HEAT TRANSFER AND THERMODYNAMICS
HT30XC Computer Controlled Heat Exchanger Service Module - Issue 3
A range of small scale heat exchangers, designed to illustrate the principles and techniques of indirect heat transfer between fluid streams. Different types of heat exchanger can be mounted on a common bench-top service unit. Small scale versions of commonly used industrial heat exchangers are available (including plate, tubular and ‘shell and tube’) for analysis and comparison. The equipment is controlled by a user supplied personal computer, which serves as the operator interface. Full data logging, control and educational software is supplied with the equipment. In addition, the equipment has been fitted with failsafe systems, including a watchdog circuit, which allows for safe operation from a remote computer.
- Benchtop service unit, designed to accommodate a range of different small-scale heat exchangers
- Comprises hot water vessel, hot water recirculation pump, cold water control system, computer interface and all necessary instrumentation
- The hot water vessel is made from clear acrylic (for visibility) and includes a 2kW heater with thermostatic over-temperature cut-out and low water level detection.
- The hot water pump is bi-directional (to allow co-current and counter- current investigations without re-configuring the hardware) and the flow rate is under computer control
- The cold water system includes a manually adjustable pressure regulator and a flow control valve which is under computer control
- Flow rates for both fluid streams in excess of 5 l/min are achievable, but this may be restricted by some designs of heat exchanger (eg HT32 & HT36 Plate Heat Exchangers)
- Up to 10 temperatures (K-type thermocouples) can be monitored using the service unit. Operating range, 0-75°C, resolution 0.1°C
- Two flow meters are included, operating range 0.2 to 9 l/min resolution 0.1 l/min
- All data is available to a (user-supplied) Windows PC, via a USB interface. This computer is also used to control the flow rates, hot water temperature, and hot water direction
- Full software for educational use is included
- A comprehensive instruction manual is included
- Small-scale, benchtop equipment
- Fast response times allow in-depth investigations in a short time
- Representative of industrial heat exchangers
- Multiple, industrially representative heat exchangers available
- All functions computer controlled, including reversing of one of the fluid streams for co-current and counter-current investigations
- Standard USB interface
- Safety functions implemented to allow for remote operation by computer
- Full educational software with data logging, control, graph plotting, and detailed ‘Help’
- Suitable for project work. The service bench provides facilities for evaluating in-house heat exchanger designs
The HT30XC is a service unit, to allow the operation of one of the Armfield range of small-scale heat exchanger systems. It provides controlled cold water flow, bi-directional hot water flow and the instrumentation required to do a series of in-depth investigations into heat exchanger performance. The individual heat exchangers can be quickly changed over, to allow comparisons between different types of heat exchanger to be made.
The HT30XC requires a user supplied personal computer for the operator interface. The computer connects the HT30XC using a USB interface, providing a simple and straightforward installation and set-up procedure.
Once the appropriate heat exchanger has been installed and setup, all other functions can be performed under computer control.
Appropriate measures have been implemented so that in the case of a computer failure or communications breakdown, the system shuts itself down in a safe manner.
The service unit provides two fluid streams to the heat exchanger, a hot water stream and a cold water stream. The hot water stream is heated in a vessel fitted with an electric heater. The heater is switched on and off by a solid state relay (SSR) which is under software control. A thermostat limits the maximum water temperature to 85°C for operator safety. A gear pump circulates water from the vessel, through the heat exchanger and back into the heater vessel. Both the pump speed and direction are under software control, allowing for co-current and counter-current investigations over a wide range of flow rates.
The cold water stream is generated from a mains water supply. The flow through the heat exchanger is adjusted by a variable flow valve, again under software control. A manually adjustable pressure regulator is used to minimise the effect of mains pressure fluctuations.
Conditioning circuits for up to 10 K-type thermocouples are included, (the thermocouples themselves are supplied with the heat exchangers). The instrumentation also includes flow meters to measure the flow rates of the two fluid streams.
Switching on the unit puts it into ‘Standby’ mode. From this mode it is necessary for a regular series of pulses to be received from the software (via the built in USB interface) to fully power up the unit. This ensures that unless the control software is running, the heaters, the pump and the cold water control valve cannot be switched on. The unit also includes an emergency stop switch. All electrical circuits are located in a bench mounted ABS supporting base, and protected by a Residual Current Device for operator safety. The ABS base includes a drip tray and drain tap in case of water spillage or leakage.
Full educational software is provided with the HT30XC for all the Armfield heat exchangers. Separate programs are provided for each exchanger, and each program contains a selection of separate exercises that can be performed. The actual details are exercise specific, but typically the following interfaces are available:
- All the temperatures and flow rates are displayed on a diagrammatic representation of the equipment
- A software button switches the equipment from standby mode to fully on
- The cold water flow control valve is operated by using up/down arrows or typing in a value between 0 and 100%. The actual flow rate can be read directly in l/min
- The hot water flow rate is set by entering a required set point into a PID control function. This use of PID control ensures the flow is stable despite changes in the viscosity of the water due to heating
- The heater is again controlled in a PID loop, by setting a required temperature set point
- Data from the sensors is logged into a spreadsheet format, under operator control
- Sophisticated graph plotting facilities are provided. Comparisons between data taken on different runs can be displayed
- Student questions and answers, including a layered ‘Hint’ facility
- Processing of measured values to obtain calculated results (this can be linked to the questions and answers to ensure student understanding)
- The data samples (measured and calculated) can be saved, or exported directly in Microsoft Excel format
- Data from the sensors can be displayed independently from the data logging. This can be in bar graph format, or a recent history graphical display (useful to check for temperature stability prior to taking a sample)
- Presentation screens are available, giving an overview of the software, the equipment, the procedure and the associated theory. This is backed up by a detailed ‘Help’ facility giving in-depth guidance and background information
User Defined Software and/or Remote Operation
Included separately on the software CD are the drivers required to allow other software applications to communicate with the HT30XC via the USB interface. This allows users to write their own software instead of using the Armfield-provided software. This software can be written in many different systems. Typically LabView, MatLab, ‘C’, ‘C++’, Visual Basic, Delphi, and any other software environment which allows calls to external drivers can be used.
In this way the user can write software to suit their specific requirements, in an environment which they are fully familiar with and which is compatible with their other equipment.
An extension of this methodology allows the equipment to be operated remotely, such as over a Local Area Network (LAN) or even over the internet. The HT30XC is ideal for this remote operation as it has been designed to ensure the unit shuts down safely in the event of a communications failure. It has also been designed so that once the heat exchanger has been installed and configured, all the controls to perform a series of investigations are under software control, and so the student does not need to be present with the equipment.
In a typical installation, the HT30XC would be connected to a local PC via the USB bus. The local PC would be connected to the user's PC via LAN. The operator interface software would be run on the remote (user's) PC and communicate to the control software on the local PC. (Armfield do not provide the software to implement this type of system).
For remote use, the appropriate heat exchanger would be installed onto the service unit, and the cold water pressure regulator adjusted to match the heat exchanger to the cold water supply. The unit is then switched on and remains in Standby mode until appropriate software is run requesting the unit to power up fully. With the HT31, HT32 and HT33, Heat Exchangers, all functions can then be operated remotely.
The HT34, HT36 and HT37 Heat Exchangers can be configured in different ways, and so the required configuration has to be manually implemented locally. However, once this has been done, a full set of investigations can be performed remotely for that configuration, including co-current and counter-current flows.
Heat Exchanger Options
A wide selection of heat exchanger options are available for use with the HT30XC, ranging from simple exchangers to demonstrate co-current and counter-current flow, to reconfigurable systems with interim temperature measurements, capable of being used for in-depth heat exchanger analysis. The heat exchangers are easily interchanged, with quick-release fittings on the flexible interconnecting tubes, and a simple location system is used to secure the exchangers onto the service unit.
Training exercises which are common to each of the heat exchangers when used with the HT30XC:
- Demonstration of indirect heating/cooling by transfer of heat from one fluid stream to another when separated by a solid wall
- Energy balance determination (heat balance) and calculation of efficiencies by measuring the flow rates and temperature changes in the hot and cold fluid streams.
- Introduction to different styles of heat exchanger and comparison of the differences in operation and performance
- Using the Logarithmic Mean Temperature Difference (LMTD) in heat transfer calculations
- Definition and measurement of Overall Heat Transfer Coefficient (U)
- Demonstration of the differences between counter-current and co-current operation, (not relevant for some HT34 configurations)
- Demonstration of the transition from linear to turbulent flow
- Effect of hot and cold fluid flow rate on the heat transfer coefficient
- Effect of driving force (temperature differential) on the heat transfer coefficient
- Investigation of heat loss and reduction in heat transfer coefficient due to fouling of the heat transfer surfaces (suitable student project using user-induced fouling)
Additional training exercises using the HT36 Extended Tubular Heat Exchanger:
- Demonstration of temperature overlaps between fluid streams in countercurrent operation
- Temperature profiles along the effective length of the heat exchanger in both counter-current and co-current operation
- Comparing the effect of different heat transfer areas
Additional training exercises using the HT37 Extended Reconfigurable Plate Heat Exchanger:
- Temperature profiles along the effective length of the heat exchanger in both counter-current and co-current operation
Demonstration of temperature overlaps between fluid streams in counter-current operation
Use of LMTD correction factor when calculating the Overall Heat Transfer Coefficient
Comparing the effect of different heat transfer areas
The use of a regeneration stage for energy efficiency, when heating and subsequently cooling a product stream
Project work to implement a wide variety of plate configurations, giving series, parallel and combined fluid passes
Additional training exercises using the HT34 Jacketed Vessel:
- Introduction to heat exchange in a batch or continuously fed stirred vessel and comparison of the differences in operation and performance when using a heating jacket or heating coil
Effects of stirring and vessel contents (volume) on the heat transfer characteristics
Additional training exercises using a user provided heat exchanger:
- Any of the above exercises can be performed, where appropriate, using a user-provided heat exchanger having appropriate characteristics, dimensions and fittings. The service unit will support evaluation of experimental heat exchangers constructed as design exercises by students
The user must have access to a PC with a free USB port, running Windows 98, or later.
At least one heat exchanger module is required, additional heat exchangers are optional.
Single Phase Mains Electricity Supply:
Cold Water Supply and Drain:
5 l/min at 1 bar gauge minimum
|Height:||0.45m (service unit only)|