Heating Temperature Accuracy Control for Unburned Cigarettes Based on POSIFA’s Thermal Flow Sensors

Xiang Zheng Tu

 

Unburned cigarettes are becoming popular because they have been proved to reduce the health risks significantly. It has been shown that when shredded tobacco sample is heated at 10 ⁰C rate in nitrogen its weight loss curve delineates four regions: region I (30-120⁰C), related to the evaporation of water absorbed in the sample; region II (120-250⁰C), related to the emission of acetaldehyde, carbon dioxide, nicotine, and water; region III (250-370⁰C), related to the emission of acetaldehyde, carbon dioxide, nicotine, and more water; and region IV (370-550⁰C), related to the emission of more carbon dioxide and carbon monoxide.

A nicotine emission rate curve for the shredded tobacco sample is shown in the above figure. As can be seen, nicotine vapor is limited to form in the heating temperature range of 175 to 350⁰C. Since in this temperature range the tobacco is only heated but not burned it is impossible for the tobacco to emit any harmful chemicals such as CO, NO and NO_x. At the heart of any unburned cigarette is a sophisticated electronic controller. With such a controller the temperature of the heater is controlled just in the predetermined range.

Again reference to the above figure an electronic controller is designed based on a POSIFA’s thermal flow sensor. The thermal water flow sensor is made up of two thermopiles and operated in conjunction with a resistive heater element for thermoelectric sensing. The mass flow rate of air passing through the thermal flow sensor is calculated on the basis of the measured temperature difference between the hot and cold junctions of the thermopile, and the thermal conductivity coefficient, electric heat rate and specific heat of air.

For air flow rate measurement the house of the unburned cigarette is selected to be a bypass configuration which has a main line and a bypass line. The thermal flow sensor is installed in the bypass line. The flow ration between the main line and the bypass line is determined in advance. Then the flow rate of the main line can be calculated by measuring the flow rate in the bypass line by the thermal flow sensor.

The output of the thermal flow sensor is sent to a microcontroller for digital processing and converted into a PWM signal used to modulate a heating voltage for heating the heater of the cigarette. The microcontroller also processes the output of a temperature sensor which is used to monitor the heated heater. The microcontroller is operated with a program so that the heater is heated up to 175 to 350°C, while monitoring the temperature to ensure a consistent taste experience for user and to avoid burning. It also has an over-heating protection function, which turns itself off if necessary.

In a traditional unburned cigarette a puff at 120 s usually create a sudden and significant temperature drop due to the cooling effect by incoming air. This temperature drop by puffing became less significant with the thermal flow sensor based microcontroller. This is because the longer puff can be detected by the thermal flow sensor and feedback to the microcontroller for providing higher heating voltage. Since any puff can be detected by the thermal flow sensor the switch function for applying electric power can be replaced by the puff itself. And the heating temperature also can be increased according to the strength of the puff so that the used more enjoy the real taste of the unburned cigarettes.

Smart House Water Consumption Systems

Xiang Zheng Tu

 

Our smart house water consumption systems are based on proven thermal water flow sensors. As shown in the above figure, the smart house water consumption system mainly consists of a variable frequency water pump, a house water filter, two POSIFA’s thermal water flow sensors and a smart phone.

A thermal water flow sensor is made up of two thermopiles, which is used as the sensing temperature difference element and operated in conjunction with a resistive heater element for thermoelectric sensing. The water mass flow passing through the thermal sensor is calculated on the basis of the measured temperature difference between the hot and cold junctions of the thermopile, and the thermal conductivity coefficient, electric heat rate and specific heat of water. Compare with other type of water flow sensors the thermal water flow sensors have the advantages as:

·       Thermal water flow sensors have no moving part and no any mechanical failures to take place.

·       Thermal water flow sensors are MEMS devices with small size, higher sensitivity, higher reliability, low power consumption, ease of fabrication, and low cost.

·       Thermal water flow sensors calculate mass flow rather than volumetric flow and do not require temperature or pressure correction, which means there is no additional expense for the purchase and installation of additional equipment.

·       Thermal water flow sensors provide excellent accuracy and repeatability over a wide range of flow rates using bypass flow tube design. The sensor is placed in a bypass around a restriction in the main pipe and is sized to operate in the laminar flow region over its full operating range. 

·       Thermal conductivity water flow sensors are not influenced by the air bubbles entrained in the water. The effect of the bubbles can be added to the series conductivity by using conductivity of the air-water mixture for the water conductivity. The thermal conductivity of continuous water phase with entrapped air bubbles can be calculated.

The variable frequency water pump is equipped with a viable frequency drive. The viable frequency drove is used to adjust the speed of an electric motor by modulating the power being delivered. It provides continuous control, matching motor speed to the specific demands of the water flow. This makes the pump more efficient and also saves the user money by reducing excess energy from being wasted. When a user implements the variable frequency pump benefits are experienced over the life cycle of the pump. On an average 85 percent of a pump’s life cycle cost is attributed to its energy consumption and only 15 percent the actual cost of the pump motor. Motors associated with pumps tend to be sized where the pump may to meet peak loads, but not necessarily for normal continuous operation. Typically, for every 1 percent reduction in the variable frequency drive output the user can save 2.7 percent of energy costs. As energy consumptions continue to rise, it will become more imperative to find ways to cut energy consumption. Variable frequency water pump application is a key aspect to this effort.

The variable frequency drive is controlled to maintain a constant water flow in the output pipe. The down thermal water flow sensor measures the flow rate in the pipe to the water service and as this change sends a signal to the smart phone, which in turn sends a speed demand signal to the drive and this in turn adjust the speed of the motor so that the water flow rate reaches the presetting value. 

The water flow date measured by the down thermal flow sensor can be reviewed and analysis by the smart phone. The screen of the smart phone displays variety of water flow readings including average, minimum, maximum water flow rate, and total water and energy consumption in a month or year. With these data users may understand exactly when, where and how much water they’re consuming in their home on a daily basis.

The water filter takes away impurities from water, like chlorine taste, odor, zinc, copper, cadmium, and mercury. There are several water filters for soft water filtration like activated carbon filters, reverse osmosis, alkaline water ionizers, UV filters, and infrared filters. These filters are inexpensive but they require frequent replacements. Replacing water filter depends on several factors. Water filters typically have an estimated life cycle. However, this is only a guideline based on average water use. This isn't always a good indicator since water use varies per user. Referencing to the figure, the up thermal flow sensor and down thermal flow sensor respectively monitor the input and output water flow rate of the water filter. When the drop in flow rate passes a predetermined value then it’s time to change the filter.

Constant Water Flow System with Thermal Water Flow Sensor and

Variable Frequency Pump

Xiang Zheng Tu

 

It has been reported that electrical energy consumed by pumps, fans and compressors represents a significant proportion of the electricity used around the world. It is estimated that in industrial processes and building utilities, 72 % of electricity is consumed by motors, of which 63 % is used to drive fluid flow in pumps, fans and compressors.

Many heating, cooling and ventilation distribution systems operate at a constant flow rate, even though peak demand may only be required for a few hours. The conventional response to meeting the changing demand for heating and cooling within a building is to restrict flow to individual rooms, while maintaining peak flow in the central system. However, through the use of this approach, considerable energy is used and equipment lifetime is shortened.

For saving energy a better approach is to use a variable speed drive on pumps and fans to vary air or water flow to meet more precisely changing load demands. As shown in the above figure, a constant water flow system comprises a variable frequency pump and a POSIFA’s thermal flow sensor. When the water flow decreases in the user pipe the thermal flow sensor measurement signal decreases. This signal feedback to the variable frequency inverter and results its output frequency decreased. With decreased frequency the operation speed of the variable frequency pump is also decreased and the water flow in the user pipe starts to drop back as to original balance. When the water flow increases the similar process will happen only the direction is opposite.

There is an everyday analogy that can help explain the efficiency advantage of a variable frequency pump.  Imagine you are driving a car. If you are driving on a highway and entering a population area, speed must be reduced so that you do not risk your own and other lives. The best possible way to do that is to reduce motor-rotation speed by taking your foot off the gas pedal and, if necessary, changing to a lower gear. Another possibility would be to use the same gear, keeping your foot on the gas, and at the same time reducing speed simply by braking. This would not only cause wear in the engine and brakes, but also use a lot of fuel and reduce your overall control of the vehicle, which is the case for a "control valve."

In most traditional cases, the variable frequency pumps are controlled to maintain a constant pressure within air ducts or water pipes in which the pressures are measured by pressure differential flow sensors. The differential pressure flow sensor is based on Bernoulli’s Equation, where the pressure drop is a squared function of the fluid velocity.

This relationship can limit the ability of differential pressure sensors to measure large flow ranges. Generally the flow measurement range of 10-100 flow units (10:1 flow turndown) would require a differential pressure flow sensor range of 1-100 differential pressure units (100:1 differential pressure turndown). Therefore, the actual 10:1 flow turndown requires a 100:1 differential pressure flow transmitter turndown.

It would be much better to use the thermal flow sensors replacing the pressure differential flow sensors for controlling the variable frequency pumps. The thermal flow sensor measurement is based on heat transfer from a heated element. The measurement is in mass flow, and additional pressure and temperature correction is not required which is not like the pressure differential flow sensors. They also provide excellent accuracy and repeatability and are easy to install.