Measurements of Local Instantaneous Convective Heat Transfer in a Pipe - Single and Two-phase Flow
April 30th, 2018
This manuscript describes methods aimed at measuring the local instantaneous convective heat transfer coefficients in a single or two-phase pipe flow. A simple optical method to determine the length and the propagation velocity of an elongated (Taylor) air bubble moving at a constant velocity is also presented.
The overall goal of this experimental procedure is to present a thermography technique, that utilizes a well designed test section to accurately measure the local instantaneous convective heat transfer coefficients, in a single or two phase pipe flow. This method can help answer key outstanding questions in transient convective heat transfer, in single and multi phase flows. The main advantage of this technique, is that it's non invasive and can measure fast variations in wall temperature, resulting from time dependent flows.
Demonstrating this procedure will be Avram Balas, and Yakov Levi, technicians from our laboratory. Begin with a segment of pipe 70 centimeters long or more. It's diameter and wall thickness, should match the pipe of the experimental facility.
Mill four adjacent narrow windows along the pipe. Each window is six millimeters wide and 80 millimeters long. The gap between windows is 25 millimeters.
Next get 12 micrometer thin stainless steel foil, and cut a long thin strip. To help weld the heating wires the strip is coated with gold near each end of the strip. Continue by measuring the foil's electrical resistance with an ometer.
Now obtain a rigid tube that fits into the pipe. The tubes outer diameter should equal the inner diameter of the pipe. Cut out a long segment of the rigid tube to create an arch.
This long arch, the basis, fits into the pipe, and will support and protect the foil. To put the foil in the test section, coat the basis with grease to aid in detaching the foil later. Then place the foil on the basis, to transfer to the test section.
Flatten the foil and use a cloth and alcohol to clean excess grease. Next, apply adhesive on the foil periphery, so it will adhere to the pipe. In addition, identify regions corresponding to the bridges between windows on the pipe and apply adhesive to them.
When ready orient the basis, so the foil faces the same direction as the test section windows. Then carefully insert the basis into the test section. Ensure the foil is aligned with the windows.
Check that each gold stripe is at an edge of an outer window. Once the foil is in place, clamp the basis to each end of the pipe. Next obtain a bicycle inner tube, folded to fit into the pipe.
Carefully insert the tube into the pipe under the basis. When done, inflate the tire. As the tire inflates, observe the adhesive spreading across the foil and reaching the basis.
Use a cloth to clear any excess adhesive in the window openings. After 24 hours of drying deflate the tire and extract it. Open the clamps holding the basis and pipe together.
Test each end of the basis to decide which side is easier to disconnect. Then use a long roller and start on the easier end. Place the roller between the basis and the pipe, and move it slowly into the pipe, until the entire basis is separated.
The foil should remain undamaged on the pipe interior. As a test of the seal, close one end of the pipe. Then fill the pipe with water and check for leaks.
Continue after unblocking the pipe and cleaning its interior. Connect electrical heating wires to the golden strips on the foil. Also connect T-Type thermocouples to the bottom of each window.
Finally, spray paint the outer side of the foil with a black matt. Now put the test section in the experimental facility. Connect the pipes with flanges.
Before continuing, fill the system with water. Move on to set up a computer for control and data acquisition. Then connect the heating wires from the foil, to a DC power supply.
Next, place a computer controlled infra red camera at a window of the test section. For calibration, place it a few centimeters from the test section surface. Measure the ambient temperature, with a thermocouple held near the experiment.
Next, focus the camera on a window of the test section to measure its temperature. Adjust the emissivity of the IR camera, so the camera and the temperature measured by the thermocouple on the pipe window match. With the camera set up, prepare the optical probes.
Each probe consists of a laser and a photodiode, that is to be connected to the data acquisition computer. Turn the laser on and point the beam at the diode. Check that the computer records a positive signal.
Place an optical probe along the test pipe, that is now filled with water. The final set up is represented in this schematic. The measurement section is in addition to the regular setup.
The computer, in addition to data acquisition from the camera, thermocouples and optical probes, governs the synchronization of bubble injection and wall temperature measurement with the camera. Now establish the desired conditions for the experiment, and perform a single phase pipe flow reference measurement. After that inject a Taylor bubble in the setup, for a two phased flow measurement.
This is an example of the optical sensor output, for a single Taylor bubble rising in a vertical pipe filled with stagnant water. The initial drop represents the sensor circuit opening due to the Taylor bubble tip. The rise represents the bubble's passing.
Later shorter drops represent bubbles in the liquid wake behind the Taylor bubble. The delay of the features in the bottom curve, is due to the sensors being in different positions. This plot represents the ensemble average results of the local convective heat transfer coefficient, due to the passage of a single Taylor bubble rising in stagnant water in a vertical pipe.
The two phase flow convective coefficient results are normalized by the single phase flow coefficient. The distance from the bubble tail moving, in a frame of reference with the Taylor bubble is normalized by the pipe diameter. This video presented measurements of the local instantaneous heat transference and slug flow.
The method can provide information on heat transfer and study stage single phase flow, as well as more complex two phase flows. Once mastered, the manufacturing of the test pipe can be done in a few hours. While attempting this procedure on transient flow, its important to remember to automate thew entire process, to insure repeated results which can later be used for an assembling averaging process.
After watching this video you should have a good understanding of how to manufacture a heat transfer test pipe, which allows a quantitative investigation of convective heat transfer in pipe flows. Don't forget that this technique of convective heat transfer measurement, can be expanded to many flow configurations, using supplementary equipment as optical prompts and high speed cameras.
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Overview
This manuscript presents a thermography technique for measuring local instantaneous convective heat transfer coefficients in single or two-phase pipe flow. The method is non-invasive and can capture rapid variations in wall temperature due to time-dependent flows.
Key Study Components
Area of Science
- Thermography
- Convective heat transfer
- Fluid dynamics
Background
- Understanding transient convective heat transfer is crucial for various applications.
- Single and multi-phase flows present unique challenges in measurement.
- Non-invasive techniques are preferred for accurate data collection.
- Elongated air bubbles can affect flow characteristics and heat transfer.
Purpose of Study
- To develop a method for accurately measuring heat transfer coefficients.
- To address key questions in transient convective heat transfer.
- To demonstrate a technique that measures fast variations in wall temperature.
Methods Used
- Utilization of a well-designed test section for measurements.
- Implementation of a thermography technique.
- Measurement of elongated (Taylor) air bubbles in pipe flow.
- Non-invasive observation of temperature variations.
Main Results
- The technique successfully measures local heat transfer coefficients.
- Fast variations in wall temperature were accurately captured.
- Results contribute to understanding transient behaviors in fluid flows.
- The method is applicable to both single and two-phase flows.
Conclusions
- The thermography technique is effective for heat transfer measurement.
- Non-invasive methods provide valuable insights into flow dynamics.
- This study enhances the understanding of convective heat transfer in various applications.
Frequently Asked Questions
Executive Industry Relevance
This thermography technique enables precise measurement of local instantaneous convective heat transfer coefficients in single and two-phase pipe flows, supporting mechanistic de-risking in thermal management systems. By capturing rapid temperature variations non-invasively, it provides quantitative data for predictive modeling of heat transfer dynamics in fluid systems relevant to bioprocessing equipment design and scale-up. The method supports target validation of thermal performance parameters in preclinical device testing and process optimization workflows.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of thermal transport mechanisms in fluidic systems, supporting hypothesis testing of heat transfer behavior under controlled flow conditions.
- Operational Value: Provides reproducible, quantitative local heat transfer coefficient data for validating thermal models in bioreactor design and microfluidic platform development.
Screening & Assay Development
- Scientific Value: Generates standardized, ensemble-averaged heat transfer metrics under defined flow regimes, enabling comparative analysis of thermal performance across fluid formulations.
- Operational Value: Supports assay readiness by delivering reliable, repeatable thermal response data under single and two-phase flow conditions for sensor calibration and system validation.
Translational & Preclinical Research
- Scientific Value: Facilitates mechanistic de-risking of thermal management strategies in implantable devices and drug delivery systems by characterizing convective heat transfer under physiologically relevant flow scenarios.
- Operational Value: Enables continuity from bench-scale thermal characterization to preclinical validation through transferable measurement protocols and normalized data outputs.
Pipeline & Workflow Integration
The method integrates into discovery workflows by providing quantitative thermal readouts that inform early-stage design decisions for fluid-handling systems, with direct relevance to lead identification phases where thermal stability and heat dissipation are critical quality attributes.
- Discovery Biology: Supports hypothesis testing of thermal behavior in fluidic microenvironments, aiding in the de-risking of targets dependent on thermal regulation.
- Screening: Delivers reproducible, quantitative heat transfer coefficient measurements under controlled flow, enabling standardized comparison of thermal performance across experimental conditions.
- Analytics: Produces localized, time-resolved temperature data and ensemble-averaged convective coefficients that facilitate statistical analysis of thermal transients in fluid systems.
- Translational Research: Connects bench-scale thermal measurements to preclinical device validation through consistent methodology and scalable test section design.
- Enterprise Reuse: Establishes a reusable thermal characterization platform applicable across multiple fluid systems and flow configurations, reducing redundant method development.
Operational & Enterprise Impact
- Scientific Value: Enhances predictive confidence in thermal modeling by delivering high-resolution, non-invasive measurements of instantaneous convective heat transfer.
- Operational Value: Ensures standardization and reproducibility through well-defined test section fabrication and synchronized data acquisition protocols.
- Strategic Value: Reduces late-stage biological risk by enabling early identification of thermal management limitations in device and process designs.
- Portfolio Impact: Informs risk-adjusted advancement decisions by providing quantitative thermal performance data for go/no-go evaluations in thermal-sensitive applications.
Implementation Considerations
- Requires expertise in thermography, fluid dynamics, and microfabrication for test section assembly and optical probe integration.
- Dependent on infrared camera systems, data acquisition hardware, and optical probes for bubble tracking and temperature monitoring.
- Necessitates cross-team standardization of flow conditions, bubble injection protocols, and reference state establishment for comparable results.
- Involves adaptation considerations when extending to different pipe diameters, fluid properties, or flow orientations beyond vertical configurations.
- Practical limitations include the need for optically accessible test sections and careful synchronization of thermal measurements with bubble passage events.
