GB2211601A - Transportable holding ovens - Google Patents

Abstract

A holding oven 1 comprises an insulated oven housing 2, one or more support shelves within the housing 2 for supporting items to be held at an elevated temperature within the oven 1, and a forced draught air heater 12. The heater 12 includes a heater casing, a fan for forcing air through the casing, a pipe 13 for supplying fuel to the casing, a spark igniter for igniting the resulting air/fuel mixture, and an outlet 16 for discharging the heated air produced by such ignition to the interior of the housing 2 to maintain the items at an elevated temperature. Such a holding oven can be made relatively compact so that it is portable and can be easily loaded into a vehicle. <IMAGE>

Description

"Transportable Holding Ovens" This invention relates to transportable holding ovens.

There is an increasing need for hot food to be transported in vehicles, for example for delivery to hospitals or elderly people in their homes. In order that the quality of the food should be maintained, it is necessary for the food to be held at a set elevated temperature during transport and up to delivery to the customer. Commonly the food is simply placed in thermally insulated containers during transport, but food held in such containers will inevitably cool over a period of time, and this method of transport is therefore not suitable for longer journeys or where delays are likely to be experienced.

It is well known to maintain food at an elevated temperature by placing it in a holding oven.

However known ovens are either too bulky to be transported or are too costly to render their use economical in most applications. It is not feasible to run an electrical holding oven off a normal vehicle battery since a reasonably sized oven would rapidly drain the battery.

It is an object of the invention to provide a novel transportable holding oven which can be constructed at reasonable cost.

According to the present invention, there is provided a transportable holding oven comprising an insulated oven housing, one or more support members within the housing for supporting items to be held at an elevated temperature within the oven, and a forced draught air heater including a heater casing, means for forcing air through the casing, means for supplying fuel to the casing, means for igniting the resulting air/fuel mixture, and an outlet for discharging the heated air produced by such ignition to the interior of the housing to maintain said items at an elevated temperature.

Such an oven enables food items to be held at an elevated temperature for an indefinite period.

Furthermore it can be made relatively compact so that it is portable, and can be easily loaded into a vehicle or transferred from one vehicle to another. The electrical requirement of such an oven can be easily met by a normal vehicle battery.

In a preferred embodiment of the invention, the air heater further includes air purifying means through which the heated air passes prior to discharge from the outlet. The air purifying means may comprise a catalytic material for receiving the combustion products produced by ignition and rendering such products substantially non-toxic.

Furthermore the air heater may further include a combustion chamber and means for mixing the air and fuel in the combustion chamber.

Preferably the means for forcing air through the casing is a fan, and the means for igniting the air/fuel mixture is a spark igniter.

Additionally temperature sensing means are with advantage disposed within the housing, and control means are provided for controlling the air and/or fuel supplied to the air heater in dependence on the oven temperature as sensed by the temperature sensing means.

In order that the invention may be more fully understood, a preferred form of transportable holding oven in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a front view of the oven; Figure 2 is a rear view of the oven; Figure 3 is a sectional diagram of the air heater of the oven; and Figure 4 is a vertical section through an optional humidifier.

Referring to Figures 1 and 2 the oven 1 comprises an insulated oven housing 2 having metal inner and outer walls 3 and 4 having thermally insulating material 5 (shown in a broken-away portion of Figure 1) sandwiched between the inner and outer walls 3 and 4. The housing 2 has two doors 6 and 7 at its front which are similarly constructed to the remainder of the housing.

Within the housing 2 are a plurality of support members in the form of shelves 8 having ventilating apertures (not shown) therein allowing a balanced flow of hot air through the interior of the housing and ensuring uniformity of temperature within the housing.

Attached to the rear of the housing 2 is a holder 9 bearing an alkane gas bottle 10, containing for example butane or propane, a control box 11 and a forced draft air heater 12. Fuel is supplied from the bottle 10 to the heater 12 by way of a feed line 13 which incorporates a cut-out device (not shown) for terminating supply of fuel to the heater 12. The control box 11 is supplied by an electrical lead 14 for connection to a 12 V battery of a vehicle. A flexible duct 15 connects the outlet 16 of the heater 12 to an inlet 17 at the bottom of the rear wall of the housing 2. Exhausted hot air from the heater 12 is supplied to the interior of the housing 2 by way of the inlet 17 and circulates through the shelving within the housing 2 before exiting through an outlet 18 in the roof of the housing.A flexible duct 19 may extend from the outlet 18 to a suitable vent in the roof of the vehicle. A variable thermostat (not shown) is disposed within the housing 2 for regulating the internal temperature of the housing in a manner which will be described in more detail below.

The basic construction of the air heater 12 will now be described with reference to Figure 3. The heater 12 comprises a casing 20 having an air inlet 21 and the air outlet 16. In order to force air through the casing 20 an electric motor 22 supplied by the control box 11 drives a fan 23 for drawing air into the casing 20 through the inlet 21 and a further fan 24 for drawing air into a chamber 25 through an inlet 26.

A combustion chamber 27 is also provided within the casing 20 and incorporates a gas jet 28. Air is supplied to the combustion chamber 27 from the chamber 25 by way of apertures 29, and fuel is supplied to the gas jet 28 by way of a fuel pipe 30. In order to promote mixing of the air and fuel within the combustion chamber 27 inclined baffles 31 are provided in the vicinity of the apertures 29 to deflect the air inwardly of the combustion chamber 27.

A spark igniter 32 is provided within the combustion chamber 27 to ignite the air/fuel mixture on start up of the heater. The mixture of air and combustion products produced within the combustion chamber 27 by means of the resulting combustion passes through a catalytic material 33 which renders the combustion products non-toxic prior to discharge of the heated air through the outlet 16. A thermocouple 34 is provided to sense the temperature of the heated air and to provide feedback control of the heater in a manner described below.

The operation of the heater 12 is controlled by the control box 11 which is electrically connected to the oven thermostat, the thermocouple 34, the spark igniter 32, the electric motor 22 and the fuel cut-out device which may be a solenoid-operated valve. On start up by operation of an appropriate switch (not shown) fuel and air are introduced into the combustion chamber by opening the cut-out device and supplying power to the motor 22 to drive the fans 23 and 24. A fuel rich mixture is provided in the combustion chamber 27 by operating the motor at reduced speed. Simultaneously the spark igniter 32 is energised to supply a spark to ignite the air/fuel mixture. When the heated air passing towards the outlet 16 reaches a pre-set temperature as sensed by the thermocouple 34 the motor 22 is caused to operate at full speed and the spark igniter 32 is switched off.In the event that an excess temperature is sensed by the thermocouple 34 or by the oven thermostat, combustion is stopped by closing off the cut-out device. The motor 22 is also stopped after a pre-set interval to provide for cooling.

Firing of the heater takes place as and when necessary to maintain a predetermined internal oven temperature.

Optionally a humidifier 50, as shown in Figure 4, is installed within the interior of the oven housing in a suitable position, for example in the vicinity of the inlet 17, so as to humidify the hot air passed into the oven housing. The humidifier 50 includes a housing 51 containing water 52 and a fan 53 for blowing water vapour, produced within the housing 51 by evaporation at the elevated temperature of the oven, through outlet apertures 54. A perforated sheet 55 floats on the surface of the water 52 within the housing 51 in order to prevent splashing of the water during transport of the oven.

Claims (10)

1. A holding oven comprising an insulated oven housing, one or more support members within the housing for supporting items to be held at an elevated temperature within the oven, and a forced draught air heater including a heater casing, means for forcing air through the casing, means for supplying fuel to the casing, means for igniting the resulting air/fuel mixture, and an outlet for discharging the heated air produced by such ignition to the interior of the housing to maintain said items at an elevated temperature.

2. An oven according to claim 1, wherein the air heater further includes air purifying means through which the heated air passes prior to discharge from the outlet.

3. An oven according to claim 2, wherein the air purifying means comprises a catalytic material for receiving the combustion products produced by ignition and rendering such products substantially non-toxic.

4. An oven according to claim 1, 2 or 3, wherein the air heater includes a combustion chamber and means for mixing the air and fuel in the combustion chamber.

5. An oven according to any preceding claim, wherein the means for forcing air through the casing is a fan.

6. An oven according to any preceding claim, wherein the means for igniting the air/fuel mixture is a spark igniter.

7. An oven according to any preceding claim, wherein temperature sensing means are disposed within the housing.

8. An oven according to claim 7, wherein control means are provided for controlling the air and/or fuel supplied to the air heater in dependence on the oven temperature as sensed by the temperature sensing means.

9. An oven according to any preceding claim, wherein humidifying means are disposed within the housing.

10. A holding oven substantially as hereinbefore described with reference to the accompanying drawings.