Title of Invention

"AN IMPROVED CONSTANT TEMPERATURE BATH "

Abstract

The present invention relates to an improved constant temperature bath having screw type vertical stirring of the liquid medium to enable to create a vertical isothermal zone for better constancy of temperature in the chamber of the bath, thereby avoiding the drawback of unwanted temperature gradients. The device of the present invention can be well used for the calibration of long stem temperature sensors.

Full Text

The present invention relates to an improved constant temperature bath Control of environmental conditions is very important in many industries and quality control systems. The main parameters are relative humidity and temperature. Control and monitoring of these parameters is very essential in industries like food processing, pharmaceuticals, electronic manufacturing, quality assurance laboratories like the standards laboratories. The present invention particularly deals with the aspect of maintenance of constant temperature isothermally in a container. Constant temperature baths are of immense use in many industrial applications where maintaining constant temperature is essential. Such constancy in temperature is required in mobile freeze devices transporting food over long distances needing days of transportation time. In industrial quality control constant temperature baths are needed for calibration laboratories for calibration of thermometers and other temperature measuring instruments. Temperature baths using liquid and gas media for heat transmission within the containers are available in the market. Notable among these, is the use of liquid medium for effecting heat distribution within the container for effecting constancy of the temperature. The range of temperature covered in these systems is between -90 ° C to 400 ° C with a stability of ± 0.05 ° C. Reference may be made to CtJSJPatent No.3985Sj>bf 1976 which describes a temperature bath mainly for laboratory use only, without any mechanism to ensure constancy of temperature. In yet anotherU.JS_Patent ( No.5092556)of Dec. 1997) a constant temperature chamber has been described which uses liquid/air exchange medium but without any system for effecting uniform heat distribution for effecting constancy of temperature. The main disadvantages of these baths have been the wider base area but of low immersion depth not exceeding about 30cm , and hence result in developing undesirable temperature gradients in the bath chamber at each level leading to low stability due to the large chamber dimensions. From the existing product survey and practical use in the laboratory, we have observed that the temperature baths of some of the imported manufacturer such as Julabo & Lauda, Germany, Haake & Rosemount, U.K. and Isothermal Technology, U.S.A. etc., though are good in temperature stability, automation and with better provision for safety measures, are not suitable for comparison of long stem type sensors due to their low depth, particularly in the area of calibration of temperature sensors. In these commercially available instruments, increase of the length to accommodate long stem sensors results in developing undesirable temperature gradients thereby rendering them unsuitable for precision calibration work. The main objective of the present invention is to provide a an improved constant temperature bath which obviates the drawbacks mentioned above. Another objective of the present invention is to provide a bath having screw type vertical stirring of the liquid medium to enable to create a vertical isothermal zone for better constancy of temperature in the chamber of the bath, thereby avoiding the drawback of unwanted temperature gradients. Still another objective of the present invention is to provide a long immersion depth enabling for the calibration of the long stem temperature sensors. Yet another objective of the present invention is to provide an economically viable, transportable and stable temperature bath. In the drawing accompanying the specification Figure-1 represents an embodiment of the improved constant temperature bath of the present invention. The cross-sectional view of the improved constant temperature bath of the present invention shows a vertical tubular chamber (1) housing another chamber (2). An insulating material with a radiation shield (3) is filled between the chambers (1) and (2). The chamber (2) has an open end at the top and is capable of being closed by a cover (4) The said cover (4) has holes to insert temperature sensing device and means for supporting stirring system (8). The chamber (2) is filled with a liquid the temperature of which is to be maintained constant. The stirring system (8) comprises a tubular bottom open shaft ( 5) connected to the cover (4). The tubular shaft (5) extending almost to the bottom of tubular container (2). The said tubular bottom open shaft (5) having a co axially placed rotatable shaft (6). The rotatable shaft (6) has attached to it angular screw type fins (7) throughout the length of the tubular bottom open shaft enclosure (5). The screw type fins are arranged at an angle of 45 to 70 ° to the vertical rotatable shaft (6). The said arrangement of screw type fins is held in position by means of a cross strip attached to the bottom of the tube (5). The stirring system is capable of being moved by a prime mover (8). A heating element (10) for heating the liquid is provided. The heating element (10) and a cooling system (11) are provided for varying the temperature of the bath . Accordingly, the present invention provides an improved constant temperature bath which comprises two co-axially placed vertical tubular containers [1] and [2], one [2] inside the )c_ v\(T*9'V«-' (_r*S*~\$ f~*&^ bv»*UA/»- other [1] and having art insulating material with\radiation shield [3] between them, the inner.' .„ j chamber [2] being provided with a top cover [4] capable of holding a stirring system f essentially consisting of a tubular bottom open shaft enclosure [5] extending almost to the bottom of the said tubular container [2], the said shaft enclosure [5] being provided with a co-axially placed rotatable shaft [6] having angular screw type fins [7] throughout its length covering the full length of the said shaft enclosure [5], the top of the said rotatable shaft [6] being connected by known means to a prime mover [8] and the bottom end [9] being rotatably fixed by known means to the bottom end of the tubular shaft enclosure [5], the said inner vertical tubular container [2] being provided by known means for controlled heating [10] and cooling [11]. In an embodiment of the present invention the insulating material used may be such as asbestos, glass wool, ceramic fibers and the radiation shield used may be such as aluminum foil. In another embodiment of the present invention the angular screw type fins may be at an angle in the range of 45 to 70° with the vertical rotatable shaft (6). In still another embodiment of the present invention the prime mover used may be such as a variable speed motor. The device of the present invention is an useful isothermal bath with an automatic temperature controlled tubular structured chamber having an apertured cover for supporting known laboratory temperature measuring instruments. An electrically heated chamber with an overflow as well as inlet pipe is provided in the bath. The bath is provided with a stirring system to produce a vertical movement of fluid vigorously inside the chamber to reduce thermal gradients. For subzero temperature range the bath is provided with refrigeration system with single stage compressor cooling. In an embodiment of the present invention the bath chamber or tank was chosen of circular cylinder to maintain uniformity in temperature distribution along the whole depth of the chamber. The chamber may be made of metals like stainless steel, mild steel, copper, brass or of nickel with mouth diameter of 100mm and depth of 450mm suitable for longer stem sensor probes. A heating system is used in the chamber. The chamber was wrapped with an insulating layer of glass wool and then heating element of nichrome wire strip was wound non-inductively all along the length of the chamber at uniformly displaced positions. This provides an uniform resistance heating to the chamber tube. The wattage of the heater was variable and kept to be of the order of 2KW at maximum temperature of 300°C and 0.5KW at lower temperature at -10°C. For use art temperatures below -10°C , a cooling system is provided . The cooling in the bath is obtained by a single stage compressor with Freon F-12 gas. The cooling pipe in the spiral form is mounted inside the bath chamber along the inner wall of the chamber to produce uniform cooling. A continuous cooling with a controlled heating at a required set temperature makes the bath stable at the set point. The balance of heating and cooling produce a significant control of bath temperature with a desired stability during operation of the bath. In an embodiment of the present invention an encased stirring system is used in the bath. The stirring is an important part of the bath which makes the bath uniquely differentiated from the other commercially available temperature baths. A screw type design of stirring is provided in the bath to maintain vertical movement of the bath liquid from upper end to lower end and a vertical isothermal condition is achieved which is important to reduce the thermal gradient along the depth of the bath chamber. The speed of the motor is so chosen to provide a vigorous movement of the bath fluid in the chamber by external coupling of motor to stirrer shaft and also not to produce gaps within the liquid otherwise thermal gradients will be produced and stability of the bath will significantly be reduced. In present invention, thermal insulation is provided in the bath. The choice of thermal insulating materials used in the bath for stablising the bath temperature is also an important part which plays a significant role for attaining the stability condition in the bath chamber. The insulation is so chosen to work at higher temperature side in a way that it should be both electrically as well as thermally to be perfectly non-conducting or with a very low thermal conductivity (K-value). For our baths which can work at an operating temperature of about 300°C or so we have used a combination of insulating material glass wool, asbestos and ceramic fibres in layer forms and provided with aluminum foil as radiation shield in the baths. These materials are suitable insulating materials in this temperature range. To provide temperature control in the baths temperature controller is used through an auto-transformer (variac). The temperature is set in the controller and variac is used to heat the bath to the set value. The controller controls the overheating above the set point due to thermal inertia so that a stable temperature of a very long duration is maintained. The RTD Pt-100 temperature sensor is used to measure the bath temperature with a precision of ±0.005°C with a digital display of resolution of 0.01°C upto 100°C and 0.1 °C used upto 300°C. The bath temperature is set in the controller at any required value. The relay of the controller operates in a way to give a continuous on-off illumination by a neon bulb indicating the condition of stability of bath temperature. A compact control panel is provided for the constant temperature bath. This panel contains all the electrical illuminated switches, fuse, and voltage and current meters, mounted to operate the bath easily and safely. The temperature controller and its operating switch is mounted separately over the bath for easy setting of temperature in the bath. The indication of the on-off neon bulb is to signify the condition of temperature stability in the bath. The principle underlying the constant temperature bath is in providing isothermal conditions in the fluid medium which houses the article to be maintained at fixed temperature. The isothermal conditions are achieved by minimising the heat leaks into and out of the system. Further, the constancy of temperature is achieved over a long working space by effecting uniform distribution of the fluid by high speed vertical notion of the liquid. The Novelty of the present invention rests in : i) the ability to produce an uniform displacement of heated /cooled liquid to obtain an isothermal condition all along the bath chamber, ii) The ability to move the bath fluid to move in the vertical direction in upward to downward motion which produces an uniformity in the constancy of temperature over the entire length of the bath. The inventive steps resides in the encased screw type stirrer having angular screw type fins along its length. The angle between the rotatable shaft and the fins being in the range of 45 to 70 . The following examples are given by way of illustration only and should not be considered to limit the scope of invention. In the following examples an embodiment of the improved 'constant temperature bath of the present invention was used. The present constant temperature bath is usable in three distinct temperature ranges namely: -20 ° C to +30 ° C, 30° C to 95°C and 50°C to 300°C with just the change in the working liquid, and adjustment of the heat load input. The depth of the inner chamber of the bath is 450 mm. The temperature sensing element is the platinum resistance thermometer. The heating is provided by a nichrome heater wound un- inductively on the outer wall of the inner chamber all along the length of the chamber. The cooling is provided by using a copper coil spread throughout the chamber and fed with a freon gas though a single stage compressor. Exsmple-1 The bath was used in the temperature tange of -20° C to + 30°C . The liquid used was reagent grade methanol. 6 Litres of methanol was filled in the inner chamber housing the stirrer. The high speed motor was switched on and the stirring started to give vertical motion to methanol to ensure uniform temperature distribution of the liquid over the entire length of the bath. Next cooling was initiated by starting the compressor and continuously monitoring the temperature. As soon as the temperature of -10° C was reached the heater was switched on to maintain the temperature around the set point of -10°C. It took 1.5 hours to reach a constant set point. The temperature of the bath was measured at various points along the length of the bath and it was observed that the uniformity of the temperature was ± 0.02 ° C and the constancy of the temperature was ± 0.05° C. the stability and uniformity of the temperature was checked over a period of 1 hr. Example-2 The bath was used in the temperature range of -20 ° C to + 30 ° C . The liquid used was reagent grade ethanol. 6 Litres of ethanol was filled in the inner chamber housing the stirrer. The high speed motor was switched on and the stirring started to give vertical motion to methanol to ensure uniform temperature distribution of the liquid over the entire length of the bath. Next cooling was initiated by starting the compressor and continuously monitoring the temperature. As soon as the temperature of 0 °C was reached, the heater was switched on to maintain the temperature around the set point of 0°C. It took 30 mins. to reach a constant set point. The temperature of the bath was measured at various points along the length of the bath and it was observed that the uniformity of the temperature was ± 0.02 ° C and the constancy of the temperature was ± 0.05 °C. The stability and uniformity of the temperature was checked over a period of 30 mins. Example-3 The bath was used in the temperature range of-20 °C to + 30 ° C . The liquid used is reagent grade acetone. 6 Litres of acetone was filled in the inner chamber housing the stirrer. The high speed motor was switched on and the stirring started to give vertical motion to methanol to ensure uniform temperature distribution of the liquid over the entire length of the bath. Next cooling was initiated by starting the compressor and continuously monitoring the temperature. As soon as the temperature of 10° C was reached the heater was switched on to maintain the temperature around the set point of 10 ° C. It took 30 mins. to reach a constant set point. The temperature of the bath was measured at various points along the length of the bath and it was observed that the uniformity of the temperature was ± 0.02 ° C and the constancy of the temperature was ± 0.05 ° C. the stability and uniformity of the temperature was checked over a period of 30 mins. Example 4 The bath was used in the temperature tange of-20 °C to + 30° C . The liquid used was reagent grade methanol. 6 Litres of methanol was filled in the inner chamber housing the stirrer. The high speed motor was switched on and the stirring started to give vertical motion to methanol to ensure uniform temperature distribution of the liquid over the entire length of the bath. Next heating was initiated powering the nichrome heater and continuously monitoring the temperature. As soon as the temperature of 30° C was reached the heater power was adjusted to maintain the temperature around the set point of 30 C. It took 30 mins. to reach a constant set point. The temperature of the bath was measured at various points along the length of the bath and it was observed that the uniformity of the temperature was ± 0.02° C and the constancy of the temperature was ± 0.05° C. the stability and uniformity of the temperature was checked over a period of 30 mins.. Example 5 The bath was used in the temperature range of 20 ° C to 95 ° C . The liquid used was distilled water. 6 Litres of distilled water was filled in the inner chamber housing the stirrer. The high speed motor was switched on and the stirring started to give vertical motion to water to ensure uniform temperature distribution of the liquid over the entire length of the bath. Next heating was initiated powering the nichrome heater and continuously monitoring the temperature. As soon as the temperature of 30° C was reached the heater power is adjusted to maintain the temperature around the set point of 30° C. It took 45 mins. to reach a constant set point. The temperature of the bath was measured at various points along the length of the bath and it was observed that the uniformity of the temperature was ± 0.003° C and the constancy of the temperature was ± 0.005° C. the stability and uniformity of the temperature was checked over a period of 30 mins. Example 6 The bath was used in the temperature range of 20° C to 95° C . The liquid used was distilled water. 6 Litres of distilled water was filled in the inner chamber housing the stirrer. The high speed motor was switched on and the stirring started to give vertical motion to water to ensure uniform temperature distribution of the liquid over the entire length of the bath. Next heating was initiated powering the nichrome heater and continuously monitoring the temperature. As soon as the temperature of 50° C was reached the heater power was adjusted to maintain the temperature around the set point of 50° C. It took 30 mins to reach a constant set point. The temperature of the bath was measured at various points along the length of the bath and it was observed that the uniformity of the temperature was ± 0.003 ° C and the constancy of the temperature was ± 0.005° C. the stability and uniformity of the temperature was checked over a period of 30 mins. Example 7 The bath was used in the temperature range of 20° C to 95 ° C . The liquid used was distilled water. 6 Litres of distilled water was filled in the inner chamber housing the stirrer. The high speed motor was switched on and the stirring started to give vertical motion to water to ensure uniform temperature distribution of the liquid over the entire length of the bath. Next heating was initiated powering the nichrome heater and continuously monitoring the temperature. As soon as the temperature of 90°C was reached the heater power was adjusted to maintain the temperature around the set point of 90° C. It took 1 hour to reach a constant set point. The temperature of the bath was measured at various points along the length of the bath and it was observed that the uniformity of the temperature was ± 0.01° C and the constancy of the temperature was ± 0.003° C. the stability and uniformity of the temperature was checked over a period of 30 mins.. Example 8 The bath was used in the temperature range of 50 °C to 300° C . The liquid used was silicon oil. 6 Litres of silicone oil was filled in the inner chamber housing the stirrer. The high speed motor was switched on and the stirring started to give vertical motion to oil to ensure uniform temperature distribution of the liquid over the entire length of the bath. Next heating was initiated powering the nichrome heater and continuously monitoring the temperature. As soon as the temperature of 100° C was reached the heater power is adjusted to maintain the temperature around the set point of 100 °C. It took 1 hour to reach a constant set point. The temperature of the bath was measured at various points along the length of the bath and it was observed that the uniformity of the temperature was ± 0.001 °C and the constancy of the temperature was ± 0.03° C. the stability and uniformity of the temperature was checked over a period of 30 mins. Example 9 The bath was used in the temperature range of 50° C to 300 ° C . The liquid used was silicone oil. 6 Litres of silicone oil was filled in the inner chamber housing the stirrer. The high speed motor was switched on and the stirring started to give vertical motion to oil to ensure uniform temperature distribution of the liquid over the entire length of the bath. Next heating was initiated powering the nichrome heater and continuously monitoring the temperature. As soon as the temperature of 200 °C was reached the heater power was adjusted to maintain the temperature around the set point of 200° C. It took 1.5 hours to reach a constant set point. The temperature of the bath was measured at various points along the length of the bath and it was observed that the uniformity of the temperature was ± 0.001° C and the constancy of the temperature was ± 0.03 ° C. the stability and uniformity of the temperature was checked over a period of 30 mins. Example 10 The bath was used in the temperature range of 50° C to 300 ° C . The liquid used was silicone oil. 6 Litres of silicone oil is filled in the inner chamber housing the stirrer. The high speed motor was switched on and the stirring started to give vertical motion to oil to ensure uniform temperature distribution of the liquid over the entire length of the bath. Next heating was initiated powering the nichrome heater and continuously monitoring the temperature. As soon as the temperature of 300 ° C was reached the heater power was adjusted to maintain the temperature around the set point of 300 °C. It took 1.75 hours to reach a constant set point. The temperature of the bath was measured at various points along the length of the bath and it was observed that the uniformity of the temperature was ± 0.008° C and the constancy of the temperature was ± 0.03°C. The stability and uniformity of the temperature was checked over a period of 30 mins. The main advantages of the present invention are - 1. The constant temperature bath accepts long stem thermometers for precision calibration . 2. The high depth of the bath (about 450mm deep) is suitable for calibration of not only of long stem glass thermometers but also long sensor probes and associated digital indicator or thermocouple based temperature sensors. 3. The insulation glass wool and fibre mat is so chosen to provide a strong barrier for arresting the set temperature value. The temperature profile of the bath with varying depths states the condition of stability in the bath. 4. The stirring mechanism can be easily replaced even during the operation of the bath. 5. Although the baths were designed and developed particularly keeping in view their use for calibration of thermometers and other associated temperature instruments but the principle used in these baths can also be utilized for other purposes such as testing of chemicals and their dependence on temperature, determination of softening points, freezing points of low melting materials and storing of food stuff, medical drugs etc. at maintained set temperature in the desired range -20°C to 300°C. 6. A very low quantity of bath fluid (4-51itres) is needed in this invention as compared to the baths available elsewhere to produce a good stability in the liquid chamber. 7. Considerable of low cost about l/5th as compared to the available liquid baths with similar features. 9. The temperature distribution by screw type stirring over the bath chamber reduces the thermal gradients as compared to the static stirring or by pump stirring. 10. The dual provision of heating and cooling system in the bath with the stirring system provides operation of the bath over a wide range of temperature namely below -10°C to +300 °C. We Claim: 1. An improved constant temperature bath which comprises two co-axially placed vertical tubular containers [1] and [2], one [2] inside the other [1] and having .aVi insulating material with [radiation snield [3] between them, the inner chamber [2] being provided with a top cover [4] capable of holding a stirring system essentially consisting of a tubular bottom open shaft enclosure [5] extending almost to the bottom of the said tubular container [2], the said shaft enclosure [5] being provided with a co-axially placed rotatable shaft [6] having angular screw type fins [7] throughout its length covering the full length of the said shaft enclosure [5], the top of the said rotatable shaft [6] being connected by known means to a prime mover [8] and the bottom end [9] being rotatably fixed by known means to the bottom end of the tubular shaft enclosure [5], the said inner vertical tubular container [2] being provided by known means for controlled heating [10] and cooling [11]. 2. An improved constant temperature bath as claimed in claim 1, wherein the insulation material used is selected from asbestos, glass wool, ceramic fibers and the radiation shield is preferably aluminum foil. 3. An improved constant temperature bath as claimed in claim 1, wherein the angular screw type fins are at an angle in the range of 45 to 70oC with the vertical rotatable shaft[6]. '4, An improved constant temperature bath as claimed in claim 1, wherein the prime mover used is a variable speed motor. 5. An improved constant temperature bath substantially as herein described with reference to the foregoing examples and drawings.

Documents:

610-del-2000-abstract.pdf

610-del-2000-claims.pdf

610-del-2000-correspondence-others.pdf

610-del-2000-correspondence-po.pdf

610-del-2000-descritpion (complete).pdf

610-del-2000-drawings.pdf

610-del-2000-form-1.pdf

610-del-2000-form-19.pdf

610-del-2000-form-2.pdf