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Arduino based temperature and humidity control for
condensation on wettability engineered surfaces
Rohit Gupta*
Department of Power Engineering
Jadavpur University
Kolkata 700098, India
*Corresponding author- rohit.ju.pe@gmail.com
Chayan Das
Department of Power Engineering
Jadavpur University
Kolkata 700098, India
Ankit Roy
Department of Power Engineering
Jadavpur University
Kolkata 700098, India
Ranjan Ganguly
Department of Power Engineering
Jadavpur University
Kolkata 700098, India
Amitava Datta
Department of Power Engineering
Jadavpur University
Kolkata 700098, India
Abstract—Condensation is a ubiquitous phenomenon which
depends on several factors, ranging from the degree of
subcooling to the relative humidity of the condensing
environment. Characterizing condensation in experimental
setups, therefore, requires a proper control strategy of
operating parameters. Although industrial vapor chambers are
available for carrying out condensation experiments under
precisely controlled environments, these setups are
prohibitively expensive. Here we have developed a low-cost,
prototype vapor chamber that is equipped with advanced
control systems. Environmental control aspects of a Styrofoam-
made condensation chamber are developed in-house for testing
condensation on wettability engineered surfaces. Peltier-heat
sink arrangement is used to cool the condenser surface under
study and the desired relative humidity is maintained within
the chamber by means of spraying deionized water with a
nebuliser. In order to automate the process, an Arduino
Duemilanove board is amalgamated with the setup.
Temperature is controlled by an ON/OFF trigger-driven
mechanical relay connected to the Arduino environment, which
in turn generates an opportunely amplified signal to control the
supply voltage of the Peltier element. A K-type thermocouple is
interfaced to the Arduino board with the help of MAX31855K
thermocouple amplifier for measuring the plate temperature.
For humidity and chamber-temperature monitoring, an
SHT35D sensor is used. The relative humidity of the chamber is
maintained by a mechanical relay-driven spray arrangement.
The time-domain plots of humidity and plate temperature
response indicates that the temperature fluctuations are within
0.25q
q
C and RH fluctuations are within 0.5% about the set-
point. Transient response of the temperature and RH data are
monitored by the Serial Monitor of Arduino software, which
indicates that the set values of temperature and RH are
obtained approximately within 0 to 1000 seconds.
Keywords—Condensation; Temperature Control; Humidity
Control; SHT35D; MAX31855K
I. INTRODUCTION
Condensation is a phenomenon that is not only
omnipresent in nature, but it also plays an important role in
wide range of industrial applications including power
generation, water desalination, industrial processes, heating
ventilation and air conditioning (HVAC). In most of these
applications, a high condensation heat transfer coefficient is
desired to improve energy efficiency. Typically it has been
seen that condensation is highly dependent on
physicochemical characteristics of condenser surface, and
the thermophysical and conditions of the condensing
medium [1]. Primarily there are two modes of condensation
heat transfer, dropwise condensation (DWC), which
predominantly occurs on hydrophobic surfaces, and
filmwise condensation (FWC), which occurs on hydrophilic
surfaces. While the literature on influence of condenser
surface wettability on DWC and FWC in pure steam has
been extensively studied over several decades [2], the
literature is still replete with controversial results when it
comes to the study of DWC in presence of noncondensable
gases (NCG) [3]. For characterizing such condensation
process on novel surfaces, controlled temperature and
humidity environment chambers (EC) equipped with precise
control systems are required. Majority of these studies have
used off-the-shelf, proprietary ECs with complex
Proportional-Integral-Derivative (PID) control algorithm for
controlling the ambient conditions. While these ECs offered
reasonably good control, inquiry by us revealed that all
these ECs were prohibitively expensive. Here, we attempted
to develop a low-cost EC that is custom-designed for
condensation experiments under NCG-vapor condition.
Such an arrangement would warrant a precise control of the
cooling plate (usually a Peltier cooler) and the temperature
and relative humidity (RH) inside the chamber.
Several researchers have previously fabricated air de-
humidifiers, based on PID that controlled the voltage to the
Peltier cooler by Pulse Width Modulation (PWM) of the
signal [4, 5,6,7, 8]. But the Peltier elements need to be
operated near their maximum efficiency point.
Implementation of PID will increase or decrease the applied
voltage too much about the Peltier set-point, which will
affect their performance.
To circumvent this problem, the authors have developed
a robust, low cost, yet accurate EC which can perform
condensation experiments over a wide range of RH (from 60
to 98 %) and a surface temperature ranging from 3 to 15 qC.
The chamber is fabricated in such a way that it enables
optical imaging and Schlieren imaging of the condensation
surface in order to study the influence of vapor-NCG
boundary layer profile on DWC or FWC heat transfer. The
whole environment control process is automated and
monitored in real-time by an Arduino processor. The paper
is structured as follows: in section II the proposed
experimental setup and its subcomponents are described.
The control strategy and connection diagrams are detailed in
section III. In Section IV the accuracy of the adopted control
algorithm is discussed and a set of successful condensate
collection data is also tabulated. Finally in section V and VI
the observed results are summarized and some future
possible developments are suggested, respectively.
II. EXPERIMENTAL SETUP
Fig. 1. Schematic of the experimental setup
In the proposed experimental setup for characterizing
condensation, the cold side of the TEC-12706 (Make –
Hebei I.T co. ltd) Peltier element (having dimensions
4u4u0.39 cm3) is attached to a copper block (Dimension –
6u6u5 cm3) using a thermal paste (Omegatherm 201,
Omega). The opposite face of the copper block is exposed to
the interior of a Styrofoam chamber of inner dimension
31u35u22 cm3 and 6 cm wall thickness. The four side-faces
of the copper blocks are insulated using double-sided Teflon
tapes. In order to maintain the cold side of the copper block
at a nearly isothermal condition (thus ensuring one-
dimensional steady heat conduction through the block), the
heat generated by the hot side of the TEG is continuously
removed by an aluminum heat sink of and a brushless DC
(BLDC) fan. The thermal contact between the Peltier
element and heat sink is also established by the same
thermal paste. The arrangement (see Fig 1) is such that the
heat sink is exposed to the atmosphere whereas the TEG is
placed within the thick wall of the EC. An aluminum
substrate (Dimension - 6.5u6.5 cm2) of known wettability is
mounted (using thermal paste) on the inner face of the
copper block, which experiences a drop in temperature as
the Peltier element is powered. When surface temperature
on the test plate drops below the dew point temperature
corresponding to the environment inside the EC,
condensation of water vapor begins on the test plate. A
fiber-glass window is installed on the opposite (to the test
plate) wall of the EC for optical imaging of the test plate.
Two windows in Line of Sight (LOS) grazing over the
condenser surface are also provided for Schlieren imaging
purpose. An effervescent atomizer-based nebulizer (Model
NE C25S) and a mixing fan arrangement is used to supply
required amount of deionized water within the EC in order
to emulate different relative humidity (RH). A K-type
thermocouple (Make - Omega) is used for measuring the
plate temperature whereas SHT35D (Make - Sensirion)
sensor module provides the temperature and RH data of
ambient condition within the EC. For comparing the
accuracy of the temperature readings of the copper block,
another K-type thermocouple is connected to a standard
DAQ (Make - Agilent). The temperature and humidity
control process is automated and monitored by an Arduino
Duemilanove development board. The details and working
principle of the different components of the controller will
be discussed in the following sub-sections.
A. ArduinoDuemilanove Development Board
The controller board used here is an Arduino
Duemilanove development board equipped with
ATMega328 running at a clock speed of 16 MHz. The
communication protocols feature UART/USART TTL (5V)
Serial communication, SPI, I2C. The board also has 14
digital I/O pins among which 6 pins can provide PWM
outputs of 8-bit/16-bit and 6 pins have a special feature of
taking analog inputs of 10-bit resolution. An
FTDI FT232RL on the board channels this serial
communication over USB.
Fig. 2. Arduino Duemilanove development board.
B. SHT35D RH and temperature sensor
The SHT35D (see Fig. 3) is a combined temperature and
relative humidity sensing breakout board which
communicates with ATMega328 using I2C protocol which
can speed up to 1 MHz. It has a typical accuracy is r1.5 %
for RH and r0.2qC for temperature readings. The SDA and
SCL pins of the breakout board are connected to the A4 and
A5 pins of the Arduino board respectively. The sensor
monitors the ambient temperature and RH % inside the
vapor chamber. An SF2 filter cap is used to prevent
penetration of water droplets inside the sensor.
Fig. 3. SHT35-D RH and temperature sensor module (by Sensirion)
C. K-type thermocouple and MAX31855K amplifier
In order to monitor and control the temperature of the
wettability-engineered test surface of condenser, a K-type
thermocouple is installed at the interface of cold side
exposed to the vapor chamber and test surface with the help
of thermal paste. The thermocouples provide a differential
voltage across its terminals for each degree of temperature
change. In order to decode that change a MAX31855 (see
Fig. 4) cold-Junction Compensated Thermocouple-to-
Digital Converters by Maxim Integrated were used to
acquire the generated Seebeck voltages. This converter
exhibits a 14-bit resolution (or 0.25°C) and a thermocouple
accuracy of ±2°C for temperatures ranging from -200°C to
+700°C for K-type.
The communication between ATMega328 and the
MAX31855K module is based on SPI (Serial Peripheral
Interface), a synchronous interface ideal for short-distance
communication. In our case we have a single master - single
slave configuration where the master is the Arduino UNO
board while the two slaves are the two MAX31855K,
selected acting on the respective ChipSelect pin. Every
second, using the SPI interface of the Arduino Duemilanove
board, a vector of temperature values is acquired and used
for further computations in the control loop.
Fig. 4. MAX31855K thermocouple voltage level booster.
D. Peltier Element
The copper block is cooled by two Peltier elements
(TEC-12706). It has maximum current and voltage ratings
of 6.4 Amps and 16.4 Volts. Heat is continuously extracted
from the hot side of the Peltier by dual-fin arrangement
equipped with a brushless DC Fan.
E. Relay Modules
Two relay breakout boards (see Fig. 5) are used, each
having two relays. One of the breakout board controls the
supply to the Peltier elements based on the temperature set-
point whereas the other board controls the stirring fan and
fogger arrangement. The Peltier relays control inputs from
two DC power supplies which are operated at 7 volts and
can supply up to 5 Amps. The Mixing fan relay bypasses 12
volt, 500 mA from another DC supply module whereas the
fogger control relay directly bypasses the 230 V, 50 Hz
household AC supply. All the relays are capable of handling
the different supply lines.
Fig. 5. Relay Module.
F. Power supply modules
In order to perform ground isolation for obtaining
uninterrupted thermocouple readings, the development
board, sensors, and logic trigger side of the relays are
powered by a 5 volt, 10000 mAh battery. The supply trigger
sides are connected to two separate variable DC supplies.
The mixing fan relay is fed with a 12 volt, 500 mA DC
supply. The Heat sink cooling fan is driven by a 12 volt, 1
amp DC adapter.
III. CONTROL STRATEGY
A. Connection layout and control sequence :-
The detailed discussion in previous section indicates that
the SHT35D should be interfaced to the I2C bus,
MAX31855 to the SPI bus and the relays will use digital
output pins of ATMega328 for their logical voltage trigger
side. Fig. 6 represents the connection diagram. The adopted
control algorithm is represented in Fig. 7. The control loop
for surface temperature is a single layer cascaded system
whereas for humidity control it is a double layer cascaded
control loop.
Fig. 6. Detailed connection layout.
Fig. 7. Process control algorithm.
IV. RESULTS AND DISCUSSION
A. Time-domain plot of condenser surface temperature:-
Fig. 8. Time domain response of temperature.
The time response (see Fig. 8) of condenser surface
temperature sensor output was plotted at different set-points
at which the condensation experiments are to be performed.
The sensor shows a nearly constant ramp down rate of
2.1qC/min for wide range of set-points. It also quantifies the
time at which the condenser surface reaches the set-point
from the start of experiment. This time can be termed as the
start-up time for the condensation experiments.
B. Time domain plot of chamber RH:-
Fig. 9. Time domain response of RH without condensation : Effect of
mixing.
For maintaining desired RH within the chamber, two
methods are adopted and compared with the help of time
domain response of RH. First method is by directly spraying
a fog of deionised water within the chamber and allowing
diffusive transport to homogenize the vapor concentration
within the EC. In the second method, a low-speed BLDC
fan is used to augment mixing of the sprayed fog droplets
within the EC. The fog-inlet port and the mixing fan are
installed far away from the condensing surface in order to
have minimal flow disturbance near the condenser plate and
ensure natural convection at the vicinity of condenser plate.
Clearly, the time domain curve (see Fig. 9) indicates that
mixing fan arrangement increases the chamber humidity at a
much faster rate and also minimizes the large amplitudes of
RH overshoot about the set-point. Therefore, the mixing fan
arrangement is chosen for the final experimental setup.
Fig. 10. Time domain response of RH : Effect of condensation (With
Mixing)
The comparison of chamber humidity response for runs
with and without condensation (see Fig. 10) is made to
ensure that the start-up time is minimal even when there is a
constant consumption of water (i.e., condensation takes
place) while the surface temperature is ramping down to
reach the set-point. For an RH set-point of 70% the
increment of charging time is nearly 50 seconds when there
is simultaneous humidity charging and plate temperature
ramp down. The same for an RH set-point of 95% is
approximately 400 seconds, which is negligible with respect
to total experimental time of 4 hours. A few random time
sampling was done for measuring the time duration of spray
(water addition time) and condensation (water consumption
time) with a stopwatch. The spray time is nearly equal to 20
seconds irrespective of the surface temperature but the
consumption time is a strong function of the difference of
chamber and surface temperature (the degree of
subcooling). Increasing the degree of subcooling will
decrease the water consumption time and will result in
frequent humidification of the chamber.
C. Condensate collection data:-
Condensation experiments were performed at different
environment and surface wettability (varying contact angle)
conditions. The measured quantity to characterize
condensation under various conditions is the amount of
condensate collected over a particular time. The area of the
condensation surface is 6.5u6.5 cm2. The salient data are
tabulated in Table-1.
Table- 1
Surface
Type
Time
of
test
(hrs)
Plate
Temp
(q
q
C)
Chamber
Temp (
q
C)
RH (%) Water
collecti
on
(gms.)
Hydrophilic
CA-81qr 1
4 8r
0.2
18r0.4 70r0.5 0.12
Hydrophilic
CA-81qr1
4 8r
0.2
18r0.4 85r0.5 1.3
Hydrophilic
CA-81qr1
4 8r
0.2
18r0.4 95r0.5 1.68
V. CONCLUSION
A simple, yet accurate control system without
implementing PID algorithm has been implemented to
design a low cost controlled humidity environment
chamber, custom-designed to perform condensation
experiments at user defined surface temperature and
humidity set-points. An Arduino Serial Monitor acquired
the real time data of the chamber humidity, chamber
temperature and condenser surface temperature. The
accuracy and stability of the experimental setup for
characterizing condensation depended on the environment.
The time response plots indicate that the temperature
fluctuations are within 0.25q C and RH fluctuations are
within 0.5% about the set-point, which is adequate for the
experimental accuracy for the study of condensation on
wettability engineered surface in presence of
noncondensable gases.
VI. FURTHER DEVELOPMENT
The future aspects of improving the environment
chamber include varying the ambient dry bulb temperature
with a help of a convective strip heater with the help of PID
algorithm. Further, for on-board process parameter
monitoring, a 16u2 LCD module can be interfaced with the
Arduino. Lastly for real time condensate collection
measurement a strain gauge load cell is to be installed.
Acknowledgment
The authors gratefully acknowledge the funding from DAE-
BRNS through the Project No. 36(1)/14/24/2016-BRNS.
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