Enhanced Heat Exchange Using Microchannel Array Architectures

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Enhanced Heat Exchange Using Microchannel Array
Architectures School of Chemical, Biological, and
Environmental Engineering Ted Carter and Paula
Pérez Rodríguez  
Results
Motivation Of all the water on Earth only 0.1 is
both potable and accessible to humans. Fresh
water shortage has become increasingly evident in
recent years as developing countries struggle to
keep booming populations hydrated. Water
pasteurization is commonly used treat
contaminated water sources. Solar energy is not
always available, and most microbes harmful to
humans can be killed at 65C. Since microchannels
provide dramatically improved heat transfer rates
as well as smaller equipment, such technology can
be used to treat water continually and
efficiently.
Heat Transfer Fundamentals
For 8 and 5 copper plates, the heat transfer was
worse than predicted, but for 1 copper plate the
heat transfer was better than predicted,. This
suggests that the copper plate temperature is not
uniform. The model assumed the system to be
adiabatic, but the heat loss was found to be
28, which may explain the differences between
the model and the experiment for 5 and 8 copper
plates.
Q Energy transfer rate (Watts) m Mass flow
rate of liquid (kg/s) Cp Liquid heat capacity
(J/kg K) U Overall heat transfer
coefficient ?T Log mean temperature difference
for parallel plates
h Convective heat transfer coefficient d
Characteristic channel dimension k Thermal
conductivity of fluid

• Objectives
• Design a small, low-cost microchannel water
• pasteurization system
• Model heat transfer within heat exchanger
• portion of device
• Measure energy recovery efficiency in
• device and compare to model predictions

Heat recovery zone of device uses copper metal to
conduct energy from the hot to cold water stream.
Thickness of copper plate is 5 to 8 times greater
than channel height.
Testing device The pump forces water into the
system, which heats the water using a
potentiometer controlled by a feedback loop. The
inlet and outlet temperatures for hot and cold
water are recorded.

• Metrics and Goals
• Maximize preheated water temperature
• Hold water at 65C for two seconds
• Maintain a pressure drop below 7 PSI
• Allow for a throughput of 20 mL/min

• Issues
• The pump does not have enough volume capacity to
  reach steady state.
• Tc1 thermocouple does not work.
• The heater does not have enough capacity to reach
  65C at high flow rates
• Thermocouple joints leak.

Think BIG, build SMALL
Looking at the heat transfer properties, the
system has its best result at higher flow rates
and smaller channel heights, but the number of
copper plates is not statistically relevant.
Pressure Drop as a Function of Channel Length and
Diameter
µ Viscosity V Volumetric flow L Length D
Channel height
Economic analysis
The maximum pressure drop allowed for this system
will be 7 psi in order to minimize the size of
the pump needed. Since the system has a total
length of 8 inches, the minimum diameter allowed
will be 250 µm for the target flow rate of 20
mL/min.

• A car battery has 12V and 40Ah ? This device can
  run for 32h
• 10 gal (38 L) per battery
• Device can be used in a stationary outlet or for
  emergency purposes.

References Introduction to Fluid Mechanics by
Fox et al, Fundamentals of Momentum, Heat, and
Mass Transfer by Welty et al.
This project was made possible by Todd Miller and
Steve Leith, our sponsors, and Dr. Philip Harding
for project guidance.