Hotstart Thermocycler

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The thermo-cycler device will be used for accelerated age testing of heaters used in the heating of diesel engines. It will significantly decrease the cycle time from on to off and allow for analysis of heater performance during testing.

Prototype showing proposed heater layout
Sponsors
Team Name Hot Testers
Duration Summer - Fall 2013
Faculty Advisers
  • Dr. Steve Beyerlein
  • Dr. David Alexander
  • Russ Porter
Mentor
  • Jeremy Cuddihy

Team

Hottesters.jpg

Left to right

  • Archana Shrestha - Electrical and Computer Engineering
  • Ahmed Al Harbi - Electrical Engineering
  • Joe White - Mechanical Engineering
  • Neal Joslyn - Mechanical Engineering
  • Joe Eckroat - Mechanical Engineering

Problem Definition

Background

The R&D lab at Hotstart is charged with testing new product designs for a wide range of markets that use diesel engines. During this testing process, a way to ensure product reliability in a short period of time is needed. Long term testing (1 year +) is not always a feasible option before releasing a product, so a way to speed up this test to the span of a month or two is necessary.

Hotstart manufactures two main types of coolant heaters. The first is a tank heater that uses the heat generated by the heating elements to force the hot coolant out of the top of the system into the engine while the colder coolant coming from the engine takes the place of the heated coolant in the bottom heater creating continuous flow (thermosyphon). The other style is forced circulation, where a pump is used to circulate the coolant across the heating elements and throughout the engine. Both styles use a bimetal snap-action thermostat to control the heating elements keeping the coolant inside the desired temperature range.

Layout Requirements

  • Maintain a small footprint to easily fit into test space
  • Be easily movable
  • Be able to simultaneously test 12 heaters (1kW or lower due to heating requirement)
  • Have adjustable flow settings if a heat transfer fluid is utilized
  • Allow for multiple voltage sources to power the heaters (1 or 3 phase, 120 – 690V)
  • Use components sourced from Hotstart’s current vendors unless absolutely not available
  • Contain all foreseeable spills automatically

Control Requirements

  • Run on 120V input voltage
  • Be capable of safely handling up to 12kW of heating input
  • Have adjustable temperature setting for heater input/output
  • Display or make available easily, critical data for each test “station” including, but not limited to: cycle count, power failure, heater failure, inlet and outlet temperatures
  • Be made from electrical components that are rated for at least 100k cycles at 50°C ambient or mitigate ambient conditions for components that are not properly rated
  • Be complete with all documentation along with a manual and troubleshooting guide. If a PLC is used, all documented code must be provided
  • Contain all branch circuit protection for all 12 heaters according to UL508A (We may need a supplier to build this part of the panel in order to get the proper sticker inside)
  • Be capable of simultaneously running multiple tests with different parameters and set points

Project Learning

Volume Testing
Experiment conducted to explore cycle times with smallest volume possible
  • Learned that volume could be reduced significantly by limiting the amount of hose and any reservoir
  • Found that heating times matched very closely with math model (curve shown below on plot)
Volume Testing
Math model created to compare cycle times achieved by relocating thermostat
  • Red line represents actual data collected from testing above
  • Due to high temperature gradients, average temperature must be much higher for thermostat to respond in its default configuration
  • Shows that cycle times also decrease by adding glycol
  • Maximum safe glycol concentration is 50%
Top-mounted thermostat
In order to further reduce cycle times of the engine heaters, we built a top-mounted thermostat. Because heat rises, the bottom mounted thermostat was not able to detect temperature changes quickly enough, which left us with huge temperature gradients in the system.
  • Much faster cycle times and less temperature variability in the heater loop
  • Utilizes the original thermostat (stock from heater) for simplicity
  • Final design enables quick installation and removal of two different types of thermostat

Design

Prototypes and testing

1st Prototype
"Sandbox" prototype.
  • Cooler full of water, cheap hoses, and some sealant
  • Roughly simulates the conditions a heater would experience in the field.
  • Learn about hose positioning and how to achieve proper thermo-siphoning behavior.
2nd Prototype
This prototype was used to test whether or not a valve could be used to prevent cold water from reaching the heater until it finishes a heating cycle.
  • Learned that without water flowing past the thermostat in the heater, the heater will not turn off
  • During testing, the heater boiled the water and was turned off before it became dangerous
  • This prototype demonstrates why it is beneficial to relocate thermostat
3rd Prototype
*Uses a small “circulation” tank so that proper thermo-siphoning can be achieved
  • The tank is small enough that cycle times can still be kept relatively short
  • When the heater has heated the volume of water, the system is flushed with water from a separate tank, and the cycle can start over.
  • Learned that there must be a breather tube on the small tank in order for air bubbles to escape the heater loop
  • Learned that, to reduce volume (and therefore cycle times), the small tank can be eliminated altogether.
4th Prototype
*Utilizes three solenoid valves per heater to trap liquid while heating (small volume=fast cycles)
  • Valves open when heater turns off, allowing a pump to flush the heater with cold liquid
  • Best performance and fastest cycle times, at the cost of added complexity and expensive equipment
5th Prototype
*Eliminates two of the three solenoid valves at each heater station, saving a lot of money
  • Valve opens when heater turns off, allowing a pump to flush the heater with cold liquid
  • Slower cycle times due to solenoid removal
  • Centrifugal pump supplying a manifold with positive pressure to flush heaters

Physical Layout

Physical layout.jpg

Rendering showing the final physical layout of the system

  • Stacked cell design saves space by putting one cell on top of the other
  • Steel table construction can be created with castors
  • Each heater station allows for mounting of 1kW heaters as well as enough room for larger tank heaters
  • Wall outlining table surfaces automatically containing spills

System Diagram

Final System Layout.jpg

This design uses two cells that can operate at independent temperatures. Each cell can be used to test six 1kW heaters at once.

Design features

  • Cold reservoir: A refrigeration unit keeps a 10 gallon tank of coolant at a constant temperature of 40 degrees F
  • Heater reservoir: Each cell contains a heater reservoir which is used to supply coolant to each heater in that cell at a desired temperature (colder than 100F)
  • Heat exchangers: A plate & frame heat exchanger is used to exchange heat between the heater tank and cold tank for each cell
    • The cold side is supplied by the cold reservoir and is pumped in series through both heat exchangers. Because of this design feature, the coldest temperature set point should be chosen closest to the cold reservoir.
    • The hot side is supplied by a pump connected to the heater reservoir. The pumps will only be used to keep the coolant in the heater reservoir within the limits of the specified temperature, for example 70F +-2F. In order to achieve this, a solenoid valve will control flow through the hot side of the heat exchanger.
  • Heating cycle: Each heater will heat a small volume of coolant in a closed loop until the coolant reaches 120F. At this point, solenoid valves will open the loop and allow coolant from the reservoir to flush the loop, and the cycle starts over.
  • Pressurized rails: Each cell uses a pump to pressurize a manifold of fluid which is used to flush a heater at the end of its cycle.
  • Valve control: Each valve in the system will be controlled by a master controller. The valves in the heating cycle loops will open or close depending on the status of the heater (on/off).
  • Thermostat override mode: Each heater will be able to operate based on user input heating temperatures rather than the automatic temperatures built into the thermostats
  • Test information: A master display will show the following information about all of the heaters
    • Cycle counter
      • Average time/cycle
      • Predicted completion time to desired cycle count
    • Heater Status (on/off)
    • Inlet/outlet temperatures of heaters as well as reservoir temperature
    • Emergency/error alarm with built-in cycle shutdown