Hopper cooling is a simple form of water cooling used for small stationary engines. The defining feature of hopper cooling, amongst other water-cooled engines, is that there is no radiator. Cooling water is heated by the engine and evaporates from the surface of the hopper as steam. [2]
Internal combustion engines are rather inefficient and require cooling to dispose of the waste heat they generate when running. Water-cooled engines remove this heat from around the cylinder head by surrounding it with a water jacket.
In most familiar engines today, this water is circulated from the hot parts of the engine to a radiator, where it gives up its heat to the air.
In early and low powered engines with hopper cooling there is little circulation. Water is instead slowly boiled off, with the heat of vaporisation needed to boil the water coming from the engine heat. The loss of heat with this departing water vapour is enough to cool the engine. [3]
As the heat of vaporisation (energy needed to vaporise water) is much larger than the specific heat capacity (energy to raise the temperature of water by one degree), relatively little water is required to replace that lost by evaporation. The heat needed to boil water is equivalent to a 540 °C rise in temperature, or about 7 times that needed to raise the temperature of the water from ambient to boiling.
| Specific heat capacity | cP | 4.1813 J·g−1·K−1 | |
| Heat of vaporisation | 2260 J·g−1 |
A typical small engine would consume a few bucketfuls in a working day.
Although hopper cooling is inefficient, in terms of the amount of heat removed for the size of the water jacket, it does maintain the cylinder temperature at a low temperature. Provided that the hopper does not boil dry, the temperature cannot exceed the 100°C atmospheric boiling point of water. This is both an advantage and a disadvantage: it maintains a low operating temperature, helping to preserve the fragile piston rings and exhaust valves of these early engines. However it also limits efficiency of operation, as the engine cannot run at a higher and more efficient operating temperature.
Large engines would use thermosyphon cooling. The hopper on the engine would be supplemented by a large drum of water above the engine. This would give some circulation between the two, but as there was no large surface area for heat transfer to the air, as with a radiator, the eventual cooling would still largely be by evaporation.
Hopper-cooled engines are usually single cylinder, and usually petrol engines rather than diesel. These are the engines that appeared in great numbers between the wars, driving a range of farm machinery by flat belt drives. These engines were used intermittently, and usually with an operator in attendance.
To avoid frost damage, the hopper could be drained easily through a large brass tap. [5] This would be done regularly, sometimes after every use, to avoid rust inside the hopper. As the cooling water evaporated continuously when running, no anti-freeze or anti-corrosion additives were used.
Hopper cooling has now largely disappeared. Lighter and more efficient engines were developed post-WWII, using air cooling. These were developed from motorcycle engines and made use of developments in aluminium casting to make thin-walled cylinder blocks with cast-in cooling fins. These are simpler in operation and do not require water, level checking or anti-freeze.
A handful of engines, now largely diesels, retained hopper cooling into the 21st century. [6] These were simply constructed engines, still using cast-iron blocks to provide more strength from a crude foundry, as a diesel engine required more strength than unsophisticated aluminium castings could provide. Single cylinder horizontal diesel engines were built in India and China and were briefly imported to the West around 2000, but were outlawed by emission control regulations. [7]
Large hot air engines, such as the Rider-Ericsson, also used hopper cooling.
Evaporative or steam cooling was used experimentally for high-powered aircraft engines in the 1930s, notably the Rolls-Royce Goshawk. [8] Although both systems rely on evaporation, they are quite different. Aircraft evaporative cooling, like radiator systems, used a pumped closed-loop for the coolant, without loss. The coolant vapour was captured in radiators, or in this case condensers and re-circulated.
A steam engine is a heat engine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a cylinder. This pushing force can be transformed, by a connecting rod and crank, into rotational force for work. The term "steam engine" is generally applied only to reciprocating engines as just described, not to the steam turbine. Steam engines are external combustion engines, where the working fluid is separated from the combustion products. The ideal thermodynamic cycle used to analyze this process is called the Rankine cycle. In general usage, the term steam engine can refer to either complete steam plants, such as railway steam locomotives and portable engines, or may refer to the piston or turbine machinery alone, as in the beam engine and stationary steam engine.
Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in cars, buildings, and electronics.
Water cooling is a method of heat removal from components and industrial equipment. Evaporative cooling using water is often more efficient than air cooling. Water is inexpensive and non-toxic; however, it can contain impurities and cause corrosion.
An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments. Common antifreezes also increase the boiling point of the liquid, allowing higher coolant temperature. However, all common antifreeze additives also have lower heat capacities than water, and do reduce water's ability to act as a coolant when added to it.
Liquid cooling refers to cooling by means of the convection or circulation of a liquid.
Internal combustion engine cooling uses either air or liquid to remove the waste heat from an internal combustion engine. For small or special purpose engines, cooling using air from the atmosphere makes for a lightweight and relatively simple system. Watercraft can use water directly from the surrounding environment to cool their engines. For water-cooled engines on aircraft and surface vehicles, waste heat is transferred from a closed loop of water pumped through the engine to the surrounding atmosphere by a radiator.
A coolant is a substance, typically liquid, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corrosion of the cooling system. Some applications also require the coolant to be an electrical insulator.
The Rolls-Royce Kestrel is a 21.25 litre V-12 aircraft engine from Rolls-Royce. It was their first cast-block engine, and used as the pattern for most of their future piston-engine designs. Used during the interwar period, it was fitted to a number of British fighters and bombers of the era, including the Hawker Fury and Hawker Hart family, and the Handley Page Heyford. The Kestrel engine was also sold to international air force customers, in this role it used to power prototypes of the German Messerschmitt Bf 109 and the Junkers Ju 87 "Stuka" dive-bomber, as the Junkers Jumo 210 engines were not ready to be fitted. Several examples of the Kestrel engine remain airworthy today.
Thermosiphon is a method of passive heat exchange, based on natural convection, which circulates a fluid without the necessity of a mechanical pump. Thermosiphoning is used for circulation of liquids and volatile gases in heating and cooling applications such as heat pumps, water heaters, boilers and furnaces. Thermosiphoning also occurs across air temperature gradients such as those utilized in a wood fire chimney or solar chimney.
The Rolls-Royce Goshawk was a development of the Rolls-Royce Kestrel that used evaporative or steam cooling. In line with Rolls-Royce convention of naming piston engines after birds of prey, it was named after the goshawk.
An absorption refrigerator is a refrigerator that uses a heat source to provide the energy needed to drive the cooling process. The system uses two coolants, the first of which performs evaporative cooling and is then absorbed into the second coolant; heat is needed to reset the two coolants to their initial states. The principle can also be used to air-condition buildings using the waste heat from a gas turbine or water heater. Using waste heat from a gas turbine makes the turbine very efficient because it first produces electricity, then hot water, and finally, air-conditioning—trigeneration. Absorption refrigerators are commonly used in recreational vehicles (RVs), campers, and caravans because the heat required to power them can be provided by a propane fuel burner, by a low-voltage DC electric heater or by a mains-powered electric heater. Unlike more common vapor-compression refrigeration systems, an absorption refrigerator has no moving parts.
Economizers, or economisers (UK), are mechanical devices intended to reduce energy consumption, or to perform useful function such as preheating a fluid. The term economizer is used for other purposes as well. Boiler, power plant, heating, refrigeration, ventilating, and air conditioning (HVAC) uses are discussed in this article. In simple terms, an economizer is a heat exchanger.
The hot-bulb engine is a type of internal combustion engine in which fuel ignites by coming in contact with a red-hot metal surface inside a bulb, followed by the introduction of air (oxygen) compressed into the hot-bulb chamber by the rising piston. There is some ignition when the fuel is introduced, but it quickly uses up the available oxygen in the bulb. Vigorous ignition takes place only when sufficient oxygen is supplied to the hot-bulb chamber on the compression stroke of the engine.
A heater core is a radiator-like device used in heating the cabin of a vehicle. Hot coolant from the vehicle's engine is passed through a winding tube of the core, a heat exchanger between coolant and cabin air. Fins attached to the core tubes serve to increase surface area for heat transfer to air that is forced past them by a fan, thereby heating the passenger compartment.
The wax thermostatic element was invented in 1934 by Sergius Vernet (1899–1968). Its principal application is in automotive thermostats used in the engine cooling system. The first applications in the plumbing and heating industries were in Sweden (1970) and in Switzerland (1971).
Oil cooling is the use of engine oil as a coolant, typically to remove surplus heat from an internal combustion engine. The hot engine transfers heat to the oil which then usually passes through a heat-exchanger, typically a type of radiator known as an oil cooler. The cooled oil flows back into the hot object to cool it continuously.
Radiators are heat exchangers used for cooling internal combustion engines, mainly in automobiles but also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating plant or any similar use of such an engine.
The Meredith effect is a phenomenon whereby the aerodynamic drag produced by a cooling radiator may be offset by careful design of the cooling duct such that useful thrust is produced by the expansion of the hot air in the duct. The effect was discovered in the 1930s and became more important as the speeds of piston-engined aircraft increased over the next decade.
An evaporator, distiller or distilling apparatus is a piece of ship's equipment used to produce fresh drinking water from sea water by distillation. As fresh water is bulky, may spoil in storage, and is an essential supply for any long voyage, the ability to produce more fresh water in mid-ocean is important for any ship.
In fluid thermodynamics, a heat transfer fluid is a gas or liquid that takes part in heat transfer by serving as an intermediary in cooling on one side of a process, transporting and storing thermal energy, and heating on another side of a process. Heat transfer fluids are used in countless applications and industrial processes requiring heating or cooling, typically in a closed circuit and in continuous cycles. Cooling water, for instance, cools an engine, while heating water in a hydronic heating system heats the radiator in a room.
