Liquid heating apparatus and operating methods

Abstract

An apparatus for dispensing a predetermined volume of a warm liquid includes a heater, a pump and a temperature sensor sensitive to the temperature of the liquid upstream of the heater. A controller is arranged to receive upstream temperature data from the temperature sensor, calculate the amount of energy required to reach a desired final temperature, energize the heater for a calculated period of ON time, and dispense liquid for a calculated period of time that is at least partly contemporaneous with the calculated period of ON time. After the heater has been de-energized, the dispensed liquid removes residual heat so that the average temperature after dispensing the predetermined volume is the desired final temperature.

Claims

1. A method of operating an apparatus comprising a heater and a pump to dispense a predetermined volume of a warm liquid, said method comprising the steps of: measuring the temperature of the liquid upstream of the heater; calculating an amount of energy required for the heater to heat the predetermined volume of the liquid from the upstream temperature to a desired final temperature; calculating a period of ON time required for energization of the heater to deliver the calculated amount of energy; energizing the heater for the calculated period of ON time; operating the pump during a first period of time to dispense a first volume of heated liquid at or above a predetermined initial temperature from an outlet of the apparatus, wherein the first period of time is at least partly contemporaneous with the calculated period of ON time; de-energizing the heater; and operating the pump for a second period of time subsequent to the first period of time, the second period of time being calculated such as to dispense a second volume of the liquid from the outlet of the apparatus so as to remove substantially all residual heat from the heater, the first and second volumes together providing the predetermined volume heated by the calculated amount of energy, wherein the average temperature of the first and second volumes of the liquid is the desired final temperature after the predetermined volume has been dispensed.

2. A method as claimed in claim 1, wherein the heater comprises a flow heater in which liquid is permitted to enter and exit the heater while heating is taking place.

3. A method as claimed in claim 1, wherein the step of calculating the energy required for the heater to heat a predetermined volume of the liquid from the upstream temperature to a desired final temperature comprises measuring the temperature of, or downstream of, the heater.

4. A method as claimed in claim 1, further comprising delivering a constant flow rate of the liquid through the heater.

5. A method as claimed in claim 1, wherein the pump is a positive displacement pump arranged to deliver a constant flow rate of the liquid through the heater.

6. A method as claimed in claim 1, wherein the desired final temperature is between 27 C. and 4 C.

7. A method as claimed in claim 1, wherein the second period of time is longer than the first period of time.

8. A method as claimed in claim 1, wherein the second volume of liquid is greater than the first volume of liquid.

9. A method as claimed in claim 1, wherein the predetermined volume of liquid is selected by a user.

10. A method as claimed in claim 1, comprising calculating the first and second periods of time for operating the pump to dispense the first and second volumes of liquid.

11. A method as claimed in claim 1, further comprising measuring the mains supply voltage and adjusting operation of the heater and/or of the pump to take into account the mains supply voltage.

12. A method of operating an apparatus comprising a heater and an arrangement for dispensing a predetermined volume of a warm liquid, said method comprising the steps of: measuring the temperature of the liquid upstream of the heater; calculating an amount of energy required for the heater to heat the predetermined volume of the liquid from the upstream temperature to a desired final temperature; calculating a period of ON time required for energization of the heater to deliver the calculated amount of energy; energizing the heater for the calculated period of ON time; dispensing a first volume of directly heated liquid from an outlet of the apparatus during a first calculated period of time, wherein the first period of time is at least partly contemporaneous with the calculated period of ON time; de-energizing the heater; and dispensing a second volume of liquid from the outlet of the apparatus for a second calculated period of time subsequent to the first period of time, the second period of time being calculated such that the second volume of liquid is heated by removing substantially all residual heat from the heater, the first and second volumes together providing the predetermined volume heated by the calculated amount of energy, wherein the average temperature of the first and second volumes of the liquid is the desired final temperature after the predetermined volume has been dispensed.

13. A method as claimed in claim 12, wherein the desired final temperature is between 27 C. and 47 C.

14. A method as claimed in claim 12, wherein the predetermined volume of liquid is selected by a user.

15. An apparatus for dispensing a predetermined volume of a warm liquid, comprising a heater, a pump, a temperature sensor sensitive to the temperature of the liquid upstream of the heater, and a controller arranged to: receive upstream temperature data from the temperature sensor, calculate the amount of energy required for the heater to heat a predetermined volume of the liquid from the upstream temperature to a desired final temperature, calculate a period of ON time required for energization of the heater to deliver the calculated amount of energy, energize the heater for the calculated period of ON time, operate the pump during a first period of time to dispense a first volume of heated liquid at or above a predetermined initial temperature from an outlet of the apparatus, wherein the first period of time is at least partly contemporaneous with the calculated period of ON time, de-energize the heater, and operate the pump for a second period of time subsequent to the first period of time, the second period of time being calculated such as to dispense a second volume of the liquid from the outlet of the apparatus so as to remove substantially all residual heat from the heater, the first and second volumes together providing the predetermined volume heated by the calculated amount of energy; wherein the average temperature of the first and second volumes of the liquid is the desired final temperature after dispensing the predetermined volume.

16. An apparatus as claimed in claim 15, wherein the heater comprises a flow heater in which liquid is permitted to enter and exit the heater while heating is taking place.

17. An apparatus as claimed in claim 15, comprising a reservoir for supplying liquid to the heating means, and optionally an intermediate holding chamber between the reservoir and the pump, wherein the temperature sensor is located in the reservoir or in the intermediate holding chamber.

18. An apparatus as claimed in claim 15, wherein the desired final temperature is between 27 C. and 47 C.

19. An apparatus as claimed in claim 15, comprising an input to allow the predetermined volume of liquid to be selected by a user.

20. An apparatus as claimed in claim 15, wherein the controller is arranged to measure the mains supply voltage and adjust operation of the heater and/or of the pump to take into account the mains supply voltage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Certain embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

(2) FIG. 1 is a perspective view of an appliance in accordance with an embodiment of the invention;

(3) FIGS. 2 and 3 are front and rear perspective views of the major internal components of the appliance shown in FIG. 1;

(4) FIG. 4 is a cross-sectional view of the water tank shown in FIGS. 2 and 3;

(5) FIG. 5 is a schematic diagram showing the flow of water, power and electrical signals through the appliance;

(6) FIG. 6 is a voltage measuring circuit diagram;

(7) FIG. 7 is flow chart outlining the main steps involved in a complete dispensing cycle according to a first embodiment;

(8) FIG. 8 is a plot of the operation of the appliance;

(9) FIG. 9 is a plot showing a temperature profile for water in the bottle;

(10) FIG. 10 is another flow chart outlining the main steps involved in a complete dispensing cycle according to a second embodiment;

(11) FIG. 11 is a plot showing operation and temperature profiles when dispensing a 120 ml volume of heated liquid according to the cycle of FIG. 10; and

(12) FIG. 12 is a plot showing operation and temperature profiles when dispensing a 330 ml volume of heated liquid according to the cycle of FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

(13) FIG. 1 is a perspective view of an embodiment of the invention and shows an appliance 1 for dispensing warm water for the preparation of infant formula milk from powdered infant formula. The appliance is shown with an outer housing 2, in which is provided a window 4 for viewing the water level in the internal water tank 6 (see FIGS. 2 and 3). On the right hand side of the housing 2 there are three user input buttons 8. These are used to set the timer when a new water filter has been installed, to run a cleaning cycle of the appliance 1, and to run a descaling cycle. A panel of LEDs 10 display various operational states of the appliance 1, i.e. a warning light to indicate that the water filter need changing. An on-off button 12 and rotatable dispense volume dial 13 are provided above the dispensing outlet 14, which is located above a drip tray 16. A baby bottle or cup 17 (shown in FIG. 5) can be placed on the drip tray 16 such that in use the heated water is dispensed into the bottle or cup 17, with the outer housing 2 having a vertically extending recess 18 between the drip tray 16 and the dispensing outlet 14 to accommodate the bottle 17.

(14) The major internal components of the appliance 1 can be seen in the perspective views of FIGS. 2 and 3, from the front and rear of the appliance 1 respectively, in which the outer housing 2 has been removed. The internal water tank 6 with its window 4 is shown on the left, and has an outlet 19 towards its base which feeds a water conduit 20. The water conduit 20 passes first through a pump e.g. solenoid pump 22 and then past a pressure relief valve 24 and through a pressure compensating constant flow valve 26. The pressure relief valve 24 vents back into the water tank 6 in the event of the water conduit 20 becoming over-pressurized. A suitable pressure compensating constant flow valve 26 is available from Netafim (www.netafim.com).

(15) After the pressure compensating constant flow valve 26, the water conduit 20 passes to a flow heater 27 in which a water flow tube 28 is brazed to a sheathed heating element 30. Cold tails 32 at either end of the sheathed heating element 30 connect it to a power supply (not shown). The water flow tube 28 passes to the final section of the water conduit 20 which then feeds to a dispensing head 34 and the outlet 14. The dispensing head 34 may take the form of an intermediate chamber receiving the liquid and/or vapor that exits from the flow heater 27. The dispensing head 34 may help to enable any steam to separate from the heated liquid so that there is a controlled flow out of the outlet 14 without any spitting.

(16) The inside of the water tank 6 can be seen in the cross-sectional view of FIG. 4 which shows that a water hopper 36 is provided inside the top of the water tank 6. It is this water hopper 36 into which untreated water, e.g. tap water, is placed. An anti-microbial filter 38 is located at the bottom of the water hopper 36 to allow water to drain into the bottom of the water tank 6 before it exits the tank via the outlet 19. Also can be seen is the inlet 37 into the water tank 6 from the pressure relief valve 24.

(17) Referring back to FIGS. 2 and 3, a number of temperature sensors are placed at various points around the heating system. First a temperature sensor e.g. negative temperature coefficient thermistor 40 protrudes through the wall of the water tank 6 to sense the temperature of the filtered water in the bottom of the water tank 6. A second temperature sensor e.g. negative temperature coefficient thermistor 42 is placed towards the exit end and on the outside of the sheathed heating element 30. Also, two bimetallic actuators e.g. half inch discs or thermal fuses 44, 46 (or other temperature sensing means) are provided on the outside of the flow heater 27, one in contact with just the water flow tube 28 and the other in contact with both the sheathed heating element 30 and the water flow tube 28. The two half inch discs or thermal fuses 44, 46 protect against the sheathed heating element 30 overheating. Such an arrangement of temperature sensing means in thermal communication with both the heating element 30 and the water flow tube 28 is also described in the Applicant's published application WO 2013/024286.

(18) The main components of the appliance 1 can also be seen in schematic form in FIG. 5, in which the flow of water, electrical signals and power is also shown. All the components are directly or indirectly controlled by an electronic controller 50 which receives electronic signals from various components and controls the power delivered to the sheathed heating element 30 and the solenoid pump 22. The electronic controller 50 is connected to a mains power supply 52 via a voltage measuring circuit 100. The sheathed heating element 30 is also connected to the mains power supply 52, with this being controlled by the electronic controller 50 via a switch 54 in the heater power supply circuit 56. In addition the pump 22 is connected to the mains power supply 52, with this being controlled by the electronic controller 50 via a pump power control 58.

(19) The electronic controller 50 receives electrical signals from the negative temperature coefficient thermistor 40 in the water tank 6 and the second negative temperature coefficient thermistor 42 on the sheathed heating element 30, as well as from the pump power control 58 and a water level sensor 60 (not shown in FIGS. 2 and 3) which detects that a minimum fill level in the water tank 6 has been reached.

(20) In accordance with other embodiments the solenoid pump 22 may be replaced with another kind of pump, for example a positive displacement pump 22 such as a piston pump. The pressure compensating constant flow valve 26 may be omitted, especially where the pump 22 is able to deliver a substantially constant flow rate through the flow heater 27 despite variations in water pressure. Yet other embodiments may omit a pump altogether, relying instead on a direct connection to an external supply such as the mains water supply and using a constant flow valve or regulator to ensure that the flow rate through the heater is known.

(21) FIG. 6 provides an example of a suitable voltage measuring circuit 100 connected between the live AC_L and neutral AC_N poles of the mains power supply 52 for the appliance 1. The circuit 100 measures the analogue voltage level AC_in and provides this to an A/D converter of the electronic controller 50 to give a digital input. The supply voltage V_in used by the electronic controller 50 is proportional to this digital input.

(22) Operation of the apparatus according to a first set of embodiments will now be described with further reference to FIGS. 7-9.

(23) When the apparatus starts a new dispensing cycle, it first conducts a preheating phase. The sheathed heating element 30 is turned on. The measured supply voltage V_in is used to calculate the instantaneous heating element power Q_dot according to Equation 1:
Q_dot=((V_in)^2/(V_cal)^2)Q_dot_cal (Eq. 1)
where V_cal and Q_dot_cal are the calibrated values of the heating element voltage and heating element power as determined during an initial calibration of the appliance (either after manufacture or when the appliance is first used). The appliance therefore accounts for variations in the mains supply voltage 52 every time it runs a dispensing cycle. Once the supply voltage V_in has been measured it is not monitored again during the same dispensing cycle.

(24) The electronic controller 50 then calculates the energy needed to heat a predetermined volume of liquid Vol_feed to a desired final temperature T_feed. The liquid volume Vol_feed may be set or selected a user via the input dial 13. The final temperature T_feed may be set or selected by a user, but for a baby formula appliance 1 it is typically pre-programmed e.g. T_feed =37 C. The temperature, T_tank, of water in the tank 6 is measured by the negative temperature coefficient thermistor 40 and provided to the electronic controller 50. Of course the ambient temperature for water in the tank 6 will vary depending on the ambient conditions. The total energy Q_total needed to heat the predetermined volume Vol_feed to the desired final temperature T_feed can then be calculated according to Equation 2:
Q_total=Vol_feedCp_waterTK1 (Eq. 2)
where T=T_feedT_tank, Cp_water is the specific heat capacity of the liquid being heated, and K1 is a compensation factor for heat losses. A typical value for K1 can be empirically determined from factory testing or calibration of the apparatus, and pre-programmed into the controller.

(25) The predetermined volume of liquid Vol_feed is dispensed in two stages, i.e. Vol_feed=Vol_initial+Vol_cold. The first volume V_initial is dispensed at a temperature T_initialdispense>70 C. to sterilize the milk powder in the bottle 17. The second volume V_cold is dispensed to remove the residual heat energy from the sheathed heating element 30 to bring the overall volume Vol_feed to the desired final temperature e.g. T_feed=37 C.

(26) It is necessary to preheat the sheathed heating element 30 to ensure that the whole of the initial dispense volume Vol_initial is dispensed hot enough. The sheathed heating element 30 is heated to a nominal target temperature e.g. T_target=210 C. to ensure that it is hot (due to the temperature gradients the water flow tube 28 should be just below 100 C. at this point). The actual temperature, T_element, of the sheathed heating element 30 is measured by the negative temperature coefficient thermistor 42 on the sheathed heating element 30. The energy needed for preheating Q_preheat is calculated according to Equation 3:
Q_preheat=mCp(T_targetT_element) (Eq. 3)
where Cp is the specific heat capacity of the heater and m is the mass of the heater.

(27) The preheat time t_preheat is then given by Equation 4:
t_preheat=Q_preheat/Q_dot (Eq. 4)

(28) The stored energy Q_stored in the system must be taken into account when calculating the total ON time (t_heater) for energizing the sheathed heating element 30. This is calculated according to Equation 5:
Q_stored=mCp(T_elementT_tank)K2 (Eq. 5)
where K2 is a compensation factor to take account of heat losses etc. which may be empirically determined and pre-programmed into the electronic controller 50. The factor K2 may be used to tune this part of the process so that the electronic controller 50 can abort a dispensing operation if the sheathed heating element 30 is detected to have overheated by one or both of the half inch discs 44, 46 on the flow heater 27.

(29) The calculated period of ON time, t_heater, for energizing the sheathed heating element 30 is then calculated according to Equation 6:
t_heater=(Q_totalQ_Stored)/Q_dot (Eq. 6)

(30) The first period of pump operation is required to dispense the first volume V_initial of heated liquid and this is calculated according to Equation 7:
Vol_initial=Q_total/(Cp_water(T_initialdispenseT_tank)K1) (Eq. 7)
where T_initialdispense is preset in the electronic controller 50 at a value of e.g. 95 C.

(31) The two periods of time for pump operation can then be calculated according to Equations 8 and 9:
t_pump1=Vol_initial/Flow rate (Eq. 8)
t_pump2=Vol_cold/flow rate (Eq. 9)
where the flow rate is that of the liquid entering the flow heater 27 as set by the pressure compensating constant flow valve 26. The flow rate is another value that may be calibrated for each appliance (either after manufacture or when the appliance is first used).

(32) FIG. 7 is a flow chart outlining the main steps involved in a complete dispensing cycle. It can be seen that the process starts by measuring the mains supply voltage V_in at that time so as to make an accurate calculation of the power Q_dot of the sheathed heating element 30. The electronic controller 50 then takes readings from the negative temperature coefficient thermistor 40 (NTC1) in the water tank 6 and the second negative temperature coefficient thermistor 42 (NTC2) on the sheathed heating element 30. From these inputs it is possible to calculate the preheat time before the pump 22 is operated for a first initial dispensing period, the time period for energization of the sheathed heating element 30, and the second period of pump operation to dispense the full volume of liquid required to make the infant feed in the bottle 17. The electronic controller 50 may be programmed to pause for a set period of time, t_pause, e.g. 30 s, 40 s, 50 s or 60 s, to allow a user to add infant formula powder to the initially dispensed water, or to stir the feed if the formula powder was already in the bottle 17. However the appliance 1 may be provided with a button or other input allowing a user to start the second dispensing period on demand.

(33) As is mentioned above, the flow rate of liquid entering the flow heater 27 is set by the pressure compensating constant flow valve 26 so as to have a constant value (e.g. 170 ml/min) regardless of any variations in the pump speed e.g. due to voltage fluctuations or as a result of age-related wear. Under certain circumstances it may be necessary to reduce the flow rate to provide the desired dispense temperature and this may be achieved by pulsing the pump on and off FIG. 8 shows a plot of the operation of the sheathed heating element 30 and the pump 22 overlaid on the temperature profiles sensed for the sheathed heating element 30 i.e. T_element 52, and the outlet temperature 54 measured at the dispensing head of the appliance. Also shown is the heater energization state 58 and the pump operation state 60. The starting temperature 56 of water in the tank 6 is constant e.g. T_tank=18 C. It can be seen that the temperature 54 measured at the dispensing head has an average value of around 85 C as the first volume of water V_initial is dispensed at this temperature T_initialdispense during the first period of pump operation t_pump1. The outlet temperature 54 then drops and rises again during the pause between the pump operation periods, as it begins to move into thermal equilibrium with the system and its stored heat. When the second period of pump operation, t_pump2, begins, there is a small volume of warm water dispensed through the outlet that has been sitting in the water flow tube 28, but this is quickly followed by most of the volume Vol_cold of unheated water that is pumped through during the period t_pump2. The outlet temperature 54 rapidly falls to match the ambient water (e.g. at 18 C.) that is being pumped through without any heating. The two volumes of water that are dispensed into the bottle 17 mix to provide the predetermined volume V_feed at the desired final temperature T_feed (e.g. set at 37 C.).

(34) FIG. 9 shows a temperature profile 62 for the dispensed water in the bottle throughout the operational cycle of the appliance. After the pump 22 is energized initially the water temperature very quickly rises to about 95 C. At the end of the first period of pump operation, t_pump1, the first volume of water, V_initial, has an average temperature of about 80 C. and this remains above 70 C. during the pause, t_pause, when the powdered infant formula is added to the bottle, ensuring sterilization of the powder. As the cooler water is dispensed during the second period of pump operation, t_pump2,the temperature 62 of the water in the bottle falls, reaching a final average of about 37 C. when the final volume of the water has been dispensed to make the overall volume, Vol_feed.

(35) As all the energy Q_dot input by the sheathed heating element 30 is used to heat the system it is not necessary for the appliance to measure the final water temperature T_feed, which can simply be calculated from Equation 10:
T_feed=T_tank+Q_dot/(m_feedCp_water) (Eq. 10)
where m_feed is the mass of the overall volume Vol_feed of liquid in the bottle 17.

(36) Operation of the apparatus according to a second set of embodiments will now be described with further reference to FIGS. 10-12. The flow chart seen in FIG. 10 shows the steps that may be taken when the apparatus is operated to continuously dispense a predetermined volume of warm liquid Vol_feed having a desired final temperature of T_feed e.g. 37 C. In this scenario the apparatus is not used to dispense a separate first volume V_initial at a particular predetermined initial temperature, i.e. no hot shot at 70 C. or higher. However, as can be seen from the heating profiles of FIGS. 11 and 12, some of the liquid may be dispensed at such temperatures during a first phase of operation but there is no pause for a user to knowingly mix infant milk formula with the liquid while it is at this temperature.

(37) According to FIG. 10 the heating element 30 is energized at substantially the same time as the pump 22, i.e. there is no preheating of the flow heater 27. As before, a voltage compensation circuit may be used to measure the voltage V_in applied to the flow heater 27. The electronic controller 50 calculates the heating element power according to Eq. 1 and then calculates the predetermined volume Vol_feed from the feed size (kg) input at the user interface MMI. The total energy Q_total needed to heat the predetermined volume Vol_feed to the desired final temperature T_feed can then be calculated according to Eq. 2. As Vol_feed is to be dispensed continuously, the time period for pump operation t_pump can simply be calculated according to Equation 11:
t_pump=Vol_feed/flow rate (Eq. 11)
where the flow rate is that of the liquid entering the flow heater 27. This flow rate may be set by an upstream pressure compensating constant flow valve 26, where provided, or it may be a known constant of the pump 22.

(38) The electronic controller 50 takes readings from the NTC1 thermistor 40 in the water tank 6 and the NTC2 thermistor 42 mounted on the heating element 30 to give temperatures T1 (=T_tank) and T2 (=T_element). The total temperature rise required to reach the desired final temperature T_feed e.g. 37 C. is DT or T=T_feedT1. The total energy required Q_total is then calculated using Eq. 2. For example, Cp_water=4180 and losses K1=1.1 (initial value of 10%). In order to take into account any heat energy stored in the system, the controller 50 also calculates G_stored using Eq. 5. The heater ON time t_heater can then be calculated from Eq. 6.

(39) The pump 22, 22 may be operated continuously or the liquid may be dispensing substantially continuously using a pulsed pump operation. For smaller volumes of liquid, the heater ON time t_heater may be almost as long as the pump ON time t_pump, at a constant flow rate, so the controller 50 checks whether pulsed pump operation is required, e.g. if t_heater>t_pump3s. The flow heater 27 is de-energized after the time t_heater has lapsed. The pump is operated (continuously or in a pulsed fashion) until t_pump has lapsed and residual heat has been removed such that Vol_feed has the desired temperature T_feed.

(40) FIGS. 11 and 12 shows the activation profiles for the heater 27 and pump 22, 22, as well as the temperature profiles for the water in the tank T_tank (measured by NTC1), the heater T_element (measured by NTC2) and the temperature of heated liquid being dispensed into a bottle at the outlet. FIG. 11 shows the profiles for Vol_feed=120 ml and FIG. 12 shows the profiles for Vol_feed=330 ml.

(41) It will be appreciated by those skilled in the art that the embodiments described above are merely examples of how the principles of the invention can be employed and there are many possible variants within the scope of the invention. For example, the principles of the invention could be used to produce water or other liquid at a different temperature and for a different purpose than the preparation of infant formula milk. Moreover, the particular type of heater shown is not essential and any other flow heater or batch heater could be used instead. Furthermore, water could be supplied from a plumbed-in source, e.g. the mains water supply, rather than from a hopper within the appliance.