation into Nozzle Vane Heating to Prevent Erosion in the Last Stages of Steam Turbines

The paper is devoted to an experimental investigation of nozzle vane heating in the last stage of a wet steam turbine. The investigation was performed at a steam-dynamic test facility whose circuit was connected to an operating cogeneration power station (TETs). The working fluid was steam from a heat extraction assembly of a steam turbine. To prepare a polydisperse wet steam flow specific for the last stages of steam turbines, a three-stage wetting system based on feedwater injection into the flow was used. The object of investigation is a flat vane cascade consisting of hollow vanes. The vane cavities are fed with superheated steam to provide heating. Experimental data are presented demonstrating that it is advisable to heat nozzle vanes: first, the economic characteristics are improved, and, second, erosion of the blades in the last stages decreases. This method can be used as an alternative to the internal moisture separation from the steam path. The experimental investigation yielded the effect of the temperature difference between the main flow and the heating steam on the amount of heat transferred to the main flow and on the steam conditions at the outlet from the heating chamber. It was found that condensation in the heating chamber decreased its outlet pressure. This should be considered in designing a similar active system to control erosion of rotor blades. The measured profile losses of kinetic energy downstream of the vane cascade for different temperature difference values are presented. The kinematic characteristics of the liquid phase downstream of the vane trailing edge are determined. Large temperature differences are found to have a negative effect on droplets and can reduce the erosion resistance of the blades as compared with profiles without any active erosion control methods.

Terrestrial and Remote Indexes to Assess Moderate Deficit Irrigation in Early-Maturing Nectarine Trees

Monitoring plant water status is relevant for the sustainable management ofirrigation under water deficit conditions. Two treatments were applied to an early-maturingnectarine orchard: control (well irrigated) and precise deficit irrigation (PDI, based on soilwater content thresholds). Moderate water deficits generated by PDI were assessed bycomparing terrestrial: stem water potential (Ψstem) and gas exchange parameters, with remote:canopy temperature, normalized difference vegetation (NDVI), and soil adjusted vegetationindex (SAVI), plant water status indicators. The Ψstem was the only indicator that showedsignificant differences between treatments. NDVI and SAVI at the postharvest period wereappropriate indexes for estimating winter pruning, although they did not serve well as plantstress indicator. Vapor pressure deficit along with Ψstem values were able to predict remotesensing data. Ψstem and canopy to air temperature difference values registered the highestsignal intensity and NDVI the highest sensitivity for detecting water deficit situations. Theresults suggest that care should be taken when using instantaneous remote indicators toevaluate moderate water deficits in deciduous fruit trees; more severe/longer water stressconditions are probably needed. The proposed PDI strategy promoted water saving whilemaintaining yield, and could be considered a promising tool for semi-arid agrosystems.

An experimental investigation on electrical performance and characterization of thermoelectric generator

Thermoelectric generator (TEG) is an attractive renewable energy source that utilizes waste heat energy from various sources to produce electricity. In this paper, a novel method has been proposed to investigate and characterize the TEG module by determining the exact maximum power point (MPP) and estimate the TEG module dynamic parameters. A DC-DC boost converter with a simple control method is proposed to obtain I-V and I-P characteristics and extract the exact MPP of the TEG module. The electrical performance and dynamic parameters such as Seebeck coefficient and internal resistance of the TEG module have been estimated at the MPP. MATLAB software package is used to model and simulate the complete system. Then, by using a low-cost Arduino microcontroller and a standard TEG module (HZ-14HV), a test rig is built to examine the electrical performance of the TEG. A comparison among simulation, experimental, and manufacturing data sheet is done to validate the accuracy of the proposed system. The proposed system tests and characterizes a TEG module at five values of temperature differences in the range from 377 K to 457 K and analyses the MPP generated in the range from 5 to 13.8 W. The obtained results confirm that there is good agreement among the simulation, experimental, and data sheet. To the best of our knowledge, it is the first time to use the boost converter to estimate the electrical characteristics and the dynamic parameters of the TEG. It can be said that the proposed DC-DC boost converter with the suggested control method is helpful for testing commercial TEG modules before implementing in a TEG system.

Investigation of a non-invasive venous blood flow measurement device

Abstract Venous blood circulation can be restricted due to various conditions commonly indicating a related medical condition. However, current non-invasive methods for determining venous blood flow are limited to be either very inaccurate or expensive. Alternatively, a method to measure sap flow non-invasively in trees is through thermal mass measurement principles. This paper investigates applying the thermal mass flow measurement principle to determine venous blood flow. A simplified finite element model (FEM) and simulation are created to determine the operating behavior and expected response of a thermal mass flow meter with venous blood flow under the skin. An initial prototype of a thermal mass venous blood flow meter is designed using a Peltier-element and RTD thermistors. Initial tests were done on N = 8 subjects identifying the presence of blood flow and, testing the devices basic functionality and performance. The simplified FEM model of venous blood flow proved the thermal mass blood flow device is feasible, and determined the initial characteristics of the first prototype. The initial prototype proved to be functional detecting rises in temperature downstream of +1.4 K (0.8 - 1.8 inter- quartile range) when the blood flow was released (t = 90 s after release), compared to when blood was not flowing. The initial prototype proved to be able to detect the presence of blood flow in all subjects. However, further work is required to increase the differences in temperature values or gradient measured for a change in flow rate so the actual flow rate can be determined.

Variations in the body surface temperature of sows during the post weaning period and its relation to subsequent reproductive performance.

ObjectiveA study was made investigate factors affecting body surface temperature changes after weaning in sows, whether these can be used to aid detection of natural estrus and how they relate to subsequent reproductive performance.MethodsA total of 132 sows were selected during summer from a breeding farm, with mean parity of 3.6±2.3 and 28.5±0.9 days lactation length. Four daily measurements (6:00, 8:00, 16:00, and 18:00) of vulva (VST), udder (UST), ear base and central back skin temperatures for individual sows were taken by an infrared thermometer, continuing up to 8 days post weaning.ResultsThe VST obtained from sows showing estrus at 4 days post-weaning (4DPW), 5DPW, and 6DPW showed a peak at the fourth day post-weaning, but then started to decrease. The VST of sows not detected in standing heat (NDPW) remained at a lower level during the experiment, but UST was increased soon after weaning. The VST-UST temperature differences during daytime of sows that were showing behavioural standing heat on 4DPW, 5DPW, 6DPW, and 7DPW were 0.46°C±0.123°C, 0.71°C±0.124°C, 0.66°C ±0.171°C, and 0.58°C±0.223°C, respectively. The NDPW sows had the highest UST observed, but also the lowest VST so that a more negative value of temperature difference (−0.31°C) was seen during first few days post-weaning. A total of 119 sows were observed to show standing heat and were bred. The later the estrus, the smaller the litter size (p = 0.005).ConclusionSows which did not show behavior indicative of stable standing heat after weaning had a VST which remained at a lower level, but the UST increased soon after weaning. Therefore, for sow heat detection under field conditions, the changes of VST and UST and difference between the two should be considered together to increase the accuracy of detection.

The deformation of the Rock wool board external thermal insulation system based on coupled temperature and relative humidity

A coupled heat and humidity transfer model of external thermal insulation wall is established. The effects of different climatic conditions (winter and summer) on the deformation of the rock wool board external insulation system were simulated and analyzed by the meteorological database from Shanghai. The results show that the changes of strain and stress are fluctuated because of the variation of temperature and relative humidity, and their extremum values appear with the extreme value of temperature and relative humidity difference. The coating mortar has the highest stress and strain, and the rock wool board has the lowest stress and strain. The maximum stress can reach 1.97×10-3MPa and the maximum strain can reach 1.36×10-4 of the rock wool thermal insulation system during the periodic changes in temperature and relative humidity within 72 hours in winter and summer.

A Novel Analytical Modeling of a Loop Heat Pipe Employing Thin-Film Theory: Part II—Experimental Validation

Part I of this study introduced a mathematical model capable of predicting the steady-state performance of a loop heat pipe (LHP) with enhanced rationality and accuracy. Additionally, investigation of the effect of design parameters on the LHP thermal performance was also reported in Part I. The objective of Part II is to experimentally verify the utility of the steady-state analytical model proposed in Part I. To this end, an experimental device comprising a flat-evaporator LHP (FLHP) was designed and fabricated. Methanol was used as the working fluid, and stainless steel as the wall and tubing-system material. The capillary structure in the evaporator was made of polypropylene wick of porosity 47%. To provide vapor removal passages, axial grooves with inverted trapezoidal cross-section were machined at the inner wall of the flat evaporator. Both the evaporator and condenser components measure 40 × 50 mm (W × L). The inner diameters of the tubes constituting the liquid- and vapor-transport lines measure 2 mm and 4 mm, respectively, and the lengths of these lines are 0.5 m. The maximum input thermal load was 90 W in the horizontal alignment with a coolant temperature of 10 °C. Validity of the said steady-state analysis model was verified for both the flat and cylindrical evaporator LHP (CLHP) models in the light of experimental results. The observed difference in temperature values between the proposed model and experiment was less than 4% based on the absolute temperature. Correspondingly, a maximum error of 6% was observed with regard to thermal resistance. The proposed model is considered capable of providing more accurate performance prediction of an LHP.

An analytical study of entropy generation in rectangular natural convective porous fins

Although, there are many studies on the second law analysis of solid fins, there are not enough investigations on the second law analysis and entropy generation of porous fins. The aim of this study is to establish a thermal analysis and to evaluate the performance of porous fins using the second law of thermodynamics. For this purpose, an analytical procedure is presented to obtain the entropy generation in two rectangular natural convective blades including very long and insulated-tip porous fins. One-dimensional heat transfer equation, the first and second laws of thermodynamics, were used to obtain two dimensionless nonlinear equations for the calculation of local temperature and entropy generation in the porous fins. The results of solving these equations showed that the entropy generation number is a function of SH, temperature ratio and non-dimensional local temperature of the porous fin. The results also indicated that, for both long and insulated porous fins, at given values of SH and the temperature ratio, the maximum entropy production occurs at the base of the fins with the maximum values of temperature difference. Moreover, based on the results of the study, two equations were proposed to estimate the average entropy generation number in long and insulated-tip porous fins. The effects of SH and temperature ratio on the local and average entropy generation number have been also investigated.

Thermally Assisted Magneto Resistance and Spin-Filtration in Single Layer MoS2

We investigate the dependence of spin polarized transport properties on temperature in single-layer ferromagnetic molybdenum disulfide (MoS 2 ). The density functional theory alongside the nonequilibrium Green's function formulation is utilized for spin polarized transport calculations. The spin dependent transmission spectrum and current are computed to clarify the impact of temperature on spin filtration and spin Seebeck effect. A high estimation of spin polarization efficiency of nearly ~100% is accomplished at small range of values of temperature difference. Large temperature distinction between left electrode (T L ) and right electrode (T R ) results in small spin polarization efficiency. The results suggest a thermal giant magneto-resistance (MR) of ~2.16 × 10 3 %, which advances with advancement in temperature gradient/difference (ΔT) among left and right electrode, MR additionally relies upon T L . The magnificent attributes, for example, high magnetoresistance and near perfect spin polarization suggests the potential of MoS 2 material in applications based on spin caloritronics.

Effect of Supertargeting and Non Isothermal Stream Mixing in Heat Exchanger Network Design Using Modified Pinch Analysis

This paper investigated the effect of minimum temperature difference as well as that of non-isothermal stream mixing in heat exchanger networks (HENs) using a modified pinch technique. Supertargeting was carried out to determine the appropriate minimum temperature difference value used to design the HENs. The networks were further optimized to remove the isothermal mixing assumption. In the four case studies used in this work, each shows how these two concepts affect the total annual cost (TAC) of HENs. These were presented in the network comparison tables where the cost of the networks using supertargeting is much lower than the cost of the ones without, and the non-isothermal mixing networks have lower costs than the ones with the isothermal mixing assumption even in the networks designed without supertargeting technique.

Research on Key Parameters Operation Range of Central Air Conditioning Based on Binary K-Means and Apriori Algorithm

As the energy-saving control of central air conditioning has been widely applied in modern architecture, research of real-time optimal control based on historical data and identification of its optimal control strategies are of great importance for reducing energy wasting of buildings. However, due to the property of easily falling into local optimum, conventional k-means approach cannot achieve the goal of real-time optimal control, we therefore propose an innovative binary k-means clustering algorithm which is used to adjust the target value of temperature difference (TD) in the control system of chilled water and cooling water of central air conditioning system (CACS). Thanks to the clustering control, among the 304 test data, the coefficient of performance (COP) of 211 sets of data, which accounted for 69.41%, are higher than those of the traditional control method. In the simulation system, the COP of 191 sets of data, which accounted for 62.83%, are higher than those of traditional control methods, achieving better energy efficiency. To achieve the goal of identify potential energy-saving control strategies, the Apriori algorithm is proposed to correlate the key parameters and energy consumption efficiency of the CACS. The results show when the chilled water temperature difference (CWTD) > 2.0 °C and the cooling water temperature difference (COWTD) > 2.4 °C, some rules are discovered as follows: 1. The probability of a larger system COP will increase if the CWTD is set lower than the third quartile value or the COWTD is set lower than the first quartile value. 2. The probability of a larger system COP will also increase if the CTWD is set lower than the first quartile and the COWTD is set between the first and the third quartile. These underlying regularity is useful for technicians to adjust the control parameters of the equipment, to improve energy efficiency and to reduce energy consumption.

Clinical evaluation of the efficacy of radiofrequency combined with ozone in the treatment of lumbar disc herniation using infrared thermography

Objective To evaluate the efficacy of radiofrequency combined with ozone in the treatment of lumbar disc herniation using infrared thermography, and discuss the application value. Methods A total of 160 patients with lumbar disc herniation were randomly divided into observation group (80 cases) and control group (80 cases). The observation group was treated with continuous radiofrequency combined with ozone injection, and the control group was treated with pulse radiofrequency combined with ozone injection. Pain visual analogue (VAS) score, Oswestry dysfunction index (ODI) score, and Japanese Orthopaedic Association (JOA) score of the patients were compared before and 1 and 3 months after the treatment. The mean temperature and temperature difference of the lower body were compared by infrared thermography before and 3 months after the treatments. The overall clinical efficacy was evaluated 3 months after the treatments using the modified Macnab criteria. Results The comparison within groups showed that the VAS, ODI and JOA scores were significant changed after 1 and 3 months of the treatment (all P 0.05), and in the temperature difference value was statistically significant between the two groups (P<0.05). The overall clinical efficacy of the observation group was better than that of the control group after 3 months of the treatment (P<0.05). Conclusions Radiofrequency combined with ozone injection is satisfactory for the treatment of lumbar disc herniation, and the continuous radiofrequency is superior to pulse radiofrequency. The clinical efficacy of radio-frequency combined with ozone injection can be effectively evaluated by Infrared thermography. Key words: Infrared thermography; Lumbar disc herniatio; Radio frequency technique; Ozone injection; Clinical research

Investigation of the combined efficiency of a solar/gas hybrid water heating system

In climate regions with large seasonal variations in solar radiation, such as the Pacific Northwest of the United States, a solar thermal energy collector might not economically satisfy year-round domestic water heating demands, requiring an auxiliary unit, such as a natural gas-fired water heater. Previous studies have shown that the burner efficiency of a gas-fired water heater varies depending on the log-mean temperature difference between the cold fluid (water) and the hot fluid (combustion gases). In a solar/gas hybrid water heating system, where solar collectors are used in conjunction with a gas-fired heater, the partial heating of water provided by solar input reduces the log-mean temperature difference value for the gas heater, reducing the efficiency of the gas burner. Since this efficiency reduction varies depending on the amount of pre-heating provided by solar energy input, it is difficult to accurately predict the actual cost and energy savings offered by solar/gas hybrid water heaters in different climates and operation scenarios. Hence, to predict the actual energy and cost savings under various design conditions, the performance of solar/gas hybrid systems must be better understood.The objective of this work is to experimentally determine the thermal performance of a solar/gas water hybrid water heating system with a 6.44 m2 flat plate solar collector array and a 22.3 kW natural gas burner in Corvallis, Oregon, USA. Under different temperature lifts and solar insolation values, the system was operated at three different modes of heating: solar, gas, and combined solar/gas mode. The overall system thermal efficiency value for each mode is calculated. The efficiency of the solar collector heating system was found to be 41.97%, 39.82%, and 35.05% at initial water temperature of 20, 30, and 51.5 °C, respectively. For initial water temperatures of 20, 30, and 51.5 °C, the efficiency of the gas burner was found to be 69.2%, 66.4%, and 65.5% at the HHV, and 76.7%, 73.6%, and 72.6% at the LHV of natural gas, respectively. In the combined solar/gas heating mode, the efficiency of the gas burner decreased with increasing solar fraction. For solar fractions of 4.93%, 9.40%, 11.39%, and 14.27%, the efficiency of the gas burner in terms of the HHV of natural gas was found to be of 69.08%, 66.80%, 66.17%, and 65.18%, respectively. Based on the experimental results, a configuration that would provide higher overall system efficiency for combined solar/gas heating is suggested.